East Malaya Research Articles

Tectonic evolution of the Sibumasu–Indochina terrane collision zone in Thailand and Malaysia: constraints from new U–Pb zircon chronology of SE Asian tin granitoids

Three principal granite provinces are defined across SE Asia, as follows. (1) The Western Thailand–Myanmar/Burma province consists of hornblende–biotite I-type granodiorite–granites and felsic biotite–K-feldspar (± garnet ± tourmaline) granites associated with abundant tin mineralization in greisen-type veins. New ion microprobe U–Pb dating results from Phuket Island show zircon core ages of 212 ± 2 and 214 ± 2 Ma and a thermal overprint with rims of 81.2 ± 1.2 and 85–75 Ma. (2) The North Thailand–West Malaya Main Range province has mainly S-type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the Sibumasu plate with Indochina during the Mid-Triassic. Biotite granites around Kuala Lumpur contain extremely U-rich zircons (up to 38000 ppm) that yield ages of 215 ± 7 and 210 ± 7 Ma. (3) The East Malaya province consists of dominantly Permian–Triassic I-type hornblende–biotite granites but with subordinate S-type plutons and A-type syenite–gabbros. Biotite–K-feldspar granites from Tioman Island off the east coast of Malaysia also yield a zircon age of 80 ± 1 Ma, showing Cretaceous magmatism in common with province 1. Geological and U–Pb geochronological data suggest that two east-dipping (in present-day coordinates) subduction zones are required during the Triassic, one along the Bentong–Raub Palaeo-Tethyan suture, and the other west of the Phuket–Burma province 1 belt. Supplementary material: A full description of U–Pb analytical methods used and data tables are available at www.geolsoc.org.uk/SUP18523 .

Palaeozoic–Mesozoic history of SE Asia

Abstract SE Asia comprises a collage of Gondwana-derived continental blocks assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones. Two major biogeographical boundaries, the Late Palaeozoic Gondwana–Cathaysia divide and the Cenozoic-Recent Australia–Asia divide (Wallace Line) are present. Palaeozoic and Mesozoic evolution involved the rifting and separation of three collages of continental terranes from eastern Gondwana and the opening and closure of three successive ocean basins, the Palaeo-Tethys (Devonian–Triassic), Meso-Tethys (Permian–Cretaceous) and Ceno-Tethys (Late Triassic–Cenozoic). This led to the opening and closing of ocean gateways and provision of shallow-marine and terrestrial land bridges and stepping-stones for biotic migration. The SE Asia core (Sundaland) comprises a western Sibumasu block, an eastern Indochina–East Malaya block, and the Sukhothai Island Arc terrane between. The Jinghong, Nan-Uttaradit and Sra Kaeo sutures represent the Sukhothai closed back-arc basin. The Palaeo-Tethys is represented by the Changning-Menglian, Chiang Mai/Inthanon and Bentong-Raub suture zones. The West Sumatra and West Burma blocks were accreted to the Sundaland core in the Late Permian–Early Triassic. SW Borneo and/or East Java–West Sulawesi are now identified as the missing ‘Argoland’ that separated from NW Australia in the Jurassic and accreted to SE Sundaland in the Cretaceous.

Submarine mass-transport deposits in the Semantan Formation (Middle-Upper Triassic), central Peninsular Malaysia

