jbkoehl

• Koehl, Jean-Baptiste P. (2025). The myth of the De Geer Zone: a change of paradigm for the opening of the Fram Strait. Open Research Europe. 4. doi: 10.12688/openreseurope.16791.2. Full text in Research Archive Show summary

  Background Cenozoic rifting in the Arctic and the resulting opening of the Labrador Sea and the Fram Strait are typically associated with the movement of the Svalbard Archipelago c. 400 km southwards and its separation from Greenland. Thus far, most of this tectonic displacement was ascribed to lateral movement along the N–S-striking De Geer Zone, a thousand-kilometer-long paleo-transform fault believed to extend from northwestern Norway to northern Greenland. Methods The study presents a new interpretation of tectonic structures on seismic reflection data north and west of Svalbard. Results The present study reports the presence of two km-thick, hundreds of kilometers long, E–W- to WNW–ESE-striking shear zones, northwest and west of the island of Spitsbergen, Svalbard, in the Norwegian Arctic. Contractional structures within the shear zones, their strike, the inferred transport direction, and the great depth at which they are found indicate that they formed during the Timanian Orogeny in the late Neoproterozoic (c. 650–550 Ma). These structures extend at least 80–90 km west of the coastline of Spitsbergen. The presence of continuous, late Neoproterozoic Timanian thrusts this far west of Spitsbergen invalidates the occurrence of c. 400 km lateral movements along the N–S-striking De Geer Zone along the western Barents Sea–Svalbard margin in the Cenozoic. Conclusions The present results suggest that the De Geer Zone does not exist and that related fault complexes (e.g., Hornsund Fault Complex) did not accommodate any strike-slip movement. In addition, the formation of major NW–SE-striking transform faults in the Fram Strait was controlled by late Neoproterozoic Timanian thrust systems. The present results call for major revisions of all current plate tectonics models for the opening of the Fram Strait and Arctic tectonics in the Cenozoic and for critical reviews of major fault zones inferred from indirect observations.

• Koehl, Jean-Baptiste P. (2024). Implications of Timanian thrust systems in the Barents Sea and Svalbard on using paleontological constraints for plate tectonics reconstructions. Open Research Europe. 3. doi: 10.12688/openreseurope.16674.1. Full text in Research Archive
• Koehl, Jean-Baptiste P.; Jolley, David W.; Peace, Alexander L.; Barrera, Jhon Meyer Munoz & Foulger, Gillian R. (2024). Impact of sub-basalt thrust systems on the Faroe continental shelf for the late Paleoproterozoic–Cenozoic tectonic evolution of the margin. Open Research Europe. 4. doi: 10.12688/openreseurope.18284.2. Full text in Research Archive Show summary

  Background The Faroe margin in the northeastern Atlantic is segmented by margin-orthogonal, WNW–ESE-striking lineaments extending several hundred kilometers out to the continent–ocean transition. Despite several earlier studies speculating that these features are the product of reactivation of pre-Cenozoic basement-seated structures at depth, the thick Cenozoic volcano-sedimentary sequences deposited along the margin mask the underburden, thus rendering the identification and interpretation of such structures and resolving the pre-Cenozoic history of the area challenging. The present study documents for the first time the existence of margin-orthogonal basement-seated thrust systems and describes their detailed geometry, kinematics, and tectonic evolution. Methods We interpreted basement-seated tectonic structures on seismic reflection data from TGS on the Faroe Platform and the Wyville–Thomson and Munkagrunnur ridges using the newly established seismic facies of major thrust systems. Results The data show that the Wyville–Thomson Ridge, Munkagrunnur Ridge, and Faroe Platform are cored by WNW–ESE-striking thrust systems hundreds of kilometers long and 30–50 km wide, showing dominantly top-SSW kinematics. The thrusts were reworked into NE–SW-striking folds during the Caledonian Orogeny and controlled the formation of Caledonian thrusts, which in turn controlled the formation of post-Caledonian faults. The pre-Caledonian nature of the WNW–ESE-striking thrusts and their geometry and kinematics suggest a relationship with late Paleoproterozoic Laxfordian shear zones onshore northern Scotland and the continuation of the coeval Nagssugtoqidian Orogen in southeastern Greenland, the Ammassalik Belt. The thrust systems also align with the Tornquist Zone in eastern Europe and the North Sea, thus suggesting either that they controlled the formation of the Tornquist Zone or a possibly much longer (Paleoproterozoic?) tectonic history for the Tornquist Zone. Conclusions The Faroe Island margin is crosscut by late Paleoproterozoic Laxfordian–Nagssugtoqidian thrust systems, which controlled further tectonic development of the margin.

• Koehl, Jean-Baptiste P.; Stokmo, Eirik & Barrera, Jhon Meyer Munoz (2024). On the Billefjorden fault zone in Garmdalen, central Spitsbergen: implications for the mapping of major fault zones during geological fieldwork and for the tectonic history of Svalbard. Open Research Europe. 4(147). doi: 10.12688/openreseurope.17826.2. Full text in Research Archive Show summary

