松辽盆地东南隆起区嫩江组泥岩段地球化学特征及地质意义

Songliao basin located in northeast China, which is well known as a Mesozoic continental rift basin in China. Previous studies mostly focus on the sedimentary characteristics of oil shale,but the provenance feature and tectonic setting of Nenjiang Formation is seldom concerned. The geochemical analysis based on the mudstone samples from Nenjiang Formation show that the Al2O3/（CaO+Na2O）ratio ranges from 1.4 to 5.3, and the parameter of（MgO+Fe2O3T）ranges from 6.5% to 12.5%. The K2O/Na2O ratio is relatively high(＞1), and the weight value of SiO2 ranges form 61.6% to 75.0%, all of which demonstrate that the mudstones contain a certain amount of femic constituents and a considerable quantity of stable components. The PAAS-standardized distribution curves of trace elements show the enrichment and depletion trends among different samples, significant variations in the REE contents, enrichment in light REE and negative anomalies of Eu. These features suggest that the material sources of the Oil Shale Member came from several provenances. The mudstone weathering and alteration indexes ranges form 63.3 to 77.0 and the Th/U ratio ranges from 2.67 to 3.98, both of which suggest that provenances had underwent moderate weathering processes. The Th /Sc and Zr/Sc ratios illustrate that these mudstones were mainly controlled by source rocks. On the basis of source rocks, discrimination diagrams of the tectonic setting and previous research material, we conclude that the provenances of the Oil Shale Member of Nenjiang Formation in Songliao Basin wrer mainly Hercynian and Yanshannian granites. Tectonic setting of the source rocks were the continental margin orogenic belt and belonged to continental island arc volcanic series.