bluuebunny/crossref_metadata_2025 huggingface dataset:
The 1988 Orange River flood, Upington Region, Northwestern Cape Province, RSA
Authors: Zawada P.K. , Smith A.M.
Published: July 2007

This paper describes aspects of the 1988 Orange River flood. The Orange River is a perennial, bedrock‐controlled river which experienced severe flooding (flood peak: 8300 m3 s‐1) during February‐April of 1988. This flood resulted in the loss of life and damage in excess of $126 million. Negligible bank erosion took place in the main channel margins due to the stabilizing effect of tree‐lined banks. In contrast, areas removed from the channel margin were characterized by erosion and deposition.

Within the confines of the natural flood channels, macroturbulence gave rise to scour holes which sometimes amalgamated into large erosion fields acres in extent. In many cases scour holes were present but macroturbulence‐originating obstacles were not, and it is suggested that these were removed by flood‐erosion processes. In some instances amalgamation of scour‐hole trails (orientated down‐current) led to the formation of steep‐sided flood channels. Deposition took the form of large sandsheets constructed from fluvial‐dune fields and braid‐bar accumulations. Post‐flood winds reworked some of the deposited sand into aeolian dunes.
GEO‐GIANTS OF THE PAST
Authors: Reyment Richard A.
Published: July 2007

A new series presenting vignettes of the life and times of early notables, confirming the fact that all is not milk and honey in the pursuit of knowledge.
Glacial rebound and sea‐level change in the British Isles
Authors: Lambeck Kurt
Published: July 2007

Observations of sea levels around the coastline of the British Isles for the past 10,000–15,000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the Late Devensian ice sheet. A high‐resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea‐level change and which demonstrates that the observations are the result of (i) the glacio‐isostatic crustal rebound in response to the unloading of the ice sheet over Britain and, to a lesser degree, of the ice sheet over Fennoscandia, and (ii) the rise in sea‐level from the melting Late Pleistocene ice sheets, including the response of the crust to the water loading (the hydro‐isostatic effect). The agreement between model and observations is such that there is no need to invoke vertical crustal movements for Great Britain and Ireland of other than glacio‐hydro‐isostatic origin. The rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea‐level change to approximate the eustatic sea‐level rise. The observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation. Preliminary solutions are presented which indicate an upper mantle viscosity of (3–5)1020 Pas, a lithospheric thickness of about 100 km or less, and an ice model that was not confluent with the Scandinavian ice sheet during the last glaciation and whose maximum thickness over Scotland is unlikely to have exceeded about 1500 m.
The present rate of uplift of Fennoscandia implies a low‐viscosity asthenosphere
Authors: Fjeldskaar W. , Cathles L.
Published: July 2007

The rate of displacement in Fennoscandia has been intensively discussed for many years. It is now widely accepted to be an isostatic response of the glacial history of the area.

The Earth's present response to deglaciation in Fennoscandia is simulated using a three‐dimensional (3D), viscoelastic model in which the asthenosphere and mantle viscosity are allowed to vary so that the maximum rate of present uplift matches its observed value. The deglaciation history is considered to be known, and the C14‐datings are converted to sidereal years. The pattern of the present uplift gives a firm match with the observed data when a low‐viscosity asthenosphere is introduced. Assuming a 15,000 years load cycle, i.e. the glacier was applied to the surface for 15,000 years before the melting started, the best fitting earth viscosity model is a 1024 Nm lithosphere overlying a 75 km‐thick 2.0 × 1019 Pas asthenosphere and a 1.2 × 1021 Pas mantle. The simulations suggest a remaining maximum uplift of 40 m.
Boussinesq's problem of viscoelasticity
Authors: Wolf Detlef
Published: July 2007

We consider an isochemical, isentropic, incompressible fluid half‐space and study quasistatic viscoelastic perturbations, induced by two‐dimensional (2D) surface loads, of a hydrostatic initial state. In view of the regional or local scale required for deformations of planets to be amenable to the half‐space approximation, the model is assumed to be externally gravitating. We derive analytic solutions for the displacement and incremental stress components and study several approximations to the expressions. Particular emphasis is placed on discriminating between the material and local incremental stresses. Based on this distinction, deeper insight is gained into the physical significance of the solution.
Oxygen and carbon isotope stratigraphy of the Palaeogene and Cretaceous limestones in the Bottaccione Gorge and the Contessa Highway sections, Umbria, Italy
Authors: Corfield R.M. , Cartlidge J.E. , Premoli‐Silva I. , Housley R.A.
Published: July 2007

