Winter semester 23/24
17.04.2024
Prof Andrea Erhardt (University of Kentucky)
Linking ocean circulation and chemistry over time - understanding unconformities, redox chemistry, and carbonate diagenesis on the Southern Campbell Plateau
Changing redox conditions with pore fluids can result in sediment precipitation, dissolution, and replacement reactions. These changes can be especially pronounced in the redox zone between where sulfate reduction and methanogenesis dominate, termed the sulfate-methane transition zone (SMTZ). At IODP Site 378-U1553 on the southern Campbell Plateau, changing circulation, sedimentation patterns, and the impact of a 26 million-year unconformity have impacted both the pore water geochemistry and likely altered sediment chemistry. This study compares the sulfur isotopes measured on pyrites from Paleocene sediments with sediment geochemistry. High sulfur isotope variability is observed in the pyrite samples and evaluated within the context of changes in paleogeography, shifts in terrestrial vs marine organic matter, and shifts in the SMTZ. Finally, we will consider the potential role methane migrations may play in this core. If the methane is migrating from deeper sediments into sulfate-bearing pore waters, this could result in an expanded SMTZ. Overall, we believe that changing depositional conditions are the overall control on the redox chemistry of this site.
08.05.2024
Prof Alexander Webb (Freie Universität Berlin)
The heat-pipe hypothesis for early Earth and hot terrestrial planetsOur rocky planet cools via plate tectonics. We have known this since the 1960's plate tectonic revolution, and there were earlier hints, most prominently Alfred Wegener's continental drift hypothesis. What remains unresolved to the present day are the origins of plate tectonic cooling. Notably, we have no dominant hypothesis for the timing, kinematics, and mechanism of the onset of plate tectonic cooling, nor for what tectonic cooling mode(s) span the period from initial crystallization of the magma ocean to the operation of plate tectonics. As such, we are in early Earth's "pre-revolutionary" conceptual period, replete with diverse hypotheses. Arguably the wildest hypothesis for Earth's pre-plate tectonic period is based on Jupiter's moon Io's heat-pipe cooling mode, in which early Earth tectonics would have been dominated by voluminous volcanism that generated a cold thick strong single-plate lid atop a partially-molten mantle. This talk will explore this hypothesis, as well as heat-pipe cooling as a mechanism for generating the lithosphere's of the solar system's remaining terrestrial bodies. The viability of early heat-pipe cooling across all of the solar system's rocky planets permits consideration of this mechanism as a general model for the transition from magma oceans to planetary lids.
29.05.2024
Prof Philipp Ruprecht (University of Nevada, Reno, and former Geoscience Master’s Student at Göttingen)
The natural laboratory of Puyehue-Cordón Caulle that links crustal scale magmatism to eruption dynamics: When and how do rhyolitic magmas blow up? Active volcanism requires a multi-disciplinary approach to forecast future unrest activity from both ongoing changes in the subsurface and from past activity. Thus, detailed timeseries of the heat and mass balance of the magmatic and near-surface hydrothermal system are necessary to constrain the state of the magmatic system as well as its transients through time. The Puyehue-Cordón Caulle volcanic complex is the site of three major subplinian to plinian eruptions that occurred in the last 100 years. These eruptions tapped a magmatic system that is thought to extend over more than 10 km laterally and currently deforms at rates of cm to dm per year. Furthermore, the most recent eruption in 2011-12 emplaced a very shallow intrusion only hundreds of meters below the surface adding to the multiple hazards associated with this volcanic complex.
In this presentation, I will give an overview of the many surface signals (geodetic, structural, hydrothermal) we can detect to estimate the thermal and mass budget of the system. I will also constrain through petrology the underlying magmatic system that represent an end-member of efficient single-step differentiation of basaltic mantle-derived melts to rhyolites. Mineral-scale geochemical records identify the conditions under which magmas are stored at depth and how the erupted rhyolite is formed and whether this rhyolite magma is approaching a critical state for future eruptions. Given the destructive nature of rhyolitic volcanism that is typically characterized by a long period of quiescence, the Puyehue-Cordón Caulle volcanic complex serves as a unique natural laboratory where pre-eruptive processes have and likely will be recorded on decadal timescales.
05.06.2024
Prof Lucie Tajcmanova (Universität Heidelberg)
Quantification of microscale processes in metamorphic rocksMetamorphic reactions within the Earth’s interior including deformation and fluid/melt flow are responsible for mountain building, volcanic eruptions and triggering earthquakes. Petrologists and structural geologists are driven by the same essential curiosity about metamorphic processes affecting the Earth’s lithosphere and use different tools to understand these processes.
Recent decades have been connected with an impressively accelerating pace in the development and availability of new analytical techniques to earth scientists. Interestingly, the smaller the scale considered, the more heterogeneous an apparently uniform rock sample is. This heterogeneity is not only characterized by variation in chemical composition but also in mechanical properties. The mechanical effects may influence element transport and mineral assemblage in rocks which can, in turn, significantly control the mechanical-chemical coupling rates and mechanisms of various processes in the Earth’s interior.
Considering the interplay of metamorphic reaction and mechanical properties in our quantification approaches is critical for correct interpretation of observations in metamorphic rocks. In my contribution, I will show major applications of the new quantification approaches, the accompanying obstacles and the consequences for our petrological interpretations.
