Controlling Factors Of Microbialites In The Lower Ordovician Fenxiang Formation-Honghuayuan Formation In Songzi Area,Hubei Province

Microbialites is not only an important reflection of the evolution of biological life,but also contributes to the reconstruction of the ancient environment.However,the main factors affecting Microbialites development are rarely mentioned.Therefore,in this paper,the Liujiachang section of Songzi area,Hubei was selected as the research object to study the controlling factors of Microbialites in the Lower Ordovician Fenxiang-Hongyuanyuan Formation,and to try to speculate the main controlling factors for the decline of microbial rocks in the study area.The Liujiachang section is known as the largest and most representative section of the Ordovician in the Central Yangtze area.Among them,the microbial rock features are obvious and widely developed,and the carbonate rock deposition is developed continuously.It is an excellent place to study the control factors of microbial rock in this paper..Based on field investigations and field surveys of Liujiachang,combined with the thin-sheet analysis results,it is considered that the three types of Microbialites such as stromatolites,thrombolite,and oncolite are mainly developed in the Fenxiang Formation-Honghuayuan Formation in the study area.In addition,the stromatolites in the study area can be subdivided into three types:corrugated stromatolites,columnar stromatolites,and mound stromatolites,and the thrombolite are subdivided into patchy and reticular thrombolite.And this article detailed description of the Microbialites mentioned in the article from the macro and micro perspectives.Based on the identification of the lithofacies and sedimentary facies in the study area,the study area is considered to be an open platform facies beneath the carbonate platform,and can be divided into platform shoal subfacies,interplatform marine subfacies,and platform biological reef subfacies.Combining the distribution characteristics of various types of Microbialites,the deposition and distribution patterns of various types of Microbialites are summarized.Among them,the wave-shaped stromatolites developed from platform biological reef subfacies to the interplatform marine subfacies,the mound-like stromatolites developed from interplatform marine subfacies,and the columnar stromatolites developed from interplatform marine subfacies.Reticulated clotstones develop from platform shoal subfacies,Patchy clotstones develop from platform biological reef subfacies,and the Oncolite developed from platform shoal subfacies.The paleo-salinity analysis showed that the Z-value curve showed a trend of slowly changing from low to high during this period,and microbial rocks were mainly developed in areas with higher salinity in the study area.Paleotemperature analysis shows that the temperature in the study area is 18.64 ??24.83 ?,the average temperature is 21.66 ?,and the suitable temperature for the development of Microbialites is about 20 ??21 ?.Paleo-oxygen phase analysis showed that the study area was generally oxygen-rich during this period,and microbial rocks were mainly developed in areas with sufficient oxygen content in the study area.The control factors of the lower Ordovician Microbialites gradually decreasing from bottom to top are discussed.It is believed that the changes of paleotemperature,paleo-salinity and paleo-oxygen phase mainly control the development of microbial communities,and sedimentation affects the Microbialites morphology.Plane changes and metazoan animals have extremely limited development of microbial rocks.Microbialites in the study area are found with metazoan fossils and a large number of biological disturbances.Combined with the large number of metazoa in the early Middle Ordovician and the gradual rise of sea level,it is believed that metazoa limit the development of microbes.Metazoans feed on fungal algae microorganisms,resulting in a continuous decrease in the number of fungal algae microorganisms and severely destroying the growth state of microbial rocks.The rise and fall of the sea level have destroyed the living environment of the ambassador's microorganisms,resulting in the phenomenon that the Microbialites gradually decrease or even disappear over time.