Palaeoenvironments of Borneo Geology and palaeogeography ... · Palaeoenvironments of Borneo...

Solving mammalian riddles Chapter 3. The palaeoenvironmental scene based on data mining

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Palaeoenvironments of Borneo

Geology and palaeogeography of Borneo

Wilson and Moss (1999) provided a detailed overview of the geology of Borneo, and

their information was used in the palaeoenvironmental reconstructions in this work,

alongside the information provided by Hall (1998). A land connection between

southern Borneo and mainland Southeast Asia is inferred to have existed during the

Eocene and Oligocene (Pupilli, 1973 in Wilson & Moss 1999). During the Late

Cretaceous–Early Tertiary, a large river (possibly the ancestral Chao Phraya/Mekong

River) ran across the length of Sundaland, from its Eurasian source areas to the central

and northern ‘Borneo fan’ area, with a delta in the Natuna Island region (Moss &

Chambers 1999). The central ranges of Borneo were uplifted towards the end of the

Oligocene, and the erosion of these areas supplied sediments eastwards towards the

Makassar Straits (Moss et al, 1998 in Wilson & Moss 1999).

Figure 3.10. Main geological features of Borneo (after Steinshouer et al. 1997); for legend refer to Fig. 3.5.

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An important aspect of the geology of Borneo was brought to light by the work of

Haile et al. (1977), who obtained palaeomagnetic data from Cretaceous igneous rocks

in West Kalimantan. They stated that, although Borneo had remained approximately

in the same paleolatitude since the late Cretaceous, it had rotated counter-clockwise

about 50º acting as a unit with the Malay Peninsula. Similarly, Nishimura & Suparka

(1997) stated that Borneo, the Celebes Sea basin and the western arm of Sulawesi

rotated 50º counterclockwise during the early Miocene (20–17 Mya). This rotation

continued until some 10 Mya (Hall 1998), although Lumadyo et al. (1990 in Lee &

Lawver 1994) had stated that the stable western part of Kalimantan has not been

rotated since the Eocene. The rotation history of Borneo and Western Sulawesi is

therefore still highly contentious (for an overview see Wilson & Moss 1999), and data

reported by Morley (2000a) suggest that significant rotation of Borneo cannot be

accommodated by Tertiary structures onshore and in the Gulf of Thailand.

Pieters et al. (1987) provided an overview of the early Tertiary development of

Borneo. In Late Eocene times the deposition of terrestrial to shallow marine sediments

began over a large part of the island of Borneo around a central highland formed by an

emergent orogenic complex (the Kuching Arch). During the Paleogene the Kuching

Arch comprised island and shallow water areas, which separated the more rapidly

subsiding portions of the Sarawak and Kutai Basins (Rose & Hartono 1978). The

continental basement of the Schwaner Mountains in Southwest Kalimantan probably

persisted as a highland area, connected by land to SE Sumatra and the Malay

Peninsula. The Meratus Mountains (Fig. 3.10) and the Barito region were still

submerged (Pieters et al. 1987), and the Paternoster Block, offshore of present-day SE

Kalimantan, was only partly emergent during the Early Paleogene, being later

transgressed during the Oligocene (Rose & Hartono 1978). In Early Oligocene times a

westward transgression of the sea reached the upper Mahakam River and the Barito

Shelf. A long and narrow arm of this sea extended westward almost across to the

present-day west coast of Kalimantan, confined between the tectonically active

emergent orogenic complex to the north and the persisting highland basement to the

south. Continuing deformation and uplift along the southern margin of the orogen led

to the demise of this central Borneo Basin and by Early Miocene times the basin had

disappeared altogether according to Rose and Hartono (1978). In Middle Miocene


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times, the Kutai Basin became separated from the Ketungau-Melawi Basin by a high

area near the present-day Müller Mountains, after which both basins slowly filled up

(Ott 1987). This resulted in volcanic activity, which formed a high plateau of tuffs and

other volcanic material (Molengraaff & Weber 1920, p. 467). This was then also the

time when the northern part of Borneo (present-day Sarawak, north East Kalimantan,

Sabah, and Brunei) became connected to the southern part (consisting of the Schwaner

Mountains). Interestingly, considering that the entire Kapuas and Mahakam River

valleys are low-lying (< 100 m a.s.l. even in the upper reaches), it is not impossible

that, during extreme sea level highstands, the two river systems became connected

again, thereby effectively separating northern Borneo from the rest of Sundaland.

Between 17 and 11 Mya, sedimentation rates rose everywhere in SE Asia,

spectacularly so in the Sarawak and Sabah Basins, north of Borneo. Rates of

deposition of carbonates and shallow-water detrital material changed from 0.17 to 0.4

mm/year. During the Pliocene, this rate increased even more to 0.69 and 0.65 mm/year

for the Sarawak and Sabah Basins respectively (Metivier & Gaudemer 1999). It

remains unclear whether this increase was due to the climatic optimum during the

Middle Miocene, which may have led to higher rainfall and erosion, or whether

increased uplift provided the sediments. Considering that the increase continued into

the Pliocene, mountain building may be a more likely explanation. Adding up the

solid phase volume accumulated in the Sabah and Sarawak sedimentary basins also

suggests the occurrence of considerable mountain areas on Borneo. Métivier et al.

(1999) provided a total estimate of 1.3 * 106 km3 of sediment accumulation in the

Sabah and Sarawak Basins since 17 Mya. Under the assumption that the Bornean

highlands were equally drained in a northern, southern, and eastern direction this

would add up to approximately 4 * 106 km3 of upland being eroded in 17 Mya, if no

further uplift occurred. The present Bornean uplands are approximately 1 * 106 km3,

which would indicate that over the last 17 Mya, a mountain area with a height of

several kilometres has been eroded. This was confirmed by R. Hall (pers. comm.),

who remarked that Borneo shed vast amounts of sediments in the last 10 Mya,

equivalent to the removal of 6 km of crust; as much as the Himalayas now but on a

third of the area. Based on research on geological and topographic criteria, Thomas et

al. (1999) estimated that in NW Kalimantan the groundsurface was lowered between

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1,200 and 1,500 m since 30 Mya, giving an average denudation rate of 40–50 mm/Kya

(which is considerably lower than the estimates by Metivier & Gaudemer 1999).

East Borneo

Zanial and Luki (1984) described the depositional cycles in the Tarakan Basin. From

the latest Oligocene to early Middle Miocene sedimentation in the basins occurred in a

marine environment. By the end of the Early Miocene the delta front had advanced

approximately 200 km eastward of the present-day coastline (Moss et al., 1997 in

Friederich et al. 1999), which brought north-east Kalimantan very close to the

Sulawesi area. At the end of this period the area was uplifted, but presumably re-

flooded during the Middle Miocene highstand. A major change in the sedimentation

history of north-east Kalimantan occurred in early Middle Miocene, when a deltaic

environment developed at the western side of the region. This delta front started to

prograde eastwards during the Miocene until all sedimentary processes in this area

were terminated by a Late Miocene uplift at approximately 6.6 Mya.

The eastern coastline of Borneo in Early Miocene times ran approximately from the

south-west corner of Kalimantan, via the area of the upper reaches of the Barito and

Mahakam to just north of the Mangkalihat Peninsula (Pieters et al. 1987). During the

Miocene, delta systems in the Kutai Basin prograded south-eastward filling the Kutai

Basin so that by the Late Miocene, deltaic deposition had generally reached a position

beyond that of today’s East Kalimantan coastline (Rose & Hartono 1978). By the end

of the Miocene, the drainage system within Borneo was similar to the present day

(Wilson & Moss 1999), although Smit-Sibinga (1953b) stated that the Mahakam River

came into being only 2 Mya, and that this river initially flowed into the very large

Kutai Lake (of which the present lakes are only remnants).

In the Late Miocene (Middle Miocene according to Ott 1987) and Early Pliocene the

Meratus Graben was uplifted and started to shed sediments to the west and to the east

(Rose & Hartono 1978; van de Weerd et al. 1987), eventually leading to the rise of the

Meratus Mountains. At that time, the Barito Basin became separated from the Kutai

Basin by the Adang Flexure/Fault, which resulted from the uplift of the Meratus

Mountains (Satyana et al. 1999). Miocene coals on the west and east side of the


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Meratus Mountains, suggests that the basins on either side of these mountains were

becoming terrestrial and that the climate was warm and wet (Friederich et al. 1999).

The uplift of the Meratus Mountains continued into the Pleistocene (Satyana et al.

1999).

East of the Meratus Mountains, a large island existed during the Tertiary (van

Bemmelen 1970). The elevated area was surrounded by the depositional basins of SE

and E Borneo, West Sulawesi, the Kangean-Madura-Rembang belt, and Bawean. Van

Bemmelen named this land area the Pulau Laut centre of diastrophism. According to

him this Pulau Laut centre was elevated at the end of the Pliocene, but the crest of this

dome was rapidly engulfed during the Pleistocene, presumably leaving only the

present-day land area of Pulau Laut. Emmet and Bally (1996) claimed that the eastern

extension of the Kangean High was emergent in the Late Miocene, but it is unclear

whether the Kangean High was part of this Pulau Laut centre.

West Borneo

Lloyd (1978 in Wilson & Moss 1999) suggested that Borneo lost its connection to the

Malay Peninsula during the latest Miocene or Pliocene, which was possibly caused by

global sea-level changes and/or plate readjustments (Wilson & Moss 1999).

Quaternary sediments on the Sunda Shelf lie directly on pre-Tertiary rocks. However,

as Wilson and Moss (1999) pointed out, it is possible that marine sediments deposited

during possible regressions of this region may have been removed by later erosion.

For further details on the divergence between the Bornean and Malay landmasses see

below in the section “Palaeoenvironments of the South China Sea”.

Ter Bruggen (1955) hypothesized on the palaeocourse of the Kapuas River. He

suggested that only in the Quaternary the present upper reaches of the Kapuas broke

through the Semitau uplands to join the Melawi River near present day Sintang (Fig.

3.11). The part of the Kapuas below Sintang, therefore, is the original continuation of

the Melawi. In that scenario, the proto Kapuas would have flowed northward through

the upper Kapuas Lakes area and followed the course of the present Batang Lupar

River.

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Figure 3.11. Map of the Kapuas River and its hypothesized change from drainage into the Batang Lupar (top) to its merge with the Melawi (bottom).

Melawi River

Kapuas River

Batang Lupar River


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A right tributary of the Melawi, now the piece of river between Sintang and Semitau,

reached the Kapuas plain by cutting back, and decapitated the Kapuas River, which

thus obtained its present course. The Kapuas Lakes area is therefore likely to consists

of the former riverbed of the Kapuas. With regard to the course of the Kapuas it is also

interesting to note that Smit-Sibinga (1953a) suggested that the Boh River, which is

now a tributary of the Mahakam, used to be part of the upper reaches of the Kapuas;

stream capture later joined it to the Mahakam River.

Sabah

Rice-Oxley (1991) and Tan and Lamy (1990) provided a detailed description of the

Early Miocene–Pliocene palaeoenvironments of north-west Sabah. The whole of

offshore NW Sabah was a realm of deep marine shale deposition during the Early

Miocene to early Middle Miocene. The coast ran approximately in the same area as

the present-day coastline and was prograding in a NW direction, while sediments were

sourced from the highlands of the Rajang accretionary prism (Tan & Lamy 1990). The

Middle Miocene to early Late Miocene saw the uplift of the Crocker Range and a

further NW shift of the coastline (Tan & Lamy 1990), while the Kinabalu intrusion

was emplaced in the middle Late Miocene (Jacobson, 1970 in Tan & Lamy 1990). Mt.

