68-6 Using conodont strontium isotopes (87Sr/86Sr) to calibrate bulk carbonate carbon (δ13C) and 87Sr/86Sr trends: refining age estimates of marine Permian-Triassic Boundary sections in the Great Basin region, western USA

Session: Climate Transitions in the Paleozoic (Posters)

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Abstract:

The Permian–Triassic interval has been the focus of numerous studies aimed addressing a range of biostratigraphic questions within a temporal framework. It was thought that complete stratigraphic successions spanning the Permian-Triassic Boundary (PTB) were rarely preserved, but advances in stratigraphic methods provide reliable methods to identify marine PTB sections, even when diagnostic fossils are scarce.  In addition, it can be difficult to demonstrate whether some sections represent continuous deposition when independent radiometric ages are not available. Due to poor biostratigraphic control, marine successions spanning the PTB have considered absent from the Great Basin region (western USA), and it is possible that ~10 Myr of geologic time is missing between the Upper Permian Gerster Formation and overlying Lower Triassic Thaynes Formation. Although recent chemostratigraphic work has improved age estimates across this stratigraphic interval, questions remain whether some geochemical data faithfully record secular trends in seawater without additional independent analysis.

In this study we measured ⁸⁷Sr/⁸⁶Sr isotopes from seven conodonts recovered from the Thaynes Fm (Smithian-Spathian; Lower Triassic) that were previously collected from sections at Spruce Mountain (NV) and the Confusion Range (UT). Paired ⁸⁷Sr/⁸⁶Sr values measured from conodonts and bulk carbonates differ by <0.00001 (avg. 0.000011, n=5). Previous work shows that conodonts can preserve seawater ⁸⁷Sr/⁸⁶Sr values when bulk rock Sr concentrations are high (>300 ppm Sr), or when conodont alteration indices are low (CAI ≤2). Conodonts from the Thaynes Fm have CAI values <2, suggesting that similar strontium isotopic values reported from conodont and bulk carbonate samples collected from these sections may faithfully record a seawater ⁸⁷Sr/⁸⁶Sr trend. Comparison of 113 ⁸⁷Sr/⁸⁶Sr values and 115 δ¹³C values to published data sets calibrated to the 2020 Geologic Time Scale suggests that the duration of time missing at the Permian-Triassic boundary between the Gerster and Thaynes fms may be <1 Myr. This revision suggests that the Permian–Triassic succession in the Great Basin region may be more complete than previously thought and worthy of additional paleontological, sedimentologic, and geochemical work aimed at characterizing environmental and climatic conditions during the extinction and recovery interval on the western Pangaean margin. Future work will include additional geochemical analysis to elucidate the plausible driver(s) of the rapid increase in ⁸⁷Sr/⁸⁶Sr values during the early Triassic.

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

doi: 10.1130/abs/2025AM-9791

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