Geochemistry on Mn-nodules from Leg81

ree types of concretions were recovered during Leg 81 from Holes 552A, 553A, and 554A, located on the west margin of the Rockall Plateau. In the sedimentary section, these concretions are located at the level of major unconformities, in condensed sequences representing a period from early Eocene to Miocene. This study is a detailed mineralogical and geochemical investigation that permits comparison among the three holes and between the fossil Leg 81 concretions and recent polymetallic nodules found on the ocean floor.