bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of a viscous model of till rheology to describe gravitational loading instabilities in glacial sediments
Authors: Hindmarsh Richard C. A. , Rijsdijk Kenneth F. 
Published: April 2008

Abstract
This paper models the operation of loading (Rayleigh-Taylor) instabilities in sediments using an effective-pressure-dependent viscosity such has been used to model the deformation of sediment beneath glaciers. A particular feature is a strong increase of viscosity with depth, resulting from the fact that the effective pressure increases with depth.
Observations suggest that more than one wavelength is generally present (e.g. diapirism and loadcasting) which requires at least three layers with uniform properties to be present. Three layers permit wavelength growth maxima at two distinct wavelengths. We investigate whether an effective-pressure dependent rheology is consistent with RT instabilities, and whether the non-uniformity it produces is able to increase the number of growth-rate maxima.
The investigation starts from the point where sediment in an underlying layer is less dense than the overlying sediment, and the Rayleigh-Taylor instability starts to operate. The mechanics of two layers of finite thickness but infinite extent are modelled by the Stokes equations. The equation set is linearized, and the Fourier transform taken in order to describe the periodic horizontal variation of flow fields at a specified wavelength.
The influences of layer thickness and viscosity ratio on the flow fields are considered. It is found that, for a given wavelength, layer thickness has a far stronger influence on flow fields than does viscosity ratio. For all configurations inspected, the dependence of growth rate on wavenumber exhibited one maximum, meaning that a variable viscosity model does not produce multiple wavelengths. Maximum growth rates occur at wavelengths corresponding to the layer thicknesses.
We infer that loading instabilities occurring at wavelengths around the layer thicknesses are consistent with the effective-pressure-dependent viscous model.
Kinematic indicators of subglacial shearing
Authors: Van der Wateren Frederik M. , Kluiving Sjoerd J. , Bartek Louis R. 
Published: April 2008

Abstract
Criteria to distinguish between sediments that have been subglacially deformed and those that are undeformed, or deformed by other mechanisms, are sparse. In this paper we develop structural criteria to reconstruct the deformation history of glacial sediments that can be readily applied in the field as well as to analyses of thin sections of tills and related materials.
Progressive simple shear is the simplest model to describe the deformation history of subglacially deformed sediments. It includes most of their characteristic structural aspects and provides tools for the kinematic analysis of subglacially deformed sediments. Progressive simple shear generates asymmetric structures, in which the principal direction of finite extension is subparallel to the direction of shearing. This is the simple shear fabric’s most distinctive characteristic, and that which most reliably defines the palaeo-ice flow direction. At a moderately strong intensity of deformation a typical shear zone in unlithified sediments may contain folded and strongly attenuated sediment layers, producing a transposed foliation which must not be mistaken for a sedimentary layering. Original sedimentary and deformation structures may completely disintegrate in the most intensely deformed sediments leading to its homogenization, although the typical shear zone fabric may still be identified in thin section.
Micromorphological evidence for polyphase deformation of glaciolacustrine sediments from Strathspey, Scotland
Authors: Phillips E. R. , Auton C. A. 
Published: April 2008

Abstract

A combination of field investigation and micromorphological analysis has been applied to polydeformed Late Devensian rhythmites and glacigenic diamicton, exposed in Strathspey, Scotland. This provided information on the geometry, kinematics and relative ages of ductile and brittle structures, and records a complex subglacial deformation history. The deformation is interpreted as resulting from a single progressive event, associated with over-riding of proglacial lake sediments by wet-based ice. The earliest deformation (‘D
1
’) resulted from compaction/loading (pure shear) and imposed a bedding-parallel (S
1
) fabric throughout the rhythmites. S
1
was subsequently deformed by kink bands and minor ductile shearing during ‘D
2
’. A later ‘D
3
’ event, characterized by soft-sediment deformation and fluidization of matrix-poor sands, was accompanied by an increase in pore water pressure. This lead to hydrofracturing of the rhythmites. The most intense deformation (‘D
4
’), which resulted from simple shear, was partitioned into the upper part of the sequence. It produced folding, thrusting and brittle microfaulting in response to NNW-directed ice-push. These findings indicate that, in general, subglacial deformation is not homogeneous and can extend to depths of >3 m below the presumed ice-sediment interface.
Large-scale glaciotectonic thrust structures in the eastern Danish North Sea
Authors: Huuse Mads , Lykke-Andersen Holger 
Published: April 2008

