Forschung - research

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Ediacaran marine dolomite and marine archives
The Ediacaran is a crucial period for the atmospheric and hydrospheric evolution in the Earth (e.g., Snowball Earth, rise of biota). Ediacaran marine dolomites, arguably precipitated directly from seawater, and are at the core of dolomite research. This because these precipitates, if well preserved, may serve as archives of deep-time oceanic dynamics and the dolomite problem. This project aims to identify the precursor mineralogies and controlling factors of exceptionally well-preserved fibrous dolomites in the Ediacaran, China. Analyses will be performed to shed lights on Ediacaran seawater properties. I intend to compare and contrast these findings with diagenetically most altered fibrous dolomites to test the effects of diagenesis on geochemical proxies. This research will be performed by establishing a very detailed and rigorous data base using the full spectrum of conventional and novel analytical tools in the sense of a multi-proxy data set (e.g., cathodoluminescence, EBSD, LA-ICP-MS, NanoSIMS, clumped isotopes, and magnesium isotopes).
Staff involved: Y. Hu, A. Immenhauser, and S. Riechelmann

Greener - Characterization and prioritization of geothermal reservoirs as energy carriers in the Rhine-Ruhr area
The conversion of the district heating network in the Rhine-Ruhr area from being fossil-fueled to being supplied by renewable energy carriers is a major task. Integrating deep geothermal reservoirs into the grid could provide the future solution. Potential geological formations in the Rhine-Ruhr area include the Carboniferous and Devonian carbonates at depths of 3,000 m to 5.000 m. The research project Greener aims to identify the spatial distribution of the Devonian reef-facies in the Rhine-Ruhr area and its respective geoscientific properties. An outcrop analogue study is conducted which includes field research like fault and fracture analysis etc. and subsequent laboratory examinations analyze the thermal, hydraulic, mechanical and chemical properties of the aforementioned stratigraphic units under surface and reservoir conditions. These correlations provide valuable information about the rock characteristics at a certain depth and thus the overall reservoir potential of the Devonian carbonates.
Staff involved: K. Lippert, A. Immenhauser, R. Bracke, M. Nehler

Relation between carbonate rock properties and fracture patterns in limestone-to-dolostone transition intervals
Understanding the relation between carbonate facies at deposition and its subsequent diagenetic pathways on one side and fracturing of these rocks during subsidence or exhumation is important. From a fluid circulation point of view, obtaining wholesale dolomitization of large bodies of rocks is not obvious as it requires a combination of flow along fractures/faults and through the country rock itself. If pathways provided by fracture networks are too efficient, fluids would not diffuse significantly inside the rock thereby only causing dolomitization very close to the fractures. The objectives of this study are to characterize and as well to produce a quantitative reconstruction of fracture networks over the full relevant range of scales and at the same time propose a model that describes the transformation in dimension of the clasts in a fault damage zone of carbonate rocks from cubic to roundness in quantitative terms. Secondly, we will perform numerical simulations testing the relative role of fractures and rock porosity in allowing flow. Staff involved: O.A. Igbokwe, M. Müller and A. Immenhauser

Assessing the resilience of carbonate archives of environmental change in limestone-to-dolostone transition zones (TP 2 of DFG FOR CHARON)
About 70% of Earth's geological history is recorded in carbonate archives that have seen varying degrees of post-depositional dolomitization. Limestone-to-dolostone transition zones are important due to the inherent depositional and diagenetic information they contain. The insufficient understanding of lateral and stratigraphic patterns within these transition zones forms a limitation in carbonate research. Similarly, early diagenetic dolomicrites, which typically record marine environmental conditions, are in the focus of this project. When altered, burial conditions may overprint the original signature but then at least provide information on burial pathways. The objective of this study is to establish a detailed framework for limestone-to-dolostone transition zones and early diagenetic dolomites from different time intervals. Upstream, a well-constrained Mg-isotope data set from all early (marine) to late diagenetic (burial) carbonate phases and complementary geochemical data constrained within fluid property context are aimed for. In foresight, this project intends to establish robust and quantitative benchmarks to test the validity of various environmental proxies in dolomitized limestones and their associated facies. Staff involved: M. Müller and A. Immenhauser

