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TitleMolybdenum speciation tracking hydrocarbon migration in fine-grained sedimentary rocks
AuthorArdakani, O HORCID logo; Hlohowskyj, S R; Chappaz, A; Sanei, HORCID logo; Liseroudi, M H; Wood, J M
SourceGeochimica et Cosmochimica Acta vol. 283, 2020 p. 136-148, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200104
Mediapaper; on-line; digital
File formatpdf; html
ProvinceAlberta; British Columbia
NTS83M/03; 83M/04; 83M/05; 83M/06; 83M/11; 83M/12; 83M/13; 83M/14; 93P/01; 93P/02; 93P/03; 93P/06; 93P/07; 93P/08; 93P/09; 93P/10; 93P/11; 93P/14; 93P/15; 93P/16
AreaDawson Creek; Peace River
Lat/Long WENS-121.0833 -119.0000 55.8000 55.0000
Subjectsfossil fuels; geochemistry; structural geology; Science and Technology; Nature and Environment; Lower Triassic; petroleum resources; hydrocarbons; hydrocarbon migration; thermal maturation; sedimentary basins; bedrock geology; lithology; sedimentary rocks; siltstones; shales; structural features; grabens; faults, extension; structural controls; molybdenum geochemistry; concentration; isotope ratios; paleoenvironment; depositional environment; hydrothermal alteration; dolomitization; diagenesis; paleogeography; spectroscopic analyses; bitumen; wells; organic geochemistry; petrographic analyses; element distribution; pyrite; oxygen; sulphur; Montney Formation; Dawson Creek Graben Complex; Western Canadian Sedimentary Basin; Pangea; Panthallassic Ocean; Phanerozoic; Mesozoic; Triassic
Illustrationslocation maps; geoscientific sketch maps; plots; tables; photomicrographs
ProgramGeoscience for New Energy Supply (GNES) Shale Reservoir Characterization
Released2020 06 12
AbstractMolybdenum (Mo) systematics (i.e., total concentration and isotope ratios) are widely used for the reconstruction of paleo-redox conditions in sedimentary records. However, the geochemical processes affecting the distribution of Mo in carbonaceous fine-grained sedimentary rocks remain unclear. This study investigates how the organic matter type may control Mo concentration and speciation in siltstone/shale strata of the Lower Triassic Montney Formation in the Western Canadian Sedimentary Basin (WCSB) to identify the effects of hydrocarbon expulsion and migration, fluid/rock interactions, and thermal maturity on Mo geochemistry when used as a paleo-redox proxy.
The bulk Mo concentration in the studied samples varies from 0.2 to 86ppm (mean = 13 ± 16.7 ppm), with Mo enrichment factors of 22.7 ± 24.4 suggesting an anoxic paleo-depositional setting. The X-ray Absorption Near Edge Spectroscopy (XANES) results show the presence of two separate Mo species within distinct geographic locations: (1) a group with a higher average Mo oxidation state where Mo is mostly surrounded by oxygen (O) atoms in an octahedral configuration, and (2) a group showing a lower average Mo oxidation state where Mo is mostly surrounded by sulfur (S) atoms in a tetrahedral configuration.
The reduced Mo species are distributed in the vicinity of fault-related hydrothermal diagenesis/dolomitization zones. In contrast, the oxidized Mo species are found associated with samples enriched with solid bitumen/pyrobitumen. The results of our study show Mo speciation can significantly help to elucidate complex paleo-redox histories.
Summary(Plain Language Summary, not published)
This study shows how diagenesis and hydrocarbon generation could change paleo-redox proxies in the sedimentary record.

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