Analysis of REE Geochemical Characteristics and Sedimentary Environment of the Early Cambrian Black Rock Strata in Daba Mountain

In this research,ICP-MS method was used to determine the abundance of REE and some trace elements,e.g.,V,Ni,Cr,U,Th,Zn,and Co,of black rock strata of Shuijintuo Formation from Early Cambrian in Chengba rift belt,Daba Mountain.By analyzing these elements,we researched the REE geochemical characteristics of black rock strata and their sedimentary environment.The results show that the black rock strata displayed LREE-enriched type in study area,were characterized by obviously negative Ce anomalies(δCeN=0.47-0.94,δCeS=0.46-0.91)and negative Eu anomalies(δEuN=0.27-1.03,δEuS=0.42-1.57),and that the ratios of U/Th range from 2.52 to 67.51,the ratios of V/(V+Ni)=0.65-0.98,Sr/Cu=5.83-27.96,V/Cr=1.35-17.79,and δU=1.77-1.99 were in relatively high level.The analysis of the NASC-normalized REE-patterns,La-Ce diagram,Zn-Ni-Co triangular diagram and La/Yb-REE diagram reveals that the black rock strata were formed in a dry,anoxic and shallow marine shelf and slope marginal environment belonging to passive continental margin affected by hydrothermal fluids.