19 Oct 2020

19 Oct 2020

Review status: this preprint is currently under review for the journal SE.

Early Cenozoic Eurekan strain partitioning and decoupling in central Spitsbergen, Svalbard

Jean-Baptiste P. Koehl1,2,3,4 Jean-Baptiste P. Koehl
  • 1Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003 NMBU, NO-1432 Ås, Norway
  • 2Department of Geosciences, UiT The Arctic University of Norway in Tromsø, NO-9037 Tromsø, Norway
  • 3Research Centre for Arctic Petroleum Exploration (ARCEx), University of Tromsø, NO-9037 Tromsø, Norway
  • 4CAGE – Centre for Arctic Gas Hydrate, Environment and Climate, NO-9037 Tromsø, Norway

Abstract. The present study of field, petrological, exploration well and seismic data shows that backward-dipping duplexes comprised of phyllitic coal and bedding-parallel décollements and thrusts, which localized along lithological transitions in tectonically thickened Lower–lowermost Upper Devonian, uppermost Devonian–Mississippian and uppermost Pennsylvanian–lowermost Permian sedimentary strata of the Wood Bay and/or Widje Bay and/or Grey Hoek formations, of the Billefjorden Group and of the Wordiekammen Formation respectively, partially decoupled uppermost Devonian–Permian sedimentary rocks of the Billefjorden and Gipsdalen groups from Lower–lowermost Upper Devonian rocks of the Andrée Land Group and Mimerdalen Subgroup during early Cenozoic Eurekan deformation in central Spitsbergen. Eurekan strain decoupling along these structures explains differential deformation between Lower–lowermost Upper Devonian rocks of the Andrée Land Group/Mimerdalen Subgroup and overlying uppermost Devonian–Permian sedimentary strata of the Billefjorden and Gipsdalen groups in central–northern Spitsbergen without requiring an episode of (Ellesmerian) contraction in the Late Devonian. Potential formation mechanisms for bedding-parallel décollements and thrusts include shortcut faulting, and/or formation as a roof décollement in a fault-bend hanging wall (or ramp) anticline, as an imbricate fan, as an antiformal thrust stack, and/or as fault-propagation folds over reactivated/overprinted basement-seated faults. The interpretation of seismic data in Reindalspasset indicates that Devonian sedimentary rocks of the Andrée Land Group and Mimerdalen Subgroup might be preserved east of the Billefjorden Fault Zone, suggesting that the Billefjorden Fault Zone did not accommodate reverse movement in the Late Devonian. Hence, the thrusting of Proterozoic basement rocks over Lower Devonian sedimentary rocks along the Balliolbreen Fault and fold structures within strata of the Andrée Land Group and Mimerdalen Subgroup in central Spitsbergen may be explained by a combination of down-east Carboniferous normal faulting with associated footwall rotation and exhumation, and subsequent top-west early Cenozoic Eurekan thrusting along the Billefjorden Fault Zone. Finally, the study shows that major east-dipping faults, like the Billefjorden Fault Zone, may consists of several, discrete, unconnected (soft-linked and/or stepping) or, most probably, offset fault segments that were reactivated/overprinted with varying degree during Eurekan deformation due to strain partitioning and/or decoupling along sub-orthogonal NNE-dipping reverse faults.

Jean-Baptiste P. Koehl

Status: open (extended)
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Jean-Baptiste P. Koehl

Data sets

Replication data for: Devonian–Mississippian collapse and core complex exhumation, and partial decoupling and partitioning of Eurekan deformation as alternatives to the Ellesmerian Orogeny in Spitsbergen Jean-Baptiste P. Koehl

Jean-Baptiste P. Koehl


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Short summary
This contribution shows that soft and coal-rich sedimentary rocks in central Spitsbergen absorbed most of the (Eurekan) contractional deformation that occurred in the early Cenozoic using seismic data and fieldwork, thus suggesting that no contractional deformation event is needed in the Late Devonian to explain the deformation differences among late Paleozoic sedimentary rocks. It also shows that the Billefjorden Fault Zone, a major crack in the Earth crust in Svalbard, is probably segmented.