Paleogene Foraminifera and Paleoecology of Thar Coal Basin, Sindh, Pakistan

Abstract

Foraminifera consisting dominantly of agglutinated forms have been observed in the Thar Coal Basin sediments. Many of these benthic forms are of small size. The preservation of fauna is rather poor; generally the specimens are strongly crystallized and partly crushed. For this study 100 samples from 10 exploratory boreholes, drilled by Geological Survey of Pakistan, were obtained. However fossils were recorded from 30 samples of 6 boreholes that consist of mainly the forms belonging to the genera Haplophragmeides, Ammobaculites, Trochomina, Osangularia, Ammosphaeraidina, together with the rare occurrence of calcarious benthic foraminifers. These foraminifers thrived in strongly different ecological conditions as far as salinity and bathymetry are concerned; other paleoecological factors have been responsible for the occurrence of agglutinated foraminifera along with non-agglutinated forms. These fauna as a whole indicated the deposition in a shallow inner neritic marine waters. The sediments are dark gray mudstone / siltstone with abundant organic matter. The depositional environment probably was one of the poorly oxygenated, slowly circulating bottom water with high CO2 content resulting from the decomposition of organic matter. The coal-bearing sequence as a whole indicates repeatedly oscillating environment ranging from delta plain marshes/ swamps to prodelta conditions. Stratigraphic data derived from the foraminiferal studies indicates that the coal-bearing rocks of Thar Coal field are of late Paleocene to early Eocene age.