Relatively fresh exposures of the Semantan Formation along the East-Coast Highway (Lebuhraya Pantai Timur - Fasa 1) between Karak and Kuantan, central Peninsular Malaysia, have given new insights into the sedimentary processes in the Triassic flysch basin that once separated west and east Malaya. An eastward change from distal to proximal facies between Karak and Maran indicates a west-facing, active continental shelf to slope sedimentation. Outcrops between Karak and Temerloh, east of the Late Triassic-Early Jurassic Bentong-Raub collisional suture, are generally characterized by classical flysch-like, thinly-bedded sandstone-mudstone facies. Further east of Temerloh towards Maran, and nearer to the paleo-shelf and slope, more sandy and thick-bedded turbidite facies occur. A proximal deep- marine facies association in the Semantan Formation is exposed at the Chenor Junction (Exit 821), kilometre 139 along the highway. South- and north-facing cuts on either sides of the highway reveal large gravity-slide blocks (megaclasts), slumps, debris flow deposits, and associated syn-sedimentary thrust faults and glide surfaces. These features are strongly indicative of large-scale submarine mass-transport processes on the palaeo-slope of the Triassic active margin. The Chenor mass-transport complex is made up of zones of incoherent slump deposits intercalated with well-bedded turbidite/debrite facies. In the lower part of the succession, there are megaclasts of sandstone-mudstone facies, measuring several metres in size, encased in a plastically deformed silty matrix. The megaclasts are highly deformed internally by numerous meso- scale normal faults, probably due to gravitationally-induced extension. Along with other smaller sandstone blocks, these megaclasts are interpreted as slide blocks due to slope failure up-dip. There are other gravity-induced structural features such as rotational slumps, glide surfaces, thrust faults and associated soft-sediment folds. The slump folds and thrusts show vergence to the west, as opposed to the generally eastward tectonic vergence. A few of the well-stratified units show strongly inclined stratal surfaces which may be attributed to lateral accretion of turbidite fan lobes. Several sets of these inclined surfaces are bounded by erosional surfaces which could have resulted from different episodes of turbidity flow. The association of incoherent mass-flow units with the more well-stratified deposits reflects the close spatial and temporal relationship between submarine mass-transport events and turbidity flows on the Triassic active slope and basin plain.

Granitic magmatism, basement ages, and provenance indicators in the Malay Peninsula: Insights from detrital zircon U–Pb and Hf-isotope data

The Malay Peninsula lies on two continental blocks, Sibumasu and East Malaya, which are intruded by granitoids in two provinces: the Main Range and Eastern. Previous models propose that Permian–Triassic granitoids are subduction-related and syn-to post-collisional. We present 752 U–Pb analyses that were carried out on zircons from river sands in the Malay Peninsula; of these, 243 grains were selected for Hf-isotope analyses. Our data suggest a more complex Sibumasu–East Malaya collision history. 176Hf/ 177Hf i ratios reveal that Permian–Triassic zircons were sourced from three magmatic suites: (a) Permian crustally-derived granitoids, (b) Early-Middle Triassic granitoids with mixed mantle–crust sources, and (c) Late Triassic crustally-derived granitoids. This suggests three Permian–Triassic episodes of magmatism in the Malay Peninsula, two of which occurred in the Eastern Province. Although the exact timing of the Sibumasu–East Malaya collision remains unresolved, current data suggest that it occurred before the Late Triassic, probably in Late Permian–Early Triassic. Our data also indicate that Sibumasu and East Malaya basements are chronologically heterogeneous, but predominantly of Proterozoic age. Some basement may be Neoarchaean but there is no evidence for basement older than 2.8 Ga. Finally, we show that Hf-isotope signatures of Triassic zircons can be used as provenance indicators.

Tectonic framework and Phanerozoic evolution of Sundaland

Sundaland comprises a heterogeneous collage of continental blocks derived from the India–Australian margin of eastern Gondwana and assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones. The continental core of Sundaland comprises a western Sibumasu block and an eastern Indochina–East Malaya block with an island arc terrane, the Sukhothai Island Arc System, comprising the Linchang, Sukhothai and Chanthaburi blocks sandwiched between. This island arc formed on the margin of Indochina–East Malaya, and then separated by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub Suture Zones. The West Sumatra block, and possibly the West Burma block, rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian and were accreted to the Sundaland core in the Triassic. West Burma is now considered to be probably Cathaysian in nature and similar to West Sumatra, from which it was separated by opening of the Andaman Sea basin. South West Borneo and/or East Java-West Sulawesi are now tentatively identified as the missing “Argoland” which must have separated from NW Australia in the Jurassic and these were accreted to SE Sundaland in the Cretaceous. Revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of Sundaland and adjacent regions are presented.

Structure of Sumatra and its implications for the tectonic assembly of Southeast Asia and the destruction of Paleotethys

