Age and Developmental History of Iowa Fens

Iowa fens are small, mineorotrophic peatlands maintained by shallow groundwater. Eighteen fen sites located across northern Iowa were mapped and radiocarbon dated to assess the timing of initial peat accumulation. The radiocarbon ages span the Holocene, ranging from 1,240 to 10,900 B.P.; however most fens postdate 5,000 yr B.P. The dominance of late-Holocene ages suggests that Holocene climatic change may have strongly influenced the record of peat accumulation. During the mid-Holocene Iowa was warmer and drier than at present, and peat was degraded or accumulated slowly in fens. The range of ages also implies that the commencement and subsequent rate of peat accumulation depends on local variations in landscape development and resultant hydrology

Surficial geologic map of the Des Moines Lobe of Iowa, Phase 5: Polk County

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Geology of Iowa Fens

Fens are peatlands which are dependent on groundwater discharge to provide nutrient enrichment. Fens are found in a variety of landscape positions and in most Iowa landform regions. This paper presents a classification system for Iowa fens based on landscape position, stratigraphy, and hydrologic factors. Iowa fens can be separated into six categories: 1) fens along valley wall slopes; the groundwater source for these fens is sand and gravel buried between glacial tills (inter-till); 2) fens in hummocky topography on the northwestern margin of the Des Moines Lobe landform region; the water source is sand and gravel buried within glacial till (intra-till) which exhibits artesian flow; 3) fens on edges of exhumed sand and gravel on the Iowan Surface; the water source is the exposed sand and gravel; 4) fens on benched alluvial terraces or glacial outwash settings; the water source is sand and gravel exposed at the surface; 5) fens recharged by bedrock aquifers; and 6) fens in abandoned channel areas whose water source is either sand and gravel exposed at the surface or bedrock aquifers. The lithology, weathering characteristics and thickness of the deposits in the fens groundwater basin influence infiltration rate, and thus recharge to the fens. The constancy of the water source and the rate of flow to the fen are important both in the long-term maintenance of the fens and in controlling their vulnerability to hydrologic and chemical disturbance

Surficial geologic materials of Linn County, Iowa

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Surficial Geologic Map of the Des Moines Lobe of Iowa, Huxley and Slater 7.5\u27 quadrangles

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Surficial geologic materials of the Marion Quadrangle, Iowa

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Surficial geologic materials of the Dixon 7.5\u27\u27 Quadrangle, Scott County, Iowa

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Surficial geologic materials of the Bertram Quadrangle, Iowa

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An Exposure of the Sangamon Soil in Southeastern Minnesota

A recent roadcut along County Road 18 in northeastern Houston County has exposed two variants of a morphologically well-expressed, Sangamon Soil. The paleosol is covered by the equivalent of the Roxana Silt, as defined in Illinois. The Farmdale Soil is developed into the Roxana Silt. The section is capped by late Wisconsinan Peoria Loess. The Sangamon Soil was developed into slope wash deposits composed of, or derived from, pre-Wisconsinan loess. No direct evidence of pre-Wisconsinan glacial till was found at the site. Two radiocarbon ages, one from the Ab horizon of the Sangamon Soil and one from the Ab horizon of the Farmdale Soil yield results of 25,690 and 23,760 respectively. These are minimum ages that suggest that the Roxana Silt buried the older Sangamon Soil prior to 26,000 radiocarbon years ago and that the Peoria Loess buried the Farmdale Soil by 24,000 radiocarbon years ago

Surficial geologic materials of the Iowa City East 7.5` Quadrangle, Johnson County, Iowa

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