/sup 230/Th-/sup 234/U dating of pedogenic carbonates in gravelly desert soils of Vidal Valley, southeastern California

Journal Article · Wed Oct 31 23:00:00 EST 1979 · Geol. Soc. Am., Bull.; (United States)

DOI:https://doi.org/10.1130/0016-7606(1979)90<1063:TDOPCI>2.0.CO;2· OSTI ID:6523432

Ku, T L ^[1]; Bull, W B; Freeman, S T; Knauss, K G

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1. Univ. of Southern California, Los Angeles

Radioactive disequilibrium relationships among /sup 230/Th, /sup 234/U, and /sup 238/U can be used to date pedogenic carbonates formed in regions of arid to semiarid climate. Samples suitable for dating consist of dense carbonate rinds around pebbles from the Cca soil horizon. Analytically, the method involves leaching the samples with dilute hydrochloric acid and measuring /sup 238/C, /sup 234/U, /sup 230/Th, and /sup 232/Th in both the leachate and residue fractions. As the soil carbonate commonly incorporates silicate mineral-bearing detritus, corrections are made to account for possible introduction of detrital /sup 230/Th and /sup 234/U into the acid leachate. The corrections are based on the assumptions that the carbonate initially contains negligible amounts of /sup 232/Th and /sup 230/Th, or has a /sup 230/Th//sup 232/Th ratio similar to that in detrital minerals; /sup 238/U, /sup 234/U, and /sup 230/Th in the detrital silicate phase are in secular equilibrium with each other; and the thorium isotopes in the detrital phase are not fractionated by the acid leaching. Application of the method to calcareous soils developed on upper Quaternary alluvial deposits of the eastern Mojave Desert in southern California gives ages that are internally consistent and that agree with the geomorphic and stratigraphic relative age relationships. Fourteen samples from an upper Pleistocene geomorphic surface, Q2b, yielded an average age of 83,000 +- 10,000 y. This age is confirmed by a different assessment of the data. On one specimen two different layers of a pebble coating were dated, and a carbonate accumulation rate of about 1 mm/8000 y was obtained. 6 figures, 7 tables.

• OSTI ID: 6523432
• Journal Information: Geol. Soc. Am., Bull.; (United States), Journal Name: Geol. Soc. Am., Bull.; (United States) Vol. 90:2; ISSN BUGMA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology &amp; Hydrology-- (-1989)
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
AGE ESTIMATION
ALPHA DECAY RADIOISOTOPES
CALIFORNIA
CARBONATE ROCKS
CENOZOIC ERA
DATA
EVEN-EVEN NUCLEI
EXPERIMENTAL DATA
GEOLOGIC AGES
HEAVY NUCLEI
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ISOTOPE DATING
ISOTOPES
NORTH AMERICA
NUCLEI
NUMERICAL DATA
QUATERNARY PERIOD
RADIOISOTOPES
ROCKS
SEDIMENTARY ROCKS
THORIUM 230
THORIUM ISOTOPES
URANIUM 234
URANIUM 238
URANIUM ISOTOPES
USA
WESTERN REGION
YEARS LIVING RADIOISOTOPES