Cryospheric and Polar Processes Seminar: Mark Demitroff

Late Pleistocene Periglacial Processes and the Origin of Pinelands Closed Basins

Mark Demitroff, Geography Department, University of Delaware

The concept of widespread permafrost and periglacial (cold, nonglacial) landforms in the Mid-Atlantic region has been controversial. Some have argued for a cool, moist Pleistocene realm, while others maintained that cold, dry, and windy conditions prevailed. This session will examine new evidence for deep seasonal frost, permafrost, and a polar desert-like environment in the Pinelands National Reserve of New Jersey. Frost cracks are commonplace. Thermokarst processes during permafrost thaw created a suite of structures that are abundantly expressed in local sand and gravel operations. Strong density-driven katabatic winds from a massive ice sheet sculpted surficial terrain through sand deposition and deflation. Closed basins, colloquially called spungs, are interpreted as blowouts. Cryogenic weathering of silicates, a process best developed in the active layer of permafrost regions, is represented in paleosols. Multiple episodes of past permafrost extended hundreds of kilometers south of the maximum limit of the continental ice sheet, and was at times continuous to Baltimore and Washington, DC.