Conference Agenda

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Session Overview
Location: Hall A (HFB)
350
Date: Monday, 04/Sept/2023
8:30am - 10:00am3.03-1 Advances in paleoclimate proxy development and application
Location: Hall A (HFB)
Session Chair: David Bajnai, University of Göttingen
 
8:30am - 9:00am
Invited Session Keynote
Topics: 3.03 Advances in paleoclimate proxy development and application

Triple oxygen isotopes of modern terrestrial mammalian tooth enamel –new implications for paleoenvironmental and physiological research

Dingsu Feng1,2, Jakub Surma3, Niklas Löffler4, Thomas Tütken5, Fabian zahnow1, Daniel Herwartz2, Andreas Pack1

1Abteilung Geochemie & Isotopengeologie, Geowissenschaftliches Zentrum,Georg-August-Universität,Goldschmidtstraße 1, D-37077 Göttingen,Germany; 2Institute für Geology und Mineralogy, Department für Geowissenschaften, Universität zu Köln, Greinstrasse, 4-6, D-50939, Köln, Germany; 3Presently at Earth-Life Science Institute, Tokyo Institute of Technology, 152-8550 Tokyo, Japan; 4Institut für Geowissenschaften, Goethe Universität Frankfurt, Altenhöferallee 1, D-60323 Frankfurt (Main), Germany; 5Institut für Geowissenschaften, AG Angewandte und Analytische Paläontologie, Universität Mainz, J.-J.-Becherweg 21, D-55128 Mainz, Germany

Triple oxygen isotope (Δ'17O) analysis has recently be shown to be a powerful tool for identifying metabolic oxygen signatures in mammalian tooth enamel (Pack et al., 2013; Feng et al., 2022). Atmospheric O2 is consumed by mammals for metabolic oxidation. The low triple oxygen isotope (Δ'17O) composition of air O2 serves as a natural tracer for identifying metabolic oxygen in body water. Bioapatite precipitates in isotopic equilibrium with its parental body water and consequently records information on the air O2. The Δ'17O of atmospheric O2 is directly linked to pCO2 and gross primary production, hence fossil teeth can be used for paleo- pCO2 reconstructions.

To provide a modern baseline for this approach, we measured 128 individual mammal teeth for their bioapatite Δ'17O by automatic BrF5 laser fluorination. The sample set includes diverse body size with a body mass range from 2 g to 6000 kg and physiology from different habitats. Taxon-specific oxygen mass balance models are developed for resolving principal dependencies and relationships.

The mass balance modelled data for all species agree within uncertainty with the measured data. The results show that Δ'17O not only correlates with body mass, but also with initial oxygen anomalies of inhaled air O2, which allows for pCO2 reconstruction on terrestrial mammalian tooth enamel. This documents the potential of tooth enamel Δ'17O analysis for metabolic rates of extinct vertebrates and paleoclimate reconstructions, especially for small mammals (Mb < 1 kg).

Pack et al. (2013) GCA, 102, 306–317.

Feng et al. (2022) GCA, 328, 85-102.



9:00am - 9:15am
Topics: 3.03 Advances in paleoclimate proxy development and application

Vital effects in biogenic carbonates in triple oxygen isotope space

Daniel Herwartz1, Swea Klipsch1, David Bajnai2, Jacek Raddaz3, Amelia Davies3, Eberhard Gischler3, Jens Fiebig3, Andreas Pack2

1Uni Köln, Germany; 2Uni Göttingen, Germany; 3Uni Frankfurt, Germany

Carbonate δ18O and Δ47 are used to reconstruct paleotemperatures. Because biogenic carbonate does not form in full equilibrium with seawater, species-specific temperature calibration curves are required for accurate temperature estimates. Apparent growth temperatures derived from corals, however, are generally inaccurate due to large and variable kinetic isotope effects, often termed “vital effect”. Triple oxygen isotope systematics can help identify if an organism forms carbonate in equilibrium with ambient water or not and thus if the δ18O and Δ47 values provide accurate paleotemperatures. In addition, the chemical nature of the “vital effect” can be identified, because individual kinetic effects fall on characteristic trajectories in triple oxygen isotope space.

To examine these concepts a series of cold water and warm water corals as well as brachiopods are analyzed for δ18O and δ17O (expressed as Δ’17O) using the CO2 spectrometer (TILDAS; Aerodyne Research) installed in Göttingen. Samples formed in equilibrium are expected to fall on the equilibrium curve. Most samples fall below the curve providing evidence that their oxygen isotope composition is biased by kinetic effects. We suggest that the “vital effect” in corals is dominated by a CO2 absorption effect. Similar conclusions are derived from dual clumped (Δ47 and Δ48) isotope analyses of the same samples [1]. These authors suggested to correct for kinetic effects by back extrapolation to the “dual clumped” equilibrium line. The same concept can be applied in triple oxygen isotope space by back-extrapolation to the “triple oxygen isotope” equilibrium line.

[1] Davies et al. (2022). GCA 338, 66–78.



9:15am - 9:30am
Topics: 3.03 Advances in paleoclimate proxy development and application

Assessing the belemnite archive for Mesozoic seawater temperature reconstruction by clumped isotope thermometry

Amelia Jane Davies1, Philip Staudigel1, Mattia Tagliavento1, Gregory Price2, Miguel Bernecker1, Julia Brugger3, Jens Fiebig1

1Goethe University Frankfurt; 2University of Plymouth; 3Senckenberg Biodiversity and Climate Research Centre

The reconstruction of Mesozoic seawater temperature is valuable to further understand the link between atmospheric carbon dioxide concentration and earth surface temperature variation. Belemnites are an effective archive for this purpose, owing to their distribution over an extensive latitudinal range in Jurassic and Cretaceous seas. However, uncertainty remains as to whether belemnites precipitate rostrum calcite in oxygen and clumped isotope equilibrium with surrounding seawater. Furthermore, recent study indicates that belemnite calcite may be more susceptible to thermal resetting of ∆47 values through oxygen isotope exchange with internal water than other calcites (Looser et al., 2023).

Here, we demonstrate identification of thermal resetting of ∆47 values in belemnite calcite using a combination of measured δ18O of fluid inclusions, δ18O and ∆47 values of belemnite calcite. We then apply dual carbonate clumped isotope thermometry (i.e. the simultaneous measurement of ∆47 and ∆48), to assess the potential importance of kinetic limitations during belemnite biomineralization (Bajnai et al., 2020; Guo, 2020). We demonstrate that Maastrichtian agebelemnites sampled at 4 sites with a range of paleolatitudes from 34 to 45 ˚N, yield ∆47 and ∆48 values that fall on the experimentally derived equilibrium calibration of Fiebig et al., (2021) indicating that rostrum calcite precipitated in clumped isotope equilibrium. ∆47-derived temperatures are combined with other proxy-based reconstructions of Maastrichtian seawater temperature to examine its latitudinal variability.



9:30am - 9:45am
Topics: 3.03 Advances in paleoclimate proxy development and application

New insights on the influence of biota on the Ce and U redox proxies: Evidence from experimental water-rock interaction with biogenic ligands under anoxic, hypoxic and oxic conditions

Dennis Kraemer1, Timmu Kreitsmann2, Stefan Weyer3, Michael Bau2

1Bundesanstalt für Geowissenschaften und Rohstoffe, Germany; 2Constructor University Bremen, Germany; 3Leibniz Universität Hannover, Germany

Microbes, plants and other organisms actively shape the Earth surface by a variety of processes. Current research on modern systems suggests that biota has a significant impact on the mobility of trace elements and there is growing evidence that it may have done so since the dawn of life. The secretion of extracellular compounds that bind strongly to iron and other micronutrients are evolutionary traits that may, besides acquiring bio-essential trace metals, also have helped in tackling with the toxicity of certain heavy metals. An example of such compounds are siderophores, which are produced today by many different plants, microbes and fungi. Besides iron, they promote the (bio)availability of different highly-charged cations in the natural environment.

In paleoclimate studies, the redox-sensitive trace elements Ce and U are commonly used as geochemical proxies (e.g., Ce anomalies, Th-U ratios, stable U isotopes) for reconstructing atmospheric oxygen levels through time. We investigated the effect of siderophores on the mobilization of rare earth elements, Th and U (isotopes) from natural rocks under anoxic, hypoxic and oxic conditions. We show that experimental water–rock interaction with siderophores under strictly anoxic conditions produces positive Ce anomalies – a geochemical signal that is usually attributed to the presence of atmospheric oxygen. Siderophores also influence the Th-U signal, but do not induce a significant U stable isotope fractionation. Thus, oxygen-independent fractionation during geo–bio interaction may hold the potential to use certain trace elements as a bio-proxy in addition to their current use as a redox proxy.



9:45am - 10:00am
Topics: 3.03 Advances in paleoclimate proxy development and application

Oxygen isotope variations in cherts from the Rhenish Massif record their diagenetic history, not climatic variations

Michael Tatzel1, Katharina Ebert1, Patrick Frings2, Tommaso di Rocco1, Andreas Pack1, N. Keno Lünsdorf1

1Universität Göttingen, Germany; 2GFZ Potsdam, Potsdam, Germany

Cherts are sturdy and ubiquitous throughout Earth history and therefore potentially ideal climatic archives, yet their diagenetic formation challenges straightforward interpretations. Previous work shows that oxygen isotope ratios (δ18Ochert) are not only controlled by seawater T and δ18Oseawater, but also by basal heat flow (Q) and burial rates, i.e. the diagenetic T-t path (Tatzel et al., 2022).

To strengthen the empirical evidence for the control of Q and burial rates on δ18Ochert we exploit the geological framework of the Rhenish Massif: During the Lower Carboniferous siliceous sediments were deposited onto stretched continental crust with variable Q across the basin. The opal mud then transformed during burial diagenesis into chert while tectonic nappes were stacked onto the autochthonous sediments during the Armorica- Laurussia collision.