Kinabalu, the highest mountain in the Sundaland area, was uplifted between 4 and 10

Mya, although uplift to its current height is thought to have occurred only within the

last 1.5 Mya (Barkman & Simpson 2001), while the mountain reached its present

height about 100 Kya (Choi, 1996 in Tanaka et al. 2001) providing suitable habitat for

mountainous species. During the Late Miocene, the northern Borneo coastline

changed from having a N-S orientation to a SW-NE orientation, similar to today

(Wilson & Moss 1999). The middle Middle Miocene to Pliocene stage is characterised

by two major depositional cycles, each starting with an initial phase of coastal plain

sedimentary upbuilding, followed by rapid transgression (see detailed maps in Rice-

Oxley 1991). Between the Late Miocene and Pliocene, the palaeocoastline in NW

Sabah was positioned off-shore the present-day coastline, approximately following the

Mangalum and Morris Faults (see Figure 3 in Tan & Lamy 1990). Early Miocene coal

finds in the Maliau Basin suggest wide tidal flats in this area and warm and wet

environmental conditions (Tjia et al. 1990).

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Sarawak

Most of Sarawak consists of deep sedimentary basins although, in the region east of

Kuching, basement rocks appear near the surface (Isaacs 1963), which suggests that

this area has been emergent for a long time. Agostinelli et al. (1990) produced

palaeogeographic maps for Sarawak. Through the Miocene, the palaeocoastline was

oriented more or less orthogonally to the present one, suggesting that a considerably

part of what is now northern and central Sarawak was below sea-level. The main

source of sediment for the coastal Sarawak area appears to have been somewhere

north of Kuching, which fits Isaacs’ (1963) hypothesis of an old emergent land area in

that region. Uplifted anticlines on the present Sarawak land area caused the deposition

of vast amounts of sediments on a rapidly prograding shelf during the early Late

Miocene (ca. 11 Mya) (Mat-Zin & Tucker 1999)), which led to the following

palaeogeography: A coastline running parallel to the present one, a broad shelf, and a

steep transition to deep water (Agostinelli et al. 1990). Towards the end of the

Tertiary, most of west Sarawak was raised above sea-level. A prolonged period of

erosion followed in the Late Tertiary and Early Quaternary times, reducing much of

the area to a peneplane (Tan 1986), probably levelling down the summits of all

mountains to the 1,500 m contour in Late Miocene times (Muller 1971). At various

times during the Quaternary, the present-day rivers were able to extend their levees

much further into the coastal shelf than at present (Andriesse, 1972 in Tan 1986).

Vegetation of Borneo

The pollen record for Brunei suggests a strongly seasonal palaeoclimate in Late

Oligocene and Early Miocene and to a lesser extent also in the Late Miocene–

Pliocene, with abundant gymnosperms such as Pinus, Abies, Tsuga, Keteleria and

Ephedra (Muller 1966, 1975). These species gradually disappeared during the Late

Miocene and Pliocene (Germeraad et al, 1968 in Watanasak 1990), although during

the Late Miocene the appearance of the seasonal mangrove taxa Aegialites and

Camptostemon in Brunei indicates a return towards a more seasonal climate (Morley

1977). Also, the conifers Phyllocladus and Podocarpus first appear in the Late

Pliocene of Borneo, with the former arriving at the Plio-Pleistocene transition,

indicating a land connection between Malaya and Borneo at that time, and either

cooler climates and/or substantially higher mountains in Borneo than at the present


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(Muller 1971). According to Morley (1977), for the montane taxa to arrive in Borneo

a direct mountainous land connection with Southeast Asia had to exist, but later,

Morley (1999) revised this idea by suggesting that cooler and drier climatic conditions

could have accounted for the southward spread of these species. Because most of these

taxa are wind dispersers, a land connection between Borneo and Malaya may not even

have been necessary.

Pollen and spores finds in Early Miocene coals in the Maliau Basin in Sabah (Tjia et

al. 1990) suggest warm everwet climates, and not strong seasonality as suggested

above, as they indicate the presence of ombrogenous peat swamps in everwet climates,

mangroves, seasonal swamp forests, and possibly other habitats (Morley 1991). This

may suggest that there was climatic variation between seasonal and everwet climates

within the Miocene. The vegetation of Middle Miocene peat swamps from SE

Kalimantan (Demchuck and Moore, 1993 in Morley 2000) and the Tarakan Basin

(Morley 1991) can be inferred from palynological analysis of coal. The presence of

mangrove and back-mangrove species suggests that the peat accumulated partly under

brackish conditions, whereas elsewhere watershed peats occurred; the presence of

Meyeripollis naharkotensis in coal suggests everwet climatic conditions. Mangrove

peats formed at a time of maximum Miocene global sea-levels and temperatures, and

it is suggested that conditions somewhat warmer than today are necessary for the

formation of these peats (Morley 2000). Further occurrence of Early–Middle and

Middle–Late Miocene coals in the Mahakam Delta, as described by Peters et al.

(2000) and coals in Miocene and Early Pliocene sequences of the Kutai, Barito, and

Asam Asam Basins (Friederich et al. 1999) suggest that overall the Miocene–Early

Pliocene climate in north and east Borneo was warm and wet.

In the Late Miocene–Pliocene the climate became cooler and drier. Gramineae

maxima in Late Miocene and Pliocene sediments of the Mahakam Delta suggest more

open savannah vegetation intermittently replacing the rain forests. Also, the

distribution of the mangrove taxa Aegialites and Camptostemon in Sarawak and the

Mahakam Delta may relate to phases of dry climate, coinciding with periods of low

sea-level (Morley 2000). East and SE Borneo are still much drier than the other parts

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of the island, and increased seasonality or reduced rainfall would have first translated

into vegetation changes on that part of the island.

I was unable to find palaeoenvironmental data for the earlier part of the Pleistocene, a

period of considerably importance to the evolution of present-day mammal species of

Borneo. However, there are several sources that suggest considerably colder

temperatures and reduced rainfall during the Late Pleistocene. Thomas (1987) found

geomorphological features in West Kalimantan that suggested that 40 Kya ago this

area underwent a 50% reduction in rainfall, and that a monsoon climate existed

accompanied by a tree-savannah vegetation. These findings were corroborated by

Thorp et al. (1990) who interpreted extensive braided and fan-like alluvial landforms

to be the results of dry, savanna-like palaeohydrological conditions during oxygen

isotope 3 (post-60 Kya). These alluvia were dissected, their surface sediments

podzolized and their incised valleys re-alluviated during the last 15 Kyr (Thorp et al.

1990). Jirin (1993) described Late Pleistocene vegetation changes in five

palynological zones from Sabah. Pollen in the oldest zone, probably representing the

penultimate glacial period, suggest a cold and dry climate, which led to the expansion

of montane vegetation. Lowland cover contracted as precipitation was reduced, while

sea-level was low, which led to the reduction of mangrove vegetation. A sea-level

high represented in the next zone caused the mangrove vegetation to expand. The

climate was warm and wet, and montane vegetation was reduced, while lowland

vegetation expanded. The next zone represents an extensive sea-level fall during the

LGM. The cooler and possibly drier climate caused montane forest to expand to lower

altitudes. Expansion of lowland vegetation at the end of this period indicates climatic

amelioration, and after the Pleistocene-Holocene boundary mangrove cover expanded,

and montane vegetation retreated to its present altitudinal range (Jirin 1993) (note that

there is no mention of grasslands). Another pollen diagram from East Borneo shows

an increase in savanna at ca. 20 Kya, which might serve as an indicator of a drier

climate than at present (Flenley 1998). Dated charcoal finds caused Goldammer and

Siebert (1989) to believe that the coastal area of East and South Kalimantan was more

continental and drier than at present and they assumed that forest formations at that

time were more seasonal and had probably a temporary fire climax character. Majid

(1982) suggested that at the height of the LGM, the Niah area in Sarawak was covered


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by deciduous monsoon forest, while Caratini et al. (1988) suggested that, during the

LGM, the hinterland of the Mahakam Delta probably consisted of grassland or

savannah.

Not everywhere on Borneo did the cooler and drier conditions lead to more open

vegetation types as shown by the findings of Anshari et al. (2000) and Kershaw et al.

(2001). Their data from West Kalimantan indicate that during the LGM the upper

Kapuas area was covered in rainforest, very similar to that found during the mid-

Holocene. Also, in the Sebangau area of Central Kalimantan, peat datings showed that

peat had started to develop at 18.3 Kya ± 0.05, and had continued to do so until c. 7

Kya, after which no peat was formed until it started again at 1.3 Kya (Page et al.

1999a); again this indicates that the climate remained relatively warm and wet during

the LGM, although peats may only have started to develop after the height of the

glacial period.

Palaeoenvironments of the Malay Peninsula and Malacca Strait

Geology and palaeogeography of the Malay Peninsula and Malacca Strait

Hutchison (1990) described the palaeogeography of the Malay Peninsula (Fig. 3.12)

during the Paleogene. The Paleogene drainage from Sundaland flowed southwards on

the tilted basement surface through the N–S Bengkalis Graben, the fault zone that

forms the eastern coast of Sumatra, the Sunda and Asri Basins offshore west Java, and

the grabens of Northern Sumatra (Hutchison 1996). The Muar River in Peninsular

Malaysia, which was still connected to the Pembeling River, is a relict of this

palaeogeography. This river system flowed south down the regional slope, probably

reaching the Indian Ocean on the South Sumatran coast. Hutchison (1990) stated that

the Paleogene Chao Phraya-Mekong River flowed southward along a regional slope as

well, a direct analogue of the Tembeling-Muar, but because the Chao Phraya-Mekong

River probably debouched near the Natuna Islands it is unlikely that the two river

systems were connected.

East of the Malay Peninsula lies the Malay Basin, which is of Oligocene to recent age.

The basin is about 350 km long and 250 km wide (Madon & Watts 1998), and it is

closely associated with the Thai Basin in the north and the Penyu and West Natuna

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Basins in the south (Fig. 3.12). It is bounded at the north-eastern flanks by the Khorat

Swell and in the south-west by the Tenggol Arch (Ramli 1988).

Figure 3.12. Main geological features of the Malay Peninsula (after Steinhouser et al. 1997); for legend see Figure 3.5.

Armitage and Viotti (1977) described the depositional environments of this basin, on a

location some 300 km east of Kuala Trengganu, which lies on the present east coast of

Peninsular Malaysia. From Early to Middle Miocene a fluvial plane existed, grading

to a coastal plain, which changed towards a brackish coastal plain with more marine

influences, while from Pliocene to recent time a marine to neretic environment existed

(Armitage & Viotti 1977). Madon and Watts (1998) also mentioned that during the

Early to Middle Miocene the basin was characterised by non-marine and brackish


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depositional environments, while Métivier et al. (1999) reported that this cycle is

composed of successive fluvio-lacustrine, littoral and deltaic or swamp deposits.

According to Ramli (1988), the southern part of the Malay Basin (at latitude 4°00 N)

started to become marine in the early Early Miocene, and by the start of the Pliocene

the entire Malay Basin was predominantly covered by holomarine inner neritic

sediments. The abundance of coal, however, suggests that the basin was at or near sea-

level during most of the Miocene and was influenced by only minor fluctuations in

sea-level; although this was questioned by Higgs (1999) who suggested that coals in

the Malay Basin were allochthonous, and that the basin was much deeper. As coals

only form in maritime climates with > 3 m of rainfall and no marked dry season (Cole

1987), we do get an idea of the prevalent climatic conditions in the Malay Basin area

during the Miocene. A similar structural history has been described in the Penyu

Basin, which lies between the Malay and West Natuna Basins (for the latter see the

section on “Palaeoenvironments of the South China Sea”). In Late Miocene to

Pliocene times, both basins developed a shallow marine environment, where water

depths probably never exceeded 200 m (Azmi et al., 1994 in Madon & Watts 1998).

