Investigating Trace Metal Sequestration of Reducing Environments in Modern and Ancient Settings
Doctor of Philosophy (PhD)
Geology and Geophysics
The incorporation of trace metals into a variety of reducing sediments are important proxies for the oxic state of the water mass in which the sediments form. While much work has been done interpreting these proxies, questions remain on the exact processes and products in which trace metal proxies form. This work employs bulk geochemical techniques to investigate circulation in the Late Pennsylvanian North American Midcontinent Sea (NAMS), and then uses sequential extractions to further understand the chemical phases in which trace metals are incorporated. Sequential extractions are then used to further investigate how trace metals are sequestered in modern environments, in environments both similar to the NAMS (Gulf of Mexico) and dissimilar (The Bahamas).
The NAMS experienced glacioeustatic rises and falls, during which repetitive sedimentary sequences termed cyclothems accumulated on a stable platform, depositing organic-rich core shales under a stratified water column with anoxic deep waters. The present study investigates circulation patterns of the NAMS by examining trace-element enrichments, organic carbon content, and carbon-nitrogen stable isotopes sampled at high resolution within a single cyclothemic black shale, the Heebner Shale, at six sites on the northern Midcontinent Shelf and two sites in the Illinois Basin. The Heebner Shale is the core shale member of the Upper Pennsylvanian (lowermost Gzhelian) Oread Limestone Formation in Kansas and Iowa, and it is correlative with the Teutopolis Shale of the Mattoon Formation in Illinois. Major elements and clay-mineral assemblages show influences from three distinct terrestrial sources, and their spatial patterns imply large-scale clockwise (anticyclonic) rotation of the NAMS watermass driven by either the Coriolis Effect or the hydrodynamics of riverine discharge into the NAMS.
In The Bahamas, syndepositional diagenesis and its effects on trace metal sequestration were investigated using stable isotopes and sequential extractions on four cores. While syndepositional diagenesis provides a pathway for authigenic enrichment of trace metals, the enrichment is sequestered in the exchangeable phase. The carbonate phase reflects concentrations similar to primary precipitates. Similar experiments were carried out in the Gulf of Mexico (GOM) “dead zone”, in which authigenic enrichment in the exchangeable phase recorded historic hypoxic levels.
Turner, Adam Charles, "Investigating Trace Metal Sequestration of Reducing Environments in Modern and Ancient Settings" (2018). LSU Doctoral Dissertations. 4580.