To isolate the effects of the T-t-path on δ18Ochert we sampled isochronous cherts and siliceous shales from the Northern and Eastern margin of the Rhenish Massif. A decreasing trend in δ18Ochert from West-to-East (by >6 ‰) testifies to differences in burial rates and paleo-Q. We derive constraints on burial rates from peak diagenetic temperatures using Raman Spectrometry of carbonaceous matter and deconvolve for paleo-Q. Triple oxygen isotope compositions (Δ’17O) show increasing variations with increasing δ18Ochert – presumably a reflection of a wider range of diagenetic conditions in low-Q settings.

Tatzel, M., Frings, P.J., Oelze, M., Herwartz, D., Lünsdorf, N.K., Wiedenbeck, M., 2022. Chert oxygen isotope ratios are driven by Earth’s thermal evolution. Proc. Natl. Acad. Sci. 119.

 
3:30pm - 5:00pm3.03-2 Advances in paleoclimate proxy development and application
Location: Hall A (HFB)
Session Chair: Amelia Jane Davies, Goethe University Frankfurt
Session Chair: David Bajnai, University of Göttingen
 
3:30pm - 4:00pm
Invited Session Keynote
Topics: 3.03 Advances in paleoclimate proxy development and application

Continental or oceanic weathering processes – What controlled the Late Cretaceous lithium cycle?

Sandra J. Huber1,2, Vanessa Schlidt1,2, Jorit F. Kniest1,2, H.-Michael Seitz1,2, Jacek Raddatz1,2, Horst R. Marschall1,2, Silke Voigt1,2

1Institute of Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany; 2Frankfurt Isotope and Element Research Center (FIERCE), Goethe University Frankfurt, 60438 Frankfurt am Main, Germany

The lithium isotopic composition (δ7Li) of marine carbonates is known as a proxy for the chemical weathering intensity of silicate rocks. To evaluate the role of weathering as a sink for atmospheric CO2 during the Late Cretaceous, we generated a 20 Ma δ7Li record (86.3–66.0 Ma) using chalk from Northern Germany as an archive. The late Santonian to Maastrichtian record shows an overall increase of ~4.5‰ with superimposed increases in the late Santonian, early Campanian and across the Campanian–Maastrichtian transition.

The overall increase in δ7Li fits with the Late Cretaceous increase in seawater 87Sr/86Sr. Further, the δ7Li record strongly resembles both the evolution of deep-sea temperatures based on benthic oxygen isotopes and modeled changes in the rate of seafloor spreading. Thereby, increases of δ7Li in the early Campanian and across the Campanian–Maastrichtian transition correspond to major sea level falls, and the latter with a negative δ13C excursion.

These coherences allow three interpretative approaches: (1) Climate cooling controlled the weathering congruency and the magnitude of Li isotope fractionation by clay mineral formation on the continents. (2) Lowland exposure promoted erosion together with enhanced soil and clay formation after sea level falls. (3) A temperature-dependent fractionation during low-temperature basalt alteration affected the seawater δ7Li signal in a time, when more fresh oceanic basalts where available due to higher spreading rates. The best possible interpretation for the Late Cretaceous δ7Li record and the often-neglected aspects of basalt alteration and reverse weathering need to be further assessed and discussed.



4:00pm - 4:15pm
Topics: 3.03 Advances in paleoclimate proxy development and application

Lithium isotope compositions of various biogenic carbonates throughout the mid-Cretaceous – Challenges of reconstructing δ7LiSW in deep time

Vanessa Schlidt1,2, Sandra Janina Huber1,2, René Hoffmann3, Ulrich Heimhofer4, Elisabetta Erba5, Cinzia Bottini5, Stefan Huck4, Hans-Michael Seitz1,2, Silke Voigt1,2

1Goethe University Frankfurt, Institute for Geosciences, Altenhöferallee 1, 60438 Frankfurt (Germany); 2FIERCE - Frankfurt Isotope & Element Research Center, Altenhöferallee 1, 60438 Frankfurt, Germany; 3Ruhr-Universität Bochum, Institute for Geology, Mineralogy and Geophysics, Universitätsstraße 150, 44801 Bochum (Germany); 4Leibniz University Hannover, Institute of Geology, Callinstraße 30, 30167 Hannover (Germany); 5Università degli Studi di Milano, Dipartimento di Scienze della Terra Ardito Desio, Via Mangiagalli 34, 0039 02 Milan (Italy)

The evolution of the seawater Lithium isotope composition (δ7LiSW) depends on the prevalent weathering regime. To reconstruct δ7LiSW, and thus, weathering congruency, two main archives are widely used: calcareous fossils and bulk carbonate sediments. Either of these archives has its strong and weak points. While carbonate sediments are prone to diagenesis and clay contamination, biogenic skeletons may exhibit strong vital effects on δ7LiSW. Here, we present δ7LiSW data for the mid-Cretaceous derived from various biogenic carbonates such as bivalves (mainly rudists), cephalopods, and brachiopods from well-known sample sites across Europe.

Additionally, we assessed the extent of taxon-specific vital effects on δ7Li for well-preserved Albian molluscs from Madagascar (Mahajanga Basin, age 110.5 +/-0.5Ma) and compared them with data for modern taxonomic groups.

Our most complete data set derives from rudist shells (mainly requieniid rudists) from the mid-Barremian to early Aptian sample locations of Sausset (Urgonian Limestone Formation, France), Ericeira (Crismina Formation, Portugal), Kanfanar (Kanfanar unit, Croatia), and Miravete (Villarova de los Pinares Formation, Spain). We compare their δ7Li compositions and trends therein with that of cotemporaneous carbonate-rich sediments. We provide preliminary δ7LiSW for several time intervals which range between 22-25‰ on average with values exceeding 30‰ in the late Barremian.

Relative to published bulk carbonate data, we observe a systematic offset for rudist-shell δ7Li values of 3-8‰ towards heavier values. We assign this offset to vital effects similar to those known for modern calcitic molluscs.



4:15pm - 4:30pm
Topics: 3.03 Advances in paleoclimate proxy development and application

Temporal and spatial distribution of modern ostracod species of Lago Enriquillo (SW Dominican Republic)

Christopher Berndt1, Torsten Haberzettl1, Lilly Biedermann1, Michael Ernst Böttcher1,2,3, Berenice Matias Marte de Reyes4, Edwin Garcia Cocco4, Claudia Wrozyna1

1University Greifswald, Germany; 2Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany; 3Interdisciplinary Faculty, University of Rostock, Germany,; 4Servicio Geológico Nacional, Santo Domingo, Dominican Republic

Understanding modern species´ ecological preferences and distribution are prerequisites for their application as proxies in paleoenvironmental reconstructions. This knowledge is, however, missing for the majority of tropical species. In order to contribute to close this gap we characterize the ostracod fauna of Lago Enriquillo in the Dominican Republic. Located in the Main Development Region of North Atlantic tropical storms it has experienced rapid water level fluctuations in the past that are assumed to be related to storm activities. This highlights the relevance of the lake for reconstructions of changes in precipitation and storm activity. Living ostracods inhabiting Lago Enriquillo were analyzed in March and September (dry and rainy season) 2022 with the aim to understand their temporal and spatial distribution and changes in morphological characteristics (valve size). Lago Enriquillo is a warm (27.8-33.8°C), mesohaline (43.7-46.3 psu) and generally slightly alkaline lake (pH: 7.5-8.1) with a max. water depth of 25 m. The spatially variable ostracod fauna is composed of Cyprideis similis, Perissocytheridea cribrosa and Thalassocypria sarbui. The three species reflect the lake’s seasonality differently in terms of their morphology and population structure. C. similis occurred continuously but is smaller in spring than in autumn. P. cribrosa inhabits the lake only in autumn and shows a distinct distribution dominating littoral areas with seasonal freshwater inflow. T. sarbui forms larger populations only in spring and forms only tentative size clusters. Their occurrence is restricted to water depths above (temporary) minima of oxygen (below 10 – 14 m).



4:30pm - 4:45pm
Topics: 3.03 Advances in paleoclimate proxy development and application

High resolution study of Glycymeris sp. shells from high energy event layers of the Cadiz Bay – a sclerochronological record for the onset of the Dark Ages Period

Alexandra Németh

Research Centre for Astronomy and Earth Sciences, Budapest, Hungary

Driving factors of shell growth of sub-fossil Glycymeris nummaria shells deposited by high energy events into layers at the Atlantic coast of the Iberian Peninsula were investigated by stable isotope analysis and analysing their growth patterns.

High energy events deposited layers of cockles along the coast of Cádiz Bay during the Roman Period (313 ± 114 AD) and the Dark Ages (648 ± 108 AD) (Gutiérrez-Mas, 2011). The climate fluctuation of the region between these two periods was largely investigated by analysing sediment cores from the pro-deltas on the Iberian margin (e.g. Bartels-Jónsdóttir et al., 2015), Glycymeris shells, however can provide seasonal data of temperature change and the seasonality in chemical characteristics of the marine ecosystems. Comparing the paleotemperature data reconstructed from oxygen isotope ratios of seasonally sampled shell carbonate indicates no significant cooling for the ‘Dark Ages Cold Period’ (DACP) for the Cádiz Bay. The seasonality of carbon isotope ratios however showed distinct changes between the Roman Period and the DACP. Seasonal maxima of δ13C values were twice as higher during the DACP which indicates seasonally intensified biological fractionation connected to enhanced primary productivity. This agrees with other studies implying intensified coastal upwelling during the DACP along the Iberian Peninsula, while they observe no significant cooling of the sea surface (Bartels-Jónsdottir et al. 2015). This case study adds to the growing number of evidence that the DACP can not be interpreted as a Europe-wide cooling event as it affected southern regions differently.



