ALTERNATION OF DUNE AND FOREST LANDSCAPES: EVIDENCE FROM PALEOSOLS IN MARINE TERRACE DEPOSITS, LINCOLN COUNTY OREGON

Mapping of sea cliff exposures in marine terrace deposits has provided evidence of alternation of dunal and forested landscapes on the Oregon coast during the Quaternary. Dune deposits are commonly interbedded with paleosols containing insitu buried tree stumps along seventy kilometers of the Oregon coast between Heceta Head and Cape Foulweather.

Radiocarbon ages on the uppermost forest layer range from 5,760 RCYBP to 3,420 RCYBP and are agreement with ages obtained on stumps of Sitka Spruce rooted on present-day wave-cut platforms of the Newport littoral cell. Several meters of truncated late Holocene dunes cover the terrace margin forest soil at elevations up to 8 meters above sea level. In places, the late Holocene forest soil is separated from underlying Pleistocene dunes by an erosional surface.

Pleistocene dune deposits are also interbedded with paleosols but they are not as well developed as the Holocene forest soil. The Pleistocene paleosols are in places continuous across small creek valleys indicating a period of stream incision and erosion occurred after formation of the Pleistocene dunes. Depending on locality, the uppermost soils developed on Pleistocene dunes are either buried by late-Holocene dunes or are still developing as modern topsoil.