Radial Ooids Dominated By Photosynthetic Biofilm

Ooids are spherical or oval,with smooth and well-developed carbonate particles(usually <2mm in diameter),which have long been fascinated by geologists,chemists and paleontologists.Unlike the well-known microbial nucleated rocks,Oolites are traditionally regarded as abiotic coated particles.There are still many controversies about the role of physical,chemical and biological processes in the growth of ooids,including whether the deposition of carbonate on the surface of Ooids is driven by the chemical or biological activities of seawater,and the role of sediment transport and loss.The study of the growing modern marine aragonite ooids gives an explanation for the specific genetic mechanism: Ooids are the product of microbial induction and microbial influence.According to the relationship between the Cambrian Miaoling oolitic sand beach and Microbial Carbonates in the North China platform,it is found that most of the ooids are developed in microbial carbonates,combined with the filaments found in the ooids and the calcification sheath of cyanobacteria,it shows that they have obvious photosynthetic biomembrane origin,which makes the hypothesis of microbial origin of ooids put forward a progressive academic challenge to the traditional view of the origin mechanism of ooids.The oolitic sand beach in the Zhangxia formation of the Cambrian Miaoling Series in the southeast margin of the North China platform is developed in the three-stage forced regression system tract,and the ooids are concentrated locally in the stromatolite,oncoids,leiolite,thrombolite,dendrolite and other microbial carbonates;and in the further observation of the microstructure,It is found that a large number of cyanobacteria calcified scabbard are accumulated in the core of the ooids in the Zhangxia group of Anjiazhuang section,while in the Zhangxia group of Xianrendong section,the twining cyanobacteria calcified scabbard and dark muddy crystal are more clearly seen in the cortex.Because the water environment and climate factors during the formation of Cambrian ooids are not consistent with those of modern marine aragonite ooids,it has become the most fascinating problem in sedimentology to explain the calcification mechanism of oolite formation before 0.5Ga through diagenetic filter.Although the detailed genetic mechanism of the ooids can not be determined quantitatively,a series of well preserved microbial fossils have appeared in the core and cortex of the calcite radial ooids,indicating that the formation of the oolite is not a simple physical and chemical coating particles.The sedimentary fabric and microscopic characteristics of the radial ooids of Zhangxia formation of Cambrian Miaolin Series in Anjiazhuang and Xianrendong sections of Shandong Province seem to emphasize the key role of microorganisms in ooid formation.