4:45pm - 5:00pm
Topics: 3.03 Advances in paleoclimate proxy development and application

Triple oxygen isotope measurements of air CO2 around Göttingen

David Bajnai, Tammo Freese, Andreas Pack

University of Göttingen, Germany

The triple oxygen isotope composition (δ18O and ∆’17O) of atmospheric CO2 provides valuable information about CO2 sources and carbon exchange fluxes between atmospheric reservoirs [1-2]. For example, stratospheric CO2 has a large positive 17O-anomaly due to photochemical processes. The ∆’17O of tropospheric CO2 is primarily influenced by carbonic anhydrase-catalyzed oxygen isotope exchange between air CO2 and water in vegetation, resulting in an air CO2 ∆’17O mainly governed by the isotope composition of local meteoric water. Additionally, CO2 from fossil fuel combustion processes shows a negative 17O-anomaly inherited from the isotope composition of atmospheric O2 [3].

Starting in April 2023, we conducted automated triple oxygen isotope measurements of air CO2 in Göttingen using tunable infrared laser direct absorption spectroscopy (TILDAS; Aerodyne, USA) coupled with a custom-built inlet system. The internal error of the ∆’17O measurements was < 10 ppm and of the δ18Omeasurements < 0.01‰.

In this report, we present our initial results and discuss the contribution of various reservoirs to the ∆’17O of atmospheric CO2 in Göttingen. We also examine daily and seasonal variations observed in our data.

[1] G. Koren et al., J. Geophys. Res. Atmos. 124, 8808–8836 (2019).

[2] M. E. G. Hofmann et al., Geochim. Cosmochim. Acta. 199, 143–163 (2017).

[3] B. Horváth, M. E. G. Hofmann, A. Pack, Geochim. Cosmochim. Acta. 95, 160–168 (2012).

 

Date: Tuesday, 05/Sept/2023
10:00am - 11:15am3.28-1 Developments and progress in regional geology
Location: Hall A (HFB)
Session Chair: Guido Meinhold, TU Bergakademie Freiberg
 
10:00am - 10:30am
Invited Session Keynote
Topics: 3.28 Developments and progress in regional geology

Shaping the northern Gondwana margin before the Variscan orogeny: large-scale geodynamic processes and paleogeography

Jiří Žák

Institute of Geology and Paleontology, Faculty of Science, Charles University, Czech Republic

The Cadomian accretionary orogeny at the end of Neproterozoic to early Cambrian was one of the principal crustal growth events in Europe, as indicated by a number and widespread distribution of Cadomian basement units within the Variscan and Alpine orogenic belts. Although the evolution of the Avalonian–Cadomian active-margin of northern Gondwana has been well established, geodynamic causes of its collapse and processes of its transition to a passive margin are significantly less understood. The particularly intriguing issues, which have a significant impact on interpretations of paleogeography and course of the subsequent Variscan orogeny, include: (1) how and when the Cadomian orogeny ended, (2) what was the provenance of the Avalonian, Cadomian, and other terranes, i.e., where they started their journey from Gondwana to Pangea, (3) how was the Cambro–Ordovician rifting phase expressed along the former active margin and what was its exact timing, duration, style, and magnitude, and (4) how far east reached the Rheic Ocean rift system and what was the nature of its eastern termination. Integrated geochronological and tectonic information suggest that (i) the active-to-passive-margin transition was step-wise, protracted over Cambrian and early Ordovician, (ii) strongly controlled by tectonic inheritance whereby an inherited suture in the Avalonian ribbon terrane facilitated complete rifting and rift–drift transition while the Cadomian terranes remained attached to Gondwana, and (iii) magmatism may have been an important geodynamic driver of rifting during at least the initial stages, before being overridden by the slab pull force of the subducting Iapetus Ocean.



10:30am - 10:45am
Topics: 3.28 Developments and progress in regional geology

The Harz Mountains (Germany) – Cadomia meets Avalonia and Baltica: U-Pb ages of detrital and magmatic zircon as a key for the decoding of Pangea´s central suture

Ulf Linnemann1, Maren Zweig2, Mandy Zieger-Hofmann1, Tim Vietor3, Johannes Zieger1, Jessica Gärtner1, Andreas Gärtner1, Katja Mende1, Rita Krause1, Friedhart Knolle4

1Senckenberg Naturhistorische Sammlungen Dresden, Germany; 2Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie, Germany; 3Nationale Genossenschaft für die Lagerung radioaktiver Abfälle (Nagra) , Switzerland; 4UNESCO Global Geopark Harz, Germany

The nature of Pangea´s internal suture in the Central European Variscides is evaluated on the example of the Harz Mountains (Germany). U-Pb ages of detrital (n = 2273) and magmatic zircon grains (n = 170) were obtained by LA ICP-MS for provenance studies and absolute age dating. Provenance studies point to a docking of East Avalonia onto southern Baltica at c. 430 Ma and to a closure of the Rheic Ocean at c. 430-420 Ma. In the aftermath, the re-opening of a narrow Rhenish Seaway happened in mid-Devonian time. Devonian aged sedimentary rocks of the Harz Mountains were formed at the north-western (Rheno-Hercynian) and on the south-eastern (Saxo-Thuringian) margin of the Rhenish seaway. Deposits formed on the Rheno-Hercynian margin display sedimentary supply from southern Baltica, while most East Avalonian sources were buried and not available for erosion. Siliciclastic shelf deposits of Saxo-Thuringia were derived from Cadomia and its West African hinterland. Provenance studies and spatial arrangement of the tectonostratigraphic units in the Harz Mountains allow to reconstruct the style of obduction of the Harz Mountains onto the southeastern margin of East Avalonia (Rheno-Hercynian Zone). As a result of the closure of the Rhenish Seaway and the collision with the Mid-German Crystalline Zone, the Harz Mountains show a building plan strongly dominated by thin skinned tectonics. Our new data favour a two-plate model for the origin of Pangea´s internal suture in the Central European Variscides, but a re-opening of a narrow oceanic seaway is necessary after closure of the Rheic Ocean.



10:45am - 11:00am
Topics: 3.28 Developments and progress in regional geology

The Ellesmerian orogeny of Laurussia – A far-field effect of the late Devonian collision of Gondwana with North America

Uwe Kroner1, Tobias Stephan2, Thorsten Nagel1

1TU Bergakademie Freiberg, Germany; 2Lakehead University, Canada

Convergent tectonics of the Ellesmerian orogeny affected Arctic Canada and Svalbard in late Devonian - early Carboniferous times. The coeval ultra-high pressure metamorphism in NE-Greenland, the formation of the Maritimes Basin in the Canadian Appalachians, and tectonic activity in the Antler orogeny (Nevada, USA), raised a controversy about whether the Ellesmerian orogeny was related to either late Caledonian plate tectonics or renewed, i.e., post-Caledonian convergence of Laurentia with the rest of Laurussia. Here, we argue that the Ellesmerian orogeny represents a far-field effect of the collision of a Gondwanan promontory with the Appalachian segment of Laurussia. This collision caused the decoupling of the North American lithosphere from Laurussia. The northward motion of this lithospheric domain relative to Laurussia explains the tectonic events along its boundaries, namely the Ellesmerian and the Antler orogenies along the frontal and the Panthalassan margins, respectively. Furthermore, it triggered the reactivation of the NE segment of the Greenland Greenland-Scandinavian Caledonides under dextral transpression causing UHP metamorphism. To the southeast, the formation of the Maritimes Basin reflects dextral transtension and associated strike-slip faults parallel to the edge of SE-Greenland. Strain compatibility requires the existence of a dextral lithospheric-scale strike-slip fault that links the tectonic structures and transects the Greenlandian part of the North American Craton. Because this proposed shear zone in SE Greenland follows small-circle trajectories of the motion of Gondwana relative to Laurussia, we interpret the southeastern edge of Greenland as a dextral transform boundary of the decoupled North American lithosphere.

 
2:00pm - 3:30pm3.28-2 Developments and progress in regional geology
Location: Hall A (HFB)
Session Chair: Jonas Kley, University of Göttingen
 
2:00pm - 2:15pm
Topics: 3.28 Developments and progress in regional geology

The Namaqua Metamorphic Complex: Geochronology and geochemical signatures of the Aus Crystalline Complex (Southern Namibia)

Jessica Haschke1, Mandy Zieger-Hofmann1, Johannes Zieger1, Ulf Linnemann1, Anja Sagawe1, Andreas Gärtner1, Sebastian Haschke2

1Senckenberg Naturhistorische Sammlungen Dresden, Germany; 2Technische Universität Bergakademie Freiberg, Germany

The Namaqua Metamorphic Complex (NMC) forms a basement unit of the Grenvillian-Kibaran collisional orogen in southern Namibia and South Africa. The Aus Crystalline Complex is a terrane within the NMC and consists, predominantly, of gneisses, granites, metavolcanites, and metasediments. The objective of our study is to generate new knowledge about crustal evolution during the Kibaran orogeny using age dating and whole rock geochemistry of various basement units of the crystalline complex around Aus.

Outcropping basement rocks were Aampled in the Namib Desert, southwestern Namibia, east of the coastal town of Lüderitz, within a 20 km radius around Aus. Rock types encountered included granulites, gneisses, charnockites, granites, and pegmatites. Geochemical and geochronological analyses were performed to gain information on the timing of crystallisation and crust production processes, using U-Pb dating on magmatic zircons with LA-ICP-MS. Analysed zircon grains are often complex, U-Pb ages range from 1700 Ma to c. 700 Ma. The oldest rock is a charnockite showing an age of intrusion of c. 1700 Ma, which represents a Palaeoproterozoic part of the cratonic basement. U-Pb zircon ages of the gneisses point to protolith ages of c. 1155 Ma – 1145 Ma. This coincides with a major tectono-magmatic event in the NMC, which occurred in a time span of c. 1190 - 980 Ma. Such processes led to the amalgamation of the supercontinent Rodinia in late Mesoproterozoic time. A younger suite of granitoids (c. 700 Ma) is most probably related to Rodinia dispersal.



