The ecological ranges of Archaeobacteria and Eubacteria are constrained by a requirement for liquid water and the physico-chemical stability limits of biomolecules, but within this broad envelope, prokaryotes have evolved adaptations that permit them to tolerate a remarkable spectrum of habitats. Laboratory experiments indicate that prokaryotes can adapt rapidly to novel environmental conditions, yet geological studies suggest early diversification and long-term stasis within the prokaryotic kingdoms. These apparently contradictory perspectives can be reconciled by understanding that, in general, rates and patterns of prokaryotic evolution reflect the developmental history of the Earth's surface environments. Our understanding of modern microbial ecology provides a lens through which our accumulating knowledge of physiology, molecular phylogeny and the Earth's history can be integrated and focussed on the phenomenon of prokaryotic evolution.
The sculpture of scales and plates of articulated anaspids from the order Birkeniida is described and used to clarify the position of scale taxa previously left in open nomenclature. The dermal skeleton of a well-preserved squamation of Birkenia elegans Traquair, 1898 from the Silurian of Scotland shows a characteristic finely tuberculated sculpture over the whole body. Rhyncholepis parvula Kiær, 1911, Pterygolepis nitida (Kiær, 1911) and Pharyngolepis oblonga Kiær, 1911, from the Silurian of Norway show three other sculpture types. Northern Hemisphere disarticulated scales and plates are described here, supporting a new anaspid taxonomy that includes both articulated and disarticulated material. The diversity, distribution, evolutionary trends and biostratigraphy of anaspids are described in the context of this new taxonomy, which includes six families (two are new) subdivided into 16 genera (10 are new) and 22 species (15 are new).
New taxa among Birkeniidae Traquair, 1898 are Birkenia robusta sp. nov. and Hoburgilepis papillata gen. et sp. nov.. Rhyncholepididae Kiær, 1924 includes Rhyncholepis butriangula sp. nov., Silmalepis erinacea gen. et sp. nov., Vesikulepis funiforma gen. et sp. nov., Maurylepis lacrimans gen. et sp. nov., and the previously described Schidiosteus mustelensis Pander, 1856 and Rytidolepis quenstedtii Pander, 1856. Tahulalepididae fam. nov. is represented by Tahulalepis elongituberculata gen. et sp. nov. and the revised T. kingi (Woodward, 1947). Septentrioniidae fam. nov. contains Septentrionia lancifera gen. et sp. nov., S. mucronata gen. et sp. nov., S. dissimilis gen. et sp. nov., S. seducta gen. et sp. nov., Liivilepis curvata gen. et sp. nov., Spokoinolepis alternans gen. et sp. nov. and Manbrookia asperella gen. et sp. nov. The family level position of Ruhnulepis longicostata gen. et sp. nov. is uncertain. Pterygolepididae Obruchev, 1964 and Pharyngolepididae Kiær, 1924 remain monogeneric.
The postcranial skeleton of Ariekanerpeton sigalovi (Seymouriamorpha: Discosauriscidae; Lower Permian, Tadzhikistan) differs from that of like-sized Discosauriscus specimens in showing: wider interclavicle anterior plate with smaller, rhomboidal sculptured field on its ventral surface not reaching plate posteromedial margins; broader interclavicle plate-stem junction; slightly narrower interclavicle posterior stem; anteroposteriorly narrower clavicle ventral plate with convex posterior margin; shorter, more robust humerus; four phalanges on fourth manus digit (five phalanges in Discosauriscus); ilium more elongate dorsoventrally with anteroposteriorly narrower neck; posterior process of iliac blade oriented distinctly posterodorsally rather than horizontally; more gracile atlantal rib; broadened distal end of second presacral rib. A revised cladistic analysis of the best known seymouriamorph species retrieves Ariekanerpeton either as sister group to both species of Discosauriscus, or to D. austriacus only.
The arid climate of the Altiplano has preserved a volcanic history of ∼11 million years at the Aucanquilcha Volcanic Cluster (AVC), northern Chile, which is built on thick continental crust. The AVC has a systematic temporal, spatial, compositional and mineralogical development shared by other long-lived volcanic complexes, indicating a common pattern in continental magmatism with implications for the development of underlying plutonic complexes, that in turn create batholiths.
The AVC is a ∼700-km ² , Tertiary to Recent cluster of at least 19 volcanoes that have erupted andesite and dacite lavas (∼55 to 68 wt.% SiO 2 ) and a small ash-flow tuff, totalling 327 ± 20 km ³ . Forty ⁴⁰ Ar/ ³⁹ Ar ages for the AVC range from 10·97 ± 0·35 to 0·24 ± 0·05 Ma and define three major 1·5 to 3 million-year pulses of volcanism followed by the present pulse expressed as Volcán Aucanquilcha. The first stage of activity (∼11–8 Ma, Alconcha Group) produced seven volcanoes and the 2-km ³ Ujina ignimbrite and is a crudely bimodal suite of pyroxene andesite and dacite. After a possible two million year hiatus, the second stage of volcanism (∼6–4 Ma, Gordo Group) produced at least five volcanoes ranging from pyroxene andesite to dacite. The third stage (∼4–2 Ma, Polan Group) represents a voluminous pulse of activity, with eruption of at least another five volcanoes, broadly distributed in the centre of the AVC, and composed dominantly of biotite amphibole dacite; andesites at this stage occur as magmatic inclusions. The most recent activity (1 Ma to recent) is in the centre of the AVC at Volcán Aucanquilcha, a potentially active composite volcano made of biotite-amphibole dacite with andesite and dacite magmatic inclusions.
These successive eruptive groups describe (1) a spatial pattern of volcanism from peripheral to central, (2) a corresponding change from compositionally diverse andesite-dacite volcanism to compositionally increasingly restricted and increasingly silicic dacite, (3) a change from early anhydrous mafic silicate assemblages (pyroxene dominant) to later biotite amphibole dacite, (4) an abrupt increase in eruption rate; and (5) the onset of pervasive hydrothermal alteration.
The evolutionary succession of the 327-km ³ AVC is similar to other long-lived intermediate volcanic complexes of very different volumes, e.g., eastern Nevada (thousands of km ³ , Gans et al. 1989; Grunder 1995), Yanacocha, Perú (tens of km ³ , Longo 2005), and the San Juan Volcanic System (tens of thousands of km ³ , Lipman 2007) and finds an analogue in the 10-m. y. history and incremental growth of the Cretaceous Tuolumne Intrusive Suite (Coleman et al. 2004; Glazner et al. 2004). The present authors interpret the AVC to reflect episodic sampling of the protracted and fitful development of an integrated and silicic middle to upper crustal magma reservoir over a period of at least 11 million years.
