Characteristics and Diagenetic Significance of Carbon and Oxygen Isotopes in the Authigenic Dolomites of Lacustrine Carbonate Rocks—A Case Study of the Paleogene Shahe Jie Formation of the Shijiutuo Uplift in Bohai Sea

Abstract

Authigenic dolomites mainly deposited like pore-lining, pore filling and metasomatic replacement in the lacustrine carbonate rocks of the Shijiutuo Uplift in Bohhai Sea. Using the laser isotope analysis method to study the characteristics and diagenetic significance of the oxygen and carbon isotopes in the authigenic dolomites with different occurrences, the research results are present as follows: 1) the authigenic dolomites formed in the salty diagenetic fluid; 2) the oxygen isotope temperatures showed that the authigenic dolomites developed in 3 periods, corresponding to the three main paleoburial depth intervals such as 75 -550 m, 700 -950 m and 1400 -2300 m; 3) the earliest authigenic dolomite with the highest δ 13 C indicates that the carbon 13 originated from the primary sedimentary carbonates; the second earliest authigenic dolomite with higher and positive δ 13 C indicates that the carbon source is still dominated by the original sedimentary carbonate and affected by the bacterial degradation during the shallow burial stage; the latest authigenic dolomite with the lowest and negative δ 13 C shows that the CO2 rich in carbon 12 produced by organic matter degradation played an important role in the carbon source; 4) the authigenic dolomites can be divided into the low temperature dolomite and the high temperature dolomite through the oxygen isotope analysis, and the low temperature dolomite formed in the reflux dolomitization process in the near surface to shallow burial stage and the high temperature dolomite formed in the middle to deep burial diagenetic environment.