2:15pm - 2:30pm
Topics: 3.28 Developments and progress in regional geology

The Early Permian Bromacker paleoenvironment: Preliminary results from scientific drilling in the Tambach Basin (Thuringia, Germany)

Jakob Stubenrauch, Thomas Voigt, Rebecca Lellau, Niklas Störer, Anna Pint, Christoph Heubeck, Peter Frenzel

Friedrich-Schiller-Universität Jena, Germany

The Bromacker Project (https://bromacker.de/) investigates the paleoecology of the Early Permian vertebrate “Ursaurier” lagerstätte of the same name in the red beds of the Tambach Formation, Thuringia. Its geologic-paleontologic subproject aims to contribute key paleoenvironmental parameters such as temperature variation, precipitation estimates, paleoelevation, soil hydrology, detailed paleogeography, and depositional environments, based on sedimentology, paleoichnology, facies analysis, petrography, geochemistry, and precise depositional ages.

Two new deep research boreholes will complement information from shallow legacy boreholes and outcrops near the Bromacker excavation site. Forschungsbohrung (Fb) Altenbergen 01/2022, 3 km to the north, cored 250 m of the Tambach Formation and terminated in conglomerates (Bielstein Member) after having cored the topmost Finsterbergen Conglomerate Member and the Tambach Sandstone Member. Contacts between members in core are gradual but differences pronounced: The basal Bielstein Member is dominated by well-rounded intermediate volcanic clasts, in contrast to felsic volcanic clasts described from outcrops. Fossiliferous pelitic-arenaceous redbeds of the overlying Tambach Sandstone Member show all indications of floodplain facies, including mudcracks, variable burrowing, root horizons, calcareous paleosol concretions, climbing ripples, and common laminated siltstones. Conglomerates of the topmost Finsterbergen Member consist of subangular plutonic, metamorphic and (sub-)volcanic clasts. Several newly documented thin felsic tuffs may be datable. Geophysical logs suggest rhythmic deposition suitable for cyclostratigraphic analysis. Fb Gallberg 01/2023, located 2 km south of the Bromacker excavation site, will complement Fb Altenbergen. Information from both boreholes will contribute to a robust sedimentologic-stratigraphic frame for paleogeographic-paleoecologic analyses. A substantial education and outreach program accompanies excavation, drilling and core analysis.



2:30pm - 2:45pm
Topics: 3.28 Developments and progress in regional geology

The geology of the South-Eastern Harz Foreland visualized in a 3D-Model

Melanie Siegburg, Alexander Malz, Tilman J. Jeske, Christian-Olaf Müller, Ivo Rappsilber

Landesamt für Geologie und Bergwesen Sachsen-Anhalt (LAGB), Halle (Saale), Germany

The Central European Basin is an intracontinental basin filled with Permian to Quaternary sediments. The southeastern basin rim, an area roughly covering the southern part of Saxony-Anhalt and eastern Thuringia (Central Germany), is characterized by complex facies distributions with a stratigraphic gap of approximately 200 Ma, where Cenozoic sediments unconformably cover the lower Triassic strata. The sedimentary rocks include several hundreds of meters thick evaporites, sandstone, shale, and carbonates of Permian to Late Triassic age, covered by unconsolidated sediments.

Various tectonic structures like NW-SE trending uplifted basement e. g. the Harz and Kyffhäuser Mountains and narrow fault zones where some abruptly ending along-strike; subordinated NE-SW trending faults sub-parallel to the Permian basin rim and salt structures characterise the area. These structures evolved during several phases of extension and contraction during Mesozoic to Cenozoic times. Due to the stratigraphic gap of the upper Mesozoic, tectonic and halokinetic processes can be well correlated with the wider Central European Basin and earlier structures. Local halokinetic processes and subrosion of evaporites indicated by the distribution of Tertiary deposits as well as variation of the thickness of evaporites influencing the geomorphology at the South-Eastern Harz Foreland until today.

Here, we used 3D modelling techniques and compiled data from drilling, seismic reflection profiles and historic mining surveys to visualize the temporal - spatial distribution and structural configuration of the South-Eastern Harz Foreland. This model will be used to unravel kinematic processes over geologic times, which will be a basis for future underground planning efforts.



2:45pm - 3:00pm
Topics: 3.28 Developments and progress in regional geology

The structure of Börnersdorf (Osterzgebirge) - an evidence of a maar volcano

Ottomar Krentz1, Frank Horna2

1Dr. Spang GmbH Witten/Freiberg, Germany; 2Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie Dresden/Freiberg

During a mapping-project in 2011, evidence of a sediment occurrence was discovered within a morphological depression of a gneiss area in the Osterzgebirge near the village of Börnersdorf (Saxony). Marls and partly sandstones, presumably Cretaceous in age, were described by means of drill cores from the 1960s.

The short wells drilled around 2010 supported this assumption. Results of several geophysical investigations displayed a basin structure with 600 m in diameter and up to 350 m in depth. Paleontological data of the examined marls pointed to a Coniacian age of the sediments that infill the structure. Until recently, the structure was interpreted as either a tectonic pull apart basin or a maar structure.

In 2021, first investigations for a new railway track from Dresden to Prague were carried out.

In order to realize this project, a tunnel of about 30 km in length crossing the Erzgebirge is planned. Therefore, several new wells were sunk in the area of investigation. One of the cores near Börnersdorf provided a breccia of grey marl and black silt pebbles and cobbles. As there is not a tectonic contact between the breccia and the surrounding gneiss, the sediment is interpreted as a collapse breccia. New paleontological examinations proof a late Turonian to middle Coniacian age of the marls.



3:00pm - 3:15pm
Topics: 3.28 Developments and progress in regional geology

The regional significance of the potash deposits in the Danakhil depression, Ethiopia

Sebastiaan van der Klauw, Christian Fritze, Stephan Pfeifer

ERCOSPLAN, Germany

The Danakhil depression is a regional structure in Ethiopia that extents over about 450 km from the Gulf of Djibouti to the NW approximately parallel to the Red Sea coast. It has a maximum width of about 75 km. On surface the SE part of the depression is dominated by recent volcanic rocks with only local windows to the sedimentary rocks below. The part NW of the Erte Ale volcanic structure at an elevation lower than 100 m below sea level is dominated by recent evaporite rocks and alluvial fan deposits with only few recent volcanic structures and is the focus for this contribution.

Although already since the early twentieth century potash and sulphur were mined from the region providing an incentive for investigations, the first regional geologic studies were published only in the 1970’s. These studies were based on interpretation of aerial photographs with minor ground checks. Although recently some further papers about the region have been published, the wealth of information about the regional geology that has been obtained from potash exploration that started in 2008 is hidden in publically accessible technical reports, not usually in focus of geo-scientists. The exploration targeted a neogene or quarternary potash-bearing evaporite sequence within the NW part of the depression. In this contribution we want to present some consequences for the understanding of the regional geology that were developed as a by-product of more than 10 years of potash exploration in the Danakhil depression.

 
4:00pm - 5:30pm3.28-3 Developments and progress in regional geology
Location: Hall A (HFB)
Session Chair: Guido Meinhold, TU Bergakademie Freiberg
 
4:00pm - 4:15pm
Topics: 3.28 Developments and progress in regional geology

New insights into the formation and distribution of Pleistocene tunnel valleys in northern Germany

Sonja Breuer, Anke Bebiolka, Axel Ehrhardt, Vera Noack, Jörg Lang

Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany

Tunnel valleys are among the deepest erosional structures in formerly glaciated areas. Our project aims to provide a synoptic model of the distribution, dimensions and evolution of Pleistocene tunnel valleys and their infills in northern Germany. The results will be used to assess the potential for future tunnel valley formation, which may pose a threat to the long-term (i.e., the next 1 Ma) safety of a radioactive waste repository.

In the first phase of our project, we produced a new overview map of the Pleistocene tunnel-valley network. From this map, we extracted the tunnel-valley thalwegs and classified them into zones of similar maximum depths. Zones of deep erosion (>400m) follow the large-scale geometry of the North German Basin. The map of maximum depth zones can be used as a planning tool for long-term safety assessments.

The next phase of our project includes a regional analysis of the tunnel valley network and local case studies. The regional analysis will compare the trends observed in the tunnel-valley network with regional geological features such as faults, salt structures and basin-fill architecture. The correlation between tunnel-valley trends and faults is ambiguous. Parallel trends occur mainly where ice advance directions were parallel to fault trends.

As a first case study, we use high-resolution 3D seismic data from the German North Sea that image two intersecting tunnel valleys. Initial results show at least three distinct seismic units correlating with different sediment types and patterns, and possible multiple use of the tunnel valley.



4:15pm - 4:30pm
Topics: 3.28 Developments and progress in regional geology

Paleoseismic and -tectonic structures in Hamburg and Peissen (Schleswig-Holstein)

Alf Grube

Geologisches Landesamt Hamburg, Germany

Paleoseismic investigations in Hamburg and Peissen document paleo-earthquake structures, e.g. large clastic dykes, infill structures, complicated folds, fault-systems and vertical injections as larger structures. Smaller structures include special forms of diapirs, seismically induced soft-sediment deformation structures (SSDS), special flame structures, shear bands, among others. Plastic deformation is dominant in Hamburg, brittle deformation dominates in Peissen. The seismic deformations can be attributed to different mechanisms, e.g. compression as a result of seismic shock or sediment intrusion, liquefaction, fluidization, strain, shear stress, volume loss and subsequent collapse as a result of blowout activity. The observed structures show certain properties that allow a distinction from non-seismic forms (e.g. glacitectonic and periglacial deformation). Dyke structures are partly of Holocene age.



4:45pm - 5:00pm
Topics: 3.28 Developments and progress in regional geology

A large regional structure from puzzle pieces - Gulf of Mexico structures on the western flank of the Eichsfeld-Altmark-Swell (EAS)?

