SE Asia Regional Geology

Variably deformed metasedimentary rocks (interbedded metaquartzite, phyllite, slate, etc.) of Paleozoic age exposed at Kg. Kuala Abang, Terengganu, are separable into two units on the basis of discernible differences in structural features. The lower unit exhibits two phases of folding; the earlier southeasterly plunging reclined fold (F1) is refolded by a later southerly plunging upright fold (F2). The divergent axial trends indicate that the two phases of folding are not coaxial. The upper unit appears to have experienced only one phase of folding corresponding to the F2-fold of the lower unit. This is also evidenced by the marked differences in the occurrence of quartz veins in the two units. The lower unit displays two sets of quartz veins corresponding to the axial planes of Fl and F2, whereas quartz veins parallel to the F2 axial plane are only present in the upper unit. The difference in the structural features between the two units suggest that the deposition of the upper unit postdated the F1 folding phase implying the probable existence of an unconformity in the Paleozoic metasedimentary sequence. The age of this probable unconformity remains uncertain and can be resolved only when the ages of the metasediments at Kg. Kuala Abang are known.

Ferrari et al. [Ferrari, O.M., Hochard, C., Stampfli, G.M., 2008. An alternative plate tectonic model for the Palaeozoic–Early Mesozoic Palaeotethyan evolution of Southeast Asia (Northern Thailand–Burma). Tectonophysics 451, 346–365. doi:10.1016/j.tecto.2007.11.065.] redefine the “Shan-Thai” terrane in Thailand as a Cathaysian Indochina-derived terrane when this has traditionally been defined and used as a Gondwana-derived continental block, hence introducing unnecessary confusion. In their definition of “Shan-Thai”, they also inappropriately combine oceanic suture zone rocks (the Palaeo-Tethys Inthanon suture) and continental arc rocks (Sukhothai Island Arc system). TheMai YuamFault, identified by Ferrari et al. (2008) as the Palaeo-Tethys suture, is in fact a Cenozoic fault and the Palaeo-Tethys suture zone is represented by the Inthanon Suture zone in Thailand which is equivalent to the previously recognised Inthanon zone. The concept of derivation of “Orang Laut” terranes from South China-Indochina by back-arc spreading is innovative but the proposed Permo-Triassic back-arc along the Song Da/Song Ma zone in Vietnam is less convincing. There is little evidence to support the proposed southwards subduction of Palaeo-Tethys beneath eastern Gondwana in the Permian.

Fragmentation, drift, and amalgamation of pieces of buoyant crustal masses like arc, continent,
micro-continent, and oceanic plateau are inevitable consequences of plate tectonics. Collision occurs
following subduction and accretion when two buoyant masses collide. Orogens – elongated regions of
crust intensively deformed, shortened, thickened, folded, and faulted – are formed during collisions,
hence they are called collisional orogens. Collisional orogen is important because it can disclose tectonic
processes that have taken place in an area.
Collisional orogens in Indonesia include : (1) the Meratus Orogen in Southeast Kalimantan
resulted from collision of the Schwaner (SW Kalimantan) continental core with Paternoster microcontinent,
(2) the Sulawesi Orogen formed by collision of Banggai-Sula microcontinent and East
Sulawesi Ophiolite, (3) the Molucca Sea Orogen resulted from collision of accretionary wedges of
Sangihe and Halmahera arc-trench systems, (4) the Seram Orogen formed by collision between
Seram/North Banda arc and the Bird’s Head micro-continent, (5) the Lengguru Orogen recording
collision between the Bird’s Head of Papua and northern margin of the Australian continent in Papua, (6)
the Papua’s Central Range Orogen resulted from collision of an island arc to the south of the Philippine
Sea plate and the northern margin of the Australian continent, and (7) the Timor-Tanimbar Orogen
formed by collision of Australian continent and Timor-Tanimbar/South Banda arc.
There are many considerations from previous authors on the origin of each orogen. Some
debates are unresolved. The previous considerations and our own view are presented in this paper. The
anatomies of the collisional orogens are various depending on many aspects such as : physical
characteristics, relative motion of colliding fragments, rate of collision, and geometry of collision. The
anatomy of most collisional orogens (continent-continent, arccontinent) in Indonesia from foreland to
hinterland comprises : foreland basin, foredeep, foreland fold and thrust belt, mélange/volcanic/ophiolitic
sutures, internal metamorphic and/or plutonic belt, and retro/back-arc fold and thrust belt. Nature of
deformation in the orogenic fold and thrust belts is complex as they are imbricated, migrate outwards
from the suture areas, giving a wedge-shaped geometry to the thrust sheets, and mostly thin-skinned.
Post-collisional escape tectonics in forms of strike-slip and extensional-faults commonly overprint the
collisional structures. Towards the core of the orogens, the deformation is extreme and thick-skinned, and
some show evidence of inversion of pre-existing rifts beneath the orogens.
Knowledge on collisional orogens of Indonesia may lead to the understanding of regional
tectonic setting and evolution of Indonesia which economically can contribute to exploration of petroleum
and mineral deposits in collisional orogen areas.

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.

The Tethys in East Asia is represented by three successive ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Palaeo-Tethys ranges in age from late Early Devonian to Middle Triassic , the Meso-Tethys from late Early Permian to Late Cretaceous, and the Ceno-Tethys from Late Triassic (west)/Late Jurassic (east) to Cenozoic. These ocean basins had a range of water depths comparable to modem ocean basins and the concept of a shallow Tethys should only be applied to the shallow regions of these oceans. All three Tethyan ocean basins, based on palaeogeographic reconstructions , had maximum widths between 2,000 and 3,000 kilometers in their eastern parts at their maximum development.

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 me´lange 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.

