The Canadian Cordillera is largely a mosaic of terranes that are allochthonous relative to the autochthonous North American craton. Palaeobiogeographic data on pectinoid bivalves from various cratonal areas and from two western Canadian terranes, Wrangellia and Stikinia, are used to estimate the amounts of latitudinal displacement and rotation of these terranes that took place during and after Early Jurassic times. Distributional patterns of various species of the distinctive, very common bivalve Weyla, and a comparison of the positions of biogeographic boundaries between high-palaeolatitude, mixed and low-palaeolatitude faunas on the terranes and on the craton indicate that Wrangellia was displaced northward relative to the craton by at least several hundred and possibly more than 1000 km since Sinemurian and Pliensbachian times. For Stikinia such estimates are even higher and exceed 1000 km. Biogeographic patterns also suggest that Wrangellia experienced at best minor rotation since Sinemurian times, while rotation from a more or less east–west alignment to its present northwest–southeast position seems possible for Stikinia prior to the Pliensbachian. Palaeomagnetic interpretations, suggesting that during Sinemurian and Pliensbachian times Wrangellia and Stikinia were in much the same latitudinal position relative to the craton as they are now, are in sharp contrast to the results from faunal data. The presence of warm oceanic surface currents, oceanographic effects of elongated barriers, climatic change and differential latitudinal displacements due to rotation appear to be insufficient explanations for the discrepancy between the interpretation of palaeomagnetic and faunal evidence.

The Dalradian Supergroup is interpreted traditionally as recording c. 300 m.y. of ‘episodic’ Neoproterozoic rifting. However, lower Dalradian (pre-Easdale Subgroup) facies architecture is incompatible with rift-basin fill, and no unambiguous Neoproterozoic extensional structures are present in those rocks. Consequently, no objective evidence exists to infer that Dalradian sedimentation was initiated during extensional tectonism. That, combined with the accumulating data for contractile deformation in Scotland at c. 870–800 Ma, the Knoydartian orogeny, permits the proposal of an alternative tectonostratigraphic evolution for the Dalradian. I propose that Dalradian basin genesis was initiated as a foredeep in response to Knoydartian orogenesis. The coarsening- and shallowing-upward, 6–8 km-thick Grampian Group–lower Lochaber Subgroup succession arguably represents a flysch to molasse Knoydartian foredeep overlain by a moderately stable post-orogenic shelfal sequence recorded by the relatively uniform thinner (c. 4 km) and compositionally more mature rocks of the upper Lochaber through Islay subgroups. Lithospheric-scale extensional tectonism and rifting did not occur until the late Neoproterozoic, as marked by the laterally variable, volcanic- and igneous-bearing Easdale Subgroup, and was followed by the late Neoproterozoic–early Palaeozoic Iapetan rift-to-drift transition through the Southern Highland Group.

A small micromonzonite pluton intruding Miocene extrusives of the Marysvale volcanic field of southern Utah has undergone a sequence of explosive brecciation, syenite veining, rheomorphism, calcium metasomatism and zeolitization. Skarn-like occurrences of magnetite and Al-spinel-rich feldspathoidal rocks within the outcrop are of two main types: (1) an olivine-bearing variety with occasional REE-rich minerals (zirconolite) occurs as veins and seams in desilicated latite screens and xeno-liths.; (2) an aluminous, corundum- and hibonite-bearing variety with accessory zirconolite, perovskite and armalcolite occurs mainly as fillings to the micromonzonite breccias. The chemically disparate types are interpreted as having initiated as propylitic, and argillic/alunitic, alterations of latite country rock in the early hydrothermal system of the pluton. Subsequent intrusion of the micromonzonite to higher levels has incorporated these products into the igneous complex, in which they have experienced varying degrees of nephelinization, pyrometamorphism, rheomorphism and veining.

Low-temperature eclogite-facies rocks from Syros and Tinos (Cyclades, Greece) include meta-igneous blocks of unclear origin (meta-olistostrome or tectonic mélange) with very high trace element concentrations (e.g. Zr up to 4850 ppm; Y up to 475 ppm). The unusual geochemistry is considered to be the result of metasomatic alteration in a subduction-zone environment. Locally, metasomatic exchange with an ultramafic matrix further enhanced compositional anomalies. A concordant U–Pb zircon age of 78±1 Ma recorded for an omphacitite from Syros is interpreted as the time of pre-Eocene high-pressure metamorphism in the Cyclades. Zircon dates of 61 and 63 Ma for a jadeitite from Tinos possibly indicate an additional discrete event (deformation?). These results are a first geochronological indication that high-pressure metamorphism in the Cyclades commenced significantly earlier than indicated by previous white mica chronology which provided ages between c. 50 and 40 Ma.

