BASEMENT ARCHITECTURE AND SEDIMENTARY FILL OF THE NORTH MAKASSAR STRAITS BASIN

摘要

The North Makassar Straits Basin (NMSB) is the deepest Cenozoic basin in Indonesia. Debate continues about whether it is underlain by continental or oceanic crust, and whether it originated as a rift or foreland basin. 2D seismic lines, gravity and well data were used to study the basement architecture and sedimentary fill of the basin. Based on those data, the NMSB is interpreted to have originated as a strongly segmented extensional basin, associated with half graben and graben structures. Mapping has revealed a system of NNW-SSE lineaments and faults intersecting the Top Basement seismic reflector. The lineaments and faults are arranged in en-echelon patterns and bound disconnected NNW-SSE trending depocentres. From comparison with sandbox analogue models, the syn-rift fault system in the NMSB seems most likely to have been produced by oblique rifting. The principal extension direction was east-west, at an angle of approximately 60° to preexisting basement structures. Rifting of this part of the southeast Eurasian continental margin occurred during the Middle to Late Eocene. The crust beneath the NMSB is interpreted to be continental. The post-rift section is subdivided into three megasequences. Post-rift Megasquence 1 was deposited during the rapid subsidence of the basin from the Late Eocene to Late Oligocene. Uplift of Kalimantan in the Early to Middle Miocene generated Post-rift Megasequence 2, an interval characterised by a prograding delta system. Late Miocene Post-rift Megasequence 3 is interpreted to contain a turbidite interval in the central part of the basin. Subsidence and deep water marine sedimentation continued to the present-day in the central NMSB but from the Early Pliocene, sedimentrnsupply from the east increased significantly as result of the westward propagation of the West Sulawesi fold and thrust belt. The NMSB became a foreland basin only from the Early Pliocene.