The older continental part of Southeast Asia is a composite of four tectonic blocks (Sibumasu, Manabor, Indochina and South China Blocks) which have had independent pre-Triassic histories.
Carboniferous sediments on these blocks are predominantly shallow marine with subordinate epicontinental and continental deposits. The Carboniferous of the Sibumasu Block consists of continental margin deposits including extensive glacial-marine diamictites. Shallow marine elastics (with reefal limestones) and abundant volcanics are the main Carboniferous deposits on the Manabor Block which is interpreted as a possible Island Arc during the Carboniferous. The central part of the Indochina Block was emergent throughout the Carboniferous and was bordered by epicontinental and shallow marine deposits.
Carboniferous faunas of Southeast Asia are predominantly of Eurasian aspect but genera typical of Australian and North American provinces also occur indicating connections between these and Southeast Asia at certain times.
Stratigraphical and palaeomagnetic evidence suggests that the Sibumasu Block was adjacent to Gondwana throughout the Carboniferous. The relative positions of the Manabor and Indochina Blocks are however uncertain.

This review combines a wide range of onshore and offshore data from Oligocene to Pliocene sediments of northern Borneo to address the following topics: (i) the stratigraphic conditions before and after the Top Crocker Unconformity [TCU], (ii) Early Miocene palaeogeography, (iii) events during later Early to mid Middle Miocene times, including the Deep Regional Unconformity [DRU], and (iv) the waning of the Sabah Orogeny in Early Pliocene times. Emphasis is placed on dating the key events, in order to consistently identify the stratigraphic and tectonic changes observed in the different data sets.

The data shows a period of uplift and deformation in the north, perhaps focussed in southern Palawan, during the Oligocene then its sudden cessation at the TCU, with strong contrast in both facies and deformation style of Late Oligocene outcrops on the Kudat Peninsula compared to the Early Miocene sediments drilled offshore. This termination of tectonic deformation coincides with published estimates for the onset of ridge-jump and sea-floor spreading in the South China Sea northwest of Sabah. Following this unconformity the deposition of sediments during the Early Miocene appears to have consisted of a fluvio-deltaic high in the south (from central Borneo) and a broad deep marine basin in the north, from west of the Kudat Peninsula to at least the western part of the Sulu Sea. For the subsequent DRU, its timing and character appears to coincide with large scale sedimentary changes in eastern Sabah and this suggests a pause in regional compression during the early part of the long lasting Sabah Orogeny.

The stratigraphic description of these events has important implications in plate tectonic reconstructions for northern Borneo and the South China Sea. The role of subduction on the eastern side of Sabah may be a key component of revised tectonic models and further evaluation of the area from the Dent Peninsula south to the Indonesian border is recommended.

East and Southeast Asia is a complex assembly of allochthonous continental terranes, island arcs, accretionary complexes
and small ocean basins. The boundaries between continental terranes are marked by major fault zones or by sutures recognized
by the presence of ophiolites, m61anges and accretionary complexes. Stratigraphical, sedimentological,
paleobiogeographical and paleomagnetic data suggest that all of the East and Southeast Asian continental terranes were derived
directly or indirectly from the Iran-Himalaya-Australia margin of Gondwanaland. The evolution of the terranes is one of rifting
from Gondwanaland, northwards drift and amalgamation/accretion to form present day East Asia. Three continental slivers were
rifted from the northeast margin of Gondwanaland in the Silurian-Early Devonian (North China, South China, lndochina/East
Malaya, Qamdo-Simao and Tarim terranes), Early-Middle Permian (Sibumasu, Lhasa and Qiangtang terranes) and Late Jurassic
(West Burma terrane, Woyla terranes). The northwards drift of these terranes was effected by the opening and closing of three sueessive
Tethys oceans, the Paleo-Tethys, Meso-Tethys and Ceno-Tethys. Terrane assembly took place between the Late Paleozoic
and Cenozoic, but the precise timings of amalgamation and accretion are still contentious. Amalgamation of South China and
Indoehina/East Malaya occurred during the Early Carboniferous along the Song Ma Suture to form "Cathaysialand". Cathaysialand,
together with North China, formed a large continental region within the Paleotethys during the Late Carboniferous and Permian.
Paleomagnetic data indicate that this continental region was in equatorial to low northern paleolatitudes which is consistent
with the tropical Cathaysian flora developed on these terranes. The Tarim terrane (together with the Kunlun, Qaidam and Ala Shan
terranes) accreted to Kazakhstan/Siberia in the Permian. This was followed by the suturing of Sibumasu and Qiangtang to Cathaysialand
in the Late Permian-Early Triassic, largely closing the Paleo-Tethys. North and South China were amalgamated in the Late
Triassic-Early Jurassic and finally welded to Laurasia around the same time. The Lhasa terrane accreted to the Sibumasu-Qiangtang
terrane in the Late Jurassic and the Kurosegawa terrane of Japan, interpreted to he derived from Australian Gondwanaland,
accreted to Japanese Eurasia, also in the Late Jurassic. The West Burma and Woyla terranes drifted northwards during the Late
Jurassic and Early Cretaceous as the Ceno-Tethys opened and the Meso-Tethys was destroyed by subduction beneath Eurasia and
were accreted to proto-Southeast Asia in the Early to Late Cretaceous. The Southwest Borneo and Semitau terranes amalgamated
to each other and accreted to lndochina/East Malaya in the Late Cretaceous and the Hainanese terranes probably accreted to South
China sometime in the Cretaceous

