Isotopic chemostratigraphy across the Early–Middle Frasnian transition (Late Devonian) on the South Polish carbonate shelf: A reference for the global punctata Event

摘要: Abstract The coupled high-resolution carbon isotope data from whole-rock limestone and organic matter samples of the transitans (Early Frasnian), punctata earliest hassi Zones (Middle Frasnian) South Polish carbonate shelf successions reveal presence a large, multi-part δ 13 C excursion, one largest known cycle disturbance Devonian period. This Early–Middle Frasnian (E–MF) perturbation consists two positive excursions (a minor event I major III) negative shifts (events II IV). up to 5‰, begins near E–MF boundary onset Middlesex transgressive–anoxic event. latter broader-scale correlates with worldwide Event documented across eastern western Laurussia as well northern Gondwana. large magnitude Isotopic Event, paired negligible biotic effects, is similar Silurian biogeochemical perturbations but contrasts markedly younger Kellwasser Events. distinctive protracted (about 1 Ma) variations may be only partly explained by escalated sea water exchange between epeiric seas anoxic open ocean during successive transgressive pulses. Very high plateau values correspond 87 Sr/ 86 Sr shift, elevated clastic input proxies magnetic susceptibility, suggesting altogether that delivery tectonically-promoted land-derived nutrients marine basins was key factor stimulating perturbation. Extreme increases in primary productivity enhanced burial restricted deeper basinal settings would promote gradual drawdown surface-water atmospheric p CO 2 , consequently climatic cooling 5 °C, indicated 18 O phosphate record.