GeologyOfSingapore Ocr

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GEOLOGY OF THEREPUBLIC OF SINGAPORE

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Published Bl'PUBLIC WORKS DEPARTMENT, SINGAPORE

December 1976

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Frontispiece: A syncline in rocks o/ the Jurong Formation at Jurong (GR 31 7458 ) showing il1lerbeds o'-thl:'fossili/erous and tu ffaceous Aver Cha wan Facies and the red- brown sandstone of the TellgallFa cies. The fold is aSVllllllet rical about a sub-horizontal axis trending at lI Do Th e inter- lilllbangle is about 80" and the axial plane o/ the/old dips at aboUl 65 ') 10 the west-south- west. Beds otboth fa cies are deeplv leached at the upper surface so that they can no longer be difTerenlialed 0 11

colou r.

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FOREWORD

The Geological Unit of the Public Works Department was formed in 1972. The main objectives for itsestablishment are:

(i) To prepare and update continuously the geological maps of the Republic of Singapore;

(ii) To assess the engineering and geotechnical characteristics of the rock formations ;

(i ii ) To study the sources of construction materials and other natura l resources; and

(iv) To provide expert an d consultative advice on geological matters .

This book attempts to fulfil some aspects of these objectives.

O ver the past years, geological data has become increasingl y important in engineering planning andconstr uction . There is a vital need for a revised and comprehensive geological reference of Singapore tosupplement the publication of F.E.S. Alexander made in 1950. This book with its nine geo logic maps a ndone locality map seeks to fulfil thi s need . It should become a useful companion to all professions connectedwi th the earth sciences.

[ wish to congra tulate every one who has made the publication of this book possible. I am confidentthat this book will be co nsidered as a major cont ri bution to the world of earth science in this region and tothe civi l engineering and allied professions .

YAP NENG CHEWDirector of Public Works

December 1976

v

PREFACE

This book aims to provide a comprehensive account of the geology of the Republic of Singapore forthe various disciplines that are involved with the ground, namely, civil engineering, land utilization, urbanplanning, agriculture, etc. For the civil engineers the nature, distribution and relationship of the variousrocks and deposits described in the book will furnish geological information for preliminary planning anddesign of foundations, roads, water supply, drainage and sewerage works and others. Those concerned withland planning and uses will find the information helpful in delineating potential areas for granite quarrying,sand washing, agriculture, brick and pottery works , etc. Besideothese practical objectives, the book aims tobecome the Republic of Singapore's contribution to the earth sciences in the South-east Asia Region as wellas to acquaint the public, teachers and students with the geological constitution and evolution of Singaporeover the past 500 million years .

This book comes in two parts. The first part features the text which relates in detail the geology of theRepublic. The summary of the text is contained in the first chapter. Some relevant aspects of the country' sgeography and a review of previous geological investigations since 1924 are described in the followingchapter. The third chapter presents, in chronological order, the definition, distribution, character, fieldrelation, and age and correlation of each of the nine rock units, namely, Sajahat Formation, the GombakNorite , the Palaeozoic Volcanics, the Bukit Timah Granite, Jurong Formation and its facies, the OldAlluvium, Huat Choe Formation, Tekong Formation and Kallang Formation and its members. Many ofthese units are introduced for the first time. Petrographic descriptions form an integral part of thepresentation in this chapter. The next chapter is concerned with fold and fault structures that had affectedthe older rock formations. The geologic evolution is discussed in the final chapter. The text's appendicesinclude a list of references; analyses of rocks and water from hot-springs and a list of fossils and theirlocations .

The second part of the book is represented by 8 coloured geological maps at a scale of I : 25,000: 1sheet of cross-sections which reveal the subsurface distribution of geologic deposits along six lines oftraverse across various areas of the Republic of Singapore and a locality map at a scale of I : 75,000 . Thegeological maps can be assembled into a convenien t wall map .

This book is prepared with the assistance of Uni ted Nations and the Government of New Zealand.Special gratitude is due to the following persons: Dr Peter Morris who worked from March 197"2 to March1973 ; Dr Hans Bader from March 1974 to February 1975 and from October 1975 to November 1975, bothUnited Nations Office of Technical Co-Operation Experts and Mr Graham Mansergh, Colombo PlanExpert from the Geological Survey of New Zealand from August 1974 to November 1975 . Gratitude is alsodue to Dr W.A . Watters, Dr I.G . Speden and Dr B.W . Collins who are staff members of the Geologi ca lSurvey of New Zealand.

The assistance of other Government Departments and Statutory Bodies, namely , Mapping Unit of theMinistry of Defence, Marine Police Department, Jurong Town Corporation, Public Utilities Board.Housing and Development Board and Port of Singapore Authority is also acknowledged.

Thanks are also due to the Department of Geology of the University of Malaya, for making relevanttheses available .

The following staff of the Geological Unit of the Public Works Department have participated in nosmall measure in the preparation of this book: Lee Kim Woon (September, 1972 - Present) , Loy WeiChoo (August, 1975 - Present), Pun Vun Tat (November, 1973 - May, 1975). The untiring support givenby the other staff members is greatly appreciated .

DR TAN SWAN BENGSenior Executive Engineer

November 1976

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CONTENTS

Page

FOREWORD . . . .. .. ..... .. . . . .. ........................... v

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII

SUMMARy .

2 INTRODUCTION .

LOCATION .

PHySIOGRAPHy .

PREVIOUS GEOLOGICAL INV ESTIGATIONS .

PRESENT GEOLOGICAL INV ESTIGAT IONS .

3 STRATIGRAPHy .

OUTLINE OF STRAT IGR APHy .

SAJAHAT FORMAT ION (S) .

Definition and Distribution .

Content. .

Field Rel a tion s .

Age and Co rrelation .

GOM BA K NORITE (GN) .


Content. .

Field Relations .

Age and Correl a tion .

PALAEOZOIC VOLCANICS (PV ) .


Content. .

Field Relation s .

Age and Correlation .

BU KIT TIMAH GRAN ITE .

Definition .

CE TRAL SI GAPO RE GRANIT E (Bt , BTh, BThy, BTb) .

Distribution .

Content. .

Granite .

Adamellite .

Granodiorite and Diorite .

FieI'd Rel ations .

INCLUSIONS IN THE CENTRAL SINGAPORE GRANITE .

Definition a nd Distribution .

Composition .

DYKE ROC KS ASSOCIATED WITH T HE CENTRALSINGAPORE GRANITE .

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CONTENTS - continued

Classification an d Distribution .

Composition .

Dy k es a/acid a/finitI' ( Da. Dp, Dg. Dt ) .D l'k es a/basic allinity ( Db . Dd. Dsp ) .

Field Rel at ions .

PULA U U BI N GRANITE (BT, 8Th, BTb, BThy) .

Dist ributi on .

Content. .

Granite .

Adalllellite .

Hybrid rock s .

Field Relations .

INCLUSIONS IN THE PULAU UBIN GRA NITE .


Compositio n .

Inclusions a/ r ocks containing pFroxene .

Inclusion.l' 0/ rock s \\JilhoUl p l' roxene .

Field Rela ti ons .

DYK E ROCKS ASSOC IATED WITH THE PULAU U BINGRANIT E .

Di st ribut ion .

Composition .

Dik es 0/ acid a/finill ' ( Da ) .

Dv kes 01 Basic a/finill{ Db ) .

Field Rel a ti ons .

Age and Correla ti on .

MINERALIZAT ION .

JU RONG FORMATION .

Introduct ion .

QUEENSTOWN FACIES (Jq) .

Definiti on and Distribution .

Co ntent. .

Field Relations .

JONG FAC IES (Jj ) .


Content. .

Field Rela ti ons .

AYER C HAWA N FACIES (Jac) .

Definiti on and Distribution .

Content. .

Field Relati ons .

RIMAU FAC IES (Jr) .


Content. .

Field Relations .

ST. JOHN FACIES (Jsj) .

Defini tio n and Distribution .

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CONTENTS - continued

Co ntent. .

Field Rela tio ns .

TENGAH FACIES (Jt) .

Definitio n a nd Di stribution .

C o nten t. .


M U RAl SC HIST .


Content. .

Field Relations .

VOLCANIC ROCKS WITHINTHEJU RONG FORMATION .

Introduction .

Spilite .Definition and Distribution .Composition .

Tuff .De finition and Distribution .Co mposi ti o n .

C hert .

D o leri te .Definiti o n and Distributio n .Co mpos itio n .Fie ld R ela ti o ns .

Age and Co rrela tio n .

OLD ALL UVIUM (OA) .

Definitio n and Di stribution .

Content. .


Age and C orrela tion .

HUAT CHOE FORMATION (HC) .

Definiti o n and Distribution .

Content. .

Field Rel a ti o ns .

Age .

TEKONG FORMATION (T) .

Definition a nd Di stribution .

Co ntent. .

Field Rel a tio ns .

Age a nd C orrela tion .

KALLANG FORMATION .


MARINE MEMBER (Km) .

Defi 'nition a nd Distribution .

Content. .

Field Relations .


ALLUVIAL MEMBER (Ka) .


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CO NTENTS - continued

Content. .

Field Relations .


LITTORAL MEMBER (KI) .


Content. .

Field Relations .


TRANSITIONAL MEMBER (Kt) .


Content. .

Field Relations .

Age · · ··· .

REEF MEMBER (Kr) .


Content. , .

Field Relations .

Age · . · · · · .

4 STRUCTURE .

PRE-MESOZOIC STRUCTURE .

MESOZOIC STRUCTURE .

Folding · .

Faulting , .

CENOZOIC STRUCT U RE .

5 GEOLOGICAL HISTORY .

REFERENCES .

Appendix I

ANAL YSES OF ROCKS

Appendix 2

ANALYSES OF HOT SPRING WAT E R

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Appendix 3

PLATEOFFOSSILS. ,.. .. ... .. ...... ..... ....... . . .. .. ... .. 74

LISTS OF FOSSILS JU RONG FOR MATI ON . . .. . .. . . .. . . . . . . .. . 75

Accompanied by geological maps, cross section sheet and localitymap .

Sheet I Geology, AMA K ENG I : 25 ,0002 Geology, NEE SOON 1 : 25,0003 Geology , CHANGI I : 25.0004 Geology. PULAU TEKO NG I : 25,0005 Geology, JU RONG 1 : 25 ,0006 Geology, CITY 1 : 25,0007 Geology, SIGLAP I : 25 ,0008 Geology , SOUTHERN ISLANDS I : 25 ,0009 GEOLOGICAL CROSS SECTIONS AND MAP LEGEND

I : 25 ,00010 LOCALITY MAP 1 : 75,000

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Fig.2 . 1

Fig. 2.2

Fig. 2.3

Fig.3.1

Fig.3.2

Fig . 3.3

Fig. 3.5

Fig. 3.6

Fig.3.7

Fig. 3.8

Fig. 3.9

Fig.3.10

Fig.3.11

Fig.3.12

Fig.3.13

Fig . 3.IA

LIST OF FIGURES

Map of the main island of Singapore showing theboundaries of the seven physiographic units. PulauBrani and Sentosa are included in area 4.Pulau Ubin is not classified .

Geological map of Singapore after Scrivenor (1924).

Geological map of Singapore after Alexander (1950).

Poorly sorted quartz sandstone from Pulau Sajahat.45X Crossed Nicols

Recrystallized quartzite of the Sajahat Formationfrom the Public Utilities Board Test Hole No. Iat Bedok.120X Crossed Nicols

Well bedded and sheared argillite from SajahatFormation exposed at Tanjong Renggam, PulauTekong Besar.

Spotted argillite from Tanjong Renggam, PulauTekong Besar.45X Plain Polarized Light

Alteration of pyroxene to coarse and fibrousamphibole in noritic gabbro from Swee ConstructionQuarry.120X Crossed Nicols

Granite intruding norite and containing xenolithsof norite , Peng Seng Quarry .

Large plates of hornblende with augite cores inhornblende gabbro from G R 404504, CentralSingapore.45X Crossed Nicols

Zoning in andesine . Sericite after a zone withinthe plagicolase in porphyritic microgranite,Singapore Granite Quarry (Mandai).45X Crossed Nicols

Rounded, well assimilated basic inclusions inadamellite, Public Works Department Quarry (Mandai).

Weathered basic dyke in granite soil, AdmiraltyRoad (G R 450611), North Central Singapore.

Phenocrysts of rounded quartz and sericitizedacid plagioclase in granite porphyry, HindhedeQuarry.45X Crossed Nicols

Radiating structure of slender feldspar andquartz in granophyre, Yun Onn Quarry.120X Crossed Nicols

Subparallel alignment of acid plagioclase laths intrachyte, Swee Construction Quarry (Bukit Batok).45X Crossed Nicols

Altered calcic plagioclase, smaller augitecrystals, and occasional quartz in altereddolerite from Swee Construction Quarry (BukitBatok). The habit of augite is in marked contrastwith that of the younger dolerite cutting theJ u rang Formation at Pulau Senang. (See Fig. 3 AI,Pg. 53 a)45X Plain Polarized Light

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LIST OF FIGURES - continued

Page

Fig.3.15 Crysta ls of a ugi te, slim laths of bio tite , and 23

patches of calcite in spessartite, Pub lic Works .,

Depa rtment Quarry (Mandai).45X Plain Polarized Light

Fig .3. 16 D olerite cutting 25 m wide microgran ite dyke in 23

norite, Chai Oh Ka ng Quarry . The yellowish-browncoloration is a stain on the acid dyke and the

norite.

Fig.3.17 Outcrop of granite at Changi . Pegm atite veins 25,..l.~

(not visible in photograph) are fo und in thisoutcrop. (G R 653540)

Fig.3 . 18 Large plates of hornblende contai ning pyroxene 25 "'7J

in hybrid granodiorite from Lian Moh Quarry ,,\

Pulau Ubin.45X Plai n Polarized Light

Fig.3 . 19 Dense clusters of biotite, hornblende, and opaque 27 .~;

grains of magnetite in granodiorite, Changi.120X Pla in Polarized Light

Fig. 3.20 D yke-like inclusions in the Housing Development 27

Board Quarry, Pulau Ubi n .

Fig.3 .2 1 C lusters of hornblende and biotite associa ted wi th 28

accessory a llani te in biotite-horn blende granitefrom K ampong Mamam, Pulau Ubin.

45X Crossed Nicols

Fig. 3.22 Numerous stubby prisms of pyroxene grains and 28

dense cluster of brown biotite in hypersthenehornfel s, Ka mpong Jelutong, Pulau U bin .

45X Plain Polarized Ligh t

Fig. 3.23 Garnet, tattered biotite nakes , and hornblende in garnet- 30

biotite hornfels at Gim H uat Quarry. Pulau Ubin.


Fig. 3.24 Rectangular-shaped inclusions in granite at the 30

H o usi ng Development Bo ard Qua rry, Pulau Ubin .

Fig. 3.25 Exposure of the Queenstown Facies showing the 33

massive character of purpli sh red mudstone,Jal an Bukit Merah, South Cent ral Singapore.

Fig. 3.26 Photomicrograph of a fine red sa nd stone in the 33

Queenstown Facies showing ve ry angular quartzdetrital g ra in s in a limonit ic clayey matrix,Kay Siang Road , (G R 467434). South CentralSingapore .120X Plain Polarized Ligh t

Fig. 3.27 Diagrammatic representation , not drawn to scale, 35

of facies relations in the J urong Forma tion .

Fig. 3.28 A 2 m thick conglomerate bed co ntaining clasts 36

of sandstone, siltstone, quartz porphyry andsch ist , Mount Faber.

Fig . 3.29 Conglomerate of the Jong Facies containing 36

sandstone, siltstone, grey mudstone, and quartzporphyry clasts at Pulau Jong.

Fig. 3.30 Heavy quartz veining in fine sandstone of the 38

Jong Facies, Pulau Senang .

Fig.3.31 A pale grey bed of mudstone exposed at ]uron'g 38

(G R 327462) showing features in dicating reworking

by biota.

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Fig. 3.32

Fig . 3.33

Fig. 3.34

Fig. 3.35

Fig . 3.36

Fig . 3.37

Fig. 3.38

Fig. 3.39

Fig . 3.40

Fig. 3.41

Fig. 3.42

Fig. 3.43

Fig. 3.44

Fig. 3.45

Fig. 3.46

Fig. 3.47

Fig. 3.48

Fig. 3.49

Fig . 4 . 1

Fig . 4 .2

Fig . 4 .3

LIST OF FIGURES - continued

Fossil collection localities of Lim (1975) (Ll - LlI)and Chin Fatt (1965)(CFI - CF8)from the Jurong Area .Locations (A) to (E) refer to Li m's detailed section.

Photomicrograph of a sandstone of the RimauFacies from Kent Ridge showing close packedsubangular quartz grains.45X Plain Polarized Ligh t

Outcrop of the St. John's Facies showing palegrey muddy sandstone and mudstone with intraformational breccia, St. John 's Island.

Schistose sandstone from the Murai Schist.45X Plain Polarized Light

A large boulder of spilite at Jurong Pier Road .

Grey spilitic body associated with coarsesandstone and chert on Pulau Salu.

Angular inclusions in a spilite boulder nearSelat Pulau Damar. (G R 352448)

Large crystals of quartz, orthoclase and acidplagioclase in rhyolitic crystal tuff, PulauPergam, North-west Singapore.45X Crossed Nicols

Relict dolerite boulders lying alo ng the strikeof a dyke cutting the Jong Facies, Pulau Senang.

Augite crystals, partly interstitial betweencalcic plagioclase, and partly enclosing some ofthe plagioclase, in dolerite , Pulau Senang .45X Crossed Nicols

Summary logs PUB Test Holes

Old Alluvium showing cross bedded angular sandwith layers of pebbles exposed near sand pit ofNam Kee Sand Quarry in Tampines Area. (G R 617511).

Clastic dyke in Old Alluvium at Bedok Sand Pit(G R 592475).

Shallow dipping beds of clay and sandy clay inthe Huat Choe Formation , near Nanyang University(GR 331494).

Terrace of the Tekong Formation on Pulau TekongKechil. It has a mean heigh t of 4 m above meansea-level. Viewed from Pulau Sajahat Besar.

Horizontal layers of peat , muddy sand and mud ofthe Alluvial Member exposed in excavation nearEwart Circus, Bukit Timah . (G R 423486)

Hard, iron-cemented beach rock of the LittoralMember exposed at low tide on the south-westcoast of Pulau Tekukor.

A dark brown pebble beach of the Littoral Memberat 2 m lying on mudstone and siltstone on Pulaulong.

Intraformational breccia of black mudstone insandstone (G R 378499), Central Singaore.

An anticlinal fold seen on Tanjong Lokos,St. John's Island .

Oblique shear developed in the Queenstown Faciesexposed in an excavation off Pepys Road.

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1 SUMMARY

A new geological map of Singapore at a scale of I : 25,000 is presented. During the survey for this maphitherto unknown Pa laeozoic sedimentary and volcanic rocks were discovered , and evidence was found forthe large-scale rafting of older rock in the Triassic granite. Considerable structural detail was recordedfrom the sedimentary Triassic rocks and lithological mapping allowed for a more detailed subdivision ofthese rocks, including the recognition of the Murai Schist as the product of dynamic metamorphism .Evidence was found showing that the Plio-Pleistocene alluvial deposits were laid down in a tectonicdepression of that age, and that their thickness in Singapo re is not purely a function of Pleistocene sea-levelOuctuations. A small Pleistocene lacustrine deposit of clay suitable for pottery was discovered also, and sixsubdivisions in the Holocene sediment were recognised based on the lithology and environmental setting ofthe deposi ts .

Three formations have been assigned a Palaeozoic age. The Sajahat Formation is a sedimentarydeposit of quartz sandstone and argillite which is intruded by both basic and acid dykes, and in placesshows evidence of contact metamorphism. It is given a lower Palaeozoic age in this report but it could beupper Palaeozoic, or even lower Triassic, should the isotopic age of the granite from Pulau Sekudu prove tobe yo unger than Triassic.

The Gombak Norite is separated from the Palaeozoic units geographically, and the time relation scannot be determined on field evidence . Its age is given o n the assumption that it represents a part of theophiolite suite of the lower Palaeozoic geosyncline, but it could also be interpreted as representing the'basic differentiate' of the Triassic granite association .

The Palaeozoic Volcanics comprise andesitic ash and tuff which are metamorphosed . They aremapped as overlyi ng the Saja hat Formation, and a re t hought to be upper Palaeozoic on correlation withsimilar rocks in Malaya . It is possible that the Sajahat Fo rmation and Palaeozoic Volcanics are of the sameage and that they represent two members of the same unit.

The Bukit Timah Granite is assigned to the lower- mid Triassic by isotope dating. There is considerablehybridization within the formation and there is much evidence of assimilation . Mixing of rock from theGombak Norite and the Bukit Timah Granite is evident , and massive rafts or inclusions of basic rocks , andsmaller inclusions of rock s of sedimentary origin can be found within the granite . Two phases of dykeintrusion are recognised . A phase of acid dyke emplacement took place during the final stages of graniteemplacement, and a second more basic phase foll owed shortly after, but before the deposition of theoverlying Triassic sedimentary rocks .

The upper Triassic Jurong Formation overlies the granite although the contact is never seen. Sixsedi menta ry facies are recognised within the formati on based on grain size, composition a nd hardness . TheMura i Schist, previ o usly thought to represent the oldest rock in the formation , is found to be a product ofdynamic metamorphi sm within the Jurong Formation and to have formed during the deposition of theform a tion. Volcanics , as tuff, spilitic lava and dyke rocks are recognised within , and are contemporaneouswith the Jurong Forma tion.

There is no direct evidence of an y further geological activity until the late Tertiary or early Pleistocene .At that time a downwa rp occurred and the resultin g trough was backfilled with a coarse sand-gravel unitreferred to as the Old Alluvium. The base of the unit is below any reasonable base level for erosionassociated with the Pleistocene low sea-levels , but the top of the unit is probably associated with a high sealevel stan d of at least 70 m*.

A lacustrine deposit, the Huat Choe Formation , was laid down , possibly at the same time, as a kaolinrich clay . It is suggested that the clay was laid down in a fault-angle depression possibly also of earl yPleistocene age.

From late Pleistocene through the Holocene, alluvial, littoral and inshore marine sediments have beenlaid down . These have been assigned to the Tekong Forma tion, a coastal terrace deposit associated with a 6m sea-level, and the Kallang Formation . Five members have been mapped within the Kallang Formation,the members being differentiated on differences in their present day depositional environment and onsediment content.

• Unless otherwise stated heights are given relati ve to present day sea-level. Positive values refer to heights above present day sealevel . and negative values to th ose below present day sea-level.

The structures in the Palaeozoic sedimentary rock s indicate a longer, more complex tectonic historythan that affecting the other rocks, but there is insufficient data to establish the full history. The intrusionand uplift of the granite presumably started in the late Palaeozoic, but there is no strong evidence of theevent until Triassic time. The Triassic sediment was lai d down in a mobile north-west trending troughbounded on either side by rising granitic hills. The lithology of the coarser clasts in the sediment suggeststhat the bulk of the granite was still buried at that time. The rate of uplift of the granite to the south-west ,the Main Range Granite, appears to have been more rap id, and the trough was tilted to the north-east, andsliding o f the sediment in that direction took place fold ing it against the uplifted Bukit Timah Granite. Thedynamic metamorphism giving rise to the Murai Schist accompanied this sliding. There is no evidence thatsedimentation persisted after lower Jurassic time, and from the evidence in Malaya, it is assumed that theMalay Peninsula was raised above the sea from that time.

Tectonic activity recommen~ed in the late Tertiary or early Pleistocene with block faulting andwarping . Depressions were formed into which Old Alluvium and Huat Choe Formations were deposited.Later in the Pleistocene, after the cessation of warping, river valleys were cut in the Old Alluvium and olderrocks to be backfilled during the last interstadial and Holocene rises in sea-level.

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2 INTRODUCTION

LOCATION

The Republic of Singapore, consisting of one larger and several smaller islands, lies at the southernend of the Malay Peninsula is a roughly diamond shaped area between latitude 1° 09' Nand 1° 28' Nandlongitude 103° 38' E and 1040 06' E. It is surrounded from north-east to north-west by West Malaysia beingseparated from it by the Selat Johor , a stretch of water varying from 0 .7 km to 2.5 km in width. To thesouth, at a distance of some 12 km to 15 km from the main island of Singapore is the Riau Archipelago ofIndonesia.

Apart from the main island of Singapore, offshore islands lie in four groups, to the north-east, south,south-west and west. The north-east group includes Pulau Ubin and Tekong, and the smaller associatedislands. The southern group includes Sentosa, Pulau Brani, Tekukor, Subar Darat and Laut and the St.John ' s Island group . The western group are those surrounding Pulau Ayer Chawan and the south-westgroup those between Pulau Bukum and Pulau Satumu.

PHYSIOGRAPHY

Singapore is of moderately low relief. The main island covers an area of 540 sq km and the offshoreislands a further 44 sq km. The climate is hot and humid with an annual rainfall ranging from 1,600 mm inthe south-west to 2,500 mm in the central regions . Under these conditions, the rocks are deeply weatheredand the drainage has developed to a stage that the rive rs are of low gradient with a mature profile. Thedrainage patterns are either consequent or structurally controlled.

Seven discrete physiographic areas can be recogn ised on the main island of Singapore as a result of fivetypes defined on the maturity of the landform developed and relief. Fig. 2.1 shows the distribution of theseareas .

Area 1, to the north and west of Nan yang University, and including the pronounced Pasir Laba Ridgeis an area of moderate relief with hills rising to a maxim um of 85 m . The hills are aligned accor9ing to thegeological structure, and the slopes are steep but soil covered. Drainage is also a function of the geologicalst ructure .

Area 2, to the east and south of area I, is of low relief with rolling hills rising to about 28 m . The area iscrossed by a line of hills trending north-west, and up to 70 m high . Drainage is partly consequent and partlycontrolled by structure.

Area 3 is the flat low-lying Jurong River Valley with virtually no relief and a consequent drainagepattern modified by man.

Area 4 is the largest area defined for Singapore. It is an area of high relief. Bukit Timah, the highest hillin Singapore rising to 166 m, lies within this area . Slopes are generally steep and drainage is controlled bythe faults and joints in the granite to give a boxwo rk dra inage pattern , and by folds , cross joints and faultsin the Triassic sedimentary rock in the south. A belt of relatively low relief cuts across the southern end ofthis a rea in a north-west direction along the line of the Singapore River and Sungei Ulu Pandan.

Area 5 lies in the central north area and shows simi lar characters to those of area 2. Most of the arealies below the 20 m contour, but hills rise to 32 m at Punggol and 33 m at Seletar North. Drainage isconsequent and to the north-east.

Area 6 is the low-lying Kallang River Basin area and shows similar characteristics to area 3.