We have made oxygen and carbon isotope measurements on limestone samples of Albian to Eocene age recovered from the Bottaccione Gorge section in the Umbrian Apennines, central Italy. Additional measurements have been made on topmost Maastrichtian and Palaeocene sediments from the adjacent Contessa Highway section. Our data from the Bottaccione Gorge show 13C maxima at the Cenomanian/Turonian boundary and during the Palaeocene, as well as a pronounced 13C minimum 7 metres above the clay layer at the K/T boundary. Our data from the Contessa Highway show a 13C minimum 9 metres above the K/T boundary clay. These minima are probably diagenetic artifacts. In the Bottaccione Gorge there is evidence for a hiatus in the early Middle Eocene. The Palaeocene of the Bottaccione Gorge appears to have been affected by slumping or faulting (in addition to the diagenetic overprinting) giving a spurious δ13C recovery after the K/T boundary, the Contessa Highway section appears to be more complete. The Coniacian‐Maastrictian is characterized by relatively stable 13C values. Our data indicate an increase in δ18O (and therefore possible cooling) across the Cretaceous/Tertiary boundary in both the Bottaccione and Contessa Highway sections.
A proposal for the kinematic modelling of W‐dipping subductions ‐ possible applications to the Tyrrhenian‐Apennines system
Authors: Doglioni C.
Published: July 2007

In W‐dipping subduction zones there is a general eastward progression of the back‐arc basin‐accretionary wedge‐foredeep complex. With the forward progression, early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle. A major shear zone should form at the new Moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle. The mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt. The retreating of the subduction hinge is interpreted as due to the push generated by the ‘eastward mantle flow detected in the hot spot reference frame. The foredeep depth is mainly a function of the radius of curvature of the subduction hinge. The frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension. In order to preserve volume balance, the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted: due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates, laterally stretched subducted lithosphere is predicted at depth. W‐dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere (the thin back‐arc) which are a key factor in controlling and generating new subductions (both E‐ and W‐dipping). This model is applied to the Apennines‐Tyrrhenian Sea system.
Eclogite formation and dynamics of crustal roots under continental collision zones
Authors: Austrheim Håkon
Published: July 2007

Field observations on deep parts of the root zone of the Caledonian orogen are combined with the geophysical data available for recent continental collision zones such as the Alps, to provide a model for dynamics of crustal root zones.

Rocks descending into the root zone are locally infiltrated by fluids which cause eclogitization along shear zones and fluid pathways. The eclogite facies rocks vary in density from 3.1 to 3.6 g cm‐3, reflecting the compositional variation in their protoliths. Where the amount of highly ductile eclogitic material reaches about 40% the descending crustal segment loses its coherence and disintegrates into a breccia where blocks of granulite facies rocks float in a matrix of eclogite material. A density‐stratified root zone develops, where light unreacted or partly eclogitized material floats on an ‘ocean’ dominated by eclogite facies rocks, the top of which may correspond to the Moho. Catastrophic decent of this eclogitic layer may (1) transport blocks of light material to depths of > 90 km, which upon further disintegration due to eclogitization are released and return by buoyancy forces to the crust; (2) result in extension and uplift of the partly‐eclogitized lighter material.
Salt diapir velocity assessment from temperature and thermal indicator anomalies: application to Lulu‐1, Danish North Sea
Authors: Thomsen R.O. , Lerche I.
Published: July 2007

A method is exhibited for assessing the time of onset of diapirism and salt flow‐speed. Using vitrinite reflectance measurements from wells drilled on top of a salt structure it is possible to determine the excess maturity caused by the focusing of heat due to the higher thermal conductivity of salt. The method is based on calculation of the thermal anomaly surrounding a rising salt diapir. For a given salt speed, predicted vitrinite reflectance values are calculated and compared with the observed values at given depths. The process is repeated with various speeds of the rising salt until consistency of predicted and observed values is obtained, thus constraining an assessment of the velocity of the salt. The method can easily be tailored to thermal indicators other than vitrinite reflectance, thereby enhancing the resolution of the thermal history, and constraining both the onset of salt rise as well as the speed. The well, Lulu‐1, from the Danish North Sea, is used to illustrate the procedure.
Long‐term seismicity of Istanbul and of the Marmara Sea region
Authors: Ambraseys N.N. , Finkel C.F.
Published: July 2007

We examine the long‐term seismicity of the Marmara Sea region in Turkey over a period of twenty centuries to attempt to answer two questions: (1) how well recorded in history is the earthquake activity of this region? and (2) does seismicity over this long period of time differ from that over the present century? We study this densely‐populated and fast‐developing region because it is one of the most tectonically active regions on the continents that appears today to be relatively quiescent.
Bustylus (Eutheria, Adapisoriculidae) and the absence of ascertained marsupials in the Palaeocene of Europe
Authors: Gheerbrant Emmanuel
Published: July 2007

