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Ages and Development of Soil Landscapes in Relation to Climatic and Vegetational Changes in Iowa¹

ABSTRACT

Radiocarbon dates in Iowa indicate that specific upland soil landscapes can be referred to age ranges before present of: (1) > 25,000 years, (2) 16,000 to 24,000 years, (3) 14,000 to 16,000 years, (4) 12,000 to 13,500 years, and (5) < 11,000 years.

Paleofloras associated with the radiocarbon horizons as well as fossil pollen sequences of geologically correlative peats permit inferences regarding the vegetative and climatic environments relative to time of the specific upland soil landscapes. In Late Sangamon time (> 25,000 years) the soil landscapes were dominantly forested under a cool, moist climate. Forest dominated the landscape during Wisconsin time (24,000 to 11,000 years) under cold, moist glacial climatic regimes and cool, moist intraglacial intervals. A warmer grassland environment may have occurred in mid-Wisconsin time (15,000 to 13,500 years). A cool, moist, arboreal environment may have culminated approximately 5,000 years ago. A warmer, subhumid to humid prairie environment became dominant at that time.

Such complex climatic and vegetative histories of soil landscapes relative to time should be considered in soil-genesis studies in Iowa as well as in other similar areas.

¹ Joint contribution of Soil Survey Investigations, Soil Conservation Service, U.S.D.A., and Iowa Agr. Exp. Sta. Journal Paper No. J-2774, Iowa Agr. Exp. Sta., Ames, Iowa. Project No. 1250.

² Research Geologist, Soil Surv. Inv., S.C.S., U.S.D.A., and Associate Professor of Soils, Iowa State College, respectively.

Received for publication June 27, 1955.