Neogene paleomagnetic chronology of the Laolongwan Basin, NW China: New insight for the northeastward expansion of the Tibetan Plateau

Abstract

The Laolongwan Basin, located on the northeastern margin of the Tibetan Plateau, has a thick layer of Neogene red sediments deposited, recording the northeastward growth process of the Tibetan Plateau. However, due to the lack of high-precision chronology of the late Cenozoic sediments in the basin, the understanding of the growth process of the northeastern margin of the Tibetan Plateau is limited. Based on regional geological surveys, this paper presents a high-precision paleomagnetic stratigraphic chronology study on the Neogene strata of the basin, and establishes a chronological framework for the Laolongwan Basin spanning from ∼ 13.61 Ma to 2.58 Ma. Integrating the paleomagnetic chronological framework with regional geological survey results, the Neogene sedimentary rocks of the Laolongwan Basin are divided into the late Miocene Xianshuihe Formation (∼13.61–8.11 Ma) and the late Miocene to late Pliocene Linxia Formation (8.11–2.58 Ma). Combined with high-precision measured stratigraphic sections, our work indicates a significant change in sedimentary facies at ca. 8.11 Ma, transitioning from siltstone and mudstone deposition to conglomerate deposition, and the sedimentation rate increased remarkably from 256 m/Myr to 544.8 m/Myr, indicating that the northeastward expansion of the Tibetan Plateau affected the Laolongwan Basin at ca. 8.11 Ma.