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The First 40ar/39ar Ages And Tephrochronologic Framework For The Jurassic Entrada Sandstone In Central Utah, Toby S. Dossett
The First 40ar/39ar Ages And Tephrochronologic Framework For The Jurassic Entrada Sandstone In Central Utah, Toby S. Dossett
Theses and Dissertations
The first 40Ar/39Ar ages of the Middle Jurassic Entrada Sandstone were derived from tephra beds found in central Utah. Eight air fall ash beds in the Entrada Sandstone, with 40Ar/39Ar biotite ages ranging from 168.1 ± 0.2 to 160.8 ± 0.2 Ma, help to establish the age of Entrada deposition. They were also used to create the first chronostratigraphic divisions within the mudstone-dominated Entrada Sandstone. Statistical cluster analysis of chemical data from electron microprobe analyses of phenocrysts were used as a second line of evidence to test absolute age and stratigraphic correlations. The first direct correlations of two distinct air …