The recent description of the new adapisoriculid placental Bustylus cernaysi from the Thanetian of Cernay, and possibly of Walbeck, permits a new assessment of the systematic position of the supposed marsupial ‘Peradectes’ marandati from the Montian of Hainin (Belgium). The affinity between the two species is demonstrated and the species ‘P.’ marandati is included in the genus Bustylus (family Adapisoriculidae) and is excluded from the direct ancestry of B. cernaysi only because of the apparent absence of the D cusp in the known sample. Comparison with the oldest known placental, Prokennalestes (otlestid), supports the eutherian nature of Bustylus marandati and B. cernaysi. It also shows that the adapisoriculids are morphologically closer to the primitive otlestids than to the paleoryctids, which are more specialized in several respects. One general conclusion is the absence of known marsupials in the Palaeocene of Europe, their occurrence in this continent being ascertained only from the beginning of the Eocene (i.e. early Sparnacian or MP 7 reference level).
A Griggs deformation apparatus set up at Lille
Authors: Ingrin J. , Doukhan J.C.
Published: July 2007

The classical solid‐medium apparatus (Griggs apparatus) is generally viewed as a machine of poor accuracy with a large amount of uncertainty. However, a new generation of equipment with new assemblies and experimental procedures has greatly enhanced the capability of the apparatus. Experiments performed on the apparatus set up in our Laboratory on T‐oriented Yule Marble samples show that the yield strength of material can be measured with reasonable precision (within 10 MPa) and a yield strength as low as 50 MPa can be detected. The apparatus is particularly adapted to work on small specimens e.g. single crystals a few millimetres in size.
Fractals, chaos, self‐organized criticality and tectonics
Authors: Turcotte Donald L.
Published: July 2007

Some geological structures have simple geometrical forms and can be analysed using deterministic equations. Examples include alluvial fans and many sedimentary basins. But most geological structures are complex and appear to defy mathematical analyses. Yet in the complexity there is an order. Complex geological structures generally obey fractal statistics. Examples include topography, distributions of earthquakes and faults, and mineral deposits. An unresolved question is whether the fractal order is simply the result of scale invariance or the result of governing equations that yield deterministic chaos. In order to try to answer this question a variety of slider‐block models have been considered. The stick‐slip behaviour of slider‐block models is a simple analogy to earthquakes. A pair of slider‐blocks has been shown to behave chaotically. Models that use many slider‐blocks exhibit self‐organized criticality and generate fractal statistics similar to the statistics of regional seismicity.
Seismic investigations along the European Geotraverse and its surroundings in Central Europe
Authors: Prodehl C. , Aichroth B.
Published: July 2007

Since 1975 several high‐resolution seismic‐refraction and reflection surveys have been carried out in western Germany to investigate the structure of the Earth's crust and uppermost mantle. The investigation culminated in the seismic‐refraction survey along the 825 km long central part of the European Geotraverse (EGT) in 1986. This contribution summarizes the main results of the more recent crustal investigations along and around the EGT.

The internal crustal structure throughout the area of the Variscides is very complex and changes laterally considerably. Distinct crustal blocks differing in their internal structure can be assigned to geologically defined units of the Variscan and Caledonian orogeny. In spite of local deviations, in general a more or less transparent and low‐velocity upper crust contrasts with a highly reflective lower crust. A subdivision of upper and lower crust by a well‐defined boundary (Conrad discontinuity) is not always seen. Towards the Alps the average velocity of the lower crust is as low as 6.2 km s−1, in contrast to the area north of the Swabian Jura where the velocities above Moho vary between 6.8 and 7.2 km s−1. In Northern Germany, the Elbe line separates the lower crust into two regions with 6.4 km s−1 average velocity in the south and 6.9 km s−1 in the north.

The total crustal thickness under the Variscan part of Germany is fairly constant between 28 and 30 km, except under the Rhine Graben area with 25–26 km and beneath the central part of the Rhenish Massif where an anomalous crustal thickening to 37 km is observed. Under northern Germany the Moho rises to about 26 km depth and the data indicate at least one fault‐like step of 1 km before the crust thickens toward the Ringkobing‐Fyn basement high. The synthesis of seismic velocity structure and petrological information from xenolith studies allows us to propose a mafic composition for the deeper levels of the crust and uppermost mantle which may be valid at least for the central part of the Variscan crust along the European Geotraverse in Central Europe.
On the structure of the Ivrea‐Verbano Zone (northern Italy) and its implications for present‐day lower continental crust geometry
Authors: Brodie K.H. , Rutter E.H. , Evans P.
Published: July 2007

The Ivrea‐Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on‐going structurally‐oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the ‘mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south‐west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c. 10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust.

