bluuebunny/crossref_metadata_2025 huggingface dataset:
On becoming cemented: evolutionary relationships among the genera in the freshwater bivalve family Etheriidae (Bivalvia: Unionoida)
Authors: Bogan Arthur E. , Hoeh Walter R.
Published: April 2008

A robust phylogeny for the Unionoida is emerging and presumed relationships of some major clades are being questioned. The Etheriidae or freshwater oysters has been a distinct family for over 160 years and currently contains three cemented genera:Acostaea(Columbia, South America),Pseudomulleria(India) andEtheria(Africa and Madagascar). Starobogatov (1970,Nauka, 1–372), Mansur and da Silva (1990,Amazoniana,11(2), 147–166) and Bonetto (1997,Biociências,5, 113–142) present conflicting testable hypotheses regarding the evolution of these taxa. Using cytochrome c oxidase subunit I DNA sequences the evolutionary relationships of these three genera has been examined, by comparing them to representatives of 30 other unionoid taxa from around the world. These analyses placeAcostaeaandEtheriawithin the Mycetopodidae whilePseudomulleriafalls within the Unionidae. A monophyletic Etheriidae, composed of cemented freshwater bivalves, is not supported by the present analyses. Furthermore, the analyses indicate that cementation in the Unionida has evolved at least twice.
Relevance of sperm ultrastructure to the classification of giant clams (Mollusca, Cardioidea, Cardiidae, Tridacninae)
Authors: Keys Jennifer L. , Healy John M.
Published: April 2008

Examination of sperm ultrastructure in six out of eight of the living species of giant clams (‘Tridacnidae’) supports reduction in status of the Tridacnidae to a subfamily of the Cardiidae (Tridacninae), as suggested by recent cladistic analyses based on shell, anatomical and molecular characters. Tridacninae spermatozoa are all of the aquasperm type, featuring, in anterior-posterior sequence: a conical acrosomal vesicle, an oblong to rod-shaped nucleus, a short midpiece region (proximal and distal centrioles surrounded by four round mitochondria); and a flagellum (9 + 2 pattern axoneme). Substantial differences occur between species with respect to the shape and length of the nucleus, and in the spatial reationship between the acrosomal complex and the nuclear apex. Although the two extant genera can be distinguished on sperm features —
Tridacna
, nuclear peg associated with acrosome, centriolar connective absent;
Hippopus
, nuclear peg absent, connective present — no defining feature of the Tridacninae can be detected. Within
Tridacna
, the species
T. (Chametrachea) maxima
and
T. (C.) crocea
are distinguished from other species of the genus by a much finer nuclear peg and a considerably smaller acrosome. In contrast, and against expectation,
T. (C.) squamosa
shows acrosomal and nuclear dimensions very close to those obtained for
T. (Tridacna) gigas
. Recently proposed phylogenies and classificatory changes for ‘tridacnids’ are discussed in the light of available sperm data.
Functional anatomy, chemosymbiosis and evolution of the Lucinidae
Authors: Taylor John D. , Glover Emily A.
Published: April 2008

All Lucinidae species studied so far possess sulphide-oxidizing, chemosymbiotic bacteria housed in bacteriocytes of gill filaments. The ecology, functional anatomy and evolution of the Lucinidae must be considered in relation to this symbiosis. The ctenidia have been extensively studied but other anatomical structures peculiar to lucinids have received much less attention. Reviewed are the morphological diversity of living lucinids, highlighting features of their anatomy including ctenidia, pallial apertures, anterior adductor mucsle, pallial blood vessel and mantle gills. The latter are much more complex than previously understood and are here redescribed. They comprise folded structures located near the anterior adductor muscle inCodakia, PhacoidesandLucina, and on the septum ofAnodontia. These are interpreted as secondary respiratory surfaces, their location enabling the separation of the anterior inflow of oxygenated water from sulphide-containing water. The latter is released from the sediment by the probing activities of the highly extensible foot and is pumped over the gill through the pedal gape and perhaps also via the exhalant tube. The shell features ofIlioniafrom the Silurian Period suggests that the lucinid chemosymbiosis is an ancient association.
Carboniferous praecardioid bivalves from the exceptional Buckhorn Asphalt biota of south-central Oklahoma, USA
Authors: Yancey T. E. , Heaney M. J.
Published: April 2008

Unusual Pennsylvanian bivalves recovered from the Buckhorn Asphalt Quarry of south-central Oklahoma are members of the Order Praecardioida, Family Lunulacardiidae. This is the youngest occurrence of praecardioids in North America. These praecardioids have an ontogeny characterized by a veneriform juvenile shell, changing abruptly to an elongate adult shell with sharp carinae, accompanied by strong rotation of the juvenile shell and change in ligament. These shells provide new evidence of dentition and ligament for lunulacardiids and the first documentation of praecardioid shell microstructure. The Buckhorn taxa possess stout hinge teeth, indicating that lunulacardiids are not edentulous. Preserved ligament in multiple growth stages indicates that beaks are prosogyrous and the flattened truncated portion of the shell is posterior. A revised diagnosis of the Lunulacardiidae is presented. New taxa:
Buckhornia carteri
n. gen., n. sp.
The nature and origin of taxonomic diversity gradients in marine bivalves
Authors: Crame J. A.
Published: April 2008

Bivalves have been fundamental in developing the understanding of large-scale biodiversity patterns in the marine realm. A new study based on 29 regional bivalve faunas indicates that both latitudinal and longitudinal gradients are not so regular in form as was once imagined. The northern hemisphere latitudinal gradient has a marked step, or inflection, at 20–30°N, and in the southern hemisphere Australia forms a distinct diversity hotspot. A longitudinal gradient runs between a large tropical high diversity focus in the southern China-Indonesia-Australia region and a somewhat smaller one in the Panamic-Caribbean region.

