A gravelly sand deposit at 103 m depth on the summit region of Mount Palinuro, a seamount approximately 100 km off the W coast of Italy, is made up of a mixture of manganese and iron micronodules with shallow water shell debris. The manganese-rich micronodules have very high Mn: Fe ratios, they are deficient in minor elements and todorokite is their principal manganese oxide phase. The iron-rich concretions are made up of smectite, probably along with amorphous iron oxides and/or hydroxides. The high degree of partition of manganese and iron and the mineralogical variation suggest that the deposit has a hydrothermal origin. The associated shell debris appears to be entirely of recent origin suggesting that Mount Palinuro has been volcanically active in historical times. This places constraints on models for the tectonism of the southern Tyrrhenian Sea.