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TitleDiagenetic evolution of a sedimentary system (Michigan Basin): insights from petrography and S-isotope micro-analysis of pyrite
AuthorJautzy, J JORCID logo; Petts, D CORCID logo; Clark, I D; Al, T A; Stern, R A; Jensen, M
SourceChemical Geology vol. 541, 119580, 2020 p. 1-14,
Alt SeriesNatural Resources Canada, Contribution Series 20190639
Mediapaper; on-line; digital
File formatpdf; html
AreaLake Huron
Lat/Long WENS -82.0000 -81.0000 45.0000 44.0000
Subjectsgeochemistry; stratigraphy; sedimentology; Science and Technology; Nature and Environment; sedimentary basins; diagenesis; petrography; pyrite; isotopic studies; sulphur isotope ratios; bedrock geology; lithology; sedimentary rocks; shales; carbonates; whole rock analyses; mass spectrometer analysis; geological evolution; hydrothermal systems; stratigraphic analyses; Michigan Basin; Cobourg Formation; Black River Group; Phanerozoic; Paleozoic; Ordovician; Cambrian
Illustrationsgeoscientific maps; lithologic sections; photomicrographs; profiles; plots; bar graphs
Released2020 03 07
AbstractThe study presents a detailed investigation of S-isotope systematics of pyrite from Cambrian-Ordovician sedimentary rocks along the eastern flank of the Michigan Basin, Ontario, Canada. Whole-rock and secondary-ion mass spectrometry (SIMS) pyrite analyses of 34S/32S were undertaken in association with a detailed petrographic investigation of the different crystal morphologies to better constrain the diagenetic history of the sedimentary rocks by informing about the processes of pyrite formation. The broad range of SIMS isotopic data (i.e., -37.1 per mille < delta-34S < +80.3 per mille) reveals that three different stratigraphic units experienced different diagenetic pathways of pyrite formation: (1) the Ordovician shales containing primarily biogenic framboidal pyrite formed during two different crystal growth phases (i.e., early diagenesis with delta-34S from ~-20 to +5.0 per mille and late diagenesis with delta-34S from ~+20.0 to +80 per mille); (2) the Cobourg formation containing relatively 34S-depleted tabular pyrite (i.e., delta-34S ~ -25 per mille) which likely reflects a late replacement phase after sulphate mineral dissolution; and (3) the Cambrian and the Ordovician Black River Group carbonates that share a genetic link in pyrite formation and a complex history of hydrothermal fluid movement. In general, the pyrite in the studied stratigraphic sequence seems to have retained S-isotope signatures indicative of a closed system at the scale of pyrite formation. This study demonstrates the importance of investigating the isotopic systematics of S-species at the microscale level to help understand the evolution of sedimentary basins over geological time scales.
Summary(Plain Language Summary, not published)
Here we present sulfur isotope abundance data measured at the 1/1000th millimeter scale on small pyrite crystals contained in an 800m long sedimentary rock core from the Michigan Sedimentary Basin. This study was carried out as part of the geoscientific characterization of a potential nuclear waste repository site led by the Nuclear Waste Management Organization. The results show that, in general, the pyrite found in this sedimentary sequence was formed at depth in isolated environments at the pyrite grain scale. These results allow us to strengthen our understanding of the evolution of the sedimentary rock over geological time scales (hundreds of millions of years) and thus inform on the ability of this rock to remain stable and isolated from the surface for the periods of time required for the safe disposal of radioactive waste.

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