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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
CretaceousEarly 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 50 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 50 counterclockwise during the early Miocene (2017 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 probablypersisted 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 Mller 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 thetime 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. Mtivier 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 4050 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 positionbeyond that of todays 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 alsointeresting 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 MiocenePliocene 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 (Morley1977). 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 thesetaxa 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 EarlyMiddle and
MiddleLate 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 MioceneEarly
Pliocene climate in north and east Borneo was warm and wet.
In the Late MiocenePliocene 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 lowlandvegetation 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 NS 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 Mtivier 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 400 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 6075 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 21.7 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 EarlyMiddle
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 60 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 EarlyMiddle 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 EarlyMiddle 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 mayhave 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 23 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 753 Kya, which is largely in agreement withthe 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 3N). 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-Wrm) interglacial, although this is speculative.
Further sediments were described by Kudrass and Schlter (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 Schlter
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 Schlter (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 190125 Kya and from 7010 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 ofDacrydium, 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 PlioceneEarly 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 andherbaceous 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 thatPinus 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 5N, 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 reviewedarguments 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
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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
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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 MioceneEarly 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 Bemmelens (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 AnambasNatuna Arc and the Riau-Bangka Arc, these musthave been much higher and wider in earlier times (Inger & Voris 2001), possibly
providing mountainous corridors. During Pleistocene low sea-level stands, these arcs
protruded 7501,000 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 MiocenePliocene 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 MiocenePliocene.
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 (MiocenePliocene 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,
Sumatras 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 riversystems, 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 1513.5 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 withthe findings by Wanget 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 ofShorea 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 coniferDacrydium 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 PlioceneMiddle Pleistocene environments of the southern SCS.
Pelejero et al. (1999a) modelled the MiddleLate 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 C,
whereas elsewhere this difference varies between 1.3 and 1.8 C. During the LGM, sea
surface temperatures in the SCS were down to 25 C. Further climatic events
suggested by the results of Pelejero et als (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 C (as
opposed to present-day 28 C) and sea-levels at 6 m higher than present-day levels
(also see below); and 3. two periods dated at 2928 Kya and 37.7 43.2 Kya that were
characterised by extreme tropical precipitation and enhanced summer monsoonactivity.
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
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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 andRhizophora),
while alsoPinus pollen was detected. Unfortunately, the exact location and age of thesediments cannot be determined from the papers 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 1524 C (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 610N, 11213E), 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.
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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
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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 doubtthat 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 OligoceneEarly 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
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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 couldcoincide 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 1120 E 11045. 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 Tertiaryseries. 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 regions biogeography were described by
Meijaard and Groves (in press-b) (see Appendix 6). This river flow model is
supported by river sedimentation calculations by Mtivier 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. Mtivier 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 7.47.0 Mya, the northern Pakistan floodplain was
dominated by closed canopy forest, with or without an understory of C3 shrubs and
3Cenograms are graphs of body weight frequencies, which, for mammals, may give some indication ofthe 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 (Morley2000). 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 7.47.0 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 7.47.0 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 (9942 E; 1327 N) probably had an environment with some mixed
vegetation with grasslands in the floodplain and forests on the surrounding limestone
hills. At 1.961.79 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 Pleistoceneearly 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 827 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 (1630 N; 10149 E), which were dated as middlelate 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 PlioceneEarly 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 MiddleLate 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 4C 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 6C. 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 andArtemisia 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 23C 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 (2015 Kyr). At that time, the vegetation in the
extreme south of China (2123 N) resembled that now growing in the Changjiang
region, indicating a fall in the mean temperature by some 6C. 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 todays, 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. 3620 Kyr), experienced
greater winter humidity and rainfall, while mean annual temperatures were onlyslightly, 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 (1610 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 912 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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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-ea