SEDIMENTARY STRUCTURE AND FACIES MODEL OF LATE PLEISTOCENE EOLIAN BIOCAL-CARENITES IN SHIDAO ISLAND OF XISHA ARCHIPELAGO, CHINA

The sequence of biocalcarenites occurred on Shidao Island,the highest one among the Xisha Archipelago,is characterized by the alternation of cross-beddings and parallel beddings,which,owing to the misinterpretation of the sedimentary structures,has caused some controversies.
Three kinds of boundary surfaces have been found in the sequence:the first-order boundaries marked with the occurrence of paleosols which is nearly horizontal; the second-order boundaries between dune deposits and interdune deposits,formed by the climbing of the dunes and interdunes under the action of NE-trade wind; and the third-order boundaries of cosets inclining exclusively windward.The dune deposits have well-preserved cross-beddings on a large scale,while the interdune deposits show roughly paralled bedding.
In conclusion,the coexistence of the three boundary surfaces and the dune and interdune deposits marks the feature of the eolian biocalcarenites.