Evolution of Miocene organic reefs and functions of algae's reef-making inXisha Islands

The data of lithology, mineralogy, lithochemistry, palaeoorganism-palaeoeco logy of 455.25 m cores from Xichen-1 well have been obtained, the character istics, types, models of fossil taphonomy and reef-making actions about dif ferent communities of 9 genera and 43 species algae have been discussed, an d the evolution process of algae's ecologic system from community successio n to community replacement has been resumed. It is pointed out that organis m evolution (phodophyta Corallinaceae Aethesolithon nanhaiensis community r eplaced by chlorophyts Halimeda community) are related to palaeo-ocean chan ges (regression 135.51 m) from late period of early Miocene to middle Mioce ne. This conclusion is identical with the cycle curve of the global sequenc e, but different from the study of sediment basin area in the northern Sout h China Sea.