Hydrothermal diagenetic alteration (experimental) of biogenic and abiogenic carbonate archives (ZP0 in the context of the Forschergruppe CHARON Phase II)
The understanding of carbonate alteration and the product of these diagenetic reactions is important, due to their common use as proxies for both depositional and burial reconstructions of environmental conditions. Our research works to analyze the petrographic and geochemical alteration of carbonate material using an experimental approach which involves the heating samples from various carbonate archives to different temporal and temperature regimes. The selected range of laboratory conditions allows the determination of the type and extent of diagenesis in the hydrothermally altered (experimental) samples, with results ranging from no alteration to full recrystallization. Staff involved at Bochum: C. Pederson, S. Breitenbach, R. Hoffmann, O. Kwiecien, S. Riechelmann, R. Neuser and A. Immenhauser

QUEST - QUantitative palaeoEnvironments from SpeleoThem
QUEST (QUantitative palaeoEnvironments from SpeleoThems) will develop new techniques for extracting quantitative information from speleothems and link field and laboratory experiments on water/mineral chemistry with innovative physical and numerical analyses on speleothems. The combination of these techniques, based on physical and chemical properties and statistical methods, will allow us to deliver quantitative reconstructions of two key parameters: hydrology and temperature. We will test our methods using speleothems from Australasia, a region vulnerable to El Niño-Southern Oscillation (ENSO) variability. At present, there is a relative dearth of millennial-scale palaeoclimate data from this region.
Our team members come from a variety of backgrounds including environmental chemistry, environmental mineral magnetism, and numerical data analysis. Each group within the team has already begun developing innovative methods for palaeoclimate reconstruction within their own subfield, but this project will be the first time these methods are combined and applied collectively to speleothems. Our combination of interdisciplinary expertise, state-of-the-art instrumentation, and novel techniques means that we are ideally placed to develop quantitative climate records from speleothems.
QUEST has received funding from the European Union’s Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie grant agreement No 691037.
Staff involved at Bochum: S. Breitenbach


Exploring the mechanisms of syn-OAE1a collapse of coral-rudist ecosystems in the Tethyan and proto-Atlantic realm
Enigmatic lower Aptian microencruster communities temporarily replacing coral-rudist ecosystems have recorded from Tethyan and proto-Atlantic localities. The driving mechanisms of these ecological patterns are unknown but the clear temporal relation to OAE1a might imply common causative reasons or linked environmental parameters. The aim of this project is to exploit microencruster community micrites for their geochemical archive of past seawater nutrient and oxygen levels. By this we aim for an improved understanding on controls of Aptian neritic carbonate systems and oceanic anoxic events in general. Staff involved: A. Hüter and A. Immenhauser (Bochum), S. Huck and U. Heimhofer (Hannover), S. Bodin (Aarhus, Denmark)

Geochemical evolution of alkaline lakes
The presence of a lake on the surface of the Earth reflects convergence of climatic and tectonic factors enabling the impoundment of a water. Hydrological closure, required to increase the salinity and alkalinity, makes lakes very responsive to environmental change. But how are alkaline lakes 'born'? Were they always closed? How long it takes to change the lake chemistry from fresh to alkaline? We use Lake Van in eastern Anatolia, Turkey, today's largest soda lake in the world as a model example to answer these questions. Complete sedimentary record of Lake Van reaches ca. 600 ka back and suggests that during its initial phase the lake hosted freshwater. Combined with data collected within ICDP PALEOVAN project, detailed analysis of inorganic and biogenic carbonates and biogenic silica will document geochemical and ecological changes in a transforming basin. Staff involved: O. Kwiecien, F.T. Meyer

Component-specific characterization of lacustrine carbonates
Commonly assumed to record surface water chemistry and temperature, lacustrine fine-grained carbonates are widely used as (paleo)environmental archives. Alas, due to their primary polygenic origin (authigenic, biogenic, microbial, detrital,) and potential secondary alteration (diagenesis) time series based on geochemistry of bulk carbonates might be difficult to interpret. This project targets sedimentary carbonates from Lake Van and aims at (1) comparing and contrasting geochemistry (δ18O, δ13C, Mg/Ca, Sr/Ca) and mineralogy of different carbonate components, and (2) relating nature of individual components with observed lithofacial changes. Our overreaching goal is a critical assessment of the utility of bulk carbonate analysis and singling out environmental factors integrated in a bulk proxy data sets. Staff involved: O. Kwiecien, J. McCormack