Area 7 lies to the east and south-west of Singapore International Airport. It can be described as adeeply dissected plateau . The relief is high and slopes steep, and a well developed dendritic drainage patternconsequent on the old surface has developed . The highest point is found just east of the airport and is 46 mhigh .

A more detailed analysis of the physiography of Singapore has been made by Wong (1969) . Herecognised nine discrete morphological units, including river valley floors , based on height, slope, relief andwhether hills or ridges dominate . He mapped some 54 areas, excluding the river valley floors, under therema ining eight headings, and for a fuller descrip tio n o f these areas , the reader is referred to his work .

3

Fig . 2.1 Map of the Main Island ofSingapore showing the boundaries of the seven physiographic units.Pulau Brani and Sen tosa are included in area 4. Pulau Ubin is not classified.

l

..,.

.:t:-.t;.:.tr ~~( ''''1>....~;l<.:.:J,1 -"""I

SHEET B

SH EET I

SHEET 5

-(

SHEET 2

6

.~ .,.;;.,~;;j>.l ....

SHEET :3

PULAU UBIN

~

, I

Km 1 0 1 2 3 4 5 6 7 ~ Km

SH EET 7

,!,.~ .. , .~-.: ·::··· ·' ·f ~· '· .. - (.~~;~..~~,;"<

PREVIOUS GEOLOGICAL INVESTIGATIONS

The most comprehensive papers on the general geology of the Republic of Singapore are those of J.B.Scrivenor (1924) and F.E.S. Alexander (1950). Other contributions have been made by Leow (1962),Burton (1964), and Hutchison (1964), and theses have been prepared by Ignatius Wong (1960), Chin Fatt(1965), Tai Say Ann (1972), SeetChin Peng (1974) and Lim Meng Sze Wu (1974) on areas within theRepublic . These latter works are of a detailed nature and concentrate on specific aspects of the geology.J .B. Scrivenor (1924) a lso prepared bibliographies of the geology pertaining to Singapore and D.J. Gobbett(1968) to that pertaining to West Malaysia and Singapore.

Scrivenor (1924) ma pped three rock units in Singapore - granite, shale and sandstone, and HighLevel Alluvium (Fig. 2.2). According to him the granite lies east of a north-west diagonal crossing theisland as a central granite mass, and appears again on Pulau Ubin and at Changi . The shale and sandstoneunit lies to the west. The High Level Alluvium is fo und to the east of the central granite separating it fromthe granite at Changi. Other igneous rocks, including quartz-norite, quartz-norite-gabbro, fine grainedrocks and enstatite-spessartite, were reported from Pulau Ubin .

Molluscs and plant rem ai ns, both as leaf impressions and fossil wood, were found by Scrivenor in thesedimentary rocks at different localities in Singapore and were described by Newton (1923) . These fossilsare poorly preserved and Newton suggested, with some reservation, a Rhaetic age for them!Scrivenorbelieved that the high inclin a tion of the sedimentary beds near the contact with granite in many places wasan indication that the sedimentary rocks were older tha n the granite,\ He suggested that the sedimentaryrocks were shallow-water deposits and that some were probably estuarine.

Alexander (1950) recognised the same three units plus a Recent Alluvium (Fig. 2.3). She divided theTriassic sedimentary rocks into three series, two of which she described as an Old Schist which was highlycontorted a nd an Argillaceous Series consisting mainly of black or grey shale , and unconformablyoverlying the older schists. Some fine and coarse sandstone and volcanic ash beds were reported asassociated with this series. The third gro up , the Arenaceous Series, was made up of sandstone,conglomerate and some shale and associated silty beds and, occasionally, thin seams of coal.

Alexander divided the igneous rocks into two groups, the Central Singapore Igenous Rocks and theChangi -Pulau Ubin Igneo us Rocks. The Central Singapore Igneous Rocks consist dominantly of granite,with less abu ndant norite and diorite, whereas the Changi-Pulau U bin Igneous Rocks are main lyhornblende-soda gran ite and fine-grained soda granop hyre. She postulated two magmas for the CentralSingapore granite, a n earlier gabbroic and a later granitic one, and she described a zone of hybrid rocksbetween the two intrusions.

The High Level Alluvium described by Scrivenor (1924) was renamed by Alexander as OlderAlluvium. The name change resulted from observations that the High Level Alluvium occurred with itsbase lying below present sea-level, and because it was older than the recent a lluvial deposits . She alsorecorded her observations on raised beaches and discussed briefly the effects of sea-level fluctuations onthese deposi ts.

Wong (1960) mapped the south-western region of Singapore. He reported three distinct conglomerate- sa ndstone - shale sets of beds each beginning with a basal conglomerate. Leow (1962), as a resul t ofheavy mineral studies of the sedimentary rocks, cou ld not accept the division of Argillaceous a ndA ren aceous Series postulated by Alexander (1950). He believed that there were several periods ofdeposition during the Triassic, each giving rise to a distinct set of beds beginning with a basalconglomerate. Later , Chin ( 1965) and Lim (1974) divided the Triassic sedimentary sequence into the Pasi rPanjang and Jurong. Formations. Lithologically, the Pasir Panjang and Jurong Formations are similar tothe Arenaceous and Argillaceous Series postulated by Alexander in 1950.

Well defined fold axes in the Triassic sedimentary rocks , which strike approximately north-west , wererecogn ised by Wong (1960). Leow (1962) concluded that the Triassic rocks contain a series of folds formingpart of a major fold syste m which plunged toward the north-west. He postulated a regional movementfo llowed by tilting as the reason for such a fold system. "Parasitic" folds due to incompetency between thestrata, and many isoclinal folds, postulated as resulting from igneous intrusion in the area, were observedby C hin and Lim . Both of them collected species of Myophoria . Pecten a nd Pteria. which suggested anUpper Triassic age for the sedimentary rocks. A detailed stratigraphic column for the Jurong and PasirPanjang Formations was given by Lim in his thesis ( 1974).

Hutchison (1964) believed that the marginal occurrence of a gabbroic body to the granodioritebatholith in Singapore was related to the Thai-Malay Orogeny and that the gabbroic rocks are preorogenic. Based on field relations as well as the chemical and petrological characters of the gabbro andgranodiorite in this area, Hutchison concluded that the granodiorite intruded the gabbro in the form of

5

6

~SEDIMENTARY ROCKS

...++ GRANITE+ALLIED ROCKS

"" HORNBLENDE GRANITE

--- HIGH LEVEL ALLUVIUM

v v v RECENT ALLUVIUIo4

to L mil, 5L·~_L-~.....J'

Fig . 2.2 Simplified Geological map of Singapore after Scriven or (1924).

!SEDIIo4ENTARY ROCKS

++ I GNEOU S ROCKS

::.-::.-- OLDER ALLUVIUIo4

RECENT SEDIIo4ENTS

N

tFig. 2.3 Simplified Geological map of Singapore after Alexander (1950).

1> ....

x-I

.n

irregular dykes, and, by thermal metamorphism and hybridization, produced a variety of hornblende-richrocks along the contact. Granodiorite dykes intrud ing the gabbro are crowded with gabbro xenoliths whichshow different stages of assimilation . Tai (1972) reported medium-grained biotite-hornblende bearingadamellite intruded by lamprophyre and apl ite dykes . He also observed some steeply dippingmetasedimentary rocks of quartz-mica-feldspar schist and quartzite intruded by granitic dykes on theeastern portion of Singapore. His full paper was not available at the time of writing and the location ofthese features is not known.

Seet (1974) carried out detailed mineralogical , petrographic and chemical studies on the igneous rocksof Pulau Ubin and deduced a complex geological history for the igneous rocks on the island. He thoughtthat the granite and granodiorite were emplaced at a high level as indicated by the low triclinicities of thealkali feldspars. He observed high AI 2 OJ but a low total alkali percentage in the granite compared with themicrogranodiorite. Based on chemical variation of the rocks, he concluded that the granite andgranodiorite were not comagmatic, and were probably derived by anatexis of sialic crustal material and notby fractional crystallization or differentiation. No correlation of this Pulau Ubin granite with those atChangi or other parts of Singapore was attempted in his thesis.

Burton (1964) in his report on the Older Alluvium of lahar and Singapore agreed with theobservations of Scrivenor (1924) and particularly Alexander (1950) . He noted a distinct deficiency ofmanganese in soil developed on the Old Alluvium, and that the weathered members of the alluvium werecharacterized by the development of ferricrete with in the staining zone, and tabular layers of pebbles atdepths varying from several cm to 3 m. From the distribution, extension and other evidence observed,Burton concluded that the Older Alluvium was related to a 75 m sea level of pre-glacial of First Interglacial(Gunz-Mindel or Aftonian) age, but the formation may have dated back to the late Pliocene.

Tai (1972) reported a definite marine fossil foun d in the Old Alluvium at a locality near the eastern endof the island.

Three unpublished geological reports were prepared by the Geological Unit of the Public WorksDepartment, Republic of Singapore (1973 A, 1973 B, 1974). These reports presented detailed geologicalmaps of Jurong-Tuas, Jurong-Pandan and the Pasir Panjang-Tanglin areas. An appendix of fieldphotographs and geological maps at scales of I : 25,000 and I : 2,500 were included in each of these reports .

The Jurong-Tuas area was found to consist only of rocks of sedimentary origin. Three units wererecognised . Two of them were described as an older a nd thicker sequence of black shale, grey mudstoneand grey tuff agglomerate, and a thinner and younge r sequence of sandstone, conglomerate and siltstone.The younger sequence was thought to lie disconformably on the older sediment. The third unit was madeup of unconsolidated Holocene sediment. The lurong-Pandan and Pasir Panjang-Tanglin areas, which lieeast and adjacent to the Jurong-Tuas area, were reported to be underlain by sedimentary rock, with somegranite lying in the north-east or northern sector of the areas . Four sedimentary units were recognised andmapped in these two areas . The oldest unit was a purple to red shale or mudstone, siltstone and fine tocoarse grained sandstone. Overlying this was a unit containing black shale, mudstone, conglomerate andtuff. On top of this uni t Ia-y a un it made up of conglo merate, sandstone, siltstone with minor red mudstone,and tuff. T he youngest unit is again an unconso lidated Holocene sediment. The lithological change fromJurong-Tuas to Jurong-Pandan and Pasir Panjang-Tanglin areas was interpreted as a facies change .

The reports showed that most folds found in these three areas were open and asymmetrical , with theiraxes trending north-west. The dips of the beds in the Jurong-Pandan and Pasir Panjang-Tanglin areas werefound to be steep . Major and minor faults in the Jurong-Tuas area strike mainly north-east and north-west.In the Jurong-Pandan area north-west faults were more common than the north-east trending faults. Smallfaults were reported from the Pasir Panjang-Tanglin area.

PRESENT GEOLOGICAL INVESTIGATIONS

Mapping at a scale of I : 10,000 commenced in September 1974 following the initial mapping projectcarried out in western Singapore at a scale of I : 2,500 and was completed by May 1975 for the whole ofSingapore except the souht-west islands and an east-west strip some 4 km wide running from Tuas to thecentral city area .' These areas had been mapped previously by the Geological Unit at a scale of I : 2,500.

Photogeological studies were used to add detail to this I : 10,000 mapping project. The aerialphotographs available are at an approximate scale of I : 15,000 and are the same as those used to compilethe base map onto which the geology has been plotted. Drilling was carried out to assist in theinterpretation in problematical areas, and use was made of the mass of drillhole data available in PublicWorks Department, and drillhole data made available by other government departments. Drillholes putdown for stratigraphic purposes are located on the map sheets.

7

3 STRATIGRAPHY

OUTLINE OF STRATIGRAPHY

In this book , nine separate formations are recogn ised in Singapore. Three of these - the SajahatFormation , a marine sedimentary unit found in the eastern part of Singapore, the Palaeozoic Volcanics,both of which are partially metamorphosed, and the Gombak Norite date from Palaeozoic times, but therelationship between them cannot be determined on field evidence. The Bukit Timah Granite was emplacednext; it has intruded and altered the Gombak Norite and is thought to be responsible for themetamorphism of the Sajahat Formation. A number of hybrid rocks are recognised within the Bukit TimahGranite . Granite emplacement is believed to have taken place in early Triassic time. The dykes associatedwith this granite can be divided into two groups, an older acid group assumed to be a cooling phase, and aslightly younge r basic set, which can be seen cutting the acid dykes. Both sets of dykes can be found cuttingthe Sajahat Formation, Gombak Norite and Bukit Timah Granite.

The Jurong Formation of late Triassic to early Jurassic age has been deposited on top of the graniteand is divided into six facies, the Queenstown, Jong, Ayer Chawan, Rimau, St. Johns, and Tengah Facies.The division is based on lithology, and rocks mapped in anyone facies do not necessarily form acon ti nuous body, now or a t the time of deposition . Deposition was either terrestrial , transitional or shallowma rine. Schist related to fa ulting and volcanic rocks cross-cutting or interbedded with the JurongFormation are included within it.

The Old Alluvium is a dominantly terrestrial deposit o f early Pleistocene age and lies unconformablyon, o r in fault contact with, the older units. No subdivi sio n has been made within this unit.

The Huat Choe Formation is a small lacu strine deposit, probab ly of early Pleistocene age and liesunconfor mably on the Jurong Formation.

The Tekong Formation is a Holocene marine and litto ra l deposit fo und with its upper depositionalsurface lying a t elevations between 3.6 m and 5.5 m above present sea-level.

The Kallang Formation includes both marine and terrestr ia l sediment laid down from late Pleistoceneto the present day. As such its time span incorporates the period of deposition of the Tekong Formation .Five members are recognised within the Kallang Formation, and further work may allow the establ ishmentof some of these members as formations . The mem bers mapped are the Marine Member, the LittoralMember, the Transitional Member, the Alluvial Member and the Reef Member. The Marine and AlluvialMembers span from the la te Pleistocene to the present day, the Littoral Member from 5000 BP to thepresent day , and the o ther two are late Holocene deposits.

SAJAHAT FORM ATION (S)

Definition and Distribution

The Sajahat Formation is defined as tho se variably metamorphosed sedimenta ry rocks comprisingquartzite, sandstone and argillite, a nd found on Pulau Saj aha t and Sajahat Kechil. Simila r rocks are founda long the north coast of Pul au Tekong as far east as T anjo ng Renggam . Quartzrich sandstone is exposed atT anjong Batu Koyok on the south-west tip ofPulau Tekong, and on the western side of Tanjong Punggo l,and these rock s have also been mapped as part of the Sajahat Formation, but in general these later rocksshow less deformation and a lower degree of lithification than those from the type locality.

A rec rys tallized qua rtzite similar to the quartzite of Pulau Sajahat was found in Public Utilities BoardTest hole No . I beneath Old Alluvium at a depth of -149 m, and a similar rock is exposed in a singleo utcrop near Tanglin (GR 46643 7). These rocks are also considered as part of the Sajahat Formation .

Content

The rocks are well lithified and vary from quartzite through quartz sandstone to argillite. Five thinsections have been prepa red from rocks assigned to th e Sajahat Formation. Two are quartzites and one is aquartz sandstone (Fig . 3.1), a ll from type locality , the fourth, also a quartzite is from a sample recoveredfrom Public Utilities Boa rd Testhole No. I at Bedok , an d the fifth is a spotted argillite from TanjongRengga m.

8

-

Quartz makes up more than an estimated 97% in the quartzites that have been sec tioned , with biotiteand a n unidentified amphibo le, possibly tremolite, making up most of the rema inder. Feldspar, usua llyrepresented only by a rat her clouded alteration product, is a lso present. The rock shows good suturedco nt acts between the grains in the purer quartz rock . In the quartz sandstone the grains are well rounded ,but poorly sorted. The quartz grains show undulose extinction in each section . Grains up to 0 .75 mm indiameter were observed.

The texture of the rocks suggests that they are ho rn felsic, and this can be explained by their proximityto gra n ite and the presence of dykes cutting the formation.

The sample from the Publi c Utilities Board Testhole No. I at Bedok is more highly altered than thosefrom Pula u Sajahat, and shows signs of shear and granulation (Fig. 3.2) as well as thermal metamorph ism .Such increase in rank is to be expected from its position close to the granite.

An argillite found at Tanjong Renggam is sheared and shows prominent spotting. In thin section therock again shows a distinct foliation, but the porphyroblasts are so strongly altered that their origin ascordierite can only be speculated from its seconda ry minerals (Fig. 3.3 and 3.4).

The rocks are well bedded, thicknesses of beds ranging from 2 cm in the finer sediments to 4 m to 5 min the quartzite. The beds are folded and sheared, with boudinage developing.

A number of dykes were mapped intruding the formation, both on Pulau Sajahat and Sajahat Kechil ,and-a long the northern coast of Pulau Tekong, but no dykes were seen in contact with the sediment on thesouth side, or at Tanj o ng Punggol. In these latter areas the bedding is more uniform and the rock less welllithified . The rock at Tanglin is well Iithified but again no dykes were seen .

Material recorded as tuff was seen in highly weathered exposures on the north coast of Pulau Tek o ngK echi! and north of Kampo ng Salabin , but no tuff was seen in fresh exposures .

Field Relations

The Saj ahat Formation is intruded by acid dykes an d basic porphy ritic dykes, somet imes carryi nginclusions of granite, in the type a rea , and is mapped as being in contact with the Palaeozo ic Vo lcanics ofeastern Pulau Tekong. The con tact between the two fo rmatio ns was not seen and the presence of thePalaeozoic Volcanics is postula ted on the identification of highl y weathered material at the eastern tip ofthe island. The bounda ry between the Palaeozoic Volcan ics and Saja ha t Formation is located by a ch angein topographic expression on Pulau Tekong. The area of Palaeozoic Volca nics shows a ro unded hill formwith the peaks usua lly below 21 m while the hill s mapped as formed of Sajaha t Formation are steeper andhave sharp ridges often ri sing to 30 m or more. .

It may be argued tha t the two formations interd igi tate and that the tuff, tentatively recognised in theSajaha t Formation, is actua lly an extension of the Palaeozoic Volcanics.

Age and Correlation

There is no direct ev idence of the age of the Sajahat Formation. It is correlated in this book withsedimentary and volca nic rocks described by Grubb (1968) from the Pengerang a rea at the southern ti p ofMalaya . Although they were not identified as such, the rocks of the Sajaha t Formation were mapped asund ifferentiated middle and upper Triassic by Gobbett (1972) . Chung ( 1973) in the 7th Edition of theGeological Map of West Malaysia excl uded Singapore but mapped the surrounding areas, those describedby G rubb (op cit) , as Permia n.

Grubb (1968) found no direct evidence for the age of the older rocks he mapped in the Pengerang area .H e m apped a belt of metasediment on the eastern side of the peninsula as older than the vo lcanics. Thevolca nics he mapped as correlatives of the ' Paha ng Volcanic Series' of Carboniferous to Triassic age.Hutchison (1973 B), later restricted tbe age of the Pahang Volcanic Series to Carboniferou s to Perma n .

In this report the Sajahat Formation is placed as older than the Jurong Forma tion because of itshigher degree of deformation, the presence of dykes within the formation which show petrographicsi milarities to th<:; dykes intruding the Bukit Timah Granite, and the evidence of contact metamorph ismwh ich has probably resulted from the emplacemen t o f the Bukit Timah Granite. The granite has beeniso topically dated as having been emplaced about 220 Ma ago.

The deformatio n of the rock indicates that it must have been deposited at leas t before the tecton is mpreceding the empl acement of the granite and thus must predate the late Palaeozoic tectonic event.

Hutchison (1973 A), in a reconstruction o f the aro system of Malaya, plots a geosynclinal trough aslying east of Bukit Timah in early Palaeozoic time and states that the subduction zo ne on the western side

9

10

~ )..~~

Fig. 3.1 Poorlv sOl'led qual'lz sandstone f ronl Pulau Sajahar.

45X Crossed Nicols

fig . 3.2 Recrvstallized quartzite o/the Sajahat FOrJ/wtionfrolll the Public Utilities

Board Test Hole No. I at Bedok .120X Crossed Nicols

----

Fig. 3.3 Well bedded and shearcd argillilc from Sajahal Formalion cxposedal Tan/ong Renggam. Plllall Tekong Besa r.

-

Fig . 3.4 Spoiled argillile / rolll Tanjong Rcnggalll. Pulau Tekong Besar.

45X Plain Polarized Lighl

I I

had migrated east to Kalimantan and the Anambas Islands by late Carboniferous time. If the deposition ofthe Sajahat Formation was in this trough, its deposition must be restricted to the early Palaeozoic .Deposition may have occurred however in the later miogeosynclinal trough lying between the upperPalaeozo ic Volcanics to the east and the granite intrusion postulated (Hutchison, op cit) as lying to thewest.

Alternatively, if the Sajahat Formation and the Palaeozoic Volcanics interdigitate, the formation isthen the time equivalent of the Paha.ng Volcanic Series.

The age of the Sajahat Formation is thus considered as probably early Palaeozoic but possiblyCarboniferous to Permian.

GOMBAK NORITE (GN)


The term norite is used here in a general sense to include the entire suite of noritic and gabbroic rocks .

A n association of noritic and gabbroic rock is found on the western side of the Bukit Timah Granite,and the unit is named from Bukit Gombak where it is well exposed in a number of quarries. Gabbro andnorite have also been reported from Pulau Ubin. Alexander (1950) reported the presence of a solitaryboulder of norite on the north coast of the island at a locality about one mile east of Tanjong Tajam. Theauthors were unable to locate any norite boulders in the area. The presence of a deep red quartz-free claysoil in the general vicinity suggests a basic parental material for the soil and thus it is suggested that anumber of basic rafts within the granite in this area have weathered to give this soil. Hutchison (1973 C)menti o ned gabbro and norite as occurring near the south coast of Pulau Ubin, but this occurrence was notrelocated .

The area of thegabbroic rocks on Singapore Island is small in comparison to that of the granite. Itoccurs adjacent to the granite and forms an alignment of hills of which Bu kit Panjang and Bukit Gombakare the most prominent. The hills form a ridge which measures some 2.5 km in length and attains amaximum width of 1.0 km. The hills support nine qu arries and they are from the north, Bluestone QuarriesPte Ltd , Lian Hup Quarry Company, Swee Construction & Company Pte Ltd, Yun ann Co Pte Ltd, GimHuat Pte Ltd , Chua Chai Seng Co Pte Ltd, Peng Seng Gra nite Quarries, Chia Oh Kang Pte Ltd and PohHua Granite Quarry Company (M a p Sheet 10) .

Chem ical analyses of a norite from Gim Huat Qua rry, and a hornblende-gabbro from Yun annQuarry are given in appendix l.

Content

The noritic body is rather variable in composition . Its overall composition can be described as rangingfrom norite through noritic gabbro to gabbro , the latter being least abundant. Noritic gabbro was found inall quarries. Norite occurs less frequently and has been sa mpled from the south and south-east faces of Yunann and Pen g Seng Quarr ies respectively. Gabbro is largely confined to the Bluestone Quarry (Hutchison.1964).

The noritic and gabbroic rocks are coarse-grained and plagioclase-rich with varying amounts of clinoand ort hopy roxene minera ls appearing as interstitial grains giving an intergranular texture. Ophitic texture ,when present , is feebly developed. Quartz has been identified in some samples of noritic gabbro and noriteobtained from Bluestone and Peng Seng Quarries . A few Oa kes of reddish-brown biotite, probabl ysecondary in origin, accompany the accessory quartz. Serpentinized crystals of olivine associated withmany opaque grains have been identified in noritic gabbro samples from the Yun ann Quarry.

The plagioclase is usually euhedral labradorite with diffuse twinning following the albite law . Thefeldsp ar is normally fresh; any significant alteration is believed to be a localized feature as only patches ofthe host rock in the Yun ann Quarry were seen showing an alteration of the plagioclase to clinozoisite,epidote and calcite. Sericitization of the plagiclase appears to be appreciable near basic and acid dykesonly .

The pyroxene minerals are represented by hypersthene and augite. Unlike the irregular crystal outlinesof the augite, the hypersthene often occurs in euhedral elongated prisms, and it is characteristically finelyfibrous. In thin section the hypersthene shows a dark grey birefringent colour. Augite is the typicalclinopyroxene. It frequently shows finely spaced lamellar structure that has been caused by the exsolutionof less calcic py ro xene. This feature is best observed in norite and noritic gabbro from Peng Seng, Poh Huaand C hia Oh Ka ng Quarries. Unlike the plagioclase, the pyroxene minerals are always altered.Serpentinization has affected many of the hypersthene minerals present in the norite and noritic gabbro of

12

--

quarries situated on the southern slopes of Bukit Gombak. Sericitization of the pyroxene minerals isseldom observed but in Yun Onn Quarry this alteration is seen together with saussuritization of theaccompanying plagioclase. The most noticeable alteration of pyroxene is to amphibo le, which formsconspicuous rims on the pyroxene (Fig. 3.5). The amphibole may be coarse or fibrous, and is usually palebrown to green. The coarse variety is generally hornblende and is characteristic of the noritic gabbro andnorite of Bluestone, Swee Construction, Yun Onn and Peng Seng Quarries. Fibrous actinolite is more oftenassociated with hypersthene and forms rims and veins on and through the hypersthene. Although pyroxenereplacement by amphibole is best observed in gabbroic rocks adjacent to the granite, such alteration ,although less spectacular, is present in all the quarries. This characteristic enrichment of amphibole reflectsa slight retrogressive metamorphism of the gabbro caused by the intrusion of the granite (H utchison , 1974).

Field Relations

The Gombak Norite lies on the western edge of the Bukit Timah Granite. Further north in lohorsimilar gabbroic bodies lie as satellite bodies along the western margin or just within the northerncorrelatives of the Bukit Timah Granite. The norite in Singapore has been penetrated by the Bukit TimahGranite and its related dykes, and zones of mixed rock associated with blocks of gabbro and norite atvarious stages of digestion can be seen in the granite (Fig. 3.6). The greatest mixing is seen in the quarries atthe sou thern end of Bukit Gombak . Acid dykes have been observed in all the quarries . A you nger set ofbasic d ykes, post dating the Bukit Timah Granite, also penetrates the Gombak Norite.

A zo ne of altered gabbro and norite characterized by hornblende gabbro has been delineated byHutchison (1964) . Such a rock is exposed behind some houses on the eastern side of Bukit Gombak (GR404504). The rock looks deceptively like a coa rse-grained, ferro mag nesian-rich granodiorite but it consistsdominantly of labrador ite and coarse pale g reen hornblende. A few of the hornblende crystals pass throughto an almost colo urless fine-grained fibrous a mphibole . Minor chlorite and sericite are also present (Fig.3.7) .