It is unlikely that the marked asymmetry in both latitudinal and longitudinal gradients can be explained entirely by either the geometric patterns of species ranges in relation to geographical boundaries (the mid-domain effect) or the operation of contemporary, or equilibrium, factors. The role of history must be considered too, and in some cases this could involve a timescale of at least 60 Ma. For example, Australia has moved progressively northwards throughout the Cenozoic era and this seems to have led to the development of a unique assemblage of both tropical and temperate taxa around the continent. When Australia eventually collided with southeast Asia, some 15 Ma ago, three previously distinct tropical marine faunas were brought into close juxtaposition.

However, something else seems to have been involved in order to generate a marked pantropical Neogene diversification event in bivalves and other marine invertebrate taxa. It is striking how this event coincided with a prolonged interval of global cooling and the suggestion has been made that glacioeustatic cycles may have promoted the formation of a tropical species diversity pump. In concert with regular and profound sea-level changes, new taxa were created in marginal tropical regions and then concentrated in certain core regions. These same glacioeustatic cycles may also have served to accentuate the latitudinal limits of many tropical taxa.

As the knowledge of large-scale taxonomic diversity gradients in the marine realm has increased, so too has the realization that they are at least the partial products of major historical events.
Analysing the latitudinal diversity gradient in marine bivalves
Authors: Jablonski David , Roy Kaustuv , Valentine James W.
Published: April 2008

Marine bivalves of the eastern Pacific continental shelf show a strong diversity gradient from the Arctic Ocean to the tropics. This gradient is underlain by strong diversity trends in both infaunal and epifaunal bivalves, contrary to Thorson’s influential hypothesis (1952,
Verhandlungen der Deutschen Zoologischen Gesellschaft
,
1951
, 267–327), and is significantly correlated with mean sea-surface temperature; either raw data or a residuals analysis yields
p
< 0.0001. Patterns differ according to trophic group and phylogeny; however, suspension feeders conform to the general bivalve diversity gradient, as do facultative deposit feeders such as tellinids, while deposit feeding protobranchs do not. Infaunal and epifaunal diversity gradients have different slopes so that their ratio changes with latitude; data on Jurassic and Cretaceous bivalves suggests that this ratio has varied in slope and intercept over geological time.
Marine bivalves of the Florida Keys: discovered biodiversity
Authors: Mikkelsen Paula M. , Bieler Rüdiger
Published: April 2008

A survey of marine bivalve biodiversity in the Florida Keys, an island archipelago off southern Florida, was compiled from original collecting, museum specimens and the literature. Assembly of over 6000 records resulted in 325 species, 47% of which can be considered common to abundant in the Keys. This represents a 100% increase over the previously known fauna, largely attributable to critical review of museum specimens. Capture of species occurrences from the literature, especially when non-traditional sources (newsletters, agency reports) are excluded, is shown to be least effective, producing only 44% of the total. Bivalve distributions within the Keys show that the fauna is tropical. One-third of the species are wide ranging along the island chain; however, a latitudinal cline in faunal similarity exists from the Upper Keys southwestwards to Dry Tortugas. The fauna of Florida Bay is the most divergent within the study region and also compared to other, ecologically complex, western Atlantic tropical-subtropical regions. Limited historical records indicate little species turnover in the Keys, although population reductions along the main highway and habitat shifts (from natural to artificial substrata) are evident. These results have implications for biodiversity survey methods and, more locally, for management of the Florida Keys National Marine Sanctuary.
Genetic relationships of
Mytilus galloprovincialis
Lamarck populations worldwide: evidence from nuclear-DNA markers
Authors: Daguin Claire , Borsa Philippe
Published: April 2008

Allozyme surveys of genetic variation in
Mytilus galloprovincialis
Lamarck throughout the world have identified three groups within this species: a northeastern (NE) Atlantic group that also includes the
M. galloprovincialis
population of South Africa, a Mediterranean group that also includes the
M. galloprovincialis
populations from the eastern and the western coasts of the North Pacific, and an Australasian group. Hypotheses that have been proposed to account for the genetic differentiation patterns and disjunct, worldwide distribution of
M. galloprovincialis
include the recent introduction of this species into the southern hemisphere and the North Pacific through human agency, and an alternative hypothesis that each of the three groups is endemic. In this study, two nuclear-DNA markers (the polyphenolic adhesive protein gene
Glu-5′
and the first intron of the actin gene
mac-1
) were used to investigate in more depth the genetic relationships among
M. galloprovincialis
populations. Samples were taken between 1996 and 1999 from California, the NE Atlantic, the Mediterranean Sea, South Africa, Korea, Western Australia, Tasmania and New Zealand. NE Atlantic
M. edulis
L. were used as an outgroup. While all
M. galloprovincialis
samples were fixed, or nearly so, for the diagnostic
G
allele at locus
Glu-5′
, correspondence analysis of
mac-1
allele frequency data highlighted the genetic distinctness of Australasian mussels relative to other
M. galloprovincialis
populations. The latter consisted of two differentiated groups (NE Atlantic and Mediterranean) as formerly reported at allozyme loci. Another sample, from Chile, was nearly identical to Mediterranean
M. galloprovincialis
. Nuclear-DNA data thus enforce the idea that
M. galloprovincialis
have probably been introduced from the Mediterranean to the North Pacific (and now Chile), and from the NE Atlantic to South Africa. It is argued in this study that Australasian mussels derive from a proto-
M. galloprovincialis
population introgressed by
M. edulis
-like genes, and should be considered as a regional subspecies of
M. galloprovincialis
.
Herring gulls feeding on a recent invader in the Wadden Sea,
Ensis directus
Authors: Cadée Gerhard C.
Published: April 2008

