The Bunga Beds outlier of the Upper Devonian Boyd Volcanic Complex, south-eastern Australia, preserves a shallow- to relatively deep-water terrigenous sedimentary rock succession, associated syn-depositional rhyolites, minor basalts, and a variety of volcaniclastic facies, all interpreted to have formed in an extensional lake basin. Basin-margin facies associations are dominated by grey mudstones, with interbedded terrigenous and volcaniclastic sandstones and conglomerates, but facies intervals dominated by tractional sedimentary structures are limited. Local horizons are significantly bioturbated. These facies associations are interpreted as fan-delta (southern association) and delta (northern association) successions. They display initial abrupt (southern association) and gradual (northern association) upward fining representing trangression, then coarsening (representing progradation of deltas) and finally fining (deepening). They pass upwards and laterally into the deep-water basin-centre facies association, which is dominated by a classic turbidite facies association, including deep-water, black, pyritic shales, graded turbidites, slump and slide deposits and debris-flow deposits. The rhyolites were high-level, syn-depositional cryptodomes and partly emergent basin-floor domes; minor dykes also occur. The basalts are exclusively dykes and irregular intrusions, some with quench-fragmented and peperitic margins. Two groups of rhyolites are identified: a crystal-poor (< 12% crystals) group, which is commonly quench-fragmented, and a relatively crystal-rich variety (12–40% crystals), which is not quench-fragmented. Massive, unbedded, jigsaw-fit to clast-rotated hyaloclastite and auto-breccia are common facies of the rhyolites, and peperite margins also occur. Because bedded, resedi-mented, dome margin autoclastic deposits are a minor facies, the majority of the rhyolites were shallow, syndepositional cryptodomes. Dome-top intralacustrine explosive activity produced two preserved, bedded, dome-top tuff cone successions dominated by diffusely bedded, water-settled fall, crystal-tuffs, and pumice lapilli-stones. The provenance of the basin-fill succession is complex. Sandstones and conglomerates in both the basin-margin and basin-centre facies associations contain dominantly basement-derived detritus, including plutonic and vein quartz, and metasedimentary lithic fragments, representing an extralacustrine terrigenous epiclastic provenance. Varying fractions of variably reworked volcanic detritus, including quartz, plagio-clase and lithic debris, are mixed with the terrigenous sediments and represent an extralacustrine volcanic epiclastic provenance. One resedimented facies, however, consists of cuspate shards, and another of basaltic scoria suggesting an extralacustrine syn-eruptive resedimented pyroclastic provenance. Hyaloclastites, autobreccias and lava-associated peperites are attributed to an intralacustrine volcanic autoclastic provenance, whereas the intrusion-associated peperites have an intralacustrine syn-depositional intrusive autoclastic provenance. The tuff and pumice cone facies have an intralacustrine pyroclastic provenance. Resedimented autoclastic facies have an intralacustrine syn-eruptive resedimented autoclastic provenance, whereas resedi-mented pyroclastic debris has an intralacustrine syn-eruptive resedimented pyroclastic provenance.

The relics of two Late Devonian subaqueous rhyolitic dome-top tuff and pumice cone successions are preserved in the Bunga Beds outlier of the Boyd Volcanic Complex, southeastern Australia. These cone successions and other rhyolitic volcanics of the Bunga Beds are associated with turbidite and other deep-water massflow sedimentary rocks. The two cone successions have a generally similar stratigraphy. At the base, flow-banded, variably autobrecciated and quench-fragmented rhyolite, representing an intrusive to extrusive dome, is overlain by rhyolitesediment breccia, representing extrusion of the dome through the deep-water sediment pile and resedimentation down its flanks. In the northern cone succession an overlying, succession of bedded pumiceous crystal-rich to crystal-poor tuffs represents the onset of pyroclastic activity and growth of a tuff cone. An overyling debris flow deposit represents degradation of part of the cone. The topmost unit, a stratified pumice succession, is thought to represent another cone-building eruptive phase, and is separated from the underlying strata by a major slide surface. The southern cone succession contains less tuff and abundant pumice, and is also terminated by a debris-flow deposit, indicating cone degradation. A modern analogue for the inferred eruptive style and sequence is the 1953–1957 rhyolite eruption that formed the Tuluman Island lava-tuff cone complex in the Bismarck Sea. The eruptions were often cyclical consisting of an initial inferred submarine-lava-forming stage, passing into a pumicecone-forming stage, in some cases a subaeriallava-forming stage, and a final stage, following the cessation of volcanism, during which the cones collapsed gravitationally or were destroyed by wave erosion. Using observations from both the Tuluman Island eruptions and the preserved stratigraphies of the Devonian tuff cones, a dynamic model is proposed for the formation of subaqueous rhyolitic dome-top tuff and pumice cones.

The Snowy River Volcanics, a belt of rhyolitic to basaltic volcanics, volcanogenic sediments and shallow intrusives, accumulated during the Early Devonian in a predominantly terrestrial continental rift basin. The uppermost part of the Snowy River Volcanics contains a complex stratigraphy of lensoidal silicic volcanics, lesser mafic volcanics and sedimentary units which can be divided into five domains displaying distinctive facies and facies associations. Recent studies of modern silicic volcanoes and their products allow the formulation of a schematic facies model for subaerial silicic centres. This model divides the silicic centre into proximal‐vent and distal facies associations. Stratigraphic complications arise from the interaction of several volcanic centres. The model is applied to facies associations recognized in the upper Snowy River Volcanics. One probable caldera succession is recognized, with indications for the existence of two other silicic centres outside the immediate area of study. The complex stratigraphy is interpreted as being due to the interaction of several silicic volcanic centres, an andesitic and a basaltic centre. The formulated silicic centre model combined with a facies approach to mapping ancient volcanic terrains could prove useful in understanding their often complex stratigraphies. Delineation of silicic centres, utilizing facies and their associations, could pinpoint areas of high potential in mineral exploration for sub‐volcanic stockwork deposits.

The strongly peralkaline Green Tuff, Pantelleria, is an example of a thin, densely welded air-fall tuff which mantles an area of at least 85 km2. Offshore the tuff is correlated with the Y-6 ash layer in the central Mediterranean Sea, and the total volume of the eruption is estimated at 7 km3 D.R.E. New petrological data suggests that the tuff was erupted from a zoned magma chamber containing a cooler, more fractionated upper zone relative to be bulk of the magma. Analysis of the distribution of accessory lithic fragments in terms of existing models of eruption dynamics indicates emplacement by a plinian-type eruption. It is shown that, due to the low viscosity of pantelleritic ejecta, dense welding can occur at moderate tephra accumulation rates and a rate of the order of 1 cm/minute is suggested for the Green Tuff; this yields an estimate for the eruption duration of rather less than one day. It is predicted that welded tuff should be formed during large plinian eruptions of pantelleritic magma, and therefore that welded airfall tuffs should be common in areas of peralkaline volcanism.