Upper Cretaceous oceanic red beds (CORBs) in the Tethys: occurrences, lithofacies, age, and environments

A major change in oceanic sedimentation from mid-Cretaceous organic carbon-enriched deep-sea deposits to predominantly Upper Cretaceous oceanic red beds (CORBs), represented mainly by deep-sea red shales and marls, occurred during the Late Cretaceous and early Tertiary in the Tethys. A variety of earth processes such as organic carbon draw-down, tectonic, palaeoceanographic, eustatic and palaeoclimatic changes, or a combination of these could cause such a change, the main significance of which is that it demonstrates that the deep ocean basins ceased to be the preferential burial site for organic carbon. A compilation of available data on CORB occurrences, composition, and age indicate that: (1) CORBs are found in a broad geographic belt extending from the Caribbean across the central North Atlantic, southern and eastern Europe to Asia; with limited occurrences in the Indian ocean; (2) both the first and the last occurrences of CORBs are diachronous; (3) CORBs are of pelagic and hemipelagic origin and were deposited in a variety of environments from continental slope to deep oceanic basin, above and below the carbonate compensation depth (CCD); (4) total organic carbon (TOC) is mostly <0.1%; haematite is relatively abundant, up to 10% in red shales; (5) the termination of CORB deposition in the Alps, Carpathians, and Himalayas was mostly a result of major tectonic events associated with intensification of continental plate migration and initial stages of collision of the Indian and Asian plates and the African and European continental plates. We suggest that changes in dissolved oxygen in the deep ocean were mainly the result of changes in the location and formation of deep water and changes in ocean circulation. It is more than probable that a score of different earth processes, including changes in climate, all acting in concert, were involved in such a major change in the deep-sea environment and location of the carbon reservoir.