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TitleMicro-scale triple sulfur isotope record of sedimentary pyrite from a complex diagenetic system - case study from the Montney Formation, Alberta, Canada
AuthorKingston, AORCID logo; Ardakani, O HORCID logo
SourceAmerican Geophysical Union, Fall Meeting 2021, abstracts; 2021 p. 1 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20210287
PublisherAmerican Geophysical Union
MeetingAmerican Geophysical Union, Fall Meeting 2021; New Orleans, LA; US; December 13-17, 2021
DocumentWeb site
Mediadigital; on-line
File formatpdf; html
NTS83C; 83D; 83E; 83F; 83K; 83L; 83M; 83N; 84C; 84D; 84E; 84F
Lat/Long WENS-120.0000 -116.5000 58.0000 52.7500
Subjectsfossil fuels; sedimentology; geochemistry; mineralogy; Science and Technology; Nature and Environment; Economics and Industry; Lower Triassic; diagenesis; pyrite; isotopic studies; isotopes; sulphur; textures; mass spectrometer analysis; petrography; crystallography; morphology, crystal; recrystallization; scanning electron microscope analyses; petroleum resources; hydrocarbons; reservoir rocks; bedrock geology; lithology; sedimentary rocks; siltstones; Montney Formation; Phanerozoic; Mesozoic; Triassic
ProgramEnergy Geoscience Clean Energy Resources - Decreasing Environmental Risk
Released2021 12 01
AbstractRecent microscale analysis of pyrite at the grain level indicates large heterogeneities in pyrite sulfur isotope composition that is frequently related to multiple pyrite textures in sedimentary systems. These different types/textures of pyrite are related to different growth phases associated with multiple post-depositional diagenetic events. Differentiation of these phases of pyrites and hence diagenetic history are lost with traditional bulk rock sulfur isotope analysis. In this study we use secondary ion mass spectrometry (SIMS) to target individual pyrite grains for triple sulfur isotope analysis to evaluate the diagenetic history of the Montney Formation, an important hydrocarbon reservoir in Alberta, Canada. The Montney Fm. is a Lower Triassic dolomitic siltstone known to have undergone multiple phases of digenesis (see Liseroudi et al., 2020). Using petrographic and SEM imagery we identified several pyritic textures including: framboidal, recrystallized framboidal, and euhedral or crystalline pyrite grains. Framboidal and recrystallized framboids have the lowest delta-34S values, however, there is also broad overlap between with euhedral grains in the intermediate to higher values. A large range in delta-34S values suggest both microbial sulfate reduction during early diagenesis and thermal sulfate reduction during later diagenesis both played a role in pyrite formation. The addition of DELTA-33S values allows us to separate framboidal grains with intermediate delta-34S values from the euhedral pyrite and indicates different sulfur sources and/or formation process(es). This indicates that framboidal formation and recrystallization was earlier and from a different sulfur source than later euhedral pyrite growth providing a timeline for the subsurface sulfur cycle in the Montney Fm. The diversity of pyrite types in sedimentary environments and especially within diagenetic systems highlights the importance of microscale analysis to create accurate models of the subsurface sulfur cycle. In addition, the use of multiple sulfur isotopes offers the advantage of a greater understanding of the sources and processes responsible for pyrite formation despite similar delta-34S composition.
Summary(Plain Language Summary, not published)
The Montney Formation has a complex history of chemical alteration which is reflected in small scale variations in the isotope compositions of pyrite and anhydrite. This report using microscale isotope analysis to investigate this small scale variability and assess the processes responsible for pyrite formation. Understanding these processes is essential in order to better evaluate the processes responsible for hydrogen sulfide production in the Montney Formation.

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