Spatiotemporal Variation in Sedimentation Pattern from the Eastern to the Western Part of the Chhattisgarh Basin and its Implication on the Tectonic Evolution Model

ABSTRACT Meso-to-Neoproterozoic Chhattisgarh Supergroup unconformably overlies the Neoarchaean to Palaeoproterozoic granitoids and meta-sedimentary rocks of the Bastar Craton. The succession consists of two major unconformity-bounded sequences, the Chandarpur-Raipur and the Kharsiya. Striking differences in the thicknesses and sedimentation patterns of the two sequences have been observed from the eastern part of the basin transitions to the western part. The maximum thickness of these sequences in the east and west of the basin is ~ 2580 and 1800 m, respectively. The thickness of the Chandarpur Group is about 1100 m in the east and merely about 300 m in the west. The thick mudstone-dominated Gomarda Formation (630 m) of the east is completely missing in the west. Conglomerate and arkose occur widely in the east but not in the west. In contrast, carbonates and fine siliciclastics occur more extensively in the west, indicating variation in the depositional environment along an east-west direction. The petrographic study indicates that the major source in the eastern part is granite gneiss, whereas in the west, the source of sediments includes both granite gneiss and meta-sedimentary rocks. The REE patterns and Eu anomalies of the shale and sandstones from the Chhattisgarh Basin are similar and resemble the granite gneiss of the Bastar Craton. The provenance analysis using trace elements and Nd isotopic ratios corroborates that the spatially extensive ~2.5 Ga granite gneisses were the major contributors of the detritus. U-Pb SHRIMP ages of detrital zircons from Lohardih and Kansapathar formations, and Deodongar Member of the Chandi Formation yield unimod-al distributions (ca. 2470 and 2485 Ma), reflecting supply from the granitic basement. The successive N-S trending faults, poorly sorted conglomerate and sandstone along the basin margin, followed by matured quartz arenite and carbonate-shale deposit with variation in thicknesses of the different stratigraphic units of the eastern and the western parts of the basin, point to the half-graben model of the basin evolution.