1:30pm - 1:45pm
Asphalt formation at the seafloor of the Campeche-Sigsbee salt province, southern Gulf of Mexico
1University of Bremen, Germany; 2National Taiwan University; 3Florida State University
Hydrocarbon seepage is widespread distributed at the southern Gulf of Mexico. During several research cruises in 2003, 2006, and 2015 (SO174, M67/, and M114) we used multidisciplinary approaches, including multi-beam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits occur at numerous knolls and ridges in water depths from 1230 to 3150 m. These striking seafloor elevations are formed by diapirs of Jurassic salt deposit associated by hydrocarbon accumulations. The deeper sites like Chapopopte and Mictlan knolls were characterized by asphalt deposits accompanied by extrusion of liquid, and very heavy oil in form of whips or sheets, and in most places by gas emissions, and the presence of gas hydrates (Tsanyao Yang, Mictlan, and Chapopote knolls). Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh solidified asphalt structures were settled by bacterial mats and vestimentiferan tube worms growing through cracks and from under the edges of pavement. The gas hydrates at Tsanyao Yang and Mictlan knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1–2 m long tube worms, bivalves, snails, and shrimps. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.
1:45pm - 2:00pm
Cliff coast collapses driven by nested biological, astronomical and meteorological activity cycles
GFZ Potsdam, Germany
Cliffs line many erosional coastlines. Localized failures can cause land loss and hazard, and impact ecosystems and sediment routing. Links between cliff erosion and forcing mechanisms are poorly constrained, due to limitations of classic approaches. Combining multi-seasonal seismic and drone surveys, wave, precipitation and groundwater data we study drivers and triggers of 81 failures along the chalk cliffs on Germany’s largest island, Rügen. We have found that marine processes are negligible in triggering failures but efficient in removing the deposits. Instead, cliff failure has been associated with terrestrial controls on soil moisture and groundwater. During the vegetative season, evapotranspiration impedes groundwater flow into the cliff face. When vegetation is dormant, failure frequency correlates with lunar-mediated precipitation. Failures are triggered by relative air moisture and rain, leading to clustered events during night time. Drier terrestrial conditions prevent smaller failures, which causes beach erosion and ultimately prepares the cliff for sector collapse.
2:00pm - 2:15pm
Hydrothermal processes related to submarine iron ore formation: Insights from Devonian Lahn-Dill-type ores
1Technische Hochschule Georg Agricola, Germany; 2Universität Innsbruck, Austria; 3Jacobs University Bremen, Germany; 4Deutsches Bergbau Museum Bochum, Germany; 5Ruhr-Universität Bochum, Germany
Numerous studies on submarine iron-rich sediments (BIF, ironstones, etc.) focus on environmental changes and ocean chemistry, however, many questions related to underlying hydrothermal processes remain unresolved. As proximal chemical sediments, Lahn-Dill-type iron ores can provide insight into mechanisms of hydrothermal seafloor alteration related metal scavenging, and subsequent Fe-mineral deposition.
Lahn-Dill-type iron ores formed during the Middle/Upper Devonian within the Rhenohercynian back-arc basin associated with intraplate alkali basaltic volcanism. Ores formed on top of volcanogenic successions proximal to centres of volcanic activity. Typically, they occur as hematite-(siderite-)quartz ores reaching up to 60 wt.% Fe. We sampled a 5 m profile within the Fortuna mine in the eastern Rhenish Massif (Lahn syncline, Germany) and conducted a detailed petrographic study and whole rock ICP-MS as well as in-situ LA-ICP-MS geochemical analyses.
Iron is commonly mobile under reducing and acidic conditions. However, geochemistry of Lahn-Dill-type iron ores indicates that hydrothermal fluids may have been able to mobilise HFSE pointing at possible alkaline fluids. This is suggested by positive correlations of Fe with certain HFSE including Zr and HREE. Upon venting into seawater, iron likely precipitated as oxyhydroxides that preferably scavenged Si, W, Mo, Pb and V complexes from seawater by sorption. Subsequent deposition on the seafloor as a Si-Fe-rich gel is indicated by crescent-shaped shrinking cracks. Today, mineral assemblages within ore are characterized by fused hematite mats, hematite dispersed in quartz and/or siderite and microcrystalline quartz that may either be interpreted as diagenetic dissolution-precipitation processes, cyclic changes in primary fluid composition, or potentially both.
2:15pm - 2:30pm
The Kieshöhe carbonatites in SW-Namibia – the role of silicatic xenoliths for REE exploration
1Karlsruhe Institute of Technology, Germany; 2Technische Universität Berlin, Germany; University of the Free State, Bloemfontein , South Africa; 3Shali Group, Windhoek, Namibia; 4University of Tübingen, Tübingen, Germany
Exploration of carbonatite-associated REE-deposits is challenging due to heterogeneous ore distribution and variable and often complex ore mineralogy. The Kieshöhe carbonatite in SW Namibia represents a subvolcanic occurrence hosting dolomite, calcite and ankerite carbonatite dykes, ring dykes and diatremes. Petrography, whole rock geochemistry and microXRF imaging provide insights into the role of silicate xenoliths for the REE mineralization in a subvolcanic environment. Xenolith-rich carbonatites are relatively REE-poor with only minor monazite mineralization, whereas xenolith-free carbonatites show high REE-contents incorporated primarily into REE-F-carbonates. Moreover, the additional presence of barite and pseudomorphic replacement of hexagonal precursor minerals suggest the former presence of burbankite, which might represent the potential REE source. The strong association of REE-minerals, barite and quartz furthermore indicates the simultaneous hydrothermal transport of REE, Ba, S and Si. In particular, Si-saturated hydrothermal fluids promote the potential of sulfate complexes to mobilize REE . Since an enhanced xenolith resorption in xenolith-rich parts of the complex increases the Si content of the hydrothermal fluid and thus the capacity of REE transport, REE precipitation is inhibited in such sections but supported in xenolith-free sections. This demonstrates that xenolith entrainment not only has a strong influence on REE mineralization in synmagmatic stages , but may also have strong effects in post-magmatic hydrothermal stages of the carbonatitic system. This observation can potentially be used as a first-order field-based exploration indicator for REE-mineralization in carbonatites.
