37-15 A Trail through Time: Retracing the Journey of the Ogallala Formation's Rhyolitic Gravels from Volcano to Sediment in the Southern High Plains of Texas

Session: Geoscience Research Poster Showcase by 2YC and 4YCU Undergraduate Students

Presenting Author:

Authors:

Abstract:

The Ogallala formation serves as a vital resource, containing one of the world’s largest aquifers used for approximately 40% of irrigation for U.S. agriculture. Despite the aquifer’s heavy usage, much of the formation’s origin and transport pathways remain a mystery. 

Several authors suggest Miocene-Pliocene paleodrainage networks responsible for Ogallala sediment in the Southern High Plains, which can be narrowed into four main paleodrainage hypotheses: a unified single source area, a 3-lobe fan configuration, a coalescing bajada (multiple sources), and a North-flowing Pecos river drainage. My research aims to build on this past research, by pinpointing the source(s) of Ogallala rhyolitic gravels in the Southern High Plains to determine where sediment travelled. Determining sediment provenance allows reconstruction of the ancient river systems that distributed material across the region, revealing how drainage patterns, sediment routing, and potentially climate conditions evolved during the Miocene epoch. To do so, I collect samples from within the Ogallala formation and potential sources and, using petrographic analysis, I compare the composition and textural patterns of site and source to see if they match. 

I started this research with petrographic analysis of rhyolitic gravels from the Ogallala formation in Texas, New Mexico and Colorado, which I referred to in my abstract and poster presentation at the ‘25 GeoConnects conference. This research noted obvious visual features with diagnostic potential, including flow banding, lithics, xenocrysts, and/or multimineralic glomerocrysts, and evidence of possible magma mixing in the form of skeletal quartz and distinct plagioclase rims around alkali-feldspar. Several samples included trace mafic minerals, including biotite and pyroxene. Through these preliminary observations, I observed five rhyolite populations present in the Ogallala formation. These observations helped guide where to sample for potential sources.

After completing this first stage of my research, I switched from a qualitative approach to quantitative, and completed point counts to determine QAP percentages. Additionally, I sampled rhyolite from potential source volcanoes in Colorado and New Mexico. This poster delves into the quartz, alkali-feldspar, and plagioclase (QAP) percentages mapped, observations from petrographic analysis of the new potential source samples, and which hypotheses my research supports or refutes.

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