Thermal histories of Tertiary sediments in western central Sumatra, Indonesia

Abstract

Apatite fission-track and organic maturity data from the central region of Sumatra suggest that Tertiary sediments exposed in the Ombilin Basin, in the northern and western margins of the South Sumatra Basin, have low to medium thermal maturities (Ro-average 0.39–0.50%). Apatite fission-track central ages and length data indicate that, at most, low levels of track annealing have occurred and the sediments have only experienced temperatures lower than 120°C. Many samples show a strong component of inherited tracks. In the Ombilin Basin we suggest that the western Talawi sub-basin was not as deeply buried as the eastern Sinamar sub-basin, and probably never received any Miocene sediments. The apatite fission-track age of one basement granite along an intra-basement high, and forward modelling of fission-track length data from the basin, tentatively suggest that cooling (?and uplift) of the western Talawi sub-basin occurred in the late Oligocene to early Miocene. The cause of the sub-division of the basin is ascribed to strike-slip tectonics. Late Eocene rocks exposed along the northern and western margins of the South Sumatra Basin, in the present-day back-arc area, are undermature. Similarly aged and younger rocks in the subsurface of the Central and South Sumatra Basins are reported to be mature/overmature. This suggests that the areas of outcrop studied were not part of the main Paleogene-Neogene graben system that was subsequently inverted. Rather the studied areas have only experienced shallow burial depths and are likely to represent marginal, rift shoulder, areas of sedimentation surrounding areas of deep rift sedimentation.