Interplay Between Tectonics & Eustacy in a Proterozoic Epicratonic, Polyhistory Basin, North Dharwar Craton

Abstract

The Kaladgi basin of the Dharwar craton is one of the smaller Purana basins of Peninsular India. It hosts two sequences of epicratonic sediments separated by an erosional and angular unconformity; that are comparable in the sedimentological contents and depositional patterns to the other Purana basins. The pervasive deformation of the older Bagalkot Group is unlike the deformation in other Purana basins. Observations and data on the distribution of sedimentary facies and their mutual interrelations, stratigraphic succession, structural patterns are used to analyze the subsidence history of this basin. It is demonstrated that an interplay between extensional tectonics and eustatic sea-level rise have resulted in the preserved contents of the basin. Two distinct transgressive cycles (with a localised subsidiary sea-level spike during the waning phase of the first cycle) flooded the northern margin of the Dharwar craton. A transtensional extension due to a contemporary reactivation of the basement shears contributed to the growth of the Kaladgi basin. Synsedimentary tectonic subsidence punctuated the relative sea-level rise and enhanced the sediment accumulation in the Bagalkot Group. An intervening phase of compressive tectonics deformed the existing sedimentary sequences into tight plunging folds and exposed them to erosional forces. The succeeding Badami Group hosts continental deposits with minor marine components. Sparse tectonic activity attended the second (Neoproterozoic) transgression that yielded this younger sequence. The Kaladgi basin is a polyhistory basin that evolved in two pulses. The early growth was of a continent-interior sag/rift driven by reactivation of basement shear zones during the Mesoproterozoic. The Neoproterozoic successor basin rests atop this as a nested continental sag basin. New geochronology of the intrusives in the basin helps correlate these events with global supercontinental events.