bluuebunny/crossref_metadata_2025 huggingface dataset:
Is the Earth too old? The impact of geochronology on cosmology, 1929–1952
Authors: Brush Stephen G.
Published: April 2008

Estimates of the Earth’s age have had significant impacts, not only on geology but also on biology, astronomy and biblical creationism. In the 1930s and 1940s, the age of the universe as estimated from the expanding universe was less than 2000 million years, but the age of the Earth as estimated from radiometric dating was perhaps as great as 3000 million years. Astronomers responded to this contradiction in at least three different ways. Some cosmologists favoured Georges Lemaître’s relativistic model, in which the universe remains about the same size for an indefinite period of time before starting its present stage of expansion. Since theories of the origin of the solar system that were popular in the early 1930s assumed an encounter between the Sun and another star, it seemed plausible that the Earth could have been formed around this epoch of ‘cosmic congestion’. Edwin P. Hubble, generally regarded as the founder of the expanding-universe theory because of his discovery of the redshift-distance law, doubted that redshifts are actually due to velocities, and seemed to prefer a non-expanding model, though he emphasized that the correct interpretation of the redshifts of distant galaxies was still an open question up until the time of his death in 1953. Fred Hoyle, Hermann Bondi and Thomas Gold proposed a ‘steady-state’ cosmology: the universe has always existed, so there is no conflict between its (infinite) age and that of the Earth. The discrepancy was finally resolved in the 1950s when astronomers revised their distance scale and boosted the age of the universe to 10 000 million years or more. The current agreement between geologists and astronomers again leaves creationists with no scientific support at all for their claim that both the Earth and universe were created only about 10 000 years ago.
The age of the Earth in the twentieth century: a problem (mostly) solved
Authors: Dalrymple G. Brent
Published: April 2008

In the early twentieth century the Earth’s age was unknown and scientific estimates, none of which were based on valid premises, varied typically from a few millions to billions of years. This important questions was answered only after more than half a century of innovation in both theory and instrumentation. Critical developments along this path included not only a better understanding of the fundamental properties of matter, but also: (a) the suggestion and first demonstration by Rutherford in 1904 that radioactivity might be used as a geological timekeeper; (b) the development of the first mass analyser and the discovery of isotopes by J. J. Thomson in 1914; (c) the idea by Russell in 1921 that the age of a planetary reservoir like the Earth’s crust might be measured from the relative abundances of a radioactive parent element (uranium) and its daughter product (lead); (d) the development of the idea by Gerling in 1942 that the age of the Earth could be calculated from the isotopic composition of a lead ore of known age; (e) the ideas of Houtermans and Brown in 1947 that the isotopic composition of primordial lead might be found in iron meteorites; and (f) the first calculation by Patterson in 1953 of a valid age for the Earth of 4.55 Ga, using the primordial meteoritic lead composition and samples representing the composition of modern Earth lead. The value for the age of the Earth in wide use today was determined by Tera in 1980, who found a value of 4.54 Ga from a clever analysis of the lead isotopic compositions of four ancient conformable lead deposits. Whether this age represents the age of the Earth’s accretion, of core formation, or of the material from which the Earth formed is not yet known, but recent evidence suggests it may approximate the latter.
Compaction experiments on wet calcite powder at room temperature: evidence for operation of intergranular pressure solution
Authors: Zhang X. , Salemans J. , Peach C. J. , Spiers C. J.
Published: April 2008

Dead weight uniaxial compaction creep experiments were carried out on fine-grained, super-pure calcite (<74 μm) at room temperature and applied effective stresses of 1–4 MPa. All samples were pre-compacted dry at a stress of 8 MPa, for 30 minutes, to obtain a well-controlled initial porosity. The samples were then wet-compacted under ‘drained’ conditions with pre-saturated solution as pore fluid. Control experiments, which were done either dry or with chemically inert pore fluid, showed negligible compaction. However, samples tested with saturated solution as pore fluid showed easily measurable compaction creep. The compaction strain rate decreased with increasing strain and increasing grain size, and increased with increasing applied stress. Addition of Mg
2+
ions to the saturated solution dramatically inhibited compaction. From the literature, Mg
2+
ions are known to inhibit calcite precipitation. By comparison with a theoretical model for intergranular pressure solution in calcite, the observed mechanical behaviour and the way that compaction responded to the pore fluid chemistry suggest that, under our experimental condition, intergranular pressure solution is the mechanism of the deformation and that precipitation is likely to be the rate-limiting step.
Numerical modelling of pressure solution in sandstone, rate-limiting processes and the effect of clays
Authors: Gundersen E. , Dysthe D. K. , Renard F. , Bjørlykke K. , Jamtveit B.
Published: April 2008

