The Response of Os Isotope in a Ferromanganese Crust from the West Pacific to Paleaoceanographic Events

This paper researches the ferromanganese crust MHD79 from bottom to top 20 Os isotope data from the Central Pacific. The results showed that: in the Ferromanganese crust MHD79, each 187 Os/ 188 Os value low point corresponds to the Os content high point, and corresponds to a large-scale volcanic (magmatic) activity or meteorite impact event. In the early three stages of the ferromanganese crust MHD79, Os content gradually increased with the decreasing of 187 Os/ 188 Os, which demonstrates that Os content correlated with 187 Os/ 188 Os negatively during this period; in the stages IV and V, the Os contents still correlated negatively with the 187 Os/ 188 Os, but the 187Os/188Os value increased gradually; in the stage VI, the Os contents increased and correlated positively with the 187 Os/ 188 Os. The evolution of Os contents and 187 Os/ 188 Os in the ferromanganese crust MHD79 suggested that, mantle and extraterrestrial material were the main contributors to the Os in the ocean relative to terrestrial material from late Cretaceous to Paleocene; Thereafter, the terrestrial material input increased gradually; after Oligocene, the terrestrial material input increased rapidly and became the main contributor for the Os in the ocean.