Observations on Ventifacts and Wind-Polished Boulders in Pleistocene Coversands, Ice-Marginal New Jersey
Monday, 15 December 2014
The nature of New Jersey Pine Barrens’ paleoenvironment biome has been problematic. The region’s Pleistocene environment has been interpreted as cool and moist, with boreal forest. A competing interpretation envisioned cold, dry, semidesert conditions. Pebble- to boulder-sized ventifacts with a wide suite of erosional forms provide evidence for strong Pleistocene wind action, which occurred when the land was sparsely vegetated allowing an abundance of abradants to be easily entrained and transported. Although commonplace, ventifact presence and utility in paleoenvironmental reconstruction is ignored. Most ventifacts occur on upland surfaces and attest to stability in this part of the region’s otherwise low-relief landscape, and their subsequent disarrangement provides clues to geomorphic processes and landscape evolution. Ventifacts progressed downslope along upper valley-side slopes largely by gravitational mass movement, particularly under periglacial conditions. Development of eolian features such as pavement einkante, scallops, and weathering pit modification can evolve only where sustained wind velocities are very high and sand sources are abundant. Pine Barrens ventifacts provide evidence that desert-like conditions prevailed. Some ventifact surfaces are covered with a silica glaze or an iron-enriched metal film, or both, indicating multiple episodes of wind abrasion. Coating study holds much promise for future dating and climate reconstruction investigations.