Ecology of foraminifera during the middle Eocene climatic optimum in Kutch, India

Abstract

The shallow marine carbonates of Kutch temporally correspond to the globally recognised warming period called Middle Eocene Climatic Optimum (MECO) that extended from later part of planktic foraminiferal zone E11 to E12 and Shallow Benthic Zone (SBZ) 17. The present study aims to investigate how foraminifera responded ecologically to the warming event. It involves identification and distribution of foraminifera, and cluster and detrended correspondence analyses of the species distribution data. Selected samples across E11 and E12 were analysed for carbon isotopes. The major conclusions are: (i) bloom of Jenkinsina columbiana in zone E11, possibly marking the initiation of warming in a shallow, eutrophic sea, (ii) increased foraminiferal diversity, appearance of Orbulinoides beckmanni and Acarinina and a sharp rise in the sea level in the early part of E12 (iii) significant jump in diversity and abundance of larger benthic foraminifera in E12, signifying warm, clear-water oligotrophic seas, promoting the formation of platform carbonates, (iv) MECO does not seem to have adversely impacted the foraminifera in shallow seas, and larger benthic foraminifera were rather ultimately superior in their diversity, abundance, size and latitudinal distribution and (v) δ13C excursions up to 1.5 ‰ are noted in the upper parts of E11 and lower parts of E12.