LOCATION THEBES IL+IAEstablished Series
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 670 feet above MSL. (Colors are for moist soil unless otherwise stated)
Ap--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. (5 to 10 inches thick)
Bt1--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--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--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 15 to 30 inches.)
2Bt4--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 iron accumulation in the matrix; slightly acid; clear wavy boundary. (5 to 20 inches thick)
2BC--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 iron accumulation in the matrix; moderately acid; clear wavy boundary. (0 to 10 inches thick)
2C--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 iron accumulation 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: The depth to the base of soil development ranges from 25 to 55 inches. Loess or other silty material ranges from 20 to 40 inches in thickness. The particle size control section averages between 27 to 35 percent clay. The average sand content is less than 15 percent in the loess and greater than 50 percent in the underlying eolian sandy material. The depth to carbonates is greater than 80 inches.
The Ap horizon has hue of 10YR, value of 4 or 5, and chroma of 2 through 4. Undisturbed pedons have an A horizon less than 6 inches in thickness that has value of 3 or 4 and chroma of 1 or 2. The Ap or A horizon is typically silt loam, but severely eroded pedons include silty clay loam. Reaction is slightly acid or neutral.
The E horizon, where present, is less than 5 inches in thickness and has hue of 10YR, value of 4 or 5, and chroma of 3 through 6. It is silt loam. Reaction is slightly acid or moderately acid.
The Bt horizon has hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 3 through 6. It commonly is silty clay loam, but some pedons have subhorizons of silt loam. Reaction is very strongly acid to neutral.
The 2Bt horizon has hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 4 through 6. It is loam, sandy loam, fine sandy loam, sandy clay loam, or clay loam. Reaction is slightly acid to very strongly acid.
The 2BC horizon has colors similar to the 2Bt horizon. It is sandy loam, loamy sand, and sand. Reaction is slightly acid to very strongly acid.
The 2C horizon has hue of 10YR or 7.5YR, value of 4 to 6, and chroma of 3 through 6. It is 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 ranges from strongly acid to neutral.
COMPETING SERIES: These are the Baraboo, Bertrand, Blackhammer, Camden, Dodge, Dubuque, Fayette, Flagg, Greenridge, Hackers, Jackson, Jemerson, La Farge, Lambeau, Martinsburg, Menfro, Middletown, Navlys, Palermo, Palsgrove, Pepin, Piscasaw, Ridgway, Rozetta, Ruma, Rush, Russell, Seaton, St. Charles, Stookey, Sylvan, Uniontown, and Yellowriver. Baraboo, Dubuque, Greenridge, La Farge, Lambeau, Palsgrove, and Pepin soils have a lithic or paralithic contact within a depth of 80 inches. 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 40 inches. Blackhammer soils have soil development below a depth of 55 inches. Camden and Ridgway soils are underlain by loamy water laid material. Dodge, Navlys, Piscasaw, Russell, Sylvan and Uniontown soils have carbonates within a depth of 60 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. 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. (Note: The Cadiz, Knowles, Lomira, Sandview, and Westbend soils have not been updated for the addition of cation exchange activity class to their taxonomy. These series may or may not compete when their taxonomy is updated. These soils are listed as Typic Hapludalfs, fine-silty, mixed mesic.)
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 20 to 40 inches of loess or other silty material and in the underlying eolian loamy sand or sand. Mean annual temperature ranges from 51 to 56 degrees F, and mean annual precipitation ranges from 35 to 40 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are Middletown soils and Alvin soils. Middletown soils have formed in more than 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 PERMEABILITY: Well drained. The potential for surface runoff is low to high. 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. The extent is moderate.
MLRA OFFICE 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 9 inches (Ap horizon);
argillic horizon - the zone from 9 to 31 inches (Bt1, Bt2, and Bt3 horizons);