Formation and Tectonic Evolution of the Pattani Basin, Gulf of Thailand
Titel:
Formation and Tectonic Evolution of the Pattani Basin, Gulf of Thailand
Auteur:
Bustin, R. Chonchawalit, A.
Verschenen in:
International geology review
Paginering:
Jaargang 37 (1995) nr. 10 pagina's 866-892
Jaar:
1995-10
Inhoud:
The stratigraphic and structural evolution of the Pattani Basin, the most prolific petroleum basin in Thailand, reflects the extensional tectonic regime of continental Southeast Asia. E-W extension resulting from the northward collision of India with Eurasia since the Early Tertiary resulted in the formation of a series of N-S-trending sedimentary basins, which include the Pattani Basin. The sedimentary succession in the Pattani Basin is divisible into synrift and post-rift sequences. Deposition of the synrift sequence accompanied rifting and extension, with episodic block faulting and rapid subsidence. The synrift sequence comprises three stratigraphic units: (1) Upper Eocene to Lower Oligocene alluvial-fan, braidedriver, and floodplain deposits; (2) Upper Oligocene to Lower Miocene floodplain and channel deposits; and (3) a Lower Miocene regressive package consisting of marine to nonmarine sediments. Post-rift succession comprises: (1) a Lower to Middle Miocene regressive package of shallow marine sediments through floodplain and channel deposits; (2) an upper Lower Miocene transgressive sequence; and (3) an Upper Miocene to Pleistocene transgressive succession. The post-rift phase is characterized by slower subsidence and decreased sediment influx. The present-day shallow-marine condition in the Gulf of Thailand is the continuation of this latest transgressive phase. The subsidence and thermal history of the Pattani Basin is consistent with a nonuniform lithospheric-stretching model. The amount of extension as well as surface heat flow generally increases from the margin to the basin center. The crustal stretching factor (β) varies from 1.3 at the basin margin to 2.8 in the center. The subcrustal stretching factor (5) ranges from 1.3 at the basin margin to more than 3.0 in the basin center. The stretching of the lithosphere may have extended the basement rocks by as much as 45 to 90 km and has led to passive upwelling of the aesthenosphere, resulting in high heat flow (1.9 to 2.5 Heat Flow Units [HFU]) and high geothermal gradient (45 to 60° C/km). The validity of nonuniform lithospheric stretching as a mechanism for the formation of the Pattani Basin is confirmed by the good agreement between the level of organic maturation modeled on the basis of the predicted heatflow history and measured vitrinite reflectance at various depths measured in some 30 boreholes.
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