Fluvial geomorphology and neotectonic activity based on field and GPR data, Katrol hill range, Kachchh, Western India

Abstract

The largely rocky and rugged landscape of the Katrol hill range, composed of Mesozoic rocks and structurally controlled occurrences of Quaternary sediments, is delimited to the north by north-facing range front scarps of the seismically active E–W trending Katrol Hill Fault (KHF). The landscape and drainage characteristics of the Katrol hill range are documented together with ground penetrating radar (GPR) investigations along the KHF to delineate its nature for understanding neotectonic activity in the contemporary tectonic setting. The overall geomorphology is controlled by the south oriented tilt block structure of the range, indicated by its pronounced influence on the morphology and drainage network. The drainage comprises north-flowing and south-flowing rivers with the drainage divide located close to the northern edge of the range, which also marks the highest topographic elevations. The narrow zone between the crest line and the drainage divide has been identified as the zone of gorges, where gorges and deeply incised fluvial valleys have been formed within Quaternary sediments by the various north-flowing streams. The Quaternary sediments consist of bouldery colluvial deposits in front of the range front scarps, valley fill miliolites and alluvial deposits of late Pleistocene age within the back valleys and scarp-derived colluvium forming the youngest deposit. Based on the geomorphic and stratigraphic evidence, three major phases of Quaternary tectonic uplift in the Katrol hill range are inferred. The oldest pre-miliolite phase (middle Pleistocene) was followed by a prominent phase of fluvial incision with formation of gorges during early Holocene, and then by the last one during late Holocene, continuing at present. Uplift of the range occurred in well-marked phases during the Quaternary in response to differential uplift along the KHF under an overall compressive stress regime. GPR investigations at selected sites show that the KHF is a steep south-dipping reverse fault near the surface, which becomes vertical at depth. This suggests neotectonic reactivation of the KHF under a compressive stress regime, responsible for active southward tilting of the Katrol hill range.