Post-caldera eruptions of Santorini, Greece, over the past 3000 years resulted in the formation of the Kameni Islands, which comprise a series of compositionally similar dacitic lava flows. Each lava flow has a distinct population of partially-crystalline mafic enclaves, which we propose were derived from the break-up of a layer of replenishing magma responsible for triggering the eruption. Five of the recent flows (erupted in 1570, 1939, 1940, 1941 and 1950) include enclaves of essentially identical andesitic bulk compositions, which formed by crystallization of originally aphyric melts prior to eruption. Detailed examination of angles subtended at the junctions between pairs of plagioclase grains demonstrates that enclaves from each flow have a characteristic textural signature, with distinct differences in the extent of quench-related modification of the original population of dihedral angles formed by impingement of growing grains. These variations suggest that the temperature difference between the host dacite and the replenishing andesite at the time of layer overturn and eruption differed between flows. The uniformity of major element compositions of both the replenishing magma and the host dacitic lava flows demonstrates that the critical parameter in determining the timing of layer-overturn is the pre-eruptive H2O content of both host dacite and replenishing magma. We suggest that the replenishing magma responsible for two of the three eruptions in the period 1939–1941 was significantly wetter than that responsible for the later 1950 eruption. The enclaves with the least amount of quench-related modification occur in the 1570 flow. We suggest that in this case the intruding magma was relatively dry.

A pair of samples, from host lava and an included segregation vein from the Reykjanes Peninsula, Iceland, allows the assessment of a complete fractional crystallization of an olivine tholeiite at low pressure. The final product consists of silicic glasses with bimodal composition: trondhjemitic and more rarely granitic. Compilation of data on major element compositions of Icelandic silicic rocks reveals a clear difference from those of the segregation glasses. Fractional crystallization of basalts at low pressure is therefore not the most likely mechanism for the origin of silicic magmas in Iceland. Similar conclusions have been reached in studies on O- and Th-isotope compositions. On the other hand, the trondhjemitic compositions of the glasses in the segregation vein from Reykjanes Peninsula suggest that fractional crystallization of olivine tholeiites could have played a significant role during the formation of the very early continental crust.

The Palaeogene Slieve Gullion Igneous Centre in southern Armagh, Northern Ireland, consists of a layered central intrusive complex surrounded by a prominent and slightly older ring-dyke that intrudes both Lower Palaeozoic sedimentary rocks and the Caledonian Newry Granodiorite pluton (452 Ma). The ring-dyke comprises two major rock types: porphyritic felsite and porphyritic granophyre. We analysed both ring-dyke lithologies, both types of country rock, and a local Palaeogene basalt dyke sample for Sr and Nd isotopes. Trace element and whole rock data for this suite suggest that there are two distinct groups of both felsite and granophyre: one Si-rich and one Si-poor, most likely representing two magmas from a zoned chamber and their mushy chamber wall equivalents (McDonnell et al. 2004). Isotope data show the low-Si rocks to be higher in radiogenic Sr than the high-Si rocks, which is inconsistent with a simple AFC-scenario of increasing sediment assimilation with higher degrees of differentiation. However, using MORB-type basalt as a starting composition, the low-Si ring-dyke rocks can be modelled through AFC with Lower Palaeozoic sedimentary rock as the contaminant. The decreasing 87Sr/86Sr trend from low-Si to high-Si dyke rocks, in turn, represents a second stage of contamination. Selective assimilation of the most fusible portions of Newry Granodiorite, which is lower in radiogenic Sr than the local sedimentary rocks, appears to be the most plausible solution. The Sr and Nd data are consistent with (a) at least a two-stage contamination history during upper crustal residence and storage, whereby fractionating magmas of basaltic and intermediate composition are contaminated by local sedimentary rocks, giving rise to rhyolite magmas that experience additional shallow contamination by Newry Granodiorite, and (b) a zoned rhyolite magma chamber where high-Si magma is stored in the upper part of the chamber where crystallization and crustal contamination are most extensive.

