COMPOSITIONS OF ORGANIC CARBON AND NITROGEN AND CARBON ISOTOPE OF POSTGLACIAL SEDIMENTS IN THE YANGTZE RIVER DELTA AND THE PALEOENVIRONMENT IMPLICATION

Postglacial deposition in the Yangtze River delta primarily consists of riverbed, flood plain as well as estuarine, shallow marine and delta facies. Compositions of organic elements, organic carbon isotope and calcium carbonate show systematic variations in core CM and HM sediments, suggesting paleoclimatic variability in the Yangtze drainage basin including the delta during the postglacial period. The analytical results correspond well with the pollen data but there are also some fluctuations. Organic matter deposited in the fluvial and delta facies mainly came from terrestrial C3 plant, and intense human activity during last 2 000 years might have changed the soil weathering and vegetation types in the drainage basin. Because of intense land-sea interaction and widespread discontinuity in the postglacial sedimentary strata of the Yangtze River delta it is difficult to reliably decipher the palaeoenvironmental changes in the estuarine and delta area just through the study of bulk compositions of organic elements, carbon isotope and CaCO₃. Therefore, seeking more sensitive and reliable proxies for palaeoenvironmental changes is urgently needed.