Abstract:
High resolution sequence stratigraphic study is conducted for the ~150 m thick tide and wave influenced Upper Barakar succession, West Bokaro Coalfield in order to delineate and reinterpret the possible controls of depositional processes. The study encompasses a systematic identification and analysis of the lithofacies types and their associations. Three major associations are identified viz., facies association 1(FA1), facies association 2(FA2) and facies association 3(FA3). FA1 consists of a tidally influenced coarsening upwards assemblage represented by coal facies , shale facies, carbonaceous shale facies and sandstone facies. FA1 is overlain by FA2, and is a fluvially influenced coarsening upwards assemblage consisting of sandstone facies and a heterolith of sandstone-mudstone. FA3 overlies FA2 and is a tide and wave influenced fining upwards sequence consisting of coal facies, shale facies , heterolith of sandstone-mudstone and medium-fine grained sandstone facies. The entire succession comprising of repeated stacking of FA1, FA2 and FA3 produced multiple coarsening-up and fining-up cycles. Lateral and vertical distribution of the facies types, facies associations and the major boundaries helped to delineate the higher order (4th and/or 5th) systems tracts and their correlations in terms of predominant transgressive-regressive cycles. Highstand systems tract(HST) is represented by the prograding FA1, lowstand systems tract (LST) by aggrading FA2 and transgressive systems tract(TST) by retrograding FA3. Such events of repeated sea-level rise and fall indicate definite marine influence during upper Barakar sedimentation and manifest complex interplay between the changing accommodation space and sedimentation rate.
