The Reef Ecosystems And Initial Forming Conditions Of Reef-building Community Of Late Carboniferous In Southern Guizhou Province

Any survey of the occurrence of reef during the Carboniferous reveals that development of reef ecosystems is a gradul re-establishment process after the reef-building community having collapsed completely up on the extinction event in late Devonian.The maturity of Carboniferous reefs is low in China.The composition of reef-building organism is very monotonous;there are only one or two main builders in each reef-building stage.The reefs are all relatively small and have not broad distribution.Carboniferous reefs of China conform well to the pattern of shallow marine level-bottom community evolution.They developed in the period of stable level-bottom community.When there had worldwide metazoan framework reef ecosystems absence in Carboniferous,larger size metazoan framework reefs developed in early and late Carboniferous of southern China.This thesis mainly focuses on the phyllloid algal reef ecosystem and the large coral reef ecosystem in Late Carboniferous of south Guizhou.The Carboniferous phylloid algal reefs are widespread and well exposed in Houchang area,south Guizhou.Affected by frequent changes of depositional environments,phylloid algal reefs,bioclastic banks and mud facies form a unique depositional sequence.The worm may taked part in the construction of reef substrate,they are the pioneer of phylloid algal reef.The phylloid algae developed on the margin of carbonate platform display a narrow spectrum of ecological environment.They favor clean,turbulence,medium energy water environments and can not live in turbid water envrionment.Through studying the characteristics of the paleoecology of phylloid algae in the Late Carboniferous in well-exposed reefs in southern Guizhou Province,we find that Phylloid algae are attached via a holdfast or similar organ to substrate.Phylloid algae have a variety of morphological forms,such as single cup-shaped,cabbage-shaped and clustering cup-shaped. Its thalli have certain tenacity and intensity.The relation between phylloid algae and other normal organisms is the competition for living space.The phylloid algal reef near Wengdao village differ frome examples reported to date by the high biodiversity of organisms other than phylloid algae,this contradicts the previous "poisoning hypothesis".Thus,in terms of biodiversity,the Wengdao example represents a unique and novel case to date.The process of phylloid algal reef building was decided by phylloid algal community evolution and sedimentary entironment.Phylloid algal have active constructional ability and they could form framestone.A large-scale Carboniferous metazon framework reef is found in Bianping Village, Houchang area,South Guizhou.The reef is scare as the huge metazon framework in Carboniferous Period all over the world.The Bianping reef is constructed mostly by big phacelloid Fomithevella and its basement is composed of patch reefs.Thus,the type of Bianping reef is unusual and unique in Carboniferous.Detailed research on the reef-building communities,especially Fomithevella community,shows that biologic and physical structures of the communities play decisive roles in constructing overall structure of reef-building communities,while tropic structure of the community is a main factor to maintain development of the communities.The combined effect of biologic structure,physical structure and tropic structure leads to ecosystem balance of reef-building communities.In the reef building process,the metazoan reef-building communities are very important,they maintain the balance development of reef ecosystem.The overall natures and ecosystem of the community are decided by the key species in the community.The character,composition and function of communities would change,if the key species were taken out.The well-preserved Pennsylvanian encrusting colonial rugose coral Ivanovia cf. manchurica is widespread and easily observed in south Guizhou,China.The documents of ecological relation between Ivanovia cf.manchurica and substrate are applied to further research the characteristic of substrate colonized by Fomitchevella reef-building community which buit a large coral reef.There are three common types of hard substrate encrusted by Ivanovia cf.manchurica:in situ carbonate hardgrounds,carbonate hardground clasts,and calcareous bioclasts.Thin,spreading sheets are the most common growth form of Ivanovia cf. manchurica in the study region.A mini-domal growth form is also found.Ivanovia cf. manchurica employed peripheral,medial and mixed growth strategies to occupy a sufficient area of substrate.It favored a shallow,warm,and clear marine environment within the photic zone and had a high tolerance of water movement.In shallow,higher energy conditions,the growth forms and internal structures of Ivanovia cf.manchurica were influenced by ambient environments.Ivanovia cf.manchurica was generally smothered and covered by mud in the studied area.The Ivanovia cf.manchurica fossil communities in south Guizhou are characterized by a low-diversity assemblage conforming to the typical pattern of hard substrate marine community evolution in the Carboniferous.Through studying the substrate colonized by reef-building community of Bianping coral reef and analyzing the initial environmental conditions of the reef-building corals,in order to seek initial forming conditions of metazoan framework reef-building community in the evolution process of Carboniferous reef ecosystem.The sedimentological and paleontological phenomena underneath the coral reef indicates that Fomitchevella colonized a hard substrate. The hard substrate offered a stable habitat for Fomitchevella during its colonization stage. Fomitchevella juveniles attached to hard substrates while the adults were free-living.The strategy employed by Fomitchevella to secure a sufficient area of hard substrate was by larval aggregation.A large number of larval Fomitchevella aggregated on areas of hard substrate to form some initial small reef-building communities.The presence of a hard substrate was the key factor in the development of Bianping coral reef.Fomitchevella initially colonized a hard substrate near wave base with medium wave energy.The sedimentation rates were low and the water was relatively clear and warm during Fomitchevella colonization.The initial colonized Fomitchevella were well-adapted to mesotrophic conditions.The transformation of Fomitchevella biostrome to coral reef well reveals that the evolution process of reef-building community from level-bottom community.On some hard substrate areas,the larval aggregation of Fomitchevella is the precondition of the framework reef-building community forming.After forming the Fomitchevella community with framework reef-building function, a relative stable depositional environment is very important for Fomitchevella community to form a reef ecosystem with the balance development.The frequent changes of environment are adverse for the development of Fomitchevella community.