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The northern part of the Svalbard-Barents margin was a shear margin from 58 Ma to 36 Ma. The strike-slip effects on Spitsbergen are evident in (a) the Central Basin, (b) the fold-and-thrust belt of western Spitsbergen, and (c) Forlandsundet Graben.
An early mid-Paleocene transtensional regime is suggested by about
500 m (1,640 ft) of deltaic deposits dispersed westward into the Central basin. These onlapped the basin margins in response to initial high rates of subsidence along the flank of the shear zone. Late Paleocene uplift and increasing transpression along the shear zone is recorded by a drainage reversal and about 2 km (1 mi) of easterly offlapping deltaic deposits.
In western Spitsbergen, deformation of late Paleocene through Eocene age represents the culmination of transpression and is characterized by thrusts, asymmetric folds, and steeply-dipping reverse faults producing approximately 10-15 km (6-9 mi) of crustal shortening.
Farther west, the Eocene to early Oligocene Forlandsundet Graben, and probably other smaller basins, originated after the climax of transpression, possibly during collapse of the uplifted axis of the orogenic belt. Although the Forlandsundet Graben contains a true vertical thickness less than 3 km (2 mi) of fan-delta to submarine fan deposits, its apparent thickness greater than 5 km (3 mi) suggests basin migration during increasing transtensional conditions. Extensional deformation of the graben sequence heralded the transition of the Svalbard margin from a sheared to a rifted regime. From 36 Ma, Spitsbergen was uplifted, and deep (> 5 km, 3 mi) rift basins developed along the new continental margin.
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