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ABSTRACT: Sequence Stratigraphy of the Offshore Tarakan

Lefort, J. J., J.P. Thiriet, P. Le Quellec, and J. B. Bailey , Total Indonesie, Jakarta, Indonesia

In the Sebawang-1 PSC (Tarakan Basin), sequence stratigraphy markers defined from well logs and cores have been correlated using a fully reprocessed seismic data set.

In an overall regressive Upper Miocene to Recent succession, major sequence boundaries indicating lowstand periods, as well as tectonically enhanced angular unconformities have been identified. Maximum flooding surfaces, well defined in the marine environment, are the lateral equivalent of thick coals and organic shales in the delta plain. The sedimentology of the limited core data indicates fluvial dominated delta-plain and delta-front deposits.

From West to East, the fluvial sediments (amalgamated channels) pass laterally into deltaic (delta-plain, delta-front) and shelfal deposits (shales and limestones).

During the Late Miocene, rapid subsidence coupled with active N-S growth faulting, trapped the deltaic sediments in downthrown paleo-troughs in the west, whilst the eastern part comprised a series of sediment starved paleo-highs with marine shales and limestones. In the latest Miocene, the western part was tilted and truncated.

During the Pliocene, subsidence slowed and growth faulting became less active or ceased. In the Bunyu area, the delta was able to prograde eastwards far towards the paleo shelf-edge, since the N-S trending paleo-highs were no longer present.

During the Pleistocene, the subsidence rate was high and NW-SE arches were set-up by reactivation of the old deep seated NW-SE lineaments.

Time isopach and paleo-geographic maps, based on the sequence stratigraphy markers, predict the clastic fairways.

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