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"Ritter, Dale F"
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Overbank Sedimentation in the Delaware River Valley during the Last 6000 Years
A thick sequence of floodplain sediments has accumulated in the Delaware River Valley by the process of overbank deposition. Textures in the sediments indicate that the sequence contains no point-bar deposits and is unbroken by periods of erosion. Fourteen radiocarbon dates show that deposition began at least 6000 years ago and has continued to the present. Because the Delaware River shifts its position laterally at a very slow rate, overbank deposition becomes dominant in the construction of its floodplain.
Journal Article
Alluvial Fan Development and the Glacial-Glaciofluvial Cycle, Nenana Valley, Alaska
Alluvial fans located downstream from Pleistocene glacial margins in the Nenana Valley of Alaska began to form immediately after outwash deposition ended. Each fan constructed by a major tributary stream rests conformably on the outwash surface of the preceding glacial episode. Outwash is unweathered where it is covered by thick fan alluvium, indicating that no significant time break separated deposition of the two material types. Except for a thin upper zone, development of each fan was completed before trunk-river entrenchment occurred prior to the subsequent glacial event. It is possible that fans were constructed in a relatively short \"paraglacial\" interval when the effects of a nearby glacier were still being felt in the tributary basins. A complete fan sequence in any tributary valley near but beyond the downvalley limits of glaciation mirrors the mountain glacial sequence and can be used as a first approximation of the number of glacial episodes.
Journal Article
Geomorphic Controls on the Origin and Location of the Tolman Ranch Ventifact Site, Park County, Wyoming, USA
Ventifaction on the Tolman Ranch Terrace surface in northwest Wyoming is controlled by factors other than intensity and direction of regional winds. Disintegration of granitic boulders in the terrace gravel causes large, fine-grained mafic boulders to be preferentially concentrated on the terrrace tread. These boulders rise above a critical height needed for ventifaction. Quartz-rich sand introduced into the system by weathering is used in the abrasive process while it is simultaneously removed from the system by topographically enhanced winds. Pronounced ventifaction in this area occurs only where granite disintegration and topography are properly combined to maximize abrasive work. Ventifaction in this setting may have been continuous or intermittent since deposition of the gravel; thus, features produced have no paleoclimatic implications.
Journal Article
Stratigraphic Implications of Coarse-Grained Gravel Deposited as Overbank Sediment, Southern Illinois
Coarse-grained gravel lifted from the channel of Sexton Creek during flash flooding was deposited on the floodplain surface in three distinct lobes. The overbank gravel was laid down passively on the floodplain and no scouring of that surface preceded the depositional event. The deposits have a flat lower surface and are convex-up in shape. Similar deposits are exposed as gravel lenses in the stratigraphic sequence underlying the floodplain. Failure to recognize the overbank origin of the gravel lenses could lead to incorrect interpretations of the paleoenvironment.
Journal Article
Problems of Stream Terrace Correlation and Reconstruction of Geomorphic History Caused by Colluvium
The ability of colluvium to mask the presence of fluvial terrace gravel is examined in and near the Beartooth Mountains of southern Montana. Two areas, different in geologic setting, have been studied in detail to demonstrate the complications created by colluvium deposition when reconstructing the geomorphic history of each region. The colluvium is topographically indistinguishable from the stream deposits it covers. The presence of the buried terrace gravel is revealed only by careful field examination of subtle textural or compositional differences between the two types of material. Colluvial deposition occurred in both areas after fluvial aggradation ceased and before entrenchment by the main river commenced. The colluvium is not moving at the present time.
Journal Article
