TWO SIDES OF THE SAME COIN: A SELECTION OF THE SWEETGRASS ARCH AND DISTURBED BELT COLLECTIONS

The USGS Denver fossil collection contains a number of particularly unique groups of fossils. Two such are the Sweetgrass Arch collection (Turonian-Campanian) and the corresponding Disturbed Belt collection (Turonian-Santonian). They were collected in the area of northern Montana that now adjoins and includes Glacier National Park. While the localities are close in proximity to one another, the preservation of the specimens is drastically different. The reason for this difference is the Disturbed Belt itself, a length of land consisting of sharp surface folds underlain by thrust faults along the cordilleran folds yielding complex stratigraphic and paleontologic problems. Along with the other similarly impressive ammonite collections, these two groups provide the basis for fine-scale lithologic and chronologic analyses of the Upper Cretaceous U.S. Western Interior research conducted by William A. Cobban and C.E. Erdmann.

We have three cases from the Sweetgrass Arch/Disturbed Belt localities, each with between 10-12 drawers. We also have two cases from the Disturbed Belt locality, each with 11 drawers. The cases are sorted by stratigraphic stage. Each drawer has approximately 40 trays with a varying number of specimens per tray. Specimens primarily consist of fossils between 3”and 6” maximum length. The fossils include Baculites, Inoceramids, Scaphitids, Ostrea, and snails. Digital photographs were taken and specimen label data were recorded. Photographs were taken in close-up view at 300 dpi, with an upper left light source displaying a standard lateral specimen view. Lighting and shadowing were adjusted to enhance the contrast of diagnostic morphologic characteristics. In addition, we whitened specimens to enhance morphology, an innovative technique introduced last year. When numerous specimens of the same species were present, the best specimens were selected to photograph.

Digital photographs and taxonomic data will augment the USGS National Paleontologic Database as well as the USGS Denver Mesozoic database. The web version will associate photographs and lithologic section, visually illustrating the Sweetgrass and Disturbed Belt collections. The database and online version of the database will allow in-house and visiting researchers to find specific specimens when needed for examination.