By the Early Miocene, the Malay Peninsula had almost reached its present-day

position, after having moved with the Indochina block in a southerly direction, but the

adjacent North Sumatra Basin and central Thailand basins were still undergoing

extension (McCabe et al., 1998 in Lee & Lawver 1995). Still, the area was affected

both by vertical movements and changing sea-levels. Scrivenor (1931) suggested that

Mt. Ophir (named Gunung Ledang on more recent maps) and Mt. Kedah were once

islands, and that a line from Alor Setar (in Kedah State) to Songkhla (in Thailand) was

the coast-line of land that was once an island, or group of islands, but had since

become the southern part of the Thai-Malay Peninsula. Scrivenor provided further

tentative evidence of former high sea-levels on the Malay Peninsula. He described

marine sponge-spicules of relatively recent age (Pliocene or Pleistocene) at an altitude

of at least 70 m in the upper Perak River area (or rather its tributary the Plus River).

Tjia (1973) also mentioned raised Quaternary shorelines in Perak, Selangor, and the

Kinta Valley which were found at altitudes of 60–75 m above present day sea-level.

He tentatively correlated these high sea-levels to the Milazzian, an Early-Middle

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Pleistocene interglacial. Possibly, these can be correlated to the high sea-levels at

about 2–1.7 Mya, as seen in sea-level curves presented by Hutchison (1989, p. 70).

These high sea-levels are correlated with the Malayan boulder beds and Old Alluvium,

which Tjia, and in the same book also Stauffer (1973), give an Early–Middle

Pleistocene age, but which others have dated as much younger (see discussion below).

The fact that the boulder beds are deformed structurally, with dips of 60º locally, and a

thickness of up to 300 m strongly suggest that considerable time has passed since their

deposition, making a Late Pleistocene age unlikely (Stauffer 1973). Burton (1964)

thought that the Older Alluvium on terraces of at most 85 m a.s.l. were deposited

during an Early Pleistocene highstand. Interestingly, Burton distinguished between

two types of Older Alluvium, i.e. wide-spread terraces with a maximum altitude of 70

m a.s.l., and older, coarser textured sediments at an altitude of between 90 and 140 m

a.s.l. In the last 5 Myr, sea levels highstands over 50 m a.s.l., have probably only

occurred 5 times, as judged from sea level curves presented by Haq et al. (1987) and

Mitchum et al. (1993): 1. During the Early–Middle Pliocene; 2. at ca. 4.0 Mya; 3. at

ca. 3.4 Mya; 4. at ca. 1.05 Mya; and at ca. 0.3 Mya. Only the Early–Middle Pliocene

highstand seems to have been close to or over 80 m a.s.l. making it a likely candidate

for the higher terraces of Sundaland.

Gupta et al. (1987), in their description of the Old Alluvium deposits, suggested that

these were associated with seasonality of water flow. Such a seasonal component may

have resulted from a dry southwest monsoon due to the increased size and relief of

Sumatra. Up until recently, the age of these deposits remained a matter of much debate

(see Batchelor 1993; Thorp & Thomas 1993). Batchelor (1993) considered the Old

Alluvium of Peninsular Malaysia and Singapore, which he correlated with the Older

Sedimentary Cover offshore Peninsular Malaysia, to be of Late Pliocene/Early

Pleistocene to Middle Pleistocene age (at least 700 Kya). Thorp and Thomas (1993),

on the other hand, disagreed with this dating and suggested that the Old Alluvium was

of much younger age (Late Pleistocene). They based this on what they considered

reliable datings by thermoluminescense. Furthermore, they were convinced that this

Old Alluvium correlated with the Late Pleistocene alluvial bodies that they found in

West Kalimantan. These latter deposits were built during a period of increased erosion

and sedimentation during the isotope 3 stage of the last glacial cycle, which was


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characterized by rainfall of 2–3 m/year over a period of probably more than 30 Kya.

Part of this debate has recently been decided in favour of Thorp and Thomas by

Teeuw et al. (1999), Kamaludin and Azmi (1997), and Kamaludin et al. (1993). The

former dated west Bornean sediments at 75–3 Kya, which is largely in agreement with

the Late Pleistocene dating by Thorp and Thomas. Similarly, Kamaludin and Azmi

(1997) and Kamaludin et al. (1993) dated the upper strata of the Old Alluvium

deposits in western Malaysia at between 67 and 29 Kya, which again agrees with

Thorp and Thomas. Still, the fact that fossils of typical Middle Pleistocene species,

such as Palaeoloxodon namadicus were found in the Old Alluvium north of Kinta

Valley (Peninsular Malaysia) indicates that at least parts of that stratum are of

genuinely Middle Pleistocene age (Stauffer 1973) (unless the species survived into the

Late Pleistocene), and it probably needs to divided into different units.

In a study of the geology of the Malacca Strait, Emmel and Curray (1982) found the

existence of a rugged basement in the southern Strait (south of 3ºN). This basement,

which they considered to be of pre- or Early Pleistocene age, consisted of low peaks,

40 m higher than the valleys. Emmel and Curray (1982) considered this basement

indicative of strong erosion during lowered sea-level. Overlying this rugged

topography were several types of sediments. Firstly, the old sea floor, like the present

one, represents an abrasion surface, formed initially during a low-level sea stand and

followed by a transgression. During the low-level phase, this surface was subaerial, as

evidenced by the small erosional valleys cut into it. Emmel and Curray correlate the

old sea floor with the low sea-level and the transgressive phase preceding the

Sangamon (Eem, or Riss-Würm) interglacial, although this is speculative.

Further sediments were described by Kudrass and Schlüter (1994). Firstly, they

discussed the sequence I sedimentary cover that was found directly on top of

sedimentary bedrock in both the northern and southern Malacca Straits. They ascribed

a tentative age to this sequence, i.e. Tertiary to Early Pleistocene, and suggested it to

be an exclusively terrestrial deposit, which could possibly suggest that Sumatra and

the Malay Peninsula were then connected. On top of sequence I, Kudrass and Schlüter

found an unconformity that was probably caused by rejuvenated fluviatile erosion

during an extended period or several periods of lowered sea-level. They tentatively

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dated the termination of this unconformity at 0.9 or 0.6 Mya, when the increased

build-up of glacial ice-sheets enhanced the amplitude of sea-level changes (Berger et

al., 1993 in Kudrass & Schluter 1994). In contrast to sequence I, sequences II and III

were deposited in an environment which was influenced by frequent shifts of the base

level of erosion. The small-scale fluctuations may be correlated to the transitional

periods from the interglacial to the glacial period, when sea-level shifted several times

across the 30 m depth contour (Shackleton, 1987 in Kudrass & Schluter 1994).

Kudrass and Schlüter (1994) found two major unconformities at the boundaries of

sequences II/III and III/IV, which they ascribed to prolonged periods of widespread

erosion caused by long periods of low sea-level. These periods were tentatively

correlated to the two last high glacial periods, when sea-level was lowered more than

50 m from 190–125 Kya and from 70–10 Kya. The final sequence IV was deposited

after the LGM. During the transgression, the Strait of Malacca was an elongated

shallow bay where a great supply of fine-grained terrigenous sediment partly

compensated the rapid sea-level rise. Up to 30 m thick Holocene coastal mud-

mangrove-peat accumulated in a short period (Kudrass & Schluter 1994) and the final

opening of the Strait between the Indian Ocean and the South China Sea may only

have occurred as recently as 5 Kya (Geyh et al., 1979 in Kudrass & Schluter 1994).

Vegetation of the Malay Peninsula and Malacca Strait

The flora in the Early to Middle Miocene Malay Basin area included species that

indicated a swamp or mangrove setting (Morley 2000), while Gramineae were also

found. Especially during the drier climate phases of the Miocene and Pliocene, which

were possibly correlated to the periods of low sea-level, Gramineae maxima in the

Malay Basin suggest more open savannah vegetation intermittently replacing the rain

forests. These Gramineae maxima are more common in Late Miocene and Pliocene

sediments than in the latter part of the Middle Miocene and Early Miocene (Morley

1999). Morley (1999) reported on a very distinctive occurrence of Dacrydium, which

is a good indicator of heath forests, within the Pliocene of the Malay and Thai Basins.

Stauffer (1973) and Hing and Leong (1990) described plant remains in Late Tertiary

coal beds in basins of the Malay Peninsula. Coal at Batu Arang near Kuala Lumpur

contained a forest flora indicating a drier climate than now, or a partly upland source

for the transported material (Stauffer 1973). More recent dating, however, suggested


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that these coals are probably of Eocene to Oligocene age (Ahmad Munif, 1993 in

Hasiah & Abolins 1998). The coal composition of Pliocene–Early Pleistocene (?)

deposits in the Kepong and Kluang-Niyor Basins (Stauffer 1973), and the Merapoh

Basin (Hing & Leong 1990) indicates that these were derived mainly from woody and

herbaceous plants as well as from spore-bearing plants, as would have been found in a

tropical forest dominated by angiosperms and to a lesser extent gymnosperms (Hing &

Leong 1990).

Morley (1999) suggested that Pinus savannah was probably widespread on the Malay

Peninsula at 660 Kya, 480 Kya, 200 Kya, and 22 Kya, while Heaney (1991)

mentioned that pine-grasslands were found near Kuala Lumpur at 160 Kya. All of

these, apart from the 200 Kya time, are periods of low sea-level and presumably drier,

slightly cooler conditions2. During the interstadials the climate in the lowlands of

Peninsular Malaysia was probably as that prevailing today, which is suggested by

pollen found at interglacial deposits dated at ca. 80 Kya and 55 Kya (Kamaludin &

Azmi 1997). Also, finds of peat, wood, laterite, and oxidized iron described by

Stauffer (1973) suggests that during the Pleistocene there were at least several periods

in which perhumid conditions existed, although these finds were not dated and can

therefore not be reliable correlated with any particular glacial or interglacial periods.

Elsewhere, Ayob (1970) provided carbon-dated peat and wood samples from deposits

containing pollen indicating perhumid vegetation; these samples were dated at ca. 36.4

Kya and 41.2+ Kya, indicating that before the LGM an evergreen vegetation type

existed in this area close to present-day Kuala Lumpur. Price et al. (1997) suggested

that bauxite formation on the Malay Peninsula took place continuously from 115 Kya

to the present, which would suggest mostly warm and wet conditions.

Geomorphological research by De Dapper (1985) on landforms in the Malay

Peninsular uplands suggested a shift from dry climatic conditions with a fairly open

vegetation (tree or grass savannah), rather unprotected slopes and braided river

systems (T2-terrace and P2 pediment) to much wetter conditions with slopes well

protected by a dense forest cover (T1-terrace). The T2 surface was locally covered by

2 According to Hantoro (1995), the 480 Kya glacial is part of tge same glacial period and sea-level low as the 450 Kya sea level low mentioned in Table 3.1.

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ashes, which X-ray microanalysis ascribed to the Toba volcano, while the ashes never

occur on T1 surfaces and are even locally covered by the T1 alluvia. The Toba ashes

could either be from explosions at 74 Kya or 30 Kya (see section on Geology and

Palaoegeography of North Sumatra), and the climatic shift probably refers to

conditions during the 80 Kya glacial and the interglacial conditions following it,

although it cannot be excluded that the terraces refer to LGM and post-LGM

conditions.

A combined coastal and offshore survey in the Strait of Malacca between Port

Dickson and Singapore yielded evidence of per-humid climatic conditions in this

region before the sea-level rise following the LGM. Between 50 and 10 Kya, dry land

conditions with peats and mangroves prevailed in most of the southern Malacca Strait,

at times in association with freshwater lakes, as indicated by the presence of diatom

ooze (Geyh et al. 1979). North of 5ºN, Emmel and Curray (1982) found evidence of

deltaic progradation. The upper Pleistocene deposits here consisted of silty clay in

which peat was regularly found, suggesting deposition in calm waters, probably into

vegetated waters or lagoons. Emmel and Curray suggested abundant vegetation in the

emergent Malacca Strait, probably resembling the lowland vegetation of tropical

regions, with mangroves in the low-lying areas and Nipah palm along the banks of

muddy creeks. Tropical rain forest would have covered the higher drier parts of this

area. These conclusions are in contrast with those by de Dapper (1987) who reviewed

arguments against and in favour of drier conditions and more open vegetation types

during the LGM in the Malay Peninsula. Based on geomorphic evidence in the

uplands of the Malay Peninsula he concluded that during the LGM vegetation in these

areas was much more open, and only reverted to tropical rainforest in the Holocene.

