Tectonic setting of Kaladgi-Badami basin and its possible connection with adjacent Proterozoic basins, Karnataka, India

Abstract

Sedimentary rock types and basin geometries are interrelated with characteristic tectonic settings. In fact, sedimentation pattern at central stable cratonic areas are not same as that on continental margins. Kaladgi-Badami (KB) basinal feldspathic arenite (i.e., arkose) dominated rocks contain more plagioclase than potassium feldspar unlike the opposite scenario of Phanerozoic sandstones. Tectonic history of the KB basin has been interpreted since basin development, sedimentation through interrupting hiatus, tectonic reworking, redeposition at later developed depocenters and later exhumation, erosion, tectonism till Deccan volcanism and finally latest configuration. As per the International commission of Stratigraphy (ICS), principles of stratigraphic classification and usages of terminology of fundamental lithostratigraphic unit ‘Formation’ is reexamined in this paper. The definition of Formation as “smallest mappable rock unit with a definite lithologic characteristic that allow it to be distinguished from other such units” is improperly used because without mentioning a specific scale every unit is mappable or traceable. Therefore, the minimum mappable unit means the unit which can be at least visible in a scale in which entire basin can be seen. Based on this slight modification is proposed in the stratigraphy of KB basin. Geochronology based radiometric stratigraphy is best tool for determination of time sequence of geological events. However, it is always a matter of concern that dating methods and materials are often not suitable in sedimentary geology. In case of passive rifted sedimentary basins like Kaladgi, Badami and Bhima of the Dharwar Craton, there is negligible igneous events and indirect dating methods are mostly available. Detrital zircon dating can give maximum age or provenance age, which cannot be of much use. However, there are other indirect tools, which are already utilized by several workers earlier and based on the reviews and present observation and mapping compilation it is proposed that KB and Bhima basins used to be a single basin, and later tectonism followed by Deccan volcanism affected the present geographic continuity. Since the distance between westernmost Bhima basinal rocks and easternmost KB basinal rocks near Mudhebihal is nearly around 15km, it is logical to consider that these were geographically connected, because there is an intense faulting near to these basin margins.