Relationship of soil properties to transformation of carbonate rocks into soils

Author

Bobby J. Miller

Date of Award

12-1972

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

M. E. Springer

Abstract

Soils developed from carbonate rocks and having thick, reddish, clayey B horizons occupy extensive areas in parts of the United States. The study was designed to determine some of the physical, chemical, and mineralogical properties of such soils and to evaluate changes that have occurred as a result of weathering of carbonate rock and ensuing devel-opment of soils. Major emphasis was placed on the zone near the soil-rock interface. Three Ultisols and one Alfisol in East Tennessee were selected for the study. The soil series represented were Dunmore, Fullerton, and Talbott. A special sampling technique assured sampling of 'in situ' residuum at one sampling location. Field studies showed variable depth to carbonate rocks. Near the rock, a thin distinctly banded zone was documented in all of the soils. An observed general decrease with depth of volumes of > 2mm fragments was documented by laboratory studies. Bulk density studies indicated maximum densities at depths between 38 and 100 cm. Particle size distribution analyses showed maximum clay contents of 70 to 80 percent in B horizons. Clay content of the zone near the carbonate rock was highly variable in the soils. Clay-free particle size distributions showed wide variations in amounts and distri-bution of sands. The thicker Dunmore and Fullerton are more highly leached than the thinner Talbott soil. Minimum pH occurs in mid-B horizons of all the soils. In the Talbott, the minimum is 6.7 while the deeper soils have minima near 5.0. Soil pH increases with distance above and below the minima. Base saturations show similar trends to pH and are highest in the zone near the carbonate rock. Amounts of extractable acidity are highest in the zone near the carbonate rock. Amounts of extractable acidity are greatest in horizons with low pH and large amounts of clay. Large amounts (3 to 6 meq/100g) of extractable acidity were measured in bands near the rock having pH ≥ 7.0. Organic matter content is greatest (1-4 percent) in surface hori-zons and decreases rapidly with depth. A unique feature of all the soils is an abrupt increase in organic matter content only a few centimeters from the carbonate rock. Total P content of the soils ranges from 40 to 600 ppm. Largest amounts are in surface horizons and in the zone near the carbonate rock. Amounts of extractable P are low (1-17 ppm) and have the same general trends as total P; however, in bands near the rock, largest amounts of extractable P do not always coincide with either largest amounts of total P or organic matter. Free iron distribution generally parallels the distribution of clay. Largest amounts (two to six percent Fe) are in B_2t. horizons. Sur-face horizons and the thin band lying on the carbonate rock contain smaller amounts; one to two percent in surface horizons compared to < 0.5 percent adjacent to the rock. Evaluation of formation and movement of clays and volume changes that result from soil formation indicate large volumes of rock are required to form the soils. Formation of clays is indicated in all the soils by a net decrease of nonclay fractions. X-ray diffraction of two clay-size fractions revealed goethite and hematite throughout B horizons in all the soils. Lesser amounts were identified in A horizons and in the bands nearest the rock. Quartz was identified as an important component of the clay fraction in all the soils. Feldspars were identified in clays from all the soils. Largest amounts were in limestone residues and in bands near the rock. In and above the banded zone, the amounts of feldspars decrease to rather small amounts throughout the soil B and A horizons. Phyllosilicate mineralogy of the soils is dominated by kaolinite, together with micaceous minerals and their alteration (interstratifica-tion) products. Residues from the carbonate rocks underlying the four soils contain three different suites of phyllosilicate minerals. They are (1) micaceous clays at the Talbott site, (2) micaceous clays and small amounts of kaolinite at the Fullerton site, and (3) micaceous clays, expanding-chlorite, and small amounts of kaolinite at both Dunmore sites. Expanding-chlorite decreases with distance from the rock in the Dunmore soils and cannot be identified in horizons more than about 20 cm from the unweathered rock. The decrease generally coincides with de-creasing pH above the rock. The micaceous clays from the carbonate rock undergo a depletion of K and subsequent interstratification. The alterations may be expressed as: micaceous minerals → interstratified minerals → soil-vermiculite. The degree of interstratification and resultant development of soil-vermiculite increases with increased intensity of weathering and thus, with increasing distance from the carbonate rock. As a result, maximum relative amounts of soil-vermiculite are in surface horizons and minima are in the bands adjacent to the rock. Small amounts of expanding-lattice layers are also present in the interstratified mineral in clays which give recognizable 10A peaks. Kaolinite is an important mineral in all horizons above the unweathered rock. The distribution in all the soils is similar whether or not the mineral is present in the underlying rock. The amounts of kao-linite increase rapidly with distance above the rock and reach apparent relative maxima within 20 cm of the rock in all the soils. Above these zones, the relative amounts remain nearly uniform with increasing distance from the rock.

Recommended Citation

Miller, Bobby J., "Relationship of soil properties to transformation of carbonate rocks into soils. " PhD diss., University of Tennessee, 1972.
https://trace.tennessee.edu/utk_graddiss/7971