Ordovician Limestone Diagenesis Of Tazhong Area In Tarim Basin

This dissertation aims to clarify the Ordovician limestone classification,lithology,diagenesis,diagenetic environment,diagenetic facies and geochemical elements characteristics of Tazhong area in Tarim Basin.Using the core description and the thin section identification confirm the lithology and classify limestone,then combine with previous research results to divide sedimentary facies.Through the analysis of geochemical elements and limestone lithology,reveal the limestone diagenesis and the environment when diagenesis happened,summarize the diagenetic facies.The result show that there are three kinds of limestone,including muddy limestone,grain limestone,bonding reef limestone.The diagenetic facies can be divided into six major categories: the first one is seawater crystal cementation facies,that the first phase cementation sediment formed in active phreatic zone of near-Surface environment,and the geochemical lelments characterized by large ratio of Sr/Ba,low ratio of Ca/Mg and rare earth element reflect the marine reducing environment without terrigenous clast;The second one is micritization facies,that the micritization sediment formed in stagnation phreatic zone in near-surface environment,and the geochemical lelments characterized by richer Sr and Ba content,poor Fe Mn Ti and K content;The third one is fresh water phreatic cementation facies,that second phase cementation sediment formed in fresh water phreatic zone of near-Surface environment,and the the geochemical lelments characterized by poor Sr contant,large ratio of Ca/Mg,and richer Fe,Mn content;The fourth is shallow phreatic dissolution facies,that the dissolution pore formed in shallow phreatic zone of supergene environment,and the geochemical lelments characterized low ratio of Sr/Ba,low ratio of V/Sc and rare earth element reflect the environment with terrigenous clast;The fifth is buried compression facies,that compression sediment formed in medium depth environment,and the geochemical lelments characterized by poor Sr,Mn content and rare earth element reflect the reducing environment;The sixth is buried dolomitizatio facies,that dolomitizatio sediment formed in medium depth environment,and the geochemical lelments characterized by definite low ratio of Ca/Mg and rare earth element reflect the reducing environment.