Diagenesis, Provenance, Tectonic Setting and Palaeoclimate of the Eocene Kopili Sandstone, Assam, India: A Petrographic Study

Abstract

Abstract The Eocene Kopili Sandstone outcropping in the North Cachar Hills (NCHs) of Assam, India, was petrographically studied to unravel its diagenetic features, provenance, tectonic setting and palaeoclimate conditions. The modal analysis of the Kopili Sandstone reveals that the detrital mineralogy is dominated by quartz (48.78 to 83.70 %), with variable amounts of rock fragments (0.37 to 7.35 %), feldspar (0.37 to 8.33 %), micas (0.36 to 7.84 %) and subordinate amount of heavy minerals. The matrix and cement content varies from 9.88 to 21.50 % and 1.12 to 19.41 % respectively. The Kopili Sandstone is classified as quartz arenite to sub lithic arenite. Compaction, cementation, dissolution and replacement are the observed diagenetic processes in the studied sandstones. Diagenetic transformations are manifested in the fractured detrital grains, overgrowth of quartz, corrosion of grain boundaries of quartz, modification of grain boundaries, and silica and iron oxide cement precipitation in the interstices of the framework grains. The provenance is of granite-gneissic rock terrain. The detritus in the depositional basin is derived predominantly from craton interior with minor input from recycled orogen. The study discerns humid palaeoclimate conditions for the Kopili Sandstone.