Reconstruction of Late Quaternary climate and seismicity using fluvial landforms in Pindar River valley, Central Himalaya, Uttarakhand, India

Abstract

Fluvial landforms in the Pindar River valley are investigated to understand the role of temporal variability in the Indian Summer Monsoon (ISM) and the spatial changes in crustal deformation. Employing the conventional geomorphological and sedimentological concepts, supported by optical dating, three major phases of valley-fill aggradation separated by phases on non-deposition are discerned. An oldest aggradation phase is dated to 33.5 ka during relatively strengthened ISM corresponding to the later part of pluvial Marine Isotopic Stage-3 (MIS-3). Following this, alluvial fan sedimentation impersistently continued during the declining phase of the ISM (until around 21 ka). A second major aggradation phase (17.5 ka–13 ka) occurred during the post-LGM/lateglacial strengthening of the ISM in which contribution from tributary valleys overwhelmed the valley-fill sedimentation. A youngest aggradation phase dated to the middle to late-Holocene (8 ka–3.6 ka), represents the transitional climate during which sporadic high sediment fluxes both from the upper catchment and tributary streams led to the development of fossil valleys (abandonment of old channels).The spatial variability in the incision/uplift rate, based on river strath terraces reveals that the terrain is undergoing differential crustal deformation. Two zones of relatively high crustal deformation are identified. These are located in the vicinity of the Main Central Thrust (MCT) and is attributed to the activity along the transverse fault and the in the inner Lesser Himalaya for which the thrust propagated fold associated with regional north-south compression is implicated. The study suggests that fluvial landforms (valley-fill and strath terraces) in the Pinder river valley are genetically related to the multi-millennial scale changes in the ISM and spatial and temporal changes in the crustal deformation associated with regional compression.