Restoration of the morphology of Angustidontus seriatus Cooper, 1936 based on complete specimens from the Famennian of Nevada and Poland, supports its affinity to the coeval alleged decapod Palaeopalaemon and suggests eocarid (possibly also peracarid) affinities. Predatory adaptation of the thoracopods and the relatively short pereion make this crustacean only superficially resemble the archaeostomatopod hoplocarids, because the large grasping appendages of Angustidontus represent the first, rather than second, maxillipeds and acted in the opposite direction: downward. Another similar adaptation of the antennae in the Viséan Palaemysis suggests a widespread adaptation to predation among early eumalacostracans. The large sample collected from the Woodruff Formation of Nevada permits biometric characterisation of the grasping maxillipeds of Angustidontus, showing that their highly variable morphology should not be used to define species. All previously described species are therefore here synonymised with A. seriatus. Differences in gnathobases of mandibles found in articulated specimens in Nevada, and associated with isolated maxillipeds and articulated specimens possibly representing another unnamed species in Poland, suggest that such mandibles may eventually prove to be taxonomically more significant.
A diverse arthropod-dominated ichnofauna, associated with a poorly preserved crustacean fauna and soft-bodied ?medusoid impressions, is described from the Blaiklock Glacier Group of the north-western Shackleton Range (Coats Land), Antarctica. The ichnofauna consists of Asaphoidichnus, Beaconites, Didymaulichnus, Diplichnites, Gordia, ?Laevicyclus, Merostomichnites, Monomorphichnus, Palaeophycus, Planolites, Rusophycus, Selenichnites , and Taphrhelminthoides (ichnogen nov.). Three new ichnotaxa are recognised: Taphrhelminthoides antarcticus n. ichnogen. et ichnosp. is a bilobate trail, composed of two parallel flat lobes, separated by a median ridge with a characteristic figure-of-eight pattern. Merostomichnites gracilis n. ichnosp. is characterised by its proportions (external:internal width ratio >3) and series of 10 to 12, thin, linear tracks. Selenichnites antarcticus n. ichnosp. is characterised by small elongate horseshoe-shaped marks, the medial portion showing three to five transverse scratch-marks.
The palaeoenvironment is interpreted as extremely shallow marine water, possibly a tide-dominated estuary, based on sedimentological evidence and the composition of the ichnofauna. Radiometric and palaeomagnetic data indicate that this assemblage is Lower Ordovician in age, representing the first autochthonous Ordovician fossiliferous succession to be described from Antarctica. The succession shows several sedimentological and palaeontological similarities with the basal units of the Ordovician Table Mountain Group in South Africa, supporting palaeogeographic models placing the Palaeozoic Blaiklock basin close to the Ordovician Table Mountain basin.
This paper evaluates the taxonomy, biostratigraphy, and palaeogeographical significance of the Cambrian bradoriid arthropods of China, the majority of which occur in the lower Cambrian of SW China. Of bradoriid faunas world-wide, Chinese occurrences yield the greatest number of specimens and a comparatively high diversity at all taxonomic levels. Nevertheless, taxonomic diversity is much less than previously supposed. Some 80 bradoriid genera and nearly 300 species have been proposed on the basis of Chinese material. By contrast, in our study, which encompasses all of the important Chinese bradoriid faunas, we recognise only 16 genera and 21 species, including those treated under open nomenclature. Interpretation of deformed specimens as discrete species and lack of application of the rules of the International Code of Zoological Nomenclature resulted in taxonomic splitting and a proliferation of names. There are an additional 12 poorly known monotypic genera of uncertain systematic status that are listed but not treated further herein. One phosphatocopid species, a group originally thought closely related to the Bradoriida, is also described.
Most Chinese bradoriid material is known from Yunnan Province; the group also occurs in Guizhou, Henan, Hubei, Hunan, Liaoning, Qinghai, Shaanxi, Sichuan, Xinjiang and Zhejiang provinces. The first bradoriids occur just below the Abadiella trilobite Biozone. They are most prolific and diverse in the Qiongzhusian Stage, constituting the most abundant animal group; the succeeding Canglangpuian Stage contains fewer individuals and species. A previously proposed bradoriid biozonal scheme lacks rigour and is of little practical value: of the five supposed biozones, two correspond to trilobite zones and three are based on taxa that herein are considered to belong to a single species.
Palaeogeographically the bradoriids occur in the Middle and especially the Western subprovinces of the Cambrian of the SW China (Yangtze) Platform. Almost all of the bradoriid genera and species are endemic to that region. The palaeogeographical links with other bradoriid faunas are mostly within the Redlichiid trilobite Realm, with areas such as N China, Australia and parts of central Asia.
Textural relations and chemical zoning of cordierites in granites act as sensitive recorders of the conditions of their crystallisation history and underlying magma chamber processes. In this contribution, we present new data on texturally distinct and variably zoned cordierites from the late-Devonian, granitic South Mountain and Musquodoboit Batholiths, and infer the conditions of their formation. Using a combined textural (grain size, grain shape and inclusion relationships) and chemical (major element composition and compositional zoning) classification, we recognise the following six cordierite types: CG1/TT1, anhedral to subhedral macrocrysts with random inclusions and patchy normal zoning; CG2a/TT2, euhedral to subhedral macrocrysts with random inclusions and normal zoning; CG2b/TT2, euhedral to subhedral macrocrysts with random or oriented inclusions, and oscillatory zoning; CG3a/TT3, subhedral to euhedral microcrysts with no inclusions and reverse zoning; CG3b/TT4, euhedral macrocrysts with no inclusions and no zoning; and CG4/TT5, anhedral macrocrysts with random inclusions and normal zoning. The textural criteria suggest that these cordierites formed as a product of cotectic crystallisation from a melt, or as the result of a peritectic reaction involving country-rock material. The combined chemical and textural criteria suggest that: (1) normal zoning results from cotectic crystallisation during cooling, cotectic overgrowths on grains formed in a peritectic reaction with country-rock material, or cation exchange with a fluid; (2) oscillatory zoning results from cotectic crystallisation during variations in XMg of the silicate melt following magma replenishment; (3) reverse zoning results from crystallisation during pressure quenching; and (4) the unzoned cordierite results from cotectic crystallisation under fluid-rich conditions.
A section of the Vitabäck Clays at Eriksdal in southern Sweden was sampled for vertebrate fossils. Large bulk samples were collected from three horizons, including two coquina beds, VC3 and VC11, and a silty clay bed, VC7. Shark teeth are very common and constitute the main portion of the vertebrate material discussed herein. The selachian tooth faunas are almost exclusively represented by hybodonts, although a single tooth from a neoselachian shark, Squatinidae indet., was recorded from one horizon (VC3). Hybodont species identified from the Vitabäck Clay samples include Egertonodus basanus , Hybodus parvidens and Parvodus rugianus . Hybodont remains, other than teeth, include five morphotypes of placoid scales, incomplete cephalic spines and fragmentary fin spines.
Other fossil groups represented in the sieved residues from the bulk samples include bivalves, gastropods and bony fish. Together with the selachians, they indicate fluctuating palaeosalinities in the area. The lower coquina bed, VC3, includes taxa indicating mesohaline conditions while the composition of the fauna in the other coquina bed, VC11, suggests oligohaline settings. In bed VC7, the presence of amphibian remains and the rarity of selachian fossils indicate an even lower salinity. Palynomorphs from the basal part of the section, immediately below bed VC3, indicate an earliest Cretaceous (Berriasian) age.
