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• Five high-precision U-Pb zircon ages in Langsettian-Bolsovian, Ruhr Basin, Germany. • No persistent 100/400-kyr pace of cyclothems; transient 1.2-Myr eccentricity. • Tropical climate decoupled from glacioeustasy on astronomical time scales. Sea-level changes recorded in coal-bearing paralic sequences or cyclothems provide a rare insight into the timing of ice sheet waxing and waning during the Late Paleozoic Ice Age (LPIA), ∼340 and 255 Ma. An astronomical origin of these cyclothems is broadly accepted, but a robust interpretation of periodicities has been challenging due to non-stationary sedimentation rates and uncertain age constraints. Here we present high-precision U-Pb dates of five Lower-Middle Pennsylvanian tonsteins from one of the key areas of coal-bearing paralic sedimentation – the Ruhr Basin, Germany. The new data lead to a substantial (up to 1.6 Myr) revision of geochronologic boundaries relative to the Geological Time Scale 2020: the onset of the Langsettian (Westphalian) is updated to 318.96 (−0.16/+0.20) Ma, onset of the Duckmantian to 316.28 (−0.43/+0.40) Ma and onset of the Bolsovian to 313.69 (−0.11/+0.12) Ma; total uncertainties are −0.40/+0.47, −0.49/+0.44 and −0.19/+0.37 Myr, respectively. The revised time scale suggests that the periodicities of 100 and 400 kyr, interpreted for Variscan and Appalachian cyclothems in previous studies, are replaced in the Langsettian by longer term patterns. A ∼ 1.2-Myr recurrence of marine transgressions is assigned here to a transient modulation of orbital eccentricity (secular frequencies g 4 − g 3 ) that distinguishes the study interval from any Cenozoic glaciations (which are superimposed upon a ∼ 2.4-Myr pace of g 4 − g 3 ). Gondwanan ice sheets were therefore subject to a distinct insolation context and their response to astronomical cycles evolved on multiple time scales. In contrast, a relatively simple periodicity in the ∼ 100-kyr band is found in coeval terrestrial strata in the tropics suggesting that the low-latitude climate was decoupled from the pace of high-latitude climatic variations. The geochronology established here will help to evaluate the non-linear record of insolation signals and climate feedbacks during LPIA.
Laurin et al. (Sat,) studied this question.