The stratigraphy, environment of eruption and age of the Faroes Lava Group, NE Atlantic Ocean

Abstract

Palaeogene volcanism on the NW margin of the Faroe-Shetland Basin is represented by the Faroes Lava Group, within an age range of 57.5–60.56 Ma. The volcanic sequence comprises >1000 m of basaltic volcaniclastic rocks deposited in estuarine or marginal lagoons, overlain by three laterally-extensive formations of subaerial facies basaltic lavas: Lower, c. 3250 m; Middle, c. 1400 m; Upper, at least 900 m (top not preserved). The Lower and Upper formations comprise high-volume sheet flows, commonly with ferrallitized tops, interbedded with reddened, thin, fluvial claystone and basaltic siltstone deposits. Laterally-impersistent coals occur within the Lower Lava Formation. The Coal-bearing Formation (c. 20 m) was deposited in an overbank floodplain environment during an hiatus in the volcanism between the Lower and Middle formations. The Volcaniclastic Sandstone Sequence comprises hydroclastic and pyroclastic deposits which post-date the Coal-bearing Formation and represent a return to volcanism, prior to the eruption of the Middle Lava Formation which is mainly characterized by inflated pahoehoe flows. The onshore sequence of the Faroes Lava Group can be correlated with basaltic flows within the Faroe-Shetland Basin, where lavas in Well 205/9-1 are interpreted to be of Lower Lava Formation affinity, possibly erupted from a local vent system. Seismic and gravity mapping and modelling suggest that the offshore extension of the Lower Lava Formation, together with the oldest part of the Middle Lava Formation, comprise subaqueous hyaloclastites deposited in a prograding Gilbert-type lava delta system. The youngest part of the Middle Lava Formation and all of the Upper Lava Formation occur as subaerial facies lavas within the basin.

Understanding the offshore flood basalt sequence using onshore volcanic facies analogues: an example from the Faroe–Shetland basin

“…The gross thickness of the volcanic succession in the Faroe Islands is thought to be 6500-7000 m, of which 3000 m are observed above sea-level (Ellis et al 2002;Passey & Bell, 2007). The onshore distribution of the formations is shown in Figure 1b.…”

“…The onshore distribution of the formations is shown in Figure 1b. The Faroe Islands Basalt Group is considered to have erupted between c. 60.56 and 57.5 Ma (Ellis et al 2002), however, the dating is poorly constrained above the Beinisvør› Formation. The Beinisvør› Formation is overlain by the Prestfjall Formation (previously termed the coal-bearing sequence), which consists of coalbearing sedimentary units and was originally dated at around 57.5 Ma (Ellis et al 2002).…”

“…The Faroe Islands Basalt Group is considered to have erupted between c. 60.56 and 57.5 Ma (Ellis et al 2002), however, the dating is poorly constrained above the Beinisvør› Formation. The Beinisvør› Formation is overlain by the Prestfjall Formation (previously termed the coal-bearing sequence), which consists of coalbearing sedimentary units and was originally dated at around 57.5 Ma (Ellis et al 2002). The most recent review of the dates for the onset and cessation of the Faroe Islands lava field, however, places the Prestfjall Formation at about 55 Ma (see Jolley, 2009) with errors of ± 0.5 Ma, and suggests an onset of volcanism more likely around 57 Ma based on correlations across the NAIP.…”

“…Additionally, within the olivine flows, two different (1981 & 1996) borehole drilled on the island of Su›uroy. The wells of Vesmanna-1 (1980) and Glyvursnes-1 (2003) are also located (after Ellis et al 2002). (c) Schematic log and approximate thickness of the stratigraphy on the Faroe Islands, including the Lopra-1/1A information.…”

“…The Enni Formation consists of a mixture of simple and compound lava flows, with a remnant thickness of 900 m with a few hundred metres removed due to erosion (Ellis et al 2002;Passey & Bell, 2007) (Figs 2e,3). The Enni Formation is considered to have erupted during magnetic chron C24R (Waagstein, 1988), which places this activity into a cycle of eruptive activity which occurred prior to the opening of the NE Atlantic Ocean.…”