The American razor clam
Ensis directus
has been a successful non-indigenous invader in the Wadden Sea since the late 1970s. It often shows poorly understood mass mortalities in the winter half-year, which are also known from its native area. During such mass mortalities
Ensis directus
partly leaves its burrow and, as it is unable to re-burrow, is an easy prey for herring gulls during low tide. During a mass mortality in March 1999,
Ensis
consumption by herring gulls was studied. Shell fragmentation was achieved by shaking the shell vigorously, not by hammering. This caused characteristic shell fragmentation ranging from small fragments broken from one or both valves near the middle, to both valves broken near the middle, but still connected by the ligament. About one-quarter of the shells remained undamaged. No other predators are known to produce similar
Ensis
shell fragments. In taphonomic studies the importance of predators in fragmenting shells should be taken into account.
Isolated carbonate platforms of Belize, Central America: sedimentary facies, late Quaternary history and controlling factors
Authors: Gischler Eberhard , Lomando Anthony J.
Published: April 2008

The closely spaced, isolated carbonate platforms of Glovers Reef, Lighthouse Reef and Turneffe Islands (Belize) differ significantly with regard to geomorphology and distribution of sedimentary facies, especially in platform interiors. Glovers Reef has a deep (18 m) lagoon with 860 more or less randomly distributed patch reefs. The interior of Lighthouse Reef is characterized by a linear trend of hundreds of coalescing patch reefs that separate a deeper (8 m) eastern and a shallower (3 m) western lagoon. Within both Glovers and Lighthouse Reefs, non-skeletal (peloidal) wackestone and packstone are found in shallow (<5 m) water depths. Deeper lagoon parts are characterized by mollusc-foram wackestones. Facies belts are circular in Glovers Reef, as opposed to linear in Lighthouse Reef. The Turneffe Islands platform has up to 8 m deep interior lagoons that are surrounded by large land/mangrove areas. These lagoons have restricted circulation, are devoid of coral patch reefs, and are dominated by organic-rich wackestone.

These differences are largely a consequence of variations in antecedent topography and in exposure to waves and currents from platform to platform. Differences in elevation and relief of the Pleistocene basement are most likely controlled by differential subsidence and latitudinal variation in karstification. Differences in exposure to waves and currents are created as the Turneffe Islands platform is in a leeward position, protected from the open Caribbean Sea by Lighthouse Reef to the east. Variation in Pleistocene elevation caused the platforms to flood successively at different rates during Holocene sea-level rise. However, all reefs investigated kept pace with the rising Holocene sea level. Sediment is now largely bypassing the margins and filling in platform interior lagoons.

These examples indicate how local attributes of antecedent topography and exposure to waves and currents can be at least as important as globally operating factors such as sea-level fluctuations. This observation should be kept in mind when interpreting palaeo-relationships in the geologic record.
Reef episodes, anoxia and sea-level changes in the Frasnian of the southern Timan (NE Russian platform)
Authors: House M. R. , Menner V. V. , Becker R. T. , Klapper G. , Ovnatanova N. S. , Kuz’min V.
Published: April 2008

The development of the Frasnian (Upper Devonian) reef complexes of the southern Timan and Pechora region of northern European Russia is described. Barrier reef complexes progressively prograded eastwards during the Frasnian but the carbonate complexes were interrupted many times by regressive events. Using new conodont and ammonoid biostratigraphical dating, the timing of reef building episodes has been established which enables international correlation with other similar Devonian areas. Basinal anoxic and hypoxic deposits associated with the reef complexes of the Domanik facies provide the major hydrocarbon source rocks of the region and the palaeoenvironmental interpretation of these is discussed. Initial transgressions appear to have been associated with the global Taghanic Onlap of the late Givetian. The new level for the base of the Frasnian and Upper Devonian lies in the Timan Formation, after the deposition of which marine conditions mostly prevailed in the area examined until the late Frasnian when a sharp regression occurred with no evidence of the typical Kellwasser facies of Western Europe and other areas. Transgressive pulses initiated ammonoid biofacies in the Regional Sargaev Stage and the widespread Timan Event was marked by the spread of
Timanites
faunas. A significant deepening event which initiated the Domanik facies correlates approximately with the Middlesex black shale of New York and the main development of the Domanik facies with the Rhinestreet black shale of New York. There are faunal and floral peculiarities of the area, shown by endemic genera and rather different ranges of cosmopolitan species than elsewhere, which complicates precise international correlation. Nevertheless, several of the main sea-level deepening pulses of the Frasnian, documented in North America, Western Europe, North Africa and Australia, are recognizable and these are thought to represent eustatic events.
Sedimentation rates and growth potential of tropical, cool-water and mud-mound carbonate systems
Authors: Schlager Wolfgang
Published: April 2008

