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The study reconstructs the Quaternary evolution of a branched tunnel-valley system in the Duck’s Beak area of the German North Sea using high-resolution 3D seismic data. Results show thick pre-tunnel-valley Quaternary deposits over Top Gelasian strata and reveal that a single, branched tunnel valley incised these units to depths of around 340 metres. The valley fill comprises a chaotic basal unit overlain by successive cut-and-fill sequences, mass-movement deposits on the flanks, and continuous marine layers. Fault mapping highlights a crestal-fault system above the ‘Belinda’ salt structure that offset both the tunnel-valley base and infill, with some faults extending into the seabed. Offsets indicate fault activity persisted into the Middle Pleistocene, and seabed-penetrating faults suggest active movements. The findings have a direct bearing on the siting of offshore wind farms and the future of deep-subsurface CO2 storage.