Age and Correlation

The age rela tion ship of the norite and the granite on Singapore Island has been di scussed byHutchi son ( 1964). The evidence avai lable suggests th at the norite body predates the granite batholith. Thisis suggested by the presence of many microgranite dykes cutting the no rite. These dykes often conta innumerou s basic xeno liths. Elsewhere , partially assimilated rocks of basic origin can be found in the granitequarries. These represent true hybrid rocks a nd not intermediate varieties that have crystallized in-situ(H utchison , 1964). Hutchison also points to the enrichment of hornblende in the norite which he stated wasca used by its reaction with a silica rich fluid which invaded the basic body before the intrusion of thegranite magma. This event has caused the replacement of the pyroxene in the norite by hornblende withou tal teri ng the texture .

Iso to pic ages of the Bu kit Timah Gr anite ra nge fro m 210 Ma to 230 M a . The latter provides aminimum age for the emplacement of the Gombak Nori te , and Hutchi so n ( 1973 C) suggested th a t theno rite Illay have represented part of the ophiolite suite of the lower Palaeozoic trench situated to the west ofa geosyclina l trough in which the Sajahat Formati on was deposited.

An a lternati ve hypothesis is that the Gombak Norite represents a part of the basic differentiate of themagma givi ng ri se to the Bukit Timah Grani te and th us the age o f the norite is associated with a Permian tolower Triassic even t.

The Gombak N orite can be correlated with bodies of similar rock found along the western edge of thegranite in the Malay Peninsula . Burton (1973 A) mapped several such bodies in lohor and named them theLinden Hill Gabbro, and Hutchison (1973 C) listed other occurrences on the Tembeling Ri ver and RompinRiver, Pahang, near Segamat in lohor , and on the Sungei Segamat and Sungei Simat in Negri Sembilan .

PALAEOZOIC VOLCANICS (PV)


Only three exposures of the Palaeozoic Volcanics were seen, two on reefs to the north-eas t of PulauTekong and one as a highly weathered outcrop at the eastern end of Pulau Tekong (GR 762568) . In eachinstance the exposure was small, and each showed a difference in general text ure , so no formal name ortype a rea is proposed for these rocks . The volcanics have been mapped as forming the reefs in the Selatlohor a nd the eastern 2 km of Pula u Tekong .

13

Fig. 3.5 Alteration 0/ pyroxene tofihrous all/phihole in noriticgahbro Irolll S\\' eeConstruction Quarry.

f20 X Crossed Nicols

Fig. 3.6 Grallire intruding l10rite alld('onraining xenoliths ofnorir e, Peng Scng Quarry.

Fig. 3.7 Large plates 0/ hornblende\\ ' ith augite cores inhornblende gabbro lrolll GR404504. Central Singapore.

45X Crossed Nicols

14

Content

On the unnamed reef in Selat Johor (GR 745588) the Palaeozoic Volcanics occur as a massive volcanicagglomerate crossed by well developed sets of vertical joints striking at 12SO and due north . The rockfragments embedded in the agglomerate are usually small, being less than 5 ern in diameter. On the secondreef, Malang Si Ajar (GR 766576), the volcanics are represented by a tuff. The deep weathering at the thirdsite on Pulau Tekong was such that the parent lithological texture could not be recognised.

One thin section only has been cut from the Palaeozoic Volcanics, and this is from the volcan icagglomerate. It shows a lithic tuff with andesitic fragments set in a ground-mass of irregular feldspar laths,glass and opaque ore, much of which has limonitic rims. Diaspore is also present in high concentration s,particularly in the lithic fragments.

Field Relations

The Palaeozoic Volcanics are not seen in contact with any other rock type in Singapore unless tuffsrecognised along the north-west coast of Pulau Tek ong are considered as part of the same formation. Th isis discussed more fully under the Sajahat Formation . The boundary between the Palaeozoic Volcanics andthe Sajahat Formation is mapped on topographic grounds and is discussed in the section on the SajahatFormation .

Age and Correlation

There is no direct evidence for the age of the Palaeozo ic Volcanics in the area mapped . Grubb (1968)mapped andesite and tuff on the eastern side of Sel at Joho r through to the east coast of Malaya where it ISintruded by granite. He recognised two types of tuff which he termed 'a shy tuff and 'agglomeratic tuff andalso recognised a metamorphosed zone extending up the eastern side of Selat Johor in which pyrophyl liteand diaspore occur as alteration products in the tuff. The Palaeozoic Volcanics are thus mapped as anextension of Grubb ' s 'Volcanic rocks' which he assigned to the Pahang Volcanic Series which are gin;n asCarboniferous to Permian in age in the more restricted sense of Hutchison (1973 B).

If it is assumed that the granite intruding the andesite is the same as that collected from Bukit La nchuand Bu kit Timah in Johor and Singapore respectivel y and dated as having been emplaced approximateh220 Ma ago (Hutchison, 1973 C), the age of th e andes ite and tuff can be restricted to the Perm IJn Carboniferous. Grubb (0(1 eil) considered the tuff to be yo unger than the andesite but made no sugges ll<-,nof any lime IIlterval between the two , so the age Permian -Carboniferous cannot be refined further for thc'setypes fo und in eastern Singapore.

From Hutchison's (1973 A, Fig . 5) palaeo-tectonic sy nthesis, the Pal aeozo ic Volcanics would apre~l r

to represent the volcanic arc rocks to the south-west of the subduction zone in the Natuna Island s.

BUKIT TIMA H GRANITEDefinition

The term granite is used here In a general sen se fo r the entire suite of acid rocks including grani te.adamellite and granodiorite, and the acid and intermedia te hybrids mainly of granodioritic and dior lt lccomposition, resulting from the assimilation of basic rock within the granite.

The Bukit Timah Granite for the purposes of discuss ion in the Report is divided informally into tIl 0

groups. The first group, the Central Singapore Granite , lies to the west of a line running from Siglap toPunggol, and the second group, the Pulau Ubin Granite, lies to the east of it. The Pulau Ubin Graniteappears to be richer in ferromagnesian' minerals and may have reached a more advanced stage ofhybridization. Insufficient data has been collected to date to separate the two groups formally, and they arenot distinguished on the map sheets.

Chemical analyses of rocks of the Bukit Timah Gra nite, and inclusions and dykes within the grani teare gi ven in Appeqdix I.

CENTRAL SINGAPORE GRANITE (BT, BTh, BThy, BTh)

Distribution

The Central Singapore Granite occupies an area in the centre of Singapore Island extending some 8km in a northerly direction and 7 km in a westerly direction where it forms hills and valleys of both highand low relief. Over most of the area the hills are less tha n 60 m high. Near its contact with the Gomb ak

15

Norite however , the granite forms steeper and more promi nent hills rising to a maximum height of 166 matBukit Tima h Hill. Less extensive areas of the Central Singapore Granite occur in the vicinity of BraddellHeights Estate, Kampong Woodleigh, a nd a ro und Seletar Airbase near Sungei Punggol.

The Central Singapore Granite is well represented by the rocks exposed in the nine quarries located onthe slopes of prominent hills to the eas t of the Gombak Norite. The Seng Kee Granite Quarries Ltd, theH o usin g Development Board Quarry, the Singapore Granite Quarry (Mandai) and the Public WorksDepartment Qua rry (M a ndai ) a re established in the Mandai Hills. On Bukit Timah Hill , the Public WorksDepa rtment Rura l Depot Qu a rry, the Singapore Granite Quarries Ltd (Bukit Timah), Hindhede agdCompany a nd Sin Seng Granite Company a re foun d . T he Swee Construction Quarry is established onBukit Batok. Samples ta ken show th a t granite in its restricted sense is the most common rock found in allthese qua rries excepting Seng Kee, Housing Development Board , and the Swee Construction Quarries,where g ra nodi orite is predomin ant. Porphyritic micrograni te has been sampled from the Singapore GraniteQua rry (Mand a i), Public Works Depa rtment Rural Depot Quarry and the Sin Seng Quarry, Adamellitehas been loca ted only in the Public Works Department Quarry (Mandai) .

Away from the qu a rries, outcrops of the Central Singapore Granite a re rare, the presence of granitebeing indicated by wea thered residua l boulders on the undulating terra in , particularly north of MandaiRoad , a nd b y cores of granitic rock s obtained from drill holes . Boulders of g ranodiorite are discoveredalong Marsiling Road in Woodlands (GR 428591 ) and in recent excavation between Sungei Kranji andWoodla nd s Road (GR 396571) . Boulders of hornblende-biotite granite have been found in a smallabandoned quarry off M andai Road (G R 461568) and on to p of a cleared hill near Sembawang Circus (G R48 1531 ). The small qua rry off Manda i Road is assu med to be the quarry described by Scrivenor (1924) asyieldin g a gra nite wi th abunda nt dark mica , with hornblende, which so metimes showed a core of pyroxene,and feldspar, together with a fai r amount of quartz . Fine-gra ined and pink-spotted adamellite rock chipshave been recovered from a depth of 6 m from a shallow d rillhole beside Track 24 off Yio Chu Kang (G R491540), an d abo ut I km wes t of the contact with the O ld Alluvium .

H ybrid rocks associa ted wi th the Centra l Singapore G ranite a re we ll exposed in the vicinity of thegabb ro-granite contact. Near this con tact numerous xenolit hs va ryi ng in their stage of hybridizat ion can befound in microgranite dyk es. In Swee Constructi on Quarry at Bukit Batok, hybrid inclusions of quartzdiorite occu r in granodio rite . These inclusions a re spotted with da rk min erals, a nd are finer gra ined tha nthe coarse grain ed granodiorite host rock .

Alexander (1950) recorded hybrid rock of diori tic composition o n 8ukit Panja ng and 8ukit Gombak,a nd on the site of the municipal flats at Monk' s Hill (GR 495450) . Monk 's Hill was removed forrecl a im a ti o n, but the other occurrences were confirmed during this sur vey.

Content

Granite , adamell ite, and granodiorite together with va ri ous hybrid rocks are found in th e area . Theirboundaries have not been mapped because it is difficult to do so due to the limi ted extent of the outcropsa nd to gradat iona l va riation s in the distribution of quartz, alkali-feldspar. sodic plag iocl ase, and theferromagnesian minerals.

Granite

The granite is generally light grey and medium grained, with gra in sizes measuring from 3 mm to 5mm. Th e main minerals can be distinguishe~ easily by the naked eye. Qua rt z, which often accounts for 30%of the minerals present, has a glassy g rey appearan ce and a rough surface. It occurs interstitially to thefe ldspar c rys ta ls a nd has interlocki ng bo unda ries with them. Feldspa r is the most abundant mineral in thesample and often constitutes 60% to 65% of the rock. It is commonly cream in appearance with the moreweat hered o nes being pa le to brownish yell ow. The pink va riety of orthoclase is present in granite of thePubli c Works Department Quarry (Mandai) and in granite boulders nea r Sembawa ng Circus (G R 481531) .Biotite and hornblende, which make up the remaining co nstituents, are easily recognised by their darkbrown co lour a nd by their cleavage.

Microscopically the granite consists predomin antly of quartz, varyi ng amo unts of alkali-feldspar, a ndacid plagioclase, with subordin a te amo unts of biotite an d hornblende .

Qu a rtz occurs mainly as anhedra l grains interst itial to the feldspar and the ferro magnesian minerals ,a nd less frequently as excellent loba te intergrowths in al kali feldspar. Such texture is well developed ingra nite and po rph y riti c microgranite sa mples from the Hindhede a nd Sin Seng Quarries only.

The a lk ali feldspar is frequently a microperthitic orthoclase. It occurs as anhedral or, rarel y, assubhedra l grai ns. The exsolution texture of the mine ral is best seen in the less a ltered grains of the granite

16

rr

from Hindhede and Sin Seng Quarries. In these same rocks the remaining orthoclase is extensively cloudedwith very fine-grained opaque dust. In rocks obtained elsewhere the orthoclase is comparatively lightl yaffected.

The plagioclase is somewhat variable in composition , ranging from oligoclase to andesine, but is morefrequently oligoclase. Andesine is present in the porphyritic microgranite from the Singapore GraniteQuarry (Mandai) . In Seng Kee Quarry, the plagioclase is albitic in composition (Hutchison, 1964) . Crudeoscillatory zoning of the mineral has been observed in the porphyritic microgranite of Singapore GraniteQuarry (Mandai) and in the pink hornblende-biotite granite from Sembawang Circus (G R 481531). One ofthe plagioclase phenocrysts present in the porphyritic microgranite from the former locality contains smallcrystals of hornblende. A ring of sericite flakes has formed as a replacement after a zone within the feldsparphenocryst (Fig. 3.8). It was possibly derived from basic rock during intrusion of the Bukit Timah Granite .Deuteric alteration of the plagioclase to calcite is infrequent, but sericitization is evident in many of therocks . Such alteration of the plagioclase is most widespread in the granite of Hindhede and Sin SengQuarries . In the rocks from these quarries, the alteration has produced a very dense concentration ofsericite in the cores of the plagioclase.

The most common ferro magnesian mineral present is reddish-brown biotite with hornblendeoccurring in sub-ordinate amounts. Much of the biotite is in part chloritized. The most severely alteredferro magnesian minerals are to be found in the granite of Hindhede Quarry, and the granite andporphyritic microgranite of Sin Seng Quarry. In these rocks the biotite has been replaced around the rimsand along the cleavage by a mass of unidentified brown cloudy material, sericite and chlorite. In additionmuscovi te may occur as pseudomorphs after biotite. The presence of secondary muscovite aspseudomorphs of biotite, and the extensive alteration of microperthitic orthoclase, oligoclase, and biotitefound in the rocks from the Hindhede and Sin Seng Quarries may have been caused by an episode ofminera lisation that has been responsible for the emplacement of veins of quartz, molybdenite and pyrite .and probable bornite. seen in these two quarries.

The usual accessory minerals in the granite are apati te and zircon. A few grains of epidote are fou ndassociated \\ith calcite in oligoclase in the porphyritic microgranite of Singapore Granite Quarry (Mandai) .Epidote in biotite has also been identified in the granite near Sembawang Circus (G R 481531).

Ada/lle/fire

In the field adamellite is indistinguisable from grani te and thus cannot be mapped separately. It hasbeen recognised in thin-section and so warrants a separa te description. It is distinguished from granite Ifbetween one third and two thirds of its feldspar is alka li.

The adamellite from the Public Works Department Quarry (Mandai) is characterized by blobs ofquart z in crudely developed myrmekitic intergrowths. T he rock chips of adamellite from a drillhole off YioCh u Kang Road consist predominantly of quartz and sericitized oligoclase, with lesser amounts of cloud edalkali feldspar and green chloritized biotite. The la tter is associated with some black opaque grains

Granodiorire and Diorite

There are gradational changes from granodiorite to diorite. Rock with an alkali feldspar content ofless than one third of its total feldspar content is called a granodiorite.

It is believed that the granodiorite is a product o f hybridization of granite and basic rock . Thisstatement is supported by field evidence in many quarries where basic rock can be seen in different stages ofassimilation within the granite (Fig. 3.9).

In th e granodiorite from Seng Kee and the Housing Development Board Quarries much of the bioti teis in part chloritized. Similar rock from Marsiling Road consists of anhedral quartz, clouded microperthiticorthoclase, sericitized plagioclase of oligoclase to andesine composition, some of which exhibit zoning. andsubordinate amounts of well developed brown biotite flakes which are often chloritized in part.

Granodiorite from the Kranji area (GR 396571) contains quartz and plagioclase of oligoclase toandesine composition. The crystals are often crudely an hedral in shape, and the feldspar has been slightlysericitized. Orthoclase is present in subordinate amounts and appears interstitially . Green hornblendedominates over partially chloritized brown biotite.

In hand specimen, the granodiorite from Marsiling Road and Kranji appears darker than that fromthe Seng Kee and Housing Development Board Quarries, and is seen in thin-section to contain moreferromagnesian minerals.

T he rock from Monk's Hill was described by Alexander (1950) as a diorite consisting of xenomorphicquart z grains containing inclusions of oligoclase, biotite and amphibole, and minute needles which were

17

18

Fig . 3. 8 Zoning in andesine. S ericit e al ter a ::one within the plagioclase inporph\"fitic /IIicrogranite. Singapore Granite Quarry ( Mandai ).

45 X Crossed S icols

Fig . 3.9 Rounded. well assi/llilated hasic inclusions In ada/llellite. Public Works

Depart/llent Quarry ( Mandai ).

......

T

thought to be apatite. She stated that the larger quar tz gra ins did not carry large inclusions, but that the segrains were usually rimmed with indistinct bands of small feldspar, b iotite and amphibole crystals.

The granodiorite rock In Swee Construction Quarry, Bukit Batok, consists of sericitized andesine ,ljuart z, subordinate orthoclase, red-brown biotite , whic h is usually in clusters, and pale green, local lyfibrous, amphibole. Hutchison ( 1964) noted that this gra nodiorite was foliated . He delineated a zone offoliation adjacent to and east of the altered zone o f gab bro and norite.

Field Relations

The contact at its western edge between the Central Singapore Granite and the Gombak Norite is notexposed. However, there is sufficient evidence within qua rries in the noritic body to establish the fact th atthe granite is younger. This has been discussed under Gombak Norite .

The contact between the granite and the Triassi c sediments is also hidden. Alexander (1950) describeda core boulder of granite some 60 cm from the granite boundary which she interpreted as a residual from anintrusive d y ke. The Geological Unit suggests that th e relict boulders observed by Alexander was not in Silll

in a dyke but was deposited in weathered granitic material at the base of the Triassic sedimentary pi le.

INCLUSIONS IN THE CENTRAL SINGAPORE GRANITE

Definition and Distrihution

Inclusion s are basic xenoliths with distinguish able boundaries that can be seen floating in the granit icrock.

Numerous ovo id shaped inclusions which appear darker than the granitic host rock, have beenobserved in the Public Works Departmen t (Mandai) an d Sin Seng Quarries (Fig. 3.9) , and in residu alboulders remote from the granite-gabbro contact at Kra nji (GR 396571) and Woodlands (GR 42859 1)

Composition

l ncllhions of hyb rId rock from the Swee C o nstruct ion Quarry (Bukit Batok) contain euhedr alplagi oc la se In a grou ndmass o f anhedral ljuart z, heav il y se ricitized in places. a nd numerous reddish bro\\ nb iotite Il~lkes. T he biotite tend s to be co nside rabl y co arser grained than the feld spar and ljuartz, and IS

widel y altered to chlorite and associated opaque grains .

The fain t o\oid inclusions found in the Public Works Department (Mandai), and Sin Sens Quarri eshave been referred to as quartz monzonite by van Bemmelen (1940) and Hutchison (1964) .

DYKE ROCKS ASSOCIATED WITH THE CENTRAL SINGAPORE GRANITE

Classification and Distrihution

Dykes associated with the Central Singapore Granite are divided into two groups, one with acid andthe other With basic affinities.

There are four varieties of acid dyke: microgranite, granite porphyry, granophyre, and trachyte. Themicrogranite forms the most conspicuous dykes an d is co mmon in the norite of Chia Oh Kang , Peng Se ngand Lian Hup Quarries . Far less conspicuous than the microgranite are the granophyre dykes cutting th enorite bodv in Peng Seng, C hia Oh Kang. and Yun O nn Quarries, and the granodiorite at the Sw eeConstruction Quarry. The granophyre is only slightly lighter in colour than the dolerite and may therefo rebe mistaken for dolerite in the field. Granite porphy ry dykes have been found in the Hindhede and theSingapore Granite (Bukit Timah) Quarries only cutt ing t he Central Singapore Granite. Trachyte has beenrecogni sed cutting granodiorite in the Swee Construction Quarry, Bukit Batok. Like the granophyre, thi Srock is also deceptively like dolerite in hand specimen .

Basic dyke s, mainly dolerite, have been observed cu tting the Gombak Norite in Bluestone, Poh Hua.Chia Oh Kang, Chua Chai Seng, and Lian Hup Qua rries and the Central Singapore Granite in theSingapore Granite' ( Mandai) , Swee Construction (Bukit Batok), and Public Works Department MandaiQuarries . One dyke in the Public Works Department Qua rry at Mandai has been identified as a spessartite .

Further north . a set of deeply weathered dykes is exposed in an excavation between Sembawang andWoodland s (G R 450611). The dykes are weahtered to a deep red clay in contrast to the pale browni shye llo w coarse sandy cla y soil derived from their granite host (Fig. 3. 10). Two other deeply weathered dyk eshave been mapped along the eastern edge of the granite, one in the Whampoa Valley and the other justno rth of the Uppe r Ka!lang Valley.

19

A spessart it e intrusive into quartz mica diorite was recorded from Seletar by Scrivenor (1931). He a lsorecorded bou lders of dolerite and quartz porphyry associa ted with andesitic ash nea r the junction ofOrchard and Grange Road. None of these rocks could be reloca ted.

Composition

Dykes of acid aflinill (Da. Dp. Dg. Dt )

In hand specimen, the microgranite is distinguished by its fine-grained, Iightcoloured appearance, andin the case of the g ra nite porphyry, by the quartz phenocrysts which can be di sti nguished as crystals up to 2mm in size.

The main minerals in the microgranite dykes (Oa) a re quartz, orthoclase, plagioclase of albite tooligoclase composition, and biotite. No hornblende has been identified . The orthoclase is heavily clouded ,and the ac id plagioclase is often crowded with individual sericite flakes. M a ny of the biotite minerals arechloritized, and epidote or sphene occurs occasionally.

The granite porphyry dykes (Op), found intruding the granite at the Hindhede and Singapore GraniteQuarries in Bukit Timah, have a distinctive porphyritic appearance in the field . Phenocrysts of quartz andacid plag ioclase up to 2 mm long are set in a fine-grained gro und mass consisting of clouded orthoclase andfeldspar, quartz, an d subordinate muscovite (Fig. 3. 11). At its contact the dyke rock shows excellentmicrogra phic interg rowths between feldspar and quartz . The dyke in the Singapore Granite Quarry is moreseverely a lte red than that in the Hindhede Quarry. It co nta ins more phenocrysts of sericitized acidplagioclase, and numerous tiny flakes of muscovite in a finer-grai ned g round mass.

The g ranophyre ( Og) is often feebly porphyritic. Un der the microscope it can be seen to containeuhedral acid plagioclase which is often heavily sericitized a nd replaced by calcite. Its groundmassinva ri ably cons ists of radiating struc tures of slender feldspa r and qua rtz (Fig. 3. 12). Small irregularlyshaped ch loritized g reen hornblende is present elsewhere in the ground mass.

The trachyte (Ot) in Swee Construction Quarry in Bukit Ba tok looks deceptively like a dolerite in thefield. Microscopically, this rock is composed of narrow elo nga te prisms of clouded acid plagioclase and afew patc hes of quart z . A few of the tabular feldsp a r phenocrysts are heavi ly dusted with fine-graineda lterati o n products . and there is widesp read fine-g rained chlor ite with min o r epidote a nd a few sericitepatches in the rock (Fig . 3. 13).

Dikes of basic a ffinity ( Db. Dd. Dsp )

The dolerite is da rk g reen and possesses a fine-grained groun d mass . It is generally porphyritic:plagioclase and augite occ ur as the phenocrysts. The plagioclase ra nges in composition from labraqorite toandesine. and is freq uentl y altered to se ricite . The g round mass is made up of al tered small pl ag ioclase lath sa nd numerous small crys tals of colourless augite and ab unda nt calcite (F ig. 3.14). Ilmenite, sphene.magneti te, epiodote, a nd sericite a re common secondary minerals.

The augite phenocrysts a nd plagioclase phenocrysts occur in dykes found in Singapo re Granite(Mandai) and Bluesto ne Quarries, a nd in the former , o liv ine is also present in the gro undmass.

In the more severely altered dolerite present in the Poh Hua, Lian H up . Swee Construction (BukitBatok). and Chua Chai Seng Quarries, most of the augite has been repl a ced by pale g reen actinoliticampnibole.

The spessartite (Osp) from the Public Works Depa rtment Qu a rry (Mandai) possesses apanidiomorphic texture typical of lamprophyres. It contains numerous well-formed small crystals of augiteand sma ll nakes of red -brown bi o tite set in a base of larger irregular crysta ls of sericitized andesine. Thereare numerous irregul a r patches of calcite and numerous tiny needles of apatite (Fig. 3. 15) .

Field Relations

R e lations between the mic rogranite, granophyre and dolerite d ykes were see n in Chi a Oh Kang andPeng Seng Quarries. A 25 m wide microgranite dyke intrusive into norite could be followed from Chia OhK a ng Quarry through to Peng Seng Quarry. In Peng Seng Quarry, a granophyre cuts this microgranite as asi nuou s dyke some 2 m wi de, and in Chia Oh Ka ng Qua rry, a dolerite dyke cuts the microgranite (Fig .3.16).

In Chua C hai Seng Quarry a set of dolerite dykes appear to be mapped as termina ting against agranite dyke. This feature is apparent. The granite dyke has been undercut from the north and the doleriteis exposed at a lower level than the granite on the south side. A fault along the northern side of the granite,shearing the granite, has removed the dolerite from the north.

No observati ons were made within the Central Singapore Granite on the relative ages of the trachyteand granite porphyry.

20

3.10 Wearhe red basic dy ke in granire soil, Admiralt\ , R oad (GR 45061 I ),

No rrh Cen tral Singapore.

' It/:.;

Fig . J.tl Phenocrysts of rounded quartz and sericitized acid plagioclase in granite

porphyry. Hindhede Quarn·.

45X Crossed Nicols

.j

21

Fig. 3 . 12 Radiaring sr ru c rure ojslender feldspar and quarrzin g ranophl/re, Yun OnnQuarry.

120X C rossed N ico ls

Fig. 3.13 Suhl}(J rallel alignmenr O!

acid plagioclase la rhs inrmehl ·rf. S\I 'ee Consrl'lleriollQuarry ( Bukir Bawk ).

';5 .\ Cro.lsfd Sim/.1

Fig . 3. 14 Alrued calcic plagioclase ,smaller aug ire crysrals, andoccasional quarrz in alrereddol e r ir e f ro m S \I ' e eConsrf/lcrion Quarry ( BukirBawk ). Th e habir 0/ augiteis in m ark ed conrrQst lVirhrheH of rh e younger doleri{(!c urrin g rh e Jur o n gForl/wrion ar Pulau S f nang .

45 X Plain Polari::fdLighr

22

Fig.3 .1 5

45X Plaill Polari::ed Lighl

Fig. 3.16 Dolerile cUlling 25 III Ivide lIIicrogranile drk e in noril e, Chia Oh KangQuarn '. Th e rellolVish-brOlVn coloralion is a slain on Ih e acid dd , e alld Ih E'noril e.

PULAU UBIN GRANITE (BT, BTh, BTh, BThy)

Distribution

The second group of the Bukit Timah Granite occurs to the east of the line running from Siglap to

Punggol.

