T158 Lakes of the World through Time and Space I: Archives of Climate Variability, Paleoenvironment, Geohazards, and Economic Resources

Tuesday, 17 October 2023
8:00 AM - 12:00 PM
334

BAYESIAN INTEGRATION OF ASTROCHRONOLOGY AND URANIUM LEAD GEOCHRONOLOGY: A CASE STUDY OF THE EOCENE GREEN RIVER FORMATION

Paper number: T158-4
Program: Technical Sessions
Time: 8:35 AM – 8:50 AM

Authors

Abstract

The Green River Formation (GRF) preserves an exceptional archive of lacustrine and alluvial sediments that offer an invaluable record of climate during the Early Eocene Climatic Optimum (EECO; ~53 - 50 Ma), a period of high atmospheric CO2 concentrations and the warmest epoch of the Cenozoic. A high precision age model that ties basin stratigraphy to numerical time is required to fully leverage this record of continental paleoclimate and link it to global paleoclimate records. Recent high-precision U-Pb zircon and 40Ar/39Ar sanidine geochronology have produced a radioisotopically calibrated age model for the Wilkins Peak Member of the GRF, and high-resolution X-ray fluorescence (XRF) scans of the GRF in a basin depocenter core reveal Milankovitch-scale rhythms in sediment accumulation. Individual major elements express these rhythms to varying degrees within the stratigraphy, reflecting the interplay between lacustrine marlstone, lacustrine evaporite and alluvial siliciclastic deposition. For example, calcium and silicon XRF data show different sensitivities to low-frequency astronomical forcing in the upper and lower intervals of the core, respectively. Given the opportunities provided by this GRF data set, we combine multiple XRF element scans, and a set of high precision U-Pb ages for interbedded tuffs to develop a new age-depth model for the Solvay core. We use a novel Bayesian method (astroBayes) to jointly invert the multi-element XRF records and radioisotopic dates using a set of target Eocene astronomical frequencies to generate an age-depth model for the Solvay core. Our results reveal fluctuations in sediment accumulation rate throughout the section, including a shift to slower rates at ~51.1 Ma which is coincident with the cessation of uplift along the Uinta fault system. Finally, we use the new age model for the GRF to test the phase of eccentricity forcing on regional hydrology and lowstand flooding surface formation during lake evolution.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-393427

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