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朱家尖岛是舟山群岛最东面的一个岛屿,四周港湾内广泛发育砾滩、沙滩和泥滩沉积.通过对该区现代海岸沉积的研究,可得出如下认识1.岛屿四周港湾内沉积物类型的分布受到波浪作用强度和基岩类型的制约.波浪作用东岸强,北岸次之,西岸微弱.导致东岸发育沙、砾滩,西岸泥滩广布,北岸仅在后滨和前滨中上部发育沙滩,外滩为泥滩沉积.在东岸,如凝灰岩为岸边基岩,常形成砾滩,而在花岗岩分布处则发育沙滩. 2.规模较大的海滩砾石坝多形成在由山地所夹持,略呈喇叭状和滨外地形坡度较大的港湾内侧,而在波潮流作用和砾石供给量适中的较开阔港湾内则发育沙质带状砾滩,从岸向海可分为五个带:(1)大盘形砾石带;(2)迭瓦构造带;(3)内侧骨架带;(4)球、杆状砾石带;(5)外侧骨架带.海滩砾石中特殊的盘状形态和较好的形态分迭可作为古海滩环境的鉴别标志,并且,盘状砾石的平均粒径大小尚能反映波潮流作用之强弱. 3.来源于中、细粒花岗岩、并经波潮流短矩离搬运的东岸沙滩物质以分迭极好,矿物成熟度较高的细砂、极细砂为特征,各亚相平均粒径、分迭差别小.来源于中、粗粒花岗岩就地风化产物的北岸沙滩为矿物成熟度较低,分迭较好到好的中粗沙沉积,各亚相结构特征显著,差异较大.层理构造和扁度特征无论是在中粗沙,还是在细沙海滩都可以作为进一步划分各亚相环境的标志. 4.泥滩物质主要来源于长江南岸沿岸流带来的物质以及流潮作用带来的部分钱塘江物质.滩面形态和沉积物分布受到季节变化影响,生物种类多,数量丰富,沉积构造受生物扰动强烈.
Zhujiajian Island is an island in the easternmost part of Zhoushan Archipelago, with gravel beaches, sand beaches and mudflats deposited extensively around the harbor. The study of modern coastal sedimentation in the area shows the following: 1. Sedimentation in the harbor around the island The distribution of the types of objects is limited by the intensity of the waves and the type of bedrock, with strong east coast, north coast followed by weak west coast, leading to the development of sand, gravel beach in the east coast and mud flats in the west coast. Sandy beaches are developed in the upper middle part of the foreshore and the mudflats are deposited on the Bund. On the east coast, such as tuffs, the shore bedrock often forms gravel beaches while the granite distributions develop sandy beaches. 2. Larger beach gravel dams are formed The inner side of the harbor, which is clamped by the mountain, is slightly trumpet-shaped and has a steep terrain on the foreshore, develops sandy ribbon-shaped gravel beach within the relatively open harbor where the wave tidal flow and gravel supply are moderate. From the shore to the sea Divided into five belts: (1) large-scale gravel belt; (2) Diego tile structural belt; (3) the inner skeleton band; (4) ball, rod gravel band; The discoid shape and the better morphological subdivision can be used as the identification mark of the ancient beach environment, and the disciform gravel The average grain size of the stone can still reflect the strength of the wave tidal current.3.The material from the finest grained granite in the East China Sea and transported by the short tide of the tidal current has excellent maturity and high mineral maturity Of fine sand, very fine sand, the average particle size of each sub-phase, sub-differential is small.From the northern coast of the weathering products of coarse-grained granite beaches for the mineral maturity is low, the sub-Diego better to good The coarse sediments and subfacies have obvious structural features and large differences, and the features of bedding structure and flatness can be used as a marker to further distinguish sub-facies environments in medium and coarse sandy beaches. The beach material is mainly derived from the material brought by the coastal flow along the south bank of the Yangtze River and part of the Qiantang River material brought by the tide-effect. The beach surface morphology and sediment distribution are affected by the seasonal variation with many species and abundances. The sedimentary structure is strongly bioturbated .