The formation of pyrite and incorporation of trace element and water inclusions: a view from modern depositional settings
EMSL Project ID
50756
Abstract
This project utilizes atom probe tomography (APT) and transmission electron microscopy (TEM) to investigate microcrystalline masses of pyrite (FeS2) at the nano-scale. These analyses will be completed on samples from different REDOX environments in the modern ocean, including the FOAM site in long island sound (oxic water column above reducing organic rich sediments), Effingham Inlet (sulfidic water column), Saanich Inlet (seasonally sulfidic), and the Derwent Estuary (high metal, oxic above reducing organic rich sediments). The analyses proposed here (APT and TEM) we be done in conjunction with several other analyses, including: iron speciation, bulk sediment chemistry, pore water chemistry, Mossbauer spectroscopy, X-Ray diffraction, Fe and S X-ray Absorption Near Edge Structure (XANES), acid volatile sulfur and chromium reducible sulfur analysis. These data will provide a detailed understanding of the chemical conditions within the sediments during earliest diagenesis. This will allow us to refine our interpretation of trace element zoning and seawater inclusions discovered during the EMSL project 49860 where APT and TEM analysis of pyrite from geologic samples (360 Ma to 0.01 Ma in age) showed saline nano-inclusions of water with major element ratios within the range expected for seawater at the time of formation and distinct zoning of trace metals. By comparing the water inclusions from pyrite formed in modern environments we will be able to assess how well they reflect the water column and pore waters from which they formed. Developing this tool will allow us to better assess ocean chemistry at different periods in Earth History. Furthermore, because trace elements were found to be strongly enriched in the later formed pyrite (cementing the microcrystals that make up framboids) rather than evenly distributed as previously thought it may be that important trace elements (co-factors for several enzymatic processes; i.e. Ni for methanogenesis) were bioavailable longer than some models say. By using APT and TEM to track the incorporation of trace elements into pyrite and the trace element abundance of pore fluids we will be able to assess how the trace element content of pyrite relates to the fluids from which they formed and whether pyrite trace element chemistry can be used to track concentrations of bioavailable trace elements at periods in Earth history when different biological mechanisms evolved and began to flourish.The resources at the Environmental and Molecular Science Laboratory at the Pacific National Laboratory are essential to complete this work because the technique of preparation of APT needles and TEM films of pyrite framboids, that are often weakly consolidated, is difficult. During EMSL project 49860 we developed the techniques to do this and the scientists at EMSL are well positioned to do this work. These techniques give us the atom scale resolution needed to identify and characterize both the nano-scale zoning of the trace elements in pyrite and the nano-inclusions of saline water that this project depends upon. Furthermore, the samples utilized are also part of EMSL project 50248 (using Mossbauer and qXRD analyses) and having both projects completed at EMSL will enable collaborations that will help the interpretations of each project.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2019-10-01
End Date
2021-12-31
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members