Ultrafine - scale magnetostratigraphy of marine 1 ferromanganese crust

12 Hydrogenetic ferromanganese crusts are iron-manganese oxide chemical 13 precipitates on the seafloor that grow over periods of tens of millions of years. Their 14 secular records of chemical, mineralogical, and textural variations are archives of deep15 sea environmental changes. However, environmental reconstruction requires reliable 16 high-resolution age dating. Earlier chronological methods using radiochemical and stable 17 isotopes provided age models for ferromanganese crusts, but have limitations on the 18 millimeter scale. For example, the reliability of 10Be/9Be chronometry, commonly 19 considered the most reliable technique, depends on the assumption that the production 20 and preservation of 10Be are constant, and requires accurate knowledge of the 10Be half21 life. To overcome these limitations, we applied an alternative chronometric technique, 22