Publications

The Eocene synrift sediments are in relative terms a frontier target in the Kutei Basin as the majority of the exploration focus in the Basin is in the younger Neogene play. Lack of Eocene sediments and basement rocks penetrated by well bores and outcropped at surface has for many years prevented clarity in the interpretation of the basement type for the Mangkalihat High. This paper will discuss the basement configuration, tectonic history, the postulated basement underlying the peninsula and the relationship to the northern part of the Kutei Basin. The Popodi PSC is located in the northern part of the Kutei Basin, to the south of the Mangkalihat High. The block is composed of two structural styles, basement involved structures in the eastern part and detachment structures in the western portion. The Mangkalihat High is located within the basement involved province. The suture of these two provinces appears to be via the formerly active NW-SE Sangkulirang fault. The NW-SE oriented rift faults appear to be the primary basement grain, and this is parallel to the suture line. This alignment is contradictory to the NNE-SSW structures found in Makassar Straits and NE-SW lineaments of the northern margin of Kutei, which may suggest that the Mangkalihat is underlain by a contrasting basement fragment. The original basement fabric of the Mangkalihat terrane is the main controlling element for graben orientation. The nature of the crust underneath Mangkalihat has been interpreted from the composition of the volcaniclastic sandstones filling the Eocene grabens. Recent exploration well drilling in the Popodi PSC suggests that the basement of Mangkalihat is probably oceanic/ophiolitic crust in nature because the Eocene volcaniclastic sands are * Anadarko Indonesia Nunukan Company composed of ultrabasic/basic rock. The Sangkulirang fault appears to mark the boundaries of different crustal fragments underneath, which are the ophiolitic or oceanic crust of Mangkalihat, oceanic affinity of the northern margin of Kutei and continental type basement of the North Makassar and also probably the Lower Kutei Basin. It has been concluded that the Kutei Basin is underlain by an amalgamated terrane which is composed of several ophiolitic/oceanic fragments and continental cust. Mangkalihat is probably a micro-oceanic fragment which was amalgamated in the eastern part of Borneo in the Jurassic period and formed the eastern portion of Sundaland.