NJG91-1/2-02
2011
Structural geology and sedimentology of Silurian metasediments in the Ulven area, Major Bergen Arc, SW Norway
91
1, 2
pp 19-33
978-82-92394-66-3

We present a structural model for a classical locality in the Major Bergen Arc and also a sedimentological description and a depositional model for rocks in the study area. Lower Silurian fine to coarse clastic metasediments that constitute the Ulven Group were deposited in a foreland basin west of the present coastline. These deposits might represent part of a greater foreland basin landward of the Caledonian mountain front. During the Scandian phase of the Caledonian Orogeny sediments were folded and squeezed between blocks of their Cambrian-Lower Ordovician ophiolitic substrate. The main structure in the area, the Ulven Syncline, changes geometry from an upright isoclinal fold at depth to a close and inclined fold at higher levels, characterized by a steep overturned NW limb and a SE limb dipping 30-40° NW. Due to a major NNE-SSW striking normal fault, with downthrow to the WNW, the SE limb of the syncline is partly or completely faulted out over a major part of the study area. Also large normal faults of a younger generation with NNW-SSE to NW-SE orientation, orthogonal to main contractional structures, have had a significant effect on the along-strike exposure of the metasediments. We infer that the main deformation that created the Ulven Syncline was Silurian whereas the final E-SE translation of metasediments to their present position, as a part of the Bergen Arcs, took place during an Early Devonian stage of Caledonian deformation.

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