FACIES ARCHITECTURAL ELEMENTS AND DIAGENETICS OF MIDDLE MIOCENE NGRAYONG CLASTIC LIMESTONE AND SANDSTONE CASE STUDY: DINGIL VILLAGE, JATIROGO, NORTH EAST JAVA BASIN

摘要

The Oligocene and Miocene of the outcrops of the North East Java Basin provide an excellent chance to compare clastic and carbonate depositional systems with eustatic and tectonic controls (Bransden & Mathew, 1992). The depositional environment of the Ngrayong Formation is still debatable. The research area located in Dingil Village, Jatirogo shows an excellent outcrop on the surface. Located within the Rembang Zone and the northern part of Randublatung Zone are several outcrops that show differences in the original terrain. The data were collected from field geological mapping and studio analysis. Four significant samples and measuring sections from several data sites were collected. Petrography analysis has been done to determine porosity. This paper will describe the facies and diagenetic process of the Ngrayong Formation. From the petrography data, a description of diagenetic and facies of limestone and sandstone has been undertaken. The clastic limestone is composed of fragments of clastic limestone: clastic limestone, coral fragment, and fossil fragments with a calcite matrix. Several diagenetic events are on the carbonate. The porosity of the carbonate samples ranges from 10-20%. The sandstone was composed of fragment clastic sandstone (MS-FS) and the matrix of mudstone had porosity between 20-30% and fossil occurrence. The petrography analysis found several diagenetic processes on the carbonate. A coal deposit was found that shows a marker of change in the depositional environment. Coal deposits show a regressive and transgressive pattern in this area. Furthermore, in thin sections, a cleat of coal and dominant ash was found. This study will bring us another perspective of the Ngrayong Formation, which will be very useful to hydrocarbon exploration.