Subhojit Saha

Chapter 13 Geology of Mesoproterozoic Chhattisgarh Basin, central India: current status and future goals

Abstract In the last two decades multiproxy studies involving process-based sedimentology, geochronology of interbedded tuff units from different stratigraphic levels, sediment geochemistry including stable isotope signatures and documentation of structural grains within selective stratigraphic intervals from the Chhattisgarh Basin, central India have resulted in a perception change on various aspects of the basin fill including its time frame, stratigraphic framework and depositional architecture in the space–time domain. In addition to establishing a Mesoproterozoic (c. 1450–1000 Ma) time frame for the basin on a strong foothold, these studies also proposed revision of its stratigraphy by introducing new stratigraphic units at ‘formation’ and ‘group’ level. From collation of available data, their critical evaluation and presentation of new data, the present work proposes a four-tier lithostratigraphy for the Chhattisgarh Supergroup, namely, Singhora Group, Chadarpur Group, Raipur Group and Kharsiya Group. Further, application of sequence stratigraphic rationale allowed the basin succession to be subdivided into four and three nonconformity/unconformity-bound depositional sequences in its eastern and western parts, respectively. The present chapter also highlights the potential of the basin for carrying out studies related to Mesoproterozoic ocean oxygenation and outlines the necessity of well-planned geophysical transects to resolve issues related to tectonic setup of the basin.

Chapter 14 c. 1450 Ma regional felsic volcanism at the fringe of the East Indian Craton: constraints from geochronology and geochemistry of tuff beds from detached sedimentary basins

Abstract New geochronological and geochemical data from bedded porcellanitic tuffs present within two sedimentary basins at the eastern fringe of the Archaean Bastar Craton, eastern India (the Ampani and Khariar basins) are presented and compared with data available from tuffaceous beds present within adjoining basins. U–Th–total Pb electron probe microanalysis data of monazite grains from the Ampani tuff revealed several age data clusters: c. 2400, c. 2130, c. 1600, c. 1450 and c. 1000 Ma. An age of 1446±21 Ma is proposed as the depositional/crystallization age for the Ampani tuff, considering its maximum probability. Comparable ages for the tuffaceous units from the Khariar (1455±47 Ma) and Singhora (c. 1500 Ma) basins allow us to infer a major felsic volcanic event during c. 1450 Ma at the eastern margin of the Indian Craton. Detailed geochemical data suggest rhyolite to andesite character for the siliceous tuff units from three geographically separated basins and point towards the presence of an active volcanic arc in a subduction-related setting in the region. The geochronological and geochemical data prompted us to search for other contemporaneous events in the Indian continent and beyond, that is, within its erstwhile neighbours in the Precambrian supercontinent ‘Columbia’.