Host: Japan Association of Mineralogical Sciences
Atmospheric oxygen increased greatly in Paleoproterozoic, and changed surface environment dramatically. In this study, I focused on the behaviors of trace elements during weathering, because they reflected the surface environment. Considering element profiles, element retentions, and thermodynamics, I discussed the change of atmospheric oxygen and ocean chemistry. The samples were paleosols which formed ~2.76-1.85Ga. They were measured the concentration of trace elements by ICP-AES/-MS, and those of major elements by XRF. I obtained element profiles and element retentions. It was conceivable that trace element distributions were heterogeneous in parent rocks, but in many cases, heterogeneity did not matter. The results are as follows. Before ~2.2-2.4 Ga, Ni, Co, and Zn flowed from the continent, and retained since then. Before ~2.4-2.4 Ga, Cu, V, Cr, Mo retained in the continent, and flowed since then. W flowed from the continent throughout Paleoproterozoic. These results suggest that atmospheric oxygen rose gradually. In addition, the behavior of trace elements can be proxies for the ocean chemistry, and continental weathering probably contributed to the ocean chemistry.
