Petrographic characteristics and carbon isotopic composition of Permian coal: Implications on depositional environment of Sattupalli coalfield, Godavari Valley, India

• Published in: International journal of coal geology Vol. 90-91; pp. 34 - 42
• Main Authors: Singh, Prakash K., Singh, M.P., Prachiti, P.K., Kalpana, M.S., Manikyamba, C., Lakshminarayana, G., Singh, Alok K., Naik, A.S.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01.02.2012; Elsevier
• Subjects: Carbon isotopes; Coal; Coal petrography; Depositional environment; Earth sciences; Earth, ocean, space; Exact sciences and technology; Godavari valley; Isotope geochemistry; Isotope geochemistry. Geochronology; Macerals; Sattupalli coal; Sedimentary rocks; Andhra Pradesh India; Asia; India; Godavari Valley; India, Andhra Pradesh; Depositional environment; Sattupalli coal; Godavari valley; Coal petrography; Carbon isotopes; Macerals; depositional environment; Permian; sandstone; rank; clastic rocks; shale; carbonaceous rocks; coal fields; stable isotopes; inertinite; C-13/C-12; coal mines; water table; inundations; concentration; Paleozoic; sedimentary rocks; correlation; upper Paleozoic; ash; fusinite; organic materials; coal; vitrinite; macerals; volatiles
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2011.10.002

The present paper entails a study carried out on selected samples of coal and carbonaceous shales of Permian age from the Sattupalli open cast coal mine of Godavari valley, Andhra Pradesh to know their petrographic and chemical characteristics. Based on these characteristics, the depositional environment has also been discussed. The study reveals that these coals are sub-bituminous in rank and are chemically characterized by low to medium moisture (4.3 to 8.6wt %) and volatile matter (24.5 to 32.6wt %) while the ash yield varies between 16.4 and 35.3wt %. Petrographically these coals are rich in inertinite. Liptinites occur in very small concentration. Collotelinite, collodetrinite and vitrodetrinite are the main vitrinite macerals whereas fusinite, inertodetrinite and semi-fusinite constitute the major proportion of inertinites. Mean ∂13C value measured for coal is −22.58±0.20‰ and for carbonaceous shale it is −23.64±0.57‰ while in the organic matter of Barakar sandstones the ∂13C is −25.2±2.1‰. Dry periods are reflected by the abundance of inertinite in some samples while more anoxic conditions are indicated by high concentration of vitrinite in some samples. Seam-II of Sattupalli coalfield initially formed in dry condition and gradually flooding took place due to rise in the water table. During the formation of the upper part of the seam, again a relatively dry phase prevailed. Moreover, a positive correlation of ∂13Corg with TOC and a negative one with TIC indicate that ∂13Corg is being modified by ∂13CDIC. ► These coals have a fluvial deposition as supported by increasing ash yield and a low (<1%) CaO content. ► Coal formation initiated under oxic condition followed by increased water cover in the paleomire. ► Carbon isotope data of coal and associated sediments indicate their terrestrial source. ► This contention is also revealed in petrography, gelification and tissue preservation indices. ► Vitrinite has enhanced the ∂13C as revealed by their correlation (r=0.849).