Sammendrag
Reprocessed regional 2D seismic reflection profiles, 3D
seismic data, available wells, and gravity and magnetic
data were used to study the pre-salt rift architecture in
the Nordkapp Basin, Barents Sea, and its impact on the
evaporite accumulations and distribution of salt
structures. The basin is subdivided into three main
segments (the northeastern, central, and southwestern
sub-basins) and has evolved over the complex
interaction between the Timanian and Caledonian
structural basement grains. Each segment is
characterized by prominent magnetic anomalies related
to the Timanian and Caledonian structural inheritance.
The rotated magnetic lineations associated with the
Caledonian structures beneath the Finnmark Platform
pass through the central segment, where the Middle
Allochthonous Front creates the major sub-division
between the two structural grains. We suggest that the
rheological properties, locations, orientations and
interaction of the parts of the basement influenced by
Timanian and Caledonian structural grains together with
two subsequent extensional phases, have strongly
influenced the shallower pre-salt rift architecture.
During the late Devonian – early Carboniferous NE-SW
-oriented extensional phase, the Nordkapp Basin
consisted of a northern and a southern regional halfgraben
separated by an elevated interbasin ridge. The
hinged margins of the northern and southern regional
half-grabens were restricted against the NW-SE-striking
graben beneath the Veslekari Dome and Troms-
Finnmark Fault Complex, respectively. The internal
configuration of the regional half-grabens was affected
by the NW-SE-striking master faults. During the late
Carboniferous to early Permian, a second extension
phase took place with a shift in stress orientation to NW
-SE and influenced the two regional half-grabens. In
particular, a transfer fault with the character of an interbasin
transfer zone (the northern transfer zone) divided
the northern regional half-graben by separating its
hinged margin (incipient northeastern segment) from the
deeper part (incipient central segment). At the same
time, the elevated interbasin ridge acted as a southern
transfer zone, separating the incipient central and
southwestern segments of the Nordkapp Basin. The
Thor Iversen, Polstjerna, Måsøy and Nysleppen basin
border fault systems were formed during the second extensional
phase and reshaped the internal configuration
of the two regional half-grabens.
The structural interaction between the spatially variable
Timanian and Caledonian structural grains overprinted
by two subsequent phases of NE-SW and NW-SE
extension caused the development of seven sub-basins
in the Nordkapp Basin. Internally within the sub-basins,
the evolving structural elements including cross-cutting
master faults and structural highs have influenced the
deposition and facies of the layered evaporitic sequences
and defined the location of subsequent salt
structures. We suggest that the relative depth of each
sub-basin, the arrangement of structural highs along
with the evolving master faults and the depositional
paleo-environment all controlled the thickness and
facies of the syn-rift layered evaporitic sequences.
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