Lithofacies And Geochemical Characteristics Of Ordovician Limestone In Shuntogol Region,Tarim

The aim of this paper is to clarify the classification,lithology,sedimentary action,sedimentary environment,lithofacies and geochemical elements of the ordovician limestone in shuntuogol and its southern region of the tarim basin.Based on the detailed analysis and description of the core and the combination with the microscopic slice,the rocks are classified and the sedimentary facies are divided according to the previous research results.The diagenesis and diagenetic environment of ordovician limestone were revealed through geochemical analysis,strontium isotope analysis and oxygen isotope analysis,and finally diagenetic facies were classified.The syntorgol ordovician limestone can be divided into micritic limestone,granulated limestone,bioskeletal limestone and conic limestone.Micritic limestone is mainly divided into two categories:?1?micritic limestone:the main structure of micritic limestone is the stucco matrix,in which there are a lot of siliciform microphytes.?2?algal micritic limestone:based on the micritic structure,it includes a lot of algal pellets;Grainy limestone is divided into:?1?internal clastic limestone,which can be divided into sand and gravel chips and powder chips according to the grain size.?2?Algal limestone:contains cryptophyta internally.There are also numerous foraminifera between the grains,including acanthosis and ostracoda,as well as brachiopods.?3?pellet limestone:the particles are mainly pellet,at the same time there will be local sand.?4?bioclastic limestone:its sort is generally more disorderly,but in the form of a good;Biological skeleton limestone can be divided into skeleton limestone,cloud-bearing skeleton limestone and cloud-like skeleton limestone.The structure is mainly composed of sand debris,usually pellet and sand debris of different types;Cone-stacked limestone usually occurs in impure limestone.Normal water environment formation limestone with high the ¹33 C,¹⁸ O,low ⁸⁷ Sr/⁸⁶ Sr,rich Sr,poor Mn,Fe and heavy metals and rare earth elements,limestone,affected by the water environment with low ¹³ C,¹⁸ O,high ⁸⁷ Sr/⁸⁶ Sr,poor Sr,rich Mn,Fe and the characteristics of heavy metals and rare earth elements.Argillaceous limestone is mainly rich in heavy metals and rare earth elements.It belongs to the weak reductive sedimentary environment near the surface where the weak hydrodynamic environment is strongly influenced by fresh water.The sand-gravel clastic limestone is mainly enriched with Ca.It is a sedimentary environment of strong reducing transition zone with strong hydrodynamics and weak influence of fresh water,and belongs to the diagenetic facies of mixed water.Algal limestone main element is rich in Sr,the main enrichment pelletal limestone Fe and Mn,similar sedimentary environment,are all affected by the hydrodynamic and fresh water are weaker strong reducing Marine sedimentary environment,particles tend to occur algae such as drilling mud crystallization effect,but the algal boundstone for mixed water main diagenesis and pelleted limestone for seawater undercurrent diagenesis;The cone-laminated limestone is mainly enriched with Sr and Ca,and developed in the environment of reducing transition zone with weak hydrodynamics.It is little affected by fresh water,and shows the diagenetic characteristics of seawater undercurrent.