LOCATION ASSUMPTION ILEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Argiudolls
TYPICAL PEDON: Assumption silt loam on a west--facing, convex, 4 percent slope in a cultivated field at an elevation of 220 meters (720 feet)above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 15 cm (0 to 6 inches); very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; weak medium granular structure; friable; many fine roots throughout; neutral; abrupt smooth boundary.
A--15 to 33 cm (6 to 13 inches); very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; moderate medium granular structure; friable; many fine roots throughout; slightly acid; clear smooth boundary. [combined thickness of A horizon is 25 to 51 cm (10 to 20 inches)]
AB--33 to 41 cm (13 to 16 inches); very dark grayish brown (10YR 3/2) and brown (10YR 4/3) silt loam, grayish brown (10YR 5/2) and brown (10YR 5/3) dry; weak medium subangular blocky structure; friable; many fine roots throughout; neutral; clear wavy boundary. [0 to 15 cm (0 to 6 inches) thick]
Bt1--41 to 66 cm (16 to 26 inches); brown (10YR 4/3) silty clay loam; weak medium prismatic structure parting to moderate fine subangular blocky; firm; common fine roots between peds; many distinct brown (10YR 5/3) clay films on faces of peds; slightly acid; clear wavy boundary.
Bt2--66 to 89 cm (26 to 35 inches); brown (10YR 5/3) silty clay loam; weak medium prismatic structure parting to moderate medium subangular blocky; firm; common fine roots between peds; many distinct brown (10YR 4/3) clay films on faces of peds; many medium distinct brownish yellow (10YR 6/6) masses of iron and common faint grayish brown (2.5Y 5/2) iron depletions in the matrix; slightly acid; abrupt wavy boundary. [Combined thickness of the Bt horizon is 38 to 76 cm (15 to 30 inches)]
2Bt3--89 to 130 cm (35 to 51 inches); yellowish brown (10YR 5/4) clay loam; weak medium subangular blocky structure; firm; common fine roots between peds; common distinct dark yellowish brown (10YR 4/4) clay films on faces of peds; many coarse prominent yellowish brown (10YR 5/8) masses of iron and common medium prominent light olive gray (5Y 6/2) iron depletions in the matrix; slightly acid; clear wavy boundary.
2Bt4--130 to 152 cm (51 to 60 inches); brown (10YR 5/3) silty clay loam; weak medium prismatic structure parting to moderate medium subangular blocky; firm; common fine roots between peds; many distinct brown (10YR 4/3) clay films on faces of peds; many medium distinct brownish yellow (10YR 6/6) masses of iron in the matrix; slightly acid; clear wavy boundary. [Combined thickness of the 2Bt horizon is 51 to 89 cm (20 to 35 inches)]
2C--152 to 203 cm (60 to 80 inches); brown (10YR 5/3) clay loam; massive; firm; common coarse faint brown (7.5YR 4/4) masses of iron and common coarse faint grayish brown (2.5Y 5/2) iron depletions in the matrix; slightly effervescent; slightly alkaline.
TYPE LOCATION: Henry County, Illinois; about 3 mile south and 1/4 mile west of Andover, 100 feet north and 300 feet east of the southwest corner of sec. 29, T. 15 N., R. 2 E. USGS Andover quadrangle; lat. 41 degrees 15 minutes 01 seconds N., and long. 90 degrees 17 minutes 58 seconds W.; UTM Zone 15, 726271 easting and 4570058 northing, NAD 83.
RANGE IN CHARACTERISTICS: The solum is 122 to 178 cm (48 to 70 inches) or more thick. The particle--size control section averages 27 to 35 percent clay. Thickness of the loess mantle is 51 to 102 cm (20 to 40 inches). Depth to carbonates is greater than 102 cm (40 inches). The till that contains a strongly developed paleosol is within a depth of 152 cm (60 inches).
The Ap or A horizon has hue of 10YR, value of 2 or 3, and chroma of 1 to 3. It typically is silt loam, but severely eroded pedons include silty clay loam. Reaction ranges from moderately acid to neutral.
The Bt horizon has hue of 10YR or 2.5Y, value of 4 or 5, and chroma of 3 to 6 in the upper part and 2 to 6 in the lower part. It typically is silty clay loam in the finest part, and some pedons contain one or more silt loam subhorizons. It typically is friable or firm. Reaction ranges from strongly acid to neutral.