AbstractIt is now generally accepted that Southeast Asia is composed of continental blocks which separated from Gondwana with the formation of oceanic crust during the Paleozoic, and were accreted to Asia in the Late Paleozoic or Early Mesozoic, with the subduction of the intervening oceanic crust. From east to west the Malay peninsula and Sumatra are composed of three continental blocks: East Malaya with a Cathaysian Permian flora and fauna; Sibumasu, including the western part of the Malay peninsula and East Sumatra, with Late Carboniferous–Early Permian ‘pebbly mudstones’ interpreted as glaciogenic diamictites; and West Sumatra, again with Cathaysian fauna and flora. A further unit, the Woyla nappe, is interpreted as an intraoceanic arc thrust over the West Sumatra block in the mid Cretaceous. There are varied opinions concerning the age of collision of Sibumasu with East Malaya and the destruction of Paleotethys. In Thailand, radiolarites have been used as evidence that Paleotethys survived until after the Middle Triassic. In the Malay peninsula, structural evidence and the ages of granitic intrusions are used to support a Middle Permian to Early Triassic age for the destruction of Paleotethys. It is suggested that the West Sumatra block was derived from Cathaysia and emplaced against the western margin of Sibumasu by dextral transcurrent faulting along a zone of high deformation, the Medial Sumatra Tectonic Zone. These structural units can be traced northwards in Southeast Asia. The East Malaya block is considered to be part of the Indochina block, Sibumasu can be traced through Thailand into southern China, the Medial Sumatra Tectonic Zone is correlated with the Mogok Belt of Myanmar, the West Burma block is the extension of the West Sumatra block, from which it was separated by the formation of the Andaman Sea in the Miocene, and the Woyla nappe is correlated with the Mawgyi nappe of Myanmar.

Late Palaeozoic and Mesozoic tectonic and palaeogeographical evolution of SE Asia

Abstract SE Asia comprises a collage of continental terranes derived directly or indirectly from the India–Australian margin of eastern Gondwana. The Late Palaeozoic and Mesozoic evolution of the region involved the rifting and separation of three elongate continental slivers from eastern Gondwana and the successive opening and closure of three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Sukhothai Island Arc System, including the Linchang, Sukhothai and Chanthaburi terranes, is identified between the Sibumasu and Indochina–East Malaya terranes in SE Asia and was formed by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo sutures represent the closed back-arc basin. The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub suture zones. The West Sumatra and West Burma blocks rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian, and together with South China formed a composite terrane ‘Cathaysialand’ in the Permian. They were translated westwards to their positions outboard of the Sibumasu Terrane by strike-slip tectonics in the Late Permian–Early Triassic at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates. SW Borneo is tentatively identified as possibly being the missing ‘Argoland’ that separated from NW Australia in the Jurassic. Palaeogeographical reconstructions for the Late Palaeozoic and Mesozoic illustrating the tectonic and palaeogeographical evolution of SE Asia are presented.

Population genetic structure and conservation implications of Ceriops decandra in Malay Peninsula and North Australia

Comprehensive information of mangrove genetic resources is requisite for developing strategies for their effective conservation and sustainable use. Genetic diversity within and among populations of a widespread viviparous mangrove Ceriops decandra was determined using inter-simple sequence repeat (ISSR). Ten natural populations were collected from Malay Peninsula and North Australia. At the species level, high genetic variation was detected ( P = 72%, H E = 0.253, and I = 0.379). The estimate of G ST was 0.882, indicating a high level of genetic differentiation among populations. When populations were grouped according to geographic regions, i.e., East Malaya, West Malaya, Southmost Malaya, and North Australia, AMOVA suggested that most of the total variation (87%) was accounted for by differentiation between regions, with only 4% accounting for variation among populations within regions, and a further 9% partitioned among individuals within a population. A UPGMA dendrogram based on genetic distance revealed a deep split between populations from the eastern Indian Ocean and all others from the western Pacific Ocean, which may result from the historical lowering of sea level at these regions during the recent Pleistocene glaciations. An understanding of the genetic structure of C. decandra provides insight for the conservation and management of this species.

Chapter 14 Tectonic Evolution

The concept that SE Asia, and indeed Asia as a whole, has been built up during the Phanerozoic by the amalgamation of allochthonous terranes derived from the northern margin of East Gondwana, is now well established in the literature (e.g. Audley-Charles 1988; Sengor et al . 1988; Metcalfe 1996, 1999 and references therein). In Early Permian time all the major continental land masses, including East and West Gondwana, were joined together in the supercontinent of Pangaea (Fig. 14.1). At this time the continental blocks of North and South China, Indochina and Simao had already separated from East Gondwana. In Metcalfe's (1999) version of the concept a series of elongated terranes separated successively from the northern Gondwana margin by the development of ocean basins behind them. These oceans are referred to as Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Indochina Block, with East Malaya, forms the core of SE Asia and is considered to have separated from Gondwana by Late Devonian times to amalgamate with the South China Block by the Early Carboniferous. Indochina is characterized by an Upper Palaeozoic to Mesozoic fauna and flora of Cathaysian and Tethyan type, exemplified by the Gigantopteris flora of Jengka Pass (Kon'no & Asama 1970; Hutchison 1994), related to those of the North and South China blocks, but with no relationship to the flora and fauna of Gondwana. To this core was added the Shan-Thai or Sibumasu Block, which separated from Gondwana in the Permian and amalgamated with the Indochina Block in the Late Permian or Triassic