Several high‐temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.

Close parallels can be drawn between the observed structure in the Ivrea‐Verbano Zone (after removing the effects of late, low‐temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province.
CO2transfer between the upper mantle and the atmosphere: temporary storage in the lower continental crust
Authors: Touret J.LR.
Published: July 2007

The CO2atmospheric content has shown large variations over geological times. High contents (up to one order of magnitude more than present‐day values) ultimately correspond to discrete episodes of mantle degassing, either juvenile, or subduction‐related (carbon recycling). A number of arguments (e.g. the continuous volume increase of carbonate‐bearing sediments with time) suggest that, throughout the Earth's history, juvenile CO2has formed a major contribution to the global carbon budget of the Earth.

The absence of a direct relationship between major volcanic episodes and the average CO2atmospheric content suggests that volcanoes might not be the only way by which mantle CO2is transported to the surface. It is proposed that large quantities of juvenile CO2could temporarily be stored in the lower continental crust during major episodes of granulite formation. These are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of CO2‐bearing, mantle‐derived magmas. Most of the CO2migrates through the crust during post‐metamorphic evolution and isostatic restoration of the normal continental thickness. However, large quantities of CO2can still be present in some areas, notably as high‐density fluids enclosed in minerals.
The evolution of the layered lower crust and the Moho through geological time in Western Europe: contribution of deep seismic reflection profiles
Authors: Bois C.
Published: July 2007

Deep seismic reflection images from a set of profiles shot in Western Europe have been reviewed and compared, and tentative conclusions have been proposed concerning the evolution of the layered lower crust and the Moho. The disappearance of Variscan mountain roots is related to the set‐up of a new Moho at a typical 30‐km depth and the creation of seismic layering in the lower crust. Deep seismic profiles suggest that these processes resulted, at least in part, from magmatic intrusion, partial crustal melting and metamorphism of deep crustal rocks into eclogite. On the other hand, the layered lower crust is greatly attenuated beneath Cretaceous basins and Tertiary rifts in relation to prominent Moho upwellings. The unusual amplitude of the Moho reflection and the presence of anomalously high seismic velocities in the lowermost crust beneath the Tertiary rifts suggest that the Moho and part of the layering are comparatively young features related to interactions between crust and mantle. Beneath Triassic‐Jurassic basins, the layered lower crust was not affected by the subsidence of the basement, with the whole crustal thinning being entirely concentrated in the upper crust. This indicates that the layered lower crust and the Moho were formed or restored during or after the main rifting phase. Seismic data reveal constraints on the processes that affect the crust‐mantle transition and seem to restore the Moho to its typical depth after any mechanical deformation of the lithosphere.
Random walk and quantitative stratigraphical sequences
Authors: Bookstein Fred L. , Reyment Richard A.
Published: July 2007

A sequence of digitized observations on short‐normal resistivity determinations seems to show trend from higher to lower values. An appropriate statistical model proves it to have less range than expected on the distribution of its successive increments. On a two‐tailed statistical procedure for testing deviations from a random walk, the series tends towards ‘stasis’ rather than trend. The random walk model is shown to be plausible for the problem considered.
Main differences between thrust belts
Authors: Doglioni Carlo
Published: July 2007

It is useful to differentiate between thrust belts that are related to east(E)‐dipping or west(W)‐dipping subduction. More precisely, these either follow or resist the overall ‘eastward’ mantle flow detected by the hot‐spot reference frame. Because of the overall ‘westward’ drift of the lithosphere we find in E‐dipping subduction that the basal decollement underlying the eastern plate reaches the surface and involves deep crustal rocks. With W‐dipping subduction, however, we find that the basal decollement of the eastern plate is warped as well as subducted. Consequently thrust belts related to E‐ (or NE‐) dipping subduction show conspicuous structural and morphologic relief, involve deep crustal rocks, and are associated with shallow foredeeps. On the other hand, thrust belts related to W‐ (or SW‐) dipping subduction show relatively low structural and morphological relief, involve only shallow upper crustal rocks and are associated with deep foredeeps as well as back‐arc extension. The accretionary wedge‐foredeep‐back‐arc basin association is visualized as an overall eastward propagating tectonic wave. The accretionary wedge forms in the frontal parts and generally below sea‐level. This is followed by forward migrating extension that cuts the earlier accretionary wedge. Typically such a system occurs in the context of overall W‐dipping subduction and is characterized by an arcuate shape (e.g. Carpathians, Apennines, Barbados, etc.). Along the branches of the arc external transpression and internal transtension co‐exist but with different sense (i.e. sinistral transpression contrasting with dextral transtension).

