PALYNOLOGY OF THE BOONEVILLE DINOSAUR SITE, MISSISSIPPI, U.S.A. – FLORISTICS, BIOSTRATIGRAPHY AND CLIMATE

We report here on a palynological assemblage recovered from a Campanian fossil site (Booneville Dinosaur Site (BDS)) near Booneville, Mississippi. The BDS, from the lower Coffee Formation, consists of interlaminated carbonaceous clays, silts, and fine-grained sands along with teredinid-bored lignitized logs, and is interpreted as a tidally influenced estuary. The faunal assemblage includes a partial skeleton of an adult hadrosaur, the most complete dinosaur found in Mississippi to date, along with the dentary of a very young hadrosaur, suggesting that this assemblage may have included a nesting site. Crocodilians, sea turtles, an aulopiform fish, sharks and macroinvertebrates are also present. Well-preserved palynomorphs were extracted from matrix associated with the dinosaur bones and from an equivalent unit about 55 m to the west. Based on 200-grain counts, angiosperms comprise about one third to one half, spores about one third, and gymnosperms about 10% of the assemblage. Algal cysts are also significant, comprising 10-20% of the assemblage. Dinoflagellates are present but rare. Species of Normapolles (= Fagales) are prominent, making up between 10% and 30% of all angiosperms. Other typical Late Cretaceous angiosperms include Holkopollenites, Tschudypollis, and Echimonocolpites (eudicots or monocots of uncertain affinity). Gymnosperms present include the Pinaceae, Araucariaceae and Cupressaceae. Diverse spores include Schizaeales, Polypodiaceae, Gleicheniaceae, Sphagnaceae, and lycophytes, along with other unknown families. Abundant algal cysts and rarity of dinoflagellate cysts indicate a strong fresh-water influence. A refined biostratigraphic age for the BDS can be proposed based on correlations with comparable palynofloral assemblages in South Carolina. The co-occurrence of Holkopollenites propinquus with a LAD in the earliest mid Campanian and Osculapollis aequalis with a FAD in the late early Campanian places it in the upper half of the Hp palynozone of Christopher & Prowell (2010), close to the early-middle Campanian boundary. The abundance of Normapolles forms suggests a warm and perhaps moderately dry climate, but the abundant and diverse ferns, lycophytes and bryophytes indicate that much of the local vegetation near the site of deposition was hydrophilic.