| This paper focus on the Dengying Formation of Sinian system,Sichuan Basin,guides by the new principles and methods of modern sedimentology,carbonate diagenesis,reservoir geology and geochemistry,bases on the core drilling,cores and field profiles,log data,combines with a series of modern analysis methods,such as the cathodoluminescence,the carbon and oxygen isotopes,the scanning electron microscope,the energy dispersion spectrum and the x-ray diffraction,makes a deep research on the stratum characteristics,sedimentary facies characteristics and litho-geochemistry characteristics.on this base,we make a deep analysis of the genesis of dolomite of dengying formation,Integrate the regional geological background and the lithofacies palaeogeographic characteristics,and finally summarized the model of dolomitization.The Dengying Formation of Sinian system could be divided into Deng 1,Deng 2,Deng 3 and Deng 4 from the bottom up,while the sedimentary system of Deng 1,Deng 2 and Deng 3 are primarily carbonate platform,the sedimentary system of Deng 3 are mixed platform and terrigenous clastic shore.during the deposition period of Deng 2 and Deng 4,the bacteria and algae have a prosperity development and build a widely distribution mud mound in the carbonate platform,the mound-beach complex subfacies consist of mud mound and grain beach become the most favourable reservoir development zone of Dengying Formation.There are quite a number of rock types in Dengying Formation,which could be divided into 5 categories,11 sub-types and a number of small cals,while the primary reservoir rock types are graindolomite,grainy dolomites and algae dolomite,and the leading reservoir rock types are(algal bound)dolarenite and algae dolomite(algal clot dolomite,algal bound frame-dolomitite,algal stromatolite)among them,on this basis,the lithofacies paleogeography of Dengying Formation,Dengl,2 member and Deng 4 member were elucidated by the method of single factor analysis and multi-factors comprehensive graphing.The Dengying formation,Dengying Formation,Dengl,2 member and Deng 4 member are maintained the sedimentary pattern of shallow in the west and deep in the east,which has the typical sedimentary characteristics of epicontinental carbonate platform,and the deposits from west to east are respectively platform facies,platform edge facies and slope-basin facies.the analysis of geochemical characteristic indicat that the dolomite samples generally have higher ?13 C,lower ?18 0,low order degree and relative higher content of K,Na and Sr as trace elements,they mainly appear dark red--dark brown under the cathodoluminescence.All the features show that the dolomite were formed in the seawater penecontemporaneous diagenetic environment,and the results of the energy spectrum analysis showed that the algal play a very important role in the formingcprocess of dolomite.Comprehensive consider the petrologic and geochemical features,combine the paleogeographic pattern of Dengying Formation,this paper believe the dolomitization of Dengying Formation is penecontemporaneous eaporation concentration and reflux permeability dolomitization,which are participated by microorganisms:during the deposion of Dengying formation,the sedimentary water was limited by the Isolation and shelter effect of palaeohigh.Additionally,the paleoclimate environment was hot and drg,the evaporation was quite intense.Meanwhile,the prolific bacteria and algae continuously consumed Ca2+and upgrade Mg2+as they grow,the normal water became high-Mg brine,and it constantly contacted with the early loose lime mud and aragonite,And eventually lead to dolomitization... |
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