Sedimentary evolution of the Holocene subaqueous Changjiang Delta, with an emphasis on contributions of the two major Rivers, the Changjiang and Yellow Rivers

Subaqueous deltas of large rivers are important repositories of historical environmental changes, and understanding the evolution of deltas is essential for extracting paleoenvironmental data. This study focuses on investigating the evolution of the Holocene subaqueous Changjiang Delta using a long core CJK11 (72.2 m long). The uppermost Holocene mud layer (36.7 m thick) is divided into three units with varying accumulation rates. Through the analysis of source-discriminating proxies, such as clay mineral composition, geochemical trace elements, and strontium isotope ratios (Sr-87/Sr-86), it is determined that a significant proportion of sediments were derived from the Yellow River (peaking at 36.6 % and averaging 18.4 %), in addition to the predominant sediments from the Changjiang River. By integrating these results with core isochronous correlations and geological contexts, this study establishes the evolution pattern of the modern subaqueous Changjiang Delta, characterized by three distinct stages. During the initial stage (10-5 ka), the study area shifted to neritic environments far from the Changjiang Estuary and experienced slow accumulation due to limited input from the Changjiang and Yellow River-derived sediments. In the middle period (5-3 ka), the study area was situated in neritic environments near the Changjiang Estuary and experienced a sedimentary hiatus due to the absence of contributions from both rivers under cold and arid climatic conditions. High accumulation rates observed locally during the earlier periods may have been influenced by marine hydrodynamic reworking and redeposition processes. In the recent period (3-0 ka), the study area transitioned to prodelta environments, with spatially and temporally varying contributions from the two rivers due to coastal changes resulting from rapid delta progradation. The sedimentary evolution of the subaqueous Changjiang Delta was primarily controlled by climate fluctuations, which may encompass specific factors such as delta progradation, Yellow River channel shifts, and coastal current processes.