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Wrench-fault structures superimposed by glaciotectonic complexes, interpreted from high-resolution reflectionseismic sections and boreholes along the western bank of Esrum Sø, north-east Sjælland, Denmark

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Wrench-fault structures below Danian limestone and Palaeogene marl, and an overlying
structural framework of Quaternary glacial deposits in north-east Sjælland,
Denmark, are interpreted from two vibro-seismic sections recorded to 600 msec TWT
depth. The main seismic section is 6.3 km long, N–S oriented, and intersected by a 0.7
km long, E–W oriented satellite seismic section. In addition, boreholes in the vicinity
of the seismic profile are used for the interpretation. The sections were acquired in
2014 along the western shoreline of the lake Esrum Sø in the Gribskov area. In the
lower part of the seismic section (the interval 100–300 msec TWT), parallel-bedded
geological layers occur along most of the profile apart from six locations, where six
wrench-fault structures displace the upper part of the Chalk Group and lower Palaeogene
marl. The northernmost of the six wrench-fault locations correlates to the
eastern slope of the buried Esrum–Alnarp valley, which suggests that the valley is
an inherited tectonic feature. The location of the wrench- fault structures supports
the outline of faults related to the Sorgenfrei-Tornquist Zone on previous geological
maps, which had almost no seismic data from the area.
Above the stratigraphic level presented by the Danian limestone and lower Palaeogene
marl, a composite glaciotectonic complex comprising two glaciodynamic
sequences is recognized by e.g. thrust-fault structures and the lithostratigraphy
of glacial successions recorded in the wells. In parts of the seismic sections, the
lowermost level of the glaciotectonic complex inherited the wrench-tectonic fault
structures, most significantly seen in the northern segment. The advance of the
Scandinavian ice sheet caused the glaciotectonic structures displayed in the seismic
section. The two sequences represent events related to the Norwegian and the
Swedish glacial advances. From the interpretation of the seismic section it is found
that the glaciotectonic complex conceals the wrench-tectonic flower structures.
OriginalsprogEngelsk
TidsskriftBulletin of the Geological Society of Denmark
Vol/bind68
Sider (fra-til)171-193
Antal sider23
ISSN0011-6297
DOI
StatusUdgivet - 7 aug. 2020

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