杭州湾南岸庵东潮坪现代沉积特征

在进行庵东潮坪水文要素定点测量的基础上,对地貌特征,沉积粒度,沉积构造及重向剖面作了全面分析与研究。结果表明,滩地位于杭州湾进、退潮流的交会点,控制其发育的主动力为潮汐作用,具明显的不规则半日潮特性,涨潮流强度远大于落潮流,造就了宽达十余公里的潮滩地貌。滩地水动力深受湾内水流影响,高潮期服从其总体潮流流向,导致潮坪上发育众多与杭州湾深槽系统相连的潮沟,破坏了沉积物正常分布规律,高潮坪存在一定向平行岸线的大型潮沟,受强劲水流影响,沉积粒度粗化,并因快冲快淤而产生变形构造;中潮坪接受退潮期潮沟漫岸物质,粒度相对较小,分选性变差,沉积构造以直脊流水波痕及板状交错层理为主;低潮坪潮流作用大、沉积粒度粗,分选性最佳,发育小型流水波痕,内部构造以槽状交错层理,“青鱼刺”层理及再作用构造为特征。潮坪近岸处潮沟迁移层序及浪成波痕层理的发现反映水动力异常强大,威胁人工海塘的安全,建议停止进一步围垦滩涂,采取促淤方法,抑制潮沟的发育,以维持滩地稳定。

INTERTIDAL FLAT SEDIMENTS OF ANDONG BEACH IN THE SOUTHERN BANK OF HANGZHOU BAY

With its hydrodynamic factors measured, the Andong intertidal flat was studied on its beach geomorphology, sedimentary grade and structure and vertical section. The results show, at the point of intersection of the flood and ebb tidal currents, in Hang zhou bay, Andong has developed a 10 KM intertidalaflat under the dominant control, of the tide, which possesses an irregular half-day tidal character with stronger flood than ebb. As its hydrodynamics is deeply influenced by the tidal currents of the embay ment, there on the flat are developed a lot of tidal channels which connect the trough system in the bay, and the normal distribution of flat sediments has been muddled. On the high tidal flat, there is a large tidal channel parallel to the shoreline and the strong tidal current leads to coarser sediments with deformanon structures; The mid-flat, which has been deposited by the overflow materials of the channel, has finer deposits, and small current ripples with straight ridge and planar cross-beddings are teen on it. The low tidal flat is characterized by the coasest sediments and there are a number of current ripples with wave ridge, trough cross-beddings, herrinbone cross laminations and reactive structures in them. Tidal flat migration sequence and wave ripple beddings in the sediments near shoreline show that the powerful tidal current s threatening the artificial seawall. It is suggested to stop further reclamation of marshes and adopt artificial methods to maintain the stability of the tidal flat.