Magnetostratigraphy of Quaternary sediments from borehole SYS90-1A in the South Yellow Sea

Quaternary sediments in the southern South Yellow Sea provide important geological archives for addressing Quaternary sea-level changes and environmental evolution. However, long sedimentary sequences with a reliable chrono-logical framework in this area are scarce. A detailed paleomagnetism study on sediments from borehole SYS90-1A (90.1 m) that located in the southern South Yellow Sea was carried out in combination with AMS¹⁴C dating data and published studies regarded. Eleven normal inclination zones and 11 negative inclination zones in the borehole SYS90-1A were revealed from the characteristic remanent magnetization after alternating-field demagnetization. The Matuyama/Brunhes boundary was found at the core depth of ～74.2 m. Meanwhile, the Kamikatsura excursion and Santa Rosa excursion were recognized at depth of 79.75～82.47m and 85.25～87.74m, respectively. The basal age of the core was estimated for about 0.96 Ma by the extrapolation of average sedimentation rate between the Kamikatsura excursion and Santa Rosa excursion. The average sedimentation rate of borehole SYS90-1A is 8.66 cm/ka in the late Early Pleistocene, 9.5 cm/ka since the Middle Pleistocene, and 12.8 cm/ka since the start of the Holocene. The sedimentation rate of the core showed an increasing trend since the late Early Pleistocene. This study provided a reliable geochronological framework of the borehole, which facilitated the stratigraphic division and tectonic evolution of the Quaternary System in the southern South Yellow Sea and its neighboring regions.