The record of Ordovician Eurypterida from New York State, USA, is shown to be largely false. Twenty-nine species in 17 genera are here recognised as pseudofossils, reducing by more than 75% the total number of named Ordovician eurypterid taxa. Consequently, 10 families now have their first occurrence either later in the Ordovician or in the Early Silurian. The implications for eurypterid palaeoecology, diversity and evolution are not as straightforward as would be expected from such a drastic taxonomic revision. All Ordovician eurypterids are now known to occur in shallow-water, near-shore shales or fine-grained carbonates. Diversity measures indicate that the end-Ordovician extinction event appears to have had less effect on eurypterids than previously known, and their turnover is level in the Ordovician.
Scotland has a magmatic record covering much of the period 3100–50 Ma. In this review, we pull together information on Scotland's igneous rocks into a continuous story, showing how magmatic activity has contributed to the country's structural development and assessing whether the effects of older magmatic events can be recognised in later episodes.
The oldest igneous rocks are part of supracrustal sequences within the Lewisian Gneiss Complex, formed when Scotland was part of the supercontinent Kenorland. The supracrustal rocks were intruded between 3100 and 2800 Ma by granodiorites and tonalites, which were metamorphosed and deformed in a major tectonothermal event between 2700 and 2500 Ma. The break-up of Kenorland (2400–2200 Ma) was marked by the intrusion of mafic dyke swarms of tholeiitic affinity. The convergence of continental masses to form the supercontinent Columbia resulted, at ∼1900 Ma, in a series of subduction-related volcanic rocks and gabbro–anorthosite masses. Subsequent continent–continent collision formed a series of granite–pegmatite sheets at ∼1855 Ma and ∼1675 Ma and reworked much of the earlier rocks in the amphibolite facies. Columbia was breaking up by 1200 Ma, an event marked by remnants of basaltic magmatism in the NW of the country. Re-assembly of the continental fragments to form the supercontinent Rodinia resulted in the Grenville Orogeny, which in Scotland was marked by basement reworking but no confirmed magmatic activity. Early attempts to split Rodinia produced a rift-related, bimodal, mafic–felsic sequence in the Moine Supergroup of the Northern Highlands, at least some of the mafic rocks having mid-ocean ridge basalt affinities. Crustal thickening during a disputed orogenic event, the Knoydartian, may have caused regional migmatisation. The final break-up of Rodinia occurred in Scotland at ∼600 Ma, when very extensive tholeiitic magmatism characterised the later parts of the Dalradian Supergroup, while a series of granites intruded the Moine and Dalradian successions.
Ordovician and Silurian times saw the closure of the Iapetus Ocean and the convergence of Laurentia, Avalonia and Baltica. The collision of a major arc system with Laurentia caused the Grampian event (480–465 Ma) of the Caledonian Orogeny, marked by ophiolite obduction, the generation of (largely) anatectic granites, volcanism in the Midland Valley and Southern Uplands, and intrusion of a major gabbro–granite suite in the NE. The late-Caledonian events (435–420 Ma) were largely post-collisional and were marked by the emplacement of alkaline igneous intrusions in the NW, calc-alkaline granitic intrusions over much of the country, widespread volcanic activity and regional dyke swarms. Laurentia, Avalonia and Baltica amalgamated to form the supercontinent Laurussia. Magmatic activity recommenced at 350 Ma, when intra-plate alkaline magmatism affected much of southern Scotland, in particular, through into Permian times. The alkaline magmatism was interrupted at ∼295 Ma by a short-lived event in which tholeiitic magmas were intruded as sills and dykes in a swarm ∼200 km wide. In the early Palaeogene, lithospheric attenuation related to proto-North Atlantic formation and the splitting of Pangaea was complemented by the arrival of the Iceland mantle plume. Huge volumes of mafic magma were emplaced as lava fields, central complexes and regional swarms, locally increasing crustal thickness by 30%
Twelve localities of Lower Carboniferous strata in Scotland (Loch Humphrey Burn, Glenarbuck, Pettycur, Oxroad Bay and the Berwickshire localities of Cove, Burnmouth, Gavinton, Edrom, Foulden) and in France (Esnost, Roannais, Montagne Noire) have been investigated with particular regard to their anatomically preserved floras. New data on the composition and preservation of the assemblages, their geological setting and stratigraphical age, using palynology in particular, are presented. Present data suggest that four successive groups of floras obtained from these localities can be recognised: from the Montagne Noire (mid to late Tournaisian) from the Berwickshire localities and Oxroad Bay (late Tournaisian to early Visean) from Loch Humphrey Burn and possibly Glenarbuck (mid Visean) and from Roannais, Esnost and Pettycur (late Visean). The similarities and differences between the floras are discussed with particular emphasis on stratigraphical as opposed to ecological controls. Comparisons are made with the New Albany Shale floras of the U.S.A., the Saalfeld and Glaetzish-Falkenberg floras from the German Democratic Republic. The data suggest that the ferns and pteridosperms show the most striking changes through the Lower Carboniferous strata.
Plants of gymnospermous affinities are the most important component of the flora at East Kirkton. Four genera of anatomically preserved gymnosperm stems with well developed secondary xylem are interpreted as arborescent. The largest specimens (trunks up to 50 cm in diameter) are attributed to the genus Pitus. Features of the wood, including ray size, are characteristic of the species Pitus withamii Lindley & Hutton which has long been described from the Strathclyde (former Oil-Shale) Group of Scotland. Decorticated axes of Eristophyton fasciculare are more common; their study has enlarged our concept of the species with regard to maximum diameter, internode length and phloem organisation. Similarly, the decorticated specimens of Bilignea solida Kidston found at East Kirkton exceed in diameter the original material described from Ayrshire. The fourth taxon is Stanwoodia recently described by Galtier and Scott (1991). In all these plants, features of leaf traces suggest that leaves were relatively large and densely borne on ultimate branches. These leaves were shed ultimately, prior to a later phase of wood development; they certainly correspond to (? most of) the compression foliage commonly found in association: Sphenopteridium, Adiantites and Spathulopteris.
Plant fossils are a common and important element in the East Kirkton biota of Brigantian (late Visean age). The most important taxa are preserved as compressions or anatomically preserved as permineralisations. The basis of the quantitative study of the flora and the distribution of individual plant species was the trenched section excavated for the East Kirkton Project. The largest diversity of compressions have been recorded from loose blocks. In the trenched section, the uppermost ashes contain only lycopsid compressions including Stigmaria. Nodules in the underlying shales yield mainly lycopsid leaf and sporophyll compressions. The uppermost limestones (Units 39-52) contain drifted fragments of pteridosperm fronds mainly Sphenopteridium crassum, S. pachyrrhachis, Spathulopteris obovata and Adiantites antiquus. Permineralised Lyginorachis spp. occur at this level. Large permineralised woody gymnosperm axes have been found loose (including Pitus, 50 cm in diameter). Permineralised axes, mainly reworked, including the gymnosperms Bilignea, Eristophyton, Stanwoodia and possibly Protopitys, have been found in Units 72-88. Poorly preserved permineralised lycopsids are rare, but include Lepidophloios. Loose chert blocks contain root mats of permineralised Stigmaria, together with Lepidocarpon, the sphenopsid Archaeocalamites and the fern Botryopteris. Similar material is found in Unit 83 of the Limestone sequence. Unit 82, the black shale containing many of the articulated vertebrates, contains predominantly pteridosperm frond and pinnule material including Spathulopteris obovata. The distinctive changes in the flora from the base to the top of the trenched sequence reflect mainly ecological and taphonomic controls upon plant distribution and preservation. Evidence suggests a close relationship between climate, fire, erosion, deposition and vegetation type through the sequence and a climatic change, from a drier to a wetter environment, is suggested at the top of the East Kirkton Limestone sequence.
