COMPOSITION AND GROWTH HISTORY OF SURFICIAL AND BURIED MANGANESE NODULES IN THE PENRHYN BASIN, SOUTHWESTERN PACIFIC

A comparative study of occurrence and composition of hydrogenetic mang anese nodules and their relation to sediment lithology were carried ou t on-material from the Penrhyn Basin in the Southwestern Pacific. The regional distribution of the nodules and compositional variations with in nodules are closely correlated to the sedimentary history of the ba sin. Radiochemical and fossil data indicate that the nodules started t o grow after the initiation of sea-floor spreading in Cretaceous time or later. Initially, Co-poor nodules grew on pelagic clay sediments as a result of continuous uplifting, although some of them were left beh ind within the sediment (old generation) through Paleogene time. More abundant Co-rich nodules followed during or after a hiatus through to the present and formed the large manganese nodule provinces. These you ng generation encrusted old small nodules, stiff pelagic clay sediment s, hydrothermal manganese deposits, and fossils. AABW played an import ant role in the formation of the young generation of nodules. It is in ferred that the AABW flows through the Aitutaki Passage into the Penrh yn Basin and runs along the western margin of the Basin. Scattered thi ck young sediments in places in the survey area have prevented the gro wth of nodules.