Preprints
https://doi.org/10.5194/egusphere-2022-164
https://doi.org/10.5194/egusphere-2022-164
 
02 May 2022
02 May 2022
Status: this preprint is open for discussion.

Geophysical analysis of an area affected by subsurface dissolution – case study of an inland salt marsh in northern Thuringia, Germany

Sonja Halina Wadas1, Hermann Buness1, Raphael Rochlitz1, Peter Skiba2,a, Thomas Günther1, Michael Grinat1, David Colin Tanner1, Ulrich Polom1, Gerald Gabriel1,3, and Charlotte M. Krawczyk4,5 Sonja Halina Wadas et al.
  • 1Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany
  • 2Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany
  • 3Leibniz University Hannover – Institute of Geology, Callinstraße 30, 30167 Hannover, Germany
  • 4GFZ – German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
  • 5Technical University Berlin – Institute for Applied Geosciences, Ernst-Reuter-Platz 1, 10587 Berlin, Germany
  • aformerly at: Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany

Abstract. The subsurface dissolution of soluble rocks, also called subrosion, can affect areas over a long period of time and pose a severe hazard. We show the benefits of a combined approach using P-wave- and SH-wave reflection seismics, electrical resistivity tomography, transient electromagnetics, and gravimetry for a better understanding of the subrosion process. The study area, ’Esperstedter Ried’ in northern Thuringia, Germany, located south of the Kyffhäuser hills, is a large inland salt marsh that developed due to dissolution of soluble rocks at approximately 300 m depth.We were able to locate buried subrosion structures, subrosion zones, faults and fractures, and potential fluid pathways, aquifers and aquitards based on seismic and electromagnetic surveys. Further improvement of the subrosion model was accomplished by analyzing gravimetry data that indicates subrosion-induced mass movement as shown by local minima of the Bouguer anomaly for the Esperstedter Ried. Forward modelling of the gravimetry data, in combination with the seismic results, delivered a cross section through the inland salt marsh from north to south. We conclude that the tectonic movements during the Tertiary, which led to the uplift of the Kyffhäuser hills and the formation of faults parallel and perpendicular to the low mountain range, were the initial trigger for subrosion. The faults and the fractured Triassic and Lower Tertiary deposits serve as fluid pathways for groundwater to leach the deep Permian Zechstein deposits, since subrosion is more intense near faults. The artesian-confined salt water ascends towards the surface along the faults and fracture networks, and formed the inland salt marsh over time. In the past, subrosion of the Zechstein formations formed several, now buried, sagging and collapse structures, and, since the entire region is affected by recent sinkhole development, subrosion is still ongoing. From the results of this study, we suggest that the combined geophysical investigation of subrosion areas can improve the knowledge of control factors, risk areas, and thus local subrosion processes.

Sonja Halina Wadas et al.

Status: open (until 13 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Sonja Halina Wadas et al.

Sonja Halina Wadas et al.

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Short summary
The dissolution of rocks (subrosion) poses a severe hazard because it can cause subsidence and sinkhole formation. Based on results from our study area in Thuringia, Germany, using P- and SH-wave reflection seismics, electrical resistivity- and electromagnetic methods and gravimetry, we develop a geophysical investigation workflow. This workflow enables to identify the initial triggers of subrosion and its control factors, such as structural constraints, fluid pathways, and mass movement.