The Late Devonian South Mountain Batholith (SMB) of southwestern Nova Scotia is the largest batholith in the Appalachian Orogen of Eastern North America and contains economic deposits of U and Sn. The SMB comprises at least 11 individual plutons, which range in composition from granodiorite to biotite monzogranite, leucomonzogranite and leucogranite. Previous studies have suggested that a combination of fractional crystallization, assimilation of Meguma Supergroup country rocks and an influx of magmatic fluids contributed to the chemical evolution of the SMB. The amount of crustal assimilation is estimated to be as high as 33%. MELTS modelling assuming a starting composition of granodiorite with H2O = 4 wt%, pressure = 4 kbar (~12 km) and fO2 = FMQ can reproduce the chemical evolution observed in the SMB. However, some leucogranites likely require an additional component (e.g. hydrothermal fluids) to explain their alkali metal enrichment (e.g. Na, K, Rb). Zircon saturation thermometry estimates indicate the Salmontail Lake and Scrag Lake granodiorite plutons had high minimum initial temperatures of 823 ± 6°C and 832 ± 2°C, respectively, which are similar to low zircon-inheritance granitoids. The TiO2/Al2O3 and alkali-lime ratios of the surrounding country rocks and the leucogranites indicate the amount of crustal assimilation is likely to be between 10% and 20%. Our findings suggest the granodiorites of the SMB were likely produced by partial melting of the sub-Meguma Supergroup (e.g. Avalon terrane) lower crust caused by the contemporaneous injection of high temperature mafic to ultramafic magmas.

The Chehugou granite-hosted molybdenum deposit is typical of the Xilamulun metallogenic belt, which is an important Mo–Ag–Pb–Zn producer in China. A combination of major and trace element, Sr and Nd isotope, and zircon U–Pb isotopic data are reported for the Chehugou batholith to constrain its petrogenesis and Mo mineralization. The zircon SIMS U–Pb dating yields mean ages of 384.7 ± 4.0 Ma and 373.1 ± 5.9 Ma for monzogranite and syenogranite and 265.6 ± 3.5 Ma and 245.1 ± 4.4 Ma for syenogranite porphyry and granite porphyry, respectively. The Devonian granites are calc-alkaline with K2O/Na2O ratios of 0.44–0.52, the Permian granites are alkali-calcic with K2O/Na2O ratios of 1.13–1.25, and the Triassic granites are calc-alkaline and alkali-calcic rocks with K2O/Na2O ratios of 0.78–1.63. They are all enriched in large-ion lithophile elements (LILEs) and depleted in high-field-strength elements (HFSEs) with negative Nb and Ta anomalies in primitive mantle-normalized trace element diagrams. They have relatively high Sr (189–1256 ppm) and low Y (3.87–5.43 ppm) concentrations. The Devonian granites have relatively high initial Sr isotope ratios of 0.7100–0.7126, negative ɛNd(t) values of −12.3 to −12.4 and 206Pb/204Pb ratios of 16.46–17.50. In contrast, the Permian and Triassic granitoids have relatively low initial 87Sr/86Sr ratios (0.7048–0.7074), negative ɛNd(t) values of −10.1 to −13.1 and 206Pb/204Pb ratios of 17.23–17.51. These geochemical features suggest that the Devonian, Permian and Triassic Chehugou granitoids were derived from ancient, garnet-bearing crustal rocks related to subduction of the Palaeo-Asian Ocean and subsequent continent–continent collision between the North China and Siberian plates.

