Structural, petrographic and metamorphic evidence is presented for localized end-Caledonian (Acadian) décollement within a ‘black shale’ formation in the central Welsh Basin, close to the Caradoc–Ashgill boundary. Similar detachments are probably widespread in other parts of the, paratectonic Caledonides with upright folds and cleavage, particularly in sequences with strong viscosity contrasts.

The first Mesozoic beds in the western Atlas (Morocco) are the Triassic redformations of the Argana valley. The present study was carried out in order to determine the tectonic pattern, especially in the lowermost formations, related to the rifting of the Central Atlantic and to the creation of the Atlas trough. The main results are: (1) from the stratigraphic point of view, the lowermost formation (the Ikakern Formation) is probably of early Triassic age; (2) the sediments of this formation were deposited in an ENE–WSW trending basin affected by northward-tilted blocks delimited by almost pure normal faults; (3) this basin, whose trend was oblique to the younger Atlantic rift, represents a failed branch of the Atlas trough; (4) the “Atlantic stage” corresponds to the creation of a NNE-SSW trending basin superimposed on the first, and the sediments were, in this area, tilted to the west by a major end-Triassic extensional event, just before the extrusion of the basalts.

A new species of the genus Worthoceras has been recognized in material from a borehole (Bóly-1) in southern Hungary. Worthoceras pygmaeum sp. nov. co-occurs with typical Upper Albian (Stoliczkaia dispar Zone) ammonites. It seems likely that the genus Worthoceras arose in early late Albian times in North America and migrated eastward (Europe). During the Cenomanian it reached the southern margin of Tethys (Madagascar, India). It reached its most widespread distribution in Turonian times (from North America to New Zealand) and then became extinct. Beside the increasing area and growing dimensions, the strengthened sculpture is characteristic of the Worthoceras evolution.

Tightly clustered Sm–Nd model ages, with an average of 1.96±0.02Ga, for the gneiss complex of Inishtrahull indicate coeval development with the earlyProterozoic gneiss terrane of Islay. The extent of this terrane, largely beneath the Dalradian Supergroup, is argued to be 100×600 km, from northeast Scotland to western Ireland. This is based on the distribution of dated basement in conjunction with Pb, Sr and Nd isotope systematics and inherited zircons in Caledonian granites of the region.

High precision U/Pb data obtained from zircons extracted from plagiogranite within the gabbro unit of the Shetland Islands oceanic fragment of northeast Scotland yield an age of 492 ± 3 Ma. Field relations indicate that the plagiogranites were generated by the partial melting of amphibolitized gabbros within high-temperature shear zones formed due to crustal deformation and fluid infiltration occurring in proximity to a spreading centre. The U/Pb data therefore constrain the crystallization age of the Shetland complex. This age is similar to U/Pb ages obtained from the Leka (497±2 Ma), Karmoy (493+7-4 Ma) and Gulfjellet (489±3 Ma) oceanic fragments of the Norwegian Caledonides, and the Pipestone Pond (4943-2 Ma) and Betts Cove (4893-2 Ma) oceanic fragments of the Canadian Appalachians.

Palynomorphs from the Stonehaven Group indicate a late Wenlock to early Ludlow age. This is older than the currently accepted Pridoli age based on fish and arthropods. Reasons for this discrepancy are discussed. A previous correlative of the Stonehaven Group has been the Old Red Sandstone of Kerrera, Argyll. However, palynological assemblages from both Kerrera and the adjacent succession at Oban are in fact younger than that from Stonehaven in being of latest Silurian to earliest Devonian age. The palynomorphs from Kerra and Oban lie beneath the important geochronological tie-point of the Lorne Lavas and suggest that the Silurian-Devonian boundary is older than currently accepted.