Effect of Bedrock Porosity on Soils Formed from Dolomitic Limestone Residuum and Eolian Deposition

Abstract

AbstractDifferences in the weathering characteristics of dolomitic limestones have resulted in the formation of Haplustalfs and Calciustolls located in the northwestern Colorado Plateau of Arizona. The establishment of effective porosity in the parent rock has controlled important pedogenic processes such as decalcification and silicate clay illuviation. The underlying carbonate strata, the Kaibab Formation, are complex limestone‐dolomite‐chert marine rocks of Permian age. Pleistocene age meteoric waters have caused the dissolution and partial removal of CaCO3 and the establishment of a porous dolomite crystal framework. Under these conditions, soils forming in residuum are able to decalcify and to form argillic horizons. However, in more resistant limestones, compaction during burial has resulted in a nonporous micrite that retards calcite removal by meteoric waters. Under these conditions, soil profiles maintain a high CaCO3 content and silicate clay illuviation does not occur. Eolian dust is also important to soil formation on the Colorado Plateau; in particular, quartz in the coarse silt fraction (31–44 µm), and quartz and biotite in the very fine and fine silt fractions (2.0–11 µm). Micaceous clay minerals of residual and eolian origin are converted to montmorillonite in the Alfisols. A probable sequence of events for this transformation to occur is: (i) the removal of calcite from the dolomitic limestone bedrock and the formation of a dolomite crystal framework, (ii) the slow dissolution of dolomite and release of Mg2+ into solution, (iii) the incorporation of Mg2+ into the octahedral layer of the mica and the release of K+ from the mica interlayer position, and (iv) the illuviation of montmorillonite to form the argillic horizon.