长江口现代潮滩沉积物粒度特征及其在沉积相识别中的应用

摘要

本研究通过对长江口现代潮滩6个柱状样沉积物的粒度精细分析，试图提取研究区潮滩沉积相识别的粒度敏感指标，并通过对长江三角洲南部平原一个全新世钻孔（SL67孔）潮滩沉积物的粒度研究，检验现代沉积粒度敏感指标在全新世钻孔潮滩沉积相识别中的应用。研究显示，长江口现代高潮滩和中潮滩的黏性颗粒（＜8μm）和粗粉砂（32～63μm）含量差异显著，可以成为区分高潮滩和中潮滩的敏感组分；在开敞型的中、低潮滩之间，砂（＞63μm）和细粉砂含量（8～32μm）也差异明显。长江口现代潮滩沉积物的粒度频率曲线及众数值也可以有效协助区分高潮滩、中潮滩和低潮滩沉积物。利用上述粒度敏感组分和众数指标检验 SL67孔全新世早中期在海平面波动控制下的潮滩演替过程，并揭示了7.5 cal ka BP前后的一次海平面加速上升事件。%This study takes detailed analyses on the sediment grain size for six cores from the modern tidal flats of Yangtze River mouth,to draw the diagnostic indexes for recognization of tidal flat facies in the study area.We also examined the grain size of a Holocene Borehole SL67 from the southern Yangtze delta plain so that to apply the sensitive indexes derived from modern sediments.Results demonstrate that the co-hesive sediment (<8μm) and coarse silt (32 ~63μm) could be the sensitive indexes for distinguis- hing upper and middle tidal flats.Sand (>63 μm)and fine silt (8 ~32μm) components differ obvious-ly for the middle and lower tidal flats of open coast.Results also show that the parameter mode derived from grain size frequency curves is an effective index to help identify the upper,middle and lower tidal flat sed-iments.Above sensitive sediment components and mode were applied to identify the successions of tidal flat in Holocene Borehole SL67,which revealed the mechanism of sea level change and an acceleration of sea level rise around 7.5 cal ka BP.