We also observe that with W‐dipping subduction the tangent to a pre‐ deformation marker is descending into the foredeep at an angle in the range of 1–10° while with E‐(or NE‐)dipping subduction the same marker would rise towards the hinterland with typical angles of about 5–10°.

Foredeep subsidence is mainly controlled by the load of the thrust sheets in thrust belts due to E‐(or NE‐)dipping subduction and by the roll‐back of the subduction hinge in accretionary wedges due to W‐dipping subduction. Subsidence or uplift rates in the foredeeps and accretionary wedges related to the two different types of subduction are very different, providing different P‐T‐t paths in the two geodynamic realms. The present shape and structure of the thrust belts belonging to one of these two general types may help us in reconstructing the location of thinned lithosphere and basin evolution in the past.
Ordovician provincial signals from Appalachian‐ Caledonian terranes
Authors: Harper David A.T.
Published: July 2007

Statistical analysis of mainly mid to deep‐shelf Ordovician brachiopod faunas from localities within and marginal to the Appalachian‐ Caledonian Orogen reveals biogeographical patterns not entirely consistent with those presumed for the progressive orthogonal closure of the Iapetus Ocean. Correspondence analysis of faunas of late Arenig‐early Llanvirn, late Llandeilo‐earliest Caradoc and late Ashgill age emphasize the importance of marginal and island faunas, the role of regressions and transgressions on faunal distributions and the effects of climatic change in the definition of biogeographical trends during the Ordovician.
Are some fossils better than others for inferring palaeogeography?: The early Ordovician of the North Atlantic region as an example
Authors: Fortey R.A. , Meilish C.J.T.
Published: July 2007

Different kinds of fossils have different patterns of palaeogeographical distribution. This has led to differing palaeocontinental reconstructions in the early Palaeozoic. We take the early Ordovician of the North Atlantic region as a test case to investigate the influence of taxonomic group upon palaeogeographical interpretation. Using both single linkage duster analysis and parsimony methods of biogeographical analysis on fossil faunas and floras of various groups within this region it is shown that the patterns of similarity obtained, and their relationship to supposed oceanic separations, vary widely from one group to another. Some planktic fossils (graptolites, acritarchs) do not ‘see’ a separation between Gondwana and Baltica which is strongly supported by evidence from other groups. Trilobites and ostracodes, in particular, reveal patterns which conform well with other geological and geomagnetic evidence. At least in the Arenig‐Uanvirn time period, geographical separation is seen as a more important control on faunal composition than was biofacies. Considering the ‘better’ fossil groups for biogeographical discrimination, different analytical methods produce similar biogeographical results.
Ordovician faunas, island arcs and ophiolites in the Scandinavian Caledonides
Authors: Pedersen R.B. , Bruton D.L. , Furnes H.
Published: July 2007

Ordovician faunal data from the Scandinavian Caledonides is tested with new geochemical information from zircons to give U/Pb ages and source origins of volcanic arc and ophiolite sequences. Early Ordovician (Arenig‐Llanvirn), low latitude, Toquima‐Table Head faunas from the upper Upper Allochthon are associated with an island arc system formed adjacent to Laurentia. Contemporaneous mafic magmas were contaminated by crustal material during subduction and associated granites contain inherited zircons of Archaean age. The nearest source for such rocks is on the Laurentian rather than the Baltic side. Higher latitude Celtic province faunas from the upper Upper Allochthon are from one insular site accessible to forms from both Laurentia and Baltica.

The late Ordovician low‐latitude Holorhynchus and subtropical Hirnantia faunas occur in overstep sequences above deeply eroded early Ordovician arc complexes. The transgression appears to be coeval with a second generation of spreading‐related complexes. Single detrital zircons from sediments show sources from Archaean, Proterozoic and early Ordovician terranes. This suggests that deposition was in a basin situated along the same continental margin (Laurentia) to which the early Ordovician ophiolite/arc sequences had already become accreted. The late Ordovician faunas link both Laurentia and Baltica at a time of narrowing of lapetus.