On the Main Island the granite was found outcropping along the beach from Fairy Point to ChangiJetty (Fig. 3.17). A deep drill hole through the Old Allu vium just north of Tampines Road (GR 634516)penetrated the Bukit Timah Granite at -54 m. Other outcrops occur on Pulau Sekudu and Pulau Ubin,from which the group is named.

Adamellite was found in the drillhole already mentioned (GR 634516) at -76 m, and a hybridgranodiorite was found in the Lian Moh, Lip Seng and Gim Huat Quarries. These quarries are on PulauUbin. Further granodiorite has been sampled from a low hill to the north-west of Sungei Jelutong, and anoutcrop at the headwater of Sungei Pulau Ubin.

Content

Granite

The Pulau Ubin Granite shows some distinctive differences when compared with the CentralSingapore Granite.

The rocks are generally richer in green hornblende and brown biotite than those from the CentralSingapore Granite. These minerals occur in clusters .

The impression one gets from hand specimen is confi rmed under the microscope. Hornblende andbiotite are the dominant ferromagnesian minerals, and occur as rather small irregular crystals spotted withopaque grains which are probably magnetite . Microperthitic texture of the orthoclase and heavysericitization of the plagioclase are prominant , but chlori tization of the biotite are comparatively rarewithin the Pulau Ubin Granite. The occurrence of allani te. pyroxene grains. and abundant magnetitegranules as accessory minerals in the Pulau Ubin Granite is yet another distinctive feature .

The granite on Pulau Sekudu is distinguished from the others by its strongly porphyritic texture withpink euhedral orthoclase crystals up to 4 cm in length set in a coarse grained groundmass. As in the othergranites. this rock also contains clusters of ferromagn esia n minerals.

Adallie /li te

The adamellite consists predominantly of quartz and clouded orthoclase in graphic intergrowth .Oligoclase occurs as euhedral phenocrysts up to 4 mm in length and also subhedral to anhedral forms in theground mass . The feldspar has been slightly sericitized on ly.

The only mafic mineral present is some irregularly shaped green hornblende. Much of the hornblendehas been chloritized. and epidote is often associated with the altered hornblende.

H l'brid rocks

A granodioritic rock from the Lian Moh Quarry area appears in hand specimen very much like thecoarse-grained granite by containing numerous clusters of ferromagnesian minerals. In thin section therocks all show a consistant mineralogy and texture . The light coloured minerals are andesine, in placesstrongly zoned, interstitial quartz, and orthoclase which occasionally form large irregular plates enclosingplagioclase grains. Some of the orthoclase crystals have irregular margins and may have been corroded.Other minerals are large Oakes of brown biotite and numerous crystals of hornblende, and the two areoften associated in clusters. Many of th.e hornblende crystals have irregular cores of pyroxene, while a fewgrade into pale amphibole (Fig. 3.18). Accessory minerals are magnetite and apatite, and rare sphene.

The rock obtained from the low hill at Kampong Jelutong is more aptly called a quartz diorite and it isprobably gradational to granodiorite. Under the microscope, anhedral oligoclase and quartz occurring asphenocrysts are seen. Clouded orthoclase, ragged green hornblende, and brown biotite are present in theground mass. Biotite occurs as dense irregular clusters of s maller crystals, and it is in places accompanied byabundant tiny opaque grains. Magnetite , sphene, and apatite are common accessories.

Precise comparison of this rock with the hybrid granodiorite obtained from Lian Moh and Lip SengQuarries is uncertain, but it appears to be similar in co mposition and shows the same tendency for theferromagnesian minerals to occur in clusters, but pyroxen e has not been recorded in the quartz diorite.

24

(

L

Fig. 3.17 Olilcrop oj' granile aI Changi. Pegillalil e veins(nol visihle in pholOgraph ) are fO llnd in IhisOlilcrop. (GR 653540 )

Fig.3.18 Large plales ofhornblende conlaining pyroxene in hrbrid granodiorilejrolilLian Moh Quarr\' , Pulau Ubin .


25

The pa rtially mixed hybrid rocks found in the Housi ng Development Board Quarry a nd Lee Hun gC heng Quarry can be compared to that from Northolt Road, Changi. There the granodiorite containsirregular agg rega tes of tin y flakes a nd prism s of biotite and ho rnblende associated with numerous opaqueg ranules (Fig. 3. 19). They a re poss ibly remnants of original basic rocks now dispersed through the pa rtl yhybridi zed g ranodiorite . Other minerals present a re albite, quartz, and orthoclase.

Field Relations

The Pul a u Ubin Gra nite is not seen in contact with the Sajahat Formation . It is believed however thatthe gran ite belongs to the sa me intrusive suite as the Central Singapore Gra nite . A number of discretebodies o f o lder rocks were seen however incorpo rated within the Pulau Ubin Granite and theirrel a tion ships are di scussed in the next section.

Alexander (1950) noted that the granite from Pulau Sekudu is not metamorphosed whereas sheco nsidered that on Pulau Ubin to be metamorphosed , and she suggested that the porphyritic granite ofPulau Sekudu is therefore younger and may be responsible for the metamorphism she recognised in theigneous rocks of Pulau Ubin .

INCLUSIONS IN THE PULAU UBIN GRANITE

Definition and DistributionInclusions ha ve been found throughout the granitic and granodioritic host rock s on Pula u Ubin and a t

C hangi . Th ey va ry greatl y in size, ranging from less than I cm in diameter to tens of metres across . Th ela rge inclusions have rendered geological interpretation particularly diffi cult in the past as rectangul arshaped slabs of foreig n rock a re o ften exposed withou t a b reak in their contin uity on a quarry face, andha ve thus been mistaken for d ykes o r even as the host rock . An incl usion can ass ume such a dimension th atit canno t be app reciated read ily, and hence may be dismissed erro neously as the host rock .

Some inc lusions and dyke like bod ies exposed in diffe rent faces of the H o using Development BoardQuarry show identica l texture and mineralogy, a nd they und o ubtedly o r iginated fro m the sa me parentmater ial. These dyke-like masses are often ve ry steeply dip ping, a nd although this or ienta tion is typica l ofdykes , they can be recogni sed as inclu sions beca use adjacent bodies of these masses ca n be seen to fi ttoge ther if the interve ning g ra ni te we re rem oved (Fig. 3.20).

Composition

T he variations in the minera logy and texture found in the inclusions ha ve given rise to the diversity ofrock na mes proposed by the previous investigators. Thi s is perhaps inevitable since the inclusions representva ri o us stages of modifica ti o n of country rock by an acidic magma .

For the purpose of di sc ussion, the inclusion s have here been classified into two g ro ups according to thep resence o r absence o f pyroxene minerals in them . Two text ura l di visions are recogni sed within each g roup ,those showing a gra no bl astic texture a nd tho se with out.

The g ra nobl ast ic texture o f the rocks described is consi dered to be caused by high temperature contactmeta morphism.

Most of the inclu sio ns seen within the granite on Pulau Ubin and at Changi represent bodies of basicroc k. Ass imila tio n has in some insta nces continued un til a g ranitic hybrid magma carrying sma ll clusters offe rromagnesia n min e ra ls (Fig . 3.2 1) as the only inclusio ns came into existence. The incorporation ofPal aeozo ic sediment is infe rred from the appearance of ga rnet and the absence of pyroxene in so me of theinclusion s. From the presence of biotite and quartz , and from the assemblage of plagioclase-hornblendediopside, often assoc ia ted with mag netite, apatite, and sphene as minor con stituents , it is taken that someinclusio ns are dervied from a ndesi te.

In clusions of rocks containing prroxene

The mineralogy o f these rocks is characterised by the presence of augite, with or without enstatitie orhype rst hene, and pl ag ioclase of oligoclase to andesine co mposition , orthoclase, quartz, hornblende andbi o tite in varying amounts. Phenocrysts of plagioclase a re fairly common, but a ugite phenocrysts arere la tive ly rare. Numerous green hornblende and brown biotite are present, generally as well-developedcrysta ls, but in those rocks th at show a granoblastic texture, the hornblende and pyroxene frequentl yap pea rs as small pri sma ti c crystals or as needles, the biotite occurs as small flakes or in clusters (Fig. 3.22) .Quartz and o rthoclase a re ab und an t only in the hornfelsic varieties. The common accessory minerals aremagnetite, apat ite a nd sph ene.

26

i~,- ' t;:':'

Fig . 3. 19 Dense clusters of biotite, hornblende, and opaque grains of magnetit e ingranodio rit e, Changi.

!20X Plain Polariz ed Light

Fi g. 3.20 Dl'ke-/ike inclusions in the Housing DevelopII/ent Board QuarrJ' , Pulau Ubin.

27

28

."~ ..:.. (f ~ \ t. '\ ;:'

~ ~ ~ " ... , '~-'" .· ~Sl~-:--"'"~:~~ I~>~'<' '~r;;'~~ .;. ,<,~', , ' . ~~~'\.~'~~.' ..~~_'"~"~-1,. ~" :1 ~ . ...--.. -'?"Jf: ..J'. ~~ . ~~~ . :..' '~~ .

V:.:...~. ,~'~' , 9:, r ~ . •' ~ . <" ::' .. ' ,~ " " • •~ . -~" .~ ', ·f;. '- 0& '" '* . ~ . - • w, • . ~ <.

'..,: ....'"1<1; , '; '/ i • -'~~\> -" A,: . ..:', , ." "" ..j " ._ ..,:..,

Fig . 3.21 Clusters of hornblende and biotite associa ted with accessor\' allanite inbiotite-hornblende granite frOIll Kampong Mamam . Pulall Ubin,

45X Crossed Nicols

Numerous stubbl' prisms of prroxene grains and dense cluster of brownbiotite in hrpersthene hornfels. Kalllpong Jelutong . Pulall Ubin,

45X Plain Polarized Light

Inclusions 0/ rock s without p vroxene

Inclusion s th a t do not contain pyroxene minerals a re simil a r in ha nd specimen to those that do. Theygenerall y con sist of a fine mosaic of quart z a nd fel d spa r as anhedral gra in s, varying amounts of sma llprism s of green hornblende and, frequently, tattered brown biotite nakes. The ferromagnesian mineralsoccur as individual crystals or associated in clusters . The occasional phenocrysts are usually of quartz a ndfeldspar with irregular crystal outlines. Common accessories are magnetite, apatite, and sphene. Garnetoccurs in some inclusions of this group (Fig. 3.23).

Field Relations

The presence of numerous dark inclusions or la rge masses of different hues , shapes, dimensions, a ndmin era logy in the granitic host rocks has presented an aura of complexity on the geology of Pulau Ubin .

The dyke-like masses are often very steeply dipping, and although thi s orientation is typical of dykes ,thei r mode of occurrence on Pulau Ubin may be explained by the incorporation of slabs of basic rock in arelatively immobile acid magm a . This setting is suggested by the linear arrangement of disjointed slabs seenfrequently on Pulau Ubin. The opposite edge of adjacent inclusions can be seen to fit if the interveninggranite were removed (Fig . 3.24). Such a fractured slab could easily be misinterpreted as a dyke if itappeared without fractures in the confines of the exposure.

DYKE ROCKS ASSOCIATED WITH THE PULAU UBIN GRANITE

Distribution

D ykes can be seen cutting the Sajahat Formatio n in the type area for this formati o n a nd alon g theno rth-east and east coast of Pul a u Tekong Kechi!. Two parallel dykes are a lso exposed , now surrounded byrecent beach sand, on the south coast of Pulau Tekong . On Pulau Ubin itsel f. dykes have been seen cuttinggra nite on a po int 0.5 km to the north-ea st o f T anjong T aja m a nd in Aik Hwa Quarry No I.

Composition

Dy k es 0/ acid a ff inity ( Da )

Sc ri ven o r ( 193 1) described acid dykes of apli te, acid gra nite, g ranophyre and ho rnblende-gra n itea pl ite on Pul au U bin. He mentioned that they rep resen t the yo un gest ph ase o f igneous ac ti vity . The dykeswere observed by him to cut o ld er dykes o f enstat ite-spessa rt it e, ho rn b lende po rph yry and ho rnble ndegrano phy re in the a rea . Vein s o f pyroxene mi c rog ran ite have a lso been reco rded by Sc ri venor ( 1931 ) tooccur a t Lian M oh Quarry and at Tanjong Jeluto ng.

An acid dyke has been mapped by the Geological U nit as intrusi ve into Palaeozoic sediment on PulauSajahat Kechil where it has been cut by a basic dyke . No thin section o f this acid dyke was prepared .

Dy k es o/ basic alfinit)' ( Db )

The basic dykes are genera ll y dolerites and la mproph yres. Dolerite dykes are observed on Pul a uSajaha t Besar and Sajahat Kechi!.

Most of the do leri te is porphyritic, with phenocrysts of severel y altered plagiocla se. The ground mass isma de up of less a ltered small plagioclase la th s, and numero us sma ll c rys ta ls of colourless augite a ndoccas ional quartz a re found interstitially to the plag ioclase . The compositio n of the plagioclase ranges fr o ma ndesine to labradorite. In the more severely a ltered d o lerite, most of the a ugite is replaced by pale greenactin o litic amphibole . Such amphibole is abundant in the dolerite dyke exposed in the south of Pula uSaj a hat Besar. Ilmenite, sphene, magnetite , epidote, calcite and sericite are very common second a ryminerals found in the dolerite.

The north-trending dyke on the west coast of Pulau Sajahat Besar is a porphyritic microdiorite . Itcontains phenocrysts of plagioclase and a few corroded quartz crystals set in a fine-grained feldspathicground mass . There are no ferromagnesian phenocrysts but the biotite and hornblende are widespread ,both as isolated small crystals or in irregular clusters . Apatite and magnetite are the common accesso rym inerals. Inclusions of granite up to 20 cm in diameter were seen in the dyke on Pulau Sajahat Besa r.

Scrivenor (1931) described a quartz norite in what is now the Housing Development Board Quarry onPulau Ubin . These rocks have not been sampled but the Geological Unit is of the opinion that theyrepresent rafted basic bodies.

The occurrence of lamprophyre dykes on Pulau Ubin and Changi have also been described byScrivenor (1931). He described dykes of enstatite-spessartite cutting the granite at Tanjong Balai, in what isnow the Housing Development Board Quarry on Pulau Ubin, and at Changi . According to Scriven or,vogesites intrusive into granite were also present in T a njong Balai and Changi . These dykes however havenot been recognised by the authors.

29

30

Fig. 3.23

Fig. 3.24

120X Plain Polarized Ligh l

Field Relations

Although the numerous acid dykes and veins described by Scrivenor (1931) on Pulau Ubin and Changihave not been seen by the authors, the presence of such dykes intruded after the emplacement of the maing ranite, can be expected . A later intrusive phase of basic dykes, already observed in the Central SingaporeGranite, is also recognised here. Such a temporal relationship is suggested by the association of the acidand basic dykes in Pulau Sajahat Besar and Sajahat Kechi!.

Age and Correlation

Hutchison (1973 A) placed the Bukit Timah Granite in with the East Coast Granites of Malaya anddiscussed the granitic associations of the Malay Peninsula and their correlations in that paper and in the"Geology of the Malay Peninsula" (Hutchison 1973 C). No further discussion on correlation is given inthis text.

The age of the Bukit Timah Granite has been obtained by isotope dating techniques. Biotite fromgranite sampled at the Public Works Department Rural Depot Quarry and Sin Seng Quarry have K-Arages averaging 200 ±9 Ma. Granite samples from the Rural Depot Quarry yield Rb-Sr ages that rangefrom 210 Ma to 221 Ma. (Bignell, 1972). An early to early-middle Triassic age is hence suggested for theBukit Timah Granite. Unfortunately, no isotopic age has yet been obtained from the Pulau Ubin Graniteto confirm a parallel age but a sample has been collected for processing. It has already been mentioned th a tthe g ranite batholith postdates the gabbro (Gombak Norite, Gn) and a consequence of this is in theformation of hybrid rocks that have been recognised o n Singapore Island and Pulau Ubin.

The porphyritic granite from Pulau Sekudu is included in The Bukit Timah Granite, but it has asimilar appearance to the late Cretaceous to early Tertia ry granite bodies situated at several points alongthe western margins of the Main Range Granite in the Malay Peninsula (Professor N.J. Snelling, pers.comm .). An isotopic age determination on this granite will be made in the near future. The authors areg rate ful to Professo r .J . Snelling for thi s.

MINERALIZATION

Evidence of minerali za tion has been found in the granitic rocks at Bukit Timah , Bukit Mandai , andBukit Panjang.

At Bukit Tima h, a minerali zed contact zone between the host gra nite rock and a dyke of graniteporph y ry in the Hindhede Quarry contains numerous na kes of sil very molybdenite crystals up to 4 cm longand patches of other sulphide minerals in qu a rtz .

On the second bench in the eastern face of Sin Seng Quarry there are thin but conspicuous veinsconsisting of quartz, pyrite, and some bornite. These minerals are restricted to the middle of the veins .

Alexander ( 1950) described the occurrence o f numerous small veins cont a ining quartz, calcite.to urma lin e sometimes as radiating needles, pyrite, molybdenite , and some cassiterite in the Public W o rk sDepartment Qua rry ( Mandai).

According to Scri venor ( 1910) tin ore was found in quantities sufficient for working at Bukit Manda i.He also recorded the presence of a pocket of cassiterite, molybdenite, chlorite, and calcite in granite atBukit Panjang.

No minerali za tion has been o bserved o n Pulau U bin.

JURONG FORMATION

Introduction

Scrivenor (1924) recorded in the southern and western parts of Singapore quartzite and shale withinterbedded limestone, which he described under the heading of 'Shale and Sandstone' ; and Alexander(1950) remapped these rocks as the 'Older Sedimentary Rocks', describing three rock types - an OlderSchist , an Argillaceous Series, and an Arenaceous Series - but not mapping their distribution .

Wong (1960) mapped the south-west coastal area and carried out petrological and sedimentologicalstudies on the sediments. He recognised three sub-divisions - A, B, and C in ascending stratigraphic order.The A series consisted of quartz conglomerate, sandstone and shale. Series B he described as a bluishconglomerate, together with sandstone and clay; and Series C is a sandstone-quartzite sequence overlying aconglomerate. He mapped a continuous anticline-syncline couplet extending north-west from TanjongBerlayar to Sungei Pandan .

3\

Leow (1962) extended the structural mapping over the whole of the western side of the island. Heco uld find no support , on hea vy minera l ana lysi s, fo r A lexander' s div ision into an Arenaceous and anArgillaceo us unit.

Chi n (1965 ) mapped the Pasir Panjang-Jurong a rea and proposed two formations, a JurongFormation and the Pasir Panjang Formation, the latter being younger. His Pasir Panjang Formation wasdescribed as a rhythmic conglomerate-sandstone-mudstone sequence with a dominant reddish colour. TheJuro ng Fo rmatio n wa s described as ma inly a n interbedded mudstone-sandstone sequence of grey to blackco lo ur.

Burto n (19 73 A) , working in southern Johor used the term Jurong Form a t io n informally for the wholeof the Triassic sedimenta ry sequence there, but stated that further work on the unit was necessary before aformal no menclature could be established. He chose 'Jurong' as he considered that area to furnish the bestd a ta for the establishment of a formal unit , possibly of group status. He recognised two members in theso uthern Jo ho r a rea within hi s informa l unit and these he na med the Gunong Pulai Member and the BukitResa m C las tic M e mber. In the " Geology of the Malay Peninsula", Burton (1973 B) discussed brieOyC hin's subdivision but considered that there was insufficient evidence at present to separate the twoformati o ns a nd al so pointed to their both being of the same age. He recast them as members of the JurongFo rmation and incorporated Chin 's Jurong Formation in his Bukit Resam Member.

Lim ( 19 74 ) however adhered to Chin's subdi visi on sta tus but postulated an upper Triassic age for theJuro ng Formation and a lower-mid Jurassic age for the Pasir Panjang Formation .

The Geological Unit agrees with Burton that Chin 's nomenclature should be abandoned, and prefersto recogni se six facies types within the Jurong Formation (used informally in Burton ' s sense). It is probablethat closely simi la r en vi ro nme nta l sett ings occ urred periodi ca lly througho ut the time o f deposition of theJ u ro ng Fo rm a t ion. so th a t simil a r sed iments co uld have been depos ited a t d ifferent times and as discretebod ies . It is no t uncommon to find ev idence o f the supe rpos ition of one fac ies o n another at one locality .~ln d th e reverse somewhere el se. Further difficul ti es were encountered in establi shing sa tisfactorypa ra meters for ma pping each me mber . and as much of the ma pping was d on e before the facie s membe rconcept was adop ted . an d by d ifferen t geo log ists using diffe rent pa ra meters. it has not a lw ays been poss ibleto establi sh \\ ith ce rt a in ty wh ich fac ies member a pa rt ic ul a r ob servation should be ass igned to.

The effe ct of weath e ring has been to reduce most of the facies members to a simil ar end pro duct. Thi stoo ha s ha mpered accura te ma pp ing.

It is proposed th a t six fac ies be establi shed to ill ustra te the va riati o ns see n in the Juro ng Fo rm a tion .T hese wi ll be refer red to as th e Queen stown F acies. Jong Facies , A yer C ha\\ an Facies. Rim a u Facies, St.Jo hn F ac ies. a nd Ten ga h F acies. Altough a general spa tia l and temporal rel atio nship ca n be recognised foreach fac ies member, no one facies ca n be assumed to form a continuou s unit.

Tec to n ic ac ti vit y has been responsible for the dyna mic metamo rph is m of parts of the JurongFormatio n . T he grade o f meta mo rphi sm is low and it is still possible to det e rm ine the fa cies tha t has bee na ffec ted. The meta mo rphosed a rea s have thus been ma pped o ver the fac ie s. a nd the rocks within th osea reas ca n b e refe rred to info rma ll y as Mura i Schi st, na me originall y intro d uced by Alexander (1950) .

Foss il collections have been made from the Juro ng Fo rmation in Singapore by Scrivenor, Alexander.C h in. Lim a nd o thers (Appendi x 3) . No systematic co llecting was ca rried out during th is survey however.M os t of the fossils a re ma rine mo lluses and are fo un d in t he Ayer C hawa n fac ies o r interbeds within it. Theage uf the fuss il s is ge ne ra ll y accepted a s upper T riassic.

QUEENSTOWN FACIES (Jq )


A 'Mudstone Unit ' was established in the Singapore Public Works Department, Geological ReportN o. 3 (1974) , and this unit and its type area is adopted here, with minor restrictions , as the QueenstownFacies. It is a distinctive purple-red clay, clayey sand, silt or fine sand with minor tuff, and was best exposedin excava tions for the Queenstown housing project extensions in the headwaters of Sungei Ulu Pandan(G R 443448). The black shale and yellow sandstone included in the Mudstone Unit are excluded from theQueenstown Facies.

The member can be found running from Peak Island north-west to Selat Johor close to the granite orOld Alluvium bound a ry, and as interbeds down the west coast and in the Jurong area . It is also found asthin bed s in the south-west and western islands . Its g reatest development is in the Queenstown-BukitMerah a rea ( Fig. 3.25). Sand is more common to the north-west, and silt and then clay to the south-east.

32

-

Fig. 3.25 Exposure of the Queenstown Facies sho wing the massive character ojpurplish red lI1udstones, lalan Bukit Merah, South Central Singapore.

Fig. 3.26 Photomicrograph 0/ a fine red sandstone in the Queenstown Faciesshowing very angular quartz detrital grains in a limonitic clayey matrix,Kay Siang Road. South Central Singapo re. (GR 467434 )

120X Plain Polarized Light

33

Content

The unit was described as consisting predominantly of thinly bedded red and purple mudstone withsome red to purple shale. The mudstone often has a white coating on the joint surfaces. Vugs, possiblyinitially con taining pyrite, are common, and these are now seen as holes up to 5 mm in diameter. Greenishstains are often found on the fracture planes. Massive red to purple mudstone is also common, and this isclosely joi nted or sheared so that on drying the rock disaggregates to a mass of len ticular fragmen ts abou t 1cm long . In the more sandy portions sharply angular quartz dominates and the quartz is coated withhaemati te and goethite to give the red-purple colour (Fig. 3.26). A thin section of this rock con tains, quartz,subordinate clouded feldspar, and a few flakes of muscovite and pale brown biotite. Tuffaceous materialcould be identified in hand specimen in some of the coarser-grained rocks in this member, particularlytowards the north-west and west, and this volcanic material may have contributed to the red colourationa lso.

Field Relations

The Queenstown Facies lies directly on the granite in places, or is separated from it by yellow clayeysand or tuff beds of the Tengah or Ayer Chawan Facies. It appears to interdigitate with the Tengah Faciesto the north-west, and appears to pass up into the main outcrops of Ayer Chawan Facies in the JurongArea, and is interbedded with it there and elsewhere (Fig. 3.27) . To the south-east the Queenstown Faciespasses into the St. John Facies. The Queenstown Facies appears to lie both above and below beds of theRimau Facies and is normally separated from it by a tuffaceous bed. A sub-member of the QueenstownFacies can be recognised lying within the Rimau Facies west of Henderson Road Extension .

The member shows marked similari ty with the Chilean red beds (Dr. H .R. Katz, pers. comm.) and it issuggested tha tit is a sub-aerial terrestri a l deposi t and the product of terrestri a l weathering. The sand bodiesare interpreted as representing ephemeral lacustrine or alluvial deposits. The existence of volcanic materialwithin th e facies , particularly in the coarse-grained horizons has added further colouration to the rock.

The o ther facies associated with the Queenstown Facies are all interpreted as subaqueo us, anddomin a ntly sha llow marine, so it is presumed that the a rea of land at that time was of limited extent.

JONG FACIES (Jj )


The Jong Facies contains a lternating beds of roundstone conglomerate and sandstone and. lessfrequently . beds of mudstone. The type loca lity is Pulau Jong, from which the facies takes its name. Bothco nglo merate a nd sa ndstone are seen on this island , but mudstone is minor.

R lKks of this facies a re found mai nly on the south-west islands, occurring on Pulau Jong, Buk o mSebarok. Semakau, Salu, Pawai, Sena ng, Biola and Satumu . It is also mapped in one locality in Jurong andon Pul a u Suba r La ut and Darat , and at Tanjong Pangkong on Pulau Ayer Chawan . It has been mapped .a lth ough no outcrop was seen , on Pulau Buk om Kechil , and a 2 m bed of conglomerate similar to that ofth e Jo ng Facies w as seen on Mt. Faber (GR 477397) but the extend of the exposure is too small to bereco rd ed on the map (Fig. 3.28).

