Jean-Baptiste Koehl, UiT, and Jhon M. Munoz-Barrera, UiB, are the authors of a new manuscript in review in the journal Solid Earth. The manuscript is titled “From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard”.
In the Devonian–Carboniferous, a rapid succession of clustered extensional and contractional tectonic events is thought to have affected sedimentary rocks in central Spitsbergen. These events include Caledonian post-orogenic extensional collapse associated with the formation of thick Early–Middle Devonian basins, Late Devonian–Mississippian Ellesmerian contraction, and Early–Middle Pennsylvanian rifting, which resulted in the deposition of thick sedimentary units in Carboniferous basins like the Billefjorden Trough. The clustering of these varied tectonic settings makes it sometimes difficult to resolve the tectono-sedimentary history of individual stratigraphic units. Notably, the context of deposition of Mississippian clastic and coal-bearing sedimentary rocks of the Billefjorden Group is still debated, especially in central Spitsbergen. We present field evidence from the northern part of the Billefjorden Trough, in Odellfjellet (Austfjorden), suggesting that tilted Mississippian sedimentary strata of the Billefjorden Group deposited during active (Late/latest?) Mississippian extension. Evidence include slickenside lineations and growth strata in the hanging wall of basin-oblique NNE-dipping faults, such as the Overgangshytta fault. These basin-oblique faults systematically die out upwards within Mississippian to lowermost Pennsylvanian strata and suggest a period of widespread WNW–ESEdirected extension in the Mississippian (rift “initiation” phase), followed by an episode of more localized extension in Early–Middle Pennsylvanian times (“interaction and linkage” and “throughgoing fault” phases). In addition, the presence of abundant basin-oblique faults parallel to the Overgangshytta fault in basement rocks adjacent to the Billefjorden Trough suggests that the formation of Mississippian normal faults was partly controlled by reactivation of preexisting Neoproterozoic (Timanian?) basement-seated fault zones. We propose that these existing faults reactivated as transverse fault or accommodation cross faults in or near the crest of transverse folds reflecting differential displacement along the Billefjorden Fault Zone, thus suggesting that normal faulting along this major fault initiated as early as the Mississippian. In Cenozoic times, the Overgangshytta fault may have mildly reactivated as an oblique thrust during transpression–contraction, and shallow-dipping bedding-parallel duplex-shaped decollements in shales of the Billefjorden Group possibly prevented further movement along Mississippian margin-oblique faults.
Koehl, J.B., Munoz-Barrera, J.M. (accepted): From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard. Manuscript in review in Solid Earth. Discussion started: 27 August 2018. DOI: 10.5194/se-2018-86 [intranet]