DETRITAL HISTORY OF THE PERMO-CARBONIFEROUS GONDWANAN SANDSTONES OF NORTHWESTERN BANGLADESH AND JHARIA BASIN OF INDIA

Permo-Carboniferous Gondwanan sequences are well-distributed in the Indian subcontinent, South Africa, Madagascar, Australia, Antarctica and South America, bearing proof that the southern continents were once united in the form of Gondwanaland. This study has been carried out focusing on petrofacies and geochronology of Gondwanan sequences of Barapukuria, Dighipara, and Khalaspir coal basins in northwestern Bengal Basin of Bangladesh and Jharia Basin in the Eastern India in order to better reconstruct regional detrital and tectonic histories of Late Paleozoic Gondwanan basins of South Asia. Sandstone petrographic studies of Permo-Carboniferous Gondwanan sequences reveal differences in sandstone modes between sediments from India and Bengal Basin. Modal composition, heavy minerals and geochemical studies vary among various basins as well as different stratigraphic levels of the same basin. These compositional differences among basins and different stratigraphic levels may be attributed to differences in source rocks, weathering conditions and fluvial networking of that time.

The detrital ⁴⁰Ar/³⁹Ar data show mostly polymodal distributions of cooling ages of detrital muscovites. The populations of age distributions from Indian sediments significantly differ from the Bengal Basin samples. Age clusters from Bengal samples strongly focuses on a narrow zone of Cambro-Ordovician whereas Indian samples are more scattered containing more Neoproterozoic cooling ages. The age distributions of the Talchir Formation significantly differ from the Barakar Sandstones. Changes in the peaks of age clusters of muscovites from different stratigraphic levels might be due to changes of source terranes through time.