  Background: The present contribution reexamines the geometry of a segment of a presumably long-lived fault in Svalbard, the Balliolbreen Fault segment of the Billefjorden Fault Zone, along which presumably two basement terranes of Svalbard accreted in the early–mid Paleozoic after thousands of kilometers strike-slip displacement. Methods: We performed structural fieldwork to Billefjorden in central Spitsbergen and interpreted satellite images. Results: Field observations demonstrate that the Balliolbreen Fault formed as a top-west thrust fault in the early Cenozoic and that weak sedimentary units such as shales of the Lower Devonian Wood Bay Formation and coals of the uppermost Devonian–Mississippian Billefjorden Group partitioned deformation, resulting in significant contrast in deformation intensity between stratigraphic units. For example, tight early Cenozoic folds are localized in shales of the Wood Bay Formation and contemporaneous top-west brittle–ductile thrusts within coals of the Billefjorden Group, whereas Pennsylvanian deposits of the Hultberget (and/or Ebbadalen?) Formation are simply folded into gentle open folds. Rheological contrasts also resulted in the development of décollements locally, e.g., between tightly folded strata of the Wood Bay Formation and Billefjorden Group and flat-lying, brecciated limestone-dominated strata of the Wordiekammen Formation. Despite the limited quality and continuity of outcrops in the area, the eastward-thickening character (i.e., away from the fault) of Pennsylvanian deposits of the Hultberget, Ebbadalen, and Minkinfjellet formations suggests that the fault did not act as a normal fault in Pennsylvanian times. Conclusions: The study suggests that strain partitioning of early Cenozoic Eurekan contraction alone may explain the deformation patterns in Paleozoic rock units in central Spitsbergen, i.e., that Late Devonian Svalbardian contraction is not required, and that a major segment of the Billefjorden Fault Zone formed in the early Cenozoic. The present work illustrates the crucial need for interdisciplinary approaches and composite educational backgrounds in science.

• Koehl, Jean-Baptiste P.; Tappe, Sebastian; Foulger, Gillian R. & Anell, Ingrid (2024). Devonian–Mississippian magmatism related to extensional collapse in Svalbard: implications for radiating dyke swarms. Open Research Europe. 4. doi: 10.12688/openreseurope.18798.1. Full text in Research Archive Show summary

  Background Despite extensive studies of the Mesozoic–Cenozoic magmatic history of Svalbard, little has been done on the Paleozoic magmatism due to fewer available outcrops. Methods 2D seismic reflection data were used to study magmatic intrusions in the subsurface of eastern Svalbard. Results This work presents seismic evidence for west-dipping, Middle Devonian–Mississippian sills in eastern Spitsbergen, Svalbard. The sills crosscut a late Neoproterozoic Timanian thrust system, which was reworked during Caledonian contraction. The sills are unconformably overlain by relatively undeformed Pennsylvanian–Mesozoic sedimentary rocks and crosscut by Cretaceous dykes of the High Arctic Large Igneous Province. The sills probably intruded along extensional fractures during post-Caledonian reactivation–overprinting of the late Neoproterozoic thrust system. Kimberlitic accessory minerals in exposed contemporaneous intrusions and the chemical composition of chromium spinel grains in Upper Triassic sedimentary rocks in Svalbard suggest that the Middle Devonian–Mississippian intrusions in eastern Spitsbergen show affinities with diamond-rich kimberlites in northwestern Russia. Overall, the sills were emplaced during a regional episode of extension-related Devonian–Carboniferous magmatism in the Northern Hemisphere including the Kola–Dnieper and Yakutsk–Vilyui large igneous provinces. Conclusions This work presents the first evidence for extensive Middle Devonian–Mississippian magmatism in Svalbard. These intrusions may be part of the Kola–Dnieper Large Igneous Province and intruded parallel to preexisting, Proterozoic–early Paleozoic orogenic structures. Their strike is inconsistent with a source from a potential mantle plume center in the eastern Barents Sea. Thus, the radiating emplacement pattern of the magmatic intrusions of the Kola–Dnieper Large Igneous Province are not the product of plume-related uplift but of structural inheritance. A similar line of reasoning is successfully applied to intrusions of the Yakutsk–Vilyui and High Arctic large igneous provinces

• Koehl, Jean-Baptiste P. & Stokmo, Eirik (2024). Caledonian reactivation and reworking of Timanian thrust systems and implications for latest Mesoproterozoic to mid-Paleozoic tectonics and magmatism in northern Baltica. Open Research Europe. 4. doi: 10.12688/openreseurope.17033.2. Full text in Research Archive Show summary

  Background The Trollfjorden–Komagelva Fault Zone is the southernmost thrust fault of the Timanian Orogen and extends for thousands of kilometers from northwestern Russia to northern Norway. Though there is little about its location onshore northeastern Norway, where it is mapped as a major fault system dominantly comprised of NNE-dipping thrust faults, its continuation to the west below Caledonian nappes and offshore post-Caledonian sedimentary basins remains a matter of debate. Methods The present study provides a more definitive answer about the continuation of Trollfjorden–Komagelva Fault Zone west of the Varanger Peninsula by using seismic reflection, bathymetric, topographic, and magnetic data onshore Finnmark and offshore on the Finnmark Platform. Results The present study demonstrates that the Sørøya–Ingøya shear zone represents a portion of the Trollfjorden–Komagelva Fault Zone that was folded into a NE–SW orientation and reactivated as a top-southeast thrust during the Caledonian Orogeny, while other portions of the Trollfjorden–Komagelva Fault Zone (e.g., on the Varanger Peninsula) were reactivated as strike-slip faults. The study also documents the presence of another major, NNE-dipping Timanian shear zone with a similar geometry to the Trollfjorden–Komagelva Fault Zone north of the Varanger Peninsula. Conclusions The Trollfjorden–Komagelva Fault Zone may continue offshore as a NE–SW-striking folded structure. This has the following implications: (1) the Seiland Igneous Province likely formed in a backarc setting, (2) metasedimentary rocks of the Kalak Nappe Complex deposited along the Baltican margin of the Iapetus Ocean, possibly in a late–post-Grenvillian collapse basin, (3) the Iapetus Ocean was much narrower than the several thousands of kilometers width commonly proposed, and (4) early Neoproterozoic magmatism in northern Norway is possibly related to the initial breakup of Rodinia.

