8 Sedimentary Systems of the Post-Alleghanian Eastern U.S. Atlantic Margin: Implications for Geologic Evolution, Resource Potential, and Carbon Sequestration (Posters)

Thursday, 28 March 2019
8:00 AM - 12:00 PM
Carolina Ballroom

RE-INVESTIGATION OF A COLLUVIALLY FILLED VALLEY CONTAINING DEEPLY BURIED ORGANIC-RICH SEDIMENTS OF PLEISTOCENE AGE, PAULINE, SOUTH CAROLINA

Paper number: 8-2
Program: Theme Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

From the mid-1930s to early 1940s the Climate and Physiographic Division of the Soil Conservation Service (SCS) conducted research on historic period erosion and Pleistocene filled valleys in Spartanburg County, South Carolina (Shape 1938; Eargle 1940, 1946, 1977). In an unsystematic study by SCS of over two dozen deeply eroded gullies, evidence was found in interfluvial uplands of previously eroded valleys partially filled with organic-rich sediments containing abundant pollen and plant macro-fossils overlain by meters of colluvium. One of the deepest of these, containing over 2.5 meters of organic-rich sediment overlain by almost 6 meters of colluvium, was the Trail Gully located near Pauline, SC. Our work summarizes contemporary investigations of these deposits and discusses their significance.

Radiocarbon and luminesence dating constrain the calendrical age of the colluvium to 3906 to 4082 yr bp (at 0.8 m) and 100k to 110k yr bp (at 4 m) respectively. Particle size analyses, pedological interpretations and magnetic susceptibility analyses indicate a complex depositional history involving multiple episodes of colluvial deposition and post-depositional soil development. Disconformities are also indicated. XRF and XRD, analyses indicate significant mineralogical differences between overlying colluvium, organic-rich sediments and underlying saprolite, and in terms of their chemical and possibly parental histories. In the organic-rich sediments (between 6 and 8 m) more negative d13C occurs where SOC concentrations increase. Replication of pollen study by Cain (1944) indicates that assemblages change with depth (from 6 to 8.5 m) The uppermost assemblage is typical of a southeastern oak-pine forest. With increasing depth percentages of pine increase and oak decrease. The deepest levels differ significantly with increased hemlock.

The presence of sediment filled valleys in interfluvial uplands is an under-appreciated aspect of the development of the Southeastern Piedmont. This research has significant implications for the conventional wisdom that piedmont soils are derived primarily from in-place weathering and that a little understood period of landscape evolution involving dissection, regolith transportation and deposition took place in the Southeastern Piedmont during the Pleistocene.

Geological Society of America Abstracts with Programs. Vol. 51, No. 3

doi: 10.1130/abs/2019SE-327726

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