Mineralogy of the Yangtze (Changjiang) shoal: Implications for provenance and land–sea interaction response to sea level changes since MIS 6

Abstract

In this study, high–resolution detrital mineral analysis was conducted on sediments from a 70.20 m borehole (core CRE–1402) located on the Yangtze (Changjiang) Shoal, which is one of the largest sheets–like sand banks globally. The research aims to offer detailed insights into the provenance of the Yangtze Shoal, as well as the corresponding sedimentary processes linked to its formation. The findings reveal that the light mineral assemblages are primarily composed of plagioclase, lithics fragments, and quartz, while the heavy mineral assemblages are dominated by epidote, hornblende, and carbonate, followed by weathered mica, biotite, actinolite–tremolit, and ilmenite. The entire suite of detrital minerals of core CRE–1402 sediments closely resemble to the lower reaches of the Yangtze River and offshore areas of Yangtze River delta. The hornblende to epidote ratios (H/E) and garnet to epidote ratios (G/E) exhibit stable values throughout the core, indicating that the sediments in core CRE–1402 primarily originated from a single terrigenous source. The Quartz–Feldspar–Lithics (QFL) ternary plot of core CRE–1402 aligns closely to the ancient Yangtze River and the subaqueous Yangtze River delta, yet far from the subaqueous Yellow River delta. Core CRE–1402 sediments were derived from Yangtze River. The Yangtze River flowed through the study area during the low sea level period of Marine Isotope Stage (MIS) 6, and to other areas from MIS 5 to MIS 2. As sea level rose during early MIS 1, the river channel incised, and the estuary shifted southward along with the formation of coastal currents. During high sea levels, the Yangtze River estuary migrated south of the study area, leading to a lack of sedimentation in the region. The Yangtze River channel likely to pass by and supply sediments to the Yangtze shoal during sea level rise. This study provides valuable insights into the history of the Yangtze River channel and estuary since MIS 6, underscoring the river's significant role in shaping the sedimentary evolution of the western coast of the South Yellow Sea.