• Janocha, Julian; Wesenlund, Fredrik; Thießen, Olaf; Grundvåg, Sten-Andreas; Koehl, Jean-Baptiste Philippe & Johannessen, Erik (2024). Depositional environments and source rock potential of some Upper Palaeozoic (Devonian) coals on Bjørnøya, Western Barents shelf. Marine and Petroleum Geology. ISSN 0264-8172. 163. doi: 10.1016/j.marpetgeo.2024.106768. Full text in Research Archive Show summary

  Upper Palaeozoic strata are potential sources for hydrocarbon plays on the Norwegian Barents Shelf. The island of Bjørnøya (Bear Island) is located on the western margin of the Barents Shelf and represents an exposed part of the Stappen High, which makes it an excellent location to investigate the source rock potential of this succession. Here, we investigate the organic geochemical composition and source rock potential of coals and organic-rich mudstones of Late Devonian to middle Permian ages. The thermal maturity of the analysed samples ranges from mature to overmature with some samples being in the late oil generation window, and thus exhibiting higher maturities than age and facies equivalent strata in central Spitsbergen in the NW corner of the Barents Shelf and on the Finnmark Platform to the south. The high maturities and thermal cracking may thus have negatively affected the applied isoprenoid and biomarker-based source facies parameters, which potentially inhibit correct source facies interpretation. However, our results and comparisons with previous studies indicate that the vitrinite- and inertinite-dominated humic coals occurring in the lower part of the succession formed by the accumulation of peat in fluvially-influenced, humid wetlands at paleo-equatorial latitudes during a pronounced episode of rifting in the Late Devonian (Famennian) to earliest Carboniferous (Mississippian). Our source rock evaluation indicates a good potential for liquid hydrocarbon generation for the coals of the Upper Devonian Røedvika Formation prior to maturation. The oil-prone organic matter of these coals is primarily considered as terrestrial and non-aqueous. Because of renewed rifting in the middle Carboniferous combined with a shift to arid climatic conditions, as well as an environmental change from dominantly terrestrial and marginal marine clastic to marine carbonate platform environments, the accumulation of wetland peats effectively came to an end. Thus, the overlying Carboniferous and Permian strata generally seems to yield poor to no hydrocarbon generation potential

• Koehl, Jean-Baptiste P.; Christophersen, Gard; Collombin, Maxime; Taule, Christoffer; Stokmo, Eirik M. B. & Allaart, Lis (2023). Devonian-Mississippian faulting controlled by WNW-ESE-striking structural grain in Proterozoic basement rocks in Billefjorden, central Spitsbergen. Geologica Acta. ISSN 1695-6133. 21. doi: 10.1344/GeologicaActa2023.21.7. Full text in Research Archive
• Koehl, Jean-Baptiste P.; Collombin, Maxime & Taule, Christoffer (2023). Middle Pennsylvanian megabreccia adjacent to the Odellfjellet Fault in Billefjorden, central Spitsbergen. Norwegian Journal of Geology. ISSN 2387-5844. 103(1), p. 1–24. doi: 10.17850/njg103-1-4. Full text in Research Archive Show summary

  The Billefjorden Trough, a well studied onshore analogue to Carboniferous rift basins in the Barents Sea, is bounded to the west by the Billefjorden Fault Zone. Structural field analysis of a megabreccia and adjacent strata of the Minkinfjellet Formation in the hanging wall of the Odellfjellet Fault segment of the Billefjorden Fault Zone suggests that slope failure occurred along the basin-bounding fault in the Middle Pennsylvanian during the “through-going fault zones” phase of extension, i.e., during decreasing tectonic activity. Structural field data acquired in the megabreccia adjacent to the Odellfjellet Fault using the scanline method show no relationship between fracture density and the presence and/or proximity to a major fault. In the early Cenozoic, mild reworking of Middle Pennsylvanian deposits, including plastic deformation within the megabreccia, reflects Eurekan strain partitioning and decoupling during reactivation of the Billefjorden Fault Zone. The study also reveals the occurrence of abundant WNW–ESE-striking faults in Middle Pennsylvanian sedimentary deposits, which probably formed parallel to the preexisting structural grain trending highly oblique to Grenvillian and Caledonian grains.

• Koehl, Jean-Baptiste P.; Marshall, John E. A. & Lopes, Gilda Maria Rodrigues (2022). The timing of the Svalbardian Orogeny in Svalbard: A review. Solid Earth (SE). ISSN 1869-9510. 13(8), p. 1353–1370. doi: 10.5194/se-13-1353-2022. Full text in Research Archive Show summary

  In the Late Devonian to earliest Mississippian, Svalbard was affected by a short-lived episode of deformation named the Svalbardian Orogeny. This event resulted in intense folding and thrusting in Devonian sedimentary successions. Deformation stopped prior to the deposition of Carboniferous to Permian sedimentary strata of the Billefjorden and Gipsdalen groups, which lie unconformably over folded Devonian strata. Later on, presumed Svalbardian structures were reworked during Eurekan tectonism in the early Cenozoic and partly eroded. At present, records of Svalbardian deformation are only preserved in narrow N–S-trending belts in central, northern, western, and southern Spitsbergen. Despite extensive field studies, the timing of the Svalbardian Orogeny is poorly constrained and remains a matter of debate in places because of conflicting ages and because of the complex tectonic history of Svalbard. The present contribution aims at reviewing and discussing all available age constraints for Svalbardian tectonism, including notably palynological, paleontological, and geochronological evidence. This has great implications for the plate tectonic reconstructions of Arctic regions and for the tectonic history of Svalbard. Palynological and paleontological evidence suggest that the Mimerdalen Subgroup is upper Givetian to lower Frasnian (ca. 385–380 Ma) in age and that the Billefjorden Group is mid-Famennian to Upper Mississippian (ca. 365–325 Ma) in age, constraining the Svalbardian event in central and northern Spitsbergen to 383–365 Ma if it ever occurred. Palynological ages indicate that the Adriabukta Formation in southern Spitsbergen is Middle Mississippian and therefore cannot have been involved in the Svalbardian event, thus suggesting that all the deformation in southern Spitsbergen is early Cenozoic in age and that strain-partitioning processes had a major role in localizing deformation in weaker stratigraphic units. The few geochronological age constraints yielding Late Devonian–Mississippian ages in Svalbard may reflect either Svalbardian contraction or extensional processes and are therefore of no use to validate or invalidate the occurrence of the Svalbardian event. On the contrary, the contradicting lines of evidence used to support the occurrence of the Svalbardian event and new regional geophysical studies suggest that Svalbard was subjected to continuous extension from the late Silurian to early Permian times.

