Evolution of the rare earth element composition of Paleogene groundwaters as recorded in vertebrate fossils from Toadstool Geologic Park, Nebraska, USA

摘要

Rare earth elements in vertebrate fossils from upper Eocene and Oligocene sediments of Toadstool Geologic Park, northwestern Nebraska, record mixing and evolution of Paleogene groundwaters and variations in paleoenvironments. REE signatures indicate that HREE-enriched alkaline groundwater reacted with LREE- and MREE-enriched sediments to produce three component mixtures. REE are paleoenvironment and paleoclimate proxies. Time series analysis suggests that REE ratios are affected by cycles of ca. 1 Ma and 700 and 500 Ka, similar to some Milankovitch periodicities.