Carbonate depositional model and facies distribution on the transpression Zone, East Kalimantan

The origin and sedimentary evolution of the Mangkalihat peninsula is still debatable and has attracted the attention of many geologists and explorationists. Miocene carbonate occurs as a primary reservoir rocks in western Indonesia, including this study area. The objective of this research is to provide a detailed examination of the previously unstudied carbonate depositinal model and diagenetic features in this area. Based on field and petrographic analysis, this study showed that the microfacies distribution of the Tendehantu Formation consist of four microfacies (MF) as follows: MF-l). Coralline-red algae boundstone, MF-2). Corraline talus-bioclastic rudstone, MF-3). Bioclastic grainstone-packstone, and MF-4), Forminiferal packstone-floatstone. The first two microfacies are considered to be deposited in the same environments, upper-middle reef front, with porosity of 10-25%. The depositional environment of the MF-3 was suggested to be an upper fore-reef and MF-4 is considered to be a lower fore-reef as a distal part of carbonate platform, with porosity of 2-5%. These four microfacies are used to interpret the depositional environment and construct a carbonate platform model. The presence of reef facies may be used as an indicator for the reservoir potential in this area.