Glacial structures in northern Germany revealed by a high‐resolution reflection seismic survey

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Abstract
In recent years, the sediments filling Pleistocene glacial structures have become of increasing importance to paleoclimate research. Climatic changes are documented by the deposition cycles in small, closed, trough or bowl‐like structures. A 2-D, high‐resolution, shallow reflection seismic survey was conducted in 1996 over such a structure near Tostedt in northern Germany. The objective was to obtain a more accurate picture of the structure and the underlying geology. Designed especially for shallow surveys, a newly developed impulse source provided sufficient energy to observe reflectors as deep as 400 m. Signals are characterized by a high‐frequency content with maximum energy between 80 and 180 Hz. The migrated section shows a distinct reflection pattern revealing local glacial dynamics. Reflectors at depths of 30, 40, and 45 m from inside the Tostedt structure correlate well with three interstadials of the Weichselian period. Weak reflections define the bottom of the structure, with a maximum depth of 70 m. The structure is imbedded in a much larger, previously unexpected depression of similar shape. The fill of this larger depression is seismically nearly transparent. High‐amplitude reflections delineate its lower boundary with a maximum depth of 130 m. Two major reflectors at depths of 170 and 270 m correlate with lower Miocene and middle Oligocene units. They indicate that subrosion, which might have been expected from the presence of a nearby salt diapir, is absent. This confirms the purely glacial origin of the two bowl‐like structures.