Historical:Farmdale Soil

From ILSTRAT
Jump to: navigation, search
Pleistocene stratigraphy of Illinois
Series Bulletin 94
Author H. B. Willman and John C. Frye
Date 1970
Link Web page
PDF PDF file

Lithostratigraphy: Farmdale Soil
Chronostratigraphy: Cenozoic Erathem >>Quaternary System >>Pleistocene Series

Authors

H. B. Willman and John C. Frye

Name origin

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. It is named for Farmdale, Tazewell County.

Type section

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.

Table 6 -- Stratigraphic Sections (partial)
The following 21 stratigraphic sections describe exposures in Illinois and illustrate many of the aspects of Pleistocene stratigraphy. These sections contain the type localities for 21 rock-stratigraphic units, 4 soil-stratigraphic units, and 3 time-stratigraphic units and include paratypes for several other units. The sample numbers preceded by "P" are the numbers used in the Illinois State Geological Survey collections. Analytical data on many of these samples are on file at the Survey. The sections are arrange alphabetically by name.

Stratigraphic relationships

The accreted organic-rich Farmdale Soil generally rests on Roxana Silt and is over lain by Morton Loess, Peoria Loess, or the Wedron Formation (fig. 8). It has been observed widely in central and northern Illinois (e.g., Campbells Hump and Tindall School Sections, table 6; Danvers, Enion Terrace, McAllister School, Perry Northeast, Richland Creek, Secor, and Union School Sections, table 7).

Table 6 -- Stratigraphic Sections (partial)
The following 21 stratigraphic sections describe exposures in Illinois and illustrate many of the aspects of Pleistocene stratigraphy. These sections contain the type localities for 21 rock-stratigraphic units, 4 soil-stratigraphic units, and 3 time-stratigraphic units and include paratypes for several other units. The sample numbers preceded by "P" are the numbers used in the Illinois State Geological Survey collections. Analytical data on many of these samples are on file at the Survey. The sections are arrange alphabetically by name.

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 the areas of sharp topographic relief adjacent to major valleys, whereas the poorly drained, and thus protected, situations where the accreted Farmdale Soil had accumulated were relatively little affected. Therefore, the Farmdale Soil in thick loess sections commonly consists of a deeply leached CL-zone, as much as 10 feet or more deep, overlain at an erosional contact by calcareous Peoria or Morton Loess (e.g., Cottonwood School, Gale, Jubilee College, Pleasant Grove, Pulleys Mill, and Zion Church Sections, table 6).

Table 6 -- Stratigraphic Sections (partial)
The following 21 stratigraphic sections describe exposures in Illinois and illustrate many of the aspects of Pleistocene stratigraphy. These sections contain the type localities for 21 rock-stratigraphic units, 4 soil-stratigraphic units, and 3 time-stratigraphic units and include paratypes for several other units. The sample numbers preceded by "P" are the numbers used in the Illinois State Geological Survey collections. Analytical data on many of these samples are on file at the Survey. The sections are arrange alphabetically by name.

A fully developed in-situ Farmdale Soil can be observed only in the areas of relatively thin loess on relatively flat uplands remote from major drainage (e.g., Henze School, New City, Rushville (4.5 W), Schuline Sections, table 7). In such places the profile generally displays a reddish brown, clayey B2-zone that grades downward to a B3-zone and a CL-zone; it is generally unstructured, and the A-zone at the top grades upward into the base of the overlying 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.

Age and correlation

The Farmdale Soil is unique in that it has yielded more than 20 radiocarbon dates (table 1), ranging from approximately 21,000 B.P. to approximately 27,000 B.P., from localities in Illinois.


Environment of deposition

Among the soil-stratigraphic units in the Pleistocene deposits of Illinois, the Farmdale Soil is unique. At its type section it is an intrazonal, organic-rich soil, formed by the accumulation of organic debris and silt from sheetwash and eolian deposition. It resembles the accretion-gley soils in that it is developed by the slow accretion of material in a poorly drained locality, but it differs from them in that it is a deposit composed largely of silt and organic debris rather than of clay and it quite clearly accumulated at a more rapid rate than did the accretion-gleys.

ISGS Codes

Stratigraphic Code Geo Unit Designation
0590
--