A Study On The Characteristics Of Carbonate Petrology And Carbonate Diagenesis Of Zhujiang Formation In The Miocene In The East Part Of Pearl River Mouth Basin

This study area is located in the Pearl River Mouth Basin,the Miocene Zhujiang Formation cabornate layers for research purposes.On the basis of the outcomes of Predecessors and guided by paleontology and sedimentology,the characteristics and diagenesis of the Miocene Zhujiang Formation carbonate rocks in the eastern part of the Pearl River Mouth Basin are studied deeply through the observation of Cores and thin sections.The study suggest that the components of carbonate rocks of the study area include created shelf biological components, bonded biological components, the barrier plot biological components, bioclastic particles, red algae stone, breccia, lumps, intraclasts, micrite, sparry and seepage silt.On this basis,using Zeng yunfu(1980)’s classification of carbonate rocks and combining Embry and Klovan (1971) Classification of biological reef,the Pearl River group carbonate have been classified in three types:reef limestone, grainstone and micrite.The reef limestone is further divided into the coral skeleton rock, sedimentary rocks of coralline algae bonding rocks and coral barrier sedimentary rocks,and coralline algae bonding rocks occupy the main position.Grainstone composed of bioclastic limestone and a small number intraclast limestones,bioclastic algal debris, foraminiferal and bone chips.The observation of cores and thin sections are used for identifing the Zhujiang Formation carbonate sedimentary structures.Reef shelf created structure, colluvium, algal layers,biological burrows and drilling and the top and bottom showing structure are identified.There also exist a small amount of mud grain structure in the deposition in the reef lagoon.As paleontology being a guide,the observation of Cores and thin sections are used in order to identify the fossils in the carbonate rocks of the study area. The identified fossils types include green algae, coralline algae, foraminifera, corals, sponges, bryozoans, bivalves, gastropods, ostracods and echinoderms.Overall, although the variety of fossils, the main distribution area is occupied by coralline algae, followed by foraminifera.Reef-building organisms are coralline algae, a small amount of coral and bryozoans and the rest are Habitat reef organisms.Zhujiang Formation carbonate pore is studied,and the pore is divided into two categories according to genesis:primary porosity and secondary porosity.The main pore types in Zhujiang Formatin carbonate rocks are Primary porosity, including original intergranular pore, remaining intergranular pore, organisms cavity hole, algae hole and so on. Secondary porosity include intragranular dissolution porosity and grain dissolution porosity, followed by casting pore.Based on previous studies and the Petrological characteristics,the facies of LF15-1-1well are divided into several subfacies including reef base, reef core, reef flat, biological beach and reef lagoon.The diagenesis of Zhujiang Formation carbonate rocks have gone through the seabed diagenetic environment, sea undercurrent diagenetic environment, atmospheric freshwater diagenetic environment and burial diagenetic environment.The seabed and seawater undercurrent diagenetic environment are further divided into the reef, beach, lagoon and tidal flat environment.Atmosphere diagenetic environment is divided into the atmosphere freshwater vadose zone, the atmospheric undercurrent of fresh water and mixing water environment of meteoric water and seawater.The burial diagenetic environment is divided into shallow buried, buried deep burial diagenetic environment.The main types diagenesis of the Pearl RiverFormation carbonate rocks in study area are bonding diagenesis,microcrystallization, cementation, dissolution, and dolomitization.There are multiple phases about the cementation and dissolution.The formation mechanism of dolomitization include the causes of biological during the synsedimentary or quasi-synsedimentary period,causes of mixed water and causes of burial.Combined with the diagenetic environment, Zhujiang Formation carbonate rocks experienced early biological bonding,microcrystallization and early cementation, dissolution, granular calcite cementation, echinoderms overgrowth, dissolution, mixing dolomitization, burial dissolution, buried dolomization in order.