These papers arise from the conference in Bristol, England, of the above international Working Group, which was held in the University of Bristol conference centre from 9–13 May, 1983. Forty-five persons attended; thirty-two were members of the Working Group (about a third of the total membership which is drawn from about twenty countries in many parts of the world from Australia to Argentina and from Korea to western Canada.)

Many explosive eruptions of dacitic magmas have occurred on St Lucia during the late Quaternary. These have produced widespread aprons and fans of pumice flow and ash flow deposits radiating around the central highlands, with co-eruptive air-fall and surge layers interbedded with palaeosols and epiclastic deposits. Vents in the highlands have not been located because of the dense tropical jungle but we suspect they are now plugged by lava domes surrounded by aprons of block and ash flow deposits. Young magmatically related dacitic lava domes have been extruded in the Qualibou depression. The pumice succession can be divided into older quartz-poor deposits forming the Choiseul Pumice and younger crystal-rich deposits with abundant large quartz which are called the Belfond Pumice. The Choiseul Pumice groups together scattered remnants of the products of many eruptions of different low-silica dacitic magma types. The Belfond Pumice is the product of several eruptions of a high-silica magma type and 14C ages have dated these between 20900 to 34200 years B.P.

The pumice flow deposits occur as small-volume valley fills. A granulometric study of Belfond pumice flow deposits shows them to be strongly depleted in finer ash and vitric components. It is suggested that the narrow, winding and vegetated valleys on the island locally induced turbulence and the flows moved with large, highly fluidized and inflated heads, resulting in substantial loss of fine vitric ash. One ash flow deposit which is extremely rich in crystals and carbonized vegetation is highly depleted in fines and shows enhanced vitric losses. This flow may have been a much more violent ash hurricane or blast which surmounted topography ingesting large amounts of lush vegetation. Ignition of this released the large quantities of gas needed to elutriate most of the fines.

A model is suggested for the recent volcanic activity on St Lucia in which separate batches of silicic magma, each having a distinctive petrological and chemical character, rose into high level chambers over a large area. Eruptions of volatile-rich magma led to highly explosive pumice-forming activity from vents in the central highlands. Degassed and more crystal-rich magma was extruded later from the same vents or in the attenuated flank of the Qualibou depression to from lava dome complexes.

The Alpine tectonics in the Pyrenean Range is controlled by motions of basement blocks (High Primary Range, North Pyrenean blocks). These blocks belong to different tectonic units; they are amygdaloid, wedge-shaped, squeezed at their roots, upthrust and displaced with their cover (detached or not) in a convergent shear zone between the European and Iberian plates. These basement blocks are distributed within isopic (isofacial) units with diachronous terrigenous prisms. The stratigraphical analysis of their Mesozoīc cover reveals their relative position during the Mid-Cretaceous continental break-up which induced the separation of the two previously joined plates.

Potassium–argon dating, field relations, geochemical and strontium-isotope compositions are reported for the island of Pantelleria (Strait of Sicily, Italy). These data support the following model for the genesis and evolution through time of the volcanic system: the peralkaline rocks originated from mantle-derived parental magmas; the trachytic magma differentiated in a low pressure magma chamber by crystal–liquid fractionation. This process led to a chemically zoned magma chamber tapped at different levels by successive eruptions. During low-pressure differentiation the 87Sr/86Sr ratios of some of the most evolved Sr-poor rhyolitic magmas increased from 0.703 up to 0.708 by contamination with crustal material.

The chemical variation displayed by the products of each of the defined eruptive cycles in the last 50000 years suggests an open system behaviour of the magma chamber which is episodically refilled by more mafic parent magma, differentiated at high rate and episodically erupted.

Modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies, supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography. A computer program has been written and used to identify modes in the zircon fission track age distribution within two Lower Cretaceous sandstone samples from the Weald of southern England. Pronounced modes appear in one rock around 119 Ma, 160 Ma, 243 Ma and 309 Ma and in the other around 141 Ma, 175 Ma, 257 to 277 Ma and 394 to 453 Ma. The geological implications of these quite dissimilar zircon age spectra are discussed. It is concluded that they support the palaeogeographical models of Allen (1981) and indicate that the provenance of the first sample, from the Top Ashdown Sandstone member at Dallington in East Sussex, was almost entirely southerly, while that of the second, from the Netherside Sand member at Northchapel in West Sussex, was more varied, but predominantly westerly and northerly.

Image analysis is rapidly becoming an integral part of scanning electron microscopy. A number of analogue and digital image analysis systems of varying sophistication are now commercially available for the SEM. This paper illustrates how one such relatively simple system, the IMAS image analyser manufactured by Cambridge Technology, can be used to obtain rapid quantitative estimates of porosity and mineral abundance in backscattered electron images of polished rock sections.

Neogene and Lower Pleistocene stratigraphy in the Southern North Sea has been investigated in four I.G.S. boreholes between East Anglia and the Netherlands. The foraminifera of the Red Crag Formation in Borehole 81/51 are closely similar to Upper Pliocene assemblages in Holland. The overlying succession is clearly punctuated by unconformities in seismic profiles, separating four early Pleistocene formations in the boreholes, and indicating intervals of significant stratigraphic hiatus offshore. The Westkapelle Ground and Smith's Knoll Formations correlate with Thurnian and Antian Stage deposits in East Anglia. Pollen spectra in the Winterton Shoal and Yarmouth Roads Formations are similar to Baventian and Bramertonian assemblages in Britain. The autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early Pleistocene palaeoclimate. The dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment. The pollen record, containing evidence of fluctuation between boreal and mixed coniferous–deciduous regional forest cover, suggests alternation between cool and warm temperate palaeoclimate.

From the Triassic to the Late Eocene, the Iberian Peninsula underwent three successive rotations with respect to the stable European plate, (a) Prior to the Late Aptian, a nearly 150 km southwestward motion resulted in stretching and thinning of the continental crust beneath the North Pyrenean zone, the Aquitaine Basin and the Bay of Biscay continental margins (rifting). Distensive structures trended 90° N to 130° N, and were shifted by 30° N to 50° N transform faults. (b) During the Late Aptian to Santonian interval, an approximately 400 km southeastward motion resulted in the opening of the Bay of Biscay and sinistral slipping of Iberia along the North Pyrenean transform zone (drifting), (c) During palaeocene–Eocene time, a 150 km northwestward convergent motion resulted in limited subduction of the oceanic crust of the Bay of Biscay beneath the Iberian plate, and folding of the Pyrenean chain. The folded belt resulted from squeezing of the former European and Iberian margins (rifted or transform margins, depending on the segment considered).

Relevant points of general principle and special application to the problem under discussion are quoted selectively from the recently published time scale by Harland et al. (1982) and critically considered. Most of the principles and the resulting names for divisions of the Precambrian–Cambrian transition used in it are accepted. The unique significance of the transition from dominantly chronometric to dominantly chronostratic boundaries based on the ‘biostratigraphic sequence’ is an additional justification for the higher ranks previously given to the Vendian (Era) and its constituent divisions: Varangian (or Varangerian) and Ediacaran (or Ediacarian) Periods. The historic transition begins with the latest of the Proterozoic glaciations (the earlier ones started about 950 m.y. ago) and ends with the exponential diversification of the Metazoa. The causal linkage of the two events is hypothetical. Their stratigraphic sequence is demonstrable on the East European platform where the type section of the Vendian is located, and on the Yangtse platform. Normative, operationally designated boundaries are required for the stratigraphic divisions. The history of life in which there are no sharp initial and terminal boundaries shows clearly a rapid transition from widespread but generally rare occurrences of Vendian, particularly Ediacaran, fossils to ubiquitous, generally ‘shelly’ Palaeozoic (initially Cambrian) faunas of unquestioned biostratigraphic importance. This biohistoric transition is the beginning of the Phanerozoic division of a unique historic process. For the Eon of the stratigraphic scale comprising Palaeozoic to Cainozoic Eras the new term Holozoic is therefore proposed.