During the last decade, a wide range of geological and geophysical data has Jed to the recognition of various continental terranes in SE Asia which, on tectonostratigraphic, palaeo­biogeographic and palaeomagnetic grounds are 'suspect' or allochthonous in nature. Some of the recognized terranes may be composite and there is some disagreement with regard to the number of terranes and their boundaries. The continental terranes are bounded by sutures (representing former oceans), by narrow mobile belts or major fault zones. Comparative studies of the stratigraphy, palaeontology, and palaeomagnetism of the various pre-Cretaceous continental terranes of East and SE Asia suggest that they were all derived directly or indirectly from Gondwanaland. Asian continental terranes that are placed on the India-Australian margin of Gondwanaland in the Early Palaeozoic include Tarim (here regarded to include the Kunlun and Ala Shan terranes), Qaidam, Indochina/East Malaya (which includes the Qamdo-Simao block of western China), North & South China, Sibumasu, Qiangtang, Lhasa, Kurosegawa, NW and SE Hai nan, West Burma and the Woy la terranes. The evolution of Gondwanaland and Tethys during the Palaeozoic and Mesozoic involved the rifting of continental slivers/fragments from northern Gondwanaland, and the northwards drift and amalgamation/accretion of these to form proto-East and SE Asia. Three continental slivers were rifted from the northern margin of Gondwanaland in the Early to Late Devonian (North China, South China, Indochina/East Malaya/Qamdo-Simao, Qaidam and Tarim terranes); Early-Middle Permian (the Cimmerian continent including the Sibumasu and Qiangtang terranes and possibly NW and SE Hainan); and Late Triassic to Late Jurassic (Lhasa, West Burma and Woyla terranes). The northwards drift of these terranes was accompanied by the opening and closing of three successive oceans, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys.
Assembly of Gondwanaland-derived Asian terranes began with the amalgamation of South China and Indochina/East Malaya along the Song Ma/Song Da zone during the Late Devonian/Early Carboniferous to form 'Cathaysialand'. Palaeomagnetic, climatic and bio­geographic data indicate that Cathaysialand and North China were located within the Palaeo-Tethys at low northern/equatorial latitudes during the Late Carboniferous and Permian. Palaeomagnetically determined palaeolatitudes are consistent with the development of tropical Cathaysian floras on these terranes. The Tarim, Kunlun, Qaidam and Ala Shan terranes accreted to Kazakstan/Siberia in the Permian. A major episode of rifting occurred on the northern margin of Gondwanaland in the Late Carboniferous-Early Permian and the Cimmerian continent separated in the late Early Permian resulting in the opening of the Meso-Tethys. Suturing of Sibumasu and Qiangtang to Cathaysialand occurred in the Late Permian-Triassic, closing a major branch of the Palaeo­Tethys. South and North China amalgamated and then accreted to Laurasia by Late Triassic-Early Jurassic times. The highly disrupted Kurosegawa terrane of Japan, possibly derived from Australian Gondwanaland, accreted to Japanese Eurasia, also in the Late Jurassic.
The Lhasa, West Burma and Woyla terranes rifted from NW Australian Gondwanaland in the Late Triassic to Late Jurassic and drifted northwards during the Jurassic and Early Cretaceous as the Ceno-Tethys opened and the Meso-Tethys was destroyed by subduction beneath Eurasia . Accretion of these terranes to proto-SE Asia occurred in the Cretaceous. The SW Borneo and Semitau terranes were derived from the South China/Indochina margin by the opening of a marginal basin in the Cretaceous which was subsequently destroyed by southwards subduction during the rifting of the Reed Bank-Dangerous Grounds terrane from South China when the South China Sea opened. The NW and SE Hainan terranes, which formed part of Early Palaeozoic and possibly Late Palaeozoic Gondwanaland, reached their current positions, relative to South China, sometime in the Jurassic-Cretaceous.

The Barito, Kutei, and Tarakan Basins are located in the eastern half of Kalimantan (Borneo) Island, Indonesia. The basins are distinguished by their di€erent tectonic styles during Tertiary and Pleistocene times. In the Barito Basin, the deformation is a consequence of two distinct, separate, regimes. Firstly, an initial transtensional regime during which sinistral shear resulted in the formation of a series of wrench-related rifts, and secondly, a subsequent transpressional regime involving convergent uplift,
reactivating old structures and resulting in wrenching, reverse faulting and folding within the basin. Presently, NNE±SSW and E±W trending structures are concentrated in the northeastern and northern parts of the basin, respectively. In the northeastern part, the structures become increasingly imbricated towards the Meratus Mountains and involve the basement. The western and southern parts of the Barito Basin are only weakly deformed. In the Kutei Basin, the present day dominant structural trend is a series of tightly folded, NNE±SSW trending anticlines and synclines forming the Samarinda Anticlinorium which is dominant in
the eastern part of the basin. Deformation is less intense o€shore. Middle Miocene to Recent structural growth is suggested by depositional thinning over the structures. The western basin area is uplifted, large structures are evident in several places. The origin of the Kutei structures is still in question and proposed mechanisms include vertical diapirism, gravitational gliding, inversion through regional wrenching, detachment folds over inverted structures, and inverted delta growth-fault system. In the Tarakan Basin, the present structural grain is typi®ed by NNE±SSW normal faults which are mostly developed in the marginal
and o€shore areas. These structures formed on older NW±SE trending folds and are normal to the direction of the basin
sedimentary thickening suggesting that they developed contemporaneously with deposition, as growth-faults, and may be the direct result of sedimentary loading by successive deltaic deposits. Older structures were formed in the onshore basin, characterized by the N±S trending folds resulting from the collision of the Central Range terranes to the west of the basin. Hydrocarbon accumulations in the three basins are strongly controlled by their tectonic styles. In the Barito Basin, all fields are located in west-verging faulted anticlines. The history of tectonic inversion and convergent uplift of the Meratus Mountains, isostatically, have caused the generation, migration, and trapping of hydrocarbons. In the Kutei Basin, the onshore Samarinda
Anticlinorium and the o€shore Mahakam Foldbelt are proli®c petroleum provinces, within which most Indonesian giant fields are located. In the o€shore, very gentle folds also play a role as hydrocarbon traps, in association with stratigraphic entrapment. These structures have recently become primary targets for exploratory drilling. In the Tarakan Basin, the prominent NW±SE anticlines, fragmented by NE±SW growth-faults, have proved to be petroleum traps. The main producing pools are located in the downthrown blocks of the faults. Diverse tectonic styles within the producing basins of Kalimantan compel separate exploration approaches to each basin. To discover new opportunities in exploration, it is important to understand the structural
evolution of neighbouring basins. # 1999 Elsevier Science Ltd. All rights reserved.

The Tethys in East Asia is represented by three successive ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Palaeo-Tethys ranges in age from late Early Devonian to Middle Triassic, Meso-Tethys from late Early Permian to Late Cretaceous, and Ceno-Tethys from Late Triassic (west)/Late Jurassic (east) to Cenozoic. These ocean basins had a range of water depths comparable to modern ocean basins and the concept of ‘Shallow Tethys’ should only be applied to the shallow regions of these oceans. All three Tethyan ocean basins, based on palaeogeographic reconstructions, had maximum widths between 2000 and 3000 km in their eastern parts at their maximum development.

