Overview of Cretaceous Oceanic Red Beds (CORBs): A window on global oceanic/climate change

Category Climate system
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Wang, Chengshan۱; Hu, Xiumian۲; Huang, Yongjian۳
Holding Date 21 September 2008

Cretaceous oceanic red beds (CORBs) are mainly pelagic red shales, marls or fine-grained limestones. They are a significant facies of deep-water pelagic deposits and pelagic/hemipelagic sedimentary systems. CORBs are globally distributed in outcrops in Europe, Asia, Africa, New Zealand, Caribbean, and at DSDP and ODP sites in the Tethys, Atlantic, Pacific, and Indian oceans. CORBs are mainly Upper Cretaceous and most range from Santonian to Campanian. Before OAE2, CORBs were limited regionally in Aptian to Cenomanian strata occurring as discrete thin beds. Upper Valanginian to Lower Hautervian CORB outcrops are even less common.
The ages of CORBs are constrained by paleontological data including planktic foraminifera and nannofossils in calcareous CORBs, and agglutinated foraminifera and dinoflagellates or radiolaria in non-calcareous CORBs. The biostratigraphic data were assembled into an integrated, testable data base by graphic correlation. The data base was then correlated to GSSPs and reference sections of Cretaceous stages. The paleoecological data support long-term climate cooling from the Turonian thermal maximum to the latest Maastrichtian.
The depositional environment of most CORB units was in relatively deep oceanic basins. Deposition was generally far from shoreline and only locally associated with coarse terrigenous clastics such as turbidites. Significant controlling factors of CORBs were slow sediment accumulation rates at great paleo-water depths. Like most marine sediments, CORBs are a complex mixture of terrigenous detritus and seawater-derived material.
According to data reported from all studied localities, the common geochemical properties of CORBs are their extremely low organic carbon content and high level of ferric oxides. The ratio between ferric oxides to the total iron is not only higher than the level of adjacent non-red sediments, but it is also higher than that of Phanerozoic normal marine oxic sedimentary rocks. These chemical properties indicate that CORBs were deposited in a highly oxic environment at or below the sediment-water interface. Other major and trace elements and isotopic data suggest an oxic, oligotrophic water mass having overall low productivity. The paleoceanographic and paleoclimatological conditions are corroborated by carbon stable isotope data, phosphorus burial records, dissolved oxygen index, and comprehensive geochemical modeling results. Paleoclimate, paleogeography, ocean currents, nutrient flux, among other processes, were related to the deposition and wide distribution of CORBs during the Late Cretaceous. The development of the paleogeographic configuration and climate cooling provided the basis for the ventilation of the deep ocean. The behavior of redox-sensitive nutrient elements like phosphorus further stimulated the development of oligotrophic conditions. All of these factors contributed to the global distribution of CORBs.