The late Precambrian–early Palaeozoic Monian Supergroup of the Mona Complex is a thick sequence of flysch-type sediments and metavolcanic rocks which were deposited during the late Precambrian–early Palaeozoic and deformed during the late Precambrian and Caledonian (Ordovician/Silurian) orogenies. The Monian Supergroup includes tectonically emplaced, geographically separated outcrops of metabasalt/andesite, gabbro and serpentinized ultramafic rocks all of ophiolite affinity. The major units of the Mona Complex are separated by important faults/fault zones which may represent terrane boundaries. New chemical analyses, together with existing ones, show that the metabasalts and meta-andesites from the older New Harbour Group of north Anglesey have characteristics of suprasubduction zone arc eruptives whereas the metabasalts from the younger Gwna Group of south Anglesey and Lleyn have MORB geochemistry. It is suggested that these volcanic rocks were produced during the late Precambrian–early Palaeozoic development of the lapetus Ocean and emplaced as separate terranes during its closure.

A new geological map, mostly subcrop, of the Brabant Massif is presented, based on a revised lithostratigraphy of the outcrop area and on recently acquired palaeontological and lithological data from boreholes in the concealed area. New interpretations of magnetic and gravity data are used to extend the lithostratigraphical units into areas with few or no boreholes. A structural model of the western, northern and southern parts of the Brabant Massif is presented. The main anticlinal axis plunges towards the west-northwest, its core comprising Upper Precambrian (?) to Lower Cambrian terrigenous rocks which outcrop in the southeast. To the north of the main axis, younger rocks appear in regular succession, but to the southwest this picture is complicated by the occurrence of a second anticlinal structure and by a subparallel magmatic arc.

The U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.

White mica (illite) crystallinity data, derived mostly from borehole samples, have been used to generate a contoured metamorphic map of the concealed Caledonide fold belt of eastern England and the foreland formed by the Midlands Microcraton. The northern subcrop of the fold belt is characterized by epizonal phyllites and quartzites of possible Cambrian age, whereas anchizonal grades characterize Silurian to Lower Devonian strata of the Anglian Basin in the southern subcrop of the fold belt. Regional metamorphism in the Anglian Basin resulted from deep burial and Acadian deformation beneath a possible overburden of 7 km, assuming a metamorphic field gradient of 36 °C km-1. Late Proterozoic volcaniclastic rocks forming the basement of the microcraton show anchizonal to epizonal grades that probably developed during late Avalonian metamorphism. Cambrian to Tremadoc strata, showing late diagenetic alteration, rest on the basement with varying degrees of metamorphic discordance. During early Palaeozoic times, much of the microcraton was a region of slow subsidence with overburden thicknesses of 3.3–5.5 km. However, concealed Tremadoc strata in the northeast of the microcraton reach anchizonal grades and may have been buried to depths of 7 km beneath an overburden of uncertain age.

Volcanic and hypabyssal intrusive rocks of the Lower Palaeozoic English Lake District and Cross Fell inliers are elements of the Ordovician destructive plate margin system of microcontinental Avalonia. Two igneous sheets within the marine sedimentary Skiddaw Group of these inliers, previously described as lavas, are reinterpreted as sills. Sedimentary rocks enclosing these sills are of late Tremadoc-early Arenig (c. 493 Ma) and early Llanvirn (> 476 Ma) age, and breccias along the upper contacts of both were produced by steam explosivity and fluidization ahead of theadvancing tips of the intrusions. Previous interpretation of the breccias on the older sheet, as sediment deposited on the eroded top of a lava flow, implied an early Ordovician onset of arc magmatism. Such early magmatism would have been virtually coincident with the latest Tremadoc initiation of arc magmatism in Wales, but evidence for such a near synchronous response tothe putative onset of subduction is lacking. Respective onsets of magmatismwere probably separated by at least 17 m.y., and possibly by as much as 29 m.y. The apparent contemporaneity of mid and late Ordovician volcanic episodes in England and Wales, and similarities in extensional tectonic style, suggest that the two areas then were part of the same subduction system responding similarly to plate-scale magma-generating and tectonic processes. The early Ordovician situation is uncertain, but the absence of arc volcanic rocks of this age in the English Lake District suggests that this area and Wales are not tectonically juxtaposed elements of a former simple linear arc.