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.

Eksplorasi hidrokarbon (minyak dan gasbumi - migas) di Indonesia telah dilakukan selama hampir 150 tahun, bermula pada tahun 1865. Penyelidikan geologi pun berjalan bersamaan dengan kegiatan ini, bahkan lebih awal lagi, yaitu sejak tahun 1850. Pada periode-periode berikutnya, baik eksplorasi hidrokarbon maupun penyelidikan geologi berjalan bersamaan dan mendapatkan percepatan yang berarti. Eksplorasi hidrokarbon berjalan dengan cepat sejak akhir tahun 1960-an ketika Pemerintah Indonesia menerapkan sistem kontrak bagi hasil untuk investasi migas. Penyelidikan geologi pun berjalan dengan sistematik ke seluruh wilayah Indonesia sejak tahun 1969 ketika Pemerintah Indonesia menjalankan sistem pembangunan berjangka Pembangunan Lima Tahun (Pelita).
Kesinambungan eksplorasi hidrokarbon dan penyelidikan geologi di Indonesia telah membuat keterpaduan yang sangat baik. Data hasil penyelidikan tersedia banyak. Perusahaan-perusahaan migas yang melakukan eksplorasi hidrokarbon dan lembaga-lembaga penelitian geologi Pemerintah yang melakukan penyelidikan geologi telah dan dapat terus saling bekerja sama untuk mendapatkan manfaat yang sebesar-besarnya. Hal ini merupakan modal yang sangat kuat untuk dapat memahami kondisi geologi Indonesia yang rumit namun menarik.
Di dalam makalah ini, penulis meringkas beberapa pemikiran tentang geodinamika Indonesia yang didasarkan kepada sintesis antara data hasil eksplorasi hidrokarbon dan data hasil penyelidikan geologi. Pemikiran-pemikiran ini mencakup : (1) Asal dan Sifat Jalur Orogen Benturan Indonesia, (2) Escape Tectonics Indonesia, (3) Akresi dan Dispersi Daratan Sunda, (4) Asal Tektonik dan Gaya Struktur Cekungan Barito-Kutei-Tarakan, Kalimantan, (5) Indentasi Tektonik Jawa Tengah, (6) Depresi Lautdalam Jawa, (7) Asal dan Sifat Sesar Mendatar Rembang-Madura-Kangean-Sakala (RMKS), (8) Pembukaan Selat Makassar, dan (9) Pembalikan Cekungan Salawati.

Petroleum exploration in Indonesia has been conducted for almost 150 years, started in 1865. Geological expedition and investigation in Indonesia, started earlier in 1850, has also been contemporaneous with petroleum and mining exploration. In the later periods, both petroleum exploration and geological investigation were simultaneously conducted and obtained significant accelerations in some periods. Petroleum exploration has been accelerated since the late of 1960’s when the Government of Indonesia offered the production sharing contract system to petroleum investors. Geological investigations were conducted systematically to cover all Indonesia region since 1969 when the Government of Indonesia started to apply the sequential Five-Year Development Plan (Pelita).
The harmony between petroleum exploration and geological investigations in Indonesia has made a very good integrity. Data resulted from these activities are much available. Companies conducting petroleum exploration and governmental institutions which made geological investigations have cooperated and can continue this cooperation for the sake of the most benefit. This harmony is a very strong basis for understanding the geology of Indonesia which is very complex but beautiful.
In this paper, I present summaries of considerations on several aspects of Indonesia’s geodynamics. These considerations were resulted from syntheses between petroleum exploration data and geological investigation data. The aspects discussed in this paper include : (1) on the Origin and Nature of the Collisional Orogens of Indonesia, (2) Escape Tectonics of Indonesia, (3) Accretion and Dispersion of the Sundaland, (4) Major Dissimilarities on Tectonics and Structure of the Barito, Kutei, and Tarakan Basins, Kalimantan, (5) Tectonic Indentatation of Central Java, (6) Deepwater Sedimentation of Java, (7) on the Origin and Nature of the Rembang-Madura-Kangean-Sakala (RMKS) Strike-Slip Fault, (8) the Makassar Straits Opening, and (9) the Salawati Basin Polarity Reversal.

The evolution of eastern Pangea and Tethys during the late Palaeozoic and Mesozoic involved rifting of continental
slivers/fragments from northeastern Gondwanaland, northwards drift and amalgamation/accretion to form proto East
Asia. Three continental slivers or collages of terranes were rifted from the northeast margin of Gondwanaland in the
Silurian-Early Devonian (North China, South China, Indochina/East Malaya, Qamdo-Simao and Tarim terranes),
Early-Middle Permian (The Cimmerian continent, including the Sibumasu, Lhasa and Qiangtang terranes) and Late
Jurassic (West Burma terrane, Woyla terranes). The northwards drift of these terranes was effected by the opening and
closing of ttu·ee successive Tethys oceans, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys.
Assembly of Gondwanaland-derived terranes to form a major part of Asia took place between the late Palaeozoic
and Cenozoic, but the precise timings of amalgamation and accretion are still controversial. Amalgamation of South
China and Indochina/East Malaya occurred during the Early Carboniferous along the Song Ma Suture to form
"Cathaysialand". Cathaysialand and North China formed large continental regions within the Palaeotethys during the
Late Carboniferous and Permian. Palaeomagnetic data indicate that these continental regions were in equatorial to low
northern palaeolatitudes, which is consistent with the tropical Cathaysian flora developed on these terranes. The Tarim
terrane (together with the Kunlun, Qaidam and Ala Shan terranes) accreted to Kazakstan/Siberia in the Permian.
Opening of the Meso-Tethys occurred as a result of the rifting and northward drifting of the Cimmerian continent from
Northeast Gondwanaland. This was followed by the suturing of Sibumasu and Qiangtang to Cathaysialand in the Late
Permian - Early Triassic, largely closing the Palaeo-Tethys. North and South China amalgamated in the Late TriassicEarly
Jurassic and finally accreted to Laurasia around the same time. The Lhasa terrane accreted to the SibumasuQiangtang
terrane in the Late Jurassic and the Kurosegawa terrane of Japan, believed derived from Australian
Gondwanaland, also accreted to Japanese Eurasia in the Late Jurassic. The West Burma and Woyla terranes drifted
northwards during the Late Jurassic and Early Cretaceous as the Ceno-Tethys opened and the Meso-Tethys was
destroyed by subduction beneath Eurasia. They were accreted to proto-Southeast Asia in the Early to Late Cretaceous.
The Southwest Borneo and Semitau terranes amalgamated to each other and accreted to Indochina/East Malaya in the
Late Cretaceous. The nature and origin of the small Hainanese terranes is still debatable, but they must have reached
their current position relative to South China sometime in the Jurassic-Cretaceous.
A series of palaeogeographic reconstrnctions of eastern Pangea and Tethys are presented which show postulated
palaeo-positions of the various continental blocks and fragments and successive Tethys oceans during the late
Palaeozoic and Mesozoic.

