@article{0221b9291e4e4bbb9f996aa554520d5b,
title = "Molybdenum speciation tracking hydrocarbon migration in fine-grained sedimentary rocks",
abstract = "Molybdenum (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 86 ppm (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.",
keywords = "Bitumen, Diagenesis, Mo concentration, Mo speciation, Montney formation, Paleo-redox",
author = "Ardakani, {Omid H.} and Anthony Chappaz and Hlohowskyj, {Stephan R.} and Hamed Sanei and Liseroudi, {Mastaneh H.} and Wood, {James M.}",
note = "Funding Information: The authors wish to thank Dr. J. Catalano (Journal Executive Editor) for the manuscript handling and Dr. B. Kendall (Journal Associate Editor), Drs. T. Algeo, and A. Dickson for their constructive comments. We thank Ovintiv (formerly Encana Corporation) for providing core samples and the permission to publish. The lead author wishes to thank S. Mackie for help with editing of the manuscript. The funding for this study was provided by the Natural Resources Canada (NRCan), Canada fund No 331403 Geoscience for New Energy Supply (GNES) program. Student support was provided by the Earth and Ecosystem Science Ph.D. program at Central Michigan University. The lead author wishes to thank the assistance of organic geochemistry and petrology staff of the Geological Survey of Canada (GSC) for their assistance. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank the beamline scientists from sector 13 GEO-CARS for laboratory and analysis at the APS. Funding Information: The authors wish to thank Dr. J. Catalano (Journal Executive Editor) for the manuscript handling and Dr. B. Kendall (Journal Associate Editor), Drs. T. Algeo, and A. Dickson for their constructive comments. We thank Ovintiv (formerly Encana Corporation) for providing core samples and the permission to publish. The lead author wishes to thank S. Mackie for help with editing of the manuscript. The funding for this study was provided by the Natural Resources Canada (NRCan), Canada fund No 331403 Geoscience for New Energy Supply (GNES) program. Student support was provided by the Earth and Ecosystem Science Ph.D. program at Central Michigan University . The lead author wishes to thank the assistance of organic geochemistry and petrology staff of the Geological Survey of Canada (GSC) for their assistance. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank the beamline scientists from sector 13 GEO-CARS for laboratory and analysis at the APS. Publisher Copyright: {\textcopyright} 2020 Elsevier Ltd",
year = "2020",
month = aug,
day = "15",
doi = "10.1016/j.gca.2020.06.006",
language = "English",
volume = "283",
pages = "136--148",
journal = "Geochimica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "GEOCHIMICA ET COSMOCHIMICA ACTA",
}