Strontium,carbon and oxygen isotopic compositions and their geological significance:the Silurian strata on the northern and southern margins of the Sichuan Basin

The Sr,C and O isotopic compositions across the stratigraphic section have been ob-tained in the light of the systematic determinations of ⁸⁷Sr/⁸⁶Sr,δ¹³C and δ¹⁸O values for the Upper Ordovician-Lower Silurian strata in the Guangyuan region of the northern margin and Qijiang region of the southern margin of the Sichuan Basin.On the basis of the isotopic data in combination with the sedimentary facies and tectonic data and the published infor-mation about the global Silurian regressive-transgressive events,the following conclusions can be drawn.