Oxygen and carbon stable isotopes of modern land snail shells as environmental indicators
Land snail shells constitute a valuable source of environmental information, especially in arid regions where other carbonate material are scarce. The oxygen isotope signal of the shell is related to temperature and a source and amount of moisture, while the carbon isotope signal reflects the dietary control. However, different cleaning techniques and sampling strategies may lead to over- or underestimating the amplitude of observed change. We use shells of land snails collected in Morocco to systematically test different methodological approaches and identify their benefits and/or limitations. Staff involved: O. Kwiecien, R. Hoffmann

Cephalopod shells as marine paleo-environmental recorder
Cephalopod shells record marine seawater properties (e.g., temperature) during growth making them ideal candidates to reconstruct paleo-environments. Due to the accretionary shell growth also ontogenetic changes of the cephalopod habitat are recorded. That allows for the reconstruction of life habits related to different shell morphologies. This project focuses on ammonoids, an extinct cephalopod. During the Cretaceous many transgressions/regressions, warming/cooling phases and oceanic anoxic events take place. Thus, making the Cretaceous ideal for studying the appearance, disappearance and distribution of specific shell morphologies. The main goals are to investigate the possible influence of changes of various paleo-ecological parameters (e.g., water depth, temperature, oxygenation of the habitat zone) on the ammonoid conch geometry. Therefore we apply geochemical analyses (δ18O, δ13C) of pristine preserved shells.

Animated micro-CT of Nautilus pompilius

Staff involved: R. Hoffmann, R.D. Neuser

Magnesium isotope signature of drip and flowing water in a former mine
The goal of this research project is to improve our understanding of the Magnesium isotope system. The former mine at Neubulach (South Germany) is especially suitable for this project, because water percolates through both siliciclastic and carbonate rocks. The differences in the Mg isotope composition between various waters and their variations over time will shed light on the fractionation processes of these rocks during dissolution. This project is undertaken in collaboration with the University Tübingen and the "Stollengemeinschaft der historischen Bergwerke Neubulach e.V". Staff involved: S. Riechelmann, D. Buhl, A. Immenhauser and G. Markl (University Tübingen).

Air and drip water monitoring of Klutert Cave, Ennepetal
Klutert Cave formed in a thin limestone layer with siliciclastic forming the underlying and overlying bed. Monitoring of drip and flowing water will improve the understanding of the hydrological connection of the different waters and their sources. Furthermore, Klutert Cave is a show cave and in order to determine the impact of tourism on the cave atmosphere the CO2-content of the cave air is measured continuously. This project is performed in close collaboration with "Kluterthöhle & Freizeit Verwaltungs- und Betriebs-GmbH & Co. KG" and "Arbeitskreis Kluterthöhle e.V." Staff involved: S. Riechelmann, D. Buhl, A. Immenhauser, S. Voigt (Arbeitskreis Kluterthöhle e.V.)

Magnesium isotope signature of dolomites
The goal of this research project is an improved understanding of the controlling factors of magnesium isotope (δ26Mg) fractionation in for instance speloan carbonates or bivalve hardparts. The main focus is on the potential of this novel isotope system as a paleo-climatological, paleo-ecological and paleo-oceanographic proxy. Staff involved: D. Buhl, A. Immenhauser, D.K. Richter

Cryogenic cave calcites
Cryogenic cave calcites (CCC) grow from freezing cave waters where slow freezing leads to a very light O-isotope composition and quick freezing leads to higher O-isotope composition. Calcites of the first group have formed in Middle European caves in water pools on ice during the transition from cold to warm periods. After the ice had molten, a polymict "crystal sand" of cryogenic calcite particles is found as a residue on the cave ground. According to morphological and structural criteria these particles can be distinguished as spherolitic, rhombohedral crystal, plait and skeletal crystal sinters. Our investigations focus on occurrences of CCC in different european caves. Staff involved: D.K. Richter, R.D. Neuser.

Crystallographic orientation of calcite crystalls in speleothems
Calcitic speleothems are known as monocrystalline (most soda straws and helictites) or polycrystalline (most stalagmites and flowstones) compositions. Crystal formation such as crystal surface limitations, crystal elongation and crystal arrangement allow a further differentiation of the speleothem patterns, but the internal crystal structure has been taken into consideration insufficiently with respect to that. Today, Electron-Backscatter-Diffraction allows the evaluation of crystal orientation parameters on oriented chemically polished thin sections. Our systematic investigations should gain new information on the in many kinds not understood genesis of speleothems. Staff involved: R.D. Neuser, D.K. Richter