Paleogene sequence framework and depositional systems in the Sunda and Asri Basins, Indonesia

Abstract

Based on seismic reflection characteristics, lithologic associations, and basin structure evolution stages, the Banuwati Formation, Zelda and Gita Members in the Oligocene could be divided into six third-order sequences. The new sequence framework has been established in the Sunda and Asri Basins. Sequence relationship between wells and seismic data has been implemented in the basin scale through the use of synthetical seismic records of 14 wells. Depositional systems, such as delta, fan-delta, nearshore subaqueous fan, and fluvial, are identified in the Banuwati Formation, Zelda and Gita Members. Alluvial fan, subaqueous fan, and fan delta occurred on the steep slopes of the basins. Deltas were mainly developed on the gentle slopes of the basins. There were three separated small basins with fluvial and shore-shallow lake deposition in the Banuwati Formation (SQ1). During the Lower Zelda (SQ2) sedimentation, the former separated small basins enlarged in a certain extent where delta and subaqueous fan were developed. Major lacustrine facies under deepwater environments and deltaic facies developed in the Upper-Lower Zelda and Middle-Upper Zelda (SQ3, SQ4). The sedimentary situation was almost the same as the Middle Zelda, but the water depth became shallower during Upper Zelda sedimentation. Later, fluvial and swamp developed in the upper part of the Upper Zelda and Gita Member (SQ5, SQ6). In general, basin sedimentary evolution is consistent with tectonic evolution. Finally, the favorable sandstone distribution in the Banuwati and Mid-Upper Zelda Member for further exploration was predicted according to the depositional systems, slope break, and present hydrocarbon occurrence. Three fields or eight favorable plays should be paid attention to for further exploration in the Sunda and Asri Basins, Indonesia.