Molybdenum and Copper Isotope Systems as Petroleum and Paleoceanographic Tracers

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With the advent of multi-collector inductively coupled plasma mass spectrometry, metal isotope systems have emerged as a new subdiscipline of isotope geochemistry. However, development of metal isotopes as an oil-oil and oil-source rock correlation tool is in the exploratory stage. This study proposes to fully assess the molybdenum and copper isotope systems as petroleum tracers using well-studied petroleum systems containing single (Siljan region, Sweden) and multiple (Western Canada Sedimentary Basin) source rocks. Experimentally produced oil (from hydrous pyrolysis of source rocks) will establish end-member isotopic compositions for each source rock and reveal if isotope fractionation occurs between a source rock and its produced oil. Isotope and multi-element data from experimental and natural oil, and potential source rock(s), will identify a multi-proxy geochemical signature in oils that can be traced to the major source rock(s). This pioneering work will pave the way for applications to other important but less-well-understood Canadian petroleum systems.Isotope data from source rocks can also be used for paleoceanography. It is well-established that molybdenum isotope compositions from anoxic and sulfidic (euxinic) black shales can be used as a tracer for the extent of oxygenated versus anoxic conditions in ancient oceans. However, paleoceanographic applications of copper isotopes are in their infancy. This study will provide the first comprehensive dataset of copper isotope compositions for Phanerozoic and Precambrian black shales, which will enable an assessment of the nature of ancient copper biogeochemical cycling. Comparisons of copper and molybdenum isotope data may shed new insights on past local and global ocean redox conditions. The data will help determine if copper scarcity in Proterozoic oceans retarded the operation of denitrification, resulting in nitrous oxide induced greenhouse warming, and/or slowed down the rate of eukaryotic evolution. Competing hypotheses for the extent of early Phanerozoic ocean oxygenation will be tested using molybdenum and copper isotope data.