Abstract:

Iron, as one of the most abundant elements in the Earth crust, cycles within a series of geochemical processes. The iron in the modern ocean mostly comes from riverine, glacial and aeolian by the input of iron oxide particles and dissolved iron ions. The iron oxides will change their form and finally be buried during the early diagenetic process characterized by the burial and degradation of organic matter, which is called the reactive iron cycling. Iron oxides would continue to be formed or at least not to be dissolved under oxic conditions, and the sediments in brown to red color will then be dominant. While in a reducing environment, iron oxides will be dissolved, with the possible migration of iron ion in the ocean, and then buried as siderite, pyrite, or other ironbearing minerals. A series of iron proxies have been suggested to distinguish the redox condition of the paleoocean, by studying iron cycling in the modern ocean. On the basis of this methodology, scientists have reconstructed the redox history of paleoocean since the Archaean as a sequential appearance of the ferrous, sulfidic and oxic ocean. Owing to the adsorption of phosphorus onto the iron oxides, and the inability of reducing ironbearing minerals to combine with the phosphate ion, more phosphorus will be buried in the sediments under oxidized conditions; while a reducing environment will enhance the release of phosphorus from the sediments. Because the phosphorus is the constraining element for the marine production, the ocean will become more productive under reducing conditions; but less organic matter will be produced under moreoxic environment. Such feedback mechanism has been preliminarily proved in the deposition of Cretaceous anoxic and moreoxic sediments. But more works are still needed to elucidate the contribution of different forms of iron burial to the occurrence of such special sediments.

Key words:

Key words: reactive iron cycle; paleoocean; Cretaceous; anoxicoxic deposition