Provenance change in the Irkutsk coal basin during the early and middle Jurassic: Geochemical and Sm-Nd isotope evidence

On the basis of the recently accepted chronostratigraphic chart, Jurassic sedimentation in the Irkutsk coal basin took place over a short time interval (~23 My), from the Pliensbachian (~191 Ma) to the Aalenian (~170 Ma). In this study, we present geochemical and Sm-Nd isotope data for sedimentary rocks of the Prisayan and Kuda formations and those in the upper course of the Angara River, which were deposited over an even shorter time interval (from ~174 to 170 Ma), as indicated by new data on biostratigraphy. Our results suggest that a greater contribution from Transbaikalia compared to that from the Siberian Platform during sediment deposition in the Irkutsk coal basin may reflect the onset of mountain building in Transbaikalia and reorganization of the river drainage network during the Middle Jurassic.