Evolution of the Late Oligocene Kujung reef complex in the western East Cepu High, East Java Basin: Seismic sequence stratigraphic study*
Margaretha E. M. Purwaningsih**, Awang H. Satyana***, Sri Budiyani****, Dardji Noeradi**, and Nanang M. Halik****
** Department of Geology, Institute of Technology Bandung, Bandung, *** Badan Pelaksana Kegiatan Usaha Hulu Minyak dan Gas Bumi, Jakarta, **** Pertamina Upstream, Jakarta
* Indonesian Association of Geologists, 31st Annual Conference, Surabaya, September 30 – October 2, 2002
Seismic sequence stratigraphic study was conducted to reveal depositional history and facies distribution of the reefs in the study area located at the western margin of the East Cepu isolated platform. Four sequences, Sequence-1 to Sequence-4, consisting of transgressive and highstand systems tracts of the Late Oligocene Kujung carbonates were identified. The sequences can be recognized as related to the synrift, postrift, and syninversion deposition. Siliclastic and carbonate sediments including facies of reefs, lagoon, talus, and marine condensed sections developed. Deposition of the upper sequences were contemporaneous with the tilting of the platform to the southwest due to a regional inversion forming a northeastward backstepping pattern. Entering the mid – Early Miocene, the episode of the carbonate deposition ended due to deposition of the Tuban silisiclastic sediments while the platform tilting more to the southwest. Seismic sequence stratigraphic study considering tectonics and eustacy is a good approach to understand stratigraphic evolution.
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