GLACIOGENIC COARSE CLASTICS IN A PERMO-CARBONIFEROUS BEDROCK TROUGH IN INDIA - A SEDIMENTARY MODEL

Physical aspects of sedimentation, particularly of coarse clastics within a bedrock trough in the basal 28.5 m of the Permo-Carboniferous Talchir Formation in West Bokaro, India have been addressed herein. The trough-fill facies assemblage bearing abundant signs of glacial activity was eventually buried under wave-agitated open nearshore and shelf sediments. Analysis of several sedimentary characteristics and their interrelationship help to recognize various types of glacial sediments and their frequent resedimentation through various mass flow processes. It brings to light plausible transportational and depositional mechanism. Facies patterns in relation to the various morphometric parts of the trough reveal a changing pattern of sedimentation whereas available palaeocurrent data indicate palaeoflows converging from the flanks and turning axis-parallel on the floor of the trough. Trough-filling through fan progradation, initially from single, but subsequently from multipoint sources, failed to impart systematic changes in bed thickness, clast size and composition in the sequence. This continued till the major coastal onlapping attributed to rapid deglaciation. A model with predictive generalization has been proposed for coarse clastic sedimentation in fjord-like coastal glacier-fed troughs on the basis of observations made herein.