Post mid-Cretaceous inversion tectonics in the Danish Central Graben – regionally synchronous tectonic events?

Abstract

Structural analysis of the Upper Cretaceous to Palaeogene succession in the Danish Central Graben suggests continuous inversion heralded in the Late Hauterivian and continuing into Palaeogene times. The following phases of increased intensity are identified: 1) latest Santonian, 2) Mid Campanian, 3) late Maastrichtian, 4) Late Paleocene – Eocene, and 5) Early Oligocene. Phases 1 through 3 are Sub-Hercynian, phase 4 is Laramide, and phase 5 is Pyrenean according to Alpine Orogen nomenclature. A temporal change in structural style is noted from early inversion confined to narrow zones associated with reverse faulting along pre-existing normal faults to late inversion dominated by gentle basinwide flexuring and folding. Inversion phases in the Danish Central Graben seem to be synchronous with inversion phases along the Sorgenfrei-Tornquist Zone. The location of inversion is generally spatially linked to Upper Jurassic – Lower Cretaceous depocentres, whereas older depocentres generally have remained intact. The origin of the compressional stress field is generally based on suggested compressional stresses transmitted into the foreland from the Alpine Orogen. In the Sub-Hercynian phase, orogenic compression dominated the Eastern Alps and Northern Carpathians to produce a likely NW oriented compression. However, structures in Denmark rather suggest a transpressional environment resulting from NNE–SSW compression. Furthermore, transmission of Alpine orogenic stresses into the foreland commenced in the Turonian, a considerable time after the Late Hauterivian and later inversion precursors. Ridge-push forces transmitted from sea-floor spreading south of the Charlie-Gibbs fracture zone, particularly from the Goban Spur SW of Ireland, acting in conjunction with Alpine orogenic stresses are suggested as the cause for the stress field.