TESTING THE VIABILITY OF CONODONTS AS A U-PB GEOCHRONOMETER USING KANSAS CORE AND OUTCROP SAMPLES

Geochronology is a powerful geologic tool with wide scientific and economic application. The vast majority of petroleum deposits are found in sedimentary rocks, ranging from limestones and shales to sandstones. Though sandstones account for only fifteen percent of all sedimentary rocks, nearly all geochronometers for sedimentary rocks are focused on minerals from sandstones (e.g. U-Pb on zircon, monazite, rutile, apatite, etc.). Consequently, most sedimentary deposits (i.e. limestones and shales) cannot be dated by traditional geochronology due to limited influx of clastic grains into most carbonate and basin depositional systems. Conodont fossils (or “elements”) are an appealing U-Pb geochronometer candidate for carbonates and shales for several reasons: they are ubiquitous in carbonates and shales from the Cambrian through Triassic, they absorb uranium post mortem, and their thermal exposure can be estimated from a series of color changes that the element undergoes (color alteration index or “CAI”). Very little work has been done in the past to test their viability for dating. The objective of this research is to test whether conodont elements can be used as a viable and accurate U-Pb geochronometer. Conodont elements of low CAI were removed from eastern Kansas Pennsylvanian cyclothem strata. Both carbonates and shales were sampled from core and outcrop. The conodonts will be analyzed via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to determine elemental distributions using depth profiling. The calculated dates will be compared to well-constrained biostratigraphic and zircon age data for their corresponding formations. Dates that match known data would suggest that conodonts are a viable geochronometer, and that rare earth elemental (REE) uptake is instantaneous (as interpreted by current conodont geochemical studies). Dates that do not match may suggest that either protracted diagenetic elemental uptake or open system behavior has occurred, contrary to current assumptions. Additionally, past work that has assumed closed system behavior and instantaneous REE uptake would need to be reevaluated. If successful, this new method of U-Pb dating has the potential to be widely applied to several areas of the geological sciences.