Sediment provenance and tidal current-driven recycling of Yellow River detritus in the Bohai Sea, China

Abstract

A detailed sediment-provenance study is presented on the modern Bohai Sea, China, the innermost gulf of the Yellow Sea, using framework petrography, heavy-mineral and grain-size analyses. A series of subaqueous river deltas, characteristic of multisource, is distinguished along the coastal zone. First-cycle fluviodeltaic sediments are attributed principally to three large source areas: the Loess Plateau, the Yanshan highlands, and the Horqin sandland. Coastal sands along eastern Liaodong Bay are produced by weathering and physical erosion of near-source Mesozoic granitoid rocks during Quaternary lowstands. Apart from subaqueous deltas and coastal sands, sediment provenance is only attributed to two end-member mixing with various proportions between recycled Holocene Yellow River sediments and ancient fluvial sediments of the Liaohe river system, even though detrital sources are multiple along the coast. Relative contributions are quantified on a ternary diagram of heavy-mineral compositions, using the proportion of relative distances between a given mixed area and the two end-member deltas. The eastern Bohai flood-tidal delta, characterized by abundant garnet and ilmenite, is regarded as a large repository of ancient Liaohe sediments, which had been intermittently accumulated during Quaternary lowstands and reworked during multiple transgressions. As a secondary sediment source detached from the present-day Liaohe River delta, it is remobilized and involved in the modern sedimentation. A complete tidal current-dominated depositional pattern is proposed throughout the Bohai Sea to explain sediment accumulation and recycling. We suggest that dominant ebb tidal currents, prevailing in the southern Bohai Strait, are a primary driver carrying fine-grained Yellow River sediments eastward to the Yellow Sea. In contrast, the recycling of Yellow River sediments is driven by flood tidal currents, prevailing in the northern Bohai Strait. The internal recycling process in the Bohai Sea builds the sand sheet and its terminal lobe, i.e., the eastern Bohai mud belt, whereas the external recycling process that involves the depocenters of Yellow River sediments in the outside North Yellow Sea builds the sand ridges and its terminal lobe, i.e., the quartz-rich area. This study improves our understanding on the Yellow River dispersal system. It also provides a typical example that demonstrates how ancient alluvial sediments accumulated during eustatic lowstands are reactivated and join the modern sedimentation processes.