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.

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This work presents a new method of coarse-grained sediment input into a deep sedimentary basin and presents a new example of igneous processes controlling sedimentary facies. The Mesozoic-Cenozoic Faroe-Shetland Basin sediments are intruded by Late Paleocene igneous sills and dikes. Sill intrusions are frequently expressed on the paleosurface as hydrothermal mounds and vents occurring directly above sill tips. Three-dimensional seismic data are used to image a Paleocene submarine mounded structure that has been penetrated by an exploration well drilled in A.D. 1984. Seismic morphology is combined with petrographic data to show that the mound was erupted from a central vent as a series of sediment pulses consisting of sediments disaggregated and recycled from depth-a submarine sediment volcano. INTRODUCTIONThe exploration well 214/28-1 was drilled in A.D. 1984 in the Faroe-Shetland Basin (Andersen, 1988;Smallwood et al., 2004); one of the targets was the mound structure that forms the basis of this contribution. The predrill interpretation was a Paleocene turbidite lobe, either mounded or subject to differential compaction, based on A.D. 1981 vintage twodimensional seismic data.The new interpretation in this paper uses recent three-dimensional seismic data and state-of-the-art seismic attribute computations to map the structure drilled in 1984. Interpretation of these three-dimensional seismic data reveals multiple subcircular mounds, along a north-south trend, dominated by a major conical mound ~380 m high and 3000 m diameter (Fig. 1), which dips 0° to 3° away from the center. The mound is linked by a chimney structure to seismically resolvable and exploration-well-penetrated transgressive dolerite sill intrusions at 0.7-3 km paleodepth below the seabed (now 2.5-4.7 km subsea) (Fig. 2, A-A′).When combined with petrological interpretation of samples taken from a cored section within the mound, it is suggested that the mounds are subsea sediment volcanoes resulting from intrusion-driven disaggregation of lithifi ed sediment, which was subsequently transported to the surface where it erupted to form the conical mounds imaged.The hydrothermal vents recognized in three dimensions in the Faroe-Shetland Basin are similar in morphology and petrography to vent complexes found in the Karoo Basin, South Africa Svensen et al., 2006), suggesting that the "chimney" structures are probably sediment pipes and dikes. Seismic morphologies of hydrothermal vents studied here are identical to those reported in the Vøring and Møre Basins (Norway) by Planke et al. (2005) and regionally by Hansen (2006). The only other offshore example that has been drilled is reported by Svensen et al. (2003) in the Vøring Basin, which is seep carbonate-rich and fi ner-grained than the 214/28-1 example. Previously, hydrothermal mounds have been linked to global climate change , but due to lack of offshore data their importance in linking igneous intrusions to offshore sedimentology has not been appreciated.It is believed this is the fi rst time the lit...

The identification of extensive intrusive igneous complexes both in subsurface data and in field studies has resulted in quantification of the volumes of igneous material. Despite this research there is still little connection established between the amount of igneous material intruded into a basin and its effect on subsequent basin evolution in terms of burial and loading. To understand how additional igneous material may influence basin evolution we investigate igneous intrusions from the Faroe-Shetland Basin (FSB) utilising subsurface data. This study highlights that the total estimated thickness of sediment during Cretaceous is likely an overestimate as the sedimentary fill consists of significant quantities of igneous material which was emplaced during the Paleocene (56-54 Ma). Previously this additional igneous material has not been accounted for in estimates of sedimentation rates and the burial history of the FSB. Importantly petroleum system modelling to understand generation and expulsion of hydrocarbons benefits from correct estimates of basin fill. The overthickening of basins by igneous material will affect the timing of hydrocarbon generation and subsequently the proper evaluation of exploration targets. In order to fully understand basin evolution the volumes of igneous material and when this material was emplaced must be acknowledged and considered. INTRODUCTION text file Click here to access/download;text file;Revisions_Overthickening by Igneous Intrusions.docx