Abstract

The Tertiary fold-thrust belt in Oscar II Land, central Spitsbergen, consists of three major zones of distinct structural style: (1) a western basement-involved fold-thrust complex, (2) a central zone of thin-skinned fold-thrust units above a decollement in Permian evaporites, and (3) an eastern zone characterized by a frontal duplex system in the fold-thrust belt, bounded eastward by steep, basement-rooted reverse faults (Billefjorden and Lomfjorden fault zones) beneath subhorizontal platform strata. Offshore seismic data from Isfjorden (Statoil) confirm the threefold zonation and document thick-skinned and thin-skinned structural interactions in both the fold-thrust belt and the foreland section. An admissible cross section yields about 45%, or 20 km, of shortening in Oscar II Land. Deeper parts of the seismic profiles show fault-bounded Devonian (central and east) and Carboniferous (west) basins. The structural grain of the Tertiary fold-thrust belt partly coincides with the margin-bounding normal faults of these basins, suggesting that preexisting structures and stratigraphy controlled the Tertiary fold-thrust belt development. A kinematic evolution of the fold-thrust belt is invoked: (1) north-northeast-directed, bedding-parallel shortening, (2) major west-southwest-east-northeast shortening, with in-sequence foreland fold-thrust propagation, (3) basement-involved, west-southwest-east-northeast uplift in the eastern foreland zone, (4) eastward out-of-sequence propagation of thrusts, and (5) west-east extension in the hinterland. Our regional structural compilation map and synthesis of the central Spitsbergen transect advocates structural variation and linked basement-involved thrusting in the hinterland and thin-skinned/thick-skinned reactivation and out-of-sequence thrusting in the east (foreland), and is new compared with previous work of the region. The synthesis also raises several important new structural play concepts for investigating hydrocarbon prospects in Spitsbergen and adjacent regions; for example, inverted Carboniferous basins, and traps produced by Tertiary thin- and thick-skinned contraction and reactivation structures.

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