The stratigraphy of the Siktefjellet and Red Bay groups of
northwestern Spitsbergen is revised in
the light of new fieldwork. An early Early Devonian (Lochkovian) age is
indicated by the rich fossil
vertebrate faunas of the Red Bay Group. The underlying Siktefjellet Group
is likely to be Late Silurian in
age, although there is no direct fossil evidence of this. The most abundant
sediment type in the two groups
is fine-grained fluvial sandstone, although conglomerates and
lacustrine siltstones also occur. The conglomerates
that predominate in the lowest parts of both groups imply the presence
of fault scarps at the surface.
There has been much debate about the importance of strike-slip faulting
in the area, particularly in relation
to the major north–south trending Raudfjorden and Breibogen faults.
Between these faults, the
Biskayerhuken–Holtedahlfonna terrane contains a zone for which the
deliberately genetic name
‘Siktefjellet Strike-slip Zone’ is proposed. This zone
is characterized by evidence for a succession of events
that, taken together, suggest a history of continuing, repeated strike-slip.
These events were: (1) the tectonism
and metamorphism of the basement (Krossfjorden Group) and the emplacement
Richarddalen Complex, (2) development of crush zones in the basement, (3)
deposition of the
Siktefjellet Group in two distinct basins (perhaps of pull-apart origin),
(4) deposition of the Red Bay Group
(first as discrete scarp-related conglomerates, and then as part of a more
stable fluvial basin), (5) localized
compressional deformation of the Siktefjellet and Red Bay groups.