Jurassic magmatism in western Gondwana produced the most voluminous episode of continental volcanism in the Phanerozoic era. During the Early to Middle Jurassic, some 2.5–3 million km3 of dominantly basalt, and to a lesser extent rhyolite, were erupted onto a supercontinent in the early stages of break-up. The major silicic portion of the Gondwana magmatic province is exposed in Patagonian South America. The volcanic rocks of Patagonia have been collectively termed the Chon-Aike Province and constitute one of the world's most voluminous silicic provinces. The volcanic rocks are predominantly pyroclastic, dominated by ignimbrite units of rhyolite composition. Volcanic rocks crop out sporadically across much of the once contiguous Antarctic Peninsula, and are considered to form an extension of the Chon-Aike Province. A continuation of the province to include the Antarctic Peninsula would extend its strike length along the active Pacific margin by c. 2000 km.

Volcanic rocks exposed along the east coast of the Antarctic Peninsula, defined here as the Mapple Formation, are also dominated by rhyolitic ignimbrite flows, with individual units up to 80 m in thickness, and a total thickness of c. 1 km. The ignimbrites vary in degree of welding, from high-grade rheomorphic ignimbrites with parataxitic textures, to unwelded, lithic-rich ignimbrites. Rhyolite lava flows, air-fall horizons, debris flow deposits and epiclastic deposits are volumetrically minor, occurring as interbedded units within the ignimbrite succession.

The lithology and stratigraphy of the Jurassic volcanic rocks of the Mapple Formation are presented, and comparisons are made to the Chon-Aike Province. A consistent stratigraphy of Permo-Triassic metasedimentary rocks, unconformably overlain by terrestrial mudstone–siltstone sequences, which are in turn conformably overlain by largely silicic, subaerial volcanic rocks, is present at several localities along the Antarctic Peninsula, and at localities in the Chon-Aike Province. Precise (zircon U–Pb) Middle Jurassic ages exist for two volcanic formations from the Antarctic Peninsula, and a Middle–Lower Jurassic age has been suggested for the underlying sedimentary formations based on fossil flora analysis. The Antarctic Peninsula chronostratigraphy, coupled with lithological similarities, indicate a close relationship to those sequences of the Chon-Aike province.

Mafic granulites from the North China craton can be divided into two textural types, referred to as A- and B-types. A-type mafic granulites display garnet+quartz symplectic coronas, and outcrop in the eastern and western zones of the craton, whereas B-type mafic granulites exhibit orthopyroxene+plagioclase±clinopyroxene symplectites or coronas, and are mainly exposed in the central zone of the craton. Most A-type mafic granulites preserve the prograde (M1), peak (M2) and post-peak near-isobaric cooling (M3) assemblages, which are represented respectively by inclusions of hornblende+plagioclase+quartz, a peak mineralogy of orthopyroxene+clinopyroxene+plagioclase+quartz+garnet, and overprinted by garnet+quartz symplectic coronas. These mineral assemblages and their P–T (pressure-temperature) estimates define anticlockwise P–T evolutionary paths. The B-type mafic granulites preserve the peak (M1), post-peak near-isothermal decompression (M2) and cooling (M3) assemblages, which are represented by the peak assemblage of orthopyroxene+clinopyroxene+plagioclase+quartz+garnet±hornblende, post-peak orthopyroxene+plagioclase±clinopyroxene symplectites or coronas, and later hornblende+plagioclase+magnetite symplectites, respectively. These mineral assemblages and their P–T estimates define clockwise P–T paths.

The anticlockwise P–T paths of the A-type mafic granulites in the eastern and western zones of the North China craton are consistent with a model of underplating and intrusion of mantle-derived magmas. In combination with lithological, structural and geochronological data, the eastern and western zones of the North China craton are considered to represent two continental blocks that developed through the interaction of mantle plumes with the lithosphere from the Palaeoarchaean to the Neoarchaean era. The B-type mafic granulites and associated rocks in the central zone represent a magmatic arc that was metamorphosed and deformed during amalgamation of the eastern and western continental blocks in the late Palaeoproterozoic era. The mineral reaction relations and clockwise P–T paths of the B-type mafic granulites from the central zone record the tectonothermal history of the collision that resulted in the final assembly of the North China craton at c. 1800 Ma.

