LOCATION SION VIEstablished Series
TAXONOMIC CLASS: Coarse-loamy, carbonatic, isohyperthermic Typic Calciustolls
TYPICAL PEDON: Sion clay. (Colors are for moist conditions.)
A1--0 to 6 inches; very dark grayish brown (10YR 3/2) clay; strong medium and coarse granular structure; firm, moderately sticky, moderately plastic; many fine and medium roots, few coarse roots; many fine and medium interstitial pores; many fine and medium wormcasts, common fine and medium insectcasts; about 10 percent, by volume, limestone pebbles; strongly effervescent; moderately alkaline; clear wavy boundary.
A2--6 to 12 inches; dark brown (10YR 3/3) clay; strong medium and coarse granular structure; firm, moderately sticky, moderately plastic; many fine and medium roots; many fine and medium interstitial pores; common fine and medium wormcasts and insectcasts; about 5 percent, by volume, limestone pebbles; strongly effervescent; moderately alkaline; gradual wavy boundary. (Combined thickness of the A horizons is 2 to 12 inches.)
Bk--12 to 16 inches; brown (10YR 5/3) gravelly clay; moderate fine and medium subangular blocky structure; firm, moderately sticky, moderately plastic; common fine and medium roots; many fine and medium vesicular and tubular pores; few fine and medium wormcasts and insectcasts, many fine and medium soft masses of calcium carbonate; about 25 percent, by volume, limestone pebbles; violently effervescent; moderately alkaline; clear wavy boundary. (2 to 8 inches thick)
CBk--16 to 24 inches; pinkish white (7.5YR 8/2) very gravelly sandy clay loam; weak fine and medium subangular blocky structure; friable, slightly sticky, slightly plastic; common fine and medium roots; many fine and medium vesicular and tubular pores; common fine and medium wormcasts and insectcasts; many fine and medium soft masses of calcium carbonate; about 30 percent, by volume limestone pebbles; violently effervescent; moderately alkaline; clear wavy boundary. (2 to 8 inches thick)
C1--24 to 32 inches; pinkish white (7.5YR 8/2) gravelly sandy loam; massive; very friable; few fine roots; common fine and medium vesicular and tubular pores; few fine and medium insectcasts; common fine and medium soft masses of calcium carbonate, about 20 percent, by volume, limestone pebbles; violently effervescent; moderately alkaline; clear wavy boundary. (2 to 8 inches thick)
C2--32 to 60 inches; pinkish white (7.5YR 8/2) loam; massive; friable, slightly sticky, slightly plastic; few fine roots; common fine and medium vesicular and tubular pores; common fine and medium soft masses of calcium carbonate; about 5 percent, by volume, limestone pebbles; violently effervescent; moderately alkaline.
TYPE LOCATION: St. Croix Island, U.S. Virgin Islands. In a pasture adjacent to the University of the Virgin Islands Agricultural Experiment Station east entrance, from the intersection of VI-70 and VI-64, about 800 feet south on VI-64, about 400 feet east in a pasture. Christiansted topographic quadrangle; lat. 17 degrees 43 minutes 19 seconds N.; long. 64 degrees 47 minutes 33 seconds W.; PRD 1940.
RANGE IN CHARACTERISTICS: Thickness of the solum ranges from 15 to 30 inches. Reaction is slightly to moderately alkaline in the A horizon, and moderately alkaline in the rest of the profile.
The A horizon has hue of 7.5YR or 10YR, value of 2 or 3, and chroma of 2 or 3. Texture is clay loam or clay in the fine-earth fraction. Content of limestone pebbles ranges from 0 to 35 percent, by volume.
The Bk horizon has hue of 7.5YR to 2.5Y, value of 3 to 8, and chroma of 1 to 6. Texture is loam, clay loam, or clay in the fine-earth fraction. Soft masses of calcium carbonate range from common to many. Content of limestone pebbles ranges from 15 to 30 percent, by volume.
The CBk horizon, where present, has hue of 7.5YR to 2.5Y, value of 4 to 8, and chroma of 0 to 4; or it is neutral with value of 4 to 8. Texture is loam or sandy clay loam the fine-earth fraction. Soft masses of calcium carbonate range from few to many. Content of limestone pebbles ranges from 15 to 30 percent, by volume.
The C horizon has hue of 7.5YR to 2.5Y, value of 5 to 8 and chroma of 0 to 4; or it is neutral with value of 5 to 8. Texture is sandy loam, silt loam, or loam in the fine-earth fraction. Soft masses of calcium carbonate range from few to many. Content of limestone pebbles ranges from 15 to 30 percent, by volume.
COMPETING SERIES: There are no competing series in this family.
GEOGRAPHIC SETTING: Sion soils are on side slopes and valley floors. They formed in alkaline marine deposits. Slopes range from 0 to 5 percent. The climate is tropical semiarid. The average annual air temperature ranges from 76 to 82 degrees F., and the mean annual precipitation is about 40 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These include Arawak, Glynn, Hesselberg, and Hogensborg soils. Arawak soils are on higher positions, are shallow, and loamy-skeletal. Glynn and Hogensborg soils are on alluvial fans and terraces. In addition, Glynn soils are clayey-skeletal. Hogensborg soils have clayey, smectitic particle-size control sections. Hesselberg soils are on ancient marine terraces, are shallow to a petrocalcic horizon, and have clayey, mixed particle-size control sections.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: Most areas of Sion soils are used for pasture. Many areas have been converted to residential or business use. The vegetation consists of introduced or native grasses.
DISTRIBUTION AND EXTENT: St. Croix Island, U.S. Virgin Islands. They are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Raleigh, North Carolina
SERIES ESTABLISHED: St. Croix, U.S. Virgin Islands; 1932.
REMARKS: Diagnostic horizons and other features recognized in this pedon include:
Mollic epipedon - the zone from 0 to 12 inches (A horizons).
Calcic horizon - the zone from 12 to 24 inches (Bk and CBk horizons).
ADDITIONAL DATA: Characterization pedon - St. Croix Island, U.S. Virgin Islands; S92VI-10-2. Sample by NSSL, Lincoln NE., 1992.
MLRA: 273.
SIR: VI0018.