Abstract
The distribution of shallow, detached thrust fault complexes in the eastern Danish North Sea has been mapped based on 6400 km of high-resolution multichannel seismic data. Individual thrust segments are 200–1000 m long and 100–250 m thick with up to 200 m of horizontal displacement. Thrusting mainly affected upper Middle Miocene to lower Pleistocene strata and predated an extensive system of now buried subglacial valleys. The thrust structures are located along a 200 km long NW-SE trend. The general thrust direction is towards the SW, parallel to inferred directions of ice movement during the Elsterian and Saalian glaciations. This direction is, however, also parallel to the dip of the underlying detachment surface. The detachment surface corresponds to the mid-Miocene unconformity in the SE and the base of the Quaternary to the northwest. Detachment is generally located at depths of 130–270 m below sea level.
The structures are interpreted as glaciotectonic thrust structures of Elsterian and/or Saalian age. The driving mechanism is interpreted to be gravity spreading in front of glaciers advancing from the north, NE and east. Thrusting was facilitated by the presence of SW-dipping detachment surfaces.
Cladistic perspectives on early bivalve evolution
Authors: Carter J. G. , Campbell D. C. , Campbell M. R. 
Published: April 2008

AbstractParsimony analysis suggests derivation of the Bivalvia from monoplacophorans rather than from rostroconchs, and additionally indicates that a phylogenetic classification of the Bivalvia can be achieved by erecting the superorder Nuculaniformiinov.and the order Nuculanoidanov.for the superfamily Nuculanoidea; relegating all other palaeotaxodonts to the superorder Nuculiformii; restricting the order Nuculoida to the families Nuculidae and Pristiglomidae; expanding the order Solemyoida to include ctenodontid genera as basal plesions; restricting the superorder Heteroconchia to palaeoheterodonts and heterodonts, exclusive of the Modiomorphidae; relegating the new family Evyanidae, the Colpomyidae, Matheriidae and Modiolodontidae to near-basal plesion status within the superorder Pteriomorphia; restricting the Mytiloida to the superfamily Mytiloidea, inclusive of modiolopsid genera as basal plesions; placingOrtonellaas a basal plesion within the Cyrtodontoida; expanding the order Pectinoida to include the Myodakryotidae and the suborders Limina and Pectinina; and expanding the superfamily Arcoidea to include the frejid genera andCatamarcaiaas basal plesions, and the family Glyptarcidae. Modiomorphid anomalodesmatans appear to be more closely related to the Pteriomorphia than to the Heteroconchia, andEvyanalies close to the common ancestry of modiomorphids and colpomyid pteriomorphians. Arcoids may have evolved from left-right symmetrical but otherwise rhombopteriid-like ancestors, rather than from actinodontoids or directly from cyrtodontids. The new family Eodonidae is proposed to distinguish the nacreous genusEodonfrom the non-nacreous Astartidae within the superfamily Crassatelloidea.
Relationships between the extant Anomalodesmata: a cladistic test
Authors: Harper Elizabeth M. , Hide Elizabeth A. , Morton Brian 
Published: April 2008

