Depositional and Diagenetic Environments Vis-à-vis Reservoir Characteristics of the Carbonates of Jhurio formation (Early Late Bathonian), Jumara Dome, Kachchh, Western India

This paper describes 10 microfacies types in the Jumara Coral Limestone and Echinoderm Packstone Members (early Late Bathonian age) of Jhurio Formation of the Jumara Dome. The temporal distribution of these microfacies associations reflects an ideal shallowing upward sequence, representing a system of bioclastic bars separating the basin from lagoon environment. Evidence suggests evolving of this bioclastic bar system upward into an oolitic Bar-to-Bank system. Three types of cements (bladed to fibrous, blocky and syntaxial overgrowth) occur in these carbonates. The study also reveals that chemical compaction followed the two phases of early mechanical compaction that largely governed porosity of these limestones. Diagenetic signatures in these carbonates suggest that marine phreatic, under saturated fresh water phreatic and mixing marine fresh water phreatic environments dominated but deep burial diagenesis also played its role in shaping these rocks through time. Evidence suggests that both primary and secondary porosity exist in these carbonates, which determine the permeability in these rocks.