Relationship Between Characteristics Of Paleocurrent And Basin-filling Evolution Of Upper Jurassic-Paleogene In Middle Yangtze Area

Study on paleocurrent direction is important to restore the tectonic setting by the paleoenvironment in basin analysis. In this paper, the provenance of Upper Jurassic-Paleogene in Middle Yangtze area and its adjacent area was analyzed combined with the diameter, composition, round and sorting of the gravels, sandstone composition, geochemistry and distribution of sedimentary facies. Further study on the evolution characteristics of the regional structure has revealed the basin-filling evolution of the study area, which is significant theoretically and practically for the oil and gas exploration of Mesozoic-Cenozoic in Middle Yangtze area. The main results are as follow:1. In Late Jurassic, the paleocurrent direction of Zigui Basin changed from S to SWW resulted from the rapid uplift of the Huangling Anticline. Thus, the northern margin of the Yangtze foreland thrust belt became the main source area of Zigui Basin. It’s proved that Huangling Anticline uplifted in late Suining of Late Jurassic and truncated the connection between Zigui and Dangyang Basin. So Zigui Basin and Sichuan Basin linked together then. It is turned out that northern margin of the Yangtze foreland fold thrust belt converged with Jiangnan-Xuefeng orogenic belts.2. In Early Cretaceous, the paleocurrent direction changed from N to SW in Shimen Age in Yichang area. According to the similarity of the composition of the gravels between upper Shimen Formation in Yichang and upper Suining Formation- Penglaizhen Formation in Zigui Basin, the thesis suggests the uplift of Huangling Anticline began to influenced the sedimentary source of Nanjinguan in Yichang, and the northern margin of the Yangtze foreland thrust belt started to be the provenance during the Shimen Age. With the northward nappe of Jiangnan orogen, Upper Cretaceous deposited thick layers of conglomerate, the paleocurrent turned to N and the Paleozoic limestone in southern margin of the basin became the main sedimentary source.3. In the Cretaceous, the paleocurrent directions of both Ezhou and Xishui area were SW. With the Qinling-Dabie Mountain southward thrusted constantly, the Dabie Mountain started to uplift and provided sufficient sedimentary source for this area. The composition of gravels in the Upper and Lower Cretaceous in Ezhou and Xishui reflects the anti-sequence of the erosion process from the Paleozoic sedimentary cover to the metamorphic basement in the source area.4. In the Lower Eocene Yangxi Formation, the paleocurrent direction mainly shows NNE, and the gravel diameter increases, which indicate that the palaeogeographic pattern of Jianghan Basin that the Northwest was higher than the Southeast since Paleocene had changed. Some alluvial fan-fan delta depositional systems were developed on the western and southern margin of the basin.