Regional magma plumbing and emplacement mechanisms of the Faroe‐Shetland Sill Complex: implications for magma transport and petroleum systems within sedimentary basins

Abstract

The movement of magma through the shallow crust and the impact of subsurface sill complexes on the hydrocarbon systems of prospective sedimentary basins has long been an area of interest and debate. Based on 3D seismic reflection and well data, we present a regional analysis of the emplacement and magmatic plumbing system of the Palaeogene Faroe-Shetland Sill Complex (FSSC), which is intruded into the Mesozoic and Cenozoic sequences of the Faroe-Shetland Basin (FSB). Identification of magma flow directions through detailed seismic interpretation of approximately 100 sills indicates that the main magma input zones into the FSB were controlled primarily by the NE-SW basin structure that compartmentalise the FSB into its constituent sub-basins. An analysis of well data shows that potentially up to 88% of sills in the FSSC are <40 m in thickness, and thus below the vertical resolution limit of seismic data at depths at which most sills occur. This resolution limitation suggests that caution needs to be exercised when interpreting magmatic systems from seismic data alone, as a large amount of intrusive material could potentially be missed. The interaction of the FSSC with the petroleum systems of the FSB is not well understood. Given the close association between the FSSC and potential petroleum migration routes into some of the oil/gas fields (e.g. Tormore), the role the intrusions may have played in compartmentalisation of basin fill needs to be taken fully into account to further unlock the future petroleum potential of the FSB.

Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data

“…via dykes) and emplacement was influenced by the E-W striking Cretaceous normal faults that formed the Canterbury Basin and dissect the basement [Ghisetti and Sibson 2012]; basement-involved normal faults have also been shown to effect magma input and sill geometry in the Faroe-Shetland Basin, NE Atlantic [Schofield et al 2015]. Initial formation of S1-S4 likely occurred in the Katiki or Moreaki formations at various structural levels, where host rock properties or stress conditions favoured sill emplacement [e.g.…”

“…Whilst borehole from the Faroe-Shetland Basins suggest that a significant proportion of sills may not be resolved or detected in seismic reflection data [Schofield et al 2015], perhaps supporting the thin sill model, a recent study has proposed that the high acoustic impedance contrast between igneous and sedimentary rocks means that even very thin sills should be detected in seismic data [Eide et al 2017]. We thus consider it unlikely that multiple, thin sills (<5 m thick) occur within the H8-H9 folded sequence of folds 1 and 3.…”

“…Reeckmann and Mebberson 1984;Holford et al 2012;Holford et al 2013]; and (iii) inelastic deformation processes involving porosity reduction (e.g. compaction and fluidization) can inhibit hydrocarbon migration and reduce reservoir quality [Schofield et al 2015]. Sill emplacement in the petroliferous Canterbury Basin throughout the Oligocene-to-Early Pliocene overlapped with the onset of hydrocarbon generation and expulsion in the mid-Miocene (Figure 2) [Bennett et al 2000].…”

“…Monreal et al 2009;Holford et al 2013]. Furthermore, it is probable that igneous bodies below the resolution of the seismic data are present and could impact maturation dynamics [Schofield et al 2015]. The forced folds deform potential Late Cretaceous and Eocene reservoir rocks, creating possible structural traps (Figure 2, 3, and 6).…”

Characterising extrusive and intrusive magmatism at the Kipper Field, Gippsland Basin, using 3D seismic data

“…Onshore equivalents are restricted to a number of small enigmatic basalts, dolerite and gabbroic dykes near Korumburra and Inverloch Green 1992, Edwards 1934) Using this data we can further investigate the igneous features associated with this rifting environment in the Gippsland Basin and create a better understanding of which structures might act as conduits for igneous material in less well imaged areas. For instance, in the Faroe-Shetland Basin and Exmouth Sub-basin, several faults have been shown to act as conduits for magma and are shown to influence the morphology and internal flow dynamics of igneous intrusions , Schofield et al 2015. …”