Shell beds as tools in basin analysis: the Jurassic of Kachchh, western India

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Abstract
Skeletal concentrations are ubiquitous in Bathonian–Oxfordian shallow water sediments of the pericratonic basins of Kachchh and Rajasthan, western India. By analysing the biofabric of the concentrations and the taphonomic signatures of individual components, it is possible to distinguish between the final concentration process (recorded by the biofabric) and events taking place prior to final deposition (recorded by taphonomic signatures). The skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations. They mainly reflect biological and hydraulic processes, and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient. Plotted against the stratigraphic sections, the skeletal concentrations show, in accordance with other sedimentological data, three orders of bathymetric trends. The first two orders are shallowing–deepening cycles which possibly correspond to eustatic changes in sea level; the third order represents parasequences with a strongly asymmetric sedimentary record. Skeletal concentrations are a useful additional tool in basin analysis, but are best used in combination with other data.