Caledonian structural development of the Oslo region, Norway

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Gabrielsen, Roy H.۱; Larsen, Bjّrn
Holding Date 03 September 2008

The Caledonian structuring of the Osle Region activated the Osen - Røa detachment along which the major displacement was to take place. Thus, this structure underlies the entire Oslo Region, but dies out to the south in the Skien – Langesund area. In the Oslo Region, the Osen - Røa detachment itself is found within the late Cambrian alum shale and is developed as an intensely deformed thrust and duplex system, from which numerous faults splay up-section into the Ordovician and Silurian strata. Although the strain intensity decreases towards the south and towards the upper part of the Cambro-Silurian section, four major structural levels, partly associated with flats of semi-regional significance in the nappe-pile, can be identified. Although the bulk transport is towards the SSE, areas of due southerly (Klekken area) and southeasterly transport (southern Ringerike) are prominent.
The detailed timing of the structuring is not well established, but the first sedimentary response to the growing mountain chain to the northwest is believed to be the fine-grained sandstones and siltstones of the Elnes Formation of late middle Ordovician age, whereas the first silisiclasic sediments of more significant thickness date to the latest Ordovician. Finally, it is evident that the up to 1250 m thick, upper Wenlock - lower Ludlow sandstones of the Ringerike Group have been affected by the contractional deformation, defining a maximum age for the latest Caledonian orogenic movements.