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Minerals 2019, 9(1), 13; https://doi.org/10.3390/min9010013

Carbon and Oxygen Isotopic Composition of Saline Lacustrine Dolomite Cements and Its Palaeoenvironmental Significance: A Case Study of Paleogene Shahejie Formation, Bohai Sea

1
State Key Laboratory of Oil-Gas Reservoirs Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
2
College of Energy Resources, Chengdu University of Technology, Chengdu 610059, China
*
Authors to whom correspondence should be addressed.
Received: 30 November 2018 / Revised: 20 December 2018 / Accepted: 21 December 2018 / Published: 25 December 2018
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Abstract

The dolomite reservoirs in the Paleogene Shahejie Formation in the Bozhong area of the Bohai Bay Basin contain a large amount of dolomite cement. Petrologic and mineralogic studies have shown that the dolomite cements can be divided into three types according to their occurrence: coating dolomite (CD), pore-lining dolomite (LD), and pore-filling dolomite (FD). The laser microsampling technique was used to analyze the C and O isotopes in the carbonate minerals. This method is an effective way to produce CO2 gas from a particular carbonate structure in a thin section, and it has a spatial resolution of 20–50 µm and an optimal precision of approximately ±0.22σ for δ13C and δ18O in carbonate standard materials. The carbon and oxygen isotopic compositions and the oxygen isotopic geothermometer results showed that the dolomitization fluid is mainly low temperature fluid, the lake basin environment is relatively closed, and the salinity index Z value is greater than 120, which indicates the invasion of seawater. CD and early-stage LD crystals were mainly very fine crystals with faint cathodoluminescence, which indicates the early formation of diagenesis. The high temperatures of late-stage LD and FD measured by oxygen isotope thermometers indicates that they formed at a deeper depth. The dolomite cements in the study area may have formed in two stages: seepage-reflux dolomitization during the penecontemporaneous period and burial dolomitization. View Full-Text
Keywords: lacustrine carbonates; dolomite cements; Shahejie Formation; carbon-oxygen isotope; dolomitization; Bohai Bay Basin lacustrine carbonates; dolomite cements; Shahejie Formation; carbon-oxygen isotope; dolomitization; Bohai Bay Basin
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Meng, H.; Lv, Z.; Shen, Z.; Xiong, C. Carbon and Oxygen Isotopic Composition of Saline Lacustrine Dolomite Cements and Its Palaeoenvironmental Significance: A Case Study of Paleogene Shahejie Formation, Bohai Sea. Minerals 2019, 9, 13.

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