Microbial mat control on siliciclastic Precambrian sequence stratigraphic architecture: Examples from India

An attempt has been made to understand, within a cause-and-effect framework, the sequence-building pattern in Proterozoic time that witnessed non-uniformiteranean microbial mat growth and epeiric sea development. Marine or marginal marine successions in three Neoproterozoic formations, the Sonia Sandstone in western India, and the Sirbu Shale and Upper Bhander Sandstone in central India have been examined here for this purpose. The strikingly common feature of all three formations is vertical stacking of highstand systems tracts without intervention of any significant transgressive deposits. In one instance only, the transgressive systems tract is represented by a thin granular transgressive lag, and in all other cases the evidence of transgression is simply marked by the presence of marine flooding surfaces. The absence of transgressive strata relates to the low sea floor gradients, which facilitated rapid transgressions, combined with a generally low sediment supply. Aggradation under normal regressive highstand conditions, in spite of the low sediment supply, was promoted by the prolific growth of microbial mats, which reduced the effects of wave and current reworking by organic binding of clastic particles.