The Composition,Ecological Function And Environmental Significance Of Coralline Algae From Well Chenke-2 In Xisha Islangs

Coralline algae belong to Rhodophyta,Florideophycidae,Corallinace,which is worldwide algae.Due to the shortage of continuous stratigraphic profile or and materials that are rich in fossil coralline algae,the study of coralline algae fossils in South China Sea has been in its infancy.On the foundational research of the phylogenetics and paleoecology of coralline algae in well Chenke-2,South China Sea,this study setted up the sequence of coralline algae assemblage,analyzed the function of coralline algae during the development of coral reefs and its environmental significance,furthermore,reconstructed the sedimentary environmental evolution form Miocene to Holocene in the South China Sea and the change of paleo-water-depth.The following understandings have been drew on the study of coralline algae:(1)This essay mainly about the preliminary study of coralline algae in well Chenke-2,Xisha Islands since the Miocene,3 families,4 subfamilies,11 genus and 29 species(17 uncertain species)were recognized,including Lithophylloideae Lithophyllum and Amphiroa;Mastophoroideae Spongites,Neogoniolithon and Lithoporella;Corallinoideae Jania and Corallina,Melobesiodideae Mesophyllum,Aethesolithon and Lithothamnion;Sporolithaceae Sporolithon.(2)Coralline algae in well Chenke-2 best developed near the bottom and in 510.00-360.00m member,the highest simple disparity occurs at its bottom.Coralline algae in 557.07-522.00m hardly developed,so as in 21.40-0m,and coralline algae in 557.07-522.00m mainly consisted of planktonic foraminifer.In 300.00-240.00m,coralline algae limited,and therefore,it presents the lowest diversity.The evolution model of coralline algae bottoms up is:geniculate developed in the lowest bottom,gradually evolved into nongeniculate and geniculate,next into nongeniculate,interspersed with a short Rhodoliths,and then into nongeniculate and geniculate,finally into nongeniculate.(3)Ranging from 309.00m to 312.00m,it can be divided into two large sedimentary cycles.The first sedimentary cycle(878.21-309.00m)coralline algae bottom-up experienced Corallina-Lithoporella assemblage,Aethesolithon assemblage,Mesophyllum-Lithothamnion assemblage,Spongites assemblage(Corallinoid-Melobesiodid-Mastophoroid),reflects the process of water from shallow to deep and shallow.The second sedimentary cycle(309.00-0m)Mesophyllum-Lithothamnion assemblage,Lithophyllum-Lithoporella assemblage,Lithophyllum assemblage(Melobesiodid-Lithophylloid),were occurd from bottom to top,reflects the process of water from shallow to deep,and finally to shallow.(4)Coralline algae play asignificant part during evolutionary processof coral reef,namely:The construction of the reef body provide about 5.21%of the calcium carbonate,up to 60.33%;Coralline algae bondstone,coralline algae and foraminifer bondstone,Rhodoliths,and coralline algae can build framework to expand and steady reef body;Fragments filled in the framework as the interstitial material,can be cemented by sparry and micrite as well.