GEOLOGY OF THE - Environment...

GEOLOGY OF THE

WAITAKI AREA

P. J . FORSYTH

( COMPILER)

BffiLlOGRAPIllC REFERENCE

Forsyth, I'J .(compiler) 200 1: Geology of the Waitaki area. Institute of Geological & Nuclear Sciences 1:250 000geological map 19. I sheet + 64p. l..ower Hutt, New Zealand. lnstitute ofGeologicaJ & Nuclear Sciences Limited.

Development and maintenance of ARCIINFO GIS database by D.W. Heron and M.S. Ratlenbury

GIS operations by D.W. Heron, B. Smith-Lyttle, B. Morri son and D.Thomas

Contributions to offshore geology by A. Duxtield, R.H. Herzer &B.o. Field

Edited by D.W. Heron and MJ . Isaac

Prepared for publication by P.L. Murray

Printed by Graphic Press & Packaging Ltd, Levin

ISBN 0-478-09739-5

© Copyright Institute of GeologicaI& Nuclear Sciences Limited 200 I

FRONT COVER

The Waitaki River valley, looking upstream from near Kurow. The modern flood plain has a vegetation cover of scrub and willow,but areas above flood level are intensively farmed. Kurow (middle distance) lies below Kurow Hill and the lower slopes of the51 Marys Range. Hydroelectric storage lakes are impounded behind the Waitaki and Aviemore dams. The ranges in view areformed of Rakaia terrane sandstone. mudstone and semischist.

Photo CN42818-20: D.L. Homer

GEOLOGY OF THE

WAITAKI AREA

Scale 1:250 000

P. J. FORSYTH

(COMPILER)

Institute of Geological & Nuclear Sciences 1:250 000 geological map 19

Institute of Geological & Nuclear Sciences LimitedLower Hutt, New Zealand

2001

CONTENTS

ABSTRACT iv TECTO IC HISTORY 40Keywords.................................................................. v

INTRODUCTION .

THE QMAP SERIES ..

Paleozoic to Mesozoic 40Late Cretaceous to Middle Miocene 40Late Miocene and Pliocene 40Quaternary tectonics.. 40Coastline 41

The QMAP geographic infom13tion system ....DaLa sources .Reliability __ _ .

REGIONAL SETTING .

GEOMORPHOLOGy ........... 3Otago Peneplain 3Central Olago ranges and basins 3North Olago ranges 3Coastal East Otago 3North Otago downlands 10Waitaki valley 10Canterbury ranges and basins 10South Canterbury downlands 10Offshore physiography 10

GEOLOGICAL RESOURCES 41

Hard-rockgold mineral isation 4 JAlluvial gold 44Scheelite 44Other meta ll ic minerals 46Coal 46Limestone and Marble 46Building stone 46Hydrocarbons 48Rip-rap and Aggregate 48Clay .... . 48Diatomite 48Silica.................................................................................. 48Groundwater 48

STRATIGRAI'HY I I ENGINEERING GEOLOGy ...... 50

GEOLOGICAL HAZARDS . 52

ACKNOWLEDGMENTS 55

Paleozoic to Mesozoic sandstone and mudstone 50Schist and semischist 50Cenozoic sedimentary rocks 50Volcanics 5 IQuaternary sediments 5 1

Lands lides 52Earthquakes 52Erosion and sedimentation 53Tsunalni 54Sea level ri se 54Groundwatercontamination 54

56

. 55

REFERENCES .

AVAILABILITYOFQMAPDATA .

CRETACEOUS TO PLIOCENE 20Mid Cretaceous sedimentary rocks 20Late Cretaceous to Early Oligocene sedimentary rocks .. 23Eocene to Oligocene sedimentary and volcanic rocks atOamaru 27Late Oligocene to Middle Miocene sedimentary rocks . 28Middle and Late Miocene volcanic rocks 3 1Latest Miocene to Early Pleistocene sediments 33Pl iocene volcanic rocks 34

PERM IAN TO TR IASS IC I ICaples terrane 11Otago Schist of Caples protolith I)

Rakaia terrane IIUndifferentiated Permian to Triassic sedimentary rocks. 14Undifferentiated Permian to Triassic volcanic andmetavolcanic rocks 16Otago Schist and regional metamorphism 16Blue Mountain Formation marble 17Kohurau Schist 17Triassic nonmarine and shallow marine rocks 17Deformation structures in Rakaia rocks 18Te Akatarawa lithologic association 19

QUATERNARY 35Landslide deposits 35Scree 35Alluvial fan deposits 35GlaciaJ and nuvioglacial deposits 35Alluvial terraces and noodplain deposits 35Peat swamp and lake deposits 36Loess 36Beach and estuarine deposits 37Deposits of human origin 37

APPENDIX I

Stratigraphic names in Nonh Otago andSouth Canterbury 64

OFFSHORE GEOLOGy .......... .... ..... .... .. ............ 39

ABSTRACT

The Waitalei 1:250000 geological map covers orth Otago,eastern Central Otago, and South Canterbury, in the SouthIs land of New Zea land . Much of the map area ismountainous. The Waitaki Ri ver, which separates Otagofrom Canterbury, rises in glaciated catchments beforeflowing through a series of bedrock gorges, then wideningto a broad plain . In Central Otago northeast-trending Oa1topped ranges of schist are separated by intermontanebasins. The so-called Otago Penepla in, a conspicuousplanar to gently rolling landform, is cut into basementrocks. In North Otago, northwes t-trending ranges, steepand deeply incised, lie between the subparallel Waihcmoand Waitalei valleys. Rising above rolling downlands ofcoastal Otago are prominent volcanic hillsand mesas andcuestas of limestone. Canterbury ranges trend generallynorth-south, and are flanked by sloping piedmont fans inthe easl, with till and glacial outwash further west.Offshore, a broad shelf is incised at its eastern edge bylarge submarine canyons feeding eastwards into theCanterbury Basin.

The map area lies on the Pacific Plate , a c rusta l blockseparated from the Australian Plate by the active plateboundary of the Alpine Faull (northwest of the map area).Basement rocksare mainly Rakaia terrane sandstone andsiltstone, of Carboniferous to Triassic age. part of theTorlesse composite terrane. Several distinctive units (BlueM ountain Form ation, Kohurau Schist, Mt St MaryFonllation, Corbies Creek Group, Otemalata Group, HaldonFormation and Spurs Siltstone) are identified, with theremainder mapped as undifferentiated. Te Akatarawalithologic association is a fault-bounded suite of uncertainaffinity surrounded by Rakaia terrane. In the southwestof the map lies an area of undifferentiated Caples terranerocks, of Permian to Triassic age. Rakaia and Caplesterranes arejuxtaposed along a complex fault system. Allthe Caples rock in the map area, and much of the Rakaiarock, is metamorphosed into Otago Schist, the degree ofmetamorphism becoming lower away from the terraneboundary.

A Cretaceous to Cenozoic sedimentary sequence ispreserved in many basinsand valleys, especially in coastalregions; it is thicker offshore in the Canterbury Basin .Rifting in late Early Cretaceous time was accompanied bythe deposition of coarse graben-fill , represented by theMatakea Group. Clastic sedimentation was at firsLaccompanied by minor silicic volcanic activity. Regionalsubsidence resulted in deposition of the transgressiveOnekakara Group over much of the eastern South Islandduring the latest Cretaceous to Early Oligocene. IL includesfluvial sandstone and conglomerate, marine sandstone,mudstone, greensand and marl. Sporadic igneous activityduring this time is represented by the Galleon andEndeavour volcani cs offshore, while onshore nearOamaru the Waiareka and Deborah vo lcani cs, wiLh

tV

associated sedimentary and intrusive rocks, comprise theAlma Group.

In mid Oligocene time, the Marshall Paraconfomlitydeveloped across the Onekakara and Alma groups, andwas succeeded by a condensed sequence of greensandand limestone (Kekenodon Group), representing a periodof greatly reduced sedimentation. Deposition resumedwith the regressive Otakou Group of Miocene age,comprising mainly marine siltstone and sandstone withsome limestone and lignite . Fluvial and lacustrinesandstone and silLstone (Manuherikia Group) weredeposited in inland basins. Intraplate volcanism duringthe Miocene resulted in theeruptionof Dunedin VolcanicGroup rocks over part ly eroded earlier Miocene and olderrocks. The regression continued through the Plioceneand Pleistocene. as detritus from rising mountain systemsbuill widespread piedmont fans and plains (HawkdunGroup and Kowai Fonllation). Onland this phase is mostlyrepresented by thick grave ls, but de position of s iltcontinued offshore. A volcanic vent near Timaru eruptedseveral lava flows in Late Pliocene time. Quaternary unitsrange from till and outwash in the mountains, throughalluvial fan and terrace deposits of inland basins andcoastal plains, to modern and older beach deposits. Loessis widespread on the downlands of South Canterbury.

Basement and covering strata have been affected by lateCenozoic faulting, including reactivation of Cretaceousfau lt sys tems, and several Late Quaternary fault and foldtraces are known. However geodetic results indicate thatstrain rates in thispart of the eastern South Island are lowto very low, though increasing westwards (towards theAlpine Faull). The Wailaki region, along with the reSI ofthe southeaste rn South Island, has had a low level oflarge earthquake occurrences in historic times, with thelargest recorded earthquakes (-5.8) occurring near Oarnaruin 1876. Paleoseismic studies 0 11 individual faults in thisarea suggest that the recurrence interva l of largeearthquakes is in the order of thousands or tens ofthousands of years, but large earthquakes centredoutside the map area (such as those on the Alpine Fault)may a lso be expected to affecl the region. Majorearthquakes can be expected to cause landsliding andliquefaction, cut transport and communication links, andthreaten many structures. Other geologica l hazardsinclude landslides, erosion and aggradation, tsunami andgroundwater contamination.

Geological resources include gold , coa l, aggregate,limestone. sa nd, dimension (bu ilding) sLone andgroundwater. These are likely to be the focus of continuedeconomic interest in the future.

Keywords

Waitaki; 1:250000 geological map; geographic information system; digital data; Caples terrane; Torlessecomposite terrane; Rakaia terrane; Blue Mountain Formation; Kohurau Schist; Mt St Mary Formation; CorbiesCreek Group; Otematata Group; Black Jacks Conglomerate; Spillway Formation; Haldon Formation; SpursSiltstone; Otago Schist; Te Akatarawa lithologic association; textural zones; isotects; isograds; prehnitepumpellyite facies, pumpellyite-actinolite facies, greenschist facies; chlorite zone; biotite-albite-garnet zone;Matakea Group; Horse Range Formation; Shag Valley Ignimbrite; Kyeburn Formation; Onekakara Group;Eyre Group; Taratu Formation; Broken River Formation; Hogburn Formation; Kauru Formation; AbbotsfordFormation; Waihao Greensand; Opawa Sandstone; Tapui Glauconitic Sandstone; Bumside Mudstone; Amurilimestone; Galleon Volcanics; Endeavour Volcanics; Alma Group; Waiareka Volcanics; Deborah Volcanics;Lorne Pyroclastics; Kakanui Mineral Breccia; Tokarahi Sill; Ototara limestone; Oamaru Diatomite; KekenodonGroup; Otiake Group; Kokoamu Greensand; Otekaike limestone; Otakou Group; Motunau Group; CavershamSandstone; Goodwood limestone; Gee Greensand; Mt Harris Formation; Southburn Sand; White RockCoal Measures; Waitangi Coal Measures;Tokama Siltstone; Manuherikia Group; Dunstan Formation; silcrete;Bannockburn Formation; Dunedin Volcanic Group; Hawkdun Group; Wedderburn Formation; ManiototoConglomerate; Kowai Formation; Timaru Basalt; Pleistocene sediments; Holocene sediments; OtagoPeneplain; Waipounamu Erosion Surface; Marshall Paraconformity; Canterbury Basin; Clipper-1 ; Endeavour1; Galleon-1; Waitaki Fault System; Waihemo Fault System; Hawkdun Fault System; Ostler Fault Zone;Hyde-Macraes Shear Zone; Gimmerburn Fault Zone; Kirkliston Fault Zone; Hyde Fault; Stranraer Fault; BlueLake Fault; Titri Fault; Ranfurly Fault; Hunters Hills Fault; St Mary Fault; Bitterness Fault; Otematata Fault;Middle Range Fault; Acaena Fault; Cap Burn Fault; Dansey Pass Fault; Waipiata Fault; Long Valley Fault;Wharekuri Fault; Waitangi Fault; Dryburgh Fault; Stonewall Fault; Fern Gully Fault; Alpine Fault; BlackForest Thrust; Bitterness Anticline; Trig E Syncline; Cannington Syncline; Rock and Pillar Antiform; activefolds; conodonts; resources; Macraes; Nenthorn; Oturehua; Barewood; Serpentine; gold; silver; tungsten;scheelite; clay; coal; diatomite; dimension stone; building stone; rip-rap; aggregate; limestone; marble;silica; hydrocarbons; groundwater; engineering geology; natural hazards; landslides; active faults; erosion;earthquakes; tsunami ; sea level rise

v

61

•9

10

36

~ ~ ~

1 Gair 1967 23 Youngson et a/. 1998 45 Mitchell 19852 Force & Force 1978 24 Grady 1968 46 McMillan 19993 Bradshaw c. 1970 25 Bishop 1981a 47 Brown 19524 Falconer 2000 26 Williamson 1939 48 Pringle 19805 Fagan 1971 27 Markley & Norris 1999 49 Martin 19996 Gair 1959 28 McCraw 1966 50 Cavaney 19667 Brown 1972 29 Liggett c. 1981 51 Tenney 19778 Mutch 1963 30 Orbell et al. 1971 52 Rae 19909 Christie et al. 1994 31 Bishop 1979 53 Turnbull 196810 Mortimer 1993a 32 Thomson 1996 54 Edwards 199111 Udy 1987 33 Pari< 1906 55 Thomson 197012 Rolfe 1993 34 Means 1966 56 Macfarlane 198813 Ryburn 1967 35 Salton 1993 57 Gage 195714 Retallack 1983b 36 McKellar 1966 58 Ward & Lewis 197515 Hada & Landis 1995 37 Brown 1968 59 Maxwell 199216 Lauder c. 1950 38 MacKenzie & Craw 1993 60 Riddolls 196617 Read et al. 1998 39 MacKenzie 1990 61 Field & Browne 198918 Marwick 1935 40 Benson 1968 62 Middlemiss 199919 Turkandi 1986 41 Brown 1963 63 Ford 199420 Bishop 1981b 42 Travis 1965 64 Fordyce 199821 Bishop 1976b 43 Dodds 1963 65 Watters 195022 Ulrich 1994 44 Macraes 1998

Figure 1 Major data sources used in compiling the Waitaki map. Unpublished maps are held in the map archive of the Institute ofGeological and Nuclear Sciences, or in university libraries and Geology Departments. Data sources are listed in the references,marked *.

VI

INTRODUCTION

THE QMAP SERI ES

This map is one of a national series known as QMAP(Quarter-million MAP; Nathan 1993), and replaces thecurrent 1:250000 geological maps of the Waitaki area (Gair1967; McKellar 1966; Mutch 1963). Since then, suchimportant geological concepts as plate tectonics andsequence stratigraphy have developed, and there hasbeen detailed onshore and offshore geological andgeophysical mapping by government, university andindustry geologists. Requirements for geologicalinfom13tion have increased as a result of the ResourceManagement and Crown Minerals acts. demands forgeological resources, a new educational curriculum, andgreater awareness of natural hazards and their mitigation.

For the QMAP series, rock types are shown primarily intenns of their age of deposition, eruption or intrusion.The colour of the units on the map face thus reflects theirprimary age, with overprints used to differentiate some

lithologies. Metamorphic rocks are mapped in tern,s ofage of the parent rock (where known), with overprintsindicating the degree of metamorphism. Letter symbolsindicate the predominant primary age of the rock unit,and either a formal lithostratigraphic name or predominantlithology. The correlation between intemational and localtime scales, and absolute ages in millions of years (Ma)or thousands of years (ka), revised as necessary forQMAP (Crampton et al. 1995.2000; Graham et al. 2000),isshown inside the front cover.

This text isnot an exhaustive description or review of thevarious rock units mapped. Names applied to geologicalunits are those already publi shed and rev ision ofnomenclature to remove anomal ies has not beenattempted. The geology shown on the map has also beengeneralised to make it appropriate for presentation at1:250 000 scale. For more detailed information onindividual rock units, specific areas, natural hazards orminerals, the reader is referred to data sources citedthroughout the text and listed in the references.

The QMAP geographic information system

The QMAP series uses computer methods to store,manipul ate and present geological and topographicalinfonnation. The maps are drawn from data stored in theQMAP Geographic Information System (G IS), a databasebuilt and maintained by the Institute of Geological andNuclear Sciences (GNS). The primary software used isARCIINFOa. The QMAP database is complementary toother digital data sets maintained by GNS, e.g. gravityand magnetic, mineral resources and localities, fossillocal ities , active fau lts and petrological sa mpl es(see page 55 for details).

The QMAP series is based on detailed geologicalinformation, plotted at 1:50000 scale on NZMS 260 seriestopographic base maps. These record sheets areavailable for consultation at GNS offices in Lower Hunand Dunedin. The detai led geology has been simplifiedfor digiti sing during a compilation stage, with lineworksmoothed and geological units amalgamated to a standardnational system based on age and lithology. Point data(e.g. dips and strikes) have not been simplified. All pointdata are stored in the GIS, but only selected structuralobservations are shown on the map. Procedures for mapcompilation and data storage and manipulation are givenby Rattenbury & Heron (1997).

Data sources

This geological map includes data from many sources,including published geological maps and papers,unpublished data from university theses, unpublishedGNS technical repoI1S and maps, mining company repoI1S,field trip guides, the New Zealand Fossil Record File(FRED), and G S digital data bases of geologicalresources and petrological samples (GERM, PET).Additional fie ld mapping between 1995 and 2000 ensureddata coverage over the whole map area. Landslides weremapped from air photos, wi th limited field checking.Offshore data were obtained mainly from published andunpubli shed s urveys by oil companies and GNS,supplemented by data from the Geology Department ofthe University of Otago. The main data sources used areshown in Figure I ; all data sources used for mapcompilation are identified by * in the references.

Reliability

This I:250000 map is a regional scale map on ly, and shouldnot be used alone for land use planning, planning ordes ign for engineering projects, earthquake riskassessment, or other work for which detailed siteinvestigations are necessary. Some of the data sets whichhave been incorporated with the geological data (GERM,for example) have been compiled from old or uncheckedinformation which may be of lesser reliability (Christie1989).

REGIONAL SETTING

The Waitaki geological map covers northern Otago andsouthern Canterbury, in the southeastern South Island,and extends 60 km offshore over the Canterbury shelfand slope. The main towns - Palmerston, Oamaru, Waimateand Timaru - lie on the coastal plains and down lands, andmuch of the interior is rugged and thinly populated withscattered villages servicing agriculture. The other mainindustries of the area are gold mining, forestry, tourismand hydroelectricity generation.

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Figure 2 Regional tectonic setting of New Zealand, showing the location of the Waitaki geological map and otherQMAP sheets, major offshore features and active faults. The relative rates and directions of plate movements areshown by the arrows.

Adapted from Anderson & Webb (1994).

2

The Waitaki map area lies on the Pacific Plate, a crustalblock separated from the Australian Plate by the activeplate boundary of the Alpine Fault (Fig. 2). Present-dayPacific Plate motion in the map area, relative to theAustralian Plale, is about 37 mm/year, and, of this, 9- 12mm/year is normal 10 the Alpine Fault, the rest being paral lelto it (Beavan el al. 1999). The easlern South Island hasbeen undergoi ng shorten ing since plate boundaryinception in th e Early Miocene, with some 90 kmaccommodated in Ihe past 6.4 Ma (Walcott 1998).

The basement rock in the map area consistsof two majortectonostratigraphic lerranes, Caples and Rakaia, whichrange in age from mid Carboniferous to Triassic. ACretaceous to Cenozoic sedimentary sequence coversthe basement rocks in many bas ins and valleys, especiallynear the coast. A thicker sequence of Cretaceous andCenozoic sedimentary rocks is present offshore (part ofthe Canterbury Basin). Eocene/Oligocene, Miocene andPliocene volcanism has left extensive remnants, in placesintercaJated with the sedimentary sequence. Pliocene toQuaternary uplift and erosion in mountainous areas hasproduced large subaerial fan complexes and alluvial plains;in coastal areas these are commonJy mantled with thickloess. The hjghest areaswere glaciated during Quaternarytime, but no glaciers remain today and glacial depositsare not extensive. Small areas of raised marine terraces,and abandoned sea cliffs, occur near the coast as a resultof the interaction of Quaternary sea level nuclUationsand local uplift.