I will also discuss new theories and quantification approaches that have been suggested based on the observations from deformation experiments focused on the calcite-aragonite and quartz-coesite transitions. I will show results from the combination of deformation experiments together with numerical modelling of rock deformation confirming the presence of stress and pressure variations during deformation of heterogeneous samples.
12.06.2024
Kurt Kment
Entwicklung der Ammonoidea nach der Trias/Jura GrenzeDie Trias-Jura Grenze ist einer der größten ökologischen Krisen des Phanerozoikums („Mass Extinction“-Event) bedingt durch massive vulkanische Ereignisse bei der Entstehung des zentralen atlantischen Ozeans (CAMP - Central Atlantic Magmatic Province). Im Bereich der alpinen Tethys kommt es zu einem Kollaps der Riffplattform Entwicklungen und generell zu einem Einbruch in der Karbonat-Bildung durch Ozeanversauerung. Mit Beginn des Jura entwickeln sich tiefere ozeanische Becken (Meliata-System), die Verbindungen zur Neotethys aufweisen. Am Ende der Trias Zeit (Rhät) kommt es zu einem nahezu vollständigen Aussterben der triassischen Ammonoidea (Ceratitida) und nur wenige Formen, vermutlich Phylloceraten-artige Ammonoidea, überlebten den gravierenden Faunenschnitt an der Trias/Jura Grenze. Diese Formen stellen sehr wahrscheinlich die Ausgangsformen der sog. Neoammonoidea dar, die mit Beginn des Juras („Recovery“-Phase) eine rapide Diversifizierung erfahren haben. Der Vortrag beleuchtet vor allem die stammesgeschichtliche der Entwicklung und biostratigraphische Bedeutung der Neoammonoidea im Unterjura des alpinen Bereichs.
19.06.2024
Habilitationskolloquium – nicht hochschulöffentlich
26.06.2024
Dr Marcus Schiedung (Thünen-Institut für Agrarklimaschutz)
The role and fate of pyrogenic carbon in permafrost affected soilsPyrogenic carbon is a product of incomplete combustion of vegetation during wildfires. It is consequently more resistant to environmental degradation compared to the initial organic matter and plays a major role in the global carbon cycle as a long-term carbon pool. However, its fate and its effect on fire-affected soils is largely unknown. The understanding of pyrogenic carbon dynamics in high-latitude regions is crucial to understand given the vulnerability of such cold regions to climate change and the vast amount of carbon stored in these ecosystems and soils. We studied the fate of pyrogenic carbon in permafrost-affected boreal mineral soils of Northern Canada by looking at short-term in-situ incubations and tracing its decomposition and stabilization within two years. Surprisingly, the persistence of pyrogenic carbon was lower in soils under continuous permafrost conditions compared to warmer soils. For the long-term dynamics, we used large-scale radiocarbon dating of the present pyrogenic carbon pool and identified its millennial age in permafrost-affected soils. We found a very consistent proportion of pyrogenic carbon on the total soil organic carbon across the permafrost-affected landscape, and its dependence on site and soil conditions that will change with the global warming
03.07.2024
Dr Anne-Katrin Broocks (Freie Universität Berlin)
Die Inklusion marginalisierter Perspektiven in sozioökologische Forschungen am Beispiel der Mangrovenforschung in Ecuador und der Klima-Kipppunkt-Forschung im Amazonas: Eine ethnografisch-wissenssoziologische HerangehensweiseBedeutungszuschreibungen auf ‚Natur‘ in Lateinamerika wurden entlang globaler Verflechtungen und ungleicher Machtverhältnisse über Jahrhunderte diskursiv konstruiert. Dominant war in vielen Fällen eine dualistische Perspektive auf ‚Natur und Kultur‘, aber auch die ‚Natur‘ selbst wurde oft entweder als bedrohlich oder ästhetisch-fürsorglich wahrgenommenen. Die bedrohliche ‚Natur‘ musste im Namen des Fortschritts dominiert und ‚entwickelt‘ werden, die ästhetisch-fürsorgliche ‚Natur‘ für den Menschen nutzbar gemacht werden. Oft wurden bedauernswerterweise auch Bewohner*innen entlang dieser Logiken ‚entwickelt‘ und ‚nutzbar‘ gemacht, also auf unterschiedlichste Art unterdrückt oder verdrängt. Dies hat zu ambivalenten Effekten in den heutigen ‚NaturKulturen‘ (cf. Latour 1993 [1991]: NaturesCultures, Gesing, Amelang et al. 2019) geführt. Anhand empririscher Beispiele der Diskurse im und über den ‚Amazonas Regenwald‘ und in den ‚MangrovenKulturen‘ der Hafenstand Guayaquil in Ecuador werde ich einige dieser diskursiven Kontinuitäten skizzieren. Die inklusive, historische Diskursanalyse (Broocks 2023), eine Erweiterung der wissenssoziologischen Diskursanalyse (WDA) von Reiner Keller (2001, 2005, 2011a, 2011b), dient als methodologischer Rahmen. Gleichzeitig zeige ich auf, wie durch die Machtverhältnisse hybride ‚mimicry‘ (Bhaba 1984:124) Lebenswelten entstanden sind, die für die Wissenschaft gerade aufgrund post-kolonialer Machtstrukturen oft nur schwer zugänglich sind.
03.07.2024, 16 Uhr, Hörsaal MN 15
Dr. Jannes Kordilla
Probevorlesung im Rahmen des Habilitationsverfahren – hochschulöffentlichMicrobial influences on groundwater quality and aquifer geochemistry
