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

摘要

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 187~Os/188~Os 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.