PALEOTECTONIC EVOLUTION OF THE EASTERN GONDWANAN RIFT BASIN FROM LATE CARBONIFEROUS-EARLY PERMIAN DEPOSITS IN THE PRESENT-DAY SUB-BASINS OF AUSTRALIA, INDIA, NEPAL AND BANGLADESH

The time from late Carboniferous to early Permian marks the initiation of rifting in eastern Gondwanaland between Australia, India and Antarctica. This rifting resulted in forming sub-basins that are distributed along the present-day south-western Australia, west-central India, discontinuous patches along the Himalayan belt in Nepal and northwestern Bangladesh. Though there have been numerous studies on the rifting basin about tectonics and sedimentation system of eastern Gondwanaland, it indisputably lacks a regional correlation that can provide the petrofacies evolution of this mega basin. Veevers and Tiwari (1995) first mentioned that the late Carboniferous Gondwanan sequences were deposited in a mega basin that had grown simultaneously with the development of the rifting. The sedimentation began with deposition of glacial diamictite as the Permo-Carboniferous glaciation ended, which can be correlated using the diamictite deposits in Tansen, Katari and Barahachettra in Nepal (Sitaula, 2009) and in Lyons Group of Southern Carnarvon, and the Nangetty Formation of Canning basin in Australia (Mory et al., 2008). This was followed by deposition of alternating sandstone, mudstone and coal layers that can be correlated in the sub-basins of central India and northwestern Bangladesh (Alam, 2011; Chowdhury, 2014). ⁴⁰Ar/³⁹Ar age dates of muscovite from sandstone samples are variable. Samples from India show an older age of 800mya peak in late Carboniferous glacio-fluvial Talchir Formation that shifts to a younger 500mya peak in lower portion of early Permian fluvial Barakar Formation (Chowdhury, 2014), which is correlatable with the samples from Gondwana Group in Bangladesh with a similar ⁴⁰Ar/³⁹Ar age peak of 500mya (Alam, 2011). In Nepal, detrital muscovite ages widely range from as early as 18mya to as late as 1000mya; the old ages reflect pre-Carboniferous orogenic systems formed during and prior to the amalgamation of the Gondwanaland, whereas the younger ages are related to the Himalayan orogenic events (Sitaula, 2009).

Ongoing research involving detrital geochronology, petrofacies, mineral chemistry, and magneto-stratigraphy on Gondwanan sequence of Indian subcontinent and Australia will provide insights reconstructing the eastern Gondwanaland.