Upper Miocene-Quaternary magnetostratigraphy and magnetic susceptibility from the Bohai Bay Basin (eastern China) and implications for regional volcanic and basinal subsidence history

Abstract

The thick Cenozoic sequence of alluvial, lacustrine, volcaniclastic, and marine sediments in the Bohai Bay Basin (BBB) of eastern China is an important sedimentary archive for studying the regional Late Cenozoic history of volcanism, tectonism, and paleoclimate changes, as well as the evolution of the East Asian monsoon system. However, well-dated deep drillcores are sparse in this region, which has prevented a comprehensive analysis of these issues. Here, we present the results of a detailed magnetostratigraphic and magnetic susceptibility study of two deep drillcores (G2 and G3) from the Huanghua Depression, with the aims of (1) refining the upper Miocene-to-Recent chronostratigraphic framework and subsidence history of the BBB, and (2) investigating its relationship to regional volcanic and tectonic events. The observed pattern of paleomagnetic polarity zones in Core G3 can be correlated well to the geomagnetic polarity time scale (GPTS). Quaternary-age peaks in the magnetic susceptibility profiles of Cores G2 and G3 may record large volcanic eruptions―they can be matched to similar peaks in other BBB drillcores, demonstrating their potential utility as regional marker horizons. Increased sedimentation rates in the study cores at ~8.0–6.4 Ma and 3.6–3.0 Ma reflect late Miocene uplift of the Taihang and Lvliang Mountains and late Pliocene BBB subsidence, respectively. Integrated into a regional framework for the upper Miocene to Recent, our magnetostratigraphic data show that subsidence of the Huanghua Depression increased from southwest to northeast.