Stratigraphy of the Purana Supergroup Around Ramgundam, Andhra Pradesh

Middle and Late Proterozoic Purana Supergroup at Ramgundam in the Pranhita Godavari valley is separated from the underlying granites and gneisses of the Basement Complex and the overlying Gondwana Supergroup by two major unconformities. Evidence is adduced to show that two other major unconformities divide the Purana sequence into three chronologically independent units correlatable with the Mallampalli Subgroup and the Mulug Subgroup, two major divisions of the Pakhal Group, and the Sullavai Group in adjacent areas, viz., Mancherial and Mulug.

Both the Subgroups of the Pakhal Group comprise of silici-clastics at the base and are followed by carbonates while the Sullavai Group is constituted entirely of siliciclastics. Detailed section measurements show rapid facies variation, both lateral and vertical, to be a characteristic feature of the Pakhal formations. Formations in the Sullavai Group are regionally more uniform in character.