The new geochemical data together with the faunal information is supported by recent palaeomagnetic studies.
Caradoc brachiopods from the Leinster terrane (SE Ireland) ‐ a lost piece of the lapetus puzzle?
Authors: Parkes Matthew A.
Published: July 2007

The recent re‐collection and examination of brachiopod‐dominated faunas from many localities in the Duncannon Group of the Leinster terrane of SE Ireland, has resulted in an improved age definition of the assemblages and a reassessment of their biogeographical affinities. The Assemblages are almost all Soudleyan to Longvillian (Caradoc) in age, and provide some constraint on the duration of volcanism related to subduction, which may have ceased in the mid‐Caradoc. At this time, they were part of a single Anglo‐Welsh Province which occupied the seas around the Eastern Avalonia plate. The province was composed of well‐established species from earlier Baltic immigrations together with endemics. Connections with the Scoto‐Appalachian and Mediterranean provinces are evident also.
Irish Carboniferous conodonts record maturation levels and the influence of tectonism, igneous activity and mineralization
Authors: Jones Gareth LI.
Published: July 2007

Organic maturation patterns in the Lower Carboniferous of Ireland have been determined from conodont colour alteration indices (CAI) for some 750 localities. Onshore Ireland conodonts record increasing maturation in the Carboniferous rocks from the oil‐window rocks of the north‐east, southwards to the greenschist meta‐argillite regime of the Munster Basin. In detail the Caledonoid trend has a marked influence in the Midlands, whilst in the south sharp variations in CAI are interpreted as being caused by thrusting of the Variscan Orogeny. In the south‐east low maturities in the Wexford Half‐graben indicate that the region was shielded from orogenic stresses, probably by the Leinster Massif. Igneous centres such as the Carlingford Complex and Croghan Hill produce local sites of increased palaeotemperature. Significant CAI variations have also been noted in proximity to major base‐metal orebodies. The CAI results highlight north‐east Ireland and the Wexford Half‐Graben as areas with hydrocarbon potential.
Chernobyl fallout and radionuclide activity in bottom sediments at the River Adige estuary (northern Adriatic Sea, Italy)
Authors: Merlin O. Hieke , Vittori L. Menegazzo , Molinaroli E. , Morani A. , Pelati L. Tassi
Published: July 2007

The artificial radionuclides 137Cs, 134Cs and 106Ru have been determined up to 16 cm deep in two sediment cores collected in March 1988 at the River Adige estuary in the northern Adriatic Sea. Interdependent relations between the properties of the sediment levels and the activity of radionuclides have been investigated using multivariate statistical analysis. The interactions between radiocontaminants and the particulate matter or water phase are discussed during their transfer processes from the river to the estuary and the marine environment. Diffusion phenomena within the sedimentary column have also been considered. The vertical distribution of the artificial radionuclides due to Chemobyl fallout in sediment cores from the River Adige mouth, compared to those from similar estuarine environments in the Adriatic Sea, point out a general rapid accumulation of river‐borne solid material in coastal zones of the North Adriatic Sea.
A 125 Kyr‐long geological record of seismic source repeatability: the Messina Straits (southern Italy) and the 1908 earthquake (Ms 71/2)
Authors: Valensise Gianluca , Pantosti Daniela
Published: July 2007

The occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century. The large 1908, Messina Straits, blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time‐scale in the order of 100 Kyr. We have compared seismological and geodetic descriptions of the 1908 rupture process with long‐term crustal deformation recorded at different stratigraphic levels by marine terraces, marine sedimentary units, and landscape features. The wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale. We investigated in detail the pattern of deformation of the 125 Kyr‐old, lowest emergent terrace, and found that it mimics the pattern of elevation changes observed following the earthquake. This suggests (1) that the 1908 earthquake is characteristic, (2) that its segment boundaries have been stationary during the past 125 Kyr, and (3) that even the locations of the regions of largest coseismic release do not change through many seismic cycles. Based on a comparison between observed heights of the 125 Kyr terrace and 1908 displacements, we estimated an average repeat time of 1000± yr for a 1908‐type earthquake. We also investigated the height, position, age and state of deformation of older terraces, and found (1) that uplift of the region started about 1 Ma and has since continued rather uniformly at 0.9–1.4 mm yr‐1, (2) that during this time the Straits have narrowed at a rate of 10–20 mm yr‐1, and (3) that all the main geomorphic features of the Messina Straits result from the interaction of fast regional uplift, 1908‐type coseismic subsidence, and global sea‐level fluctuations.
A dislocation model of aseismic fault slip under nonuniform friction
Authors: Dragoni Michele
Published: July 2007

A model is proposed for studying the mechanical behaviour of faults during their interseismic periods. The model considers a plane fault surface in an elastic medium, subject to a uniform shear stress which increases slowly with time. A1‐D friction distribution is assumed on the fault, characterized by asperities and a weaker zone. The traction vector on the fault plane has an arbitrary orientation: in particular, it can be nonperpendicular to the asperity borders. Aseismic fault slip takes place when the applied stress exceeds the frictional resistance: slip starts in weak zones and is confined by asperities, where it propagates at increasing velocity. Propagation into asperities is characterized by a dislocation front, advancing perpendicularly to the asperity border. Fault slip does not take prate in the direction of traction, except when traction is perpendicular or parallel to the asperity border. The propagation of such aseismic dislocations produces a stress redistribution along the fault and can play a key role in determining the conditions which give rise to earthquakes.
Modelling the Biosphere
Authors: Westbroek Peter , Muyzer Gerard
Published: July 2007

