Lacunes de sedimentation, series condensees et nodules de manganese dans les depots neogenes et quaternaires des bassins de l'ocean Indien austral

Abstract

Abstract This is a detailed stratigraphic study of core samples from basins in the southern Indian Ocean used to characterize early milieux which controlled neogenic and quaternary sedimentation. Distribution of the principal pelagic facies identified--coccolithic calcareous oozes, red clays, grey and brown diatoms--depended more on depth than on latitudinal hydrologic zonation. Stratigraphic succession of neogenic and quaternary sediment layers--in general, red clays at the bottom, calcareous oozes above--is usually discontinuous. Condensation sequences and manganese nodules are comparable to those from the Jurassic, Cretaceous and Paleogene in alpine areas. Their stratigraphic character indicates that lithological condensation was due to carbonate dissolution and sedimentation hiatuses. Their formation seems to depend on 3 principal phenomena: depth variation of the accelerated calcium zone in the course of time; crustal subsidence produced by dorsal ridges; and winnowing of sediments by deepwater movement. These results suggest a solution to the paradoxical problem of slow nodule growth--that it takes place during breaks in the sedimentation process.