A comprehensive study of the similar to 2200-Ma-old Kuetsjarvi Sedimentary Formation (KSF), NW Russia, was undertaken to contribute to our understanding of palaeoenvironments associated with the global perturbation of the carbon cycle between 2330 and 2060 Ma. Closely spaced drill core samples (n=95) were obtained from a 150-m-thick unit deposited in rift-bound fluvial-deltaic and shallow-water lacustrine settings with a short-term invasion of sea water. Apart from a very few de-dolomitised samples, all other carbonate lithologies are represented by C-org-free, S-poor, quartz-rich dolostones, stromatolites and travertines which have high Sr concentrations (51-1069 ppm) and low Mn/Sr ratios (2.9 +/- 2.1). The carbonate succession, excluding travertines, shows high delta(13)C (+7.5 +/- 0.6 parts per thousand, n=95) with a limited variation (+5.8 to +8.9 parts per thousand). Fluctuating delta(18)O values (10.8-20.4%) were overprinted during diagenesis, regional greenschist-grade and later retrograde metamorphism. Several short-term stratigraphic excursions of delta(13)C were apparently governed by evaporation and CO2 degassing combined with pulses of C-12-rich hydrothermal waters precipitating travertines. However, the C-13-rich nature of the dolostones reflects the global isotopic signal, which was modified in a shallow water lacustrine environment by evaporation, enhanced uptake of C-12 by cyanobacteria, and pene-contemporaneous oxidation and loss of organic material. The best proxies to delta(13)C and Sr-87/Sr-86 of coeval sea water recorded in the KSF dolostones are likely to be around +5-6 parts per thousand and 0-70406, respectively. The study of the KSF has shown that circumspection is necessary when attempting to model the behaviour and evolution of the global C-cycle in Deep Time. Models which purport to explain global oceanic-atmospheric evolution without first adequately accounting for the possibility that many Precambrian carbonate deposits might be non-marine, or at least influenced by non-marine fluids, should be viewed with caution.
The very large trilobite Taihungshania miqueli occurs abundantly in siliceous nodules in the Ordovician of the Montagne Noire, southern France, but in these, larval individuals are not preserved. At a new locality at Peret, near Cabrieres, protaspid and early meraspid growth stages occur in great abundance, together with a few complete specimens belonging to meraspid degrees 1, 2, 3, 5 and 7, and a single young holaspis. Although this material is largely flattened, and the originally globular protaspides crushed, it is still possible to establish the development of several axial rings before the transitory pygidium becomes liberated. In the degree 0 meraspis, the cephalon and transitory pygidium are about the same size, and the presence of a partially enrolled degree 3 meraspis indicates that protective coiling was possible by this early stage. Palpebral lobes are incipient in degree 2 meraspides, and fully formed by degree 7, otherwise the morphology of the cephalon becomes quite adult-like by degree 4. The pygidial spines begin to appear in degree 5, at which stage there are about 10 axial rings; there are about 13 in a degree 7 meraspis, and in the adult, when the posterior contour is semi-elliptical, there are some 22. The smallest hypostomes present belong to a degree 6 meraspis, and these are morphologically similar to those of adults. Observations on the later growth stages were made on material from another locality (Caramaou), as well as that from Peret. In the eye the upper lenses an large and slightly separated, but those towards the base are much diminished in size, this is a function of an unusual growth geometry. At Peret, all stages of development, at least as far as young adults, are represented, albeit often in a fragmentary state. As with other asaphines, the protaspides are assumed to be planktic, and T. miqueli presumably left the plankton and became benthic between the protaspid and meraspid periods.
A new crustacean, Castracollis wilsonae is described from a loose block of the Early Devonian Rhynie chert, found in the vicinity of Rhynie, Aberdeenshire, Scotland. It differs markedly from Lepidocaris rhyniensis, Scourfield 1926, the only other crustacean found in the Rhynie chert. The material comprises complete individuals up to 8 mm long and fragmentary remains. The head is normally damaged and detached from the body, and damage to the anterior of the trunk suggests the specimens are exuviae. The head appears domed with a labrum, robust mandibles, and long biramous antennae. A few specimens exhibit a probable detached cephalo-thoracic shield. The trunk is multi-segmented, comprising similar ring-like somites. The thorax variably comprises up to 26 segments. The anterior 11 segments possess similar long, phyllopodous appendages, the remainder variably possess 10 to 15 phyllopodous appendages with a disposition of one per somite. The abdomen comprises up to 28 apodous segments. The posterior of the body comprises a telson with two furcal rami. The crustacean is most probably a calmanostracan branchiopod. It occurs associated with Lepidocaris, charophytes, cyanobacteria and coprolites within a 'clotted' chert texture, indicating subaqueous deposition, most probably in a temporary freshwater pool in area of surficial hydrothermal activity.
Geological and palaeontological research in the Rhynie area, Aberdeenshire, Scotland, has progressed in several stages. Following early surveys in the nineteenth century, Dr William Mackie mapped the western margin of the basin in 1910-1913, and discovered the plant-bearing chert. Following trenching of the chert in 1913, Kidston & Lang described the plant fossils between 1917 and 1921 and Scourfield, Hirst and Maulik the arthropods in the 1920s. Following a 'dark age' of some 30 years, Geoffrey Lyon awakened interest in the late 1950s. Trenching in 1963-1971 provided Lyon and his co-workers with new material, and resulted in finds of new plants and reinterpretations of earlier work. The next phase was initiated by Winfried Remy's discovery of gametophytes in material given to him by Lyon. Since 1980, the Munster school has continued to make exciting discoveries. Aberdeen University involvement began in 1987 with geochemical work confirming a hot spring origin for the chert. Drill cores taken in 1988 and 1997, and further trenching have allowed structural, sedimentological and stratigraphic reappraisals, and resulted in the discovery of a new biota in the Windyfield chert. Long-term collaborative international research continues to advance interpretation of this unique Early Devonian hot spring system, and the remarkably diverse freshwater and terrestrial biota of the cherts.
