PROVENANCE OF EXPOSED TIPAM SANDSTONE FORMATION, SURMA BASIN, SYLHET, BANGLADESH

The modal composition of the sandstones of Tipam Sandstone Formation in the Surma Basin of the Bengal Basin is studied to infer provenance, tectonic setting and paleoclimatic condition during deposition. The sandstones are mainly lithic arkose, feldspathic litharenite with lithic arenite in nature. These sandstones are composed of quartz (av.52.33%), rock fragments (av.20.53%), feldspar (av.12.46%), mica (av.9%), heavy mineral (av.2.93%) and matrix (av.2.66%). The sedimentary rock fragments such as sandstone, siltstone and shale, metamorphic lithic fragments like mica schist and sillimanite and igneous rock fragment of granite suggest the sources of these sandstones are the pre-existing sedimentary, metamorphic and igneous rocks respectively. According to the ternary diagrams, the provenance of the Tipam Sandstone Formation is suggested to be a quartzose recycled orogen and mixed provenance field. The petrographic study on quartz grains indicates that sediments were derived from a low rank metamorphic rock. Using the ternary diagrams of Suttner and Dutta (1986) and Basu (1985), it is found that the Tipam Sandstone Formation was deposited under semi humid to humid climatic conditions.