The age of granophyric diorite from the Sosnowiec IG-1 borehole (Brunovistulia Terrane) was studied by means of U–Pb single-grain zircon analysis performed on a SHRIMP (sensitive high-resolution ion microprobe) IIe device. The isotope ages and provenance of zircons from the Emsian tuffs cropping out in the southern part of the Holy Cross Mountains (Małopolska Terrane) were also investigated using the same method. The age of the diorite intrusion (420 ± 2 Ma) is comparable with the combined Ar–Ar/magnetostratigraphic age of the Bardo diabase intrusion from the northern part of the Małopolska Terrane. These intrusions were emplaced during the same event of regional tectonic extension associated with the Rheic Ocean closure and the onset of processes creating the Rheno-Hecynian Basin near the Silurian/Devonian boundary. A negative Nb anomaly characteristic of both intrusions could be linked with the subduction of the Rheic oceanic crust under the SE margin of the Old Red Continent. Emsian magmatic activity in the distant Rheno-Hercynian Zone provided several tuff layers in the northern part of the Małopolska Terrane. As can be inferred from zircon ages, these tuffs were derived from mafic eruptions that cut sedimentary rocks containing detrital zircons transported from Baltica. This interpretation fits the existing models of development of the Rheno-Hercynian Basin in the Emsian.

The discovery of volcanogenic ‘brown beds’ in Dalradian and Torridonian (Sleat Group and Diabaig Group) sequences in Scotland has raised questions about their origin and provenance. New discoveries of a grey facies cognate to the ‘brown beds’ have led to an hypothesis which proposes that these beds originated as tephra-fall deposits of intermediate to mafic composition. Subsequent prehnite–pumpellyite- and greenschist-facies metamorphism generated an albite–chlorite–muscovite–quartz–calcite assemblage. Recent sub-aerial weathering selectively dissolved interstitial calcite and oxidized iron, which left an albite-rich ‘brown bed’ with a porous saccharoidal texture. Field relationships and mineralogy support their origin as tephra-fall deposits and their widespread occurrence suggests they are not localized phenomena. Crucially, the weathered ‘brown beds’ point to the existence of otherwise cryptic grey metamorphosed tuffs which tend to blend in with their host metasediments.

Tephra-fall deposits in the Late Mesoproterozoic Sleat Group (Torridonian) from Skye, Scotland, are described for the first time. Two individual beds occur within the Loch na Dal Formation which represents sedimentation in a shallow marine environment. Each bed has a distinctive brown, crumbly, amorphous appearance in the field and has sharp contacts with its host metasediment. This unique lithology is identical to that of albitic schists described recently from the Southern Highland Group, Dalradian Supergroup, which were identified as air-fall tuffs.

Volcanogenic sediments form a significant part of the East Kirkton Limestone, with thin tuff units occurring at several levels and pyroclastic fragments being an important constituent of the coarser clastic limestone units.

The tuffs have been extensively altered during diagenesis but recognisable pseudomorphs after olivine and plagioclase phenocrysts confirm the basaltic nature of the volcanism. The considerable lateral variations in thickness of the tuff horizons in conjunction with the poorly sorted and lithologically heterogeneous nature of the tuffs indicate an epiclastic origin for the volcanogenic sediments. Well-rounded volcanic rock fragments—products of erosion—occur with angular fragments within the tuffs. Blocky tuffs in the lower part of the formation contain charred wood fragments, rip-up clasts of limestone and disarticulated amphibian bones. Graded bedding at several horizons and the presence of ostracods within some tuffs confirms subaqueous deposition.

The findings are consistent with the usual, dominantly epiclastic products of basaltic volcanism, in an equatorial, continental, humid environment, with assorted debris being washed from the flanks of a volcano into a shallow lake.