FLORAL COMPOSITION AND PALEOECOLOGICAL IMPLICATIONS OF A LATE NEOGENE FLORA FROM THE GRAY FOSSIL SITE, NORTHEASTERN TN: RESULTS FROM POLLEN ANALYSIS

The Gray Fossil Site is a proximal depositional basin with a complex filling history located in northeast Tennessee. The site is covered with lacustrian sediments of latest Miocene – earliest Pliocene age. A rich vertebrate fauna was recovered including over 80 tapirs, the short-faced bear (Plionarctos), alligators (Alligator), rhino (Teleoceras), elephants, etc. The fossiliferous lacustrian sequence is primarily dated in the light of co-occurrence of Plionarctos and Teleoceras. Interestingly, an abundant flora is also preserved in the sequence, in which plant organs, such as wood fragments, leaves, fruits/seeds and pollen, are represented.

A palynological analysis was conducted on 46 samples collected from 6 test pits at the site. Comparative modern pollen data were acquired from 144 sites from the North America and Greenland Modern Pollen Database. These sites were carefully chosen using the presence of crocodilians (Alligator sp.) as a proxy for temperature; hence, we only selected those sites where Alligator currently occur. To quantitatively compare the floral composition from the fossil site at Gray with those modern floras, we used the following three methods, e.g., Detrended Correspondence (DCA), Hierarchical Cluster (HCA), and Discriminate Analyses (DA). The GFS pollen profiles exhibit a low diversity and little variation in the pollen assemblages throughout the site. Over 90 % of the palynoflora is dominanted by Quercus, Carya, and Pinus, and less than 10 % of the flora is comprised of Pterocarya, Juglans, Ulmus, Tsuga and Chenopodiaceae-Amaranthaceae among other rare taxa. Fossil charcoals are common throughout the section, suggesting wildfires may have been a significant disturbance factor. The DA was employed to help identify the best comparable modern pollen assemblages, which are distributed mainly along the Mississippi river valley and the northern limit of the Atlantic coastal plain. The dominance of Oak – Hickory elements and the abundant occurrence of charcoals in the flora suggest that the Mio-Pliocene GFS region may have been subject to a distinct wet-dry seasonal pattern and the frost-line was shifted further north, permitting a more northern distribution of warm temperate – subtropical elements, e.g., alligators, Nyssa, and Pterocarya, as seen at the Gray Fossil Site.