A Fine Study Of The Botryoid Structure Of The Sinian Dengying Formation In The Sichuan Basin

A special type of carbonate fabric was developed in the Sinian Dengying Formation of Sichuan Basin.The shape of carbonate rock is like Grapes,so it is called botryoidal structure.In this paper,the botryoidal structures that are developed in the sections of Wangcang,Qingping,Yangba,Qianjiang,Songlin and other places are chosen as the object of study.Starting from the single laminar layer,from the point of view of the laminated periodicity,on the basis of spatial distribution and external morphology analysis,the advanced analytical techniques are used to subtly study its internal structure,material composition,geochemical characteristics and other aspects,so as to further find out the internal laminar structure of botryoidal structure and its material characteristics and differences,illustrate the construction mechanism of its prosody laminated structure,and finally establish the genetic model of the botryoidal structure of Sinian Dengying Formation of Sichuan Basin,which makes contribution to the research development of botryoidal structure.1?Through the observation of wild field section,it is found that the outcome state of botryoidal structure has two characteristics.One is that three types of combinations come along at its vertical direction:The first type of combination at vertical direction is the cyanobacteria bonded dolomite-botryoidal structure;the second type of combination at vertical direction is nucleoid-karyotype and micrite dolomite interlayer-botryoidal structure;the third type of combination at vertical direction is nucleated stone-seepage beans-botryoidal structure.These three types of combination indicate that the botryoidal structure was developed near the exposed surface of the top of upward gyratory water that became shallow.The second is that the botryoidal structure can't be only developed from the bedding,but also can be developed in the cave of structure solution fissure,and meanwhile the two production sites are connected with the same environment.The botryoidal structure developed from the bedding was formed in sedimentary-quasi-identical environment with two characteristics of stratum and cyclicity,but the botryoidal structure formed in the dissolution fissure is located nearby and connected each other.Furthermore,it can be seen that the botryoidal structure has the characteristics of stratum and cyclicity.2?By using the electron microscope,cathode luminescence microscope,scanning electron microscope and other technical means,the botryoidal structure samples and its grinding sheets are observed.It can be seen that the surface characteristics and evolution of overlaying lamina of botryoidal structure play an important role in the construction of the botryoidal structure.Meanwhile,from the observation and analysis of the microstructure of the botryoidal structure,it can be learn that the botryoidal structure was formed in the oscillating water,the development of cyanobacteria was key importance to the formation of botryoidal structure,and its development degree is related to the slight change of water depth.3.By using the advanced instruments such as LA-ICP-MS and others,the main elements,microelements,rare earth elements,carbon and oxygen isotopes of botryoidal structure are analyzed and studied.The characteristics of carbon and oxygen isotopes reveal that the botryoidal structure was formed in the seawater environment,the composed dolomite was formed in sedimentary-quasi-syndiagenetic stage,and the construction of the lamina was controlled by changes in the depth of water;Oxygen isotopes reveal ancient temperature characteristics,indicating that the botryoidal structure was formed in a warm climate;the salinity characteristics obtained from calculation of carbon and oxygen isotopes,indicating that the water salinity in the formation of botryoidal structure was higher;the distributed model of rare-earth elements,?Ce,Sr/Ba and Sr/Ca values further confirm that the botryoidal structure was formed in the seawater environment;V/(V+Ni)reveals that high degree of anoxia is beneficial to the development of dark lamina.4?Through a systematic analysis of the outcome state and internal structure of botryoidal structure,and by using the combination between micro and Marco means,and between geology and geochemistry means,finally it is verified that the botryoidal structure was formed in the shallow-water place of seawater environment that was confined in the oscillation.