Stable carbon and oxygen isotope composition of Recent, Tertiary and Cretaceous foraminifera (Table III)

Comparison of carbon isotope ratios of adult and juvenile forms indicates that either the source of the carbon found in the shell or the carbon isotopic fractionations which occur during calcite secretion change during the development of individual foraminifera. The carbon isotopic ratios do not provide a reliable means for reconstructing the depth habitats of ancient species. Temperature-depth profiles for tropical Tertiary oceans have been reconstructed from the isotopic temperatures of planktic and benthic foraminifera.

The vertical thermal structure of Oligocene oceans resembled that of modern oceans most closely. Those of Paleocene and Maastrichtian times differed most from that of modern oceans.