Conodont colour alteration index (CAI) values from Upper Paleozoic rocks in the Cantabrian zone of northern Spain show that temperatures during Hercynian metamorphism locally exceeded 300 °C. Various temperature domains have been defined, which are generally separated by fundamental structures. These domains do not correspond with the tripartite subdivision based on stratigraphic analysis.

The observed CAI values of conodonts are in general agreement with the mineral paragenesis. Areas with high CAI values display extensive alteration and mineralization, and where CAI values exceed 4–4.5 (>200 °C) slaty cleavage has developed.

The Cantabrian zone is an area of very low grade metamorphism, where peak conditions were reached in Upper Carboniferous to Lower Permian times. The characteristics of the metamorphism and its spatial relationship with major faults suggest that fluids were the main source for regional heating and that fluid transport was focussed along crustal-scale structural features.

The overall deformation regime in this part of the Variscan orogen of western Europe is interpreted to be large-scale transtension. This is in agreement with earlier proposed models for the formation of Upper Palaeozoic basins in this area.

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.

Carbon isotopic data from the Selinde section in the southeastern part of the Siberian platform area are correlated with the reference isotopic profile from the Lower Cambrian stratotype sections of the Lena–Aldan region, but also show additional δ13C excursions unrecognized there. The chemostratigraphic correlation suggests that the geological and fossil record of the lower Pestrotsvet Formation in the Selinde section has a deeper history than the stratotype region. This conclusion is important for both constraining the age of the earliest Cambrian marine transgression on the Siberian platform and providing a clearer understanding of the pace and order of early Cambrian geochemical and biological events.

The lithostratigraphic characteristics of the iconic Blue Lias Formation of southern Britain are influenced by sedimentation rates and stratigraphic gaps. Evidence for regular sedimentary cycles is reassessed using logs of magnetic susceptibility from four sites as an inverse proxy for carbonate content. Standard spectral analysis, including allowing for false discovery rates, demonstrates several scales of regular cyclicity in depth. Bayesian probability spectra provide independent confirmation of at least one scale of regular cyclicity at all sites. The frequency ratios between the different scales of cyclicity are consistent with astronomical forcing of climate at the periods of the short eccentricity, obliquity and precession cycles. Using local tuned time scales, 62 ammonite biohorizons have minimum durations of 0.7 to 276 ka, with 94% of them <41 ka. The duration of the Hettangian Stage is ≥2.9 Ma according to data from the West Somerset and Devon/Dorset coasts individually, increasing to ≥3.7 Ma when combined with data from Glamorgan and Warwickshire. A composite time scale, constructed using the tuned time scales plus correlated biohorizon limits treated as time lines, allows for the integration of local stratigraphic gaps. This approach yields an improved duration for the Hettangian Stage of ≥4.1 Ma, a figure that is about twice that suggested in recent time scales.

Two-phase packets of crystals plus liquid form rapidly at a magma contact having a high thermal contrast with its surroundings. The packets can detach from an upper contact and settle rapidly with respect to crystal settling or turbulent stirring velocities. They carry crystals and supercooling downward and act as heat sinks for crystallization of floor cumulates. Evolution of picritic magma toward neutral buoyancy and overturn into overlying basalt magma proceeds most efficiently with two-phase convection. Sinking of hot bronzite-laden liquid into cooler anorthositic liquid destroys the liquid stratification within a day or so. Two-phase convection rarely yields crystal mush thicknesses suitable for compaction of cumulates, which occurs only for a narrow window of cooling rates. Two-phase convection leads to cool, thin boundary layers above and below hot interior magma and may tend to prevent or control turbulence. The critical timing and scale of two-phase layer detachment need further study.

Teeth from the Early Cretaceous Napai Formation of Fusui County, Guangxi Zhuang Autonomous Region (South China), initially described as the sauropterygian Sinopliosaurus fusuiensis, are redescribed as belonging to a spinosaurid theropod closely allied to Siamosaurus suteethorni, from the Early Cretaceous of Thailand. This identification extends to China the geographical range of Asian spinosaurs, previously reported from Thailand and Japan.

Fieldwork forms the basis of geoscience studies. However, field activities present limitations for people with mental or physical impairments. This aspect can preclude participation in field trips by certain groups of students or limit their experience. In recent years, new types of supporting material and the development of accessible field trips have been a step forward towards the reduction of barriers to inclusion and equal opportunity. In the present work, normal practices of field teaching and potential solutions (and their limitations) to foster inclusion and accessibility to fieldwork are presented.

A study of the morphometry of an ephemeral stream system which is incising itself into a terrace of the Farmington River, Connecticut, supports the regional relationship between stream-channel gradient and valley-side slope angle suggested by Strahler (1950). The continuing areal extension of the system allows stream order to be employed here as a relative measure of the passage of time. Thus it is possible to recognize that steepening and parallel development of a given valley-side slope may have their place in a sequence of early stage erosional development characterized by headward channel extension and ramification.