Palaeobiogeographic implications of Middle Permian brachiopods from Johore (Peninsular Malaysia)

A new Middle Permian locality in northern Johore, Peninsular Malaysia, yields a small-sized, but compositionally unique, brachiopod fauna consisting of eight species: Pseudoleptodus sp., Caricula cf. salebrosa Grant, Neochonetes (Nongtaia) aff. arabicus (Hudson & Sudbury), Karavankina sp., Transennatia cf. insculpta (Grant), Hustedia sp., Orthothetina sp., and martiniid indet. The first four genera are new records for Malaysia; in particular, the rare taxa Pseudoleptodus and Caricula characterize the fauna. The brachiopods occur together with the ammonoid Agathiceras sp., the nautiloid Foordiceras? sp., bivalves, and crinoid stems. The locality belongs to the East Malaya terrane of the Cathaysian biotic region, but some affinities to species of the Sibumasu province are recognized. The Malaysian forms of Pseudoleptodus, Caricula and Transennatia are similar to those of the Ratburi Limestone (southern Thailand). A Roadian–early Wordian age is interpreted for the Johore fauna. The similarity of brachiopods reported here with those from the Ratburi Limestone suggests that there was species interchange or one-way migration between shallow waters of East Malaya and Sibumasu across the main Palaeo-Tethys. The Tethyan seaway between the two terranes must have been narrower than previously interpreted by some authors to allow such faunal traffic during the Roadian–Wordian time period.

A Permian phillipsiid trilobite from Peninsular Malaysia

Pygidia of the trilobitePseudophillipsia sp. are reported from the Permian Bera Formation, Pahang, Peninsular Malaysia, in association with a moderately rich brachiopod fauna of early Capitanian (Guadalupian) age. It resembles a slightly younger Capitanian speciesPseudophillipsia acuminata Mansuy, 1912 of northern laos. This find suggests an additional faunal link between Indochina and Peninsular Malaysia (the East Malaya terrane) during Capitanian time.

The Bentong–Raub Suture Zone

It is proposed that the Bentong–Raub Suture Zone represents a segment of the main Devonian to Middle Triassic Palaeo-Tethys ocean, and forms the boundary between the Gondwana-derived Sibumasu and Indochina terranes. Palaeo-Tethyan oceanic ribbon-bedded cherts preserved in the suture zone range in age from Middle Devonian to Middle Permian, and mélange includes chert and limestone clasts that range in age from Lower Carboniferous to Lower Permian. This indicates that the Palaeo-Tethys opened in the Devonian, when Indochina and other Chinese blocks separated from Gondwana, and closed in the Late Triassic (Peninsular Malaysia segment). The suture zone is the result of northwards subduction of the Palaeo-Tethys ocean beneath Indochina in the Late Palaeozoic and the Triassic collision of the Sibumasu terrane with, and the underthrusting of, Indochina. Tectonostratigraphic, palaeobiogeographic and palaeomagnetic data indicate that the Sibumasu Terrane separated from Gondwana in the late Sakmarian, and then drifted rapidly northwards during the Permian–Triassic. During the Permian subduction phase, the East Malaya volcano-plutonic arc, with I-Type granitoids and intermediate to acidic volcanism, was developed on the margin of Indochina. The main structural discontinuity in Peninsular Malaysia occurs between Palaeozoic and Triassic rocks, and orogenic deformation appears to have been initiated in the Upper Permian to Lower Triassic, when Sibumasu began to collide with Indochina. During the Early to Middle Triassic, A-Type subduction and crustal thickening generated the Main Range syn- to post-orogenic granites, which were emplaced in the Late Triassic–Early Jurassic. A foredeep basin developed on the depressed margin of Sibumasu in front of the uplifted accretionary complex in which the Semanggol “Formation” rocks accumulated. The suture zone is covered by a latest Triassic, Jurassic and Cretaceous, mainly continental, red bed overlap sequence.