Carbonate fixation in the ocean proceeds in three basic modes: abiotically, biotically induced (with organic trigger), and biotically controlled (where organisms determine timing, location and composition of the product). The three modes combine in a variety of ways to produce carbonate sediment. When viewed on the scale of formations and global facies belts, three benthic carbonate production systems, or ‘factories’, emerge: (1) the tropical shallow-water system, dominated by biotically controlled (mainly photoautotrophic) and abiotic precipitates; (2) the cool-water system, dominated by biotically controlled (mainly heterotrophic) precipitates; and (3) the mud-mound system, dominated by abiotic and biotically induced (mainly microbial) precipitates.

The sedimentation rates of all three factories decrease as the time span of observation increases. This scaling trend is not just an artifact of ratio correlation; it is almost certainly related to the episodic, pulsating nature of sedimentation.

The growth potential of the three systems can be estimated by drawing the envelope of the maximum observed rates of aggradation. The tropical system shows the highest rates: 10
4
μm a
−1
at 10
3
years, decreasing to 10
2
μm a
−1
at 10
7
years. The maximum rates of the cool-water system are comparable to those of the tropical carbonates for intervals shorter than 2 × 10
5
years but they amount to only 25% of the tropical standard in the domain of 10
6
–10
8
years. The high short-term rates of cool-water carbonates are probably caused by reworking and local trapping of sediment. The growth rates of the mud-mound system significantly exceed cool-water rates and rival the aggradation rates of tropical shallow-water carbonates. However, the mud-mound system exports less sediment than its tropical counterpart and is, therefore, somewhat less productive.
From Cadomian subduction to Early Palaeozoic rifting: the evolution of Saxo-Thuringia at the margin of Gondwana in the light of single zircon geochronology and basin development (Central European Variscides, Germany)
Authors: Linnemann U. , Gehmlich M. , Tichomirowa M. , Buschmann B. , Nasdala L. , Jonas P. , Lützner H. , Bombach K.
Published: April 2008

Saxo-Thuringia is classified as a tectonostratigraphic terrane belonging to the Armorican Terrane Collage (Cadomia). As a former part of the Avalonian-Cadomian Orogenic Belt, it became (after Cadomian orogenic events, rift-related Cambro-Ordovician geodynamic processes and a northward drift within Late Ordovician to Early Silurian times), during Late Devonian to Early Carboniferous continent-continent collision, a part of the Central European Variscides. By making use of single zircon geochronology, geochemistry and basin analysis, geological processes were reconstructed from latest Neoproterozoic to Ordovician time: (1) 660–540 Ma: subduction, back-arc sedimentation and tectonomagmatic activity in a Cadomian continental island-arc setting marginal to Gondwana; (2) 540 Ma: obduction and deformation of the island arc and marginal basins; (3) 540–530 Ma: widespread plutonism related to the obduction-related Cadomian heating event and crustal extension; (4) 530–500 Ma: transform margin regime connected with strike-slip generated formation of Early to Mid-Cambrian pull-apart basins; (5) 500–490 Ma: Late Cambrian uplift and formation of a chemical weathering crust; (6) 490–470 Ma: Ordovician rift setting with related sedimentation regime and intense igneous activity; (7) 440–435 Ma: division from Gondwana and start of northward drift. The West African and the Amazonian Cratons of Gondwana, as well as parts of Brittany, were singled out by a study of inherited and detrital zircons as potential source areas in the hinterland of Saxo-Thuringia.
Chronological constraints on the pre-Variscan evolution of the northeastern margin of the Bohemian Massif, Czech Republic
Authors: Kröner A. , Štípská P. , Schulmann K. , Jaeckel P.
Published: April 2008

New single zircon ages enable us to provide an evolutionary scenario for the Neoproterozoic to Cambro-Ordovician tectonic history of part of the easternmost Sudetes along the northeastern margin of the Bohemian Massif. The easternmost crustal segment (Brunia) yields Neoproterozoic ages from both autochthonous and allochthonous Variscan units; these ages document a Cadomian (Pan-African) history that may be linked with the northern margin of Gondwana. A Cambro-Ordovician magmatic-thermal event in Brunia is represented by granitic to pegmatitic dykes intruding Neoproterozoic crust and by localized partial anatexis. Farther west a narrow zone of Cambro-Ordovician rifting is identified (Staré Městro belt), marked by gabbroic magmatism, bimodal volcanism and medium-pressure granulite facies metamorphism. The westernmost crustal domain (Orlica-Sniezník dome) is represented by Neoproterozoic crust intruded by Cambro-Ordovician plutons consisting of calk-alkaline granitoid rocks and affected by widespread Cambro-Ordovician anatexis. The geodynamic setting of the Neoproterozoic and Cambro-Ordovician domains is similar to that of the Western Sudetes, where both Cambro-Ordovician rifting and calc-alkaline magmatism were identified. We discuss the rifting mechanics in terms of sequential crustal thinning along the northern margin of Gondwana. The calc-alkaline magmatism, in conjunction with crustal rifting, is related to a back-arc geometry in front of a retreating south-dipping subduction zone during progressive closure of the Tornquist Ocean southeast of Avalonia.
Heat flow evolution, subsidence and erosion in the Rheno-Hercynian orogenic wedge of central Europe
Authors: Littke R. , Büker C. , Hertle M. , Karg H. , Stroetmann-Heinen V. , Oncken O.
Published: April 2008