Finally, Taylor et al. (2001) investigated cores of sediment from Nee Soon, a peat

swamp in the perimarine zone of Singapore, which yielded a record of environmental

change comprising the LGM and Holocene periods. The evidence indicated the

occurrence of swamp conditions at Nee Soon during the late glacial and early

Holocene and taxa presently associated with highland areas in dryland forest at low

altitude. This would suggest either temperatures substantially lower that those at


98

present and, possibly, humid conditions, or cold, seasonally dry climates and reduced

levels of atmospheric CO2.

In summary, on and around the Malay Peninsula, there appears to be evidence of

alternating phases of open, grassy vegetation types during glacials to closed evergreen

forest during interglacials.

Palaeoenvironments of the South China Sea

Geology and palaeogeography of the South China Sea

The South China Sea, in very broad terms, is that part of the Pacific Ocean generally

west of the Philippines and north and west of Borneo. During the Palaeocene to

Middle Miocene, the South China Sea opened, leading to a southward migration of

mainland Asian continental crust of about 700 kilometres in 25 Mya. This spreading

of the South China Sea carried the present-day areas of Palawan and Mindoro from the

Asian mainland to their present position in the Philippine archipelago (Holloway

1982).

Sundaland, or the Sunda Shelf Plate, is considered to be composed of a mosaic of

continental and oceanic microplates accreted and sutured together in the Late Triassic

(Pulunggono 1985; Cole & Crittenden 1997). Since the Early Tertiary, the Sunda

Shelf plate has generally tilted southward and has been subsiding (Ponto et al. 1988).

This resulted in the development of a large basin in the Gulf of Thailand and the

Sunda Shelf (White & Wing 1978), between the Natuna Ridge, an extension of the

Sunda landmass and the Khorat Con Son Platform, which was part of the Asian

mainland. The eastern part of the basin extends from offshore Vietnam, across

Indonesian and Malaysian waters into Sarawak and Brunei (White & Wing 1978). The

Natuna-Khorat Ridge appears to have had enough local topographic relief to prevent a

marine environment from penetrating the West Natuna Basin until the Middle

Miocene when this sill was breached and a more marine environment developed in the

West Natuna Basin (White & Wing 1978). By the early Middle Miocene, the entire

oceanic crust of the South China Sea appears to have been subducted beneath the

Borneo accreted continental crust, and the continental crust of the South China Sea

Platform collided with Borneo. The more rigid and buoyant continental crust does not

99

bend as much and this resulted in a period of regional uplift and erosion throughout

early Middle Miocene times in the South China Sea area (Tan & Lamy 1990).

The East Natuna Basin and most of the West Natuna Basin indicate Miocene

deposition in deltaic or littoral environments (Wongsosantiko & Wirojudo 1984). The

area west of the Natuna Islands was uplifted during the Miocene and became

temporarily emergent in Late Miocene to Early Pliocene (Holloway 1982). Similarly,

the East Natuna area emerged in the Late Miocene–Early Pliocene, probably as a

result of a sea level lowstand (Martono 2000). Later in the Pliocene open marine muds

once more buried the Natuna Basins (White & Wing 1978). Hall (2002) suggested

uplift of this part of the Sunda Shelf (the area between Borneo, the South Malay block,

and Sumatra, i.e. the Singapore Platform) from about 15 Mya because of the presence

of thick Neogene sediments filling the offshore NW Java basins. This appears to fit

van Bemmelen’s (1970) theory of an emergent Singapore Platform during the

Miocene and Pliocene that supplied sediments to northern Java. Also, Tjia and Liew

(1996 in Hanebuth et al. 2000) claimed that the Singapore Platform was tectonically

stable during the Pliocene and Pleistocene, and may have been emergent during most

of that time. Ben-Avraham and Emery (1973) similarly suggested that after the Early

Miocene, the Singapore Platform, Lampung High, and Karimunjawa Arch were the

main high areas supplying sediments to the surrounding basins. Furthermore,

considering the age of the Anambas–Natuna Arc and the Riau-Bangka Arc, these must

have been much higher and wider in earlier times (Inger & Voris 2001), possibly

providing mountainous corridors. During Pleistocene low sea-level stands, these arcs

protruded 750–1,000 m above the surrounding flatlands, trapping moisture on one side

and creating a rain shadow on the other.

Hall (in litt., 20 March 2000 and 12 November 2001; 2002) remarked that on the

Sunda Shelf generally marine conditions come in the Late Miocene (later to the NW

and earlier to the NE) and may be as late as Pliocene, while at the same time global

sea-level was falling. Preceding this marine transgression, there was probably a

tectonic subsidence event, since there is a major unconformity in this area, not seen

further north in the Gulf of Thailand. The result of this event was to remove about


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2,000 m of strata in the Malay Basin, and further south, the ridge connecting Borneo

and the Malay Peninsula has only Quaternary strata resting directly on basement.

Isaacs (1963) reported on a minor sedimentary basin about 80 km west of the

Tambelan Islands (west of Borneo), which reached a depth of ca. 700 m below sea-

level. This area is probably where Borneo and the Malay Penisula were first separated;

considering the amount of sediment, it may have remained submerged during most of

the Quaternary. This basin which has become filled with sediments can tentatively be

followed further south towards the islands of Tujuh, Karimata, and Bangka. Aleva et

al. (1973) reported on a Miocene–Pliocene sedimentary cover, with a thickness of

over 100 m in some areas; on top of this they found a sequence of sedimentary layers

and erosional surfaces. Only one of these erosional surfaces, the Red Clay Formation,

clearly developed when the area became emergent, which, according to Aleva et al.,

happened during the LGM. An older terrestrial deposit also existed, the Alluvial

Complex, which may have been deposited during the Late Pliocene sea-level lowstand

(but see discussion on the age of the Alluvial Complex in the section on

Palaeoenvironments of the Malay Peninsula). It consisted of valleys and depressions,

which deeply incise the Older Sedimentary Cover (which Aleva and colleagues

considered to be of Late Tertiary age). The occurrence of peat layers and the

alternation of deep incisions of valleys with thinly stratified sedimentation indicate

frequent vertical oscillation in relation to the sea-level (Aleva et al. 1973). Aleva et al.

mentioned that the pollen content of the Alluvial Complex and the Older Sedimentary

Cover are rather similar, and that the latter had been dated as Miocene–Pliocene.

The above information suggests that the opening-up of the land between Borneo and

the Malay Peninsula started in the north, possible in relation to the deepening of the

Malay Basin. A sea inlet developed west of the Tambelan Islands, which moved south

towards the Karimata, Bangka, and Belitung Islands. This presumably happened

during the Pliocene. The data suggest that this sea inlet reached the Java Sea at the

time when the Older Sedimentary Cover was deposited (Miocene–Pliocene according

to Aleva et al., but possibly younger). This first sea connection between the South

China and Java Seas probably closed again during a major sea-level lowstand,

possibly the one at 2.4 Mya, as evidenced by the Alluvial Complex. The area once

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more became inundated, presumably separating Borneo from Malaya and Sumatra,

and then re-emerged during the LGM.

Molengraaff and Weber (1920) and Verstappen (1975) hypothesized that during

Pleistocene low sea-levels the rivers of west Borneo and SE Sumatra formed part of

one river system, the North Sunda River. Two other rivers emptied into the present

day South China Sea: the Mekong, and the Chao Phraya and tributaries collected

south to the tip of peninsular Malaysia. The drainage of the present day Java Sea was

eastward and a ridge along the islands of Bangka-Belitung-Karimata separated this

system from those to the north (Verstappen 1975). During the Late Pleistocene glacial,

Sumatra’s rivers flowed into a number of major river systems. The flowage between

the Malay Peninsula and Sumatra had as tributaries the north-eastern Sumatran rivers,

such as the Simpang Kanan, Panai, Rokan and Siak, and also several large rivers from

the west of the Malay Peninsula, i.e. the Perak, Bernam, Muar and Lenek Rivers

(Voris 2000) (note that according to Scrivenor 1931, the Pahang River flowed until

recently through the Tasek Bera area and the present Muar River to debouch into the

Malacca Straits). Further south along the Sumatran coast the Indragiri, Hari and Musi

joined the river systems from West Borneo to form the North Sunda River System or

Molengraaff River (also see Wyrtki 1961). Judging from the 120 m sea-depth contour,

the mouth of this river would have been at approximately E 109.60 and N 5.11,

between the northern and southern Natuna Island groups. In between these two river

systems, a third river system existed according to Voris (2000), which drained the

present Kampar River (running through the Singapore Straits) and was joined by the

Johore River before flowing into the large river system from the Gulf of Thailand.

These rivers all disappeared when the shelf area became inundated once more.

Pelejero et al. (1999a) found evidence for the beginning of the inundation of the Sunda

Self at 14.9 Kya, although this could also have happened at 13 Kya, as suggested by

Broecker et al. (1988). A reconstruction of this inundation suggests that at the

beginning of the deglaciation the position of the Molengraaff River mouth remained

unchanged during the first small step in sea-level rise, due to the morphology of the

shelf break. It is not until 15–13.5 Kya that a fundamental change occurred in the

oceanographic setting of the southern South China Sea, when the Sundashelf was


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flooded across the threshold depth of –70 m. At this time, the river mouth was rapidly

displaced landward by more than 200 m/year. The last stage of the flooding and

submergence of Sundaland was accomplished at about 10 Kya, when the 30 m depth

of the present Karimata Strait was reached (Pelejero et al. 1999b). This is in line with

the findings by Wang et al. (1994) who suggested that the gateway between the Java

and South China Seas (sill depth 36 m) opened at about 10.5 Kya.

Vegetation of the exposed South China Sea area

Land exposure on the Sunda Shelf was often linked to drier and colder climates, and

possibly increased seasonality (Verstappen 1975, 1980, 1997; Gupta et al. 1987;

Stuijts et al. 1988; Thorp et al. 1990; Thomas et al. 1999). Some authors have

therefore suggested that the land connection between Borneo, Sumatra, Java and the

mainland was covered in savannah-type vegetation (Muller 1975; Morley 1981;

Morley & Flenley 1987; Broecker et al. 1988; Caratini & Tissot 1988; Heaney 1991),

although monsoon forest (Morley, pers. comm., in Whitmore 1981; Whitten et al.

1996; Adams & Faure 1997; Taylor et al. 1999) has also been suggested. Adams and

Faure (1997) and Chappell and Thom (1977) suggested that, at least in the final glacial

stages of the Pleistocene, rainforest colonisation rates may have been insufficient for

rainforest to recolonize the exposed land between Java, Sumatra, and Borneo, because

of the brackish soils left behind as the sea retreated. Here, I investigate the evidence

for drier, more open vegetation types on the exposed Sunda Shelf.

Based on pollen data Morley (1978, in Morley & Flenley 1987) suggested that in the

Early Miocene, Late Miocene and Pliocene, much of the South China Sea (SCS)

experienced a strongly seasonal climate. Earliest Miocene palynomorph assemblages

from the Natuna and Malay basins are thought to reflect drier climates than those in

the Late Oligocene, due to the common occurrence of Gramineae, and the low

representation of fern spores and spores characterizing peat swamps. Interestingly,

pollen, comparable to that of Shorea and Hopea, was common, which suggests that

low diversity Dipterocarp monsoon forests must have been widespread at this time.

