Buried ferromanganese nodules of the Magellan Seamounts

Resumo

Buried ferromanganese nodules and their stratiform accumulations (nodule horizons), which are widespread in sedimentary sequences of the Magellan Seamounts, have been studied in core obtained by shallow drilling on its guyots in the course of expeditions of the R/V Gelendzhik in 2001–2010. The study included description of morphological features, structure, and composition of buried nodules, the assessment of their geological age, and the analysis of host geological environments. It was revealed that nodule horizons are developed in areas with unstable hydroand lithodynamic conditions. The frequent changes of these conditions were responsible for the formation of such nodule horizons and overlying ferromanganese crusts. It is shown that the crusts and nodules developed at the surface of bottom sediments and nodules buried within them are characterized by the similar structure and composition, which indicates their belonging to the same ore formation, i.e., ferromanganese ores of seamounts. The age of buried nodule horizons is correlated with that of layers in ferromanganese crusts, on the one hand, and with the age of host sedimentary complexes defined in the Magellan Seamounts area. The buried nodules include both Cenozoic and Late Cretaceous varieties. The finds of Cenomanian nodule horizons provide grounds for the assumption that the formation of ferromanganese ores on gyuots of the Magellan Seamounts could start prior to the Senonian.