Depositional Environment of the Sangkarewang Oil Shale, Ombilin Basin, Indonesia

Abstract

Abstract. Five samples from a 56 m long drill core that was recovered from the lacustrine Sangkarewang oil shale have been studied by means of petrography and organic geochemistry in order to investigate the organic matter composition and depositional environment of the shale. The organic matter consisted of abundant lamalginite (30%, v/v) and a very limited amount of vitrinite, suggesting an aquatic depositional environment with minor terrestrial influence. Organic geochemical analysis exhibited the dominance of pristane, phytane, and generally n-alkane compounds. These compounds may have originated mostly from aquatic photosynthetic organisms. The oil shale was likely deposited in an anoxic lake environment as suggested by the presence of framboidal pyrite (6%, v/v) and preserved organic matter with a total organic carbon (TOC) percentage of about 4.9%. The pristane/phytane ratio was relatively high (about 3.9) and thought to be source sensitive rather than redox sensitive. Hopanoid and aryl isoprenoid compounds were present in minor amounts. The latter compounds are interpreted to be derived from green sulfur bacteria dwelling in an anoxic environment with the presence of H 2 S in bottom water.

Precipitation of Calcite during the Deposition of Paleogene Sangkarewang Oil Shale, Ombilin Basin, West Sumatra, Indonesia

“…The Sangkarewang oil shale is calcareous as reported by e.g. Koesoemadinata and Matasak (1981) with carbonate content in Talawi area is up to 55% (wt) (Anggayana et al, 2014). The mineralogy of Sangkarewang oil shale has been discussed in detail by Fatimah and Ward (2009).…”

“…Journal homepage: h p://ijog.bgl.esdm.go.id ISSN 2355-9314 (Print), e-ISSN 2355-9306 (Online) I J O G petrology (Fatimah and Ward, 2009;Widayat et al, 2013) and organic geochemistry (Anggayana et al, 2014;Widayat et al, 2013). With respect to the presence of organic matter in the oil shale, the authors have demonstrated the depositional environments responsible for the organic matter preservation.…”

“…With respect to the presence of organic matter in the oil shale, the authors have demonstrated the depositional environments responsible for the organic matter preservation. Euxinic bottom water existed in the former Ombilin lake was thought as the key factor for the preservation of organic debris sinking from top water into sediment zone (Anggayana et al, 2014;Koesoemadinata and Matasak, 1981).…”

“…However, anoxia has also been ascribed to the higher accumulation of organic matter in sediments (Demaison and Moore, 1980) as anaerobic degradation of organic matter is thermodinamically less efficient than aerobic degradation (Claypool and Kaplan, 1974). Anoxia in the Lake Ombilin has been reported by some authors and considered as the significant factor on the abundant of preserved organic matter (Koesoemadinata and Matasak, 1981;Anggayana et al, 2014).…”

Penentuan Peringkat Dan Pengaruh Karakteristik Batubara Terhadap Nilai Kalori

“…Batubara merupakan salah satu batuan sedimen padat yang mudah terbakar dan terbentuk dari hasil rombakan tumbuhan pada masa lampau, berwarna coklat-hitam, mengalami proses perubahan fisika dan kimia yang mengakibatkan pengayaan pada kandungan karbon (Anggayana & Widayat, 2007). Peringkat batubara adalah posisi batubara pada peningkatan kandungan karbon dari lignit hingga antrasit dan pada umumnya akan berbanding lurus dengan kualitas batubara.…”