Alexander Malz1, Jonas Kley2, Heinz-Gerd Röhling3

1Landesamt für Geologie und Bergwesen Sachsen-Anhalt, Germany; 2Georg-August-Universität Göttingen, Germany; 3DGGV e.V., Germany

We discuss the structures associated with the Eichsfeld-Altmark-Swell (EAS) in Central Germany, using observations from published cross-sections, outcrops, few boreholes and reflection seismics in a some 200 kilometres long swath in Central Germany. The EAS is well-documented as an approximately NNE-SSW-trending Permo-Triassic intrabasinal high, expressed by reduced thickness, facies changes and unconformities. It was accompanied by depocenters trending parallel to its axis, which changed in position and magnitude during geologic epochs. North of the Harz Mountains an approximately 10 km wide strip of the EAS´s western flank is strongly structured by faults of the Braunschweig-Gifhorn-Fault Zone (BGFZ). There, local thickness reductions of several hundred meters, in places culminating in complete absence of Lower and Middle Buntsandstein and apparently often associated with salt tectonics, are documented by seismics and well data, contrasting with the regional thickness reductions in the range of tens of meters typically attributed to the EAS. In Keuper time areas with large Buntsandstein hiatuses turned into depocenters. The spatial relationships of these depocenters with bordering normal faults and associated salt structures indicate that the western flank of the EAS was influenced by strong extension (up to 5 km) along low-angle normal faults detaching in Zechstein evaporites. No prominent basement offsets are observed, although they become prominent along trend of the BGFZ in the aligned westward terminations of the Flechtingen High, Harz and Thuringian Forest basement blocks. We discuss solutions for the mismatch of strong thin-skinned extension and apparently little deformed basement.



5:00pm - 5:15pm
Topics: 3.28 Developments and progress in regional geology

The role of Regional Geology as key aspect in the planning of large subsurface infrastructures

Marius Waldvogel1, Raphael Burchartz2, Bjorn Vink3, Pooya Hamdi2

1Geological Institute, RWTH Aachen University, Germany; 2Chair for Engineering Geology and Hydrogeology, RWTH Aachen University, Germany; 3NIKHEF

The Einstein-Telescope (ET), a next-generation gravitational wave-detector, is a triangular shape underground facility with 10 kilometres long arms to be constructed at a depth of 200-300 meters below surface. A potential location is the Meuse-Rhine Euroregion. The success of such mega-project requires a comprehensive understanding of regional geology in terms of lithology, lithological variations and dominant structures. A solid regional geology study, combining literature review, reconnaissance study, surface and subsurface mapping, sample collection, geophysical data collection, and remote sensing methods to identify the rock units and structures present, is part of assessing the feasibility of the area. The lithology consists of soft Upper Cretaceous sediments resting unconformable on Silesian, Dinantian and Famennian units. The Dinantian carbonates and the Famennian sandstones are the preferred target units for the cavern construction. A major goal is to understand the spatial distribution of the different rock units that may be encountered during construction of caverns and tunnel. Structurally, the region shows a complex pattern of NE- SW striking Variscan folds and thrusts and (N)NW –(S)SE striking faults linked to the Lower Rhine Embayment. Changes in the lithology due to folds and thrust are important in terms of tunnel planning. The (N)NW – (S)SE structures provide pathways for fluids and are potentially seismic active and hence may affect the construction and the operation of the ET severely. Understanding the regional geology allows for optimization of the location and orientation of the ET infrastructure and identifies the potential impacts during construction and operation of the ET.

 

Date: Wednesday, 06/Sept/2023
10:00am - 11:15am-
Location: Hall A (HFB)
2:00pm - 3:30pm3.21-1 Tectonic Systems - TSK Open Session
Location: Hall A (HFB)
Session Chair: Armin Dielforder, Leibniz Universität Hannover
Session Chair: Michael Stipp, Martin-Luther-Universität
 
2:00pm - 2:30pm
Invited Session Keynote
Topics: 3.21 Tectonic Systems - TSK Open Session

Sedimentary basins: Fingerprinting the lithospheric-scale processes

Nevena Andrić-Tomašević

Karlsruhe Institute of Technology, Institute of Applied Geosciences, Karlsruhe, Germany

This talk focuses on disentangling the signatures of the lithospheric scale processes such as slab break-off and/or tearing within the sedimentary basin architecture. Sedimentary basins are sensitive recorders of the interplay between dynamic processes controlling the deformation of the lithosphere, climate and sea-level variations. Variations in sedimentary succession, recorded as variable grading, thickening and/or depositional trends across the basin or series of basins, are often attributed to a wide range of lithospheric-scale processes. This cause-and-effect relationship is based on deductive reasoning and so far, a direct link and quantitative assessment of the effect of these processes on the basin(s) architecture are missing. The inversion of basin fill data to derive the dominant mechanism responsible for the observed basin architecture is complicated by incomplete preservation in the geological record or sparseness in data coverage. Furthermore, many processes may have operated coevally or at different spatiotemporal scales or at different amplitudes, making retrieving the information challenging. Therefore, to distinguish slab break-off and/or tearing-induced signals within sedimentary basins from other signals (e.g., climate, sea level variations) an interdisciplinary approach is needed. In this talk, field observations and results of 3D geodynamic and stratigraphic numerical models inspired by the Molasse Basin and Dinaridic Lake System are combined to understand the set of parameters leading to the preservation of these signals in sedimentary records.



2:30pm - 2:45pm
Topics: 3.21 Tectonic Systems - TSK Open Session

The Importance of Rift Inheritance in Understanding the Early Collisional Evolution of the Western Alps

Gianreto Manatschal1, Pauline Chenin1, Gianluca Frasca2

1University of Strasbourg, CNRS, ITES UMR 7063, F-67084 Strasbourg, France; 2Institute of Earth Sciences and Georesources, National Research Council (IGG-CNR), 56124 Torino, Italy

We reassess the architecture and tectonic history of the Western Alps based on recent knowledge developed at rifted margins. First, we replace the main Alpine units of our study area into a synthetic rifted margin template based on diagnostic petrologic, stratigraphic, and structural criteria. We find that some units previously attributed to the internal part of the thick-crusted Briançonnais domain may rather derive from the thin-crusted Prepiemonte hyperextended domain. We assert that the Briançonnais and Prepiemonte domains were separated by a mega-fault scarp. Second, we revisit the Paleogeography of the Alpine Tethys, suggesting that the Briançonnais was a ribbon of little thinned continental crust between two overstepping en-échelon rift basins, namely the Valais domain to the northwest and the Piemonte domain to the southeast. We affirm that this uneven-margin architecture can explain most of the Western Alps’ complexity. In our kinematic model, convergence between Adria and Europe was mainly accommodated by strike-slip movements in the Western Alps until the late Eocene. Orogeny began with the reactivation of the mega-fault scarp between the Briançonnais and Prepiemonte domains, which we name Prepiemonte Basal Thrust. Once hard collision started, the main shortening stepped inboard into the Valais/Subbriançonnais domain along the Penninic Basal Thrust.



2:45pm - 3:00pm
Topics: 3.21 Tectonic Systems - TSK Open Session

The Cadomian Orogeny in the northern Bohemian Massif – geochronology, basin development, crustal growth, and geotectonic setting

Ulf Linnemann1, Mandy Zieger-Hofmann1, Johannes Zieger1, Jessica Gärtner1, Andreas Gärtner1, Linda Marko2, Richard Albert Roper2, Axel Gerdes2

1Senckenberg Naturhistorische Sammlungen Dresden, Germany; 2Institut für Geowissenschaften, Goethe-Universität Frankfurt, Germany

During Ediacaran to earliest Cambrian times, the Cadomian Orogen formed a system of magmatic arcs and marginal basins at the northern periphery of the Gondwana supercontinent. The orogenic belt was structured in the geotectonic style of the recent western Pacific. The Saxo-Thuringian Zone forms part of the northern Bohemian Massif and contains a number of good preserved fragments derived from the peri-Gondwanan Cadomian Orogen (e.g. the Schwarzburg Antiform, the Lausitz Block, the Eastern Sudetes). Here, we present a massive dataset of LA ICP-MS U-Pb ages and Hf-isotopes from detrital and magmatic zircon of sedimentary and igneous rocks from these areas. Sedimentary rocks are represented by arc-derived greywacke and mudstone turbidites in a back-arc and retro-arc setting. Further, glacio-marine diamictites and high-mature quartzites display passive margin deposits situated more proximate to the cratonic hinterland. U-Pb ages of detrital zircon form populations, which point to a West African hinterland during the time of deposition. The stratigraphic age of the basin fillings is bracketed between the maximum depositional age of the sedimentary rocks at c. 560 Ma and the age of intrusion of c. 539 Ma old granodiorite plutons, which intruded the isoclinal deformed greywacke-mudstone deposits of the marginal basins in the Cadomian orogenic system. The Cadomian crustal evolution is dominated by the recycling of continental crust from the West African hinterland as suggested by the dominance of zircons with negative εHf values. Juvenile arc magmas became contaminated by the recycling of Eburnian and Archaean crust during long Cadomian magmatic arc activity.