In the Miocene fluvial system of the Huesca area, in the Ebro Basin, northern Spain, rivers radiated outwards, to the south and west, from a small sector of the northern margin of the basin. The deposits of the system extend about 60 km radially from this sector and then pass into calcareous and gypsiferous deposits.

The magnetostratigraphy of two logged sections, 1 km apart, within this system consists of an upper zone of normal polarity and a lower zone of reversed polarity. The lithostratigraphy and magnetostratigraphy are parallel.

The sands and silts are dominated by angular quartz, intraformational clay lithograins and calcite lithograins. They are mainly pale yellow brown to dusky yellow, and magnetic tests indicate that the magnetization is carried dominantly by ferric oxyhydroxides (haematite and gôethite). The higher temperature Natural Remanent Magnetization is probably due to detrital haematite which would have been partially aligned during fluvial deposition. Post-depositional modification (PDRM) may have occurred during dewatering.

Haematite pseudomorphing pyrite framboids indicates that early reducing conditions were succeeded by a more oxidizing regime which produced secondary magnetizations associated with fine-grained haematite and goethite.

Complete polarity zones are not delineated, but the thicknesses present are not excessive compared with other continental Miocene deposits. The average palaeolatitude of 22° is lower than would be expected for the Miocene of northern Spain, probably due to incomplete averaging of secular variations and other sources of error including possible ‘inclination error’.

We present chemical data on magmatically heterogeneous pyroclastic deposits of late Quaternary age erupted from zoned magma systems underlying Tenerife (Canary Islands), Sao Miguel and Faial (Azores), and Vesuvius. The most fractionated magmas present at each centre are respectively Na-rich phonolite, trachyte, and K-rich phonolite. Within any one deposit, chemical variation is either accompanied by changes in the phenocryst assemblage (petrographic zonation) or is largely manifested in trace element abundances, unaccompanied by any petrographic change (occult zonation). Zoning is analogous to that in calc-alkaline systems where the most fractionated products are high-silica rhyolites. When a range of magma types are considered, a correlation emerges between roofward depletion of trace elements (especially REE) in the zoned system and compatability of those same trace elements in the accessory phenocryst phases present. Thus, allanite- or chevkinite-bearing rhyolitic systems are light-REE depleted roofwards, the sphene-bearing Tenerife system is middle-REE depleted roofwards, the melanite-bearing Vesuvius system is heavy-REE depleted roofwards, while the Azores systems, which lack these phases, display roofward REE enrichment. Therefore, the behaviour of trace elements may in each case be explained by fractionation of observed phenocryst assemblages. The resemblance between features of zoned magma systems and published work on the dynamic consequences of cooling saturated aqueous solutions prompts us to suggest that sidewall crystallization and consequent boundary-layer uprise to form a capping layer at top of the system may be a plausible mechanism for the generation of both petrographic and occult zonation. Reverse zoning occurs among the first-erupted tephra of some deposits, demonstrating that the most highly differentiated magma available is not always the first to be tapped during an eruption from a zoned system.

The Tremadoc Series and series of the Ordovician System are widely used in international correlations, and this review explains and summarizes how the base of each of these series is recognized in Britain. No type section in which the base of any one of them is displayed has ever been selected and formally designated, hence the basal horizon of each series is a matter of general understanding rather than precise definition. This general understanding is of particular biozones, or of assemblages of fossils and their relative ages. The geographical separation between type sections of series, and differences in facies, complicate the understanding of relative ages of biozones. Brachiopod and trilobite faunas of the Llandeilo, Caradoc and Ashgill Series have been studied in detail in recent years, and biozones proposed. These biozones have proved difficult or impossible to recognize outside their type areas in Britain, and brachiopod–trilobite faunas of the Tremadoc, Arenig and Llanvirn Series are likewise highly provincial. Thus for correlation within and outside Britain attention has been focused on the ‘standard’ graptolite biozones, particularly since such conodont faunas as have been found have not proved useful. Yet there are problems associated with these ‘standard’ biozones; for example, the Tetragraptus approximatus Biozone is unknown in Wales or England, the relationship between the base of the Glyptograptus teretiusculus Biozone and the earliest Llandeilo shelly faunas requires clarification, and at what level the base of the Caradoc Series may lie in the Nemagraptus gracilis Biozone is unknown.

