Pedogenesis on the Edwards Plateau, Texas: III. New Model for the Formation of Petrocalcic Horizons

Abstract

AbstractPetrocalcic horizons occur in a number of soils formed from Cretaceous limestone in central and west Texas (Edwards Plateau land resource area). Microfabric and stable C isotope analyses confirmed that the indurated carbonate zones are mostly of pedogenic origin. Multiple lines of evidence indicate that the petrocalcic horizons in these soils form through a process of limestone alteration by in situ dissolution and reprecipitation of carbonates. Evidence includes: (i) very low noncarbonate residue levels in petrocalcic horizons, which are comparable to levels in limestone bedrock; (ii) lithologic discontinuities between petrocalcic horizons and the overlying sola; (iii) presence, concentration, and particle size distribution of flourite in some petrocalcic horizons; (iv) presence of secondary silica within petrocalcic horizons indicating limited movement of components within this zone; and (v) microfabric analysis. This in situ process is in distinct contrast to commonly held models depicting translocation and accumulation of carbonates within a solum that was initially nonindurated. A model is proposed to describe the genesis of limestone‐derived petrocalcic horizons.