Late Quaternary Carbonate Deposits of Saurashtra, Western India: Insights from Petrographic Analysis of OSL Dated Sequences

Popularly known as ‘Miliolite' or ‘Miliolitic limestone', the late Quaternary carbonate deposits of Saurashtra, western India is a unique sequence that has been geochronologically constrained recently using Optically Simulated Luminescence (OSL) technique. The sequence contains three distinct type of depositional units, viz., (i) coastal shell limestone, (ii) coastal and inland aeolianites, and (iii) fluvial reworked sheets. Petrographic study has shown that the shell limestone units are mainly biomicrite, biopelmicrite and biopelsparite whereas, the coastal and inland aeolianites are biopelsparite and pelsparite. The allochems are mainly molluscan shell fragments, echinoid grains, bryozoan fragments, coralline algae, peloids, vadoids and intraclasts. The detrital grains in some case reach up to 45% having its minimum value around 2%. The cement is calcareous being mainly law magnesian sparite and microsparite with occasional presence of micrite. Overall the diagenesis of these units must have occurred in fresh water meteoric condition.