Tuffs form key stratigraphic markers which assist with determining the timing of volcanic margin development. A number of laterally extensive tuffs are preserved along the North Atlantic Margin in the offshore Faroe-Shetland Basin (FSB), a product of early Palaeogene volcanism associated with the break-up and seafloor spreading between Greenland and northwest Europe. These tuffs, which are dominantly basaltic in composition, are widely preserved in the contiguous North Sea Basin. However, less attention has been paid to them in the FSB. This study integrates multiple regional datasets, including 3D seismic and released commercial well logs to detail the character and distribution of early Palaeogene tuffs in the FSB. The earliest tuffs are more locally identified by their presence in core, whereas later tuffs are more regionally recognisable, highlighting more widespread volcanism with time. The distribution of tuffs also reveals the timing of formation of the previously enigmatic volcanic centres. Importantly, due to constraints of vertical resolution in well data, we argue the number of tuffs in the North Atlantic Margin is likely underestimated, and biased towards basaltic tuffs which are easier to identify on well logs. Volcanic tuffs are recognised as an almost ubiquitous component of flood basalt provinces globally (Ross et al. 2005), and are invaluable in event stratigraphy and stratigraphic correlation (Fisher & Schmincke 1984). The North Atlantic Margin experienced widespread volcanic activity during the early Palaeogene (66-54 Ma), associated with continental break-up and seafloor spreading between Greenland and the northwest Europe (Passey & Hitchen 2011). A manifestation of this volcanism was the widespread deposition of basaltic tuffs throughout the offshore basins of northwest Europe. In the Faroe-Shetland Basin (FSB) these tuffs are
Igneous sills and dykes that intrude pervasively into prospective sedimentary basins are a common occurrence in volcanic rifted margins, impacting the petroleum system and causing geological and technical drilling challenges during hydrocarbon exploration. The Faroe-Shetland Basin (FSB), NE Atlantic Margin, has been the focus of exploration for over 45 years, with many wells penetrating igneous intrusions. Utilising 29 FSB wells with 251 intrusions and 3D seismic data, this study presents new insights into the impacts that igneous intrusions have on hydrocarbon exploration. Examination of cores reveals that there can be up to 35% additional igneous rock in individual wells compared to estimates using seismic or petrophysical data alone, leading to potential underestimation of the igneous component in a basin. Furthermore, analysis of petrophysical data shows that within the FSB there are evolved intrusions such as diorite and rhyolite in addition to the commonly encountered basaltic intrusions. These evolved intrusions are difficult to recognise in seismic and petrophysical data and have historically been misidentified on seismic as exploration targets. Drilling data acquired through intrusions provide valuable insight into the problems exploration wells can encounter, often unexpectedly, many of which can be detrimental to safe drilling practice and result in prolonged nonproductive time.
Rift-related magmatism resulting in widespread igneous intrusions has been documented in various basins, including the Faroe Shetland Basin (UK), Voring and Møre Basins (Norway) and along the NW Shelf of Australia. Seismic mapping, combined with field work, has resulted in greater understanding of subsurface intrusive plumbing systems, but knowledge of emplacement style and the mechanisms by which intrusions propagate is limited. The interpretation of a 3D seismic dataset from the Exmouth sub-basin, NW Shelf Australia, has identified numerous igneous intrusions where a close relationship between intrusions and normal faults is observed. These faults influence intrusion morphology but also form pathways by which intrusions have propagated up through the basin stratigraphy. The steep nature of the faults has resulted in the intrusions exploiting them and thus manifesting as fault-concordant, inclined dykes, whereas in the deeper parts of the basin, intrusions that have not propagated up faults typically have saucer-shaped sill morphologies. This transition in the morphology of intrusions related to fault interaction also highlights how dykes observed in outcrop may link with sills in the subsurface. Our interpretation of the seismic data also reveal subsurface examples of bifurcating intrusions with numerous splays, which have previously only been studied in outcrop.
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