Geochemical characteristics and genesis of lower Paleozoic dolomites in the central Bohai Sea

• Published in: Arabian journal of geosciences 2021-09, Vol.14 (17), Article 1716
• Main Authors: Song, Xiuzhang, Lv, Zhengxiang, Qin, Binchuan, Wang, Honghui, Qing, Yuanhua, Zang, Chunyan, Zhao, Wei, Hao, Peng, He, Yinjun
• Format: Article
• Language: English
• Subjects: Carbonates; Cathodoluminescence; Diagenesis; Dolomite; Dolomitization; Dolostone; Earth and Environmental Science; Earth science; Earth Sciences; Fluids; Geochemistry; Isotopes; Original Paper; Paleozoic; Rare earth elements; Salinity; Salinity effects; Seepage; Terrestrial environments; Titanium dioxide; Trace elements; Uplift; X-ray diffraction
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-021-08145-5

Dolomite diagenesis is a key issue in the evolution of dolomite reservoirs. Hence, lower Paleozoic carbonate samples from the Bonan Low Uplift are analyzed. Data collected from thin sections, cathodoluminescence, X-ray diffraction, major and trace elements, rare earth elements, isotopes, and other experimental work to determine the types, diagenetic environment, and fluid characteristics of dolomite, are used to determine its genesis. Three main dolomite types are identified: D1 with a very good original structure, D2 without an original structure, and D3 with a poorly preserved original structure. The concentrations of many geochemical indicators follow the order of D1>D2>D3. The ratios of MnO to TiO 2 in both D2 and D3 are >0.5, and the Rb concentration of D2 is greater than that of D3. δCe shows that D1 and D2 are partially oxidized, while D3 is not. The D1, D2, and D3 diagenetic temperatures are 49.28, 54.96, and 50.23°C, respectively. The order degrees of D1 and D2 are 0.56 and 0.75, respectively, while that of D3 ranges widely. Comprehensive data show that D1 originated from evaporative dolomitization in the syndiagenetic period, and the diagenetic fluid was sea-sourced fluid mixed with terrestrial fluids. D2 was generated by seepage reflux dolomitization, which occurred in the penecontemporaneous-shallow burial period, and its high-salinity diagenetic fluid is inherited from sea-sourced fluids, with the participation of pore fluids. D3 was formed in shallow burial dolomitization, and its diagenetic fluid inherited from sea-sourced fluids and pore fluids is characterized by low salinity.