T113 EARTHTIMEs and EarthRates: Exploring the Tempo and Mode of Earth-System Processes and Evolution (Posters)

Monday, 5 November 2018
9:00 AM - 6:30 PM
Halls J-K

ASSESSING URANIUM HETEROGENEITY AND U-PB GEOCHRONOLOGY VIABILITY IN CONODONT ELEMENTS USING KANSAS OUTCROP SAMPLES

Paper number: T113-2
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

U-Pb geochronology is a powerful geologic tool with wide scientific and economic applications. However, obtaining robust depositional ages using the U-Pb system remains a challenge, particularly for carbonates and shales that commonly lack datable material. Conodonts, tooth-like microfossils (or “elements”), are appealing candidates for U-Pb geochronology because they are ubiquitous in carbonates and shales from the Cambrian-Triassic, they are widely applied as a biostratigraphic and thermal maturity tool, and they are syndepositional fossils that could yield absolute ages in both carbonates and shales. Conodonts have been and continue to be collected routinely, so the application of such a method could be a profound improvement. Little work has been done to test their viability for dating, and their use in geochemical applications has been hindered by their elemental heterogeneity and small size (some < 40 microns – the diameter of a typical LA-ICPMS spot). The objective of this research is to test whether conodont elements can be used as a viable and accurate U-Pb geochronometer, as well as to assess U heterogeneity within the conodont element. Conodont elements of low CAI and large size (>150 microns) were removed from eastern Kansas cyclothem outcrop samples. The conodonts will be analyzed via laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) to determine elemental distributions using depth profiling and grain mapping. The calculated dates will be compared to well-constrained biostratigraphic and geochronologic age data for corresponding formations. Dates that match known ages would suggest that conodonts are a viable geochronometer, and elemental uptake is instantaneous, as interpreted by current geochemical studies and models. Dates that do not match may indicate that either protracted diagenetic elemental uptake or open system behavior has occurred, contrary to current assumptions. Finally, this study will assess whether geochemical heterogeneity of different conodont tissues impacts U uptake and mobility within a single conodont element, and will contribute to a greater understanding of the conodont U-Pb dating method and accuracy and reliability of dates. If successful, this new U-Pb geochronometer has the potential for broad application in the geosciences.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-323364

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