The REE geochemistry and heavy mineral composition of BS24 core: implication to the Late Holocene sedimentary evolution in the North Yellow Sea

The mud area of the North Yellow Sea is characterized by unique geographical location, abundant terrestrial sediment supply, and complex sedimentary environment. Therefore, revealing the sedimentary evolution of the mud area of the North Yellow Sea is of great significance for systematic understanding of “source-sink” scheme in the North Yellow Sea under the impact of global change. In this paper, AMS¹⁴C dating, grain size, clay grain size, and REE (rare earth element) and heavy mineral composition of BS24 core sediments in the margin of the mud area of the North Yellow Sea were analyzed to identify the provenance and environment characteristics of the sediments. Furthermore, the sedimentary evolution process in the North Yellow Sea was discussed. Results show that the BS24 core has obvious differentiation of LREE and HREE, the chondrite normalized partition curve of REE inclines to the right, LREE is enriched, HREE is depleted, and had no obvious anomalies of δEu and δCe normalized in the overland crust. The variation trend of REEs is relatively consistent, a boundary at 170 cm, large fluctuation range in the upper segment, and a relatively stable content in the lower segment. A total of 30 heavy minerals were identified, of which biotite (37.46%) and authigenic pyrite (22.39%) are most common, and pyroxene, ferric oxide and unstable minerals were low in content. The clay grain size and very fine sand composition of the BS24 core indicate that the source was mainly from the Yellow River since the Late Holocene. The variation of authigenic pyrite content in BS24 core reflected the variation in cold water mass strength in the North Yellow Sea. Since 650 cal. a BP, the strength of the cold water mass in the North Yellow Sea increased and the authigenic pyrite content decreased. During 650-1 560 cal. a BP, the study area was in a reductive environment, and the strength of the cold water mass in the North Yellow Sea was weakened. The lack of convective environment was favorable for the formation of authigenic pyrite.