Pressure solution is an efficient mechanism for ductile deformation and local mass transport in the upper crust. In this paper we model pressure solution as a mechanism involving four steps: (1) dissolution at the grain contacts; (2) diffusion of solutes through fluid films at the contact between two grains; (3) transport of solutes by diffusion through the pore fluid into other adjacent open pores; and (4) precipitation on the surface of grains at their contact with the pore fluid. In this study we constrain under which conditions pressure solution is limited by one of the four processes: dissolution; contact diffusion; precipitation; and global diffusion. From our model of pressure solution, based on thermodynamic relationships we derive three dimensionless numbers which represent the competetion between the four mentioned processes. With these numbers we can define the crossover from a situation where one process acts as the limiting process to a new situation controlled by another process. We also see how the different rate-limiting processes influence the amount of mass transported during the compaction process. In addition we study the effect of clays, as it has been suggested that these minerals speed up the rate of pressure solution. We propose two models, a chemical related and a mechanical model for how the clay particles may affect the dissolution process of quartz.
Effects of stress on the anisotropic development of permeability during mechanical compaction of porous sandstones
Authors: Zhu Wenlu , Montési Laurent G. J. , Wong Teng-Fong
Published: April 2008

To investigate the influence of stress on permeability anisotropy during mechanical compaction, a series of triaxial compression experiments with a new loading configuration called hybrid compression were conducted on three porous sandstones. The effective mean and differential stresses in hybrid compression tests were identical to those in conventional triaxial extension tests. Permeability was measured along the axial direction in both hybrid compression and conventional extension tests, which corresponds to flow along the maximum principal stress direction in the former case and the minimum principal stress direction in the latter case. Since their loading paths coincide, the comparison of permeability values from the two types of tests provides quantitative estimates of the development of permeability anisotropy as a function of effective mean and differential stresses. Our data show that the permeability evolution is primarily controlled by stress. Before the onset of shear-enhanced compaction
C
*, permeability and porosity reduction are solely controlled by the effective mean stress, with negligible stress-induced anisotropy. With the onset of shear-enhanced compaction and initiation of cataclastic flow, the deviatoric stress induces enhanced permeability and porosity reduction. The permeability tensor may show significant anisotropy. Our data indicate that the maximum principal component of permeability tensor
k
1
is parallel to the maximum principal stress σ
1
, and the minimum principal component
k
3
is parallel to the minimum principal stress σ
3
. During the initiation and development of shear-enhanced compaction,
k
1
can exceed
k
3
by as much as two orders of magnitude. With the progressive development of cataclastic flow, changes of permeability and porosity become gradual again, and the stress-induced permeability anisotropy diminishes as
k
1
and
k
3
gradually converge. Our data imply that permeability can be highly anisotropic in tectonic settings undergoing cataclastic flow, inducing the fluid to flow preferentially along conduits subparallel to the maximum compression direction. However, this development of permeability anisotropy is transient in nature, becoming negligible with an accumulation of strain of about 10%. The anisotropic development of permeability in a lithified rock is dominantly controlled by microcracking and pore collapse. This is fundamentally different from the mechanisms active in unconsolidated materials such as sediments and fault gouges, in which the permeability evolution is primarily controlled by the development of fabric and shear localization via the accumulation of shear strain.
The numerical simulation of microstructure
Authors: Jessell Mark W. , Bons Paul D.
Published: April 2008

This review discusses the attempts that have been made by geologists to numerically simulate the evolution of microstructures in rocks. The strengths and weaknesses of the differing techniques are compared and equivalent materials science results are included. In particular we focus on the application of techniques that have been used to predict texture development, grain boundary geometries, deformation in one and two-phase systems and crystal growth.
Dynamic recrystallization of quartz: correlation between natural and experimental conditions
Authors: Stipp Michael , Stünitz Holger , Heilbronner Renée , Schmid Stefan M.
Published: April 2008

Quartz veins in the Eastern Tonale mylonite zone (Italian Alps) were deformed in strike-slip shear. Due to the synkinematic emplacement of the Adamello Pluton, a temperature gradient between 280°C and 700°C was effected across this fault zone. The resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization, subgrain rotation recrystallization and grain boundary migration recrystallization. The transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature. Differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships. Deformation temperatures are obtained from metamorphic reactions in the deformed host rock. Flow stresses and deformation temperatures are used to determine the strain rate of the Tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10
−14
s
−1
to 10
−12
s
−1
. The deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of Hirth & Tullis. Linking the microstructures of the naturally and experimentally deformed quartz rocks, a recrystallization mechanism map is presented. This map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known.
The effect of static annealing on microstructures and crystallographic preferred orientations of quartzites experimentally deformed in axial compression and shear
Authors: Heilbronner Renée , Tullis Jan
Published: April 2008