• Koehl, Jean-Baptiste P.; Bergh, Steffen Gunnar & Sylvester, Arthur G. (2022). Tectonic evolution of the Indio Hills segment of the San Andreas fault in southern California, southwestern USA. Solid Earth (SE). ISSN 1869-9510. 13(8), p. 1169–1190. doi: 10.5194/se-13-1169-2022. Full text in Research Archive Show summary

  Transpressional uplift domains of inverted Pliocene–Pleistocene basin fill along the San Andreas fault zone in Coachella Valley, southern California (USA), are characterized by fault linkage and segmentation and deformation partitioning. The Indio Hills wedge-shaped uplift block is located in between two boundary fault strands, the Indio Hills fault to the northeast and the main San Andreas fault to the southwest, which merge to the southeast. Uplift commenced about or later than 0.76 million years ago and involved progressive fold and faulting stages caused by a change from distributed strain to partly partitioned right-slip and reverse/thrust displacement on the bounding faults when approaching the fault junction. Major fold structures in the study area include oblique, right-stepping, partly overturned en echelon macro-folds that tighten and bend into parallelism with the Indio Hills fault to the east and become more open towards the main San Andreas fault to the west, indicating an early and close relationship of the macro-folds with the Indio Hills fault and a late initiation of the main San Andreas fault. Sets of strike-slip to reverse step-over and right- and left-lateral cross faults and conjugate kink bands affect the entire uplifted area, and locally offset the en echelon macro-folds. Comparison with the Mecca Hills and Durmid Hills uplifts farther southeast along strike in Coachella Valley reveals notable similarities, but also differences in fault architectures, spatial and temporal evolution, and deformation mechanisms. The present work contributes to better understand the structure and tectonic history of a major fault system along a transform plate boundary

• Koehl, Jean-Baptiste Philippe; Magee, Craig & Anell, Ingrid (2022). Impact of Timanian thrust systems on the late Neoproterozoic–Phanerozoic tectonic evolution of the Barents Sea and Svalbard. Solid Earth (SE). ISSN 1869-9510. 13(1), p. 85–115. doi: 10.5194/se-13-85-2022. Full text in Research Archive Show summary

  The Svalbard Archipelago consists of three basement terranes that record a complex Neoproterozoic– Phanerozoic tectonic history, including four contractional events (Grenvillian, Caledonian, Ellesmerian, and Eurekan) and two episodes of collapse- to rift-related extension (Devonian–Carboniferous and late Cenozoic). Previous studies suggest that these three terranes likely accreted during the early to mid-Paleozoic Caledonian and Ellesmerian orogenies. Yet recent geochronological analyses show that the northwestern and southwestern terranes of Svalbard both record an episode of amphibolite (–eclogite) facies metamorphism in the latest Neoproterozoic, which may relate to the 650–550 Ma Timanian Orogeny identified in northwestern Russia, northern Norway, and the Russian Barents Sea. However, discrete Timanian structures have yet to be identified in Svalbard and the Norwegian Barents Sea. Through analysis of seismic reflection, as well as regional gravimetric and magnetic data, this study demonstrates the presence of continuous thrust systems that are several kilometers thick, NNE-dipping, deeply buried, and extend thousands of kilometers from northwestern Russia to northeastern Norway, the northern Norwegian Barents Sea, and the Svalbard Archipelago. The consistency in orientation and geometry, as well as apparent linkage between these thrust systems and those recognized as part of the Timanian Orogeny in northwestern Russia and Novaya Zemlya, suggests that the mapped structures are likely Timanian. If correct, these findings would imply that Svalbard’s three basement terranes and the Barents Sea were accreted onto northern Norway during the Timanian Orogeny and should hence be attached to Baltica and northwestern Russia in future Neoproterozoic–early Paleozoic plate tectonics reconstructions. In the Phanerozoic, the study suggests that the interpreted Timanian thrust systems represent major preexisting zones of weakness that were reactivated, folded, and overprinted by (i.e., controlled the formation of new) brittle faults during later tectonic events. These faults are still active at present and can be linked to folding and offset of the seafloor

• Koehl, Jean-Baptiste P. & Allaart, Lis (2021). The Billefjorden Fault Zone north of Spitsbergen: a major terrane boundary? Polar Research. ISSN 0800-0395. 40. doi: 10.33265/polar.v40.7668. Full text in Research Archive Show summary

  The Billefjorden Fault Zone is a major terrane boundary in the Norwegian Arctic. The fault separates basement rocks of Svalbard’s north-eastern and north-western terranes that recorded discrete Precambrian tectonothermal histories and were accreted, intensely deformed and metamorphosed during the Caledonian Orogeny. Although the fault represents a major, crustal-scale tectonic boundary, its north-ward extent is not well constrained. The present short contribution addresses this issue and presents new seismic mapping of structures and rock units north of Wijdefjorden, where the Billefjorden Fault Zone may continue. This study shows that there is no evidence for major faulting of the top-basement reflection, and therefore, that the Billefjorden Fault Zone may die out within Wijdefjorden–Austfjorden, step ≥ 20 km laterally, or be invisible on the presented seismic data. Seismic data also suggest that Caledonian basement rocks in Ny-Friesland (north-eastern terrane) are not significantly different from basement rocks below the Devonian Graben in Andrée Land (north-western terrane). Potential implica-tions include the absence of a major terrane boundary in northern Spitsbergen

• Koehl, Jean-Baptiste P. (2021). Early Cenozoic Eurekan strain partitioning and decoupling in central Spitsbergen, Svalbard. Solid Earth (SE). ISSN 1869-9510. 12(5), p. 1025–1049. doi: 10.5194/se-12-1025-2021. Full text in Research Archive Show summary