When sea-levels rose and land became submerged at approximately 20 Mya, this

association disappeared (Morley 2000). The common occurrence of temperate

conifers, such as Abies, Picea and Tsuga in north Borneo, the Natuna and Malay

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basins and Indochina, probably relates to cooler climatic conditions in the low

latitudes in Late Oligocene and Early Miocene (Morley 2000). Further north, on the

northern Sunda Shelf, the Pliocene is characterised by the presence of abundant pollen

of the conifer Dacrydium and pollen of the Polystachyus type, which indicates either

montane environments, or heath forest, especially where there is impeded drainage,

with or without peat formation (Morley 1977, 1999). No further data were found on

the Pliocene–Middle Pleistocene environments of the southern SCS.

Pelejero et al. (1999a) modelled the Middle–Late Pleistocene climate of the SCS area

by looking at a wide range of biomarkers. They found that sea surface temperatures in

this shallow enclosed system showed much more variation between glacial and

interglacial times than open ocean areas at the same latitude. For instance, the

difference in SCS temperature between present-day times and the LGM is 2.8 ºC,

whereas elsewhere this difference varies between 1.3 and 1.8 ºC. During the LGM, sea

surface temperatures in the SCS were down to 25 ºC. Further climatic events

suggested by the results of Pelejero et al’s (1999a) research include the following: 1.

at 19.5 Kya a period of extreme precipitation and river run off; 2. a very warm period

between 127 and 116 Kya, with sea surface temperatures between 28.7 and 29.9 ºC (as

opposed to present-day 28 ºC) and sea-levels at 6 m higher than present-day levels

(also see below); and 3. two periods dated at 29–28 Kya and 37.7– 43.2 Kya that were

characterised by extreme tropical precipitation and enhanced summer monsoon

activity.

Pollen spectra from the southern SCS indicate that during the last glaciation, the

lowland was covered by tropical lowland rainforest, and mangroves grew along the

river mouths and along the coasts. The periodic expansion of montane gymnosperms

implies falling temperature, at least on the mountains of surrounding islands, but no

desiccation was found during the glacial period (Sun et al. 2000). There is further

support for the maintenance of high rainfall and rainforest in the southern part of the

SCS. Pollen data from peat sediments taken from the Pulau Tujuh area, southeastern

Sumatra, strongly suggests rainforest or peat swamp forest vegetation during the

LGM. Pandanus is common, while values for Cyperaceae are low and Poaceae occurs

at a low percentage. In 4 samples, there are significant percentages of Rhizophoraceae


104

suggesting increased proximity of mangroves (van der Kaars, unpubl. data in Kershaw

et al. 2001). Also Kawamura (1998) found Late Pleistocene to Holocene pollen on the

Sunda Shelf suggesting the presence of mangroves (with Sonneratia and Rhizophora),

while also Pinus pollen was detected. Unfortunately, the exact location and age of the

sediments cannot be determined from the paper’s abstract.

In the northern South China Sea, high levels of the herb Artemisia may indicate that

during the LGM at least parts of the exposed continental shelf of the northern South

China Sea was occupied by grassland, dominated by this species. This would indicate

an annual precipitation of between 300 and 500 mm and an average July temperature

of around 15–24 ºC (Sun & Li 1999; Sun et al. 2000). Interestingly these data suggest

that in the northern part of the South China Sea frequent changes occurred in the

character of the exposed shelf vegetation during glacial times (Sun & Li 1999; Sun et

al. 2000). These changes were mostly from a relatively cool and humid climate to

more drier and/or temperate conditions. During the drier and temperate conditions the

shelf was covered by Artemisia, while other species indicate the presence of swamps

or wetlands scattered on the shelf. Similar cycles were detected by Li (1997, in Sun &

Li 1999) in the southern part of the South China Sea (at 6º10’N, 112º13’E), where the

pollen diagram shows alternative predominance of upper montane rain forest and of

lowland rain forest with mangrove. Meijaard (2003, also see Appendix 1) provided

further information on Late Pleistocene environments of the SCS area.

105

Palaeoenvironments of southern mainland Asia

Geology and palaeogeography of southern mainland Asia

Thailand is located on what is considered to be a stable land area compared to adjacent

regions in SE Asia (Dheeradilok 1995). The western coast of the Thai Peninsula has,

however, been affected by crustal movement. The distinctive coastal landform with

steep cliffs and short but steep-gradient river courses suggest uplift. This uplift

resulted in the emergence of thick Tertiary coal beds and associated terrestrial fossils

(Dheeradilok 1995). During the Oligocene and Miocene the ca. 30 intermontane

basins of mainland Thailand and the Gulf of Thailand were occupied for long periods

by lakes, as indicated by extensive lacustrine (or fluvio-lacustrine) deposits. By the

end of the Miocene, many of these lakes were replaced by a fluviatile, erosional

regime similar to that of the present time (Roberts & Jumnongthai 1999).

Figure 3.13. Main geological features of Indochina (after Steinshouer et al. 1997); for legend see Fig. 3.5.

The Quaternary deposits of the Lower Central Plain of Central Thailand represent a

complex sequence of alluvial, fluvial, and deltaic sediments. About 2,000 m of


106

Pleistocene and Holocene sediments were deposited in the basin, of which only the

uppermost 300 are known (Sinsakul 2000). In the Late Pleistocene, the sea

transgressed over the Lower Central Plain beyond Uthai Thani, and subsequently

receded during the last glacial period (Dheeradilok 1995). There seems little doubt

that high sea-levels occurred in Thailand during the Mid Holocene (ca 6 Kya) and that

it reached as far land inward as 70 km north of Bangkok (Dheeradilok 1995;

Woodroffe 2000).

South of the Lower Central Plain, the Gulf of Thailand is a shallow epicontinental sea

(maximum depth 86 m) that separates the Thai-Malay Peninsula to the west from the

Indochina massif to the east. It is composed of a series of north-south trending ridges,

which separate 12 major basins (Fig 3.13). These basins are divided by the Kro Kra

Ridge into the Westerns Graben Area that contains 10 basins, and the Eastern Graben

Area that contains the Pattani and Malay Basins (Watcharanantakul & Morley 2000).

The Pattani Basin was probably temporarily emergent at 14 Mya due to low sea-

levels; tectonic uplift at 5 Mya, however, did not lead to its emergence (Pigott &

Sattayarak 1993). Sedimentary units in the Thai basins are identical to those found in

the Western Malay Basin (Metivier & Gaudemer 1999). In Oligocene–Early Miocene

times, depositional sequences in the Pattani Basin are dominated by continental

lacustrine, fluvial, and delta plain deposits. After this, marginal marine and fluvial

deposits show increasing marine influence towards the Malay Basin, although

according to Martens et al. (2000) fluviatile sedimentation in the Pattani Basin

continued into the Pliocene. Tertiary sedimentary fill in the Gulf of Thailand

(predominantly Neogene) varies in thickness from about 8,000 m in the deepest parts

of the basins to less than 300 m over some of the basement highs (Highton et al.

1997). The Middle Miocene unconformity represents the onset of a regional marine

transgression in the Malay Basin and a return to the delta plain environments during

the Late Miocene in the Pattani Basin (Watcharanantakul & Morley 2000). Another

unconformity at 10 Mya may have some tectonic significance, as it seems to mark the

end of a major inversion in the Malay and W. Natuna Basins. However, it also

coincided with a major sea-level low stand. Several million years may be absent in

this unconformity (Morley et al. 2001). The Gulf of Thailand environment from the

Late Miocene to recent was described as ‘flood plains with more mangrove swamp

107

and marine deposits in the upper part (Lian and Bradley, 1986 in Watcharanantakul &

Morley 2000). During the Pliocene and Pleistocene, in the northern part of the Gulf

near Bangkok, there were at least three major breaks in deposits, probably associated

with sea-level changes. The first of these was deposited when the sea transgressed in

the Pliocene (Dheeradilok & Kaewyana 1986).

The thin sedimentary cover on the basement highs of the Gulf of Thailand (as little as

300 m) (Highton et al. 1997) suggests that these structures would have been emergent

thoughout most of the Pleistocene and possibly Pliocene. If the Kro Kra Ridge was

one of these structures, it would effectively divide the Gulf of Thailand into two seas.

Also, the Ko Phangan Ridge (see Pigott & Sattayarak 1993), would add to the

watershed division in the Gulf of Thailand. Between these two ridges lies the 250 km

long and 50 km wide Kra Basin, which received more than 2.5 km of predominantly

lacustrine Tertiary sediments (Pigott & Sattayarak 1993). These distinct valleys are

also mentioned by Sawamura and Laming (1974), who recognized three sea floor

valleys in the northern part of the Gulf of Thailand. My investigation of bathymetric

maps (Hydrographic Department of Thailand 1978) showed that the most eastern

valley, which appears to connect with the present Chao Phraya River, closely follows

the eastern shore of the Gulf of Thailand. The western valley is less clearly defined,

but seems to closely follow the western shore of the Gulf, thereby diverging from the

eastern valley. The two seem to be separated by a shallower area, which could

coincide with the Kro Kra Ridge as described by Watcharanantakul and Morley

(2000) and Highton et al. (1997). It would be interesting to know whether the western

river at an earlier time could have flowed west of the Kro Kra Ridge, across the low

part of the Malay Peninsula near Krabi into the Andaman Sea. The ‘ridge’ can be

followed to ± N 11°20’ E 110°45’. The question is whether the two valleys and

associated rivers would have merged downstream or whether they stayed separated

during periods of low sea-level. In the latter case it becomes conceivable that the

western river system would have crossed the present-day Malay/Thai Peninsula and

flowed into the Indian Ocean. There is some support for this model. Garson et al.

(1975) describe the Tertiary Krabi Series in the lowland areas north of Krabi. These

deposits appear to fill shallow marine or lacustrine basins in a Tertiary landscape, and

primarily lie unconformably on and between limestone sediments. The Krabi Series


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seem to consist primarily of deposits, which were tentatively dated at Middle-Tertiary

or later. Ducrocq et al. (1995) estimated mammal fossil in these deposits to be of Late

Eocene age, but considering that such fossils would most likely be found in lacustrine

environments, it could well be that later marine deposits occur in the same Tertiary

series. Interestingly, Garson and colleagues stated that the land area of the present-day

Phangnga Bay was submerged in the Late Tertiary or Quaternary due to a relative sea-

level rise, while also on Phuket Island small areas of marine sediments suggest that

high eustatic sea-levels once inundated a much larger area than today. Overall, it

therefore seems likely that this whole land area between Surat Thani and Krabi was

low-lying during the Late Tertiary and Quaternary and that during periods of high sea-

levels at least parts became submerged. Whether this led to the development of a

complete sea strait cutting the Thai-Malay Peninsula into two halves remains unclear,

while there is also further need for supporting evidence regarding a river that flowed

from central Thailand, west of the Koh Kra Ridge, past Surat Thani and into the

Indian Ocean near Krabi.

Of great importance to the biogeography of non-volant, terrestrial species in Indochina

and China are the three main rivers, the Salween, Mekong, and Yangtze. The changes

in these river courses and their effect on the region’s biogeography were described by

Meijaard and Groves (in press-b) (see Appendix 6). This river flow model is

supported by river sedimentation calculations by Métivier and Gaudemer (1999). They

found that sedimentation in all SE Asian rivers, apart from the Mekong, Red River,

and Chao Phraya has remained constant during the Quaternary. In the case of the

Mekong River, the present-day load is much larger than the average filling rate over

the last 2 Myr. Métivier and Gaudemer suggest that the Mekong River discharged into

the Gulf of Thailand or the Malay Basin before shifting its course to the Mekong

Basin. There does, however, not seem to be much support for a direct connection

between the Salween and Chao Phraya Rivers, as suggested by Attwood and Johnston

(see above). For further discussion of this see Appendix 6.

