Modern Applied Science; Vol. 13, No. 8; 2019 ISSN 1913-1844 E-ISSN 1913-1852 Published by Canadian Center of Science and Education 22 Sediment Fasies of Upper Part of Late Miocene Halang Formation in Kali Tajum, Gumelar Area, Banyumas - Central Java, Indonesia Yan Rizal 1 , Ricky Andrian Tampubolon 1 , Wahyu Dwijo Santoso 1 & Alfend Rudyawan 1 1 Geological Study Program of Institut Teknologi Bandung Jalan Genesha 10 Bandung 40132, Indonesia Correspondence: Yan Rizal, Geological Department of Bandung Institute of Technology, Bandung- Indonesia. E-mail: yan@gl.itb.ac.id Received: June 26, 2019 Accepted: July 22, 2019 Online Published: July 25, 2019 doi:10.5539/mas.v13n8p22 URL: https://doi.org/10.5539/mas.v13n8p22 Abstract A detailed stratigraphy description and measurements of the sedimentary facies within the Halang Formation has been carried out to provide a thorough assessment of the architectural facies and depositional environment. The study area is located along the Tajum River in the District of Gumelar, Banyumas, Central Java-Indonesia where most of the Halang Formation is preserved in a good condition. Three cycles of facies association from basin plain, in channel to channel overbank deposits were able to be determined from the formation which indicate very active changes of sub-depositional environment that related to transgressive response influenced by the local tectonic during sedimentation takes place. Keywords: Halang formation, Turbidite, lithofacies, Kali Tajum 1. Introduction The stratigraphy of the study area follows the stratigraphy of the Majenang area (Kastowo & Suwarna, 1996). The area is underlain by the deep marine to transitional sediments which belong to Halang Formation, Kumbang Formation and Tapak Formation. Mulhadiyono (2006) stated that within the deep-sea sediments, particularly the Halang Formation, there are traces of hydrocarbon that probably came out via fractures in sandstones (Tobing, 2002). Fanani (2012) suggested that based on the analysis of TOC content of the mudstone, by pyrolysis analysis and vitrinite reflectance analysis and the type of kerogen, the mudstone of Halang Formation have the ability to produce hydrocarbons by primary products such as gas (kerogen type III). The Halang Formation is a turbidite deposit formed in the fore arc basin (Ardenta et al. 2016) at the time of the Miocene. This formation has a wide spread in Java, especially in Central Java (Praptisih and Kamtono, 2011; Ardenta, et Al, 2016; Rizal, et Al, 2016; Rizal et Al, 2017) and some in West Java (Abdurrokhim, et al, 2017). Identification of the body shape of the deep marine deposits in turbidite facies is very important especially with regard to the determination of the geometry of a reservoir. The problem that arises is the geometry of deep marine deposits in these turbidite facies is very complex and varied, and its existence depends on how, when, and the type of depositional environment (Slatt, 2003). The paper aims to study the individual facies and the vertical architectural facies association of the Halang Formation that could unravel the change of their sub-depositional environment and its relationship with the presence of hydrocarbons. Tajum River in the Gumelar District of Central Java is selected as a study area because the river preserves outstanding and continuous sequence of the Halang Formation of which a detailed stratigraphic measurements can be carried out. 1.1 Study Area Administratively research locations are in the Tajum river in Gumelar subdistrict, Banyumas, Central Java Province (Figure 1).