Cathodoluminescence features and diagenetic stage division of the carbonate rocks in Buqu Formation of Jurassic,Southern Qiangtang Depression,Tibet

Based on petrographic characteristics and cathodoluminescence analysis, combined with the corresponding Fe-, Mn-, the Sr and oxygen isotope data, this article studies the cathodoluminescence features and diagenetic stage division in Buqu Formation of Jurassic carbonate rocks in Angdaercuo area of Southern Qiangtang Depression, Tibet. The results show that:(1) Carbonate rocks of Buqu Formation generally have dull cathodoluminescence, which results from lower Fe and Mn contents, indicating the limited influence of non-marine fluid during post-sedimentation and the diagenesis of the carbonates should have been governed by the marine fluid. (2) Different types of rocks with the increase of the strength of diagenesis, the content of Mn elements increased gradually, the content of Sr elements decreased gradually, the oxygen isotope values generally show the evolution characteristics of high negative direction migration, the corresponding cathodoluminescence intensity is gradually enhanced. (3) The mud-microcrystalline dolomite has the strongest cathodoluminescence and the highest Mn content. It may be related to the weakly reducing environment near the surface during dolomization. Evaporation pump and permeate reflux may be the main mechanism of the dolomization of these rocks. The crystalline dolomite has weak cathodoluminescence and low Mn content. The pore fluid may be far away from atmospheric freshwater, and the homogenization temperature of the inclusion shows that the dolomitization occurs in a deep-buried environment. (4) The Buqu Formation carbonate rock experienced a contemporaneous-penecontemporaneous stage of seawater diagenetic environment→Early diagenetic stage of near-surface -shallow burial diagenesis weak reduction environment→Middle-deep diagenetic stage of mid-deep burial of deep-cycle water and high-salinity formation water environment → Late-Cretaceous-Paleogene early tectonic thermal events hydrothermal reform stage → The exodiagenesis stage.