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Browsing by Author "Hannah, Judith, advisor"

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    Deciphering the Late Jurassic paleoenvironment through Re-Os isotope geochemistry of the Agardhfjellet Formation, Svalbard
    (Colorado State University. Libraries, 2017) Connors, Marisa Leigh, author; Hannah, Judith, advisor; Stein, Holly, advisor; Borch, Thomas, committee member; Hammer, Øyvind, committee member
    Accurate interpretations of environmental change throughout Earth's history rely on robust correlations of sedimentary systems. The Late Jurassic has been difficult to correlate regionally and globally due to sparse radiometric ages and lack of cosmopolitan fossils. The rhenium-osmium (Re-Os) geochronometer provides an excellent platform to approach this problem. Re-Os geochemistry provides a way to directly date organic-rich shales which can then be used to: 1) place numerical ages on boreal fossil zones and Geologic Time Scale stage boundaries, 2) correlate with regional or global units, and 3) enhance the understanding of oceanic anoxic events (OAEs) and climactic shifts when paired with additional chemical and lithological data. The Agardhfjellet Formation of Svalbard, Norway has multiple intervals of organic-rich mudrocks which are ideal for Re-Os geochemistry. Presented here are Re-Os ages which confirm placement of the Agardhfjellet Formation within the Late Jurassic to Early Cretaceous (157.9 ± 2.9 Ma to 141 ± 20 Ma). We provide an age immediately above the Kimmeridgian-Oxfordian boundary, within the Amoebocera subkitchini zone, at 153.2 ± 5.0 Ma in agreement with previous work. Furthermore we present evidence that: (1) the Agardhfjellet Formation was deposited in fluctuating anoxia conditions; (2) increasing initial 187Os/188Os (0.401±0.007 to 0.577±0.054) coupled with a decrease in δ13Corg (-25.26‰ to -29.63‰) through the Late Jurassic signifies a changing climate represented by an increase continental weathering with a warming climate and/or an increase in continental freeboard.
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    Redox-sensitive trace elements document chemical depositional environment and post-depositional oxidation of the Ediacaran Biri Formation, southern Norway
    (Colorado State University. Libraries, 2014) Marolf, Nathan J., author; Hannah, Judith, advisor; Stein, Holly, committee member; Butters, Gregory, committee member
    The Ediacaran Biri Formation comprises carbonate and silisiclastic facies including a ~ 70 m thick organic-rich shale facies exposed 9 km west of Biri, Norway in a steep bedrock stream channel at Djupdalsbekken. This outcrop is overlain by ~ 30 m of coarse-clasitic conglomeritic facies of the Ring Formation, deposited in the southern and western portion of the Hedmark basin as prograding subaerial and submarine delta fans. Concentrations and distributions of some redox-sensitive trace elements, specifically molybdenum and uranium, within the Biri Formation shale indicate deposition under sub-oxic to anoxic conditions. Pyrite framboid size distribution corroborates trace element evidence and suggests that sulfidic conditions existed within the sediment with a chemocline at or near the sediment-water interface. An attempt to date the Biri Formation shale by Hannah et al. (2007) found disturbed Re-Os isotope systematics from samples in the first 8 meters of the exposure, while data obtained from samples further down section were undisturbed. Here, an attempt to understand these disturbed and undisturbed sections using redox-sensitive trace element chemistry suggests the disturbed data was a result of post-depositional re-oxygenation within the upper few meters of the Biri shale. This is indicated by concentration peaks in trace element profiles that result from remobilization and subsequent re-fixation of these elements at different locations in the shale. A well constrained hypothesis constructed using uranium and molybdenum as proxies for rhenium shows that rhenium was likely remobilized after deposition of the Biri Formation and either subsequently re-deposited, or flushed out of the system. In this scenario, the post-depositional remobilization of rhenium (and most likely osmium also) resulted in disturbed Re-Os isotope systematics described by Hannah et al. (2007). Trace element geochemistry, petrographic, and δ13C and δ18O stable isotope evidence document post-depositional re-oxygenation of the Biri Formation shale. Re-oxygenation occurred either synchronous to deposition of the overlying Ring Formation or during a later event, the Caledonian orogeny (~ 440 Ma) being the most likely candidate. While the geochemical evidence does not preclude one time period or the other, disturbed Re-Os isotope systematics and resulting dates given by Hannah et al. (2007) can only be supported by re-oxygenation of the Biri Formation shale during the Caledonian orogeny.
