Geochronology of a sedimentary core in the northwest of South China Sea and regional paleoenvironmental changes over the last million years

The South China Sea (SCS) is ones of the largest marginal seas on the Earth. Apart from IODP/ODP sites, limited progress has been made in establishing chronostratigraphy for long-term geological sequences spanning millions of years. In this study, we present findings from a sediment core (NH-01) collected from the eastern part of Hainan Island, northwest SCS, in terms of magnetostratigraphy and sedimentary/paleoenvironmental changes in the past 1 Myr. The main findings are as follows: (1) Two magnetic polarity zones in core NH-01 can be preliminarily correlated with the upper part of the intervening Matuyama chron and the Brunhes normal chrons, respectively. (2) By tuning the color indices of core NH-01 to the stacked benthic delta 18O record, the age-depth model was refined, and the sediment accumulation rates are estimated as 10-30 cm/kyr (3) The sedimentary processes in the study area display a dominant 100-kyr cycle, with contributions from precession and obliquity bands, underscoring the influence of regional sea-level changes and monsoonal evolution. Comparisons between the NH-01 sedimentary record and various global climate proxies indicate a significant shift in regional sedimentary processes around 430 kyr, which can be attributed to the pronounced impact of the Mid-Brunhes event, potentially linking it to climatic changes in the Southern Hemisphere. Consequently, sedimentary records from the northwest SCS not only capture regional environmental history but also provide insights into potential connections between different climatic systems.