Clastic limestone dikes from the late Proterozoic Bhima Group, South India

Abstract

Clastic dikes of the late Proterozoic Bhima Group, South India, intruding the Kasturpalli Glauconitic Member are reported from two localities. These glauconitic sediments of the Rabanpalli Formation form the oldest transgressive sequence of the Bhima Group, which starts with basal conglomerates and grades upward into supermature quartz arenites. These are followed successively by glauconitic fine-grained sediments and shales. This sequence is capped by thick deposits of micritic flaggy limestones of the Adki Formation. The dikes are generally emplaced vertically, but also have small lateral apophyses along the bedding planes of the host rocks. The clastic dikes are chiefly composed of a matrix of micritic calcite along with quartz, clay minerals, etc. In places, crystals of calcite are observed in the form of veins. In one locality the dikes are emplaced in the vicinity of a post-depositional fault. This faulting seems to have triggered the intrusion of the clastic material, which shows a thixotropic behaviour, into the glauconitic sandstones and siltstones.