PREHISTORIC ANTHROPOGENIC EVENT II (AE-II) AND ITS INFLUENCE ON EARTH SURFACE PROCESSES ALONG THE MIDDLE DELAWARE RIVER VALLEY, USA (Invited Presentation)

Quaternary geologists and geomorphologists are increasingly examining the effects of anthropogenic impact on the environment. To this end, geoscientists have proposed the Anthropocene Epoch or Age as a new stratigraphic interval documenting sedimentary and biogeochemical evidence of human impact on the geologic record. Although human impact on the surrounding environment is notable, it is time-transgressive, likely occurred in multiple, discrete, short-lived events, and is of varying spatial extent. To address this complexity, we propose identifying and measuring anthropogenic impacts on the environment using INQUA-based event stratigraphy. Much like a debris flow, volcanic ash deposit, or eustatic flooding surface, anthropogenic impacts on the environment can be classified as events. Using a suite of methods we demonstrate evidence for a prehistoric anthropogenic event recorded in the Quaternary geologic record of the middle Delaware River Valley. Anthropogenic Event II (AE-II: 1.0 – 0.4 ka) is characterized by increased sedimentation, coarsening flood deposits, enriched soil carbon isotope values, C₄ phytoliths, increasing frequency of artifacts, and maize-based agricultural intensification during the Late Woodland cultural period. These data suggest that the combined effects of prehistoric land-use (farming and forest management) operating within the late Holocene climatic context impacted eastern North American floodplain sedimentation and development several hundred years prior to the onset of major European Settlement. AE-II is followed by AE-I, a Euro-American anthropogenic event resulting from widespread upland forest clearance documented in many river valleys in the Northeastern USA. The systematic study of anthropogenic event complexity in time and space will likely shed more light on the historic- and process-based geomorphic interpretations of human impact. We also contend that continued mapping of anthropogenic events will lead to a more practical and useable Age/Epoch designation for the Anthropocene.