New paradigms to evaluate the stratigraphy for the geological and geoarchaeological prospects of the upper and post-Siwaliks in the Soan Valley, Upper Indus Basin, Pakistan

Abstract

The Upper Siwalik (US) of the Late Pliocene to the Middle Pleistocene and the Post-Siwalik (PS) of the Late Pleistocene to the Holocene are extensively distributed in the Upper Indus Basin. These deposits have geological and geoarchaeological significance, but they are least explored in the northwestern Himalaya, specifically in Pakistan. The current fieldwork was conducted in the Soan Valley of the Upper Indus Basin, Pakistan, through detailed stratigraphic and sedimentological investigations to address the existing research gap. Multiple methods and datasets are employed, including outcrop investigation, loss on ignition analysis, literature review, and well top data from five wells. The study identified thirteen lithofacies and six lithofacies associations, distinguished by multiple coarsening-to-fining upward cycles. These deposits indicate a transition from fluvial channel to floodplain and from alluvial to aeolian environments, showing progradation, aggradation, and retrogradation patterns across high to low accommodation system tracts (HAST and LAST). Five sequences (Sq1-Sq5) are recognized in the upper and lower Soan Valley. Sedimentary evolution was controlled by active tectonism and paleoclimates. Together with tectonic activities, LOI values indicate a transition between arid to semiarid and humid conditions, influencing the transformation of LAST and HAST, and creating a dynamic landscape for hominins in the Soan Valley. Previous studies have linked Paleolithic artefacts to these sequence stratigraphic cycles. This research lays the foundation for further geological and geoarchaeological investigations in the Soan Valley. Sequence stratigraphic and sedimentological approaches establish new paradigms, opening avenues for researchers to explore the Quaternary strata of the Himalaya and Paleolithic sites of the Soan Valley.