Very large volume (>1000 km3 of magma) crystal-rich dacitic ignimbrites that lack pronounced evidence of fractional crystallization or vertical zonation erupt in some continental magmatic arcs (e.g. the Lund Tuff of the Great Basin and the Fish Canyon Tuff of Colorado in western USA). Apparently, their magma chambers were only modestly heterogeneous and not systematically zoned from top to bottom. These ignimbrites have 40 to 50% phenocrysts set in a high-silica rhyolite glass. Mineral assemblages and mineral compositions suggest pre-eruption temperatures were 730 to 820°C and water and oxygen fugacities were relatively high. We have speculated that these very large volume ignimbrites are unzoned because crystallization and convection in slab-shaped magma chambers inhibited separation of crystals from liquids and resulted in a chamber filled with compositionally heterogeneous magma that lacked systematic chemical zonation or strong fractionation. However, many other very large volume silicic ignimbrites are strongly fractionated and may be vertically zoned (e.g. tuffs related to the Yellowstone hotspot). These rhyolitic tuffs typically have few phenocrysts, anhydrous mineral assemblages, low oxygen fugacities, crystallization temperatures of 830 to 1050°C, and a strong imprint of fractional crystallization. Yet these Yellowstone-type rhyolites are derived from chambers 40 to 70 km across which have sill-like shapes (depth/diameter ratios much less than 1). Thus, factors other than chamber shape must be important for establishing the degree of evolution and nature of zonation in silicic magma chambers. Here, the role of crystallinity-dependent viscosity on the evolution of these two types of contrasting magmas is explored. Calculated magma viscosities for the hot, dry, crystal-poor rhyolites are significantly lower than for the cooler, wetter, crystal-rich dacites. Perhaps these hot rhyolites had low enough crystal contents and viscosities to allow efficient crystal–liquid separation, probably by a combination of unhindered crystal-settling, floor crystallization (including compaction), and crystallization on the walls of large chambers. Clean separation of melt from residual solids at their sources may have been promoted by their high temperatures and low viscosities (<104.5 Pa s). In contrast, monotonous dacitic magmas may never have been crystal-free near-liquidus magmas. Their large magma chambers may have developed by progressive growth at a shallow level with repeated input of intermediate to silicic magma. Crystallization of the water-enriched dacitic magmas occurred at lower temperatures (<800 °C) where crystallinity and hence magma viscosity (>106.5 Pa s) were significantly higher. These characteristics inhibited all forms of crystal–liquid separation, hindered development of systematic vertical zonation, and promoted quasi-equilibrium crystallization in small domains within large heterogeneous magma chambers. Eruptions of these crystal-rich dacites may only occur if the roof fails over a growing magma chamber that is becoming increasingly molten.

The purpose of this paper is to integrate, or even modify where necessary, the geo-volcanological setting outlined by other authors on the history of the small volcanic field of San Venanzo (Umbria, Central Italy). To attain this goal, new accurate field investigations were carried out in that area, coupled with detailed stratigraphic studies and laboratory analyses, to support field evidence with experimental results. The first objective was to stress the importance of a groundwater reservoir whose interaction with magma at various degrees was responsible not only for the explosive character of volcanism in that area, but also for the complex morphology of the volcanic deposits that are widely scattered on the underlying sedimentary basement. Another objective was to clarify the role played by tectonic activity in enhancing the fast and discontinuous ascent of batches of magma from the mantle to the surface, through two different sets of faults, opened by tectonic unrest into the crust, that were also responsible for the morphology and spatial distribution of volcanic centres. This was considered to be very important in consideration of the still-active stress field of the region. Finally, special attention was focused on the presence of a palaeosol between two eruptive sequences, as it most likely denoted a split in the volcanic activity of this site into two separate phases. This observation leads to the conclusion that, in spite of its eruptive characteristics, the small volcano of San Venanzo is not monogenic. For all of these topics, a number of conclusions have been drawn and they are reported with more data in the following sections of this paper.

Mudstones and shales in the Lower Cambrian Shipai Formation in the Three Gorge area, Hubei, China, are richly fossiliferous, containing common shelly fossils and some soft-bodied fossils. The latter provide important new information about the nature and variety of Cambrian soft-bodied organisms. Identifiable, non-mineralized taxa include components of the Chengjiang fauna, such as Vetulicola Hou, 1987, a palaeoscolecidan referable to Maotianshania Sun & Hou, 1987, and a brachiopod Diandongiapista with pedicle preserved (not illustrated). Cambrorhytium Conway Morris & Robison, 1988, co-occurring both in the Burgess Shale and the Chengjiang Lagerstätte, was also recovered. Additionally, a new worm is described based on two specimens. This taxon, in common with many other fossil worms, has a slender, cylindrical body with annulations, but it is characterized by each annulus bearing an elevated ridge and lacking surface ornamentation. The occurrence of exceptional preservation in the Shipai Formation has likely been overlooked due to the relatively poor resolution of soft-bodied fossils; nevertheless, this occurrence is an important extension of the Burgess Shale-type biotas in China, over 1500 km northeast of the provenance of the Chengjiang Lagerstätte.

