Late Miocene to Present Paleoclimatic and Paleoenvironmental Evolution of the South China Sea Recorded in the Magneto-Cyclostratigraphy of IODP Site U1505

The continuous sedimentary cores recovered at the International Ocean Discovery Program (IODP) Site U1505, Expedition 368, provide an opportunity for paleoceanography and paleoclimate reconstruction in the continental margin of the northern South China Sea (SCS). In this study, we conducted detailed rock- and paleomagnetic studies on 420 discrete samples from the top similar to 200 m of the synthetic records of Holes U1505C and U1505D. Rock magnetic analyses indicate that low-coercivity pseudosingle domain magnetite dominates as the primary ferromagnetic mineral of Site U1505. The magnetostratigraphic age model was constructed by correlating the interpreted polarity sequence with the Geomagnetic Polarity Time Scale 2020 with the constraints of the biostratigraphic data and the distribution probability of the age of each polarity zone provided by a Dynamic Time Warping algorithm. The Milankovitch cycles of the short eccentricity, obliquity, and precession cycles were identified in the magnetic susceptibility (MS) and natural gamma radiation (NGR) series based on paleomagnetic results. We established an similar to 9 Myr high-resolution astronomical time scale by tuning the MS and NGR records to the global oxygen isotope curves, the obliquity, and the eccentricity curves of the La2004 astronomical solution. Our new age model reveals detailed sedimentation rate variations and a similar to 500 kyr hiatus across the Brunhes-Matuyama boundary related to local tectonic activity. These results lay the foundation for understanding the paleoceanography and paleoclimate evolution of the SCS.

Automated summary

The continuous sedimentary cores recovered at IODP Site U1505 in the South China Sea provide an opportunity for paleoceanography and paleoclimate reconstruction. Detailed rock- and paleomagnetic studies were conducted, revealing the prevalence of low-coercivity pseudosingle domain magnetite in the sediment samples. By correlating the polarity sequence with the Geomagnetic Polarity Time Scale 2020 and using biostratigraphic data, a magnetostratigraphic age model was constructed. This study also identified Milankovitch cycles and established a high-resolution astronomical time scale, providing insights into sedimentation rate variations and a hiatus across the Brunhes-Matuyama boundary.