Numerical, thermal and rheological modelling techniques are applied to unravel the basin-forming processes and the heat flow and burial history of the Rheno-Hercynian fold belt (Rhenish Massif), the adjacent Subvariscan foreland (Ruhr Basin), and the intramontane Saar-Nahe Basin. Thermal history and crustal architecture in the study areas were affected mainly by the Variscan Orogeny during late Palaeozoic times. Calibration of the simulated thermal histories is primarily based on vitrinite reflectance and fission-track data. Mechanical modelling reveals average
β
values of 1.7, reaching a maximum of 2.4 in the central basin (Mosel Graben) and at the transition to the Giessen Ocean to the south during Early Devonian rifting. This stage was associated with tholeitic magmatism and an elevated heat flow of up to 110 mW m
−2
, preserved in weakly overprinted syn-rift sediments. Average basal heat flow during maximum burial at the end of the Carboniferous period (i.e. the end of crustal shortening) was between 50 and 70 mW m
−2
with a slight decrease from the Subvarian foreland basins towards the Rheno-Hercynian in the south. The values suggest average crustal thicknesses of between 32 and 36 km during late Carboniferous time. For the Saar-Nahe Basin, values between 50 and 75 mW/m
2
represent the thermal regime in the upper crust during the late Stephanian and early Permian time. Estimated eroded thicknesses of Palaeozoic sediments vary between 2500 m in the northern and central Ruhr Basin and more than 6000 m in the Osteifel and the Siegen Anticline within the Rheno-Hercynian, and between 1800 and 3600 m in the Saar-Nahe Basin. Fission-track data provide evidence for significant reheating during the Mesozoic era within the entire study area. This phase of heating, probably linked to North Atlantic rifting, coincides with post-Variscan ore formation and with major tectono-magmatic events in central Europe.
White mica
40
Ar/
39
Ar ages of Erzgebirge metamorphic rocks: simulating the chronological results by a model of Variscan crustal imbrication
Authors: Werner Olaf , Lippolt Hans J.
Published: April 2008

In the Erzgebirge, which is part of the Saxo-Thuringian Mid-European Variscides, an
40
Ar/
39
Ar study was performed on white mica and hornblende separates from 68 metamorphic rocks of varying lithologies. Two groups of late Early Carboniferous cooling ages of 340 ± 2 Ma and 329.7 ± 1.5 Ma are distinguished by evaluating spectra shapes. A third group of rocks yielded intermediate argon ages, presumably related either to thermal rejuvenation or to neoformation of white mica during a reheating process 330 Ma ago. A model that explains rejuvenation is proposed. The observed age patterns and the shape of the age spectra cannot be simply explained by assuming a single uplift and exhumation process set in motion by extensive forces. Chronological and structural arguments favour the idea that Variscan crustal imbrication took place during the mineral cooling phase. A tectonic process that intercalated, at about 20 km depth, a unit of cool rocks into a much hotter environment suitably models the chronological results. This is shown by a simulation of the age record. Temperature profiles are calculated for both intercalation and subsequent uplift models. Rocks in these profiles, which preserved their 340 Ma signature, are distinguished from those heated 330 Ma ago by contact with adjacent hotter rocks and reset isotopically to varying degrees. The agreement between analytical results and modelled ages favours the crustal imbrication hypothesis as explanation for the age distribution throughout all lithologies.
Exhumation of high-grade rocks in the Saxo-Thuringian Belt: geological constraints and geodynamic concepts
Authors: Franke W. , Stein E.
Published: April 2008

The Saxo-Thuringian Belt on the northern flank of the European Variscides resulted from SE-ward subduction of a Cambro-Ordovician rift basin under the Teplá-Barrandian (Bohemian) margin. It contains ultra-high-pressure (UHP) metamorphic rocks, which are now exposed in different tectonic settings, and were exhumed in different modes, under different thermal regimes. Eclogites of the upper allochthon (tectonic klippen of Münchberg, Wildenfels and Frankenberg) originated from early Devonian (
c.
400 Ma) subduction. Cooling ages in the klippen, combined with clast spectra and ages of detrital minerals in the foreland flysch record exhumation in Famennian time. The high-pressure (HP) rocks rose in a narrow corridor along the suture zone, were retrogressed under amphibolite facies conditions, and rapidly recycled into the foreland flysch. Rocks of the lower allochthon are exposed in dome structures emerging from under the relative autochthon. The HP Saxonian Granulites were formed at
c.
20 kbar/1050 °C, and the Erzgebirge contains diamond-bearing quartzo-feldspathic rocks, associated with eclogites. Peak temperatures of the lower allochthon were attained at
c.
340 Ma. Immediately afterwards, these rocks were emplaced under the floor of the relative autochthon, which, at this time, was a foreland basin receiving clastic sediments from the orogen adjacent to the SE. Emplacement of the lower allochthon is most clearly documented in the Saxonian Granulite Dome, in which HP granulites are juxtaposed against low-pressure-high-temperature (LP-HT) rocks of the hanging wall. The interface is a zone of HT shear, which cuts out ⩾ 60 km of crustal thickness. In more internal parts of the belt (Erzgebirge), the newly emplaced lower allochthon was subsequently reworked by thrusting and polyphase refolding. Emplacement of the hot, low-viscosity lower allochthon was probably driven by buoyancy and the hydraulic gradient between the crustal root to the SE and the lower crust of the foreland. Unlike the earlier HP rocks exposed in the upper allochthon, the 340 Ma HP rocks of the lower allochthon were thermally softened, and, instead of piercing their cover, intruded into the foreland. Therefore, the 340 Ma rocks do not appear in the clastic record of the flysch. The two contrasting mechanisms of exhumation observed in the upper and lower allochthon are apparently due to different thermal regimes.
The fundamental Variscan problem: high-temperature metamorphism at different depths and high-pressure metamorphism at different temperatures
Authors: O’Brien Patrick J.
Published: April 2008