Quartzite samples were experimentally deformed with partial to complete dynamic recrystallization by axial compression (strain magnitude of 0.8 to 1.4) and by general shear (strain magnitude of 1.3 to 2.8) in each of the three dislocation creep regimes, and subsequently annealed with complete static recrystallization at the deformation temperature for 120 hours. The
c
-axis crystallographic preferred orientation (CPO), 3D grain size distribution, grain boundary surface shape, and misorientation density were measured before and after annealing. The effect of annealing on the CPO was minor, but the microstructure was greatly changed. All of the annealed samples were completely recrystallized. The recrystallized grain size increased by a factor of 2 to 5, and was greatest for samples deformed at lowest temperature. The grain boundary lobateness (PARIS factor) and misorientation density were reduced significantly. The CPOs for all the deformed samples were relatively unchanged by annealing, although the strengths are somewhat decreased; for sheared samples the asymmetry was preserved. The results suggest microstructural criteria for recognizing the occurrence of static annealing and for estimating the dynamically recrystallized grain size relevant for paleopiezometry from annealed samples.
Stress and deformation in subduction zones: insight from the record of exhumed metamorphic rocks
Authors: Stöckhert Bernhard
Published: April 2008

High pressure (HP) and ultrahigh (UHP) metamorphic rocks are exhumed from subduction zones at high rates on the order of plate velocity (cm/year). Their structural and microstructural record provides insight into conditions and physical state along the plate interface in subduction zones to depths of >100 km. Amazingly, many identified (U)HP metamorphic rocks appear not to be significantly deformed at (U)HP conditions, despite their history within a high strain rate mega-shearzone. Other (U)HP metamorphic rocks seem to be deformed exclusively by dissolution-precipitation creep. Indications of deformation by dislocation creep are lacking, apart from omphacite in some eclogites. Available flow laws for dislocation creep (extrapolated to low natural strain rates, which is equivalent to no deformation on the time scales of subduction and exhumation, i.e., 1 to 10 Ma) pose an upper bound to the magnitude of stress as a function of temperature along the trajectory followed by the rock. Although the record of exhumed (U)HP metamorphic rocks may only be representative of specific types or evolutionary stages of subduction zones, for such cases it implies: (1) strongly localized deformation; (2) predominance of dissolution-precipitation creep and fluid-assisted granular flow in the shear zones, suggesting Newtonian behaviour; (3) low magnitude of differential stress; which (4) is on the order of the stress drop inferred for earthquakes; and (5) negligible shear heating. These findings are easily reconciled with exhumation by forced flow in a low viscosity subduction channel prior to collision, implying effective decoupling between the plates.
On estimating the strength of calcite rocks under natural conditions
Authors: De Bresser J. H. P. , Evans B. , Renner J.
Published: April 2008

Field studies of calcite mylonites often document microstructures produced by dislocation creep. In contrast, flow laws derived from experiments predict that calcite rocks should deform mostly by diffusion creep during tectonic processes. To investigate this apparent discrepancy, we compare stresses estimated by microstructural piezometers to those obtained by extrapolation of experimentally derived flow laws. Considering shear zones from different geological settings, a clear trend is observed of increasing recrystallized grain size with increasing temperature. However, there is a large spread in grain size and associated stress. Because separate flow laws have been defined for various different marbles and limestones, the strengths predicted for a given set of conditions differ significantly. The stress estimates based on the piezometers and strength extrapolated from the various experimentally derived dislocation creep flow laws agree qualitatively, but no single flow law predicts all the palaeostress estimates. Even if experimental data are disregarded, the field observations are not consistent with a hypothetical law for Coble creep; they are consistent with a power law for dislocation creep, but only if the material constants are different from those currently determined in laboratory experiments.
Deformation of the continental lithosphere: Insights from brittle-ductile models
Authors: Brun Jean-Pierre
Published: April 2008

2D deformation experiments on multilayer models of a brittle-ductile lithosphere are reviewed. The experimental method consists of simulating simplified strength profiles which incorporate brittle (frictional) and ductile (viscous) rheologies with gravity forces. A selection of models built with sand and silicone putties to represent brittle and ductile lithosphere layers, respectively, is used to illustrate the effects of variations in strength profiles on deformation patterns. Models of extension first consider lithosphere necking and the development of narrow rifts, with application to continental rifts and passive margins, and, second, lithosphere spreading with application to the development of wide rifts and core complexes. Models of compression compare sandbox-type and brittle-ductile multilayer-type experiments. Results are applied to mountain belt formation and, in particular, to the Pyrenees and the western Alps. Both extensional and compressional experiments demonstrate that the presence/absence of a sub-Moho brittle mantle and the coupling/decoupling between brittle and ductile layers play a dominant role on localized versus distributed deformation, at lithosphere scale.
Evidence for steady fault-accommodated strain in the High Himalaya: progressive fault rotation of the southern Tibet detachment system in NW Bhutan
Authors: Wiesmayr G. , Edwards M. A. , Meyer M. , Kidd W. S. F. , Leber D. , Häusler H. , Wangda D.
Published: April 2008