East and Southeast Asia is a giant "jigsaw puzzle" of continental blocks (terranes) which are bounded by faults, narrow mobile belts or sutures that represent the sites of former ocean basins.  Comparative studies of the tectono-stratigraphy, palaeontology, and palaeomagnetism of the various terranes suggests that they were all derived directly or indirectly from Gondwanaland and that they formed part of a "Greater Gondwanaland".

Rifting and separation of three continental slivers occurred on the northern margin of Gondwanaland, in the Devonian, Early-Middle Permian, and Late Triassic to Late Jurassic.  The northwards drift of these terranes was accompanied by the opening and closing of three successive oceans, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys.

Amalgamation and accretion of Asian terranes occurred progressively between the Late Devonian and the Cretaceous, beginning with the intra-Tethyan amalgamation of South China and Indochina to form Cathaysialand in the Late Devonian-Early Carboniferous, followed by the accretion of the Tarim terrane to Kazakhstan/Siberia in the Permian.  Suturing of Sibumasu and Qiangtang to Cathaysialand and amalgamation of this super-terrane with North China occurred in the Permian - Triassic, and accretion to Laurasia was completed by Late Triassic-Early Jurassic times.  The highly disrupted Kurosegawa terrane of Japan, possibly derived from Australian Gondwana, accreted to Japanese Eurasia in the Late Jurassic.  The Lhasa, West Burma and Woyla terranes, which rifted from NW Australian Gondwana in the Late Triassic to Late Jurassic were accreted to proto-Southeast Asia in the Cretaceous.  The SW Borneo and Semitau terranes were derived from the South China/Indochina margin by the opening of a marginal basin in the Cretaceous which was subsequently destroyed by southwards subduction during the rifting of the Reed Bank-Dangerous Grounds terrane from South China when the South China Sea opened.  Following the final breakup of Gondwanaland, India travelled rapidly northwards to make its initial contact with Eurasia at the end of the Cretaceous.  Reconstructions showing the postulated positions of the various terranes and the distribution of land and sea in the Palaeozoic and Mesozoic are  presented.

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.

Field evidence from Upper Palaeozoic and Mesozoic strata exposed in Peninsular Malaysia demonstrates that the structural style, degree and orientation of folding, axial-plane cleavage , and faulting in the Triassic, Jurassic and Cretaceous rocks of the central basin are remarkably similar. In contrast, the Upper Palaeozoic strata, especially the Carboniferous rocks exposed in the eastern part of the peninsula, show multiple phase folding and regional metamorphism unlike anything seen in the Mesozoic rocks . These observations demonstrate that two important compressional events affected Peninsular Malaysia , one in Late Permian times and the other in the mid- to late Cretaceous. The Late Palaeozoic compressional event was a major orogenic mountain building phase with associated emplacement of major Permo- Triassic granite plutons that form the eastern and main ranges . No indications were found of the widely reported Triassic orogenic compression. The palaeotectonic and palaeogeographical implications of these discoveries are important for interpreting the evolution of eastern Gondwana and Tethys. The Raub-Bentong line was an important fault zone active during the Mesozo ic but does not appear to have been a major tectonic suture since the Late Palaeozoic . We postulate that the Permo-Triassic granites of the eastern belt and those presently exposed in the main range were originally about 30-50 km apart, and that Triassic and Jurassic crustal attenuation and subsidence led to the separation of these two granitic belts by more than 100 km.

The Phanerozoic tectonic evolution of Southeast Asia has involved the dispersion of continental terranes from the margin of Gondwanaland, their northwards drift and amalgamation/accretion to form present-day East and Southeast Asia. The continental terranes of mainland Southeast Asia include the South China (which may be composite), Indochina, Qamdo-Simao (possibly an extension of Indochina), Sibumasu (including the Baoshan and Tenchong blocks of Yunnan), South West Borneo, Semitau, West Burma, Sikuleh, Natal, Bengkulu and Hainan Island terranes. These terranes rifted and separated from Gondwanaland during three episodes; in the Devonian (South China, Indochina, Qamdo-Simao, Hainan); late Early Permian (Sibumasu); and Late Triassic-Late Jurassic (West Burma, Sikuleh and Natal). During the separation of the three collages of terranes from Gondwanaland, three Tethyan ocean basins opened, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Southeast Asian terranes were assembled during Carboniferous to Cretaceous times, ftrst with the amalgamation of South China and Indochina in the Lower Carboniferous, followed by the amalgamation of this superterrane with Sibumasu in the Triassic and then the accretion of the other smaller Southeast Asian terranes in the Mesozoic. The various terranes of Southeast Asia are bounded by suture zones that represent the remnants of the various Tethyan ocean basins, or by major strike-slip faults. The main Palaeo-Tethys ocean basin, which separates Late Palaeozoic Gondwanaland terranes to the west from Late Palaeozoic Cathaysian terranes to the east, is represented by the Lancangjian and Changning-Menglian sutures of SW China, the Nan-Uttaradit and Sra Kaeo sutures of Thailand, and the Bentong-Raub suture zone of Peninsular Malaysia. Other subsidiary branches of the Palaeo-Tethys are represented by the Ailaoshan suture in Yunnan, the Song Ma suture in Vietnam and other possible suture segments in North Thailand and southern Guangxi, South China. Radiolarian biostratigraphic and geochemical studies of ribbon-bedded cherts of the main Palaeo-Tethys, together with other constraining data, suggest that the Palaeo-Tethys opened in the Mid-Late Devonian and closed in the Triassic.

