摘要：The present study of field, petrological, exploration well, and seismic datadescribes backward-dipping duplexes comprised of phyllitic coal andbedding-parallel décollements and thrusts localized along lithologicaltransitions in tectonically thickened Lower Devonian to lowermost Upper Devonian;uppermost Devonian–Mississippian; and uppermost Pennsylvanian–lowermostPermian sedimentary strata of the Wood Bay and/or Wijde Bay and/or Grey Hoekformations; of the Billefjorden Group; and of the Wordiekammen Formation,respectively. The study shows that these structures partially decoupleduppermost Devonian–Permian sedimentary rocks of the Billefjorden andGipsdalen groups from Lower Devonian to lowermost Upper Devonian rocks of theAndrée Land Group and Mimerdalen Subgroup during early Cenozoic Eurekandeformation in central Spitsbergen. Eurekan strain decoupling along thesestructures explains differential deformation between Lower Devonian to lowermost Upper Devonian rocks of the Andrée Land Group and/or Mimerdalen Subgroup andoverlying uppermost Devonian–Permian sedimentary strata of the Billefjordenand Gipsdalen groups in central–northern Spitsbergen without requiring anepisode of (Ellesmerian) contraction in the Late Devonian. Potentialformation mechanisms for bedding-parallel décollements and thrustsinclude shortcut faulting and/or formation as a roof décollement in afault-bend hanging wall (or ramp) anticline, as an imbricate fan, as anantiformal thrust stack, and/or as fault-propagation folds overreactivated or overprinted basement-seated faults. The interpretation ofseismic data in Reindalspasset indicates that Devonian sedimentary rocks ofthe Andrée Land Group and Mimerdalen Subgroup might be preserved east ofthe Billefjorden Fault Zone, suggesting that the Billefjorden Fault Zone didnot accommodate reverse movement in the Late Devonian. Hence, the thrustingof Proterozoic basement rocks over Lower Devonian sedimentary rocks alongthe Balliolbreen Fault and fold structures within strata of the AndréeLand Group and Mimerdalen Subgroup in central Spitsbergen may be explainedby a combination of down-east Carboniferous normal faulting with associatedfootwall rotation and exhumation, and subsequent top-west early CenozoicEurekan thrusting along the Billefjorden Fault Zone. Finally, the studyshows that major east-dipping faults, like the Billefjorden Fault Zone, mayconsist of several discrete, unconnected (soft-linked and/or stepping) or,most probably, offset fault segments that were reactivated or overprinted tovarying degrees during Eurekan deformation due to strain partitioning and/ordecoupling along sub-orthogonal NNE-dipping reverse faults.