There is abundant evidence of injury, teratology and pathological conditions in trilobites although it is commonly difficult to distinguish between their morphological results. Many injuries were probably sustained during moulting, with spines, bilamellar fringes and narrow gaps between dorsal exoskeleton and doublure being most vulnerable. Some injuries were the result of predaceous attack and provide important clues to the trophic structure of Palaeozoic communities. Many injuries show evidence of repair. Some supposedly teratological conditions, most notably the number of paradoxidid thoracic segments, are so common that they must be considered part of normal variation. Others represent genetic mutation or ontogenetic malfunction, the latter possibly externally induced. Undoubted pathological conditions are restricted to swellings and borings presumably caused by parasitic infestation. Abnormalities affecting lateral areas are more common than those involving the rachis and glabella and this probably reflects both greater mortality when the axial region is involved, and greater vulnerability of peripheral regions to predaceous and moulting damage. The first explanation also accounts for the rarity of cephalic abnormalities compared to those of the pygidium. -Author
The zoned McMurry Meadows Pluton has been examined for REE and trace element variations in hornblende, sphene, apatite, allanite and zircon. Mineral separates (17), were analysed by INAA from four granitoids spanning the compositional range of the pluton (60%-75% SiO2). All of the phases examined exhibit significant compositional variations, with sphene having the largest changes in chondrite normalised REE patterns. Compositional variations in these minerals are related to paragenetic sequence and, as the whole rocks become more evolved, increases in partition coefficients; not subsolidus re-equilibration. Hornblende is only a dominant site for REE in granites where sphene is a later crystallising phase, otherwise allanite (LREE only) and sphene are the dominant whole rock sites for REE. Zircon and apatite normally contribute less than 10% each to the whole rock abundance of REE. Three zircon samples contain only small compositional differences and are interpreted as having crystallised from the bulk magma prior to differentiation. Zr variation in the pluton is nonlinear, first increasing and then decreasing with whole rock fractionation. A simple process, analogous to "restite unmixing' applied to the Zr variation, defines a bulk magma composition of about 63% SiO2, before differentiation of the zoned pluton. The modelled bulk magma need only have evolved by about 2.5% silica and still have produced the entire compositional range (60-75% SiO2) observed in the pluton. -Author
The Late Cretaceous granites of the eastern Mojave Desert, California, have heretofore provided useful but poorly focused images of their source regions. New studies of lower crustal xenoliths and inherited accessory minerals are sharpening these images. Xenoliths in Tertiary dykes in this region are the residues of an extensive partial melting event. A link between these xenoliths and the Late Cretaceous granites is probable; in any case, they provide invaluable clues concerning a crustal melting event, recording information about nature of source material (heterogenous, supracrustal-rich), conditions of melting (moderately deep, moderately high T, accompanied by partial dehydration), and melt extraction (highly variable, locally extensive). The Old Woman-Piute granites contain a large fraction of inherited zircon and monazite. The zircons record a Proterozoic history similar to that which affected the Mojave region. Zonation patterns document multiple phases of igneous, metamorphic, and sedimentary growth and degradation, commonly several in a single grain. -from Authors
Late Palaeozoic alkali basalts in the Midland Valley contain a variety of 'plutonic' xenoliths. The upper mantle is dominantly magnesian peridotite in which a younger component is represented by pyroxene-rich xenoliths (wehrlites, clinopyroxenites and garnet pyroxenites). Biotite-rich ultramafic xenoliths are probably samples of metasomatized upper mantle facies. Xenoliths of plagioclase and clinopyroxene + or - orthopyroxene + or - magnetite are common and may represent lower crust; garnet granulites are rare but anorthosites common. The lower crust may consist largely of stratified metacumulate bodies. Tonalitic and trondhjemitic gneisses probably represent a mid-crustal domain beneath deformed Upper Precambrian and Lower Palaeozoic supracrustals. Widespread metasedimentary rocks are also regarded as mid-crustal.-I.P.
Agnostid trilobites are relatively abundant and taxonomically diverse in outer shelf facies of the Yangtze Platform and Jiangnan Transitional Belt regions of the South China Plate. Nine Arenig and Llanvirn species, representing at least five genera or subgenera in the Agnostidae, Diplagnostidae and Metagnostidae, are treated in a taxonomic review of the South Chinese Agnostida, based on new material from the Dawan and Kuniutan formations of W Hubei and the Zitai and Jiuxi formations of N Hunan. The new genus Han is established to incorporate the globally youngest known diplagnostid species. The new species Han solo, Geragnostus (Geragnostus) balanolobus and G. (G.) waldorfstatleri are established. G. carinatus is recognised as being based on inaccurately interpreted material, and is only tentatively retained within Geragnostus. Three further taxa represented by poorly preserved material are left in open nomenclature. The geographic distributions of different agnostid species across the South China Plate, and the endemicity to the palaeoplate displayed by all Arenig-Llanvirn South Chinese species, suggest that these agnostids at least were either benthic or epibenthic.
Little is known regarding the internal anatomy of thelodonts, with most of the available information coming from a single specimen. the holotype of Turinia pagei (Powrie). Previous descriptions have led to many partial, or conflicting interpretations. Herein, we describe fully the anatomy of T. pagei based on the holotype and additional material. T. pagei possessed a branchial system composed of eight pairs of gills, a buccal/nasohypophyseal region lined with minute denticles, comparable to buccopharyngeal denticles of sharks, and possessed a stomach which is preserved by sediment infill in the holotype specimen. Contrast between the petrological character of the gut infill and the sediment in which the animal is preserved suggests that the gut was infilled in vivo and that T. pagei was probably a deposit feeder. Phylogenetic analysis resolves T. pagei and the Galeaspida as sister-taxa. comprising a sister-group to the Osteostraci plus jawed vertebrates. In contrast to the view that has prevailed hitherto. thelodonts with a dorsoventrally compressed cross-sectional profile comprise a monophyletic group. of which T. pagei is the least derived member. The furcacaudiforms are resolved as an unnatural group, one taxon being the sister taxon to the 'conventional' thelodont clade, and the other, the sister taxon to this clade plus galeaspids, osteostracans and jawed vertebrates. The analysis agrees with the earlier view that thelodonts lack distinct synapomorphies, but we argue that distinct synapomorphies are not a requisite of monophyly.
The skull roof, palate and lower jaw of the seymouriamorph Utegenia shpinari (?Upper Carboniferous-Lower Permian; Kurgalin Formation, Kazakhstan) are described in detail, and a new cranial reconstruction is presented. Important features include: skull slightly longer than broad; elongate nasals; deep, elongate posterior cheek region; long, dorsoventrally deep posterior jugal ramus; flat, recurved, blade-like tabular process; denticle-covered anterior ventral part of pterygoid quadrate ramus; transverse pterygoid flange; low radiating ridges with denticle rows on pterygoid and parasphenoid cultriform process; incipient anterior wedge-like process on posterior end of parasphenoid cultriform process; distinct, robust posterolateral processes of posterior plate of parasphenoid. Degree of skull ossification, ornamentation, and absence of ossified quadrate, articular and endocranium suggest that large Utegenia specimens correspond to larval Discosauriscus. In such specimens, dentine infolding extends for almost half of the crown in premaxillary and largest maxillary teeth, as in late larval/metamorphic Discosauriseus. Preliminary results of a regression analysis through some simple skull measurements indicates that, although the preorbital and interorbital regions elongate isometrically relative to the posterior skull table, they do not show a particularly strong linear correlation with the widening of the skull during ontogeny.