The evolution of the crystalline internal zone of the European Variscides (i.e. Moldanubian and Saxo-Thuringian) is best understood within a framework of two distinct subduction stages. An early, pre-Late Devonian (older than 380 Ma), subduction stage is recorded in medium-temperature eclogites and blueschists derived from low-pressure basaltic and gabbroic protoliths now found as minor relics in amphibolite facies meta-ophiolite or gneiss-metabasite nappe complexes. A second subduction and exhumation event produced further nappe complexes containing different types of mantle peridotites, along with their enclosed pyroxenites and high-temperature eclogites, associated with large volumes of high-
T
-high-
P
(900–1000°C, 15–20 kbar) felsic granulites. Abundant geochronological evidence points to a Carboniferous age (
c.
340 Ma) for the high-
P
-high-
T
metamorphism as well as an extremely rapid exhumation because the fault-bounded, granulite-peridotite-bearing tectonic units are also cut by late Variscan granitic plutons (315–325 Ma). The massive heat energy for the characteristic, and most widespread feature of the Variscan event, the low-
P
-high-
T
metamorphism (750–800°C, 4–6 kbar) and voluminous granitoid magmatism (325–305 Ma), comes from three sources. An internal heat component comes from imbrication of crust with upper-crustal radiogenic heat production potential in the region parallel to the subduction zone; an external mantle heat component is undoubtedly contributing to the transformation of crust taken to mantle depths (i.e. the granulites); and a heat component advected to the middle and lower crust seems inescapable if the hot granulite-peridotite complexes were exhumed and cooled as rapidly as petrological and geochronological evidence seems to suggest. Major mantle delamination and asthenospheric upwelling as a cause of heating in Early Carboniferous times is not supported by geochemical, geophysical or petrological-geochronological studies, although slab break-off probably did occur.
The Variscan lower continental crust: evidence for crustal delamination from geochemical and petrophysical investigations
Authors: Wittenberg A. , Vellmer C. , Kern H. , Mengel K.
Published: April 2008

Seismic observations along the European Geotraverse (EGT) Central Segment indicate an overall felsic composition of the Variscan crust, including 15 vol. % of mafic lower-crustal (MLC) rocks. As the Variscan continental crust is largely post-Archaean, its bulk composition should be basaltic andesitic rather than felsic (tonalitic), because primitive post-Archaean crust was formed by mantle extracted basaltic andesite magmas. The observed proportions of the Variscan continental crustal layers do not match the requirement of a mafic overall crust. Combining laboratory-derived,
in situ
seismic data (
V
P
) with the refraction seismic data and the evidence from geological and geochemical investigations suggests that large amounts of MLC rocks are missing in the present-day lower crust. A mass balance calculation of the basaltic andesite bulk crust, considering a refined compilation of the Variscan MLC, gives a volume proportion of 37 vol. % for the felsic and 63 vol. % for the mafic components, for primitive crust prior to collision tectonics and orogenic root delamination. If large parts of this MLC have undergone eclogite-facies metamorphism at the orogenic root, large amounts of former basaltic-gabbroic and MLC cumulates could have been subtracted from the crust by its subsequent delamination processes which results in the currently observed proportion of the continental crust of the Variscan Orogen with a predominance of felsic rocks.
Chronostratigraphic framework for the Devonian and Old Red Sandstone
Authors: House Michael R.
Published: April 2008

Boundaries for all the Devonian series and stages have now been proposed by the Subcommission on Devonian Stratigraphy (SDS) of the International Commission on Stratigraphy (ICS) and have been ratified by the International Union of Geological Sciences (IUGS). A summary of these decisions is given. All the defined Global Stratigraphic Section and Points (GSSPs) are in the marine realm, and in pelagic facies. Much work is still needed to correlate the new boundaries into neritic and terrestrial facies.
Kinematics and dynamics of Old Red Sandstone basins
Authors: Friend P. F. , Williams B. P. J. , Ford M. , Williams E. A.
Published: April 2008

