Framework Mineralogy and Texture of the Upper Palaeocene Sandstones from Laitrengew-Cherrapunji area of East Khasi Hills, Meghalaya

The Laitrengew-Cherrapunji area of East Khasi Hills, Meghalaya exposes a complete Palaeocehe sequence of sedimentary rocks. The coal-bearing sandstone around Laitrengew-Cherrapunji area is regarded as Lakadong Sandstone Member of the Sylhet Formation. The Lakadong sandstones are quartz dominated, fine to medium grained, well to very well sorted, and have not been subjected to significant alteration. The intensive solution effect lowers the packing index values for the underlying Therria Formation around Laitrengew. The quartz arenite type of Therria and Lakadong sandstones is indicative of intense paleoweathering processes under humid climate and low relief. The sediments were derived from the exposed shield areas of plutonic rocks and low to medium grade metasedimentary rocks. The structural, textural as well as compositional attributes of the Therria and Lakadong sandstones indicate that the sediments were deposited in a slowly subsiding, stable depositional area in which the sediments were subjected to higher hydraulic energy winnowing processes. During the period, the paleoclimate was humid and tropical. The intermittent subaerial exposure of the depositional surface and development of shallow swampy lagoons in the coastal environment was supported by the palyontological evidences such as trace fossils and pollen grains of Arecaceue family.