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Projekt
Methane-induced carbonates along the Cascadia Margin: Archives of episodic methane seepage
Antragstellerin
Dr. Barbara Teichert
Fachliche Zuordnung
Paläontologie
Förderung
Förderung von 2012 bis 2016
Projektkennung
Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 224645753
The Cascadia Margin has been studied thoroughly with ODP (Legs 146 and 204) and IODP Expeditions (Exp. 311) with respect to the occurrence of gas hydrates within the hemipelagic silts and clays and sandy turbidites forming the accretionary wedge. The abundant occurrence of methane-induced carbonates at different depth intervals in sedimentary cores drilled during Expedition 311 at the northern Cascadia Margin provides the ideal opportunity to test if their formation has been triggered by episodic methane seepage due to climatic-controlled sealevel changes. This process has been proven for the southern Cascadia Margin and the question that is to answer is, if all methane-induced carbonates precipitated along the Cascadia Margin are archives of these glacial/interglacial sealevel variations or if regional factors (e.g. tectonics, bottom water temperature) also influenced the intensity of methane seepage over time. The paragenesis of different carbonate phases within one carbonate sample also indicates that they bear information on a 'geochemical' chronology. While authigenic carbonates get successively buried they pass through different geochemical zones like anaerobe methane oxidation and methanogenesis. In each zone, a carbonate with a different mineralogy might precipitate and create in the end a very complex mineralogical mixtures. Finally, a process that is occurring deep in the sedimentary column, the smectite-illite transformation, can be studied in a natural laboratory from the retrieved porewater samples. The chlorinity profiles show an increasing freshening with distance from the accretionary toe due to release of mineral water during illitization. For magnesium isotopes it has been hypothesized that this process will lead to a heavy magnesium isotope signature in the porewater. The porewater samples from IODP Exp. 311 will provide the opportunity to verify this hypothesis and increase the knowledge about magnesium cycling in marine sediments.
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