3:00pm - 3:15pm
Topics: 3.21 Tectonic Systems - TSK Open Session

Zircon U-Pb-Hf isotope systematics of southern Black Forest gneiss units (Germany) – implications for the Pre-Variscan evolution of Central Europe

Armin Zeh1, Magdalena Zimmermann1, Kirsten Drüppel1, Richard Albert Roper2, Axel Gerdes2

1KIT, Germany; 2FIERCE, Frankfurt, Germany

We present the first systematic U-Pb-Hf isotope data of detrital zircon grains from gneiss units of the southern Black Forest, preserving different stages of the pre-, syn- and post-Cadomian evolution. Protoliths of Murgtal metagreywackes were deposited during the Ediacarian at <550 Ma and sourced from the Avalonian-Cadomian Belt (550-700 Ma; ~70%) and Sahara Metacraton (760-1045 Ma, 1850-2250 Ma, 2720-3230 Ma; ~30%). In contrast, metasedimentary rocks of the Wiese-Wehra and Todtmoos gneiss units reveal late Devonian depositional ages at <370 Ma, but in different geotectonic settings. Wiese-Wehra metagreywackes provide evidence for the existence of pre-Cadomian oceanic crust formed at 610 Ma (εHft = +5 to +8), accreted to the Cadomian Belt at ca. 540 Ma, and successively reworked between 490 and 430 Ma (εHft = +1 to +6). Finally, these rocks became part of an early Variscan arc-back arc system with juvenile input at 370 Ma (εHft = 0 to +10). Todtmoos metaarkoses mainly reflect subduction-related magmatism at 490-420 Ma (~88%), and at 380 Ma (~10%) in an evolved continental arc setting (εHft = -2 to -8). In combination, existing data from the Black Forest and other basement units throughout Europe provide evidence for the amalgamation of pre-Cadomian juvenile terranes along the northern margin of Gondwana until 540 Ma, followed by a complex rift history, accompanied by subduction between 500 and 400 Ma. They further point to the existence of an oceanic arc-back arc system, which has been located south of the Armorican terrane assemblage at 380-365 Ma.



3:15pm - 3:30pm
Topics: 3.21 Tectonic Systems - TSK Open Session

Microstructures and absolute ages of brittle structures in the Weschnitz Pluton (Southern Odenwald, Germany)

Filip Loeckle1, Axel Gerdes2, Gernold Zulauf3

1BGR Hannover, Germany; 2FIERCE-Lab, Goethe University Frankfurt, Germany; 3Institute for Geosciences, Goethe University Frankfurt, Germany

We present new microstructural evidence and geochronological data from brittle structures sampled in an active quarry located in the Weschnitz Pluton in the southern Odenwald Crystalline Complex (OCC). Open joints and fractures are the primary pathway for fluids in crystalline rock and thus crucial in the utilization of crystalline formations for geothermal energy and long term nuclear storage.
The quarz-monzodioritic wall rock was emplaced around 344.4+-0.6 Ma ago into a considerably thickened crust in in about 18 km depth in a continental arc setting (Altenberger & Boesch, 1993; Altherr, 1999; Henes-Klaiber, 1992). Visean lamprophyre dikes bound to NNE-SSW striking normal faults relate to post-orogenic collapse and mark the onset of a multiphase history of extension and uplift, during which pre-existing variscan structures were repeatedly reactivated (von Seckendorff et al., 2004). While the variscan evolution is fairly well constrained (e.g. Todt et al., 1996; Krohe, 1996; Reischmann, 2001; Stein et al., 2022), brittle structures in the southern OCC have not yet been dated directly.
Most of the sampled joints measure between 2 and 10 mm and are sealed, one specimen has a thickness of 15 cm and is not sealed completely. In thin section, several types of joint mineralizations were identified, with syntaxial elongate blocky quartz with growth zoning and syntaxial blocky calcite with growth zoning being the most common types. Fractured calcite veins are often associated with hematite indicating later reactivation. U-Pb data obtained from LA-ICP-MS analyses on 15 samples splits into 2 age groups of around 300 Ma and 60-50 Ma.

 
4:00pm - 5:30pm3.21-2 Tectonic Systems - TSK Open Session
Location: Hall A (HFB)
Session Chair: Ruth Keppler, Universität Bonn
Session Chair: Kamil Ustaszewski, Universität Jena
 
4:00pm - 4:15pm
Topics: 3.21 Tectonic Systems - TSK Open Session

Do thermomechanical heterogeneities in the upper mantle control crustal deformation?

Judith Bott1, Magdalena Scheck-Wenderoth1,2, Ajay Kumar1, Mauro Cacace1, Sebastian Noe3, Jan Inge Faleide4

1GFZ German Research Centre for Geosciences, Germany; 2RWTH Aachen, Faculty of Georesources and Materials Engineering, Aachen, Germany; 3ETH Zürich, Department of Earth Sciences, Zürich, Switzerland; 4University of Oslo, Department of Geosciences, Oslo, Norway

The architecture of the crust in intracontinental Western and Central Europe is well constrained by multidisciplinary geoscientific data. This low-strain intraplate setting is known for its widely distributed seismicity with earthquake localization, however, being difficult to explain by the observed crustal configuration. Also, observed variations in crustal thickness do not provide clear evidence to explain lateral shifts in depositional and erosional centers over geological time. This raises questions regarding the underlying forces controlling crustal tectonics in this region, located far from active plate boundaries. Shear-wave velocity models obtained from seismic full waveform inversion methods show that the upper mantle is strongly heterogeneous pointing to thermomechanical contrasts that potentially could impact crustal tectonics. Therefore, we convert mantle shear-wave velocities to thermodynamically consistent temperature and density configurations by following a Gibbs's free energy minimization approach. We find spatial correlations between lithospheric thickness, respectively shallow lithospheric temperature and density variations, and crustal deformation patterns (including seismicity). This indicates that thermomechanical instabilities in the mantle could be the origin of relative vertical movements which would (i) cause laterally variable surface uplift and/or subsidence and (ii) facilitate strain localization in the mantle (ductile shear movements) above which the overlying crust would locally respond by brittle deformation.



4:30pm - 4:45pm
Topics: 3.21 Tectonic Systems - TSK Open Session

Detailed investigation of the Asse salt structure (Subhercynian Basin) based on new 3D seismic data

Michael Warsitzka1, Jan Witte2, Kai Gruschwitz3, Maximilian Scholze1, Christoph Nachtweide1, Christian Buxbaum-Conradi1

1BGE Bundesgesellschaft für Endlagerung, Germany; 2Falcon Geo-Consulting, Germany; 3Notting Hill Geoconsulting Limited

The Asse salt structure is a salt-cored anticline with steep, locally overthrusted flanks located in the Subhercynian Basin. It is an excellent example of salt structures in the North German Basin containing a wedge-shaped intrusion of Upper Permian into Upper Triassic salt (‘salt wedge’). The Asse is also known as a location for the disposal of low- and intermediate-level radioactive waste emplaced in the former salt mine Asse II during the 1970s. Detailed knowledge of the tectonic structures is indispensable for planning new retrieval infrastructure and for long-term safety analysis. The Asse salt structure has been thoroughly explored for over 100 years by surface geological mapping, 2D seismic and drilling. Ongoing exploration provides further insights into the salt structures and strengthens our understanding of its evolution.

A new 3D seismic data set (2019-2020) provides new insights into the details of this salt structure. Here we present first results of the seismic interpretation revealing substantial changes in the structural style opposing previous geological models. It can be shown that the sub-horizontal northern flank terminates at the base of the southern flank implying a north-ward instead of a south-ward directed overthrusting. Small-scale faults crossing the crest were previously interpreted as transpressional faults developed during the Late Cretaceous inversion. Ongoing kinematic modeling suggests that these faults originated as steeply dipping pre-Cretaceous normal faults that were overprinted during flank-rotation. These implications as well as observations of thickness variations and unconformities in Mesozoic layers will help to reconstruct the evolution of the Asse salt structure.



4:45pm - 5:00pm
Topics: 3.21 Tectonic Systems - TSK Open Session

Response of salt structures to loading and unloading by ice-sheets – insights from numerical modelling

Jörg Lang1, Andrea Hampel2

1Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany; 2Institut für Geologie, Leibniz Universität Hannover, Germany

Salt rocks are mechanically weak and behave like viscous fluids when deforming at geological time scales and strain rates. The weight of an ice sheet advancing into a salt-bearing basin may cause sufficient differential load to induce salt flow. Ice loading has been postulated as a trigger for Pleistocene deformation at a number of salt structures in the Central European Basin System. We conducted 2D-finite-element models (ABAQUS) with a setup representing a simplified salt diapir to test existing conceptual models and evaluate the controlling factors. Different parameter sets for the rheology of salt and overburden rocks, including linear versus non-linear viscosity of the salt, were tested. Model results show lateral salt flow into the diapir and diapiric rise during the ice advance, while a transgression of the diapir by the ice sheet leads to overall downwards displacement. During unloading, displacements are largely restored due to the dominance of the elastic response. Displacements never exceed few metres and are always larger in models with linear viscosity than in those with non-linear viscosity. Linear viscous salt behaviour seems reasonable, considering the low differential stresses caused by the load of a few hundred-metres-thick ice sheet and the time-scale of several thousand years. The elastic parameters also have a strong impact, with lower Young's moduli leading to larger displacements. Our findings demonstrate that both the viscosity and the elasticity exert a fundamental control on ice-load driven salt movement during glacial-interglacial cycles and highlight the importance of a careful parameter choice in numerical modelling.



5:00pm - 5:15pm
Topics: 3.21 Tectonic Systems - TSK Open Session

Insights Into the Edifice Stability of Anak-Krakatau (Sunda Strait, Indonesia) Before the Lateral Collapse in December 2018 from Direct Shear Experiments and Finite-Element Models

Fiene Matthies1, Morelia Urlaub1, Matt Ikari2

1GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel; 2MARUM Zentrum für Marine Umweltwissenschaften

The lateral collapse of oceanic volcanoes poses a high risk for the population living in coastal areas since the sudden displacement of large amount of material can trigger tsunami waves impacting the surrounding coastlines. One recent example is the lateral collapse of the SW-flank of Anak-Krakatau (Sunda Strait, Indonesia) in December 2018 that generated a tsunami wave impacting the Sunda Strait coastlines and causing several hundred fatalities. Even though, the lateral collapse of oceanic volcanoes are hazardous events, the precursors of such events are poorly understood. It is suggested that external triggers such as the movement of a décollement, the rise of magma during enhanced activity, or earthquakes can cause a lateral collapse. Yet, the internal state of stability of a volcano needs to be known to evaluate the impact of external triggers. We carry out direct shear tests on samples from Anak-Krakatau and implement the results into finite-element models to evaluate the influence of the volcano’s geometry and the rock mechanical properties on the stability of Anak-Krakatau’s flank before the collapse in 2018. The preliminary results suggest that the volcanic edifice of Anak-Krakatau was unstable before the collapse in 2018 solely due to the geometry of the volcano and the rock mechanical properties. Whether the instability of the volcanic edifice is enough to cause the lateral collapse of Anak-Krakatau in 2018 or whether an external trigger is needed, needs further testing.