Late Paleozoic radiolarians from the Bentong‐Raub suture zone, Peninsular Malaysia

Abstract Radiolarians extracted from marine siliceous sediments from the Bentong‐Raub suture zone, Peninsular Malaysia have indicated a range of ages for olistostromal blocks of bedded chert, siliceous argillite and tuffaceous argillite, and chert clasts and lenses within the mélange from the suture zone. Late Devonian (Faniennian), Early Carboniferous (Tournaisian and Viséan) and Early Permian (Wolfcampian and Leonardian) ages are represented by seven radiolarian zones from ten localities along the suture zone. In stratigraphic order these include Holoeciscus 2–3 Assemblage Zones, Albaillella paradoxa Zone, Albaillella dejendrei Zone, Albaillella cartalla Zone, Pseudoalbaillella lomentaria Zone, Albaillella sinuata Zone and Pseudoalbaillella longtanensis Zone. Fifteen genera are represented by 35 species. The range of ages from Late Devonian to Early Permian suggests that an ocean existed between the Sibumasu and East Malaya terranes from at least Late Devonian to late Early Permian time and that closure of the ocean between the two terranes could not have occurred until after late Early Permian time. The range of ages and rock types from different depositional environments, indicate that the Bentong‐Raub suture zone includes a disrupted accretionary complex.

Late Palaeozoic radiolarians from the Bentong-Raub suture zone, and the Semanggol formation of Peninsular Malaysia—initial results

Cherts and tuffaceous siltstones from the Bentong-Raub suture zone, Peninsular Malaysia, have yielded radiolarians indicating Late Devonian (Famennian) and Early Carboniferous (Tournaisian, late? Tournaisian and Viséan) ages. Cerium anomalies from these Devonian and Carboniferous cherts indicate deposition in an open ocean. This ocean is interpreted to be the Palaeo-Tethys ocean which existed between Sibumasu and East Malaya during at least the Devonian and Early Carboniferous. Radiolarians extracted from siliceous sediments of the Semanggol Formation of NW Peninsular Malaysia have indicated both Early Permian and Late Permian (Guadalupian) ages. This extends the age of the Semanggol Formation down to the Early Permian and confirms the presence of a deep-marine basin in what is now NW Peninsular Malaysia during the Permian.

Tectonic Patterns and Cenozoic Basalts in the Western Margin of the South China Sea: ABSTRACT

The allochthonous fragments - Indosinia, Sibumasu, East Malaya, and Southwest Kalimantan - rifted from Gondwanaland and drifted northward. Indosinia collided with the Yangzi-Huanan terranes in Devonian or Early Carboniferous period and became part of the East Asia continent. Sibumasu collided· with East Asia continent and East Malaya during the Indosinian Orogeny (220-200 Ma). The Southwest Kalimantan terrane probably rifted from the northeast margin of Indosinia in the Cretaceous. ·At about 50 Ma the collision of the Indian continent into the Eurasian continent led to the fragmentation of Asia and was followed by the opening of the Andaman Sea, the clockwise rotation of the Indochina plate, and the rifting and the opening of the South China Sea. The Late Cretaceous alkaline intrusions in the Red River area of northern Vietnam formed during initial stage of rifting of the South China Sea. The Indian-Eurasian collision has successively pushed the Indochina Peninsula in the east­ southeast direction. Most of the Middle Tertiary movements probably occurred along the left-lateral Red River, Tonle Sap-Mekong faults concurrent with the opening of most of the eastern South China Sea. The extensional tectonics along these predominantly strike-slip faults may be responsible for the Pliocene­ Pleistocene alkaline basalts, which extend from the Mekong Delta northwestward into Thailand. Some basalt outcrops in Thailand, Kampuchea and Vietnam appear to trend north-south. The composition of basalts ranges from tholeiitic to alkalic. The basanitoid basalts contain abundant megacrysts of zircon, ruby, sapphire, and spinel. The megacrysts probably originated through assimilation of metamorphic rocks deep in the continental crust. The cores from the South China Sea indicate that the increase in subsidence rate appears in wells during the Quaternary. It may be related to the increase in Quaternary basalt and high heat flow in the western part of the South China Sea basin.