The dominant structure controlling the disposition of Dalradian stratigraphy in mid-Ulster has hitherto been regarded as a southeast-facing gently inclined F1 anticline, a gross geometry modelled on, and thought to be a possible correlative of, the Tay Nappe in Scotland. Remapping of the supposedly inverted southern limb of this major fold reveals that much of it is in fact the correct way up. However, a stratigraphie repetition coupled with a reversal in younging does occur in the Sperrin Mountains, much further south than previously realized. This hitherto unrecognized upward southeast-facing isoclinal Sperrin Nappe is, however, a D2 structure, traceable for at least 40 km along strike and responsible for a regional stratigraphie inversion over an area of 300 km2. Following D2, a major 10 km thick D3 ductile shear zone resulted in translation towards the east-southeast. In the south, this deformation carried the Dalradian over Ordovician volcanics of the Tyrone Igneous Complex along the Omagh Thrust. Penecontemporaneity of magmatism with deformation clearly demonstrates that D3 is Caledonian (Arenig-Llanvirn). This deformation correlates with similar southeast-directed Caledonian thrusting in southern Donegal and Connemara. The apparent absence of Dalradian deformation of this age in southwestern Scotland may imply that Caledonian collision of outboard terranes with the miogeoclinal margin was initiated in Ireland and/or subsequent strike-slip has removed the evidence for deformation of this age from southwestern Scotland. The D3 shear zone in the Sperrin Mountains affects a very large volume of psammitic rocks. Within this shear zone the strain is not markedly higher than surrounding areas; however, its existence is demonstrated by the reorientation of mineral lineations over a large area. Such broad zones of only moderate strain may, we believe, be typical of translatory tectonics in areas of the mid-crust where there is little lithological diversity.

Twenty-five Ordovician K-bentonite samples ranging in age from Llanvirn to Ashgill and representing both sides of the lapetus suture were analysed by INAA and XRF and compared on magmatic and tectonic discrimination diagrams. The proportional distribution of Nb, Y, Ti, Zr, Hf, Ta, Th and REE indicates that source volcanics were erupted in a setting that changed from subduction-related in the Llanvirn/Llandeilo to marginal basin extensional volcanism in the Caradoc/Ashgill. Welsh K-bentonites appear to be derived from volcanoes within the Welsh Basin, but K-bentonites from the Southern Uplands to not have characteristics consistent with a fore-arc setting, further suggesting a source related to ensialic marginal basin extensional volcanism.

The 170 Ma Straumsvola nepheline syenite complex in western Dronning Maud Land, Antarctica, is located on the eastern edge of the Penck-Jutul Trough, a major tectonic feature which may be a Palaeozoic-Mesozoic rift system. The 5 km diameter pluton consists entirely of nepheline syenite and can be divided into two volumetrically important units: a relatively structureless outer zone which is overlain by a layered zone. The latter exhibits continuous rhythmic alternations of layers containing different proportions of alkali feldspar to amphibole+Na-rich pyroxene+biotite+nepheline throughout its 350 m thickness. The mafic zone is a volumetrically minor unit which unconformably overlies the layered zone and consists almost entirely of mafic minerals and nepheline. The layered zone shows no systematic stratigraphic variation in major or trace composition or mineral chemistry which is interpreted as being due to a combination of migration of intercumulus liquid and action of deuteric fluids. The remarkably constant thickness of successive layers throughout the layered zone suggests that layering resulted from an internally self-regulating process(es). The layering is defined by changing proportions of alkali feldspar to mafic minerals+nepheline which is consistent with layering being caused by differences in nucleation rate during eutectic crystallization. Dykes associated with the complex show wide-ranging compositions and include both over-and undersaturated types. Low σ18O values of the nepheline syenites (mean 5.9%, n = 9) suggest that the magma from which the nepheline syenites crystallized was mantlederived. Peralkaline microgranite dykes have higher σ18O values (mean 7.3%, n = 4) and it is suggested that they are either undersaturated liquids contaminated by siliceous crust, or derived by partial melting of partly fenitized gneiss. Oxygen isotope ratios of the surrounding gneiss indicate that the intrusion of the nepheline syenite did not cause extensive circulation of meteoric or magmatic hydrothermal fluids.

