[Objective]The early Cambrian was a pivotal period of oceanic environmental evolution in Earth history.To grain the insight into evolutions of oceanic redox condition and nitrogen cycle,which can favor to ascertain the dominant control on coeval organic matter enrichment.[Methods]The present study conducted the iron speciation,nitrogen and sulfur isotopes analyses for the Qiongzhusi Formation in the Weiyuan area.[Results]The oceanic redox condition experienced several transitions in response to coeval sea-level fluctuations during the early Cambrian.In the Cambrian Age 2,the deep euxinic watermasses expanded to the shallow-water shelf environment,and intense denitri-fication resulted in the persistent consumption of NO-3 in seawater,which eventually caused the nitrogen cycle domi-nated by biological nitrogen fixation.Synchronously,the low δ15N values imply the relatively low primary productivity level in the Cambrian Age 2.The obviously increased δ15N values in the Cambrian Age 3 suggest the stepwise expan-sion of NO-3 reservoir and extension of surface oxygenated seawater.[Conclusions]The organic matter enrichment of the Qiongzhusi Formation in the Weiyuan area was dominantly controlled by redox conditions in the sedimentary envi-ronment,where the severe anoxia caused by transgression resulted in three significant organic matter enrichments.The redox conditions,nitrogen cycle,and enrichment of organic matter in inner shelf environments of South China were influenced by sea-level eustacy during the early Cambrian.
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