H. B. Willman and John C. Frye
The Yarmouth Soil was named and described by Leverett in 1898 from its occurrence in a well at Yarmouth in Des Moines County, Iowa. Leverett proposed Yarmouth as a replacement for the older term Buchanan, and his new type locality demonstrated occurrence of the soil below deposits of Illinoian age. He described the soil as the weathered zone on the Kansan drift.
Yarmouth Soil is described in six of the geologic sections in this report (table 6). In the Cache and Gale Sections it is an in-situ soil developed in Mounds Gravel and overlain by Loveland Silt. In both of these localities the period of soil formation may have been much longer than the Yarmouthian Stage, and the soil was truncated before deposition of the overlying Loveland Silt. At the Enion Section the Yarmouth Soil is developed in sand and gravel of the Banner Formation, and at the Tindall School Section it is developed in till of the same formation. At both localities it is a deeply developed in-situ profile that had been somewhat truncated prior to the deposition of the overlying Glasford Formation. At the Petersburg Dam and Zion Church Sections it is an accretion-gley assigned to the Lierle Clay Member of the Banner Formation.
|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.
The mineral composition and sequence of mineral alteration has been described for Yarmouth Soil in the Fort Madison, Iowa, area (Willman, Glass, and Frye, 1966), at the Rushville (4.5 W) Section, Schuyler County, Illinois (Willman, Glass, and Frye, 1963), where the soil occurs on till of Kansan age and is overlain by till of Illinoian age, and at the Dixon Creek Sections in Jo Daviess County (Willman and Frye, 1969), where the soil is developed in dolomite gravel and in dolomite of the Galena Group (Ordovician) that is overlain by Loveland Silt. The soil has been described in the Independence School Section (table 7), at several localities in Fulton and Peoria Counties by Wanless (1957), and in Christian, Menard, and Sangamon Counties by Johnson (1964).
Yarmouth Soils of all classes are sharply bounded at the top by overlying deposits of the Loveland, Petersburg, Glasford, or Pearl Formations.
The Yarmouth Soil occurs both as an accretion-gley and as an in-situ profile developed in older deposits.
The Yarmouth Soil occurs as three distinctly different types of profiles. The accretion-gley profiles consist of slowly deposited clay, silt, and some sand that accumulated
in poorly drained or undrained areas on the till plain. The sediment was moved to the low spots by sheetwash and deposited in an intermittently wet, reducing environment. These deposits (formerly called "gumbotil") possess a distinctive mineralogy (Frye, Willman, and Glass, 1960; Willman, Glass, and Frye, 1966) characterized by a very high percentage of expandable clay minerals, a gray to gray-black color, and a massive and highly plastic character when wet. The accretion-gley deposit overlies the till with a sharp contact, and the contact at the top with overlying Petersburg Silt, till of the Glasford Formation, or Loveland Silt, is equally sharp. At some localities the uppermost part of the accretion-gley was secondarily oxidized before burial by sediments of Illinoian age. Because of its distinctive lithology and generally sharp contacts, the accretion-gley is differentiated in rock-stratigraphy as the Lierle Clay Member of the Banner Formation.
The second type of Yarmouth Soil contains the zonal profiles that developed in sediments of Kansan age under conditions of moderate to good surface drainage. These profiles are more or less oxidized and mineral alteration decreases downward. The solums are characterized by clay of a heterogeneous swelling type. They have typically gray-brown to red-brown B-zones and contain pellets and platelets of Mn-Fe, clay skins, and strongly developed peds (soil structure). The maximum depth of profile development is more than 20 feet.
The third type of Yarmouth Soil contains a wide range of profiles developed in sediments older than Kansan that extend to dolomites of Ordovician age. Most striking in this type is the residual geest developed on dolomite that displays clay pendants extending downward into the widened joints of the bedrock to depths of 6 to 8 feet below the top of the soil (e.g., Christian Hollow Church Section, table 7). Such soils are overlain with sharp contact by tills and silts of Illinoian age, are predominantly massive clay of strongly degraded clay mineral types, and are red-brown to mahogany in color. Yarmouth Soils of this class have been observed in southern Illinois developed in shales of Pennsylvanian age (e.g., Marion Northwest Section, table 7). Also in this class are soils developed in colluvium (e.g., Seehorn Section, table 7).
FRYE, J. C, H. B. WILLMAN, and H. D. GLASS, 1960, Gumbotil, accretion-gley, and the weathering profile: Illinois State Geological Survey Circular 295, 39 p.
JOHNSON, W. H., 1964, Stratigraphy and petrography of Illinoian and Kansan drift in central Illinois: Illinois State Geological Survey Circular 378, 38 p.
LEVERETT, FRANK, 1898c, The weathered zone (Yarmouth) between the Illinoian and Kansan till sheets: Iowa Academy of Science Proceedings, v. 5, p. 81-86.
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey Bulletin 82, 233 p.
WILLMAN, H. B., and J. C. FRYE, 1969, High-level glacial outwash in the Driftless Area of northwestern Illinois: Illinois State Geological Survey Circular 440, 23 p.
WILLMAN, H. B., H. D. GLASS, and J. C. FRYE, 1963, Mineralogy of glacial tills and their weathering profiles in Illinois. Part I— Glacial tills: Illinois State Geological Survey Circular 347, 55 p.
WILLMAN, H. B., H. D. GLASS, and J. C. FRYE, 1966, Mineralogy of glacial tills and their weathering profiles in Illinois. Part II— Weathering profiles: Illinois State Geological Survey Circular 400, 76 p.
|Stratigraphic Code||Geo Unit Designation|