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Marine to continental transition in Himalayan foreland

M.K. Bera¹, A. Sarkar^1,, P.P. Chakraborty², R.S. Loyal³ and P. Sanyal⁴

¹ Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India
² Department of Applied Geology, Indian School of Mines, Dhanbad 826 004, India
³ Centre of Advanced Study in Geology, Panjab University, Chandigarh 160014, India
⁴ Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India

Correspondence: E-mail: anindya{at}gg.iitkgp.ernet.in

Mapping, sedimentological studies, and sequence stratigraphic analysis in parts of the Himalayan peripheral foreland basin of northwest India suggest that deposition of basinal turbidites, derived from both the orogenic and ramp sides, took place due to progressive uplift of the basin margin, causing forced regression. The forced regressive wedge of shoreface white sandstone, thus deposited throughout the foreland basin across the regressive surface of marine erosion, cannot be included in the alluvial sediments of Dagshai Formation. Contrary to earlier inferences, the unconformity between the Subathu and Dagshai Formations is found to occur at the top of the white sandstone marked by caliche development or erosion by Dagshai channel sand interpreted as a Type 1 sequence boundary. The reworked fossils in calciturbidite units suggest that the upper limit of the Subathu Formation must be significantly younger than ca. 44 Ma, and the proposition of a synchronous orogen-scale unconformity of >10 m.y. duration and early exhumation of Himalayan rocks should be reassessed. The duration of unconformity between Subathu and Dagshai Formations is interpreted to be 3 m.y. The sea-level fall and shoaling of Subathu Sea that was already set in by forced regression received tectonic enhancement only at the beginning of the Dagshai Formation, which resulted a total turnaround from a marine to a continental alluvial system.

Key Words: forced regression • turbidites • Paleogene foreland basin • India • northwest Himalaya • tectonism