Carbon isotopes across the Eocene-Oligocene boundary sequence of Kutch, Western India: implications to oceanic productivity and pCO₂ change

Abstract

Analyses of foraminiferal δ¹⁸O (δ¹⁸O_carb), δ¹³C (δ¹³C_carb) and bulk organic matter (d13Corg) across a tropical Eocene/Oligocene boundary (EOB) section from Kutch basin, western India show that the ocean cooling (at least ~3°C) is coincident with a rapid enrichment (~3‰) in δ¹³C_org but depletion (~1.5‰) in δ¹³C_carb. The decrease in pCO₂ in ocean-atmosphere system across the boundary, possibly resulting from enhanced silicate weathering in rising Himalayas and accompanied organic carbon burial in ocean, caused the cooling and δ¹³C_org enrichment. The end-Eocene climatic stress decreased the oceanic productivity (and δ¹³C_carb) eventually causing extinction of larger benthic foraminiferal community. The data suggest a critical role of tropical ocean and direct forcing of CO₂ on global climate change at least for this crucial Cenozoic transition.