Abstract
Although ancient anomalodesmatans were apparently abundant shallow and deep burrowers, in Recent seas the subclass comprises some of the most specialized rarest of all bivalves. The morphological adaptations associated with diverse life habits has persistently frustrated attempts to achieve a widely accepted scheme for the relationships between extant families.
A cladistic analysis, using 43 informative anatomical and shell characters for each of the extant anomalodesmatan families has produced a single, reasonably robust tree which is in broad, albeit imperfect, agreement with the known fossil record of the subclass. This total evidence tree places the Pandoridae, Lyonsiidae, Cleidothaeridae and Myochamidae, and also the Thraciidae, Periplomatidae and Laternulidae in monophyletic groups. Carnivory appears diphyletic, with the Parilimyidae separated from the ‘septibranch’ families (Cuspidariidae, Verticordiidae, Lyonsiellidae and Poromyidae) which form a monophyletic group. The enigmatic tube-dwelling Clavagellidae appear as a sister group to the ‘septibranchs.’.
Re-analysis of the data matrix using only those 18 characters which could be socred from shell characters alone, produced a tree which contradicted the total evidence tree rather than producing a poorly resolved version. The degree of convergence shown by shell characters make it, at least at present, difficult to include the extinct anomalodesmatan families in a cladistic analysis.
Comparative sperm ultrastructure in pteriomorphian bivalves with special reference to phylogenetic and taxonomic implications
Authors: Healy John M. , Keys Jennifer L. , Daddow Lina Y. M. 
Published: April 2008

Abstract
Pteriomorphian spermatozoa, like those of most other bivalves, are of the classic aquasperm type (conical acrosomal vesicle, short to rod-shaped nucleus, short midpiece composed of two centrioles and a ring of spherical mitochondria, a simple flagellum). Whereas most other bivalve subclasses show at least some defining acrosomal feature(s), this does not appear to be the case within the Pteriomorphia. While this could indicate non-monophyletic status, it also correlates with the fact that the Pteriomorphia are a very old and very successful group of bivalves. Acrosomal similarities suggest a close link between the Ostreoidea and Limoidea (acrosomal vesicle with wedge-shaped apical zone; radiating plates present but not well developed); and between the Pterioidea, Pinnoidea and Pectinoidea (dense anterior layer; very well developed radiating plates). For supposedly closely related taxa, the Arcoidea and Limopsoidea (both Arcoida) differ markedly from each other in acrosomal shape and substructure. The affinities of the Anomioidea and even more so the Mytiloida remain uncertain, the latter possibly connected with the Pterioidea or, more likely, removed from the rest of the Pteriomorphia (mytiloid acrosomes show concentric lamellae). A very close relationship between the Pectinidae and Spondylidae of the Pectinoidea is demonstrated (dense anterior layer of acrosome recurved). Within the Mytilidae (Mytiloidea) there is substantial variation in sperm morphology between supraspecific taxa especially at the subfamial level.
Growth patterns of noetiid ligaments: implications of developmental models for the origin of an evolutionary novelty among arcoid bivalves
Authors: Thomas R. D. K. , Madzvamuse A. , Maini P. K. , Wathen A. J. 
Published: April 2008

Abstract
The dorsal ligaments of arcoid bivalves typically consist of oblique, lamellar and fibrous sheets, alternating along the hinge so that their attachments from characteristic chevron patterns. New elements are added at or near the middle of the pattern, as the ligament grows ventrally and gets longer. Most Palaeozoic arcoids exhibit this growth pattern, which still predominates among their living descendants. Early in the Cretaceous, a novel pattern emerged, with vertical strips of lamellar ligament embedded in grooves in the sheet of fibrous ligament which is attached to each valve. In contrast with the chevron, duplivincular ligament, new elements are added to each end of the noetiid ligament, anteriorly and posteriorly. This distinctive growth pattern is the defining character of the family Noetiidae.

