Study On Carbonate Petrology Of Jialingjiang Formation Of Lower Triassic Series In Northeastern Sichuan

Carbonate diagenesis, as the most important and active field of sedimentology, has played a vitally important role in reservoir study for decades of years. Based on the predecessors’ research, in order to study petrologic characteristics of carbonate rocks, the author choose carbonate rocks of the Jialingjiang Formation, lower Triassic of the Bailixia section in Xuanhan area, the northeast Sichuan. For this, a lot of work has been done, such as observing and measuring the field section, dealing with samples, including choosing sample, grinding thin sections, and so on. Furthermore,correlative experiment has been made, such as the thin section analysis, the cathodoluminescence analysis, and so on. By comprehensive analysis, some points of view as follows:(1)There are 617.8m thicknesses in the Jialingjiang Formation, Bailixia section, Xuanhan area. The sediment develops in open platform and restricted platform in this area. Based on the lithology and sedimentary facies features of study area, there are three sections has been divided, namely the first section of the Jialingjiang Formation, the second section of the Jialingjiang Formation, the third section of the Jialingjiang Formation. In the first section of the Jialingjiang Formation, they are mainly politic microcrystalline limestone, vermicular limestone and bioclastic limestone. Those form in beach interact sea of open platforms. In the second section of the Jialingjiang Formation, the main rock types are micritic dolomite, karst breccia, a little oolitic limestone and bioclastic limestone. The sedimentary environment is the lagoonevaporated tidal flat facies of circumscribed-evaporated conditions in this section. In the third section of the Jialingjiang Formation, they are microcrystalline limestone, a few karst breccia and bioclastic limestone, all of which develop in lagoon facies of circumscribed conditions.(2)The carbonate rocks of the Jialingjiang Formation are composed by carbonate minerals, a little idio-noncarbonate minerals and terrigenous detrital minerals. Carbonate minerals are consisted of calcites and dolomites, including a few ankerites. Among those idio-noncarbonate minerals, the pyrite is the most common mineral.(3)Based on the basis of mineralogy and petrology, bying observing different diagenetic characteristics of rocks, the complicated diagenetic characteristics of the Jialingjiang Formation have been restored. It has developed those stages, such as seawater environments, fresh water environments, buried environments, and surface environments. The main diagenetic characteristics are micritizations and foliated cements, which existed in grains’ surrounding. Besides, the crystal powder dolomite, as production of penecontemporaneous dolomitizations, is the important characteristic of seawater diagenetic environments. The granular calcite cement and the selective corrosion show that it has experienced freshwater diagenetic environments. In addition, there are some diagenetic characteristics, such as the compation, the pressolution and the filling of the late calcite vein, all of which relect buried conditions. In my opinion, the dolomitization and the recrystallization of oolitic limestone are productions of shallow-middle depths of buried environments. One of the important marks of shallowmiddle depths of buried environments is the occurrence of saddle dolomites. Moreover, the occurrence of karst breccia represents the exodiagenesis in Jialingjiang Formation, lower Triassic of the Bailixia section in Xuanhan area.(4)The vermicular limestone has multiple origins. And there are essential differences in different vermicular limestone. The vermicular limestone, which belongs to descriptive term, doesn’t have genesis significance. Even though the vermicular limestone has a lot of origins, the genesis of the most of vermicular limestone is related to the participations of the creature. The biogenic origin is the major in the Jialingjiang Formation, lower Triassic. Based on different origins of vermicular limestone, four types could be divided as follows: the genesis of the bioturbation, the genesis of the dwelling burrow, the genesis of the chemical coagulation, which connected with sulfate reduction, and the genesis of the compaction.