Correlation of widespread Holocene and Pleistocene tephra layers from Newberry Volcano, Oregon, USA, using glass compositions and numerical analysis

During the last ca. 500,000 years, Newberry Volcano in Oregon has produced at least 50 rhyolitic and dacitic tephras ranging from locally distributed pumice rings and cones to ignimbrites to widely dispersed plinian fallout deposits. To date, 13 tephra units with ages ranging from about 1525 14C years BP to >200,000 years BP have been traced to 20 sites across five western states of the USA. Correlations have been established by applying similarity coefficient and discriminant function analysis to major element compositions of tephra-derived glasses determined by electron microprobe analysis. Newberry Pumice correlates to four locations in Oregon and Idaho. East Lake or Central Pumice Cone tephra correlates to two locations in Oregon. Paulina Creek, Ice Quarry, 9912D, 9920C, 984F, 984G5, 9917C, and 9881C tephras correlate to ash beds at Summer Lake, Oregon. Paulina Creek tephra also correlates to several locations in northern California and is equivalent to the Olema ash bed. Tephra 9917C is very similar to tephras K and D at Pringle Falls, Oregon. Lava Pass or a related tephra correlates to an unnamed tephra in the Bonneville basin, Utah.