Well records on the Phanerozoic stratigraphy in the Fennoscandian Border Zone, Denmark: Hans-1, Sæby-1, and Terne-1 wells

The Hans-1, Sæby-1, and Terne-1 wells are located within the Danish part of the Fennoscandian Border Zone and provide significant new data pertaining to the evolution of this important tectonic belt. All three wells encountered Palaeozoic rocks; the Terne-1 well extended into the lower Palaeozoic. Two of the wells are located in the Danish waters of the Kattegat, and thus yield the first deep well data from this part of the border zone. The wells encountered Cambrian to Silurian, Carboniferous to Zechstein and Triassic to Upper Cretaceous successions. The Cambrian to Lower Silurian section is interpreted to represent shelf and shallow marine deposits comparable to those known from Scania and Bornholm. The inferred Upper Silurian section is calculated to be up to 2600 m thick and may represent the fill of a foreland basin in front of the Caledonian 4 deformation front. A hiatus comprising the Devonian to Lower Carboniferous is inferred. A 550 m thick Rotliegende sequence was drilled in the eastern part of the Sorgenfrei-Tornquist Zone; changes in structural dip indicate a syn-depositional faulting. Palaeozoic tectonism is also indicated by Late Carboniferous intrusive and extrusive volcanic rocks. Reworked volcanic rocks characterize the Rotliegende elastic sequence. A thin siliciclastic Zechstein sequence is recognized. The lithology and stratigraphy of the Mesozoic sections are in accordance with well data from the Danish Subbasin. The presence of a Middle Jurassic depocenter within the Sorgenfrei-Tornquist Zone may indicate a tectonically controlled subsidence of the zone. The occurrence of a Late Cretaceous to Early Tertiary inversion tectonism is supported by these new data.