Pearl River sediment dispersal over its associated delta‐estuary‐shelf system during the Holocene

Abstract

To understand the Holocene sedimentary evolution of the Pearl River associated delta–estuary–shelf system, high‐resolution seismic data were acquired from Lingdingyang Bay to the inner shelf. A Pearl‐derived Holocene subaqueous clinoform developed over the pre‐Holocene incised channel/valley network. Overlying the Holocene ravinement surface, progradational highstand and acoustically semi‐transparent or transparent transgressive system tracts are separated by a maximum flooding surface. Restricted and thick in‐channel/in‐valley retrogressive deposits represent an earlier transgressive deposit. Displaying a westward‐oriented along‐shore extent, the highstand sediment accumulated asymmetrically within 30 m water depths, corresponding to a modern hydrodynamic environment. The wedge‐shaped highstand unit thickened landward with a depocentre (>15 m) located in western Lingdingyang Bay, possibly because of higher sediment trap efficiency inside the salinity front. Preliminary analyses suggest that the Pearl River has been trapping sediment to fill its extensive estuarine system for most of the Holocene and its sediment trap efficiency is greater since the sea‐level highstand. Since ca 7.5 ka bp, the total volume of highstand sediment accumulated in the entire delta‐estuary‐shelf dispersal system was approximately 128.36 × 109 m3. The calculated highstand riverine sediment flux was 16.01 to 16.50 Mt/yr. This value is equivalent to approximately one‐fifth of the flux that occurred prior to widespread dam construction and likely related to late‐Holocene intensified anthropogenic influence in South China. Since ca 7.5 ka bp, only ca 35% of the Pearl‐derived sediment has been dispersed to offshore shelf areas from the delta‐estuary system. With the dramatic decrease in river sediment discharge in recent decades, a larger fraction of Pearl‐derived sediment transported to the shelf might have been interrupted and changed.