GEOMORPHOLOGY

Otago Peneplain

The so-called Otago Peneplain is a conspicuous landformin the southwestern pan of the Waitaki map area andthroughout the Otago region (Fig. 3). It is part o f theWaipounamu Erosion Surface (LeMasurier & Landis 1996;Landis & Youngson 1996; see below). As nOI all parts ofthe surface were formed so lely by rivers, the term"peneplain" isnot strictly accurate, but it iswidely used.The planar to gently rolling landform is cuI inlo Caplesand Rakaia terrane basement rocks and is widely used asa slructural marker fordeternlining offset on major faultsand folds (e.g. Bishop 1994; Markley & Norris 1999;Fig. 4). The present-day surface on the range tops is anexhumed one, which shows the original form but has hadsome material (including overlying sediments) strippedoff.

The Otago Peneplain is particularly well preserved southof the Waihemo Faull System (Figs 5 and 6), on the topsof Blackstone Hill, North Rougb Ridge, Rough Ridge,Rock and Pillar Range, and the Lammennoor - BarewoodNenthorn plateau, and is also preserved on the Hawkdun

plateau and the Kakanui Range. Where it is underlain byschist, upstanding tors are characteristic (Fig. 7) but theseare not developed in lower-grade rocks. North of theWaitaki Fault System, infaulled areas of low relief withoverlying Cenozoic sediments in the Hunters Hill s,Campbell Hills, Kirkliston, Waitangi and Benmore areasare interpreted as peneplai n remnants (Fig. 8); widespreadsummit accordance in these ranges also suggests theformer peneplain landform. The "top of basement"reflector in offshore seismic sectionsprobably correlateswith the Otago Peneplain.

Central Otago ranges and basins

The soulhwest of the map includes part of Central Otago,aregion of northeast-trending depressions (Manuherikia.Ida, Maniototo, Strath Taieri and severaJ smaller basins)separated by asymmetric ranges of schist (Rock and Pillar,Rough Ridge, orth Rough Ridge, Little Rough Ridge,Blackstone Hill ; Fig. 9). These landforms have developedby folding, and some faulting, above a series of reversefaultswhich result from late Cenozoic defonnation . M ostranges are still rising, and mass wastage by large scalelands liding (sagging) is typical of the Sleeper range fronts(MeSaveney el al. 1992).

In the intervening basin s, Quaternary sedimentscommonly overlie sedimentary rocks of Miocene andPliocene age (the Manuherikia and Hawkdun groups;Fig. 10). Spectacular meanders are developed in the basinsof the upper Taieri River (Fig. II ).

'orth Otago ranges

The Kakanui , St Marys, Hawkdun and St Bathans rangeslie between Ihe subparallel Waihemo and Waitaki faultsystems, and many subsidiary faults on the same trendrun through these mountainous areas. In contrast to thenat-topped northeast-trending ranges, these northwestIrending ranges are mostl y steep and deeply incised,although ageneraJsumm it accordance remainsand someextensive relictsof the Otago Peneplain survive (e.g. theHawkdun plateau and parts of the Kakanui Mountains).Small moraine ridges were left by Quaternary ice-capsand cirque glaciers. The ranges are composed of Rakaiaterrane sandstone, mudstone and semischisl, andalthough semischist is more prone to large sca lelandsliding than sandstone, nowhere in these ranges ismass movement as prevalent as in schist terrain.

Coastal East Otago

Prominent hills formed of more resistant DunedinVolcanics (Puketapu, Mt Royal , Derdan Hill , Mt Baldie)rise above Ihe generall y rolling landscape (Fig. 12). Theestuaries orthe Shag, Pleasant and Waikouaiti riversare

3

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<J> :i'"E 0-J!! ~<J> Ol>- 0<J> -iii:; >-.c~ 0-c c-iii -iii::;; ::;;

Figure 3 Computer-generated digital terrain model of the Waitaki map area, derived from 20 m contour data andilluminated from the northeast. The major fault systems are shown in simplified form, and the major physiographicfeatures are labelled_

4

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--Otago Peneplain

surface eroded on faultscarps or in deep gorges

surface concealed byMiocene and youngersediments

Figure 4 Structure contours on the Otago Peneplain. Major faults which offset the erosion surface are shown,together with Cenozoic folds in foliation which deform the erosion surface. Digitising by B. Smith-Lyttle.

5

Figure 5 On the unfaulted eastern side of the Strath Taieri basin, the peneplain surface cut in Otago Schist of Rakaiaterrane protolith dips to the northwest. The trellis drainage pattern is controlled by the direction of slope and jointsets. Photo CN31924-8: D.L. Homer

Figure 6 The landscape around the Poolburn reservoir is dominated by the Otago Peneplain, cut in Otago Schist ofRakaia and Caples terrane protoliths. The prominent scarp of the Long Valley Fault, immediately beyond thePoolburn reservoir, offsets the peneplain surface; beyond are a faulted basin in the upper Taieri River and thesouthern Rock and Pillar Range. Photo CN38396-14: D.L. Homer

6

Figure 7 Tors in schist are generallycores of less weathered rock betweenjoints, which remain as upstandingblocks when erosion has removed softermaterial. Lines of tors probably resultfrom the intersection of joint sets withlineations (often fold hinges) inschistosity; more rarely, these lines reflectresistant lithologies such as massivepsam mite or chert. This view isnorthwest towards Sutton Stream, southof Strath Taieri.


Figure 8 The northern Hunters Hills andthe upper Pareora River. The westdipping surface in the middle distancehas a relict Cenozoic sedimentary veneerin places and is an Otago Peneplaincorrelative. To the right of this, the PareoraRiver has cut an antecedent gorge inAakaia terrane sandstone andmudstone.

Figure 9 A fau lt-angle basin nearMoonl ight , in the Nenthorn structu ralblock, with Shark Hill in the foregroundand Strath Taieri and the Rock and PillarRange distant. Sediments in the basinare those of the "Moonlight lake", theancient shoreline of which can be seenin the foreground and to the right of SharkHill.


7

Figure 10 The basin of the upper Manuherikia River (right), with the Hawkdun Range, of Rakaia terrane sandstoneand mudstone, beyond. The low hills in the foreground and right middle distance are underlain by ManuherikiaGroup and Hawkdun Group sedimentary rocks, bevelled by later erosion. This area includes at least 812 milliontonnes of Manuherikia Group lignite. Photo CN4408-5: D.L. Homer

Figure 11 The scroll plain at Serpentine Flat, upper Taieri River. The uplifted Rakaia terrane schist block beyondincludes (from left) , the snow-capped southern Rock and Pillar Range, the antecedent gorge of the Logan Burn,and Logan Burn reservoir, formerly the Great Moss Swamp. Photo CN39501-10: D.L. Homer

8

Figure 12 The East Otago landscapenear Palmerston. Puketapu (centre) iscapped by Dunedin Volcanic Groupbasalt, while coastal clifts are cut inGoodwood Limestone. The KakanuiMountains (right background), of Rakaiaterrane textural zone llA semischist, areon the upthrown side of the WaihemoFault System.


Figure 13 Along the steep eastern faceof the Kirkliston Range, sloping piedmontgravel fans have forced the HakatarameaRiver to the eastern side of its valley(foreground) . The Kirkliston Range isformed mainly of textural zone I Rakaiarocks, and the outcrops in the foregroundare of semischist on the eastern side ofthe Kirkliston Fault Zone.


Figure 14 The loess-covered CollierDowns lie at the eastern foot of theHunters Hills in South Canterbury. Thisview to the northwest up the Makikihi Riverand Peters Stream shows the asymmetryof the stream valleys: the northern bankis generally much steeper than thesouthern .


9

separated by c1iffed coastlines with bold headlands. Tothe west lies the dissected schist catchment of theWaikouaiti River, which famls the more deepl y incisedeastern part of the Nenthorn plateau. The coastal areasouth of the Waihemo Fault System is underlain by gentlydeformed Cretaceousand Cenozoic rocks, someof whichare clay-rich and prone to slumping.

North Otago downlands

Rollingdownlands south of the Waitaki Ri verstrctch fromthe M aerewhenua River to thecoast. Thisarea isunderlainby generally east-dipping Late Cretaceous and Cenozoicrocks, with the morc resistanlun ils (such as the OtckaikeLimestone and the Tokarahi basalt sill) forming mesasand cueslas. The morc seaward parts are capped byweathered gravels, which partly predate present-daydrainage. and loess layers represcrlling several glacia l!interglacial climatic cycles. The seaward edge of thedownland is truncated by a degraded sea cliff. and itsnorthern edge is partly fault-controlled and partly cut bytheWaitaki River. Thedownlandshave a composite origin,partly aggradational and partly degradational. Althoughoverlain in places by loess and weathered gravels, thelandform may be inherited from a Late Miocene erosionsurface. The distinctive planar surface. as seen from CapeWanbrow. has a seaward tilt of a few degrees.

Waitaki valley

The Ahuriri, Ohau , Pukaki and Tekapo rivers rise inglaciated catchments outside the map area. They flowfrom the Mackenzie basin into Lake Benmore and thenceform the Waitaki Ri ver (front cover). Several bedrockgorges, separated by small tectonic basins, lie beneath astring of artificial lakes (Benmore, Aviemore, Waitaki)occupying the middle reaches of the fault-controlledWaitaki valley. Below Kurow, the va lley widens to a plain,with paired alluvial terraces on either side of a braidedri ver channel. The arcuate seaward edge of the plainreflects a wave-dominated coastline with strong longshoredrift.

10

Canterbury ranges and basins

The Hunters Hills, Kirkliston, Benmore and Diadem rangestrend north-south and are composed of Rakaia terranesandstone and mudstone. The steep eastern faces of theHunters Hill s, Kirkli ston and Benmore ranges areprominent landscape features (Figs 13 and 14) controlledby Quate rnary faults which may be aClive. Largecomposite fan systems at the range-frontsrepresent partof the material removed from these mountainsduring theQuaternary. while the older Kowai Formation gravels mayrepresent some of the debris shed from the Hunters Hillsin the Pliocene . Where uplift has been less, OtagoPeneplain remnantsare preserved.

In the east, the intervening Hakataramea. Waihao andCannington basins contain mainly Quaternary fluvialsediment. Basins further west (Ohau, Mackenzie) arecharacterised by Quaternary till and Ouvioglacial outwash.[n the Ohau basin, a line of hills (including the Clay Cli ffs)is uplifted along the acti ve Ostler Fault Zone.

South Canterbury downlands

These downlands comprise stream and fan alluvium, withridges composed largely of loess up to 20 m thick.Multiple loess layers, locally separated by peat, showthat these areas have remained out of reach of marine orfluvial erosion for a long time. The landscape has beenformed by the aggradation of loess on interOuves, anddiffers from the North Otago downlands which wereformed by Ouvial dissection of older rocks.

Offshore physiography

The continental shelf is relatively narrow near thesouthern map boundary (35 km wide), but broad east ofthe South Canterbury coast, where the shelf/s lope breakis 140 km offshore (Fig. 3). Northwest-southeast orientedsubmarine canyons are incised into the continental shelfand slope, the largest (the Waitaki Canyon) beingopposi te the mouth of the Waitalei Ri ver. The geology ofthe offshore area is well known from marine geophysicalsurveys and three petroleum exploration wells, two ofwhich (Cli pper- I and Oalleon- I) were sited close to u,eshelf/s lope break (Field, Browne ef at. 1989).

STRATIGRAPHY

Paleozoic to Mesozoic quartzofeldspathic sandstone,mudstone, semischist and sch ist outcrop over about 60%of the Waitaki map area. Remnants of Cretaceous andCenozoic nonmarine and marine cover sediments arepreserved overlying basement in the basins of CentralOtago and in areas close to the coast. Quaternaryf1uvioglacial and alluvial deposi ts are widespread.

The basement rocks are mapped in tectonostratigraphicterranes (Fig. 15, also Monimer I993a; Bradshaw 1993),within which, in some areas, traditional lithostratigraphicfonnations and groups are also recognised. Two majorunits (Caples and Rakaia terranes) and one minor unit ofuncertain affinity (Te Akatarawa lithologic association)are recognised. The basement rocks have been subjectedto regional metamorphism and defonnation; they are heredescribed according to their parent terrane, lithology, and(where schi stose), their textural development. Theschistose parts of the Caples and Rakaia terranes areknown collectively as the Haast Schist, which is dividedinto Otago, Alpine and Marlborough schists on the basisof geography.

Caples - Rakaia terrane boundary

Rakaia and Caples terrane rocks, originallydeposited in widely separated basins, werejuxtaposed along a complex fault zone duringJurassic to Cretaceous colHsion tectonic events(Graham & Mortimer 1992; Little et al. 1999).Differentiation of protoliths in the centre of IheHaast Schist depends on geochemical orisotopic crUeria because of structural complexityand metamorphic overprinting of the CaplesRakaia terrane boundary; a belt of rocks withuncertain affinity was mapped in Otago byMortimer (1993a). Recent geochemical samplingin the map area (N. Mortimer & D. MacKenziepers. comm. 2000) has resulted in the boundarybeing more closely constrained, but it is still notsharply defined, even at 1:250 000 scale. Theboundary is close to major fold hinges mappedby Means (1966) and Brown (1968) and may bedeformed by such macroscopic structures.

PERMlAN TO TRIASSIC

Caples terrane

Otago Sch.ist of Caples protolith

Caples terrane rocks range from non-schistose sandstoneand mudstone, west of the Waitaki map area, to stronglyfo liated Otago Schist which is a component of the HaastSchist (Bi shop et al. 1976; TumbuIl 2000). In west Otago

and Marlborough, the Caples terrane has a volcaniclasticprovenance, a distinctive geochemistry, and a mappablestratigraphy (Mortimer & Roser 1992; Begg & Johnston2000; T urnbu ll 2000). Only the southwestern corner o fthe Waitaki map area is Caples terrane (c. 460 km'); theCaples-Rakaia terrane boundary (see text box) trendsnorthwest-southeast , across the Lammermoor andLammerlaw ranges.

Caples rocks in the Waitaki map area are textural zone illschistsof the biotite-gamet-albite zone, greenschist facies(Yc; Monimer I993a). The dominant lithology is layeredpelitic schist, with minor metachen (Yct). There is nomappable stratigraphy, as the rocks have been overprintedby at least two phases of deformation (see below) withmost original features destroyed. A major macroscopicfold which extends into the map area from the west isdefined by steeply dipping foliation and changes inmesoscopic fold vergence (Means 1966). Elsewhere,foliation dips gently north or northeast and lineationsplunge gelllly nonh or south. Cenozoic folding of foliationis seen above blind reverse faults, for example at thesouthem end of the Hyde Fault. The depositional sellingsof the protolith Caples terrane sediments are inferred tohave ranged from trench slope, to trench-slope basi ns,and possibly, trench fl oor (Can er el al. 1978; Turnbu ll1979; Roser et al. 1993).

Rakaia terrane

The Rakaia terrane forms pan of the larger Torlessecomposite terrane, which comprises much of the SouthIs land (Fig. 15). The Rakaia terrane differs from the Caplesterrane in hav ing a granitic rather than a volcaniclasticprovenance, a di stincti ve quartzo feld spathi cgeochemistry, and a stratigraphy which in most areas isdifficult to map. Rakaia terrane rocks extend over the wholemap area, except for the small area southwest of theCaples-Rakaia terrane boundary. In the nonh the Rakaiarocks are mainly quartzofeldspathic sandstone andmudstone, but schistosity increases towards the terraneboundary (Fig. 16). The textural zones (see text box)increase from t.z. I sandstone and IlA semischist in theCanterbury ranges, th rough IlA and lIB sem ischi st inNorth Otago, to t. z. IV schi st in Centra l Otago and southof the Waihemo Fault System.

Rakaia terrane rocks are typically quanzofeldspathicsandstone and mudstone or argillite (Fig. 17), withsandstone generally dominant, or their regionallymetamorphosed equivalents, the pelitic and psammiticOtago Schist. The coarser-grained clastic lithologies areinferred to have been deposited by g ra vity -flowmechanisms (such as turbidites); some mudstone mayrepresent hemipelagic background sedimentation (e.g.Andrews et al. 1976; Hicks 198 1). Raka ia rocks are

II

_ f a Ak:atarawa lithologic association

c:=I Cenozoic to Holocene sediments

-- Gaples-Rakala terrane boundary

-......-

Pahaum••Rakaia •;"0

~<,n

•"0::;

~:l:5"ii83

Median Batholith

Karamea Batholith

Paparoa Batholith

Hohonu Batholith

Takaka terrane lTuhua

Butler terrane compositeundifferentiated terrane

Caples tenane

Dun Mountain - Maitai terrane

Murihlku terrane

Brook Street terrane

200 km

REGIONAL TECTONICMETAMORPHIC OVERPRINTS

Esk Head and Whakatane Melanges

II Haasl (including Otago) SChist

Gneiss

PLUTONIC ROCKS

SEDIMENTARY AND VOLCANIC ROCKS

_ Northland and East Coast Allochthons

Waipapa composite terrane(western North Island)

II Morrinsville-Manaia Hill

Hunua-Bay of Islands

Figure 15 Tectonostratigraphic terranes of New Zealand, after Mortimer et al. (2000) . Waitaki area basement rocks(inset) consist mainly of Rakaia and Caples terrane, with a small area of Te Akatarawa lithologic association. Thebasement terranes were in mutual juxtaposition by the Late Cretaceous,

12

(

Metamorphic facies_ prehnite·pumpellyite

pumpellyite·actinolite• chlorite greenschist_ biotite greenschist

Textural zones

• I• IIA• liBIII

• IV

Figure 16 Mineral and textural zonations within the Otago Schist of the Waitaki map area. Only major faults areshown.

13

interpreted to have been deposited in a huge submarinefan complex developed on an actively subducting oceanfloor during Late Carboniferous, Permian and Triassictime. at the Pacific margin ofGondwanaland. Incorporationofshallow marineand nonmarine sediments could indicatethat in Triassic time, pm1softJle fan complex wereelevatedabove sea level, but the shallow marine and nonmarinebeds are fault-bounded and their re lationship with themore typical. deeper water sediments remains unknown.Some of the inclusions and slivers of volcanic rocks,limestone, chen and red mudstone are inferred to havebeen incorporated tectonically during accretion (Campbell2000). The source of the Rakaia terrane sediment is stilldebated; (MacKi nno n 1983) suggested an Antarcticprovenance, but more recent studies of detrital zirconpopulations suggesl a source in north Queensland,Australia (Adams & Kelley 1998; Pickard et al. 2000;however see also Roser & Korsch 1999).

Undifferentialed Pennian 10 Triassic sedimentary rocks

Undifferentiated Rakaia terrane rocks in South Canterbury(Hunters Hills to the Ohau Range) are inferred to be mainlyPermi a n (Y t) in age, from poor ly preservedatomodesmatinid bivalve remains (Campbell & Warren1965; Pringle 1979; MacKinnon 1983). Conodonts nearMeyers Pass have close affinities wi th Early Permianfaunas of the onhem Hemisphere and are the oldestPennian fossils recognised from the Rakaia terrane (Fordet al. 1999; Campbell 2(00). Probable Triassic rocks (Tt)

liewest of Black Forest, in tJle Benmore and Ohau ranges;Triassic fossils occur in the Ohau Range (Andrews et al.1976) and Grays Hills (Force & Force 1978),just north ofthe map boundary. Detrital zircons in sandstones fromLake Aviemore and Pareor"" Gorge are mainly 260-270 Ma(S HRIMP V-Pb metllod; Ireland 1992; Pickard et al.2(00),with fewer Early Paleozoic and Proterozoic grains. Theabsence of Triassic zirconssupports the inferred Permiandepositional age. Sandstones compri se two majorpetrofacies. In the Benmore and Kirkli sLOn ranges andthe Hunters Hills, sandstonesare lithic feldsarenites withtypi ca l detrita l q uartz;feldspar: li thi cs (QFL) rat io of20:50:30; detrita l homblende and volcanic li thic grainsare common. In the Diadem Range, the QFL ratio istypically 30:50;20 with detrital biotite common. Thesedifferences partly correspond to Permian and Triassicpetrofacies outlined by MacKinnon ( 1983) and Roser &Korsch (1999).

