Nøvling: An unusual salt structure on the soutbern margin af the Danish Basin

Abstract

The N~vling salt structure is located on the southern margin of the Danish Zechstein Basin. The present study of this structure is based on a detailed gravity survey, reflection and refraction seismic data, and well information. Apart from the exploratory well NØvling-l, and a shallower well Herning-l, a number of wells, mainly 20-30 m deep, were drilled in this general area (by the Geological Survey of Denmark). Through this combined study using geological and geophysical methods it is possible to distinguish several stages in the development of the N~vling structure. It is shown that these stages are closely related to faulting at the base Zechstein level. The faulting, which apparently started as normal faulting in the Triassic, triggered the first salt movements from the deeper parts of the basin to this peripheral area. The faulting was reactivated during the late Jurassic, resulting in the formation of a salt pillow. The tectonic regime changed in the post-Paleocene tertiary when transpressional movements along a prominent basement wrench fault became dominant. This ultimately resulted in the formation of a positive flower structure and the uplifting of the Saale Quatemary surface. At shallow depths the salt became dissolved creating a topographic depression above the flower structure. The present depression was formed at the beginning of the last late glacial time. Quatemary landforms in the N~vling area are therefore greatly influenced by recent tectonic events.