Tephrostratigraphy and potassium-argon age determinations of seven volcanic ash layers in the Muddy Creek Formation of southern Nevada
Geological Sciences and Engineering
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Seven silicic tephra layers occur in alluvial deposits of the Muddy Creek and equivalent formations at three localities in southern Nevada. Chemical and petrographic characterization indicate the tephra were derived from seven different volcanic eruptions and do not represent any previously known tephra layers. K-Ar age determinations on minerals or glass from each layer yielded 6 to 12 m.y. ages. Discordant ages were obtained on multiple mineral phases due to incorporation of detrital contaminants. The tephra are sufficiently distinctive to constitute stratigraphic marker horizons in the Muddy Creek and equivalent formations. Derivation from the southwestern Nevada volcanic field, active 16 to 6 m.y., is highly likely for some of the tephra. The K-Ar results suggest substantial parts of the Muddy Creek Formation and equivalent basin-fill are 6 to 12 m.y., indicating basin- range faulting began prior to 12 m.y. Little tectonic deformation or physiographic change has occurred in the past 6 m.y.
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Subjectsilicic tephra layers
K-Ar age determinations
stratigraphic marker horizons