摘要
1974—1976年,我们三次到我国西沙群岛进行了地质地貌考察,在各岛洲采集了大量海滩岩和松散堆积物样品,大部分采自海滩,部分采自其他地形部位(包括岛屿陆上、中部泻湖、礁平台和较深处),并对14个主要岛屿上的24个松散堆积物样品,进行了粒度和基本生物碎屑组分的分析。
On the basis of geological and geomorphological observations for a number of years in the Xisha Islands,24 samples of sediments have been selected from 14 coral reefs and bars for microscopic analysis of grain size and biological composition.6 categories have been identified according to quantity and gravimetry.They are:gravel,grouan,coarse sand with fine granels,medium coarse sand with fine gravels,coarse sand and medium sand.The mixed types of fine gravel and coarse sand predominate,amounting to 62.5%.A common characteristic of the sediments is their well sorting,high sphericity,and low sphericity.On the same island,grain size differs in different localities.Of the Xisha Islands,the Pyramid Rock is a unique volcanic island,where ash deposits are found.Elsewhere,the loose materials are mainly of coral fragments which may amount to 55-80%.Shell fragments come next,being about 15%.Calcareous algae,foraminiferal duricrust,zooecia stereoplasm,make up 1-6%.All these are principally carbonates in composition,with a small percentage for the non-carbonates.The analysis shows that the curve of grain size percentage does not conform with that of gravity percentage(Fig.1-4).It necessitates some consideration regarding nomenclature.The growth rate of the Xisha coral reefs has been proved to be faster than that of the sediments(0.3 cm/yr.against 0.15cm/yr.).Three types of sediments have been recognized.They are,according to the sequence of development,the tidal sand bank-the sand bar-the sand island.Mostof the sediments extend S or SW-wards,reflecting the action of N and NB winds.These sandy sediments are not protected by vegetation,and are frequently changed in shape and size.The beach sediments are the source of beach rocks representing the earliest type of carbonate rocks.Annular cementation of the beach rocks is composed principally of aragoniteneedles.Another type"of cementation is achieved by the porefilling with aragonite and high Mg-Calcareous muds.
作者
钟晋樑
黄金森
Zhong jinliang;Huang jinsen(South China sea Institute of Oceanology,Academia Sinica)
出处
《海洋与湖沼》
1979年第2期125-135,共11页
Oceanologia Et Limnologia Sinica
