Discussion on ‘Palaeoseismic structures in Quaternary sediments, related to an assumed fault zone north of the Permian Peissen-Gnutz salt structure (NW Germany) – Neotectonic activity and earthquakes from the Saalian to the Holocene’ (Grube, 2019)

Abstract

We discuss the significance of deformation structures in Quaternary sediments observed by Grube (2019) in the Peissen quarries (NW Germany) in light of the geological context. Evidence for polygonal patterns visible in aerial images in the study area shows that the wedge structures interpreted by Grube (2019) as earthquake-induced sand blows may rather correspond to thermal contraction cracks filled with aeolian sand in a permafrost environment. In the study sites, brittle deformations caused by (i) the rise of a salt diapir, (ii) salt dissolution, (iii) the development of Pleistocene permafrost and (iv) possibly, water circulation under pressure in the Scandinavian ice sheet margin may have coexisted. We support the idea that, while the morphology of deformation generally makes it possible to determine the stress state to which the sediments have been subjected and the quantity of water available in the system at the time of deformation, the nature of the factors causing the stresses remains difficult to identify. In the end, we highlight other useful criteria that should be privileged for palaeoseismic research in such complex geological settings.