The major fault zone of central Vestspitsbergen

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Abstract
Summary: A deformation belt runs southwards from Wijdefjorden through the length of central Vestspitsbergen, a distance of over 190 miles. From the stratigraphical summary several factors emerge that are relevant to the structural history. 1. The pre-Downtonian rocks are crystalline schists with a general N.-S. trend resulting from an earlier orogeny. 2. There was a basin of sedimentation in the Billefjorden area in Lower and Middle Carboniferous times. 3. The Carboniferous to Lower Permian succession is concordant in the central portion of this basin. 4. A strip of coarse conglomerates overlying an old fault-line suggests weak faulting activity in Middle Carboniferous times. Fault activity occurred in Upper Devonian times, probably with a strong compressive phase in the earlier part which was followed by weaker gravity faulting 1 near the end of the period. Again in Tertiary times, either gravity faults or flexures formed, depending on the competence of the rocks affected. Parallelism with the trend of the pre-Downtonian metamorphic rocks is striking and renewed dislocations along the Upper Devonian fractures seem to be common. It is concluded that the major Upper Devonian fractures are not gravity faults. Two theories of genesis are possible : firstly, transcurrent faulting with associated upthrust wedges; secondly, high-angle thrusting with a later phase of gravity faulting. The data available appear to favour the second.