Paleopedology of the Sangamonian-Wisconsinan transition in loess of the upper Mississippi Valley Driftless Area, Wisconsin
- Univ. of Georgia, Athens, GA (United States). Geography Dept.
The late Quaternary Sangamonian-Wisconsinan transition in loess deposits of the Driftless Area is characterized by syndepositional weathering and upward growth of the Sangamon Soil'' within thin deposits of the early to middle Wisconsinan Roxana Silt. Complete pedologic separation of a Sangamon Soil'' and a Farmdale Soil'' in the strict sense does not occur in upland loess settings in Driftless Area. Radiocarbon ages indicate that the Roxana Silt accumulated between about 55,000 and 27,000 C-14 yr B.P. at a maximum bulk sedimentation rate of only about 5 to 10 cm/1,000 yr. Plant macrofossils throughout the thickness of the Roxana Silt, and other paleobotanical evidence, indicate that the uplands of the Driftless Area probably were characterized by a conifer forest throughout the early to middle Wisconsinan. Sedimentological characteristics separate the Roxana Silt from bounding lithostratigraphic units, but the Roxana Silt is pedogenically welded'' to underlying units which contain well developed paleosols with argillic horizons. The Roxana Silt is overlain by apedal late Wisconsinan Peoria Loess dated between 25,000 and 12,000 yr B.P. Pedologic features in the Roxana Silt is overlain by apedal late Wisconsinan Peoria Loess data between 25,000 and 12,000 yr B.P. Pedologic features in the Roxana Silt suggest cumulic A-horizon and cambric B-horizon development, indicating that weathering intensities were slight to moderate during the period of loess sedimentation. Pedologic and geochemical characteristics, including soil structure, argillans, and phosphorus concentrations, suggest that weathering intensities progressively decreased during the early to middle Wisconsinan time period. This is consistent with other proxys for paleoclimate which indicate progressive global cooling from the Sangamonian to late Wisconsinan time.
- OSTI ID:
- 5807834
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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