23 Quaternary Geology along the Southeast U.S. Coast: Contrasting Recent Change with Long-Term Evolution

Friday, 1 April 2016
8:00 AM - 12:00 PM
Richland C

THE CAROLINA SANDHILLS OF THE SOUTHEASTERN UNITED STATES ARE EOLIAN SAND SHEETS AND DUNES THAT WERE ACTIVE DURING THE LAST GLACIATION

Paper number: 23-2
Program: Theme Sessions
Time: 8:20 AM – 8:40 AM

Authors

Abstract

The Carolina Sandhills is a 15 to 60 km wide physiographic region in the southeastern United States, extending from the western border of Georgia to central North Carolina along the updip portion of the Coastal Plain province. In Chesterfield County (South Carolina), the “sandhills” occur at ca. 60 to 150 m elevation and in most places consist of <1.5 m thick sand that blankets the landscape, but in areas of higher elevation the sand forms subdued hills (<7 m relief) with steeper sides on the east and southeast. The sand is grayish orange (with some brown, yellow, and white), composed predominantly of quartz with <1% mica and opaque minerals, and rests on an unconformity above poorly indurated sandstone of the Cretaceous Middendorf Formation. The sand is moderately sorted to poorly sorted, and the grain size mode of individual samples varies from fine (lower) to coarse (lower) sand. Outcrops of the sand display evidence of bioturbation by vegetation, pedogenic soil lamellae, and argillic horizons, but no primary sedimentary structures. Ground-penetrating radar (GPR) data, however, reveal 2 to 5 m thick sets of cross-bedding at depths below 2 m. Optically stimulated luminescence (OSL) dating of the sand has yielded 11 ages from ca. 73 to 19 thousand years ago (ka) and 6 ages from ca. 12 to 8 ka.

The “sandhills” are interpreted as eolian sand sheets and dunes that were active predominantly during the last glaciation. The poor sorting, coarse grain size, and spatial association with poorly indurated Cretaceous sandstone suggest that the sand has not traveled far and was derived from the underlying Cretaceous strata. The OSL ages suggest that the sand is not beach deposits (because sea level was well below 60 m elevation during 73 to 19 ka) or fluvial deposits (because the sand blankets the landscape and is not associated with obvious fluvial channels). The hill morphology is interpreted as relict dunes because the steeper sides of hills are consistent with most cross-bedding dip directions in GPR data. The predominance of sand sheets over dunes is attributed to the coarse grain size and the likely presence of some vegetation when the sand was mobile. It is easier for wind to entrain sand at lower air temperatures (such as were present during the last glaciation), and eolian sand sheets of similarly coarse grain size are present in high latitudes today.

Geological Society of America Abstracts with Programs. Vol. 48, No. 3

doi: 10.1130/abs/2016SE-271938

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