Carla Gray

Honors in Geography

Major: Geography

Supervisor: Michael Benedetti, Geography and Geology

Buried Soils as Stratigraphic Marker Horizons on the Cape Fear River Floodplain, Bladen County, North Carolina

Over the past 40 years, studies have shown that buried pre-settlement soils can be used to determine historical deposition rates in river systems across North America. Previous studies in the Coastal Plain of the Southeastern USA have not often cited buried soils, and it is unclear whether they are not present, or have simply not been identified. Several factors might explain the lack of buried soil evidence in this region. First, poor drainage causes soil-forming conditions, such as bioturbation and redoximorphic features, to mask the appearance of buried soils in swampy floodplains of the Coastal Plain. Second, deposition rates on the Coastal Plain are generally low, relative to the rates of pedogenesis and bioturbation. Third, the long colonial history of the Southeast means that the postsettlement stratigraphic record in floodplains is older and more complex than elsewhere in the US. The purpose of this study is to show that a pre-settlement soil is present and can be used as a stratigraphic marker horizon to determine overbank deposition rates on the Cape Fear River floodplain in Bladen County, North Carolina. Buried soils were identified by careful field description, supported by organic carbon determination. Organic carbon results showed a slight increase in the buried horizon. pH analyses were also performed and showed trends that correlated with A horizon levels. Radiocarbon dates suggest an age of approximately A.D. 1630 for the earliest burial of this soil, with a vertical accretion rate of approximately 1.9-2.2mm/year since then. Cesium-137 results indicate a vertical accretion rate of approximately 1.7-2.8mm/year since 1964.