Characteristics of Paremba Sandstones in Bantimala Complex: The Implication of Oil Exploration in Eastern Indonesia

Abstract

This research aims to determine the characteristics and provenance of paremba sandstones as an implication of oil and gas reservoirs potential. Paremba sandstone is a shallow marine sedimentary rock in the Bantimala tectonic complex, which is composed of flysh-type sedimentary rocks, interbedded sandstone, shale and conglomerates. The field data retrieval are using measuring section method. There are 31 thin section samples, including 5 blue day thin section samples for provenance analysis based on the percentage content of monocrystalline quartz, polycrystalline quartz, plagioclase, K-Feldfar and rock fragments. Paremba sandstone lies on the Bontorio River consist of conglomerates, very coarse - fine sandstones, siltstone, claystone and fosilliferous limestone with an almost vertical slope of 70 ° - 80 ° and NW - SE direction. Conglomerates are divided into two types, namely cherty conglomerate which is grayish-red colored, the sizes of the grain are pebble - boulder, open-packing, bad sorting, fragments consists of schist and quartzite, matrix in sandy-silt and cement consists of silica (chert) and grayish conglomerates which is similar to a cherty conglomerate, but it has gray colored and absen of chert. Sandstone have coarse - fine grain sizes, sub-angular - rounded grain shapes, in the form of arkose and litharenite which have flame structures (load cast: sole mark), slump structure, parallel lamination and ripple lamination. The presence of mosaic textures on sandy limestones, epidote in sandstones and graphite shows that paremba sandstones had undergone low-grade metamorphism. Based on the Qm-F-Lt diagram, the Qm-PK diagram and the Qt-F-L diagram, the paremba sandstones are from recycled orogen to interior craters, whose rocks had undergone Lithic recyled, transitional recycled, until quartoze recycled so it is interpreted that paremba sandstone comes from the Recycle orogenic tectonic environment. Petrographic observations of five blueday samples found that two of them had porosity <1% with fracture porosity-type. This is indicates that paremba sandstones are not suitable as oil and gas reservoirs.