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上海滨海平原上现发现约12条贝壳砂堤,它们厚一般0.5～1M,宽100～150M,在剖面上呈厚、宽比为1:100左右的薄层状透镜体;它们主要由贝壳和细砂组成,含较多的重矿(5～23％);其内部构造为近于水平的斜层理,无交错层出现,纹层一般厚几个毫米,由上部的贝壳层及下部的砂层联合组成。贝壳砂堤的下伏层含大量的植物根茎、铁锰结核、虫穴,结构也与现代潮上带的相似,表明它们的形成位置是潮上带。它们形成于基本稳定-微蚀、岸坡1～8％的海岸,是波浪长期改造、反复簸选的产物。它们大致形成于距今6400、5230、730、600、580年,其中早期贝壳砂堤可能与全新世的最大海进有关,后期的则与长江河口砂坝的阶段性发育有关。上海滨海平原从早到晚成陆速度加快,其中7000～4000 B.P.,成陆速度1公里/750～2000年;4000～1500 B.P.,1公里/125年;1500～580 B.P.,1公里/40年。
About 12 shell sand banks are found on the coastal plains of Shanghai. They are generally 0.5-1M thick and 100-150M wide. They are thinly lenticular lenses with thicknesses and width ratios of about 1: 100 in the cross section. They are mainly composed of shells and Fine sand composition, with more heavy ore (5 ~ 23%); its internal structure is nearly horizontal oblique bedding, no staggered layer occurs, the pattern layer is generally a few millimeters thick, the upper shell layer and the lower Sand composition. The underlying layer of shell sand dike contains a large number of plant rhizomes, ferromanganese nodules and wormholes, and the structure is also similar to the modern tidal zone, indicating that they are formed in the tidal zone. They formed in the basic stability - micro-erosion, coast 1 to 8% of the coast, is the wave of long-term transformation, repeatedly elected products. They are generally formed in 6400, 5230, 730, 600, 580 years ago, of which the early shell dike may be related to the maximum sea age of the Holocene, while the later stage is related to the stage development of the sand bar of the Yangtze estuary. Coastal plains in Shanghai have been accelerated from early to late into the sea, of which 7000 ~ 4000 BP and 1 km / 750 ~ 2000 into the land; 4000 ~ 1500 BP, 1 km / 125; 1500 ~ 580 BP, 1 km / 40 years .