| The Archean atmospheric oxygen concentration and sulfur cycle was long debated. The banded iron formation (BIF) is a special type of the sedimentary formation, which has truly recorded the atmospheric and oceanic conditions at that time. We have measured the silicon isotope composition of the banded iron formations (BIFs) and the multiple sulfur isotope ratios (δ34S/δ33S/δ32S) for sulfides bedded in the BIFs (~2.7Ga) from Anshan-Benxi area, northeast of China. BIFs have lowδ30Si values from -2.0‰to +0.3‰with a mean value as -0.8‰, similar with clay minerals, sinter and modern seabed black funnel. Theδ18O values varied from +10.5‰to +17.4‰, these values between those of igneous quartz and hydrothermm solution induced quartz.δ30Si values in the magnetite band is lower than that in the neighbor siliconous band, while theδ18O values in the magnetite band is higher than that in the neighbor siliconous band in the same sample. This indicates that the BIFs were formed by the early terrestrial ocean floor gas ejection process and the periodic activity of the ocean bottom gas ejection formed the regulation bands. Theδ34S values shift from -22.0‰to +11.9‰, and the△33S (△33S =δ33S-1000[(1+δ34S/1000)0.515-1]) values varied from -0.89‰to +1.21‰. The non-zero△33S values indicate the Archean sulfur cycles were different than it is today. Gas phase sulfur-bearing species like volcanic SO2 radiated by solar UV can produce S0 with positive△33S and sulfuric acid with negative△33S in an anoxic atmosphere. Especially, theδ34S were varied from -22.0‰to +11.8‰, this signature indicates biological sulfate reduction was existed in local area and UV induced sulfate were not the only source of marine sulfate. Combined with the contemporaneous existence of the hematite, magnetite and the occurrence and preservation of the sulfur MIF, it can be inferred that the Archean atmospheric oxygen level must be at 10-2~10-3 of the present atmospheric level (PAL).
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