The principal continental lithospheric terranes that existed in the Permian, and that now comprise SE Asia, are the South China/Indochina Super Terrane, and the Sibumasu, Simao, West Burma and SW Borneo/Semitau terranes. The Simao Terrane is here regarded a separate terrane, rather than an extension of Indochina, derived from South China by back-arc spreading in the Lower Carboniferous. The main Palaeo-Tethys ocean in Thailand is identified as the Chiang Mai and Sra Kaeo Sutures and the eastern boundary of the Sibumasu Terrane is thus interpreted farther west in Thailand than previously inferred. The Nan-Uttaradit Suture is interpreted as representing a marginal back-arc basin, and contiguous with the Ailaoshan and Jinshajiang Sutures in SW China. The South China/Indochina Super Terrane, and the Simao Terrane were located within the Palaeo-Tethys in equatorial latitudes during the Permian, where they, together with North China, exhibit Cathaysian floras and faunas. The Sibumasu Terrane was located on the NW Australian margin of Gondwanaland until the Sakmarian. Major shifts in faunal affinities from Gondwanaland province faunas to an independent Sibumasu Province and then assimilation into the Cathaysian Province records Separation and rapid northward drift of Sibumasu from the Late Sakmarian. The principal Permian palaeogeographic models for the region are assessed for internal consistencies and conflicts.

East and Southeast Asia comprises a complex assembly of continental fragments (terranes), the boundaries of which are marked by suture zones that represent the remnants or sites of former ocean basins. Late Palaeozoic data from East Asia indicates the incongruous present juxtaposition of cold Gondwana sediments, faunas and floras, and warm Tethyan faunas and floras. The boundary between the cold western Gondwana elements and the eastern warm Terthyan elements is formed by the Lancangjiang, Changning-Menglian, Nan-Uttaradit, Sra Kaeo and Raub-Bentong Suture zones that represent the main Palaeo-Tethys ocean basin. All of the principal East and Southeast Asian continental terranes were located on the Himalayan­Australian margin of Gondwana in the Early Palaeozoic where they formed a "Greater Gondwana". The Asian terranes rifted and separated from Gondwana as three continental slivers in the Devonian, Early-Middle Permian and Late Triassic-Late Jurassic. During the separation of these continental slivers, three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys opened between each successive sliver and Australian Gondwana. The first sliver separated in the Devonian and included North China, South China, Tarim and Indochina. By the Carboniferous, faunas and floras of terranes that formed the first sliver to separate had no Gondwana connections, and palaeomagnetic data indicate that these terranes were separated from the parent craton. The Upper Carboniferous clockwise rotation of Gondwana around 320-300 Ma sent Australia into high southern latitudes and the Gondwana glaciation affected much of Australia during the Upper Carboniferous and Early Permian (from 320 to 270 Ma). During this time, glacial ice reached the marine environment of the northeast Gondwana margin and glacial-marine sediments were deposited on the cold Gondwana margin including the Sibumasu, Qiangtang and Lhasa terranes now located in East and Southeast Asia. Typical Gondwana fossils are also found on these terranes in the Lower Permian and cold-water faunas and cold­water oxygen isotopic signatures are associated with the Lower Permian glacial-marine sediments. Late Carboniferous-Early Permian rifting led to the separation of the Sibumasu and Qiangtang terranes from the Himalaya-NW Australian margin of Gondwana at the end of the Early Permian. These terranes drifted rapidly northwards between 270 and 250 Ma. Rifting and separation of a third continental sliver from Gondwana began in the Late Triassic with the separation of the Lhasa block and progressed eastwards with separation of West Burma and the small Sikuleh terrane of SW Sumatra and other small microcontinental fragments now located in Borneo and West Sulawesi in the Late Jurassic. Following the final break-up of Gondwana, both India and Australia travelled northwards to collide with Eurasia.

