Sea-level, climate, and oceanographic controls on recent deepwater hyperpycnites: A case example from the shenhu slope (northern South China Sea)

Abstract

Hyperpycnites record information on sedimentary processes and climate change and play a significant role in hydrocarbon exploration. However, deep-water hyperpycnites can hardly be differentiated from intrabasinal turbidites since their control factors are not well understood. More detailed studies are needed to improve the knowledge of hyperpycnites. This study aims to identify and characterize hyperpycnites in the Shenhu slope and investigate their evolution in response to sea-level and climate changes using sediment gravity cores, combined with detailed grain size analysis, X-ray fluorescence scanning, X-ray computed tomography scanning, radiocarbon dating, and microscopic observations. Hyperpycnites and internal wave redistributed deposits were identified in core S19 since 42 cal ka BP. Internal wave redistributed deposits served as background deposit and dominated in the middle-late Holocene, while hyperpycnites dominated the Marine Isotope Stage 3 sequence form the early Holocene. The hyperpycnites facies S3 interbedded with S2L occurred during Marine Isotope Stage 3, facies L appeared in Last Glacial Maximum (LGM) strata, while facies S2L dominated the strata after LGM to the early Holocene. The facies distribution suggested that the strength and distribution of hyperpycnal flow were higher in warm and humid stages with low sea-level. Lower flood flows discharge in cold and dry stages limited the generation and extensional distance of hyperpycnal flows, although the sea-level was low in this stage. However, high sea-level combined with longshore and Surface waters in warm and humid stages, prevented the travel of hyperpycnal flows into deep basin. The study of hyperpycnites in the Shenhu slope reveals that the formation of deep-water hyperpycnites is influenced by a combination of factors, including sea-level fluctuations, climate change, and oceanographic processes. The amount of precipitation in the drainage basin determines the intensity and generation of hyperpycnal flows, while sea-level fluctuations affect their travel distance to the deep-water setting. Additionally, oceanographic processes such as longshore current can significantly alter hyperpycnal flows near the river mouth and shelf area, preventing them from reaching the deep basin.