37-20 Paleoxygenation Trends Reveal Environmental Conditions Caused Delays in Recovery: Evaluating the Virgin Limestone following the Permian-Triassic Mass Extinction

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

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The Permian-Triassic mass extinction was the most devastating extinction in the history of the Earth. Biotic recovery from the Permian-Triassic mass extinction was sporadic across the Early Triassic, with diversification beginning in earnest only in the early Middle Triassic. Harsh environmental conditions, likely associated with the cause of mass extinction, persisted across the Early Triassic by way of global hothouse climates and anoxic conditions in the oceans. These environmental stresses narrowed the area of habitable environments and likely reset recovery multiple times. This study focuses on the Virgin Limestone at Lost Cabin Springs, NV locality, where interbedded carbonate and siliciclastic beds were deposited from the Smithian (middle Early Triassic) until the Anisian (early Middle Triassic) in a deep outer carbonate shelf environment. The Virgin Limestone offers a unique setting whereby environmental conditions can be determined by examination of shale interbeds, and the degree of biotic recovery can be estimated from the fossils and trace fossil content of the limestone interbeds. A total of 47 shale samples were subjected to trace element analysis to determine paleoxygenation via U, V, and Mo contents, while biotic recovery in intervening beds was estimated using ichnofabric indices. Initial results suggest that suboxic to anoxic conditions were often associated with deposition of the shale interbeds, and this biotic stress is reflected in ichnofabric indices, supporting the hypothesis that environmental conditions determined the timing and shape of recovery. Further study will refine recovery estimates and separate local environmental controls from longer-term recovery trends.

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