Understanding landform evolution in dryland fluvial systems by examining relict paleochannels in the Kachchh mainland, western India

Abstract

Dryland rivers are sensitive indicators of both long‐term and short‐term climatic fluctuations. These rivers are also useful archives for understanding tectonic responses superimposed on climatic fluctuations, which eventually provide important data for paleoclimatic and paleoseismic studies. In this context, we investigated fluvial sediments along the tributary‐paleochannels of the Khari River, which is a major dryland river of the Kachchh region in western India. This study reconstructs sedimentation patterns using lithofacies, architectural elements, facies associations, and Optically Stimulated Luminescence dates and indicates that the Khari River and its paleochannels have evolved in eight phases since MIS‐4, depicting both the climatic fluctuations and sedimentation response to tectonics. The adjoining Katrol Hill Fault, the Kachchh Mainland Fault, and their splays tectonically modulated the topography of the Khari basin. Two tectonically induced base‐level lowerings at ~74 ka and ~20 ka beveled the Mesozoic bedrocks underlying the alluvium and were followed by high‐magnitude‐low‐frequency ephemeral floods. Climatically induced aggradation phases occurred between approximately 67 ka and 59 ka, 48 ka and 37 ka, and 9 ka and 7 ka, showing a floodplain environment and sustained and wetter hydrological conditions. The lateral erosion of the underlying Mesozoic bedrock at ~50 ka and vertical incision at ~30 ka are marked as climatically governed phases. An uplift event (tectonic activity) is marked at ~7 ka, which led to debris‐flow deposition followed by vertical incision of the paleochannel and the Khari River. This study revealed that ephemeral floods, which are characteristic features of drylands, dominated fluvial sedimentation. The combination of enhanced precipitation and steepened topographic relief serves as two essential criteria for sedimentary discharge in these rivers.

Bibliographic Information