At the eastern margin of the southern part of the northwest-trending Kalamata Basin, four small extensional sub-basins were formed during the Plio-Pleistocene period. These sub-basins developed on the footwall of a major north-northwest-trending marginal fault, which separates the Taygetos mountains from the Kalamata Basin. Two different basin configurations, mostly resulting from different subsidence/sedimentation ratio (R), produced two different depositional types. In the first type, where R>1, gravelly alluvial fans were deposited in narrow and restricted sub-basins. In the second type, where R<1, braid-deltas were deposited in open, low-gradient sub-basins with marine influence. Braid deltas consist mostly of sandstone and mudstone, and only in the northern part of one sub-basin did gravel accumulate. The paucity of gravel is associated with rapid basin subsidence. Since factors such as climate and source-rock lithologies were essentially similar for the different basins, these different alluvial stratigraphies result principally from tectonic processes. Maximum sediment thickness formed on the hangingwall of faults parallel to the major basin-margin fault. Transfer faults at right angles to this major fault have strongly influenced the pathways of braided low-sinuosity streams. The initial open-channel width-to-depth ratio of the channels in this study (range 5–20) is comparable to suspended load channels and channel-fill deposits.

Whole-rock major and trace element compositions of quartzofeldspathic Permian–Cretaceous sandstones of the Torlesse terrane, New Zealand, display progressive changes which compare well with published petrographic data. Chemical indices in three Permian–early Late Triassic Rakaia subterrane petrofacies show small contrasts, as do the modes, reflecting original source compositions. A Late Triassic Rakaia petrofacies displays sharp increases in SiO2/Al2O3, K2O/Na2O, Th/Sc, La/Sc, Ce/Sc, LaN/YN and decreases in Ti/Zr and V/La, consistent with partial cannibalistic recycling and a small influx of lithic volcanic detritus. In the post-collisional Late Jurassic–Early Cretaceous Pahau subterrane, SiO2/Al2O3 remains high, but other indices decrease to levels seen in the Permian, due to recycling of the earlier Rakaia petrofacies and influx of 10–30% mafic-intermediate volcaniclastic detritus derived from inboard volcanogenic terranes. The results are confirmed by additional suites, including mudstones, which cover a larger area, but also show that some spatial variation occurs within the terrane as a whole. Whole-rock data and Chemical Index of Alteration indices indicate that the Torlesse was derived from a relatively unweathered source with granodioritic bulk composition. Comparisons with data from a proposed Rakaia source in the New England and Hodgkinson orogens of eastern Australia suggest that the observed chemical and modal compositions cannot be simply derived from that area as presently exposed.

A geochemical and mineralogical study of thin (2–20 cm) clay-rich beds found in Turonian–Coniacian chalks from the Anglo-Paris Basin has been undertaken. On the basis of their rare-earth element (REE) and mineralogical composition it is possible to subdivide beds into bentonites, characterized by a negative Eu anomaly and elevated smectite content, and detrital beds (characterized by a minimal or absent Eu anomaly and a greater proportion of illite). Six beds are considered to be bentonites (Glynde 1, Southerham 1, Caburn, Bridgewick 1, Lewes and Shoreham 2). Trace-element discriminant diagrams add support, as does comparison with similar studies undertaken in eastern England and northern Germany. Geochemical evidence demonstrates that the tephra was variably acidic in composition (rhyodacite–rhyolite–comendite/pantellerite), and was probably derived from crustal melting associated with initial rifting of the North Atlantic. Correlation of bentonites between the Anglo-Paris Basin, eastern England and northern Germany can be demonstrated and independently tested, establishing a tephro-event stratigraphy across northwest Europe for this period.

