STUDI MIKROFASIES DAN DIAGENESIS BATUAN KARBONAT FORMASI POH, CEKUNGAN LUWUK - BANGGAI, KECAMATAN PAGIMANA, KABUPATEN BANGGAI, PROVINSI SULAWESI TENGAH

Abstract

Poh Formation is one of formation which sedimented at Tertiary age in Luwuk – Banggai basin, Central Sulawesi. This basin is very interesting, because it’s exposed all kind of rock from PreTertiary to recent. Poh Formation litology composed of limestone with insert of carbonic siltstone. This study aimed to determine microfacies and depositional environment of carbonate rocks,find out the process that develops and environmental diagenesis of carbonate rocks, to determine the relative age based on the abundance of foraminifera in the rocks, and the latter determines the dynamics of microfacies stratigraphy sequence based on petrography and paleontology data that observed. The methodology used in this research is descriptive and analytical methods. Descriptive methods performed to test hypotheses, make predictions and get the benefit of a problem to be solved, while for the method of analysis used is the petrographic analysis, mikrofacies analysis, analysis of large foraminifera, and analysis sequence stratigraphy. Analysis mikrofasies done to interpret facies, depositional environment, platform type, process and environmental diagenesis, where as foraminifera analysis is needed to determine the age of rocks. Based on the results of the analysis made facies zoning columns are arranged vertically for easier detection of a parasequence stacking pattern set. From the observation of thin section obtained 13 types of carbonate rock classifications Dunham (1962), a modified Flugel (2010), namely: Large Bioclast Packstone forams, Bioclast Plangtonik Forams Packstone, Bioclast Plangtonik Forams Packstone with Quartz, Red Algae Bioclast Wackstone, Bioclast Red Algae Grainstone, Packstone with Dolomitation, Ooid Grainstone, Ooid Packstone, Bioclast Coral Rudstone, Bioclast Milliolids Grainstone, Bioclast Plangtonik Forams Packstone with Microspar, Interdeterminate Bioclast Packstone and Bioclast Red Algae Packstone with Microspar. To thirteen types of rocks are scattered into six facies zoning Wilson (1975), namely FZ 1 Deep Sea, FZ 3 Toe-Of-Slope Apron (Deep Shelf Margin), FZ 4 slope, FZ 5 Platform-Margin Reefs, FZ 7 Open Marine, and FZ 8 Platform Interior – Restricted. Depositional environment of the outcrop rocks is shallow marine shelf with to be rimmed carbonate platforms. The process of developing such cement diagenesis isopach marking the marine phreatic environment, which marks the formation of cement circum granular meteoricphreatic environment, as well as the growth of equant calcite mineral, grain deformation, and neomorfism which marks the burial. Relative age out crop shows the range of ages P21 to N11 End the Oligocene-Middle Miocene. The data collected from the analysis of the incision can be used to identify the sequence boundary of the parasequence set that show agradation and retrogradation stacking pattern, of a system tracts which estimated as transgressive system tract and highstand system tract. Keywords: Poh Formation, microfacies, facies zoning, diagenesis, sequence stratigraphy