Provenance and Paleoclimate Characteristics of the Upper Cretaceous Yaojia Formation Clastic Rocks in the Northeastern Songliao Basin, China: Evidence from Elemental Geochemistry and Zircon U-Pb Geochronology

The Yaojia Formation in the northeastern Songliao Basin is a primary target horizon for sandstone-type uranium mineralization in the area. Understanding its provenance, composition, and depositional paleoclimate is of great significance for uranium exploration in the region. This study analyzed 58 sandstone and mudstone samples using petrographic thin-section observation, elemental geochemistry, and detrital zircon U-Pb geochronology. The results show that Yaojia Formation sandstones are feldspathic lithic quartzose sandstone (averaging 47% lithics, 32% quartz, and 21% feldspar, mainly K-feldspar), with moderate sorting and predominantly angular to subangular grains, indicating rapid denudation in the source area, medium- to short-distance transport, and rapid deposition. The chemical weathering index (CIA, 52–68) and the index of compositional variation (ICV, 0.83~1.26) are generally low, indicating moderate chemical weathering. Rb/Sr, Sr/Cu, Al₂O₃/MgO, CIA, MgO/CaO ratios indicate that the Yaojia Formation was deposited under predominantly arid–semiarid conditions, with later stages being wetter than earlier ones. Rare earth element (REE) characteristics indicate light REE enrichment, heavy REE depletion, and significant negative Eu anomalies. Combined with A-CN-K diagrams and discriminant plots such as La/Th-Hf and Co/Th-La/Sc, the provenance is primarily derived from felsic magmatic rocks in a post-orogenic extensional tectonic setting. Detrital zircon U-Pb ages are mainly concentrated at 119–153 Ma (64%), 160–183 Ma (14%), and 318.3–327.7 Ma (6%), showing the highest similarity to zircon age spectra from magmatic rocks in the Great Xing’an Range. The comprehensive results indicate that the clastic rocks of the Yaojia Formation in the study area were mainly sourced from Early Cretaceous felsic magmatic rocks in the Great Xing’an Range and have undergone short- to medium-distance transport and sedimentation under arid to semi-arid paleoclimatic conditions.