A rock accumulation curve is presented for the Ordovician-Silurian Welsh Basin, based on the volume of sediment entering the basin during each graptolite biozone. Even allowing for its inherent uncertainties, the curve still illustrates a significant and sudden increase in the rate of sedimentation in early Silurian time. This may be explained by submarine fan migration, large scale climate change, or river capture in the hinterland, but is most likely caused by tectonic uplift at source. This would support models for either an early Silurian, or late Ordovician closure of the Iapetus Ocean

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.

A fluvial /wave-dominated delta was formed during late Pliocene times in southwestPeloponnesus, influenced by NNW—SSE and ENE—WSW trending faults. The depositional patternremained unchanged through early Pleistocene times, when the pre-existing active faults with WNW—ESE extension were combined with an eastward asymmetrical subsidence of the graben. Inthe deltaic environment, marshes, lakes and lagoons were created in the western parts, whereas largequantities of sediments were deposited in the central and eastern parts adjacent to basin marginsof steeper relief.

This study combines grain size parameters, total organic matter, carbonate and clay mineralogyand structural analysis to: (a) determine the pattern of sedimentation in sub-environments and (b)create a fluvial/wave-type deltaic depositional model, and distinguish between delta-plain, delta-front and pro-delta environments. The Pliocene-Pleistocene, fluvial/wave-dominated delta model inthis study can be used to predict deltaic sedimentation in analogous basins.

The well-preserved Tvären crater is noteworthy for being one of a small number of Early and Middle Ordovician impact structures formed in a marine environment. It is demonstrated to be an impact structure by the presence of a breccia lens, consisting of crystalline basement rocks, and shocked quartz. The breccia lens formed under dry-hot conditions after expulsion of sea-water by the impact. Resurging sea-water thereupon deposited a positively graded, 60 m thick turbidite-like unit. This graded resurge deposit is a previously unknown feature, to be expected in open-sea impacts. Breccia in the lower part of this graded deposit contains fragments of a remarkably complete orthoceratite limestone succession that existed at the site of impact, resting on non-lithified sand of probably Early to earliest Middle Cambrian age. A sedimentary succession was deposited inside the crater at depths decreasing from more than 200 m in the initial stages to some 100 m at the time of deposition of the youngest preserved beds. The environment within the crater thus favoured deposition of an essentially complete stratigraphic succession with depth-controlled palaeoecology for a significant time interval after the impact. Whereas planktonic members, like graptolites and chitinozoa, are present throughout the post-impact succession, and asaphids, almost as persistent, became established at an early date, burrowers were somewhat reluctant to enter and remopleuridids and small strophomenids came in at a late stage. We suggest as a result of this study that structures formed by impact may offer unique information about the palaeogeology and palaeoenvironment of the region hit by the impact.

The distribution and stratigraphic position of porphyry copper and epithermal gold deposits in andesitic arcs of the western Pacific and eastern Europe suggest that porphyry copper and epithermal vein deposits of adularia–sericite type develop successively under different stress regimes in an evolving arc, rather than being genetically related as commonly supposed. Absence of coeval high-level stocks in the root zones of many adularia-sericite deposits suggests that circulation of the dominantly meteoric hydrothermal fluids is not driven by shallow intrusions. The location of several world-class deposits on basement geanticlines, and on more localized antiforms of which at least one has been interpreted as a metamorphic core complex, implies that elevation of the arc, emplacement of magmatic sills at depth and adularia–sericite type gold mineralization are genetically related to subduction-induced crustal extension. Ascent of deep hydrothermal fluids, predominantly meteoric but with a metamorphic or magmatic component, may be controlled by regional low-angle structures at depth, analogous to those inferred for some mesothermal gold deposits. Mineralization at shallow (epithermal) depths in high-angle structures largely reflects the high geothermal gradient and mixing of deep fluid with cool meteoric water in or at the base of the permeable volcanic cover. Andesitic magmatism may resume following porphyry copper mineralization, adularia–sericite epithermal gold mineralization, or continued extension to form a ‘back arc’ spreading system, depending on the relative plate motion.

Vitrinite reflectance data from Namurian rocks in west Clare suggest that high maturation levels, corresponding to palaeotemperatures of 340–370 °C, were attained prior to Variscan deformation. Fluid inclusions in syntectonic quartz veins homogenize between 330 °C and 50 °C with an accompanying decrease in salinity from 27 to 5 eq. wt % NaCl. Maximum fluid inclusion entrapment temperatures ranged from more than 300 °C to 250 °C during Variscan folding in County Clare. The observed maturation levels (c. 7.5% Rmax) far exceed values for simple burial maturation based on the estimated burial history and ‘normal’ geothermal gradients, and do not increase with depth in the Doonbeg No. 1 exploration well. Fluid advective heating is suggested as the most likely mechanism consistent with the Clare reflectance and thermometric data. Vein and shear zone dimensions preclude rapid vertical movements of hot fluids through the section, and extensive lateral fluid migration from sedimentary basins undergoing tectonically driven dewatering to the south or west is therefore proposed.

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.

