The geology and distribution of oriented landforms and associated features in northeastern Nebraska

• Main Author: Guthrie, Robert Scott
• Format: Text
• Language: English
• Published: DigitalCommons@University of Nebraska - Lincoln 1990
• Subjects: Geology; Sand Hills; Ice; permafrost; wedge*
• Online Access: https://digitalcommons.unl.edu/dissertations/AAI9030120

A distinctive northwest-to-southeast topographic grain consisting of fluted-ridge and trough landforms, aligned drainages, and elongated basins extends across much of northeastern Nebraska. Late Wisconsinan wind-scouring superimposed these oriented topographic features upon an existing dissected landscape composed mostly of older Pleistocene sediments. Subsequent loess deposition covered this deflated land-surface and preserved the character of former surficial elements. These paleosurface components include cover sands, ventifacts, wind-polished pebbles, sand wedges, ice-wedge casts, soil flow deposits, and scattered, predeflationary paleosol remnants. Ventifact fabric diagrams conform to landform alignments and independently substantiate the existence of northwest paleowinds. Locally, up to 20 meters of sediment may have been deflated from the till/outwash substrate to produce the fluted landforms. Cold, dry climatic conditions have been interpreted for this deflationary episode based upon comparable Atterberg Limit values between deformed and undeformed active layer sediments, and the scarcity of cryodisturbance structures. In northeast Nebraska, sand wedges and polygonal patterned ground are landscape position-dependent. This and the association of cover sands with fluted landforms suggest that a combination of aspect, stratigraphy, thermal contraction, and particle abrasion promoted the development of the oriented topography. Sieve analysis reveals that an upward-fining, particle-size continuum exists between sand wedges, cover sands, and sandy loess. The trend of lineated landforms in northeast Nebraska is similar to orientations observed elsewhere in the central mid-continent. Wind-aligned landforms discontinuously parallel the Late Wisconsinan glacial margin from central Montana to western Illinois. This geographic landform assemblage is associated with evidence of past permafrost conditions, suggesting the presence of an ice-marginal, cryodeflationary belt. This wedge-shaped, permafrost/paleowind ...