Evolution of the sedimentary environment on the continental shelf of southeastern Hainan Island under the influences of sea level and climate during the Holocene

Abstract

The South China Sea, which connects the Indian Ocean and the Pacific Ocean, is an important part of the Indo-Pacific Warm Pool. This study examined the provenance and evolution of the sedimentary environment on the southeastern Hainan Island continental shelf in the northwestern South China Sea through AMS 14C dating, grain size analysis, and clay mineral analysis of sediments from Core QZ4. The clay mineral analysis indicated that the terrigenous detritus originated from Hainan Island, while the grain size data identified three endmembers: EM1 and EM2, corresponding to the fine-grained material transported by the oceanic current system, and EM3, corresponding to the coarse-grained material input by rivers from proximal sources. The sedimentary environment in the study area underwent three stages: foreshore (11.2–9.2 ka BP), nearshore (9.2–6.2 ka BP), and shallow shelf (6.2 ka BP to present). From 11.2 to 6.2 ka BP, the sedimentary environment was mainly controlled by sea level changes, although extreme cold events (such as the 9.4 ka BP and the 8.2 ka BP event) had a significant effect on the southeastern continental shelf of Hainan Island. From 6.2 ka BP to the present, the sedimentary record has mainly been influenced by climate change, and an increase in riverine contribution and the enhancement of chemical weathering may have been caused by rising typhoon intensity or frequency and possibly by an increase in human activities. These findings will be valuable for conducting high-resolution research on typhoons by analyzing sediments on the eastern Hainan Island shelf and neighboring areas.