57 Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part II

This session welcomes submissions related to applications of geochronology (e.g., U-Pb, 40Ar/39Ar) in stratigraphic research, including topics such as eruption and maximum depositional age estimation, provenance analysis, numerical modeling of geochronological data, and multi-disciplinary chronostratigraphic characterization.

Sunday, 19 October 2025
1:30 PM - 5:30 PM
HBGCC, 304C

Building Bayesian Bridges Between Anchored and Floating Timescales

Paper number: 57-5
Program: Technical Sessions
Time: 2:40 PM – 3:00 PM

Authors

Abstract

Relating stratigraphic position to time is critical  for interpreting the timing and rate of geologic, biologic and climatic processes throughout deep-time. Astrochronology, which uses  quasi-periodic solar system motions recorded in strata to infer the passage of time, has become an invaluable technique for generating deep-time floating age-depth models for rock records. However, anchoring these models in numerical time requires stratigraphic levels of known age. Radioisotope geochronology (U-Pb, 40Ar/39Ar) provides these anchoring points, albeit usually randomly distributed throughout stratigraphy. Integrating these two chronometers can produce age-depth models that capture the strengths and minimize the weaknesses of both systems, reducing model uncertainties and allowing high-resolution examination of Earth-system processes in deep time. However, age-depth models are sensitive to the types and quality of the input data, and ambiguities in either the astrochronologic records or radioisotope dates can lead to models that do not accurately reflect the true distribution of time in the rock record. 

astroBayes is a Bayesian age-depth model algorithm that probabilistically inverts astrochronologic and radioisotopic data, while incorporating prior information about superposition, sedimentation rate, and the presence or absence of major hiatuses. We demonstrate the application of astroBayes to three cyclostratigraphic datasets that include high-quality radioisotopic constraints. First we present the evaluation of a greyscale record from the Bridge Creek Limestone (central Colorado) that contains the Cenomanian-Turonian GSSP (93.98 ±0.10 Ma). Second, we develop a new age-depth model for the Ocean Drilling Program Site 1000 core, using previously published δ13C and δ18O values and U-Pb ages. We use this model to estimate the timing of the onset of the Miocene Climatic Optimum (17.13±0.05 Ma). Third, we use oil-yield and XRF core-scanning data from the Green River Formation to test the phasing of astronomical forcing on terrestrial hydroclimate during the Eocene Climatic Optimum (~52 - 50 Ma). These datasets contain different types of astrochronologic proxy data (greyscale, stable isotopes, oil yield & XRF) with different signal-to-noise ratios, astronomical periods, and sampling resolutions. The resulting age-depth models capture subtle changes in sedimentation rate and major hiatuses, suggesting that the astroBayes algorithm is robust, and is able to dynamically integrate multiple types of astrochronologic data and radioisotopic dates.

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

doi: 10.1130/abs/2025AM-412593

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.