Vegetation of southern mainland Asia

Toward the end of the Early Miocene, rising global temperatures and sea-levels

corresponded with a change to predominantly moist forests in Indochina, and tropical

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and paratropical rain forests became established beyond the tropics. From this time,

Dipterocarpaceae became prominent in Thailand (Watanasak, 1990 in Morley 2000)

and alternating wet and dry climates were characteristic of Vietnam (Dzanh, 1994 in

Morley 2000). Palynological study of coal deposits in northern Thailand confirms this

change from a more temperate climate in the Oligocene to more tropical conditions in

the Miocene. Between the Early and Middle Miocene these deposits suggest a mixed

environment of lakes and forest swamps, with Pinus and Florschuetzia trilobata

possibly indicating some seasonality (although coal formation would suggest mostly

everwet conditions) (for detail see Figure 1 in Ratanasthien et al. 1999). Similarly,

palynological studies of coals in the Krabi Basin, southern Thailand, suggest wet

conditions and also proximity to mangroves (Watanasak et al. 1995). The Middle

Miocene vegetation of the Pong area in eastern Thailand suggests a bushy mangrove

environment (Vozenin-Serra et al. 1989), which would indicate that the coast was

considerably further inland than today. However, Ducrocq et al. (1994) reported that

neither the vertebrate, nor invertebrate fossils indicate a mangrove environment during

the Middle Miocene in the named area. Instead, they suggested that between 16 and

14 Mya, a stable palaeoenvironment existed, with wet and warm characteristics.

Cenograms3 of the Middle Miocene faunas suggest a quite open habitat, or possibly

small areas of forest intermixed with grassland. These faunal structures indicate a

tropical climate characterized by an alternation of dry and rainy seasons. The

cenograms exclude the possibility of environments dominated by either closed forest

or steppe (Ducrocq et al. 1994). The Miocene palaeoenvironments, further south in the

Pattani Basin consisted of low-lying swamps (in a subsiding basin) dissected by rivers

(Jardine 1997).

Based on an ecological shift from C3 to C4-dominated vegetation types in central Asia,

Quade et al. (1989) described major climatic changes that occurred towards the end of

the Miocene (C3 plants include all trees, shrubs and herbs, and grasses favoured by a

cool growing season, whereas C4 plants include grasses favoured by a warm growing

season). From at least 18 until 7.4–7.0 Mya, the northern Pakistan floodplain was

dominated by closed canopy forest, with or without an understory of C3 shrubs and

3 Cenograms are graphs of body weight frequencies, which, for mammals, may give some indication of the kind of vegetation type in which a community occurred.


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herbs, while early Middle Miocene (16 Myr) Siwalik deposits in Himachal Pradesh

clearly indicate the presence of evergreen tropical rainforest of Malesian affinity

(Morley 2000). Towards the end of the Miocene, evergreen forest still existed in

Nepal, but after that time they were gradually replaced by deciduous forests (Morley

2000). Similarly, coal-bearing sediments in northern Vietnam considered to be of Late

Miocene age are indicative of a humid, subtropical climate (Covert et al. 2001).

Between 7.4–7.0 Myr and 5 Myr, a vegetation mosaic of grasslands and forest was

probably present in the Himalayan foothills (Quade et al. 1989; Awasthi, 1992 in R.J.

Morley 2000). After 5.0 Mya, up until 0.4 Mya, grasses by far dominated the

vegetation, possibly interspersed with riparian habitats in which some C3 trees and

shrubs grew. Drier Pliocene climates in Rajasthan are shown by the presence of fossil

woods, which indicate deciduous forest at that time (Guleria, 1992 in Morley 2000).

Elsewhere, palaeobotanical data from India and from Myanmar indicate that a rich

tropical to subtropical vegetation covered the region ca. 5 Mya under a prevailing

warm humid climate (several authors in Poole & Davies 2001). However, during the

Pliocene, the increasingly arid climate, engendered by the rising Himalayas, caused a

consequent change in the vegetation of this region (Poole & Davies 2001). During the

Pliocene, an alpine flora would have occupied the higher ranges of the Himalayas and

the plateaux of Yunnan and North Burma, while during the cold stages of the

Pleistocene, these areas were covered by glaciers (Kingdon Ward 1939). Quade et al.

(1989) speculated on the cause of the vegetation change around 7.4 Mya, as it remains

unclear whether this happened due to climatic changes or because of the evolutionary

first appearance of C4 plants. They do, however, suggest that a strong intensification

of the monsoon system at 7.4–7.0 Mya played an important role. The vegetation

changes are also reflected in faunal turnovers: browsers are replaced by grazers;

rodents show considerable turn-over; and Sivapithecus (a possible ancestor of the

Orang-utan) disappears from the record (Barry et al. 1985; Quade et al. 1989; 1991;

2002). These palaeoenvironmental changes are also reflected in north Thailand, where

the Li Basin contains Oligocene and Early Miocene coal (C.K. Morley et al. 2000),

indicating a wet and warm, fluvial or lacustrine environment. Coals in Middle

Miocene sediments still indicate a peat swamp, fluvial or lacustrine environment, but

in the Late Miocene, Pliocene and Quaternary sediments no coal was found (C.K.

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Morley et al. 2000), possibly indicating a climate that was either too cool or dry for

coal formation.

Mammalian fossil assemblages in Yunnan Province (also see Chapter 4.1) indicate

that between Early and Middle Pliocene a mixed forest, and open bush-grassland

vegetation existed, with several carnivores typical of forested areas, and ungulate

species suggesting more open, grassy vegetation (Pan 1993). Slightly wetter

conditions seem to have prevailed further east and southeast of Yunnan.

Reconstructions of the climate and vegetation of this area in the Middle Pliocene (3

Mya) indicate that there was a considerable expansion of evergreen forest in southern

China, whereas Indochina was mostly covered by rainforest, possibly with patches of

deciduous forest in the area of present-day Burma (Dowsett et al. 1994).

Based on rodent fossils distributions, Chaimanee (1998) reconstructed Late Pliocene–

Early Pleistocene palaeoenvironments for several locations in Thailand. Khao

Samngam (99°42’ E; 13°27’ N) probably had an environment with some mixed

vegetation with grasslands in the floodplain and forests on the surrounding limestone

hills. At 1.96–1.79 Myr, Longgupo, in South China, 15° latitude north of Khao

Samngam had a forest community, but of different vegetation composition than that in

Thailand. Early Pleistocene–early Middle Pleistocene fossil communities indicate a

typical forest faunal assemblage, probably of a dry evergreen type with some open

patches. At this time, the boundary between the Indochinese and Sundaic faunistic

subregions may have been about 500 km south of the present Kra boundary [Note that

this line further south would approximately have been in the same location as the

Kangar-Pattani floristic boundary (Whitmore 1984), which separates Indochina from

Malesia]. This situation occurs also in some more recent, probably Middle

Pleistocene, localities from Peninsular Thailand, when several Sundaic endemic taxa

moved north, with some typical Indochinese forms moving south. Chaimanee (1998)

suggested that these localities (at 8°27’ N) are indicative of dense evergreen forest

with no indication of grassland, and they probably correspond to an interglacial stage

of the earliest part of the Middle Pleistocene. The Snake Cave deposits in northeast

Thailand (16°30’ N; 101°49’ E), which were dated as middle–late Middle Pleistocene

(minimum age 169 Kyr), suggest cooler climatic conditions than today, probably with


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dry evergreen forest with some clearings with grasses or bamboo. The present-day

vegetation in this area is dense evergreen forest (F. Blasco, pers. comm. in Chaimanee

1998).

According to Dongsheng and Menglin (1984), Indochina and southern China were

still covered by humid rainforest at the Pliocene-Pleistocene boundary, although this

rainforest zone was progressively pushed south during the Pleistocene until no

rainforest remained in China. By the Middle Pleistocene, the subtropical and tropical

zones had shifted south- and eastward, and by the Late Pleistocene, these zones had

migrated even farther southward and were considerable reduced in area (Jablonski &

Whitfort 1999). Evidence for grasslands is very limited through most of the Pliocene,

but subsequently shows a marked increase, together with charred grass cuticle, during

the Early Pleistocene, indicating the expansion of savannah vegetation, which was

subject to burning (Morley 1999). Thick laterites of Pliocene–Early Pleistocene age in

the Lower Central Plain of Thailand (Thiramongkol 1986) may also indicate

seasonality in a generally humid tropical climate (Whittow 1984). In Yunnan

Province, towards the Late Pliocene, the fossil assemblages indicate a forest and

woodland environment, while also appearing to reflect a period of rapid faunal and

environmental change. In the Early Pleistocene, the fauna indicates a more open,

grassland-bush environment, whilst pollen analysis suggests a fairly cool subtropical

climate. Finally, towards the end of the Pleistocene most likely a grassland-dominated

environment existed (Pan 1993).

The Middle–Late Pleistocene in the eastern parts of SE Asia led to some considerable

changes in vegetation distribution. For instance, Zheng and Lei (1999) provide

palaeoenvironmental data for the Leizhou Peninsula, north of Hainan Island, for the

last 400 Kyr. Between 400 and 340 Kya, pollen data indicate slightly drier and cooler

conditions compared to today with an increase of montane forest formation. Between

340 and 280 Kya this was replaced by a wetter and warmer climate with predominant

evergreen oak forest. Between 280 and 240 Kya, mean annual temperatures were more

than 4ºC lower than today, which led to a substantial increase in typical montane

conifer forest elements. Between 240 and 180 Kya, significant warming occurred and

montane elements were replaced by fagaceous evergreen forest, while tropical

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lowland rainforest taxa increased significantly. Between 180 and 125 Kya, vegetation

changes in tropical China were less drastic and only the coldest glacial stadials

affected the local forest. The inter-glacial stage between 125 and 65 Kya, was

accompanied by a warmer climate and dense forest, which, between 65 and 29 Kya,

was followed by a drop in temperature of between 5 and 6ºC. The period between 29

and 15 Kya was the first during the whole study period in which the Pleistocene dense

forests were transformed to grassland or savanna vegetation. Furthermore, the

dominance of Poaceae and Artemisia implies not only a cooler, but also a much drier

climate. After 15 Kya the pollen assemblage shows the resurgence of montane forest,

and the disappearance of savanna formation (Zheng & Lei 1999). Zheng and Lei

(1999) also found that a fundamental change from densely forested formation to

savanna did not occur until the LGM. The replacement by grassland in southeastern

China during the LGM could be a result of extremely dry conditions caused by the

increased continentality in southern China and SE Asia, the reduction of the South

China Sea, as well as the lowering of sea surface temperatures. As Zheng and Lei

showed that precipitation during earlier glacial-interglacial cycles may have been very

stable, and that even during the cooler period wet conditions prevailed, it can be

hypothesized that the South China Sea area did not become subaerial in any other

periods during the last 400 Kyr. Only, during the LGM did the exposure of the South

China Sea area lead to both dry and cold conditions, which caused forest formations to

change to savanna.

Ferguson (1993) reviewed the Late Pleistocene environmental changes for south and

southwest China. Judging from the vegetational changes in the Late Pleistocene cold

phases, the mean annual temperature in south and southwest China was normally no

more than 2–3°C lower than at present (Luo, 1991c; Tong and Shao, 1991; Wu, 1991,

all in Ferguson 1993). Probably the only exception was the extremely cold and arid

phase at the end of the Pleistocene (20–15 Kyr). At that time, the vegetation in the

extreme south of China (21–23 °N) resembled that now growing in the Changjiang

region, indicating a fall in the mean temperature by some 6°C. In the interstadials,

warm temperate taxa were replaced by tropical elements. In Jiangxi Province, central-

southeast China, the Late Pleistocene climate (between 12.8 and 10.5 Kya) was

similarly drier and cooler than today’s, and the subtropical, mixed deciduous-


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evergreen broad-leaved forest, which is now in the area, was reduced and herbaceous

cover expanded (Jiang & Piperno 1999). Data by Liu et al. (1986) suggested that

Yunnan, at a time approaching or including the LGM (ca. 36–20 Kyr), experienced

greater winter humidity and rainfall, while mean annual temperatures were only

slightly, if at all, lower than present. Yunnan may therefore have represented a

Chinese tropical refugium. Other such extensions of the tropical belt in China during

the LGM were suggested for Guangxi and Guangdong, although this remains

contested (see Ferguson 1993).

