Formation of Calcic and Argillic Horizons in Selected Soils of the Texas Coast Prairie

In a previous paper the soil‐geomorphic relationship and microtopographic expression were described for Mollisols with calcic horizons and associated noncalcareous Alfisols of the Texas Coast Prairie. This paper describes the development of calcic and argillic horizons in the above soils. Microfabric of soil carbonates, carbonate clay depth functions, and acid residues from carbonate nodules confirm the pedogenic nature of carbonates in the Mollisols. Carbonate contents in the calcic horizons range up to 40%, with up to 50% of the total carbonates in the clay‐size fraction. Clay‐size carbonates have impregnated the soil matrix in the upper part of the main zone of carbonate accumulation, forming a dense K‐fabric. Such abundance and expression decrease with depth. Complex pedological features—fine‐grained calcans, crystallaria, and coarse‐grained carbonate glaebules—in lower horizons of the Mollisols suggest a fluctuating water table within 1 m. Carbonate‐free clay distribution data supported the microfabric analyses, which indicate the lack of argillic horizons in the Mollisols. Associated leached Alfisols have well‐expressed argillic horizons. Lateral redistribution of allogenic and authigenic carbonates from microdepressions to adjacent micro‐highs via saturated and unsaturated moisture flow is proposed to explain carbonate distribution in some landscapes of the Texas Coast Prairie. A weathering origin for the carbonates was discounted because weatherable minerals in parent sediments were insufficient to account for the 550 to 750 kg/m 2 of carbonate in the calcic horizons. Carbonates inherited with fluviatile‐deltaic sediments are considered the single most plausible carbonate source for these soils.