Impacts of fault-sill interactions on sill emplacement in the Vøring Basin, Norwegian North Sea

Abstract

Pre-existing faults may facilitate subsurface magma transport and sill trangression in sedimentary basins. Although widely recognized, interaction between faults and intrusion networks in sedimentary basins remains poorly imaged by seismic reflection data. To understand how sills interact with pre-existing faults in sedimentary basins, we use high-resolution 3-D seismic reflection data from the Naglfar Dome, Vøring Basin to examine the seismic expression of sills, interpret fault geometries and displacement patterns, and characterize sill-fault interactions. The sills are expressed as tuned reflection packages, meaning they are below ∼<50 ± 5 m thick, with saucer-shaped, transgressive, and strata-concordant morphologies that range in area from 6 km2 to 180 km2. The interconnected sills form a sill-complex, which was emplaced during the Eocene and cross-cuts three main stratigraphic intervals (i.e. the Nise, Tang, and Brygge Formations). Faults are of Early Paleocene to Early Eocene age, tectonic in origin and dominated by normal faults that are up to 28 km long. Fault and sill interactions define a spectrum, which we sub-divide into five categories (i.e. Type 1a, 1b, 2, 3 and 4); the two main end-member fault-sill relationships documented here are (a) sills stepping up stratigraphy short distances via faults and (b) those with inclined limbs intruded along fault planes. Whilst interactions between the faults and the sills are common, quantitative displacement analysis reveals fault displacement did not influence where sills exploited faults. In the study, the intricate interaction of fault and magmatic sills and its broader implications to structural compartmentalization and outcrop-scale studies in many magma-rich continental margins are demonstrated.