Hydrothermal links between ocean plateau formation and global anoxia at the Cenomanian-Turonian boundary Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gt54kr21f

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  • The Cretaceous was a period of extreme climatic conditions accompanied by major perturbations in ocean-atmosphere biogeochemical cycles. One of the most intriguing features is the sporadic interruption of normal marine pelagic sediment deposition by organic rich sediments deposited during oxygen-deficient conditions (ocean anoxic events OAEs). A current model for the abrupt onset and conclusion of these events relates increased trace metal delivery to the ocean during volcanic activity associated with ocean plateau construction, to the eventual depletion of oxygen and deposition of organic rich sediments. A majority of the trace metals are most likely released in eruption related "event plumes", degassed magmatic fluids mixed with seawater, rather than typical hydrothermal activity dominated by water/rock exchange. An important aspect of volcanic "event plumes" is that trace element concentrations are controlled by volatility into magmatic gases rather than solubility in water-rock reactions and therefore, the abundance pattern of released elements is fundamentally distinct from background hydrothermal venting. This study specifically evaluates a proposed link between "event plumes" associated with the construction of the Caribbean ocean plateau and OAE2 at the CenomanianlTuronian (C/T) boundary (-93 Ma) by examining five globally distributed CIT boundary sedimentary sections for major, minor and trace elemental abundance patterns. Resulting trace metal anomalies are evaluated in terms of their timing and relationship to the other major biogeochemical perturbations at this time. After normalizing element concentrations to Zr to remove the effect of variable terrigenous input to these sediments, an interval of metal anomalies, at approximately the same stratigraphic location, is present in four of the five sites. I interpret the presence of metal abundance anomalies, and their stratigraphic position relative to events associated with OAE2, to suggest that hydrothermal activity could be the causative agent in pushing the ocean abruptly into anoxia. Also, the changes in trace metal patterns and intensities at all five sites are consistent with a source of metals being the Caribbean ocean plateau and modeled late-Cretaceous surface circulation.
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