We present fault analyses from the exhumed middle crustal slab of the High Himalaya in eastern Lunana in NW Bhutan. Fault planes from within two-mica, tourma-line-bearing leucogranites, leucogranitic rocks and migmatites indicate a complex brittle fault pattern with two distinct fault groups. A first group of faults (D
1
) characterized by chlorite, quartz and tourmaline slickenfibres is mainly defined by steeply SSE-dipping oblique-slip normal faults, and by shallowly NNW-dipping normal faults. A second, younger group of faults (D
2
) characterized by cataclasis products comprises strike-slip faults displaying conjugate patterns and E- and W-dipping conjugate normal faults, all which indicate E-W extension. Cross-cutting relationships amongst the D
1
fault group demonstrate that progressively steeper members of the fault group become younger within the NNW-dipping faults and become older within the SSE-dipping faults. These are all post-dated by the D
2
fault group. The D
1
fault group indicates that the slab experienced ongoing NNW-SSE extension (i.e. flow) via brittle fault accommodation, contemporaneous with fault rotation. This may reflect rotation of the entire upper orogen due to movement over deeply located major ramp structures formed by out-of-sequence thrusting (Kakhtang Thrust) within the High Himalayan Slab of the Bhutan Himalaya.
A GPR study of sedimentary structures within a transgressive coastal barrier along the Danish North Sea coast
Authors: Møller Ingelise , Anthony Dennis
Published: April 2008

The Danish North Sea coast is characterized by the presence of coastal barrier systems. One of these systems, the Holmsland Barrier, is a transgressive wave-dominated barrier. For the purpose of studying large-scale architecture in a transgressive barrier, as well as small-scale sedimentary structures, a ground penetrating radar (GPR) field experiment has been carried out. The study focuses on the identification of high-amplitude reflections of the large-scale architecture of the barrier and the recognition of small-scale structures for interpretation of coastal processes. The observed radar facies fall into two groups, both interpreted as storm washover deposits. One group, dominated by parallel to subparallel reflection, is related to the seaward horizontal stratification in the washover fans. The other group, dominated by sigmoid and oblique clinoforms, is related to delta foreset stratification, indicating that the washover fans are terminated in standing water. The observations derived from the GPR study of the Holmsland Barrier suggest that this transgressive barrier is composed almost entirely of washover deposits with local small amounts of aeolian deposits. This study has shown that the GPR method is outstanding in mapping both large-scale architecture and small-scale internal structures in a coastal barrier.
Sedimentary architecture and radar facies of a fan delta, Cypress Creek, West Vancouver, British Columbia
Authors: Roberts M. C. , Niller H. -P. , Helmstetter N.
Published: April 2008

Fan deltas are common depositional features along the macro-tidal, fjorded coast of southern British Columbia. To determine the sedimentary architecture of the Cypress Creek fan delta, West Vancouver, British Columbia, a combined ground penetrating radar and geomorphological study was carried out. Five radar facies were identified and their associated geomorphic environments were established: oblique clinoform radar facies (delta front); mounded radar facies (debris-flow deposits); undulating subhorizontal radar facies (beach zone); concave radar facies (river channels) and horizontal radar facies (salt-water intrusion). The delta plain was formed primarily by debris flows, some of which reached the delta front to form prograding foreset beds. Radar facies analysis established the occurrence of arcuate scars and masses of slumped material, signifying mass movement on the delta front. Wave action, working over a 4.9 m tidal range, has reworked the distal delta-plain debris-flow sediments into an armoured gravel beach. A depositional model is proposed for a fan delta in a macro-tidal fjord setting.
The use and application of GPR in sandy fluvial environments: methodological considerations
Authors: Woodward John , Ashworth Philip J. , Best James L. , Sambrook Smith Gregory H. , Simpson Christopher J.
Published: April 2008

Ground penetrating radar (GPR) is a popular technique for imaging and interpreting sedimentary architecture. However, current literature shows a wide range in the quality of information provided on the GPR methodology and processing technique. It is therefore difficult to judge the validity of the GPR interpretations and this produces inherent difficulties for comparison between surveys. This paper describes the key steps required to collect, process and interpret GPR surveys in sandy fluvial sediments. GPR data from the South Saskatchewan River, Canada, are used to illustrate each stage of data collection and processing. Particular attention is given to the appropriate set-up conditions for the GPR software and hardware, the selection of data-processing techniques and velocity analysis. Methods for the interpretation of GPR reflectors are also investigated using ground-truth control provided by a cut-face exposure. This paper presents recommendations for a systematic and rigorous methodology for the collection, processing and interpretation of GPR data in sandy fluvial environments. The paper suggests that all data-collection parameters and processing steps should be recorded or tabulated in any GPR publication to facilitate comparisons between surveys.
GPR derived architecture of November 1996 jökulhlaup deposits, Skeiðarársandur, Iceland
Authors: Cassidy N. J. , Russell A. J. , Marren P. M. , Fay H. , Knudsen Ó. , Rushmer E. L. , Van Dijk T. A. G. P.
Published: April 2008

