Spatial Distribution Of Trace Metals In Anoxic Shale And Its Implication For Paleoenvironment During The Late Ediacaran,South China

Ediacaran(~635–541 Ma)was a key period characterized by significant shifts in life evolution and ocean oxygen levels in the history of the earth.Redox-sensitive trace metals(RSTEs)are one of the key proxy to explore ocean redox conditions and their relationship with life evolution on Earth.Some studies argued that RSTEs of anoxic shales in South China can reflect ocean redox conditions globally,and this ocean redox conditions globally has a key role in life evolution during the Ediacaran.However,this hypothesis remains to be debated.Thus,we wish to conduct the spatial distribution of RSTEs in anoxic shales during the Ediacaran,South China,which can provide a new insight to constrain oceanic redox conditions and life evolution based on RSTEs from the spatial angle.In order to get our goal,we conduct multiple geochemical proxies from the basinal Sandu section,including redox(Fe species and RSTEs),watermass restriction/upwelling(Mo/TOC and Co×Mn-Cd/Mo),terrigenous fluxes(Ti fluxes),hydrothermal activity(rare earth element),and salinity(B/Ga).These new data integrated with similar geochemical data from other sections deposited under different water depths(the inner-shelf Jiulongwan and Three Gorges core #1,slope Rongxi and Wuhe)provide the spatial distributions of marine redox conditions and RSTEs.Our results suggest a highly spatial heterogeneity of marine redox conditions during the late Ediacaran,where the mid-depth euxinic conditions develops between the surface-water oxic conditions and deep-water ferruginous conditions.Our results further indicate a spatial heterogeneity of RSTEs in anoxic shales during the late Ediacaran,in which the inner-shelf(Jiulongwan,Three Gorges core #1),slope(Rongxi,Wuhe),and basinal(Sandu)settings are characterized by high,moderate,and low RSTEs.Our results suggest that terrigenous fluxes and hydrothermal activities paly minor roles in the spatial heterogeneity of RSTEs in anoxic shales,whereas local marine redox conditions,watermass restriction,and salinity have profound effects on a spatial heterogeneity of RSTEs in anoxic shales.Our study thus suggest that the relationship between global redox conditions and the diversifications of algae and animals during the Ediacaran should need to be made carefully.