Palaeoecological Analysis of Benthic Molluscs from the Eocene of Kutch, Gujarat Reveals an Event of Storm Induced Concentration of Shells in a Quiet Marginal Marine Environment

Abstract

The Eocene deposits of the Kutch basin are characterized by predominance of plane-laminated shales and low diversity mollusc faunas. These features reflect a low energy, restricted environment. A thin molluscan shell bed stands out in this backdrop because it produced a very diverse assemblage of bivalves and gastropods. Palaeosynecological analysis of the benthic mollusc assemblages from different stratigraphic levels of the Eocene of Kutch, including the shell bed, was carried out by testing for standard ecological models of rank-abundance. The specific abundance data from the shell bed c onform to the log-normal model indicating stable, resource-rich environment. On the other hand, low diversity and often high abundance of opportunist species from other levels reflect harsh ecological conditions for molluscs. Analyses of habitat preferences and habits of the genera from the shell bed indicate shallow to very shallow shelf environment. It is inferred that this exotic assemblage of shells was brought in this quiet, restricted environment by storm surges from open part of the sea. High degree of shell fragmentation and high content of micrite matrix corroborate this interpretation.