Calciustolls in Central Texas: II. Genesis of Calcic and Petrocalcic Horizons
- L. T. West *,
- L. P. Wilding and
- C. T. Hallmark
Soils on hillslopes in the Grand Prairie and eastern Edwards Plateau regions of Texas are developed from multiple facies of interbedded weakly to strongly indurated Cretaceous limestones. Most contain either calcic or petrocalcic horizons. Stable C isotope analysis of the carbonate-enriched horizons from seven pedons sampled in this area permitted quantification of the amount of pedogenic carbonates. Features indicative of carbonate translocation and accumulation were observed in the soils. However, reconstruction analysis indicated that none of the calcic horizons and few of the petrocalcic horizons contained more carbonates than the parent limestone. Microfabric development in calcic horizons supports loss of carbonates as a major process in these horizons. The pedogenic nature of most of the carbonates in calcic horizons is attributed to in situ recrystallization of the parent limestone. Petrocalcic horizons commonly had areas of strongly indurated limestone in matrix interiors, and micromorphic observations indicated that much of the pedogenic carbonates in these horizons was also the result of in situ recrystallization of the limestone. Petrocalcic horizons occurred on all landscape positions. Their occurrence and position in the profile appears to be related to an indurated limestone bed within the normal depth of wetting. The development of calcic and petrocalcic horizons primarily by recrystallization rather than translocation and accumulation of carbonates contrasts with the commonly accepted model for formation of these horizons.
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