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1701 - Tephra layers of blind Spring Valley and related upper pliocene and pleistocene tephra layers, California, Nevada, and Utah : isotopic ages, correlation, and magnetostratigraphy [texte imprimé] / Andrei M. Sarna-Wojcicki, Auteur . - 2005 . - 1 vol. (69 p.) : ill. en noir et coul., cartes, couv. ill. en coul. ; 28 cm. Langues : Américain | Catégories : | Régions
Nevada
| | Résumé : | Numerical ages have been determined for a stratigraphic sequence of silicic tephra layers exposed at the Cowan Pumice Mine in Blind Spring Valley, near Benton Hot Springs, east-central California, as well as at Chalk Cliffs, north of Bishop, Calif. The tephra layers at these sites were deposited after eruptions from nearby sources, most of them from near Glass Mountain, and some from unknown sources. The ages were determined primarily by the laser-fusion 40Ar/39Ar method, mostly on sanidine feldspar; two were determined by conventional K-Ar analysis on obsidian clasts. These tephra layers, all underlying the Bishop ash bed and listed in order of concordant age and stratigraphic position, are: Tephra Unit Method Material Age Bishop Tuff (air-fall pumice) Ar/Ar sanidine 0.759?0.002 Ma* Upper tuffs of Glass Mountain Ar/Ar sanidine 0.87?0.02 Ma Upper tuffs of Glass Mountain Ar/Ar sanidine 1.13?0.19 Ma Lower tuffs of Glass Mountain K-Ar obsidian 1.86?0.09 Ma (avg of 2 dates) Ar/Ar sanidine 1.92?0.02 Ma (avg of 2 dates) Tuffs of Blind Spring Valley Ar/Ar sanidine 2.135?0.02 to sanidine 2.219?0.006 Ma (10 dates) Tuffs of Benton Hot Springs Ar/Ar plagioclase 2.81?0.02 Ma *Date published previously The above tephra layers were also petrographically examined and the volcanic glass shards of the layers were chemically analyzed using the electron microprobe and, for some samples, instrumental neutron activation analysis and X-ray fluorescence. |
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Faire une suggestion Affiner la recherche1689 - Quaternary paleoseismology and stratigraphy of the Yucca Mountain area, Nevada (Bulletin de U.S. Geological Survey professional paper, 1689 [01/01/2004])
