Syntectonic controls of palaeoflow reversals and variability: sediment-vector sequences in the late orogenic fluvial Siwalik basin, Panjab sub-Himalaya, India

Abstract

The Siwalik late orogenic basin is a response to the final stages of tectonic activity in the continent to continent collision zone of the Himalaya. The basinal evolution and the nature of the lithic fill are largely determined by syntectonic activity. Data have been collected on the temporal variability in palaeoflow of four formations of the Upper Siwalik Subgroup (˜1 to ˜3 m.y.) Analysis of the bed-by-bed directional measurements has resulted in the identification of three sediment-vector sequences (G_a, G_b, G_c) in the Ghaggar section, and four sediment-vector sequences (K_a, K_b, K_c K_d in the Khetpurali section. Palaeodrainage patterns during Siwalik sedimentation have been shown to flow from the orogenic highlands in the north. In the present study, palaeodrainages from the south controlled by intrabasinal tectonic highs are recognised. The four major sediment-vector trends in two measured stratigraphic columns have been related to two tectonic highs along the northern basin margin within the main orogen and to one intrabasinal subsurface tectonic high lying in the south, the existence of which was already proved from different lines of evidence-gravity and seismic.