The Lower Cambrian in northwest Scotland is one example of a Lower Palaeozoic ‘orthoquartzite-carbonate’ succession deposited on a slowly subsiding, peneplained Precambrian basement during a period of relative sea-level rise. This particular setting led to the development of a very wide, low gradient shelf which was extremely sensitive to minor sea-level changes. The basal quartz arenite section (Lower Member-Pipe Rock) is a transgressive, tide-dominated systems tract, but lacks a systematic parasequence architecture because of three factors: a fluvial sediment flux was insufficient to induce shoreline progradation, accommodation space was limited during sea-level falls (which are commonly expressed by widespread erosional surfaces), and sediment yield to the shelf by transgressive reworking was a major contributor towards the preserved stratigraphy. The storm-dominated Fucoid Beds represent a condensed section and also show the effects of rapid and widespread facies belt oscillations because of the low shelf gradient. An overlying highstand systems tract is also lacking, partly due to the absence of a large fluvial sediment yield and also due to lowstand and transgressive reworking. An erosively based tidal sandsheet at the top of the Fucoid Beds, interpreted to be a lowstand systems tract, therefore rests directly on the condensed section of the underlying sequence. This was in turn reworked into linear tidal sandbanks (Salterella Grit) during slow sea-level rise, prior to the next major transgression. The limited accommodation space therefore introduced a preservational bias towards deepening-upward trends on a parasequence and sequence scale. The oscillations in facies belts, episodic subareal exposure and the potential to remove substantial portions of systems tracts suggests that Lower Palaeozoic ‘orthoquartzite’ successions may exhibit regular and abrupt vertical shifts in depositional environment which, given their subtle lithological character, may require detailed analysis to identify. Such successions may also display incomplete development of several components of transgressive-regressive sequence architecture.

A new discovery of in situ amber is reported from the southwest coast of the Isle of Wight. The productive site is located within the Wealden Marls (Wessex Formation), generally regarded to be of earliest Barremian (early Cretaceous) age; also making this amber amongst some of the oldest known occurrences in the world. Amber globules can be found within two thin, black lignite horizons which form a channel-lag deposit exposed in the cliffssoutheast of Chilton Chine. Examination of plant material above and below this site by other workers, combined with infrared spectra of the amber in this study, implies a coniferous (possibly taxodiaceous) origin for this resin. Palaeoenviron-mental interpretation of the Chilton Chine site suggests that the amber was exuded locally, and in some cases the globules have beenpartly replaced by iron pyrite.

The Skiddaw Group comprises a marine sedimentary sequence deposited on the northern margin of eastern Avalonia in Tremadoc to Llanvirn times. It is unconformably overlain by subduction-related volcanic rocks (the Eycott and Borrowdale Volcanic groups) of mid-Ordovician age, and foreland basin marine strata of late Ordovician and Silurian age. The Skiddaw Group has a complex deformation history. Syn-depositional deformation produced soft sediment folds and an olistostrome. Volcanism was preceded (in late Llanvirn to Llandeilo times) by regional uplift and tilting of the Skiddaw Group, probably caused by the generation of melts through subduction-related processes. The Acadian (late Caledonian) deformation event produced a northeast- to east-trending regional cleavage, axial planar to large scale folds, and a later set of southward-directed thrusts with associated minor folds and crenulation cleavages. This event affected the northern Lake District probably in the late Silurian and early Devonian. The Skiddaw Group structures contrast strongly with those formed during the same event in the younger rocks of the Lake District inlier. The contrasts are attributed to differing rheological responses to varying and possibly diachronous stresses, and to possible impedence of thrusting by the combined mass of the Borrowdale Volcanic Group and the Lake District batholith.

Detailed mapping of the Precambrian rocks of the Llangynog Inlier, made possible by a series of new exposures, has allowed the establishment for the first time of the 1100 m thick succession within the Precambrian rocks of the area. All boundaries of the Precambrian rocks with younger strata in the area are either faults or unconformities. Some 350–400 m of rhyolitic lavas form the oldest rocks seen in the area; they are extensively silicified and devitrified and show little of their original texture, although flow-banding is visible in some outcrops and the presence of perlitic and snowflake textures imply that originally they were glassy in part. These lavas are succeeded by a varied succession dominated by volcaniclastic siltstones showing evidence of shallow water deposition and containing medusoids and trace fossils of Ediacaran age. Interbedded in the sediments are basaltic lavas, autobreccias and rare hyaloclastites displaying textural features characteristic of submarine eruption, and rhyolitic pumiceous and shardic ash-flow tuffs. The name Coomb Volcanic Formation is proposed for this succession, within which are recognized two members, a lower Castell Cogan Rhyolite Member succeeded by the Coed Cochion Volcaniclastic Member. In association are varied intrusions, comprising both dolerites and dacites. A palaeoenvironmental model, built on evidence of petrography, palaeontology and sedimentology is that of shallow water to emergent volcanic islands.

