Sediment flux variation and environmental implications in the East Hainan Coast, South China Sea during the last 20 ka—a luminescence chronological investigation

Abstract

Sediments deposited on the continental shelf are indicative of paleo sea-level and terrestrial-marine interaction. A reliable chronology of the continental shelf sediments is required for paleoenvironmental and paleoceanographical investigations. In this study, the chronology of the terrestrial-to-marine sedimentary sequence in the East Hainan Coast, South China Sea (SCS), was established using luminescence and radiocarbon dating approaches. The luminescence characteristics of quartz post-infrared (pIR)-blue and pIR-pulsed OSL signals, K-feldspar and polymineral IR and post-IR IRSL (pIRIR) signals, were thoroughly studied and compared using six representative samples. The quartz pIR-blue and pIR-pulsed OSL ages are generally consistent with each other. The pIRIR₁₅₀ (subscript shows the stimulation temperature) ages slightly underestimate the associated quartz luminescence ages, likely due to fading under-correction. Chronology of the sediments was established using the post-IR blue OSL ages, indicating the terrestrial-to-marine sedimentation occurred during the last 20 ka. Episodic sedimentation in the East Hainan Coast was revealed by slow sedimentation during the periods of pre- (19.7–11.5 ka) and mid-Holocene (8.7–7.0 ka), while rapid sedimentation occurred during the early Holocene (11.5–8.7 ka). The exposed environment and the Younger Dryas cold event may be attributed to the slow sedimentation during the periods of ca. 19.7–14.3 and 12.9–11.5 ka, whilst the rapidly rising sea-level during 14.3–12.9 ka resulted in rare sedimentation under the coastal to neritic environments. Tremendous fluvial input corresponding to considerable precipitation resulted from intensification of the East Asian Summer Monsoon during the early Holocene (11.5–8.7 ka). Deepening water level, inundation of the Qiongzhou Strait and vegetation densification, may change the process of sediment transportation, source and flux, causing slow sedimentation in the eastern inner shelf to the Hainan Island in the mid-Holocene (8.7–7.0 ka).