On the evolution of the Pranhita-Godavari Gondwana Basin, Andhra Pradesh, India

The Pranhita-Godavari Basin is located within a complex milieu of different structural grains of great antiquity, i.e., Dharwar (2800 Ma), Eastern Ghats (1625 + 75 Ma), Pakhal (1300 Ma), Sullavai (880 Ma) of Proterozoic,-indicating a successor-type of basin evolution. The basin configuration, the deposition of the major lineaments, and the more convincing geophysical data, suggest a structural, and not an erosional feature, carved by glacial scouring of this Gondwana basin. The block fault movement, which was initiated during the pre-Pakhal (Precambrian time), has continued spasmodically till the end of the Gondwana period. A broad, four-stage episodes/pulses for the Pakhal, Sullavai, Permian, and Triassic/post-Triassic sedimentation is discernible. The Gondwana basin has a far greater southeasterly strike extension, than the Proterozoic basins, as it cuts across both the Proterozoic basin and the structural grain of the Eastern Ghats. The tectono-stratigraphic synthesis indicates that this master Gondwana basin, comprises, at least four major basins i.e. Godavari, Kothagudem, Chintalapudi and Krishna-Godavari. Though interconnected, within themselves, they display subbasinal structure, highs, a varied floor relief, hingelines, etc., denoting the basin differentiation and subtle variation in its long and complicated geological history. The Permian coal measures appear to have been subjected to folding and faulting initially in the pre-triassic times itself, as documented in some of its faulting pattern. This is also punctuated by a short break in sedimentation, as an overlap between the Permian sequence and the Triassic sequence (hill-forming Kamthi). The coal measures along with the Triassic sediments, appear to have been further subjected to faulting, in the post-Triassic times, as seen in the Chinnur coalbelt area.