Fashion and phases of late Pleistocene aggradation and incision in the Alaknanda River Valley, western Himalaya, India

Abstract

We study the aggradation and incision of the Alaknanda River Valley during the late Pleistocene and Holocene. The morphostratigraphy in the river valley at Deoprayag shows the active riverbed, a cut terrace, and a fill terrace. The sedimentary fabric of the fill terrace comprises four lithofacies representing 1) riverbed accretion, 2) locally derived debris fan, 3) the deposits of waning floods and 4) palaeoflood records. The sedimentation style, coupled with geochemical analysis and Optically Stimulated Luminescence (OSL) dating, indicate that this terrace formed in a drier climate and the river valley aggraded in two phases during 21–18 ka and 13–9 ka. During these periods, sediment supply was relatively higher. Incision began after 10 ka in response to a strengthened monsoon and aided by increase of the tectonic gradient. The cut terrace formed at ~ 5 ka during a phase of stable climate and tectonic quiescence. The palaeoflood records suggest wetter climate 200–300 yr ago when the floods originated in the upper catchment of the Higher Himalaya and in the relatively drier climate ~ 1.2 ka when locally derived sediments from the Lesser Himalaya dominated flood deposits. Maximum and minimum limits of bedrock incision rate at Deoprayag are 2.3 mm/a and 1.4 mm/a.

Late Quaternary paleoclimatic and geomorphological evolution at the interface between the Menyuan basin and the Qilian Mountains, northeastern Tibetan Plateau

“…Pan et al, 2009) have shown that fluvial aggradation took place during periglacial conditions on the Tibetan Plateau during the Pleistocene, caused by changes in precipitation, cessation of soil development and decrease of vegetation cover as a response to climate deterioration, which is in agreement with general observations (e.g. Vandenberghe, 1995Vandenberghe, , 2003Bridgland and Westaway, 2008;Srivastava et al, 2008;Vandenberghe, 2008). In addition, investigations have shown that fluvial landforms in the northeastern Tibetan Plateau were controlled by both climate change and tectonic uplift (Lu et al, 2004;Vandenberghe et al, 2011;Wang et al, 2012).…”

Feasibility of the Sar Technique on Quartz Sand of Terraces of NW Himalaya: A Case Study from Devprayag

“…Phyllite is a low-grade metamorphic rock formed intermediate between slate and schist. The details on the geomorphology, luminescence chronology and climatic interpretations are discussed in detail in Srivastava et al (2008). In order to determine the source of sediments and the contribution of sediments from the host rock (phyllite) and rocks from the upper reaches (mainly gneisses and granites from Higher Himalayan crystalline rocks), geochemical analysis was carried out.…”

“…The site was explored to study the palaeoflood record of the region and to assess the provenance (for details, please see Ahmad et al, 2000). Alakananda River catchment and has been discussed in detail by Srivastava et al (2008). CIA values suggests that DP-8 has around 62% of phyllite, DP-4 and DP-11 have 33% and 40% phyllite respectively and DP-7, DP-9, DP-10, and DP-13 have phyllitic contribution of around 50%.…”

“…In this process, the luminescence characteristics of quartz were studied and further evaluated the source of quartz received from different rocks on the basis of luminescence properties. Luminescence chronology and climatic implications has been discussed in detail by Srivastava et al (2008).…”

Climate induced temporal change in Sr-Nd isotope ratios in the valley-fill deposits of the Ganga river

“…The rivers that drain the Himalaya respond to varying climate and tectonic conditions and acts as a medium for sediment erosion and evacuation (Gupta, 1997;Goodbred, 2003;Srivastava et al, 2008). The Himalayan rivers like Ganga and Yamuna, travels through different lithology and provide variable amount of sediments into the Ganga Plain.…”