  The present study of field, petrological, exploration well, and seismic data describes backward-dipping duplexes comprised of phyllitic coal and bedding-parallel décollements and thrusts localized along lithological transitions in tectonically thickened Lower Devonian to lowermost Upper Devonian; uppermost Devonian–Mississippian; and uppermost Pennsylvanian–lowermost Permian sedimentary strata of the Wood Bay and/or Wijde Bay and/or Grey Hoek formations; of the Billefjorden Group; and of the Wordiekammen Formation, respectively. The study shows that these structures partially decoupled uppermost Devonian–Permian sedimentary rocks of the Billefjorden and Gipsdalen groups from Lower Devonian to 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 Devonian to lowermost Upper Devonian rocks of the Andrée Land Group and/or 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 or 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 consist of several discrete, unconnected (soft-linked and/or stepping) or, most probably, offset fault segments that were reactivated or overprinted to varying degrees during Eurekan deformation due to strain partitioning and/or decoupling along sub-orthogonal NNE-dipping reverse faults.

• Koehl, Jean-Baptiste P.; Bergh, Steffen G; Osmundsen, Per Terje; Redfield, Thomas Fitzmaurice; Indrevær, Kjetil & Lea, Halldis [Show all 7 contributors for this article] (2019). Late devonian–carboniferous faulting and controlling structures and fabrics in NW finnmark. Norwegian Journal of Geology. ISSN 2387-5844. 99(3), p. 1–39. doi: 10.17850/njg99-3-5. Full text in Research Archive Show summary

  In the SW Barents Sea, Devonian–Carboniferous collapse led to the formation of major basins and faults, e.g., the Hammerfest Basin bounded by the Troms–Finnmark Fault Complex, and rhomboid- to sigma-shaped (half-)grabens on the Finnmark Platform. High-resolution aeromagnetic and bathymetry data from the shallow shelf show that analogue fault systems are present in coastal and onshore areas of NW Finnmark. We provide new documentation for the Langfjorden–Vargsundet fault, a post-Caledonian, NW-dipping, zigzag-shaped, margin-parallel fault complex consisting of alternating linear to sub-linear, NNE–SSW- and ENE–WSW-striking, down-NW normal fault segments. This fault formed as an extensional splay-fault of inverted, Caledonian, brittle–ductile thrusts, e.g, the Talvik and Kvenklubben faults, which the fault eventually truncated and offset. In northern Finnmark, the Langfjorden–Vargsundet fault is offset laterally by up to 28 km by a system of WNW–ESE-trending faults notably including potential segments and splays of the Trollfjorden–Komagelva Fault Zone, a reactivated Neoproterozoic, margin-orthogonal transfer fault, separating NW Finnmark from the eastern Finnmark Platform. This fault system likely dies out westwards, and portions of the system’s process zone may crop out on the island of Magerøya. Similarly, the WNW–ESE- to ENE–WSW-striking Akkarfjord fault offsets the Langfjorden–Vargsundet fault by c. 2 km left-laterally. This fault may have formed as a conjugate to the Trollfjorden–Komagelva Fault Zone in Neoproterozoic (Timanian?) times. Steeply NW-plunging, upright and gently NE-plunging, inclined folds in Archaean–Palaeoproterozoic basement rocks and margin-parallel Caledonian thrusts may have controlled the formation and geometry of post-Caledonian faults. A Late Devonian–Carboniferous age for the Langfjorden–Vargsundet fault is supported by geochronological dating of onshore dykes and fault gouge, and by syn-tectonic sedimentary wedges along the offshore extension of the Langfjorden–Vargsundet fault. Mini-basins bounded by the Langfjorden– Vargsundet fault on the Finnmark Platform and on the shallow shelf, e.g., the Ryggefjorden trough, may represent analogues to deep, offshore, Devonian–Carboniferous basins, like the Nordkapp Basin, prior to the deposition of late Palaeozoic evaporites.

• Koehl, Jean-Baptiste P. & Barrera, Jhon Meyer Munoz (2018). From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard. Solid Earth (SE). ISSN 1869-9510. 9, p. 1535–1558. doi: 10.5194/se-9-1535-2018. Full text in Research Archive Show summary

  In the Devonian–Carboniferous, a rapid succession of clustered extensional and contractional tectonic events is thought to have affected sedimentary rocks in central Spitsbergen, Svalbard. 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 sometimes makes it 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 (e.g., growth strata and slickensides) from the northern part of the Billefjorden Trough, in Odellfjellet, suggesting that tilted Mississippian sedimentary strata of the Billefjorden Group deposited during active (Late/latest?) Mississippian extension. WNW–ESE-striking basin-oblique faults showing Mississippian growth strata systematically die out upwards within Mississippian to lowermost Pennsylvanian strata, thus suggesting a period of widespread WNW–ESE-directed extension in the Mississippian and an episode of localized extension in Early–Middle Pennsylvanian times. In addition, the presence of abundant basin-oblique faults 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 preexisting faults reactivated as transverse or accommodation cross faults in or near the crest of transverse folds reflecting differential displacement along the Billefjorden Fault Zone. In Cenozoic times, a few margin-oblique faults (e.g., the Overgangshytta fault) may have mildly reactivated as oblique thrusts during transpression–contraction, but shallow-dipping, bedding-parallel, duplex-shaped décollements in shales of the Billefjorden Group possibly prevented substantial movement along these faults.

