New Methods in Stratigraphic Correlation

Patrick, Doreena¹, Paul N. Wegleitner², James E. Martin³ (1) GeoChemical Solutions LLC, North Wales, PA (2) GeoChemical Solutions LLC, Fort Pierre, SD (3) South Dakota School of Mines and Technology, Rapid City, SD

Our recent research has involved new methods for stratigraphic correlation including Rare Earth Element (REE) and trace element (TE) analyses of both fossil bioapatite and associated sediments and unit cell dimension (UCD) analysis of fossil bioapatite. REE and TE analyses use variations within fossil bioapatite and sediment fractions to identify a unique signature for stratigraphic units. The REE composition and UCD of fossil bioapatite are dependent upon the conditions of diagenesis and thus dependent upon availability of TE for substitution during bioapatite per mineralization. REE and TE signatures and UCD variations identify distinct intervals within lithologic formations. Because these intervals represent an averaging of periods of certain depositional environments, these distinct intervals can be correlated over significant areas. REE and TE analyses of fossils and sediment fractions and UCD analysis of fossil bioapatite define an environmental package that relies on several analytical methods and more than one variable to determine a “fingerprint” for lithologic units. As a test, fossil vertebrates and sediment samples were obtained from the Pierre Shale, at various localities in South Dakota. Samples were collected from the lower, middle and upper Sharon Springs, Gregory, Crow Creek, DeGrey and Verendrye members. REE signatures and UCD variations were found to be consistent within individual lithostratigraphic units but are significantly different between units. Therefore, REE signatures and UCD act as markers for their units and are used to discriminate between units for purposes of stratigraphic correlation.