Special Aspects of the Application of Lithogeochemical Indicators for Reconstructing the Paleoclimate and Composition of Source Areas in the West Siberian Late Jurassic–Lower Cretaceous Sedimentary Basin

For Upper Jurassic–Lower Cretaceous rocks of the Bazhenov Formation, a significant positive linear correlation of the content of Th, Hf, Sc, and La with the Al₂O₃ content was revealed, and their terrigenous genesis was confirmed. It has been determined that the samples, in which the distribution of Sc/Al₂O₃ and La/Al₂O₃ values does not satisfy the linear correlation, represent the mixed clayey–siliceous rocks (with P₂O₅ > 1 wt %) or the substantially pyritized rocks (with the pyrite content exceeding the OM content and C/S ≤ 1), as well as siliceous mudstones (with the SiO₂ content > 70 wt %). It is concluded that, in addition to carbonatized rocks, rocks of the above-mentioned types, as well as rocks subjected to the late diagenetic kaolinization, should be excluded before analyzing the geochemical indicators for reconstructing the formation conditions of the Bazhenov Formation. The formation conditions of these rocks were reconstructed based on the analysis of values of several geochemical modules and indicators. Based on the study of CIA and CIW variations, it was confirmed that the Late Jurassic–Early Cretaceous climate in the West Siberian sedimentary basin was warm and semiarid, and it did not change significantly during the entire period under consideration. For rocks of the Bazhenov Formation, several indicators, such as (La/Yb)_N and Eu/Eu*, as well as the distribution of trace elements in the Th‒La‒Sc triangular diagram, suggest that rocks of the Bazhenov Formation were deposited in the central and southeastern regions, with the dominant impact of source areas of mafic rocks.