The radiolarian Beothuka terranova occurs in the Arenigian Didymograptellus bifidus Biozone (uppermost Lower Ordovician) of Spitsbergen (Svalbard), associated with a diverse and well-preserved radiolarian fauna. The presence of typical Cambrian spicular radiolarians associated with derived spherical forms shows a gradational faunal change from the Cambrian to the Ordovician. The genus and species Antygopora ordovicica n. gen. et n. sp. is described.

Secular variations in the carbon isotopic composition of organic and carbonate carbon characterize the Lower to Middle Cambrian transition that is exposed on the Yangtze Platform at Taijiang, Guizhou Province, southern China. δ13C values for organic matter range between −33.4 and −26.5‰. The carbon isotopic composition for carbonate carbon fluctuates between −2.7 and +3.1‰. A progressive decrease in the isotopic difference (Δδ) between these two isotope records reflects a decrease in the proportional contribution of bacterial biomass to the total sedimentary organic matter. In general, the observed changes are interpreted to reflect primary depositional values, notably variations in the burial rates of organic matter. These, in turn, are linked to biological changes across the Lower to Middle Cambrian transition. No distinct shift in the carbon isotopic composition marks the proposed Lower–Middle Cambrian boundary.

Since 1990, the Kundur locality (Amur Region, Far Eastern Russia) has yielded a rich dinosaur fauna. The main fossil site occurs along a road section with a nearly continuous exposure of continental sediments of the Kundur Formation and the Tsagayan Group (Udurchukan and Bureya formations). The sedimentary environment of the Kundur Formation evolves from lacustrine to wetland settings. The succession of megafloras discovered in this formation confirms the sedimentological data. The Tsagayan Group beds were deposited in an alluvial environment of the ‘gravel-meandering’ type. The dinosaur fossils are restricted to the Udurchukan Formation. Scarce and eroded bones can be found within channel deposits, whereas abundant and well-preserved specimens, including sub-complete skeletons, have been discovered in diamicts. These massive, unsorted strata represent the deposits of ancient sediment gravity flows that originated from the uplifted areas at the borders of the Zeya-Bureya Basin. These gravity flows assured the concentration of dinosaur bones and carcasses as well as their quick burial. Such taphonomic conditions allowed the preservation of sub-complete hadrosaurid skeletons unearthed at the Kundur site. Palaeobotanical data indicate a subtropical climate during the deposition of the Kundur and Udurchukan formations. Several elements in the composition of the Kundur vertebrate fauna suggest a strong influence of the North American late Cretaceous vertebrate communities: the abundance of corythosaur-like lambeosaurines, the probable presence of a nodosaurid dinosaur and of a eucosmodontid or microcosmodontid multituberculate. A late Maastrichtian age is tentatively proposed for the dinosaur-bearing sediments in Amur Region, by comparison with the information collected in the Western Interior Basin of North America. As it is also observed in the latter area, important floristic changes (diminution of angiosperm pollens and predominance of modern families) and the disappearance of dinosaurs mark the end of the Maastrichtian age in the Amur Region. Late Maastrichtian dinosaur localities from Amur Region are dominated by lambeosaurines, whereas these dinosaurs apparently disappeared from western North America long before the iridium horizon that defines the K/P boundary. This local disappearance is therefore probably due to ecological factors rather than indicating a gradual extinction of the dinosaurs long before the K/P boundary.

The Lower Cambrian Pardailhan Formation of the Montagne Noire (Southern France) has yielded a diverse fossil assemblage including bivalved arthropods (the bradoriids Monceretia erisylvia gen. et sp. nov., Cambria danvizcainia sp. nov. and Matthoria? sp., together with Isoxys sp.) associated with trilobites, hyolithids, inarticulate brachiopods, sponge spicules, ichnofossils and chancelloriid sclerites. This assemblage provides new evidence about the biodiversity of Early Cambrian marine communities in palaeocontinental Gondwana. The bradoriids are Cambriidae, a family with widespread distribution in offshore shelf marine environments during Early Cambrian times. The present study confirms the presence of cambriids within a subtropical latitudinal belt that encompasses Laurentia, Siberia and the Gondwanan margins from Southern France to South China. Although knowledge of the distribution of fossil cambriids is patchy, at the generic level they appear to be provincial, with Petrianna from Laurentia, Shangsiella and Auriculatella from South China, Cambria from Siberia and Gondwana (Armorica), and Monceretia gen nov. from Gondwana (Armorica). The presence of Isoxys in the Montagne-Noire confirms the cosmopolitan distribution of this genus in the Early and Middle Cambrian tropics. Cambriid bradoriids occupy a biostratigraphically narrow time interval, probably equating to part of the Atdabanian and Botomian stages of Russian terminology. Their presence in the Pardailhan Formation supports the notion of a Botomian age, determined from archaeocyathan evidence. The North American bradoriid genus Matthoria, also possibly present in the Pardailhan Formation, is reassigned to the Cambriidae.