Mafic–ultramafic Quaternary lava flows form the Tigris volcanic field (covering 1750 km2) at the northeastern tip of Syria and extend into Turkey. This volcanic field occurs between the Euphrates graben and the Bitlis–Zagros collision suture that forms the boundary between the Arabian and Eurasian plates. The rocks are made up of labradorite, clinopyroxene, olivine and opaque phases. The Tigris lavas are compositionally restricted to basanites and alkali basalts, having a narrow range of major element compositions (SiO2, 42.2–48.2 wt%; MgO, 5.7–9.0 wt%, with Mg numbers ranging from 0.51 to 0.62; TiO2, 1.7–3.2 wt%), and are alkaline in nature. The rocks are enriched in HFS elements such as Zr (119–231 ppm), Nb (14–43 ppm) and Y (17–22 ppm). The REE patterns are strongly fractionated ((La/Yb)N = 10.6), indicative of a garnet-bearing source. The 143Nd/144Nd isotopic compositions range from 0.512803 to 0.512908, and 87Sr/86Sr from 0.70327 to 0.70403 (εNd = 3.2–5.3) suggesting strong affinities to ocean island basalts. Modelling using a variety of mantle source materials and different degrees of partial melting indicates that the magma was produced by a small degree of batch partial melting (F = 1.5%) of a primitive, garnet-lherzolite fertile mantle source. The overall petrological/chemical nature supports this interpretation. Shear heating at the base of the lithospheric mantle of the northern boundary of the Arabian plate, caused by a change in plate motion as the Arabian plate moved in a more easterly direction during the Plio-Quaternary, could represent a possible source of the heat necessary for partial fusion and magma generation. Adiabatic decompression and melting represents a more likely process for the generation of the Tigris magma. Elemental ratios such as K/P (4.6), La/Ta (12), La/Nb (0.90), Nb/Y (1.22) and Th/Nb (0.09) indicate that the magma was subjected to minimal crustal contamination.

New U–Pb ID-TIMS geochronological and whole-rock geochemical data from the Hurry Inlet Plutonic Terrane in Liverpool Land provide evidence of a Late Ordovician to Silurian magmatic arc in the East Greenland Caledonides. These voluminous granitoid rocks range from meladiorite to monzonite and granite, they are alkali-calcic to calc-alkaline and magnesian, and have characteristic arc granitoid trace element signatures. Zircon data give ages of 446 ± 2 and 438 ± 4 Ma for two phases of the Hurry Inlet Composite Pluton, 426 ± 1 Ma for a meladioritic xenolith in the anatectic Triaselv granite, and 424 ± 1 Ma for the Hodal-Storefjord Pluton. The Late Ordovician plutons can be correlated with similar plutons in the uppermost nappes of the Scandinavian Caledonides, likely representing the northern branch of magmatic arcs formed on the Laurentian margin. Magmatism appears to have continued sporadically until about 425 Ma when a major, short-lived, magmatic event formed the bulk of the batholith on Liverpool Land. This activity was likely mantle-driven and can be correlated with the Newer Granites in Scotland, for which a slab break-off mechanism has been proposed. The increased heat flow from this process can also explain the generation of the crustally derived, syntectonic, two-mica granites, which are the areally most important Caledonian suite in East Greenland.

Forming a northern continuation of the Moldanubian Thrust Zone, the Staré Město Belt comprises an E-verging thrust stack of three narrow lithotectonic units that exhibit variations in their respective P–T records. The upper and lower units form the respective margins of the hanging wall and footwall of the suture zone and are dominated by amphibolite grade metasedimentary successions. The middle unit is defined by an elongated body of MORB-like amphibolites that contains inserts of migmatized mica schists. Integrating both structural studies and pseudosection modelling in the MnNCKFMASH system shows that the present-day tectonic architecture of the Staré Město Belt is the result of a polyphase Variscan evolution. During a frontal, WNW–ESE-directed (in present-day coordinates) collision between the Bohemian Massif terranes and the Brunovistulian terrane, the metasedimentary rocks of the Staré Město Belt experienced tectonic burial to depths corresponding to 7–9 kbar. The continuous indentation and underthrusting of the Brunovistulian terrane led to top-to-the-ESE folding and uplift of these rocks to depths corresponding to 5.5–6.0 kbar at peak temperature. At depths corresponding to 5.5 kbar, the Staré Město Belt underwent subsequent dextral (top-to-the-NNE) shearing that was locally associated with nearly isobaric heating, possibly related to the emplacement of a Carboniferous tonalite body in the axial part of the Staré Město Belt. Subsequent tectonic compression resulted in the Variscan WNW-dipping metamorphic foliations becoming locally (N)NE- or ESE-dipping.

