Latest Cretaceous-Early Neogene oxygen and carbon isotopic record at DSDP sites in the Indian Ocean

Abstract

Stable isotopic data of calcareous nannofossil, monogeneric and monospecific planktic and benthic foraminifera from five Indian Ocean DSDP sites (212, 217, 220, 237, and 253), leads to the following paleoclimatic and paleoceanographic conclusions: • — The latest Cretaceous oxygen isotopic record implies a cooling (3–4°C) during the Maastrichtian. At the Cretaceous/Tertiary boundary only a minor warming (about 2°C) has been recorded. The parallel δ 13 C decrease of more than 1‰ indicates a significant decrease in productivity. • — During the latest Paleocene a positive δ 13 C excursion was detected in Sites 217 and 237. This transient enrichment in δ 13 C may be due to productivity changes on continents and/or a change in the storage rate of organic matter in marginal basins or shelf areas. • — The most striking feature in the oxygen isotopic record is noted at the Early/Middle Eocene transition. The shift towards more positive values (which were probably enhanced to a certain extent by a preceding diagenetic alteration) delineates a dramatic climatic deterioration at high and mid latitudes during the earlier Tertiary. • — Near the Eocene/Oligocene boundary a cooling is evident within the latest Eocene interval. During the earliest Oligocene time a hiatus at Sites 217 and 253 partially obscures the climatic record. • — Several climatic fluctuations have been noted during the Oligocene: a cooling at the base of Zone NP 23, a warming at the top of Zone NP 23 through NP 24, and a cooling during Zone NP 25. • — The Miocene oxygen isotopic record is dominated by changes in surface and bottom water environments during Zone NN5. The decreasing and then increasing δ 18 O values, together with the subsequent steepening of the vertical δ 18 O gradient, point towards major climatic instabilities. These events coincide with the Mid-Miocene build-up of Antarctic ice-sheets. During the latest Miocene to the earliest Pliocene the δ 18 O record of planktic foraminifera indicates a significant warming of the Indian Ocean at mid-latitudes. • — The δ 13 C record during the Oligocene and Miocene reveals several cycles ( δ 13 C enrichments: NP 24, NN2, NN5, NN9, and base NN 11) which are most likely related to changes in storage rates of organic matter and biological productivity due to climatic changes and transgression/regression cycles. In addition, changes in the circulation patterns may also have influenced the carbon isotopic record.