Sedimentology and provenance of Cenozoic molasse and pre-molasse sandstones, Sulaiman Range, Pakistan

This study uses changes in facies, paleoccurents, and provenance to reconstruct the depositional history of Upper Cretaceous through Plio-Pleistocene sandstones in the northern and southern ends of the Sulaiman Range, north-central Pakistan.; Pre-orogenic Cretaceous shelf sandstones show westward dispersal (from the Indian craton) and a cratonic provenance. However, Paleocene marine sandstones and Eocene deltaic sandstones show more eastward dispersal and a mixed provenance of cratons and recycled orogens. Dispersal onto the Indian craton indicates slope reversal of the Cretaceous shelf. Uplift and reversal of the Cretaceous shelf was probably due to initial docking of the Indo-Pakistani plate with parts of Eurasia.; The basal molasse comprises deposits of clayey to sandy meandering rivers that flowed S in the northern site and SSW in the southern site. A sandstone-dominated middle unit in the south represents large sandy braided rivers that flowed SW. The conglomeratic uppermost units in both sections show characteristics of gravelly to cobbly braided rivers that flowed SW in the south and ESE in the north. Overall, the northern and southern sections show similar fluvial histories.; The post-Eocene molasse sandstones are derived from collision orogens, involving continental blocks, dissected arcs, recycled orogens, and fold-thrust belt settings. Most of the detritus seems to have been derived from igneous, metamorphic, meta-sedimentary and sedimentary rocks in the northern Himalayan convergence zone and was dispersed by a large river that flowed southward, parallel to the modern Sulaiman Range. This was probably a precursor to the modern Indus River.; Compositions also suggest sporadic influx of sedimentary detritus from the west. Eastward drainage transverse to the Sulaiman Range was marked in north by a sudden influx of boulder conglomerates and a transition from sandy meandering rivers to gravelly braided rivers. The conglomerates occur on the order of 700 m lower in the north than in south, which suggests that the northern end of the Sulaiman range uplifted much earlier than the southern end. The southern end shows only a gradual transition from meandering through sandy braided to gravelly braided rivers, together with a consistent SW flow obliquely into the Sulaiman Range, suggesting only a coarsening and "proximalization" of the pre-Indus trunk river system, and little or no uplift of the SE corner of the Sulaiman Range, until a very late influx of fold-belt detritus.; The study shows that, in collision orogens caused by oblique convergence, the obliquity plays an important role in limiting the amount of detritus shed from the orogens, the development of transverse rivers and their fan-plains, and the interaction of transverse and longitudinal rivers in adjacent foredeeps.