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ABSTRACT: Tectonically influenced Miocene sequence stratigraphy in the Kutei basin, East Kalimantan, Indonesia

Stuart, Charles J. , Unocal Corporation, Sugar Land, TX

The early Kutei basin formed as a composite rift during the Eocene. Collision of the Australia plate w/Sulawesi beginning in the early Miocene (circa-18-20Ma), caused c-clockwise rotation of Borneo until the end of the middle Miocene (circa-10 Ma). Rotation and regional compression caused episodic uplift of central Kalimantan and upper Kutei fault blocks, providing the sediment for Miocene and younger deltaic systems. Linked, syndepositional listric and toe-thrust faults and folds significantly influenced deltaic sedimentation in offshore areas.

Deltaic sediments prograded into the basin from west to east beginning in the early Miocene. In offshore parts of the basin, cycles of progradation are punctuated by flooding and aggradation. Each of the major depositional cycles consists of smaller-scale coarsening- and fining-upward intervals. Some flooding events are widespread and serve as valuable correlation horizons. Seismically imaged unconformities and onlap relations are poorly developed except in basin margin areas.

Four major progradational pulses are recognized in the late early Miocene to early Pliocene section with durations on the order of 2-4 Ma. These cycles (megasequences) are closely related to regional inversion events. Delta lobes prograded rapidly eastward until reaching tectonic hinge points or listric faults. Subsequent decrease in sediment supply or more rapid subsidence forced aggradational stacking and transgression. Abrupt, smaller-scale basinward and landward shifts in facies were probably forced by global-eustatic cyclicity. Sand deposition in deep water appears to be most extensive during periods when eustatic and tectonic forcing coincide.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia