Anisotropy of magnetic susceptibility of the Late Cretaceous–Eocene sediments in the southeastern Fenwei Graben and its tectono-sedimentary significance

The Fenwei Graben located in the conjoint region between the Neo-Tethys tectonic domain and the western Pacific tectonic domain is key to understanding the tectonic evolution of the East Asian interior. Extensive Late Cretaceous–Paleogene fluvial and lacustrine deposits within the southeastern Fenwei Graben, provide ideal archives of early tectono-sedimentary evolution in Fenwei Graben. Recently, we find two complete Late Cretaceous–Cenozoic sections in the Lingbao Basin. These unique sections provide an excellent opportunity to investigate regional tectono-sedimentary evolution and its potential dynamic mechanisms in Fenwei Graben. The anisotropy of magnetic susceptibility (AMS) is an effective and economic method to obtain information about tectonic and/or sedimentary evolution recorded in deposits. To this end, we present an integrated rock magnetism and AMS study of 36 sampling sites from these two sections that span the interval from the Late Cretaceous to the Early Eocene. Our rock magnetism results suggest that hematite and magnetite are the main magnetic carriers of remanence, and paramagnetic minerals and hematite are major contributors to AMS in the Lingbao Basin. In addition, the reverse, intermediate and anomalous magnetic fabrics are found in these two sections, which may result from the contribution of iron-bearing carbonates in deposits. The AMS of the Lingbao Basin is a primary sedimentary fabric with the K 1 direction antiparallel to the preferential paleocurrent direction. During the Paleocene, the clockwise rotation of the paleocurrent directions in both sections is more likely to be caused by the rotation of the Lingbao basin or the relatively rapid uplift of western provenance under the influence of the India–Eurasia convergence. Moreover, the inferred early evolution of the Fenwei Graben is likely controlled by both the western Pacific plate subduction and India–Eurasia convergence.