• Koehl, Jean-Baptiste; Bergh, Steffen G; Henningsen, Tormod & Faleide, Jan Inge (2018). Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea. Solid Earth (SE). ISSN 1869-9510. 9(2), p. 341–372. doi: 10.5194/se-9-341-2018. Full text in Research Archive Show summary

  The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle–Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and (iii) the Troms–Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE–SW-trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya–Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top–NW normal displacement in Middle to Late Devonian–Carboniferous times. The Troms–Finnmark Fault Complex displays a zigzag-shaped pattern of NNE–SSW- and ENE–WSW-trending extensional faults before it terminates to the north as a WNW–ESE-trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the western Finnmark Platform and the Gjesvær Low in the southwest. The WNW–ESE-trending, margin-oblique segment of the Troms–Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjorden–Komagelva Fault Zone, which is made of WNW–ESE-trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjorden–Komagelva Fault Zone dies out to the northwest before reaching the western Finnmark Platform. We propose an alternative model for the origin of the WNW–ESE-trending segment of the Troms–Finnmark Fault Complex as a possible hard-linked, accommodation cross fault that developed along the Sørøy–Ingøya shear zone. This brittle fault decoupled the western Finnmark Platform from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Middle to Upper Devonian sedimentary units resembling those in Middle Devonian, spoon-shaped, late- to post-orogenic collapse basins in western and mid-Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE–WSW- to NE–SW-trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Middle to Late Devonian–early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya–Ingøya shear zone truncated and decapitated the Trollfjorden–Komagelva Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjorden–Komagelva Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea.

• Koehl, Jean-Baptiste P.; Bergh, Steffen G & Wemmer, Klaus (2018). Neoproterozoic and post-Caledonian exhumation and shallow faulting in NW Finnmark from K–Ar dating and p/T analysis of fault rocks. Solid Earth (SE). ISSN 1869-9510. 9(4), p. 923–951. doi: 10.5194/se-9-923-2018. Full text in Research Archive Show summary

  Well-preserved fault gouge along brittle faults in Paleoproterozoic, volcano-sedimentary rocks of the Raipas Supergroup exposed in the Alta–Kvænangen tectonic window in northern Norway yielded latest Mesoproterozoic (approximately 1050 15 Ma) to mid-Neoproterozoic (approximately 825–810 18 Ma) K–Ar ages. Pressure–temperature estimates from microtextural and mineralogy analyses of fault rocks indicate that brittle faulting may have initiated at a depth of 5–10 km during the opening of the Asgard Sea in the latest Mesoproterozoic–early Neoproterozoic (approximately 1050–945 Ma) and continued with a phase of shallow faulting to the opening of the Iapetus Ocean–Ægir Sea and the initial breakup of Rodinia in the mid-Neoproterozoic (approximately 825–810 Ma). The predominance and preservation of synkinematic smectite and subsidiary illite in cohesive and non-cohesive fault rocks indicate that Paleoproterozoic basement rocks of the Alta–Kvænangen tectonic window remained at shallow crustal levels (< 3.5 km) and were not reactivated since mid-Neoproterozoic times. Slow exhumation rate estimates for the early–mid-Neoproterozoic (approximately 10–75mMyr^-1) suggest a period of tectonic quiescence between the opening of the Asgard Sea and the breakup of Rodinia. In the Paleozoic, basement rocks in NW Finnmark were overthrusted by Caledonian nappes along low-angle thrust detachments during the closing of the Iapetus Ocean–Ægir Sea. K–Ar dating of non-cohesive fault rocks and microtexture mineralogy of cohesive fault rock truncating Caledonian nappe units show that brittle (reverse) faulting potentially initiated along low-angle Caledonian thrusts during the latest stages of the Caledonian Orogeny in the Silurian (approximately 425 Ma) and was accompanied by epidote–chloriterich, stilpnomelane-bearing cataclasite (type 1) indicative of a faulting depth of 10–16 km. Caledonian thrusts were inverted (e.g., Talvik fault) and later truncated by high-angle normal faults (e.g., Langfjorden–Vargsundet fault) during subsequent, late Paleozoic, collapse-related widespread extension in the Late Devonian–early Carboniferous (approximately 375–325 Ma). This faulting period was accompanied by quartz- (type 2), calcite- (type 3) and laumontite-rich cataclasites (type 4), whose cross-cutting relationships indicate a progressive exhumation of Caledonian rocks to zeolitefacies conditions (i.e., depth of 2–8 km). An ultimate period of minor faulting occurred in the late Carboniferous– mid-Permian (315–265 Ma) and exhumed Caledonian rocks to shallow depth at 1–3.5 km. Alternatively, late Carboniferous (?) to early–mid-Permian K–Ar ages may reflect late Paleozoic weathering of the margin. Exhumation rates estimates indicate rapid Silurian–early Carboniferous exhumation and slow exhumation in the late Carboniferous–mid- Permian, supporting decreasing faulting activity from the mid-Carboniferous. NW Finnmark remained tectonically quiet in the Mesozoic–Cenozoic.

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• Distlebrink, Amber; Shephard, Grace; Koehl, Jean-Baptiste P.; Bergh, Steffen Gunnar & Beniest, Anouk (2024). Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years. Full text in Research Archive
• Cooke, Frances Ann; Faverola, Andreia Aletia Plaza; Bünz, Stefan; Amrouch, Khalid; King, Rosalind & Koehl, Jean-Baptiste P. (2023). High resolution fault analysis of the Vestnesa Ridge: a highly complex deep water fluid flow system in the east Fram Strait. Full text in Research Archive
• Plaza-Faverola, Andreia; Cooke, Frances Ann; Vachon, Remi Elie Celestin; Waghorn, Kate Alyse; Koehl, Jean-Baptiste P. & Beaussier, Stefan Jon [Show all 7 contributors for this article] (2022). Coupling between rifted oceanic crust and sedimentary deformation in the Fram Strait: implications for seafloor seepage and gas hydrates dynamics. Full text in Research Archive Show summary

