Analysis Of Structural Characteristics Of Creatures And Their Relationship With Phosphorus Formation In The Cambrian Phosphorites,Zhijin,Guizhou

Phosphorus rock series at the bottom of the Cambrian system in Guizhou have rich rare earth resources with large deposit scale,so the deposit genesis has been of concern all the time and a large number of relevant researches on it has been carried out.However,as the current research is mainly confirmed to the enrichment of rare earth resources in the phosphorites and causes of the phosphorites and it is seldom on the relationship between the large number of biologic fossil assemblage and phosphorus formation in the phosphorites.This paper takes the fossils in the phosphorites at the bottom of the Cambrian system as the entry point,carries out research by centering on the biologic fossil assemblages in different phosphorus environment,microstructure and phosphorus-containing characteristics of fossils and their relationships with the enrichment of phosphorus through a large number of field investigation,sampling,rock-mineral determination,analysis of element geochemistry,statistics by microscope,electron microscope based analysis and EDS,and obtains the following results:a.Through field measurements and analysis of the sedimentary characteristics in the phosphorus-containing section in Zhijin County,it is discovered that the depositional environment has undergone the change from the subtidal-intertidal deposits to the supralittoral ones,the abundance and diversity of the fossils are low with poor condition of phosphorus formation in the area of the scutching plant-Yinchanggou-Xiongjiachang;in the area of Lianxing-Gezhongwu which is the subtidal-intertidal zone,the condition of phosphorus formation is good,the abundance and diversity of biological fossils are high and the high-grade and great-thickness phosphorites are also formed.Through the statistical analysis of the fossil assemblage of small shelly animals in the phosphorites in the six sampling sections: Xiongjiachang,Lianxing,Yinchanggou,the scutching plant,Gaoshan and Gezhongwu,this paper combines with the sedimentary environment of the phosphorus-containing rock series in the section,draws the characteristics of the biological fossils in the phosphorus-containing rock series at the bottom of the Cambrian system in Zhijin County in Guizhou and the relation schema of them with the change in the sedimentary environment,analyzes the relationships between the characteristics of biological assemblage and phosphorus formation and considers there are obvious positive relationships between biologic fossil assemblage and phosphorus formation,that is,the high the degree of biological enrichment and the diversity are,the more likely for phosphorus formation it is.b.Early Cambrian period is that of big fossil radiation of the fossils of small shelly animals globally when the phosphorites contain a large number of different fossils of small shelly animals.Through the observation by microscope of the fossils of small shelly animals such as Turcutheca,Paracircotheca,Zhijinites,Loculitheca zhijinensis and Protospongia,this paper describes their microstructure characteristics.It discovers the shell wall of Turcutheca is mainly of concentric multilayer structure and the number of the unit layer is related with its age;the shell wall of Paracircotheca exists the structure of gas cell,similar to Nautilus and ammonites;the wall shell of Zhijinite is of obvious medullary cavity structure,elliptoid in the cross section and the shell cavity is of fibrous structure parallel to the extension of the shell;Loculitheca zhijinensis' s shell wall is monolayer and inside the shell wall is the two-level cyclic next-door structure,so Loculitheca zhijinensis is considered coelenterate;in addition,it also discovers that Protospongia which is with the triradiate biaxial needle is siliceous in its spicule with microcrystalline structure and that the higher the abundance and diversity of creatures are,the more favorable for phosphorus formation it is.c.Through EDS and contrastive analysis of element characteristics of the core padded section,shell wall and wall rocks of Turcutheca,this paper determines the main components of Turcutheca's shell wall to be francolite.Through the micro-zone analysis by microscope,it discovers not only small shelly animals are the enrichment of phosphorous,the surroundings of their fossils are also that of phosphorous,which displays that creatures probably have the effect of absorbing phosphorous from the sea and play an important role in the sedimentation of phosphorous,and what's more,they break down a large number of organic substances after their death,changing the PH value of the sea and providing physicochemical conditions favorable to phosphorous sedimentation with the further depositions of phosphorites.d.Through the element geochemical analysis and comparison of phosphorites in different sections in Zhijin County,it considers in the deposition of phosphorites in Zhijin,the environment of phosphorus formation is basically that of rich oxygen and the ascending current brings a large number of deep-sea of phosphorus enrichment which is rich not only in phosphorus,but also in Se,U,V and rare earth elements.Thus,the enrichment of rare earth in the phosphorites and element geochemistry characteristics characterized by hot-water deposition are caused.The ascending current brings a large number of nutrient elements such as phosphorus,which provides the condition for the prosperity of small shelly animals and algae;meanwhile,the biochemical action also plays an important role in the deposition of phosphorites.