Paleoecology of middle siwalik sediments and faunas, northern Pakistan

Abstract

The Siwalik deposits of northern Pakistan are distinctive for their excellent sedimentary record and Neogene mammal faunas that include a family of homonoids, the Ramapithecidae. A 160-m interval was chosen from 3500 m of local section for study of lateral lithofacies variation, microstratigraphy and taphonomy of selected fossil localites. Field data consists of: (1) stratigraphic sections that span 30 km of lateral exposure, (2) microstratigraphic sections of fossul localities in presentative deposional environments, and (3) taphonomic sampling of a subset of these localities. These data form the basis for landscape, habitat, and community reconstruction. The physiography of the paleoenvironment was determined by braided and meandering river channels. Lateral distribution of channel and floodplain deposits suggests that a mosaic of vegetation types covered the entire drainage basin, including constantly renewed plant succession along channel margins and more stable associations on floodplains. Vertebrate fossils occur in three major depositional settings: channel-lags, channel-margin swales, and floodplain land surfaces. Most collected fossils come from channel-lag conglomerates. The predominant taphonomic influence on the overall fossil assemblage from this interval has been fluvial transport and sorting resulting in a sampling bias toward medium-sized taxa. However, rank abundances from the fossil samples may be valid for these taxa. Fluvial processes probably harvested bones from all habitats present, but no habitat associations of major taxa are detectable. A relatively high species richness of small to medium ungulate herbivores suggests the presence of diverse vegetation types that probably included forest, woodland, and grassland. The ramapithecids were uncommon, medium-sized members of this community.