The 5th International Conference of Geobiology

Marine red beds (MRBs) are important sedimentary archives for reconstructing paleoceanography. Numerous hypotheses have been proposed to account for the formation of MRBs, but a general consensus on the long-term variations in MRBs over the Phanerozoic is lacking. Here, we compiled a geo-dataset comprising the frequency of calcareous MRBs (Ca-MRBs) occurrence throughout the Phanerozoic coupled with redox conditions (δ²³⁸U), temperature changes, weathering rates (⁸⁷Sr/⁸⁶Sr) and carbon isotopic compositions (δ¹³C) to investigate the factors affecting Ca-MRB genesis. The results show that the abundance of Ca-MRBs varied appreciably over Phanerozoic time, with seven peaks occurring at the Middle Ordovician, Early Devonian, Late Devonian, Early Triassic, Early- and Late Jurassic, and middle to late Cretaceous. All the Ca-MRB peaks are closely related to oceanic anoxia during greenhouse phases, high weathering rates and large carbon isotope perturbations probably triggered by intense volcanism. It is thus suggested that oceanic anoxia in the context of global warming might have a profound impact on Ca-MRB genesis by controlling the global seawater ferrous Fe inventory.
 

marine red bed,oceanic anoxia,global warming,weathering