An earliest Llanvirn age is established on micropalaeontological grounds for the interbedded lava–pelite sequence at the base of the Binsey Volcanic Formation in the northern Lake District. The northern volcanic sequence, here termed the Eycott Volcanic Group, is earlier than, and chemically distinct from, the main Borrowdale Volcanic Group. The evidence precludes a regional unconformity between the Skiddaw Slates and the overlying volcanic rocks, but is compatible with the hypothesis that the vulcanicity occurred in an island arc environment.

A detailed investigation of a glauconite bed within the Late Cretaceous Bryozoan Limestone Formation of the Bagh Group in central India, as well as the study of existing records, reveals the existence of a ‘glauconitic sea’ along the margins of the Palaeo-Tethys Ocean during the Late Cretaceous Epoch. The authigenic green mineral formed abundantly on shallow seafloors unlike in its modern, deep-sea counterpart. We present an integrated petrographical, geochemical and mineralogical investigation of the glauconite within Late Cretaceous transgressive deposits to highlight its unique geochemistry with moderate Fe2O3 and high Al2O3, SiO2, MgO as well as K2O contents. X-ray diffractional parameters identify the ‘evolved to high evolved’ nature of the glauconite while Mössbauer spectroscopic study reveals the dominance of Fe3+ compared to Fe2+ in the atomic structure. The rare earth elements (REE) pattern of glauconite reveals moderate light-REE/heavy-REE (LREE/HREE) fractionation and weak negative Eu anomaly. The Ce anomaly of the glauconite indicates a sub-oxic diagenetic condition. We propose that Late Cretaceous glauconites formed within a shallow marine depositional setting across the Tethyan belt because of enhanced supply of K, Si, Al, Fe, Mg cations through continental weathering under the extant greenhouse climate.

Geochemical (δ13C, δ18O and Mn) compositions of Lower Jurassic shallow-water carbonates cropping out in Croatia were analyzed to elucidate the impact of the early Toarcian oceanic anoxic event (T-OAE) on the Adriatic Carbonate Platform (AdCP). The bulk-rock carbon-isotope records through the studied sections (Velebit-A, Velebit-B and Gornje Jelenje) are characterized by two significant excursions: (i) an initial positive trend interrupted by a pronounced negative shift (c. 2.5‰) that is followed by (ii) an increasing trend of positive values (up to 4.5‰). A comparison with δ13C trends obtained from well-calibrated sections from other localities in Europe shows that the overall character of the early Toarcian negative excursion is clearly reproduced in the curves derived from Croatian shallow-water deposits, which helps to date the sequences and reinforces the global character of the carbon-cycle perturbation. Lower Jurassic sedimentary successions in the studied area show a gradual deepening trend corresponding to deposition of the Toarcian spotted limestones. Assuming that the distinctive negative excursion in the carbon-isotope curves is synchronous across the AdCP, the contact between the spotted limestones and the underlying beds rich in lithiotid bivalves appears to be diachronous within the study area. The Mn record through the Croatian Velebit-A section and, in particular, the rise in concentration (up to 100 ppm) coinciding with the beginning of the δ13Ccarb positive shift, reflects a change in the redox conditions in seawater that allowed diagenetic incorporation of reduced manganese into the calcite structure of the carbonate sediment during the onset of the T-OAE.

A recent hypothesis concerning the age of orogenic deformation of the Skiddaw Slates in the English Lake District has proposed that the main slaty cleavage (S1) and superimposed subhorizontal crenulation-cleavage (S2) are of intra-Ordovician age. A study of the fabric of the aureole of the (end-Silurian) Skiddaw granite shows that the granite was emplaced towards the end of the D1 deformation phase, but before the formation of S2. These structures are therefore of broadly end-Silurian age, and evidence of an intra-Ordovician orogeny in this area is lacking.

Detailed analysis of trilobite assemblages at the Cambrian–Tremadoc transition reveals the presence of four, possibly five, biogeographic provinces: Baltic, North China, Southeast China, North American, and possibly Siberian. One or more discrete biofacies characterize the transition in each province. When plotted palaeogeographically these appear to be largely temperature controlled. Interdigitation of provincialized trilobite biofacies is recognized by the representation of dominant types of trilobite, olenaceans, ceratopygaceans, remopleuridaceans, dikelocephalaceans and leio-stegiaceans in particular, on key boundary sections. These sections, at Nochixtlán, Mexico; Batyrbay, southern Kazakhstan; Broken Skull River, District of Mackenzie, Canada; and Jiangshan–Chang-shan, western Zhejiang, China, permit the correlation of biogeographic provinces globally. As a result of the application of trilobite biostratigraphy relatively few problems prevent the maintenance of a Cambrian–Ordovician Boundary stratotype section in its traditional Baltic biogeographic setting.

Tightly clustered Sm–Nd model ages, with an average of 1.96±0.02Ga, for the gneiss complex of Inishtrahull indicate coeval development with the earlyProterozoic gneiss terrane of Islay. The extent of this terrane, largely beneath the Dalradian Supergroup, is argued to be 100×600 km, from northeast Scotland to western Ireland. This is based on the distribution of dated basement in conjunction with Pb, Sr and Nd isotope systematics and inherited zircons in Caledonian granites of the region.

