The structure of the post-Caledonian strata within the West Spitsbergen Fold Belt is dominated by a Palaeogene compressive tectonic event, though earlier deformation also is documented. The Sørkapp-Hornsund area shows abundant evidence for the nature and the relative ages of these events. A multiphase tectonic history can be devised with implications for the post-Caledonian tectonic history of Svalbard.

1. Post-Caledonian basin formation (Devonian), faulting and considerable uplift at the end of the Devonian. The so-called 'Svalbardian Phase' of fold ing cannot be seen in the Sørkapp-Hornsund area.
2. Folding and thrusting along a NNW -SSE trending belt within the area of the former Devonian basin during the Early (or Mid-) Carboniferous, the so-called 'Adriabukta Phase'.
3. Synsedimentary faulting during the Middle Carboniferous, and the establishment of the Sørkapp-Hornsund High, which remained a land area until the earliest Triassic.
4. Compressive reactivation of the same mobile zone during the Palaeocene/ Eocene with formation of a complex thrust system leading to a crustal shortening of minimum 8 km across the Hornsund area. Deformation presumably dies out towards the south, but is tak en over by another fold-thrust zone offshore to the west.
5. Subsequent faulting along with the opening of the Atlantic/Arctic Oceans produced the dominating structures of the present setting.

The majority of these movements are related to a defined zone of weakness within the basement, here called the 'Sørkapp-Hornsund mobile zone'. It comprises, besides other structures, the previously defined Carboniferous 'Inner Hornsund Fault Zone' and the southern part of the 'Tertiary fold-and-thrust belt'. This mobile zone is supposed to be one of several long-lived tectonic lineaments that have controlled the tectonic development of Svalbard. The pre-existing orientations of these lineaments are thought to be responsible for apparent disagreements between regional stress fields and modes of deformation.

W. K. Dallmann, Norsk Polarinstitutt, P.O.B. 158, N-1330 Oslo Lufthavn, Norway.