Skeiðarársandur in southeastern Iceland, with an area of > 1000 km
2
, is the world’s largest active proglacial outwash plain. In July–August 2000, a total of over 10 km of ground penetrating radar (GPR) profile data (at 50 MHz and 100 MHz) was collected from a variety of proglacial outwash sediments across the Gígjukvísl channel region of the Skeiðarársandur plain. GPR-profile results and their corresponding facies interpretations are presented for the flood deposits of a single supraglacial outwash fan and its associated source-proximal ice-walled canyon created entirely by the November 1996 jökulhlaup event. By combining the GPR data with ground surveying, photogrammetry and detailed sedimentary outcrop evidence, this study adds a new perspective to the large-scale analysis of single, high-magnitude flood events and the sedimentary record of former, ice-proximal outwash plains. The GPR derived architectures point to a higher degree of sediment reworking than predicted by previous sedimentary models and may provide a useful analogue for the study of sedimentation within similar bedrock fluvial and alluvial fan feeder systems.
Visualization and characterization of active normal faults and associated sediments by high-resolution GPR
Authors: Reiss Stefan , Reicherter Klaus R. , Reuther Claus-Dieter
Published: April 2008

Ground penetrating radar (GPR) is applied here to visualize sedimentary structures related to recent deformation. Several 200 MHz GPR profiles perpendicular to active normal faults in Spain and Italy were analysed. The El Camp normal fault with associated sedimentary and tectonic patterns in northeastern Spain serves as test site. Faulted alluvial and colluvial sediments of the Pleistocene were studied in a trench for direct comparison with GPR profiles. GPR investigations across buried faults from several localities are compared to these observations in a case study. The hanging walls of these faults form half-grabens or grabens, which are generally characterized by internal asymmetric, concave, displaced reflectors or wedge-like features comparable to sedimentary features in adjacent outcrops. The examples demonstrate that high-resolution GPR profiling provides not only the possibility to trace and map active normal faults but also to visualize the associated sedimentary hanging-wall patterns in the subsurface, such as heterogeneous graben and half-graben structures, including coarse-grained clastic wedges. Quantitative and qualitative GPR evaluation of those wedges yields a certain possibility of estimation of palaeomagnitudes and slip rates on active normal faults. We regard high-resolution GPR as an additional tool in pretrenching palaeoseismological investigations.
Tectonic control on changes in sediment supply: Quaternary alluvial systems, Körös sub-basin, SE Hungary
Authors: Thamó-Bozsó Edit , Kercsmár Zsolt , Nádor Annamária
Published: April 2008

The Pannonian Basin of Hungary is Europe’s largest inter-mountain basin, where an evolution in drainage development patterns during the Quaternary was caused by changes in sediment flux to the basin, the dynamics of basin morphology development and the uplift history of the Apuseni Mountains source area, all directly or indirectly related to the tectonic systems operating in the region. Micro-mineralogical data of detrital heavy minerals from modern rivers and two key boreholes covering a time span from the present back to 2.6 Ma have been grouped by statistical analysis into two main clusters and some sub-clusters. The samples within the same cluster have a similar composition, and originated from the same source area. Based on the similar palaeogeographical setting of the potential source areas during the Quaternary, it has been possible to extrapolate the present transport directions of the rivers with a well-known catchment area geology and the heavy mineral composition to Pleistocene borehole data. The changes in transport directions were clearly sharp and related to significant changes in the uplift history of the Apuseni Mountains catchment area. During the Pliocene and Early Pleistocene the compressional stress field operating in the East Carpathians region resulted in the thrust-driven uplift of the Apuseni Mountains and the formation of a syn-sedimentary trap at the western margin of the source area, which captured the sediments of short, transverse rivers. During this period the drainage of the study area was characterized by axial drainage parallel to this trap, and sediments were transported from the northeast, also shown by micro-mineralogical data of detrital heavy minerals. At about 1.95 Ma this trap stopped being active due to the release of the compressional stress field and the isostatic uplift of the Apuseni Mountains, together with the adjoining basin area. This resulted in the filling of the thrust-bounded trap, and the development of transverse drainage, which was shown by characteristic SE transport directions, based on micro-mineralogical data in the study area, and also by an increase of sediment flux. The axial capturing shifted further to the west, developing a configuration approaching to the present river course pattern. By analogy with the Himalayan foreland and retro-arc basins of the Cordilleran-Andean ranges, it was demonstrated that tectonic activity exerts a strong control on the drainage pattern through its influence on variations in sediment supply.
Sediment budgeting techniques in gravel-bed rivers
Authors: Brewer P. A. , Passmore D. G.
Published: April 2008

