Pitambar Pati

Use of digital elevation models and drainage patterns for locating active faults in the Upper Gangetic Plain, India

Twelve normal, active faults transverse to the regional Ganga and Yamuna longitudinal faults have been identified in the western part of the gently sloping Upper Gangetic Plain from the interpretation of digital elevation models (DEMs), prepared by manual digitization of spot heights from 1 : 50 000 scale topographic maps. High vertical exaggeration of these DEMs reveals artefactual morphostructures such as ‘cliffs’ and ‘significant breaks in slopes’ that are indicative of faults. Convergent drainage on the upthrown blocks, initiation of new streams on the downthrown blocks, offsetting of drainage and anomalous sinuosity of streams close to faults have provided additional corroborating evidence of the faults. Detailed field investigations indicate relatively steeper slopes close to the inferred faults than the adjoining areas. Erosion of the upthrown blocks and deposition of sediments on the downthrown blocks in the form of terminal fans under a semi‐arid climate formed features typical of many such faults.

Paleoweathering and Paleoclimatic Reconstructions using Neoproterozoic Paleosol in the Eastern Margin of the Pranhita-Godavari Basin, India

A thin, weakly-developed palaeosol horizon within the Neoproterozoic Sullavai sandstone in the eastern margin of the Pranhita-Godavari basin was studied. Field observations, thinsection studies and geochemical analyses of the palaeosol horizon were carried out to reconstruct the palaeo-weathering and palaeoclimatic conditions. The palaeosol developed on sandstone parent rock. Morphological features of this palaeosol are not distinct, perhaps due to very ancient nature as well as thin occurrence. A few of which that can be mentioned include weakly developed peds and calcareous nodules of size <1 cm -.2 cm. The lower part of the profile preserves incipient parent rocklamination. Major micromorphological features of this palaeosol include weakly-developed sub-angular blocky structure and redoximorphic features showing redox enrichment and redox depletion of Fe oxides and oxyhydroxides. XRD analysis of the palaeosol reveals the presence of glauconite and illite, suggesting deposition of sediments under shallow marine conditions, and prevalence of cold climate, respectively. This is also supported from Chemical Index of Alteration (CIA)and presence of illite. Further, Chemical Index of Weathering (CIW), Clayeness, and Salinization data of the palaeosol clearly suggests an environment where chemical weathering was feeble and cold (11-14°C) palaeo-temperature. XRF results show abundance of K, Ca and Mg which suggest the area was poorly drained along with cooler palaeoclimate during the late Neoproterozoic. Al2O3 concentration at the middle of the soil profile suggests weakly-developed B-horizon, however it is hardly observed in the field. Parent material, cold climate and less time of exposure only resulted in the formation of a thin and weaklydeveloped soil profile. This ancient soil may represent an unconformity at the basin boundary suggesting a local regression and exposure of the fluvio-marine deposits along the basin boundary. It further needs detailed such studies at various spatiotemporal basinal scales.