In the late Palaeozoic fore-arc system of north-central Chile at latitudes 31–32°S (from the west to the east) three lithotectonic units are telescoped within a short distance by a Mesozoic strike-slip event (derived peak P–T conditions in brackets): (1) the basally accreted Choapa Metamorphic Complex (CMC; 350–430°C, 6–9 kbar), (2) the frontally accreted Arrayán Formation (AF; 280–320°C, 4–6 kbar) and (3) the retrowedge basin of the Huentelauquén Formation (HF; 280–320°C, 3–4 kbar). In the CMC, Ar–Ar spot ages locally date white-mica formation at peak P–T conditions and during early exhumation at 279–242 Ma. In a local garnet mica-schist intercalation (570–585°C, 11–13 kbar) Ar–Ar spot ages refer to the ascent from the subduction channel at 307–274 Ma. Portions of the CMC were isobarically heated to 510–580°C at 6.6–8.5 kbar. The age of peak P–T conditions in the AF can only vaguely be approximated at ≥ 310 Ma by relict fission-track ages consistent with the observation that frontal accretion occurred prior to basal accretion. Zircon fission-track dating indicates cooling below ~ 280°C at ~ 248 Ma in the CMC and the AF, when a regional unconformity also formed. Ar–Ar white-mica spot ages in parts of the CMC and within the entire AF and HF point to heterogeneous resetting during Mesozoic extensional and shortening events at ~ 245–240 Ma, ~ 210–200 Ma, ~ 174–159 Ma and ~ 142–127 Ma. The zircon fission-track ages are locally reset at 109–96 Ma. All resetting of Ar–Ar white-mica ages is proposed to have occurred by in situ dissolution/precipitation at low temperature in the presence of locally penetrating hydrous fluids. Hence syn- and postaccretionary events in the fore-arc system can still be distinguished and dated in spite of its complex heterogeneous postaccretional overprint.

Organic petrography and geochemical analyses have been carried out on shales, carbonaceous shales and coals of the Shemshak Group (Upper Triassic–Middle Jurassic) from 15 localities along the Alborz Range of Northern Iran. Thermal maturity of organic matter (OM) has been investigated using vitrinite reflectance, Rock-Eval pyrolysis and elemental analysis of kerogen. Reflectance of autochthonous vitrinite varies from 0.6 to 2.2% indicating thermally early-mature to over-mature OM in the Shemshak Group, in agreement with other maturity parameters used. The shales of the Shemshak Group are characterized by poor to high residual organic carbon contents (0.13 to 5.84%) and the presence of hydrogen-depleted OM, predominantly as a consequence of oxidation of OM at the time of deposition and the hydrogen loss during petroleum generation. According to light-reflected microscopy results, vitrinite/vitrinite-like macerals are dominant in the kerogen concentrates from the shaly facies. The coals and carbonaceous shales of the Shemshak Group show a wide range in organic carbon concentration (3.5 to 88.6%) and composition (inertinite- and vitrinite-rich types), and thereby different petroleum potentials. Thermal modelling results suggest that low to moderate palaeo-heat flow, ranging from 47 to 79 mW m−2 (57 mW m−2 on average), affected the Central-Eastern Alborz basin during Tertiary time, the time of maximum burial of the Shemshak Group. The maximum temperature that induced OM maturation of the Shemshak Group seems to be related to its deep burial rather than to a very strong heat flow related to an uppermost Triassic–Liassic rifting. The interval of petroleum generation in the most deeply buried part of the Shemshak Group (i.e. Tazareh section) corresponds to Middle Jurassic–Early Cretaceous times. Exhumation of the Alborz Range during Late Neogene time, especially along the axis of the Central-Eastern Alborz, where maximum vitrinite reflectance values are recorded, probably destroyed possible petroleum accumulations. However, on the northern flank of the Central-Eastern Alborz, preservation of petroleum accumulations may be expected. The northern part of the basin therefore seems the best target for petroleum exploration.