Content

Co nglomerate with subrounded to rounded clasts, usua lly abo ut 6 cm to 10 em in diameter, butfrequently up to 30 cm , occurs in beds from 50 cm to 6 m thick and possibly thicker. These beds grade upinto a muddy fine to coa rse sandstone to make up the bulk of the facies. Beds of hard muddy sand grit.ranging from 20 cm to 2 m thick, form most of the remainder. Mudstone beds, often dark grey to black .and seldom more than I m thick, are less frequent. The sand in the unit is qua rtz rich, with lithic-volcanic,tuffaceous, and pumiceous fragments also present.

The clasts in the conglomerate are dominantly siliceous as fine sandstone or siltstone, or as quartzporphy ry . Dark grey mudstone clasts are also common (Fig. 3.29). Fragments of vein quartz, as seen in theRimau Facies, are conspicuously absent. Chert fragments are common within the facies, and chertreplace ment of the origina l sediment can be seen in some beds.

Occasional lensoid spilitic bodies have been observed within the member; one on Pulau Salu was some25 cm thick a nd 2 m long. Heavy veining by quartz was also common within the facies (Fig. 3.30).

34

_._ , I

Y"'

<J ;;' V

Z O

, ~ ~

I Z

~ 2- 2- 2- :i..

0"':

2-

.,...J

Z

. Vl

~Z

1--

(5

Vl

Z «I« I

I I-

0 ::> u if)

l.? , « l.?Z

Zn: w

w ,..: 2 w z W

I- if) n: ~0 ::>

g!

, 0

35

36

Fig. 3.28 A 2 m thick conglomerate bed con taining clasts of sandstone. silts(one.quartz porphl'ry and schist..\1t. Faber.

Fig . 3.29 Conglomerate of the long Facies contammg sandstone, siltstone, greymudstone, and quartz porphyry clasts at Pulau long.

- l '

Field Relations

The Jong Facies is seen to lie below the Ayer Chawa n Facies on both Pulau Salu and Pulau Senang,but a bove it on Pulau Bukom . At Jurong it is interbedded within the Ayer Chawan Facies, and beds ofTengah Facies also interdigitate with the Ayer Chawan Facies in the same section. At Jurong, and on PulauSenang, the Ayer Chawan Facies is represented by sediment, but on Pulau Salu it is represented by massivelithic tuff which overlies the Jong Facies, each bed being I m to 2 m thick, and the Jong Facies isrepresented by a well cemented slightly tuffaceous muddy coarse sandstone or grit, but without anyconglomerate beds .

AYER CHAW AN FACIES (Jac)


The Ayer Chawan Facies is dominated by tuffaceous debris and the presence of black sand andmudstone beds and minor black to red conglomerate. Spilitic lava is present in this facies also.

The type section is defined as the west coast of Pulau Sakra in the Ayer Chawan Group of islands, notbecause it is the best section available, but because it is the one least likely to be obliterated by civicdevelopmen t.

The member is found in the Jurong area (see frontispiece), particularly towards the south-west, in theAyer Chawan group of islands, and as a single bed overlying the Rimau Facies running from Sungei UluPan dan to the southern end of Sentosa Island and again as a conglomeratic bed underlying the RimauFacies on Sentosa Island . Sub-members are also found towards the base of the Queenstown and TengahFacies close to the granite contact.

Content

The Ayer Chawan Facies is generally a well bedded tuffaceous muddy sandstone facies. Bed thicknessvary between I mm and 1 m . Graded beds are co mmon but few other sedimentary structures are seen;minor scour channels in the top of mud beds, and fill ed with sandy foreset beds , are the most common.Quartz grit beds, silt and clay beds, tuff and tuffaceo us conglomerate, often red in colour , are commonwithin the member. There is considerable evidence of reworking of the sediment by the biota at the time ofdeposi tion (Fig. 3.31).

Chin (1965) recorded the presence of a volca nic breccia on Pulau Samulun, and Lim (1974) notedboulders of spilite some 400 m north of Sel at Pulau Damar both of which are here included in the AyerChawan Facies . Further boulders were found during this survey in the Jurong area and their 10cations aregiven in the section on the volcanic rocks within the Jurong Formation. Alexander (1950) recorded lavas atTanjong Kling, Tanjong Gul and Pulau Sakra, on each occasion associated with chert, and a coarse tuff,again associated with chert, on Pulau Pergam. Spilite flows occur as beds, I m to 2 m thick on Pulau Saluand a spilitic dyke cuts the facies on Pulau Senang .

Li m (1974) produced detailed sections of sediments he put in Chin's Jurong Formation, and discussedthe petrology of the various lithologies he recognised. His sections A, B, C , D and E come from areasmap ped in this report as Ayer Chawan Facies with interbeds of the Tengah Facies, and the followingdescriptions are based on his work.

The sandstone usually comprises a fine to medium grained sand made up of quartz, with a significantamount of polycrystalline quartz grains, tuffaceous clasts and secondary chalcedony and chert. Biotitemica is also present and zi rcon, tourmaline and opaque ore, sometimes rimmed with haematite occur. Upto 20~o clay can be found in the rock.

The finer sediments are more characteristically black or grey and contain a few angular grains of sandsize quartz in a clay silt matrix of silica minerals, sericite, opaque ore and heavy minerals. No detailed workwas done on the mudstone, but both Lim (1974) and Chin (1965) commented on the presence ofcarbonaceous matter. Chin (op cit) reported 6.5% carbonaceous matter determined by loss of weight onignition of a dry sample heated for a period of 2 to 3 days. It is suggested that part of the weight loss mayhave resulted from a driving out of water from the clay lattices under such severe treatment, and that thisfigure may be overestimated. It is also thought unlikely that 6.5% carbonaceous matter would impart thedegree of colouration observed in the Ayer Chawan Facies. Alexander (1950) suggested that the colourresulted from the presence of finely divided iron sulphide and the authors support this view. Lim (1974)observed pyrite in one bed on Bukit Susop and sulphur efflorescence was observed by the writers as beingcommon on the black sediments.

With the exception of the Mt. Guthrie and Alexa ndra Brickworks collections, it appears that all fossilcollections from the Mesozoic rocks in the Republic of Singapore come from the black sediment of the

37

38

Fig . 3.31 A pale grey bed of mudstone exposed at Jurong (GR 327462) showingfeatures indicating reworking by biota.

-- 1.......

Ayer Chawan Facies or from sandstone, presumably of the Tengah Facies, intimately associated with it.Most of the collections came from a restricted area in Jurong (Fig. 3.32), but collections have also beenmade from Pula u Ayer Chawan a nd from a black sediment near Mt. Faber (Br Lawrence pers. comm.) .

The first well documented collection of fossils fro m rocks assumed to belong to the Ayer ChawanFacies was made by Alexander. In her report (1950) she described them as lamellibranchs, gastropods,probably crustacea, and the brachiopod Lingula. At that stage they still awaited identification andAlexander did not give their location. Burton (1973 B) quoted a written communication from Cox listing anumber of species from near Huat Choe Village (see Appendix 3) and ESlheria mangalensis from PulauAyer Chawan, which represent Alexander's collections.

C hin (1965) collected from the Jurong area . The specimens found were casts, as have been allsubsequent finds. His localities CF 3 to 6 were in interbeded mudstone-sandstone, while the other four werein black mudstone (Fig. 3.32).

Li m (1974) collected from eleven localities, designated Ll-II in Fig. 3.32, his localities Ll and L9 beingequivalent to Chin's localities CFI, CF2 a nd CF8 respectively, and L5 probably being similar toAlexander's Huat Choe collection. Lim recognised two different faunal groups, one in the black mudstone,and the other in the sandstone, thus supporting Chin's inference that these groups indicate at least two setso f depositional environments. Both had recognised Conodon and Posidonia from the sand beds whileMyophoria dominated in the black mudstone. Chin also recorded a fragment of an ammonite from one ofthe sand beds.

An effort was made to relocate the site of the Morse Road collection of Scrivenor (Newton 1923 ), andas a consequence a single broken cast was found in place at the head of the va lley above Morse Road . Thecast was in a g rey and pink tuffaceous and carbonaceous muddy fine sandstone sequence in excess of 25 mthick, and it is assumed that this is the horizon from which Scrivenor made his collection. The bed ismapped as belonging to the Ayer Chawa n Facies on lithology . It is capped by a 2 m bed of roundstoneconglomerate similar to th at of the Jong Facies, and the mudstone-congl omerate beds lie between beds ofangular quartz conglomerate of the Rimau Facies (co mplete faunal lists a re given in Appendix 3).

The collection from black sediment near Mt. Faber was a private collection made by Br Lawrence andha s not been described . It cannot now be traced .

The age of the fossils co ll ected is discussed in the section on age and correlation .

Field Relations

The Ayer Chawan Facies appears to interdigitate with the upper portion of the Tengah Facies and alsothe Queenstown Facies, and a limb of the facies is also found to overlie the Rimau Facies. In the Jurongarea the Ayer Chawan and Tengah Facies interdigitate extensively, but much of the material identified asTengah Facies may in fact be leached Ayer Chawan Facies.

Lim ( 1974) reco rded six stratig raphic columns from this facies with his sec tion A passing up into hisPa sir Panjang Formation. The present a uth o rs map Tenga h Facies in this area overlying the Ayer ChawanFacies bu t there is insu fficient evidence to sta te ca tegorica ll y that this con tact represen ts the top of the AyerChawan F acies. Nor is there sufficient evidence to place column 'A' relative to the other given sections.Remapping however confirms Lim's general sequence but places columns ' B' and 'C' at the samestratigraphic level.

The sediments of the Ayer Chawan Facies are dominantly fine grained with lamella bedding and onlyminor current features. These features, together with the occurrence of finely disseminated carbonaceo usma tter suggest a low energy environment. The characteristic black colouration, due, it is believed, to thepresence of finely divided pyrite, points to a reducing environment. It is thought that these anaerobi cconditions occurred after phases of volcanic ac tivity and were responsible for the elimination of the biotapresen t.

Dr. I.G . Speden (pers. comm.) recognised six mode-of-life elements in the Myophoria assemblage(Table I) . Of these, group T requires a firm to moderately firm substrate containing organic material forfood , and reasonably oxygenated sediments, altho ugh its members can tolerate lower oxygenconcentrations than most infaunal bivalves. The other five groups require moderately firm to firm,relatively stable substrates which can provide suitable holdfasts (shells, pebbles, wood or grain fragments ,and marine plants), in a low to moderate energy environment with adequate oxygen and food. The specieswould not tolerate anaerobic or high energy scouring environmental conditions, nor excessive turbidity .Most species in group '5' can rebury themselves if exhumed by currents or buried to a moderate depth , butwould not tolerate frequent displacement. Dominance, both numerically and in diversity , of the assemblageof suspension feeders, indicates low turbidity .

39

+>oFig. 3.32 Fossil collection localiries of Lilli ( /974) (Ll - Ll/ ) and Chin Fall (/965) (CFl - CF8 )

j i'Ol li th e Jurong area . Locations (A ) to (E ) refer to Lims detailed sect ions.

r 11 \\ I ~ jI.l, 7000 m NI I I II

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All groups frequently occur together in the stra tigrap hic record and are characteristic of shallow shelfto enclosed m a rine bay habita ts of normal sa linity, turb idity, oxygenation, and low to moderate energycond itions.

The evidence of bioturba ti o n a nd frequent incursion of sand often carrying the Gonodon-Posidoniafauna a lso argues against an anaerobic deep barred basin type setting but rather a shallow water, sheltered,low energy setting, possibly similar to the brackish coastal areas found in tropical areas at the present time,but with a volcanic province nea rby to supply the tuffaceous material. The Gonodon bearing sand bed spossibly arose thro ugh longshore drift during the longe r periods of volcanic quiescence. Lim noted that theGonodon a nd Posidonia shells we re all orientated and co nvex upwards suggesting transport and reworkingbefore burial.

TABLE I

Mode of life elements for species listed by Lim (1974) as having been fo und in sediment mapped asAyer C ha wa n Facies in this report.

I . Infaunal mobile deposit feeders: Pa/aeonei/o sp ., Pa/aeonucu/a sp .

2. Endobyssate and epibyssate suspension feeders : Cassiane//a sp . Pteria pahangensis. Posidonia sp .,Ha/obia sp., Buchia sp.*, Pa/aeo/ima sp., A vicu/ima sp ., Lima spp. (2), Pa/aeopharus sp.

3. Epifaunal free -swimming suspension feeder s: Amusiw/1 sp ., S ync)'c/onema* (? = EnlO/ium) sp., andpossibl y the Pecten spp'* ('J4).

4. Epifaunal ce mented suspensio n feeders: P/icalU/a sp., Spondy /us dubiosus ( Bittner).

5. S hallo\v b u r row in g siphona te and non-siphonate suspen sion feeders: Trigo nodus sp.,AllodolllOphora spp. ('In Costatoria spp'* ('76), Gruemva/dia sp ., Ml 'ophoria sp., Neoschizodus sp ..Gonodon sp., Cardium scrirenori.

6. Other: Gastropod sp .

RIM Al) FACIES (Jr )


The Rim au Facies is na med from Saran g Rim au at the north-west tip of Sentosa Isl and where thefaci es is well exp osed . The typ e secti o n is defined as those beds lying above (to the south-west of) the redmud sto ne exposed beneath the Siloso Jetty (GR 46 1393). A no rth-west trending fold axis lies 100 m southwest of the jetty a nd the section is re peated to the south-west 160 m of sed iment being exposed .

The Rim au Facies is found on Mt. Faber and Kent Ridge as far north-wes t as Sungei Ul u Pandan , onthe north side of Pul au Brani, and forms the sou th- west coastline of Sentosa Isla nd an d the bulk of PulauTekuk o r, and the St. Johns Island group. It is also found on the south-eastern side of the m ai n g ranite masson Singapore Island.

Content

The Rimau Facies is typified by quartzite and conglomera te. Both rock types are welllithified and assuch fo rm the backbone of the prominent north-west tre nding ridges of Mt. Faber, Kent Ridge, and thesouthern islands.

In these areas the conglomerate contains sub-angular to rounded fragments, usually less than 5 em indiameter, but so metimes of cobble grade, of qu artz, tu ff, quartz sandstone, chert, rhyolite , bas ic igneouspebbles, and pebbles of red sandstone presumed to be derived from the Queenstown Facies and schistpresumably deri ved from the Mura i Schist. Quartz, probably a vein quartz, is by far the dominant lithologyof the clasts however. The ryJatrix is usually a coa rse sub-angular quartz sand, but feld spar has beenrecognised, usually having wea thered to clay . Tourmaline, fluorite and zircon occur as heavy minerals andhaematite and magnetite were recorded by Chin (1965) as the only observable opaque minerals. Wong(1960) also recorded limonite and leucoxene.

• Dr . I.G. Speden (pers. com m.) stated that Pecten and Costatoria may be conspecific and that SI'ncyclonema may be Ento/ium sp. H ea lso sa id that Buchia sp. is on ly know n fro m late Jurassic to early Cretaceous and must therefore be a misidentification in thesecollections.

41

Thin sections of the sandstone show a typical arrangement of close packed sub-angular well-sortedgrains (Fig. 3.33). Quartz may form up to 98% of the rock, with biotite, to urmaline and traces of iron oxide,usually as a coating on the quartz grains , also being present. Quartz sandstone fragements can also be seenin the rock. In other thin sections, chlorite, illite and do ubtful kaolinite were recognised as alterations offeldspar.

The quartz conglomerate beds of the Pasir Panjang coast and southern islands are usually a grey whitecolour, but the associated quartz sandstone is often stained pink, and hence shows similarities to thecoarser horizons in the Queenstown Facies. On the southern islands the pink colouration is also seen in theconglo mera teo

Beds of the Rimau Facies are usually 0.5 m to 1.5 m thick and coarse cross beddings and scour featuresare common. Beds between I cm and 10 cm thick o f silt and fine sand grade may be seen between thethicker beds , and these may show a greater variety of sedimentary current features .

Field Relations

Although the Rimau Facies is a distinctive member in the field, its field relationships are not alwaysclear. It can be seen to lie conformably on a volcanic co nglomerate of the Ayer Chawan Facies on SentosaIsland and on the St. Johns Facies on Lazarus Islan d and is intimately associated with the QueenstownFacies and Ayer Chawan Facies along Kent Ridge . To the north-west it appears to wedge out and passlaterally into Queenstown Facies and Ayer Chawan Facies . Identical rocks have been described by Priem(1975) from the Bintan Formation from the Riau Archipelago.

The general coa rse nature of the facies and the presence of cross-bedding and current-bedding featuressuggest a shallow water, near-shore , probably deltaic en vi ronment close to a rising land mass that has beendeeply leached. The clay residual has been removed , poss ibly to be incorporated in the Queenstown andTengah Facies prior to the deposition of the Rima u Facies.

The juxtaposition of the Rimau Facies to the dom ina ntly terrestrial Queenstown Facies and marine St.John Facies support s the argument for a near-shore envi ronment.

ST. JOHN FACIES (Jsj)


The SI. John Facies is a pale grey mudstone and m uddy sandstone found in the Southern Island groupand pOSSibly MI. Guthrie, and the type area is defin ed as the south-west coast of Lazarus Island, andincluding tho se beds below the lowest quartz pebb le bed exposed at the south-west tip of the island.

Content

The rock is a pale grey muddy sandstone with we ll defined ripple marked beds, current bedding ,graded bedding and minor intraformational breccia (Fig. 3 .34). Lenses of coal, less than 2 mm thick, arealso characteri s tic of thi s facies , and were not reco rded in any other facies . No petrographic orsedimentological studi es were carried out on this facie s. Because of the presence of coal and a marine fauna ,the MI. Guthrie rocks, although now removed , are ma pped as part of the St. John Facies .

Newton (quoted by Burton 1973 B) suggested that the Mt. Guthrie collection was taken from anestuarine or lagoonal deposit, and the n ysch-lik e cha racter of the rest of the other facies suggests a shallo\\but un stable marine basin.

Field Relations

The SI. John Facies appears to pass laterally into the Queenstown Facies to the north-west and isinterbedded with it on Sentosa Island and also with tuffaceous beds mapped as Ayer Chawan Facies . It isfound mainl y below the Rimau Facies but it is also fo und within the Rimau Facies at Mt. Chermin.

TENGAH FACIES (Jt)


This member includes all those rocks of the Jurong Formation found in Singapore that have not beenincluded within the other five facies. No formal type area or definition is therefore proposed. They arerecognised however as being typically a muddy fine to medium grained poorly lithified sandstone, and asthey show this specific unifying characteristic, are no t mapped as undifferentiated Jurong Formation. Forthe same reason they are not mapped as a continuation of the Bukit Resam Member of Burton (1973 A) .

42

Fig. Fa cies f rom Kent Ridge

45 .'( Plain Polarized Light

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.:.;<::~ , -.. " ':-\.' "" .•.t-"

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mudstone with intraformational breccia, St. John's Island.

..,

43

The facies is found extensively in the area from Tengah west towards the coast and south to lurong. Itis also found lying between the Rimau and Queenstown Facies betwee n Sun gei Ulu Pandan and Keppe lH arbo ur and is assumed to be present in contact with the Rimau Facies to the east of the granite .

Content

o detailed work has been done on the sedimentology or petrology of this facies, but the poor sortingof the sa ndstone and conglomerate, and the rapid change in grain size from mudstone to grit suggests afl ysch-like deposition. The sediment is a muddy quartz-rich fine to medium sandstone, usually only poorlyindurated , so that as a result of weathering there a re few natural outcrops. The member is usually wellbedded with beds being 2 em to 30 em thick , but moderately welliithified beds up to I m thick can be seen .Such beds are well exposed in a n excavation I km north of the Jurong Road (G R 387498) . The weillithifiedbeds are generally quartz-rich and appear to have been cemented by silica.

Occasional yellow-brown roundstone conglomerate and grit beds are found, particularly to the northwest of Nanyang University, along the Pasir Laba Ridge, and along the ridge north ofSungei Murai. Manyo f the pebbles, some of which are up to 10 cm in di a meter, appear to be derived by the contemporaneouserosion of the Jurong Formation.

Lim (1974) collected his Gonodon fauna from sediments assumed to be part of the Tengah Facies.These have been discussed together with his Myoph oria collections under the Ayer Chawan Facies.

Field Relations

The Tengah Facies is seen to be interbedded with all the other facies with the exception of the St. John sand Jong Facies. It appea rs to be the la teral equivalent of the Queenstown and Rim a u Facies and passes upinto the main body of the Ayer C hawan Fac ies .

T he presence of Gonodon an d Posidonia in rock s supposed to belong to this facies suggests a marin een vironment and the general bedding characteristics support this. Bo th species a re bottom surface dwellin gor shallo\", borrowing marine types preferring moderate to firm su bstrates. They could be exhumed andredeposited by low energy currents ( Dr . l.G. Speden , per comm.). The orientation of Gonodon shells asdisc ussed by C hi n ( 1965) points to the periodic influx of s teady directional ocean currents for this purpo se.

MURAl SCHIST


It is not proposed th a t the Murai Schist be recognised as a formal geological unit but rather a zone ofwell developed cleavage in rocks otherwise recognised so fa r as sediments of the Queenstown, Jong andTengah Facies.

The Schist Zon e form s a belt up to 0.5 km wide trending north-east from Tanjong Skopek to includethe a rea origi nal ly described by Alexander ( 1950). A sm aller schist zone was found o n the no rth arm of th ePasi r Laba Ridge (G R 295494) and ano ther , not recorded on the map, in the Jo ng Facies in Jurong (G R332452 ).

Content

The unifying characte ri stic of the Murai Schist is the well developed cleavage in the pelitic sedimen tand a coarser fracture or folia tio n in the arenaceous sediment, in both cases subparallel to the bedding (Fig .3.35) . While the cleavage planes a re planar, the foliation planes in the coarser sediment are knotted , andelongatio n, with lenticular nodules lying along the foliat ion planes, is obvious. The harder tuffaceousmaterial within the schist zone has resisted shear.

I t is not clear in thin section if any metamorph ic minerals have formed, white mica being the onlyprobability. An apparent spotting, formed by the presence of a few small areas rich in fine-grained whitemica , was recognised in one thin section of slate. In the slate, quartz is the main recognisable mineral.Slately cleavage is well shown by the parallel orientation of small mica flakes and lines of iron oxidegranules. There are a few small irregular areas rich in fi ne-grained white mica . The coarse arenite can beseen in thin section to form a poorly schistose rock formed from a quartz rich sandstone. There appears tohave been an overall reduction in average grain size by pronounced shearing . Many of the quartz grainsshow undulose extinction while others have been reduced to a mosaic of tiny interlocking grains. A fewlarge grains have conspicuous lamella structures, probably resulting from crushing . In addition to thequartz, there is also occasional fragments of very fine-gra ined chert, usually grey or dark grey in colour ,

44

because of the finely divided opaque inclusions. There are scattered aggregates and streaks of mica , manyof wh ich are clouded by fine-grained alteration, while the bo rders between many of the quartz and othergrains are o utlin ed by opaque material, probably iron oxide.

Field Relations

The rocks of the schist zone are in fault contact with the Tengah Facies to the north-west and there is amarked angular unconformity across this fault. To the south-east however, the schist is seen to pass up intonon-sheared Queenstown and Tengah Facies rocks, and bedding is concordant.

VOLCA IC ROCKS WITHI N THE JURONG FORMATIO

Introduction

Volcanic activity comtemporaneous with the sedimentary deposition of the lurong Formation hasgiven rise to spilite, tuff, chert a nd dolerite within the formation.

Spilite


The spilite is defined as those soda rich basalts found as lavas an d relict boulders in or associated withrocks of the Ayer Chawan and long Facies.

Alexan der ( 1950) recorded lavas at T anjong Kling, Tanjong Gul and on Pulau Sakra , on eachoccasion associa ted with chert . C hin ( 1965) recorded the presence of a volca nic breccia on Pula u Samulu nand Lim (1974) noted boulders of spilite some 400 m no rth of Selat Pul au Damar.

The present auth ors can co nfirm the find of Lim north of Selat Pul au Damar (GR 352448). Spili teboulders have also been found during this sur vey in the Jurong area at GR 350452 and GR 363466 (Fig3.36). On each occasion the boulders have been left afte r excavation activities within the Ayer Chaw JIlFacies , an d the relationship with the host rock cannot be seen. The on ly spilite found interbedded wi th theJurong Formation lies in sandstone of the Jong Facies on the northern shore of Pulau S;l lu. There the rocforms an elongated pillow approximately 2 m long and 25 em thick (Fig . 3.37).

Composition

The spilite is described by Lim (1974) as being a dark green amygdaloidal rock containing phenocrystsof albite and epidote in a matrix o f small albite laths showing a trachytic texture in a matt of chlorite . H eidenti fi ed six groups of amygdales; those filled with ca lcite , calcite and quartz, quartz, chlorite andplagioclase, quart z a nd plagioclase, and plagi oclase. Large angular inclusions were observed by the autho rsin boulders near Selat Pulau Da m ar (Fig. 3.38), bu t they were not mentioned by Lim and ha ve not beenstudied by the a utho rs.

Tuff


Lithified tuff only, found within the lurong Formation, is included under this heading. It appears as acrystal tuff and is made up mainly of crystals in a chloritized matrix. The poorly lithified ashy tuff cann otrealistica lly be separated from the sediment and hence is not discussed under this heading .

Alexander (1950) recorded a coarse tuff associated with chert on Pulau Pergam . This occurrence wasconfirmed during the present investigation . Tuff interbedded with sandstone and also associated with chertwas also found on Pulau Salu . The beds· are approximately I to 2 m thick and are well exposed on thewestern shore of the island .

Composition

In hand specimen the tuff appears as a hard, dense, green rock, containing phenocrysts up to 2 mm ,which consist of feldspar and quartz. The tuff on Pulau Pergam is coarse grained, showing crystals up to Icm in length.

The rock from Pulau Pergam has been described by Dr . W .A . Watters (pers. comm.) as a rhyoliticcrystal tuff containing numerous crystals of acid plagioclase, orthoclase, and quartz set in a fine-gra inedmatr ix with abundant pale green chlorite. A few irregular elongate aggregates made up of chlorite and

45

46

F ig. 3.35 S chistose sandstone f rom the Murai S chist .

45 .\ Plain Polari::ed Light

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Fig. 3.36 A large boulder of spilite at Jurong Pier Road.

! .

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" 40 ',

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Fi g. 3.37 Grey spilitic body associated\I'ith coarse sandstone andchert on Pulau Salu.

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Fig. 3. 39 Large crystals of quart z .o rth o cla se and a c idplagioclase in rhy olithiccrystal tulI Pulau Pergam .Nort h- west Singapore.

45X Crossed Nicols

.+7

sericite may represent original fragments of pumica . There are also a few small areas of calcite and tin yaggregates of granular sphene (Fig. 3.39) .

