THE BIAK BASIN AND ITS SETTING IN THE BIRD’S HEAD REGION OF WEST PAPUA

摘要

The Bird’s Head region of West Papua is dissectedrnby several major strike-slip faults, namely thernSorong, Ransiki and Yapen faults. Although the agernand current activity of these faults is disputed, it isrngenerally accepted that they were initiated withinrnthe last 23 million years. Several sedimentaryrnbasins, including the Biak Basin, filled largely byrnCenozoic (mainly Neogene) carbonates, are foundrnin close proximity to these faults, indicating arnpotential genetic link between faulting and basinrnformation.rnThe Biak Basin is situated between the islands ofrnBiak and Yapen, north of Cenderawasih Bay. Thernbasin fill consists of three sequences with boundingrnunconformities traceable across the wider Bird’srnHead region. These sequences form a completernmegasequence that records changes in relative sealevelrndriven by uplift and subsidence within thernregion.rnThe lowermost sequence comprises island arcrnvolcanics accreted to the northern New Guinearnmargin at the end of the Paleogene. The top isrnmarked by a Lower Miocene angular unconformityrnthat can be traced to basins in the Bintuni region tornthe west. The middle megasequence within thernbasin is composed of Lower Miocene platformrncarbonates possibly correlative with the KaisrnLimestone found in the Salawati Basin to the west.rnThe final sequence is marked by an unconformityrncaused by diachronous regional subsidence acrossrnthe northern Bird’s Head that led to the drowning ofrnlocalised carbonate platforms, including therncollapse of the Kais Platform, and the initiation ofrnstrike-slip faulting. The movement along thesernfaults has led to the formation of many of thernmodern sedimentary basins in the region.