37 Undergraduate Research IV (Posters)

Friday, 13 April 2018
1:30 PM - 5:30 PM
Room 301 DE/Henley Concourse

LATE QUATERNARY CLIMATE AND LANDSCAPE HISTORY OF THE GRAFTON PONDS NATURAL AREA PRESERVE, YORKTOWN, VIRGINIA

Paper number: 37-20
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

The Grafton Ponds Natural Area Preserve (GPNAP) is a complex of shallow ponds situated on the Coastal Plain in Yorktown, Virginia. The ponds are depression wetlands, formed in the mid-Pleistocene age Chuckatuck Formation as a result of the dissolution of the underlying carbonate-rich Yorktown Formation. Here we investigate sediment accumulated in two of the ponds for their potential as archives of late Quaternary paleoenvironmental information. We collected sediment cores from two ponds in the northern region of the preserve and analyzed them for magnetic susceptibility, bulk density, total organic and inorganic content, carbon: nitrogen ratios, and grain size. Select radiocarbon samples were analyzed from the upper sections of both cores. Additionally, a geomorphic landscape analysis was preformed using existing LiDAR data. Geomorphic analysis and on-site observations indicate approximately 20-30 shallow ponds with no major feeder stream systems in a 5,500 m2 area with a total relief of less than 5m. The basal sediments in both ponds, ~3-0.8m, are a clayey fine to coarse pebbly sand that transitions into an upper unit with finer grained, faintly laminated, more organic rich sediment at ~80cm. This transition is also defined by a gradual decrease in the magnitude and variability of C:N ratios from 20 to 15. The basal unit is characteristic of the Chuckatuck Formation marked by deposition in an estuarine environment. The change in sedimentation in the upper unit appears to be distinct and likely indicates subsequent late Quaternary sedimentation in a wetland pond environment. Radiocarbon results suggest this transition occurred in the late 1700’s, which is surprising considering the rate of accumulation and evidence of older ages documented previously by others at another site in GPNAP. However, an 18th century age for this transition does coincide with the end of a significant interval of regional drought, as well as an increase in early colonial landscape activity. These preliminary data provide new perspective on the landscape history of GPNAP and more broadly on sedimentation in coastal plain depression wetlands, and their viability as a climate archive

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-312896

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