EP41A-0905
Fluvial fan evolution during Late Quaternary climate changes: field and chronological constraints from the Indo–Gangetic basin
Thursday, 17 December 2015
Poster Hall (Moscone South)
Ajit Singh1, Sanjeev Gupta2, Rajiv Sinha3, Alexander Densmore4, Kristina J Thomsen5, Nibedita Nayak3, Suneel Kumar Joshi3, Wout Matthijs van Dijk4, Jan-Pieter Buylaert6, Setbandhu Mondal7, Dewashish Kumar7, Philippa J Mason2, Andrew Sean Murray8, Manoranjan Kumar9, Shashank Shekhar9 and Shiv Prakash Rai10, (1)Imperial College London, Earth Sciences and Engineering, London, United Kingdom, (2)Imperial College London, London, United Kingdom, (3)Indian Institute of Technology Kanpur, Kanpur, India, (4)University of Durham, Durham, United Kingdom, (5)Technical University of Denmark, Kgs. Lyngby, Denmark, (6)Technical University of Denmark, Center for Nuclear Technologies, DTU Risø Campus, Roskilde, Denmark, (7)National Geophysical Research Institute, Hyderabad, India, (8)Aarhus University, Risø Campus, Nordic Laboratory for Luminescence Dating, Department of Geoscience, Roskilde, Denmark, (9)University of Delhi, Geology, Delhi, India, (10)National Institute of Hydrology, Roorkee, India
Abstract:
The stratigraphic evolution of fluvial fans is to a large extent governed by channel avulsion. Spatial variations in alluvial architecture are influenced by avulsion magnitude and frequency. However due to the absence of long–term chronostratigraphic records of fan stratigraphy, it has proved difficult to test patterns of fan evolution against records of climate variability. In order to understand the processes of channel avulsion during fan evolution, it is important to determine the spatio–temporal pattern of fluvial channel aggradation, incision, and migration. In this study, we reconstruct the shallow sub–surface alluvial stratigraphy of fluvial fan systems formed by the major Himalayan rivers, the Sutlej and Yamuna, in the northwestern Indo–Gangetic basin. We map the spatial distribution of channel sand bodies deposited by these rivers and develop a chronostratigraphic model for the fluvial succession in a depositional dip perpendicular transect. Sediment cores up to ~50 m deep along two transects are used to reconstruct the shallow stratigraphy of the fan systems. Discontinuous channel sand bodies are separated by floodplain fines which occasionally show weak pedogenesis that mark the end of episodes of channel aggradation. Optically stimulated luminescence (OSL) dating is used to bracket the timing of channel–filling episodes, and their spatial distribution. Mapping of sand bodies coupled with chronostratigraphic constraints allows reconstruction of channel migration patterns and their timing across the Sutlej–Yamuna fans. Chronostratigraphy permits temporal correlation with published measures of monsoon variability. We find that fluvial aggradation at the western end of studied transects, near the middle of the Sutlej fan, terminated around ~20 ka. We also show that abandonment of the paleo–Sutlej and major fan–scale avulsion occurred after ~15 ka, and was followed by formation of incised valleys that confined the modern fluvial system in northwestern Indo–Gangetic basin. Our study has importance for groundwater management policies in this water–stressed agricultural hotspot of India, because the sub–surface sand bodies form excellent fluvial aquifers. Thus, understanding the variability in sand body stratigraphy is important for understanding aquifer geometry.