The tuff from Pulau Salu is also a rhyolitic crystal tuff. It shows a fine-grained groundmass consistingmainly of plagioclase and quartz with subordinate orthoclase. All the minerals appear to be fresh (Fig.3.39) .

Chert

The chert is a cryptocrysta lline form of silica which occurs as bands or layers in the sedimentary rockso f the Jurong Formation . The chert is interstratified with spilitic lava , and it is therefore assumed that thesilica owes its origin to the volcanism associated with the spilitic lavas.

Chert was found abundantly on Pulau Salu where it forms bands, layers , small lenses, and redepositedfragments within the long Facies immediately below the spilite .

No thin sections were made of the chert, so no comment can be made of their contents.

Dolerite


The dolerite is a medium grained basic hypabyssal igneous rock , mineralogica lly and chemicallyequ ivalent to gabbro or basalt .

Scri venor ( 1924) repo rted the occurrence o f do leri te bo ulders at the site o f the T a n Tock Seng Hospita lres ting o n the Juro ng Fo rmati o n. At the Hospit a l site sedimentary rock o f the Rima u Facies is seen tooutcrop. b ut no igneo us bo ulders have been loca ted du ring th is survey despite det a iled wo rk and drilling inthe a rea. We suspect tha t the bo ulders reported by Scriven o r were not residua l bo ulders weathered outfro m dykes cutting the Tri ass ic sedimentary rock, but tha t they were derived fr o m dykes in the gran itewhi ch lies abo ut 40 m to the west.

There is eviden ce o f o nl y one do lerite dyke cutt ing the Jurong Form a tion. On the western shore o fPul a u Sen a ng , an alignment o f bo ulders. each abo ut 60 cm in diameter, indicates the presence of the dykewhose stri ke is readil y inferred (Fig. 3.40).

Composition

The dark grey medium-grained rock from Pulau Senang is an olivine bearing undersaturated dolerite .The rock is holocrystalline and is made up of long slender laths of calcic plagioclase whose intergranula rspaces are filled with anhedral augite crystals. Occasi o nal phenocrysts of strongly serpentinized olivinewere found.

The abundance o f a ugite a nd the rel a tivel y un a ltered sta te of the feldspar and pyroxene of this basicdyke o n Pul a u Sen ang a re in ma rked contrast with the dolerite dykes a ssoci a ted with the Bukit TimahGra nit e (F ig. 3.41 ).

Field Relations

The field relatio ns of each of the volcanic roc ks lis ted above ha ve been discussed in the sections dealingwit h the respecti ve host fa cies.

Age and Correlation

Scrivenor (1924) specified two fossil collections, o ne from "a cutting near the top of the road that leadsto the Mt. Faber Ridge by way of Morse and Pender R oads" and the other from Mt. Guthrie . Newton(1923) reported on both collections and assigned them to the Upper Triassic (Rhaetic) and ? MiddleJurassic respectively . Scrivenor considered however tha t the sediment predated the granite because thesedimentary beds dipped away from the granite, and there was no evidence of the folding, common in thesediment, continuing into the granite.

Alexander (1950) accepted the same time sequence as Scrivenor and described a core boulder ofgranite which she interpreted as a residual of an intrusive dyke penetrating 60 cm into the sediment. Sheextended the time range of the lurong Formation to span from? Carboniferous to ? Jurassic. Her fossilcollections had not been studied at the time she wrote her report but were later reported by Cox (Burton1973 B) as being upper Triassic . Later collections by C hin (1965) and Li m (1974) confirm this upperTriass ic age.

48

. _1

l

Fig . 3.40

Fig. 3.4\ Augite crvstals , partly interstitial between calcic plagioclase, and partlyenclosing some of the plagioclase , in dolerite, Pulau S enang.

45X Crossed Nicols

49

The age of the M t. G uth rie collecti on was reassessed by Kobayash i and Tam ura ( 1968), who suggesteda lower Jurassic age for this assemblage . With the stratig ra phic detail now a vailable , the Mt. Guthrie sitea ppea rs to lie so me 200 m above the Morse Road site (Section E map 9) but still a t least 400 m below thetop o f the Jurong Formation. Their relationship to the collections in the Jurong area cannot be established .

No evidence of contact metamorphism of the Jurong Formation was found during this survey, and noevidence o f intrusi o n was seen. The example of intrusion cited by Alexander (1950) could not be relocated:she described a s ingle residual boulder in deeply weathered material close to the granite pluton asrepresenting a d yke . In view of the more recent datings obta ined for the two formations it is thought thatshe mi sin terpreted this outcrop. In this report the Jurong Formation is interpreted as being younger thanthe granite. The palaeontologica l evidence suggests an upper Triassic age for the Jurong Formationwherea s the isotopic age for the Bukit Timah Granite is approximately 220 Ma (early to mid Triassic) oreven older depending on the decay factor used in the isotopic age determinations.

The age of the Jurong Formation is thus deduced to be mid-Triassic to early Jurassic . Fig. 3.27.illu stra tes diagrammatically the relationship of the various facies.

The Jurong Formation is correlated with the Bukit Resam Member (Burton 1973 A) in Johor. Noequivalent of the Gunong Pulai of Burton (op. Cil) is recognised in Singapore. The spilite noted by Lim( 1974 ) a nd by the authors , and the lavas reported by Alexa nder (1950) are mapped in the Ayer ChawanFacies a nd a re thu s too high in the stratigraphic sequence to be correlated with the Gunong Pulai Member.

The Jurong Formation is also correlated with the Bintan Formation described by Priem (el at) (1975)from the Riau Arc hipelago, and Proffeso r H.N.A. Priem (pe rs. comm.) stated that sediment of the RimauFacies sho ws a m a rked similarity to th ose sediments of t he Bintan Formation. Burton (1973 B) has alsoco rrelated th e J u ro ng F o rm a tio n with the Kerd a u and Jel ai Fo rm a tio ns o f ax ial M a laya , and the top of theJuro ng F o rmati o n w ith the Mura u C o nglome rate a nd the base of the Tembeling Formation .

The period of faultin g of the Jurong sediment which gave rise to the M urai Schist is discussed in thecha pte r o n stru ctu re .

OLD ALLLVI UM ( OA)


The te rm 'O lder Allu vium ' was in troduced by Alexa nder (19 50) to repl ace the term 'High Level,-'\llu v ium ' fi rst used by Scri venor (1924 ) to describe the a llu via l sa nd forming the hills traversed 'by theT a mpin es, C hang i a nd East Co ast Roads. Walker (in Stauffer , 1973) introduced the term 'Old Alluvium'together with ' Yo ung Alluvium' for the depo sits in th e Kint a Valley in West Malaysia and the term 'OldAllu viu m ' has bee n adopted by Stauffer (1973 ) for th e Jo ho r-Singapore a rea.

l\i o fo rmal de finiti o n o f the Old Allu vium has been prese nted a nd it is therefo re proposed that th osesedimen ts exposed in t he Bedo k Sa nd Quarry, (G R 595475) a nd recorded in Public Utilities Board Testhol e No . I at G R 598465, Bedok, be ta ken as the type 'Old Alluvium' for the Singapore-Johor area. Asumm3n log for Public Utilities Board Test hole N o. I is given in Fig. 3.42.

The Old Allu vium is fo und lying to the north and no rth-east of the Kallang River Basin between thece n tra l gra nite a nd the g ra nite a t C ha ng i. Simil a r sed imen ts , a lso assigned to the 'Old Alluvium' , a re foundin the no rth-west pa rt o f the island in the Buloh Besar a rea where they lie again s t the Jurong Formation .

In Public Utilities Board Test hole No. I the Older Alluvium was found to lie at a depth of -149 mdirectl y o n a quart z sandstone of the Sajahat Formation that has been contact metamorphosed, and thenearby hill s rise to 35 m giving a thickness of a t least 184 m , and to 45 m 3 km to the north-west giving ap oss ible aggrega te thickness of 195 m . To the north between ee Soon a nd Seletar North the granitebase men t is thought to lie at a depth of -20 m to -40 m as a solid substrate which has been encountered butnot penetrated by drilling in that area . To the north-east a granite basement was encountered in PublicUtilities Board Test hole No.4 at a depth of -53 m . The Older Alluvium cuts out against the oldersedimentary rock at Punggol, and the Bukit Timah Granite at Se\etar North. As Pulau Ubin is also anigneous mass , there is little room to carry the Older A lluvium through to its correlatives in Johor at orbelow present sea level. On the western side of the island however, the Older Alluvium can be mapped ascontinuing through in a north-west direction into Joho r.

Content

Detai ls of the content of the Old Alluvium have been documented by Alexander , (1950) , Burton (1964 ,1973 A ), and Stauffer (1973).

50

5 6 2 3 4

20M

+ ++

SEA + +f----4'h.Uj~---....F;,, :-"'I."t-----L VEL +

+ +C W

+ ++

+ +20M + + +

+MW+

+ +40M

bOM

8 0 M

100M

120M

140M

160M

180M

LEGEND

GRAVEL

SAND

SILT

CLAY

OLD ALLUVIUM

+ +IGNEOUS ROCK + BUK IT TIMAH GRANITE

+ +-200M SANDSTONE SAJAHAT FORMATION

CW COMPLETELY WEATHERED

FIG.3.42 SUMMARY LOGS P.U.B TEST HOLESM W M ODERATELY WEATHERED

SW SLIGHTLY WEATHERED

51

.-\: :C-. ::: : : :-:le of mapping, the Old Alluvium was well exposed in excavations a t Bedok , a nd in the m a nysend :- .:- : :- : h e north, as well as in coasta l exposures between Bedok and C ha ngi, a nd on the north-westcoas: _- -:-: :: <::: Pulau Sarimbun. In a ll exposures the forma tion is seen to be a clayey coarse a ng ular sa ndwith ~:-:::-. ~:::-~ of subrounded pebbles up to 4 cm in diameter (Fig. 3.43). The beds are often cross-beddedwith .:: .: ,,::: :'-::.::knesses up to 1.5 m . Cut and fill structures are a lso common a nd rare clas tic dykes can beseen I F' : ~ : -H l.

F:- ::: -~:-';' : :-j ed beds a re also present, usually as small lent icula r bodies . Alex a nder (1950) mentioned onefoun e -:::,;, ~ \1.::Pherson Road about 30 cm thick and 14 m in length . Several fine-grained horizons werereco r-= ::- :: :- : 'l :: Pu b li c U tilities Boa rd Test holes , usually as fine sand and silt beds, and one clay layer at -36m to -:. ~ ~- "3., recorded in Publi c Utilities Boa rd Test ho le No. I.

TC-:::: ;-,:: :--bles within the Old Alluvium are dominantly quartz, but , with rhyo lite, chert, and argillitepebb l::-- .=. :-::- 31 , 0 found. The quartz pebbles are generally more angular, the others subrounded to rounded .No g:-.:..:-: !::: t'ebb les have yet been found in Singapore but Burton (1973 A) recorded them in the OldAllu\ ' -.::-:- c~:' Johor. The sand is qua rtzo-feldspathic with the feldspar weathering to clay to varying depth s,usu a ! ~ ::-. excess of 8 m. Alexander (1950) found that 75% of the heavy mineral suite from a samplecolle.:::::-c ::::-3. r K a mpo ng Mata Ikan (GR 640477) was made up o f magnetite and ilmenite, a nd that zircon,cassit c ' :e. 3n d a few grains of monazite made up the rest. Scrivenor (1924) also found staurolite. Burton(196..h :;-, di scussi ng the Old Alluvium in both Singapore a nd lohor listed in addition topaz, tourmaline ,py rit e . 3.T12t3 Se. a nd sphalerite . No plant matter has been fo und in Singapore but again Burton (1973 A)recorc~ ,u.::h fin ds in l o hor. Tai (1972) co llected a single ma rine fossil from the Old Alluvium in Singaporeand .-\ j::-\3.T1der ( 1950) recorded the presen ce of a water-wo rn gastro pod preserved in black silica atK anE" ,::g E unos Earth Quarry, but from her descripti on it is ass umed to be a derived specimen with acoat ir:~ cy ' ~h e seconda ry sil ica minera l.

T:-.::- ;'c' ~ m3 tion is usuall y uncemented but quite dense an d with a low permea bility . Pfeiffer (1972) givesfigu r::-~ c'I l eV to 10-i" m / s for the permeability in the weathered zone of th e Old Alluvium. Zones ofcemeri : ., : ic'n :, re found but the cemented rock often disin tegrates after a few days exposure. Alexander( 195 S I :, u g"e;;ted that the rock was li ghtl y cemented with sil ica o r possibly a lumina . She then proceeded tosho\\ :h:: : .: Il'ss in we ight o n ex posu re to the Singapore climate ca n be recorded for water clear qu a rt zcrys u ls. .: nd thus suggested that the silica cement dissolved on exposure di sagg rega ting the rock. H e runcc~ m;:, I ::- : ed experiment showed an average loss of 0.005% by we ight over 6 weeks, but it is co nsidered bythe aut hc'r , Il~ be LOO slow to exp lain the breaking down of la rge blocks within days of exposure. A colloid als ili ca .:e m e nt is t ho ught mo re li ke ly to respond to wea thering wit hin thi s interval of time. Fu rther s tudy ofthe ce men t hC1\\e\er. co uld usefully be ca rri ed out.

Sl'me :ife:lS of ce mented Old Alluvium have been exposed for several yea rs and yet ha ve rem a in edcement ed. these a reas are plotted o n the map. N o study of the cement in these areas has been made .

Field R elations

The Cl)nt:lc t between the Old A llu viu m and o lder for mations is at present buried or obscured by deepweather ing ·\\exander ( 1950) observed tongues of Old Alluvium lying on c lay that she identified asweath ered granite at Changi. The Old Alluv ium is co nsidered to li e on sandstone in Publi c Ut ilities BoardTest hc)!e :" LI. I and gra nite in Public Utilities Boa rd Test ho le NO.4 at depths of -149 m and -53 mrespec ti \ely. Baseme nt had not been reached when Public U tiliti es Boa rd T est hole No.3 (GR 604501) wasterminated at -122 m.

T o the north near Punggo l, the Older Alluvium has been la id down against the Palaeozo ic sedimentsand in the Buloh Besa r area against the lurong Formation . In neither case is the co ntact seen. It is possiblethat part o f' the co ntact in the Buloh Besar a rea is faulted.

The ge neral texture of the Old Alluvium as exposed in Singa pore is consistent with tha t o f an alluvi alfan or piedmont plain type deposit. No evidence of' marine incursion could be see n, but the presence of9 mof clay in Public Uti lities Bo a rd Test hole No . I , other fine-g rai ned layers in that and o ther deep boreholes,may indicate marine deposition . No firm correlation s coul d be m ade however from one hole to another.

Yerstappen ( 1975) discussed the changes in clim ate that can be expected inthe South-East Asian areaduring the Pleistocene, and described conditions that would a llow the development of such piedmontpl a in s.

Age and Correlation

There is no direct evidence for the age of the Old All uvium in Singapore . Scrivenor (1924) originallyassumed it to be o f Quaternary age and Alexander (1950) listed it as? Pleistocene. Burton (1964) stated thatits deposition may extend back a t the most to la te Pliocene.

52

Fig. 3.43

'~ (l~'.~;.~. ~~~~f'

Fig. 3.44 Clastic dl'k e in Old AlluviulII at Bedok Sand

Pit (GR 592475 ).

53

Sta uffe r ( 1973) li sted find s of a mid Pleistocene elephan t too th ( Palaeoloxodon nallladicus) from th eKinta Va ll ey , M alaya a nd remain s of a rhinocero s, suid d eer , turtle sh ells , a nd ca tfi sh spines , which areregarded as probab ly o f Pleistocene age.

Three radi o metric ages were li sted by Stauffer (op cit), fro m Sungei Besi , M alaya . Two samples gaveC I4 ages of> 41,200 and > 41,500 respectively and a re thus beyond the limit of the method, and the thirdyie ld ed a n age o f 36,420 (+ 1255-1085) BP from wood ap pa rently in the po siti o n o f growth . Radioca rbo ndete rmi na ti ons on wood and peat fro m the Kinta Va ll ey proved to be beyo nd the ra nge of the method. Thege ne ra l ch a rac te r o f the fo rmati o n h owever suggests a g rea ter age th an 36,000 yea rs a nd the authorsco nside r tha t thi s da te should be accepted with cautio n . It wo uld require less tha n 1% contaminatio n bypresen t day orga nic ma te ria l to produce a figure o f th is o rder.

A part fr o m the cha racteristi cs of deep weathering , the common occurrence of slumping due to theso luti on of the unde rlying bedrock, and the degree of dissection , listed by Stauffer (1973) , the occurrence ofO ld All uvi um in deep tro ughs must also be con sidered in a di scussio n o f its age. The Old Alluvium is fo undto a dep th of -149 m in Singa po re. Aleva (1 97 3) plotted , by use o f an aco usti c continuous profiler, cha nnel scut to a dep th of -1 00 m and filled with an ' Allu vial Co mplex' , between the Singkep a nd Bangka Islands,and aga in a ro u nd the K a rima ta Island s, a n a rea abou t 3° o f la titude to the south and south-eas t ofSingapo re . These cha nnels li e benea th a ' Younger Sedimenta ry C over' and below an extensive 'M arin eAbras ion Surface ' now a t a depth of -20 m to -30 m , It would a ppea r rea sona ble to correla te Aleva'sA ll uvial Co mp lex with the Old A llu vium and his ' You nger Sedimentary Series' with members o f theKallang Forma tion .

H e desc ribed th e Alluvi a l C o mplex a s ly in g o n an 'Ol der Sedimenta ry Cover' and fillin g deep tro ugh swithin thi s Older Sedimenta ry Cover. He recogni sed evi dence fo r repea ted ve rtica l movements o f theeros io nal base level , and sma ll sca le b lock fa ult ing during the depos it ion o f hi s Older Sedimenta ry Cover.Pa lyno log ical de te rmin a tion s o n the O lder Sedi mentary C ove r indica te a Mi o cene-Pliocene age, but gi veno clear di stinction be tween the O lder Sedimenta ry Cove r a nd th e Allu via l Co mplex. The two unit s a lsos howed similar li thologies in drill cores . A leva sugges ted that an upper Tertiary to Pleistocene age wo uld bereaso nab le for t he depos ition of bo th the O ld er Sedimenta ry Cove r and th e overly in g A llu vial Co mplex.

Fro m t he e\ide nce c ited above it ap pea rs that th e Old A lluviu m o f S ingapo re must da te fr o m a peri oddur ing which tectonic movements were sti ll tak ing place. It ca nn o t reaso nab ly be a rgued th at e ros io n hascut a channel In Sin ga po re to a de pth of 149 m below sea -leve l so far from the postul a ted edge of th ePle is tocene S unda la nd with o ut it be in g a mo difi ca tion o f a downfa ulted o r dow nwa rped zo ne . It is possibl eho \\ever that th e buried va ll ey is pa rtl y fill ed wit h the equ iva lent of A leva's O lde r Sedimenta ry C-ove r, butthi s ha s not been recogn ised in d rill ho le o r geo phys ica l exp lo ra ti o n .

Terti a ry \\arp ing has been recognised in the semi-c rato n o f the Asian lith ospheric pla te . Folding o fTerti a ry sediment accom p a nying fa ult ing has been recog nised alo ng th e Kua la Lumpur- Enda u faultzone in Ma lays ia (Gobbett a nd Tj ia 1973) and Renwick a nd Ri shwo rth ( 1966) repo rt ed la te T e rti a rysedi me nts d ipping a t up to 25" to a leve l o f a t least 144 m belo w sea-leve l fr o m ka mpo ng Bukit Kepo ng inJo hor. T he areas o f block fa ult ing cited a bove a nd th ose recog nised by A leva ( 1973) a lso li e withi n th eAsian lithosp he ri c plate.

As wa rp ing or fa ultin g ap pea rs to continue through at least to la te Tertia ry time , a nd deposition of th eOld A ll uvium ap pea rs to be tied to th is fa ul ting, deposition mu st h ave co mmenced by the end of theTert ia ry.

The re is in su ffic ient d a ta to recon struct the o riginal agg ra da tion a l surface o f th e Old Alluvium . Thetop of the unit in Singa po re li es at 46 m but in Jo hor is reco rded up to 70 m with ma rine beds occurring a tthi s height and do ubtfull y to 138 m . As the Old Allu viu m is do min a ntly a terrestria l de posit , thi s depo sit io nmust be tied in to a base level which wa s a t times as high as 70 m . Aleva (1973) mapped his Allu vialComp lex as pred a ting hi s up per pla na tio n surface which he co rrel a ted with the Riss-Wurm Interg laci a l.Ve rstap pen ( 1975) showed tha t a clim a tic change with lower precipita tion , ra infa ll , a nd tempera ture woulda llow for the d epos ition of a coa rse poorly wea thered sediment similar to that o f the Old Alluvium, andthu s depositi o n ca n be associa ted with clima tic changes accompanying the Pleistocene glaci a tions . It wouldfo ll ow th a t d ur ing the wa rm interglacial s, a mo re deeply wea thered finer-grained sediment would bedeposited . Such sedimentation has not been recogn ised within the Old Alluvium , but erosion of the OldAlluvium durin g the Wurm Glaci ation is recognised and fine sediment is deposited in the eroded channel s.

T he uppe r lim it o f the Old A llu vium is thus taken to coin cide with the c lim a t ic wa rming fo llowing , a tthe la test , the R iss Glacia ti o n, but beca use o f the absence o f ' normal' sedimenta tion within the OldA lluvium , it is proba bly ea rlier.

54

Variations in the term Old Alluvium and it s predecessors have been used in Singapore and WestMalaysia since Scrivenor first recognised the unit in Si ngapore, and the correlatives in this area have beendiscussed by Stauffer (1973) . The Alluvial Complex of Aleva et af. ( 1973) is also correlated with the OldA Iluvium a nd deposits underlying the Palembang peneplain and described by Verstappen (1975) alsoappear to be correlatives.

HUAT CHOE FORMATION (HC)


The formation is defined as those mostly fine-g rai ned, ponded , terrestrial sediments exposed in claypits 1.5 km north of Huat Choe Village and I km north-east of Nanyang University (Fig . 3.45) . Suchdeposits do not appear to have been recorded in Singapore before.

The formation has been recognised in one area o nly and is of limited extent. It covers an area ofapproximately 400 by 200 m and from the lowest exp osure to the upper eroded surface it is not more than 6m thick. It has been separated out from the other Quaternary deposits because of its different deposition a lsetting , its supposed age, and its economic use.

Content

The formation is made up of a poorly bedded white kaolin-rich clay with minor amounts of quartzgravel. The clay is similar to that in the low-lying areas of deeply leached Jurong Formation rocks nearby,and it is probable that the clay was derived from these rocks . Plant remains , mainly sedges, and the shells ofan unidentified land snail were found within the deposits, but no systematic work has been done on theseremains . Although the sedges were in situ, it needs to be established that the land snails, whose shells shO\\littl e sign of leaching, have not been introduced accidently into the clay pits during extraction of the clay.

Field Relations

Exposures show the formation as lying uncon forma bly on an eroded , moderately weathered surface ofmoderate relief cut in the Jurong Formation. It liesjust to the east of a fault bounding, and thus within thedown thrown Jurong area, and it is suggested that it was laid down as a lacustrine sediment within this areaduring the period of faulting. It is probable that other , as yet unrecognised deposits occur close to the faul t.

Age

There is little ev idence as to the age o f the Huat C hoe Formation. There is no evidence of Lithificat io nor obvious in-situ weathering, unless it was leached in place, suggesting any great age. Its position does notrelat e to the present-day drainage pattern, but m ore to the position of the fault mentioned a bove . There isno evidence to date the las t faul t movement. Burton ( 1973 A) observed tight folding and minor faultin g inthe Old Alluvium in Joh o r and thus movements in the ea rly Pleistocene, or even younger can be postulated .It is sugges ted that th e Huat Choe Formation is take n as lower mid-Plei stocene or younger.

TEKONG FOR MATION (T)


The sediments forming the wide terraces stan ding between 3.6 m and 5.5 m , usually a round 4.0 m,above sea-level on Pulau Tekong Kechil and Pu lau Tekong are assigned to the Tekong Formation (Fig .3.46). Sediments beneath surfaces within the same height range on Pulau Ubin and at Changi, a ndremnants of terraces along the north-east and south-west coasts of Singapore are also correlated with theTekong Formation, as also are terrace deposits found at a similar height in the tidal reaches of SungeiSerangoon, Sungei Seletar, Sungei Kranji and Sungei Pandan, and above base level in the Bedok Valley .

Bore holes in the type area on Pulau Tekong Kechil pass through some 5 m of sand beforeencountering a yellow clay containing quartz pebbles. As drilling did not continue into this clay it is notknow if this represents the base of the formation . Quartz pebble beds were not recognised in the underlyingPalaeozoic rocks although quartz veins were seen . Quartz pebbles were recognised within the TekongFormation at the type locality.

Content

The borehole records describe the formation as being a loose fine to very fine light brown sand withpeat and wood fragments, and occasional quartz pebbles. An exposure by the river at Changi (G R 659538 )reveals a well sorted light brown slightly iron-stained fi ne to medium quartz sand. The drilling records alsoreport the presence of fragmented shells within the cu ttings.

55

_ . _.J

56

Fig. 3.46 Terrace of the Tekong Formation on Pulau Tekong Kechil. It has a meanaverage height of 4 111 above mean sea-level. Viewed from Pulau SajahatBesar.

Field Relations

The base of the unit has not been recognised with certainty, but the formation is seen to overlie each ofthe pre-Tertiary formations, and it is assumed that it lies unconformably on these formations . Youngterraces have been cut into the Tekong Formation , particularly along the Pasir Panjang coast.

Apart from being finer grained, the unit shows similar characteristics to the present day sand bankssouth of Pulau Tekong, and it is suggested that the formation represents beach and off-shore sand bankdeposits tied to a previous higher sea-level stand at about 6 m. The presence of shell fragments in the PulauTekong Formation supports this suggestion.

Age and Correlation

The Tekong Formation is assumed to have been deposited at a period when sea-level stood at about 6m, and its deposition could thus be tied to the 'Daly Levels' variously quoted as 5 m or 6 m and dated ashaving occurred between 6,000 and 7,000 BP (Tjia , 1970, Tjia, et al. 1972, and Fairbridge, 1961).

It ha s been argued by Nossin (1964) that beach ridges are at present being constructed to heights of 6m along the east coast of Malaya, but surfaces recognised in Singapore all lie in sheltered zones, on islandswithin the Johor River mouth area, and within the sheltered tidal reaches of rivers flowing north into theSelat Johor, and hence such aggradation is not to be expected. Even around the more exposed southern andsouth-western islands, wave energy is low. Swan (1971 ) stated that waves of I m height were exceptional ,and these were observed to the so uth-west at Raffles Lighthouse on Pulau Satumu.

