Trace element geochemistry of the Middle and Upper Ordovician strata in the Guanyinqiao section,Qijiang,Chongqing

The complete Middle and Upper Ordovician strata are of widespread occurrence in the middle-upper Yangtze area.The geochemical examination of the Middle and Upper Ordovician strata in the Guanyinqiao section,Qijiang,Chongqing have disclosed that the Baota Formation displays V and Ni depletion,low V/(V+Ni) ratios,and high Th/U and Ni/Co ratios.These values imply that there was once one phase of transgression during the deposition of the Baota Formation under the highly oxidized climatic conditions.The geochemical anomalies in the Middle and Upper Ordovician strata may be attributed to the interaction of the Cathaysian plate and Yangtze plate.