Silicic pyroclastic deposits at the base of the Paleogene Skye Lava Field: Evidence from An Carnach, Strathaird Peninsula

Abstract

Synopsis Silicic pyroclastic deposits, attributed to two discrete volcanic phases, are reported from a basal sequence of the Paleogene Skye Lava Field, NW Scotland. Phase 1 comprises relict silicic fall deposits that have been subsequently altered to a bed of K-bentonite. These fall deposits pre-date a thick ( c . 70 m) sequence of basaltic plateau lavas and a later underlying tholeiitic sill. The K-bentonite bed has a fabric that strongly resembles that of eutaxitic welded ignimbrite. Phase 2 comprises both basic and silicic ignimbrites that post-date the lowermost plateau lavas. The nature of these distinct ignimbrite lithofacies can be used to infer that eruption parameters, such as chemistry, intensity and flux output, underwent temporal variations. The recognition of these two phases of pyroclastic volcanism has major implications for the established sequence of the Skye Lava Field and gives important new insights into the nature of these Paleogene eruptions.

A large explosive silicic eruption in the British Palaeogene Igneous Province

“…Coupled with the occurrence of widespread ash beds in E-Greenland, Denmark and the North Sea as well as with eroded ignimbrite vents elsewhere in the BPIP 4,9–11,33,67,68 , our results imply that large-scale explosive silicic eruptions have likely been common during both phases of volcanic activity during the opening of the North Atlantic, including the British Palaeogene Igneous Province. This realisation paints a more violent picture of the rift to drift transition of the North-Atlantic region between 61 and 56 Ma than previously assumed.…”

“…The basalt-dominated British Palaeogene Igneous Province (BPIP) records silicic magmatism as small plutons and intrusive sheets, as downfaulted extrusive rocks in central calderas, and as thin silicic tuffs in the associated lava fields, but large-volume pyroclastic eruptions from any of the Scottish Palaeogene centres are not known (e.g. refs 1–4 ). On the one side, uplift and erosion could have obliterated the former evidence, whereas on the other side, large silicic eruptions may not have been a characteristic feature in the BPIP during the initiation of the North Atlantic (e.g.…”

Catastrophic caldera-forming eruptions and climate perturbations: the result of tectonic and magmatic controls on the Paleocene-Eocene Kilchrist Caldera, Isle of Skye, NW Scotland

“…Whilst much BPIP research has concentrated on the gabbroic and granitic central complexes (Figure 1B-D) together with the basaltic lava fields [Bell 1966;1976;Bell and Williamson 1994;Williamson and Bell 1994;Goulty et al 1996], less attention has been paid to silicic volcanic rocks. However, detailed mapping, logging, and re-interpretation of silicic volcanic sequences has recently been conducted on Eigg [Brown and Bell 2013], Skye [Drake and Beard 2012], Arran [Gooday et al 2018],…”