RESEARCH OF THE SEDIMENTARY SEQUENCES IN THE NORTHERN OLD YELLOW RIVER DELTA SINCE THE LAST GLACIAL MAXIMUM

This paper focuses on the sedimentary features of the upper part (1.0~22.0 m) of the core ZK4, which is located in the northern Old Yellow River Delta, northern Jiangsu Province. The results, together with AMS ¹⁴C dating, suggest that a hard clay bed and fluvial sediments (between the core depth 22.00 and 16.63 m) be deposited during the Last Glacial Maximum (LGM) and the early Holocene, overlaid by the sediments (16.63~1.00 m) of tidal flat, shallow sea and Old Yellow River Delta from early Holocene to AD 1185. The core consists largely of clayey silt and silt intercalating a small number of thin layers of fine-grained sands. The grain-size frequency curves of the core sediments above 16.63 m are characterized by the alternation of unimodal and bimodal distributions, while the deposits under 16.63 m show a pattern of trimodal distribution, which changes to unimodal and bimodal distributions downwards. The sediment grain-size parameters fluctuate frequently in the core, indicating the complexity of the sediment sources (fluvial and marine) and sedimentary dynamics (freshwater runoff, tide and wave). The sedimentary sequence since the LGM, as revealed by the core ZK14, was developed under the joint interaction of sea level, sediment source and sedimentary dynamics.