Detailed Structural Investigation of the Bjørnøyrenna Fault Complex

Abstract

The NE-SW and N-S trending, Bjørnøyrenna Fault Complex is obviously belongs to an extensional regime. It is comprised of three main master faults (MF1, MF2 & MF3) in the study area. This large array of master faults further characterized by different segments termed as (MF1a, MF1b; MF2a, MF2b; MF3a, MF3b & MF3c) which constitute linked fault system with variable soft-linked and hard-linked elements. In a cross-sectional view, the fault geometries exhibit a distinct contrast between deepest (late Carboniferous-early Permian) and shallowest (intra Triassic -Cretaceous) stratigraphic levels. On the basis of regional significance and thick skin nature, MFCP1 qualified as a “First class” fault. On the other hand, MF1 & MF2 are not basement involved but shows reactivation with time and exhibits a regional significance. Therefore, it could be termed as a combination of “First or Second class” fault. Subsequently, the fault complex is subdivided into platform and sub platform on the basis of intrinsic fault frequency, pattern and dip dimensions of the reflection packages. On the platform, the fault at deeper level MFCP1 is characterized by planar fault geometry whereas; MF1 at shallowest level is dominated by strong listric configuration. Additionally, relatively simple listric detachment has been recognized within Permian succession. However, rotated fault blocks geometry has been recognized along planar normal faults (MF2a & MF2b) in sub platform. Fault dating was performed by using the methods of expansion growth index and recognition of syn-rift sedimentation. On the behalf of these methods, the N-S striking, MFCP1 was active in the late Carboniferous-early Permian whereas, NE-SW striking master fault MF2a & MF2b demonstrates an age of mid/late Jurassic – early Cretaceous. Moreover, an age of MF1 could be younger than the intra Triassic. An evidence of positive structural inversion is recognized in the present study. The analysis of such feature suggests that the strike slip movement could be responsible for the generation of this mild inversion. Therefore, an age of inversion structure can be related to the late Jurassic to the early Cretaceous. The evolution of the Bjørnøyrenna Fault Complex was started in late Carboniferous-early Permian. The late Permian-early Triassic period was characterized by the uplift of the Loppa high and significant subsidence recognized in the fault complex. The mid-late Triassic period was characterized by growth faulting. The mid Jurassic-early Cretaceous time was marked by an extensive uplifting followed by tremendous erosion of sediments. The early cretaceous time is characterized by positive inversion resulting in strike slip movement. In addition, late Cretaceous time is followed by post rift subsidence.