Remarkable variation among individuals within populations of a living limopsid arcoid includes forms with vertical strips of lamellar ligament. These variants suggest how the noetiid growth pattern could have been derived from the duplivincular pattern. Computer simulations show that such patterns can be generated by a reaction-diffusion mechanism of the sort first conceived by Turing (1952,
Philosophical Transactions of the Royal Society, London, Series B
,
237
, 37–72). Moreover, the noetiid growth pattern can simply be derived from the duplivincular pattern by a developmental switch based, for example, on a change in boundary conditions. These results indicate that striking differences in form may arise from modest changes in the developmental process. The evolution of the Noetiidae, members of which are quite disparate in overall shell form, should be reassessed. The derived character on which this family is based may not be uniquely shared, so the group could well be polyphyletic.
The Queen Scallop
Aequipecten opercularis
: a new source of information on late Cenozoic marine environments in Europe
Authors: Johnson A. L. A. , Hickson J. A. , Swan J. , Brown M. R. , Heaton T. H. E. , Chenery S. , Balson P. S. 
Published: April 2008

Abstract

Few data exist on seasonal variation in the temperature (or other aspects of the environment) of late Cenozoic shelf seas in Europe. Ontogenetic records in the shell of
Aequipecten opercularis
, a widespread, fast-growing and typically well-preserved bivalve, are a potential source. Study of modern forms has shown that oxygen stable isotopes are incorporated in equilibrium with surrounding seawater (hence providing a faithful record of temperature) and data from late Holocene
A. opercularis
of the southern North Sea Basin (SNSB) indicate that extreme winter (as well as summer) temperatures are registered. Oxygen isotope data from apparently well-preserved, mid-Pliocene shells of the SNSB indicate seasonal temperatures similar to present, whereas microgrowth increment data suggest substantially warmer conditions, in accordance with other evidence. The balance of evidence thus implies cryptic diagenetic corruption of the isotopic temperature signature in mid-Pliocene shells. However, it would be premature to discount the possibility of cooler mid-Pliocene conditions than currently recognized. Ontogenetic variation in carbon isotopic composition within shells is minor and apparently unrelated to environment, but differences between mid-Pliocene, late Holocene and modern shells probably relate to changes in atmospheric CO
2
concentration. Unlike certain taxa, seasonal variation is not evident in the strontium or magnesium contents of the
A. opercularis
shell, but may be displayed by other trace elements, hence affording (together with seasonal increment width variation) a means of independent temporal calibration of isotope profiles. Ontogenetic records of environment from
A. opercularis
can be complete (and, in the case of increment data, easily recovered) but are of short duration. They must be complemented by (less complete) records from longer lived taxa to obtain the fullest possible environmental history. Seasonal cycles in ontogenetic records afford a means of establishing age and growth rate, and can therefore provide information of value for evolutionary studies and management of living populations.
The myth of metabolic cold adaptation: oxygen consumption in stenothermal Antarctic bivalves
Authors: Peck Lloyd S. , Conway Lucy Z. 
Published: April 2008

Abstract

Antarctic marine ectotherms are often described as only being capable of living in a restricted temperature range, i.e. they are stenothermal. However, few data exist demonstrating that for a given group this is the case. The Antarctic bivalve molluscs
Laternula elliptica
and
Limopsis marionensis
are similar to other Antarctic invertebrates and can only exist within a temperature window of 6–12°C. This is two to six times smaller than the range for temperate and tropical bivalves, thus demonstrating their stenothermal nature. The possibility of elevated metabolic rates of cold-water ectotherms has been a topic of debate over many years. Recently, the suggestion that metabolic rates must be elevated at low temperatures to overcome constraints has been supported by findings that mitochondrial contents of muscles in ectotherms are higher at low temperatures. Data, presented here for standard or routine metabolic rates of 41 species of bivalve mollusc from polar, temperate and tropical sites, indicate that oxygen consumption is not elevated at low temperatures. Indeed, analysis of Q
10
coefficients between 0 and 25°C suggests that metabolic rates of polar species may be lower than would be expected by comparison with temperate bivalves.
Marine mussels, their evolutionary success, ecological significance and use as chronometers of environmental change
Authors: Seed R. , Richardson C. A. , Smith K. 
Published: April 2008

