98-5 Ichthyolith Evidence for Depth-Stratified Ecological Stress Across Late Triassic Ocean Anoxic and Acidification Events in Eastern Panthalassa

Session: Linking Biodiversity Loss to Environmental Stressors Through Integrated Approaches

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Vertebrates are critical components of marine ecosystems, yet their fossil record is often fragmented due to selective preservation, complicating efforts to resolve diversity patterns at high stratigraphic resolution. Microscopic ichthyoliths—sand- and silt-sized vertebrate remains—offer a promising proxy for tracking vertebrate diversity and ecological shifts, particularly during episodes of environmental stress. This study examines ichthyolith assemblages across two major Late Triassic events: the ocean anoxic event at the Norian–Rhaetian boundary and the ocean acidification event spanning the Triassic–Jurassic boundary. Samples from marine carbonates in the New York Canyon area (west-central Nevada, U.S.A.), representing platform environments across both intervals, were processed using heavy liquid separation of buffered acid residues. These ichthyolith data are integrated with sedimentological observations, macrofossil invertebrate assemblages, and carbon and strontium isotope records.

Ichthyolith samples indicate a marked decline in marine vertebrate diversity, abundance, and ecological breadth across the Norian–Rhaetian boundary, paralleling negative carbon and strontium isotope excursions and reductions in shelly invertebrate diversity. Tooth morphologies suggest a significant loss of durophagous and generalist feeders, with piscivory and filter-feeding dominating the Rhaetian ichthyolith record. This dietary shift reflects a faunal composition increasingly reliant on open-water niches, likely tied to comparatively oxic conditions in the upper water column. These patterns underscore the vulnerability of benthic and near-benthic vertebrates to oxygenation changes and demonstrate the high utility of ichthyoliths in reconstructing paleoecological dynamics at fine temporal scales.

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

doi: 10.1130/abs/2025AM-10539

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