The Old Red Sandstone basins of the North Atlantic borderlands provide a record of diverse dynamics in very different settings, related to the Variscan, Caledonian and Ellesmerian orogenies. This paper is a first attempt to review much new information on the basins, including information presented, for the first time, in this book. Five basin groupings are distinguished: (1) Scandinavian basins of, syn- to post-Scandian (Caledonian) age, formed on greatly thickened crust by extension or transtension (Western Norway, East Greenland, Spitsbergen); (2) NE Scotland, Orcadian Basin, mid Caledonian setting, formed by extension; (3) Scotland (Midland Valley) and related Irish basins, north of the Caledonian Iapetus Suture Zone, formed by extension; (4) southern Britain and Ireland, basins south of the Iapetus Suture Zone, related to collision of Eastern Avalonia with Laurentia, and Maritime Canada and the Catskills related to collision of Western Avalonia; these are load-induced flexural basins; (5) Southern margin of Eastern Avalonia, (Munster, South Wales, SW England), of Late Devonian age, extensional basins of various (Early to Late) Devonian ages.
The geometry, flow patterns and sedimentary processes of Devonian rivers and coasts, New York and Pennsylvania, USA
Authors: Bridge John S.
Published: April 2008

The Middle-Upper Devonian strata of New York and Pennsylvania were deposited in a foreland basin adjacent to the Acadian fold-thrust belt. Fluvial (Catskill) strata in the east thin to the west into marine (Chemung) strata. The overall sequence is marine regressive, but there numerous superimposed marine transgressions. The Catskill river channels changed character with distance from the palaeoshoreline. Sinuous, single-channel rivers (widths tens of metres, maximum bankfull depths 4–5 m, sinuosity 1.1–1.3, mean bankfull flow velocity 0.4–0.7 m s−1) occurred near the coast. With increasing distance from the coast, rivers increased in slope, became wider (up to hundreds of metres) and deeper (up to 15 m), coarser grained, and possibly braided. This suggests that rivers were distributive near the coast. Furthermore, muddy floodplain areas were more extensive near the coast than up-valley, such that the proportion of channel deposits increased up-valley. Coastal areas comprised tide-influenced channels and mouth bars, wave-influenced sandy shoals and washovers, sandy and muddy tidal flats, and muddy interdistributary bays and lakes. Major marine transgressions are thus represented in wholly fluvial successions by a decrease in the proportion of channel sandstone bodies, and a decrease in channel size and grain size. Marine transgressions in near-coastal successions are represented in places by an increase in sandstone proportion associated with progradation of coastal sands over muddy backswamps and interdistributary areas. Small-scale marine transgressions and regressions in coastal deposits (i.e. metres-thick parasequences) are probably associated with switching of coastal channels or delta lobes. There is no evidence for the preservation of incised valleys, nor for any changes in coastal channel patterns associated with these parasequences: therefore, major regional sea-level changes were not responsible. However, large-scale (tens to hundreds of metres) transgressive-regressive sequences were due partly to eustatic sea-level change (e.g. in mid-Givetian time) but also due to changes in the balance between sediment supply and subsidence associated with tectonic uplift of the hinterland and peripheral bulge. Such uplift may have induced some kind of climate change. However, climate changes in the depositional basin are not supported by sedimentological evidence. Further understanding of the origin of these strata will require higher precision in the biostratigraphic correlation of marine and non-marine strata (using miospores), and quantitative interpretation of depositional environments from other regions.
Taking the roof off a suture zone: basin setting and provenance of conglomerates in the ORS Dingle Basin of SW Ireland
Authors: Todd Simon P.
Published: April 2008

The Late Silurian to Mid-Devonian Dingle Basin occupies a central position within the Iapetus Suture Zone of SW Ireland. The basin is believed to have formed from late Silurian times onwards as a product of sinistral transpression along several major faults within this suture zone. Conglomeratic sediments were deposited by moderately large gravelly fans shed into the basin from the NW (Glashabeg Formation) and the SE (Trabeg Conglomerate Formation). The systems fed into a large apparently through-going sandy, axial river (Slea Head Formation) that flowed towards the NE. The lateral, basin-margin systems were sourced from two disparate source terranes. To the NW lay a basic volcanic hinterland with some intermediate volcanic rocks and limestones, mudstones, sandstones and chert. During the Early Devonian time the SE drainage basin was underlain by sandstones, quartzites, phyllites and limestones probably intruded by a granite. Some of these lithologies can be found in outcrop in the pre-Dingle Group of the peninsula. Others need to be correlated with rocks of the oceanic terranes in the northern part of the suture zone. The southerly derived clasts have corollaries in the rocks of the Avalonian Leinster Terrane south of the suture. Following partial inversion of the Dingle Basin, the southerly hinterland was apparently further unroofed during mid-Devonian time, when the Inch Conglomerate Formation was deposited by alluvial fans shed northwards from a source area formed along the Dingle Bay Lineament. The Inch conglomerates are characterized by distinctive clasts of schist, gneiss, mylonite, tourmalinite and granite. The general picture of the Early Devonian deformation, intrusion by granite and unroofing of terranes currently partially exposed in central and southern Ireland within the Iapetus Suture Zone is largely consistent with clast lithotypes. However, some exploratory isotopic data indicate at least two possible vagaries in the interpretation. First, model ND
T
DM
ages of Trabeg sedimentary clasts yield several results older than typical southern Iapetean or Avalonian crustal material. This suggests a complex history of sedimentary mixing of material across the developing Iapetus Ocean. Second, two of three Rb-Sr muscovite-whole-rock dates of Inch metamorphic clasts indicate Silurian ages. These data similar to Rb-Sr dates derived from the Carnsore and Saltees granites in the Rosslare Terrane, perhaps extending the geographical spread of this Silurian deformation.
Progress in reconstructing vegetation on the Old Red Sandstone Continent: two
Emphanisporites
producers from the Lochkovian sequence of the Welsh Borderland
Authors: Edwards Dianne , Richardson John B.
Published: April 2008