The subsequent cutting of terraces in the Tekong Formation on the south-west coast lends support to

the hypot hesis that these terraces are not present-d ay features.

Deposits of a similar elevat ion have been reported fro m Indonesia and Malaysia , and are correlatedwith the Tekong Formation, and Tjia (1970) listed terraces at 6 m to 8 m on Bangka and Billiton, andreferred to the presence of further terraces of similar heights in the Indonesian Archipelago .

KALLANG FORMATION


This formation includes the sedi mentary deposit s discussed by Alexander (1950) under the heading of' Recent Alluvium a nd related deposits' and the recent deposits referred to by Scriven o r (1924) . Theformation is na med from the Kallang River Basin where it is most extensive, but no type area is proposedas the formation is poorl y exposed . Most of the evidence for the existence and subdivision of this formati oncomes from boreholes. and the physiographic setting of the deposit. The formation is found along thecoast line a nd extending into th e hea dwa ters of the rivers draining Singapore, its most extensivedevelopment being around Sungei Kallang, Sungei Jurong, Sungei Kranki. Sungei Serangoon and Sunge iSeletar. Extensive deposit s are a lso found on Pulau U bin and the so uth-west and southern islands , and asreef deposits exposed to the south and south-west of Singapore at low tides.

The deposits are generall y low lying, and are seldom recognised more than 4 m above sea-level excep tIn the more inland a reas .

Five members are recognised within the formation , an d these are referred to informally as the Marin eMember, Alluvial Member , Littoral Member , Transitional Member, and Reef Member. Two di visions canbe recogni sed in the Marine Member in certain dril l holes.

MARINE MEMBER (Km)


Two divisions can be recognised within the member in boreholes, but the member is not recognisedanywhere a t the surface. The two division s, referred to as the Upper Marine Member and the LowerMarine Member, are best known in the Kallang River Basin area where they can be found within one metreof the surface.

Undifferentiated Marine Member sediments are fo und in Sungei Jurong, Sungei Pandan, SungeiKranji, Sungei Seletar, Sungei Bedok and Sungei Punggol and also at Changi. The member has beenrecognised in boreholes as extending inland at least as far as Stevens Road in the Bukit Timah Valley (G R479461), Thomson Road in the Whampoa Valley (GR 499459), and Braddell Road in the Kallang Valley(G R 514485). The maximum thickness recorded to date is some 35 m close to the Rochore Canal (G R518553) and again one kilometre to the west at GR 511435 where the upper surface may lie between 1.0 mand 1.8 m above sea-level.

57

Content

The base of the member is usually c haracter ized b y a peaty clay sa nd , seld om more tha n 3 m thi ck, andthi s passes up into a so ft blue g rey mud, or sa nd y mud . Tan ( 1972) stated that the mud contained on anaverage a 50~/~ clay fraction . Thin san d and pea t layers may occur within the sequence.

If the two d ivisions occur, the boundary is recognised at the to p of a stiff reddish brown si lty clay , orsometimes a loose sa nd , w hich li es on top of the lower of the two sepa rate, but otherwise indisting ui sha ble ,blu e grey mud s. This boundary usuall y lies a t -10 m to -20 m but ca n be found down to -28 m . Peat depositsm ay also be assoc ia ted with this ho rizon . It is assumed tha t the stiff silty clay represents a zone ofdesicat ion, a llu vial o r m ari ne reworki ng , a nd co lonization b y plants during a period of low sea- leve l.

Shell fragments are found frequentl y in the Marine Member a nd these have been identified by Dr. LimChuan Fong (pers. comm.) as belo nging to a shallow muddy marine environment. Similar fa una lassemblages are found in si mil ar settings o ff the coast of Singapore at the present time.

Fie ld Relations

The Marine Member is th e oldest unit in the K alla ng Formation and it lies unconform ably withinva lleys cut in the Buki t Timah Granite , Juro ng Formation and Old Alluvium . The basal contact has been

recog nised in drill ho les on ly a nd the rocks beneath a re usua lly o nly modera tely weathered .

These drill hol es which show th e inland exte nt of the Marine Member a lso indicate that the Marine

M e mber interdigitats wit h th e Alluv ia l Member.

Age and Co rrelation

The M a ri ne M ember fili s va ll eys cu t to at least 35 m below sea-leve l at a ti me of low sea-l eve l and has

been deposited in two phases to attain a maximum height of 1. 8 m . It is thus sugges ted that deposition

started during a period of m arine transgression. foll o wi ng a low sea-level stand. Deposition was interrupted by a seco nd lowering of sea-level to a depth of at least -28 m after which sea- level rose again to 1.8 m.

Biswas ( 1973), working off the no rth-east coast of Mal aya, recogni sed the last Quaternary fa ll in sealevel as corresponding with th e Holocene-Pleistocene bou nda ry , a nd has dated plant matter from a buriedmangro ve swamp now at + 65 m below sea- level as having been deposited 11 , 170 ± 150 BP. As there is n oevidence of any subsequent lower ing of sea-level of the order required to erode ch a nnel s ir. Si ngapore to adept h of -28 m . and as th e re is no evidence to suggest a ny major ea rth movements in Singapore during theH olocene. it is sugges ted that the U pper M a r ine Member was depos ited during the tran sg ressi o n .fo ll o \\ ingthe 11 .000 B P low sea-level. Deposition presum abl y continued until t he fall in sea-l evel from 1.8 m t opresent sea-leve l some 5.000 BP (Tjia, 1970) . It follows that the Lower M ar in e Member was depos iteddu r ing the penultimate Wurm sta di a l.

ALLUVIAL i\!l EM BER ( Ka )


The A llu vial Member is found as val ley fill throug hout the Republi c and as a thin ve neer on the floorof the K a ll ang and Juro ng Ri ver Basi ns. It is of limited exten t in the off-shore islands. It has been mappedfr o m it s phy siog raphic set ting a nd from drill ho le data.

Content

T he A llu via l Member deposits vary from pebble bed s throug h sand, mudd y sa nd, a nd clay, to peat(Fig. 3.47). N o stud y has been made of these va riations. Ex ten sive peaty sand a nd mud is found in theK a ll a ng an d Juro ng R ive r Basi ns .

Field Relations

T he Alluvial M ember overlies the older form ations and is seen in drill ho le evidence to interdigitatewith the Marine Member, and can be assumed to interdigitate with the other me mbers of the K a llangFormation .

Age and Correlation

Interbedding of the Alluvial Member with the M a rine Member can be recognised in drill h o les at leastto the base of the U pper Marine Member. The age of the Alluvi a l Member is thus g iven by correlation asspa nning the Holocene.

58

LITTORAL MEMBER (KI )


The Littoral Member includes those sediments deposited in active coastal regions as beach deposits,immediate offshore deposits, and as tidal sand banks.

It is found along the southern and eastern coast of Singapore, and on the offshore islands. It alsooccurs as shoals south of Pulau Tekong and east of Pulau Ubin and Pulau Seletar, and as small isolatedstrips along the northern coast. The member is recognised in drill holes between Kallang and Bedok to-10 m, but it is normally less than 5 m deep. It is found building beach ridges and as terraces up to a heightof 2.8 m on Singapore and the islands to the north-east, and up to 3 m on the more exposed islands to theso uth-west. Beach rock found on the southwest facing coast of Pulau Tekulor an d St. John Island is alsoincluded within this member.

Content

Clean sand and pebbly sand is the most common lithology within the member. The sand is dominantlyof quart z, but lateritic, shell , and lithic fragments also occur. Swan (1971) stated that the sand may containup to 600 ° calcareous matter. He also repor ted feldspar as being present in the sa nd at Kampong Bahru onPulau Ubin and on Pulau Sekudu, and heavy minerals derived from the igneo us rocks may also be foundon Pulau Ubin.

The beach rock is an iron-cemented quartz sand or lithic conglomera te and dips seawards at the sameslope a s the present beach (Fig. 3.48). It lies a t a height of I m or less above the present beach and extendsbeneath present low tide level. Alexander (1950) reponed the presence of primitive stone tool s in the beachdeposits.

Field Relations

The Littoral Member is seen to lie conformably on the Marine Member in drill holes, andunconformably on the older formations. It is assumed to interdigitate with the Transitional , Alluvial. andReef Members and can also be expected to interdigita te with the Marine Member.

Age a nd Correlation

The Littoral Member is essentially a present-day deposit , but terraced deposits associated with it arefound up to a height of 2. 8 m and are associated with the 'Da ly' periods of higher sea-level whicli ha ve beenda ted at 5.000 BP and 3,500 BP (Tj ia 1970) (F ig. 3.49 ). The extension of beach sa nd to -10m ma y ind icatedeposition during the later stages of the post Wurm transgression, but it is considered more likely torepresent more recent off-shore deposits laid down below sea -l evel.

The presence of beach rock belo\\' present 10\\ tide level suggests deposition when the sea stood I 111 to

2 m below the present level. Tjia (1970) has recognised a -2 m sea-level as common on the Sund a Shelf andgives an age range (Tjia Of! Ci l , Table II) of 1,500 BP to 3,000 BP for thi s.

It is therefore suggested that the Littora l M ember ranges in age from 5,000 BP to the present day.

TRANSITIO:\AL MEMBER (Kt)


The Transition a l Member is found in the ri ve r mouths and tidal swamps surrounding Singapore,particularly those at the western end of the island , and is typified by the presence of mangrove swa mps.Ex ten sive areas of Transitional Member may be found on Pulau Ubin, Pulau Ketam, and Pulau Seletar.The member however is not now recognised in the Kallang Basin, but mangrove swamps were plotted onthe early maps of Singapore . These areas are now buried under reclamation.

Content

The Transitional Member is deposited in a low energy environment. It is an unconsolidated black toblue-grey mud, muddy sand or sand with a high organic con tent. The high organic content and general lowenergy conditions, together with the slow rate of deposition, give rise to a general reducing environ ment.The sand is mainly of quartz derived from the nearby rocks, and mica is found with the finer-grainedsediments.

59

Fig . 3.47 Horizontal lavers 0/ peat,mudd\' sand and mud 0/ theAlluvial Member exposed inexcavation near EwartCircus. Bukit Timah (GR423486)

Fig. 3.49 A dark broli'n pebble beacha/the Littoral Member at 2m lying on mudstone andsill-slone on Pulau long .

60

Fig. 3.48 Hard. iron-cemented beachrock o/the Littoral Memberexposed at 10\\' tide on the.loll1h-west coasl 0/ PulallTckllkor.

Field Relations

This member is found from borehole evidence to overlie the Marine Member and also the LittoralMember. It is a lso seen to li e on the cut surface of the older formations on Pulau Ubin and the southwestislands. It was seen in excavations at Sungei Kranji (GR 378573) to interdigitate with the Marine Member .

Age

This member has been ma pped on its physiographic setting in the present day environment and henceby definition is a recent deposit and postdates the las t sea-level Ouctuation .

REEF MEMBER (Kr)


This member is recognised around the southern, western, and south-western islands only. The reefs areexposed during periods of low tide as broad platforms surrounding the islands, or as disconnected Oattopped shoals associated with former islands.

The coral sand making up this member is quite thin in the central portion of a number of the reefs , andmay wedge out exposing the underlying Jurong Formatio n. The thickness of the fore reef deposits howeveris unknown .

Content

The reefs are made up of cora l and its detrital frag ments . These fragment s grade down to sand-sizeparti c les. Swan (1971) stated that 99.9 0

0 of the sand o n the coral reefs is calcareous but that quartz andheavy seco ndary ferr uginous grains are also found. On the reefs attached to present day islands a higherpe rcentage of quartz and seconda ry minerals can be found.

Field Relations

The Reef Member lies un co nformab ly on a ma rine cut surface in the Jurong Formation but mavinterdigitate with the Littoral and Alluvial Members.

Age

The coral on the reefs is still actively growing a nd the top surface is thus related to presen.t sea-level.The underlying Jur ong Formation rocks have been pl a nned off to a level correspo nding to present low tideleve l. or to a level associated with a sea-level I m to 2 m below that of the present day; thus the base of themember is also related to these sea- levels .

The age of the Reef Member is thus about 3,000 BP to the present.

61

4 STRUCTURE

Singa pore lies at the southern tip of the Mal ay Peninsula and is structurally an integral part of it. Therl)cb ,)f the Republi c show the same north-west trend as that running through from Kulau Lumpur toJol1l'r Ra hru in West Ma lays ia and on south through the islands of the Ri a u Archipelago , Banka andBillit l)n . The st ru ct ures th at have affected the Tri ass ic sediment are thought, in the Singapore area, to haveresul ted frl)1l1 tectonic activity which started prior to the ir deposition in lower Triassic time and continuedthr,)ugh as a rela ti vely mild process until as least early Jurassic time. The tectonism appears to have beenless \il)!en t than th a t recognised in Malaya and also to ha ve lagged slightly behind it in time.

I're-t\lesozoic rocks recogni sed in Singapore include the gabbro-norite described by Hutchison (1964)from Rukit Gomba k a nd the Palaeozoic volcanic and sedimentary rock s of the Sajahat Formation.

:\ secl)nd peri od of faulting, dominantly a block faulting, occurred, probably in Pliocene time, and isevidenced by the topog raphic expression in the Triassic sediment and granite, and by the depth to basementheneath the Old Alluvium.

PRE-MESOZOIC STRUCTURE

T he sedi ment of th e Palaeozo ic Sajahat Formation is both folded and stretched as well as faulted, butthe c\idence for a pre-Mesozoic age is not positive . The style of folding in the fine sandstone of the SajahatFnrm;\til1l1 is diffe rent from th a t in the younger rocks and hence it is considered that the diastrophismatlel'ti ng them is o lde r. The minor folds are angu la r rat her than rounded, the cleavage is better developedthan in the Triassic rocks, and bou din age is mo re common . The rocks are no t s ufficiently well exposed toalll"l the co llecti on of data for st ru ctura l analysis, but those observations ma de show the two dominantst rike directions to be c lu stered a ro und 030°, dip 45W and 155°, dip 25E. No majo r folds were recognisedand Ill) data was co llected o n the minor folds, joints, or fau lt s. Jo ints in the Pa laeozoic Volcanics, quotedearlier as being verti ca l and trending due north or at 125°, were seen in one locality o nl y. Grubb (1968)recll~ l lised a west -n orth-wes t ( 11 2.5°) a nd north-east (4 5°) t rend in joints throughout the Pengera ng area.Snuth-Llst Johor. a c lockw ise rota tion of 20° to 40° from those observed in the Singa pore a rea.

MESOZOIC STRUCTURE

II 1It ch ison ( 1973 B) postulated tha t the gra nit e in Malaya was forced up during the uplift o f the axialLO ne ;lnd spread out to fo rm the M a in R a nge and East Coast Bat ho lith system s. The gra nite of Singaporelies ill the East C oas t Ba tholith sys tem ( Hu tchison 1973 A) .

.\ s u[li lft co ntinued. a north-west t rend ing downwa rp paralleled the a xi s o f uplift. The troug h sofnrtllcd is the back a rc sedimentary basi n of Hut ch ison ( 1973 A. Fig. 7). That thi s trough was mobilet h ro ll ~ h l)lIt t he Tria ss ic is ev idenced by the presence of intrafor ma ti o nal brecc ia (F ig. 4.1) . and by the ra pi dvari ;ll1(ln In fa cies and a ltern ation s of biofacies within it.

Sedimentation in th is trough co ntinued through to at least th e lowe r Jurassic when the St. John FaciesconLlllling the Mt. Guthrie fos sil fauna was depos ited . The locus of uplift pres umably migra ted so uth sothat the sed imentati on was termin ated by a later phase of the same event respo nsible for the uplift of theMalaY;ln Peninsula in Triassic time.

Folding

II is suggested that the fo lding of the Triassic sedi menta ry pile started before the cessation ofsedimentation in lower Jurassic time by a sliding of the rock mass to the no rtheast against the buttress ofgranite. The fold s va ry in style from open through vert ica l isoclinal to isoclin al over-folds but a re normallyopen folds (Frontispiece & Fig. 4 .2) . Parasitic folds can be fo und on the limbs of larger folds and these areresponsible for the rapid variation in the strike and dip that may be observed . Most beds strike north-westbutthe dip may vary over a short distance from \00to vertica l, and field studies show that overturned bedsdipping between 70° an d 90° are co mmon ; shallower dips in overturned beds were not found . Few fold axescan be followed for mo re than I km, a nd although in general the fold axes a re seen to be sub-horizontal,folds may plunge steeply at either end.

62

The fine-grained sediment, particularly that of the Queenstown Facies, is sheared obliquely to thebedding (Fig. 4.3), and it is suggested that these beds frequently failed incompetently during folding whilethe more rigid sandstone beds and conglomerate beds, particularly those of the Rimau Facies, were foldedor tilted, possibly as discontinuous bodies.

Isoclinal overfolds are recognised both in the city area and at Jurongjust south of Nanyang University(Cross-section B), and these show translation to the northeast. It is from these data, together with theexistence of a low angle thrust striking south-south-east from Nanyang University, that the north-easterlydirection of stumping is postulated.

Faulting

Very few faults are exposed, and those that have been observed are usually small-scale features . Mostof the faults plotted have been recognised on the alignment of erosional features, abrupt changes intopography. or detailed field evidence of litholog ica l discontinuities . There is little evidence for the age ofthe faults. The only faults that can be assigned positively to the Mesozoic period are the three thrust faultsand associated tear faults which are named as the Murai, Nanyang, and Pasir Laba faults (Map Sheets Iand 5). The Murai Fault trends north-east for 3.2 km and then swings around to the south-east for a further0.6 km. Movement on this fault has been sufficiently intense to be responsible for the dynmaicmetamorphism of the Triassic sediment on the southern overthrust side . It is suggested that the principalhorizontal stress was from the south-west with the main thrust front now being represented by thecomparati\'ely small south-east trending arm, and that the south-west trending arm is a tear fault with areverse component. The whole mass has over-ridden the normally, north-west trending Triassic sediments.

Schist IS found associated with the Pasir Laba fault, but not with the Nanyang fault. Schist is alsofo und within the Jong Facies in Jurong but no associ ated fault was recognised. The sediment associatedwith the ]\;anyang fault is a muddy and tuffaceou s sand, compared with the dense mudstone or sandstonefound met a morphosed at the other two faults , and hence a more plastic type failure is proposed.

Schist pebbles have been found in the Triass ic conglometrate in Singapore and these are identical tothe Mu ra i Schist. and thus it must be argued that the thrusting described above occurred be fo re thecessation of Mesozoic sedimentation in the Singapore area. The apparent association of an isoclinaloverfold. assumed in the previous section to have been developed in Mesozoic time, with the Nanyang fa u lt(c ross-section B). also suggests that faulting too k place in Mesozoic time.

Most o f the fault affecting the Jurong Formation strike between north-north-east and north-east, witha smaller percentage striking between north and north-east. In the granite the faults strike between northeas t and east-north-east or around west-north-west.

The north-east trending faults affecting the Jurong Formation are also considered to be tear fault sbetween rafts of sediment sliding to the north-east. The Henderson Road fault (Map Sheet 6) is well definedby the offset of conglomerate at Tanjong Berlayar and the discordance of bedding on either side ofHenderson Road (GR 475408), and the Tanjong Lokos fault (Map Sheet 8) and Pepys Road fault (Ma pSheet 6) by the juxta-position of anticlinal and synclinal axes across the faults. In no case is the fault plan eexposed, but on the position of the nearby ou tcrops, they must be high-angle faults .

The north-west trending faults are less common a nd possibly are thrust or bedding faults ca used by thenorth-east translation of the Jurong Formation . These faults were seldom seen in exposure. One, howe\ er.at Pearl Hill was seen to be near vertical and two at Kent Ridge were also near vertical. It is also suggestedthat Selat Jo hor on the western and northern sid e of Singapore west of Sembawang has formed by erosi onalong north-east and north-west trending fault s.

It has not been possible to determine whether the lineations seen in the plastonic rocks are faults ormajor joints. The lineations have been mapped mainly from topography with the aid of aerial stereophotographs. No offset features were recognised , but step downs in topography were recognised associatedwith the Nee Soon Fault (Map Sheet 2) and the western end of the Seletar Fault.

As these lineations are confined to the granite their age of formation is taken as being associated withthe tectonic uplift of the granite in early Triassic or during the period of block faulting in early Pleistocenetime.

CENOZOIC STRUCTURE

A series of blocks can be recognised, both in the Jurong Formation and Bukit Timah Granite.standing at different elevations, and the existence of a down faulted block has been suggested earlier asoccurring beneath the Old Alluvium . This form of topographic relief suggests a period of block faulting,

63

Fig. 4.1 Intra(o rmational breccia ofblack mudstone in sandstonef CR 378499 ) , CentralSingapore.

Fig. 4.2 .-1/1 anticlinal fo ld seen 0/1

Tan;ong Lokos, 51. John sIsland.

Fig . 4.3 Oblique shear developed inthe Qu eens t own .Faciesexposed in an excavation offPepI 's Road.

64

1"

~

II

possibly accompanied by warping, at a period prior to or during the early phases of deposition of the OldAlluvium , but sufficiently recent to control the present-day topography. It has been suggested in thedi scu ss ion of the age of the Old Alluvium that such fa ulting occurred in late Tertiary time.

It is not possible on the evidence available to separate those faults showing Mesozoic movement fromthose showing Cenozoic movement. It is probable that some of the older fault planes were reactivatedduring the Cenozoic, particularly those to the west of Sungei Jurong and east of and including the NeeSoon Fault. The Ama Keng fault (Map Sheet I) in particular bounded a down thrown granitic block andallowed Old Alluvium to be deposited in the north-west of Singapore against the Jurong Formation .

It appears that tectonic activity was minimal after the deposition of the Old Alluvium. Burton (1973 A)recognised tight folds and a fault with a throw of about 6 m in Old Alluvium in Johor. Small faults havebeen observed in the sand quarry at Bedok. A clastic dyke was seen associated with one of these faults butthe faulting and dyke were interpreted as compaction feature rather than of tectonic significance (Fig.3.44 ).

Recent seismic activity in Singapore has been reported by early writers, but their papers were notavailable to the authors. It is suggested that the epicentres lay close to the subduction zone west of Sumatraa nd that these seismic waves do not necessarily reflect any activity in Singapore itself.

65

5 GEOLOGICAL HISTORY

The earl iest geo log ica l reco rds in Singapore are gi ven by the Gombak Norite, Pa laeozoic Volcanicsa nd Sajahat Form a ti o n sediments. Hutchison ( 1973 A) has rel a ted the Gombak Norite to th e LowerPa laeozoic Malaya n Geosyncline. He drew the boundary o f the subducting plate as passing throughSingapore , and suggested th at the norite represented a portion of the ophiolite suite emplaced immediatel yto the west o f the subducti on zo ne . The Sajahat Formation sediments lie to the east a long the s it e of theassociated Malayan Geosyncline a nd co uld thus be interpreted as representing Lower Pa laeozoicgeosyncl inal sediment.

As th e geosynclina l axis mig rated to the north-east , the sediment of the Saja hat Formation was foldedaga in st the sta ble shelf to the southwest and a genera l north-west structural trend imposed o n it.

It would follow that the Palaeozoic Volcanics represen t rock from the volcanic arc which followedbehind the subdu ction zone as it mig ra ted to the north-east, and Hutchison h as plo tt ed the volca nics insuch a position in his palaeotectonic reco nstruct io n (Hutchison 1973 A, Fig. 5).

A n alterna ti ve interp re tation is to consider the Gombak Nori te as represe nting th e primary stage ofthe Triassi c granite associati on and the Sajahat Fo rmati on as being co ntact metamo rph osed by a you nger '?C retaceou s g ra nit e, possibly represented by the roc ks of Pulau Sekudu. If thi s interpre ta tion is co rrect , theSajahat Fo rm at ion cou ld be metamorphosed Juron g Formation, a nd the dykes c utting it would beassociated with the C retaceous pl utonic intru sio n . The presence of the Pa laeozoic Volcanics, which G rub b( 1968) believed wre metamorphosed by Triassic granite, and the occurrence of sedimentary intrusions inthe Bu kit Timah Granite, which were presumably deri ved fro m the Sajahat Formation make this theoryun a tt ractive.

Granite emplacemen t in cent ral and eastern Singapore may have co mmenced in la te Permi an time butwas mo st pro nounced in early Triass ic time. The granite was considered by Hutchi so n (1973 C) to bemesozonal , but Seet ( 1974) concluded fro m the st ud y of the triclinicities of the feldspar that th e rocks ofPu lau Ubin \\ere emplaced at a hig h level.

There is evidence in the Bukit Timah Granite of assimilation, and the producti on of several pha.ses ofhyb rid rock, and a mix ing of th e hybr id rock types can be observed . Large rafts of co untry rock andn umerous smaller in c lusions at various stages of digestion ca n be seen. As th e larger rafts bear little sign ofmetamorphism, and they li e usuall y in a nea r vertical pos ition , it is suggested th a t the y have beeninco rp o rated at a relatively sha ll ow depth , probably in a fa irly visco us magma. The evi dence of grea terass imilati on of the s ma ller inclusions, and prod uction of comp lete ly Iluid hybrid magma s, suggestscons iderable assimilation at depth as well.

The evidence of rafting , ass imil ation, mi xing and re- mixing s uggests that there co uld ha ve beencons iderable tectonic acti vity accompanyi ng the e mpl aceme nt and crystallisa tion of the acid magma.

'The inclusions indicate a va riety of host rocks , norite, rhyolite, andesite, argillite a nd qu a rt zite, anda lth o ug h most of these rock types ca n be fo und in the Gombak Nori te, Sajahat Formation a nd PalaeozoicVolcanics, on ly the norite ca n now be seen in con tact with the g rani te. At the con tact, th e norite ismetasomatized and the granite penetrates through the metasomatic zone into the relativel y un alte red rock.

La te cooling phases of the acid intrusion have been injected into th e g ranit e pluton a nd o lderformation s to form a se t of dykes of va ryi ng composition . Th is has been followed quit e closely by a secondph ase of dyke empl ace ment , this time of a basic na ture . This event probably accompanied the further upliftof the batholith.

Dur ing coo ling and uplift of the g rani te and associated no rite , joints have developed and fa ultingoccurred. 0 det ai led study was carried out during the survey on the joint pa tterns.

The pluton co ntinued to ri se, initi a lly at a fairly slow pace to a llow for the deep weathering of thecovering strata . As the pluton continued to rise, deposition of the Jurong Formation took place in the backa re sedimentary basin . This basin was highly mobile throughout sedimentation as evidenced by the rapidvariation in facies with ch anges from marine to terrestrial sedimentation a nd vice-versa. Towa rds themiddle of the sedimen tary cycle, quite coa rse-g ra ined facies become prominent , suggesting a more rapiduplift of the surrounding land. With the exception of the norite at Bukit G o mbak, the quartzite fro m PublicUti lities Boa rd Test ho le No . I at Bedok, the Palaeozoic rock a t Punggol a nd near Tanglin , the rock

66

1

T

I

enclosing the original batholith has either been removed from the main island of Singapore or is nowburied beneath younger rock.

