Cenozoic thermotectonic history of the Sunda–Asri basin, southeast Sumatra: new insights from apatite fission track thermochronology

The tectonic and thermal history of Cenozoic rocks from four wells (Asri-1, NE Ria-1, Hariet-1 and Yani-2) in the Sunda–Asri basin has been reconstructed using apatite fission track (AFT) analysis combined with modelling of previously determined vitrinite reflectance (VR) measurements. The wells all penetrate Recent to middle Eocene successions, in which only the Eocene to Oligocene successions have been subjected to temperatures suitable for partial annealing, due to rapid late Miocene to Recent burial. With respect to organic thermal maturities, the zone of minimum annealing coincides with undermature heating and records provenance AFT ages, whilst the zone of partial annealing agrees well with mature heating suitable for generation of hydrocarbons. The integrated AFT and VR data suggest that the Sunda–Asri basin continues subsiding, probably due to extension initiated in the late Eocene, and the successions near the base of the wells were recently exposed to the high present-day temperatures. The recent heating of rocks is consistent with up to 800 m of Plio–Pleistocene burial. Both the AFT and VR results indicate that geothermal gradients remained relatively constant through the Cenozoic.