Southeast Asia is a complex assembly of allochthonous continental terranes now far removed from their original sites of origin together with island arcs, accretionary complexes and small ocean basins. The boundaries between these terranes are marked by major fault zones or by sutures recognised by the presence of ophiolites, melanges and accretionary complexes. Stratigraphical, sedimentological, palaeobiogeographical and palaeomagnetic data suggest that most, and probably all, of the Southeast Asian continental terranes were derived directly or indirectly from Gondwanaland. These terranes were assembled between the late Palaeozoic and Cenozoic, but the precise times of rifting from Gondwanaland and timings of amalgamation and accretion are still contentious. The continental 'core' of the region comprises four principal continental blocks: South China, Indochina, Sibumasu and East Malaya. Palaeomagnetic and fauna! data suggest that South China rifted from Gondwanaland in the Silurian or Devonian. Indochina and East Malaya may also have rifted from Gondwanaland in pre-Carboniferous times because their late Palaeozoic faunas and floras do not appear to show any Gondwanaland affinities and there are no Carbo-Permian glaciogenic sediments recorded on these blocks. Indochina and East Malaya also exhibit extremely similar late Palaeozoic and Mesozoic geology which suggests that they were already amalgamated by the late Palaeozoic. Amalgamation of South China and Indochina-East Malaya occurred during the Early Carboniferous along the Song Ma Suture to form "Cathaysialand". Cathaysialand, together with North China, formed a large continental region within the Palaeotethys during the Late Carboniferous and Permian. Palaeomagnetic data indicate that this continental region was in equatorial to low northern palaeolatitudes which is consistent with the tropical Cathaysian flora developed on these terranes.
Palaeozoic (Cambrian - Early Permian) faunas of Sibumasu show strong affinities with NW Australia and indicate that this block formed part of the north-eastern margin of Gondwanaland along with the small Hainanese terranes, the Lhasa Block and Changtang Block (part) of Tibet, which have similar stratigraphy and fauna! affinities. This is supported by the presence of Late Carboniferous - Early Permian glacial-marine diamictites, Early Permian cool-water and low­diversity faunas and palaeomagnetic data suggesting southern hemisphere palaeolatitudes during Carboniferous and Early Permian times. A major rifting phase occurred on the north and east margin of Gondwanaland in the Early-to-Middle Permian, and palaeomagnetic and fauna] data suggest that Sibumasu (as part of the elongate Cimmerian continent) rifted from NW Australian Gondwanaland at this time. Collision between Sibumasu and Indochina-East Malaya probably occurred within Palaeotethys in Early Triassic times to form the continental core of Southeast Asia. The Early Triassic suturing age is indicated by melange ages, ages of collision-related plutons, palaeobiogeographic data and development of Late Triassic post-orogenic basins. The Early Triassic suturing of Sibumasu to Cathaysialand was followed by collision with North China in the Late Triassic, as evidenced by palaeomagnetic data, resulting in an overall consolidation of the Southeast Asian cratonic 'core'.
Other smaller terranes including West Burma, the Woyla terranes (Sikuleh, Natal), Semitau and SW Borneo were accreted to this core during the Jurassic and Cretaceous to form 'Sundaland'. The West Burma terrane and possibly some of the Woyla terranes, together with other unidentified crustal blocks may represent the material that provided sediment to the Triassic intracratonic basin of Timor and which rifted from NW Australia in the Middle Jurassic. The origin of the Southwest Borneo and Semitau terranes is still unclear. Palaeomagnetism indicates that they have been located in equatorial palaeolatitudes since the Cretaceous. Triassic and Jurassic fauna! affinities are with Indochina, South China and Japan which suggests a possible Cathaysialand origin.
Eastern Southeast Asia is composed of continental fragments, rifted from the Australian and South China margins during the Late Mesozoic and Cenozoic, together with subduction complexes, island arcs and marginal seas. The spatial distribution of the small continental fragments in eastern Southeast Asia is a result of the interaction between the Eurasian, Indo-Australian and Philippine Sea plates during the Cenozoic. A series of palaeogeographic maps are presented showing interpreted palaeopositions of the various Southeast Asian terranes in the Palaeozoic, Mesozoic, and Cenozoic, in relation to Gondwanaland and Tethys, consistent with the current geological and geophysical constraints.

The main branch of Palaeo-Tethys in East Asia is represented by the Lancangjiang and Changning-Menglian suture zones of western China, the Nan-Uttaradit and Sra Kaeo suture zones of Thailand and the Bentong-Raub suture zone of Peninsular Malaysia. Other subsidiary branches are represented by the Jinshajiang, Ailaoshan and Song Ma suture zones of western China and Vietnam and the Qinling-Dabei suture zone of north and central China. A further possible Palaeo-Tethyan suture zone segment has also been recognised in southern Guangxi, south China. New data from the PalaeoTethys remnants along these sutures, particularly in Yunnan, Thailand and Malaysia, suggest that the Palaeo-Tethys opened in the Devonian when the first of three continental slivers (comprising North China, South China, Tarim, Indochina and Hainan) rifted and separated from northern Gondwanaland. The branch of Palaeo-Tethys which separated South China and Indochina closed by Early Carboniferous times in its eastern part along the Song Ma suture, but much later in the west along the Ailaoshan suture during the Triassic. Radiolarian biostratigraphic and other data suggest that the main Palaeo-Tethys was closed when the Sibumasu-Qiangtang terranes amalgamated with Indochina/South China in the Permian-Triassic.

Two contrasting parallel tectonic sutures can be recognised through the Yunnan–Thailand region of mainland Southeast Asia; they are sutures of the Devonian–Triassic Palaeo-Tethys Ocean and a Permian back-arc basin. The Changning–Menglian and Inthanon suture zones are regarded as the Palaeo-Tethys Suture Zone. The Jinghong–Nan–Sra Kaeo suture is regarded as a closed back-arc basin. The Sukhothai Zone is no longer treated as a part of the Sibumasu Terrane, but is defined as the core part of the Permian island-arc system developed on the western margin of the Indochina Terrane. Two tectonic events are interpreted from the parallel sutures; a Late Permian collapse of the back-arc basin and a mid-Triassic collision of Sibumasu to the Sukhothai Arc of Indochina (= closure of the Palaeo-Tethys). The Early–early Middle Triassic thermotectonism of Vietnam as linked to the Indosinian orogeny by some authors is incompatible with the suggested timing of Sibumasu collision, but instead it is temporally closer to the back-arc compression of western Indochina.

A new lithostratigraphic subdivision for the Carboniferous sediments of the Panching area, Pahang is proposed as follows; Charu Formation (Visean-basal Namurian), Panching Limestone (Namurian A) and Sagor Formation (?Late Carboniferous). These three formations are defined as constituting the Kuantan Group.

The Charu Formation consists predominantly of interbedded sandstones, siltstones and shales. Brachiopods, found abundantly at a number of localities indicate the formation is of Visean-basal Namurian age. The sedimentary features and fossil assemblage suggest the formation was deposited in a shallow marine near shore environment.
The Panching Limestone consists of biomicrites, biosparites, biosparudites, oomicrites and recrystallised micrites. It contains a very rich macro- and microfauna which indicates a Namurian
A age. The limestone is interpreted to have formed in a warm shallow marine reefal environment. Five penecontemporaneous facies are recognisable in the limestone: micritic facies, biomicrite facies, crinoidal facies, biosparite facies and carbonaceous limestone facies. The overall fauna of the formation represents a reefal pre-climax community. A new species of heterocoral, Hexaphyllia concavia sp. nov. is described from the Panching Limestone.
The Sagor Formation is a sequence of conglomerate, sandstone, shale, mudstone and radiolariao mudstone, with rare limestone lenses, deposited in a relatively shallow marine environment. The precise age of the formation is not known but is interpreted to be Late Carboniferous.

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-amalgama- tion-accretion history of Southeast Asia are presented.

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.

