RARE EARTH ELEMENT (REE) ANALYSES OF FOSSIL VERTEBRATES IN THE PIERRE SHALE: FOSSIL PROVENIENCE

Rare earth element concentrations 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 REE signatures similar to one another, but statistically different from those of other members. Fossils collected from the Sharon Springs Member have distinctive REE signatures that may be further subdivided statistically into three superposed groups that correspond with the upper, middle, and lower Sharon Springs Member. Because REE signatures differ between members, fossil bones removed from stratigraphic context can be assigned to a member based on REE signature comparisons. A sample of a mosasaur originally collected in the early 1800's that was known to have come from the Pierre Shale in central South Dakota but which could not be assigned to a particular member due to limited collection information was tested and compared with the already analyzed in-situ fossils. Discriminant analysis grouped this fossil statistically with those of the DeGrey Member; therefore, the provenience of this fossil could be assigned using REE analysis.