LOCATION THEBES                  IL+IA

Established Series
Rev. GWH-JBF-JWS-JKH
02/2011

THEBES SERIES

The Thebes series consists of very deep, well drained soils. They are on windblown sandy hummocks, on outwash plains, alluvial terraces, and on upland ridges adjacent to stream valleys. These soils formed in 20 to 40 inches of loess or other silty material and the underlying eolian loamy sand or sand. Slopes range from 1 to 35 percent. Mean annual precipitation is about 940 mm (37 inches), and mean annual temperature is about 11.7 degrees C (53 degrees F).

TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Typic Hapludalfs

TYPICAL PEDON: Thebes silt loam on a north-facing slope of 7 percent under cultivation at an elevation of about 204 meters (670 feet0 above mean sea level. (Colors are for moist soil unless otherwise stated)

Ap--0 to 23 cm (0 to 9 inches); dark grayish brown (10YR 4/2) silt loam, light brownish gray (10YR 6/2), dry; moderate medium granular structure; friable; slightly acid; clear smooth boundary. [13 to 25 cm (5 to 10 inches) thick]

Bt1--23 to 36 cm (9 to 14 inches); yellowish brown (10YR 5/4) silty clay loam; weak fine and medium subangular blocky structure; friable; few distinct brown (10YR 5/3) clay films on faces of peds and in pores; strongly acid; clear wavy boundary.

Bt2--36 to 66 cm (14 to 26 inches); dark yellowish brown (10YR 4/4), silty clay loam; moderate medium subangular blocky structure; friable; common distinct brown (10YR 4/3) clay films on faces of peds and in pores; moderately acid; clear wavy boundary.

Bt3--66 to 79 cm (26 to 31 inches); dark yellowish brown (10YR 4/4) silty clay loam; moderate medium subangular blocky structure; friable; common distinct brown (10YR 4/3) clay films on faces of peds and in pores; few medium faint pale brown (10YR 6/3) and few medium distinct strong brown (7.5YR 4/6) masses of iron accumulation in the matrix; slightly acid; clear wavy boundary. [Combined thickness of the Bt horizons is 38 to 76 cm (15 to 30 inches).]

2Bt4--79 to 102 cm (31 to 40 inches); dark yellowish brown (10YR 4/4) loam; moderate medium subangular blocky structure; friable; few distinct brown (10YR 4/3) clay films on faces of peds and in pores; common coarse faint pale brown (10YR 6/3) and common coarse distinct strong brown (7.5YR 4/6) masses of oxidized iron in the matrix; slightly acid; clear wavy boundary. [13 to 51 cm (5 to 20 inches) thick]

2BC--102 to 127 cm (40 to 50 inches); 55 percent yellowish brown (10YR 5/4) and 45 percent brown (7.5YR 4/4) stratified sandy loam and loamy sand; weak medium subangular blocky structure; friable; few medium distinct pale brown (10YR 6/3) masses of oxidized iron in the matrix; moderately acid; clear wavy boundary. [0 to 25 cm (0 to 10 inches) thick]

2C--127 to 203 cm (50 to 80 inches); dark yellowish brown (10YR 4/4) stratified loamy sand and sand; single grain; loose; common medium and coarse faint brown (7.5YR 4/4) masses of oxidized iron in the matrix; slightly acid.

TYPE LOCATION: Mercer County, Illinois; located about 3 miles southeast of Aledo, Illinois; 1060 feet west and 1800 feet south from the northeast corner of sec. 3, T.13 N., R. 3 W; U.S.G.S. Aledo East topographical quadrangle; latitude 41 degrees, 09 minutes, 02 seconds North and longitude 90 degrees, 42 minutes, 30 seconds West; NAD 27.

RANGE IN CHARACTERISTICS:
Depth to the base of soil development: 64 to 140 cm (25 to 55 inches)
Thickness of the loess or other silty material: 51 to 102 cm (20 to 40 inches)
Average content of clay in the particle size control section: between 27 to 35 percent
Average content of sand in the loess: less than 15 percent, and greater than 50 percent in the underlying eolian sandy material
Depth to carbonates: greater than 203 cm (80 inches)

Ap horizon:
Hue: 10YR
Value: 4 or 5
Chroma: 2 to 4
Texture: typically silt loam, but severely eroded pedons include silty clay loam.
Reaction: slightly acid or neutral

A horizon [less than 15 cm (6 inches in thickness)]:
Hue: 10YR
Value: 3 or 4
Chroma: 1 or 2
Texture: silt loam
Reaction: slightly acid or neutral.

