Magnetic fabric study of the Cambrian Stage 3 sedimentary rocks in Eastern Yunnan and its implications for paleocurrent direction

In this paper, a total of 42 sites from the Early Cambrian Shiyantou Formation, Yulingshan Formation and Hongjingshao Formation were collected in Zhujiaqing section and Guliancun section for the study of rock magnetism and anisotropy of magnetic susceptibility. The experimental results show that the magnetic minerals in the samples include magnetite, hematite and a small amount of goethite, while paramagneticminerals are the main contributors to the AMS. In both sections, the magnetic foliation is relatively developed and the degree of anisotropy is low, showing typical sedimentary characteristics. However, considered the relationship between bedding strike and the distribution of AMS ellipsoid principal axis, the AMS results of Zhujiaqing section reflect the initial deformation fabrics under the late compressive stress near E-W direction, while the AMS results of Guliancun section retain the primary imbricated sedimentary fabrics, including flow fabrics and transverse fabrics. Through further analysis of shape factor (q) and imbricated angle (β) of samples in Guliancun section, it is found that during several million years of deposition from Yuanshan to Hongjingshao Formation, the hydrodynamic conditions gradually increased, and the paleocurrentic direction was SW-NE without significant change, and the sedimentary source area may be the Kangdian old land to the west.