A wide spectrum of macroscopic and microscopic features preserved on the bedding planes or frozen between the laminations of fine-to medium-grained sandstones are described from a number of stratigraphically and geogr...A wide spectrum of macroscopic and microscopic features preserved on the bedding planes or frozen between the laminations of fine-to medium-grained sandstones are described from a number of stratigraphically and geographically separated localities within the Chhattisgarh(Bhalukona and Kansapathar Formations)and Khariar basins(Lower sandstone Formation),India and attributed to microbial mat related sedimentary structures.These include bedding plane features viz.wrinkle structures,palimpsest and patchy ripples,spindle-shaped and sub-circular microbial shrinkage cracks indicating original cohesiveness in sand-sized sediments,fragments of torn mat spread on bed surface suggesting mat erosion under high energy flow etc.and bed-perpendicular features e.g.wavy-crinkly laminae,iron oxide specks and stringers etc.The structures suggest different mat-induced biophysical interactions viz.growth,biostabilisation,binding,baffling and trapping or a combination of all.Mat growth also favoured preservation of setulf structure that usually has low preservation potential.The stratigraphic intervals from where the structures are described are assigned Mesoproterozoic time frame(~1.4 Ga)and modelled as products of near-shore environment i.e.wave-influenced shoreface-beach under widely different sea level stands viz.forced regression,low-stand and transgression.It is proposed that prolific mat growth may act as facilitator for preservation of thin forced regressive deposits in Proterozoic low-gradient epeiric basins.展开更多
文摘A wide spectrum of macroscopic and microscopic features preserved on the bedding planes or frozen between the laminations of fine-to medium-grained sandstones are described from a number of stratigraphically and geographically separated localities within the Chhattisgarh(Bhalukona and Kansapathar Formations)and Khariar basins(Lower sandstone Formation),India and attributed to microbial mat related sedimentary structures.These include bedding plane features viz.wrinkle structures,palimpsest and patchy ripples,spindle-shaped and sub-circular microbial shrinkage cracks indicating original cohesiveness in sand-sized sediments,fragments of torn mat spread on bed surface suggesting mat erosion under high energy flow etc.and bed-perpendicular features e.g.wavy-crinkly laminae,iron oxide specks and stringers etc.The structures suggest different mat-induced biophysical interactions viz.growth,biostabilisation,binding,baffling and trapping or a combination of all.Mat growth also favoured preservation of setulf structure that usually has low preservation potential.The stratigraphic intervals from where the structures are described are assigned Mesoproterozoic time frame(~1.4 Ga)and modelled as products of near-shore environment i.e.wave-influenced shoreface-beach under widely different sea level stands viz.forced regression,low-stand and transgression.It is proposed that prolific mat growth may act as facilitator for preservation of thin forced regressive deposits in Proterozoic low-gradient epeiric basins.
