Astronomical calibration of the middle Cambrian in Baltica: Global carbon cycle synchronization and climate dynamics

The Alum Shale Formation of Baltica preserves one of the most continuous and fossil-rich records of the Cambrian, making it a key sedimentary archive for refining global chronostratigraphy, reconstructing carbon cycle perturbations, and assessing astronomical forcing on high-latitude systems during an early Palaeozoic greenhouse world. A high-resolution cyclostratigraphic and multiproxy study of the middle Cambrian succession from the Albjära-1 drill core (southern Sweden) establishes a 173 kyr obliquity-tuned astronomical time scale (ATS), anchored by a high-precision U–Pb age. Integration of this time scale with new carbon isotope data and refined biostratigraphy positioned the Albjära-1 core as a global reference record. This framework provides the first numerically constrained ages and durations for the Drumian Carbon Isotope Excursion (DICE), enabling worldwide synchronization of biostratigraphy and carbon cycle events. Coupled elemental geochemistry and time calibration reveal that obliquity- and eccentricity-driven climate oscillations modulated sea-level and dust fluxes governing middle Cambrian outer-shelf sedimentation at high-latitudes. These results highlight the sensitivity of early Paleozoic greenhouse Earth systems to astronomical forcing.