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 for the Cambrian Period. Thus, the Alum Shale is a key sedimentary archive for refining global chronostratigraphy, reconstructing carbon cycle perturbations, and assessing astronomical forcing of high-latitude systems during an early Palaeozoic greenhouse world. Here we present a high-resolution cyclostratigraphic and multiproxy study of the middle Cambrian succession from the Albjära-1 drill core (southern Sweden), anchored by a high-precision U–Pb age. Integration of our astronomical time scale with carbon isotope data and refined biostratigraphy places the Albjära-1 core as a global reference record. This framework provides 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 orbital eccentricity-driven climate oscillations modulated sea-level and dust fluxes, highlighting the sensitivity of Earth’s early Paleozoic greenhouse systems to astronomical forcing.