[M-IS46] Marine manganese deposits: Origin, growth processes, and environment

[MIS46-P06] Comparison of the microscopic growth structure of the ferromanganese crusts with the glacial-interglacial cycles

*Hironori TAKAHASHI¹, Akira USUI¹, Takashi ITO² (1.Faculty of Science, Kochi University, 2.Faculty of Education, Ibaraki University)

Keywords:ferromanganese crust, northwestren Paciffic, growth layer

Hydrogenetic ferromanganese crusts are iron-manganese oxide chemical precipitates on the sea?oor that grow over periods of tens of millions of years. The marine environmental changes and events of a long range are possible recorded in microstructure (Sorem and Foster, 1972; Usui, 1998). For example, the crust (D96-m4) dredged on the floor of the Philippine Sea Plate in the northwestern Pacific Ocean, shows periodical lamination of characteristic pouch? or lobe? like structures.
Intervals of each lamination is about 500 μm, which bounds to about 100 k.y. when assumed the average Be-10 growth rate of 4.9 mm/m.y.. The structure was observed in the crusts from other near by seamounts.
The controlling factors will be discussed geological and environmental in the paper.