238 JOUR.GEOL.SOC.INDIA, VOL.94, SEPT. 2019 JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.94, September 2019, pp.238-244 A Field-scale Overview of Facies Architectures and Depositional Environment Integrating Core and Geophysical Log Data: Study from a Marginal Gondwana Basin, India Souvik Sen 1, * and Joyjit Dey 2 1 Geologix Limited, Dynasty Building, Level-4, Wing-A, Andheri Kurla Road, Andheri (E), Mumbai - 400 059, India 2 School of Earth and Environment, University of Leeds, Leeds, UK *E-mail: souvikseniitb@gmail.com ABSTRACT Karanpura field is the western most member of the E-W trending Damodar Valley basin, belonging to Indian Gondwana sedimentation. This paper aims to provide a field-scale depositional model of Permian Barakar Formation from Karanpura field in order to enlarge the knowledge of stratigraphic and facies architecture. The study reviews the findings from extensively available cores. Four major facies were defined, which represented a fluvial depositional environment. Observations from core analyses were integrated with high resolution geophysical log data to understand the stacking pattern and depositional cyclicity of Barakar Formation. The lateral and vertical distributions of the facies associations were highlighted by well correlations, which established major fining upwards depositional cycles in the area. The depositional model has been interpreted on a regional scale. INTRODUCTION Facies analysis helps to understand the sedimentary structures and architectural elements, deciphers the depositional environment. This is the basic building block for sub-surface characterization, which is a primary step for any basin exploration work. Karanpura field is the western most part of the large east-west trending Damodar valley b asin, an important unit of Gondwana deposits in India (Dey and Sen, 2018; Kumar et al., 2018). Middle Permian Barakar Formation is the major stratigraphic unit. Few researchers (Casshyap and Kumar, 1987; Gupta, 1999; Hota, 2010; Mukhopadhyay et al., 2010; Bhattacharya et al., 2012; Mendhe et al., 2016; Tewari et al., 2017; Dey et al., 2018; Dey and Sen, 2018, Kumar et al., 2018) have published their work on various aspects of Permian Barakar Formation from various parts of Karanpura area and adjacent sub-basins belonging to Gondwana (Raniganj basin, Durgapur depression etc.), but only a few publications are available on field scale interpretation. This paper aims to: (i) summarize the various sedimentary architectures and facies associations from the Karanpura field, (ii) establish a regional sub-surface correlation and (iii) unravel a conceptual field-scale depositional model of Permian Barakar Formation integrating the available dataset. To reach these objectives, a coherent workflow combining extensively available core and high resolution well log analysis was used (data from Dey et al., 2018; Dey and Sen, 2018). Sedimentary structure and sub-surface facies analysis and well log correlations (field scale, i.e. regional) were then performed which shows a vertical and lateral facies variation and depositional environment of the Barakar Formation throughout Karanpura field. GEOLOGY OF THE AREA Karanpura field, one of the major coal bearing unit of Gondwana basins in peninsular India, spread over Hazaribagh, Ranchi and Palamau districts of Jharkhand state, India (Sen and Dey, 2018), with an area of about 2280 sq. km (Dey and Sen, 2018). This is the western most part of the vast east-west chain of Damodar valley basin (Fig.1). It is a saucer shaped basin, having a maximum length of 64 km in the east-west direction and a width of about 36 km in the north-south direction (Priyadarshi, 2004; Dey et al., 2018; Dey and Sen, 2018). Stratigraphy of the Karanpura field consists of thick sedimentary succession from Carboniferous to Cretaceous; lower to middle Gondwana Group of rocks from Talchir to Mahadeva Formation (Dey et al., 2018). Karharbari, Barakar, Barren Measures and Panchet formations with thick shale beds with cumulative thickness of about 500-800 m are present in the Karanpura area (Mendhe, et al., 2016). In the easternmost part of this coalfield, Precambrian basement rocks (metamorphic rocks) and small patchy occurrence of Talchir formation is noted. Barakar Formation occurs in north, south and western parts of the basin with patchy occurrence in eastern part (Dey et al., 2018). Barren Measures Formation is exposed mainly in north and west parts of the basin. Central part of the basin is occupied with Panchet Formation. The study area lies between 23°43' N to 23°47' N and 84°47' E to 84°53' E (Fig.1, same as in Dey et al., 2018). The coal bearing formation was deposited unconformably over the Archean basement of quartzite and quartz mica schists. The regional stratigraphic sequence of Karanpura coal field is presented in Table 1. BARAKAR FORMATION – LITERATURE STUDIES The Gondwana group of basins of India are intra-cratonic basins which occur along rifted grabens (Biswas, 1999). Approximately 5.5 km thick Gondwana sediments, mainly of fluviatile/lacustrine origin were deposited from Upper Carboniferous to Lower Cretaceous and are preserved in the linear rift basins (Hota, 2010; Tewari, 2005; Tewari and Maejima, 2010, Kumar et al., 2018). The Damodar Valley Gondwana basin of eastern India consists of a sequence of east-west aligned sub-basins. Karanpura field is the western most member of the set of sub-basins. The major part of Barakar Formation consists of buff or dull brownish medium to coarse grained compact feldspathic sandstone with interbedded clay bands, grey shale and coal seams (Singh et al., 2003), the average thickness of coal seam varies from 1- 20 m and has its dip towards SE (Singh and Singh, 1996; Dey and Sen, 2018). The occurrence of Glossopteris, Gangamopteris and Cyclopteroids fossil leaves were also observed in their usual state of preservation from the carbonaceous shale and clay band of Barakar Formation (Srivastava and Agnihotri, 2010; Tewari et al., 2017). Casshyap and Tewari (2001) have extensively worked on Barakar Formation, especially coal seams. Their detailed studies from various coal mines and surface exposures suggest that Barakar coals were DOI: 10.1007/s12594-019-1302-x | 0016-7622/2019-94-3-238/$ 1.00 © GEOL. SOC. INDIA