Submitted: Devonian–Carboniferous collapse and segmentation of the Billefjorden Trough, and Eurekan inversion–overprint and strain partitioning and decoupling along inherited WNW–ESE-striking faults

An article by Jean-Baptiste Koehl, former ARCEx PhD student, and co-authors has been submitted for review to the Norwegian Journal of Geology. The submitted article can be viewed in the ARCEx intranet.

Abstract

The Billefjorden area is located in central Spitsbergen where Lower–lowermost Upper Devonian deposits of the southeastern part of the northern Spitsbergen Devonian collapse basin presumably affected by Late Devonian Ellesmerian folds and thrusts are juxtaposed against Proterozoic basement rocks overlain by uppermost Devonian–early Permian rift deposits of the Billefjorden Trough along the Billefjorden Fault Zone. Field, seismic, and bathymetric data and satellite images reveal the existence of WNW–ESE-striking faults that acted as oblique-slip normal faults during Early Devonian late–post-Caledonian collapse (e.g., Odindalen fault), and during the latest Devonian–Mississippian “initiation”, latest Mississippian–earliest/Early Pennsylvanian “interaction and linkage”, Middle Pennsylvanian “through-going fault zones”, and latest Middle Pennsylvanian–early Permian latest–post rift phases of the Billefjorden Trough, e.g., localizing the deposition of thick coal-rich deposits of the Billefjorden Group. In the Carboniferous, extensional deformation progressively localized along fewer faults starting in the earliest Pennsylvanian, probably reflecting decreasing amount of tectonic extension, and terminating with the formation of the NNE–SSW-trending Petuniabukta Syncline through upwards propagation of the Billefjorden Fault Zone during limited renewed extension. In the early Cenozoic, mild reactivation and overprinting of Early Devonian–Middle Pennsylvanian WNW–ESE-striking faults accommodated strain partitioning and decoupling, resulting in intense deformation within Lower Devonian rocks that acted as a weak buffer, and in the formation of bedding-parallel décollements, e.g., between the Wood Bay and Wordiekammen formations, thus suggesting that intense deformation within Devonian rocks in Dickson Land can be explained by Eurekan deformation alone. Finally, Early Devonian–Middle Pennsylvanian WNW–ESE-striking normal faults merge at depth with similarly trending and dipping ductile fabrics and shear zones in Proterozoic basement rocks that are oblique to Grenvillian and Caledonian grains. This suggests that Devonian–Carboniferous collapse- and rift-related normal faults and their early Cenozoic Eurekan overprints formed along inherited Timanian grain.