[M-IS27_2PM1] MarineMarine manganese deposits: Origin, growth processes, and environment

[MIS27-05] Paleoceanographic Record on the Dual Structure of Hydrogenetic Ferromanganese Crusts

*Keisuke NISHI¹, Akira USUI¹, Yoshio NAKASATO¹, Sato HISAAKI¹, Graham IAN², Kyoko YAMAOKA³, Kosuke T. GOTO³ (1.Kochi University, 2.The Institute of Geological and Nuclear Science, 3.National Institute of Advanced Industrial Science and Technology)

Keywords:ferromanganese crust, marine environment, pacific, seamount

Most Hydrogenetic ferromanganese crusts in the Pacific consist of two growth generations: a phosphatized older grows generation and a non-phosphatized growth generation. This study attempts some detail analyses such as macroscopy, microscopy, chemistry, mineralogy, age and growth rate determination to consider how the dual structures are formed. As a result of age growth rate determinations supported by GNS, the boundary of two growth generations concentrates approximately 15-10 Ma regardless of water depth and region. In the middle to late Miocene, the climate was prominently cold by Antarctic glaciation. As a result, a phosphogenesis of ferromanganese crusts may have occurred because the dissolves phosphate rich and oxygen rich deep water were redistributed to the intermediate water depths by upwelling at the seamounts.