TAPHONOMY OF THE BLUE SPRINGS LOCALITY, COON CREEK FORMATION (LATE CRETACEOUS), MISSISSIPPI: PRESERVATION OF A DECAPOD LAGERSTATTEN

The Late Cretaceous (Maastrichtian) Coon Creek Formation of Mississippi and Tennessee contains a diverse and abundant assemblage of decapods including lobsters, ghost shrimp, and crabs. Such an assemblage is rare in the fossil record. The formation lies in a temporally and paleogeographically significant location, situated between the Atlantic Coastal Plain and the Western Interior Seaway, shortly before the closing of the seaway.

Coon Creek decapods have been little studied since the fauna was first described in the 1920’s. A large collection of specimens, ranging in preservation from poor to excellent, has recently become available for study. Because of the visible variation in preservation, the abundant material, and the paucity of cuticular data of this type of preservation, an investigative study of elemental composition of the sediment and cuticle of six species of decapod from six families (Palinuridae, Nephropidae, Callianassidae, Dakoticancridae, Raninidae, and Retroplumidae) is being conducted from material collected at the Blue Springs Locality in Mississippi.

Cuticle, concretions, a decapod burrow, and sediment from the site were analyzed with X-Ray Florescence and Elemental Reflectance for preliminary elemental composition and subsequent mineral composition. Concretions and the burrow were observed in thin section and were mapped for elemental distribution using Energy-dispersive X-Ray spectroscopy and dot mapping. The six species of decapod were analyzed using the same techniques. Preliminary results suggest that the decapod cuticle was either degraded or altered to apatite during diagenesis, much like the decapod cuticle of the Late Cretaceous Bear Paw Shale Formation of Montana. Elemental analysis of the sediment will help to confirm the diagenetic pathway for the cuticle.