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    Residency of rhenium and osmium in a heavy crude oil
    (Colorado State University. Libraries, 2017) DiMarzio, Jenna, author; Stein, Holly, advisor; Hannah, Judith, advisor; Georgiev, Svetoslav, committee member; Finke, Richard, committee member
    The Re-Os geochronometer is an emerging tool for the study of oil formation and migration processes, and a new technology for petroleum exploration. Very little is known, however, about the residency of Re and Os within asphaltene and maltene sub-fractions of crude oil. This information is crucial for better understanding of petroleum systems in general, and especially for successful geochronology of key processes such as oil formation, migration, or biodegradation. In this work, a heavy crude oil was separated into soluble (maltene) and insoluble (asphaltene) fractions using n-heptane as the asphaltene-precipitating agent. The asphaltenes were separated sequentially into sub-fractions using two different solvent pairs (heptane-DCM and acetone-toluene), and the bulk maltene was separated into saturate, aromatic, and resin (SAR) fractions using open column chromatography. Each asphaltene and maltene sub-fraction was analyzed for Re and Os. The asphaltene sub-fractions and bulk samples were analyzed for a suite of trace metals by ICP-MS. Our results show that Re and Os concentrations co-vary between the asphaltene sub-fractions, and that both elements are found mostly in the highly polar, highly aromatic sub-fractions; significant Re and Os are also present in the aromatic and resin fractions of the maltenes. However, each asphaltene and maltene sub-fraction has a distinct isotopic composition, and these sub-fractions are not isochronous. This may suggest that asphaltene sub-fractionation separates Re-Os complexes to the point that the isotopic integrity of the geochronometer is undercut. The decoupling possibilities of radiogenically produced 187Os from Re remain elusive, and more work is needed to determine the mobility of radiogenically produced 187Os. Re-Os and Ni-V budgets track each other, suggesting that some Re and Os may form metalloporphyrins. On the other hand, Re correlates strongly with Mo and Cd in the asphaltene sub-fractions; as Re and Os track each other, this suggests that Re-Os, Mo, and Cd occupy similar sites. Finally, we suggest that progressive asphaltene precipitation during migration and mixing of oils can change the resultant oil's isotopic ratios. This is key to interpretation of Re-Os data for tar mats and live oils, whether the data form an isochron or scatter. By combining data from source rocks, oils, and asphaltenes generated along the migration pathway, we are constructing temporal histories for whole petroleum systems.
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    Rhenium-osmium geochronology and geochemistry of the Upper Jurassic marine black shales, Agardhfjellet Formation, Central Spitsbergen, Svalbard and mercury degradation of Upper Permian shales, East Greenland and mid-Norwegian shelf
    (Colorado State University. Libraries, 2024) Park, Junhee, author; Hannah, Judith, advisor; Harry, Dennis, committee member; Borch, Thomas, committee member; Georgiev, Svetoslav, committee member; Hammer, Øyvind, committee member; Olaussen, Snorre, committee member
    Every rock has its own story. Rocks are categorized as igneous, metamorphic, and sedimentary types based on their origins and overprinting processes. The human species is confronting the crisis of climate change and some rocks hold a climate story from the past, permitting speculation on the future. On the geological time scale, Earth has experienced both scorching and freezing environments, the latter referred to as Snowball Earth. A critical key to resolving the problems we are facing lies in geology, which deconvolutes environments where specific rocks have formed. This dissertation addresses Boreal sedimentary sections during the Late Jurassic period by conducting three projects; Project I pinpoints depositional ages for black shales from the Agardhfjellet Formation and discusses Os isotopic ratios in the Boreal ocean during the Late Jurassic. Project II evaluates the depositional environments of the Agardhfjellet Formation, which was deposited during a shelf dysoxic-anoxic event. Project III focuses on Hg degradation incurred during incipient weathering and calls attention to interpreting Hg signals of sedimentary rocks, which have been used as an indicator of ancient volcanism. This dissertation provides new radiometric ages and detailed geochemical discussions of the Late Jurassic Agardhfjellet Formation and cautions the use of Hg concentrations when interpreting from outcrop sections. The findings herein significantly enhance our understanding of shelf dysoxic-anoxic events compared with oceanic anoxic events and Hg behavior during the early stage of weathering.