The occurrence of hydrocarbons in back-arc basins of Indonesia has been known since the beginning of this century, but its relation to the formation and evolution of sedimentary basins is rather poorly understood. This can be resolved by explaining the origin of a basin in terms of extensional tectonics. This approach has been applied to the Makassar basin. Data provided by well records and multichannel seismic reflection profiling indicate that the observed subsidence can be explained by the thinning of continental crust by a factor of between 2 and 2.9. Stretching

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and initial fault-controlled subsidence commenced during early-middle Eocene time (or perhaps earlier), and had ceased by early Miocene time. Since middle Miocene time, there has been thermally-controlled subsidence due to conductive cooling of the lithosphere, and post-lower Miocene sediments have been deposited across the basin with little or no internal deformation.

Assuming the pre-stretched thickness of the crust to be 22 mi (35 km), the thickness of the crust in the Makassar basin is about 12 mi (19 km) at the basin margin, and it decreases to about 9 mi (15 km) in the abyssal plain. Evaluation of the degree of hydrocarbon maturation indicates that the pre-lower Miocene sediments have reached sufficient temperatures for hydrocarbon generation, assuming an initial heat flow of 1.6 HFU with crustal contribution of 0.8 HFU, and thermal conductivity of 5 × 10^-3 cal/cm.s.°C.

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