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Oxygen Isotopic Ratios of Quartz from Wind-Erosive Soils of Southwestern United States in Relation to Aerosol Dust¹

ABSTRACT

The oxygen isotopic ratios (expressed as parts per thousand relative to mean ocean water, SMOW, ¹⁸O) of the quartz from 13 soils undergoing much wind erosion during the study period of 1972–1975 in four southwestern states and from comparison areas were determined. The ¹⁸O for quartz from eight Texas (TX) and Arizona (AZ) soils range from 13.0 to 15.9 . The quartz of the sands and silts coarser than 20 µm from three of the soils had ¹⁸O values ranging from 13.1 to 15.1 , characteristic of an ultimate igneousmetamorphic origin. The ¹⁸O values increase greatly with decreasing particle size of quartz from three soils ranging from loamy fine sand to loam to clay in texture. The ¹⁸O of the 1–10 µm quartz fraction (aerosol size) ranged from 19.2 to 20.2 (19.55 ± 0.28 ; ± sigma) for the thirteen soils most affected by dust storms. The higher values are suggestive of an admixture of some quartz crystallized at low temperature to quartz of high temperature origin. These results are not significantly different from the mean of 20.73 ± 1.82 found earlier for the same fraction from 30 shales of the midcontinental United States, but are 4 to 7 higher than those reported for New Zealand, Australian, and southern African soils. The 1–10 µm quartz from the comparison areas of TX and AZ soils in Fluvial materials further southeast and southwest has a ¹⁸O mean of 17.7 ± 0.6 , reflecting the influx of a slightly higher proportion of quartz from igneous sources than in the soils most affected by wind erosion. The oxygen isotopic ratios of 1–10 µm quartz from three Hawaiian soils and two sediments from Lake Waiau occurring at 3,970 m altitude on the Mauna Kea summit on the Island of Hawaii give a ¹⁸O mean of 18.3 ± 0.2 . Quartz of the above soils, including sandy, loamy, and clayey soils of southwestern United States, in addition to shales reported earlier, are source reservoirs of quartz having intermediate oxygen isotopic ratios characteristic of mixtures of two sources of quartz, one crystallized at high (e.g., ¹⁸O = 11 ) and one at low temperature (e.g., ¹⁸O = 30 ).

¹ Research supported in part by the School of Nat. Resour., College of Agric. and Life Sci., Univ. of Wis., Madison, projects 1336 and 1123; in part by the Ecological Sci. Branch, Div. of Biomedical and Environ. Res., U.S. Energy Res. and Develop. Administration Contract EY-76-S-02-1515-Jackson (Pap. COO-1515-75); and in part by the Nat. Sci. Found. (Nat. Center for Atmospheric Res., Boulder, CO-Gillette), EAR76-19783-Jackson, and GA-22711-Clayton; through an International Consortium for Interinstitutional Cooperation in the Advancement of Learning (ICICAL). We thank Toshiko Mayeda, Univ. of Chicago, for assistance with the oxygen isotopic analyses. Presented before Div. S-9, Soil Sci. Soc. of Am., Houston, TX, 30 Nov. 1976.

² Project Associate and Franklin H. King Professor of Soil Science, Univ. of Wis., Madison, WI 53706; Professor of Chemistry, Univ. of Chicago; Atmospheric Scientist Natl. Center Atmospheric Res., Boulder; and Geologist, New Mexico Bureau of Mining and Mineral Resourc., Soccoro, N. Mex., respectively.

Received for publication . Accepted for publication September 27, 1977.