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Abstract

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Interaction of Basement-Involved and Thin-Skinned Tectonism in the Tertiary Fold-Thrust Belt of Central Spitsbergen, Svalbard1

Steffen G. Bergh, Alvar Braathen, and Arild Andresen4

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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,


©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.

1Manuscript received October 30, 1995; revised manuscript received June 5, 1996; final acceptance October 28, 1996.

2Institute of Biology and Geology, University of Tromsø, N-9037 Tromsø, Norway.

3Geological Survey of Norway, P.O. Box 3006, N-7002 Trondheim, Norway.

4Institute of Geology, University of Oslo, P.O. Box 1047, N-0316, Oslo, Norway.

Field work for this project was funded through the University of Tromsø, University of Oslo, RNF/NAVF (grant 440.92/057), VISTA-Statoil, Norwegian Petroleum Directorate, and Norsk Hydro/SNSK. We thank Statoil for access to seismic lines from Isfjorden, and the Norwegian Polar Institute for logistical support. K. Kleinspehn, R. Gries, and J. D. Lowell are acknowledged for fruitful review of the manuscript.

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