LOCATION SEPO ILEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Fluvaquentic Endoaquolls
TYPICAL PEDON: Sepo silty clay loam - in a nearly level cultivated field. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 8 inches; black (10YR 2/1) silty clay loam, dark gray (10YR 4/1) dry; weak fine subangular blocky structure; firm; many very fine roots; about 1 percent shell fragments; slightly effervescent; neutral; abrupt smooth boundary.
A1--8 to 12 inches; black (10YR 2/1) silty clay loam, dark gray (10YR 4/1) dry; moderate fine and medium subangular blocky structure; firm; common very fine roots; about 1 percent shell fragments; strongly effervescent; slightly alkaline; abrupt smooth boundary.
A2--12 to 19 inches; very dark gray (N 3/0) silty clay loam, gray (N 5/0) dry; moderate fine angular blocky structure; firm; common very fine roots; about 1 percent shell fragments; few fine prominent strong brown (7.5YR 4/6) masses of iron accumulation with diffuse boundaries lining pores; strongly effervescent; slightly alkaline; abrupt smooth boundary. (Combined thickness of the A horizons is 10 to 24 inches.)
Bg1--19 to 28 inches; dark gray (N 4/0) silty clay loam; moderate fine prismatic structure parting to moderate fine angular blocky; firm; few very fine roots; common distinct dark gray (10YR 4/1) pressure faces; about 1 percent shell fragments; few fine prominent strong brown (7.5YR 4/6) masses of iron accumulation with diffuse boundaries lining pores; strongly effervescent; slightly alkaline; abrupt smooth boundary.
Bg2--28 to 32 inches; dark gray (N 4/0) silty clay loam; moderate fine subangular blocky structure; firm; about 4 percent shell fragments; common fine prominent strong brown (7.5YR 4/6) masses of iron accumulation with diffuse boundaries lining pores; strongly effervescent; moderately alkaline; abrupt smooth boundary. (Combined thickness of the Bg horizons is 10 to 21 inches.)
BCg--32 to 42 inches; dark gray (N 4/0) silty clay loam with strata of loam; weak coarse subangular blocky structure; firm; about 1 percent shell fragments; common fine prominent strong brown (7.5YR 4/6) masses of iron accumulation with diffuse boundaries lining pores; violently effervescent; moderately alkaline; abrupt smooth boundary. (0 to 15 inches)
Cg--42 to 70 inches; grayish brown (10YR 5/2) silty clay loam with strata of silt loam; massive; firm; many fine distinct yellowish brown (10YR 5/6) masses of iron accumulation with diffuse boundaries lining pores; strongly effervescent; moderately alkaline.
TYPE LOCATION: Fulton County, Illinois; about 1 1/4 miles northwest of Havanna; 1,465 feet east and 333 feet south of the northwest corner of sec. 17, T. 4 N., R. 4 E.; USGS Havana topographic quadrangle; lat. 40 degrees 20 minutes 04 seconds N. and long. 90 degrees 04 minutes 54 seconds W., NAD 27.
RANGE IN CHARACTERISTICS: The depth to the base of the cambic horizon ranges from 30 to 50 inches. The mollic epipedon ranges from 10 to 24 inches thick and extends into the upper part of the B horizon in some pedons. Organic matter content decreases irregularly with depth. Carbonates are within a depth of 40 inches and commonly are present throughout the series control section. These soils typically contain small snail shell fragments throughout. The upper and middle parts of the series control section average between 27 and 35 percent clay. Individual subhorizons range to as much as 42 percent clay. Sand content ranges from 8 to 15 percent. The lower part of the series control section averages between 18 and 30 percent clay and between 10 and 40 percent sand.
The upper part of the series control section (Ap and A horizons) has hue of 10YR, 2.5Y or is neutral, value of 2 to 3, and chroma of 0 to 2. Redox concentrations are present in the lower part, commonly as masses of iron accumulation lining pores and root channels. Reaction ranges from slightly acid to slightly alkaline.
The middle part of the series control section (Bg and BCg horizons) has hue of 10YR, 2.5Y, 5Y or is neutral, value of 3 to 6, and chroma of 0 to 2. It dominantly is silty clay loam but thin subhorizons of silty clay are in some pedons. It often is stratified in the lower part with textures of more sand and less clay. Redox concentrations are present as masses of iron accumulation lining ped surfaces and pores. Reaction ranges from neutral to moderately alkaline.
The lower part of the series control section (Cg horizon) has hue of 10YR, 2.5Y, 5Y or is neutral, value of 4 to 6, and chroma of 0 to 2. It is silty clay loam with strata of silt loam, loam, sandy loam, fine sandy loam, or very fine sandy loam. Sand content averages less than 40 percent. Redox concentrations are present as masses of iron accumulation lining pores. Reaction ranges from neutral to moderately alkaline.
COMPETING SERIES: These are the Beaucoup, Blackoar, Bridgeson, Ettrick, Gorham, Leshara, Lummi, Sauvie, and Wapato soils. Beaucoup soils lack free carbonates above a depth of 40 inches. Blackoar, Ettrick, and Leshara soils average less than 27 percent clay in the particle size control section. Bridgeson, Lummi, Sauvie, and Wapato soils are dry in all parts of the soil moisture control section for more than 45 out of the 120 days following the summer solstice. Gorham soils average more than 40 percent sand in the lower part of the series control section.
GEOGRAPHIC SETTING: Sepo soils are in abandoned shallow lakes on flood plains. Slope ranges from 0 to 2 percent. These soils formed in slackwater sediments and are often stratified in the lower part of the solum and in the C horizon. The strata are typically loamy sediments. Mean annual air temperature ranges from 50 to 54 degrees F, and mean annual precipitation ranges from 35 to 40 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ambraw, Tice, and Titus soils. The Ambraw and Titus soils are in low-lying areas nearby. Ambraw soils average more than 15 percent sand and Titus soils average more than 35 percent clay in the control section. The somewhat poorly drained Tice soils are on summits of broad rises.
DRAINAGE AND PERMEABILITY: Poorly drained. Runoff is slow or ponded. Permeability is moderately slow. Flooding from stream overflow is occasional during the spring. These soils have an apparent water table at a depth of .5 foot above the surface to 1.5 feet below during the spring in most years.
USE AND VEGETATION: Most areas of Sepo soils are cultivated. Corn and soybeans are the principal crops. Native vegetation is water-tolerant grasses and deciduous trees.
DISTRIBUTION AND EXTENT: Western Illinois; MLRA 115. The soils of this series are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES PROPOSED: Fulton County, Illinois, 1995. Named for a town in Fulton County.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface to a depth of approximately 19 inches (Ap and A horizons); cambic horizon- the zone from 19 to 32 inches; fluventic properties: stratification and irregular decrease in organic carbon; endosaturation; aquic conditions - chroma of 2 or less and redox concentrations in all layers below the A1.