Over small areas the dominanllithology is mudstone (Yti);the distinctive, maroon and green Domet Phyllite is over40 m thick (Bishop 1976) and is a useful stratigraphicmarker bed, as are thinner layers of coloured mudstoneand argi ll ite e lsewhere. Black siltstone with thin beds ofsandstone crops out in the HuntersHi llsnear Mt Nimrod.Pebble and cobble conglomerates (VIc) are known fromDanseys Pass (e.g. the Cone Conglomerate of Bishop1976), Meyers Pass (Ford 1994), Kakanui Mountains(Tumbull 1968), Kirkliston Range, Black Forest (Fig. 17c)and Hunters Hi lls. Most are dominated by quartz clasts,

Textural zones

Textural subdivision is a uselul method lor mapping low grade metamorphic rocks and major structures withinthe Haast Schist and has been widely applied (e.g. Bishop 1974; Turnbull 1988; Mortimer 19938). Texturalzones (t.z.) separated by "isotects' are independent of metamorphic facies boundaries, and can cut acrossisograds or foliation.

The application of the textural zonation system established by Bishop (1974) has been revised by Turnbull etal. (2000). Characterislics of these revised textural zones are summarised:

t.z. I: Rocks retain their sedimentary (primary) appearance. Detrital grain texture is preserved, and beddint;l(when present) dominates outcrops. Metamorphic minerals may be present, but are very line-grained «75 pm),and there is no foliation.

t.z. IIA: Rocks retain their primary appearance and sedimentary texture, although detrital grains are /faltened.Metamorphic minerals are line-grained «75 pm), and impart a weak cleavage to sandstones. Mudstones haveslaty cleavage. Bedding and foliation are equally dominant in outcrop. Rocks are termed semischist.

t.z. liB: Rocks are well loliated, although primary sedimentary structures may still be seen. Bedding istransposed or /fattened. Clastic grains are /fattened and metamorphic overgrowths are visible in thin section.Metamorphic mica grain size is still <75 pm and metamorphic segregation appears. Mudstone is changed tophyllite; meta-sandstone is well loliated and forms parallel-sided slabs. Rocks are termed semischist.

t.z. 11/: Planar schistosity identified by metamorphic micas is developed in all rocks. Bedding is barelyrecognisable, and is transposed and parallel to folia lion. Claslic grains may still be recognisable in sandstones,but are recrystallised and overgrown, and melamorphic segregation laminae are developed. Rocks aretermed schist. Quartz veins develop parallel to folia lion, or are rotated and /fattened. Metamorphic micas aretypically about 75-125pm long (very line sand size).

t.z. IV: Primary sedimentary structures and clastic grains are destroyed at a mm-cm scale, although primarysedimentary units may be discernible in outcrop. Schistosity tends to be irregular due to porphyroblastgrowth. Metamorphic mica grain size is t25-500 pm. Schistosity and segregation are ubiquitous and rocks aretermed schist. Gneissic textures may be developed. Quartz veins are abundant in most lithologies.

14

Figure 17 Rakaia terrane lithologies.

(a) massive textural zone (I.z.) Isandstone dominated by joints(Hunters Hills) .

Photo: J.G. Begg

(b) alternating sandstone andsiltstone of I.z. I (Hunters Hills) .

(c) pebble conglomerate of I.z. I(Black Forest Station , SouthCanterbury).

15

wi th subordi nate c lasts o f dark grey argi llite flakes,sandstone, semischist, silicic and basic volcan ics andgranitoids, and they lack the common plant materialpresent in Triassicconglolneratessuch as the Black JacksConglomerate (see below). They are interpreted as coarseturbidite or grain-fl ow deposits (Bishop 1974), with someautocannibalistic reworking of older Torlesse rocks(MacKinnon 1983). Though on ly 8 m thi ck, ConeConglomerate hasbeen traced laterally for more than 8 km.Other conglomerates are up to 100 m thi ck but areapparently lenticular, or channel- fill s. Clasts becomeprogressively deformed wi th increasing schistosity( onis & Bishop 1990).

Undifferentiated Permian to Triassic volcanic andmetavolcanic rocks

Metavolcanic units and associated minorlithologies (Ytv)occur in the KirkJiston Range. Waihao, Pareora andWaianakarua rivers, Black Forest, and near Danseys Pass(Bishop 1976; Pringle 1980). At higher metamorphic gradesmetavolcanics are represented by greenschists (Ylg),which typically contain metamorphic chlorite, epidote,muscovite. albite, calcite, and locally, magnetite. TheKirkliston metabasite is3 15 m thick and at Danscys Passthere are at least 550 m of intercalated metavolcanics.Primary basalt textures which have survived low-grademetamorphism include coarsely porphyritic (Waianakaruaand Waihao Forks), coarsely variolitic piJlows (BlackForest), and hig hl y vesicu lar spilites (Green Gullynorthwest of Danseys Pass). Metado lerite is present inthe KirkJislon Range and at Danseys Pass; the latter isinterpreted as a sill (Bishop 1976). Associated with themetavolcanic rocks are minor hematitic argillite,marble (Ytf) and c hert (YII), the la tter commonl ymanganiferous. An area of broken formation in theKirkli ston Range, along strike from the Kirk lis tonmetabasi te, includeschert, sandstone and igneous rocksin a matrix of sheared red and grey argillite (Fig. 18).Conformabl e contact s show tha t some of themetavolcanics in the map area are coeva l with the

Figure 18 Manganiferous chert and red mudstone inbroken formation (Waitangi Station, South CanterbUry).

16

enc losing sedi mentary rocks (pringle 1980), and in theWaianakarua River a pi llowed metaporphyrite isintrudedby sandstone dikes. Elsewhere in the Rakaia terrane.metavolcanics are generally found in melanges, or alongfaults (e.g. Begg & Johnston 2000; Turnbull 2(00).

Otago Schist and regional metamorphism

Only a quarter of the basement rocksof the Waitaki areaare unfo liated ; all the Caples rocks and the greate r part o fthe Rakaia rocks are Otago Schi st (Fig. 19). Layeredsemischist and schist are composed of distinct alternatingquartz-albite and mica-rich laminae; quartz and albiteconstitute 40-60 % of the rock (Mortimer & Roser 1992).Massive semischist and schist are generally unlayeredwi th weakly to moderatel y developed fo li a ti on andcompri se 50-80 % quartz and albite. These two sch isttypes represent metamorphosed argillite and sandstonerespective ly. Metamorphosed volcanic rocks, metachertand marble are minor lithologies.

Almost all the unfoliated sandstonesand mudstones, andtheir schi stose equi va lents, contain the metamorphi cmineralsquartz, albite, chlorite, white mica and titanite.Metamorphic mineral zones and facies (Fig. 16) are basedon the additional presence of one to three index minerals,namely prehnite, pumpellyite, actinolite, stilpnomelane,epidote , biotite and garnet. The textural zones (see textbox) used in field mapping are independent of metamorphicfacies, although rocks of higher textural grade also tendto be of higher metamorphic grade. Both isotects andisograds are generalised on the map. lsotects are basedmainly on fi eld determinati ons, supplemented bymicroscopy, and isograds on petrographic examinationof more than 200 thin sections.

Zeolite facies laumontite-bearing luffs have beendescribed from Benmore Dam (Coombs 1993) but the areaof known zeolite facies rocks istoo small to be shown inFigure 16; the unfoliated (t. z. I) rocks are mainly prehnitepumpellyite facies. There is a progressive increase inmetamorphism through the pumpellyi te-actinolite faciesto chlorite zone, then to biotite-gamet-a1bite zone of thegreenschist facies in the centre of the Otago Schist belt,as part of a moderate Pff facies gradient (Mortimer 1993a,I993b, 2(00); the highest grade schists are present in thesouthwest of the map area. Semischist (t.z. II) rocks are ofprehnite-pumpeUyite and pumpe llyite-actinolite fac ies.The transition to greenschist facies typically occurswithin t.z. III ; fuU y schistose rocks are of greenschistfacies (Mortimer 2(00).

Little ef al. ( 1999) suggested that metamorphism peakedat c. 170- 180 Ma (M iddle Jurassic), fo llowed at 135 Ma(Early Cretaceous) by rapid uplift and cooling below theargon retention threshold (see also Adams el al. 1985 ;

Figure 19 Otago schist structures.

(a) Textural zone (t.z.) liB semischist in the KakanuiRiver has transposed bedding subparallel toschistosity. Because the two structures are slightlyoblique, bedding appears as strong lineations onschistosity surfaces (b, below).

(c) Quartz rodding in t. z. III schist (Shag River) hasformed parallel to axes of minor folds.

Adams& Robinson t993; M ortimer t993a, 2(00). Adamsand Graham ( 1997) inferred initial metamorphismat c. 200 Ma (Late Triassic), and a second metamorphicevent before 11 5 Ma (Early Cretaceous), followed byuplift, or alternatively, a single metamorphicevenr in LateTriassic-Early Jurassic time, followed by slow uplift .

Blue Mountain Formation marble

M arble of the Blue M ountain Formation (Ytb) occurswithin t.z. II A semi schi sl at Blue Mountains, in theKakanui Range near Palmerston; much smaller outcropslie up to 30 km to the northwest (Hector 1884; McMillan1999; M artin 1999). A t Blue M ountains, blue-greycrystalline marble with intercalated argillite is about200 m thick. A t Conical Peak about 100 m of pure andimpure marble, hematitic and chloritic slate, and red andgreen chert are interbedded with grey sandstone andargillite; further to the no rthwest, pinkish calcareoussiltstone is interbedded with sandslOneand argill ite. LateMiddle Carboniferous conodonts have been reportedfrom Conical Peak (Martin 1999; S. Yamaki ta pers. comm.2000), but no diagnostic fossi ls have been found at BlueMountains. Initial stronti um isotope ratiosofa limestonefrom thequarry at Blue M ountainsareconsistent with anEarly Permian or Late Carbon iferous age. A K-Ar agedetemlination of 189 ±5 Ma(Early Jurassic) on slate fromthe southwest margin of the quarry is interpreted as ametamorphiccooling age and isconsistent with aTriassicor older age ofdeposition (C,J . Adamspers. comm. 1998).Limestoneand marbleoccurring in associationwith Rakaiaterrane elsewhere are of Carboniferous and Pennian age(Hitching 1979; Hada& Landis t995).

K ohurau Schist

Pale green schistose metasandstone with rare purplishgreen ph yll ite is present between the St M ary andWharekuri fau lts, on the north flank of the St Marys Rangebetween Otematata and Kurow (Kohurau Schist, Ytk;Bishop 1976). Discontinuousth indark micaceouslayersseparated by thicker paler quartzofeldspathic layers aredistincti ve; the quartz-rich layers are veins but may bepartly inherited from asiliceousprotolith . A lthough rocksappear well fol iated, detrital textures are visible betweenthe veinsand the rocks are classified as t.z. 11. The foliationis commonly folded about a strong mullion lineation.Pumpellyi te-epidote mineral assemblages are common;K ohurau Schist has a different metamorphic anddefoml ational history from adjacent rocks.

Triassic nonmarine and shallow marine rocks

M t St Mary Formation (T tm; Rybum 1967; Bishop 1976)is one of four simjlar units containing plant fossils andmai nly shallow marine macrofoss il s of latest M iddle

17

Triassic age (Kaihikuan local stage; Canlpbell 1994). Themajn lithologies are sandstone and siltstone, wi th minorlenses of conglomerate containing pebbles of silicicvolcanics and plulonics, chert, quartz, sandstone, schistand phyllite. The fonnation is slightly schi stose in thesoutheast (I.z. IIA) and rich ly fossili ferous in parts. It isbounded by the Bitterness and St Mary faults and fo ldedinto the Bitterness Anticline. Corbies Creek Group (Tic;Retallack & Ryburn 1982) comprises several fonnationsof fossi liferous marine sandstone and si ltstone. gradingup to nonmarine carbonaceous sandslOne, siltstone andcoal and fOfming a regress ive sequence which wasprobably deposited in a large delta. It is bounded by theOtematata and Middle Range faults and folded into aseries of synclines and anticlines. Kaihikuan marinemacrofossilsfrom near the base are similar to those of theMt St Mary Fonnation, though more diverse. Fossil plantsfrom the top of the sequence (Retallack & Ryburn 1982)are similarto those from lhe Mt Potts Group in Canterbury,which is also of Kaihikuan age. Otematata Group (Tlo;Retallack 1983a. 1983b) comprises nearly I()()() m ofterrestrial to shallow marine. massive to crudely bedded.sandstone pebble conglomerate, with minor intercalatedsandstone and mudstone (the Black Jacks Conglomerate;Hada & Landis 1995). overlain by coarse-grained lithicsandstone w ith interca lations of conglomerate andinterbedded siltstone and shale (Spillway Fonnation). Therocks have been metamorphosed to prehnite-pumpellyitefacies (Retallack 1983a). Black Jacks Conglomerate isbounded at the base by the Acaena Fault, but the natureof the upper contact of the Spillway Formation is stillunknown. Sandstone and siltstone lithofacies of theHaldon Formation plus gradationally overlying SpursSiltstone (both Tlh) were deposited on the upper to middleportions of a submarine fan (Force & Force 1978). Therocks are sheared and weakly foliated, but still within t. z. I,and contain a Triassic fauna. Both formations are lightlyfolded into a series of synclines and anticlines. SpursSiltstone is separated from adjacent undifferentiatedRakaia terrane rocks by the Black Forest Thrust, whilethe base of the Haldon Formation is not seen. The nearbyMt Maggie Fonnation (Force & Force 1978) has not beendifferentiated on the map because of its small area,unknown age and unknown relationships with namedfonnations.

Deformation structures in Rakaia rocks

Outcrop-scale tight and isoclinaJfoldsarecommon in t. z. Isandstone- and mudstone-dominated beds (Fig. 20a);younging directions can commonly be determined fromfacing indicators such as graded bedding and so lestructures. An early axial plane slaty cleavage is commonlydeveloped. Over much of the map area the regionalcleavage and sc hi stos it y are ori ented northwestsoutheast, and the ori entat ions of these relative to

18

Figure 20 Some folding slructures in Rakaia terranerocks .

(a) disharmonic folding in alternating sandstone andmudstone (Lake Benmore area) .

(b) gently-dipping bands of small folds deformingmore steeply dipping regional schistosity in t.z. IVschist (Rough Ridge). Photo: I.M. Turnbull

(c) kink swarm in pelitic t.z. liB schist (upper KakanuiRiver). Photo: I.M. Turnbull

bedding can typically be detennined for rocks of texlUralzone as hi gh as Lz. lIB . With increasing strain andrecrystallisation, early folds and sedimentary structuresare obliterated, and progressive deformation refoldsfoliation (Fig. 20b). Up to four generations of structureshave been identified (Table I), but where bedding isobliterated deformation events can be assigned only

Table 1 Overview of structures in Caples and Rakaia terrane rocks of the Waitaki map area. Amended from Coxet af. (2000).

Generation Structure Inferred Age

0 Bedding Carboniferous -Permian- Triassic

I transposed bedding. schistosity, cleavage, mineral Jurassicsegregation, steeply plunging folds, tight-isoclinal folds (Early regional metamorphism)

2 recumbent folding, nappe sheets & high strain zones, Jurassicstretching lineations. veins. foliation, schistosity (Late regional metamorphism and terrane(Manorbum generation of Means 1966) juxtaposi tion)

3 brittle-ductile fault zones (e.g. Hyde-Macraes CretaceousShear Zone), mainly normal faul ts. mineralisation (Uplift and exhumation of schist prior to& veins, joints peneplanation)

4 open, broad antifonns (e.g. Rock & Pillar), Latc Cenozoicmainly reverse fauhs, kinks, chevron folds, joints (Related to Alpine Fault development

and crustal shortening across Otago)

relative ages. Foliation symbols on the map face showthe dominant foliation at any outcrop and do notdifferentiate between the different generations. Earlyregional -sca le folding is associated w ith reg ionalmetamorphism, for example, folds south of Strath Taieri(Brown 1968) and at Blackstone Hill (Grady 1968). Rocksof different metamorphic grade were juxtaposed alongpost-metamorphic normal faults before the OtagoPeneplain was formed. Such faults include the HydeMacraes Shear Zone and the Cap Burn Fault in thenorthem Rock and Pillar Range, both of which dip gentlyto moderately to the north and northeast. Rocks of lowmetamorphic grade occur in the hanging walls, showinga net normal sense of offset. Normal faulting along theWaihemo Fault System (including Stranraer Fault) fornledbasins which are now present on the hanging wa ll ,demonstrating subsequent reversal of movement. Faultsin the Waitaki Fault System may also have been active asnormal faults at this lime.

Renewed faulting in Miocene and Pleistocene time fonnedrange fronts such as the Kirkliston Range and HuntersHills (Figs 13 and 14). Some older faults were reactivatedwith reversal of movement, for example, the Dansey PassFault (Bishop 1974) and the Waihemo and Wai taki faultsystems. Reverse faulting and folding is also associatedwith the northeast-trending Otago ranges (Markley &Norris 1999). Kink and chevron folds in foliatio n arecommon along the Cenozoic faults (Fig. 2Oc).

Te Akalarawa lithologic associalioll

A fault-bounded suite of clastic, carbonate and volcanicrocks on the north side of the Waitaki valley east ofBenmore Dam issufficiently distinct in age, lithology andmetamorphic grade from the surrounding Rakaia terraneto have been classed as a separate terrane or subterrane

(B ishop el al. 1985; Hada & Landi s 1995; Cawood el al.200 I); it is described here as a litho logical association ofuncertain affinity. Te Akatarawa lithologic association(Yk) is present in a fault-bounded block comprising anea r- isoc lina l southw es t- p lungin g fo ld, theTri g E Sync lin e . Roc k types inc lude interca iatedsand stone, mud ston e and minor co nglomerate,significcwtly more quartz-rich than surrounding Rakaiarocks (Smale i980), and mudstone-matri x melange withclasts of fragmented hyaloclastite and scoria. rare pillowlava , and limestones. Te Akatarawa rocks are ofpumpellyite-actinolite metamorphic facies, and texturalzones lIA and []B , significantly higher than adjoi ningRakaia terrane rocks. lIIite crystallinity is also higher(Hada & Landis 1995).

The absence of Atomodesma serves 10 differentiate TeAkatarawa limestones from most other Pennian Torlesselimestones. The Te Akatarawa limestones containfragments of crinoids. algae, cora ls, ammonoids,brachiopods and fusulinid foraminifera; the faunasuggests Te Akatarawa lithologic association isallochthonous to the ew Zealand region. Though poorlypreserved, the fusulinid foraminifera indicate a MiddlePeml ian age. and correlate best with Eurasian faunas ofTethyan affin ity (Leven & Campbell 1998).

Te Akatarawa rocks are interpreted to have fonned as anoceanic basalt/ limestonel chert! hemipelagite sedimentarymelange or olistostrome, which originated as talus andslide-blocks oflithified limestone emplaced in a matrix ofbasaltic detritus along the flanksof a submarine volcanoo r seamou nt (Hada & Landi s 1995). Subsequentdeformation has superimposed a shear fabric. TheTe Akatarawa lithologic association is inferred to havebeen tectonically emplaced into the Rakaia terrane duringa subduction-related accretionary event.

19

CRETACEOUSTO PUOCENE

Full descriptions of [he Cretaceous [0 Plioce nesedimentary succession in southeastern ew Zealandhave been given by Carler ( 1988), Field, Browne ef al.( 1989) and Cook ef al. ( 1999). Different stratigraphicnomenclature has been used by the different authors(Appendix I); this publication follows Carler's scheme,as did the previously published 1:250 000 map of theadjacent Dunedin area (Bishop & Turnbull 1996).

Rifting associated with separation of New Zealand frol11Australia and Antarctica in late Early Cretaceous timewas accompan ied by deposition of coarse graben-fi lldeposilS (Matakea Group), accompanied a[ first by minorsilicic volcanic activity. Regional subsidence in LateCretaceoustime resulted in deposition of the transgressiveOnekakara Group across the east of [he South Island.Deposition of nuvial sandstone and conglomerate wasfollowed by deposition of marine sandstone, mudstone,greensand and marl. Sporadic igneous activity from latestCrelaceous to Early Oligocene lime produced localvolcanicedifices, with associated limestone and diatomitedeposits. Some of these (the Galleon and Endeavourvolcanics) lie entirely offshore. The onshore Waiarekaand Deborah volcanics near Oamaru and their closelyassociated sedimentary rocks comprise the Alma Group.