The Rhizodontida (Pisces: Sarcopterygii) is a clade of predatory fishes from the Upper Devonian (Aztecia; ?Givetian of Antarctica) through to the Upper Carboniferous (Strepsodus; Moscovian of northern Europe and North America). They form the most basal plesion within the tetrapod stem-lineage. The mandibles were dominated by large symphysial tusks on the dentary. Not much else is known of the mandibles in primitive rhizodontids. However, later forms show several derived characters: the mandible is very deep dorsoventrally and narrow linguolabially; the coronoid fangs bear only a single fang and no other dentition; the Meckelian element was unossified, leaving the adductor fossa unfloored by bone; the prearticular produced a large dorsal process lingual to the adductor fossa, presumably for muscle attachment. These and other characters are discussed in the context of the evolution of the tetrapod stem-group. The mandible appears to have been split into two functional units, one comprising the firmly sutured prearticular, coronoids and dentary, the other comprising the firmly sutured infradentaries. The connection between the two units was weak, suggesting a longitudinal intramandibular hinge. The possibility that this acted as a 'torsion grip' during feeding is discussed.
Musculature of the pectoral and pelvic appendages and girdles of adult and nestling Maiasaura peeblesorum (Dinosauria: Ornithischia: Hadrosauridae) from the Late Cretaceous of Montana is restored according to a phylogenetically based methodology. This methodology uses an explicit, independently derived phylogenetic hypothesis of the fossil taxon and related extant taxa to generate a series of inferences regarding the presence of a muscle, its number of components, and the origin(s) and insertion(s) of these components. Corroborative osteological evidence is sought on the fossil in the form of scars and processes that fulfill the criteria for muscular attachment according to generalisations based upon extant vertebrates. A total of 46 muscles are restored, although separate attachment sites for numerous muscles cannot be discerned on the fossils. Osteological evidence for several muscles can be found in nestlings of Maiasaura despite their skeletal immaturity. Results of the phylogenetically based approach and new hypotheses for homologies of deep dorsal thigh muscles suggest that it is more parsimonious to restore the femoral insertions of M. iliofemoralis on the greater trochanter and M. puboischiofemoralis internus on the anterior (lesser) trochanter, a reversal of the traditional interpretation. The often-cited osteological specialisations of birds for flight are not accompanied in all instances by profound myological transformations, and birds must be included in any attempt to restore the myology of extinct dinosaurs.
Microstructural features of eurypterid cuticles are analysed from a biomechanical viewpoint: some fibrous elements are now considered to resemble the macrofibres of extant arthropod cuticles; possible preferred orientation zones in Mycterops are related to directional stresses; pore canals are not viewed as acting as crack-stoppers but laminae (sensu Dennell 1978) may have served this function. Could some eurypterids have walked on land? - this problem is approahced by using extant Limulus as a model. It leads on to the use of scaling exponents to determine the limits that possessing an exoskeleton places on the size of land arthropods: moulting may be the limiting factor. Possble critical factors limiting the size of aquatic arthropods are discussed briefly. -Author
A new hypothesis of the relationships between arachnomorph arthropods, and the origin of chelicerates, is presented based on a cladistic analysis of 34 taxa and 54 characters. The present study provides a detailed discussion of primary hypotheses of homology and includes a more complete range of terminal taxa than previous analyses. The analysis provides the first convincing synapomorphies for the Arachnomorpha, and suggests that the marrellomorphs are not arachnomorphs. The assignment of Cambrian 'great appendage' (or megacheiran) arthropods to the Arachnomorpha is confirmed, and potential synapomorphies uniting them with chelicerates are discussed and tested. Principal amongst these are the loss of the first cephalic appendages (the antennae), loss of the exopods of the second cephalic appendages and modification of the endopods of these appendages into spinose grasping organs. The Arachnomorpha consists of two major clades: (1) a 'chelicerate-allied' clade, including chelicerates, megacheirans, Emeraldella, Sidneyia, cheloniellids and aglaspidids, in which chelicerates and a paraphyletic group of megacherian arthropods form the sister group to the remaining taxa; and; (2) a 'trilobite-allied' clade, including trilobites, xandarellids, helmetiids, tegopeltids and naraoiids, the relationships of which are more fully resolved than in previous studies.
Microdecemplex rolfei, gen. and sp. nov., a new microarthropleuridean less than 5 mm long, is described from the Middle Devonian Panther Mountain Formation of New York State, U.S.A. The specimens consist of organically preserved cuticle, with some preserving the only cephalic structures known for arthropleurideans. A new order, Microdecemplicida, and a new family, Microdecemplicidae, are established. The probable phylogenetic position of the Microdecemplicida as one of the basal clades of Diplopoda is proposed.
Diapirism has been discredited as a transport mechanism for magmas partly because diapirs seem to be unable to bring magmas to shallow crustal levels (< 10 km) and partly because recent developments in the theory of dyke propagation have shown that sufficiently wide dykes are able to efficiently transport felsic magmas through the crust. However, it is still unclear how felsic dykes grow to widths that allow them to propagate faster than they close by magma freezing. Ultimately, it may be the ability of felsic dykes to grow within the source that controls which mechanism dominates ascent. The ability of dykes to propagate from the top of rising diapirs depends among other factors on the changing temperature gradient of the wall rocks. The steep gradient around rapidly rising diapirs in the low viscosity lower crust will cause dykes to freeze. As diapirs rise to colder stiffer crust and decelerate, heat diffuses further from the diapir, resulting in shallower temperature gradients that favour dyke propagation. The mechanism may thus swap, during ascent, from diapirism to dyking. Calculations of the thermal evolution of diapirs and their surroundings show that basaltic diapirs may never form because they would be drained by dykes at a very early stage; felsic diapirs may be unable to give rise to successful dykes, whereas diapirs of intermediate magmas may propagate dykes during ascent.
The ascent of silicic magmas in dykes and diapirs on Venus is investigated using magma transport models for granitic melts on Earth. For fixed planetary thermal and melt properties, differences in critical minimum dyke widths, and hence magma ascent rates, are controlled by gravitational strength alone. For density contrasts of 200-600 kg/m3 and a solidus temperature of 1023 K, minimum critical dyke widths (wc) on Venus range from c. <1-1200 m for a transport distance of 20 km. Dyke widths are especially sensitive to small changes in the far-field lithospheric temperature at values close to a critical Stefan numbers (Soocrit) of 0.83 where dyke magma temperatures are equal to the mean surface temperature. Typical magma ascent rates range from 0.02 m/s (nm = 105 Pa s) to 10-9 m/s (nm = 1017 Pa s) giving transport times of between 12 days and c. 105 years. Dyke ascent velocities for highly viscous melts are compared with diapiric rise of a hot Stokes body of radius comparable with the pancake dome average (c. 12 km), and require dyke widths of the order of 100 times the average width of low viscosity flows to prevent freezing. In both cases, magma flow is characterised by Péclet numbers between 1 and 4, although even at high viscosities (> 1014 Pa s), dyke ascent is still 100 to 1000 times faster than diapiric rise. At a melt viscosity of 1017 Pa s, critical dyke widths are between c. 1% and 5% the diameter of an average width pancake dome on Venus, indicating that even for extreme melt viscosities, domes can easily be fed by dykes. Given the abundance of dome structures and associated surface features related to hyperbasal magmatism, batholithic volumes of silicic rocks may be present on Venus. Intermediate to high silica melts formed by partial melting of the Venusian crust should be compositionally more akin to Na-rich terrestrial adakites and trondhjemites than calc-alkaline dacites or rhyolites.
