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Willman, H. B., and John C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.

H. B. Willman and John C. Frye

Farmdale Soil (Willman and Frye 1970).

It is named for Farmdale, Tazewell County.

The Farmdale Soil has not previously been described formally as a soil-stratigraphic unit though the peaty deposits of the Farmdale Silt (now the Robein Silt) and the Farmdalian Substage were described many years ago.

Its type section is the Farm Creek Section (table 6), NE SW SE Sec. 30, T. 26 N., R. 3 W., Tazewell County, which was the type section for the Farmdale Loess and Farmdale Silt and also serves as the type section for the Robein Silt and the Farmdalian Substage. <center> '''Table 6 -- Stratigraphic Sections (partial)'''<br> The following stratigraphic sections illustrate exposures in Illinois and document type localities and analytical samples for Pleistocene units. <gallery widths=250px heights=250px perrow=4> File:94-tb_6-d.jpg|alt=Stratigraphic section table showing part of Illinois exposures used to define Pleistocene soil and sediment units.|{{File:94-tb_6-d.jpg}} </gallery> </center>

The accreted organic-rich Farmdale Soil generally rests on Roxana Silt and is overlain by Morton Loess, Peoria Loess, or the Wedron Formation. <center> <gallery widths=250px heights=250px perrow=4> File:94-fig_8.jpg|alt=Diagram showing stratigraphic relationships of Farmdale Soil with underlying Roxana Silt and overlying loess and glacial units.|{{File:94-fig_8.jpg}} </gallery> </center> <center> '''Table 6 -- Stratigraphic Sections (partial)''' <gallery widths=250px heights=250px perrow=4> File:94-tb_6-a.jpg|alt=Stratigraphic section table illustrating documented Illinois exposures and sample data.|{{File:94-tb_6-a.jpg}} File:94-tb_6-i.jpg|alt=Stratigraphic section table showing detailed field descriptions and sample records.|{{File:94-tb_6-i.jpg}} File:94-tb_6-j.jpg|alt=Stratigraphic section table illustrating variation in Pleistocene exposures across Illinois.|{{File:94-tb_6-j.jpg}} </gallery> </center> In-situ profiles of the Farmdale Soil, where they occur in relatively thick loess sections and, particularly, close to the valleys of the Mississippi and Illinois Rivers, are nearly everywhere truncated into or below the B₂-zone of the soil. The episode of widespread erosion that coincided with the advance of the Woodfordian glaciers was particularly effective in areas of sharp topographic relief adjacent to major valleys, whereas poorly drained locations where the Farmdale Soil accumulated were less affected. Therefore, the Farmdale Soil in thick loess sections commonly consists of a deeply leached CL-zone overlain at an erosional contact by calcareous Peoria or Morton Loess. <center> '''Table 6 -- Stratigraphic Sections (partial)''' <gallery widths=250px heights=250px perrow=4> File:94-tb_6-b.jpg|alt=Stratigraphic section table showing exposures and analytical sample records.|{{File:94-tb_6-b.jpg}} File:94-tb_6-c.jpg|alt=Stratigraphic section table illustrating variation in soil and sediment units.|{{File:94-tb_6-c.jpg}} File:94-tb_6-e.jpg|alt=Stratigraphic section table documenting additional Illinois exposures and samples.|{{File:94-tb_6-e.jpg}} File:94-tb_6-f.jpg|alt=Stratigraphic section table showing field observations across multiple sites.|{{File:94-tb_6-f.jpg}} File:94-tb_6-h.jpg|alt=Stratigraphic section table illustrating detailed stratigraphic data.|{{File:94-tb_6-h.jpg}} File:94-tb_6-i.jpg|alt=Stratigraphic section table showing additional sample records and descriptions.|{{File:94-tb_6-i.jpg}} File:94-tb_6-l.jpg|alt=Stratigraphic section table illustrating regional variation in Pleistocene units.|{{File:94-tb_6-l.jpg}} File:94-tb_6-m.jpg|alt=Stratigraphic section table documenting further Illinois exposures.|{{File:94-tb_6-m.jpg}} </gallery> </center> A fully developed in-situ Farmdale Soil can be observed only in areas of relatively thin loess on flat uplands remote from major drainage. In such places the profile generally displays a reddish brown, clayey B₂-zone that grades downward and is overlain by Peoria Loess. The Farmdale Soil is exceeded only by the Sangamon Soil in its use as a widespread stratigraphic datum within the Pleistocene deposits of Illinois.

The Farmdale Soil has yielded more than 20 radiocarbon dates ranging from approximately 21,000 to 27,000 years before present. <center> <gallery widths=250px heights=250px perrow=4> File:94-tb_1.jpg|alt=Table showing radiocarbon age data for Farmdale Soil samples across Illinois.|{{File:94-tb_1.jpg}} </gallery> </center>

The Farmdale Soil formed as an organic-rich, intrazonal soil through accumulation of organic debris and silt in poorly drained environments, with contributions from sheetwash and eolian deposition.

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