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.
Structural geology and sedimentology of Silurian metasediments in the Ulven area, Major Bergen Arc, SW Norway