Small coalified fossils (mesofossils) have yielded new insights into vegetation of the Old Red Sandstone Continent in early Devonian times. Particularly useful are those containing spores that can be placed in dispersed spore taxa, although patinate and emphanoid spores have not hitherto been found
in situ. Emphanisporites
cf.
micrornatus
Richardson & Lister is described in a bifurcating cylindrical sporangium preserved as a cuticular sheath. A terminal dehiscence feature is compared with that in
Horneophyton
. The sporangium is encased in amorphous detritus with some tubular fragments. Similar associations occur on other sporangia, e.g.
Tortilicaulis
and axes at this North Brown Clee Hill locality, and they are interpreted as remains of a microbial or fungal film. Fragmentary cuticles, interpreted as isolated sporangial valves, bear an undescribed species of
Emphanisporites
with fine interdigitating proximal muri and laevigate distal surfaces referred to
Emphanisporites
sp. A Richardson & Lister. Analysis of dispersed spore assemblages from the locality and others in the Welsh Borderland indicate that the two emphanoid taxa were not common components of the spore ‘rain’. This evidence, coupled with the dearth of mesofossils of the producers, suggests that the plants grew at the upper reaches of the drainage basin of the river that deposited the sediment, although the paucity of sporangia may also be attributed to their low fossilization potential.
Depositional setting of the Lower Old Red Sandstone at Pantymaes Quarry, central South Wales: new perspectives on the significance and occurrence of ‘Senni Beds’ facies
Authors: Owen Geraint , Hawley Duncan
Published: April 2008

The 200 m long face of Pantymaes Quarry, central South Wales, exposes part of the upper (Dittonian) Red Marl Group (Lower Old Red Sandstone). A lower Sandstone Facies Association (up to 15 m thick) comprises interbedded grey-green micaceous sandstones, pebbly intraformational conglomerates, and grey siltstones. Major bounding surfaces define stacked channel complexes, representing the deposits of braided river systems. An erosively overlying Mudstone Facies Association (up to 15 m thick) comprises tabular-bedded, bioturbated and calcretized red siltstones and fine sandstones representing overbank deposits, possibly from a meandering system. The change in fluvial style is interpreted as a local response to pulses of oblique-slip movement on nearby fault systems. The period of fault activity resulted in the braided Sandstone Facies Association, the Mudstone Facies Association recording a gradual return to a meandering system. Individual pulses of activity produced the stacked channels within the Sandstone Facies Association. The Sandstone Facies Association is similar in character to the overlying Senni Beds, suggesting that ‘Senni Beds’ may describe a recurring, possibly tectonically controlled, braided channel facies in the Lower Old Red Sandstone.
Old Red Sandstone basins and alluvial systems of Midland Scotland
Authors: Bluck B. J.
Published: April 2008

Old Red Sandstone rocks of the Midland Valley of Scotland record the amalgamation history of blocks widely separated from each other in Ordovician times. As a response to the lateral juxtaposition of the Midland Valley against the Highland block, the Midland Valley, weakened during its long history of igneous activity, was subjected to transtension and transpression, which opened and closed basins resulting in much recycling of sediment and the renewed development of intermittent and sometimes prolific volcanic activity. The Old Red Sandstone comprises two cycles of basin fill: the older (the Lower Old Red Sandstone) is separated by a major unconformity from the younger (the Upper Old Red Sandstone). Each cycle begins with conglomeratic sedimentation in pull-apart basins then fines and petrographically matures upward. The cycles, initiated by faulting, record the decline in tectonic influence and the concomitant reduction in source relief. The sediment source to the Old Red Sandstone is enigmatic. The Dalradian basement to the north and Southern Uplands to the south were, in many places, extensively eroded by Late Silurian-Early Devonian times. The thickest sequence of coarse sediment in the UK, if not in Europe, therefore has no obvious nearby uplift to provide both the sediment and the persistent, substantial slopes required to deliver sediment of that calibre to the basin. To the northeast, the Greenland-Baltica collision had created a major Silurian-Carboniferous (Scandian) uplift. Major river systems draining this mountain belt entered the Lower and Upper Old Red Sandstone basins at a late stage in their development when relief was lowered sufficiently to allow access to them.
Age and provenance of limestone clasts in Lower Old Red Sandstone conglomerates: implications for the geological history of the Midland Valley Terrane
Authors: Armstrong Howard A. , Owen Alan W.
Published: April 2008

Conodont-bearing limestone clasts in Lower Old Red Sandstone conglomerates in the Lanark and Strathmore basins and the Pentland Hills Inlier, Midland Valley, Scotland, indicate a source in a cryptic arc terrane with a mid-Ordovician (
P. serra-P. anserinus
Biozone) limestone cover. Simpson coefficients of similarity indicate that the faunas from the limestone clasts are closer to conodont faunas from the Holy Cross Mountains, Poland, and the Wrae Limestone in the Northern Belt of the Southern Uplands, than to those in coeval strata from the Laurentian margin including Girvan. Conodont colour alteration index values indicate separate thermal histories for the limestone clasts and coeval strata in the Girvan Inlier. The cryptic arc was located to north of the Northern Belt of the Southern Uplands during Ashgill time and to south of the Midland Valley in Late Silurian-Early Devonian time and clearly had a complex tectonic history.