The 2Bt or 2Btg horizon has hue of 7.5YR, 10YR, 2.5Y, or 5Y; value of 3 to 6; and chroma of 1 to 6, and commonly has redoximorphic features in some part. In some pedons the redoximorphic features have a redder hue or chroma as high as 8 or both redder hue and higher chroma. The texture is clay loam, silty clay loam, loam, clay or silty clay. This horizon typically contains more clay than the Bt horizon and always a higher content of sand. It averages 30 to 45 percent clay and 15 to 35 percent sand. It is firm or very firm. Reaction ranges from strongly acid to neutral.
The 2C or 2Cg horizon has color and textures similar to the 2Bt horizon. Reaction ranges from slightly acid to moderately alkaline.
COMPETING SERIES: These are the Aviston, Barrington, Blackberry, Buckhart, Catlin, Clare, Dana, Danabrook, Geryune, Graymont, Harrison, Keltner, Saybrook, and Totanang series. All of the competing soils except Barrington, Graymont, Harrison, and Keltner soils average less than 30 percent clay in the lower part of the series control section. Barrington soils are less than 122 cm (48 inches) to the base of the solum. Graymont soils are calcareous within a depth of 102 cm (40 inches). Harrison soils are greater than 102 cm (40 inches) to a sand content of more than 15 percent. Keltner soils have a lithic contact within a depth of 152 cm (60 inches).
GEOGRAPHIC SETTING: Assumption soils are on side slopes and some ridge tops on gently sloping to moderately steep till plains and moraines. Slope gradients range from 2 to 18 percent. These soils formed in 51 to 102 cm (20 to 40 inches) of loess and in the underlying till that contains a strongly developed paleosol. Some pedons contain a layer of silty or loamy pedisediment of variable thickness between the loess and the underlying till. The mean annual temperature ranges from 8 to 12 degrees C (46 to 54 degrees F), mean annual precipitation ranges from 810 to 1020 mm (32 to 40 inches), and frost free period is 140 to 180 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Atlas, Coatsburg, Keller, Osco, and Velma soils. The somewhat poorly drained Atlas soils and poorly drained Coatsburg soils are on similar landscape positions as Assumption soils or are down slope. Atlas and Coatsburg soils have a thinner surface mantle of loess or other silty material. In addition, Atlas soils do not have a mollic epipedon. The somewhat poorly drained Keller soils are on similar parts of the landscape nearby and have redox depletions or 2 chroma matrix colors throughout the lower 3/4 of the control section. Osco soils are on nearby ridge tops and slopes above Assumption soils and formed in loess. The well drained Velma soils formed in Illinoisan till below the paleosol and are down slope from Assumption soils.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Moderately well drained. Saturated hydraulic conductivity is moderately high and high (4.23 to 14.11 micrometers per second) (moderate permeability) in the loess, moderately high (1.41 to 4.23 micrometers per second) (moderately slow permeability) in the pedisediment, and moderately low and moderately high (0.42 to 4.23 micrometers per second) (moderately slow or slow permeability) in the till that contains a strongly developed paleosol. The potential for surface runoff is medium on gentle slopes and high on steeper slopes. Seep spots on side slopes are common as the result of perched water above the paleosol.
USE AND VEGETATION: Almost all areas of Assumption soils are cultivated. Corn, soybeans, small grain, and meadow are the principal crops. Native vegetation is prairie grass.
DISTRIBUTION AND EXTENT: Central, western, and northern Illinois. LRR K and M, MLRAs 95B, 108B and 115C. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Christian County, Illinois, 1946.
REMARKS: The 2Btg or 2Bt horizon of Assumption soils is the lower part of the solum superimposed upon a Sangamon paleosol in the Illinoisan till. Many of the properties of those horizons are believed to have been inherited from the paleosol. It is difficult to differentiate the properties of the lower part of the modern solum from those of the paleosol in many pedons. The variability of the properties is related to the degree of geologic truncation of the paleosol before it was buried by loess, and to the extent of modern soil development into the old materials. Some pedons have a dark--colored layer at the top of the paleosol that was the surface layer of the paleosol, and is now part of the 2Bt or 3Bt horizon of the modern soil. In pedons that do not have the pedisediment layer, the Peoria loess lies directly on the paleosol. The paleosolic Bt horizon typically is gray, but ranges to brown in some pedons. Calcium and other bases have been replenished in the paleosol in some pedons after burial by loess by seepage from the mantling material up slope.
Diagnostic horizons and features recognized in this pedon are:
mollic epipedon -- from a depth of 0 to 41 cm (0 to 16 inches) [Ap, A and AB horizons]
argillic horizon -- from a depth of 41 to 152 cm (16 to 60 inches) [Bt1, Bt2, 2Bt3, and 2Bt4 horizons];
lithologic discontinuity at 89 cm (35 inches)
ADDITIONAL DATA: The typical pedon is 79IL073113.