Programmes for the study of global change correctly identify the development of integrated numerical models of earth dynamics as an ultimate goal. But ongoing research and plans for future investigations suffer from a major flaw: they fail to treat life as a global phenomenon. We propose a long‐term strategy for the incorporation of the biosphere as a module into general circulation models (Gas).
Magma mixing processes in volcanic contexts, a thermodynamic approach with the examples of St Vincent Soufrière volcano, West lndies and Cerro Chiquito, Guatemala
Authors: Bardintzeff Jacques‐Marie
Published: July 2007

Different modalities and thermodynamic conditions of magma mixing are compared: heterogeneity and chemistry, temperature and water pressure, volatile (= water) content and water solubility, density and viscosity. Such data are somewhat scarce in the literature.

Two case studies have been studied in detail to highlight this review. (1) St Vincent Soufrière (West Indies). Magma mixing may have been a major process in triggering the 1979 explosive phase. All products (whole rock analyses) are basaltic andesite (52.3–56.2 wt% SiO2) but dacitic (60–64 wt% SiO2) glass occurs as micropumice or inclusions in crystals. (2) Cerro Chiquito (Guatemala). A Quaternary extinct dome consisting of dacite (62.5–67.1 wt% SiO2) enclosing 20–30% in volume of basaltic andesitic (54.9–55.3 wt% SiO2) enclaves.

The nearly thorough mixing process of case 1 strongly differs from the commingling process of case 2. The main phases may be mafic (case 1) or acidic (case 2). Thermodynamic parameters are calculated using classical geothermometers and formulae. The range of values and errors are estimated (60–80°C in case of temperature). In addition, other processes, such as crystallization of mineralo‐gical phases and fluid vesiculation, may modify thermodynamical conditions. Difference of magma temperature ranges from about 60°C (case 1) up to about 130°C (case 2). Water concentrations of 2.5 wt% in mafic magmas and 4 wt% in acidic magmas, are always lower than the upper limit of water solubility at depths where contrasting magmas were mixed. The difference between the viscosities of the two magmas varies from one order of magnitude up to five.

Various mixing scenarios may occur, each of them being linked to different petrological processes including effusive or explosive volcanism as well as plutonism.
The role of transcurrent intra‐arc tectonics in the configuration of a volcanic arc
Authors: Tibaldi Alessandro
Published: July 2007

Field investigations show that Plio‐Quaternary Mexican and Quaternary Ecuadorian volcanic arcs are coeval with intra‐arc transcurrent or transtensional tectonics with motions along faults parallel or subparallel to the arc. This relationship can also be observed in the Quaternary Kamchatka arc. These arcs have an anomalously wide distribution of volcanic centres which cannot be explained simply by a low dip in the subducting lithosphere. Comparison with the intra‐arc tectonics and geometry of other Quaternary arcs reveals that strike‐slip fault zones, parallel to the arc, favour magma rising in a broad surficial zone and may channel magma feeding mainly huge stratovolcanoes.
A revised census of European Late Cretaceous nodosaurids(Ornithischia: Ankylosauria): last occurrence and possible extinction scenarios
Authors: Pereda‐Suberbiola Javier
Published: July 2007

ABSTRAT

Nodosaurid ankylosaurs illustrate well the differences between European and North American faunal assemblages during the Late Cretaceous. A revised checklist of the nodosaurid specimens from the Late Cretaceous (mainly Campanian and Maastrichtian) localities of Europe reveals a more important diversity than commonly envisaged, with at least two distinct species represented.Struthiosaurus nustriacusand a new nodosaurid from the Basque‐Cantabric Basin were small (body length about 3 m), presumably dwarf insular forms. AIthough a detailed stratigraphic correlation is not yet availabIe, the disappearance orrelationisnotof the nodosaurids in the Western Interior of North America and in Europe may not be simultaneous but asynchronous. If so, the extinction of the Nodosauridae occurred in the latest Maastrichtian andStruthiosaurus couldbe the last representative of the group.
Stratigraphic evidence for the extinction of the ichthyosaurs
Authors: Bardet Nathalie
Published: July 2007

