Abstract
ABSTRACTTunnel valleys are assumed to form near the margin of ice sheets. Hence, they can be used to reconstruct the dynamics of former ice margins. The detailed formation and infill of tunnel valleys, however, are still not well understood. Here, we present a dense grid of high‐resolution 2D multi‐channel reflection seismic data from the German sector of the southeastern North Sea imaging tunnel valleys in very great detail. Three tunnel valley systems were traced over distances ranging between 11 and 21 km. All tunnel valleys are completely filled and buried. They differ in incision depth, incision width and number of incisions. The tunnel valleys cut 130–380 m deep into Neogene, Palaeogene and Cretaceous sediments; they show a lower V‐shaped and an upper U‐shaped morphology. For individual tunnel valleys, the overall incision direction ranges from east–west to northeast–southwest. Two tunnel valleys intersect at an oblique angle without reuse of the thalweg. These valleys incise into a pre‐existing glaciotectonic complex consisting of thrust sheets in the northwest of the study area. The analysis of the glaciotectonic complex and the tunnel valleys leads us to assume that we identified several marginal positions of (pre‐)Elsterian ice lobes in the southeastern North Sea.
Highlights
Major ice sheet advances beyond the polar limits in the northern hemisphere are well documented for the Quaternary; the last 900,000 years are assumed to be the period with the most prominent ice sheet advances (Ehlers et al, 2018)
We use a more general approach delineating the seven main seismic units (SU) up to 800 ms penetration that have been correlated to the seismic stratigraphy framework of the Federal Agency of Geosciences and Resources of Germany (BGR), which is based on the results of Thöle et al, 2014 and Kockel, 2002
These sediments are overlain by Plio‐Pleistocene sediments, which build the foundation for the Holocene drape (Thöle et al, 2014)
Summary
Major ice sheet advances beyond the polar limits in the northern hemisphere are well documented for the Quaternary (last 2.6 Ma); the last 900,000 years are assumed to be the period with the most prominent ice sheet advances (Ehlers et al, 2018). Surface and subsurface landforms serve as an archive that can be used to reconstruct past sedimentation and erosion processes. Identifying these landforms and the corresponding mechanisms of formation can support the reconstruction of ice sheet configurations during the Pleistocene (Aber and Ber, 2007; Dowdeswell et al, 2016). Fluctuations in oxygen isotopes found in deep sea cores have been linked to major cold and warm phases of the planet. The rhythmic pattern of gradual cooling and rapid warming of the climate has been defined as Marine Isotope Stages (MIS). The dating of glaciogenic sediments enabled the scientific community to assign the well‐known glaciations around the globe to specific MIS (Ehlers and Gibbard, 2004)
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