 Cui et al. (2020). Geology, 48(2), 145-148.
 Giebel et al. (2019). Journal of Petrology, 60(6), 1163-1194.
2:30pm - 2:45pm
Reservoir characterization of the coal-bearing Upper Carboniferous clastic succession, Ruhr area, Germany
1Geological Survey of North Rhine-Westfalia; 2Structural Geology & Tectonics, Karlsruhe Institute of Technology
Due to the closure of coal mining in the northwestern German coalfields, active mine water drainage becomes technically redundant. As a result, the rising mine water table affects the subsurface stress conditions and may induce heterogeneous ground movements of fault blocks. Petrophysical properties of the Upper Carboniferous (Westphalian A and B) rocks are crucial to understand subsurface behavior during mine water rise. As a part of the interdisciplinary FloodRisk project, we present a petrophysical and petrographical characterization of Westphalian A and B drill cores from the Ruhr area.
Based on fining-upward cycles consisting of basal sandstones (medium-grained, planar laminated) followed by siltstones with intercalated lower (planar/wavy laminated to bioturbated/rooted) mudstones and coal seams at the top, that are locally overlain by clayey deposits, the rock succession was interpreted as fluvio-deltaic facies association. Petrophysical measurements on core plugs indicate that most samples are generally tight (mean permeability: 0.26 mD; mean porosity: 6.4 %) but reservoir properties vary by grain size and facies. Petrographic analyses indicate that sandstone cementation is dominated by ferroan carbonate (mostly siderite and Fe-calcite) and quartz overgrowth in the pore space. Locally, veins are cemented by ferroan calcite or sulfides. Feldspar-rich rock fragments are often replaced by kaolinite, reducing the secondary porosity.
The outcome of this investigation will be integrated into an interdisciplinary model that involves geomechanical, geodetic and geophysical data in order to understand subsurface flow. Furthermore, data can be used to consider the fluid distribution for potential geothermal energy use.
2:45pm - 3:00pm
Das natürlich geschlossene System (NGS) – Inzidenz der reflexiven und transitiven Eigenschaften in der Geologie
Das natürlich geschlossene System (NGS), das von (Stensen Niels 1669) begründet wurde, ist ein Modell des Komplexes von exakt gemessenen Parametern dualer Gesteinssysteme der Geologie. Die angewandte Messtechnik in den Geowissenschaften deduziert funktionale Zusammenhänge der Proportionalität (h = m) und (h = - m + C). Die Umformung der Funktionen liefert die Invarianten des geologischen Binärsystems (h/m = ±1). Die Funktionen stehen orthogonal aufeinander, sie sind symmetrisch, invers und relational. Reflexive Messwerte (Offhaus 2020) bestimmen die Lagerung der Gesteinssysteme, während die Lote (geologische Profile), im Unterschied zur Lagerung, transitive Eigenschaften aufweisen. Transitive und reflexive Werte liegen in der Geologie partiell übereinander. Die arithmetische Relation (h = - m + C) hat neben der Transitivität die besondere Eigenschaft der Identität von Funktion und Umkehrfunktion durch den Betrag des Anstiegs von (- 1). Inzidenzmatrix und gerichteter Graph (Metz 2010) belegen die Einheit und Verflechtung der Eindeutigkeit dualer Gesteinssysteme in der Geologie. Das NGS hat die Eigenschaften der Symmetrie, der Reflexivität, der Transitivität, es ist nicht antisymmetrisch und nicht asymmetrisch, somit ist es Äquivalenzrelation und Halb- oder Quasiordnung.
Die mathematischen Anwendungen in der Geologie, wie z.B. (Bentz A. 1961); (Eisbacher Gerhard A. 1996), die Verknüpfung von geologischen Prozessen der Tektonik mit der mathematischen Eigenschaft von „Umkehrfunktionen“ zum geologischen Begriff „Inversionstektonik“ (Kley J. 2013) oder die Anwendungen der Session „vorwärts und inverse Modellierung“ von geologischen Daten (Matenko L. u.A. 2020) verifizieren das NGS. Ebenso bestätigt die ausführliche Formenanalyse von Windkantern (R. Schwenecke 2020) die theoretischen Aussagen des NGS mit gemessenen Daten von ca.1000 Windkantern in vollem Umfang, darüber hinaus Verbindungen zur Skaleninvarianz und zur Selbstähnlichkeit.
Das geologische Modell des NGS ist ein mathematisches Objekt, das sich zur Entwicklung einer theoretischen Geologie eignet.