Osmium isotope stratigraphy of a ferromanganese crust

Abstract

In order to test the growth hiatus hypothesis of a ferromanganese crust (Fe-Mn crust), we conducted Os isotope analysis of Fe-Mn crusts collected from the Takyo 5th and Ryusei seamount. The Os isotope compositions in the younger parts of Fe-Mn crusts are almost the same as the seawater Os isotope record from present to 15 Ma. However, in the older parts of Fe-Mn crusts, the Os isotope compositions show large deviation from the seawater Os isotope record. This deviation in the Fe-Mn crusts of the Takyo 5th seamount can be explained either by the existence of growth hiatus or the diagenetic effect during the phosphatization. By contrast, the deviation in the Fe-Mn crust of the Ryusei Seamount may be caused by the complex growth structure in this sample.