Petrography and Stable Isotope Geochemistry of Middle Eocene Garampani Limestone (Assam), India: Implications for the Depositional Environment and Diagenesis

Abstract

Petrography and stable isotopic (carbon and oxygen) studies of the Middle Eocene of Garampani limestone from Jamunagar limestone quarry of the Umrangso area, North Cachar Assam, were carried out to determine the environment of deposition and the level of diagenesis to improve our understanding of the climate at the time of formation. The major petrographic types documented here are include wackestone, packstone and grainstone which fall into the type I and II categories of the triangular classification scheme indicating formation in a short-lived, high-energy environment that was dissipating at the time of deposition. The samples have a distinct signature that includes extensive diagenesis with varying intensities of compaction, recrystallization, pressure solution, and neomorphism. Most of the samples produced positive δ13C ‰ ranges from 1.64 to 0.76‰ (PDB) and correlated with a transgressive phase. The negativeδ18Ovalues range from − 6.25 to -4.67‰ (PDB) suggesting that the Middle Eocene was generally characterized by a warmer climate.