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

Key words: 
• dune rock /
• beach rock /
• sedimentology /
• petrology

Abstract: Dune rock is a special type of rocks in tropic and subtropic areas. Although dune rock is similar tobeach rock in the external figure, their origins and features are quite different. By the study on some rep-resentative 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 asummary to the sedimentological, petrological characteristics of dune rocks and their differences frombeach rocks. Dune rocks in South China are formed by the cementation of island limesands and coastal bioclasticdensands. which can be dstributed in the zone(with an altitude over bom).Th ere are high angle plate cros s一bedding, megatrough cro ss一bedding, conv ex cross- bedding, pares- parallel bedding, megatrough croc s一bedding, conv ex cross- bedding, Parallel bedding, and cacting tubes(mould) of tree roots in therocks. The elastic materials of dune rock inherit the characters of the beach sands, but also carry on thefeatures 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 arewell sorted with variableand negative Ywhich are quite different from those of beach sands. The cement miner一als and fabrics, Peculiar in the fresh water vadose environment, are welldevoloped in dune rocks. Al-though the Ca Mg} and Sr contents and proportions in dune rocks are different from those of beachrocks, 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 outcropo ccur-rence, sedimentary structure, granulometry，cement and〔ement fabric，etc·