The exposed Precambrian cratonic crust in South Korea is divided into two massifs - the Gyeonggi massif to the north and the Yeongnam massif to the south. Mesozoic granites intruded into both massifs and are mostly I-types. The Jurassic granites form extensive deep-seated batholiths. the Triassic granites are deep-seated stocks and the Cretaceous granites occur as volcanic-plutonic complexes. The systematic variation of c,, and SrI in the Korean Mesozoic granites could result from the mixing of two components in different proportions to produce the source of the granites. Although most Mesozoic I-type granites were apparently derived from more juvenile crust, the old evolved crustal components seem to have been incorporated in the magmas in various proportions. Mantle-crust mixing can account for the generation of the source of the Triassic and Cretaceous granites in the Gyeongsang basin. On the other hand, crust-crust mixing can feasibly produce the source of the Triassic and Jurassic granites in the Yeongnam massif, the Jurassic granites in the Gyeonggi massif, and the Cretaceous granites in the Yeongdong-Gwangju basin and the Okcheon belt. However, some Jurassic granites in the Yeongnam massif and Cretaceous granites in the Yeongdong-Gwangju basin can be also explained by the mantle-crust mixing. Combined geochemical and isotopic signatures indicate that a simple binary mixing model is inadequate to explain both the geochemical and isotopic data. The chemistry of the granites is considered likely to reflect the composition of the igneous protolith that derived from depleted mantle, which explains why most Mesozoic granites in South Korea are represented by I-types, regardless of their temporal and spatial position. Nd-Sr isotopic signatures of the Mesozoic granites and basement rocks indicate that the continental crust beneath the Korean peninsular is vertically structured by the successive underplating of mantle-derived materials. It is postulated that the crust is vertically stratified from the surface to the lowermost crust with late Archean to early Proterozoic, early to middle Proterozoic (ca. 1(.)9 Ga), middle Proterozoic (ca. 1(.)5 Ga), and late Proterozioc (younger than 1(.)5 Ga) components.
The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calc-alkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion. Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive (epsilon)(Nd)(T) values and young Sm-Nd model ages (T-DM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their 'juvenile' character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative (epsilon)(Nd)(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes. The evolution of the CAOB is probably related to accretion of young are complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.
The tetrapod Caerorhachis bairdi, probably from the Pendleian Limestone Coal Group in the Scottish Midland Valley, is rediagnosed and redescribed, and its affinities are discussed. Caerorachis was originally interpreted as a temnospondyl amphibian, based on characters that are now regarded as primitive for tetrapods, or of uncertain polarity. Several features of Caerorhachis (e.g. gastrocentrous vertebrae, curved trunk ribs, reduced dorsal iliac blade, L-shaped tarsal intermedium) are observed in certain primitive amniotes. In particular, Caerorhachis resembles 'anthracosaurs', generally considered to be among the most primitive of stem-group amniotes. The phylogenetic position of Caerorhachis is considered in the light of recently published cladistic analyses of Palaeozoic tetrapods. Most analyses place Caerorhachis at the base of, or within, 'anthracosaurs'. When multiple, equally parsimonious solutions are found, its 'anthracosaur' affinities are shown in at least some trees, and are supported by several informative and, generally, highly consistent characters. Alternative phylogenetic placements (e.g. sister taxon to temnospondyls) are usually less well corroborated. If the fundamental evolutionary split of most early tetrapods into stem-group lissamphibians (e.g. temnospondyls) and stem-group amniotes (e.g. 'anthracosaurs') is accepted, then the revised interpretation of Caerprhachis sheds light on near-ancestral conditions for Amniota.
A strong correlation exists between the Li isotopic compositions of Carboniferous-Triassic granites from the New England Batholith, and the previously inferred involvement of sedimentary and mantle/infracrustal source components. Isotopically (Nd and Sr) juvenile, low-K, Cordilleran I-type granites of the Clarence River supersuite have delta Li-7= +2 center dot 2 to +8 parts per thousand similar to those of arc magmas, the inferred source of these granites (Bryant et al. 1997). Isotopic variability within this supersuite probably arises from heterogeneity within primary mantle-derived magmas, combined with subsequent modifications through interactions with crustal materials. Oxidised, high-K granites of the Moonbi Supersuite have more homogenous and slightly lighter Li isotopic compositions (delta Li-7=+1 center dot 9 to +4 center dot 2 parts per thousand). The observed range of values lies within the range of arc magmas. and is consistent with partial melting of arc shoshonites within the crust (cf. Chappell 1978) or the involvement of high-K mantle-derived magmas (cf. Shaw & Flood 1981; Landenberger & Collins 1998). S-type granites of the Bundarra (delta Li-7= -0 center dot 1 to +2 center dot 1 parts per thousand; average= +1 center dot 3 parts per thousand; n=6) and Hillgrove supersuites (delta Li-7=+0 center dot 4 to +1 center dot 7 parts per thousand; average= +0 center dot 8 parts per thousand) define a narrow range of isotopic compositions which are, overall, lower than those observed in NEB I-type granites or generally observed in primary arc magmas. Their isotopic compositions are equivalent to those typically observed in shales (primarily delta Li-7= - 3 center dot 2 to +2 center dot 0 parts per thousand; Moriguti & Nakamura 1998; Teng et al. 2004). No difference is evident in the isotopic compositions of the two S-type supersuites despite inferred differences in the degree of weathering experienced by the sedimentary protolith, or differences in mineralogy of the granites. Granites of the Uralla Supersuite, which have been have formed from mixtures of local meta-igneous and meta-sedimentary components, span a broad range of values (delta Li-7= - 1 center dot 3 to +3 center dot 9 parts per thousand) which overlap with both the sediment-poor New England Batholith I-type intrusions of the Clarence River and Moonbi supersuites, and the S-type granites of the Bundarra and Hillgrove supersuites. Lower delta Li-7 values primarily occur in lower-K plutons from the northern portion of the Uralla Supersuite. Overall, anatexis and magma differentiation do not appear to contribute to significant fractionation of Li isotopes relative to the inferred source components. However, subtly lower delta Li-7 values, evident in the three leucogranites analysed herein, imply that subtle Li isotopic fractionation may occur in association with the exsolution of an aqueous fluid. Like most isotopic systems, the Li isotopic composition of rocks is not a definitive guide to source rock compositions, but given the results herein, the present authors suggest that it may play a very useful role in understanding crustal processes.
