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Soil-Carbonate Genesis in the Pinacate Volcanic Field, Northwestern Sonora, Mexico

Published online by Cambridge University Press:  20 January 2017

Janet L. Slate
Affiliation:
Department of Geosciences, University of Arizona, Tucson, Arizona 85721
William B. Bull
Affiliation:
Department of Geosciences, University of Arizona, Tucson, Arizona 85721
Teh-Lung Ku
Affiliation:
Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741
Muhammad Shafiqullah
Affiliation:
Department of Geosciences, University of Arizona, Tucson, Arizona 85721
Daniel J. Lynch
Affiliation:
Department of Geosciences, University of Arizona, Tucson, Arizona 85721
Yi-Pu Huang
Affiliation:
Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741

Abstract

Uranium-series methods were used to date and evaluate pedogenic CaCO3 genesis in the Pinacate volcanic field, northwestern Sonora, Mexico. Soils are developed in eolian deposits on lava flows. 230Th/234U dates of pedogenic carbonate are mininum soil ages because of (1) the time needed to yield clasts from flows and to accrete enough carbonate to sample, (2) subsequent additions of uranium, and (3) continued solution and reprecipitation of carbonate rinds. K-Ar dates of basalt flows are maximum soil ages. Maximum and minimum rates of CaCO3 accumulation are calculated from the Th/U dates and K-Ar dates, respectively. The mean maximum rate is 0.13 g CaCO3/cm2/1000 yr and the mean minimum rate is 0.05 g CaCO3/cm2/1000 yr. Least-squares regressions of pedogenic carbonate and clay content and of Th/U ages against K-Ar ages suggest additions to soils from atmospheric sources throughout the late Quaternary. Morphology of pedogenic carbonate and laboratory data for soluble salts indicate that the climate of the Pinacate has not changed significantly during the past 150,000 yr. Soil variability is influenced by proximity of the eolian source. Near the periphery of the Pinacate, carbonate and clay are evenly distributed throughout soil profiles. Within the volcanic field, carbonate and clay are concentrated in soil horizons, suggesting that additions from atmospheric sources are slow enough to allow translocation.

Information

Type
Research Article
Copyright
University of Washington

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