Age of a Fe-Mn crust on the Gagua Ridge and applicability studies of dating methods

Precise dating of deep-sea Fe-Mn crust is crucial to the research of paleoceanographic changes. In this paper, dating methods of ¹⁰Be/⁹Be, Co empirical formula, ²³⁰Th_ex/²³²Th and paleomagnetic stratigraphy are comparatively used for systematical chronological studies of a Fe-Mn crust sample collected from the Gagua Ridge. Different growth rate or different age figures are observed as different dating methods are adopted due to large inputs of terrigenous materials. Co content is diluted by the excessive amounts of ²³²Th brought in by the terrigenous inputs, and the Co flux in certain layers and initial ²³⁰Th_ex/²³²Th flux at the surface layer are both greatly fluctuated, which will render greatly influence onto the dating results of the two methods. Although the ¹⁰Be/⁹Be initial flux is also influenced by terrigenous inputs, it remains relatively stable. Therefore, ¹⁰Be/⁹Be can be regarded as the most precise dating method in the case. Paleomagnetic stratigraphy dating results may provide several age controlling points after referring to other dating results. Finally, the initial growth age of the Fe-Mn crust is confirmed as 7.09 Ma. For more precise age figure, further studies are required on the occurrence of nuclides in the Fe-Mn crust.