Proterozoic intracontinental basin: The Vindhyan example

摘要

The Vindhyan basin is a classic example of Proterozoic intracontinental basin that developed in the central part of the Indian shield along with several other basins such as Cuddapah, Chattis-garh, etc. The strata are exposed in three major sectors: Son valley, Bundelkhand and Rajasthan. Substantially thick Vindhyan rocks have also been recognized under the Gangetic alluvium. The constituent stratigraphic units of the Vindhyan Supergroup are laterally correlatable and vertically stacked in similar fashion in individual sectors, but their stratigraphic and sedimentologic attributes vary from one sector to the other. The basin fill in the Son valley (around 3 km thick) exhibits an asymmetric cross-sectional geometry normal to the regional strike (ENE-WSW), with the thickest part occurring to the south, and is divisible into four groups: Semri, Kaimur, Rewa and Bhander, from bottom to top. The boundary between the Semri and Kaimur Groups is marked by a pronounced unconformity. The dominant lithologies include conglomerate, sandstone, shale, limestone as well as volcaniclastics. The Vindhyan strata define a broad, regional syncline trending ENE-WSW. The axis of the syncline is slightly curved (convex towards north) and plunges gently towards west. The average dip of the southern limb is greater than that of the northern limb rendering the axial plane to dip southerly.