Neogene subsidence and stratigraphy of the Simeulue forearc basin, Northwest Sumatra

Interpretation of new multi-channel seismic data reveals the Neogene subsidence history of the Simeulue forearc basin, located off northwestern Sumatra. The trench-parallel elongated basin extends over 260 km in NW–SE direction and 100 km in SW–NE direction. Maximum water depth is about 1300 m and the Neogene sedimentary fill shows a thickness of up to 5 s two-way traveltime. We identified three stages of subsidence evolution after the formation of a regional basal Neogene unconformity which are characterized by changing accumulation space, sedimentation rates, source areas and tectonic phases. An Early/Mid Miocene stage is marked by occurrence of subsidence in several half grabens forming along the western border of the basin. During the Late Miocene/Pliocene this small scale subsidence changed to a steadily subsiding trench-parallel trough. The present setup of the forearc region under the influence of strike-slip faults due to oblique subduction is active at least since this time as evidenced by wrench faulting. At the end of this stage subsidence expanded significantly eastwards drowning a large carbonate platform that evolved in the then shallow southern and eastern parts of the basin. Presently, the central part of the Simeulue basin is subject to inversion, probably related to reactivation of Early/Mid Miocene half grabens.