Very thick shallow water sedimentary sequences were deposited in Neoproterozoic time along the future margins of Laurentia. On the eastern margin these include the Eleonore Bay and Hecla Hoek sequences of Greenland and Svalbard; these are described and their geotectonic context briefly reviewed. They present both geotectonic and geodynamic problems: why did subsidence continue for some 300 Ma prior to the opening of Iapetus, and how could 15–20 km of sediment be accommodated in an ensialic environment?

Prolonged slow stretching appears to have affected the eastern margin of Laurentia while the western (Cordilleran) margin progressed through the rift-drift transition as the Pacific opened. It is proposed that expansion of the Pacific was associated with both the convergence of Proto-Gondwanan continental terranes during the Pan-African orogeny (the extended SWEAT hypothesis) and also the maintenance of very slow extension rates on the future Iapetus margin. The strain-hardening effect of slow stretching may have been inhibited by a continuous basin-fill of juvenile heat-producing Grenville detritus. The onset of subduction in the Pacific freed up this margin; major rifting took place between East Greenland and possibly the Tornquist margin of Baltica in Vendian time, followed by the opening of northern Iapetus.

Isotopic chemostratigraphy has proven successful in the correlation of carbonate-rich Neoproterozoic successions. In successions dominated by siliciclastic rocks, chemostratigraphy can be problematic, but if thin carbonates punctuate siliciclastic strata, useful isotopic data may be obtained. The upper Pocatello Formation and lower Brigham Group of southeastern Idaho provide an opportunity to assess the potential and limitations of isotopic chemostratigraphy in overwhelmingly siliciclastic successions. The 5000 m thick succession consists predominantly of siliciclastic lithologies, with only three intervals that contain thin intercalated carbonates. Its depositional age is only broadly constrained by existing biostratigraphic, sequence stratigraphic and geochronometric data. The lowermost carbonates include a cap dolomite atop diamictites and volcanic rocks of the Pocatello Formation. The δ13C values of these carbonates are distinctly negative ( −5 to −3), similar to carbonates that overlie Neoproterozoic glaciogenic rocks worldwide. Stratigraphically higher carbonates record a major positive δ13C excursion to values as high as +8.8 within the carbonate member of the Caddy Canyon Quartzite. The magnitude of this excursion is consistent with post-Sturtian secular variation recorded elsewhere in the North American Cordillera, Australia, Svalbard, Brazil and Namibia, and exceeds the magnitude of any post-Varanger δ13C excursion documented to date. In most samples, Sr-isotopic abundances have been altered by diagenesis and greenschist facies metamorphism, but a least-altered value of approximately 0.7076 supports a post-Sturtian and pre-Marinoan/Varanger age for upper Pocatello and lower Brigham rocks that lie above the Pocatello diamictite. Thus, even though available chemostratigraphic data are limited, they corroborate correlations of Pocatello Formation diamictites and overlying units with Sturtian glaciogenic rocks and immediately post-Sturtian successions in western North America and elsewhere.

Observations on pyritized graptolites have revealed a variety of pyrite morphotypes, several of which often coexist within the same fossil steinkern. The commonest forms of pyrite are those consisting of size-sorted microcrysts, which show degrees of ordering ranging from well-ordered framboids to a more homogeneous, unordered groundmass. Larger, euhedral pyrite crystals may be scattered throughout the microcrystalline groundmass, or be the dominant pyrite form in themselves. ‘Floriform’ pyrite frequently overgrows earlier framboids and may act to mould the inner periderm microstructure of the graptolite. Overpyrite occurs either as a primary ‘overspill’ of internal pyrite, or as a separate, later phase.

All of the diagenetic pyrite has light sulphur isotope compositions, indicating formation during early diagenesis; isotopic evidence of the relative timing of pyrite generations matches the morphological paragenesis. Under most conditions, available iron appears not to be a limiting factor in pyrite formation, with reactive organic matter only being limiting at the lowest concentrations encountered in these sediments. The availability of organic matter does, however, exert a control on the timing of fossil pyritization. At one locality, a change in diagenetic conditions has allowed for the formation of a morphologically late generation of pyrite with isotopically light and therefore apparently early diagenetic signatures.

