RECONSTRUCTION OF AN ACTIVE MARGIN COASTAL WETLAND FROM THE LATE PLEISTOCENE TO THE PRESENT: IMPLICATIONS FOR A COASTAL MIGRATION INTO THE NEW WORLD

Archaeological evidence indicates that humans occupied the Northwest Coast by 12,000 years ago. However, the viability of coastal Oregon as a migration corridor for the first humans into North America depends, in part, upon whether the coast provided environments suitable to human needs. Ethnographic and archaeological studies suggest a long history of human occupation of estuary and wetland settings. This study explores the depositional environment evolution of an active margin, coastal wetland/estuary locality in the Sixes River Valley, southern Oregon coast, USA.

Detailed diatom assemblage analysis coupled with lithostratigraphic investigations of long sediment cores from this coastal wetland/estuary setting reveal a transgressive facies evolution from the late Pleistocene to the present that differs from models of transgressive coastal facies, as well as from studied estuarine life histories from other localities along the Northwest Coast. The results of this study indicate that freshwater, fluvial environments did not dominate the lower Sixes River Valley until at least 9400 cal yr BP. Instead, a tidally influenced estuarine setting or intertidal wetland occupied the site during the late Pleistocene and early Holocene. Local features, such as river valley width, upper-plate tectonic deformation, or higher rates of sedimentation may have had a significant effect on the timing of estuary and tidal wetland existence at the site. If this is the case, then the exact location and timing of early human use of highly productive, active margin, coastal landscapes, such as estuaries and tidal wetlands, depend upon the interactions of coastal tectonics, geomorphology, and local, relative sea level rise. A search for evidence of late Pleistocene human occupation of coastal river valleys will have to be considered on a case-by-case basis.