The Marshall Paraconformity, a regionally extensivesurface of erosion or nondeposition of mid Oligoceneage, is developed across the Onekakara and Alma groups(Carler & Landis 1972; Carler 1985; Ful[horpeef al. 1996).The paraconformi[y and [he overlying Kekenodon Grouprepresent a period of greatly reduced sedimentation.Deposition continued with the regressive Otakou Groupof Mioceneage, comprising mainly marine mudstone andsandstone, but with minor limestone and nonmarinedeposits, including li gnite. Flu vial and lacustr inesandstone and mudstone (Manuherikia Group) weredeposited in inland basins. Intraplate volcanism duringthe Miocene resulted in the eruptionof Dunedi n VolcanicGroup rocks over partly eroded earlier Miocene and olderrocks. In Pliocene and Pleistocene time, detritus shed fromrising moul1lain systems built extensive piedmont fansand plains (Hawkdun Group, Kowai Forma[ion and othercoarse gravel deposits), while deposition of marinemudstone continued offshore. A volcanic vent nearTimaru erupted several lava flows in the Late Pliocene.

Some of the facies variations and unconformities withinthe Cretaceous to Pliocene sedimentary succession reflectchanges in global sea level or ocean currents, while othersresult from pla[e boundary events and regional or localtectonic activ ity (McMillan & Wilson 1997; King ef al.1999). The resulting lithofacies have been given manylocal and regional formation names (Table 2, also

20

Appendix I). Fossil assemblages in these rocks, especiallymolluscs and foraminifera, are of great imporlance to bothlocal and ew Zealand paleon[ological studies (e.g.Homibrook I% I; Homibrook ef al. 1989; Beu & Maxwell1990; Maxwell 1992).

Mid Cretaceous sedimentary rocks

Matakea Group comprises predominanlly coarse clasticsed iments deposited in fault-angle basins on thedownthrown (nor[hern ) side of [he Wai hemo Faul[System. Three formations are differentiated.

The Kyeburn Formation (Kek) crops out over 80 km'nOrlh of [he Maniototo basin (Bishop 1976; Bishop &Laird 1976). lIS southern and eastern boundaries are [heS[ranraer Faull (of the Waihemo Faul[ System) and theDansey Pass Fault, and to the northeast and northwest itun conformabl y overli es Rakaia terrane schist andsemischist. Kyebum Formation consistsof over 3000 mof terres[ ri a l red a nd blue-grey schist-derivedconglomerate. with some breccia, sandstone andcarbonaceous siltstone. The upper and lower parts aredominantly conglomeratic, whi le the middle part includescalcareous sandstone, carbonaceoussandstone, siltstoneand coal. Lmbrication. cross-bedding and facies changesindicate derivation from thesouth and east. Biotite-bearingsilicic tuff layers (Eweburn Tuft) near [he base of theformation now contain alteration minerals such asmontmorillonite and zeo lites. Sandstones ha ve ametamorphic mineral assemblage ofquartz-albite-chloriteseri cite-pumpellyite ± calcite. The formation wasdeposited on a surface of low relief, as lalus, alluvial fans,and overbank and lake deposits. Eweburn Tuff is of lalestEarly Cretaceous age ( 105- I07 Ma) and the remainder ofthe fonnation, as determined from microflora. islate Earlyto Late Cretaceous (Motuan-Mangaotunean; Adams &Raine 1988).

Horse Range Formation (Keh) is presem in an elonga[estrip in eaSlern Otago; about 400 m of induratedconglomerate, brecc ia , sandstone, siltstone andcarbonaceo lls mudstone with thin coal lenses lieunconformably over relati vely unweathered Rakaiasemischis[ (Douglas 1970; Mi[chell 1990). A basal brecciaof quartz clasts occurs closest to the Waihemo FaultSystem and is succeeded by conglomerates, locallyseparated by a sandstone-muds[one-coal facies. Pebblesand cobbles of Rakaia terrane rocks dominate theconglomera[es (Fig. 2 1); in higher beds the c1as[s are morerounded and better sorted. Horse Range Formationgrades into the overlying Taratu Formation of theOnekakara Group. The formation was deposited in anorthwest-southeast oriented half-graben associated withnormal movement on theWaihemo Fault System. Roundedsandstone and mudstone pebble conglomerates were

REGIONALUNCONFORMITY


LOCALUNCONFORMITY


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deposited by an axial braided river system, whereassubangular schist-quartz conglomerate and breccia werederived from fans coming off the uplifted rift shoulder tothe southwest (Douglas 1970). A fault-bounded strip ofconglOinerate within the Horse Range Fonnation includesthe Shag Valley Ignimbrite (Kei; Steiner e' al. 1959); it

comprises rhyolitic tuffs in a primary pyroclastic nowdeposit and isof latest Early Cretaceousage ( 10I - I03 Ma).Palynology indicates the Horse Range Fomlation is lateEarly Cretaceous to Late Cretaceous in age (Adams &Raine 1988).

Figure 21 Horse Range Formation is dominated byconglomerate of Aakaia terrane sandstone andsemischist clasts, in places highly altered by postdepositional processes.

Figure 22 Taratu Formation quartz conglomerate and coal have been mined at Cameron's Pit in the lower Waitakivalley. Several generations of quarry are visible in this view southwest towards Big Hill.

Photo: Tasman Aerial Photography

22

Late Cretaceous to F..a rly Oligocene sedimentary rocks

Onshore the Onekakara Group is up to 1500 m thick;offshore it is as thick as 3000 m (Carter 1988). The basalbeds in eastern Otago include quartzose conglomerateand sandstone (Fi g. 22), mudstone and coal (TaratuFormation; IKt); north of the Waitaki River the lateralequivalent is Broken River Formation (Eeb). Taratu andBroken Ri ver formationsunconformably overl ie leachedRakaia terrane schi st, semischist or sandstone/mudstone,the leaching being attributed to alteration after thedeposition of sediments (Craw 1994) rather than priorsubaerial weathering. Taratu Formation is up La 120 mthick, buttypicaIJy less than50 m. Broken River Formationis also of variable thickness and is absent locally, as inthe upper Waihao River. Variations in thickness resultfrom irregularities in the underlying ancient land surfaceand marine erosion before deposition of the overlyingunits. Taralll and Broken River formations accumulatedin valleys, flu vial plains. swampsand estuaries as the seatransgressed northwestwards. Sedimentary structurestypical of stream systems, such as trough cross bedding,

are common in the lower part, but towards the top of theunits the better sorting, very low-angle crossbeds,hummocky cross stratification, increased bioturbation andpresence of marine dinonagellates indicate marineinnuence (Aitcbi son 1988; McMillan 1999). Silica- andlimonite-cemented layers are common, especially near thebase.

CoaJseamsare up to 8 m thick at Ngapara but elsewhereare typically 3 m thick or less. Taratu mudstone and lignitehave yielded a well preserved leaf fossil assemblage (pole1992, 1995; Fig. 23), which grew in mild temperateconditions, was dominated by angiosperms, and includedlesser components of coni fers and ferns (E. Kennedypers. comm. 2000). Taratu Formation ranges from LateCretaceous to Eocene in age (Couper 1960; Pole 1992,1995), the base generall y becoming younger inland;however no definite Paleocene ages have beendetermined. Thiscould be an artefact of the sampling orit could result from erosion at the transition to marinesedimentary environments. In South Canterbury. BrokenRiver FOimation is Early Eocene in age (Wilson 1995).

Figure 23 At Cameron's Pit (Fig. 22), Taratu Formationcontains well preserved leaf lossils of latest Cretaceousage. The diverse flora is mainly angiosperm form s, withrelatively minor components of other plant groupsincluding araucarians , podocarps and ferns.

Photos: E. Kennedy

23

Hogburn Formation (Eh) quartzose sandstone (Fig. 24a),conglomerate. carbonaceous mudstone and ligni teunconformably overlie weathered Rakaia terrane schist;it is the inland equiva lent of the youngest TaratuFormation. It occurs in inland Nonh Otago along theWaihemo Fault System and on the Nenthom plateau. Inthe area of the Waitaki map, dating of overlyingfossiliferous marine sedimentary rocks suggestsa MiddleEocene age; further south Hogburn Formation isMiddleto Late Eocene (J.t. Raine ill Bishop & Turnbull 1996).

The stratigraphically higher, marine formations (mappedas undifferentiated Onekakara Group marine units; Eo,Porn) are present in a coastal strip up to about 15 kmwide, and up to 70 km inland in the Shag, Waitaki andHakataramea valleys. The contact between the nonmarineand marine units is either an angu lar unconformity ordisconformity, interpreted as a wave-cut surface (theWaipounamu Erosion Surface of LeMasurier & Landis1996; see also Landis & Youngson 1996). Many localformation names are applied (Table 2). The more extensiverock types include limonitic and micaceous sandstone(Kauru Formation), concretionary si lty sand sLOne,

glauconit ic sandstone and ca lcareous mudston e(Abbotsford Formation and Waihao Greensand; Fig. 24band c), well sorted sa ndstone (Opawa Sandstone),

glauconitic sandstone (Tapui Glauconitic Sandstone),ca lca reous mudston e and clayston e ( Burn si deMudstone), and impure limestone or marl (A muriLimestone). Kapua Tuff, within Burnside Mudstone, isrelated to the Waiareka Volcanics (see below).

These rocks were deposited in a wide range of shallowmarine environments, ranging from shoreface to outershelf and offshore bars. Deta il ed paleogeographicinterpretations have been published elsewhere (Carter1988; Field, Browne eta/. 1989; Wilson & McMillan 1996;McMillan & Wilson 1997; Kinge/al. 1999). Gage(1957),Gair ( 1959), Bishop (1979), Fordyce e/ al. (1985), Maxwell( 1992) and McMillan (1999) have given formation andoutcrop-scale descriptions. South of the Waihemo FaultSystem, the marine beds are as old as Late Cretaceous; alatest Cretaceous fossil locality at Shag Point has yieldedplesiosaur and mosasaur skeletons (Cruickshank el al.1999). Most of the sequence is Paleocene to Eocene,with some Early Oligocene rocks in North Otago.Archaeocete whale fossils and a fossil turtle have beencollected from the Middle Eocene Waihao Greensand(Fordyce 1985; Kohler 1995; Kohler & Fordyce 1997). InSouth Canterbury the known age range is Earl y Eoceneto Early Oligocene. The upper limit of the OnekakaraGroup sequence isthe Marshall Paraconformity.

The Marshall Paraconformity

The Marshall Paraconformity (Carter & Landis 1972; Carter 1985; FUlthorpe et al. 1996) is a regionally significantsurface of erosion or nondeposition in the South Island. It is commonly marked by a burrowed or bored surface,phosphatised in places, in the underlying Onekakara Group rocks. Its type locality is in the Pareora district (Gair1959; Carter & Landis 1982), in the northeast of the Waitaki map area. The unconformity and the overlyinggreensand plus limestone (Kekenodon Group) coincide approximately with a prominent seismic reflector whichcan be traced offshore into the Canterbury and Great South basins.

The formation of the Marshall Paraconformity was probably related to a glacio-eustatic sea level faJJ (Loum et al.1988) which occurred during the period of almost maximum submergence of the New Zealand subcontinent, whenterrigenous sediment supply was greatly reduced (Carter 1985). Strong, cool water currents derived from theAntarctic circumpolar current also developed about this time, and were responsible for widespread submarineerosion, winnowing and nondeposition. The unconformity represents a period of about 2-4 Ma and spans theboundary between the Early and Late Oligocene (Fulthorpe et al. 1996).

24

Figure 24 Some Onekakara Group lithologies.

(a) burrowed fine sandstone (HogburnFormation, Siberia Hill).

(b) heavily burrowed greensand (AbbotsfordFormation, Shag valley) .

(c) concretionary mudstone (AbbotsfordFormation, Katiki Beach).


25

Figure 25 Alma Group lithologies.

(a) Layers of tuff (bottom), limestone,sandstone , siltstone and pillowbreccia (top) of Waiareka Volcanicsat Boatmans Harbour, CapeWanbrow, Oamaru.


(b) Carbonate-cemented agglomerate,Waiareka Volcanics at BoatmansHarbour.


(c) The Kakanui Mineral Breccia atKakanui North Head, part of theDeborah Volcanics, contains avariety of mantle-derived crystals,nodules and lithic clasts.

26

Eocene to Oligocene sedimentary and volcanic rocks atOanlllnl

Waiareka and Deborah volcanics, together with theassociated OlOlara Limestone. form the Alma Group(Gage 1957). Ototara Limestone (Elo) includes Gage'sTotara and McDonald limestones and is equivalent tothe expanded Totara Limestone ofField & Browne (1986).Ototara Limestone is massive or indistinctly bedded andmainly comprises bryozoan remains with little terrigenousmaller; in places it contains tuff and pebbles of basalt.Though macrofossils are not common, turtle, bivalve,shark and penguin fo ss ils have becn collected(Fordyce 1979. 1985). The limestone is interbedded withrocks of the Waiareka and Deborah Volcanic formations(Edwards 1991), is up to 60 m thick, and of Eocene toEarly Oligocene (Runangan-Whaingaroan) age. It wasdeposited on submarine platforms. in a shallow marine,shelf setting.

The Waiareka Volca nics (Elw) arc present close to thecoast between Moeraki and Oamaru and as far inland asMaerewhenua. Correlative thin tu ffs are present as farafield as Kapua in South Canterbury. The Debora hVolcanics (Old) are recognised between Oamaru andKakanui (Edwards 199 1). Thc two erupt ive phases wereformcrly thought to be separated by a layer of limestone(Gage 1957) bu t th is is now rega rded as anoversimplificmion (Edwards 199 1).

Waiareka Volcanics comprise basaltic tuff. agglomerateand pillow lavas, basaltic to doleritic dikes and sills, andlayers of coeval sediment; the dominant lithology is tuff(Fig. 25a and b; Gage 1957; Coombs & Dickey 1965). n,egreatest known thickness is at Cape Wanbrow where over200 m are present, with the base not exposed. Tuffs arewell bedded and well sorted; they include planar-Ian,inatedash beds, current-bedded tuff, and reworked unitscontaining brachiopods and molluscs. Volcanic debrisflows with fragments of pillows, dikes and bombs are wellexposed at Bridge Point south of Kakanui , and pyroclasticsurge deposits occur near Cape Wan brow. Severalmembers have been recognised (Edwards 1991) and twoare differentiated (by overprint) on the map; the LornePyroclastics comprise breccia, tuff, agglomerate andmudstone and are up to 120 m thick. Fossi liferous horizonscontain molluscs, brachiopods, echinoderms, corals,bryozoa and foranninifera. Oamaru Diatomite, up to 45 mthick, includes massive, soft, pale grey si ltstone composedof diatOinswith other micro-organisms, and intercalatedtuff beds. It is overlain by, and grades laterally in to, theOtotara Limestone.

The spectacular exposures of pillow lava at BoatmansHarbour, uear OamaTu (back cover), have been studiedintensively since first being recorded in 1905 (see Coombs

el al. 1986 and references therein). Thcre. tuffs a minimumof 150 m thick are overlain by about 30 m of tholeiiticpillow lava, basanitic tuffs and impure calcareous beds,and at least 40 m of coarse tholeiitic pillow brecciacontaining local pockets of fossiliferous sandstone andlimestone. At Moeraki Peninsula, basaltic inlrusionsanda dolerite sill intrude coeval tephra and underlyingmudstone; the sedimentary rocks have been baked nearsome contacts. A large dike at Enfield may have been afeedcr for ncarby intrusive basal tic sheets (Coombs el al.1986). The olivine tholeiite Tokarahi Sill (Gage 1957) wasintruded into wet, unconsolidated sediment of MiddleEocene (Bortonian) age, concordant with bedding. It hasprominent columnar jointing and associated pillow lavas.

Deborah Volcanics comprise pyroclastic deposits,including the Kakanui Minera l Breccia, and severalintrusive dolerite or basalt masses in the area betweenOamaru and Kakanui (Edwards 1991). Tuffs at Kakanuiwere deposited in shallow water by mass now processes,the youngest being the Kakanui Mineral Breccia (Fig. 25c).It contains bombs and lapilli of basic volcanics, blocks ofschist, exotic xenocrysts (garnet, pyroxene, amphiboleand fe ldspar) and xenoli ths (Iherzoli tes, pyroxenites andgranul ites (Reay & Sipiera 1987).

T he ages of A lma Group volcanic units have beendetermined from tl,e study of fossi ls (mainly foraminifera)in the intercalated sandstones, limestones and tuffs.Waiareka Volcanics are Late Eocene (late Kaiatan Runangan) and the Deborah Volcanics are Early Oligocene(early Whaingaroan). K-Ar whole-rock dates fromWaiareka Volcanics in the Maheno area (40 Ma;C.J. Adamspers. comm. 1998) and from the Kakanui Mineral Breccia(32.4 Ma and 31.6 Ma; Coombs el al. 1986; Reay & Sipiera1987) are consistent with the biostratigraphic ages. Thereis also some evidence for Middle Eocene volcanism;basalts from the offshore well Galleon-I have been datedby K-A r at 46-47 Ma and Middle Eocene sedi mentaryrocks in the well contain volcanic rock fragments.

The volcanoes near Oamaru apparently erupted on therelatively shallow continental shelf (Coombs el al. 1986;Cas el al. 1989). Surtseyan eruptions projected ash, lapilliand blocks into the atmosphere from vents below sealevel. Much of the ejected material was reworked by massflows and by wave and current action. The volcanoesand adjacent sea floor were colonised by brachiopods,bryozoans, foraminifera and other organisms. Cas et al.(1989) and Maicher (1999) have described smallmonogenetic cones south of Kakanui in detail.

27

Late OUgocene to Middle Miocene serumenlary rocks

The Kekenodon Group (eMk), of latest Oligocene toearl iest Miocene age, typically consists of the KokoamuGreensand and overly ing Otekaike Limestone (Table 2).The greensand is usually ca lcareo us , with somephosphate nodules, abundant macro- and microfossilsand bioturbation. It grades into the overlying limestone,which is generally much thicker. Locally the OtekaikeLimestone is represented by calcareous sandstone.Though massive in places, the limestone is typically wellstratified, with bands of nodular concretions and crossbedding on several scales (e.g. in the Waihao area; Fig. 26)(Ward & Lewis 1975). Notable fossils have been collectedfrom both the greensand and limestone (Fig.27), includingthe remains of penguins, an early dolphin, several ornercetaceans, bony fishes, molluscs and brachiopods(Fordyce & Jones 1990; Fordyce 1994).

The Kekenodon Group varies in thickness from less thana metre to a maximum of 75 m at Trig Z. Waitaki va lley.South of Oamaru it is represented only by greensandcavity fiJlings in a bored surface (Gage 1957) and onlygreensand is present in inland Otago (for example. at

Naseby). In the mid Waitaki valley Otekaike Limestone is

up to 30 m thick (Turkandi 1986) and in the Shag valley itreaches 60 m (Cavaney 1966). In the Parcora and Otekaiekedi stric ts. thi ck limestone forms extensive plateaus(Fig. 28). However in many areas the Kekenodon Groupis represented on the map as a hori zon, either because itis very thin or because it forms venical cliffs. KekenodonGroup beds in the Waitaki valley and eastern Maniototobasin may represent the maximum inland extent of marinetransgression. Further inland, either marine sedimentswere not deposited, or have subsequently been removed

by erosion. The Kekenodon Group rocks are a condensedsequence. deposited in shallow, sediment-starvedplatform environments. Sedimentary structures suggest

strong current activity at times (Ward & Lewis 1975).Differential warping and/or sea level falls resulted in localunconformities and paleokarst.

The predominantly marine Otakou Group (Mo) occurs incoastal areas except between the Waihemo Fault Systemand Waianakarua Ri ver. The sequences arc somewhatdifferent on either side of this gap (Table 2; Gage 1957;Gair 1959; RiddoUs 1966; McMillan 1999; Morgans et (II.1999). To the south, well sorted medium- to fine-grainedsandstone (Caversham Sandstone) and impure limestone(Goodwood Limestone) were deposited in an outer shelf

Figure 26 Large-scale channelling and cross bedding in Otekaike Limestone cliffs at Waihao Downs. The broadchannels are oriented roughly north-south, while most of the cross beds were formed by currents flowing from thewest.

