华南海岸沙丘岩的特征及其与海滩岩的区别

沙丘岩是热带亚热带的一种特殊的岩石类型，尽管外貌相似，但它们成因和特征上有别于海滩岩。作者通过对西沙石岛、海南岛文昌和临高、广东阳江青洲岛、汕头广澳等处具一定代表性的沙丘岩的研究，总结了沙丘岩的沉积学、岩石学特征及其与海滩岩的区别。华南沙丘岩由岛屿上的灰砂和含生物碎屑的海岸风成沙丘物质胶结而成。分布高程可达＋６０ｍ以上，岩石中发育板状交错层理、大型槽状交错层理、上凸层理、似水平层理以及根管构造；其物质来源与海滩砂具继承关系，兼具风成砂的特点，部分沙丘岩还混有坡积物及陆生生物壳体。沙丘岩的颗粒多为中砂粒径，普遍分选好，（ＳＫ１）偏度变化比较大，ＫＧ峰度较小，Ｙ１值为负值，与海滩砂、海滩岩差别较大。沙丘岩中发育各种淡水渗流环境中特有的胶结物和胶结组构。虽然沙丘岩与现代海滩岩相比，其Ｃａ、Ｍｇ、Ｓｒ元素的含量及比例不同，但可以完全与上升海滩岩相似。本文作者认为:辨别沙丘岩主要从产状、沉积构造、粒度分析、胶结物及组构诸方面进行研究。

Characteristics of Dune Rocks in the South China Coast and Their Differences from Beach Rocks

Dune rock is a special type of rocks in tropic and subtropic areas.Although dune rock is similar to beach rock in the external figure,their origins and features are quite different.By the study on some representative outcrops of dune rocks in Shidao (Xisha Islands),Wenchang and Linggao (Hainan Island),Qingzhou Island(Yangjian,Guangdong) and Guang-Ao (Shantou,Guangdong),the author makes a summary to the sedimentological,petrological characteristics of dune rocks and their differences from beach rocks. Dune rocks in South China are formed by the cementation of island limesands and coastal bioclastic dune sands.which can be distributed in the zone (with an altitude over bom).There are high angle plate cross-bedding,megatrough cross-bedding,convex cross-bedding,para-parallel bedding,megatrough cross-bedding,convex cross-bedding,Parallel bedding,and casting tubes (mould) of tree roots in the rocks.The clastic materials of dune rock inherit the characters of the beach sands,but also carry on the features of eolian sands.Some of them contain the collision sediments or bodies of terrestrial organisms. The grains of dune rocks which are, in general, middle-fine sands are well sorted with variable SK 1, lower KG and negative Y 1, which are quite different from those of beach sands.The cement minerals and fabrics,Paculiar in the fresh water vadose environment, are welldevoloped in dune rocks.Although the Ca,Mg,and Sr contents and proportions in dune rocks are different from those of beach rocks, they can be very similar to those of uplift beach rocks. So,the author considers that the main way to recognize dune rocks is to study their outcrop occurrence,sedimentary structure,granulometry,cement and cement fabric, etc.