Recent collecting in the Lower Lias of localities at St Audrie's Bay, north Somerset, Sedbury Cliff, Gloucester and Lavernock Point, South Glamorgan has yielded Psiloceras planorbis (J. de C. Sowerby) in beds considered by some to be of Rhaetian, Triassic age. These are the earliest records of this ammonite to date in southwest Britain. Evidence is provided of a major facies change at the top of the pre-planorbis beds followed by the diachronous first occurrence of Psiloceras planorbis. These new data have implications for the use of earliest occurrence of Psiloceras planorbis as a chronostratigraphic marker in defining the base of the Jurassic System, and for the definition of the base of the Hettangian Stage in the recently proposed candidate Global Stratotype Section at St Audrie's Bay.

The Sunnfjord Melange is a strongly tectonized sedimentary assemblage occurring tectonostratigraphically below the Solund–Stavfjord Ophiolite Complex of Ashgill age, and upon continental margin deposits of Wenlock or older age. The Sunnfjord Melange, which probably started to form within an oceanic transform fault, developed further during obduction of the Solund–Stavfjord Ophiolite Complex. The Sunnfjord Melange is divided into two units, the lower Øyravatn Unit of predominantly fine grained calcareous quartz-bearing chlorite–muscovite schists, and the upper Markavatn Unit, mainly metagreywackes. Both units contain blocks of metabasalts, marble and meta-arkose. Serpentinite blocks are restricted to the Markavatn Unit. The appearance of serpentinite detritus is marked by much higher contents of Cr and Ni in the metasediments of the Markavatn Unit than in those of the Øyravatn Unit. The geochemistry of the metasediments from the Øyravatn Unit and the Markavatn Unit is compatible with mixing of detritus from continental and ophiolitic sources. Despite the strong and pervasive deformation of the Sunnfjord Melange, its geochemical composition from the lowest to the highest tectonostratigraphic levels reflects that of the inverse pseudostratigraphy of the Solund–Stavfjord Ophiolite Complex. Thus, only metabasalts of the Solund–Stavfjord Complex and continental meta-arkoses yielded detritus to the schists of the Øyravatn Unit. The compositions of the schists and metagreywackes of the Markavatn Unit, on the other hand, show that a multicomponent detritus derived from metabasalt and serpentinite of the Solund–Stavfjord Ophiolite Complex, mixed with the detritus from continental meta-arkoses.

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 Pioneer Formation of southwestern British Columbia (Canada) is composed predominantly of middle to late Triassic pillow basalts. These rocks are an integral part of the Cadwallader and the Bridge River terranes that were delaminated from the oceanic lithosphere and stacked against the continental margin of the North American craton by middle Jurassic time. The basalts are underlain and locally intercalated with ribbon cherts and argillites that range in age from Mississippian to Triassic. The Triassic basalts are conformably overlain by clastic sediments containing late Carnian–Norian conodont fauna. The tholeiitic basalts have enriched and depleted REE patterns, and have been emplaced in an oceanic environment. The compositional variations of the basalts are attributed to dynamic partial melting of source rocks that are believed to have been part of the rising mantle diapir. According to our model, after initial melting in the garnet stability field, the mantle diapir rose up to the spinel stability field where it underwent subsequent melting. The reconstructed stratigraphy of the Bridge River area may be interpreted in terms of an oceanic plate moving over a mantle plume and into a trench where offscraping preserved tectonic lenses of the subducting plate in an accretionary prism.

The Croghan Kinshelagh alkali granite intrudes a cleaved volcano-sedimentary sequenceon the border of counties Wicklow and Wexford in southeast Ireland. U-Pb dating of zircons fromthe granite indicate a mid-Caradoc emplacement age of 454 ± 1 Ma. The Duncannon Group hostrocks form the southwestern end of the Avoca Volcanic Belt, a Mid-Ordovician (Caradoc) sequenceof acid and intermediate lavas and volcaniclastics. Dolerite dykes intrude the granite; elsewhere in theregion dolerites are generally associated with volcanic rocks. The main, Dl deformation within theDuncannon Group rocks is manifest as a steep Dl cleavage generally regarded as a product of LateCaledonian regional deformation in southeast Ireland. The Croghan Kinshelagh granite showsstrong geochemical coherence with subalkaline varieties of the Caradoc volcanic rocks; relativelyhigh Th, Y, Nb and REE contents set it apart from any other known granite type in southeastIreland. Together with the geochemical evidence, the age determination of 454 Ma indicates that theCroghan Kinshelagh granite was generated and emplaced during Ordovician volcanism in southeastIreland. Volcanism was closely followed by penetrative deformation and emplacement of the granite.The intra-Ordovician deformation may have been a consequence of closure of the Iapetus Ocean ormore localized events such as accretion on the hanging wall of the subduction zone. The age of theCroghan Kinshelagh granite provides an important datum for Ordovician volcanism and subductionin southeast Ireland.