  The continent–ocean transition along the passive margin off western Svalbard is, in places, only a few kilometers away from the formerly glaciated continental shelf. Strong bottom currents in the Fram Strait have led to the deposition of several kilometers thick sedimentary ridges that extend from continental to oceanic crust all the way onto the flanks of the oblique-spreading Molloy and Knipovich mid-ocean ridges. The sedimentary ridges represent large contourite drifts and are characterized by faults that extend to the present-day seafloor. Generally, it is argued that gravitational forcing or flexure due to fast sedimentation and/or erosion is the main force leading to deformation of Quaternary sediments, and that horizontal forcing is negligible. However, high resolution 2D and 3D seismic data along the western Svalbard margin reveal that sedimentary faults commonly propagate from the termination of rift-related faults in the oceanic crust, and are not always favorably oriented to accommodate gravitational collapse. We suggest that coupling between the slow-spreading oceanic crust and the sedimentary cover results in a transfer of stress and strain that influences near-surface sedimentary deformation. Deep crustal fluids are also transferred into the Quaternary succession utilizing faults as migration pathways. Such faults sustain shallow gas accumulations, wide-spread gas hydrate formation and cold seeps. Simultaneously, glacial isostatic rebound leads to additional lithospheric deformation and also exerts a control on fault kinematics and gas seepage. We discuss seismic examples of deep marine seepage systems and the potential implications of coupling between lithospheric deformation and sedimentation on the spatiotemporal evolution of seafloor seepage at Arctic margins

• Koehl, Jean-Baptiste P. (2021). Impact of Timanian thrusts on the Phanerozoic tectonic history of Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste P.; Cooke, Frances Ann & Plaza-Faverola, Andreia (2021). Formation of a transform-parallel oceanic core complex along an inherited Timanian thrust, and impact on gas seepage in the Fram Strait. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2021). Impact of Timanian thrusts on Arctic Tectonics (ArcTec). Full text in Research Archive
• Koehl, Jean-Baptiste P. (2021). Impact of Timanian thrusts on Arctic tectonics. Full text in Research Archive
• Koehl, Jean-Baptiste Philippe (2021). Seismic study of major faults in Svalbard and the Barents Sea. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2020). Impact of Timanian thrusts on the Phanerozoic tectonic history of Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2020). Late Neoproterozoic–Cenozoic tectonic evolution of Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2020). Tectonic connections between the Norwegian Arctic and Antarctic. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2019). WNW-ESE-striking Timanian faults in Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2019). Påvirkning av Timanianske forkastninger på Svalbards Fanerozoiske tektoniske historie. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2019). Forseglingsanalyse og risiko for gass og olje lekkasje. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2019). WNW-ESE-striking Timanian faults in Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2019). Mississippian rocks and WNW–ESE-striking faults in Spitsbergen. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2019). Impact of Timanian thrusts on the Phanerozoic tectonic history of Svalbard. Full text in Research Archive Show summary

  Despite more than a century of investigation, the relationship between basement rocks throughout the Svalbard Archipelago is still a mystery. Though these rocks display similar geochronological ages, they show significantly different metamorphic grades and structures. Thus far, Svalbard was believed to be composed of three terranes of rocks formed hundreds–thousands of kilometers apart and accreted in the mid-Paleozoic. New evidence from seismic, gravimetric, aeromagnetic, seismological, bathymetric, and field data show that these terranes might have already been accreted in the late Neoproterozoic. Notably, the data show that at least three–four, crustal-scale, WNW–ESE-striking thrust systems crosscut Spitsbergen and merge with Timanian thrusts in the northern Barents Sea and northwestern Russia. These thrusts were reactivated as sinistral-reverse oblique-slip faults and partly folded during the Caledonian and Eurekan orogenies, and reactivated as sinistral-normal faults during Devonian–Mississippian extensional collapse, thus offsetting N–S-trending Caledonian grain and post-Caledonian basins. The presence of these faults explains the juxtaposition of basement rocks of seemingly different origin throughout the Svalbard Archipelago, the distribution of Mississippian rocks and Early Cretaceous intrusions along a WNW–ESE-trending axis in central Spitsbergen, the west vergence of Cenozoic folds in Devonian rocks in central–northern Spitsbergen (previously ascribed to Late Devonian Ellesmerian contraction), the arch shape of the Cenozoic West Spitsbergen Fold-and-Thrust Belt in Brøggerhalvøya, and the strike and location of transform faults west of Spitsbergen. Further implications of this work might be that the tectonic plates constituting present-day Norwegian Arctic regions (Laurentia and Baltica) have retained their current geometry and alignment for the past 600 Ma, that the Timanian Orogeny and associated WNW–ESE-striking faults extend from northwestern Russia to Svalbard, and, possibly, to Greenland and Arctic Canada, and that the transport of Svalbard from next to Greenland in the early Cenozoic to its present position (ca. 400 km southwards) might have been accommodated exclusively by break-up and displacement along transform faults (strike-slip movements), and by top-SSW thrusting and folding (horizontal shortening) along inherited Timanian grain instead of dextral strike-slip movement along the De Geer Zone.

• Koehl, Jean-Baptiste P.; Bergh, Steffen G; Henningsen, Tormod; Faleide, Jan Inge; Smyrak-Sikora, Aleksandra & Olaussen, Snorre [Show all 7 contributors for this article] (2018). Mid/Late Devonian-early Carboniferous collapse basins in the Barents Sea and Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste P. (2018). Devonian core complex exhumation and Cenozoic decollements as alternatives to the Ellesmerian Orogeny. Full text in Research Archive Show summary

  The Ellesmerian Orogeny (Piepjohn et al., 2000) is a short-lived contractional–transpressional event that occurred in the Late Devonian–Mississippian, i.e., after Devonian collapse of the Caledonides and prior to Carboniferous rifting. Thus far, this episode of contraction–transpression was required to explain the presence of undeformed Carboniferous–Permian sedimentary rocks on top of folded Upper Devonian strata in central Spitsbergen. The orogen is poorly constrained in other parts of the Arctic due to the lack/poor exposure of Devonian–Carboniferous sedimentary rocks (Rippington et al., 2010). We present an alternative model involving core complex exhumation through continuous, decreasing, Devonian–Carboniferous extension during the collapse of the Caledonides, and (partial) strain decoupling during Cenozoic transpression in Svalbard.