The Mississippian Strathclyde Group of the Midland Valley of Scotland yields some of the earliest non-marine ostracods. The succession records shallow marine, deltaic, estuarine, lagoonal, lacustrine, fluvial and swamp environments representing a series of staging-posts between fully marine and limnetic settings. Macrofossils and ostracods are assigned to marine, marginal marine, brackish and freshwater environments based on their faunal assemblage patterns. Key brackish to freshwater ostracods are Geisina arcuata, Paraparchites circularis n. sp., Shemonaella ornata n. sp. and Silenites sp. A, associated with the bivalves Anthraconaia, Carbonicola, Cardiopteridium, Curvirimula, Naiadites, the microconchid ‘Spirorbis’, Spinicaudata and fish. Many Platycopina and Paraparchiticopina ostracods are interpreted as euryhaline, which corresponds with their occurrence in marine to coastal plain water bodies, and supports the ‘estuary effect’ hypothesis of non-marine colonization. The success of non-marine colonization by ostracods was dependent on the intrinsic adaptations of ostracod species to lower salinities, such as new reproductive strategies and the timing of extrinsic mechanisms to drive non-marine colonization, such as sea-level change. The genus Carbonita is the oldest and most common freshwater ostracod, and went on to dominate freshwater environments in the Late Palaeozoic.

We describe the geometry and kinematics of a Jurassic to Early Cretaceous transpressive sinistral strike-slip system within a metamorphic basement inlier of the Mesozoic magmatic arc near Bahia Agua Dulce at latitudes 31–32°S in north-central Chile and discuss possible relations with the Atacama Fault System further north. Sinistral transpression overprints structures of an accretionary system that is represented by the metamorphic basement. Sub-vertical semi-ductile NNW-striking strike-slip shear zones are the most conspicuous structures. Chlorite and sericite grew, and white mica and quartz dynamically recrystallized, suggesting low-grade metamorphic conditions during semi-ductile deformation. Folds at the 10–100 metre scale developed before and during strike-slip shearing. The folds are deforming a former sub-horizontal transposition foliation that originated during prior accretion processes. The folds have axes sub-parallel to the strike-slip shear zones and sub-vertical axial surfaces indicating a component of shortening parallel to the shear-zone boundaries, suggesting an overall transpressive deformation regime. Transpressive strike-slip deformation also affects Middle Triassic (Anisian) basal breccias of the El Quereo Formation. 40Ar–39Ar laser ablation ages of synkinematically recrystallized white mica in one of the shear zones provide an age of 174–165 Ma for the waning stages of semi-ductile strike-slip shearing. The semi-ductile shear zones are cut by mafic and rhyolite dykes. Two rhyolite dykes yield 40Ar–39Ar ages of 160.5 ± 1.7 Ma and 131.9 ± 1.7 Ma, respectively. The latter dyke has been affected by brittle faulting. Fault-slip analysis shows that the kinematics of the faulting event is similar to the one of the semi-ductile shearing event, suggesting that sinistral transpression continued after ~130 Ma. Timing, kinematics and geographic position suggest that the shear zones at Bahia Agua Dulce represent a southern continuation of the prominent Atacama Fault System that affected the Jurassic/Early Cretaceous arc over its ~1400 km length.

