ABSTRACT: Eocene Deep-Marine Clastic Sedimentation in Southwest Java, Indonesia: An Example of a Quartz-Rich Turbidite System on the Flank of the Sunda Shield
SCHILLER, D. M., P. T. Robertson Utama Indonesia, Jakarta, Indonesia, R. A. GARRARD, Atlantic Richfield Indonesia Inc., Jakarta, Indonesia, and L. PRASETYO, P. T. Robertson Utama Indonesia, Jakarta, Indonesia
Deep-marine sandstones can be important exploration targets but have yet to be widely exploited as potential oil and gas reservoirs in the Indonesian region. Very few have been drilled or recognized in the subsurface, even though they should be relatively frequent given the active tectonic setting of the area. There are many reasons why these deposits have received so little attention, including the lack of a well described ancient example within the region. Well-exposed coastal outcrops of the middle to late Eocene Ciletuh Formation located in the Ciletuh Area, Southwest Java, have been described on the basis of field study and laboratory analysis, and interpreted as a sand- and gravel-dominated deep marine sediment gravity flow complex. The outcrops consist of fine to very coarse gr ined sandstones and sandy conglomerates with a number of classic sediment gravity flow features. The sediments are believed to have been deposited in a series of parallel slope grabens oriented perpendicular to slope. Two separate lithofacies are recognized in the Ciletuh Formation; a quartzose lithofacies composed of mostly quartz (58-84%) and lithic rock fragments; and a less pervasive volcanic lithofacies composed of volcaniclastic sediments. Mesozoic granitic continental crust and Late Cretaceous subduction complex areas lying to the north supplied the majority of quartz and lithic fragments, while a local Eocene volcanic arc is believed to have sourced most volcanics. The quartzose sandstone reservoir quality is poor due to near complete destruction of a large percentage of the poro ity. Even though the deposits have very low reservoir potential, they present a useful local example of a sand- and gravel-rich turbidite complex and indicate that deep marine sandstones elsewhere in Indonesia could provide a viable petroleum reservoir under more favorable tectonic or diagenetic conditions.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)