C-S-Fe relationships and the isotopic composition of pyrite in the New Albany Shale of the Illinois Basin, USA

Journal Article · Thu Oct 01 04:00:00 EDT 1987 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(87)90159-1· OSTI ID:7000736

Anderson, T F; Kruger, J ^[1]; Raiswell, R ^[2]

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1. Univ. of Illinois, Urbana (USA)
2. Leeds Univ. (England)

The relationship between pyritic sulfur content (S{sub pyr}) and organic carbon content (C{sub org}) of shales analyzed from the New Albany Group depends upon C/{sub org}. For samples of <6 wt.% C{sub org}, S{sub pyr} and C{sub org} are strongly correlated (r = 0.85). For C{sub org}-rich shales (>6 wt.%), no S{sub pyr}-C{sub org} correlation is apparent. The degree of Fe pyritization (DOP) shows similar relationships to C{sub org}. These C-S-Fe relationships suggest that pyrite formation was limited by the availability of metabolizable organic carbon in samples where C{sub org} < 6 wt.% and by the availability of reactive Fe for samples where C{sub org} > 6 wt.%. Apparent sulfur isotope fractionations relative to contemporaneous seawater sulfate ({Delta}{sup 34}S) for pyrite formation average {minus}40 {per thousand} for non-calcareous shales and {minus}25 {per thousand} for calcareous shales. {Delta}{sup 34}S values become smaller with increasing C{sub org}, S{sub pyr}, and DOP for all C{sub org}-poor (<6 wt.%) and some C{sub org}-rich (<6 wt.%) shales. These trends suggest that pyrite formation occurred in a closed system or that instantaneous bacterial fractionation for sulfate reduction decreased in magnitude with increasing organic carbon content. The isotopic trends observed in the New Albany Group are not necessarily representative of other shales having a comparable range of organic carbon content, e.g. Cretaceous shales and mudstones from the western interior of North America. {Delta}{sup 34}S values in the remainder of the C{sub org}-rich New Albany Group shales are relatively large ({minus}38 to {minus}47 {per thousand}) and independent of C{sub org}, S{sub pyr}, and DOP, which suggests that pyrite in these shales formed mostly at or above the sediment-water interface by precipitation from an isotopically uniform reservoir of dissolved H{sub 2}S.

• OSTI ID: 7000736
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 51:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CARBON COMPOUNDS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
DEVONIAN PERIOD
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
ILLINOIS BASIN
INTERFACES
IRON COMPOUNDS
IRON SULFIDES
ISOTOPE RATIO
MINERALS
ORIGIN
PALEOZOIC ERA
PENNSYLVANIAN PERIOD
PRECIPITATION
PYRITE
REDUCTION
ROCKS
SEDIMENT-WATER INTERFACES
SEDIMENTARY ROCKS
SEPARATION PROCESSES
SHALES
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
SULFUR CONTENT
TRANSITION ELEMENT COMPOUNDS