Tertiary structure of the Sørkapp-Hornsund Region, South Spitsbergen, and implications for the offshore southern extension of the fold-thrust Belt
pp. 43-60

The Sørkapp-Hornsund region of southern Spitsbergen has undergone a complex Tertiary tectonic history, including contractional and transpressional uplift and transtensional subsidence and reactivation. Major Palaeozoic features such as the Sørkapp-Hornsund High and related basins, greatly influenced Tertiary structural development. The main elements of the region include, from west to east; the Hornsund Fault Zone (offshore), the Lidfjellet-Øyrlandsodden Fold Zone, the Øyrlandet Graben, the Sørkapp-Hornsund High, and the Tertiary fold-thrust belt. Offshore seismic data indicate that Tertiary structural features similar to those of the Sørkapp-Hornsund region are present below the shelf extending south to 75°50’N, including terraces, detached fold-thrust structures, and steep basement-involved extensional and strike-slip faults that delimit basement highs and basin margins. South of 75°50’N, the contractional structures diminish abruptly in frequency and are replaced by a geometry more characteristic of a passive margin and reflecting rifting phases dating back to the Late Cretaceous.

A multiple-event Tertiary tectonic history is proposed to explain the present day onshore-offshore structural pattern: Phase A (Paleocene – possible Early Eocene) involved WSW-ENE directed contraction and formation of the fold-thrust belt and the Lidfjellet-Øyrlandsodden Fold Zone. The Sørkapp-Hornsund High was inverted as a foreward propagating wedge along basement-involved, ENE-vergent thrusts. During phase B (Mid-Late Eocene?) local transtensional basins such as the Øyrlandet Graben, formed obliquely (NNE) to the Sørkapp-Hornsund High and the fold-thrust belt, in a right-stepping transfer zone between the two segments of en echelon contractional deformation zones. Paleocene-Eocene strata of the graben were tilted southwards and the basin margins reactivated by dextral strike-slip movements directed subparallel to the NNW-striking Hornsund Fault Zone, situated offshore. Phase C (possible Late Eocene) included reactivation of the Lidfjellet-Øyrlandsodden Fold Zone by sinistral strike-slip duplexing that also affected the fold-thrust belt and the Sørkapp-Hornsund High by means of sinistral transtension, producing NNW-striking normal faults. A south-plunging basement uplift was produced by reorientation of strata adjacent to the Sørkapp-Hornsund High, possibly due to local NW-SE contraction and/or movements along a ENE-striking transfer fault zone situated offshore and to the south of Sørkapp. Phase D (Late Eocene - possible Oligocene?) resulted in ENE- and WNW-striking transfer fault zones that offset and partition all the main structural elements, onshore and offshore.