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Environments favoring dolomite formation at cold seeps: A case study from the Gulf of Mexico
Tong, Hongpeng; Feng, Dong1,2; Peckmann, Joern3; Roberts, Harry H.; Chen, Linying; Bian, Youyan5; Chen, Duofu1
Source PublicationCHEMICAL GEOLOGY
AbstractDolomite rarely occurs in modern marine environments, while it is ubiquitous in the geological record. This apparent contradiction made the formation mechanism of dolomite a long-standing problem haunting sedimentologists. However, dolomite is a constituent of many modern seep carbonates, providing an opportunity to investigate the conditions favoring dolomite formation at low temperatures in the shallow subseafloor. This study reports the petrology, mineralogy, carbon and oxygen stable isotopic compositions, as well as sulfur isotopic compositions of both carbonate-associated sulfate (CAS) and chromium reducible sulfur (CRS) of a set of dolomite-bearing carbonates from two seep sites (GC140 and GB382) on the northern slope of the Gulf of Mexico. The delta C-13 values of carbonates vary from -50.0 parts per thousand to 3.2 parts per thousand (V-PDB), confirming that carbonate minerals mostly resulted from methane oxidation. The corresponding delta O-18 values range from 2.6 parts per thousand to 5.9 parts per thousand (V-PDB), reflecting formation close to equilibrium with seawater composition. All carbonate samples with dolomite show similar petrologies and lack skeletal remains of seep-dwelling metazoans. The homogenous texture of microcrystalline dolomite agrees with its formation in the shallow subseafloor. Dolomite-bearing samples reveal delta O-18(CAS)/delta S-34(CAS) slopes of 0.425 and 0.435 for the two study sites, respectively. Such high slopes are significantly different from the smaller slopes of seep carbonates consisting of calcite from Gulf of Mexico seeps, suggesting low overall sulfate reduction rates during dolomite formation. This explanation is also supported by relatively high delta S-34(CRS) values ranging from -29.4 parts per thousand to 19.0 parts per thousand (V-CDT) and the positive correlation of these values with dolomite contents. Interestingly, an approximately stoichiometric dolomite sample yielded the most positive delta S-34(CRS) value, indicating a formation environment typified by low replenishment of seawater sulfate at a supposedly relatively deep sulfate methane transition zone (SMTZ). Overall, these results confirm that dolomite formation is facilitated where the SMTZ is situated at relatively great depth, where sulfate reduction rates are slowed down due to the buildup of high contents of dissolved sulfide and low seawater sulfate replenishment.
KeywordDolomite Seep delta O-18(CAS)/delta S-34(CAS) slope delta S-34(CRS) Sulfate reduction
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Document Type期刊论文
Affiliation1.Shanghai Ocean Univ, Coll Marine Sci, Shanghai Engn Res Ctr Hadal Sci & Technol, Shanghai 201306, Peoples R China
2.Qingdao Natl Lab Marine Sci & Technol, Lab Marine Mineral Resources, Qingdao 266061, Shandong, Peoples R China
3.Chinese Acad Sci, South China Sea Inst Oceanol, CAS Key Lab Ocean & Marginal Sea Geol, Guangzhou 510301, Guangdong, Peoples R China
4.Univ Hamburg, Ctr Earth Syst Res & Sustainabil, Inst Geol, D-20146 Hamburg, Germany
5.Roberts, Harry H.] Louisiana State Univ, Coll Coast & Environm, Coastal Studies Inst, Baton Rouge, LA 70803 USA
6.Chinese Acad Sci, Guangzhou Inst Geochem, CAS Key Lab Ocean & Marginal Sea Geol, Guangzhou 510640, Guangdong, Peoples R China
Recommended Citation
GB/T 7714
Tong, Hongpeng,Feng, Dong,Peckmann, Joern,et al. Environments favoring dolomite formation at cold seeps: A case study from the Gulf of Mexico[J]. CHEMICAL GEOLOGY,2019,518:9, 18.
APA Tong, Hongpeng.,Feng, Dong.,Peckmann, Joern.,Roberts, Harry H..,Chen, Linying.,...&Chen, Duofu.(2019).Environments favoring dolomite formation at cold seeps: A case study from the Gulf of Mexico.CHEMICAL GEOLOGY,518,9.
MLA Tong, Hongpeng,et al."Environments favoring dolomite formation at cold seeps: A case study from the Gulf of Mexico".CHEMICAL GEOLOGY 518(2019):9.
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