STRATIGRAPHY OF THE LATE OLIGOCENE JONES BRANCH VERTEBRATE FOSSIL SITE, LOWER CATAHOULA FORMATION, WAYNE COUNTY, MISSISSIPPI

The Jones Branch fossil site was discovered by local rockhounds, Andy Weller and Roger Rains of Waynesboro, Mississippi. The geology of Wayne County, Mississippi was mapped by state survey geologist, James H. May in 1974. His test hole MGS N-12 in close proximity to the fossil site is the basis for the stratigraphic division of the site. The Tertiary units exposed in Jones Branch occupy Planktonic Foraminiferal Zone P22 thus, are of Chattian age, and are stratigraphically below the last regional occurrence of the benthic foraminifera, Heterostegina. The base of the exposed section is the Late Oligocene fossiliferous, glauconitic, sandy-clay marl and soft limestones of the Paynes Hammock Formation. The Paynes Hammock occupies the upper Calcareous Nanofossil Zone NP24 and is dominated by thin discontinuous reefs of the large oyster, Crassostrea blanpiedi. The contact with the Paynes Hammock and the overlying Catahoula Formation (Calcareous Nanofossil Zone NP25) is marked by a thin, fine-grained, sandy, indurated ledge, exhibiting preserved primary structures interpreted as ripple marks on a sandy tidal flat. The basal Catahoula Formation is composed of gray-green-colored, fissile, high-alumina clays of an emergent delta with both brackish water and terrestrial influences marked by excellently preserved flora of lignitized broadleaf and palmetto fossils and silty to fine-sandy shell hash seams along partings grading upwards to massive, uniform, freshwater clays. The basal clays contain a series of thin sandy tidal channel lag lenses, containing mollusks, marine and terrestrial vertebrates, and phosphatic pebbles and coprolites. Much of the larger marine vertebrate and invertebrate fauna contained in these channel lags show signs of reworking from older, up-dip units, while the terrestrial vertebrate assemblage, tentatively assigned by Barry Albright to the Early Arikareean North American Land Mammal Age, are syndepositional to the channel lag deposits.