Morphological variability of stromatolites and their cyclicity: Examples from a Proterozoic carbonate platform of Vindhyan Supergroup, India

Abstract

In the exploration of well-preserved Proterozoic stromatolites in the Bhander Limestone Member and the basal horizon of the Sirbu Shale Member within the Vindhyan Supergroup of central India, various challenges arise due to the emergence of abiogenic features resembling their biogenic counterparts. This investigation utilized sedimentological, microscopic, and ultramicroscopic methods to unravel the origin of these intricate organo-sedimentary structures. Within the studied stratigraphic sections, six distinct stromatolite morphotypes were identified, including large-scale laterally linked domal stromatolites (S1), columnar stromatolites forming biostromes (S2) and bioherms (S3), small-headed stromatolites (S4), stratiform stromatolites (S5), and cabbage-shaped domal stromatolites (S6). Microscopic analysis revealed varied microfabrics, such as alternating dark-colored micritic and light-colored spar calcite-bearing laminae. Raman spectra analysis confirmed the presence of carbonaceous material within the darker micritic laminae. The diversity in macro-scale morphological variations and their cyclical patterns, coupled with in-depth microstructural investigations, strongly suggest a significant role of microbial communities in the formation of these stromatolites. The presence of different stromatolite morphotypes and their cyclical patterns further supports the hypothesis that microbial processes responded to changing energy conditions and subsidence-induced spatial alterations in a shallow marine environment, ultimately indicating a biogenic origin for these stromatolites.