Conference Agenda

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Session Overview
3.28-2 Developments and progress in regional geology
Tuesday, 05/Sept/2023:
2:00pm - 3:30pm

Session Chair: Jonas Kley, University of Göttingen
Location: Hall A (HFB)


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 ( 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


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.