Paleocurrent, Deformation and Geochemical studies of Lower part of the Bagalkot Group of Kaladgi Basin at Ramthal and Salgundi: Implications on Sedimentation History

Abstract

The lithounit conglomerate of the thickness about 6m - 30m is seen exposed at Ramthal and Salgundi belonging to the Salgundi Conglomerate Member of the Ramdurg Formation in the Bagalkot Group of the Kaladgi-Badami sequence of rocks. Even though this basin is studied extensively by many workers on a larger scale, the minute intricacies have remained untouched. This includes studies on individual lithounit with respect to its lithological characters, textural features, provenance, deformation history, paleocurrent directions and mapping on a larger scale of the area. Therefore, this lowermost rock unit provides an opportunity to understand the paleocurrents, provenance and deformation history of the Mesoproterozoic Bagalkot Group. To understand this, field studies were combined with analytical studies to come to a conclusive result. To understand the deformation history of the area, field studies were combined with micro section observations. The deformational mechanisms of grain boundary migration, overgrowths in crystallographic continuity, recrystallisation of quartz, neocrystallisation of micas, indicate the deformation involved a low temperature (<300°C) regime. Further, based on the imbrications of the pebbles observed in the field and reconstruction to a prefolding position of the limbs of the fold based on the dip directions recorded at two places Ramthal (dipping North) and Salgundi (dipping South) suggests the upstream side of the basin to be probably towards the western side of the basin. The rock is mineralogically matured with abundance of silica varieties and lack in feldspars. While percentage of Fe2O3 increases along with SiO2 at both places that of Al2O3, K2O, CaO and Na2O is much less. The Al2O3+Na2O+K2O versus SiO2 plot indicates Compositional Maturity Index is relatively higher at both the study areas suggesting removal or lack of mobile elements like Na2O and MgO. The lower concentrations of U and Th in the samples with lower ΣREE probably reflects a control by grain size fractionation during transport suggest a contribution from a mafic source with lesser concentration of such elements. Bivariant log/log plot of the ratio of Qp/F + R values represent the region to have been a moderate to low lying plain experiencing hot, tropical, oxidizing, humid climatic conditions.

Keywords: Mesoproterozoic, provenance, deformation, imbrications