Contents lists available at ScienceDirect International Journal of Coal Geology journal homepage: www.elsevier.com/locate/coal Paleoenvironment of Eocene lignite bearing succession from Bikaner-Nagaur Basin, western India: Organic petrography, palynology, palynofacies and geochemistry Alpana Singh a , Mahesh Shivanna b,⁎ , Runcie P. Mathews a , Bhagwan D. Singh a , Hukam Singh a , Vikram P. Singh a , Suryendu Dutta c a Birbal Sahni Institute of Palaeosciences, 53-University Road, Lucknow 226 007, India b Instituto de Geociencias, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Goncalves, CEP 91509-900 Porto Alegre, RS, Brazil c Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai 400 076, India ARTICLE INFO Keywords: Organic petrography Palynofacies Palynology Biomarkers Eocene lignites Bikaner-Nagaur Basin ABSTRACT Lignite and associated shale samples from the Matasukh mine of western India have been studied by petro- graphic, palynofacies, palynological and organic geochemical parameters. The objective is to understand the floral (organic) composition, and palaeo depositional conditions (ecology and climate) of the lignite-bearing sequence. Petrographically, the low rank B lignites are dominantly composed of huminite macerals, followed by moderate liptinite and low inertinite macerals. The predominance of detrohuminite (attrinite + densinite) with respect to telohuminite (textinite + ulminite) suggests that the woody vegetation has undergone higher degree of degradation during the peat accumulation, as is also indicated by the frequent occurrence of funginite. The TPI, GI, GWI and VI indices point towards limno-telmatic condition of the palaeomire during the deposition of lignite-forming peat under mesotrophic to rheotrophic basin conditions. The reducing conditions in the de- positional site are evident from the frequent pyrite content. The studied samples had a high organic matter yield, which showed a co-dominance of phytoclasts and AOM. This nexus is indicative of a marginal marine deposi- tional environment, also evident from Tyson's APP diagram. The palynofloral assemblage is dominated by an- giosperm pollen, especially those having affinity with the family Arecaceae. The presence of palynomorphs of the family Dipterocarpaceae indicates the existence of rain-forest vegetation in the vicinity of the depositional site. The degradation products of oleanane and 23-norlupane in the sediment extracts also suggest that the angiosperm dominant higher plants served as the source for the peat-forming biomass. The presence of hopanes indicates high microbial activity during the formation of lignites. The high CPI and TAR values also indicate the large input of terrigenous higher plant materials. 1. Introduction The north-western state of Rajasthan in the Indian subcontinent has been considered as a highly potential region for fossil fuel resources. Rich in highly carbonaceous sediments such as lignites and shales along with hydrocarbon reserves, this part of the country serves as one of the important producer of oil and natural gas and occupies a significant position in the mineral map of the country. Lignites are reported from the Tertiary sediments extending an area of 1700 km 2 in Nagaur, Jalore, Bikaner, Barmer and Jaisalmer districts of Rajasthan. A recent investigation suggests that the lignite of Rajasthan can serve as a po- tential source of unconventional oil (Raju and Mathur, 2013). The present study focuses on the lignite-bearing sequence exposed in the Matasukh mine located in Nagaur district of central Rajasthan (Fig. 1A). The lignite is being commercially exploited by the Rajasthan State Mines and Minerals Limited (RSMML) since 2003, mainly for thermal power generation. The conventional organic petrographic analysis is the widely used method for evaluation and evolution of coal/lignite deposits (Stach et al., 1982; Diessel, 1983; Kneller William and Wu, 1985; Diessel, 1986; Calder et al., 1991; Kalkreuth et al., 1991; Taylor et al., 1998; Kalaitzidis et al., 2000; Flores, 2002; Bechtel et al., 2004; Dai et al., 2007; Životić et al., 2010; Suárez-Ruiz et al., 2012; Stock et al., 2015). Economic evaluation and palaeoenvironmental re- construction of lignite, using multidisciplinary analysis of the organic matter in lignite, has gained immense significance in the past few years (e.g. Bechtel et al., 2005, 2007; Dutta et al., 2011a; Zdravkov et al., http://dx.doi.org/10.1016/j.coal.2017.08.009 Received 13 January 2017; Received in revised form 21 June 2017; Accepted 18 August 2017 ⁎ Corresponding author. E-mail address: mahesh.shivanna@ufrgs.br (M. Shivanna). International Journal of Coal Geology 181 (2017) 87–102 Available online 30 August 2017 0166-5162/ © 2017 Published by Elsevier B.V. MARK