A CAMPANIAN PERSPECTIVE ON THE EVOLUTION OF MARINE COMMUNITIES: PALEOECOLOGICAL ANALYSIS OF THE COFFEE SAND

The late Mesozoic is generally seen as a pivotal time in the evolution of benthic communities but the details of the timing of these changes are poorly known. The Coffee sand formation is one of the oldest (lower/middle Campanian: Late Cretaceous) units on the U.S. Gulf Coastal Plain (N.E. Mississippi) that contains original aragonitic material preserved in unconsolidated sediment. The preservation makes it ideally suited to ecological analysis.

Several bulk samples were wet-sieved and all specimens greater than one millimeter were identified to species level and counted. Each sample contains over a thousand "countable" specimens. These samples are compared to Late Cretaceous and early Cenozoic faunas from similar depositional environments. The Coffee Sand samples have a highly skewed species-abundance distribution that are very "modern" in several respects. The Coffee contains a large number of presumably predatory early Neogastropod species, although at lower abundance than found in Cenozoic samples. Certain taxa appear to have suffered significant drilling predation, although at lower frequencies than that found in many Cenozoic samples. Preliminary analyses indicate that the Coffee Sand is ecologically similar to the better studied H. bilira zone (Maastrichtian) in terms the of abundance of predatory taxa and degree of infaunality and contrasts with descriptions of Early Cretaceous faunas.