First Description of Cosmic Spherules In Situ in Ferromanganese Crust from the Alba Guyot (Magellan Seamounts)

In polished thin sections of ferromanganese crust from the Alba guyot (Magellan Seamounts), nine cosmic spherules of type I were found in undisturbed occurrence. They consist of Fe oxides and sometimes contain a core of Fe–Ni alloy. The spherules are 40–250 µm in size and are confined to porous phosphate-clay material filling spaces between columns composed of Fe and Mn oxyhydroxides. Phosphates in the matrix hosting the spherules are represented mainly by bone detritus. Barite grains, zeolites, and foraminifera were found. The presence of spherules in situ in the Fe–Mn crust excludes contamination during sample preparation and indicates that the spherules accumulated almost simultaneously with the host layer. Spherules from crushed crusts of the Alba and Fedorov guyots were also studied; the presence of a ferromanganese shell with a concentrically layered structure was noted in some of them.