Enry Horas Sihombing

Geomorphology of normal fault footwalls and fault scarps: Greater Tampen Spur Area, northern North Sea

Enry Horas Sihombing

Late Jurassic rifting in the Greater Tampen Spur area created a network of major normal faults, the footwall crests and fault scarps of which show major variations in their geomorphology.  In this study we characterise this variable footwall geomorphology using a ~3700 km2 3D PSDM seismic volume and several key wells from the Snorre and Visund fault blocks. Our objectives are to: (1) document the different geomorphic characteristics of major footwall blocks; (2) illustrate the variable geomorphology of fault-controlled scarps; 3) define the syn- and early post-rift depositional systems in the immediate hanging walls of major normal faults and their relationships to the geomorphology of the adjacent footwalls; and 4) understand the tectonic, stratigraphic and surface processes responsible for developing varied footwall and fault scarp geomorphology. Visund and Snorre footwall blocks exhibits differing styles of footwall crest shape and internal morphology. The Snorre fault footwall has a broad, 10-14 km wide and 60 km long, gently west-dipping plateau whereas the Visund fault footwall has a curved convex-up, east-dipping, nearly 50 km long and 6-8 km wide crest in cross section which gives way to a westward facing dip-slope. The fault scarps associated with the Snorre, and Visund fault blocks host collapsed and rider blocks of different stages of maturity, mass wasting complexes and canyon systems. Rider blocks and fault scarp collapse structures are most common along the Snorre fault zone and are located at the point of maximum fault displacement (3-5 km throw). In areas of lower displacement, both fault blocks exhibit canyon systems along their southern extents, with canyons 1-2 km in width and <0.5 km deep. Canyons are consistently observed where the footwall and fault scarp host the Late Trassic Lunde Formation in the subcrop of the Base Cretaceous Unconformity (BCU). The variability of fault scarps may be controlled by interactions of mechanical strength of pre-rift stratigraphy and the tectonic setting and evolution. Along-strike and temporal variability in displacement along the fault segments would also produce differing uplift histories along, and between fault segments. Furthermore, strain migration towards the rift axis is interpreted to produce different depositional environments (a subaerially exposed Snorre footwall and largely subaqueous Visund footwall) during much of the Late Jurassic, which likely created different erosion potential and geomorphic responses between the two fault blocks. The study highlights the importance of integrating both local and regional tectono-sedimentary factors when characterising the highly variable character of fault scarp degradation.