5:15pm - 5:30pm
Topics: 3.21 Tectonic Systems - TSK Open Session

High-stress crystal-plasticity versus creep of rock-forming minerals – the importance of stress-loading rates indicated by deformation microfabrics

Claudia Trepmann

Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Germany

There is ample evidence of transient high stresses of several hundred MPa at the base of the seismogenic zone in the continental crust, i.e. at greenschist-facies conditions. The microstructural evidence from these depths includes twinning and kinking of jadeite and amphibole, as well as quasi-instantaneous cataclastic deformation of garnet and quartz. At interseismic strain rates, known flow laws for dislocation creep of the rheological dominant mineral, quartz, and/or dissolution precipitation creep of crustal rocks predict lower stresses at the given pressure-temperature conditions. Thus, fast stress-loading rates are required to explain the inferred high-stress crystal-plasticity at greenschist-facies conditions, i.e. loading rates from few tens of MPa to several hundred of MPa within minutes, corresponding to the rupture times for major earthquakes in the seismogenic zone. Although high-stress crystal-plasticity is not allowing to accumulate a high amount of strain, as high stresses prevail only transiently, it provides a driving force for accelerated but rapidly decaying creep, where higher amounts of strain can be accumulated. The strength of both, fault rocks and their host rocks, is strongly depending on the stress conditions that control whether they behave by high-stress crystal-plasticity or creep at given pressure-temperature conditions. Thus, the rheology of crustal rocks is dependent on the stress-loading rates during the seismic cycle controlled by the distance to the tip of the seismic active fault.

 

Date: Thursday, 07/Sept/2023
10:00am - 11:15am3.05-1 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science
Location: Hall A (HFB)
Session Chair: Anne Bernhardt, FU Berlin
 
10:00am - 10:30am
Invited Session Keynote
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Linking source to sink in active rifts: Insights from the Gulf of Corinth, Greece

Alexander Whittaker

Imperial College, United Kingdom

The volume and grain-size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite this, few studies have constrained sediment budgets and grain-size exported into an active rift and compared this to the characteristics of depositional stratigraphy. Here, we use the Gulf of Corinth as a natural laboratory to quantify the controls on sediment export within an active rift. We measured the hydraulic geometries, surface grain-sizes of channel bars and full-weighted grain-size distributions of river sediment at the mouths of multiple catchments draining the rift, which constitute 83% the Gulf’s drainage area. Results show that grain-size increases westward along the southern coast of the Gulf and that median and coarse-fraction of the sieved grain-size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. We also demonstrate that the median and coarse-fraction of the grain-size distribution are predominantly transported in bedload; however, typical sand-grade particles are transported as suspended load at bankfull conditions, suggesting disparate source-to-sink transit timescales for sand and gravel. Using this data, we derive both a Holocene sediment budget and a grain-size specific bedload discharged into the Gulf of Corinth using the grain-size measurements and previously published estimates of sediment fluxes and volumes. Finally, we demonstrate that at the scale of individual fault blocks, these sedimentary signals fundamentally control the nature of basin deposition, including the characteristics and architectures of hangingwall Gilbert deltas. Our results therefore highlight the importance of linking geomorphic and stratigraphic approaches in areas of active extension.



10:30am - 10:45am
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Sediment transfer and recycling in segmented sedimentary systems: An example from the Aare river (Switzerland)

Laura Stutenbecker1, Matthias Hinderer2, Daniela Krieg2, Fritz Schlunegger3, Michael Schwenk4

1University of Münster, Germany; 2Technical University of Darmstadt, Germany; 3University of Bern, Switzerland; 4Bayerisches Landesamt für Umwelt, Germany

Environmental signals produced by changes in climate or tectonic regime are transferred and modified through sedimentary systems from source to sink. Sediment (and therefore signal) transfer in segmented systems is interrupted through sediment storage in e.g. lacustrine sinks. The Alpine orogen is a mountain chain characterized by high denudation rates that sources important rivers such as the Rhine river. This study focuses on the Aare river, a tributary to the Rhine, that originates in the Swiss High Alps. The course of the present-day Aare river is controlled by an overdeepened valley carved during the Pleistocene glaciations, and segmented by several lakes. We present a provenance dataset based on detrital garnet geochemistry from modern river sands, Pleistocene deposits from drill core samples and river terraces, a Pliocene river terrace, and the Miocene Molasse bedrock. We show that before the Pleistocene, i.e. before valley incision, detritus was transferred directly from the High Alps to the Rhine river plain. After the incision in the Pleistocene, the Aare river recycled the incised local Molasse bedrock. Today, the Aare river is in turn recycling those Pleistocene river terraces as well as the local bedrock. First-cycle detritus from the High Alps is instead stored in man-made and natural lakes. Our data shows that the “erosional engine” of sedimentary systems changes drastically in response to geomorphic reorganizations, and that provenance analysis is a prerequisite to locate the sediment source, as well as the origin of any environmental signal produced in that source.



10:45am - 11:00am
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Sedimentological record of a river mouth in Northern Lebanon during the Holocene

Martin Trappe1, Sender Christian1, Rom Jakob1, Kopetzky Karin2, Genz Hermann3

1Catholic University Eichstaett-Ingolstadt, Germany; 2Austrian Archaeological Institute Vienna, Austria; 3American University of Beirut, Lebanon

Within the framework of a geoarchaeological project to reconstruct the environmental conditions in the hinterland of an archaeological excavation in Northern Lebanon a drilling core near to the Nahr-El-Jaouz river mouth was taken in 2022. The core exhibits a 10,50m thick succession of Holocene fluvial deposits. Sampling comprised more than 100 samples. Sedimentological techniques using grain size distributions and textural parameters were applied for the assessment of facies type and the conditions of sediment transport and deposition.

At a drilled depth of 10,00-10,50m gravelly sediments occurred representing the deltaic foreset followed by an alternating sequence of muds and sandy muds deposited directly at the river mouth or somewhat upstream (deltaic topset). The section above consisting of sandy to muddy sediments was formed by temporarily floods or stagnant water showing mainly suspension transport of the particles. The facial interpretation indicates a transition between a lagoonal environment of the topset and a distal floodplain far from the main river.

Most of the upper core (9,35m to the surface) shows sediments formed within a wetland environment. Frequent facial changes from distal to proximate floodplain positions with muddy and sandy deposits can be observed. Gravelly layers occur as occasional intercalations deposited by more turbulent floods of different reach and force.

The drill core indicates a former sea arm of several kilometres in length for the Nahr-El-Jaouz river mouth. Unfortunately, at present no age data from 14C analyses of taken charcoals or from OSL dating are available. These analyses are still in progress.



11:00am - 11:15am
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Using Laser-Diffraction Grain-Size Analysis and End-Member Modelling Analysis (EMMA) to understand laminar to turbulent flow transitions in deep-water systems

Hannah Louise Brooks1, Yvonne Therese Spychala2, Elisabeth Steel3

1RWTH Aachen, Germany; 2Leibniz University Hannover, Germany; 3Queen's University, Ontario, Canada

Hybrid beds or linked debrites are deposits that form under bi- or tri-partite flow conditions, involving transitions from turbulent to laminar flow conditions. Often, hybrid beds occur with distal or lateral flow transformation following significant entrainment of a muddy substrate and/or declining turbulent energy. Hybrid beds have been noted to make up significant proportions of deposits within basin-floor setting worldwide, most commonly within the distal fringes of lobe systems. The stratigraphic distribution of hybrid beds has been linked to the character of the supply slope and seafloor relief, where hybrid beds are invoked to develop during periods of disequilibrium in out-of-grade slopes.

The mechanisms of formation and evolution of flows that deposit hybrid beds have been significantly studied and debated over the past decades. The aim of this study is to utilize techniques not commonly used in this area, namely Laser-Diffraction Grain-Size Analysis and End-Member Modelling Analysis (EMMA) to undertake a detailed study of lateral and down-dip changes within targeted deposits, to interpret more accurately how and when turbulent to laminar fluctuations occur, as well as adding quantitative analysis to previously established qualitative models. Samples were taken from the Marnoso-Arenacea Formation, the Castagnola Formation, and the Gottero Formation.

Initial findings show significant correlation between grain-size distribution from similar facies across different formations. Despite variability in the median grain-size between formations, similar end members can be extracted from each, indicating deposition under similar flow conditions.