Southeast Asia is a complex assembly of allochthonous continental terranes.
Palaeontological, stratigraphical anJ palaeomagnetic data indicates that all of these terranes were
derived directly or indirectly from Gondwana. Assembly of the terranes took place between the Late
Palaeozoic and Cenozoic but the precise sites of original attachment, and timing of rifting from
Gondwana and of amalgamation and accretion are still contentious. The continental 'core' of the region
comprises four principal terranes, South China. Sibumasu, Indochina and East Malaya. Early
Palaeozoic, and in particular Ordovician, faunas of South China and Sibumasu show strong affinities
with N and NW Australia and Tasmania and include forms otherwise endemic to Australia and
Gondwana. Middle and Late Palaeozoic faunas of Sibumasu also show NW Australian affinities and
the presence of Late Carboniferous-Early Permian glacial-marine diamictites with associated cool-water
faunas suggest attachment to N. W. Australia at this time. The affinities of Early Palaeozoic faunas of
Indochina and East Malaya are not yet known but Late Palaeozoic and younger faunas and floras do
not appear to be related to Gondwana.
Biogeographic, stratigraphic and palaeomagnetic data suggest that South China and Sibumasu, along
with the North China, Tarim, Tsaidam, Lhasa, Changtang and possibly Indochina and East Malaya
blocks formed part of the NE Gondwana margin in the Ordovician. Specific sites of attachment are
indicated by stratigraphic and biogeographic evidence together with palaeomagnetic data. North China
is placed near North Australia, Sibumasu adjacent to NW Australia and the South China, Indochina,
Tarim, Tsaidam, Lhasa and Changtang blocks as forming part of the North India-Iran margin of
Gondwana. Palaeobiogeographical and palaeomagnetic data suggest that South and North China
(possibly along with Tarim, Indochina and Tsaidam) rifted from Gondwana in the Silurian. South China
appears to have been isolated from other continental masses during the Devonian as evidenced by its
high degree of faunal and floral endemism, but appears to have amalgamated with Indochina to form
"Cathaysialand" by the Early Carboniferous.
An elongate continental sliver, the 'Cimmerian Continent', including the Lhasa, Changtang, and
Sibumasu blocks, rifted from Gondwana in the Early-Middle Permian and travelled rapidly northwards
across the Tethys, fragmenting on its journey. Amalgamation of Sibumasu and Cathaysialand occurred
in Late Permian-Early Triassic times along the Uttaradit-Nan and Bentong-Raub sutures.

Remnants of the Palaeo-Tethys ocean are preserved within a number of suture zones that separate allochthonous continental terranes in East and Southeast Asia. The main Palaeo-Tethys ocean is represented by the Lancangjiang and Changning­Menglian sutures in Tibet and Yunnan, and the Nan-Uttaradit and Bentong-Raub sutures in Thailand and Malaysia respectively. To the west of these sutures, terranes exhibit Gondwanaland faunas and floras and marginal Gondwanaland stratigraphies up until the Lower Permian. To the east, the terranes exhibit Lower Palaeozoic Gondwanaland faunas but Tethyan/Cathaysian Late Palaeozoic faunas and floras and show no evidence of Gondwanalad related stratigraphy in the Late Palaeozoic. Other branches of the Palaeo­Tethys are represented by the Ailaoshan suture in Yunnan and the Song Ma suture in North Vietnam. New data from the Palaeo-Tethys remnants along these sutures, particularly in Yunnan, Thailand and Malaysia, suggest that the Palaeo-Tethys opened in the Devonian when the first of three continental slivers rifted and separated from northern Gondwana­land. It is proposed that this continental sliver comprised North China, South China, Tarim, Indochina, Qaidam and Hainan. The branch of Palaeo-Tethys which separated South China and Indochina closed by Early Carboniferous times in its eastern part along the Song Ma suture, but much later in the west along the Ailaoshan suture during the Triassic. Radiolarian biostratigraphic and other data suggest that the main Palaeo-Tethys was closed when the Sibumasu-Qiangtang terranes amalgamated with Indochina/South China in the Triassic. Ongoing problems relate to the correlation and contiguity of the Palaeo-Tethyan sutures in south Yunnan, northern Thailand, Laos, Burma and Vietnam.

Southeast Asia comprises a complex assembly of continental fragments (ter­ranes), bounded by suture zones that represent former ocean basins. ln the Early Palaeozoic (545-410 Ma), all the principal Southeast Asian continental terranes were located on the Hima­layan-Australian Gondwanaland margin, where they formed part of a "Greater Gondwanaland". Multidisciplinary studies suggest that the Asian te1nnes rifted and separated from NW Austra­lian Gondwanaland as three continental slivers around 350, 270, and 200-140 Ma. During the separation of these continental slivers, three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys, opened between each successive sliver and Gondwanaland. The first sliver, inter­preted to have separated at 350 Ma, included North China, South China, Tarim, and Indochina. By 325 Ma, these terranes had no Gondwanaland faunas and floras, and palaeomagnetic data indicate that they were separated from the parent craton. Clockwise rotation of Gondwanaland around 320-300 Ma sent Australia into high southern latitudes, and glaciation affected much of Gondwanaland from 320 to 270 Ma. During this time, glacial ice reached the marine environ­ment and glacial-marine sediments were deposited on the Sibumasu, Qiangtang, and Lhasa ter­ranes now located in South and Southeast Asia. Gondwanaland cold-climate faunas and floras and cold water oxygen isotopic signatures are also found in Lower Permian rocks of these ter­ranes. Rifting, starting at about 300 Ma, led to separation of the Sibumasu and Qiangtang ter­ranes from Gondwanaland at approximately 270 Ma. These Cinunerian terranes drifted rapidly northwards between 270 and 250 Ma and significant changes in both brachiopod and fusulinid biogeographic provinces on these between 300 and 250 Ma are interpreted as being primarily due to the separation and northwards drift of the Cimmerian continental terranes, coupled with climatic amelioration following retreat of the Gondwanaland glaciation. Rifting and separation of a third continental sliver from Gondwanaland began 230 million years ago with the separa­tion of the Lhasa block and progressed eastwards with separation of West Burma and possibly the small Sikuleh terrane of SW Sumatra and other small microcontinental fragments now lo­cated in Borneo and West Sulawesi around 160 Ma. Amalgamation and accretion of Gond­wanaland-derived Asian terranes occurred progressively between the Late Devonian and Creta­ceous.

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 Visran) 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.