The westward continuation of the Highland Border fault of Scotland (HBFZ) into Ireland is problematic. It is widely thought to follow a pronounced magnetic and gravity lineament, the Fair Head-Clew Bay Line (FCL). The advantage of this interpretation is that it places all the Ordovician ophiolitic complexes and associated sedimentary basins to the south of the FCL, which would represent the contact between Laurentia and the outboard terranes. Its main shortcomings are that both the deep structure and timing of strike-slip are different on the HBFZ and FCL. In Ireland the FCL is a north-dipping feature that can be traced to the Moho on BIRPS profiles, while the HBFZ has no such signature. Terrane amalgamation in western Ireland was completed by the late Ordovician, while in Scotland the Midland Valley terrane did not finally dock until the early Devonian. These considerations suggest that in western Ireland a branch of the HBFZ exists, which was active in post-Ordovician time and must lie south of Connemara. An examination of Irish geological, geophysical and image-processed magnetic data shows that a profound lineament can be traced from Antrim to Galway Bay (the Antrim–Galway Line). Stitching plutons date movement on it as pre-405 Ma. We propose that the Antrim–Galway Line represents the continuation of the Scottish HBFZ, while the FCL is a preserved Ordovician splay of the HBFZ system whose northdipping geometry is a product of Ordovician collapse of the orogen in western Ireland.

Curved and other variably oriented minor F1 folds with a common axial–planar cleavage are described from the Dalradian of the South-West Scottish Highlands. An explanation for the varying orientations is offered in terms of progressive deformation following the arguments of Flinn (1962) and Ramsay (1967).

Six sections through lower Ordovician shale and limestone at Hunneberg have been sampled for conodonts. Forty-nine limestone horizons and 34 shale surface samples yielded over 40000 conodont elements. The degree of biostratigraphic resolution permitted further subdivision of the post-Tremadoc Paroistodus proteus Zone into four successive intervals. Preliminary studies of coeval rocks in other areas of Sweden show that this subdivision applies elsewhere as well. Comparison with published sections from, for example, Newfoundland, Estonia and Kazakhstan indicates that the fourfold subdivision of the P. proteus Zone proposed here could significantly increase the correlation accuracy, even internationally, within this critical part of the Ordovician. Graptolites and trilobites found together with the conodonts at Hunneberg indicated that the new subdivision could help to correlate biostratigraphic units based on these fossil groups. Thus the two lower intervals of the P. proteus Zone correspond to the M. (E.) armata trilobite Zone, and the upper two are approximately equal to the M. (V.) planilimbata Zone. The base of the T. phyllograptoides graptolite Zone at Hunneberg lies close to the boundary between the upper middle and uppermost intervals of the P. proteus Zone, but the graptolitic chronozonal boundary may be lower. The overlying Prioniodus elegans Zone is mainly represented by graptolitic shale at Hunneberg, but conodont faunas have been found in it, and co-occurrences of conodonts and graptolites have been noted.

In the Early Cambrian, there were two peaks of the increase in number of new archaeocyathan genera. These diversification bursts are, perhaps, related to significant changes in Early Cambrian palaeogeography. The first burst at the beginning of the Atdabanian was, perhaps, connected with the initiation of archaeocyathan expansion beyond the Siberian Platform. During the second half of the Atdabanian, closely related archaeocyathan assemblages were established from North Africa to Australia because neither climate, nor geographic isolation could have affected their differentiation in that time. At the end of the Atdabanian and the beginning of the Botomian the number of archaeocyathan genera again increased sharply, and isolated provinces were established. The American–Koryakiyan province was formed in western North America (from Alaska to Sonora) and included the Koryakiya, while the Afro–Siberian–Antarctic province probably extended from North Africa and Western Europe to Siberia, Australia, and Antarctica. The main difference between the regular archaeocyathan assemblages lies in what skeletal elements filled the intervallum. There was a certain stability in the distribution of skeletal elements of high taxonomic rank and an interchangeability of elements of low taxonomic rank.

The pattern of crustal warping in northern Spitsbergen as a result of widespread deglaciation is plotted. This is facilitated by the occurrence on ancient strandlines of pumice fragments at 4 major horizons 14C dated at 6500 (A), 6200 (B), 4100 (C) and 2200 years b.p. (D). Trace element analyses indicate an origin for the pumice in the Jan Mayen area. At least 2 pumice horizons are thought to be contemporaneous with eruptions at 6500 and 4100 years b.p.

The concept of tectonic regimes is developed so as to specify the symmetry and orientation of bulk deformation for use in tectonic analysis. Four symmetry patterns combined with possible arrangements of principal axes in vertical and horizontal directions as in a compression belt give thirteen regimes which are in turn defined and tentatively related to some known tectonic structures. A theoretical orogenic sequence of regimes is developed and the paper concludes with a review of some of the difficulties.