The Characteristics And Paleoceanographic Environment Of Carboniferous Coral Reef In Guangxi

Throughout the development and evolution of worldwild reef in geological history, Carboniferous is a gradual re-establishment process for the reef-forming organisms affected by extinction events and global climate. Metazoan framework reef were relatively absence in the Carboniferous, however some larger sized metazoan have been found in south China. Carbonate platform well developed in the southern China during Carboniferous, in which the shallow sea environment was quite favourable for organisms, especially the benthic organisms, and as a result different types of reef-building communities formed. Despite all this, the maturity of Carboniferous reefs is low in China. The composition of the reef-building organism is very monotonous, and the scales of these reefs are all relatively small. This thesis mainly focus on the characteristic, evolution model, and the paleoceanographic environment of carboniferous reefs in the Langping area of Guangxi province. This thesis also comprehensively summarize the reefs formed at the same period all over the world.There are many metazoan framework reefs developing in the Langping area of Guangxi province, in which Xiadong coral reef is in Visean, and Longjiangdong coral reef, Longjiangdong patch reef and Xinzhai benthic communities are in Bashkirian. The Longjiangdong patch reef was earlier than Longjiangdong coral reef. The body parts of these carbonate buildings are built by rugose corals, which include Diphyphyllum, Siphonodendron, Lithostrotion, Antheria, Thysanophyllum, Paralithostrotion, Palastraea, Lonsdaleia and Caninia. Moreover, Syringopora and microbialite are also vital participants. From Visean to Bashkirian, the evolution of the reef-building organisms in the study area was characterized by succession and continuity. But the structure of reef-building organism communities is relatively single, in which there are only one or two main builders. The Xiadong coral reef is characterized by a large-scale, relatively complete structure, rich organisms and a relatively high diversity of reef-building organisms. And the reef was controlled by the gradually descending sea-level and increasing water dynamics, and built by Diphyphyllum community, Siphonodendron-Lithostrotion community and Diphyphyllum-Syringopora community continuously. In contrast, in the Longjiagndong coral reef, the reef-building organism communities had a low species diversity, and was only built by Diphyphyllum communities. Its growth environment was relatively complex, and controlled both by sea level and nutrition level. The growth and development of Longjiangdong patch reef basically belong to an incomplete part of Longjiangdong coral reef. The patch reef is built by Diphyphyllum community and Diphyphyllum-Caninia-Lithostrotionella community successively. The distribution of benthic communities in Xinzhai village are scattered, they are in a stage of trying to form reef without typical reefs. In these reefs and benthic communities, there is competition for spaces between individuals in phacelloid rugose corals, as well as for substrates between frame-building corals and crinoids. The individual of frame-building corals deserved to win in clonal budding and bending growth avoiding obstacle. The competition is controlled by the environment between frame-building corals and crinoids, which leads to an increase in one and a decrease in the other in biomass.Base on the carbonate stable isotopes analysis, the?18OPDB and ?13CPDB values of matrix micrite vary from -5.892‰ to -2.957‰, and 2.632‰ to 3.672‰ respectively. Firstly of all, the range of values is in accordance with the objective law of historical development in Carboniferous carbon and oxygen stable isotope. Secondly, these dates reflects temperatures ranging from 17.1? to 30.8?, the average is 22?, which shows a warm to hot climate. The water temperature in Xiadong coral reef is high in favour of reef-building corals growth in the Visean, while the low water temperature in the Bashkirian just meet the minimum requirements of growth and development for reefs. This might be affected by the glaciation of Gondwanaland. Moreover, these data indicate the reefs grew in the normal salinity marine environment in the Carboniferous.According to the comparison, induction and summary with the same period of reefs worldwide, the coral reefs mainly developed around the Paleo-Tethys Ocean. Rugose corals are an important part of the coral reefs in the Visean, and they had potential to build the large ecological reef. The Bashkirian reefs scattered on the Paleo-Tethys Ocean and its extending area, which may have inherited the paleogeographic distribution in the Visean. Furthermore, both the Visean and Bashkirian reefs are characterized by a short developing period, small thickness, simple shape, low-diversified reef-building corals and low-relief in morohology.The Bashkirian reefs inherited and develop the reef-building organisms, tectonic setting, and paleogeographic distribution of Visean reefs. Whereas the water environment for reef growth in Bashkirian was less favorable than in Visean.