A strong correlation exists between the Li isotopic compositions of Carboniferous-Triassic granites from the New England Batholith, and the previously inferred involvement of sedimentary and mantle/infracrustal source components. Isotopically (Nd and Sr) juvenile, low-K, Cordilleran I-type granites of the Clarence River supersuite have δ 7Li = +2·2 to +8‰ similar to those of arc magmas, the inferred source of these granites (Bryant et al. 1997). Isotopic variability within this supersuite probably arises from heterogeneity within primary mantle-derived magmas, combined with subsequent modifications through interactions with crustal materials. Oxidised, high-K granites of the Moonbi Supersuite have more homogenous and slightly lighter Li isotopic compositions (δ7Li = +1·9 to +4·2‰). The observed range of values lies within the range of arc magmas, and is consistent with partial melting of arc shoshonites within the crust (cf. Chappell 1978) or the involvement of high-K mantle-derived magmas (cf. Shaw & Flood 1981; Landenberger & Collins 1998). S-type granites of the Bundarra (δ7Li = -0·1 to +2·1‰; average = +1·3‰; n=6) and Hillgrove supersuites (δ 7Li = +0·4 to +1·7‰; average = +0·8‰) define a narrow range of isotopic compositions which are, overall, lower than those observed in NEB I-type granites or generally observed in primary arc magmas. Their isotopic compositions are equivalent to those typically observed in shales (primarily δ 7Li = -3·2 to +2·0‰; Moriguti & Nakamura 1998; Teng et al. 2004). No difference is evident in the isotopic compositions of the two S-type supersuites despite inferred differences in the degree of weathering experienced by the sedimentary protolith, or differences in mineralogy of the granites. Granites of the Uralla Supersuite, which have been have formed from mixtures of local meta-igneous and meta-sedimentary components, span a broad range of values (δ7Li = - 1·3 to + 3·9‰) which overlap with both the sediment-poor New England Batholith I-type intrusions of the Clarence River and Moonbi supersuites, and the S-type granites of the Bundarra and Hillgrove supersuites. Lower δ 7Li values primarily occur in lower-K plutons from the northern portion of the Uralla Supersuite. Overall, anatexis and ma gma differentiation do not appear to contribute to significant fractionation of Li isotopes relative to the inferred source components. However, subtly lower δ7Li values, evident in the three leucogranites analysed herein, imply that subtle Li isotopic fractionation may occur in association with the exsolution of an aqueous fluid. Like most isotopic systems, the Li isotopic composition of rocks is not a definitive guide to source rock compositions, but given the results herein, the present authors suggest that it may play a very useful role in understanding crustal processes.
The Tombstone, Mayo and Tungsten plutonic suites of granitic intrusions, collectively termed the Tombstone-Tungsten Belt, form three geographically, mineralogically, geochemically and metallogenically distinct plutonic suites. The granites (sensu lato) intruded the ancient North American continental margin of the northern Canadian Cordillera as part of a single magmatic episode in the mid-Cretaceous (96-90 Ma). The Tombstone Suite is alkalic, variably fractionated, slightly oxidised, contains magnetite and titanite, and has primary, but no xenocrystic, zircon. The Mayo Suite is sub-alkalic, metaluminous to weakly peraluminous, fractionated, but with early felsic and late mafic phases, moderately reduced with titanite dominant, and has xenocrystic zircon. The Tungsten Suite is peraluminous, entirely felsic, more highly fractionated, reduced with ilmenite dominant, and has abundant xenocrystic zircon. Each suite has a distinctive petrogenesis. The Tombstone Suite was derived from an enriched, previously depleted lithospheric mantle, the Tungsten Suite is from the continental crust including, but not dominated by, carbonaceous pelitic rocks, and the Mayo Suite is from a similar sedimentary crustal source, but is mixed with a distinct mafic component from an enriched mantle source. Each suite has a distinctive metallogeny that is related to the source and redox characteristics of the magma. The Tombstone Suite has a Au-Cu-Bi association that is characteristic of most oxidised and alkalic magmas, but also has associated, and enigmatic, U-Th-F mineralisation. The reduced Tungsten Suite intrusions are characterised by world-class tungsten skarn deposits with less significant Cu, Zn, Sn and Mo anomalies. The Mayo Suite intrusions are characteristically gold-enriched, with associated As, Bi, Te and W associations. All suites also have associated, but distal and lower temperature Ag-Pb- and Sb-rich mineral occurrences. Although processes such as fractionation, volatile enrichment and phase separation are ultimately required to produce economic concentrations of ore elements from crystallising magmas, the nature of the source materials and their redox state play an important role in determining which elements are effectively concentrated by magmatic processes.
Diverse and abundant brachiopod faunas, associated with unstable outer shelf and slope environments., occur through the Upper Ardmillan Group (upper Caradoc-upper Ashgill) in the Girvan district of SW Scotland. Representatives of the deep-water Folioniena fauna occur intermittently throughout the group, appearing in both the Whitehouse and Drummuck subgroups. This distinctive assemblage of small, thin-shelled brachiopods, including Dedzetina. Christiania, Cyclospira and Foliomena itself, first appeared in South China during the early Caradoc but had colonised the Laurentian margins by the late Caradoc. Within the upper Caradoc-lower Ashgill Whitehouse Subgroup, the Foliomena fauna is interbedded with a variety of other less cosmopolitan deep-water assemblages including the Onniella-Skenidioides and Lingulella-Trimurellina associations. Shallower-water environments in the middle Ashgill Lower Drummuck Subgroup hosted the Fardenia-Eopholidostrophia association in sands, and the Christiania-Leptaena association in muds and silts. The remarkable Lady Burn Starfish Beds in the upper part of the group contain a variety of brachiopod-dominated assemblages including the Eochonetes and Plaesiomys-Schizophorella associations. transported from various shelf locations, within a very diverse mid-Ashgill biota. Nevertheless, elements of the Folioniena fauna persisted to near the top of the Drummuck Subgroup, occurring as rare assemblages in more muddy and silty facies. The upper Ashgill High Mains Formation contains abundant elements of the terminal Ordovician Hirnantia fauna including Eostropheodonta, Hindella and Hirnantia itself, but also some taxa more typical of the Laurentian Edgewood Province. As a whole, the changing brachiopod biofacies monitor environmental fluctuations, on part of the Laurentian margin, driven by mainly eustatic and tectonic events.
The Late Ordovician-Early Silurian succession in Jamtland includes the marine Kogsta Siltstone, which is unconformably overlain by the shallow-water Ede Quartzite that grades into the open-marine Berge Limestone. A Hirnantia shelly fauna dates the uppermost Kogsta Siltstone as Hirnantian, and shelly fossils indicate an Aeronian age for the Berge Limestone. Biostratigraphically highly diagnostic conodonts of the early-middle Aeronian Pranognathus tenuis Zone provide the first firm date of the Upper Ede Quartzite and the lowermost Berge Limestone. The Lower Ede Quartzite has not yielded fossils, but sedimentological data suggest it to be of Hirnantian age and reflect the glacio-eustatic low-stand. The contact between the Lower and Upper Ede Quartzite, here taken to be the Ordovician-Silurian boundary, appears to be an unconformity associated with a stratigraphic gap that at least includes the Rhuddanian Stage. The biostratigraphically important conodonts Pranognathus tenuis, Kockelella? manitoulinensis, and Pranognathus siluricus are recorded from Sweden for the first time, and these and other conodonts are used for correlations with coeval units in Europe and North America. In a regional review of Aeronian conodont faunas, three intergrading, apparently depth-related, conodont biofacies are recognised, the Jamtland conodonts representing the one characteristic of the shallowest water.