The discovery of ferrous bottom water conditions in the sealed mid-Proterozoic marine basin, northern part of North China Block: implications to evolution of ocean chemistry

How the ferrous deep water keep as long as one billion years and why sulfidic water wedge come out near the terrestrial sources supplementary zone are the focus of the evolution of ocean chemistry in mid-Proterozoic. The study of the sealed mid-Proterozoic marine basin found that the low level of pyrite in the black shale of Kuancheng where is far from the terrestrial sources supplementary zone, nevertheless, the level of black shale of Jixian where is far near the terrestrial sources supplementary zone is higher. This may reflect that the shallow-to-deep sulfate concentration gradient the sealed marine basin. The ferrous and deficit of sulfidic bottom water conditions in the sealed marine basin is the great advances in the study. It was proved that the existence of Supercontinent Nuna made the aerobic weathering and the importation of sulfate dropping to the critical point though the bottom water is ferrous in the case of sufficient terrestrial sources supplementary. Due to the long-term stabilization of Supercontinent Nuna, it is possible that the ferrous bottom water conditions in the open ocean in mid-Proterozoic. It is referential for how the global tectonics control the evolution of ocean. The focus for the study of the evolution of ocean chemistry in mid-Proterozoic is how the ferruginous deep water can maintain as long as one billion years, and why sulfidic water wedge would come out near the terrestrial sources region. The present work on the sealed mid-Proterozoic marine basin found the trace level of pyrite exists in the black shale of Kuancheng far away from the terrestrial source region. Nevertheless pyrite is more abundant in the black shale of Jixian nearer from the terrestrial source. This may reflect that the shallow-to-deep sulfate concentration gradient in the sealed marine basin. However the most significant discovery in present work is that the prevailing ferrous bottom water conditions in the sealed marine basin deficit of any sulfidic indicators. Based on comprehensive evidences, we conclude that it was the occurrence of Supercontinent Nuna that decrease the aerobic weathering and sulfate input to a certain critical point that make ferrous bottom water condition in the sealed marine basin possible. The existence of Supercontinent Nuna would be also one of the reason for the wide-spread ferrous condition in the open ocean during that time. The discovery of this work would be of value for exploring the effects of global tectonic development on the evolution of chemistry of paleo-oceans.