The Heligoland Glacitectonic Complex in the southeastern North Sea: indicators of a pre‐ or early‐Elsterian ice margin

Abstract

Glacial landforms are abundant in the North Sea basin and are often used to reconstruct the impact and dynamics of ice sheets during the Pleistocene. Geophysical methods have allowed the mapping and structural analysis of glacial landforms at the surface and in the subsurface to estimate the position of former ice margins in the North Sea. However, the glacial history of the southeastern North Sea remains underexplored. In this study, we present a structural analysis of Late Pliocene to Late Pleistocene sediments based on a dense grid of 2D high‐resolution multi‐channel reflection seismic data from the German sector of the southeastern North Sea. We show that the Heligoland Glacitectonic Complex (HGC) is larger than previously assumed (700 km2, 32×22 km) and characterized by three distinct zones of thrusting and deformation on two décollements. The kinematic restoration of seismic cross‐sections and dip measurements of thrust faults demonstrate that the HGC was formed by an ice lobe advancing from the southeast. To explain the origin of the HGC, we provide alternative models for its formation during a single ice advance or two ice advances in the study area. Furthermore, we validate the early or pre‐Elsterian age of the HGC based on nearby Elsterian tunnel valleys, and conclude that salt structures in the subsurface may have influenced its location.

Tunnel valleys in the southeastern North Sea: more data, more complexity

“…TV0 is oriented in a SE-NW direction and therefore parallels the identified thrust direction of the Heligoland Glacitectonic Complex (HGC) towards the northwest postulated in that area (Fig. 2; Winsemann et al, 2020;Lohrberg et al, 2022).…”

“…400 m and to extend the data set westwards. Based on earlier results (Lohrberg et al, 2020), we were able to plan selected survey lines precisely along the (Winsemann et al, 2020;Lohrberg et al, 2022). (b) Depth profiles for the base of TV1-TV3 inferred from longitudinal seismic profiles following the thalweg of the TVs.…”

“…The acquisition setup and data processing were highly similar for both surveys, and details are described in Lohrberg et al (2020Lohrberg et al ( , 2022. We used a sound velocity of 1600 m s −1 for the depth conversion for lack of a detailed velocity model, and depths are provided in reference to the water level.…”

New insights into the structural development and shortening of the southern Jasmund Glacitectonic Complex (Rügen, Germany) based on balanced cross sections

“…Pedersen 2000;Bennett 2001) and offshore (e.g. Pedersen and Boldreel 2017;Lohrberg et al 2021). In such complexes, thrust faults dip towards the proximal zone of the complex and towards the proposed ice margin (Vaughan-Hirsch and Phillips 2017).…”

“…Dahlstrom 1969Suppe 1985). This approach has already been successfully applied to other glacitectonic settings (Croot 1987(Croot , 1988Boulton et al 1999;Pedersen 2005;Benediktsson et al 2010;Lohrberg et al 2021).…”