The trilobite fauna of the upper Ordovician (middle Katian) Pyle Mountain Argillite comprises a mixture of abundant mesopelagic cyclopygids and other pelagic taxa and a benthic fauna dominated by trilobites lacking eyes. Such faunas were widespread in deep water environments around Gondwana and terranes derived from that continent throughout Ordovician time but this is the only known record of such a fauna from North America and thus from Laurentia. It probably reflects a major sea level rise (the ‘Linearis drowning events’) as does the development of coeval cyclopygid-dominated deep water trilobite faunas in terranes that were marginal to Laurentia and are now preserved in Ireland and Scotland. The Pyle Mountain Argillite trilobite fauna occurs with a deep water Foliomena brachiopod fauna and comprises 22 species. Pelagic trilobites (mostly cyclopygids) constitute 36% of the preserved sclerites, and 45% of the fauna is the remains of trilobites lacking eyes, including one new species, Dindymene whittingtoni sp. nov. Three species of cyclopygid are present, belonging in Cyclopyge, Symphysops and Microparia (Heterocyclopyge). Cyclopygids are widely thought to have been stratified in the water column in life and thus their taxonomic diversity reflects the relative depths of the sea-beds on which their remains accumulated. A tabulation of middle and upper Katian cyclopygid-bearing faunas from several palaeoplates and terranes arranged on the basis of increasing numbers of cyclopygid genera allows an assessment of the relative depth ranges of the associated benthic taxa. The Pyle Mountain Argillite fauna lies towards the deeper end of this depth spectrum.

Two strikingly different successions of Lower Carboniferous (mainly Tournaisian) sedimentary rocks are closely juxtaposed on the NE coast of the island of Arran, SW Scotland. Near the village of Corrie a thin succession (~ 17 m) of Tournaisian rocks is preserved, whereas in the neighbouring Fallen Rocks–Laggan area, correlative rocks are > 300 m in thickness. These contrasting successions are separated by the Laggan Fault, which is a landward extension of the submarine Brodick Bay Fault, marking the SW boundary of the Northeast Arran Trough. The contrasting thickness and stratigraphy of the two sequences of sedimentary rocks result from juxtaposition of shoulder and trough deposits along the Laggan–Brodick Bay Fault. Although originally a normal, basin-defining fault, later sinistral movements caused significant displacement of the NE Arran Trough, together with a segment of the Highland Boundary Fault, from their original positions. The most northerly occurrence of the Highland Boundary Fault on Arran is thought to be the truncated northern end of the Corloch Fault. To the SW the surface trace of the Highland Boundary Fault is largely obscured by a Palaeogene granite body but it is present on the west side of the island, near Dougrie. The Highland Boundary Fault appears to be displaced to the south, in Kilbrannan Sound, by a series of NW-trending sinistral transcurrent faults. Thus the ‘anomalous’ trend of the Highland Boundary Fault and narrowing of the Midland Valley of Scotland in the Firth of Clyde area may be explained by later fault movements and intrusion of the Palaeogene North Arran Granite Pluton.

The Mesozoic fore-arc of the Antarctic Peninsula is exposed along its west coast. On Adelaide Island, a 2–3 km succession of turbiditic coarse sandstones and volcanic rocks is exposed. Four U–Pb (zircon) ages are presented here that, in combination with a new stratigraphy, have permitted a robust chrono- and lithostratigraphy to be constructed, which in turn has allowed tentative correlations to be made with the Fossil Bluff Group of Alexander Island, where the ‘type’ fore-arc sequences are described. The lithostratigraphy of Adelaide Island includes the definition of five volcanic/sedimentary formations. The oldest formation is the Buchia Buttress Formation (149.5 ± 1.6 Ma) and is correlated with the Himalia Ridge Formation of Alexander Island. The sandstone–conglomerate dominated succession of the Milestone Bluff Formation (113.9 ± 1.2 Ma) is tentatively correlated with the Pluto Glacier Formation of Alexander Island. Three dominantly volcanic formations are recognized on Adelaide Island, akin to the volcanic rocks of the Alexander Island Volcanic Group; the Mount Liotard Formation is formed of 2 km of basaltic andesite lavas, whilst the Bond Nunatak Formation is also dominated by basaltic andesite lavas, but interbedded with volcaniclastic rocks. The Reptile Ridge Formation has been dated at 67.6 ± 0.7 Ma and is characterized by hydrothermally altered rhyolitic crystal-lithic tuffs. Tentative correlations between Adelaide Island and Alexander Island preclude the two areas forming part of distinct terranes as has been suggested previously, and a proximal source for volcaniclastic sediments also indicates an exotic terrane origin is unlikely.

