PALYNOMORPHS OF THE ARKADELPHIA FORMATION AND MIDWAY GROUP TRANSITION (MAASTRICHTIAN-DANIAN), HOT SPRING COUNTY, ARKANSAS

Near Malvern, Hot Spring County, Arkansas, the contact between the Arkadelphia Formation (Late Maastrichtian) and the overlying Midway Group (Danian) is represented by a macrofossil lag deposit rich in Maastrichtian age chondrichthyan teeth; other vertebrate remains; and in invertebrates, corals and bivalves in particular. Sediment samples from the lag, and from the beds immediately above and below it, contain a palynomorph assemblage comprised of a relatively small number of poorly preserved dinoflagellate cysts, pollen grains, and spores. Representative dinoflagellate genera include Ceridinium; Paleocystidinium, and Paleoperidinium. Other palynomorph genera are Aquilapollenites; Proteacidites; Tricolpites; Triporopollenites, and trilete spores such as Cardioangulina. Stratigraphic ranges of these genera are consistent with the Maastrichtian-Danian age of the transition beds. However, poor preservation and the small number of constituent taxa in the assemblage have so far precluded the use of palynomorphs in correlating the macrofossil lag with the presumably impact generated tsunami deposit that marks the Cretaceous-Paleocene boundary in other regions of the Gulf Coastal Plain and Mississippi Embayment. Wind-driven pollen and spores of land plants are as abundant in the samples as dinoflagellates. This evidence suggests that the depositional setting of our Malvern locality was probably close to the Cretaceous-Paleocene shoreline. This interpretation is consistent with habitat preferences inferred for the invertebrates, and for the chondrichthyans, teleosts, and other vertebrates preserved in these beds. This view is also supported by lithologic and macrofossil evidence suggesting a freshwater/brackish influence in these marine deposits.