The difficulties in obtaining reliable sediment transfer data from direct field measurement or from sediment transport formulae are widely recognized by geomorphologists and river engineers. Quantifying morphological changes (erosion and deposition) in rivers by the analysis of archive data or by field survey, however, can overcome many of these difficulties and provide a mechanism by which sediment budgets can be calculated over a variety of spatial and temporal scales. This paper applies three sediment budgeting methods based on morphological changes in a hypothetical braided reach. These methods range from a simple two-dimensional planform budget to more sophisticated three-dimensional cross-profile and morphological budgets. The development of each budget technique is described and the limitations and applicability of each identified. The three methods are then used to calculated sediment transfer rates in a multi-thread reach on the River Severn in mid-Wales, UK. Results show that across four budget periods spanning 2.5 years the reach was a net exporter of sediment. Application of the planform budget to eight time periods since 1836 shows a similar pattern of net sediment export in the nineteenth century, but during the majority of the twentieth century the reach was a net sediment sink. Finally, the applicability of applying budgeting techniques to extended centennial and millennial timescales is discussed and an assessment made of the role they might play in advancing our understanding of Holocene river dynamics and informing sustainable river management practices.
Transverse rivers draining the Spanish Pyrenees: large scale patterns of sediment erosion and deposition
Authors: Jones Stuart J.
Published: April 2008

Data collected from six transverse rivers draining the Spanish Pyrenees highlight how the rate of change in river gradients downstream controls long-term deposition and erosion patterns acroos the mountain belt. The rivers draining the Spanish Pyrenees provide evidence for an important relationship between gradient (
S
) and distance from the drainage divide (
x
), such that
S
is proportional to
x
Ω
. This can be expressed quantitatively as a power function relation
S
∞
L
−R
. In areas dominated by erosion Ω has a value > − 5, while in areas of deposition Ω has a value < −0.4. The contrast between areas of erosion and deposition is also reflected in downstream increases and decreases, respectively, in stream power and bed shear stress along the whole of the mountain front.

It is proposed, based upon previous empirical studies of loose to semi-armoured channels, that the downstream variations of stream power and bed shear stress result in variations of bed-load transport rates, which in turn create the erosional and depositional patterns associated with variations of channel gradient.

These results highlight the complex response of the fluvial system, emphasizing the need for regional approaches for examining long-term changes in rivers draining orogenic belts and the importance for incorporation of hydraulic data into geomorphological models to assist interpretations of the mass distribution of sediment.
The flux of siliciclastic sediment from the Iberian Peninsula, with particular reference to the Ebro
Authors: Evans Graham , Arche Alfredo
Published: April 2008

Today, the main flux of sediment from the Iberian Peninsula is carried to the Atlantic Ocean by westerly or northwesterly flowing rivers. The only major contribution of sediment from Iberia to the Mediterranean is that carried by the Ebro River, which flows along a foreland basin before cutting through the Catalan Ranges to form a delta in the adjacent Valencian Trough of the Mediterranean. During the Cretaceous and Early Eocene the sediment flux was to the northwest in this part of Iberia. During Late Eocene-Tortonian times it was mainly centripetal, as in other Tertiary Basins in Iberia. Beginning in the Seravallian-Tortonian the main flux of sediment has been to the adjacent Valencian Trough of the Mediterranean. This change in direction, it is proposed, was initiated in Pre-Messinian times by a small river cutting back into the Ebro Basin by headward erosion and was possibly aided, or even induced, by changes in palaeo-slope during contemporaneous rifting along the Mediterranean coast.
Geology: from an Earth to a planetary science in the twentieth century
Authors: Marvin Ursula B.
Published: April 2008

Since the opening of the Space Age, images from spacecraft have enabled us to map the surfaces of all the rocky planets and satellites in the Solar System, thus transforming them from astronomical to geological objects. This progression of geology from being a strictly Earth-centred science to one that is planetary-wide has provided us with a wealth of information on the evolutionary histories of other bodies and has supplied valuable new insights on the Earth itself. We have learned, for example, that the Earth-Moon system most likely formed as a result of a collision in space between the protoearth and a large impactor, and that the Moon subsequently accreted largely from debris of Earth’s mantle. The airless, waterless Moon still preserves a record of the impact events that have scarred its surface from the time its crust first formed. The much larger, volcanic Earth underwent a similar bombardment but most of the evidence was lost during the earliest 550 million years or so that elapsed before its first surviving systems of crustal rocks formed. Therefore, we decipher Earth’s earliest history by investigating the record on the Moon. Lunar samples collected by the
Apollo
astronauts of the USA and the robotic
Luna
missions of the former USSR linked the Earth and Moon by their oxygen isotopic compositions and enabled us to construct a timescale of lunar events keyed to dated samples. They also permitted us to identify certain meteorites as fragments of the lunar crust that were projected to the Earth by impacts on the Moon. Similarly, analyses of the Martian surface soils and atmosphere by the
Viking
and
Pathfinder
missions led to the identification of meteorite fragments ejected by hypervelocity impacts on Mars. Images of Mars displayed landforms wrought in the past by voluminous floodwaters, similar to those of the long-controversial Channeled Scablands of Washington State, USA. The record on Mars confirmed catastrophic flooding as a significant geomorphic process on at least one other planet. The first views of the Earth photographed by the crew of
Apollo 8
gave us the concept of ‘Spaceship Earth’ and heightened international concern for protection of the global environment.
Arthur Holmes’ unifying theory: from radioactivity to continental drift
Authors: Lewis Cherry L. E.
Published: April 2008