The North Dogger Fault Zone is located at the northern margin of the UK Southern North Sea Basin, at the edge of the mobile Zechstein Supergroup, and was particularly active during late Triassic and early Jurassic times. It resembles geometrically, and is related tectonically to, the Dowsing Fault Zone which was initiated in late Scythian time along the southwestern edge of the mobile salt. It is proposed that both of these basin-bounding fault systems were initiated in response to the buoyant growth of salt swells in the centre of the Southern North Sea Basin. Passive folding of the Triassic strata over the swells, which accommodated the shape changes caused by halokinesis, led to extension on the fault zones at the edge of the mobile Zechstein salt.

Dropstones are clasts which pose a hydrodynamic paradox or which have an exotic lithology with uncertain provenance. Dropstones are usually associated with glacial processes and have recently been used to substantiate the presence of cool climatic phases in the geological record. The aim of this paper is to demonstrate, using an example from southeast Spain, that dropstones can be unreliable palaeoclimatic indicators, and that greater care is required in their interpretation.

‘Lower Old Red Sandstone’ deposits preserved by cauldron subsidence at Glen Coe, Scotland have hitherto lacked secure biostratigraphical age constraint. A sporomorph assemblage recovered from basal sediments of these deposits permits age determination, despite being highly carbonized. The sporomorph assemblage is correlated with the micrornatus-newportensis Sporomorph Assemblage Biozone, indicating a late early-early late Lochkovian age (early Devonian). Sporomorph assemblages from basal sediments of the ‘Lower Old Red Sandstone’ sequence at nearby Lorne, a suggested correlative of the Glen Coe deposits, are older (latest Pridoli-earliest Lochkovian age). However, the new biostratigraphical data do not preclude the possibility that the Glen Coe and Lorne deposits are lithological correlatives and the basal sediments are diachronous.

Silurian mudstones and siltstones in the region south of Colwyn Bay, North Wales, contain numerous ‘disturbed beds’, with folds, fabrics, and other features resulting from pre-lithification deformation at or near to the sea floor. Orientation data are presented for slump folds in four areas of Ludlow rocks where the exposure allows three-dimensional measurement. The data show considerable scatter, perhaps reflecting an irregular slope morphology, and the palaeoslope inferred for each of the areas is slightly differently orientated. In general, however, the palaeoslope directions indicate that the slumps moved not eastwards, along the axis of the Denbigh Trough, as most recently suggested, but down the southern flanks of a gentle, intra-basinal swell.

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.

The uppermost Windermere Supergroup (Kendal Group) of northwest England records the passage from Wenlock and lower Ludlow deep water ‘flysch’ deposits to upper Ludlow and Přídolí shallower water ‘molasse’ deposits within an evolving foreland basin. An upwards progression is preserved from oxygen-poor basin-slope turbidite deposits through more oxygenated, bioturbated dilute density flow deposits, to storm and wave-influenced sediments. The storm-influenced sediments display hummocky cross-stratification, a Skolithos ichnofacies, shelly lags, and symmetrical wave ripple cross-lamination. Convolute lamination increases in magnitude and frequency in the upper part of the sequence, apparently nucleated above ripple crests. Tropical hurricanes probably controlled storm deposition, as suggested by late Silurian palaeogeographic reconstructions. Structures in the heterolithic muddy siltstones suggest deposition in a lower energy, wave-influenced setting. Mud-drapes, short wavelength symmetrical ripples and multi-directional ripple cross-lamination are common. The Kendal Group shows a regional palaeocurrent distribution consistent with an arcuate basin geometry, bounded to the northwest and northeast by topographic slopes. As well as a temporal trend, facies and faunal diachroneity imply a southwards migration of the foreland basin depocentre through Ludlow and Přídolí time, probably ahead of a rising mountain front to the north. The increase in pre-lithification sediment disturbance may reflect greater earthquake activity as this mountain front advanced and the basin began to invert.

Broad zones of distributed shear operating through mid-crustal regions of orogenic belts may incorporate narrow horizons of intense localized deformation culminating in discrete, large magnitude displacements. The relative importance and relationship between distributed and localized shear are influenced by a variety of factors including lithological variation, pre-existing structural anisotropy, strain rate and migration of fluids. Rigorous structural analysis of lower amphibolite facies Dalradian metasediments in northwestern Ireland demonstrates that an early (D1) discrete ductile detachment was subsequently reactivated during distributed non-coaxial D2 deformation operating in a broad zone through the structural pile. Regional shear was directed towards the southeast and resulted in the generation and translation of kilometre-scale, isoclinal, recumbent sheath folds which close and face towards the transport direction. The D1 detachment is clearly folded around the hinges of these major folds, whilst on fold limbs it was reactivated and acted as a local décollement within the zone of distributed shear. Shear criteria along the detachment indicate a southeast-directed translation of the major folds, in sympathy with regional shear. A broad zone of D3 translation operating through the nappe pile resulted in coaxial refolding of large scale F2 folds by the D3 Ballybofey Nappe producing a complex fold interference pattern. Non-coaxial D3 deformation resulted in continued reactivation of local decollements, together with the initiation of east-southeast directed oblique thrusts and partial dismemberment of D2 folds. Detailed structural investigation allows concepts of distributed and localized shear to be evaluated and models of crustal deformation to be assessed.