Periglacial Sediment-Filled Wedges, Northern Delaware, USA By: - - PowerPoint PPT Presentation
Periglacial Sediment-Filled Wedges, Northern Delaware, USA By: Mary D. Lemcke and Frederick E. Nelson Relict periglacial features associated with Late Quaternary glaciations have been used to reconstruct the periglacial environment south of
Relict periglacial features associated with Late Quaternary glaciations have been used to reconstruct the periglacial environment south of the glacial border (Brown and Péwé, 1973; Washbrun, 1980, Péwé, 1983) Project goals: To determine the origin of wedge-like sediment-filled structures in northern Delaware, we generically refer to as “sediment-filled wedges”, and determine their possible paleoenvironmental significance.
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Delaware New Jersey Pennsylvania Maryland
Sand and Gravel Pit, Kenton DELDOT Sand and Gravel Pit, Middletown
Map of northern Delaware showing the locations of the DELDOT sand and gravel pit south of Middletown and the privately owned sand and gravel pit near Kenton.
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1 2 3 4 5 phi scale % Middletow n Kenton
Grain-size distribution of sediment samples from a typical wedge structure from the Middletown quarry and the
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1 2 3 4 5 phi scale % top middle bottom
Grain-size distribution of samples taken from the top, middle, and bottom of a wedge from the Middletown quarry
Dylik and Maarleveld (1967)
1. Maximum width exceeding 10 cm 2. Rapid decrease of width downward 3. Infill material different than surrounding material 4. Bending of layers along wedge wall 5. Swellings bordering top of wedge 6. Polygonal pattern exceeding 7 m in diameter 7. Distance between wedges of several meters
Murton, Worsley, and Gozdzik (2000)
1. Large-scale polygonal network 2. Vertical to steeply dipping lamination 3. Elementary sand veins extending from sides and toes of sand wedges 4. Inclusions of host material cross-cut by sand veins 5. Pebbles near top of wedge, gravel content decreases with depth 6. Ventifact lags 7. Infill indicates greater aeolian abrasion than that of host material
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New Jersey Maryland Delaware Pennsylvania
Middletown Pollack's Farm Kenton West Berlin Haleyville South Bound Brook Manville Lewisburg Benfer
Map of the mid-Atlantic region showing the locations of sediment-filled wedges (▼ indicates the location of reported relict sand and frost wedges and field located sediment-filled wedges; ▽ indicates the location of reported ice-wedge casts).
The sediment-filled wedges located near Middletown and Kenton, Delaware, are morphologically and sedimentologically similar to wedges formed by thermal contraction cracking and filled with aeolian sediments.
information indicate that permafrost was present during their formation. Although the exact time in which the wedges formed has yet to be determined, based on ancillary evidence, we can infer that they formed during the peak of the last ice age.
ACKNOWLEDGEMENTS We are grateful to Dr. Thomas Meierding and Dr. Kelvin Ramsey for providing critical expertise in developing the thesis from which this paper was distilled. Jim Doolittle (U.S. Department of Agriculture) conducted ground penetrating radar investigations and provided interpretive expertise. Jim Black and the Department of Geology (University of Delaware), Dr. Robert Jordan, Dr. Scott Andres, and the Delaware Geological Survey made laboratory equipment available and discussed local geology with the first author.