Zircon U–Pb ages, major and trace element geochemistry and Sr, Nd and Pb isotope compositions of diorite and diorite porphyry dykes from the Jinchanggouliang (JCGL) gold ore field on the northern margin of the North China craton (NCC) were studied to investigate their sources, petrogenesis and geodynamic significance. LA-ICP-MS zircon U–Pb dating reveals three major age groups of 2500 Ma (n = 2), 253 ± 7 Ma (n = 5) and 227 ± 1 Ma (n = 9). The inherited ages of 2500 Ma, contemporary with the Archaean NCC continental growth, imply that crustal material was involved in the magma source. The igneous zircons with a concordia age of 227 ± 1 Ma may record the emplacement age of the JCGL dykes. Both diorite and diorite porphyry exhibit a wide range of SiO2 and MgO contents and are characterized by high concentrations of Na2O+K2O and Al2O3, and low abundances of P2O5 and TiO2. They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies, and depleted in high-field-strength elements; all are categorized as shoshonitic rocks. All samples show a narrow range of Sr isotope compositions with initial 87Sr/86Sr ratios from 0.70394 to 0.70592, variable εNd(t) values (1.1 to −12.0) and TDM2 ages of 913–1972 Ma. Their Pb isotope compositions form continuous variation trends and plot in the fields between enriched mantle 1 (EM1) and lower continental crust (LCC). The above results suggest that the JCGL dykes studied could have been derived from mixing of lower crust, lithospheric mantle of the NCC and ascending asthenospheric melt in a post-orogenic extensional geodynamic setting. These shoshonitic dykes, together with the geochronological data of regional ENE-trending retrograded eclogites, ophiolites, continental arc magmatic belt, A-type granite, alkaline intrusions and metamorphic core complex from the northern NCC and Central Asian Orogenic Belt (CAOB) suggest that closure of the Palaeo-Asian Ocean (i.e. stage of pre-collision to collision) had completed during latest Permian to earliest Triassic time, and that the CAOB was subsequently tectonically dominated by post-orogenic extensional regimes. The involvement of asthenospheric melt in the magma source implies that the sub-continental lithospheric mantle (SCLM) of the NCC had been modified, and the onset of lithospheric destruction and thinning beneath the northern NCC may have occurred in Middle–Late Triassic time as a result of post-orogenic subducting slab detachment and lithospheric delamination.

The calc-alkaline, gneissic El Shalul granite is the westernmost gneiss dome or core complex within the Arabian–Nubian Shield. Previous studies have indicated that it represents either a window into the underlying pre-Neoproterozoic Sahara metacraton or a melt derived from the metacraton. U–Pb LA-ICP-MS dating of magmatic zircons from two samples of the variably foliated El Shalul pluton gives ages of 637 ± 5 Ma and 630 ± 6 Ma, excluding it from representing exhumed cratonic rocks. The ages are, however, indistinguishable from the age of the Um Ba'anib pluton, constituting the core of the Meatiq Gneiss Dome, as well as several other plutons in the Eastern Desert, indicating an important magmatic pulse in the Arabian–Nubian Shield in Late Cryogenian time. Major and trace element data indicate a within-plate setting. Bulk rock Nd-isotope and Hf-isotope data on zircons from the El Shalul pluton indicate derivation of the primary melt from a relatively juvenile source, either the lower crust of a mid-Neoproterozoic volcanic arc or as a result of fractionation of a mantle-derived mafic melt. Sm–Nd bulk rock isotopic data indicate a model age of c. 720 Ma for the protolith from which the melt was derived. Time-corrected Hf-isotope data obtained on the magmatic zircons indicate that the bulk of the source rock was extracted from the mantle around 810 Ma.