28

(b) partly excavated fossil baleen whale jaws inOtekaike Limestone at Earthquakes near Duntroon.

Figure 27 Fossils from Otekaike Limestone.

(a) skull and jaws of the fossil dolphin Waipalia(Fordyce 1994).

(c) fossil teeth and vertebrae of the Late Oligoceneshark Carcharodon anguslidens.

Photos: R.E. Fordyce

29

.~ ' ..r

setting; to the north, mid shelf sandstone and siltstone(Mt Harris Formation) are succeeded by shallow marinesandstone (Southburn Sand) and the paral ic q uartzsandstone, carbonaceous mudstone and lignite of theWhite Rock Coal Measures. Both northern and southernsequences are glauconitic near the base. Onshore, thetop of the group is a Miocene regional unconformity, butdeposition of similar sediments continued offshore untilLate Pliocene time (Field, Browne et 01. 1989). Most Ot..lkouGroup formations are fossil iferolls. Severa l hundredspecies of molluscs have been collected from Mount HarrisFonnation localities within the area covered by the Waltakimap_

Fluvial and lacustrine sediments of the ManuherikiaG r oup (OlM Ol) are present in Central OtllgO (Douglas1986), in the Maniototo bllsin (Youngson et 01. 1998) andthe Waitaki vlllley (Waitangi Coal Measures ofTurkandi1986) (Table 2). Two fornlations (not differentiated on themap) are recognised in Centrol Otago. Dunstan Formationcomprises quartz conglomerate and sandstone (Fig. 29),with minor mudstone and lign ite seams, deposited indeltaic, nuvial, and lake marg in settings (Douglas 1986;

30

Figure 28 Spectacular si nkholes(dolines) in Otekaike Limestone atCraigmore, South Canterbury. Thetableland in the distance is the TimaruBasalt sheet.

Photo CN42743- 11: D.L. Homer

Pole & Douglas 1998). In places the basal conglomerateand sandstone are silica-cemented, and presem as a lagof sarsen stones (s ilcrete). The stratigraphically higherBannockburn Formation is mainly interbedded cl aystoneand si ltstone, with minor sandstone and fresh- waterlimestone. Macrofossils include leaf fossils (Pole 1993a;Pole & Douglas 1998), algal stromatolites (Lindqvist 1994),fish bones and bird bones (Lindqvist & Craw 1992;Turkandi 1986). The lake in which Manuherikia Grouprocks were depos ited extended from northern Southlandto north of the Lind is Pass, and as far west as TheRemarkables (Dougills 1986; Turnbull 2(00). In the eastthe White Rock Coal Measures, which include estuarinebeds in the Hakataramea valley (Falconer 2(00), mayrepresent the coastlll margin (Pole & Douglas 1998).Manuherikia Group beds in the Manuherikia and Idavalleys are Early to M idd le Miocene (Mi ldenhall &Pocknall 1989; Pole 1993a; Pole & Douglas 1998). Thereis less age control for Manuherikia beds in the ManiOlolObasin, where the sequence in the Haughton Hill drillholeis debated (Mildenhall & Pocknall 1989; Pole & Douglas1998), but an Early to Midd le or Late Miocene age isprobable.

Figure 29 Sluiced cliffs at the former Surface Hill gold workings, east of St Bathans, expose Dunstan Formationquartz sandstone and conglomerate. The sediments were deposited by a braided river entrenched into Rakaiaterrane basement (the darker grey rock exposed at left) . Both the basal unconformity, and the Dunstan Formation,dip gently eastwards.

Middle and Late Miocene volcanic rocks

The large, panly eroded shield volcano in the area ofDunedin City and the Otago Peninsula was intenniuentlyactive in late Middle Miocene time (Coombs el al. 1960,1986; Bishop & Turnbull 1996). Within the area of theWaitaki map are many small volcanic centres formerlymapped as Waipiata Volcanics and Molehill Basalt (e.g.Mutch 1963; Gage 1957) which are now included in theDunedin Volcanic Group (Md). The westernmost is atHaughton Hill , in the western ManiOloto basin, and thenonhernmost is near gapara, 12 km south of the WaitakiRiver. At Kauru Hill and Lookout Bluff, and perhapselsewhere in the Oamaru area, Dunedin Volcanicsunconfom13bly overlie earlier Waiareka Volcanics.

Most of the vents were small , with activity short-lived,producing on ly a few flows or a tuff ring (Fig. 30).However at Siberia Hill and Round Hill in the Waihemoarea, vents produced flow s of di stinctly differentcomposition (Brown 1955; Cavaney 1966; Rae 1990),suggesting activity over a longer period (Fig. 31).Relatively extensive lava sheets are preserved or implied,notably the Waipiata doleritic basalt, which extends overan area of about 130 km' (MUlCh 1963), and the olivinedolerite flow at Swinburn Peak. Bishop (1979) mappeddikes in the Waihemo area.

Tuffs and agglomerates underlie the lowermost flow s.Though typically only a few melfes thick, they are over

50 01 thick at eruptive centres in the Shag valley andPaJmerston areas (Bishop 1979: McMillan 1999). Locallyderived xenoliths in the tuff include schist fragments,rounded quanz pebbles and calcareous sediments (Brown1955; McMillan 1999). Bedded surge deposits in theWaihemo and Karitane districts probably originated duringphreatomagmatic eruptions, and there is apossible pumiceignimbrite near Waikouaiti . Near Middlemarch, localcoll apse features or maar craters were filled by a varietyof deposits including breccias derived frolll the underlyingschist and Cenozoic sedimentary rocks (Coombs el 01.

1986). The nonmarine diatomite (Mdd) of Miocene age atFouJden Hills is over 75 mthick and possibly accumulatedin a volcanic maar lake; pollen and leaf fossils suggest awarm cJimateand a diverse flora (Travis 1%5; Pole 1993b).

The rocks range from basanites and alkalic o livine basaltsthrough arange of intermediate rock typesto nephelinilesand phonolites. Geochemical data suggest that most lavaswere of mantle derivation, and rose rapidly to the surfacewith relatively linle fractionation. Mantle-derived ncx:lulesare common, predominantly spinel Lherzolites which maybe up to 50 Col across, and megacrysts of pyroxene andamphibole (Reay & Sipiera 1987). Magma compositionssuggest that the Dunedin Volcanic Group was fonnedduring a pericx:l of extensional tectonism (Coombs el 01.

1986). K-Ar ages for Dunedin Volcanic Group rocks in theWaitaki area are in the range 10-16 Ma (cf. 10- 13 Ma forthe Dunedin volcano itself; Coombs et al. 1986; Reay &Sipiera 1987).

31

Figure 30 The Crater, a tuff ring of the Miocene Dunedin Volcanic Group, overlies t.z. IV schist (Rakaia terrane) onTaieri Ridge, near Middlemarch. This view is to the east over the Nenthorn area, where the exhumed OtagoPeneplain is offset by parallel, northeast-trending faults. Photo CN42731-3: D.L. Homer

Figure 31 Mt Dasher (foreground) consists of Dunedin Volcanic Group basalt. The smaller peak in the right middledistance, Kattothyrst, is composed of cOlumnar-jointed lava and the broad summit beyond is Siberia Hill, formed ofseveral different basalt flows. Extensive boulder fields are derived from the outcrops. Underlying the volcanic rocksand the dissected tableland beyond is Rakaia terrane t.z. IIA semischist. A thin interval of Onekakara Group beds ofEocene age lies between the Otago Penep lain and Dunedin Vo lcan ic Group basa lt at Siberia Hill.


32

Latest Miocene to Early Pleistocene sediments

Late Miocene tectonic uplift of Central Otago ranges andreworking of quartzose cover sediments gave rise to thecoarsen ing-upward, sandslone- and cong lomeratedominated Hawkdun Group (I'd; Youngson el al. 1998),which is widespread in the Maniololo basin and in theWaitaki valley from Clay Cliffs (Fig. 32) to Kurow. Thebasal Wedderburn Formati on is quartz-lithic sandstoneand conglomcralc. Overlying Maniotolo Conglomerateis composed of well rounded, imbricated clasts of Rakaiaterrane sandstone with some schist. Clasts and matrix aregenerally weathered to a rusty red-brown colour. althoughin reducing environments the conglomerate may be bluegrey (Bishop 1979). In places the Hawkdun Group isimerfingered with upper pans of the generally underlyingManuherikia Group (Youngson el al. 1998). Bothcon Fonnable and unconfonnable contacts are known, withthe laner tending to be near teclonically deformed rangefronts, where H awkdu n Group sedimentscharacter istica ll y dip s teeply (Bi shop 1979).

Hawkdun Group represents alluvial braid plain deposilsand proximal alluvial fa ns, deri ved from ri si ng ranges,for example, the Hawkdun and St Bathans ranges (Fig.10). Schmitt (1984) considered that mudstones in thewestem Maniototo basin weredista] fluvial and lacustrinefacies within the same depositional setting. HawkdunGroup in eastern Central Otago has been dated bypalynology as Late Miocene to Pliocene in age: howeverthe lower pan of the unit in the Swin Burn is MiddleMiocene where it is overlain by a lava now with a K-Ardate of 13.4 ± 0.3 Ma (Youngson el al. 1998).

Early Pliocene (Opoitian) marine shells have been foundjust south of Oamaru; shells of this age have been washed

up on beaches in the area. and dredged from about 2 kmoffshore (Fordyce 1985). Celacean bones found at CapeWanbrow may be from the same deposit.

Weathered red, orange and brown gravel. sand and mudpresent on the flank s of the Hunters Hills, from theHakataramea valley in the west to the coast at Timaruand M akikihi , and as far south as the Waitaki River aremapped as Kawai Formation ( i'k ; Field & Browne1986); they include the Cannington Gravels (Gair 1959)and the Elephant Hill Gravels (Riddolls 1966). KowaiFormation iscommonly cemented by clay and iron oxides.Intercalated sand and mud layers, some with plantfragments, are planar and continuous over tens of melres.At Makikihi the lower pan of the formation is marine(Collins 1953) and the foreset bedding ofintercalated sandand gravel indicates deposition in shallow water, withstrong currents (Field & Browne 1986). Macrofossils ofLate Pliocene age include crabs. oysters and cetaceanbones. Marine gravels are also present at Timaru (Gair196 1) and possibly elsewhere, as shells have been reportedfrom dri llholes al Pareora.

At White Rock River, the Kowai Formation restsunconformably on underlying units (Gair 1959) but inElephant Hill Stream there is no unconfonnity wi th theunderlying Otakou Group. The Kowai Formation iscommonly tilted, the tilting and some erosion predatingerupti on of overlying Timaru Basalt (dated atabout 2.5 Ma). Moa bones collected from beneath thebasalt are probably a later fissure-fill deposit(Worthy el al. 1991). Kowai Formation was probablyderived from the rising Hunters Hills. It spans thePliocene-Pleistocene boundary (Gair 1961) and isapparently youngerthan the Hawkdun Group (Mildenhall1999).

Figure 32 Hawkdun Groupsediments, uplifted and tilted by theOstler Fault Zone, form the ClayCliffs near Omarama. The pale greymaterial near the base has morequartz and less lithic gravel than thedarker material overlying it.


33

Pliocene volcanic rocks

Timaru Basalt (1'1) crops oul over an area of aboul130 km' immedialely west of Timaru. At Mt Horrible itis about 25 m thick, whileonthecoast it may bejust overa metTe thick. It was apparently eXlruded subaerially froma vent near Mt Horrible onto a surface sloping I - 2° tothe southeast. The presenl extent is probably close to theoriginal ex lenl (Gair & Rickwood 1965).

There are a number of individual nows - up to fi ve inanyone outcrop - of oli vine, hypersthene and oli vinehypersthene basalts (Duggan & Reay 1986). The basaltsare typicalJycoarse-grained. vesicular and nonJX)rphyritic.with well defined columnar j ointing (Fig. 33). Apan fromsegregation veins, the lavasare relatively unfractionated.About I mof basaltic tu ff commonly underli es the lowestnow. A K -Ar whole-rock date of 2.52 ± 0.74 Ma hasbeen reponed (Matthews& Curtis 1966, recalculated byN. M ortimer using new decay constants). This iscompalible with latesl Pliocene (lower Nukumaruan)fossils found beneath the basalt in adrillhole (Gair 1961 )and with the reponed reverse magnetisation (Matthews& Cunis 1966).

Figure 33 Columnar-jointed Timaru Basalt at Taiko,15 km inland of Timaru, is underlain by 1.5m of beddedash. Here the ash rests on grey silt but elsewhere itoverlies Kowai Formation gravel.

Figure 34 Cirques, till and tarns at the head of Clear Stream, on the east side of the Hawkdun Range crest, probablydate from the last (Otiran) glaciation. The highest small moraines may have formed during colder periods of theHolocene. The view is west towards the St Bathans Range. Photo CN42857-16: D.L. Homer

34

QUATERNARY

Quaternary sediments are widespread and have been

mapped on the basis of geomorphology and lithology,with extensive air photo interpretation supplemented byfield checking. On the map lhey are coded by inferredage, with overprints for fan, fluvial, lake, glacial andnuvioglacialorigin. Some units(suchas landslides) covera wide age range, and no age differentiation has beenattempted. Where absolute age control is lack ing, agesare inferred from geomorphic correlation with datedsequences, from degree of weathering and preservationof landforms, and by "counling back" through g lacialevents. Previously, moraine and outwash deposits havebeen given a varielyoffonnalion names (e.g. MUlCh 1%3).These are rationalised here by correlation with theappropriate oxygen isotope (01) slage, prefixed by "'Q".

Landslide deposits

Landslides are widespread lhroughoul the map area andthose over I km2 in area are shown on the map face by anoverprint. Large complex landslides may have beenmoving for many thousands of years (McSaveney el at.1992) and many are sti II acti ve. They are more commonand more extensive in schist, and dominate the landscapeof many Central Otago ranges. Release surfaces includefoliation planes, especially dip slopes, andjoinls. Schistlandslide debris consists of unsorted mixtures rangingfrom clay to boulders. Some landslides consist of largeblocks of schist which have moved only slighlly, or mergeinlo superficial solinuction deposits affecting only thetop few metres of soil. Deeply weathered, clay-rich zonesin schist, especially lhose associated with the OtagoPeneplain, commonly form extensive landslides. Clay-richCenozoic rocks such as mudstones of the Onekakara,Manuherikia and Otakou groups become plastic whenwet and are prone to sliding. Landslides in colluvium areusually too small to show on a map of thisscale.

Scree

Areas of scree (Qls) large enough to map at 1:250 ()()() aredeveloped in sandstone and semisch ist in the St Bathansand St Marys ranges. Scree is typically angular, unsortedgravel, deposited by rockfall or mass movement at or nearthe base of steep slopes. In cross section it may showvariable layering. The screes mapped are probably upto 50 m thick. Boulder fields in volcanic rocks near SiberiaHill are grouped with screes on the map.

Alluvial fan deposits

Alluvial fans (Q1a, Q2a etc.) are characteristic of rangefronts, valley sidesand smal l tributilly streams; they gradedown slope into alluvial telT3ces. Fans have steeper slopes

than terraces, and clearly defined radial drainage. Theyare composed of locally derived. commonly angulargravel, and may include debris flow as well as streamdeposits. Both fans and aJiuvial deposits may grade upslope into scree and colluvium, which in most places arenot mapped separalely.

Glacial and nuvioglacial deposits

The major morainesofthe Waitaki catchment are mainlyto the north of the map area, but distal moraines of theOhau sequence and outwash from the Pukaki and Tekapovalleys are present near Omarama. Till forming the Ohaumoraines (Q2t, Q4t, Q6t, Q8t) comprises very largeangular blocks in poorly sorted deposits with sand orclay matrix, while outwash (Q2a, Q4a, 063) is the nuviallysorted down-valley equivalent in which clasts are morerounded with increasing distance from the moraine.Moraines and outwash older than oxygen isotope stage4 are deformed by the active Ostler Faull Zone. Outwashgravels (Q2a) are also mapped al the head of the Tekapoarm of Lake Benmore.

Previously unrecognised till deposits of subdued formon the Hawkdun Range imply former ice caps; their age(Q2-Q4) is inferred from known snowline elevations inOlago during the Otira Glaciation (Fig. 34). Cirques(particularly in the Hawkdun and Sl Bathans ranges) arecommonly noored or fronled by bouldery angular till(Q2t), typically with well preserved terminal moraine form.Several moraine loops may be preserved. Rock glacierdeposits (Fig. 35) are grouped Wilh these tills, thoughsome may actually be Holocene (Q I) in age.

Alluvial terraces and noodplain deposits

WealilCred quartz-schist gravel (eQa) filling channelseroded into schist along the Taieri River comprisesrounded and angular quartz gravel with angular schistclasts up to bou lder size. It representsManuherikia Groupand older sediments recycled by an ancient ri ver. Thegravel has been extensively sluiced for gold, for examplein the upper Taieri - Lammermoor area. and at PatearoaPower Station and Matarae. further downstream.

Moderately to highly weathered gravel-dominatedalluvium, mantled in places by multiple loess layers, capsmany ridges in east and orth Olago (mQa). IL has alsobeen mapped as Smilie, Georgetown and Tumai formations(Mutch 1963; McMillan 1999) and as "gravels of highterraces" (Gage 1957). This alluvium is part of a fomlerlyextensive piedmont gravel su ite, derived mainly from theranges of Rakaia terrane rocks but also containingCenozoic sedimentary and volcanic clasts. It predatesmodern drainage patterns and some may be as old asearly Quaternary.

35

Terrace and nood plain deposits of unconsolidated gravel,sand and mud (Qla, Q2a etc.) fill most val leys. The braidedgravel noodplain of the lower Waitaki River, and thegenerally finer grained sediments of the upper Taieribasins, are conspicuous examples of postglacial alluvium(front cover and Fig. I I). Older deposits are moreweathered and some are mantled with loess (see below).In most catchments. flights of several terraces arepreserved, recording in part the aggradational anddegradational history ofthe valley system (Read & Blick1991 ; Read & Barrell 1998; Barrell e1al. 1998; McMillan1999).

Peat swamp and lake deposits

Peat swamps (Q l a with overprint) are still fornling inpoorly drained valley headsand. on the lOpS of ranges inCentral Otago, under periglacial conditions impoundedby vegetation barriers in string bogs. Lacustri ne sandand mud (Qlk) are present in two areas. The formerTaieri Lake existed at the time of European settlement(Wi lliamson 1939) but has since been drained. Aprehistoric lake at Moonlight (Fig. 9) is marked by welldefined beaches and wave-cut cliffs (R. Thomson pers.comm. 2(00).

--

Loess

A thin (1-2 m) layer of loess is widespread but notdifferentiated. Loess cover is commonly patchy on Q4aterraces but th icker on Q6a and Q8a terraces. Loess ismapped separately where it is more than 3 111 thick (mQe,Q8e, Q6e); typically such deposits are formed of severalindividual loess units, separated by discontinuities(Fig. 36). Thick loess is present mainly on the downlandsofSouth Canterbury (up to 19 m thick; Tonkin e1 al. 1974)and North Otago (7 to 10m maximum; Young 1964; Gage1957), from about 200 m altitude dowll lO sea level (andloca ll y, be low). In places loess is dramat ica ll yovenh ickened by down slope movement but this loesscolluvium has been grouped with hiJifoot alluvial fans.

The age and stratigraphic details of the various loessdeposits are poorly constrained, but most of the loess isprobably of middle to late Quaternary age (Young 1964;Ives 1972; Tonkin e1 al. 1974). It is derived from Rakaiaterrane rocks of the Southern Alps and subsidiary rangesand consists mainly of quartz and plagioclase, withsignificant, mica-derived clays (Young 1964; Raeside1964). Sponge spicules fou nd in coastal loess decreasein size and abundance with distance inland, suggesting

36

Figure 35 Rock glaciers on the westside of the Hawkdun Range may haveformed in the Last Glaciation or in theHolocene, and may still be active. Theview is northeast towards the BellmoreRange.

