The Temporal And Spatial Evolution Of CORBs

With analyzing the transition of the Cretaceous sedimentary, we found out that, from early Barremian to Cenomanian-Turonian boundary, the stratigraphy is mainly characterized by the widespread of back shales and CORBs. Some units are mainly consisted of black shales, while others are composed of CORBs. It is possible that the alternation of black shale and CORBs occurs in certain units. By correlating the globally distributed CORBs from Barremian to Maastrichitian, this paper discussed the temporal and spatial evolution of CORBs and its implications for paleoceanography and paleoclimatology.Firstly, this paper analyzed the features of the CORBs in Southern Tibet. And then on the basis of distribution of the CORBs in the world, we found out that they are located in five regions, which are Tethys region, North Altantic Ocean, South Atlantic Ocean, Indian Ocean and Oceania. We study and correlate the characteristics of the CORBs located respectively in different area. The software GRAPHYCOR was used for the correlation as well. The results show that: 1) the globally distributed CORBs were mainly present in late Cretaceous; 2)the paleoenvironment of the CORBs is deep water of low latitude area in general; 3)the lithologies are mainly consisted of red shale, red limestone, red marlstone, red mudstone and red siliciclastic shale; 4) the content of organic carbon is quite low.Secondly, according to the the temporal and spatial distribution of CORBs, we signed the expose of CORBs on the paleogeography map from Baremian to maastrichtian. In combination with the plate tectonics, we explored what causes the formation of CORBs. We inferred that the formation of CORBs is related to the open of south Atlantic and the connection between north Atlantic and Tethyan ocean. Because of the connection of south Atlantic, north Atlantic and Tetheyan ocean, the Oxygen-rich down-welling water can be brought to deep sea and have the capacity of fluidness, which lead to the formation of CORBs in these areas.Finally, the late Cretaceous circulation between South Atlantic, North Atlantic and Tethys Ocean was simulated, based on the relationship between the paleogeography and distribution of the CORBs. We suggest that the circulation leads to oxic bottom water and even the cooling of world.