Only ten years after the discovery of radium in 1897, Arthur Holmes (1890–1965) began his studies at the Royal College of Science in London where he completed the very first U/Pb age determination designed specifically for that purpose. His continued interest in radioactivity and its effect on the thermal history of the Earth led to his early recognition that the age of the Earth should be measured in thousands, not hundreds, of millions of years, a subject he pursued for the rest of his career, despite considerable opposition from traditional geologists. Following a short period in Burma, he returned in 1922 to find that not only had attitudes to the age of the Earth changed, but that geologists were embroiled in a new controversy over continental drift. Evidence is put forward that suggests Holmes may have been aware of Wegener’s theories virtually from the time they were proposed, and that by 1924 he was already searching for his own theory which would explain all geological processes. His profound understanding of the effects of radioactivity on the internal processes of the Earth, and his advanced knowledge of petrology, placed him in a unique position to develop a mechanism for driving continental plates around the globe. The progression of his ideas for this mechanism — convection currents in the mantle — and the unifying theory that that led to, is traced through his papers and letters to colleagues.
Russian geology and the plate tectonics revolution
Authors: Khain Victor E. , Ryabukhin Anatoly G.
Published: April 2008

The suggestion of the concept of ‘scientific revolution’ by Thomas Kuhn in 1962 was, in itself, a significant event in the history of science, and ‘crucial’ episodes or ‘paradigm shifts’ have come to be of special interest in the history of geology (as in other sciences). The appearance of a new paradigm is commonly associated with attempts by the most talented and well-established practitioners to consolidate or sustain the position of the previously prevailing paradigm. For almost 40 years, global theories in geology have been developing under the influence of mobilist ideas. It is no secret that in Russia the mobilist school initially met with serious opposition, and that even up to the present it has had numerous opponents. However, Western, and especially popular, scientific literature usually exaggerates the intensity of the situation and underestimates the contribution of Russian geologists and geophysicists to the development of mobilism and plate tectonics. The present paper describes some of the debates in Russia concerning mobilist doctrines, the work done in that country in the last three decades of the twentieth century from a mobilist perspective, and various theories that had currency in Russia at the end of that century.
‘As chimney-sweepers, come to dust’: a history of palynology to 1970
Authors: Sarjeant William A. S.
Published: April 2008

A brief overview is given of the various fields of palynology, their practical applications being stressed. Particular attention is thereafter paid to the history of palaeopalynology, here considered as the study of pre-Quaternary palynomorphs. This is presented as three stages: the period of pioneer discoveries (to 1918); years of slow progress (1919–1945); and a post-World War II period of accelerating discoveries (1946–1970). Developments concerning the different groups of palynomorphs during these periods are successively presented, under six headings: spores and pollen; dinoflagellates (and acritarchs); prasinophytes; scolecodonts; chitinozoans; and other palynomorphs. The changes brought about in palynology by improving preparation techniques and microscopical equipment are stressed. A brief overview is attempted concerning the developments since 1970, consequent upon ever-expanding research, new preparation techniques and new technology. As conclusion, an overview is presented of the history of palynology and likely future developments are discussed.
Collecting, conservation and conservatism: late twentieth century developments in the culture of British geology
Authors: Knell Simon J.
Published: April 2008

The last three decades of the twentieth century saw a transformation of the place and influence in British society of two cultural themes: environmental conservation and the values of political conservatism. These are here used to examine cultural change in the science of geology at two levels of resolution. First, the micropolitics of the science are revealed through a study of collecting in an era of conservation. Here the scientific hegemony confronted the more populist and commercially driven wings of geology. This was a period of campaign and conflict, leading to the eventual accommodation of opposing views. The second section examines the macropolitics of the science’s institutional infrastructure through a study of a science in a period of recession and under the control of an ideologically motivated Conservative government. The challenge for science was to acquire appropriate government patronage. Here patterns of decline and growth in the science are revealed, driven by supposedly ‘external’ factors. Both perspectives show how the notion of accountability became critical to the science at all levels, and how, in an era which saw the revolutionizing of mass communication, language became fundamental to the political progress of the science.
Phylogeny of the Reedocalymeninae (Trilobita): implications for Early Ordovician biogeography of Gondwana
Authors: Turvey Samuel T.
Published: April 2008

