Characteristics of grain size and magnetic susceptibility of the Late Quaternary sediments from core 07SR01 in the middle Jiangsu coast and their paleoenvironmental significances

The grain size and magnetic susceptibility of sediments from core 07SR01 in the middle Jiangsu coast were measured, as well as their variation and correlation were analyzed. Combined with the chronological framework and sedimentary facies data from the core, plus the research results of the Northern Hemisphere climate and relative sea level changes since the Late Pleistocene, the paleoenvironmental evolution of the study area was further established. It is found that the study area has experienced three periods of environmental changes from late MIS 5 to MIS 3: (1) The period of marginal bank and riverbed developed in the tidal estuary during late MIS 5 (36.10～26.65 m) which was under relatively high sea level and strong hydrodynamic conditions, the sediments deposited during this period were mainly affected by the provenance of old Yangtze River and characterized by coarse grain size, dramatical variations in sorting coefficients (0.55～2.35), extremely positive deviation with a high-narrow peak near 3 Φ and a thin tail in the frequency curve, and high magnetic susceptibilities with small fluctuations in the range of (5.81～42.16)×10⁻⁸ m³·kg⁻¹ and strongly and positively correlated with sand (＜4 Φ); (2) The period dominated by fluviolacustrine and littoral environments with weak hydrodynamics during MIS 4-3, in which the climate changed from cold and dry to warm and humid as the sea level rose after a drop (26.65～15.77 m), the sediments deposited at this period are characterized by fine grain size, stable sorting coefficients (1.51～3.03), positive deviation with a low-broad peak near 4.75 Φ in the frequency curve, low values and small variations of magnetic susceptibilities (6.46～20.04)×10⁻⁸ m³·kg⁻¹, which are weakly and positively correlated with coarse silt (4～5 Φ); (3) The period of distributary channel in the tidal estuary with relatively high sea level and strong hydrodynamics during MIS 3 (15.77～0 m), the sediments deposited at this period were strongly influenced by the old Yellow River of North Jiangsu and characterized by relatively coarse grain size and large variations in sorting coefficients (0.94～2.82), extremely positive deviation with a high-narrow peak near 3.75 Φ and a thin tail in the frequency curve, and relatively high magnetic susceptibilities with great fluctuations in the range of (10.21～57.25)×10⁻⁸ m³·kg⁻¹ and weakly and positively correlated with sand and coarse silt (＜5 Φ). To reveal the paleoenvironmental significances for combination of grain size and magnetic susceptibility of coastal sediments, will provide a necessary basis for further study on their genetic mechanisms.