T230 From Hudson Bay to the Coastal Plain: Comparisons of Pre-LGM (Last Glacial Maximum) Quaternary Records in Glaciated and Unglaciated North America II

Thursday, 29 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

LATE PLEISTOCENE, PRE-LGM COLLUVIAL AND ORGANIC-RICH SEDIMENTS IN THE INTERFLUVIAL UPLANDS OF THE SOUTHERN PIEDMONT: A CASE STUDY FROM NW SOUTH CAROLINA

Paper number: T230-4
Program: Technical Sessions
Time: 6:05 PM – 6:20 PM

Authors

Abstract

The Piedmont physiographic province of the SE US is widely touted as a region of type-section localities for stable uplands with deep, bedrock-derived weathering profiles. Over 40 upland, low-order watershed localities in NC, SC and GA, however, suggest that many locations in this region preserve rich records of pre-LGM landscape evolution and climate. Gully profiles, borings and geophysical surveys reveal meters-thick deposits of colluvium underlain by organic-rich sediment deposits, providing irrefutable evidence that many uplands comprise inverted topography of past filled-paleochannels or filled-valleys. This study is a detailed description of one such site near Pauline, SC.

Analyses of particle size, elemental and mineralogical composition (XRF, XRD, total and stable isotopic carbon and nitrogen, magnetic susceptibility), and pedological analyses of the 9m section show significant lithostratigraphic and pedologic differences between the upper 6m of overlying colluvium, lower 3m of organic-rich sediments and underlying saprolite. A complex history of episodic development is indicated.

Discontinuities and unconformities suggest seven distinct allostratigraphic units, dated by 14C and IRSL, spanning late Holocene, MIS 4, MIS 5d, and probably MIS 5e-6. Observed periods when deposition exceeds erosion appear to correspond to cooler climatic stages.

Palynological evidence from the lower organic-rich sediment document a vegetational and climatic shift from cool-temperate forests during stadial/glacial conditions to warm-temperate forests during interstadial/interglacial conditions, sometime prior to 110kyr BP.

Continued analysis of this and other sites with polygenetic histories has the potential to improve understanding of late Quaternary history of the Southern Piedmont region. This ancient landscape is not as stable as traditionally viewed, involving much more dynamic systems of erosion, transportation and deposition.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357572

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