Analysis of ferromanganese deposits from the West African margin and the Mediterranean Sea

The type of lamina depends on the general hydrologic conditions of the bottom waters (currents activity, nutriments and Mn availability) but, also, on the microtopography of the sea water-lamina interface, probably because it introduces significant differences about Eh and Mn fluxes. Considering the low accretion rate of this type of deposit, it appears that the biofilm growth may be controled by a self-regulating process: the initial period of active production is followed by a long time interval of low production or of equilibrium between accumulation and removal of slime.