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AAPG Rocky Mountain Section Meeting

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Report on an unusual Cody Shale Fossil Assemblage from Casper, Wyoming


A construction site in Casper, Wyoming has produced an unusual suite of fossils from the late Cretaceous Cody Shale. Fossils in the Cody Shale and similar black shales of the intermountain west (e.g. Pierre Shale) are generally found in concretions. The concretions from this Casper site, called “27th and McKinley”, have produced numerous inoceramids and some baculites, but fossils at this site are also found in the shale itself. The invertebrate fossils in the shale are preserved primarily as slightly flattened orange-colored impressions and steinkerns, most often lacking actual organic material. Vertebrate material in the shale are preserved as three dimensional remains. Fossils collected in the shale include baculites, Previous HitghostNext Hit shrimp claws, gastropods, pelecypods, fish scales, fish bones, shark teeth, crab carapaces and claws, ammonite pieces and echinoderms. The fauna suggest an early Campanian age. The presence of a large number of Previous HitghostTop shrimp claws suggest deposition was in a shallow-water or tidal environment. The fossils were collected by Tate Geological Museum crews in the mid-2000’s. The site is now a collection of houses.