The major fault zone of central Vestspitsbergen

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.

Revision of the Stratigraphical Scheme for the Carboniferous and Permian Rocks of Spitsbergen and Bjørnøya

“…Part 3 dealing with the remaining areas was prepared in manuscript by McWhae and Forbes but not published. Details of Billefjorden fault belt and Carboniferous breccias were given by McWhae, 1953aMcWhae, , b. 1951: (Harland and Hollin, 1953) sections in south-east Ny Friesland.…”

The Geology of the Land between Ekmanfjorden and Dicksonfjorden in Central Vestspitsbergen

“…The NNW-SSE trend of the fault is parallel to the block-faulting of the more northern Devonian Sandstones. This might suggest that the fracture follows earlier lines of weakness similar to the faults in the Billefjorden area (see McWhae, 1952).…”

The main features of the tectonic structure of Spitsbergen

“…McWhae (1953) and Harland (1959) regarded this fjord as coinciding with a great dislocation, namely an overthrust, steeply dipping eastward with a vertical displacement not less than 4,000 m. Taking into consideration that in the Wijdefjorden area the upper part of the Devonian succession is obscured, and that the total thickness of Devonian rocks is up to 6,500 m, the amplitude of this overthrust is obviously about 6,000 m. The asymmetrical structure of the graben is evident in the quite different amounts of vertical displacement along the western and eastern faults, which was pointed out by Orvin as far back as in 1940. This asymmetrical structure is represented by a general dip to the east of the Devonian beds, which results in the appearance of younger horizons of this sequence in the east.…”

“…In western Vestspitsbergen this mantle was characterized by the great intensity of the block-folded deformations. The existence of a narrow zone of dislocated Upper Palaeozoic and Mesozoic deposits near the west coast of Vestspitsbergen was the basis upon which most geologists assigned the westernmost part of the archipelago to the Alpian fold belt (Ermolaev, 1937 ;McWhae, 1953 ;Orvin, 1940 ;Rozycki, 1959). However, in the early works these dislocations were said to be associated with block movements (De Geer, 1909 ;Holtedahl, 1926 ;Nathorst, 1910).…”

“…The displacements along the ancient faults amount to several kilometres, and those of the younger faults are less, decreasing to 50-350 metres. In the MesozoicCainozoic deposits south of Isfjorden the Eastern Zone is represented only by two faults with displacements ranging from 140-350 m, and associated anticlines (Livshitz 1965;McWhae, 1953;Parker, 1966).…”