Abstract:

Ningwu-Jingle basin and Hunyuan basin are located within the north-central of North China craton, and the Jurassic sedimentary sequences are complete from Early Jurassic to Late Jurassic, whose provenance came from the middle of Yinshan-Yanshan orogenic belt. Therefore, we may infer the orogenic process by the research of sedimentary sequences in these basin. According to U-Pb dating for the tuffaceous micritic limestone at the top of the Yungang Formation in the Middle Jurassic and the basalt-andesite at the bottom of the Tiaojiashan Formation, the recommended age of the Middle Jurassic in the international stratigraphic chart and the sedimentary rate of it, the key limit of the change of Jurassic sedimentary sequences was determined. The Jurassic sedimentary sequences experienced a conversion from the early lacustrine transgressive sedimentation to the late lacustrine regressive one at the bottom of the Middle Jurassic Yungang Formation (J₂yg). It was indicated that the regional tectonic stress field converted from extensional environment to compressional one, giving birth to the beginning of the Jurassic orogenic movement, and the time limit is about 168 Ma. The colors of the tuffaceous micritic limestone on the top of the Yungang Formation in the Middle Jurassic varied from celadon to fuchsia , indicating a suddenly uplift of the lake basin topography and a quick strengthen of regional oxidizing. The Jurassic orogenic movement experienced a stage of quick development, and the time limit is about 161.0-159.0 Ma. The sedimentary sequence from the Middle Jurassic to the Late Jurassic is continuous and inherited. With the further uplift of the lake basin topography, the sedimentary scope of Jurassic retreated quickly the leading edge of the orogenic belt. It is characterized by the synorogenic conglomerates, while Jurassic orogenic movement reached to the peak period, and the time limit is about 159.0-153.0 Ma. In the Late Jurassic, the regional sedimentary sequences consisted of  basalt-andesite and the tuffaceous breccia, the Jurassic orogenic movement came into a post-orogenic adjustment stage.

Key words: North China craton, Jurassic, sedimentary rocks, the tuffaceous micritic carbonates, basalt-andesite, zircon U-Pb age