Petrological Investigations of Oligocene Coals from Foreland Basin of Northeast India

Abstract

The results of the petrological investigations carried out on coal samples from the Oligocene deposits of Northeastern India (Assam, Arunachal Pradesh and Nagaland) have been discussed. These deposits occur in the Tikak Parbat Formation (Barail Group) and were probably deposited in the foreland basin. Petrographically, these coals are enriched in vitrinite macerals (65.8-96.6 vol %, mean 87.2 vol %) with variable concentrations of liptinite macerals (2.7-35.4 vol %, mean 11.9 vol %). They contain low concentration of inertinite (nil-3.3 vol %, mean 0.9 vol %) macerals. The microlithotype is dominated by vitrite (61.5-100 vol %, mean 90.8 vol %). An elevated volatile matter (44.15 -60.20 wt %, mean 52.90 wt %, d.a.f. basis) and reflectance values (VRr 0.39-0.61%) put their rank as sub-bituminous type 'C' to high volatile bituminous type 'C'. The GI and TPI values favour telmatic conditions of origin with high tree density and prolonged wet conditions. This is in agreement with the paleoenvironment interpreted from the vitrinite and liptinite-rich microlithotypes, which suggested a forest and reed facies. However, the presence of inertinite in some coal seams indicates tectonic upheavals / regression of the sea resulting to periodic and short span dryness of the basin.

Leaching of trace elements from Indian coal

“…Navale and Saxena (1989) indicated the deposition of West Bokaro coal under freshwater environment, while Neyveli coal was deposited in deltaic to near-shore backswamp environment (Sidhanta, 1986). The petrographic and chemical imprints also indicate that Makum coal and other coals of northeast India were deposited under marine influence as deciphered from its mineralogy (Singh et al, 2012;Singh et al, 2013).…”

“…Coal seams occur in Tikak Parbat Formation of Oligocene age, and mainly comprises of fine grained sediments consisting of sandy shale, siltstone, shale, mudstone and clay units. These are high sulphur coal, and are classified into sub-bituminous rank on the basis of studies on their chemical composition and physical characteristics (Chandra and Chakrabarti, 1989;Singh et al, 2013).…”

“…Goodarzi et al (2006) reported that high carbonate content in the coal resulted from the carbonate bed rock geology. Dominant pyrite in Makum coal is due to the influence of marine environment during coal formation (Chandra and Chakrabarti, 1989;Singh et al, 2012;Singh et al, 2013). Cohen et al (1984) reported that marine to brackish peat contains more pyrite than the fresh water type.…”

Coal petrology analysis and implications in depositional environments from Upper Cretaceous to Miocene: a study case in the Eastern Cordillera of Colombia

“…From the petrographic results, models, and indices (GI, TPI, GWI, VI) proposed by different authors in recent decades were used to identify the facies and deposit environment of the coals (Smyth 1979;Mukhopadhyay 1986;Calder et al 1991;Diessel 1992;Singh and Singh 1996;Rimmer et al 2000;Singh and Singh 2000;Singh et al 2013). Regarding the current knowledge about the stratigraphy and sedimentology of the Eastern Cordillera, different studies were integrated to analyze our results, we took into consideration mainly the outcomes of Ulloa (1976), Guerrero and Sarmiento (1996), Dueñas and van der Hammen (2007), Bayona et al (2007Bayona et al ( , 2008, Parra et al (2008), Terraza et al (2013), Pardo and Jaramillo (2014), and Caballero et al (2020).…”

“…These disciplines are essential to support and restore the deposit environment and infer the origin of vegetal matter, facies, processes, and conditions of the coal formation. Petrology provides indices and ternary diagrams as elements for this sort of interpretations (Teichmüller and Teichmüller 1982;Diessel 1986Diessel , 1992Mukhopadhyay 1986;Calder et al 1991;Singh and Singh 1996;Singh and Singh 2000;Rimmer et al 2000;Staub 2002;Singh et al 2013;Bechtel et al 2014;Sen et al 2016;Singh 2016). Some authors argue the disagreement on the use of diagrams and indexes (Dai et al 2020).…”