Thus to bring precision to definitions of Ordovician Series in Britain the identification of continuous, fossiliferous sequences that will serve as stratotypes, is required. Such a section for the basal portion of the Tremadoc Series has recently been proposed. Systematic studies related to particular biozones are needed, for example early Caradoc and early Ashgill brachiopods, and graptolites of the Didymograptus bifidus and Glyptograptus teretiusculus Biozones. The stratigraphical ranges and abundances of species in particular sections require documentation, so that the type of biozone (assemblage, acme, concurrent-range, etc.) may be recognized. Such work could lead towards chronostratigraphy, the provision of a standard stratigraphical scale in Britain for the Tremadoc Series and Ordovician series.

Recent interpretations of Cenozoic arc systems and collision belts facilitate reinterpretation of some aspects of British Caledonide evolution. End-Cambrian ‘Grampian’ collision of the passive ‘Dalradian’ foreland following southeastwards subduction beneath an island arc was accompanied by initiation of the Highland Boundary Fault as a high-angle south-directed oblique-slip thrust. Mid-Ordovician to early Devonian northwestward oblique subduction of the Iapetus Ocean beneath the Grampian orogen resulted in a continental margin magmatic arc, back-arc thrusting and development of an accretionary prism, while southeastward subduction led to arc magmatism and back-arc extension followed by initiation of the Rheic Ocean as a back-arc marginal basin; this syn-subduction N–S asymmetry of the Iapetus Ocean margins was analogous to the E–W asymmetry of the modern Pacific. Closure of Iapetus was diachronous, earlier in the northeast: during end-Silurian collision the southern Caledonides behaved as a passive foreland; post-collision foreland thrusting resulted in deposition and deformation of Lower Old Red Sandstone foreland basin deposits in Wales, and probably in northwest-directed back-thrusting in the region of the Longford-Down accretionary prism. Subsequent dextral movement in the suture zone juxtaposed the southern Caledonides with Scotland and northern Ireland, beneath which northwestward subduction had continued into the early Devonian.

During the Palaeogene Alpine compression three units were differentiated in the studied area (south of the Ebro Basin): the Catalan Coastal Range, dominated by NE–SW major basement faults with a sinistral movement; The Iberian Range, where the important basement faults have a NW–SE direction and a reverse movement (often with a dextral component); the Linking Zone, between these two ranges, where an E–W dominant structural direction is marked by an array of folds and thrusts (with a northward vergence) in the Mesozoic cover.

From the analysis of both these major structures and the small-scale structures, it can be deduced that the compression in the studied area has evolved from a NW–SE direction (lower-middle Eocene) to a N–S direction and to a NE–SW one (uppermost Oligocene). The major structures are due to the N–S compression. Later, the stress-field progressively changed to a distensive regime.

We suggest a relation between the compressive phases and the displacement direction of the Iberian Plate with reference to the European Plate.

Being located in Jinning County, Yunnan Province, approximately 103° E, 25° N, the Meishucun section has a long history of study, convenient accessibility, mild spring-like climate all the year round and good exposures of the relevant strata. In the particular area there occur monofacial transitional carbonate deposits of marine origin, yielding in great abundance both small shelly fossils and trace fossils, which are present in close association and in some cases on the same bedding surface. The sequence of biotic assemblages is clearly evident and can be used for wide intercontinental correlation.

In the lower part of the Qiongzhusi Stage, stratigraphically higher, there appear the oldest trilobites, archaeostracods and Baltisphaeridium characteristic of the Early Cambrian.

