Valleys of the Gangetic Plains, India: Multiple Origins and Moving Targets

S. K. Tandon¹, Martin Gibling², Rajiv Sinha³, Parviz Ghazanfari⁴, Ananda Dasgupta⁵, Mayank Jain⁶, and Vikrant Jain^5
1 University of Delhi, Delhi 110007, India
² Dalhousie University, Halifax, NS
³ Indian Institute of Technology, Kanpur 208016, India
⁴ Department of Geology, University of Delhi, Delhi 110007, India
⁵ Department of Civil Engineering, Indian Institute of Technology, Kanpur 208016, India
⁶ Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, United Kingdom

Many Gangetic Plains rivers of the Himalayan Foreland Basin occupy valleys created by tectonism, sea-level and climate, the effects of which have varied in time and space. Valleys near the Himalayan thrust front are incised through areas of active uplift. In the western and southern plains where tectonic activity is minor and subsidence rates are low, monsoonal precipitation, discharge and sediment transport capacity have varied on 10³ to 10⁴ year timescales, controlling incision and accumulation and creating disconformity-bounded floodplain sequences. In the eastern plains, aggradation is rapid and megafans and interfan rivers are not incised. Below the Ganga-Brahmaputra Delta, thick valley fills extend several hundred kilometers inland, reflecting sea-level fluctuation. A widespread recent phase of valley formation is a response to continent-wide strengthening of the monsoon following the Last Glacial Maximum. Many Gangetic rivers have migrated progressively southward over 10⁶ to 10⁷ year timescales in response to India / Eurasia collision and Himalayan uplift. Thus, short-term cycles of valley incision and aggradation will be superimposed on long-term valley migration in many parts of the plains. Unlike coastal valleys created and filled by sea-level fluctuations, alluvial valleys such as those of the Gangetic Plains are likely to be “moving targets” that vary from prominent to cryptic both spatially and over short time-scales. Valley formation and filling across wide areas may be synchronous if precipitation changes regionally, or may be out of phase if tectonism and sea-level change are involved.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005