Fluid sources and formation environment of Late Triassic seep carbonate in eastern Oregon,United States
As an important carrier of the anaerobic oxidation process of hydrocarbons in seep systems,the petrological and geochemical characteristics of seep carbonate play a crucial role in tracing the source of fluids and the redox environment.A large number of Late Triassic seep carbonates were developed in the Oregon region of the United States.In order to investigate the characteristics of the diagenetic fluids and to reconstruct the sedimental redox environment,comprehensive petrological,carbon and oxygen isotope,trace and rare earth element content analyses were carried out in this paper.Our findings reveal that these carbonates are predominantly composed of microcrystalline calcite,preserving the needle and banded structure of aragonite,indicating that it was formed in pore water with high sulfate concentration.The carbon isotopic values(δ13C)range from-32.7‰ to-5.1‰,and a large amount of native bitumen is also visible under the microscope,suggesting that the carbon sources of the carbonate were methane,crude oil,and seawater.Rare earth elements(REEs)exhibit characteristics of light REEs depletion and heavy REEs enrichment,with a pronounced negative anomaly in Ce and an average Y/Ho ratio of 45.30,which is similar to the seawater partitioning pattern.In summary,above results indicate that the Oregon seep carbonates were formed in a shallow oxidized sedimentary environment close to the seafloor.
seep carbonatecarbon and oxygen isotopesrare-earth elementOregon,USA
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