Crustal structure in the transition zone from the Precambrian to Palaeozoic platform in the southern Baltic Sea – inferences from newly acquired potential field and seismic data

The southern Baltic Sea area is in the transition zone between the Fennoscandian Shield as part of the East European Craton (EEC) and the West European Platform. This area is characterised by a mosaic of various geological blocks separated by several fault zones formed throughout the Phanerozoic. The most prominent tectonic feature is the NW–SE trending Sorgenfrei-Tornquist Zone, crossing the southern Baltic Sea area between Scania in Sweden and Pomerania in Poland. Recently, this area was covered with the new multi-channel seismic data (MCS), acquired during the “BalTec” cruise of the German R/V Maria S. Merian. In addition to MCS data, hydroacoustic and gravity data were collected along the same profiles.

The new data, acquired during the “BalTec” cruise in 2016, include 3500 km of MCS data and 7000 km of gravity data. This is the first such a regional survey in the southern Baltic Sea, which provides a gapless image of sedimentary layer with a high resolution from seafloor to the base of Permian salt (North German-Polish Basin) or Palaeozoic strata (EEC). In addition, a 230-km long refraction/wide-angle reflection (WARR) profile was acquired across the transition zone to image its deeper structure. This profile is nearly parallel to the western Polish coast in half a distance to Bornholm.

The main topic of our study is the structure of Phanerozoic sedimentary cover in the southern Baltic Sea and its relationship to the geological evolution of the area situated at the junction of two major tectonic units of NW Europe. In the methodological part of our research, we are going to develop the process of integration of potential field modelling into seismic interpretation workflow. Another important point is testing the capability of marine versus satellite gravity data to reflect the geometry of shallow tectonic structures.

The first step in analysis of potential field data was integration of marine gravity with a regional gravity dataset. The result was a coherent gravity grid, which was used for further advanced processing, involving calculation of transformations and derivatives. We also included a regional magnetic grid in the advanced processing. Calculated derivatives and filters of gravity and magnetic data were applied for qualitative interpretation, i.e., compilation of a structural map based on the location and nature of gravity and magnetic anomalies. In addition, a preliminary 2D forward model was produced for the WARR profile to provide an image of the broad crustal structure. The next 2D models will be built upon seismic reflection profiles acquired during the “BalTec” cruise. The results will be eventually used to calibrate the three-dimensional model for the top of crystalline basement derived from gravity inversion.

This study was funded by the Polish National Science Centre grant no UMO-2017/25/B/ST10/01348.