A DIGITAL ATLAS OF UPPER CRETACEOUS SHORELINES IN THE WESTERN INTERIOR OF THE UNITED STATES, INCLUDING GEOGRAPHIC DISTRIBUTION OF ZONAL FOSSIL LOCALITIES

This atlas is being developed to show the approximate shoreline positions and index fossil localities for 55 ammonoid biostratigraphic zones in the Upper Cretaceous of the Western Interior of North America. Shoreline positions and fossil localities are shown for the early Cenomanian Neogastroplites haasi zone (Lower Cenomanian) through the late Maastrichtian Hoploscaphites birkelundae zone (lower Upper Maastrichtian). This atlas was developed from over 100 scanned hand-drawn maps and from the fossil collections of Bill Cobban at the U.S. Geological Survey in Denver, Colorado. The scanned maps have been rectified for use in a geographic information system (GIS), using the Albers Equal Area Conic Projection, and the shorelines have been traced as line shape files. Each map file includes the location of collection sites, the geographic distribution of both zonal fossils and other fossils collected with them, and county and country political boundaries for accurate reference. Collection locality accuracies are described in the shape files along with associated full fossil descriptions, along with stratigraphic and lithological information. These maps are GIS-compatible and are completely scalable for the addition of higher resolution data. It is intended that these maps provided by Bill Cobban will be a starting point and that collaboratively-developed data, including more detailed shorelines and fossil localities, can be added in the future. This GIS-compatible atlas of Western Interior shorelines and zonal fossils will enable paleontologists, sedimentary geologists, and stratigraphers to test various hypotheses on, among other topics, the paleobiology of Western Interior organisms, the interplay between environmental factors and the distribution of key fossil groups, the processes driving the dynamic migrations of the western shoreline, and the nature of sediment accumulation within the Western Interior basin. This atlas and subsequent collaborations will be housed online at the U.S.G.S. Paleo website.