 
1:30pm - 3:00pm3.05-2 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science
Location: Hall A (HFB)
 
1:30pm - 1:45pm
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Responses of alluvial river networks to environmental change: Integrating geomorphic and stratigraphic archives

Fergus McNab1, Taylor F. Schildgen1,2, Jens M. Turowski1, Andrew D. Wickert1,3,4

1Helmholtz Centre Potsdam, GFZ German Centre for Geoscience Research, Germany; 2Institute for Geosciences, University of Potsdam, Germany; 3Saint Anthony Falls Laboratory, University of Minnesota, USA; 4Department of Earth & Environmental Sciences, University of Minnesota, USA

Alluvial river networks are key components of sedimentary systems. They transport sediment, supplied from eroding source regions, to downstream depositional sinks. Their slopes and the rates at which they transport sediment are controlled by their water and sediment supplies, which are sensitive to environmental conditions: temperature and precipitation rates influence erosion rates, and hence sediment supply; precipitation rates are also a first order control on water supply. Changes in sediment and water supply therefore drive changes in channel slope, which may be preserved in fluvial terrace sequences, and sediment-transport rates, which may be preserved in downstream stratigraphic records. Consequently, if we can understand this behaviour, we may be able to use geomorphic and stratigraphic archives to reconstruct past environmental change and its influence on landscapes. Here, we apply a physically based model describing the coupled evolution of sediment transport and slope along alluvial rivers. We show that aggradation, incision, and variation in sediment-transport rates can be damped and lag significantly behind environmental change, depending on the forcing timescale, and on network geometry and hydrology. When water supply is varied, variation in sediment output can in some cases be amplified and appear to lead the imposed forcing. These effects should be taken into account when interpreting fluvial terrace and sedimentary records. Contrasting patterns of aggradation and incision compared with sediment-transport rates implies that integrating information from geomorphic and stratigraphic archives will provide deeper paleo-climatic insights and a powerful test of our understanding of sedimentary systems.



1:45pm - 2:00pm
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Headward drainage basin expansion drives Miocene incision along the Yangtze River, China

Alexander Rohrmann1, Eric Kirby2, Wolfgang Schwanghart3

1Freie Universität Berlin, Berlin, Germany; 2University of North Carolina, Chapel Hill, NC, USA; 3Universität Potsdam, Potsdam, Germany

Along the southeastern margin of the Tibetan Plateau, the onset of rapid fluvial incision during the Miocene is commonly attributed to growth of high topography. Recent recognition of lacustrine strata preserved atop interfluves, however, suggest that headward expansion of river networks drove migration of the topographic divide. Here, we explore the impact of this process on fluvial incision and sediment transport along the Yangtze River. Landscape evolution simulations using TopoToolbox (TTLEM and TVD-FVM) demonstrate that expansion of the Yangtze watershed into previously internally-drained basins since the Late Miocene could be responsible for 1-2 km of fluvial incision. The distribution of modern knickpoints and river profiles are consistent with this hypothesis. We suggest that increased erosive power associated with capture and basin integration drove accelerated incision and sediment transport during the Late Miocene. Progressive captures and integration of sub-basins could have driven punctuated episodes of rapid incision as drainage divides were progressively breached. Our results support the notion that the low-relief landscape atop the eastern Tibetan Plateau was elevated prior to Miocene time, and that basin integration and headward incision into this high-standing plateau drive rapid incision downstream of this former topographic divide.



2:00pm - 2:15pm
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Modelling the detrital signals of cosmogenic nuclides concentrations coupled with landscape evolution

Sebastien CARRETIER, Vincent REGARD, Youssouf ABDELHAFIZ, Bastien PLAZOLLES

Geosciences Environnement Toulouse, GET, CNRS, IRD, CNES, Universite de Toulouse, 14 avenue E. Belin, F-31400, Toulouse, France

The measurement of cosmogenic nuclide (CN) concentrations in riverine sediment has provided breakthroughs in our understanding of landscape evolution. Yet, the link between this detrital CN signal and landscape evolution is based on hypotheses that are not easy to verify in the field. New applications could arise from a better understanding of the statistics of CN concentrations in sediment grains. In this work, we present the coupling between the landscape evolution model Cidre and a model of the CN concentration in distinct grains. These grains are exhumed and detached from the bedrock and then transported in the sediment to the catchment outlet with temporary burials and travels according to the erosion-deposition rates calculated spatially in Cidre. The concentration in the various CN can be monitored in these grains. Because the CN concentrations are calculated in a limited number of grains, they provide an approximation of the whole CN flux. Thus, this approach is limited by the number of grains that can be handled in a reasonable computing time. On the other hand, part of the variability in the erosion-deposition processes can be recorded in the grain-by-grain distribution of the CN concentrations by monitoring the CN concentrations in distinct grains using a Lagrangian approach. We illustrate the robustness, the perspective and the limits of this approach by deriving the catchment-mean erosion from the 10Be mean concentration of the grains leaving a synthetic catchment uplifting at different rates and by comparing this derived erosion rate to the actual one calculated by Cidre.



2:15pm - 2:30pm
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Late Quaternary deformation, strain partitioning, and growth of the fold and thrust belt of The Western Himalaya

Saptarshi Dey1, Rasmus C. Thiede2, Kordt Jonas2, Bodo Bookhagen3, Ramon Arrowsmith4, Naveen Chauhan5

1IIT Gandhinagar, Gandhinagar, Gujarat, India; 2Christian Albrecht Universität zu Kiel, Germany; 3Universität Potsdam, Germany; 4Arizona State University, Tempe, U.S.A.; 5Physical Research Laboratory, Ahmedabad, India

Constraining millennial-scale fault slip rates and understanding the related structural architecture in active orogenic wedges might provide important assessment of future seismic risk evaluations. An increasing number of Holocene and Late Pleistocene deformation rates have been reported throughout the Western Himalayan frontal fold-and-thrust belt (FTB), which have illustrated that the deformation is divided along several arc-parallel fault splays rooted to the Main Himalayan Thrust décollement. Studies also report complex pattern of out of sequence faulting, as well as spatiotemporal variations in fault growth and lateral heterogeneity of the FTB. However, what drives this lateral heterogeneity is debated until now.

Late Pleistocene – Holocene deformed fluvial strath terraces across active faults in western Himalayan provide a measure of time-averaged fault slip rates along the Himalayan Frontal Thrust (HFT) and the Medlicott Wadia Thrust (MWT). While the Quaternary slip rates along the HFT varies from 3 – 12 mm/y, the slip rates from the ~700 km- long MWT is steadily high (7 – 9 mm/y).In contrast, previously published balanced cross-sections proposed slip rates of ~1 – 2 mm/y along the MWT. So from million-year to millennial timescale, there exists a significant temporal variation in fault activity. Single fault system like the MWT accommodate up to 50 - 60% of the total measured geodetic rates on Holocene/Late Quaternary timescales. These results document significant strain partitioning within the Sub-Himalaya and steady - high slip on the MWT which, beside the HFT could host the next big seismic event and damage the human-infested north India.



2:30pm - 2:45pm
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

Middle to Late Pleistocene alluvial surface ages recorded by their spectral reflectance in Patagonia.

Andreas Ruby1, Taylor Schildgen1,2, Henry Crawford3, Mitch D'Arcy3, Victoria M. Fernandes1, Hella Wittmann1, Fergus McNab1

1German Research Centre for Geosciences (GFZ) Helmholtz Centre, Potsdam, Germany; 2Institute for Geosciences, Potsdam University, Potsdam, Germany; 3Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, Canada

The age of alluvial surfaces can play a key role in deciphering surface processes and landscape evolution. However, the most common dating methods (e.g. with cosmogenic nuclides like 10Be) are expensive and time-consuming. We propose an approach that utilizes a limited number of 10Be samples in combination with hyperspectral data to estimate surface ages.

Specifically, we make use of known alterations of the spectral reflectance of geochemical surfaces caused by weathering processes, e.g., clay mineral and iron oxide formation. Changes consist of an overall increase in reflection, but mainly the development of characteristic absorption features. Our aim is to detect these weathering features via hyperspectral satellite imagery to build a ground-truthed spectral-age model for estimating alluvial surface ages over large regions.

To test this approach along the Río Santa Cruz in southern Patagonia, we dated 7 out of 13 fluvial terrace levels that yielded exposure ages up to 1.5 My, and we conducted in situ spectral measurements using a field spectrometer. By comparing these observations to satellite data (Landsat 8 and EnMAP), we can estimate ages and make better correlations of undated surfaces along the 250-km length of the river. Surprisingly, the age range of the model indicates slower than expected weathering rates and a major methodological advance in the detection of weathering processes via hyperspectral satellite.



2:45pm - 3:00pm
Topics: 3.05 „Geomorphology and Sedimentology Beyond Boundaries“ - towards integrating geomorphology and sedimentary system science

The temperature control on the intensity of silicate weathering

Kai Deng1,2,3, Shouye Yang2, Yulong Guo2

1GFZ German Research Centre for Geosciences, Earth Surface Geochemistry, Telegrafenberg, 14473 Potsdam, Germany; 2State Key Laboratory of Marine Geology, Tongji University, 200092 Shanghai, China; 3Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland

Chemical weathering of silicate minerals plays a vital role in maintaining the long-term habitability of Earth’s climate over geological timescales via a negative feedback mechanism. But much debate concerns the response strength of silicate weathering to each climatic factor and its evolution with land surface reorganisation. Such discrepancy arises from lacking weathering proxy validation and scarce quantitative paleo-constraints on individual forcing factors. Here we examine the catchment-scale link of silicate weathering intensity with various environmental parameters using a global compilation of modern sediment dataset for calculation of weathering intensity proxies, including chemical index of alteration (CIA) and weathering index of Parker (WIP).

We show the primary control of temperature on silicate weathering given the monotonic increase of feldspar dissolution (constrained by CIA) with it at 0-30 oC, while controls of precipitation or topographic-lithological factors are regional and subordinate1. We interpret the non-linear forcing of temperature on feldspar dissolution as depletion of more reactive plagioclase (relative to orthoclase) at higher temperature. Accordingly, the surface temperature decrease could be accompanied with a higher proportion of more reactive plagioclase available for weathering, supporting the hypothesis that land surface reactivity has increased during the late Cenozoic cooling2. We also propose a first-order quantitative relationship between surface temperature, feldspar dissolution and CO2 consumption that will be of great potential for deep-time temperature reconstruction and carbon cycle modeling.

References

1. Deng, K., Yang, S. & Guo, Y. (2022) Nat Commun 13, 1781.

2. Caves Rugenstein, J.K., Ibarra, D.E. & von Blanckenburg, F. (2019) Nature 571, 99–102.