During Cretaceous time, before the opening of the northernmost Atlantic Ocean, western Spitsbergen lay opposite northeastern Greenland. With the opening of the Norwegian Greenland Sea during early Tertiary time, Spitsbergen slid past northeastern Greenland along a transform fault zone. This strike-slip displacement was accompanied by a strong transgression of the adjacent rocks, causing uplift of crustal blocks in a narrow belt along the western coast of Spitsbergen. Eastward from this coast, three structural zones can be recognized; (1) a 30-km-wide coastal zone of Hecla Hoek strata (upper Precambrian-lower Paleozoic) which was strongly deformed during the Caledonian orogeny and uplifted during early Tertiary time; (2) a 10-km-wide disturbed zone of Devonian-Cretaceous s rata with some sills; tilted, folded, and faulted during early Tertiary time; and (3) an interior zone of flat-lying Tertiary sedimentary beds. Most Hecla Hoek structures are probably pre-Devonian, but a prominent westward-dipping foliation may be Tertiary in age. The beds of the disturbed zone display an impressive variety of folds and faults related to uplift, tilting, and slippage between beds; one cliff shows a sequence with large recumbent folds resting in fault contact upon an unfolded sequence. Other structures, however, are related to eastward thrusting of the massive Hecla Hoek rocks onto the younger beds. A graben in the coastal zone, with nearly horizontal Tertiary beds, probably reflects a new tectonic regime (transtension) that formed after Spitsbergen had moved clear of Gre nland.

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