| Abstract:Based on field observations, thin section identification and cathodoluminescence analysis, combined with elemental and isotope geochemical analysis, the petrological and geochemical characteristics of the Middle Permian carbonate rocks in northwestern Guizhou were studied. The results show that: 1) Grainstone and micritic limestone are dominated in the Middle Permian strata, and the rock samples are characterized by non-luminescence to weak luminescence. Dolomitization mainly occurs in the upper part of Qixia Formation and the first member of Maokou Formation, and the dolomites have dark rose cathodoluminescence. 2) The carbonate rocks of Qixia-Maakou Formation are relatively rich in Ni, V, Cr and U, and poor in chalcophile elements. They generally have a left-leaning REE distribution pattern with low total REE (∑REE 2.11-8.10 μg/g), relative deficit of LREE and relative enrichment of HREE. 3) The contents of elements such as Ti, Al, Zr and Th, which are easy to be enriched in terrigenous components, are low. The low Mn content (<50×10-6) and Mn/Sr ratio (<1), combined with characteristics of cathodoluminescence and REE composition, indicate that the middle Permian carbonate samples in the study area are less affected or modified by terrigorous materials. The extremely low Re, Cd, Mo, U, Cu content and obvious negative Ce anomaly indicate that the study area was dominated by oxidation environment during the Middle Permian. 4)The δ13CPDB and δ18OPDB ranges from 1.2‰ to 4.6‰ (mean 3.6‰), and from 7.4‰ to 10.1‰ (mean 9.08‰), respectively. There is no obvious correlation between δ13CPDB and δ18OPDB. The variation of carbon isotope is consistent with the transgression-regression cycle in the area, while the negative oxygen isotope is mainly the result of burial diagenesis. |