An enigmatic buried structure, located in Mesozoic sedimentary rocks in the Perth Basin, Western Australia, was discovered in 1990 by Ampol Exploration. The basin-like Yallalie structure (centred on 30° 26′ 40.3″ S, 115° 46′ 16.4″ E) is circular in plan view and about 12 km in diameter. High-resolution, seismic-reflection profiles across the structure show a basin-shaped area of chaotic reflections that extend to a depth of approximately 2 km below the surface. The structure has sharp boundaries with surrounding faulted, but otherwise relatively undisturbed, rocks. In the centre of the structure there is an uplifted area approximately 3–4 km across, similar to those described from complex meteorite impact structures. The seismically defined structure coincides with a circular topographic depression, and image processing of digital elevation data has allowed recognition of concentric and radial structures extending as far as 40 km from the centre of the depression. Gravity surveys show the structure to be associated with a positive gravity anomaly of about 30 gu. Aeromagnetic surveys have defined annular anomalies associated with the central uplifted section, and possibly margins, of the structure. A search for siderophile element enrichments (by neutron activation analysis) in the rocks of the structure, which would indicate the presence of a meteorite component, proved negative. Quartz grains in cores that penetrate the structure show the development of prismatic cleavage fractures and irregular, slightly curved planes formed by brittle fracture. An allochthonous breccia of Late Cretaceous rocks occurs a few kilometres west of the western margin of the structure. Quartz grains from a thin veneer of Tertiary sediments that drape the structure are essentially undeformed. However, multiple sets of closely spaced planar deformation features in quartz, characteristic of highly shocked rocks, have yet to be observed in the rocks of the Yallalie structure and the allochthonous breccia. The morphology of the Yallalie structure determined from topographic and geophysical data suggests strongly that it is of impact origin. Geological and geochemical evidence is equivocal, but is not inconsistent with this interpretation.

A collection of conodonts, including Dapsilodus obliquicostatus (Branson & Mehl), Distomodus cf. kentuckyensis Branson & Branson, Ozarkodina oldhamensis (Rexroad), and Panderodus sp., has been obtained from brachiopod coquinas in the lower part of the La Chilca Formation in the Precordillera of west-central Argentina. This conodont fauna, the first to be recorded from the Llandovery in South America, can be referred to the D. kentuckyensis Biozone, and is interpreted to represent an interval in the middle Rhuddanian to lower Aeronian stages. This age assignment is supported by graptolite data from the lower third of the La Chilca Formation beneath the conodont-bearing interval. The brachiopods associated with the conodonts belong to the Afro-South American Realm, but include a high percentage of North Atlantic and cosmopolitan genera. The conodont taxa present are widespread in the tropical zone (Laurentia, Baltica, etc.). This suggests that the pronounced conodont faunal provicialism in the Upper Ordovician had disappeared in the Lower Silurian, where high- and low-latitude conodont faunas appear to be closely similar.

The Upper Cretaceous chalk of northwest Europe was deposited in an open epicontinental sea during a period of high global eustatic sea-level – a unique depositional setting requiring modification of the sequence-stratigraphical approach. In this paper, a framework for the sequence-stratigraphical analysis of the Upper Cretaceous chalk is discussed, and an ideal sequence model presented.

Analysis of the Coniacian succession has identified eight third-order (short-term) cycles of relative sea-level change (∼400 Ka duration), superimposed upon a second-order (longer term) cycle (∼3.2 Ma duration). The third-order cycles represent frequent, basin-wide oceanographic changes for which there are no known tectonic mechanisms. These cycles show a visual correlation with both the δ13C and the δ13C stable isotope curves, indicating a climatic control on sedimentation, probably linked to a Milankovitch eccentricity rhythm.

The long-term trend in independently derived δ13C stable isotope values parallels the long-term relative sea-level curve, reflecting increased production as the shelf area expands. By contrast, the δ18C stable isotope values show little change over the long term, suggesting that tectonics, rather than climate, was the controlling factor on second-order relative sea-level change. This is corroborated by the fact that the long-term cycle is coincident with a phase of increased activity at the mid-ocean ridges, which is thought to allow for a 60 m rise in global sea level.

The Leonian (early Middle Cambrian) regional Stage of Iberia is revised from a lithostratigraphic and biostratigraphic point of view in order to propose it as a chronostratigraphic unit for the Mediterranean subprovince (outcrops in Spain, France, Italy, Germany, Morocco and Turkey). This revision now permits a correlation of the Leonian Stage with the other early Middle Cambrian regional Stages. For this correlation the first appearance datum (FAD) of Eoparadoxides mureroensis, Macannaia spp., Schistocephalus antiquus and Oryctocara granulata are employed for the lower boundary; while the FADs of Badulesia tenera, Ctenocephalus (Hartella) spp., Parasolenopleura aculeata and Triplagnostus gibbus are employed for the upper boundary.

