TWO MAIN FORMATION EPISODES OF FERROMANGANESE CRUSTS IN THE PACIFIC OCEAN

Abstract

By the synthesis study for three central Pacific ferromanganese crusts (hereinafter for short as crusts) of their biostratigraphy, structure and element geochemistry on the section along their growth directions, it was found that the formation of the crusts concentrate on two different formation stages which were controlled by the different factors. The first formation stage which corresponds to the new layers of these crusts is the stage whose degree of oxidation of their ore-forming environment after about 25Ma obviously controlled by the Antarctic bottom water (AABW), and the other formation stage which corresponds to the old layers of these crusts is the stage whose degree of oxidation of their ore-formingenvironment before Oligocene controlled by surface and middle-level ocean currents which surrounds the earth's equator and the sinkage of high density warm saline surface water, and in early and middle Oligocene the ore-forming environment belonged to their turnaround time of those two stages, which was also a period of marine regression, low oceanic primary productivity, low CCD and low production of the biogenetic carbonate, the crusts' main growth hiatus occurred. This research finding is significance to the further study of the Pacific paleoceanography and its palaeoenvironment.