LOCATION ATLAS IL+OHEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Aeric Chromic Vertic Epiaqualfs
TYPICAL PEDON: Atlas silt loam -on a 8 percent slopes in a pasture that was formerly cultivated at an elevation of about 665 feet (203 meters). (Colors are for moist soil unless otherwise stated.)
Ap--0 to 7 inches (0 to 18 cm); dark grayish brown (10YR 4/2) silt loam, light brownish gray (10YR 6/2) dry; weak fine granular structure; friable; common very fine and fine roots in cracks; many very fine and fine continuous tubular pores; common medium prominent irregular strong brown (7.5YR 5/8) and few fine prominent irregular yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few fine prominent irregular black (2.5Y 2.5/1) iron and manganese masses throughout; slightly acid; clear smooth boundary. [10 to 20 cm)(4 to 8 inches) thick]
BE--7 to 13 inches (18 to 33 cm); brown (10YR 5/3) silty clay loam, light brownish gray (10YR 6/2) dry; weak medium subangular blocky structure; friable; common fine roots throughout; many fine continuous tubular pores; few fine faint distinct light brownish gray (10YR 6/2) clay depletions on faces of peds; common fine distinct irregular yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; slightly acid; clear wavy boundary. [0 to 20 cm (0 to 8 inches) thick]
2Btg1--13 to 26 inches (33 to 66 cm); dark gray (10YR 4/1) silty clay loam; moderate thick platy structure parting to weak fine subangular blocky; firm; many fine and few medium roots throughout; many fine and few medium continuous tubular pores; many distinct very dark gray (10YR 3/1) organo-clay films on faces of peds; few fine prominent irregular yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few very fine prominent irregular white (10YR 8/1) masses of barite throughout; moderately acid; clear wavy boundary.
2Btg2--26 to 37 inches (66 to 94 cm); dark gray (10YR 4/1) silty clay; weak medium prismatic structure; firm; common fine and medium roots throughout; common fine and medium continuous tubular pores; common distinct very dark gray (10YR 3/1) organo-clay films on faces of peds; common fine prominent irregular yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few fine faint irregular gray (10YR 5/1) iron depletions in the matrix; few very fine prominent irregular white (10YR 8/1) masses of barite throughout; about 1 percent fine rounded and subangular chert gravel; neutral; clear wavy boundary.
2Btg3--37 to 47 inches (94 to 119 cm); gray (2.5Y 5/1) silty clay; weak coarse prismatic structure; firm; common fine and medium roots throughout; common fine continuous tubular pores; few prominent very dark gray (10YR 3/1) clay films lining root channels and/or pores; few fine prominent irregular yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few fine distinct irregular gray (10YR 6/1) iron depletions in the matrix; few fine prominent irregular white (10YR 8/1) masses of barite throughout; about 1 percent fine angular feldspar gravel; neutral; clear wavy boundary.
2Btg4--47 to 61 inches (119 to 155 cm); gray (2.5Y 5/1) clay loam; weak coarse prismatic structure; firm; few fine roots in cracks; few prominent very dark gray (10YR 3/1) clay films lining root channels and pores; few fine prominent irregular black (2.5Y 2/1) masses of iron and manganese oxide throughout; few fine prominent irregular white (10YR 8/1) masses of barite throughout; about 1 percent very fine chert gravel and about 1 percent medium rounded granite gravel; neutral; clear wavy boundary. [The combined thickness of the 2Btg horizons is 91 to more than 203 cm (36 to more than 80 inches).]
2BCg--61 to 80 inches (155 to 203 cm); light brownish gray (2.5Y 6/2) clay loam; weak coarse prismatic structure; firm; few fine prominent irregular yellowish brown (10YR 5/6) and common medium prominent brownish yellow (10YR 6/8) masses of iron accumulation in the matrix; about 2 percent fine subangular chert gravel; neutral. [0 to 50 cm (0 to 20 inches) thick)
TYPE LOCATION: Adams County, Illinois; about 4 miles northeast of Coatsburg; 1,200 feet west and 50 feet south of the northeast corner of sec. 7, T. 1 N., R. 6 W.; U.S.G.S Coatsburg, IL topographic quadrangle; Latitude 40 degrees, 5 minutes, 39.9 seconds, North and Longitude 91 degrees 7 minutes 51.5 seconds West. NAD 27.
RANGE IN CHARACTERISTICS: The depth to the base of the argillic horizon is greater than 42 inches. The dominant clay mineral in the upper part of the 2Btg horizon is smectite. The content of illitic clays increases with depth. The particle-size control section ranges from 35 to 45 percent clay, from 10 to 35 percent sand, and from 0 to 5 percent gravel.
The Ap, A, E, EB, or BE horizon has hue of 10YR, value of 2 to 5 (6 or 7 dry), and chroma of 1 to 4. It is silt loam or loam. Severely eroded pedons can be silty clay loam or clay loam. Reaction is very strongly acid to neutral.
The E, EB, or BE horizon, where present, has hue of 10YR, value of 4 or 5 and chroma of 1 to 4. It is silt loam or silty clay loam.
