Geomorphic history and Pleistocene stratigraphy of the Pecatonica River valley, Wisconsin and Illinois
The Pecatonica River valley in southwestern Wisconsin and northwestern Illinois lies in both driftless and glaciated terrain. Therefore the stratigraphy of Pleistocene sediments in the valley is a complex of alluvial, colluvial, and lacustrine material, glacial till, loess, and weathered bedrock residuum. In the middle reaches of the stream system, the bedrock valley is incised 30 to 60 m below the ridge tops and is nearly half-filled with Pleistocene sediments that now have a stepped topography due to erosion surfaces and terraces. The oldest known sediments are preserved in erosional remnants protected in abandoned valley meanders. The sediment units recognized in the erosional remnants include pre-glacial alluvium, fine-grained lake deposits (Silveria Silt-Clay), and the Sinslow, and Ogle tills. They were deposited as glacial ice dammed the valley drainage from the east and south and advanced to the margin of the Driftless Area. Three bodies of sand found in the Driftless Area might be shoreline deposits formed by the Illinoian age lake at 860-870 feet elevation. Surrounding the silty erosional remnants are high-level terraces containing thick beds of poorly-sorted stony silt. These layers of diamicton are interpreted as solifluction deposits, possibly formed during intense periglacial conditions during early Wisconsinan time. Sandy alluvium (Blanchardville Sand), in places younger than the erosion surfaces, formed broad terraces throughout the driftless and glaciated portions of the valley. Isolated low dunes and sheets of eolian sand of Holocene age are also present in the valley.
- Research Organization:
- Wisconsin Univ., Madison (USA)
- OSTI ID:
- 5473336
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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