Biological Reef Succession Of The Lower Ordovician In Liujiachang Area Of Songzi County,Hubei Province

In the past 30 years,the research on reefs at home and abroad has also achieved certain results,but there are also many shortcomings,such as the research on the biology reefs formed by microorganisms and the succession relationship of metazoan reefs,and the mainstay of reef succession.There are also many problems in the understanding of control factors.Based on careful observation and actual measurement of the relevant Orta system profiles of the Songzi Liujiachang and the systematic research studies,the theories and methods of bioreef geology,sedimentary petrology and paleoecology are adopted as the guide.Based on the introduction of the regional geological background and the types of reefs,the research on the succession of reefs and its controlling factors was carried out,and the following understandings were made:The research on the types of reefs in the Liujiachang area shows that the types of reefs in the Lower Ordovician in this area include microbial reefs and metazoan reefs.Among them,micro-reefs mainly include bonded reefs and stucco reefs.The bonded reefs are mainly stromatolites.It can be seen in the Nanjinguan Formation,the Fenxiang Formation,and the Honghuayuan Formation.Metazoan reefs mainly include barrier reefs,bond-barrier reefs,and barrier-bonded reefs,with cyanobacteria-bottlestone-blocking reefs,echinoderms-cyanobacteria-bonded reefs.bottle stone-cyanobacteria barrier-bonded reef and echinoderms-cyanobacteria-bonded reef-based,can be seen in the Nanjinguan Formation,the Fenxiang Formation,the Honghuayuan Formation.The succession study of Nanjinuan Formation,the Fenxiang Formation and the Honghuayuan Formation reef in the Lower Ordovician was systematically carried out.It is believed that the Lower Ordovician reef succession is characterized by the fact that the Nanjinguan Formation has a smaller biological thickness and thickness.It is characterized by thin and wide distribution,as well as microbial reefs and macroscopic organisms.The Honghuayuan Formation is characterized by a slightly larger body,larger thickness and wider distribution,as well as macro-reefs and micro-organisms.The Fenxiang Formation has the transitional characteristics of the Nanjinguan Formation and the Honghuayuan Formation.The succession process revealed that after the decline and disintegration of the Middle Cambrian bone reef,the succession of the Lower Ordovician reef experienced the recovery from the Nanjinguan Formation to the Honghuayuan Formation.The succession process is as follows: the Nanjinguan Formation reef has experienced the Pelmatozoan barrier reef? Pelmatozoan-cyanobacteria reef succession process,and the subgroup reef has experienced Batostoma reef?Calathium?blue-green algae reef?Archaeoscsyphia reef ? The succession process of the Batostoma reef.The Honghuayuan Formation experienced the Pelmatozoan reef?blue-green algae-bottle stone Calathium bond-barrier reef?Calathium barrier reef succession process.Analysis of the control factors of biological reefs shows that the sedimentary environment is one of the main controlling factors for the development of reefs.The sedimentary environment of the Lower Ordovician reefs in the study area has undergone a process of deepening the water body.It is semi-closed in the middle of the sedimentary period of the Nanjinguan Formation,with high salinity and temperature,making the succession of the stromatolite reefs to a cactus reef.The decline of the bottleneck reefs in the stratified reefs and the Honghuayuan Formation of the Fenxiang Formation was caused by the deepening of the water in the paleoenvironment and the increase of turbidity.Therefore,the development and succession of reefs are obviously constrained by the paleoenvironment and its changes.The succession of the Early Ordovician reefs in the Songzi Liujiachang area was significantly affected by changes in sea level.The formation of the early echinoderms in the Nanjinguan Formation benefited from the first sea level rise.In the middle of the sedimentary period of the Nanjinguan Formation,the crust reef replaced the stromatolite due to the decline of sea level.The decline of the shoal reef and the Honghuayuan Formation of the basket reefs in the Fenxiang Formation is the result of a rapid rise in relative sea level.Therefore,the development and succession of reefs are obviously constrained by sea level and its changes.During the formation and succession of early Ordovician reef-buiding organisms and reefs,the Lower Ordovician micro-organisms such as Gewan algae are the main contributors to the reef.These microorganisms can not only participate in the formation and reef-building of stromatolites,clots,but also promote the formation and evolution of the mid-late macroscopic reefs in the Early Ordovician.More importantly,these microbes played a very important role in the recovery of the Early Ordovician reefs after the extinction of the skeletal reefs in the Middle Cambrian.In the process of biological reef formation and succession,paleontology,hydrodynamic conditions and storm action may have a certain control effect on the succession of reefs.Paleontology itself can participate in the formation of biological reef.Hydrodynamic conditions affect the external morphology of stratified rock reefs.Storm action may play a role in the formation and transformation of biological reef-based reefs.