Late palaeozoic and mesozoic palaeogeography of Southeast Asia

Southeast Asia comprises a complex assemblage of allochthonous terranes derived directly or indirectly from Gondwana Land and assembled between the Late Palaeozoic and Cenozoic. The continental “core” of the region is made up of four principal continental blocks, South China, Indochina, Sibumasu and East Malaya. South China, Indochina and East Malaya were rifted from northeast Gondwanaland during the Silurian or Devonian and amalgamated to each other during the early Carboniferous. Sibumasu remained attached to northwest Australian Gondwana land until the late early Permian when it rifted away as part of the elongate Cimmerian continent. Collision between Sibumasu and Indochina-East Malaya probably occurred in the early Triassic forming the continental core of Southeast Asia. Other small terranes including Mount Victoria Land, Sikuleh, Natal, Semitau and southwest Borneo were accreted to this core during the Jurassic and Cretaceous to form “Sundaland”. A series of palaeogeographic maps are presented showing interpreted palaeopositions of the various Southeast Asian terranes in the Late Palaeozoic and Mesozoic which are consistent with the current geological and geophysical constraints.

Significance of Monodiexodina (Fusulininacea) in geology of Peninsular Malaysia

Monodiexodina sensu stricto is a very rare genus of the Fusulinacea which was found in the Permian deposits. Its distribution is restricted to a narrow sliver extended from the central of Afghanistan in the west to Japan, Eastern Russia and Malaysia in the east. Only three species of the genus have a wide distribution in the south Asia and Southeast Asia. They are Monodiexodina sutschanica, Monodiexodina shiptoni and Monodiexodina kattaensis. Their restricted geographic distribution may reveal their paleobiogeographic province which is very important for establishing paleogeography. Monodiexodina shiptoni is a good index fossil which was used as a zonal marker for the Artinskian, late Early Permian. The geographic distribution of the species suggests that the species were warm-water species which occupied the tropical or subtropical shallow seas. In Sibumasu block, only Monodiexodina sutschanica and Monodiexodina shiptoni were found in either limestone or calcite cemented sandstone which overlies the pebbly mudstone of glacio-marine origin. In East Malaya block, two species of Monodiexodina were found in the Sumalayang limestone. They are Monodiexodina kattaensis and Monodiexodina shiptoni. They are associated with many species of Fusulinacea. Their occurrence may give some clues to the evolution of the paleoclimate and tectonic history of the two blocks during the Permian. Monodiexodina is a very rare genus of the Fusulinacea. It first appeared in the Middle Cordilleran region, became widespread during the Sakmarian, and restricted to the Tethyan region during the Artinskian and the early Late Permian (Ross, 1967). There are two groups of Monodiexodina. The first is Monodiexodina sutschanica group which consists of Monodiexodina sutschanica (Dutkevitch), Monodiexodina shiptoni (Dunbar) and Monod'iexodina matsubaishi (Fujimoto) which is considered as Monodiexodina proper. The second is Monodiexodina kattaensis group which includes Monodiexodina kattaensia (Schwager), Monodiexodina bispatulata Williams, Monodiexodina prolongata (Berry), Monodiexodina steinmanii (Dunbar and Newell), Monodiexodina wanneri (Schubert) and Monodiexodina wanganensis Sossina. This group is morphologically intermediate between Monodiexodina strict sense and genus Parafusulina (Choi, 1973). Recently, two species of Monodiexodina, Monodiexodina sutschanica and Monodiexodina shiptoni (plate 1) were discovered from the calcareous sandstone bed of the top part of Kubang Pasu Formation, at the excavation site of Timah-Tasuh Dam in Perlis (Basir Jasin and Koay, 1990). The

Stratigraphic and tectonic implications of Triassic conodonts from northwest Peninsular Malaysia

AbstractThe Chuping Limestone of northwest Peninsular Malaysia, until recently considered entirely of Permian age, has yielded late Triassic (early Norian) conodonts. TheLimestone thus spans the time interval late Early Permian–Late Triassic and is in part equivalent to the Kodiang Limestone (Late Permian–Late Triassic) in Kedah andsimilar limestone sequences in south Thailand and north Sumatra. Early Late Triassic (Carnian) conodonts are also reported from pelagic limestones associated with bedded chertsof the Chert Member of the Semanggol Formation in Kedah. The Chert Member, previously considered of Middle Triassic age, is re-interpreted to represent Early, Middle and early Late Triassic deposition. The Triassic sedimentary rocks of the Malay Peninsula represent three distinct sedimentary regions: a stable shallow marine carbonate complex (ChupingLimestone, Kodiang Limestone), which forms part of an elongate carbonate platform on theSibumasu block; a deep water pelagic/turbidite basinal sequence (Semanggol Formation) which accumulated in either a foredeep basin or an intracratonic pull-apart basin related to strike-slip faulting; and a volcanic-sourced volcaniclastic basinal sequence on the East Malaya block (Semantan Formation and equivalents) which accumulated in either a forearc/intra-arc setting, or in a post-orogenic rift basin.

