USE OF SEDIMENTARY DIATOM ASSEMBLAGES TO ASSESS ENVIRONMENTAL CHANGES DURING THE LATE PLEISTOCENE AT A MASTODON SITE IN HYDE PARK, NEW YORK STATE

This study assesses changes in the environmental conditions of the Mid-Hudson River Valley, New York State, from analyses of diatom assemblages (microscopic algae, Class Bacillariophyceae) preserved in a sediment core from a small lake (Lozier Pond) during the period ~15,000 to 9,000 yr BP, when mastodons were abundant to the time of their extinction. This research project is focused on the site of one of the most complete mastodon skeletons ever discovered in the American Northeast (Hyde Park, Dutchess County, New York), and forms part of a multidisciplinary paleoecology research project organized by the Paleontological Research Institution (PRI, Ithaca, NY). The resulting diatom analysis revealed that the diatom taxa dominating the assemblages are typical of late Pleistocene and early Holocene diatom communities seen in sediments of many lakes.

The earliest period of the sediment core (~15,000-12,400 ¹⁴C yr BP) reveals a lack of planktonic diatom taxa and the dominance of small, benthic Fragilaria species, suggesting a turbid, low-light, aquatic environment, possibly fed by glacial meltwater. At ~12,400 ¹⁴C yr BP, there is a decrease in Fragilaria species and a change to a more diverse diatom flora with the introduction of numerous new epiphytic species including Amphora pediculus and Navicula diliviana, possibly indicating the growth of aquatic weeds under more clear-water conditions. This trend continues for another ~1,700 years until a major change occurs at ~10,700 ¹⁴C yr BP. This change is indicated by the dominance of Navicula diluviana and a further decrease in relative abundance of Fragilaria species, possibly indicating a further expansion of weeds. Two very significant climatic warming events (centered around 12,400 ¹⁴C yr BP and ~10,700 ¹⁴C yr BP respectively) correspond with the observed major changes in diatom assemblages, and they appear to be tightly coupled with changes in forest composition as recorded by a regional pollen record. The closest modern conditions that exhibit similar diatom assemblages are in small lakes in the high arctic and present-day periglacial environments.