Geological and petrographic investigations of the Miocene Molasse deposits in Sub-Himalayas, District Sudhnati, Pakistan

The provenance of Molasse deposits is a debatable topic due to the active tectonics and complex geological nature of Sub-Himalayas. The research aim is to find out the geological and petrographic understanding of the Molasse sandstone in the Sub-Himalayan slab of Pakistan. The primary sedimentary structures suggested the fluvial depositional environment in the arid paleo-climatic condition. The repetition of strata and soft sedimentary structures are the indication of active tectonic influence. The pi-beta (π-β) and rose diagrams depict the area that lies away from the Indo-Eurasian collision zone. The mineralogical composition of sandstone has a mixed source of detrital fragments. The quartz-feldspar-lithic fragments (QFL) and monocrystalline quartz feldspar lithic (QmFLt) diagram suggest quartzose to transitional recycled Himalayan orogeny. The diamond diagram plot suggests the provenance of quartz are plutonic and middle to upper rank metamorphic. The low abundance of feldspar in most of the sandstone samples suggests semi-humid depositional conditions supported by plotting polycrystalline quartz/feldspar+lithic fragments [Qp/ (F+L)] against quartz/ feldspar+lithic fragment [Q/ (F+L)]. Therefore, it is concluded that these Molasse deposits were derivative from metamorphic and igneous rocks of the Higher Himalayas which were deformed, uplifted consequent to Himalayan orogeny. The detritus was eroded by active river systems and finally, it was deposited in the Sub-Himalayas.