Photo CN3S9S5-16: D.L. Homer

that some loess was blown inland from the exposedcontinental shelf during periods of lowered sea levels(Raeside 1964). Loess colour ranges rrom pale yellow rorthe youngest, to darker yellow, orange and brown for theolder deposits. Loess deposits are compact and stand insteep cliffs when dry, but are prone to gu llying and tunnelerosion. Venical polygonal jointing and grey veins arecharacteristic.

Beach and estuarine deposits

Recent and mobile beach deposits of gravel, sand andsilt (Q l b) are present in estuaries aL Timaru, WainonoLagoon and Waikouaiti. Most are backed by a low seacliff which marksthe 6 500 year culmination of postgJacialsea level. The modern gravel beach stretching betweenOamaru and Timaru isgenerally too narrow to be shownon a map of this scale.

Deposits of shelly gravel and sand (Q5b) resti ng on aplaned sunace (Fig. 37) underlie low coastal terracesextending from the Waikouaiti estuary to Oamaru. Thetop of the deposits is typically 4-5 m above sea levelbut a 3-10 m range is recorded (Gage 1957 ; Barrell el a/.1998; McMillan 1999), which may reflect local variat ionsin cover bed thickness. The deposits have been mappedas Hill g rove Formati o n (Mutch 1963); thegeomorphological featuresare the 015 coastline terracesof Barrell ef a/. (1998). Geomorphology and loess coversuggest a Last Interglacial (oxygen isotope stage 5) age,which is supported by a n optically s timulat edluminescence date determined on material from CapeWanbrow (Grant-Mackie & Worthy 2(00). Fossil Tawerashells from the terrace 5 m above sea level at CapeWanbrow yielded an ami no acid D/L rat io = 0.25±0.04.Using the approach orOta el al. ( 1996) and allowing ror atemperaturec. 2.5°C colder at Oamaru than at Wanganui ,the estimated age is 130000 ± 35 000 years (B. Pillanswrinen comm. 2(00).

Remnants or higher beach deposits (shelly sand) presentat up to 13 m above sea level between Pleasant River andOamaru, and at Cape Wan brow and Shag Point areincluded in the Boatmans Formation (M utch 1963). Theyare typica lly poorly defi ned, have a cover or loess, andare in areas too small to be shown on a map of this scale.McMillan ( 1999) mapped Boatmans Formation in manyplaces between Cornish Head and Shag Point, and atKakanui . It has not been dated but is probably older thanoxygen isotope stage 5. At Shag Point, Goodwood andPleasant River. even higher remnants or beach pebblesand sand are present at c. 50 m above sea level (mQb);they are probably or oxygen isotope stage 7 or older(Barrell el al. 1998; McM illan 1999). Otherrem nants orpossible 0 17 and 019 marine terraces were reported byBarrell el al. ( 1998) at Trotters Creek, Katiki.

Figure 36 At Normanby, on the coast 5 km south ofTimaru, Kowai Formation gravel (lower metre) is overlainby multiple loess layers. Near this locality loess isexposed on the beach below high tide level.

Deposits of human origin

Waste from gold mining operations isextensive enoughto map at Serpentine Diggings and Macraes Flat (Q l n).Smaller areas of tailings are present wherever alluviaJ goldhas been worked (see below). Major areas of fill wereplaced during reclamation at the Port ofTimaru and duringconstruction of hydroelectricity worksat Ohau C PowerStation and Benmore Dam (Fig. 38). Other areas of fillassocimed with the Waitaki and Taieri damsand reservoirs(Aviemore, Waitaki, Logan Burn, Pool Burn , Paerau) andat the Port of Oamaru are too small to show on thi smap.

37

Figure 37 Beach gravels underlying the raised marine terraces at Kakanui North Head probably date from oxygenisotope stage 5.

Figure 38 The Benmore earth dam, on the Waitaki River, was commissioned in 1965. It contains nearly 28 milliontonnes of material and impounds a lake covering an area of 8000 hectares. The dam and lake are surrounded byt.z. I Rakaia terrane sandstone and mudstone of probable Triassic age. Photo CN42766-24: D.L. Homer

38

OFFSHORE GEOLOGY

Thick Cretaceous and Cenozoic sedimentary rockspresent offshore lie within the Canterbury Basin, whichpasses southeast into the Great South Basin. Detaileddescriptions and interpretations oflhese rocks have beenpublished elsewhere (Carter 1988; Field, Browne el al.1989; Raineelal. 1994; King el al. 1999;Cooketal. 1999).Seismic data is avai lable for 1110St of the offshore part ofthe map; it hasbeen used to define areas of volcanic rock(not necessarily forming sea-floor outcrops), areas wheremid Cretaceous sed imenls are thicker than 1000 m, areaswhere total Cretaceous-Cenozoic sediment thickness isgreater than 2000 m, and major faults. Three petroleumexploration wells have been drilled offshore (Galleon-I,Endeavour-I and Clipper-I). Summary well logs are shownon the map face.

The basement rocks are presumed to be sandstone,mudstone, semischisl and schist of the Rakaia terrane, asseen onshore. The sandstone to schist transition has 110t

been recognised in seismic data (Mortimer el al. 200 1).Evidence for schist basement isprovided by clastswithinthe Late Cretaceous Galleon Volcanics(Wilson& Dernie1986) and schi st of lextural zone III encountered inClipper-I (Hawkes & Mound 1984; N. Mortimer pers.comm.2ooo). Endeavour-l did not reach basement butthe lowest units drilled contain clasts of schist or phyllite(BP Shell & Todd 1971).

Seismic surveys suggest that local sub-basins (Cl ipperand Galleon) contain mid Cretaceous sedimentary rocksequivalent to Matakea Group; the greater part of theClipper Sub-basin lies northeast of the map boundary.The GaJleon Sub-basin is in a structural setting similar tothat of the onshore areas with Matakea Group rocks, inthat it Iies on the nortJl side of the Waihemo Faull System(and also at its intersection with the Titri Fault). TheClipper Formation is interpreted as a terrestrial andnearshore marine deposit, laterally equi va lent to theHorse Range Formation, and of early Late Cretaceousage (Raine el al. 1994). The Late Cretaceous terrestrialand paralic Pukeiwilahi Formation is probably anequivalent ofTaratu Formation onshore. Both Clipper andPukeiwitahi fonnations are coal bearing. with hydrocarbonsource potential.

Following Late Cretaceous erosion and marinetransgression (identified in Clipper-I and Endeavour-I).Onekakara Group mudstone with subordinate sandstoneand limestone were deposited. A thin carbonaceousmudstone of Paleocene age is correlated with the WaipawaFormation of eastern North Island basins; it has beenstud ied in detail because of itspotential as a hydrocarbonsource rock (Killops el al. 20(0). Several intervals ofvolcanic rocks have been drilled and GaJleon- 1bottomed

in weathered. fractured microgabbro alleast 46 m thick,of uncertain affinity. The Galleon Volcanics (Kx) atGalleon-I are dated as latest Cretaceous (Haumurian) bytheir enclosing sediments. CUllings are of amygdaloidalsil icic igneous rock and tuff with sch ist clasts in acarbonate and si liceous matrix (Wilson & Oemie 1986).Paleocene Endeavour Volcanics (Pn) basaltic tuffs arepresent in all three wells. Volcanic fragments of middleEocene (Heretaungan-Porangan) age in Galleon-I mayalso be correlatives of the Endeavour Volcanics (Field,Browne el al. 1989), or may be part of a mid-Eocenevolcanic suite. Undifferentiated Alma Group volcanics,of Lale Eocene to Early Oligocene age, extend a shortway offshore from Moeraki to nonh ofOamaru.

Between Late Eocene and late Early Miocene time nosediments were deposited over the northeast trendingEndeavour High (Field, Browne ef al. 1989, Field &Browne 1993). Elsewhere Kekenodon Group greensandand limestone overlie the Marshall Paraconformity(recognised in Clipper-I but not Galleon-I, where agecontrol is inadequate; Field, Browne el al. 1989: Fulthorpeel al. 1996). Sedimentary rocks of the regressive OtakouGroup occur in all three drillholes. Clinoforms showingeastward progradation are conspicuous in the seismicsurveysand reflect increased sediment supply from upliftto the west (Field & Browne 1993). Increasi ngly coarseprograding wedges (Southburn Sand, Kowai Formation)may not have reached far beyond the present coastline,as they are not recorded in drillholes or seismic surveys,but an up-sequence shallowing trend is apparent (Field& Browne 1993).

Offshore from Timaru. a thin layer of marine very finegrained sand and mud of the Holocene Pegasus BayFormation is underlain by the lithologically more variableCanterbury Bight Formation, of Last Glacial and LastInterglacial age (Herzer 1981). East of Karitane, Cenozoicsedimentary and volcanic rocks crop out in places on thesea floor. River channelsincised into these rocks are fil ledwith Late Pleistocene sediments and capped by postglacial sand and mud (Carter el al. 1985). Submerged relictfluvial bedforms and coastal landforms such as spits andbars are recognised as far offshore as the shelf edge. Acut terrace near the shelfbreak (at depths of 110-120 m) isthought to represent the shoreline at the Last Glacialmaximum.

Some of the faults shown offshore (east of Shag Pointand east ofTimaru, for example) cut Cenozoic rocks andare inferred to have been active in the Pliocene (Allan1990). No fault mapped offshore in the map area is knownto have been active in the Quaternary.

39

TECTONIC HISTORY

Paleozoic to Mesozoic

The Caples and Rakaia terranes amalgamated in theJurassieduring continental collision (Mortimer I993e) andconvergent margin tectonics continued into the EarlyCretaceous, with the aeerelion of the Caples-Rakaiaagainst Gondwana margin terranes across theLivingstone Fault (Lill ie e1 at. 1999). In mid Cretaceoustime, extensional basins fOfmed along the Waihcmo FaultSystem. By Late Cretaceous time a passive continentalmargin had evolved, with regional subsidence andwidespread deposition of clastic sediments.

Late Cretaceous to Middle Miocene

Following rifting from Gondwana and thennal relaxationof the continental crust, mllch of southern New Zealandremained relatively tectonicaJly stable. Erosion and marinetransgression formed the Waipounamu Erosion Surface(LeMasurier & Landis 1996). Tectonic basins on theWaihemo and Waitaki fault systems formed localdepositional centres within the general Late Cretaceousto Oligocene marine transgressive sequence. Furtherinl and, a large shallow basin that developed duringMiocene time was filled wi th fluvial and lacustrinedeposits of the Manuherikia Group. A local mid-Miocenetectonic episode is recorded in the sediments of LakeManuherikia (Lindqvist & Craw 1992).

Late Miocene and Pliocene

In the Late Miocene and Pliocene, North Otago and SouthCanterbury were affected by tectonic events along theAustralian - Pacific plate boundary. The effects includedregional uplift and broad scale deformation, formation ofintermontane basins, erosion of Manuherikia Groupcover, and deposition of great quantitiesof sediment fromthe rising ranges (Hawkdun Group, Kowai Formation). InCentral Otago, northeasl-trending schi st ranges formedas growing fold s above reverse faults (Sa lton 1993;Jackson et al. 1996; Markley & Norris 1999), and in placescrush zones and offset structural markers (Bishop 1976,1979) demonstrate brittle faulting. Some faults mayrepresent a series of imbricate thrusts over a deeperdecollement surface (Beanland & Benyman 1989).

Significant reactivation of Late Cretaceous faulls isdemonstrated by the Waihemo Fault System. Thesouthern side was initially upthrown, to exhume t.z. lilschist, but reversal raised the lower grade rocks of theKakanui ranges about 800 m higher than the schistexposed on the southem side. The Waitaki Fault Systemprobably behaved similarly, although the contrast ofbasement grade across it is not as marked. While throwon the Waihemo Faull System increases towards thesoutheast, on the Waitaki Fault System it increases to the

40

northwest. North of the Waitaki Fault Syslem in theElephant Hill - Ml Harri s area, Otakou Group and KowaiFormation sed iments are deformed into south-plungingfolds, which extend beneath the Quatemary gravels ofthe Lower Waitaki Plains (based on Macfarlane 1980).

Quaternary tectonics

Southwest-directed ob lique convergence at the plateboundary isresulting in contraction of the eastern SouthIsland. though most of the shortening is accommodatedwest of the Waitaki map area (Pearson 1990; Beavan e1al.1999; Walcott 1998). The northeast-trending, mainlyreverse faults at the range fronts which bound theManuherikia, Ida, Maniototo and Strath Taieri halfgrabens are classed as active faults , in that they areinferred to have moved within the last 125000 years. Thcassociated folds mapped along the range crests (such asRock and Pillar Antiform and Blackstone Hill Antifoml)may also be active. South Canterbury ranges (such asthe Kirkliston Range and Hunters Hills; Figs 8, 13 and 14)were also rising during the Quatemary, and active faulttraces have been ident ified within the associated basins,1-5 km from the range fronts. Near Otaio Gorge theactivestructure isexpresst:d as amOlloclinal fold, with 110 surfacebreak. It is probably related to the hidden thrust modelledfrom gravity data c. 4 km east of the Hunters Fault(Langdale & Stem 1998).

The Maniototo basin is apparently bounded by activefaults on the east (Rock and Pillar), west (Rough Ridge)and north (Waihemo) sides. There is al so activedeformation within the basin, expressed at the surface asfault traces and sma ll folds of the Ranfurly andGimmerburn fault zones. ear the southern margin of thebasin movement on the Waipiata Fault has progressivelydeformed alluvial surfaces, though there is no offset ofthe modern floodplain of the Pig Burn. The Long ValleyFault near Poolburn Reservoir (Fig. 6) is an active reversefault with discontinuous linear traces, which displacealluvial fan surfaces of probable lalesl Pleistocene agebut Holocene surfaces are not offset (M. Stirling &K. Benyman, pers. comOl. 2(00).

The Waitaki Fault System includes the Waitaki, Waitangi,Dryburgh, Clarkesfield , Stonewall, Fem Gully, MiddleRange and Wharekuri faults, several of which have activetraces. These faults have been studied in detail duringinvestigations for Waitaki valley hydroelectric powerdevelopment (e.g. Macfarlane 1980, 1988). Reverse dipslip faulting and dextral strike-slip movements have beenreported.

Where measured, slip rates of South Canterbury faultsare of the order of I mOl/year or less (Read & Blick 1991 ;Pettinga e1 al. 1998). In the wider region of the

southeastern South Island, characteristic slip rates forsimi lar faulting are O. I - I mm/year (Stirling ef al. 1998).Geodetic results indicate that strain rates are low to verylow in the area covered by the Waitaki map, and highertowards the northwest (Beavan ef al. 1999).

Coaslline

T he coastline is tectonically relati vely stable by NewZealand standards. At Blueskin Bay, immediately southof the map area, all available data from sediments in theestuary suggest tectonic stability during the mid and lateHolocene (Gibb 1986; Thomas 2(00).

Raised beach deposits at and south of Oamaru (Fig. 37)reveal minor tectonic uplift, and seismi c ev idencesuggests uplift of the continental shelf offshore fromKaritane (Carter ef al . 1985). North of Tintaru, there hasbeen gradual subsidence beneath the eastern CanterburyPlains and offshore region (Wellman 1979; Field & Browne1993). Thi s overall northward tilting may be responsiblefor the asy mmetri c vall eys of Collier D owns andCannington basin east ofthe Hunters HiJls (Fig. 14), whererivers and streams are eroding their northern banks,leaving a suite of slip-off terraces preserved on theirsouthern sides. A lternati vely, the cause could beclimatic(Gait 1959).

GEOLOGICAL RESOURCES

The Waitaki map area is well endowed with geologicalresources. Gold mining was widespread in the late 19th

and early 20 th centuries, notably in central and easternOtago (Figs 39 and 40), where prospecting played a majorpart in the exploration and settlement of the region. Coalmining was also at its peak during the gold mining era,but coal isno longer an imp0l1ant commodity. Explorationfor hydrocarbonshas taken place offshore. Groundwater,limestone, aggregate, building stone and diatomite arecurrently extracted. The mineral potential of the map areahas been described by Christie ef al. (1994), who alsogave past mineral production figures based on GeologicalResource M ap of New Zealand data; more recent annualproduction statistics are available from the Min.istry ofEconomic Development.

Hard-rock gold mineralisation

Hard rock gold-quartz deposits within the Otago Schistare almost entirely restricted to rocks of t.Z. lJI and IV(greenschist facies and above); sandstone-dominatedterrain in South Can terbury has no reported go ldminerali sati on. The most important hard-rock goldoccurrences in the map area are at M acraes Fl at,Barewood, Nenth orn , O turehu a and Serpentine(Williamson 1939; Williams 1974). ALI were worked between1868 and 1920, but the only working mine (in 200 I ) is atMacraes Flat (Fig. 40). Recent exploration at the otherfi elds has included rock chip sampling, regional streamsediment and soil surveys, geological mapping, groundbased geophys ics, trenching, channel sampling and

drilling.

Otago occurrences are either isolated veins in fault!fractures with limited wall-rock deformation, or morecomplex multiple vein systems in highly deformed shearzones. Veins typically dip steeply and cut across theschistosity formed during Earl y and Middle Jurass icregional metamorphism. Vein mineralsprecipitated fromhyd ro thermal fluid s that c ircula ted thro ugh faults,fractures and shear zones. Almost al1 structures hostingvein depos its strike northwest-southeast, generall yparallel to either a local lineation in schist wal1 rocks orthe strike of schistosity.

The deposits were formed over a wide range of pressureand temperature conditionsduring waning metamorphism(Craw & Norris 199 1; Craw 1992). Preliminary datingsuggests that mineralisation was episodic, with at leasttwo phases during 40-50 Ma of coo ling. Micaceousselvedges and veins at Macraes Flat and Oturehua yieldLate Jurassic-Early Cretaceousages, whereas Barewoodand Nenthorn samples give mid Cretaceous ages (Angusef al. 1997; Adams & Graham 2000). Ore-bearing fluidsmay have been metamorphic or magmatic in origin(McKeag & Craw 1989; de Ronde el al. 2(00), with somecontribution from meteoric water.

41

The Macraes Gold Project operated by GRD MacraesLid. is one of the largest gold mines in New Zealand,having produced more than 3 1 000 kg (over a mill ionounces) of gold since renewed development in the late1980s (Fig. 40b). Open pits exploit re lat i vely high-gradepodsof ore (Macraes 1996), hosted in the Hyde-MacraesShear Zone. This relatively planar structure strikesnonhwest and dips 15-20° northeast. with minor rampsand flats. and changes in oriemation from offset on latestage faults. Current mining is mainly within a 5 x 3 kmportion of the shear zone, to depths of c. 200 m, butsignificant potential exists along the remaining 30 kmexposed strike lenglh of the shear zone. T he ore isrefractory and contains carbonaceolls material (Windleel 01. 1999), but profi lable gold recoveries have beenachieved using pressure oxidation and a carbon-ill-leachcircuit. Minor amounts of silver are also recovered.Scheelite is present but nOI worth recovering at presentprices. The current resource estimate is83 million lannesof ore al an average grade of 1.53 gil Au, equivalent 10

127 518 kg (4. 1 million ounces) of contained gold, andexpected to provide the mine with ore reserves for at least

another decade at present rates of extraction (Gold &Resource Developments 1999).

Harewood was mined for gold and scheelite from 1888 to1919. A northwest-trending nonnal fault dipping al55° tothe northeast hostsqumtz veins formed about 125 millionyears ago (Adams & Graham 2000) at re lat ively shallowlevels (P - 2 kbar, T - 300°C, M acKenzie & Craw 1993).The mineralisation is younger than that of Macraes Flat,and formed at shallower deplhs. The mineralised rockaverages 1.3- 1.6 m wide, but reaches 5 m where the faultsplays locally inlo the hanging wall. The fault al Barewoodis known along a slrike length of 5 km. and may eXlend10 km - similar in scale to the area of advanced miningnear Macrae Flat. Extensional movemeJ1l(s) accompaniedmineralisation. The historic workings are spaced regularlyat intervalsof c. 900 m and suggest a number of northeasttrending ore shoots. Secondary mobility resul ted incoarser, more easily won gold near the surface, with morerefraclory ore at depth (MacKenzie & Craw 1993). Al leaSI379 kg ( 12 183 oz) ofgold were recovered from 32 374 Ionsofore ( 11.5 gil recovery grade). with 600 Ionsofscheelileproduced (Ingram 1982; Jeffery 1987).