The geochemistry of Tertiary igneous rocks from Arran, western Scotland, provides a probe for the structure of the crust in the region of the Highland Boundary Fault (HBF). New Nd isotope data, coupled with other geochemical evidence, point to variable contamination of primitive mantle-derived magmas during magmatic differentiation in the crust. Two different isotopic contamination trends are seen. The northern granite was generated by contamination of basic differentiates by crust resembling exposed Dalradian units. Data for the central granite, and several other minor intrusions from south of the HBF, trend towards the reported isotopic signatures of granulite-facies xenoliths from the Midland Valley. However, quartz porphyry intrusions in the south of the island are compositionally similar to the nothern granite, and were probably intruded southwards across the HBF in dykes. Hence the isotopic signatures of the Tertiary intrusions reflect the different character of the crustal units on either side of the fault.

Lithostratigraphic units of early to late Cambrian age established by T. C. Nicholas in 1915 in the St Tudwal's Peninsula are revised. They comprise, in ascending order: Hell's Mouth Formation (> 190 m); Trwyn y Fulfran Formation (37 m);Cilan Formation (400 m); Ceiriad Formation (40 m seen); Nant-y-big Formation (> 110 m seen); Maentwrog Formation (in part, 50 m seen, an estimated 250 m concealed); Ffestiniog Flags Formation (in part, c. 120m seen). The ‘calcareous grit’ at the top of Nicholas's Nant-pig Mudstones spans the unconformable boundary between the Nant-y-big and Maentwrog formations. Previously described limestone clasts in the ‘grit’ are probably erosional remnants of an in situ bioclastic limestone bed; their contained trilobites include genera and species found in the Andrarum Limestone (late Middle Cambrian) of Scania, Sweden. Acritarchs are documented and compared particularly with those from eastern Newfound-land. Those from the highest part of the ‘calcareous grit’ include Cymatiogalea sp. and are of late Cambrian age. One new species, Heliosphaeridium? llynense Martin, comes from the lower part of the Nant-y-big Formation (middle Middle Cambrian), where it appears a little earlier than the Adara alea Biozone.

All bentonite and bentonite-resembling layers thicker than a few millimetres from a 120m-thick Early Silurian sequence on Gotland, Sweden, were searched for shocked quartz grains of comet or asteroid impact origin. Although more than 200000 quartz grains from 86 bentonite samples were studied, not one single grain with multiple planar shock features was found. The studied sequence represents sedimentation during a period of about 2 million years. Impact frequencies, estimated from the cratering record and astronomical observations, indicate that during a 2-myr- period on average 20 comet or asteroid bodies larger than 0.5 km in diameter strike the Earth. The number of smaller impacting bodies is many times higher. In the light of this high frequency of impacts, the absence of any shocked-quartz-bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small- and medium-scale impact events.

The results also show that shocked quartz in general is absent or extremely rare in volcanic ash. This strengthens the case for an impact-related origin of shocked quartz grains in the Cretaceous–Tertiary boundary days.

