Seawater Redox Conditions in the Late Paleoproterozoic: Insight from the North China Craton

The "Boring Billion" (BB, similar to 1800-800 Ma) is characterized by the perceived stasis of carbon isotopes within the geological record of that time. However, geochemical data obtained from global Paleo-Mesoproterozoic strata indicate heterogeneity and complexity of oxygen contents in the oceans, which hinder paleoenvironmental reconstructions from this period. Furthermore, there has been a dearth of studies focused on the Paleoproterozoic strata in the western and southern parts of the North China Craton (NCC). In this paper, we report elemental abundances and Fe speciation data from the Huangqikou Formation in the Ordos Basin, western NCC, and the Dagushi, Bingmagou, Baicaoping, and Puyu Formations in the Xiong'er Basin, southern NCC. Our latest findings, integrated with prior research, indicate that sedimentary environments in these parts of the NCC in the late Paleoproterozoic were uniformly anoxic and ferruginous. During a marine transgression, we see limited evidence of oxic surface waters entering the sedimentary water and resulting in intermittent oxygenation events in the Ordos Basin. However, microbial respiration of oxygen and/or limited oxygen replenishment under sluggish circulation in the basin might have caused the consistently anoxic conditions in the Xiong'er Basin during the late Paleoproterozoic.