Tectonic and climatic controls on late Quaternary bajada sedimentation along Narmada-Son Fault (NSF), Gujarat, Western India

Abstract

An alluvial bajada has been recognized along a part of the active Narmada-Son Fault (NSF) and confined by the Karjan River on the eastern side and by the Madhumati River on western side. The bajada sequence exposed along the incised cliffs of various north flowing parallel streams has been studied in their proximal, medial and distal part. The sediments are characterized on the basis of grain size, fabric, sedimentary structures, bed geometry and sorting, and lithologs prepared from the mapped cliff sections. Detailed study of sedimentary characteristics, lithofacies analysis and facies associations indicate that sediments are mainly of three types - sediments that were deposited by debris flows and sediment gravity flows, and as extensive bar deposits. Three major aggredational sequences are recognized. Each sequence is composed of coarsening-upward sequence of proximal facies overlain by fining-upward sequence of distal facies. Coarsening upward sequence record periods of tectonic activity related to uplift along the NSF and fan progradation, whereas fining-upward sequence results from tectonic quiescence periods. The presence of rhizocretions, calcium carbonate nodules and calcite sheets within the basal debris flow and sediment gravity flow indicate semi-arid climate, whereas the formation of pedoginized paleosol indicate relatively wetter climate prevailing in the study area. Tectonic activity along the NSF has played dominant role by controlling the geometry and volume of bajada sediments. Climate is found to be responsible for compositional and temporal distribution of bajada sediments. OSL dating suggests that the bajada sediments were deposited during the later part of late Pleistocene. The incision of the sediments is attributed to uplift due to inversion of the lower Narmada basin during the early Holocene.