Allochthonous terrane processes in Southeast Asia

Southeast Asia comprises a complex agglomeration of allochthonous terranes located at the zone of convergence between the Eurasian, Indo-Australian and Philippine Sea plates. The older continental ‘core’ comprises four principal terranes, South China, Indochina, Sibumasu and East Malaya, derived from Gondwana-Land and assembled between the Carboniferous and the late Triassic. Other terranes (Mount Victoria Land, Sikuleh, Natal, Semitau and S.W. Borneo) were added to this ‘core’ during the Jurassic and Cretaceous to form ‘Sundaland’. Eastern Southeast Asia (N. and E. Borneo, the Philippines and eastern Indonesia) comprises fragments rifted from the Australian and South China margins during the late Mesozoic and Cenozoic which, together with subduction complexes, island arcs and marginal seas, form a complex heterogeneous basement now largely covered by Cenozoic sediments. Strike-slip motions and complex rotations, due to subduction and rifting processes and the collisions of India with Eurasia and Australia with Southeast Asia, have further complicated the spatial distribution of these Southeast Asian terranes. A series of palinspastic maps showing the interpreted rift-drift-amalgamation-accretion history of Southeast Asia are presented.

Origin and assembly of south-east Asian continental terranes

Abstract The pre-Tertiary continental core of south-east Asia is a composite of at least four tectonostratigraphic terranes; Sibumasu (Shan States of Burma, north-west Thailand, Peninsular Burma and Thailand, Western Malaya, and north-western Sumatra), Indo-China (east Thailand, Laos, Vietnam south-west of the Song Ma-Song Da zone and Kapuchea), East Malaya (including south-east Sumatra and Natuna) and south-west Borneo. These terranes are separated from each other by sutures, and are now joined to South China along the Song Ma-Song Da zone. Stratigraphic, palaeontological, and palaeomagnetic evidence suggests that all of these crustal blocks probably had their origin on the north-eastern margin of Gondwanaland where they formed part of a complex continental margin. The Indo-China and East Malaya terranes both have typical late Palaeozoic Cathaysian floras, which indicate that they were close to South China in the Permian. Stratigraphic studies in northeast Vietnam suggest that Indo-China and South China may well have sutured as early as the late Devonian to early Carboniferous. Carboniferous and Permian faunas and floras of these blocks do not appear to be related to those of north-eastern Gondwanaland, indicating that they rifted away at some earlier time. The Sibumasu block remained on the north-western Australian margin of Gondwanaland until the late Lower Permian, and was in continuity with the Tibetan Lhasa and Changtang blocks (south of the Langcangjiang Fracture Zone) and the proto-Kreios microcontinent further to the west. Late Carboniferous and Lower Permian sediments of the Sibumasu, Lhasa, and Changtang blocks, and the Iranian and Afghan portions of proto-Kreios include extensive glacial-marine deposits. Early Permian shallow-marine faunas were of cold-water type until a major change occurred in late Lower Permian times, with Middle Permian faunas becoming typically warm-water Tethyan in aspect. It seems most likely that Sibumasu (still attached to the Lhasa and Changtang blocks and proto-Kreios) rifted from Gondwanaland in the late Lower Permian. Amalgamation of the south-east Asian blocks was probably completed by the end of the Triassic. This is indicated by terrestrial vertebrate biogeography and palaeomagnetism. It is still a matter of debate whether Indo-China sutured to South China in the Devonian-Carboniferous along the Song Ma line, or in the late Triassic along the Song Da zone. Evidence seems stronger for a late Triassic suturing of Sibumasu to the other ‘Cathaysian’ southeast Asian blocks, although a Permian closure of ‘palaeo-Tethys’ has recently been proposed for the Shan-Thai-Indo-China region. The south-west Borneo block probably rifted from the margin of Indo-China in the Cretaceous, and travelled south to its present position during the opening of the proto-South China Sea.