The shallow-water
Neseuretus
Association has been recognized by many authors as an important indicator of the former extent of Gondwana during the Early Ordovician. Phylogenetic relationships of the Reedocalymeninae (Arenig-?Early Silurian) were investigated using cladistic analysis, incorporating 22 species of
Neseuretus
as well as representatives of all other reedocalymenine genera. The area cladogram derived from this analysis contains four subclades each containing areas that span much of the palaeogeographic extent of Gondwana, which are interpreted as representing separate biogeographic events during the evolution of the subfamily. As the majority of taxa included in the analysis are associated with shallow shelf facies, this suggests that no significant environmental barriers existed across the continent during the Early Ordovician. Consideration of area relationships both for different subclades within the area cladogram, and within a consensus area cladogram, also supports the idea of a faunal cline between eastern and western Gondwana during this time interval. Further cladistic analysis of different trilobite taxa can be used to test these ideas.
Euconodont diversity changes in a cooling and closing Iapetus Ocean
Authors: Armstrong H. A. , Owen A. W.
Published: April 2008

Constrained seriation of euconodont generic presence-absence matrices for four time slices between the late Llanvirn and late Llandovery provides a qualitative method for defining shelf and oceanic biofacies, recosntructing biofacies architecture and analysing biodiversity within a regional context.

We propose many North Atlantic Province taxa had a pelagic mode of life and ranged widely across the Iapetus Ocean. Oceanic biofacies are considered to reflect water mass structure. Changes in vertical distribution of one such biofacies (including
Amorphognathus
and
Spinodus
) suggest adaptation to cold, nutrient-rich, oxygen-poor upwelling water. Biofacies distributions suggest that upwelling occurred along the Avalonian margin throughout the Ashgill, but was only initiated along the Laurentian margin immediately prior to the Hirnantian glacial maximum.

Clade diversities and trajectories differ between biofacies and latitudes, reflecting different causal mechanisms. In Laurentia, diversity fell in the early Ashgill, coincident with the onset of ocean cooling. Diversity declined in Avalonia when the microcontinent drifted into tropical latitudes. The stability of euconodont biofacies architecture during the Late Ordovician indicates that global cooling and plate reorganization had a low palaeoecological impact despite decreases in alpha and beta diversity.
The role of pyroclastic volcanism in Ordovician diversification
Authors: Botting Joseph P.
Published: April 2008

Pyroclastic volcanism has been tentatively correlated with Ordovician faunal diversification, but it is unclear whether the volcanism itself or associated tectonic effects were more influential. Elevated nutrient flux from uplifted areas has been widely discussed, but the link between enhanced productivity and diversification is unclear. Ecosystem compartmentalization due to irregular topography was probably significant, but it is debatable whether this was sufficient to explain the entire diversification. This paper introduces a further volcanic process, which may have been more significant than these established hypotheses, although it is emphasized that all relevant factors acted in combination. Recent studies of the local ecological effects of ash-fall have revealed dramatic post-depositional plankton and benthic blooms associated with overturning of a stratified water mass. The data are consistent through all studied sections from the Builth Inlier, Central Wales, while deeper-water sediments showed plankton blooms only. Repeated bloom events over localized dysaerobic shelf areas may have produced temporary benthic ‘islands’, enhanced genetic heterogeneity within affected regions, and increased speciation rates. In order to maximize bloom intensity (and possible effects on evolution), this process requires widespread pyroclastic volcanism combined with extensive shelf areas with well-developed stratification. The hypothesis potentially allows explanation of the differential rates of evolution between different groups, particularly the decoupled planktic-benthic patterns. A preliminary test using Welsh Basin ostracodes is presented, with predictions for the global database results.
Opening of the Hispanic Corridor and Early Jurassic bivalve biodiversity
Authors: Aberhan Martin
Published: April 2008

The Hispanic Corridor is a postulated marine seaway linking the eastern Pacific and western Tethyan oceans as early as Early Jurassic times. Two existing hypotheses relate the Pliensbachian-Toarcian bivalve extinction and recovery to immigration of bivalve species through the Hispanic Corridor. The extinction hypothesis implies that, in South America, the Pliensbachian-Toarcian extinction can be partly explained by the immigration of bivalves through the Hispanic Corridor and subsequent competitive replacement. The recovery hypothesis states that, in NW Europe, the renewed rise in diversity in the late Toarcian/Aalenian was largely a consequence of immigration of taxa from Andean South America via the Hispanic Corridor.

To test these hypotheses, I calculated immigration and origination rates of bivalves per million years. In both regions, early Pliensbachian to Aalenian immigration rates remained at low levels, thus disproving both hypotheses. By comparison, the origination of new species generally played a much more important role than immigration in controlling overall diversity of both regions. Future research should investigate if this is a more general pattern in the recovery of post-extinction biotas.

The apparently global Pliensbachian-Toarcian diversity crisis may be best explained by a combination of physicochemical factors, invoking intense volcanism, sea-level highstand and widespread anoxia, as well as biological factors. Recovery from this mass extinction commenced when origination rates increased again, which, in the Andean basins, was in the Aalenian and in NW Europe, the late Toarcian.