A set of continuous and stable clastic deposits rock developed after volcanic rocks of the Batamayneishan Formation in Shiqiantan sag, Eastern Junggar Basin. The study of the Upper Carboniferous mudstones are of great significance for restoring the weathering characteristics and paleoclimate of the late Carboniferous source area in Eastern Junggar and judging the properties and tectonic setting of the source rocks.Methods: In order to systematically study the whole- rock geochemistry of the fine- grained sedimentary rocks, the author have combined with the XRD, major and trace element results of the outcrop samples.Results: Mudstones from the Upper Carboniferous mudstones are all have low quartz contents. The Batamayneishan Formation mudstones have high clay contents, whereas those of the Shiqiantan Formation have high andesine contents. The clay compositions both of them are montmorillonites (content>99%), reflecting dry and cold climate characteristics and long- term alkaline deposition medium conditions. The CIA results show that the Batamayneishan and Shiqiantan Formations experienced moderate to weak chemical weathering and had the characteristic of alternating dry and wet climate change. The major trace elements and related discriminant diagrams shows that the provenance of tow formations are dominated by felsic, mixed with a few meso- mafic and acidic sources, and most of them come from undifferentiated arcs. The element- geochemical characteristics of the mudstones reflect that the tectonic background of the provenance is mainly the continental island arc.Conclusions: Combined with the peak age of detrital zircon in Shiqiantan Formation and the analysis of the main provenance area, it is concluded that the Yemaquan terrane and the northeastern Junggar terrane began to change from subduction to collision orogeny around 335 Ma.