JOUR.GEOL.SOC.INDIA, VOL.84, OCT. 2014 406 ALI ADNAN AND U. K. SHUKLA A Case of Normal Regression with Sea Level Transgression: Example from the Ganurgarh Shale, Vindhyan Basin, MaiharArea, M.P., India ALI ADNAN and U.K. SHUKLA * Center of Advanced Study in Geology, Banaras Hindu University, Varanasi-221005. *Email: shukla_umakant@yahoo.com Abstract: The Ganurgarh shale, a formation belonging to the Bhander Group of Vindhyan basin is investigated using field based detailed lithofacies and petrofacies analyses in order to interpret the depositional environment in a sequence stratigraphic context. Five major lithofacies have been recognized consisting of calcareous sandstones, laminated mudstones, rippled siltstones, red-grey shales and sandy limestones characterized by small to large-scale cross-bedding, ripple cross-lamination of wave and current origin, parallel lamination, low-angle horizontal bedding, flaser and lenticular bedding, mud-cracks, salt pseudomorphs, convolute bedding and load structures. The constituent lithofacies are recurring and grouped into three lithofacies associations where, the association A is composed of fining upwards and B with coarsening upwards cycles at the lower and middle levels of the succession respectively, are dominantly arenaceous whereas, the association C occurring at upper levels is fining upwards (FU) and becomes calcareous with meager representation of clastics. Petrographically, the section offers three main petrofacies viz., (a) sandstone- (b) siltstone- (c) sandy limestone-petrofacies. Lithofacies characters complimented with petrography show that deposition occurred within the shoreface (subtidal) to foreshore intertidal domain involving tidal flats with sub-environments ranging from intertidal to supratidal. However, lithofacies associations within the Ganurgarh shale of Maihar area represent a case of normal regression during sea level transgression. In the beginning, probably because of excessive sediment supply the sea level had a falling trend during an overall transgressive phase ultimately culminating into limestone sedimentation. Keywords: Neoproterozoic, Lithofacies, Tidal-Flats, Normal Regression, Vindhyans, Ganurgarh shale, Madhya Pradesh. environment ranging from marginal continental to shallow marine domains (Akhtar and Srivastava, 1976; Chakraborty et al. 1998; Bose and Choudhuri, 1990; Bose, et al. 2001). An attempt has been made in the present study to interpret its depositional environment, using detailed lithofacies analysis and petrographical evidence. The objective has been to identify mode of sedimentation in specific geomorphic domains in response to sea level changes. GEOLOGICAL SETTING Maihar, the studied area, lies geologically between Bundelkhand granite (Basement) in the northwest, Deccan traps in the west, Central Indian tectonic zone separated by Son-Narmada lineament in the south and east (Fig. 1 a). The Vindhyan Supergroup has been sub-divided into four groups namely (a) Semri- (b) Kaimur- (c) Rewa- and (d) Bhander- Group in stratigraphic order (Auden, 1933; Banerjee et al. 2006) (see Table 1). The thickness of sediments varies in different areas with time, implying shifting of depocenters (Banerjee, 1964). During deposition INTRODUCTION The Ganurgarh shale of the Bhander Group of the Vindhyan basin belonging to late Precambrian or Neoproterozoic age (Valdiya, 1969; Crawford and Compston, 1970; Sarkar, 1974; Kumar, 1976; Rao et al. 1977; Prasad, 1980; Prasad and Ramasamy, 1980; Ray et al. 2003; Ray, 2006) exposed in and around Maihar area in Satna district of Madhya Pradesh, India, is studied keeping in view to bridge the gap in the Vindhyan stratigraphy existing mainly due to fragmentary nature of outcrops in the study area as compared to other areas of the Son valley.The Ganurgarh shale, litho-stratigraphically, is the basal formation of the Bhander Group and conformably overlies Govindgarh sandstone of the Rewa Group (Table 1). Lithologically, it is constituted of mostly clastic sediments like calcareous sandstones, siltstones, shales and a sandy limestone unit on top. Literature survey makes it obvious that this formation is the least studied from the sedimentological point of view and controversy prevails regarding its depositional setting. Different workers have given varied interpretations for its depositional JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.84, October 2014, pp.406-416 0016-7622/2014-84-4-406/$ 1.00 © GEOL. SOC. INDIA