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The Genesis of Certain Calcareous Floodplain Soils of Virginia¹

ABSTRACT

A study was made to determine the origin of the calcareous material found in certain floodplain soils of the limestone valleys of Virginia. The CaCO₃ in these soils was derived from the highly fractured and faulted limestone underlying the area. Groundwater, high in dissolved CO₂, percolated through the crushed limestone, dissolving an appreciable amount of Ca and Mg carbonate. This water issued at the surface in the form of large springs and lost some of the dissolved CO₂ which resulted in a saturated solution with respect to calcium. The CaCO₃ depositing alga Oocardium stratum Näg was found below the point of saturation in the streams and was thought to be of major importance in the deposition of CaCO₃. In a 200-foot section of stream channel beginning 450 feet below a spring having a rate of flow of 104 gallons/min, approximately 2.85 tons of CaCO₃ were deposited annually as tufa. Algal-deposited tufa is torn from stream channels during heavy rains and redeposited downstream by flood waters. Calcareous material occurs several miles from the source area and is a constituent of the flood plain soils along the creeks and rivers of the area.

¹ Contribution of the Agronomy Department, Virginia Polytechnic Institute, Blacksburg, Va. This material is taken from a thesis submitted as partial fulfillment of the M.S. degree. Presented before Div. S-5, Soil Science Society of America, Ithaca, N. Y., Aug. 21, 1962.

² Instructor, Department of Agronomy, Virginia Polytechnic Inst.; Professor of Botany and Plant Pathology, Michigan State Univ.; and Professor of Agronomy, Virginia Polytechnic Inst., respectively.

Received for publication August 20, 1964. Accepted for publication July 7, 1965.