Major lode fields

0 Oturehua

M Macraes

S Serpentine

N Nenthorn

B Barewood

... alluvial gold workings

- lode in schist

D covering sediments

• Rakala terrane

• Caples terrane

Caples-Rakaiaterrane boundary

........ Hyde·MacraesShear Zone

Figure 39 Alluvial gold workings and gold-hearing lodes within lhe Otago Schist, in re lation to major fauit sytemsand terranes. The Macraes lodes are associated with the Hyde-Macraes Shear Zone, a major Late Jurassic - EarlyCretaceous metamorphic and textural boundary. Data derived from QMAP and GERM.

42

Figure40a

Underground gold workings atGolden Bar, near Macraes Flat,date from the 19~ century. Nearhorizontal to gently dipping quartzlodes cut the t.z.1I1 schist host rock.


Figure40b

Large scale open pit gold miningnear Macraes Flat, operated byGRD Macraes Limited . Thetailings dam and treatment plantappear at upper left; the main pitsare, from left, Golden Point Oustbeyond tailings dam), Round Hill,Southern , Innes Mills andFrasers. One of several wastedumps is in the foreground. Thephotograph was taken in March2001.


43

entborn was discovered in 1888 but worked for only afew years before the companies failed (Hearn 1988). Aseries of northwest-striking, normal fault s dippingnortheast at 60-80° host banded veins ofquartz and quartzbreccia. generally less than 0.4 m wide. The two mainlodes, Croesus and Consolidated - Homeward Bound,are continuous along a strike length ofalm0512 km. Theyare oriented at I 15° and 140°, parallel to the strike ofschi stosity and trend of lineation in the host rocksrespectively. Gold isassociated with pyrite, arsenopyrite,stibnitc and minor galena, but no scheelitc or si lver hasbeen reported (cf. Macraes Flat and Barewood).Mineralisation occurred from bo iling low-salinity waterat very sha llow, near-s urface conditi ons (c. J90°C.<0.3 kbar;McKeag & Craw 1989; Craw 1992). The recordedproduction is 112 kg (3593 oz) of gold from 7 157 tons ofore (15.6 glt recovery grade) but the reliability of this datais uncertain. Secondary near-surface gold mobi lity isindicated by blebs of native gold in the matrix of breccias.Returns decreased as mining proceeded.

Oturebua was worked intermittently from 1868 to 1887and from 193 1to 1936. The only poppet head remainingin Central Otago stands over a shaft 83 m deep dug duringthe latter period. Minerali sation is hosted in a swarm ofsteeply northeast-dipping, fracture-hosted veinsless thana metre thick, which cut across the schistosi ty. The GoldenProgress - Lloyds lode is the most continuous, persistingalong strike for about I krn. The veins are infi lled tensionalfracture cavities. in which gold is assoc iated witharsenopyrite, pyri te, sphaleriteand galena, and with minorchalcopyrite and smal l amounts of si lver (Hesson 1988).Preliminary nuid inclusion studies and dating suggestdeposition at 250-300°C and I32±2 Ma (Grieve 1997;Adams & Graham 2000), equivalent 10 the latter stages ofmineral isation at Macraes Flat. Early production figuresare not available, but 122 kg (3898 oz) o f gold wasrecovered from 2346 tons of ore (recovery grade 52.0 glt)during 193 1-1936(WiILianlson 1939).

Hard-rock mining at Serpentine from 1877 to 1890exploited a northwest-trending. steeply dipping quartzvein (Williams 1974) but there are apparently no recordsof the production. The extent of o ld workings andneighbouring aJluvial deposits suggeststhe principal lodeat Golden Gully is probably continuous forc. 1.5 km alongstrike. An old tramway, battery and waterwheel remain atthe site.

Alluvial gold

Alluvial gold in Cretaceous-Cenozoic rocks and inQuaternary sedimentsisultimately derived from lodes inthe Otago Schist. The Horse Range, Taratu and Hogburnfonnations were all mined for alluvial gold in North Otago.In Central Otago, gold was recovered from Miocene and

44

Pliocenesediments, and from Quaternary alluvial gravels(Figs 4 1 and 42). Youngson and Craw ( 1995, 1996) havedescribed recycling and chemical accretion of gold inthese placer deposits. Comprehensive historical accountsof the goldfields and mining methods include those ofMcKay ( 1897) and Wi II iamson (1939).

Manuherikia and Hawkdun Group rocks in the upperManuherikia valley and Maniotolo basin were workedby hydraulic sluicing in the late 19" century, and many ofthe water races that provided water for sluicing still ex ist.Spectacular sluicings at Surface Hill and Blue Lake, in theSt Bathans area, are the result of work which continuedinto the 20" century (Figs 29 and 41). Hawkdun Groupconglomerate was worked at Naseby, where sluicings,races and dams are still evident. Quaternary terrace gravelsderived from older sedimentary rocks were worked in theKyeburn vall ey. Manuherikia Group and HogburnFormation were slu iced at several sites near Hyde, wheredeep shafts were sunk to the rich basal lead . Uplifted orinfaulted remnants of Manuherikia Group and HogburnFormation on the schist ranges hosted diggings such asGaribaldi, Mt Buster, Gemlan Hill , Firemans Hut, Hamiltons3ndStation Hill (Will iamson 1939). Hogburn Formationquartz gravels and younger stream gravels were sluicednear Macraes Flat (Fig. 42). Taratu Formation was workedat Maerewhenua and Li vingstone, where gold wasconcentrated at the top of Eocene alluvial gravels bybeach processes (Thomson 1970; Aitchison 1988). Similarreworking of slightl y auriferousHorse Range Formationnear Palmerston resulted in richer layers within theoverlying marine sandstone (A.R. Mutch, unpublishedresearch), which were probably the sources of gold andscheelite recovered from M oeraki and Katiki beach sands(McKay 1897).

High gravels on the Lammermoor Range (deposits of anancient Taieri River; eQa) were worked by hydraulicsluicing in the early 20th century. and sluicing was alsoattempted in younger gra vels at Canadian Flat, in theupperTaieri River (Hamel 1995). Old Taieri gravels werealso sluiced at the upper end of Serpentine Flat (near thePatearoa Power Station) and at Matarae nearMiddlemarch.

Scheelite

Scheelite is assoc ia ted with the quartz lode goldmineralisation at Macraes Flat and Barewood, but atpresent it is not economic to recover. Scheel ite is alsopresent in Rakaia terrane metavolcanics near DanseysPass and in quartz veins in nearby schist (Christie et al.1994), and is widespread in catchments draining theKakanui Mountains. Demand for scheelite peaked duringWorld Wars I and II as the mineral is lIsed for hardeningsteel. About 2200 tonswere extracted from Macraes and

Figure 41 Blue Lake, adjacent to the settlement of 5t Bathans, was formed by hydraulic elevating and sluicing forgold . The pit was excavated in west-dipping, basal Manuherikia Group quartz conglomerates. Rakaia terrane schistis exposed in the eastern (left) face of the open pit. Photo CN4446a: D.L. Homer

Figure 42 Murphy's Flat, near Macraes Flat, was worked for alluvial gold over a period of about 40 years, beginningin 1862. The tailings cover about 1 ha and are registered as an historic site. Photo CN39451-2: D.L. Homer

45

Barewood between c. 1905 and 1920, with minor workingduring the 1940s.

Other metallic minerals

Antimony, bismuth, lead, manganese, monazite, sil ver andzinc have been reported from quartz lodes in l.z. IV schist,mainlyal Rough Ridge, Oturehua, Nenthom, Barewoodand Macraes Flat (Christie e1 af. 1994). Manganese hasalso been repo rted from Nenthorn . M anganeseminerali sation in l.Z. I and II Rakaia terrane rocks of theKakanui and Kirkl iston ranges occurs in metac hertassociated with metavolcanics. Detrital monazite andzi rcon have been reported from the auriferousconglomerates and gravels at St Bathans, aseby andLivingstone (Thomson 1970; Christie et al . 1994).

Coal

The earliest and 1110St productive coalfie ld was at ShagPoint, where underground mines worked high volatilebi tuminous coal from the early 1840s until 1984 (Christiee1af. 1994). Poor quality seams are known in the HorseRange Formation but the seams mined are within TarmuFormation. They are upto 3 m thick, with medium sulphurand high ash contents. Total production was about 1.84million tonnes (Christie e1 af. 1994).

Mines in the Herbert d istrict worked lignite and subbituminouscoal in the Taratu Formation. The coal hasamedium sulphur content and seams are mainly thin anddiscontinuous. Several underground mines were workedbetween 1884 and 1952, by which time the deposits wereassessed as "well-nigh exhausted" (Gage 1957). Furthernorth, sub-bituminouscoal in the Taratu Formation wasmined at Big Hill , Ngapara, Airedale, Bortons, Otiake,Awakino and Wharekuri , from 1869 onwards (Gage 1957;Christie et al. 1994). A 7.5 m seam at Ngapara was thethickest recorded.

In South Canterbury, Broken Ri ver Fonnation coal wasworked insmall underground operationsat Waihao, Otaioand Hakataramea.The Waihao field was worked from 1869to 1933, ten mines producing 22 500 tonnes of lignite(Christie e1 al. 1994).

Lignite seams within the Manuherikia Group of CentralOtago have been worked in small mines at Idaburn ,Naseby, Kyebllrn, Gimmerbllrn , Wedderburn, Waipi ataand Hyde. The Idaburn Pit, near Blackstone Hill , wasworked fromabout 1870 (Williamson 1939) unti l the 1990s.Small underground workings at Aviemore are in equivalentsediments (Waitangi Coal Measures). Between 1978 and1986, the lignite deposi ts of Central Otago were assessedas part of the New Zealand Coal Resources Survey.Dri ll ing and seismic surveys confirmed that major lignite

46

deposits are present at ldaburn-Oturehua (50 milliontonnes coal-in-ground; Bowman 1980), Home Hills (346million tonnes; Isaac 198 1; Hooper e1 al. 1983) andHawkdun (Fig. 10; 8 12 million tonnes; Isaac 198 1; Hoopere1 al. 1983). Hawkdun was one of three lignite depositsinvestigated as asource of feedstock for a plant to convertcoal to liqu id fu el. Min ing feas ibility studies werecompleted for a pit designed to produce II million tonnesof lignite annually for a period of 30 years (Dames &Moore 1987).

Limestone and Marble

Limestone and a lesser amount of marble are quarried foragriculture, building stone, industria l use and roadaggregate. lnfonnationonthe resource isgivenby Cooper(1966), Warren ( 1969) and Christie et af. ( 1994).

Blue Mountain Formation marble worked by the largequarry near Dunback is up to 99% CaCO, (Fig. 43). It hasbeen used for agricultural lime, roadi ng, and riprap. InSouth Canterbury and North Otago, th ick limestones ofthe Ke ke nodon Group (Cra igmo re a nd Ote ka ikelimestones) are worked for agricultural lime and reservesare practically un limi led. M ajor quarries are siluated atGordons Valley and Frenchmans Gully (South Canterbury)and in the Tokarahi area (North Otago), with small quarriesin the Waihao and Hakataramea areas. Further south theselimestones are not well developed and the youngerGoodwood Li mestone (Otakou Group) is of much lowergrade. In the Oamaru district, near Weston, major quarri eswork Ototara Limestone (Alma Group) for both agriculturaluse and building stone (Fig. 44).

Building stone

Otolara Li mestone (commonly knownasOamaru Stone)isone of New Zealand 's most important and widely usedbuilding stones, and has been quarried since the 1860s.Soft and easily worked, it isalso used for slone carving.The main quarry is Parks ide, in the Weston area (Fig. 44).

"Otepopo slale" isRakaia terrane pelitic schist oft .z. lIB,worked on a small scale near The Dasher in McKerrasCreek for decorative roofing chip. The rock containstoomany defects 10 produce large roofing slates. A largerquarry works l.z. lIB schist at Pennyweight Hill , betweenthe Manuherikia and Ida valleys, for walls and claddi ngs.Schist of th is grade spl its easily and is the most suitablefor building work. Reserves are practically unlimited.

Lava flows can provide durable rock in large regular blocks."Kokonga Basalt" fromthe Dunedin Volcanic Group wasworked close to the rai lway between Hyde and Ranfurlyin the I860s. It was used in the bu ildi ng of Dunedinrailway station and has more recently been used for

Figure 43 Blue Mountain Formation marble from this quarry near Dunback is processed to produce GaO for use atthe Macraes gold mine and for other industrial purposes. The marble is also used for agricultural lime, roading,and rip-rap. Photo CN40560-12: D.L. Homer

Figure 44 The Parkside Quarry near Oamaru works the Ototara Limestone (widely known as Oamaru Stone); thehorizontal lines are artefacts of the limestone cutting process, not horizontal stratification.


47

decorative stone in Dunedin.Timaru Basalt hasalso beenused in local buildings.

Hydrocarbo",

Five holes have been drilled within the Waitaki map areafor petroleum exploration . Two shallow holes drilledonshore at Oamarn in 1961 found no hydrocarbons, andthree wells were subsequently drilled offshore. Thepetroleum geology of the offshore Waitaki area isdescribed in detail elsewhere (Crown Minerals 2(00).

Endeavour- I, drilled 20 km offshore in 1970, was pluggedand abandoned as a dry hole. Clipper-I was drilled 60 kmfrom shore in 1984, to test an anticlinal structure identifiedfrom seismic surveys; gas-condensate shows werepresent in the mid Cretaceous, nonmarine, coal-bearingClipper Formation (Hawkes & Mound 1984; Field, Browneel al. 1989). Galleon- I was drilled 26 km from shore in1985 to test the nonhem of two weakly faulted anticlinaldrapes above a basement high. It proved a 21 m gas!condensate column in a good quality Late Cretaceousreservoir (2632-2653 m), which nowed up to 2240 bbVdayof condensate and up to 30 x 10' m'lday of gas; lhediscovery was considered to be subcolllmercial (Dernie& Mound 1986; Wilson & Demie 1986). The source ofhydrocarbons in Galleon-I and Clipper-I was probablythe Clipper Formation (Killops el al. 1997). Some marinestrata in all three drillholes have potential as petroleumsource rocks, particularly a carbonaceous Illudstonewithin the Onekakara Group that is correlated with theWaipawa Fonnation, but no hydrocarbonsgenerated fromthese sources have yet been identified (Killops el al. 1997).

Rip-rap and Aggregate

Aggregate resources in the map area are abundant. Portworks at Timaru and Oamaru have used large quantitiesof volcanic rock from local quarries in Timaru Basalt andOamaru Volcanics. Hydroelectricity structures in theWaitaki valley, such as the large Benmore and Aviemoreearth dams and the Ohau canals, have been built usinglocal sandstone and allu vial grave l. Holocene (Q I a)gravelsprovide material suitable for concrete aggregate,while older gravels (04 and older) have been used forcanal linings in the Upper Waitaki power scheme(Macfarlane 1980). Roading materials are obtained fromTaratu Fonnation quartz conglomerate (" Ngapara gravel".Fig. 22) and Alma Group volca ni cs. Unweatheredsandstone and sandstone-derived gravel provide materialsuitable for road sealing chip.

Clay

Manuherikia Group clays in Central Otago are suitableforcerrunjcsand mineral fil lers. The most important deposit

48

is at Hyde, where the main mineral is kaolin ite but withsome montmorillonite (Christie el al. 1994). In SouthCanterbury loess has been quarried for bricks, for examplein the centre ofTimaru and at nearby Kellands Hill.

Diatomite

Large deposits exist at Foulden Hills near Middlemarchand in the Oamaru distric!. The Foulden Hills deposi t hasbeen worked sporadically since 1941 and was thoroughlyprospected in the 1950s (Gordon 1959a, 1959b). Anextensive new quarry was proposed in 2000, citingreserves equivalent to 2 million tonnes of processedproduct (Otago Daily Times, 26 June 2(00). The Oamarudiatomjte, which ismore extensive but less pure, has beenquarried on a small scale (Edwards 1991).

Silica

High-purity quartz sand for glassmakjng and ceramicglazes has been extracted from Manuherikia Groupsediments at Hyde and Kokonga (Christie e1 al. 1994).Potentially economic deposits of silica sand are alsopresent in the upper part of the Taratu (Papakaio) andBroken Ri ver formations, notably at Kapua, Elephant HillStream, Hakataramea valley, Ngapara and Windsor (Gage1957; Christie e1 al. 1994). Sources of lump silica arenumerous in the lower parts of the Manuherikia Group,and include silica-cemented sandstones and quartzpebble conglomerates. Many localities are known in theManuheriki a valley, Ida valley and Maniototo basin(Christie el al. 1994).

Groundwater

Groundwater is extracted from aquifers below the Shagvalley, Kauru and Kakanui va ll eys, Enfie ld basin ,Maniototo basin. Strath Taieri . lower Waitaki Plains,Hakutaramea valley. Waimate and Waihao Downsareas,Otaio - Pareora district and Timaru City (Fig.45). Detailedinvestigationshave been carried out in only a few areas.and in general the hydrogeology is poorly known . TheWaitaki map area is drought- prone and at tim esgroundwater-based irrigation and stock water suppliesare placed under severe pressure.

The widespread Papakaio Formation (mapped with TaratuFormation; IKt) forms a significant confined aquifer(lrricon 1993; Otago Regional Council 2000). The waterquality in the Papakaio aquifer (low pH. high iron andsulphate content) issuch that the water is used primarilyfor pasture irrigation. In the Enfield basin, hydraulic headin the Papakaio aquifer has decreased over the past 15years as abstraction has increased, and usage may haveto be restricted in the near future. The age of the waterranges from about 8000 years, to over 20 000 years, in

different parts of the basin (Otago Regional Council 2(00).The Waiareka and Deborah Volcanics near Oamaru, andalluvium in the Kakanui , Kauru, Shag and Taieri valleys.are typically unconfined aquifers (Otago Regional Counc~1999, 2(00). Water from the Waiareka and DeborahVolcanicsaquifer is high in bicarbonate, consistent witha reservoir in marine sediments and volcan ic rocks.

In South Canterbury, shallow unconfined aqui fers inalluvial gravels predominate (Aitchison-Earl 2000) andthere are about 160 water bores in the area of the plainsbetween the Waitaki and Waihao rivers alone. Monitoringof the Waihao - Wainono aquifers shows a complexinteraction between river and lagoon levels and flows,coastal processes and contributions from the M orvenGlenavy Irrigation Scheme. while the Pareora aquifer

Maniototobasin

responds in sympathy with river nows, suggesting that ithas limited storage. Much water from these aquifersprobably passes out to sea in submarine leakage. Waterquality problems in these shallow aquifers are largelycaused by contamination from surface runoff (see below).Deeper wells (>50 01) at Waimate and Pareora tap aquifersin earlier Quaternary or Kawai Formation gravels. and afew wells penetrate to basal quartz gravels (equivalentlothe Papakaio aqui ferof north Otago) or to Rakaia terranebasement for significant yie ldsofgroundwater (AitchisonEarl2000).

Water at temperatures above normal has been foundbeneath Timaru (Christie et al. 1994) and warm water hasbeen encountered locally in the Papakaio aquifer (OtagoRegional Counci l 2(00).

TimaruBasalt

Pareoravalley

Otaio valley

Makikihi valley

WaihaoWainonoaquifers

Waitaki valley

Waiareka-DeborahVolcanics

Kauru and Kakanui valleys

Shag valley

Figure 45 Principal groundwater basins in the Waitaki map area. The aquifers in alluvial gravels (shown in yellow)and in volcanic rocks (pink) are generally unconfined and at shal low depths. The Papakaio aquifers (Taratu Formation,shown in green) are confined; they lie just above Rakaia terrane basement rocks north and south of the WaitakiRiver.

49

ENGINEERING GEOLOGY

This section provides generalised background infonnfltionbut is not a substitute for detailed geotechnica l siteinvestigations and hazard assessments. Characteristicsof some units that are relevant to engineering arehighlighted.

Paleozoic to Mesozoic sandstone and mudstone

Unfoliated Rakaia terrane sandstones are generally strongand hard when unweathered. Rock strength decreasesmarkedly with increasing weathering, and joints are verysignificant defects in fl uenc ing rock mass stab ility(Macfarlane 1988; Read 1999). Bedding is a significantrock defect main ly in fine-grained lithologies. Slopes cutin fresh rock with appropriate batters are generally stableand natural slopes stand at relatively steep angles, thoughthey are prone to rock falls. Deep-seated landsliding israre.

Schist and semischist

Rock propenies in the schists tend to be highly variable.

