A belt of folded and faulted Carboniferous-Cretaceous platform cover strata lies parallel to and inland of much of Spitsbergen's west coast. Uplifted older basement rocks along the coast have been thrust eastward into and over these younger platform cover strata. This deformation occurred in early Tertiary time and was related to dextral movement of the Barents Shelf past northeastern Greenland during the opening of the Norwegian-Greenland Sea. On Midterhuken, a peninsula in Bellsund, an uplifted, tilted, and faulted sequence of the cover strata forms a 3.3-km-thick, 12-km-wide margin on the eastern side of the basement crustal welt. A series of closely spaced detachment horizons within Triassic strata occurs at the boundary between a lower unit of mainly sandstones and an upper unit of mainly thin-bedded shales and siltstones. The lower unit is tilted 60°–70° to the northeast but unfolded, whereas the upper unit is tightly and disharmonically folded. Hanging-wall–down movements on these and other detachment surfaces are indicated by offset of a dike and by fold-and-fault patterns. These foreland-dipping faults might be southwest-dipping thrusts later rotated, but more likely these faults and associated folds represent detachment structures formed close to their present position in response to the uplift and tilting of these strata.