In this paper thermal patterns based on conodont Colour Alteration Indices (CAI) have been studied in the Devonian and Carboniferous rocks from Belgium, northern France and western Germany. Four maps (with the exception of the southeastern Rheinisches Schiefergebirge) have been compiled for the investigated area: one for the Eifelian and Givetian, a second for the Frasnian, another for the Famennian and one for the Tournaisian and Viséan. Conodonts have not been found in Cambrian rocks from Belgium and northern France and as they are scarce in the Ordovician to Lower Devonian formations of this area, it was impossible to integrate these CAI data into an isograd map. In Germany (in the eastern Rheinisches Schiefergebirge) only a few CAI values for the Lower Devonian strata are available. In contrast to the Ardennes where in general conodonts show CAI values of 3.0–5.0, indices in areas adjacent to the Anglo-Brabant Massif, e.g. in the western Namur Synclinorium and in the Eifel Hills, range between 1.5 and 2.0. Slightly higher values occur in the Campine Basin north of the Anglo-Brabant Massif. By comparison with CAI data from Belgium, conodont colour alteration indices from the same stratigraphic horizons in some areas of the northern and eastern Rheinisches Schiefergebirge are up to one index higher. In most areas of the Rheinisches Schiefergebirge the level of metamorphism corresponds to the anchizone. Regional variations in CAI data appear to be related to buried intrusions and associated hydrothermal activity. In the southeastern Rheinisches Schiefergebirge CAI data are not completely consistent but it is possible to discern an increase in coalification from the north to the south. High index values in the southern Rheinisches Schiefergebirge are believed to result from regional metamorphism and heating related to numerous intrusive bodies.

In the northwestern part of the Wessex Basin of southern England, interpretation of seismic reflection and recently released borehole data provides detailed information of the major unconformity at the base of the sedimentary-fill. Seismic mapping of the top of Variscan basement reveals a concealed, faulted, dome-like Palaeozoic basement culmination or structural ‘high’ lying within the larger Cranborne–Fordingbridge High, southwest of Shaftesbury. This structure profoundly affected the deposition of the overlying Permo-Triassic sequence. The culmination, composed of Carboniferous Limestone, lies to the south of northwards-throwing, basement-controlled, syn-sedimentary faults which form the southern margin of the Mere Basin. In this area, the main phase of faulting occurred during Permo-Triassic times with little or no faulting during the Jurassic. Triassic strata onlap the basement culmination which was overstepped and finally submerged in late Triassic times. The structure has much in common with the basement ‘highs’ at Bruton and in the Mendips and provides further evidence for the existence of such features close to the main lines of Mesozoic faulting within the Wessex Basin. It is considered that differential subsidence related to syn-depositional normal faulting was the dominant factor controlling development of the highs. The simple infilling of a pre-existing post-orogenic topography played a minor role.

Arthropod trace fossils are described from the Borrowdale Volcanic Group, a sequence otherwise devoid of faunal evidence. Two forms, both made by the same probably myriapod-like organism, are assigned to the ichnogenera Diplichnites and Diplopodichnus. The lithologies preserving the trace fossils are non-marine and may have been deposited in a freshwater lacustrine environment; some of the traces were probably made in temporarily emergent conditions. The change from one form of trace to the other reflects drying out of the substrate. The trace fossils probably record some of the earliest freshwater arthropods, before the widespread colonization of land by the group.

The Portsoy–Duchray Hill Lineament has been widely quoted in the literature as a major zone of discontinuities, running from Portsoy on the Banff coast to the Duchray Hill area in Perthshire. A review of the evidence indicates that there is no single structural entity running from Portsoy to Duchray Hill; the term ‘Portsoy-Duchray Hill lineament’ should be avoided. There are, however, significant along- and across-strike variations in geological history across a zone which extends from Portsoy to the Cabrach (the ‘Portsoy Line’). Certain elements can be identified also in areas further south, e.g. the Coyles of Muick shear zone and Glen Doll fault.

The Portsoy Line was initiated as a zone of syn-depositional faulting, with resulting facies variations similar to those seen across the Glen Doll fault. The Portsoy Line was reactivated as a ductile shear zone during Caledonian orogenesis, while the Glen Doll fault is a later, more brittle, structure. The shear zone from Portsoy to the Cabrach forms the western branch of a system of shears which acted to focus syn-orogenic basic magmatism, and differential movement during post- metamorphic uplift. The Coyles of Muick shear zone is the most southerly example of the system of shears, and there is probably a transfer zone along Deeside between it and the Portsoy-Cabrach shear zone, now obscured in part by the Ballater Granite. The focused shear zones serve to delineate the Buchan area, with its low pressure metamorphism and distinctive structural style, from areas to the south and west where the structural level was deeper, and deformation more pervasive.