ECOLOGICAL RESPONSE OF SHALLOW-MARINE FORAMINIFERA TO EARLY EOCENE WARMING IN EQUATORIAL INDIA

Abstract

The Earth’s climate was marked by a pronounced warming at the onset of the Eocene Epoch, followed by successive short-lived warmings in the later part of the early Eocene. The carbon isotope (δ 13 C) excursions, the fingerprints of the Eocene hyperthermal events, have been established in the geological sections in India that lay across the equator in the early Eocene. The present study examines how shallow-marine foraminifera responded to the thermal events. The hyperthermal events, identified in sections of Kutch and Cambay basins corresponding to Shallow Benthic Zones (SBZs) between SBZ 5/6 to SBZ 11, have been examined for their foraminiferal assemblages, which indicate a shallow-marine environment. A significant change in the foraminiferal assemblage occurs from SBZ 5/6 to SBZ 11. The SBZ 5/6 to SBZ 10 interval (corresponding to Paleocene–Eocene Thermal Maximum, Eocene Thermal Maximum 2 and Eocene Thermal Maximum 3) is characterized by (i) low diversity and dwarfed foraminifera, (ii) rectilinear benthic foraminifera, and (iii) biserial and triserial planktic foraminifera that are known to survive in areas of high runoff, upwelling or otherwise eutrophic conditions. The stressed environments of the SBZ 5/6 to SBZ 10 appear to have ameliorated in SBZ 11 (corresponding to Early Eocene Climatic Optimum) with significant increase in abundance and diversity of foraminifera, dominance of K- strategists, and a switch from eutrophic to oligotrophic environments.