135-12 Multi-proxy investigation of the paleobotanical community at Waco Mammoth National Monument (Waco, Texas, USA) and re-evaluation of paleoclimatic interpretations

Session: Science and Stewardship of U.S. National Park Service Paleontological Resources

Presenting Author:

Authors:

Abstract:

Waco Mammoth National Monument (WMNM) is a Late Pleistocene paleontological locality containing the remains of at least 29 Columbian mammoths (Mammuthus columbi) along with isolated specimens representing approximately 20 additional vertebrate taxa. Within the WMNM Dig Shelter, vertebrate remains have been discovered in at least three stratigraphic units situated within the second alluvial terrace between the Brazos and Bosque Rivers. Sedimentological analyses indicate the deposits are dominated by clay-silt fractions with interspersed fine sand (< 158 μm), consistent with deposition in a distal flood plain or other low-energy fluvial system. Weathering indices and paleoclimatic estimates suggest stable environmental conditions that were cooler and drier than present day. Precipitation values of 470-647 mm are indicative of a semi-arid to sub-humid climate during the transition from Marine Isotope Stage (MIS)-5 to MIS-4.

Although ongoing research has focused on the vertebrate assemblage and sedimentary context, the composition and structure of the paleobotanical community remains largely unexplored. Columbian mammoths, which dominate the faunal assemblages, were primarily grazers, and isotopic data indicate diets comprised of 70-80% C₄ grasses. However, limited information is currently available regarding the broader plant community. To address this gap and further refine reconstructions of paleovegetation and paleoclimate at WMNM, sediment samples were studied for phytolith assemblage, lipid molecular fossils (biomarkers), and stable carbon isotopes. Eight samples, from three successive stratigraphic units, were collected from oriented sediment blocks removed from the WMNM Dig Shelter. Phytoliths were concentrated using dense liquid separation, mounted on glass slides, and morphotypes were identified and counted via microscopy. Biomarker lipids were extracted by pressurized solvents and identified by gas chromatography/mass spectrometry. Phytolith morphotypes, biomarkers, and isotopes will be reconciled with existing bulk geochemical evidence from the paleosol present to reconstruct local vegetation and further contextualize Late Pleistocene ecological conditions of the Waco Mammoth National Monument.

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

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