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ABSTRACT: Controls on sediment dispersal patterns in the deepwater neogene Kutei Basin, East Kalimantan, Indonesia

Bransden, Paul1, Martin Smith1, Paul Sherwood1, Ralph Gillcrist2, and Rhys Schneider3
(1) Lasmo Indonesia, Jakarta, Indonesia
(2) Lasmo Plc, London, England
(3) Unocal Indonesia, Balikpapan, Indonesia

As well as regional uplift of Borneo, local uplift of the Kutei foldbelt has provided sediment provenence. Continuous uplift from mid Miocene is dated by AFTA and seismic onlap patterns. Delivery of sediment to slope canyons could occur either by eustatic sea level fall, or forced regression. Age equivalent sequences in the deepwater are largely deposited in highstand and transgressive systems. Intervening lowstand packages are more consistent with eustatic curves than a long-lived period of forced regression. Subsurface facies patterns and modern observations on the shelf suggest that with no fluvial flood phase, and little reworking on the shelf, coarse clastics are trapped on the delta top and delta front.

At the shelf edge, coarse clastic sediment entry points are locally fixed by carbonate buildups, which themselves may be reworked into the deepwater. Sediment thicks in the deepwater occur either in the hangingwall of major growth faults, or in long-lived palaeotopographic lows. Growth faults and related toe-thrusts are driven by delta loading, whereas regional thicks show underlying control from the Palaeogene rift fabric. Toe-thrusts in the south were mostly active in the mid Miocene. In the north onset was mid Miocene, with major late Miocene gravity movement. The central delta has little growth faulting, and an oversteepened carbonate-rich margin, which may represent a basement high. Final accumulation of coarse clastics on the slope and basin floor is controlled by entry points and palaeogradient. High relief toe-thrusts with surface expression have ponded sediment locally, but are frequently degraded by slumping.

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