7 Undergraduate Research, Part I (Posters)

Session showcases undergraduate research. Topics include geoscience-related fields (e.g., resources, hydrology, oceanography, climate, environmental science, geospatial, informatics, health, policy, & education). Undergraduate student/s must be the lead author/s presenters with faculty mentor/s as co-author/s. This session welcomes both poster and oral presentation submissions.

Monday, 9 March 2026
9:00 AM - 5:00 PM
RCC, Lower Level Hall

Chronostratigraphy of Volcanic Ash Beds in the Ash Hollow Formation, Ogallala Group, Panhandle Region of Nebraska, USA

Paper number: 7-35
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

The Miocene Ash Hollow Formation (AHF) is a complex sequence of alluvial deposits in the upper Ogallala Group in Nebraska.  The Ogallala Group consists of terrigenous sediments shed eastward from the Rocky Mountains onto the Great Plains as a series of clastic wedges during the Miocene from approximately 18 Ma to 5.5 Ma. The cut and fill geometry and extreme heterogeneity of the AHF and the Ogallala Group in general complicate local and regional geochronology and correlation of these units. In the southern panhandle of Nebraska, more than 100 separate volcanic ash beds are exposed in the AHF along the North and South Platte river valleys.  Most are less than 2m thick, but up to 6m thick beds are reported. The ash is mostly silvery gray and unaltered, though some are cemented in whole or part by calcium carbonate and form resistant ledges. Most of these ashes were likely produced by volcanic eruptions emanating from the Snake River Plain-Yellowstone hotspot track in Idaho and coincident with AHF deposition. Six vertical sections, each containing 3–5 superposed ash beds, were examined along the North Platte River escarpment for a total of 23 individual ash samples. At least 100 zircons will be collected for U-Pb dating from each sample to estimate depositional ages and provenance of sediment source areas. To date, samples from one locality (BG) have produced 3 youngest single grain dates: 10.2 ± 0.6 Ma, 10.6 ± 0.5 Ma, and 12.3 ± 0.5 Ma in stratigraphically descending order. These dates correspond to a series of Plinian eruptions from the Bruneau-Jarbidge volcanic field that was active from 12.7 to 10.5 Ma. Determination of absolute ages and provenance of the AHF ashes is ongoing, with the intent of establishing a regional chronostratigraphic framework of the Nebraska panhandle region and beyond. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411889

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