Sedimentary evolution of the Xiamaling Formation-Longshan Formation-Jing’eryu Formation (IMAGE)
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Accompanied by the global scale Columbia supercontinent rifting peak around 1.4 Ga in the Mesoproterozoic, strong crustal extension occurred from the western part of Yanshan Mountain to the northern part of Taihang Mountain with the formation of the Large Igneous Province. This formed a narrow and deep aulacogen basin extending over 500 km from east to west and 120 km wide, with the deepest rift located in northwestern Hebei. The largest rifting area in the basin is from Changping to Huailai and Xuanhua in the west, with a thick accumulation of grayish-green and black illite shales and carbonaceous shales. Meanwhile, to the east of Changping, the water depth becomes shallow, and siltstones and sandstones are dominant. In the middle stage, mudstones and shales with intercalated sandstones in a shallow shelf environment are dominant, and in the late stage, mudstones and siltstones in a tidal flat with thin interbeds of calcareous nodules have predominantly developed. This indicates sedimentary evolution and a sediments infilling response from the initial strong subsidence of the rift valley, to the drift of rift valley in the middle and late stages. Therefore, the area with the largest stratigraphic thickness in the west Beijing-Zhangjiakou area has become the sedimentation and sub sidence center of the rift basin and the deep-water basin area (Liu and Zheng, 1994). From west to east, the transition from a narrow and deep basin center to an open and shallow sea on the shoulder of the rift valley has been recorded (Song and Zhang, 1983). At the end of the deposition of the Longshan-Jing’eryu formations, the east Liaoning rift valley maybe have started rifting. Thus, the paleogeographic pattern started to shift from the high in the east (Shanhaiguan-east Liaoning) and low in the west (Yanliao) of the Longshan-Jing’eryu stage to the high in the west (Yanliao) and low in east (Shanhaiguan-east Liaoning) of the Diaoyutai-Nanfen stage. The Diaoyutai-Nanfen formations may be contemporaneous with or slightly later than the Longshan-Jing’eryu formations. After that, Yanliao areas uplifted, and deposition did not occur in the Jiao-Liao-XuHuai areas
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