Depositional Environment Of Yixian Formation Of Lower Cretaceous In Northern Hebei And Western Liaoning Province And Basin Evolution

Study area is in northern Hebei and western Liaoning province, located at the north edge of North China plate and middle-east part of the Yanshan Belt. In the Early Cretaceous, a series of rift basins formed in the area with NE-NNE strike because of the extension. However, the scientific issue that these basins formed at same time or not has not yet been solved. In western Liaoning, volcanic rocks intercalated with sediments characterize the widespread Lower Cretaceous especially the Yixian Formation aged early stage of Early Cretaceous, whereas in northern Hebei this Formation consists mainly of sedimentary rock. It results in the difficulty in correlation of Yixian Formation between northern Hebei and western Liaoning. As we know, the Jehol Biota was found in this Formation; therefore, the investigation of depositional environment of it is important for the study of the occurrence and development of Jehol biota. Base on previous study of this area, this paper carries on sedimentology study including facies analysis, provenance analysis, paleocurrent analysis and sequence stratigraphy study on the sedimentary rock of Yixian Formation in Fuxin-Yixian basin, Jianchang basin, Lingyuan basin and Luanping basin. The primary objective is to discuss the depositional environment of the Early Cretaceous basins and the characteristics of basin evolution.The architectural elements analysis indicates that the sedimentary rock of Yixan Formation is continental deposits including alluvial fan, river, fan delta and lake deposits, with differences between basins. There are three sedimentary cycles developed in each basin, relating to three times of deepening and shoaling of the lake. At last, most of the sedimentary units were covered by volcanic rocks.Three sequences are identified in the Yixian Formation in each basin based on the Sequence stratigraphy study The maximum lake flood surface occurred in sequence â…¡of Fuxin-Yixian basin, sequenceâ… of Jianchang and Lingyuan basin and sequenceâ…¢of Luanping basin.Sandstones of Yixian Formation are composed of quartz, feldspar and debris. In general, the debrises are trachytes, andesites and basalts with a few sedimentary and metamorphic debrises, which indicate they are originated from island arc. Abundant unstable debrises indicate an adjacent provenance. Combined with the Dickinson debris triangle map, the tectonic setting of the provenance area is island arc. Paleocurrent analysis shows that the provenance area is located in the NW to the basins in western Liaoning and the provenance areas of Luanping are located in the NW and SE to the basin.The correlation of Yixian sedimentary units among basins shows that the Cretaceous basins of study area are formed from east to west except Luanping basin.