Deformation of the Old Red Sandstone of NW Spitsbergen; links to the Ellesmerian and Caledonian orogenies

Abstract

Abstract The Late Silurian?-Devonian fluvial deposits of northern Spitsbergen were deposited on basement with Caledonian and earlier metamorphic ages in which two distinct terranes are recognized (Biskayerhalvøya and Krossfjorden). These form part of the central of three major terranes in Svalbard, assembled during the Caledonian Orogeny. The subsequent geological history of the Svalbard area has been strongly influenced by the north-trending structures which were active as transcurrent fault zones at this time. The unconformable base of the Siktefjellet Group, a Late Silurian?-earliest Devonian sequence of coarse conglomerates and breccias, overlain by fluvial sandstones, is preserved only on the Biskayerhalvøya terrane, and the final juxtaposition of the two terranes (during the Haakonian sinistral strike-slip phase) is interpreted to post-date the deposition of these sediments. The Lochkovian Red Bay Group, a sequence of conglomerates, fluvial sandstones and siltstones, was deposited on both terranes. This has been mapped and correlated throughout the basin exposure, allowing the reconstruction of the tectonic history. Sedimentation was influenced by active faulting during deposition of the oldest Wulffberget Formation, but subsequent deposits show little evidence of this. Deposition was interrupted in latest Lochkovian time by renewed sinistral strike-slip faulting, which broke up an area of the basin into rotating fault blocks, across which about 30 km of extension occurred. This was followed by east-west shortening, which uplifted the Red Bay basin and underlying basement, developing large folds, locally with related thrusting. The Monacobreen phase is defined to involve this deformation. The Andr0.000000e+00e Land Group reflects a subsequent renewal of subsidence, and re-establishment of an extensive fluvial basin, occupying an area east of the inverted Red Bay basin. Conglomeratic units that overlie the Red Bay Group are interpreted as the products of the reworking of the uplifted Red Bay basin and its basement. The Latest Devonian-Earliest Carboniferous Svalbardian phase again involved east-west shortening, with limited strike-slip faulting, but it is difficult to discriminate these effects from the Monacobreen phase in the Siktefjellet and Red Bay groups. A review of North Atlantic and Arctic Devonian basins shows that during deposition of the Red Bay and Andrée Land groups, the tectonics of Svalbard was more similar to that of the developing Ellesmerian orogen, than to that of the collapsing Caledonian orogen. A model is proposed that links the repeated extension and shortening seen from Early Devonian time in north Spitsbergen to anticlockwise rotation of the Chukotka-Alaska plate, about an axis near the position of Svalbard during Ellesmerian collision, coupled with minor Caledonian-related strike-slip movement along reactivated fault zones.