60-53 Following the Volcanic Trail: Petrographic Provenance Analysis of Rhyolitic and Intermediate Clasts in the Ogallala Formation, Southern High Plains, Texas

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

Presenting Author:

Authors:

Abstract:

The Miocene-Pliocene Ogallala gravel deposits serve as a valuable record of paleodrainage networks across the Southern High Plains, preserving clasts that were transported from distant source regions during this critical period of landscape evolution. Petrographic analysis of these gravels can identify distinctive rock types and textures that fingerprint specific source areas, while geochemical analysis—including trace element signatures, isotopic ratios, and mineral chemistry—provides quantitative constraints on provenance and transport pathways. Together, these sediment provenance techniques allow 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.

I conducted provenance analysis on rhyolitic and intermediate fluvial gravels of the Ogallala in the Southern High Plains of Texas and New Mexico to test whether these volcanic clasts derive from a northerly source in New Mexico and/or southern Colorado versus a southerly source in the Trans-Pecos region. Through thin-section petrography, I estimated percentages of quartz, alkali-feldspar, and plagioclase (QAP) compositions to determine the igneous lithotype. I observed trachyte, latite, and rhyolite compositions. Several samples included trace mafic minerals, including biotite and pyroxene. In addition to determining lithotype, I observed distinctive igneous textures and features. I found several samples showcasing flow banding, lithics, xenocrysts, and/or multimineralic glomerocrysts. Other samples show evidence of possible magma mixing in the form of skeletal quartz and distinct plagioclase rims around alkali-feldspar.

Future work will focus on these samples, using electron-probe microanalysis across the feldspar rims and whole-rock trace-element geochemistry. In addition, I will collect and analyze samples of possible source areas, such as the Tuff at Tetilla Peak, New Mexico and/or the Amalia Tuff near Questa, New Mexico for the northerly sources. Alternatively, the rhyolites and intermediate lithotypes could be derived from the Brack Rhyolite in the Trans-Pecos region, indicating a southerly source. By tracing the gravels back to their source areas, the paleodrainage networks present during the Miocene-Pliocene may be elucidated.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9056

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