The trace metal content of modern and ancient peritidal and shallow subtidal dolomites: significance and systematics

• The trace metal content of modern and ancient shallow marine dolomites: significance and systematics

• Author / Creator

  Petrash, Daniel A.

• Dolomitization has traditionally been regarded as being related to the interaction of thermally active Mg-rich fluids with poorly ordered carbonate precursors of elusive origin. Our ideas on how such precursors form have evolved rapidly since the late 1990s, and microbes are now considered key players — i.e., by providing nucleation sites and due to their capacity to regulate pore water alkalinity. Outstanding questions include what triggers the low-temperature reactions conducive to dolomite stabilization and whether or not subsurface chemolithotrophs participate in the catalysis of these reactions. Here these aspects are evaluated throughout three independent but complementary textural and spectroscopic examinations of shallow marine dolomites. First, fine-scale analyses of modern carbonate cements point to biologically mediated manganese and sulfur co-recycling as a necessary control for dolomite stabilization. Second, similar analyses of mid-Cretaceous dolomitic marlstones suggest that in the Aptian-Albian epicontinental sea of northern South America, dolomite precipitation was linked to the utilization of metals and sulfur for organic matter respiration. Reactants were transported to the extended shallow marine setting in association with episodic orbital perturbations, which also triggered high organic matter productivity and burial, and ultimately led to interstitial organogenic dolomite formation. Third, stromatolitic rocks from the Paleoproterozoic Gunflint Formation (Ontario, Canada) were interrogated in order to interpret the variable redox states of pore waters at the time of stromatolite accretion and diagenetic mineral stabilization. This study shows that diagenetic shifts associated with exogenous water mixing, together with variable burial and exhumation histories, led to the development of the temporarily and spatially restricted reaction fronts responsible for the pervasive replacement of early formed carbonate cements. Such diagenetic complexity adds difficulty to the interpretation of paleomarine geochemical conditions. Overall, this work reveals that the trace metal content of shallow marine dolomite provides information useful for the evaluation of redox conditions that govern mineral authigenesis. However, autocycles and their effect on the activity of subsurface microbes, and thus over the saturation state of minerals in coastal sediments should be carefully considered prior to regional scale paleoceanographic interpretations.

• Subjects / Keywords

  • Gunflint Formation, Ontario, Canada
  • Archipelago Los Roques, Venezuela
  • Grupo Cogollo, Cretaceous Venezuela
  • Dolomite
  • Peritidal
  • Microbial
  • Stromatolites, microbial mats

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R37P8TN0D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.