The purpose of this study is to use the mechanisms of deformation band formation to help with interpreting the timing of phases of deformation in an area with a complex geological history. Deformation bands and zones of deformation bands are described from the quartzites of the Lower Devonian Muth Formation in the Pin Valley, NW Himalayas. Thin-section analyses show that the deformation bands in the Muth Formation formed early in the diagenetic history before porosity was lost. Deformation mechanisms involved cataclasis, translation, rotation of quartz grains and effective porosity reduction. The orientations of the deformation bands cannot be reasonably grouped with the orientations of faults related to Himalayan deformation in the Pin Valley. Additionally, the deformation bands are deformed by Eo-Himalayan (Eocene) folds, which in turn are cut by later faults. The later faults that cross-cut the Eo-Himalayan folds developed in the already-cemented Muth Formation at much higher temperature and pressure conditions by crystal plastic deformation mechanisms, indicated by quartz crystals with undulatory extinction, abundant kink bands, dislocation glide, elongated subgrains, slightly curved deformation lamellae and pronounced shape-preferred orientation. These two completely contrasting deformation mechanisms on the microstructural scale characterize two distinct fault sets that formed at different depths in the crust. Based on these differences, a pre-Himalayan origin of the deformation bands is concluded, thus representing a set of rare pre-Himalayan deformation structures. After unfolding to remove Eo-Himalayan crustal shortening, the orientation of the deformation bands and restored relative offsets of sedimentary bedding are most compatible with ∼ E–W-oriented shortening associated with N–S extension. The age of the deformation bands in the Muth Formation is bracketed by an early Devonian sedimentation age of the Muth Formation and a middle Cretaceous age of considerable cementation as deduced from compiled burial histories. Accepting a pre-middle Cretaceous age of the deformation bands, maximum conditions of about 80°C and 60 MPa lithostatic pressure during their formation are estimated from the amount of overburden during the middle Cretaceous. We suggest the deformation bands are a result of either the Neo-Tethys rifting event beginning in the early Carboniferous or the extension related to late Carnian/early Norian rapid subsidence, although a hitherto unknown deformation event cannot be excluded.

Seventy-five samples from the classic sections through the historical type area of the Ashgill Series in the Cautley district and along Pus Gill in the Cross Fell Inlier have been examined for chitinozoans. The results of this study allowed the recognition of five internationally recognized biozones and the definition of two new Avalonian chitinozoan zones. From bottom upwards, these are: the Fungochitina spinifera, the Tanuchitina bergstroemi?, the Conochitina rugata, the Spinachitina fossensis, the Bursachitina umbilicata sp. n., the Ancyrochitina merga and the Belonechitina postrobusta zones. One new species is described: Bursachitina umbilicata sp. n. This biozonation enables a correlation between the Cautley district and the Baltoscandia and Gondwana palaeocontinents based on chitinozoans. The Baltoscandic chitinozoan zones are, therefore, now better correlated with the British chronostratigraphical scheme, which is still widely used. It is stratigraphically significant that the base of the Ashgill in its type area does not fall within the Tanuchitina bergstroemi Zone, as widely believed before, but in the Fungochitina spinifera Zone. In addition, chitinozoans from the Onnian (Caradoc) section of the Cross Fell Inlier provide a link with the type Caradoc section in Shropshire.

Mudstones above coals in the eastern part of the South Wales Coalfield have yielded diverse and well-preserved palynofloras. They indicate that the Llantwit No. 1 and No. 2 seams are Stephanian in age, and thus correlate with the Household Coals Member in the Forest of Dean. Until the formation of the highest coal seam in the succession (No. 1 Llantwit Seam), conditions were progressively becoming wetter, as indicated by an increase in abundance of lycophytes and a decline in the cordaites. However, after the formation of this stratigraphically highest coal, the lycophytes declined significantly, indicating that conditions suddenly became drier, perhaps as a result of uplift of the area as the Variscan Front to the south steadily pressed forward.