The biostratigraphic significance of the bivalves Buchia and Aucellina in northeast China is assessed. Buchia is abundant in four assemblages of the Dong'anzhen Formation, spanning the Jurassic-Cretaceous boundary: B. russiensis-B. fischeriana (Middle Volgian), B. fischeriana-B. unschensis (Upper Volgian), B. volgensis-B. cf. subokensis-B. cf. okensis-B. unschensis (Berriasian), and B. pacifica (Lower Valanginian). Aucellina is common in two Middle Barremian-Aptian assemblages: A. caucasica-A. aptiensis-A. jeletzkii in the lower part of the Upper Yunshan Formation, Longzhaogou Group, and in the lower part of the Chengzihe Formation, Jixi Group; A. cf. caucasica-A. cf. aptiensis in the upper part of the Upper Yunshan Formation. These assemblages can be correlated on a global scale and are particularly significant in dating the Early Cretaceous coalbearing measures of eastern Heilongjiang.

The multiphase Strath Ossian Pluton was intruded into metasedimentary rocks of the Neoproterozoic Grampian and Appin groups (Grampian Highlands, Scotland) during Silurian or early Devonian times. Emplacementfollowed the main ductile tectono-thermal history of the area and took place during post-orogenic regional uplift and cooling. Early emplacement of dioritic magma in the northern part of the pluton resulted in migmatization of its immediate country rocks with the generation of new ductile structures. The main granodiorite was then emplaced with magma migrating towards the southeast where wall-rock stoping took place. Elsewhere the pluton created its own space with little stoping or veining. Thermal metamorphism caused by granodiorite emplacement resulted in the progressive development of the assemblage quartz+ plagioclase + biotite+ cordierite +andalusite ± K-feldspar in the metapelitic country rocks. Six prograde mineral assemblage zones are identified in the aureole. Final emplacement of a marginal porphyritic microgranite was accompanied by the release of alkaline fluids into the thermal aureole. This produced sillimanite (fibrolite) in association with hydrous phases such as chlorite and white mica. The development of andalusite and cordierite-bearing assemblages is estimated to have occurred at temperatures of 650±50 °C at an estimated pressure of 3.2±0.5 kbars. An approximately isobaric temperature change of 300±50 °C across the width of the main aureole is deduced. The migmatization close to the plutons margins took place at temperatures of about 700 °C. An estimated depth of emplacement of about 11 km is obtained for the Strath Ossian Pluton. This implies considerable regional uplift both prior to, andimmediately after its emplacement. Thus it has been estimated that at the peak of regional metamorphism, probably during the Ordovician Period, the country rocks were at a depth of 15 to 18.5 km, whereas the early Devonian dykes of the Etive dyke swarm, which cut the Strath Ossian Pluton, were emplaced at, or near surface.

Investigations into the micromorphology of the Pwll Du Red Beds in Gower, South Wales, have revealed pedo-features in the form of compound void coatings. Overlying marine deposits dated to the Ipswichian (Oxygen Isotope Substage 5e), the Red Beds are interpreted as the product of sedimentation and pedogenesis during Early Devensian time.

Acritarchs of Lower Cambrian age have been recovered from a clay horizon within conglomerates 6 m above the unconformity described by Cope & Gibbons (1987). The Wrekin Quartzite (34 m thick) represents beach deposits grading upwards into shelf sandstones. The stratigraphie evidence and recent age determinations suggest that although the granophyre was intruded at 560 ± 1 Ma the Cambrian Unconformity is younger than 533 ± 13 Ma.

A concentration of exceptionally well-preserved large tubular foraminifera occurs on a specimen from the sole of a sandstone bed from the Eocene Zumaya flysch. The foraminifera were probably washed out from the sediment by a weak bottom current, orientated and concentrated in a pre-existing depression on the ocean floor. Fortunately, subsequently deposited turbidite sand, which forms the host bed, only disturbed the fossils to an infinitesimal degree.

Regional variation of white mica (illite) crystallinity in the Skiddaw Group is set against the structural interpretation of Hughes, Cooper & Stone (1993, this issue) in which early- or pre-Ludlow deformation and slaty cleavage development (S1) were succeeded by southward thrusting and an associated development of S1 and S1 crenulation cleavages, possibly during early Devonian times. Kubier index (KI) values are plotted in relation to geological structure for a major part of the Skiddaw Group, and cross-sections constructed. The pattern is interpreted in terms of three processes: (1) diagenetic to low anchizonal burial metamorphism under a relatively high geothermal gradient during the late-arc stage (early to mid-Silurian) which preceded the orogenic phase and formation of S1; (2) upper anchizonal to epizonal metamorphism due to tectonic thickening and slaty cleavage development during the early to pre-Ludlow orogenic phase following closure of Iapetus; (3) late-tectonic uplift of already metamorphosed rocks by southward-directed movement on the Loweswater, Gasgale Gill and Causey Pike Thrusts possibly during early Devonian time. An analogous interpretation is made for the Skiddaw area, though with the addition of major post-S1 contact metamorphism.