Study On The Palaeoecology Of Coral-microbial Reef Of Middle Ordovician In Haoshi River,Southern Ordos Basin

In this paper,the coral-microbial reefs and reef-building corals and microorganisms developed in the middle Ordovician Pingliang Formation in the Yongshou Haoshi River in the southern margin of the Ordos Basin are taken as the main research objects,and the species of Tabulate corals are identified,their systematic paleontological characteristics are described,and 2 genera and 2 species of Tabulate corals are identified.For Lichenaria and Amsassia,to identify calcified cyanobacteria: Acuasiphonoria,Ortonella,Proaulopora.According to the field survey data,the average height and width of the coral mass in the study area are about3.7cm and 8.1cm,and nearly 20 coral mass can be found in the outcrop with some layers of 9 meters.In some local areas,the coral mass forms a skeleton supporting structure,and most of the coral mass is wrapped and tied by the laminaceous cryptobacteria algae microorganisms.It is speculated that the coral growth was vigorous during the deposition period,although it was entangled,the development of coral reef was not affected.According to the laboratory study,the data of paleontological fossils in the microscopic thin sections of two sections in the study area were collected.The microscopic study found that cyanobacteria had two phenomena: the attachment between the calcified bones of coral and the entangling on the outside of the coral mass.Cyanobacteria were symbiotic organisms during the development of coral.The development stages of the Ordovician coral-microbial reef in the Haoshi River reflect the ecological competition between the coral and the microbiome: In the early stage of coral growth,the bloom of cyanobacteria and other microorganisms does not block the light or affect the growth and development of plexiform complex coral.Instead,because it is wrapped around the calcified skeleton of coral,the coral blocks are connected together,which can resist wind and waves and form a coral reef.In the late period,cryptococcus algae microorganisms dominated,resulting in a sharp decrease in the number of corals.In the survival competition between bacteria algae and corals,a large number of bacteria algae flourished in the late period,destroying the material cycle needed for coral growth,leading to the gradual extinction of corals.The Ordovician coral-microbial reef on the Haoshi River is the first organic reef in the North China Plate after the beginning of the Ordovician benthic radiation,and its development model is a major change based on the reef system dominated by microorganisms,which has epoch-making significance.In this paper,through field measurement and laboratory study,the data of the size of paleontological fossils and the size of coral mass in the microscopic sections of two sections in the study area were collected,and the stratigraphic lithology,the development characteristics of the reef and the composition of the paleontological community in the study area were obtained,so as to explore the paleoecological relationship between the reef-building coral,cyanobacteria and cryptococcus algae in the study area.