Field Characteristics of Sedimentary Rocks in the Dohol Formation, Johor, Peninsular Malaysia

Abstract The Dohol formation is predominantly composed of sedimentary rocks; however, the black shales attract much attention because of their potential to generate hydrocarbons. Black shales generally have a high organic matter content and can serve as good source rocks for hydrocarbon generation. Therefore, this study was conducted to characterize the sedimentary rocks, including the black shales, which are of great importance and discover new areas where these rocks can be located. Four distinctive lithofacies of shales were observed on the field; the massive black shales facies, light grey shales facies with quartzite intrusion in some areas, the red sandy shales, and the dark brown shales facies. The black shales are dark-coloured, laminated, and some parts are fissile. The second type of shale, light grey, looks similar to the dark shales, but it probably contains less organic matter. In other areas, these grey shales have intrusions of quartzite. The third type of shale facies are the red shales which are sandy, fissile, and highly weathered, and pebbly sands overlie it. Finally, the dark brown shale facies are fissile, flaky, and weathered. The sandstones encountered are massive cream-colored, and composed of mainly quartz with a few scour marks in some areas. Several new outcrop locations of these sedimentary rocks were discovered, and they are spread across Jemaluang, Kota Tinggi, and the outskirts of Mersing town in East Johor. From the outcrop trends and the sedimentary features of the shale rock sequence, the deposition environment of the shales is probably from shallow to deep marine.