Dolomitisation in the Northern Part of the Chhattisgarh Basin, Bilaspur District, Madhya Pradesh

Dolomite, occurring in the shale-limestone sequence of the Raipur Stage of the Precambrian sedimentaries of the Raipur Series in the northern part of the Chhattisgarh basin, was formed by dolomitisation of the calcium carbonate sediments in two phases. The dolomitised sediments were deposited in a linear, shallow, near-shore, uneven basin, which was divided into (i) closed or partly connected, shallow, sub-basin and (ii) isolated, comparatively deeper and 'starved' sub-basin. Higher values of pH, PCO₂, Mg/Ca ratio and CO₃ ion concentration prevailing in the closed, shallow sub-basin gave rise to an early replacement forming extensive dolomite bodies. The second phase, responsible for veins and smaller irregular dolomite bodies was effected by the Mg-ions released during the recrystallisation of calcite and labile material of the limestones and their subsequent diffusion by the squeezed out connate waters.

Solution features developed during dolomitisation and subsequently by surface and groundwaters have induced secondary porosity in the dolomite. These are therefore significant for groundwater exploration in the area.