• Brönner, Marco; Gellein, Jomar; Henningsen, Tormod; Forthun, Tore; Grundvåg, Sten-Andreas & Johannessen, Erik [Show all 9 contributors for this article] (2017). Insights in the basement characteristic and structural settings of Bjørnøya, derived from the first geophysical campaign on the island. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Henningsen, Tormod & Faleide, Jan Inge (2017). Mid/late Devonian-Carboniferous collapse basins along the SW Barents Sea margin. Full text in Research Archive
• Koehl, Jean-Baptiste (2017). Faults. Full text in Research Archive
• Koehl, Jean-Baptiste; Kvanli, Tor-Einar; Rowan, Mark G. & Faleide, Jan Inge (2017). Late Carboniferous salt tectonics in the southwesternmost Nordkapp basin. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Indrevær, Kjetil; Faleide, Jan Inge; Henningsen, Tormod & Lea, Halldis [Show all 7 contributors for this article] (2016). Nearshore half-grabens as analogues for offshore, early Carboniferous rift-basins. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Indrevær, Kjetil; Lea, Halldis; Bergø, Espen & Henningsen, Tormod [Show all 8 contributors for this article] (2016). Nearshore half-grabens as analogues for offshore, early Carboniferous rift-basins along the SW Barents Sea Margin. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Indrevær, Kjetil; Faleide, Jan Inge; Henningsen, Tormod & Lea, Halldis [Show all 7 contributors for this article] (2016). Nearshore half-grabens as analogues for offshore rift-basins on the Finnmark Platform. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Henningsen, Tormod; Forthun, Tore; Faleide, Jan Inge & Kvanli, Tor-Einar [Show all 7 contributors for this article] (2016). Prospectivity of the Late Devonian-early Carboniferous rift, SW Barents Sea. Full text in Research Archive
• Koehl, Jean-Baptiste (2016). The "wider" Late Devonian-early Carboniferous rift. Full text in Research Archive
• Koehl, Jean-Baptiste; Wemmer, Klaus & Bergh, Steffen G (2016). Shallow faulting and westwards migration of rifting from mid-Permian times in North Norway, evidence from K/Ar dating. Full text in Research Archive
• Koehl, Jean-Baptiste; Tveranger, Jan; Osmundsen, Per Terje; Braathen, Alvar; Taule, Christopher & Collombin, Maxime (2016). Fault-growth deposit in a Carboniferous rift-basin: the Billefjorden Trough, Svalbard. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Indrevær, Kjetil & Henningsen, Tormod (2015). Onshore-offshore realtionships on the SW Barents Sea with emphasis on the Troms and Finnmark coastalareas: fault correlation, tectonic landscape and margin architecture. Full text in Research Archive
• Koehl, Jean-Baptiste & Bergh, Steffen G (2015). Onshore-offshore relationships on the SW Barents Sea Margin with emphasis on the Troms and Finnmark coastal areas: fault correlation, tectonic landscape and margin architecture. Full text in Research Archive
• Koehl, Jean-Baptiste & Bergh, Steffen G (2015). Onshore-offshore relationships on the SW Barents Sea Margin with emphasis on the Troms and Finnmark coastal areas: Fault correlation, tectonic landscapes and margin architecture. Full text in Research Archive
• Koehl, Jean-Baptiste & Bergh, Steffen G (2015). Onshore-offshore relationships on the SW Barents Sea Margin with emphasis on the Troms and Finnmark coastal areas: fault correlation, tectonic landscape and margin architecture. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G; Indrevær, Kjetil; Stunitz, Holger; Henningsen, Tormod & Ingebrigtsen, Arild (2015). Onshore-offshore fault correlation on the SW Barents Sea margin. Full text in Research Archive
• Koehl, Jean-Baptiste; Bergh, Steffen G. & Stunitz, Holger (2013). Late Paleozoic-Cenozoic fault correlation and characterization of fault rocks in western Troms, North Norway. UiT Norges arktiske universitet. Full text in Research Archive Show summary

  The present work focuses on the mapping and description of onshore brittle fault zones on the SW Barents Sea Margin, within gneisses and granitic intrusions belonging to the West Troms Basement Complex. The description of the brittle structures includes the geometry, kinematics and fault rock characteristics, using DEM satellite imaging, structural field work and a microstructural analysis of the fault rocks. As a result of the present study,two major sets of onshore brittle faults have been observed, trending NNE-SSW and ENE-WSW,and they are tentatively correlated in two, NE-SW trending fault complexes: the Rekvika and the Vestfjorden-Vanna fault complexes. These fault complexes run parallel to the Troms-Finnmark fault complex that borders major offshore sedimentary basins in the NW. On the one hand, the Vestfjorden-Vanna fault complex defines the southeastern boundary of the West Troms Basement Complex towards the Caledonian nappes, and is made of wide fault zones that have experienced major displacement (ca. 1-3km). On the other hand, the Rekvika fault complex is considered as an intra-horst fault system composed of narrow fault zones that are thought to have accommodated low amounts of displacement (> 250 m). On a local scale, the fault zones display similarities in attitude (trend and dip) with the Caledonian and Precambrian fabrics, indicating a possible influence of pre-existing zones of weakness on brittle faulting. The dominant deformation mechanism (cataclastic flow) indicates pressure range about 0.2-0.3 GPa, i.e. 5-10 km depth for the formation of the cataclastic fault rocks, and these fault rocks contain mineral assemblages that generally indicate temperatures about 350-500ᵒC. This suggests that the West Troms Basement Complex has been largely uplifted later on, until present level. The NNE-SSW and ENE-WSW trending fracture sets are believed to have formed synchronously due to WNW-ESE extension, during an early stage of rifting in the Permian-Early Triassic. The NNE-SSW trending faults likely represent the main fault system, orthogonal to the extension direction, and the ENE-WSW trending faults may correspond to oblique transfer zones that link the NNE-SSW fault segments. An alternative model implies NW-SE trending transfer zones to link the NNE-SSW trending faults. A late stage of minor reverse reactivation of the NNE-SSW and ENE-WSW trending faults, and the development of NW-SE striking fractures are tentatively correlated to ridge-push forces during the opening of the North Atlantic in the Eocene.

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