138 The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms

The Cretaceous-Paleogene boundary interval witnessed extreme geological events: the Chicxulub impact and Deccan Traps volcanism, and a biological catastrophe. New proxy-records, coupled with numerical modelling, unravel the mechanisms driving the environmental change and mass extinction.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 304A

Integrated Astrochronologic-Geochronologic Modeling of the Cretaceous-Paleogene Boundary with Globally Distributed Terrestrial and Marine Records

Paper number: 138-15
Program: Technical Sessions
Time: 5:15 PM – 5:30 PM

Authors

Abstract

The Cretaceous-Paleogene Boundary (KPB; 66 Ma) represents one of the most dramatic and sudden changes in the history of life on Earth. As such, the KPB is exceptionally well described and documented, with multitudes of analyses having been performed to characterize and identify its stratigraphic position and precise age in terrestrial and marine sections worldwide.

Among these sections, there are a few uniquely important cyclostratigraphic records for reconstruction of Solar System dynamics. A ~60 Ma “chaos boundary” has been established by astronomical modeling to indicate that the planetary orbits are inherently chaotic. The consequence of this boundary is that from ~60 Ma backward in time, the usual data-model role is reversed: geological data must inform astronomical models.

Prior to 60 Ma, the first well-defined geologic time point is the KPB, which has an estimated age of 66.038±0.025 Ma to 66.021±0.024/0.039/0.081 Ma. Cyclostratigraphy that includes the KPB can be used to steer astronomical modeling toward best-fit planetary orbital parameters and Earth axial precession rate. Recent work has extended such geologically informed astronomical models from 50 Ma to the KPB with data from ODP Site 1262, Walvis Ridge, and from the KPB to 70 Ma with data from Zumaia, Spain. The results show strong matches between specific models and the data, the latter, however, are not precisely anchored to time.

We present comparisons between astronomical models and cyclostratigraphy from marine ODP Site 1262 and the continental Kiowa core, Colorado, USA for the C29r magnetochron. The Kiowa core consists of fluvial sedimentary cycles and magnetic reversal stratigraphy constrained by high-precision U-Pb geochronology. Kiowa chronostratigraphy is formulated into a Bayesian time scale, supplemented with astrochronology from Kiowa and Site 1262. Both sites have eccentricity-modulated precession cycles that end with a minimum at the KPB. The timing of the final precession cycle leading into the KPB determines the best astronomical/precession model for the KPB time interval.

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

doi: 10.1130/abs/2025AM-414277

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