Neotectonic deformation of a Late Weichselian outwash plain by deglaciation‐induced fault reactivation of a deep‐seated graben structure

• Published in: Boreas
• Main Authors: Sandersen, Peter B. E., Jørgensen, Flemming
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Ice Sheet
• Online Access: http://dx.doi.org/10.1111/bor.12103; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fbor.12103; https://onlinelibrary.wiley.com/doi/pdf/10.1111/bor.12103

The L ate W eichselian T inglev outwash plain in southwestern D enmark slopes gently from east to west, but certain areas of the topography show unusual irregularities. Analysis of LiDAR data reveals a mosaic of smaller areas with pronounced changes in slope magnitude and orientation between neighbouring areas. The outwash plain also features notable changes in elevation across kilometre‐long lineaments and areas lying lower and higher than the expected level. The depressions in the area have previously been interpreted as the result of melting dead‐ice blocks left by the L ate W eichselian ice sheet. However, borehole samples from L ake T inglev on the outwash plain show that lake sedimentation did not start until the early H olocene (9000 years ago), which is more than 9000 years after the ice sheet had retreated. The topographical irregularities are located above the T ønder G raben structure, and we interpret these as the result of H olocene strike‐slip movements along the graben faults resulting in areas of both subsidence and uplift. The deformations of the outwash plain are interpreted as the effect of deglaciation tectonics acting within a limited time frame at the beginning of the H olocene. As the event can be related to stress release from the weight of the S candinavian I ce S heet, we expect that other fault zones in northern E urope would be equally prone to reactivation. Tectonic events related to deglaciation would most likely be recurrent, and the stress changes appear to have been able to induce short‐lived tectonic instability to areas normally considered tectonically stable. We conclude that this type of tectonics has had a significant impact on topography and sedimentation throughout the Q uaternary.