E horizon (where present):
Hue: 10YR
Value: 4 or 5
Chroma: 3 to 6
Texture: silt loam
Reaction: slightly acid or moderately acid

Bt horizon:
Hue: 10YR or 7.5YR
Value: 4 or 5
Chroma: 3 to 6
Texture: commonly silty clay loam, but some pedons have subhorizons of silt loam.
Reaction: very strongly acid to neutral

2Bt horizon:
Hue: 10YR or 7.5YR
Value: 4 or 5
Chroma: 4 to 6
Texture: loam, sandy loam, fine sandy loam, sandy clay loam or clay loam
Reaction: slightly acid to very strongly acid

2BC horizon:
Hue: 10YR or 7.5YR
Value: 4 or 5
Chroma: 4 to 6
Texture: sandy loam, loamy sand or sand
Reaction: slightly acid to very strongly acid

2C horizon:
Hue: 10YR or 7.5YR
Value: 4 to 6
Chroma: 3 to 6
Texture: loamy sand, fine sand, loamy fine sand or sand that is more than 6 inches thick. Some pedons contain thin strata of sandy loam, fine sandy loam, or silt loam.
Reaction: strongly acid to neutral

COMPETING SERIES: These are the Bertrand, Blackhammer, Camden, Dodge, Dubuque, Fayette, Flagg, Greenridge, Hackers, Jackson, Jemerson, Knowles, La Farge, Lambeau, Lomira, Martinsburg, Menfro, Middletown, Navlys, Palermo, Palsgrove, Pepin, Piscasaw, Ridgway, Rozetta, Ruma, Rush, Russell, Seaton, St. Charles, Stookey, Sylvan, and Yellowriver. Bertrand, Fayette, Martinsburg, Menfro, Middletown, Palermo, Rozetta, Ruma, and St. Charles soils have less than 15 percent sand in all horizons within a depth of 102 cm (40 inches). Blackhammer soils have soil development below a depth of 140 cm (55 inches). Camden and Ridgway soils are underlain by loamy water laid material. Dodge, Navlys, Piscasaw, Russell, and Sylvan soils have carbonates within a depth of 152 cm (60 inches). Dubuque, Greenridge, Knowles, La Farge, Lambeau, Palsgrove, and Pepin soils have a lithic or paralithic contact within a depth of 203 cm (80 inches). Flagg and Hackers soils have hue of 5YR or redder in some part of the series control section. Jackson, Jemerson, Seaton, and Stookey soils average less than 27 percent clay in the particle size control section. Lomira soils are less than 102 cm (40 inches) deep to the base of the argillic horizon and to carbonates. Rush soils have coarse fragments in the lower part of the series control section. Yellowriver soils average less than 50 percent sand in the underlying material.

GEOGRAPHIC SETTING: Thebes soils are on wind-blown sandy hummocks, on outwash plains, alluvial terraces, and on upland ridges adjacent to stream valleys. Slope gradients commonly are between 5 and 15 percent but range from 1 to 35 percent. These soils formed in 51 to 102 cm (20 to 40 inches) of loess or other silty material and in the underlying eolian loamy sand or sand. Mean annual temperature ranges from 10.6 to 13.3 degrees C (51 to 56 degrees F), and mean annual precipitation ranges from 890 to 1016 mm (35 to 40 inches).

GEOGRAPHICALLY ASSOCIATED SOILS: These are Middletown soils and Alvin soils. Middletown soils have formed in more than 102 cm (40 inches) of loess or other silty material and are in similar positions. Alvin soils have more sand in the particle size control section and are on similar positions.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained. The potential for surface runoff is low to high. Saturated hydraulic conductivity is moderately high to high (4.23 to 14.11 micrometers per second) in the loess and high to very high (41.34 to 141.14 micrometers per second) in the underlying material. Permeability is moderate in the loess and rapid in the underlying material.

USE AND VEGETATION: The soils are used principally for growing cultivated crops. Principal crops are corn, soybeans, small grain and meadow. Native vegetation was hardwood trees.

DISTRIBUTION AND EXTENT: Central and northwestern Illinois, and eastern Iowa in MLRAs 108B, 113, 114B. and 115C. The extent is moderate.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana

SERIES ESTABLISHED: Shelby County, Illinois, 1932.

REMARKS: With this update the typical pedon is relocated to Mercer County, Illinois. Thebes soils were previously correlated as fine-silty over sandy or sandy skeletal in Illinois and Iowa. However, based on field investigations in Illinois and additional documentation, it is proposed, with this update, to classify the Thebes soils as fine-silty.

This pedon was checked in the field by SLE 2/17/1998 and adjustments were made in the description on depth of soil development, colors, and redoximorphic features. The pedon number is 84IL-131-44.

Diagnostic horizons and features recognized in this pedon are:
ochric epipedon - the zone from the surface to a depth of 23 cm (9 inches) (Ap horizon);
argillic horizon - the zone from 23 to 79 cm (9 to 31 inches) (Bt1, Bt2, and Bt3 horizons);

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National Cooperative Soil Survey
U.S.A.