Abstracts of Symposium 55 and some papers from other related Symposia.

Mid and Late Pleistocene Paleopedology of the Upper Mississippi Valley Driftless Area, USA

Peter JACOBS, Dept. of Geology, Valdosta State University, Vladosta, CA, 31698, James KNOX and Joseph MASON, Dept. of Geography, University of Wisconsin, Madison, WI, 53706, David LEIGH, Dept. of Geography, University of Georgia, Athens, GA, 30602.

Pleistocene soils older than Wisconsin Age are preserved only locally in the Driftless Area of Wisconsin, USA. Most have been eroded in response to continued Quaternary valley entrenchment and periglacial erosion when ice sheets were nearby. Loess is the primary parent material. All known loess deposits are < 790 ka, even thought glacial outwash > 790 ka is present in the region. Our longest known sequence is at Oil City, Wisconsin, were a 9 m section contains 5 loesses and 3 colluvial deposits with 5 buried soils; all are < 790 ka.

Except the mid-Wisconsin Farmdale soil, all of the buried soils at Oil City have argillic horizons and are intensely weathered. Intense weathering is indicated by relatively high clay enrichment of originally silty soils and the lack of silt-size mica observed in this section. Mosaic speckled b-fabrics indicate weathering of micas to plasma domains and XRD indicates micas are depleted in favour of expandable and kaolinite minerals. Compound and cross-cutting argillans of various compositions, and linear concentration features, among other pedofeatures indicate complex pedogenic histories as environments changed and younger soils formed in newly deposited sediment. Were not truncated the Sangamon Soil often has a thick epipedon with granular structure, suggesting it supported grassland (i.e. a Molisol), until the mid-Wisconsin when spruce forest became dominant. However, few buried soils have all genetic horizons preserved. Truncation and welding (overprinting) by younger soils is common. At Oil City, the Sangamon Soil and two morphologically distinct argillic horizons beneath are welded into a pedocomplex. Argillic horizons are interpreted as evidence of continental climates with seasonal contrasts in temperature and precipitation. Pedogenic evidence of permafrost in the loess soils is not overwhelming, even though ice wedge casts are present locally. Only the Mid-Wisconsin Farmdale Soil and buried soil 4 at Oil City, formed in loamy colluvium, have well-sorted silt cappings and platy structure.

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