Overall, mainland SE Asia appears to have been cooler and more seasonal than today

during much of the Late Pleistocene. For instance, between 62 and 28 Kya and

between 28 and 19 Kya, the reworking and redeposition of aeolian sands along the

southeastern Vietnam coast points to reduced vegetation cover and landscape

instability in this area (Murray-Wallace et al. 2002). Also, Nutalaya et al. (1986)

described loess deposits in the Khon Kaen district near the Mun River and also in

North Thailand. Again, these indicate dry climates and devegetation, which possibly

occurred during the LGM and/or the penultimate glaciation at 130 Kya. Further to the

north in north-east Thailand (17 °N, 103 °E), the pollen assemblages in the Late

Pleistocene/Early Holocene (16–10 Kya) suggest xeric, species poor, and strongly

seasonal vegetation, with seasonally inundated floodplains or stream margins

(Kealhofer & Penny 1998). Follow-up work by Penny (2001) described

palaeoenvironments from the same region in north-east Thailand from 40 Kya.

Between 40 and 10 Kya the vegetation in this area, consisting of Fagaceous-

Coniferous forest, is remarkably stable, with clear evidence of lower temperatures and

possible geomorphic evidence of significant drying in that region. At the start of the

Holocene, at ca. 12 Kya, a rapid transition occurred from the pine/oak forests to

tropical broad-leaf taxa.

Finally, after the LGM, climatic conditions rapidly improved in much of SE Asia. In

Thailand, along the eastern coast of the peninsula, peat deposits and lateritic layers

that were dated as post-LGM, but before 9–12 Kya, suggest a warm and wet climate in

that period (Dheeradilok 1995). Meanwhile, in eastern Cambodia, the climate was still

relatively cool and dry at 9.3 Kya with vegetation being at least partly semi-evergreen,

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but of a drier type than present. Also, open forest with grasses was common at this

time. At ca. 8.4 Kya grasses disappeared, and other signs indicate an abrupt transition

to a warmer, more humid climate (Maxwell 2001). This resembles patterns described

for Sichuan and, possibly, Yunnan (Sun et al., 1986; Li and Liu, 1988; Jarvis, 1993,

all in Maxwell 2001), although the dry late glacial period may have lasted longer in

Indochina than in southwest China. A possible reason for this may have been that the

source of Indochina’s monsoon precipitation lies in the Gulf of Thailand, which even

by 8 Kya was still 20 m lower than today, and large areas were therefore still dry. At

ca. 5.3 Kya, changes in pollen indicate a climatic shift to drier conditions, which

lasted until ca. 2.5 Kya with a recovery of the monsoonal strength.

The Palaeogeography of Sulawesi, Nusa Tenggara, and the Philippines

Zoogeographic evolution in island SE Asia cannot be investigated without observing

the environmental and geological changes that have occurred in Sulawesi, the lesser

Sundas, and the Philippines. Many mammalian taxa now found in the latter areas are

closely related to Sundaland forms, although it still remains largely unclear how they

migrated between those areas. The Borneo-Palawan-Calamian-Mindoro link seems to

have been one migration route, while another one may have followed the Sulu

Archipelago, connecting Borneo and Mindanao. It remains unclear whether mammals

also migrated from north Sulawesi, across the Sangihe Islands to Mindanao. The

biogeography of these areas is outside the scope of this thesis, but some aspects will

be highlighted below, as they are important to the discussion of some species groups

studied here, e.g. the Sus barbatus group (Appendix 8), mouse-deer (Tragulus sp.,

Appendix 5), and Cervinae (Appendix 7).

One of the key questions regarding mammalian biogeography in Sulawesi is whether

at any time in the Late Tertiary or Quaternary there was a land connection between

this island and Sundaland. Groves (1976) suggested that Sulawesi and Java were once

connected, as did Hooijer (1975) who postulated the existence of what he named

Stegoland. A similar idea was proposed by P. and F. Sarasin (in Weber 1902) who

followed and measured a ridge from Madura to the Kangean and Sabalana Islands, and

on to the southern-western tip of Sulawesi, and suggested that this once provided a

land link between Java and Sulawesi. More recent data, however, suggest that


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Sulawesi has had no land connections with either Java or Borneo since the Eocene. It

is indeed now generally accepted that in the Middle Eocene, the southwest arm of

Sulawesi formed part of a low-lying swampy area along the south-eastern margin of

Sundaland. Part of this arm became submerged from the Late Eocene to Middle

Miocene, but the presence of a continuous pollen record in clastic sediments indicates

that some areas remained emergent when the arm drifted away from Sundaland,

during the opening of the Makassar Straits (Morley 2000). The north arm of Sulawesi

was nearly in its present-day orientation by the end of the Early Miocene (Lee &

Lawver 1995), while East and West Sulawesi collided sometime during the Middle

Miocene (Audley-Charles et al., 1988 in Lee & Lawver 1995).

Wilson and Moss’ (1999) suggestion that western Sulawesi was connected to Borneo

and emergent up until the Eocene cannot explain the presence of recent Sulawesi

faunas. They do, however, suggest that island hopping routes may have existed along

volcanic arcs, such as the long-lived arc along the north arm of Sulawesi and the

Cagayan and Sangihe arcs, and later along the younger Sulu arc. Furthermore, they

concluded that the uplift and subsequent erosion of Borneo from the Late Oligocene to

the present day and the emergence of more extensive land areas in Sulawesi led to the

progressive reduction in width of the Makassar Straits. This may have facilitated

interchange of biota in the Late Tertiary, especially during times of low sea-level.

Data provided by Guntoro (1999) suggested that the Straits were at their shallowest

during the Early Miocene, and between mid-Miocene and recent times as then shallow

marine limestones were deposited. Also, Pulau Laut was once much larger (see

Borneo section) providing another stepping stone between Borneo and Sulawesi.

The age of the volcanic islands in the inner Banda Arc (consisting of the islands in a

chain along Bali, Lombok, Sumbawa, Flores and Banda) is not known accurately, but

Burrett et al. (in Schmitt et al. 1995) indicated that they are post-Miocene, and some

(e.g. Bali) may be only about 3 Myr old. Similarly, Lombok and Sumbawa were

elevated only in the relatively recent past (Hall 2002). Komodo is the exception

among the mainly Tertiary volcanic islands, with a history dating back to the Late

Mesozoic (Auffenberg, 1980 in Monk et al. 1997). At one time, Flores was also

thought to be a geologically old island that existed before the Miocene, but it is now

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thought to have its origins in the Mio-Pliocene (Monk et al. 1997). Table 3.2 shows

the time since several of the islands of Nusa Tenggara have been last emergent,

although it should be realized that many of these islands have complex histories and

may have been emergent and subsequently submerged before their latest emergence.

They could therefore have provided stepping-stones for dispersing species (Monk et

al. 1997).

The exact geographical arrangements of the land masses during the Pleistocene glacial

maxima are uncertain, partly because the available bathymetric maps lack detail

(Schmitt et al. 1995). Heaney (1991, in Schmitt et al. 1995) estimated that, during

periods of low sea-level, the present islands formed six islands: Greater Sumbawa

(Lombok, Sumbawa and Moyo); Sangeang; Greater Flores (Komodo, Flores,

Adonara, and Lembata); Pantar; Alor; and Sumba. There may, however, have been

additional ridges connecting some of these islands (Schmitt et al. 1995).

Island Age or epoch of emergence Sumbawa Plio-Pleistocene Atauro Pliocene Sumba 1 Mya Timor Quaternary Tanimbar Quaternary Kai Quaternary Buru Plio-Pleistocene Seram Pliocene

Table 3.2. Nusa Tenggara islands and the time when they became last emergent (after Monk et al. 1997).

The Philippine archipelago first appeared as dry land during the late Eocene or early

Oligocene (Peterson & Heaney 1993). At about 25 Mya, the Philippines were part of

an arc that connected them with Sulawesi and Halmahera. This arc created a

discontinuous land connection between these island areas (Hall 1998). Between 15

and 5 Mya, the deep marginal basin of the South China Sea was eliminated and in the

Early Pliocene an area of shallow sea run from the northern end of the Philippines to

the south coast of present-day China (Hall 1998). Morley (2000) suggested that the

Palawan microcontinent that rafted from south China to its present position may have

acted as a dry-land raft for mainland Asian species. It should be noted, however, that

sediments on Palawan appear to indicate that Palawan was submerged for much of its


118

rafting time (Hall 1996). Still, Holloway (1982) described late Middle Miocene

unconformities in Palawan and in the neighbouring areas of the Sulu Sea and offshore

west and north-west Palawan. These, possibly correlated, unconformities indicate a

phase of uplift at that time, resulting in emergence and non-deposition. None of the

other parts of the Philippines had any land connection to Sundaland. Also, volcanic

arc activity occurred along the Cagayan and Sulu ridges during the Miocene and Plio-

Pleistocene, respectively, and probably resulted in emergent chains of islands (Rangin

and Silver, 1991 in Wilson & Moss 1999); these may have been times when migration

from Borneo to Mindanao via these arcs was possible, although a continuous land

connection probably never existed.

Most of the growth of the Philippine islands has occurred since the beginning of the

Miocene, and much since the Pliocene. Because the islands are on a shallow platform,

they were heavily influenced by repeated Pleistocene changes in sea-level (Heaney

1985). Heaney (1985) reviewed the distribution of many animal species in the

Philippines. Based on this, he concluded that there has been no land bridge to the

Philippines from Asia during the Late or Middle Pleistocene, with the exception of a

Middle Pleistocene connection from Borneo to Palawan. Reis et al. (2001), however,

suggested that this Pleistocene land connection did not exist, but a narrow water gap

instead, which prevented some species from colonizing. According to others (e.g.,

Earl of Cranbrook 2000), Palawan was connected to northern Borneo during the LGM

and only became separated at about 14 Kya.

Heaney (1985) found some evidence from the primary fresh-water fish (those that are

never found outside freshwater habitats) for the existence of a land-bridge from

Palawan to Mindanao during the Early Pleistocene or (more likely) the Pliocene,

although this remains somewhat speculative. During Late Pleistocene climatic

fluctuations, the islands of Luzon and Catanduanes merged to form Greater Luzon,

while Leyte and Biliran merged to form Greater Mindanao (Peterson & Heaney 1993).

In a paper on the stratigraphy of Palawan, Wolfart et al. (1986) provided evidence for

the Pliocene inundation of parts of the southern end of Palawan. The Pusok

Conglomerate found in the eastern side of southern Palawan is thought to be of

Pliocene age, has a thickness of some 100 m, and overlies pre-Tertiary rocks

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transgressively, suggesting submergence during a sea level highstand. This is further

supported by Pliocene limestones that were found at the southern edge of Palawan,

southeast of Canipaan. These deposits are unconformably overlaying Miocene

sediments in much of southern and central Palawan, which suggests that, in the Late

Miocene or Early Pliocene, this area was emergent, possibly providing dispersal

opportunities for terrestrial mammals. Southern and central Palawan—at least their

coastal areas—became emergent on the Pliocene-Pleistocene boundary (Wolfart et al.

1986). Northern Palawan, on the other hand, probably became emergent in the Early

Miocene and was not or only to a slight extent submerged during any of the later high

stands. South-west of Palawan, parts of Balabac Island also have Pliocene sediments,

while raised beaches and drowned valleys suggest that during high sea levels parts of

the island became submerged (John 1963).

