Magnetostratigraphy and tectonic implications of Paleogene-Neogene sediments in the Yinchuan Basin, western North China Craton

Abstract

The Yinchuan Basin, one of the Cenozoic faulted basins in the western margin of the North China Craton (NCC), was filled by thick Cenozoic fluvial-lacustrine sediments, which documented tectonic-sedimentary processes. However, many debates were highlighted in the Cenozoic tectonic evolution processes due to a lack of ages of the Cenozoic sediments in the basin. In this paper, we provide a high-resolution magnetostratigraphic records of the Yinchuan Basin based on the XL15-1-01 borehole in the southwestern basin. Detailed magnetostratigraphy of the 850-m-thick sedimentary sequences record C2An.1n to C8n.2n of the Geomagnetic Polarity Timescale (GPTS) with the age span of ∼26.06 Ma to ∼2.77 Ma, corresponding to the middle Oligocene–Pliocene, which delimits the depositional periods of the Qingshuiying, Zhangnengbu, and Ganhegou fomations in the Yinchuan Basin. The upper age limit of the Qingshuiying Formtion is 21.32 Ma, the Zhangnengbu Formation extends from 21.32 to ∼10.17 Ma, and the Ganhegou Formation spans the interval of ∼9.58 to ∼2.77 Ma. The sedimentary discontinuity between the Ganhegou Formtion and the Zhangnengbu Formation in the Yinchuan Basin initiated at ∼10.17 Ma, which is interpreted as the initial time for the northeastward expansion of the Tibetan Plateau impact on this region, and continued for ∼0.59 Myr. The depth-age correlation determined from magnetostatigraphy reveals a distinct increase in sedimentation rate at ∼9.58 Ma, responding to an intensive uplift of the Tibetan Plateau.