Uplift of the back arc basin continued with the uplift of the Main Range Granite* to the south-westoutpacing that of the east coast granite so that the basin tilted to the north-east and the Jurong Formationslid to the north-east. The failure within the Jurong Formation can be looked on as a semi-incompetentfailure with slabs of coarse-grained sandstone tilted and folded in a more plastic fine-grained matrix. Tearfaults in the direction of translation, and thrust and bedding plane faults normal to the direction oftranslation occurred, and in some places the rocks were sufficiently rigid, and the energy applied duringfailure sufficiently intense, for local dynamic metamorphism to occur.

Both marine and terrestrial deposition, accompanied by volcanic activity giving spilite , dolerite andtuff, continued during this faulting, but by mid-Jurassic time Singapore was above sea-level andsedimentation ceased. Faulting and folding may have continued however for a short period.

There is no evidence of any further events affecting Singapore from early Jurassic until late Tertiarytime . The Old Alluvium was then deposited as a thick pile of alluvial to deltaic coarse sand with occasionalincursions of marine sediment. Sedimentation continued through into the Pleistocene. The nature of thesediment suggests the existence of a well exposed qua rtz- rich, probably granitic terrain, and a far lower rateof chemical weathering than is experienced today . Verstappen (1975) suggested that such conditions wouldbe expected during glacial periods.

Faulting activity appears to have recommenced in late Tertiary time giving rise to a trough which nowplunge~ to the south beneath the Old Alluvium on the eastern side of Singapore. A second down-thrownblock formed in the Buloh Besar area in north-west Singapore, and Old Alluvium was deposited in thisbaSin too. It IS probable that a number of faults in the Jurong area were also reactivated, despite their beingsurface tear faults only, during this time. The main movement was apparently vertical as the evidence ofreju ve nation is based largely on the existence of block s of different height, but this topographic expressionmay also result from the juxtaposition of elements with different weathering characteristics by lateralmovement. Some adjustment also took place on faults cutting the granite .

The Old Alluvium was deposited as a delta-like body which extends back into Johor along the courseof Sungei Skudai, and was probably fed by the ancestral Sungei Johor as well. In Singapore the deposit isover 195 m thick and extends down to at least -149 m. In Johor it is found up to 70 m above sea-level butbasement is unknown. There is a threshold of grani te and Palaeozoic rock across the north of Singaporefrom Sembawang through Seletar North, Punggol, and Pulau Ubin to Changi and, unless the granite wasupli fled after the deposi tion of the Old All uvi um , the sedi men t must ha ve been carried across th is th resholdabove present sea-levels to be deposited in the trough plunging down to Bedok. This implies th a t thedeposition of the Old Alluvium must have been tied to a base level above present sea-level, or was graded toa more di s tant coastline. An approximation of the gradient of the depositional surface of the Old Allu vi ummeasured from the maximum of 47 m above sea-level recorded from the Old Alluvium immediately northof Johor Bahru. and the maximum of 43 m above sea-level measured just east of Singapore InternationalAirport, gives a gradient of I : 750 and would place the coast some 350 km distant. a very unlikely

proposition.

A second depression must have formed in the nort h-west of Singapore and across into South Johor.There is little evidence to suggest that there was much fa ulting during the main period of deposition of theOld Alluvium, so It is assumed that trough formati on terminated before the cessation of deposition of theOld Alluvium. Alluvial sedimentation must have kept pace with depression in the area as there is noevidence of any major marine incursion. Burton (1973 A) stated that marine incursions can be found inJohor up to 70 m. or possibly higher, and thus It can be assumed that the sea stood at that height o r higherduring the deposition of the Old Alluvium.

Because of the requirement of a cool dry clim ate to provide the necessary detritus, and the observationof a maximum sea-level of 70 m, it appears that the Old Alluvium must have been deposited rapidly in aninitiall y subsiding trough during a transition from glacial to interglacial conditions.

Efforts to recognise distinct erosion levels subsequent to the deposition of the Old Alluvium as a resultof Pleistocene sea-level fluctuations were unrewarding. Alexander (1950) recorded beaches between 21 III

and 27 m near Punggol and Kampong Wood leigh and at 17 m near Seletar, and beach sand was found at 12m by the authors adjacent to Changi Aerodrome and is mapped as Tekong Formation.

Ho, in Burton's paper (1964) drew attention to the common breaks in slope of the Old Alluviumerosional surface between 15 m and 23m and Burton (op Cif) related these to a temporary Pleistocene highsea-level stand.

* It follows that the Main Range Granite lay to the south-wes t of Singapore in late Triassic - early Jurassic time , not acrossSingapore as shown by Hutchi so n (1973 A, Fig. 7).

67

A hypsometric study was carried out by the Geologica l Unit over the area of Old Alluvium inSingapore using 10 ft contour maps prepared at a sca le o f I : 2,500. Three possible surfaces were indicatedat 30 m , 24 m and 17 m on either side of an east-west ridge east of Singapore In ternationa l Airport. Fields tudies however suggested that these surfaces, identified fro m the plotting of spot heights, a re nothing morethan the ge ntly sloping sp urs of the deepl y dissected Old All uvium . The existence of the 17 m surface on theri ght bank o f Sungei Seletar may be mo re realistic. In genera l however, the Old Alluvium is too sensitive toerosion and weathering for the preservation of ancient eros ional surfaces.

A hypsometric study of the whole of Singapo re ( Pun 1975) showed a dominance of heights between15 m and 33 m and hence revealed no additional informat ion .

During the period of early Pleistocene faulting, ponded areas isolated from the zone of deposition ofthe Old Alluvium were also formed, and a deposit in one such area in Western Singapore is recognised asthe Huat Choe Formation.

Reworking and redeposition of the Old Alluvium is also recognised at two places , both at a height of36 m just east of Singapore I nternational Airport and at either end of the runway. The material islith o logica ll y similar to the Old Alluvium but th e bedd ing is better defined a nd mo re continuous . The depthof weathering howeve r is such that the environment of deposition cannot be determined.

The next event of which there is record is that of the low sea- levels associated with the interstadials ofthe last Wurm Glaciation. Erosion was vigorous throughout Singapore and rivers downcut their va lleys toat least -35 111. T hese val leys were back filled with both the Alluvial and M a rine Members of the Kall angFormation as the sea rose , but during the regression o f the sea accompanying the next stadia l cooli ng , th erivers re-excavated their beds , this time to a depth of a bout -28 m. The older deposits of the KallangFormation \\"ere exposed to the a tmosphere at thi s t ime and were both dessicated and weathered to formthe stiff red brown clay fo und within the Marine Member. At the end of the Pleistocene co ld period, sealevel again rose to abou t 6 m above present sea-level a bout 6,000 BP to 7,000 BP. (Tjia 1970) to allow forthe deposition of the Tekong Format ion, and a lso the renewed deposition of the Alluvial and MarineM embers in the dro\\ned ri ve r valleys. Minor nuctuati o ns of sea- level con tinu ed through to the present.Tj Ia recogni sed two hig h level s, o ne at 1.5 m to 2 m (5 ,000 BP) and one at 0.5 m to I m (3,500 BP) in th egeneral Sunda Shelf area , and beach ridges associated wi th these levels can be seen arou nd Singapore .Subsequent to these times, sea-level is assumed to have been lowe r than at present. Beach ro ck on PulauTekukor \\as form ed at a lower sea-leve l th an that of toda y, a nd rock of the Jurong F orma tion forming aba se for th e Reef Member cora ls must have been planned o ff a t a time when the sea was at its present levelo r o nl y I m to 2 m bel ow present day le vel.

68

REFERENCES

ALEXA NDER, F.E.S . (1950) : The geology of Singapore and the surrounding islands. Appendix I inRepon on the availabilitl ' of granite on Singapore and the Surrounding islands. Singapore GovernmentPress. pp 24.

ALEVA, GJJ.; BON, E.H.; BaSSIN, U.; SLUITER, WJ . (1973): A contribution to the geology of thepart o f Indonesian tin belt: the sea areas between Singkep and Banka Islands and around the KarimataIslands . Bulletin No.6 Geological Societ) , of Mala)'sia. pp 257-72.

BI GN ELL, J. D . (1972) : The Geochronolog)' of the M ala)'an Granite. Unpublished Doctor of Philosophythesis. University of Oxford .

BISW AS B. (1973) : Quaternary changes in sea-level in the South China Sea. Bulletin 6. Geological Societ)'0/ Malalsia. pp 229-56 .

BURTON, C.K. (1964): The Older Alluvium of Johore and Singapore. 10urnal o/Tropical Geograph)'. 18 .pp 30-42.

---- (1973 A) : Geology and mineral resources . Johore Bahru-Kulai area, South Johore . Map BulletinNo 2 Geological Survey of Mala)'sia. pp 72.

---- (1973 B) : Mesozoic. Chapter 5 in Geolog)' o/the Mala)' Peninsula: West Mala)'sia and Singapore .Eds DJ. Gobbet! and e.S. Hutchison . John Wiley-Interscience, New York. pp 97-142 .

C HI N, F. ( 1965) : The Upper Triassic sedilllents of Pasir Panjang-lurong area 0/ Singapore. UnpublishedHonours thesis. Department of Geology. University of Malaya .

C H UNG. S.K. (1973) : Geological Map of West Malarsia. Geological Survey of Malaysia .

FA I RB R IDG E, R. W . (1961) : Eustatic changes in sea-level. In Ph)'sics and Chell/istr)' o/the Eanh. Ed L. H.Ahrens el at. Pergamon Press. London . pp 99-1 85 .

GOBBETT , DJ . (1968): Bibliography and Index of the Geology of West Malaysia and Singapore, Bullelin2 . Geological Societl' of Malal'sia .

---- (1972) : Geological Map 0/ the Malal' Peninsula. Geological Society of Malaysia .

---- and TJIA , H.D. (1973): Tectonic History . Cha pter 10, in Geolog\ ofthe Mala)' Peninsula: WeslMalalsia and Singapore: Eds DJ. Gobbett and e.S . Hutchison. John Wiley-Interscience, New York .pp 305-330.

GRUBB, R.L.e. (1968) : Geologl' and Bauxite deposits o/the Pengerang area , Southeast 10ho;e. DistrictMemoir 14. Geological Survey of West Malaysia.

HUTCHISON, C.S. (1964): A gabbro-granodiorite association in Singapore Island . Quarterl) ' Journal 0/Ihe Geological Societv. London. 120 pp 283-97.

- --- (1973 A) : Tectoni c evolution of Sundaland : a phanerozoic synthe sis. Bulletin 6 Geolog)' S ocienof M alalsia pp 61-81.

---- (1973 B) : VolcanIC Activity . Chapter 7 in Geologl' o/the Malal' Peninsula : Wes[ Malal 'sia andSingapo re. Eds D.J. Gobbett and e.S. Hutchi son . John Wiley-Interscience, New York. pp 117-214 .

- --- (1973 C): Plutonic Activity. Chapter 8 in Geologl' o/the Malal' Peninsula: Wesl Mala\sia andSingapore. Eds D.J . Gobbett and C.S. Hutchiso n. John Wiley-Interscience, New York . pp 215-52.

LEOW , J .H . (1962): A glimpse of the sedimentary structure of Singapore. Malal'Gn Nature Journal. 16. pp54-60 .

LIM , M.S.W. (1974) : Biostratigraphl ' 0/ [he lurong area, Singapore. Unpublished Honours thesis,Department of Geology, University of Malaya .

NEWTON, R .B. (1923) On marine Triassic shells from Singapo re. Annals and Magazine oj NaturalH islorl (ser 9) 12. pp 300-21.

PFEIFFER, D. (1972) : Investigations for groundwater, Singapore Islands, eastern end . No.2 (FinalReport). U.N. E.C.A.F.E. Natural Resources Division, Mineral Resources Seclion. Sala Santitham .Bangkok 2. Thailand.

PUN, V.T. (1975) : Report on the geolog)' of Singapore. Unpublished Report. Singapore Public WorksDepartment Geological Unit.

PRIEM , H .N .A .; BOELRIJK , N.A.I.M.; BON, E.H .; HEBEDA, E.H .; VERDURMEN , E.A.Th.; andVERSC H U RE, R .H. (1975) : Isotope geochronology in the Indonesian tin belt. Geologie en Mljnbouw .54 pp 61-70.

69

Appendix I

ANALYSES OF ROCKS

2 3 4 5 6 7 8 9 1O II

Si0 2 76.55 75.60 69 .98 68.98 59.83 51.52 49 .95 69 .92 69.39 69.69 72.80

AI2O , 12.78 13 .03 14 .58 14 .80 16.21 13.29 21.03 14.30 14.33 14.82 13.90

Fe 20 .1 0.38 0. 11 0 .84 0.48 1.33 0.30 Nil n.d. n.d. n.d. n.d.

FeO 0.37 1.44 2.35 3.44 5.64 9.91 7.76 n.d . n.d. n.d. n.d .

Total Iron as FeO 3.78 3.87 3.82 3.06

MgO 0.12 0.21 0.98 1.56 2.43 12.31 5.95 0.8 1 0.89 0.81 0.44

CaO 1.46 0.84 3.19 4.32 4.57 8.77 10.56 2.88 2.48 2.28 1.66

Na 20 2.56 3.58 3.38 2.06 3.90 1.01 2.27 3.67 4.40 3.77 3.95

K , O 5.04 4. 17 3.60 3.26 2.63 0.39 0.19 3.32 3.36 3.29 3.29

H2O+ 0.33 0.57 1.13 0.Q7 2.02 1.54 1.39 n.d . n.d . n.d . n.d.

H , O- 0.22 0.13 0.28 Nil 0.42 Nil n .d . n.d . n.d. n.d . n.d .

Ti02 tr. 0.16 0.47 0.49 0.84 0.58 0.58 0.27 0.24 0.24 0.14

P205 tr. 0.06 tr. 0.08 tr. 0.06 0.06 0.05 0.07 0.11 0.08

MnO tr. Nil 0.04 0.02 0. 10 0.29 0.24 0.08 0.05 0.05 0.01

CO 2 n.d. N il n.d. 0.03 n.d. Nil Nil n.d. n.d . n.d. n.d.

Total 99 .8 1 99 .90 100.52 100.22 99.92 99.97 99 .98 99.08 99.08 99.28 99.33

12 13 14 15 16 17 18 19 20 21

Si0 2 70.00 7 1.69 68 .33 71 .6 1 64.58 66 .75 52.4 1 48. 12 64.50 72 .19

AI 20 1 18. 13 17.26 19. 11 17.71 14 .5 1 14. 79 15.57 22 .51 15.96 13.25

Fe a ; n.d. n.d . n.d. n.d . n.d . n.d. n.d . n.d. n.d. n.d .

FeO n.d. n.d. n.d. n.d. n.d . n.d . n.d . n.d. n.d. n.d.

Total Iron as FeO 2.52 2.47 2.80 1.30 6.99 6.73 9.52 10.01 5.08 3.23

MgO 0.23 0.28 0 .30 0.29 0.69 0.69 6.67 7.40 1.58 0.29

CaO 2.02 2.63 2.\3 I. 1J 3.78 3.48 8. 16 7.5 1 4. 52 2.38

Na2a 2.93 3. 16 2.98 3.69 5.09 3.20 2.25 1.60 2.81 3.37

K20 3.44 2.0 1 3.34 3.11 1.25 2.92 2.92 0.66 4.10 2.95

H2O + n.d . n.d. n.d . n.d . n.d. n.d . n.d. n.d. n.d . n.d.

H2O- n.d . n.d. n.d. n.d. n.d . n.d . n.d. n.d. n.d. n.d .

T i0 2 0.21 0.23 0.23 0 .16 0.68 0.73 1.1 6 0.98 0.64 0. 17

P20 5 0.10 0.1 3 0.09 0.07 0.25 0.21 0.05 0. 80 0.19 0.65

MnO 0.07 0.06 0.06 0.01 0.08 0.0 1 0. 16 0.24 0.13 0.05

CO 2 n.d . n.d. n.d . n.d . n.d. n.d . n.d. n.d. n.d. n.d .

T otal 99.66 99 .92 99 .30 99 .06 97.90 99.61 98 .69 99.83 99.51 98.89

tr. = trace n.d. = not determined

(1) Ap1itic granite , Public Works Department Quarry (M andai)(2) Adamellite, Singapore Granite Quarry (Bukit Timah)(3) Biotite-granite, Public Works Department Quarry (Mandai)(4) Biotite-hornblende-granodiorite, Swee Construction Quarry (Bukit Timah)(5) Quartz-monzonite xenolith, Public Works Department Quarry (Mandai)(6) Hornblende-gabbro , Yun ann Quarry(7) N orite, Gim Huat Quarry

71

72

ANALYSES OF ROCKS - continued

(8) Hornblende microgranite, Gim H uat Quarry(9) Hornblende microgranite, Gim Huat Quarry

(10) Hornblende microgranite, Aik Hwa Quarry No . I(II) Porphyritic biotite granophyre, Lee Hung Cheng Quarry(12) Hornblende granite, Public Works Department Quarry (Pulau Ubin)(13) Hornblende granite, Housing Development Board (Pulau Ubin)(14) Hornblende granite, Tanjong Chek Jawa (Pulau Ubin)(15) Hornblende granite, Aik Hwa Quarry No . 2(16) Actinolite hornfels, Aik H wa Hung Cheng Quarry(17) Actinolite hornfels, Lee Hung Cheng Quarry(18) Amphibolitized dyke rock, Lee Hung Cheng Quarry(19) Amphibolitized dyke rocks, Housing Development Board Quarry(20) Granodiorite, South Coast of Pulau U bin(21) Granodiorite, East Side of Pulau Ubin

Analyses Nos . I - 7 from Hutchison (1 964)

Analyses Nos . 8 - 21 from Seet (1974)

Appendix 2

ANALYSES OF HOT SPRING WATER

I 2

PH value 8.1 7.0

Total dissolved solids 914.0 10170.0

Loss on ignition of solids 191.0 298.0

Silica (as Si02) 16.0 22.0

Ferric Oxide Nil 0.02

Calci um Oxide 29.1 1032 .0

Magnesium Oxid e 3.2 96.5

Chlorine Nil Nil

Sulphate (as S0 3) 45.0 190.0

Carbonate (as CO 3) 18.0 Nil

Colour(Hazen Unit) 5 5

Result s of analyses in milligra ms per litre except for pH and colour values.

(1) Hot springs in Kua la Simpang Kiri, South of Chong Pang Village , Sembawang. (G R 4755 86) .

(2) Hot spring issuing through swamp, 300 m west of Sungei Belang, North Pula u Tekong . (G R740591 ).

Analyses from the Depa rtmen t of Chemistry, Outram Road, Singapore .

73

Appendix 3

PLATE OF FOSSILS

Myophoria sp ? '

L ow- Upper T ··.. .GR n asslc

. 316468X4

~alaeonucula sp .,.?n asslc-Jurassic

GR . 333463X2

RY coUR T ESY O F MR. I.I M .\1 ENG SZ ' .. E\\U(1974)

74

--l - r

LIST OF FOSSILS: JURONG FORMATION

--.IVI

FOSS IL LOCATION I 2 3 4 5 6 7 8 9 10 I I 12 13 14 15 16 17 18 19

Allllllonite (Fragments) N

AlIIusiw/l sp. L L L L

Anodontaphora A sp. (Kobayashi &Tamaru) K L L L

Anodontaphora 8 sp. (Kobayashi &Tamaru ) K L L

Area sp. N Co

Astarte guthriensis (Newton) N

Astarte scrivenori (Newton) N

A viculinia sp. L

Buchia sp . L

CardiulII scrivenori (Kobayashi &Tamaru) L

CardiulII scrivenori, Nov. K L

Carpolithes sp. N

Cassianella cf. tenuistriata(Munster) N K

Cassianella cf. verbeeki (Kobayashi &Tamaru) K

Cassianella sp. Co L L L

Chlamys cf. vo loniensis (Deferance -Leymerie) N

Cos tatoria aff. goldfussi K

Costa toria cf. myophoria (Boettiger,1880) K L L

Cos tatoria chegarperah ensis (Kobayashi) L L L LCos tatoria lIIalayensis (Newton , 1900) L

Costa toria pahangensis (Ko bayash i) L LCostatoria singapurensis (Kobayashi) K L L L L L

--.l0\

FOSSIL LOCATION I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 \7 18 19

Costatoria (7) sp. ex. gr. go ldfu ssi(Zieten) L L L

Cuculaea scrivenori (Newton) N

Cucullaea (7) sp. N

Cuspidaria sp . C

Estheria mangalensis Co

Gastropod sp . L L L L

Gen . et. sp. indet (Kobayashi & Tamura) K

Gervillia hanitschi (Newton) N

Gervillia scrivenori (Newton) (Nov .) N

Gervillia sp. Co

Goniomya scrivenori (Newton) N

Goniomya singapurensis (Newton) N

Gonodon sp . (Schafhautl, 1863) C C

Gonodon sp . (Schafhaut l, 1950) L L

Gruenewaldia sp . L

Halobia n. sp. (Kobayashi & Tamura) K

Halobia sp . L

Halobia sp . ex . gr. H. verbeek i K

Halobia (7) sp. indet. K

Lima (Plagiostoma 7) sp. K

Lima sp.

Lima sp. A Co L

Lima sp. B L

Lima sp. Brugu ie, 1797 C C

Lopha of Montis-caprilis (K lipstein) N

Lucina (7) sp. N Co

~- I - I I~

--.J--.J

FOSSIL LOCAT ION 1 2 3 4 5 6 7 8 9 10 I I 12 13 14 15 16 17 18 19

Modi%psis gonoides (Healey) N

M odio/us cf. nachamensis Co

M.I'oconcha sp. Co

M yophoria A & 8 sp. indet. N

M yophoria billneri Newton (Nov .) N

M yophoria cf. go ldfu ss i Co

M yophoria cf. go ldfuss i Alberti N

M vophoria cf. harpa? C C

M yophoria in aeq uicos tata Co

Myophoria ornata (Wissman) N

Mvophoria sp. C L

Mrophoria sp. A, (Brown 1834) C

Mvophoria sp . 8 C

M yophoriopsis cf. carina ta Co

M vophoriopsis sp. Co

Neo.l'hizodus (Leviconcha cf. Ovatus L

Nuc/oid gen. et. sp. indet. N

Nucu/ana (?) sp. N

Nunda sp . A. C C C

Nun da sp. B. C C C

Opis cf. heo ningha usi (K lipstein) N

Pachvcardia ? sp . Co

Pa/aeocardita cf. crena ta (Goldfuss) N

Pa/aeonei/o A. sp. (K obayash i &Tamura) K L L

Palaeoneilo 8 sp. (Kobayashi &Tamura) K L L L L

-..l00

FOSSIL LOCATION I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19

Pa/aeonucu/a sp . L

Pa/aeopharus sp. L

Pa/eo/ima sp. L

Pa/eopharus sp. L L L

Paralle/odon M eek, / 866 C C C

Pecten (Entolium ?) sp. K

Pecten (Entolium) sp. Meek , 1965 C C

Pecten sp . Co C

Pecten sp. A. L L L

Pecten sp. B. L L L

Pecten sp. C. L

Pecten sp. D. L L

Pecten (Syncyclonema) sp. Meek , 1864 C C

Pleuromya sp. Co

Plicatula cf. Healey L L L L L

Podozarnites cf. lanceolatu s (Lindley &Hutton) N

Posidonia sp . Co L L

Posidonia sp. (Brow n) C C C

Posidonia sp. indet. KPro/aria sp. Co

Proma/thildia co lon ? (Wissman) N C

Prosospondy/us comt us (Goldfuss) N

Pteria pahangensis L

Pteria sp . Co C C C

Schaufh aulia astarti(orlllis (Wi ssman) N

Spondy lus dubiosus (Bittn er) N L L

-..J\0

FOSSIL LOCAT ION I 2 ] 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19

Sprijerina cf. fragi Iis (Sc hlot heim) N

S V/l c.l'c!oncllw sp . N L L L L

Terebratu/oid shell N

Thra cia (?) sp. N

Trigonia cf. zlambachensis Co

Trigonodus sp . Co L L

Va/sella cf. compressa (Go ld fuss) N

(I) Mount Guthri e, Sin ga pore (Newton , 1906)(2) Mou nt Faber, Singapore (New ton, 1923)(3) Nea r H uat Choe Village (Cox, 1952)(4) Pul au Ayer Chawan (Cox , 1952)(5) From 24 points on the Jurong Industria1 Estate, about 3 miles sq uare (Kobaya shi & Tamura )(6) Behind Crown Co rk Co mpan y: CF I, F IG . 3.32. (C hin , 1965)(7) Opposite Crow n Cor k Co mpan y: C F2 & L1 , FIG . 3.32. (Chin, 1965 and Lim , 1975)(8) Drain cu ttin g beside Jalan Buroh; CF4, F IG. 3.32. (C hin , 1965)(9) Floo r of leve lled hill heside Jalan Buroh; CF5, FIG . 3.32. (Chin, 1965)

(10) North face of Bukit Susap behin d General Electric Factory ; CF6 , L7 & L8, F IG. 3.32. (C hin , 1965 & Lim , 1975)(I I) Hill cuttin g beside Pioneer Road; CF7, F IG. 3.32. (Chin , 1965)(12) Drain cutting abou t 8 m so uth of Pioneer Circu s; CF8 & L9, F IG. 3.32 (C hi n, 1965 & Lim, 1975)(13) Leve lled area 27 m NE of Jurong Pier C ircus; L2, FIG. 3.32. (Lim, 1975)( 14) Drain cu tting 13 m west o f Jurong Pier C ircu s; L3 , FIG . 3.32. (Lim, 1975)(15) Drain cutting beside S.T.1. Factory; L4 , F IG. 3.32. (Lim , 1975)(16) East face of Bukit Sembawang; LS, FIG . 3.32 (Lim , 1975)(17) Hill rese rve for Singapore Port Authority: L6, FIG . 3.32. (Lim, 1975)(18) Drain cu ttin g opposi te Singapore Clay Pr odu cts: L10, FIG . 3.32 . (Lim, 197 5)(19) Benoi Sectors syncline: L1 1, F IG. 3.32. (Lim, 1975)

NOTES:(i) N = Newton, Co = Cox , K = Kobayash i & Tamura , C = C hin and L = Lim Meng Sze Wu

(ii ) Locality 13, a ll fo ss il s co ll ec ted from thi s loedi ty ha ve been doubtfull y id ent ifi ed.

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