Neogene Evolution of Northern Mahakam Delta, East Kalimantan, Indonesia

R. A. Armin, R. Abdoerrlas, W. D. de Boer, H. L. Heitman, R. A. Leveque, C. J. Stuart, S. K. Wiman, and Y. Yusuf

A regional sequence-stratigraphic study of the lower Kutei basin, embracing present coastal and offshore East Kalimantan, was undertaken to decipher the Neogene history of an important oil-producing province. The chronostratigraphic framework developed during this study was applied to facies analyses, organic geochemistry, and 2-D basin modeling. Integration of these disciplines powerfully illuminated the relationships between structuring, sedimentation, and hydrocarbon migration. Sedimentation in the lower Kutei basin since the late Middle Miocene has been dominated by the tidal-fluvial Mahakam delta system. During this time the principal river transport system has remained in about the same location as the present-day Mahakam River. Thick successions of monotonously sim lar deltaic facies were stacked vertically, punctuated by progradational or backstepping (flooding) units. Middle to Upper Miocene shelf edges of the delta platform, which are commonly sites of carbonate buildups, offiap from west to east towards the present-day shelf edge. Growth faults active during ca. 12-9 Ma are clustered just basinward of a prominent aggradational Middle Miocene shelf margin, and they exerted profound control on facies distribution. Tectonic quiescence prevailed during ca. 9-4 Ma, and in this period widespread regressive deltaic deposition over a broad, stable delta platform created the most important reservoirs. Subsequently, during Late Pliocene and younger time, many early growth faults were reactivated, and new faults also formed eastward toward the present she f margin. Here, economically significant intervals consist mainly of lowstand deposits that accumulated in shelf-margin half-grabens created by these Plio-Pleistocene faults.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California