开敞型潮坪潮汐层偶形成和保存的若干问题

简要综述了中国开敞型潮坪的分布与特征,总结了多年来在开敞型潮坪所做的野外观测结果,包括不同时间尺度沉降板观测分析潮汐层偶的生成和保存,插桩观测季节性潮滩冲淤和研究砂、泥质单层的形成与保存.结果表明,潮流和波浪侵蚀造成开敞型潮坪潮汐纹层的保存率极低,连续性差.季节性强风浪和平静天气交替形成的小型层序,其中砂、泥质纹层厚度的变化与大小潮旋回所形成的沉积序列类似,但二者的成因不同,所代表的时间尺度差别较大.因此,在进行高分辨率古潮汐环境研究时需严格分析潮汐沉积的连续性.

Some Problems on Tidal-couplet Formation and Preservation on Open-coast Tidal Flats

After a brief review of the previous studies on distributions and physical environments of Chinese open-coast tidal flats,this paper focuses on analyses of the continuity of tidal flat deposits based on our long time field observations.Different time scales tile observations were carried out to understand the link of tidal-couplet formation and preservation to processes during calm weather conditions.Elevation monitoring by the graduated stakes was carried out to study formation and preservation of sand-dominated and mud-dominated layers.The results show that preservation rates of tidal couplets is very low due to erosion by tidal-currents and waves,and the continuity of the open tidal flat deposits is poor.A small sequence,consisting of a sand-dominated layer and a mud-dominated layer,results from seasonal alternation of storm and calm weather conditions.Small sequences share the similar trend of lamia-thickness variations with neap-spring cycles,but they are different in genesis and the former represents a time unit much longer than the latter.Therofore,it is emphasized that the continuity of ancient tidal rhythmites should be strictly examined when they are used to study paleotides.