We report a U–Pb monazite age of 23.0±0.2 Ma for the Shivling leucogranite, a tourmaline+muscovite±biotite leucogranite at the top of the High Himalayan slab in the Garhwal Himalaya, north India. The Shivling–Bhagirathi leucogranite is a viscous near-minimum melt, emplaced as a foliation parallel laccolith via a dyke network not far from its source region. Prograde heating occurred soon after the India–Asia collision at c. 50 Ma up to melting at 23 Ma and high temperatures (>550 °C) were maintained for at least 15 Ma after garnet growth. The leucogranite was emplaced at mid-crustal depths along the footwall of the Jhala fault, a large-scale low-angle normal fault, part of the South Tibetan Detachment system, above kyanite and sillimanite grade gneisses. The geometry of the leucogranite laccolith shows biaxial extension and boudinage both perpendicular (north-northeast–south-southwest) and parallel to the strike (west-northwest–east-southeast) of the mountain range. Unroofing occurred by underthrusting beneath the High Himalayan slab along the Main Central Thrust zone, progressively ‘jacking up’ the leucogranites, removal of material above by low-angle normal faulting, and erosion. Very rapid cooling at rates of 200–350 °C/Ma between 23–21 Ma immediately followed crystallization, as tectonic unroofing and erosion removed 24–28 km of overburden during this time. K–Ar muscovite ages are 22±1.0 Ma and fission track ages of zircons from >5000 m on the North Ridge of Shivling are 14.2±2.1 and 8.8±1.2 Ma and apatites are 3.5±0.79 and 2.61±0.23 Ma. Slow steady state cooling at rates of 20–30 °C/Ma from 20–1 Ma shows that maximum erosion rates and unroofing of the leucogranite occurred during the early Miocene. This timing coincides with initiation of low-angle, north-dipping normal faulting along the South Tibetan Detachment system.

Lower Palaeozoic outcrops near Kemer comprise only Ordovician and Silurian strata in the Upper Antalya Nappes, and are described in detail for the first time. The oldest rocks, Seydişehir Formation (lower Arenig), resemble those of the central Taurides. A disconformity is probable, though unexposed, below the succeeding Şort Tepe Formation (Ashgill), a unit seen elsewhere only in south central and southeastern Turkey; sparse trilobites include Cyclopyge, Cyphoniscus, Panderia, Symphysops, Ulugtella, and one new species Placoparia (Hawleia) marcouxi. Silurian rocks (Sapandere Formation) differ from those further east in the Taurides, and are of Llandovery (Telychian), Wenlock and ?Ludlow age, based on conodonts, graptolites and trilobites (Cerauroides, Otarion (Aulacopleura), Sphaerexochus) the affinities of which lie with the Carnic Alps and western Europe. The Sapandere Formation is unconformably overlain by red sandstones at the base of the Armutlugözlek Formation (Devonian).

The graptolite biozonation of the Wenlock Series in the Builth Wells district is reassessed. The graptolite fauna is dominated by relatively few, but variable, species of Monograptus s.s., Pristiograptus and Monoclimacis. These species are mostly long-ranging and are of limited biostratigraphical use. Biozonation is based largely on the relatively rare cyrtograptids. The lower Wenlock Series of the district comprises the widely recognized centrifugus, murchisoni and riccartonensis biozones. The middle to upper Wenlock biostratigraphy differs from that previously recognized in the UK. Above the riccartonensis Biozone, dubius, rigidus and lundgreni biozones are distinguished. Separate flexilis and ellesae biozones are not recognized: Monograptus flexilis appears earlier than, then largely co-exists with, Cyrtograptus rigidus s.l.; while Cyrtograptus ellesae appears later than Cyrtograptus lundgreni. The uppermost Wenlock nassa–ludensis Biozone is sparsely fossiliferous; its subdivision has not proved possible. This revised biostratigraphical scheme for the Wenlock Series of the Builth Wells district suggests that the Sheinwoodian–Homerian boundary, as defined in the Welsh Borderland, might occur within, rather than at the base of, the lundgreni Biozone. However, difficulties in correlation with other Wenlock sequences, particularly overseas, suggest significant biofacies control, with the Wenlock seas of the Builth Wells district appearing to have been periodically inhospitable to graptolites.

The Chianti Mountains is an important sector of an E-verging regional thrust-related fold (the so-called Tuscan Nappe) extending along the whole length of the Northern Apennines. This thrust system involves the Tuscan Sequence superposing the Macigno sandstones onto Cervarola-Falterona sandstones, both of which are sedimented in adjacent foredeep basins. Detailed field mapping and analysis of superposition relations among tectonic structures, as well as correlation between structures and syntectonic deposition, has allowed Chianti Mountain evolution to be interpreted in terms of three main stages of deformation.

