Petrologic Characteristics And Diagenesis Environment Analysis Of Dengying Formation Dolomite In Jinsha, Yankong, Guizhou

Guided by multiple theories involving petrology,carbonate sedimentology andgeochemistry and so on, the dolomite in upper Sinian in northern Guizhou have beenstudied.Based on outcrops such as Jinsha Yankong as well as other typical wellsections or outcrops, and carry on field measurements, description, sampling andindoor cathodoluminescence, isotopes, REE, fluid inclusions, and organicgeochemistry, the types, the sedimentary facies, diagenesis, development andforming mechanisms are comprehensively studied with the following mainprogresses:According to the metasomasis view, the genesis-texture classification has beenproposed; two types and eight kind of dolomites have been identified. Namely algallaminae dolomite, algal lime dolomite, algal dolomite, algal oncoids dolomite, oolitic-beans dolomite, grape and snowflake shaped dolostone and fine crystalline dolomite;structure mainly including algal bonded structure (foam, sponge layered, bond-like),gravel debris structure, pellets structure, bright crystal structure and fine grainstructure; cements are composed of calcite and dolomite,they have multiplegenerations; develop dissolved pores between grains, mould pore,crack and othersecondary pores, etc.;Sedimentary structures are mainly laminae, grape lace-likestructure, laminated structure, birds-eye structure (panel hole), etc.; authigenicminerals are quartz, calcite, dolomite, fluorite and pyrite.Also, the sedimentary facies have been researched by the type and structure, theyare Tidal flat,Lagoon, shoal facies, Dolomite obviously controlled by sedimentaryfacies types.The diagenetic evolution has been founded, there are three diagenetic stages,Syngenetic, Diagenetic and Supergene. In those stages Compaction, pressure solution,dolomitization, recrystallization, silicification, rupture, cementation, dissolution andfilling have happened. On diagenetic sequence, overlay or similar diagenesis canhappened in the same stage, and multiple diagenesis extension at different stages, andoriented and multi-period in diagenetic stage also verified of Dengying Formationdolomites. The diagenetic environments are researched based on the geochemistrycharacteristics of the dolomites. The dolomitization mechanisms is clarified: burieddolomitization. And The Distribution and physical properties of reservoir controlledby diagenetic environments through the type and stage. Dolomite elements Ca/Mgaverage value reached1.34, reflecting the strong dolomitization; Significantcorrelation in the rock Fe, Mn content and its cathode luminescence, under reducingconditions, Fe, Mn ions more easily into the mineral lattice and enhancedluminescence; Dolomite and dolomite cements δ18O high negative bias, buried bythermal fractionation process significantly, its δ13C between0~2‰, Z value of122to135, reflecting the characteristics of the sea of the original fluid;dolomite, calcitecement and quartz fluid inclusions are Features with high temperature and highsalinity, the lowest homogenization temperatures greater than100℃, the highestvalue reached225.1℃, on behalf of burial diagenetic environment;Asphalt organicvitrinite Ro1.91~2.92%, the average reached2.64%, higher thermal evolution,reflecting the reservoir had entered the narrow burial environment, experienced a hightemperature thermal evolution;Rock REE value is very low, ranging between1.27~4.24ppm, light rare earth elements (ΣLREE) relative losses associated with highconcentrations of brine conditions, δCe δEu weak negative anomalies and anomaliesare the result of acid by the reduction of environmental impact.At last, we point out that the sandy dolarenite of Dengying Formation has goodexploration prospects, in north Guizhou.