Controlling Factors Of Microbialites In The Lower Ordovician Nanjingguan Formation In Songzi Area,Hubei Province

Studies have shown that microbes Ordovician carbonate rocks under Songzi more developed regions,they are not only rich types and phenomena,but also with domestic and foreign microbes on rocks synchronization.I carefully observed,theories and methods related to research base for Measured Songziliujiachang Ordovician profile as well as the systematic study and research have been published in order to reef geology,sedimentary petrology,geochemistry and ancient ecology as a guide,the study of regional geological background and relevant information on all aspects of microbial rock,rock and carried out the study of microbial control factors,made the following understanding:Through the analysis of the external geometry and the internal structure of microbial carbonate rock,the microbial carbonate rock is divided into stromatolite,nucleated stone and clotstone.Among them,clotstones can be divided into porphyrites and banded clotstones;stromatolites can be divided into layered stromatolites,corrugated stromatolites and columnar stromatolites.The lithology,characterized in depositing a deposition environment configuration flag,and the flag microbiolite Geochemical analysis region,and the study area nanjinguan component and open platform with platform limitations,which can be divided into restricted platform relative to granulocytes beach debris lagoon facies and facies;open platform and can be divided into sub-phase and a shallow beach between Yahya phase.The analysis results show that,in the limited platform facies,the water body has poor circulation,low energy,and the overall salinity is relatively high.It is suitable for the growth of microbial carbonate rocks,with layered stromatolite and columnar stromatolite developed;In the platform facies,the water body has good circulation and high energy,but the salinity is lower than that of the limited platform,and there are wavy stromatolites,mat-shaped stromatolites,and clotstones.Based on the analysis of the controlling factors of microbial rock,it is believed that the sea level of the Nanjinguan Formation has undergone two cycles of change.The analysis of the change of Ca / Mg ratio showed that the Ca / Mg ratio of the first stage of the Nanjinguan Formation was higher and the paleotemperature was slightly higher.Analysis of the characteristic changes of oxygen isotopes shows that the values of ?18O in the second and third sections of the Nanjinguan Formation are higher than those in the first and fourth sections,and the paleotemperatures of the first and fourth sections are higher.Seawater has a certain evaporation effect,which is more conducive to the reproduction and growth of stromatolites,which is also consistent with the development of sedimentary facies in the study area.By comparing the indication significance of the Sr / Ba value to the paleo-salinity,it is concluded that the Sr / Ba value of the first segment of the Nanjinguan Formation is continuously decreasing,reflecting the continuous decrease of the paleo-salinity;The value increases first and then decreases,and the ancient salinity also increases first and then decreases.Therefore,the increase of paleo-salinity is beneficial to the reproduction and growth of microbial carbonate rocks.On the whole,the changes of carbon,oxygen isotope elements and Sr / Ba ratio in the study area show two major cycles,which are basically consistent with the relative sea level change trend,and also reflect the periodicity of the changes of paleosalinity and paleotemperature.Paleo-oxygen phase also has a certain control effect on the development of microbial rocks.In an oxygen-rich environment,the temperature and salinity of the paleo-seawater are more conducive to the development of microbial carbonate rocks and the development of biological reefs.By analyzing the trace element Th / U ratio and V / V + Ni ratio in the study area,the paleo-oxygen phase changes in the study area were analyzed,and combined with the types and characteristics of the rocks collected,most of the Nanjinguan Formation in the study area was anoxic reducing environment However,in the oxygen-rich environment,there are stromatolites,clotstones,and nucleated stones,indicating that oxygen-rich conditions are conducive to the development and growth of microbial carbonate rocks.According to the analysis,the effect of metazoan on the microbial carbonate rock is mainly manifested in that gastropods have eaten and destroyed the bacteria and algae in the microbial carbonate rock.At the same time,the echinoderm fossils and blue-green algae can also form a reef together.Therefore,the change in the abundance of microbial carbonate rocks has a certain relationship with metazoa,but it is also the result of the ecological environment.