Abstract
The evolution of the heteromyarian form and neotenous retention of the byssus into the adult stage were central to the colonization of hard substrata and the subsequent evolutionary success of epibyssate mytilids. In addition, these mussels are supreme filter feeders and exhibit many structural, behavioural and life-history traits which make them particularly successful colonizing species. As competitively dominant species, mussels can potentially monopolize epibenthic communities with a consequent reduction in diversity of the primary space-occupying species. However, mussel patches themselves are extremely diverse, offering numerous resources which are exploited by a range of associated organisms from most animal phyla. Mussel beds can influence large-scale coastal and estuarine processes such as productivity and eutrophication, and can significantly alter sediment biogeochemistry. Annual growth lines and tidal bands in mussel shells have been used to estimate age, and to investigate the effects of environmental factors such as seawater and air temperature, spring-neap lunar tidal cycles and exposure to chlorination regimes in power station culverts. Analysis of the elemental composition of the incremental record in long-lived mytilids has been used to assess the effects of anthropogenic inputs into coastal waters.
A temperate reef builder: an evaluation of the growth, morphology and composition of
Sabellaria alveolata
(L.) colonies on carbonate platforms in South Wales
Authors: Naylor Larissa A. , Viles Heather A. 
Published: April 2008

Abstract

Sabellaria alveolata
(Linné) (Polychaeta: sabellariidae) is a sedentary polychaete that builds wave-resistant reefs from sand-sized particles. Reefs are formed in areas with a large, continuous supply of sand-sized sediment and turbulent water, such as the Bristol Channel, UK. Although several studies have documented the extent, growth, form and geological importance of Sabellariidae, their bioconstructive role has not been adequately assessed.
S. alveolata
occurs rarely in the UK and is classified as a distinct ecological unit by the Marine Nature Conservation Review, yet it has been little studied. Thus, there is a need for greater understanding of the species’ role in UK coastal ecology and geomorphology. An evaluation of reef development in terms of composition, growth and extent of
S. alveolata
constructions on carbonate shore platforms in South Wales is presented here. Results indicate that
S. alveolata
is a fast-growing species capable of juvenile settlement, tube formation and growth of 2.5–5.0 cm in as little as two months after installation of exposure blocks of artificial substrata. Particle size analysis of 24 randomly selected reefs and ten adjacent sand samples shows a significant difference in mean grain size, with worms consolidating particles of a coarser size distribution than the mean particle size of surrounding sand. Preliminary scanning electron microscope observations indicate preferential use of flat, platy and elongate particles in the worm tubes. This research forms part of a larger study concerned with quantifying the bioconstructive capability of
S. alveolata
.
Skeletal growth rates of Upper Cretaceous rudist bivalves: implications for carbonate production and organism-environment feedbacks
Authors: Steuber Thomas 
Published: April 2008

Abstract

The skeletal growth rates of late Cretaceous rudist bivalves have been inferred from cyclic variations of isotopic and chemical compositions which are found in sclerochronological profiles of outer shell layers. Annual shell accretion of 11 studied shells from different environmental settings was in the range of less than 10 to 54 mm. CaCO
3
production of individual rudists was calculated to range from 12 to 214 g a
−1
, and estimates of annual production of rudist communities assuming dense growth fabrics range from 4.6 to 28.5 kg m
−2
. These production rates are not significantly higher when compared to modern mussel or oyster beds but, in contrast to modern analogues, rudist associations were much more important for the sedimentary budget of low-latitude shallow-water depositional environments.

Controlling factors for the formation of growth fabrics and carbonate production are evaluated in a case study of rudist formations from a single depositional sequence. From turbulent outer platform environments to lagoonal inner platform settings, a decrease both in carbonate production and size of shells was found among specimens of a single species. No differences in carbonate production are evident when carbonate production in siliciclastic and calcareous environments is compared. Potential feedbacks between rudists and their environment induced by vertical growth, large production of bioclastic sediment and ejected biodeposits are discussed.