Glaciodynamic sequence stratigraphy

Abstract

The glaciofluvial deposits are by volume and permeability the most important unit in the terrestrial glacial successions, and they are the obvious target for groundwater as well as hydrocarbon reservoir exploration. The dominant glaciofluvial units are related to the proglacial setting in the foreland of an advancing ice margin, which results in a coarsening-upwards sequence with fine-grained beds at the base and glaciofluvial gravel at the top. In a complete sequence a till caps the unit, and at its base a glacitectonite is formed by shearing related to the development of the deformational layer below the ice. The glacial deposits laid down during the same glacial advance represent a glaciodynamic sequence. An important feature added to this is the proglacial glaciotectonic deformation. The glaciotectonic architectural elements comprise thrust faulting, folding of hanging-wall anticlines, thrust-sheet duplexes, hydrodynamic breccias and mud diapirs, the structural style of which define the glaciotectonic complex. The glaciodynamic sequence corresponds to the glaciodynamic event related to one major ice advance. The glaciodynamic processes representing the event comprise deposition as well as deformation, creating a glaciogenic sedimentary succession and a set of glaciotectonic structures. These constitute the elements to be recognized for defining a glaciodynamic sequence.

Glaciotectonic deformations in the Jammerbugt and glaciodynamic development in the eastern North Sea

“…The earliest ice advance in the Saalian was from Norway and is commonly referred to the Drenthe stadial (Pedersen, ). The last ice advance derived from the east and is referred to Baltic ice advance during the Warthe stadial (Larsen et al ., ).…”

“…Here the dislocated Skærumhede Group has been described from coastal cliff at Hirtshals (Lykke‐Andersen, ) and from the Rubjerg Knude Glaciotectonic Complex (Pedersen, ), where glaciotectonic deformation is determined to be late Middle Weichselian (about 30–28 ka BP). The general sequence stratigraphy in the area was outlined by Pedersen (), and when the conditions of the Jammerbugt Glaciotectonic Complex are included the following glaciodynamic development is suggested.…”

“…In this part of the area a succession of horizontal reflectors onlap the erosional unconformity at the tail end of the thrust‐fault complex (Figs and 8). The horizontal reflectors are interpreted as a highstand marine transgressive sequence in a glaciodynamic sequence system (Pedersen, ). The erosional unconformity at the base of this sequence may be defined as the second first‐order surface in relation to the glaciotectonic architecture (Pedersen, ).…”

“…() the lowermost part of the Skærumhede Group constitutes the latest Saalian transgressive systems tract. During the sea‐level highstand systems tract in the Eemian time, the deposition of the Skærumhede Group continued, and in the Early Weichselian glaciomarine conditions prevailed during progressive deposition, which terminated in the Middle Weichselian (Sejrup and Knudsen, ; Pedersen, ). In the Vendsyssel well the base of the Skærumhede Group is marked by a 20‐m‐thick Saalian till deposited during a Warthe ice advance (160–140 ka BP, Larsen et al , ).…”

“…Most of these were formed during the Saalian and Weichselian glaciations, and in general the Saalian glaciotectonic complexes are preserved onshore Europe with glaciotectonic–geomorphic features south of the Main Stationary Line of the Weichselian Scandinavian Ice Sheet (Aber and Ber, ). North of the Main Stationary Line the preserved and landscape‐forming glaciotectonic complexes were formed during the last Weichselian glaciation, and older glaciotectonic complexes are only known from superimposed deformations or deformed Quaternary successions (Ehlers, ; Pedersen, , , ). The major complexes incorporate thrust sheets of bedrock displaced from a décollement surface more than 100 m below the surface of the foreland fringing the thrust fault margin.…”