186-5 From Integrated Geochronology to Earth-System Evolution: Refining the Cretaceous Time Scale and Paleoceanographic History

Abstract:

Since our collaboration began in 2008—building from the pioneering synergy between Bill Cobban and John Obradovich—advances in ⁴⁰Ar/³⁹Ar and U-Pb geochronology, astrochronology, biostratigraphy, and chemostratigraphy have transformed understanding of the chronology and paleoceanographic evolution of the Cretaceous Period. Our overarching aim has been to reduce temporal uncertainty sufficiently to resolve the sequence and rates of Earth-system processes during the Cretaceous. Beginning with the first direct intercalibration of radioisotopic and astronomical time scales across the Cenomanian-Turonian boundary in the Western Interior Basin, this research established a chronologic framework that integrated independent geochronometers while substantially reducing uncertainties in numerical ages. Subsequent expansion of this framework through the Turonian-Campanian interval refined the ages of Cretaceous stage boundaries and demonstrated that integrated radioisotopic, astrochronologic, and biostratigraphic approaches provide the most robust calibration of the geologic time scale. These advances also resolved longstanding discrepancies between ⁴⁰Ar/³⁹Ar and U-Pb chronometers through astronomical calibration of the Fish Canyon sanidine standard.

The resulting temporal framework enabled quantitative investigation of Cretaceous Earth-system processes. High-resolution chronostratigraphy and chemostratigraphy constrained the timing and duration of Oceanic Anoxic Event 2, demonstrated near-continuity of Western Interior Basin reference sections, and established the temporal relationships among volcanic activity, osmium- and carbon-isotope excursions, and environmental change. Extension of high-precision geochronology into the Albian-Cenomanian interval refined correlations among North American, European, and northwest Pacific successions in Japan, culminating in an updated synthesis of the Western Interior Basin and global timescales. Most recently, integrated U-Pb, ⁴⁰Ar/³⁹Ar, carbon-isotope, and osmium-isotope records from Hokkaido, Japan, have provided new constraints on the age of the Albian-Cenomanian boundary and the timing of Oceanic Anoxic Events 1a and 1d, strengthening evidence that large igneous province volcanism exerted a primary influence on multiple Cretaceous carbon-cycle perturbations. Ongoing efforts are expanding this approach to Valanginian through Barremian strata in Japan.

Together, these studies illustrate how progressively improving temporal resolution has shifted Cretaceous research from establishing numerical ages to quantifying the rates, durations, and causal relationships of major paleoceanographic events. The resulting chronostratigraphic framework now provides a foundation for global correlation and for testing hypotheses linking large igneous province volcanism, carbon-cycle perturbations, oceanic anoxia, and biotic change during one of Earth's most dynamic greenhouse intervals.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.