Oxygen and Carbon Isotope Measurements of Late Cretaceous and Early Tertiary Foraminifera

Oxygen and carbon isotope measurements on paleontologically inferred and foraminifera of Late Cretaceous and Early Tertiary age have shown that the foraminifera indeed inhabited surface waters of the oceans, while the foraminifera inhabited deep waters. Over a five-million-year period near the end of the Cretaceous, various planktonic foraminiferal species retained the same order of depth stratification beneath the surface of the ocean. The surface water in the Cretaceous had temperatures and 6C13 values for dissolved bicarbonate similar to those existing today in South Atlantic surface waters. The bottom-water temperature, however, was perhaps about 10? C warmer than today. Oxygen isotope studies of the Cretaceous pelecypod Inoceramus reveal that it had a benthonic habitat and that it shows consistently heavier oxygen isotope values than the benthonic foraminifera values. Isotope results from the foraminifera clearly indicate that there was a sharp climatic deterioration from middle to late Maastrichtian (68 to 66 million years B.P.). Whether or not this climatic change was the primary cause of the massive extinction of taxa near the end of the Cretaceous can not be proven, but the timing of these two events is sufficiently coincidental to suggest causal effect. Oxygen and carbon isotope measurements of Late Cretaceous and Early Tertiary foraminifera