Research In Nannofossil Stratigraphy On The Growth Age Of The Co-rich Ferromanganese Crust From The Western Pacific

As a significant solid mineral resource in ocean, Co-rich ferromanganese crust is rich in many economy value mental elements, such as Mn, Co, Pt, Ni et al, which has became one of the most potentially valuable mineral styles in modern ocean.Chronology study of Co-rich ferromanganese crust is a key process and the analysis foundation which relate to the formation cause, growth process and the paleo-ocean environmental evolvement of the crust.The analysis of the Calcareous nannofossils in two Co-rich ferromanganese crusts, CLD01-1 and CLD11-4 coming from the Western Pacific Marshall Island seamount chain, is in order to estimate their depositional ages. The nannofossil deposition has not be found in CLD01-1 since Miocene. From the variety and distribution of nannofossil, we can conclude that this crust may start grow at early Eocene(51.5Ma) and stop at Late Eocene(34.2Ma). CLD11-4 crust may start grow at early Eocene(52.9Ma), the upper layer of this crust was deposited since Pleistocene(0.96～0.46Ma), while the middle layer had formed from Oligocene(27.5～23.9Ma) to Middle to Late Miocene(11.8Ma). Therefore this crust deposit from middle layer to upper layer maybe has a long time sedimentation hiatus, or this was because of the absence of time fossils. We can not conjecture whether there is sedimentation hiatus in the progress from lower layer to middle layer.Synthesizing the former studies of various methods to dating the Co-rich ferromanganese crust in Western Pacific, we can conclude that Co-rich ferromanganese crust in study area formed since Late Cretaceous. Co-rich ferromanganese crust grows in every period of the Cenozoic, whereas in affect of paleo-ocean environment, geological construct activities and some important ocean events, sedimentation hiatus maybe exist in the progress of its growth.Based on the chronology analysis of the two crust samples, the paper studies their growth rate. CLD01-1 crust deposits grow at the rate of 1.73mm/Ma, while CLD11-4 crust's growth rate is different in every layer, the average is about 0.8 mm/Ma. They were comparatively accord with the general use rate of the former study: 1～6mm/Ma.