Southeastern Section - 68th Annual Meeting - 2019

Paper No. 31-17
Presentation Time: 8:00 AM-12:00 PM


CHILDS, Briana D.1, BALASCIO, Nicholas L.1 and RAMSEY, Kelvin W.2, (1)Department of Geology, College of William & Mary, Williamsburg, VA 23187, (2)Delaware Geological Survey, University of Delaware, Newark, DE 19716

The Cypress Swamp Formation (CSF) is a late Pleistocene to early Holocene deposit located on the Delmarva Peninsula in Sussex County, Delaware. It is up to ~9 m thick and is generally mapped as having a composition of unconsolidated silty sand, organic silts, and peat beds. Here we present a detailed stratigraphic analysis of the CSF in an attempt to better understand the relationship between sedimentation in this region and paleoclimate and paleoenvironmental conditions. In particular, previous mapping has defined a distinct organic-rich unit within the lower CSF that appears to be laterally extensive and that has been dated in places to sometime within Marine Isotope Stage (MIS) 3. Here we present data from two new 10-meter cores from the CSF that were recovered and analyzed to develop detailed profiles of changes in organic matter content and grain size. Based on these data we define four lithostratigraphic units and show a distinct interval near the base of the CSF with higher organic content values (7-15%) and a finer grain size (80% silt) than the overlying units. Six radiocarbon dates within this organic-rich unit show that it accumulated from c. 25-37 cal ka BP. The overlying units are primarily low in organic content and silty sand to sand silt in composition. The age range that defines deposition of the organic-rich unit with the CSF formation falls near the end of MIS 3 and may represent a period of wetter or less windy environmental conditions just prior to the LGM when a cold, dry, and windy climate persisted into the Holocene, as previously interpreted based on sediments in the upper CSF and other records from the region.