RARE EARTH ELEMENT SIGNATURES OF FOSSIL VERTEBRATES COMPARED WITH LITHOSTRATIGRAPHIC SUBDIVISIONS OF THE UPPER CRETACEOUS PIERRE SHALE, CENTRAL SOUTH DAKOTA

Abstract

Rare earth elements were measured in mosasaur bones collected from five members (Sharon Springs, Gregory, Crow Creek, DeGrey, and Verendrye) of the upper Cretaceous Pierre Shale at localities near the Missouri River in Brule, Buffalo, Hughes and Hyde counties. Fossils from each member of the Pierre Shale have different REE signatures. Signatures of fossils from individual members may be distinctive over wide areas; fossils from the Verendrye Member have REE signatures that are consistent over 250 square kilometers. Fossils from the Sharon Springs Member have distinctive REE signatures that may be further subdivided into three superposed groups that correspond with the upper, middle, and lower Sharon Springs Member. Because REE signatures may differ