Frontier exploration and the North Atlantic Igneous Province: new insights from a 2.6 km offshore volcanic sequence in the NE Faroe–Shetland Basin

Abstract

The Lagavulin exploration well 217/15-1Z penetrated a ~2.6 km thick volcanic sequence dominated by extrusive basaltic rocks spanning the Palaeocene-Eocene boundary in the NE Faroe-Shetland Basin (FSB). The well comprises one of the thickest drilled sequences through the North Atlantic Igneous Province. Integrated analysis of drill cuttings and wireline-log data reveals key volcanic lithofacies: i) tabular lava flows; ii) compound lava flows; iii) hyaloclastite; and iv) volcaniclastic rocks. The volcanic facies reveal two major sub-aqueous to sub-aerial sequences consistent with lava delta progradation. These sequences are separated by a volcanic hiatus represented by extensive reddened soils which preceded the re-submergence of the area. Emergence followed by submergence of the first lava delta is interpreted to record an intra-T40 transient uplift event near the Palaeocene-Eocene boundary. Basalts from the lower ~1.3 km have low TiO 2 (<1.5 weight %) and low Zr/Y (2-3), with olivine-phyric picrites towards the base (Mg# 70-82; olivine Fo 85-91). The hiatus correlates precisely with a change to high TiO 2 (2.5-3.2 weight %) high Zr/Y (>4) compositions which dominate the upper sequence. The associated change in lava geochemistry, transient uplift and volcanic hiatus appears consistent with a transient pulse of hot buoyant plume material passing beneath the area.

Geochemical stratigraphy and correlation within large igneous provinces: The final preserved stages of the Faroe Islands Basalt Group

“…However, in many other cases, the uniformly low primary gamma response of thick lava packages (e.g. Planke, 1994;Nelson et al, 2009;Millett et al, 2015) may limit the viability of geophysical means for borehole correlation, outside of facies characterization (e.g. Nelson et al, 2009) which, as demonstrated by this study, does not form a robust criteria for correlation by itself.…”

“…(Jerram, 2015;Millett et al, 2015) along with the potential for CO 2 sequestration (Zakharova et al, 2012) and natural gas storage (Reidel et al, 2002). Understanding the potential but also the limitations of geochemical correlation within LIP sequences is therefore important for the effective exploration and development of resources associated with LIPs.…”

“…Where drill cuttings of sufficiently good quality , core or sidewall core data are available from boreholes, the chemical composition of thick lava sequences may be revealed (e.g. Millett et al, 2015). In such cases, lava flow geochemistry opens the potential for igneous geochemistry to play an important role in subsurface correlation.…”

Igneous seismic geomorphology of buried lava fields and coastal escarpments on the Vøring volcanic rifted margin

“…Jerram et al, 2009;Planke et al, 2015;Schofield et al, 2016), as well as an understanding of the petrophysics of the volcanic rocks from borehole core and wireline data (e.g. Planke et al, 1999;Japsen et al, 2004;Nelson et al, 2009;Watton et al, 2014;Millett et al, 2015). With these advances in our understanding of volcanic margins, targeted 3D seismic data over key volcanic areas will provide valuable insights into how these margins develop through time and are preserved in the offshore rock record.…”

Inelastic compaction and permeability evolution in volcanic rock

“…Often, the interpretation of logging data from volcanic materials (e.g. Millett et al, 2016) is non-trivial due to the variable quality of density logs and variations in the relationship between density and porosity with depth, alteration, or the intersection of distinct facies (Li et al, 2009), as well as gaps in the stratigraphic record due to incomplete core recovery. An example of a study with an excellent degree of core recovery -99.7 % -is reported by Jónsson and Stefánsson (1982): these authors calibrate porosity and density data obtained by the Iceland Research Drilling Project from a borehole cored continuously to a depth of 1919 m near Reyðarfjörður in Iceland.…”