Major and rare earth elements geochemistry of the Cretaceous ocean red beds: Implications for the terrestrial silicate weathering and marine sedimentary environment

During the Cretaceous, global ocean redox state fluctuated dramatically, resulting in the deposition of black shales and Cretaceous Ocean Red Beds (CORB). Herein, the chemical weathering intensity indexes calculated by major elements and the geochemical behaviors of rare earth elements (REE) were investigated in the late CORBs and the underlying shales deposited in southern Tibet and the Northern Atlantic. The original deposition environment of CORBs from both sites showed intensified chemical weathering extent under relatively warm and humid conditions, despite an overall global cooling trend during the late Cretaceous. The large variations of Ce anomalies (0.65–1.46) and LREE/HREE ratios (0.60–0.94) normalized by Post-Archean Australian Shale (PAAS) in the shale layers were the results of Fe mineral transformation, and the generally positive PAAS-normalized Eu anomalies (0.93–1.50) were likely controlled by the material sources. The CORBs displayed higher contents of total REE and Fe₂O₃ than the underlying shales, and had a similar covariant relationship with the chemical weathering intensity. This study suggested that a large amount of terrigenous iron was transported into the oxic Cretaceous Ocean by continental weathering, and REE fractionations were potential indicators to reflect sedimentary location and relatively sedimentation rate of ocean red beds formation across the Ediacaran and Phanerozoic.