LOCATION TARRANT TX+OKEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic, thermic Lithic Calciustolls
TYPICAL PEDON: Tarrant cobbly clay--native pasture.
(Colors are for dry soil unless otherwise stated.)
A--0 to 8 inches; very dark grayish brown (10YR 3/2) very cobbly clay; very dark brown (10YR 2/2) moist; compound strong very fine subangular blocky and strong medium granular structure; very hard, firm; common fine roots; common fine pores; about 35 percent by volume of cobblestones and 5 percent pebble-size fragments of limestone; stone fragments are randomly oriented and coated with secondary calcium carbonate; calcareous; moderately alkaline; clear irregular boundary. (4 to 11 inches thick)
Ak--8 to 13 inches; dark brown (10YR 4/3) extremely cobbly clay, dark brown (10YR 3/3) moist, occupies about 15 percent by volume in vertical bands as much as 2 inches wide and horizontal bands as much as 1 inch wide; compound moderate very fine blocky and moderate medium granular structure; very hard, firm; common fine roots in both vertical and horizontal bands; calcareous; moderately alkaline; 85 percent by volume of cobblestone and stone size fragments of limestone that have thin patchy calcium carbonate coatings and pendents; abrupt wavy boundary. (2 to 10 inches thick)
R--13 to 30 inches; fractured indurated and platy limestone bedrock and strata of strongly to weakly cemented limestone about 1/2 to 6 inches thick; about 1 percent by volume brown (10YR 4/3) clay, dark brown (10YR 3/3) moist, in vertical and horizontal bands 1/32 to 1/2 inch wide; moderate very fine subangular blocky structure; very hard, firm; few fine roots extend into the crevices and clay between the plates of the limestone; thin patchy calcium carbonate coating on limestone plates.
TYPE LOCATION: Menard County, Texas; in native pasture 150 feet west of edge of U.S. Highway 83, 1.2 miles south of the intersection of U.S. Highway 83 and Ranch Road 2291 in Menard.
RANGE IN CHARACTERISTICS: Thickness of the solum ranges from 6 to 20 inches, and corresponds to the depth to indurated limestone. The solum contains 35 to 85 percent coarse fragments, the amount ranging from 10 to 60 percent in the A horizon and from 50 to 90 percent in the Ak horizon. Coarse fragments are dominantly limestone but some pedons include quartziferous fragments. The fragments greater than 3 inches in diameter comprise 25 to 70 percent of the soil and consist of cobbles, flags and stones. Fragments less than 3 inches in diameter are mostly larger than 0.75 inch in diameter. Secondary coating of calcium carbonate on the fragments is lacking in the upper 4 inches of some pedons, but is 1 cm or more thick on some fragments immediately above the R layer. Carbonates are in the form of coatings and pendants.
The A horizon has hue of 7.5YR to 10YR, value of 2 to 5, and chroma of 1 to 3. Chroma of 1 is not associated with wetness. It is clay, or silty clay, or their cobbly, very cobble, stony or very stony counterparts. Many pedons have an extremely cobbly or flaggy layer immediately above the bedrock. Clay content of the fine earth fraction is 40 to 60 percent.
The strata of the underlying fractured bedrock range from 2 to 24 inches. In some pedons, massive pulverulent lime is interbedded with bedrock.
COMPETING SERIES: There are no competing series in the same family. Closely similar soils are Eckrant, Ector, Eddy, Kavett, Maloterre, Purves, Talpa, and Yates series. All these soils except Eckrant and Purves soils have less than 35 percent clay in the fine-earth fraction. Eckrant soils lack calcic horizons and Purves soils, as well as Kavett, Maloterre, and Talpa soils have less than 35 percent coarse fragments in their control sections. Ector and Maloterre soils have carbonatic mineralogy. Eddy and Yates soils, as well as Maloterre soils, have ochric epipedons.
GEOGRAPHIC SETTING: Tarrant soils are on convex to plane slopes of ridgetops and breaks of erosional uplands. Slopes are mainly 1 to 8 percent, but some are as much as 50 percent. The soil formed in residuum weathered from limestone of lower Cretaceous age, and includes interbedded chalks, marls, and marly earths. The mean annual precipitation ranges from 20 to 34 inches, Thornthwaite annual P-E indices are about 30 to 44, and mean annual temperature is about 62 to 70 degrees F. Frost free days range from 230 to 260. Elevation ranges from 1000 to 2400 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Kavett series and Brackett, Crawford, Denton, Tobosa, and Valera series. Brackett soils are light colored, shallow soils underlain by softer limestone. Crawford, Denton, Tobosa, and Valera soils are more than 20 inches deep.
DRAINAGE AND PERMEABILITY: Well drained. Runoff is negligible on 0 to 1 percent slopes. Very low on 1 to 3 percent slopes, low on 3 to 5 percent slopes, medium on 5 to 20 percent slopes and high on 20 to 50 percent slopes. Permeability is moderately slow.
USE AND VEGETATION: Used entirely as rangeland. The original vegetation included little bluestem. The present range is buffalograss, Texas wintergrass, green sprangletop, threeawn, panicum, agarito, pricklypear, few mesquite, many live oak and yucca.
DISTRIBUTION AND EXTENT: West-central Texas, and Oklahoma, mainly in the Edwards Plateau, but some areas are on Grand Prairie, Pennsylvanian, or Permian limestones in the same climatic zone. The series is extensive.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: McLennan County, Texas; 1947.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 13 inches.
Calcic horizon - 8 to 13 inches, and upper few inches of limestone contain secondary carbonates.
Lithic contact - at 13 inches.
The province of occurrence for the Tarrant series has been recently redefined. Tarrant soils are now limited to the Edwards Plateau materials with a P-E index of 30 to 44.
ADDITIONAL DATA: Lincoln Laboratory Sample Nos. 20207, 20208, 20209, 20210, 20255, 20226, 20227, 20228, and 20229.