Fluvial history of late Cenozoic molasse, Sulaiman Range, Pakistan

Abstract

Two measured sections show that Himalayan molasse in west-central Pakistan is 3850m thick at the northern end of the Sulaiman Range and 3150m thick at the southern end. The basal units in both sections are made up principally of channel lags, in-channel megaripples, point bars, floodplain, and crevasse-splays. These represent clayey to sandy meandering rivers that flowed SE in the north and SSW in the south. A sandstone-dominated middle unit in the south is made up of channel lag and fill, in-channel megaripples and large transverse bars, and some overbank material. These are thought to have been large sandy braided rivers that flowed S W. The conglomeratic uppermost units in both sections are channel lag and coarse longitudinal bars, fine longitudinal bars, megaripples, and some overbank material. These were deposited by gravelly to cobbly braided rivers that flowed SW in the south and SE to ENE in the north. These changes in facies, drainage, and fluvial style can be related to the uplift and eastward advance of the orogenic front of the Sulaiman Range. In the south, the gradual transition from meandering through sandy braided to cobbly braided rivers and a consistent SW flow obliquely into the modern Sulaiman Range indicate little or no uplift of the immediately adjacent orogen. In the north, clayey and Sandy meandering rivers change abruptly to cobbly braided rivers and flow simultaneously changes from SE (longitudinal) to E (transverse). The onset of boulder conglomerates occurs about 700m lower in the north than in the south, which suggests that the northern end of the Sulaiman Range was uplifted slightly earlier.