Indones. J. Chem., 2022, 22 (6), 1512 - 1522 Praptisih et al. 1512 Geochemistry and Potential Hydrocarbon Source Rocks of Rambatan Formation in Karangkobar Area, Central Java Praptisih Praptisih 1,2* , Yoga Andriana Sendjaja 1 , Vijaya Isnaniawardhani 1 , Anggoro Tri Mursito 2 , Purna Sulastya Putra 3 , and Septriono Hari Nugroho 3 1 Faculty of Geological Engineering, Universitas Padjajaran, Jl. Raya Bandung Sumedang Km 21 Jatinangor, Sumedang 45363, Indonesia 2 Research Center for Georesources, Research Organization of Earth Science and Maritime, National Research and Innovation Agency, Jl. Sangkuriang, Bandung 40135, Indonesia 3 Research Center for Geological Disaster, Research Organization of Earth Science and Maritime, National Research and Innovation Agency, Jl. Sangkuriang, Bandung 40135, Indonesia * Corresponding author: tel: +62-81320465935 email: praptie3103@yahoo.com Received: February 20, 2022 Accepted: July 22, 2022 DOI: 10.22146/ijc.73162 Abstract: The purpose of the study in the Karangkobar area was to investigate the source rock potential of the fine-grained surface samples of clastic sediments. The use of surface samples for source rock potential study in Indonesia is still limited. We conducted geochemical laboratory analyses in this research, including Total Organic Carbon (TOC), Rock-Eval Pyrolysis (REP), and Gas chromatography–mass spectrometry (GCMS). Seventeen samples have been analyzed for their TOC content. The result shows that TOC values varied between 0.36–1.55%, indicating that the source rock potential level based on the surface samples is poor to fair organic richness. REP was conducted on 16 samples, and the results show that the hydrocarbon-generating characteristics (HI values) ranged from 15 to 163 mg HC/g TOC. The kerogens identified included type II and III kerogen, which indicated the oil and gas-generating potential. Pyrolysis temperature is at maximum (T max ) in the 276–458 °C, indicating that the samples were thermally immature to mature. GCMS analysis of source rock indicated that the depositional environment of the organic material derived from an open marine and plankton environment. This study is essential to complete the understanding of the petroleum system in Central Java. Keywords: fine-grained sediment; TOC; REP; hydrocarbon; source rocks; potential; Karangkobar Central Java ■ INTRODUCTION Hydrocarbons are an important energy resource for the Indonesian economy. The increasingly limited discovery of oil fields in conventional areas, as has been found so far, has spurred the thought of oil exploration towards basins in the frontier region. The understanding of the frontier here is mainly intended not on the geographical aspects, but more emphasized on the geological aspects. In the petroleum system, in addition to the cover rock (seal layer), there are two main elements associated with the presence of hydrocarbons in a basin. These two important elements are the presence of source rock and reservoir rock [1]. Source rocks are generally fine- grained rocks that are rich in organic materials, while reservoir rocks are formed from clastic (siliciclastic) and non-clastic (carbonate) rocks. Therefore, concerning the study of source rock, especially in conventional exploration, there is a tendency for more exploration activities to be carried out to determine the type of hydrocarbon traps and detailed studies of the bedrock from which the seepage originated.