The Bt, Btg, 2Bt, or 2Btg horizon is neutral or has hue of 10YR, 2.5Y, 5Y, value of 4 to 6, and chroma of 0 to 2. In some pedons the upper part of the Bt or 2Bt horizon has one or more subhorizons with dominant chroma of 3 or 4. Redoximorphic features have hue of 10YR, 7.5YR, 2.5Y, or 5Y, value of 4 to 6, and chroma of 1 to 8. In some pedons the Bt or Btg horizon is silty clay loam that averages less than 10 percent sand. These pedons have 2Bt or 2Btg horizons within a depth of 20 inches that average between 10 and 35 percent sand. The texture is clay loam, clay, silty clay loam, or silty clay. Reaction is very strongly acid to neutral in the upper part and ranges to slightly alkaline in the lower part.
The 2BCg or 2Cg horizon, where present within 80 inches, has hue of 10YR, 7.5YR, 2.5Y, 5Y, or is neutral, value of 4 to 6, and chroma of 0 to 6. It is clay loam, clay, or loam. Rock fragment content ranges from 2 to 15 percent. Reaction is slightly acid to slightly alkaline.
COMPETING SERIES: These are the Ashgrove, Hurst, and Kernan series. Ashgrove soils average more than 45 percent clay in the upper 20 inches (51 cm) of the argillic horizon. Hurst soils typically have less sand, average less than 2 percent rock fragments, and formed mainly in lacustrine sediments. Kernan soils average less than 10 percent sand in the particle size control section and formed in 35 to 55 inches (89 to 140 cm) of loess and the underlying lacustrine sediments.
GEOGRAPHIC SETTING: Atlas soils are on the upper ends of incised drainageways and on backslopes and shoulder slopes. They formed in 0 to 20 inches (0 to 51 cm) of loess or silty sediments overlying Illinoian till or accretion gley that contains a strongly developed Sangamon paleosol. Slopes range from 2 to 20 percent. The mean annual temperature ranges from 50 to 58 degrees F. (10 to 14 degrees C), mean annual precipitation ranges from 36 to 48 inches (914 to 1219 mm), frost free days range from 160 to 200 days, and elevation ranges from 340 to 1,020 feet (104 to 311 meters) above mean sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Blair, Coatsburg, Fishhook, Hickory, Elco, Keller, and Keomah soils. Blair, Elco, Fishhook, and Keller soils are upslope from Atlas soils. Also, Blair soils are fine-silty and formed in pedisediment above the paleosol. Coatsburg soils are on similar slopes nearby. Elco and Keller soils formed in 20 to 40 inches of loess (51 to 102 cm) and the underlying till that contains a paleosol, with or without a layer of pedisediment in between. In addition, Keller soils have a mollic epipedon. Hickory soils average more than 15 percent sand in the particle-size control section, formed in Illinoian till, and are downslope from Atlas soils. Keomah soils formed in loess and are on convex crests and summits upslope from Atlas soils.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Atlas soils are somewhat poorly drained. These soils are seasonally wet and seepy. The seasonal high water table is 0.5 foot to 1.5 feet (15 to 46 cm) below the surface in spring. Saturated hydraulic conductivity is low or moderately low (0.07 to 0.42 micrometers per second) in the slowest layers. Permeability is slow or very slow (0.01 to 0.42 inches per hour). The potential for surface runoff is high to very high.
USE AND VEGETATION: Most areas of Atlas soils are used for forage, hay, or pasture. Cultivated crops are on less sloping areas and trees are on steeper areas. The native vegetation is hardwood forest.
DISTRIBUTION AND EXTENT: Southern, western, and northwestern Illinois and southern Ohio. Moderately extensive in MLRA's 108B, 113, 114A, 114B, 115A, 115B and 115C.
MLRA OFFICE RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Stephenson County, Illinois, 1969.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from the surface of the soil to a depth of 13 inches (33 cm), (Ap and BE horizons);
Albic horizon - the zone from a depth of 7 to 13 inches (18 to 33 cm), (BE horizons);
Argillic horizon - the zone from approximately 13 to 61 inches (33 to 155 cm), (2Btg1, 2Btg2, 2Btg3, 2Btg4 horizons);
Episaturation - redox depletions in those horizons above argillic horizon and paleosol.
Aquic moisture regime - redox features in all layers between lower boundary of Ap and 16 inches (41 cm), and less than 2 chroma matrix within top 5 inches (12 cm) of argillic;
Mesic temperature regime.
The concept of the Atlas series is that of soils formed in Illinoian till or accretion gley that contains a strongly developed Sangamon paleosol. There is a minor occurrence of Atlas soils in Illinois, generally in the area west of the Illinois River, that have a paleosol formed in Pre-Illinoian till. Those soils are similar to the Atlas soils and are included with them. The variability of the properties in the Atlas series is related to the geologic truncation of the paleosol before it was buried by loess, and to the extent of modern soil forming processes on the old materials. Many of the properties of the Btg horizon are believed to be inherited from the paleosol. Calcium and other bases have been replenished in many pedons after burial by loess by seepage water from upslope or from the mantling material. The brighter colors allowed in the 2BC or 2C horizons of some pedons represent soils that extend through the gray paleosol into the less weathered or unweathered till below. It is difficult to differentiate the properties of the lower part of the modern solum from those of the paleosol in many pedons. Some pedons contain buried horizons of the paleosol beneath the modern solum.
Described from a core taken from near the previous OSD type location.
ADDITIONAL DATA: Particle size data are on file for several pedons of the Atlas soils at the Illinois State Office and at the NSSL.