The D1 stage resulted in the NE-directed synsedimentary thrusting of the Macigno onto the Cervarola-Falterona sandstones, while large NE to ENE-vergent thrust-related folds developed during the two successive deformation stages (D2 and D3). Fault-propagation folds developed during the D2 stage, and were affected by the Main Chianti Mountains Thrust (MCMT) during the successive D3 stage. In particular, the D3 stage has been correlated to the development, during the Pliocene period, of the hinterland Upper Valdarno Basin, which was previously considered to be an extensional basin. In fact, this continental basin formed along the eastern margin of the Chianti Mountains, ahead of the MCMT that also produced a shortening of the basin fill. With the beginning of the Quaternary period, the tectonic regime switched to extensional, as manifested by the development of a normal fault system on the opposite basin margin.

The data presented here allow us to infer that the Chianti Mountains thrust system (D2 and D3) developed during a time interval spanning from the Late Miocene (∼12 Ma) until the Late Pliocene (∼2 Ma) periods. In the Northern Apennines, polyphase thrusting recorded by cover rocks has been related to the activity of basement thrusts, which have been recently evidenced by geophysical data. In this context, the two latest stages of deformation recognised in the Chianti Mountains have been attributed to the activity of the Abetone–Cetona crustal thrust, the deformational effects of which propagated forward in the sedimentary cover.

Three elements of the ‘Ediacara fauna’ are described from lower Cambrian strata on the Digermul Peninsula, Norway. Nimbia occlusa Fedonkin, 1980 and Tirasiana sp. occur approximately 80 m above the base of the Lower Breivik Member, which approximately coincides with the Neoproterozoic–Cambrian boundary. A specimen of Cyclomedusa sp. has also been found in the Lower Duolbasgaissa Member about 600 m above the boundary, in rocks of trilobite-bearing age.

These discoveries add to a growing body of evidence that some elements of the dominantly Neoproterozoic Ediacara fauna continue into the Phanerozoic, thereby diminishing the scope of a possible late Neoproterozoic mass-extinction event.

The taxa described here, particularly Nimbia and Cyclomedusa, also occur at many other localities within Neoproterozoic strata and, in common with other elements of the Ediacara fauna, display remarkable morphological variation. Some of this diversity in form is probably caused by environmental and preservational factors. The possibility that it may, at least in part, reflect an inability of these early life forms to replicate faithfully their genes during reproduction should, however, not be overlooked.

Significant volumes of partial melt developed in the arkosic contact aureoles of two of the numerous mafic and ultramafic minor intrusions found in the northern parts of the Isle of Rum, Scotland. Melting was essentially static, with little movement of melt even on a thin-section scale, and no segregation. The relative proportions of (now inverted) tridymite and high quartz inferred to have crystallized in the silica primary-phase field constrain the pressure of metamorphism to 150 ± 50 bars. Melting attained 95 vol. %, and occurred up to 15 m from the contact with the 50 m diameter gabbro plug. Melting around the adjacent 200 m diameter peridotite plug reached ≈ 70 vol. %, and occurred up to 6 m from the contact. Simple thermal models for the two aureoles, based on the isograds given by the onset of melting, the breakdown of chlorite and the disordering of microcline, support the hypotheses that the peridotite plug was injected as a crystal-rich mush close to its solidus, whereas the gabbro plug was a relatively long-lived feeder conduit. Time scales for the melting events are of the order of forty years for the aureole of the gabbro and ten years for that surrounding the peridotite body. The melt distribution resulting from the heating part of the thermal history is controlled by reaction, and is far from textural equilibrium. Crystallization was abrupt, being complete in ten years for the gabbro, and in only four for the peridotite, resulting in a fine-grained cotectic intergrowth and preservation of the melt distribution.

The full stratigraphical context of the type materials of Psigraptus arcticus and P. lenzi from Rock River are given, as well as a new occurrence of the Psigraptus–Adelograptus Zone in the Upper Canyon, Peel River of Canada's Yukon Territory. A new monotypic genus Chigraptus is created for a quadriradiate anisograptid graptolite with four unbranched first-order stipes, a horizontal to slightly reclined rhabdosome and isolate autothecae. The genus is found only at the base of the Early Tremadoc Anisograptus–Staurograptus Zone. Chigraptus may have given rise to the Late Tremadoc Psigraptus by a reduction in first-order stipes and by increased reclination.