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Geological Society, London, Special Publications; 1997; v. 126; p. 311-339;DOI: 10.1144/GSL.SP.1997.126.01.19

1997Geological Society of London

The tectonostratigraphic evolution of SE AsiaIan M. LongleyWoodside Offshore Petroleum Pty Ltd, 1 Adelaide Terrace, Perth, Western Australia 6000,Australiaian.longley@woodside.com.auA new model for the Tertiary tectonic and stratigraphic evolution

of SE Asia is presented integrating

stratigraphic data frommany of the major sedimentary basins in the area. The model

can be divided into

four phases.

(1) Stage I (5043.5 Ma) during which the India-Eurasiacollision was initiated and proceeded

contemporaneously withoceanic subduction beneath southern Eurasia. The continental

collision caused a

slow-down in the oceanic spreading ratesin the Indian Ocean reducing the convergence velocity

along

the Sunda Arc subduction system and resulting in a phase of

extension in the adjacent fore-arc andback arc areas. The isolatedrift basins in the fore-arc and the East Java area were filled

with

transgressive then open marine sediments since these basinswere on the low-lying edge of the Sunda

craton whereas the mid-Eocenesea was not able to penetrate in to the more cratonic backarc

rift basins

of Sumatra or NW Java which were filled with fluvio-lacustrinesequences.

(2) Stage II (43.532 Ma) was triggered by the terminationof oceanic subduction beneath the India-

Eurasia collision zone.This locked up the spreading system in the Indian Ocean and

caused a major plate

reorganization effective in the Indian,Southern and Pacific oceans. The plate reorganization in the

Indian

Ocean slowed convergence rates yet again along the SundaArc producing a second phase of rifting and

rift basin deposits.The plate reorganization in the Pacific Ocean resulted in the

onset of extension in the

South China Sea and the depositionof fluvio-lacustrine sequences in the isolated rift basins whereas

in

the East Kalimantan area a failed rift system in the MakassarStraits resulted in isolated rift basins filled

with deltaic

and marine sequences which were overlain by more extensive post-rift

marine shales. Thefirst major collision of the Luconia Shoalsblock with a subduction system along the NW Borneo margin

resultedin the deposition Balingian delta sequence.

(3) Stage III (3221 Ma) is contemporaneous with the firstphase of seafloor spreading in the South China

Sea during whichthe entire continental area south of a line bisecting and joining

the South China Sea and

the Gulf of Thailand rotated clockwiseabout a pole near the head of the Gulf of Thailand. This

blockrotation formed the Malay Basin within which a large fluvio-lacustine

sequence was deposited. The

rotation also produced a phase ofincreased plate convergence rates and inversion along the Sunda

Arc

ending the rifting in these basins. The subsequent sedimentaryfill in these basins records a marine

transgression which isinterpreted to be partially eustatic in origin and partly a

result of the subsidence

associated with the onset of post-riftthermal sag phases. Elsewhere in East Kalimantan extensive

marineand carbonate sequences were deposited whilst in the South China

sea the incursion of marine

environments led to the deposition

of inboard transgressive deltaic and marine deposits and marine

andcarbonate deposits offshore in more distal settings.

(4) Stage IV (210 Ma) was initiated by the cessationof the first phase of seafloor spreading in the South

ChinaSea caused by the collsion of the Baram block with the NW Borneo

subduction system. This event

is interpreted to be contemporaneouswith the onset of continental shortening in Tibet via block

rotation

and lateral extrusion along strike-slip faults. Majorcollisions, an inevitable result of the particular

configurationestablished by the plate-reorganization at 43.5 Ma, occurred

throughout this stage in the NW

Borneo, Sulawesi and Timor areasand together with the rotation of Sumatra, and extrusion-

relatedwrench faulting in the Malay-West Natuna and Bac Bo/YinggehaiBasin areas resulted in a

http://www.geolsoc.org.uk/http://www.geolsoc.org.uk/http://www.geolsoc.org.uk/mailto:ian.longley@woodside.com.aumailto:ian.longley@woodside.com.aumailto:ian.longley@woodside.com.aumailto:ian.longley@woodside.com.auhttp://www.geolsoc.org.uk/

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extensive structural invertsion andhighly variable basin fill sequences. A eustatic high in the

middle

Miocene marks a period of maximum marine transgressiononto the Sunda craton and the deposition of

extensive marineshale deposits. This was followed by dominantly regressive sequences

puctuated by

major eustatic sea-level falls at about 5 and 10Ma.

Particular structural styles and eustatic models are discussedin relation to the proposed model and the

distribution of hydrocarbons

in the Tertiary basins of southeast Asia is presented. This

distribution isexplained in terms of the different types ofsource rocks present in the different basins.