Characteristics and impacts on favorable reservoirs of carbonate ramp microfacies: A case study of the Middle-Lower Ordovician in Gucheng area, Tarim Basin, NW China

LIU Yini,HU Mingyi,ZHANG San,ZHANG Junlong,GAO Da,XIAO Chuantao

Table 1 Characteristic parameters of sedimentary microfacies of the Ordovician carbonate ramp in the Gucheng area, Tarim Basin

Subfacies Microfacies Hydrological dynamics Back ramp Argillaceous dolomitic flat: Laminar powdered-fine crystalline dolomite; dolomite lagoon: micrite dolomite Between the highest and the mean sea levels Shallow ramp inner zone Dolomitic shoal: fine-middle crystalline dolomite with residual sand debris; top flat: coarse-middle crystalline dolomite with well-developed dissolved pores; inter-shoal flat: powder crystal dolomite Between the mean and the lowest sea levels Shallow ramp outer zone Medium-high energy shoal: sparry conglomerate and sandy limestone, oolitic limestone; low-energy shoal: micrite- sparry sandy and silty limestone; inter-shoal sea: micrite limestone Between the lowest sea level and the sunny wave base Deep ramp Storm shoal: thin micrite- sparry conglomerate limestone; static mud: micrite limestone Between the fair wave base and the storm wave base Outer ramp- basin Static mud facies: widely developed marl and dark mudstone Below the storm wave base