With increasing mctamorphic grade in l.z. rill,mand rvschists, rock strength decreases due to development ofmicaceous segregations. Jointing usually formsperpendicular and parallel to foliation, and multiple jointsets may be present, panicularly close to faults. In thehighest grade schi sts, rock strength ishighl y anisotropic.and fo liation dip slope landslides are common. Schistderived landslide debris is extremely variable in character.ranging from large intact blocks separated by shear zones,to internally chaotic masses.

Cenozoic sedimentary rocks

The wide lithological variation in these rocks is reflectedin a range of rock strengths and properties, but most areclassified as "soft rocks" in the engineering sense. TaratuFormation quanz conglomerate is widely used for roadsurfacing but contains significant plastic si lt and clayand becomes slippery when wet. Some Taratu beds aresands that may l iquefy under earthquake loadings(Macfarlane 1988). The stability of faces in this materialdepends on the degree of quartz, iron or clay

Figure 46 On the eastern Otago coast at Seacliff, the road and railway (middle of picture) Iraverse a complex activelandslide terrain which is underlain mainly by mudstones of the Burnside and Abbotsford formations (OnekakaraGroup). Several other transport corridors in the eastern part of the map area are at risk of landsliding.


50

cement.Onekakara Group mudstones are very prone toslumping (Fig. 46) and batters tend to fret. The somewhatyounger Otakou and Manuherikia group mudstones arealso prone to landslides, creating engineering difficultiesin road bauers. These impermeable sediments contributeto subsurface problems such as roadbed heaving.Manuherikia Group sedimentshave developed swallowholes along the western Maniototo water race, and naturalsinkholesin thismalerial are widespread in the Ida valley.Otekaike Limestone is generally a competent lithologythat stands well in steep faces, but the degree ofcementation varies significanLly over short distances. IIis prone to block fall s and to slumping where underlainby weaker units (Fig. 47). Sinkholes in limestone unilsmay need 10 be taken into account when planning waterstorage dams and canals (Fig. 28).

Volcanics

Basalts in lava flows are strong but defects such as verticaland horizontal joints can allow block faJls. Less densevolcanic units may also be strong (e.g. the agglomerateand pillow breccia at Oamaru Harbour). Weatheringsignificantly weakens these rocks.

Qualemary sediments

Quaternary gravel and sand deposits in moraines, outwashplains. alluvial terraces and fans are all loose, weak rocks(or soils, in engineering terms) which do not stand insteep faces. Regolith on slopes isparticularly vulnerableto shallow landsliding. Loess is prone to tunnel gullyingand slope movement, and forms small landslides whensaturated.

Figure 47 Clay-rich Cenozoic rocks may be involved in large landslides even on gentle slopes. This landslidedeposit west of the Maerewhenua River comprises a chaotic mixture of Tapul and Burnside formations (OnekakaraGroup), and Otekaike Limestone. Photo CN38985-16: D.L. Homer

51

GEOLOGICAL HAZARDS

Geological hazards within the Waitaki map area includelandsliding, earthquake shaking and liquefaction, anderosion. More local hazards include tsunami andgroundwater contaminati on. All these hazards areinfluenced by geological factors such as rock propertiesand distribution, the occurrence and activity of faults,and geomorphological factors such as slope angle. Thehazards are summarised here, but this map and text shouldnot be used for zonation or detailed hazard assessmentof specific si tes. Recording of si te-specific hazardinformation is the responsibility of local authorities. andan awareness of the presence of majorhazards. and theirpotential for recurrence, isessential fordi slrict and townplanning purposes.

Landslides

Major landslides have occurred in the past and willcertainly occur in the future, with extreme rainfall eventsand earthquakes the most likely triggers. Areas underlainby sch ist or Cenozoic clay-rich rocks are inherentlyunstable (Figs 46 and 47). Only the largest landslides areshown on the map. Many are at least partly active,reacting to major rainfall events and to undercutting bystreams. Minor slope fai lu res in regolith may also beexpected during extreme rainfall eventsor longer periodsofsoi l saturation. A combination of slope angle, directionof fo liation or bedding, jointing, groundwater, and rocktype can be used to model and predict landslide hazardzones.

Earthquakes

Earthquakes are measured in terms of their released energyaccording to the Richter magnitude (M) scale. The effectsof earthquakes, or felt intensi ties, are assessed accordingto the Modified Mercalli In tensity Scale which has 12levels. MM 12 represents very strong shaking with totaldestruction of property and struclUres; MM lOis thehighest intensity that has so far been rel iably observedin New Zealand. Part of the scale most relevant to theWaitaki map area is shown (text box; summarised fromDowncs 1995).

The southeastern part of the South Island (including thearea of the Waitaki map) has had a low level of earthquakeactivity relative to orner areas of the country since recordswere kepI. Three earthquakes of approximate Richtermagnitude 5.8 occurred near Oamaru in 1876. Chimneyswere brought down at Oamaru and Kakanui and numerouss lips were triggered between Herbert and Hampden.Many aftershocks were feil (Downes 1995). The Waitakimap area has also experienced minor damage fromearthquakes occurring just outside its boundaries, forexample, the May 8 1943 magnitude 5.9 earthquake nearthe head of Lake Hawea.

52

MM 3 Felt indoors: hanging objects may swing, vibrationsimilar to passing oflight trucks.

MM 4 Generally noticed indoors but not olllside. U ghtslee{Jers may be awakened. Vibration may belikened to passing of heavy traffic. Doors andwindows ranle. Walls (lfId/rames o/I)lIildings maybe heard to creak.

MM 5 Generally felt olllside. (Uul by almost el'eryoneindoors. Most sleepers awakened. A few peoplealamled. Some glass''''are and crockery may bebroken. Open doors may swing.

MM 6 Felt by all. People alld animals alarmed. ManynUl outside. Objects fall from shelves. Glas.nvareand crockery broke n. Unstable fllmiwreoverturn ed. Slight damage to some types ofbuildings. Afew cases ofchimney damage. Loose11Ill1erial11llly be dislodged from sloping ground.

MM 7 General alantl. Furniture mOl'es on smoothfloors.Unreinforced stOlle and brick walls (·rack. Somepre-earthquake code buildings damaged. Rooftilesmay be dislodged. Man y domestic chimneysbrokelL Small slides such asfalls ofsandand grcl\'elbanks. Somejine cracks appear ill sloping ground.Afe", installce.\·o/liquefaction.

The significant upgrade of the ational Seismographetwork in 1964 made it possible to locate earthquakes

more accurately, and thi s has shown that two parts of theWaitak i map area are more seismically acti ve thanelsewhere in the region (Fig. 48). Sporadic eaJ1hquakeactivity south and southwesl of Lake Benmore and theBenmore Dam has occurred between 1964 and the presentday; some may be related to the filling of the lake in 1964.Adams ( 1974) suggested that there was a significantincrease in seismicity within 80 km of the dam followingits completion. The largest earthquake recorded in theBenmore area (magnilUde5.00n Apri l 6 1971) was one ina series of shallow earthquakes. It was strongly felt, butcaused no damage. Another series of earthquakesoccurred near Omarama in May 1999; the largest had amagni tude of 4.9 and caused minor damage. Althoughclose to the acti ve Ostler and Otematata faults. thelocations of the 1999 earthquakes are not accuratelyenough determined to link them with activity on eitherfaull.

The Danseys Pass area is also active seismically, thelargest recorded earthquake being a magnitude 5. 1eventon February 8 1998. It caused minor damage and wasfollowed by numerous aftershocks.

Seismic hazard in ew Zealand has been evaluated byStirling et al. ( 1998), who modelled the likely groundmotion levels at any po int based on the hi storicearthquake record and the paleoseismic record. Seismic

hazard in the Waitaki map area is low compared to regionsclose to the Alpine Fault, where most of the plate boundarymotion in the South Island is accommodated (Fig. 48).Large earthquakes on the Alpine Fault are considered torecur every few hundred years, the most recent beingabout 300 years ago. For individual faults within the areaof the Waitaki map the recurrence interval of largeearthqu akes is in the order of thousands or tcns ofthousands of years. Trenching on the northern sectionof the Ostler Fau lt Zone (north of the map area) showsthat th e three 111 0st recent surface ruptures were

approx imately 10000,6 000, and 3 600 years ago, withmetre-scale displacements (i.e. a recurrence interval ofabout 3 000 years; van Dissen et 01. 1993). Salton (1993)estimated the return period for a magnitude 7 event on

the Hyde Fault at c. 5000 years. The faults mapped asactive within the Waitaki map area have the potential toproduce moderate to large earthquakes (magnitude 5 to7.5); earthquakes cou ld also occur on faults not knownto be active, or even on fau lts that have not yet beenrecognised.

Areas of soft and unconsolidated sediment are likely toamplify ground shaking during an earthquake, such thatfelt intensities could be up to two MM units higher thanonadjacent areas underlainby hard rock. Liquefactionof

loose, water-saturated sand and silt layersis likely whenshaking intensities exceed MM7 (text box). Majorearthquakes can be expected to produce landslides,blocking ri ver gorges with temporary dams. Floods ofwater and sediment would result if dams break or areovertopped. Landslides into lakes could generate largewaves, threatening hydroelectricity structures. Largevolumes of mobili sed sediment in rivers could causeaggradation downstream for many years following theevent. Landslides would also be likely to cut road and raillinks.

Erosion and sedimentation

In the lower Waitaki valley, bank erosion and channelswitching during high river nows affects farmland androads on the modern noodplain . A dam failure orovertopping upstream could result in similar but moreextensive damage. Marine erosion is active where themodem sea cliff is cut into unconsolidated gravels. as formuch of the North Otago and South Canterbury coastline.Gibb ( 1978) listed net rates of erosion in the range 0.21.97 m per year, with significant accretion occurring onlyat Timaru . Erosion ismost severe during periodsof hightides with heavy seas; in June 2000 a stretch of coastnear Oamaru receded several metres in a month.

ca o

-----144

Q> O

•co 0

O ' 0~ 45

0

0, 0, 0

Figure 48 Locations of0 shallow (depth .: 40 km)

0 o' earthquakes in the0

southeastern South

" • magnitude 6 Island with· 0 0

magnitude 5 magnitudes ~ 3.5, for<> • 46

0 magnitude 4 the period 1964 - June2000. Low and

00 magnitude 3 moderate earthquake

activity in New Zealandrarely delineates

:.4.-0

0known major faults

200 km,'. 0 expressed at the168 169 170 171 172 173 174 surface.

53

oo

o

Tsunami

Coastal flooding due to tsunami (seismic sea wave) ispossible a long much of the coastline and inland in [helower reaches of rivers. Large earthquakes on offshorefaults could cause significant tsunami, either by suddenlyraising or lowering the sea floor or by triggering submarineslumps. In hisloricaltimes no large earthquakes are known[ 0 have occurred offshore. Ear[hquakes off the coast ofSouth America have generated tsunami that causeddamage at several locations along the eastern coast of

New Zealand. At Oamaro in 1877, the breakwater wasovertopped and bOals damaged. The breakwater wasovertopped a[ Timaru in 1868 and 1877, but no damageresulted. Tsunami from distant sources often consist ofmany successive rises and falls in water levelsover adayor two. while tsunami from local sources may persist forup to half a day. In 1868 [he larges[ tsunami waves almos[certainly arrived at low tide, which would have minimisedthe damage caused.

Sea level rise

Sea level may rise significantly over the next century,

perhaps by almost a metre, as a result of global warming.This would result in accelerated coastal erosion andincreased flooding of coastal wetlands and estuaries.

Communities, transport links, recreation facilities andenvironmentally sensitive si tes could be adverselyaffected, and the raised base level at river mouths would

resu lt in more severe flooding of low-lying areas.

Groundwalercontamination

Shallow un co nfined aquifers are suscept ib le LoconL.1.mination, especially from stock and human effluent,pesticides, and leaching of chemicals from landfill andindustrial sites. For example, between the Waihao andWai[aki rivers, 66% of wells were found to be cont,unina[edby faecal colifonns. H igh nitrate/n itrogen levels have

been found near Morven, and other problems (low pH ,salinity, high iron and manganese levels) were alsorecorded from some wells in this area (Canterbury RegionalCouncil 1996). There isa contaminated groundwater plumenear an industrial site on the Levels Plai n, immediatelynorth of the map area.

54

AVAILABILITY OF QMAP DATA

The multi-purpose geological map accompanying thisbooklet is based on infonnation stored in the QMAPGeographic [nfonnation System. Other single or multifactor maps can be produced on demand from the G IS, forexample maps showing single rock types, or minerallocalities in relation to host rocks and road networks.Other digital data sets which may be integrated with thebasic geology include gravity and magnetic surveys,active faulls, earthquakes, landslides, mineral resourcesand localities (from GERM), fossi l localities (from FRED),and petrological samples (from PET). This informationcan be presented at varying sC~lles. bearing in mind thescale of data capture and the general isation in volved indigilising; maps produced at greater than 1:50000 scalewill not show accurate, detailed geological informationunless they are based on poi nt data (e.g. s tructuralinfonnat ion). [f required, the QMAP series maps can alsobe made available in digital ronn, usi ng standard datainterchange formats.

The data record maps on which the digital geology isbased are filed in GNS offices at Dunedin and Gracefield(Lower HUll) and, although unpubli shed, are availab lefor consultation. The legends and mapping phi losophyused on the detai led maps are based on traditionallithostratigraphy, and map units may differ from those onQMAP for this reason.

The QMAP database will be maintained and updated asfurther geologic mapping is undertaken, and updatedversions o fQMAP sheets will be produced in futu re. Fornew or additionaJgeologicaJ information. for prints ofthis map at other scales, for selected data or combinationsofdata sets, or for derivative or single-factor maps basedon QMAP data, please contact:

The QMAP Programme LeaderIIlSliwle of Geological & Nuclear Sciences LId.P. O. Box 30 368Lower HuttNew Zealalld

ACKNOWLEDGMENTS

The Waitaki geological map was compiled by PJ. Forsyth,with assistance from PJ . Glassey (NZMS 260 sheets141 & 143), DJ.A. Barrell (H39 & 140), MJ . Isaac, J. Leeand CR. Anderson (H39) and I.M . Turnbull (139 & 139).Add itional mapping and assistance in the field wasprovided by CR. Anderson, DJ.A. Barrell, J.G. Begg, TJ.Chinn, CElms, MJ . Isaac, J. Lee, B. Morrison and B.Smith Lyttle. Field mapping by D.G. Bishop and N.Mortimer made major contributions to the project and isg ratefull y acknowledged. Aerial photographicinterpretation of landslides was undertaken by R.Thomson.

Contribut ions to this project from staff of the GeologyDepartment, University of Otago, are acknowledged withthanks. Professor RJ. orris gave permission to useinfonnation from a large number of unpublished theses,notably those of Allan ( 1990), Cavaney (1966), Dodds(1963), Douglas (1970), Fagan (1971), Falconer (2rxxJ), Ford(1994), Grady ( 1968), MacKenzie ( 1990), Maicher (1999),Martin ( 1999), Middlemiss ( 1999), Pringle ( 1980), Rae(1990), Rolfe (1993), Ryburn (1967), Salton (1993), Schmitt(1984), Tenney ( 1977), Thomas (2000), Travis ([965),Turkandi (1986), Udy ( 1987) and Ulrich (1994). Numerousthird year projects by Otago students have also beencompleted within the map area. Use of the CanterburyUniversity thesis by Riddolls ( 1966) is acknowledged.

Additional infonnation for the text was provided by thereviewers listed below, and also by C J . Adams, G.H.Browne, G. Downes, E. Kennedy, D.C Mildenhall , J .1.Raine, and GJ. Wilson, of the Institute of Geological &Nuclear Sciences, TJ. Chinn of the National Institute ofWater & Atmospheric Sciences, and S. Yamakita ofMiyazalki University, Japan. Offshore data was providedby A. Duxfield, R.H. Herzer & B.D. Field, of the Insti tuteof Geological & Nuclear Sciences.

The map was digitised by B. Smith Lyttle, D. Thomas, J .Arnst, and C Thurlow. Map and legend layout, checking,and production from the digital database were by D.W.Heron, B. Morrison, B. Smith Lyttle and M.S. Rattenbury.

All or part of the map and text were reviewed by DJ.A.Barrell, K.R. Berryman, HJ . Campbell , R.M . Carter, S.CCox, D. Craw, B.D. Field, R.E. Fordyce, MJ . Isaac, M.R.Johnston, CA. Landis, D. Lee, P.A. Maxwell , N. Mortimer,S.A. L. Read, A. Reay, I.M. Turnbull, R. van Dissen, P.R.Wood and J.H. Youngsol1 . The reviewershave improvedbOtll map and text, and I thank them for their time andenergy during many valuable discussions.

Funding for the QMAP project was provided by theFoundation for Researc h, Science and Technologycontracts C0 56 19, C05809 and C05XrxxJ3. Topographicdata is sourced from Land Information New Zealand.Crown copyright reserved.

55

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56

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63

APPENDIX 1

Stratigraphic Names in North Otago and SouthCanterbury

The Late Cretaceous to Miocene sedimentary successionin southeastern New Zealand comprises rocks depositedduring a transgression, a stillstand and a regress ion.Recognising thi s pattern, Field & Browne ( 1986; alsoField, Browne el (II. 1989) and Caner ( 1988) publishedtwo different. but largely equivalent. selS of stratigraphicnam es. Thus sed iments laid down during thetransgression are named Onckakara (Caner 1988) or Eyre(Field & Browne 1986) Group; the condensed sequenceof the stillstand Kekenodon or Otiake Group, and theregressive suite Gtakou or Motunau Group. The authorsalso recognised that many local formation names wereredundant and could be grouped to emphasise similaritiesrather than differences (see Table 2).

The names proposed by Field & Browne ( 1986) werebased mainly on detailed section measurement ofonshoreoutcrops from orth Canterbury to South Otago, andcompilation and synthesisof these data into a monographfor the Cretaceous-Cenozoic Project of the New ZealandGeological Survey (Field, Browne et (I I. 1989). The namesproposed by Carter ( 1988) were more widely based ingood offshore seismic data, which led to the rea lisationthat the fragmentary onshore record lies near the edge ofmajor offshore basins containing a much more completesedimentary record.

The stratigraphic scheme of Carter ( 1988) was used forthe Dunedin sheet, the first of the QMAP series (Bishop& Turnbull 1996), and it has also been fo llowed bere.

64

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This full colour, large format geological map illustrates the geology of the Waitaki area, whichcomprises orrh Otago and South Canterbury in the South Island of New Zealand, at a scale of1:250 000. The map is partof a series initiated in 1996, which will coverthe whole country.

Onshore geology and offshore bathymetry and geology are shown, derived from published andunpublished mapping by the Institute of Geological and Nuclear Sciences, rhe ationa] Institute forWater & Atmospheric Research, university staff and slUdents, and exploration company geologists. Allgeological map data are held in a geographic information system and are available in digital form, and asthematic maps at various scales. The accompanying illustrated text summarises the regional geology,teclOnic development, economic geology, engineering geology, and the potential geological hazards.

Paleozoic to Mesozoic indurated sedimentary rocks of the Rakaia and Caples terranes, and theirmetamorphosed equivalents which form the Otago Schist, underlie rhe whole Waitaki area and areexposed in the mountain ranges and upland plateaus. A Cretaceous to Cenozoic sedimentary sequenceis preserved in many basins and valleys, especially in coastal regions. These rocks include marinesandstone, mudstone and limestone, commonly rich in fossils, and non-marine sandstone, mudstone,conglomerate and coal. Igneous activity from Cretaceous to Pliocene time has left mainly basaltic lavaflows, ash and a few intrusive rock bodies. Quaternary sediments are dominated by alluvial gravels,with some glacial, lake and beach deposits.

The area is crossed by many major faults, some of which are active. Landsliding is common in areasunderlain by schist and Cenozoic sedimentary rocks. Geological resources include gold and othermetals, coal, aggregate, limestone, building stone and groundwater.

Spectacular pillow lavas, exposed near Oamaru, occur within the Eocene Waiareka Volcanics.Pillow lavas form when molten lava flows into water, and are associated with the quieter phases ofundersea volcanic eruptions. Each pillow has one or more dark skins of quenched volcanic glassaround a centre of grey basalt. The pale limestone between the pillows originated as calcareousmud on the sea floor.

Photo CNJJ409-24: D.L. Homer

ISBN 0-478-09739-5

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