A new odontopleurid trilobite, Meadowtownella serrata, is described from a new Llanvirnian (Darriwilian; Didymograptus murchisoni Biozone) locality in the Builth Inlier, Mid-Wales. This unusually spinose species displays a remarkable array of pygidial spines and extends the stratigraphic range of the genus back into the Abereiddian. Benthic faunas are rare in the predominantly ‘anoxic’ D. murchisoni Biozone of the Welsh Basin, and these beds are an unusual habitat for odontopleurids. Environmental analyses (framboidal pyrite and associated total organic carbon) in this study, together with the distribution of benthic faunas (described and figured) in the section, indicate a likely oxic water column and episodically oxic bottom waters. A new diagnosis for Meadowtownella is presented with a review of the genus, as a clarification of previous work. The greater spinosity of earlier members of the lineage may reflect either changing environmental preferences, or the derivation of Meadowtownella from an original more spinose lineage.

Lacustrine sediments of the Hajnáčka I maar of southern Slovakia contain teeth and skeletal remains of a mammal fauna, including index Early Villanyian arvicoline rodents. U–Pb dating of magmatic zircons extracted from the redeposited fossiliferous maar sediments revealed a total of six volcanic events. The oldest age of 3.43 Ma was interpreted as that corresponding to the initial phreato-magmatic eruption that created the maar. Most zircons grouped around 3.06 ± 0.03 Ma, the age attributed to the catastrophic eruption that killed the mammal assemblage thriving within and around the maar studied. This age coincides with the 3.1 Ma boundary between the MN 16a and 16b subzones of the European Mammal Neogene chronostratigraphic scale estimated from the succession of Early Villanyian palaeontological localities according to the hypsometry of rodent teeth. Younger zircon ages overlapped those of the neighbouring basaltic lava flows, necks and dykes, thus recording superimposed effusions. The youngest 1.58 Ma old zircon defines the age limit for the final redeposition of the fossiliferous sediments in the maar drainage lake regime.

Data on the first appearances of major animal groups with mineralized skeletons on the Siberian Platform and worldwide are revised and summarized herein with references to an improved carbon isotope stratigraphy and radiometric dating in order to reconstruct the Cambrian radiation (popularly known as the ‘Cambrian explosion’) with a higher precision and provide a basis for the definition of Cambrian Stages 2 to 4. The Lophotrochozoa and, probably, Chaetognatha were first among protostomians to achieve biomineralization during the Terreneuvian Epoch, mainly the Fortunian Age. Fast evolutionary radiation within the Lophotrochozoa was followed by radiation of the sclerotized and biomineralized Ecdysozoa during Stage 3. The first mineralized skeletons of the Deuterostomia, represented by echinoderms, appeared in the middle of Cambrian Stage 3. The fossil record of sponges and cnidarians suggests that they acquired biomineralized skeletons in the late Neoproterozoic, but diversification of both definite sponges and cnidarians was in parallel to that of bilaterians. The distribution of calcium carbonate skeletal mineralogies from the upper Ediacaran to lower Cambrian reflects fluctuations in the global ocean chemistry and shows that the Cambrian radiation occurred mainly during a time of aragonite and high-magnesium calcite seas.

