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

Olaf Michelsen,Lars Henrik Jensen

doi:10.34194/seriea.v29.7049

Abstract

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.

Highlights

The Kattegat region has previously only been known from geophysical data, and published models of basin development through geological time have mainly been based on seismic data and data from the adjacent onshore areas
The primary goals of this paper are 1) to interpret the data available from 3 newly released wells located within the Danish part of the Fennoscandian Border Zone and 2) to describe the dynamic stratigraphic development of the zone during the Phanerozoic
The SorgenfreiTornquist Zone is defined as a strongly faulted zone primarily characterized by Late Cretaceous to Tertiary inversion tectonics

Summary

Introduction

The Kattegat region has previously only been known from geophysical data, and published models of basin development through geological time have mainly been based on seismic data and data from the adjacent onshore areas. The Kattegat region is transected by a strongly faulted zone that separates the Fennoscandian Shield to the northeast from the Norwegian-Danish Basin to the west and southwest. The EUGENO-S Working Group (1988) considered the structural line through the Kattegat region as being a discrete structural element rather than an integrated part of the Tornquist Zone It was termed the Sorgenfrei-Tornquist Zone, whereas the Polish-Ukrainian element was referred to as the Teisseyre-Tornquist Zone The SorgenfreiTornquist Zone is defined as a strongly faulted zone primarily characterized by Late Cretaceous to Tertiary inversion tectonics The area between this zone and the Fennoscandian Shield was named the Skagerrak-Kattegat Platform The term Fennoscandian Border Zone will, be used for the structural region comprising the Sorgenfrei-Tornquist Zone and the Skagerrak-Kattegat Platform The third well, Sreby-1, is located in North Jylland, but still within the Skagerrak-Kattegat Platform (fig. 1)

Material and methods

Findings

Conclusions