Hydrogen and oxygen isotope composition of selected Cretaceous and Paleogene/Neogene kaolins from Nigeria: Paleoclimatic inferences

The < 2 mu m fractions of Cretaceous and Paleogene/Neogene kaolins from Eastern Dahomey and Niger Delta Basins, Nigeria were selected. Oxygen and hydrogen stable isotopic kaolinite geochemistry were used to estimate the paleoclimatic conditions under which they were formed. Nine (9) samples comprising of five (5) Cretaceous and four (4) Paleogene/Neogene kaolins, respectively, were collected. The delta O-18(19.1 to 21.6 parts per thousand) and delta D (-66 to -49 parts per thousand) values for the Cretaceous - Paleogene/Neogene kaolinites suggest equilibration with meteoric waters which support a weathering origin before its sedimentation. The calculated paleotemperature range from 17.0 and 32.2 degrees C are characteristic of tropical climate. In addition, kaolinisation temperatures during the formation of the Cretaceous kaolins (30.7 degrees C) were warmer than those for the Paleogene/Neogene kaolins (20.5 degrees C) based on their respective average paleotemperatures. The isotopic composition of the paleometeoric water in equilibrium with the kaolinites from Cretaceous kaolins were enriched relative to the kaolinites from the Paleogene/Neogene kaolins.