Cryogenic sediment‐filled wedges, northern Delaware, USA

• Published in: Permafrost and Periglacial Processes
• Main Authors: Mary D. Lemcke, Frederick E. Nelson
• Format: Article in Journal/Newspaper
• Language: unknown
• Subjects: Ice; Ice Sheet; permafrost; Tundra; wedge*
• Online Access: https://doi.org/10.1002/ppp.481

Wedge‐like sedimentary structures at two sites in northern Delaware USA are located at the erosional surface of, and extend into, channel deposits of the fluvial, mid‐Pleistocene Columbia Formation. The wedges are 0.25–0.60 m wide at the top, 1.0–1.5 m in vertical extent, contain moderate to poorly sorted, and vertically‐stratified sediment, and are overlain unconformably by a layer of wind‐blown silt. Several hypotheses for the formation and infill of the wedges were evaluated using detailed physical, stratigraphic, and sedimentological information. The most likely explanation for the features is that they are relict cryogenic structures formed by thermal‐contraction cracking in permafrost, and filled with wind‐blown sediments derived from the Columbia Formation. The wedges are believed to have formed in the tundra environment that existed in northern Delaware, south of the Laurentide Ice Sheet, during the coldest parts of the Wisconsinan glaciation. Copyright © 2004 John Wiley & Sons, Ltd.