During the last six years great progress has been made in the study of the particular section through lithostratigraphic, biostratigraphic, geochronological, magnetostratigraphic and seismostratigraphic approaches, thus making the Meischucun Stage and the Sinian–Cambrian boundary stratotype section in the Meishucun area a Chinese candidate for global stratotype section and point for the Precambrian–Cambrian boundary.

Reconnaissance geological mapping (1962–75) followed by detailed geological investigations (1979–80) in the Ellsworth Mountains of west Antarctica have established the existence of extensive Middle and Late Cambrian strata. Forms tentatively referred to Archaeocyatha have been examined by F.D. and A.R., who concluded that, despite the commonly held opinion that the phylum became extinct at the boundary of the Lower and Middle Cambrian, the Ellsworth Mountains' forms represented Irregularian Archaeocyatha which survived in protected niches into the Late Cambrian. The age of the fauna containing the archaeocyaths is firmly dated by abundant trilobites including species of Homagnostus, Pseudagnostus, Kormagnostella, Erixanium and Onchopeltis.

The structure of the northern part of the Arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region. The Palmyra and Sinjar zones share a common history of development involving two stages of rifting, one in the Triassic–Jurassic and the other during late Cretaceous to early Tertiary times. Deformation of the Palmyra zone during the Mio-Pliocene is attributed to north–south compression on the eastern block of the Dead Sea transcurrent system which occurred after continental collision in the north in southeast Turkey. The asymmetry of the Palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow Triassic evaporites. An important NW-SE cross-plate shear zone has been identified, which can be traced for 600 km and which controls the course of the River Euphrates over long distances in Syria and Iraq. Transcurrent motion along this zone resulted in the formation of narrow grabens during the late Cretaceous which were compressed during the Mio-Pliocene. To a large extent, present day structures in the region result from compressional reactivation of old lineaments within the Arabian plate by the transcurrent motion of the Dead Sea fault zone and subsequent continental collision.

On the basis of previous work in Northern England and in Southern Scotland the Pusgillian Stage is in turn related to the stratigraphical ranges of selected trilobite species and to the standard graptolite zonal scheme. Thus characterized it can be recognized in rocks of ‘shelly’ facies at localities in the northwest, southeast and south-central Berwyn Hills of North Wales and possibly in the Llandeilo area of South Wales, but does not seem likely to be developed in any rocks of graptolitic facies in Wales.

Primary compact bone is ignored in some recent discussions of claims that dinosaurs were endotherms, but forms the basis of one of the arguments from bone, and part of the basis of another. This paper explains its histology and discusses its possible significance. In dinosaurs the primary compact bone was commonly fibre-lamellar bone, resembling bone seen in many large mammals, and implying a capacity to sustain rapid growth to large sizes. This probably indicates some physiological difference between dinosaurs and modern types of reptiles; but similar bone is present in early therapsids, which were probably not endotherms, and bone with typical reptilian ‘growth rings’ was sometimes formed. Endothermy is also unlikely in most kinds of dinosaurs, if its evolution requires a trend to small sizes; but perhaps they were ‘failed endotherms’.

The present work describes the quartz geodes (cauliflower-like) that appear in a specific level of the Late Cretaceous (north of Burgos). Due to their special characteristics, principally anhydrite relicts and spherulitic quartz (length-slow chalcedony), they are considered as pseudomorphs of anhydrite nodules, formed during early diagenesis. At the same level compact chert nodules sporadically appear, presenting a considerable amount of sponge spicules with fibrous texture (length-fast chalcedony). The silicification of the anhydrite nodules took place before total compaction and cementation of the sediment. The source of silica is principally biogenic (sponge spicules). We offer a hypothesis to explain the formation of the anhydrite nodules since there is no link between the depositional environment and the existence in itself of anhydrite nodules. Indirectly it is possible to see the effects of an arid climate, which have not been recorded in the lithologic column here described.