黄河三角洲东营港潮坪上的贝壳沉积

黄河三角洲东营港的泥质潮坪上发育大量的贝壳沉积。贝壳的特殊形态使其很容易被水流搬运,波浪的簸选、泥坪表面的侵蚀坑穴和植物根、堤坝等障碍物对贝壳的拦阻、与地形地貌或涨潮流的水流形态有关的流速降低都可以形成贝壳堆积。潮坪表面贝壳的沉积形态包括:与涨潮流有关的坑穴状、密集窝状、陡坎状、垄沟状、席状、带状以及潮汐水道中的混合沉积等类型;与波浪作用有关的堤坝状、堤坝遮挡沉积等类型。涨潮流流速降低的方式不同,贝壳沉积形态也会相应有较大的差别。另外,潮坪表面的细微起伏、潮坪底质类型和粘结性都会对贝壳的沉积形态造成较大影响,其中尤其是以密集窝状和陡坎状为特征。从东营港贝壳的沉积特征上看,潮坪上贝壳沉积的水动力条件与常见的砂砾滩、鲕粒滩、内碎屑滩有很大的不同,不能将介壳的富集一概归为滩坝相沉积。

Shell sediments on tidal flat near Dongying Harbor of Yellow River Delta

Abundant shell sediments are developed on the muddy tidal flat near the Dongying Harbor of Yellow River Delta. Shells can be easily transported by water due to their special shapes. Many factors can lead to the formation of shell sediments such as winnowing of wave,barrier of eroded crater and plant,block of bank,decline of flood current speed related to topographic and geomorphologic features and shape of flood current. These shell sediments show many different depositional configurations,including some configurations related to flood current such as pit,glomerate socket,steep chimb,groove,sheet,zone,and mixing deposition of tidal channel and some configurations related to wave such as bank,obstructed deposit by mound. Shelly depositional configurations change greatly with the declining manner of flood current speed. Small fluctuation of tidal flat surface,sediments of tidal flat surface and its cohesiveness all can influence the depositional configuration of shell sediments,especially the glomerate socket and steep chimb. Depositional hydrodynamic force of shell sediments on the tidal flat is obviously different from the normal sandy conglomeratic beach,oolitic shoal and intraclastic beach. Thus the abundance of shell sediments can not generally be grouped to beach or bar sediments.