Chromium-spinels have been widely used as petrogenetic indicators to infer parent melt compositions and the tectonic setting of their formation. This study integrates petrographic, quantitative textural and geochemical analyses of Cr-spinel seams within the Dawros Peridotite, NW Connemara, Ireland to determine the composition of their parental magmas. Calculation of Cr no. (Cr/(Cr + Al)) (0.50–0.77) values and TiO2 (0.18–0.36 wt%) contents of the Cr-spinel seams, coupled with an estimation of the Al2O3 and TiO2 contents (~11.86 wt% and ~0.39 wt%, respectively) of their parental melts, indicates that they probably formed from boninitic melts sourced from a highly depleted mantle. This implies that the Cr-spinel seams formed in a supra-subduction zone undergoing high degrees of partial melting. The Cr-spinel data support tectonic models for the formation of the Dawros Peridotite (and Connemara Metagabbro-Gneiss Complex) during island arc collision, immediately prior to Grampian orogenesis at ~470 Ma. The occurrence of the Dawros chromitite seams at the approximate transition between the lower harzburgite sequence and the upper lherzolite sequence bears marked similarities to the positions of such seams in larger anorogenic layered mafic-ultramafic intrusions, and implies that the Dawros Peridotite behaved as an open-system magma chamber.

Out of the 14 agnostoid species/subspecies so far recorded from the Furongian of Scandinavia, seven are excellent biostratigraphical indices and important for correlation between Baltica and other palaeocontinents. Glyptagnostus reticulatus, Aspidagnostus lunulosus and Agnostus (Homagnostus) obesus first appear at the base of the G. reticulatus Zone, allowing a precise correlation of the base of the Paibian Stage into Scandinavia. Tomagnostella orientalis and Pseudagnostus cyclopyge appear near the base of the Parabolina brevispina Zone, suggesting a correlation with the uppermost Paibian through the lowermost Jiangshanian stages. Lotagnostus americanus and Pseudagnostus rugosus have an intercontinental distribution and their first appearance in Scandinavia allows for a correlation with one of the most favourable levels for defining the base of Cambrian provisional Stage 10. In the Furongian of Scandinavia, agnostoids are conspicuously assembled in three different intervals: the lower Glyptagnostus reticulatus Zone, the lower Pseudagnostus cyclopyge Zone and the Lotagnostus americanus through lower Trilobagnostus holmi zones. The agnostoid-barren and largely unfossiliferous succession separating the lower and middle agnostoid-bearing intervals can be explained by means of subsequent dissolution of the calcareous fauna and/or a hostile environment. The middle agnostoid-bearing interval is succeeded by an anomalous succession dominated by the orthide brachiopod Orusia lenticularis, reflecting a regressive event coupled with increasing levels of oxygen at the sediment/water interface. This shallowing evidently resulted in unfavourable conditions for agnostoids.

Mafic flows of the Middle to Upper Ordovician Dunn Point Formation of eastern Canada were deeply weathered under warm and relatively humid conditions before being buried by subsequent flows. In the absence of superior plants, and in the context of relatively low atmospheric carbon levels, the soils developed alkaline groundwater conditions through mineral–water interactions, which resulted in an enhanced mobility of Al relative to Si in most palaeosols of that formation. Although the vegetation cover was volumetrically insignificant compared with that of subsequent geological times, it was apparently producing very efficient chelates, which, for most palaeosols of the succession, generated a well-defined cheluviation pattern for not only Al and Fe, but also and mainly Ti, which is typically immobile in modern soils. The resulting soils developed an Al–Fe–Ti-depleted upper horizon that was enriched in Si, probably through periodic ground saturation. Long-term climatic variations related to orbital cycles are inferred to have accounted for a second type of soil in the succession, which contrasts with the former by showing a Si-depleted and less Al–Fe–Ti-depleted upper horizon. Some soil material was substantially reworked by surface runoff, but such occurrences can be easily differentiated from in situ soil material in terms of texture, structure and composition. A thick overlying rhyolite flow is thought to be responsible for providing abundant K in solution, which was incorporated in the underlying basalt palaeosols as exchangeable cations within a probably montmorillonitic clay precursor to the Fe–Mg-rich phengite that later developed during deep burial and orogenic compression.