NEW DATA ON FERROMANGANESE NODULES GROWTH -RATES IN THE SOUTH-EAST PACIFIC

Nine pelagic ferromanganese nodules from the South-East Pacific have b een analyzed by the alpha radiographic technique using the nitrate cel lulose LR- 1 15. The obtained growth rates vary from 1 to 16 mm/Ma. Th e growth of three nodules was analyzed in two opposite directions: two of these nodules have grown only in one direction during the last 300 thousand years and in the third nodule growth rate differs by a facto r of 2. The sedimentation rates of the surrounding deposits were deter mined by the radiocarbon and excess Th-230 methods. These rate values are approximately equal to 0.4 mm/Ka. The difference between the sedim entation rates and nodule growth rates is caused by the activity of th e benthic fauna which is confirmed by the inversion of the radiocarbon dates with depth.