Summary of palaeoenvironmental and palaeogeographical reconstructions

Above, I have provided detailed information on the changes in land/sea distribution

and the most important vegetation types in island SE Asia since the Early Miocene. In

the next section, I have mapped these changes and these maps will be used to see

whether mammalian evolution can be linked to the most important

palaeoenvironmental and palaeogeographical changes. For that purpose I will provide

each map with a code which will be used later to refer phylogenetic events to these

coded palaeogeographies:

1. Early Miocene (MIO 1)

2. Middle Miocene (MIO 2)

3. Middle to early Late Miocene (MIO 3)

4. Late Miocene (MIO 4)

5. Early Pliocene lowstand (PLIO 1)

6. Early to Middle Pliocene highstand (PLIO 2)

7. Middle Pliocene (PLIO 3)

8. Late Pliocene (PLIO 4)

9. Early Pleistocene (PLEI 1)


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10. Early to Middle Pleistocene (PLEI 2)

11. Early to Middle Pleistocene highstand (PLEI 3)

12. Middle Pleistocene lowstand (PLEI 4)

13. Late Pleistocene (PLEI 5)

In summary, during the Early Miocene, Sundaland existed as an extension of the

Asian mainland, and primarily covered the western part of Borneo, the Sunda Shelf

and the Malay Peninsula; at that time a warm and wet climate existed. During the

Miocene, the land areas of Java and Sumatra slowly started to shape up, initially as a

chain of small volcanic islands. Much of the land area was flooded during the Middle

Miocene highstand. Towards the end of the Miocene, when global climatic conditions

had cooled and become drier, more land was exposed, leading to connections of parts

of Sumatra and Java to the rest of the Sundaic land mass. Vegetation became

increasingly open, and grasses started to become more common. During the Pliocene,

the sea between the Malay Peninsula and Borneo started to open, eventually leading to

the latter becoming an island. At that time the climate was becoming increasingly dry

and environmental fluctuations increased. It appears that an Early-Middle Pliocene sea

level high caused a break-up across the Malay/Thai Peninsula which could have lasted

for as long as 1 Myr. During the Pleistocene, Java and Sumatra started to take on their

present-day shape. The considerable fluctuations in sea level at that time led to

alternating connections and disconnections between the different islands of this

region, but the exact sequence of this remains unclear. It appears that during a Middle

Pleistocene glacial Java was directly connected to the Malay Peninsula by a land

bridge that followed the Riau and Lingga area, Bangka and Belitung, and reached Java

via the Karimun Jawa area. During the Pleistocene glacials, tropical wet evergreen

rainforest probably became restricted to refugia, as suggested by the vegetation

patterns that existed during the LGM.

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3.5 PALAEOGEOGRAPHICAL RECONSTRUCTIONS

Early Miocene (MIO 1)

During the Early Miocene, the islands of Sumatra and Java did not exist as we know

them today. Instead several smaller islands were in place, none of which probably

connected to Sundaland. At this time, it appears that northern Borneo with the

Kuching High was separated from the rest of Sundaland. The location of upland areas

(see Fig. 3.14) outside the area of present-day Borneo is largely hypothetical. The

presence of marine influences in the Malay and Thai Basins suggested that the eastern

coastline of Sundaland was located considerably further west than suggested by Hall

(1998). This was also suggested in the palaeoenvironmental maps by Jinmin (1994).

Pollen findings suggest a markedly seasonal climate in Borneo and Sumatra. The key

biogeographic issues are that Borneo was part of Sundaland, while parts of Sumatra

were possibly connected. Most of Java had probably not yet emerged.

Figure 3.14. Palaeoenvironmental reconstruction for the Early Miocene. The grey areas show the land area at this time in relation to the present-day shape of the region; black areas are uplands, and the dotted lines are rivers.


122

Middle Miocene (MIO 2)

The Early–Middle Miocene saw the re-expansion of tropical and sub-tropical forest

zones as the climate became warmer, and wet forest types such as peat swamps

developed in Sundaland. This was also a time of generally high sea-levels. Sundaland

is still one landmass and connected to the Asian mainland. Sumatra probably consisted

of an island arc, while Java was still mostly submerged.

Figure 3.15. Palaeoenvironmental map for the early Middle Miocene (for legend see Fig. 3.14)

An important period of low sea-levels occurred between 16.5 and 16.2 Mya, which

may have led to a brief reconnection of Sumatra with Sundaland. However, the further

sea-level rise during the Early–Middle Miocene resulted in inundation of most of

northern Sumatra, which suggests that no terrestrial mammals survived in that area

until later in the Miocene. At 16 Mya, however, a faunal turn-over occurred in

southern Asia (Barry et al. 1985), and this may have resulted in an influx of new

mammal taxa into Sundaland. Figure 3.15 shows the palaeoenvironmental map at the

height of the early Middle Miocene climatic optimum.

123

Middle to early Late Miocene (MIO 3)

Compared to the palaeoenvironmental reconstructions by Hall (1996; 1998), the data

in this research suggest less emergent land in Java and on Sumatra, which are here

shown as a chain of several islands rather than the two larger land masses of proto-

Java and proto-Sumatra shown by Hall. In Fig. 3.16 I hypothesize that the Lampung

High in southern Sumatra provided a link between the Sumatran land mass and

Sundaland. The climate would have been mostly hot and humid and a tropical

evergreen vegetation would probably have covered most of Sundaland. The river

courses are largely hypothetical, although it could be that the Mae Khlong and Chao

Phraya/Mekong Rivers were separated by the upland area of the the Koh Kra Ridge. A

large island, in the present-day Pulau Laut region, may have existed south-east of

Borneo.

Figure 3.16. Palaeoenvironmental reconstruction for the late Middle to early Late Miocene (for legend see Fig. 3.14).


124

Late Miocene (MIO 4)

Similarly to the preceding reconstruction, it was still found that only small parts of

Java had emerged in this period, as opposed to the complete emergence of Java

suggested in Hall’s (1996; 1998) reconstruction. West Java was probably a small land

area now, connected to the Lampung High, while in the central Java area some small

islands may have occurred that were however flooded again later in the Pliocene and

did therefore not play a role in Tertiary mammal evolution. Towards the Late

Miocene, the climate in mainland Asia was becoming drier and cooler, although it is

unclear whether that significantly changed the vegetation of Sundaland. Judging from

the vegetation for Indochina, it is likely that Sundaland remained largely covered in

tropical evergreen forest.

Figure 3.17. Palaeoenvironmental reconstruction for the Late Miocene (for legend see Fig. 3.14).

125

Early Pliocene lowstand (PLIO 1)

In the Early Pliocene, the prograding southern Sunda Shelf edge ran quite close to the

Java area, but it is unclear whether the Sundaland area actually connected with the

exposed parts of Java. In Fig. 3.18 I have still drawn a connection between Sundaland.

southern Sumatra, and west Java, but this is also the time when the Sunda Dome

collapsed which probably led to the break-up of this connection. The further

deepening of the Malay and Thai Basins probably also led to the opening up of the sea

between Borneo and the Malay Peninsula, although the timing of this is poorly known.

Similarly, I have drawn a connection between north Sumatra and the Malay Peninsula

via the Asahan Arch, but again the timing of the submergence of the arch is unclear.

Figure 3.18. Palaeoenvironmental reconstruction for the Early Pliocene lowstand (for legend see Fig. 3.14).


126

Early to Middle Pliocene highstand (PLIO 2)

The Early–Middle Pliocene sea level highstand (ca. 4.5–3.5 Mya) (e.g. Haq et al.

1987; McNeill et al. 1996; McNeill et al. 1998), which Haq et al. estimated at ca. 100

m above present-day sea levels, could have significantly changed the geography of the

region (see Woodruff 2003). It is possible that it cut the Malay/Thai Peninsula in two,

while it is also possible that Borneo was separated, or almost separated into two parts

when the valleys of the Kapuas and Mahakam Rivers became sea arms within close

reach of each other. It was probably also at this stage that the land connection between

Borneo and the Asian mainland was first broken, or at least narrowed down to a small

land corridor. This is likely to have happened somewhere along the

Riau/Lingga/Belitung/Bangka ridge. The high sea levels suggest warm and wet

conditions, although no detailed vegetation information is available for this period.

Figure 3.19. Palaeoenvironmental reconstruction for the Early–Middle Pliocene highstand (for legend see Fig. 3.14).

127

Middle Pliocene (PLIO 3)

During the Middle Pliocene, sea levels remained relatively high and I hypothesize that

at that time the connection between Borneo and the Malay Peninsula was severed (but

exact information on this is lacking). This would have been the first time that Borneo

became an island (unless it happened earlier during the Pliocene), which would have

led to the divergence of Bornean species. Also the Sumatra and Javan islands were

isolated.

Figure 3.20. Palaeoenvironmental reconstruction for the Middle Pliocene (for legend see Fig. 3.14).


128

Late Pliocene (PLIO 4)

The Late Pliocene glacial led to very low sea levels and cool and dry conditions. I

think that at that time Borneo became reconnected to the rest of Sundaland (as sea

levels were at a similarly low level as during the LGM). I have also drawn

connections between Sumatra and the Malay Peninsula. At this time it is likely that

evergreen rainforest became restricted to refugia although their locations remain

unknown.

Figure 3.21. Palaeoenvironmental reconstruction for the Late Pliocene (for legend see Fig. 3.14).

129

Early Pleistocene (PLEI 1)

During the Early Pleistocene, sea levels were generally high which presumably led to

the fragmentation of the large area that resulted from the lowstand between 2.8 and 2.4

Mya. Data for this period are tentative, however.

Figure 3.22. Palaeoenvironmental reconstruction for the Early Pleistocene (for legend see Fig. 3.14).


130

Early–Middle Pleistocene (PLEI 2)

The arrival on Java of the Ci Saat Fauna at this time suggests that a land bridge or an

arc of small islands connected central Java to the Asian mainland. This could either

have been a direct connection between Bangka, Belitung, and Karimun Jawa, or one

via the southwest of Borneo (see Figs. 5.8 and 5.9).

Figure 3.23. Palaeoenvironmental reconstruction for the Early–Middle Pleistocene (for legend see Fig. 3.14); see Fig. 5.8 for an alternative scenario.

131

Early–Middle Pleistocene highstand (PLEI 3)

The landbridge described on the previous page (via the Karimun Jawa Islands) was

probably low-lying and would have been affected by sea level changes and the general

subsidence of the Java Sea area. Intermittently it would have provided dispersal

opportunities for species from the Asian mainland to Java and vice versa.

Figure 3.24. Palaeoenvironmental reconstruction for the Early–Middle Pleistocene highstand (for legend see Fig. 3.14).


132

Middle Pleistocene lowstand (PLEI 4)

The Middle Pleistocene lowstand occurred during one of the more severe glacials of

the Pleistocene. It led to the dispersal of many new species to Java, which at that time

was presumably connected to the Asian mainland. Java had quite an open environment

at that time, which was probably also found in south-eastern Borneo, and possibly on

the central Sunda Shelf.

Figure 3.25. Palaeoenvironmental reconstruction for the Middle Pleistocene lowstand (for legend see Fig. 3.14).

133

Late Pleistocene (PLEI 5)

The palaeogeography of the LGM is reasonably well known. At this time, Sundaland

was connected into one landmass, probably the largest it had ever been. This area was

dissected by some very large rivers of which the courses are known with considerable

accuracy. Tropical evergreen rainforest did probably not occur anywhere on Java

(apart maybe from some mountain areas) and may also have been absent from south-

eastern Borneo, the central Sunda Shelf and from parts of the Malay Peninsula. In

these areas, the evergreen forest was probably replaced by more open deciduous forest

types or wooded grasslands. Tropical evergreen forest remained on Sumatra’s west

coast and the Mentawai Islands, around the Natuna area, and around the Bornean

mountains.

Figure 3.26. Palaeoenvironmental reconstruction for the Late Pleistocene lowstand (for legend see Fig. 3.14).

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