T198 Radiogenic Isotopes as Tracers of Geologic Processes: Dates, Rates, and Proxies (Posters)

Tuesday, 11 October 2022
2:00 PM - 6:00 PM
Exhibit Hall F

DEFINING GEOLOGIC VARIABILITY IN CONODONT 87SR/86SR AND CHRONOSTRATIGRAPHIC IMPLICATIONS

Paper number: T198-14
Program: Technical Sessions
Time: 2:00 PM – 6:00 PM

Authors

  • Julie Griffin Presenting Author
    California State University, Sacramento, Sacramento, CA
  • Isabel Montanez
    University of California, Davis, Davis, CA
  • Justin Glessner
    University of California, Davis, Davis, CA
  • Jitao Chen
    CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing
  • Malte Willmes
    University of California, Santa Cruz, Santa Cruz, CA

Abstract

Conodont microfossils record seawater strontium isotope values (87Sr/86Sr), permitting chemostratigraphic correlation for tectonic and climatic reconstructions of the Paleozoic and early Mesozoic (541–201 Ma). Advances in laser ablation multiple collection inductively coupled plasma mass spectrometry (LA MC-ICP-MS) enable rapid, high resolution 87Sr/86Sr analyses of conodont bioapatite, but require validation by comparison with solution analysis. We compare solution and LA MC-ICP-MS 87Sr/86Sr analyses of Carboniferous-age conodonts. The two analytical methods generally agree for conodonts from the same stratigraphic level. In addition, we find that individual conodonts from the same stratigraphic level exhibit 87Sr/86Sr variability beyond the precision of reference materials. This finding suggests that solution 87Sr/86Sr values determined by dissolving multiple conodonts are homogenizing distinct 87Sr/86Sr signatures of individual conodonts. As such, the precision of these solution measurements does not capture the geologic variability of conodont 87Sr/86Sr within a stratigraphic level. We explore possible reasons for this geologic variability including time averaging, spatial variability in in seawater 87Sr/86Sr, and differential diagenesis. We further calculate what fraction of the geologic variability in conodont strontium isotope values contributes to the uncertainty in age estimations based on correlations to the seawater strontium isotope curve. Conodont 87Sr/86Sr measurements that do not account for geologic variability are at risk of false calibrations with the paleo-seawater 87Sr/86Sr curve, which has implications for the timing of geologic events and reconstructions of paleo-environmental changes.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382463

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