Harmonizing Late Devonian Cyclostratigraphy Across Europe, North America, and China

Establishing a globally consistent Late Devonian timescale requires the harmonization of cyclostratigraphic records across paleogeographically distinct basins. However, differences in depositional environment, sedimentation rate, and stratigraphic completeness complicate the alignment of orbitally forced signals at high temporal resolution. This contribution evaluates the extent to which cyclostratigraphic patterns can be correlated across Europe, North America, and China, using key Late Devonian intervals including the Kellwasser Crisis, the Annulata and Dasberg events, and the Hangenberg Crisis. Cyclostratigraphic studies from European mixed carbonate–siliciclastic shelf successions in the Rhenish Massif provide high-resolution records of precession- and eccentricity-paced variability, forming the basis for floating astrochronologies that resolve multiple astrochronozones across the Frasnian–Famennian transition and the Famennian stage. Equivalent cyclic patterns are increasingly recognized in North American siliciclastic systems, such as the Appalachian Basin, where astronomical forcing is preserved despite fundamentally different depositional environments. Chinese records, encompassing both carbonate-dominated and mixed systems, further extend this framework, although published duration estimates and tuning approaches show considerable variability. Across these regions, first-order agreement is emerging in the total duration of key Late Devonian intervals. For example, the Kellwasser Crisis consistently spans over three consecutive 405-kyr eccentricity cycles (i.e., astrochronozones), and different astrochronological frameworks suggest a pacing of Famennian global carbon-cycle perturbations by the very-long ~2.4-Myr eccentricity cycle. However, higher-resolution analyses reveal substantial discrepancies in the internal expression of these intervals. Organic-rich horizons and lithological markers associated with events such as the Kellwasser, Annulata, Dasberg, and Hangenberg crises vary markedly in thickness, continuity, and number of cycles represented, reflecting strong environmental filtering of the orbital signal. New cyclostratigraphic results from the Walnut Creek section (Appalachian Basin, USA) illustrate this challenge. While the total duration of the Kellwasser interval aligns with European and Chinese estimates, its internal structure is expressed as multiple precession-paced black shale layers rather than as single, laterally continuous beds. These observations demonstrate that harmonization of Late Devonian cyclostratigraphy is achievable at the scale of orbitally modulated bundles (e.g., eccentricity-paced groupings), but becomes increasingly uncertain at finer scales. Lithostratigraphic markers associated with global events may represent composite or diachronous features when examined at precessional resolution, even if their broader placement within the astrochronological framework is consistent. We argue that a robust global timescale must be built on the integration of cyclostratigraphic patterns across multiple basins, rather than on the direct correlation of individual beds or event layers. Harmonizing these records requires explicit consideration of how astronomical forcing is recorded differently in carbonate versus siliciclastic-dominated systems, as well as in deep versus shallow to marginal depositional environments. Careful evaluation of the reproducibility of high-resolution signals across a wide range of boundary conditions provides a pathway toward a more consistent and testable Late Devonian astrochronology.