The extinction of ichthyosaurs is not well understood both in terns of time and of causation although it is supposed to have happened at some point of the Late Cretaceous. Four species of ichthyosaurs attributed to the single cosmopolitan genus Platypteygius Huene, 1922 are currently recognized from the Albian and Cenomanian, but after that time only fragmentary remains have been described. A review of these available post‐Cenomanian ichthyosaur remains reveals that all are doubtful either from a stratigraphic or a systematic point of view. Ichthyosaur extinction may be tentatively correlated with the Cenomanian‐Turonian boundary events. During this interval, biological factors such as a break in the food chain attested by severe extinction in marine invertebrates, especially belemnites, may have led to the extinction of ichthyosaurs.
Global change: anthropogenic forcing—the moving target
Authors: Fyfe W.S.
Published: July 2007

If we are to develop valid models for predicting the future of the global environment, anthropogenic forcing must become the major component of study. The technological developments needed to supply food, water and materials for 10 billion humans will dominate environmental change over thenext decades.
Global change in Earth history: a personal point of view
Authors: Wezel Forese‐Carlo
Published: July 2007

The global changes of the past took place during the progress of geological cycles and marked a drastic passage from an ancient Pangaean regime of continental emergence to a new Tethyan regime of submergence. They occurred with a certain violence and rapidity, and represented critical phases in the destabilization and subsequent reorganization of the geosphere and biosphere. This process resulted in the destruction of certain assemblages (e.g. biotic mass extinctions) and the rise of new ones (e.g. the emergence of new taxa). These major phases of evolution and growth were probably connected to the upwelling of hot mantle material from great depths and a subsequent process of lateral spreading and outward migration of the mantle melt. The ensuing marked increase in mantle activity, degassing and explosive volcanicity produced catastrophic environmental perturbations with turning points in tectonics, global climate, sea level, ocean and atmospheric chemistry, palaeocirculation and palaeogeography.
Relative sea‐level rise and climate change over the last 1500 years
Authors: Varekamp J.C. , Thomas E. , Van de Plassche O.
Published: July 2007

We constructed a detailed relative sea‐level rise curve for the last 1500 years using a novel approach, i.e. charting the rate of relative sea‐level rise using microfaunal and geochemical data from a coastal salt marsh sequence (Clinton, CT, USA). The composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively. The resulting sea‐level rise curve, with age control from 14C dating and the onset of anthropogenic metal pollution, shows strong increases in the rate of relative sea‐level rise during modern global warming (since the late nineteenth century), but not during the Little Climate Optimum (ad 1000–1300). There was virtually no rise in sea‐level during the Little Ice Age (ad 1400–1700). Most of the relative sea‐level rise over the last 1200 years in Clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years. Changes from slow to fast rates of relative sea‐level rise apparently occurred over periods of only a few decades. We suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea‐level rise along the northeastern USA seaboard. Relative sea‐level rise in that area is currently faster than the worldwide average, which may result partially from an ocean surface effect caused by hydrodynamics. Our data show no unequivocal correlation between warm periods (on a decaal to centennial time‐scale) and accelerated sea‐level rise. One period of acclerated sea‐level rise may have occurred between about ad 1200 and 1450, which was the transition for the Little Climate Optimum to the Little Ice Age, i.e. a period of cooling (at least in northwestern Europe). Local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea‐level, however. The second period of accelerated sea‐level rise occurred during the period of modern global warming that started at the end of the last century.
Global change and long‐term geomorphology
Authors: Ollier C.D.
Published: July 2007

Landscape evolution is on the same time‐scale as global tectonics, biological evolution, and major climatic change. Some features of global change reflected in landscape evolution result from the breakup of Pangaea. Others relate to major climatic changes, and yet others to a major change from a dominantly plains landscape of the Mesozoic to an increasingly mountainous landscape in the Tertiary. Worldwide deep weathering profiles of Cretaceous and early Tertiary age suggest widespread planation and warm, moist climates. Erosion of deeply weathered regolith following the formation of new continental margins and tectonic uplift led to the deposition of unusual mature sediments. Many river patterns can be traced to early Tertiary or older antecedents.

Some climatic changes are due to orbital forcing, but others may be related to changing positions of continents, creation of new seaways, or to mountain building. The timing of mountain uplift, climatic changes and biological changes must be resolved to test models of their mutual interaction. Geomorphic input on tectonics, drainage evolution, and deep weathering will be an essential component in dealing with these problems.
Tectonics and global change ‐ inferences from Late Cenozoic subsidence and uplift patterns in the Atlantic/ Mediterranean region
Authors: Cloetingh Sierd , Kooi Henk
Published: July 2007

Quantitative subsidence analysis for a number of rifted basins in the northern Atlantic/Mediterranean region provides evidence for rapid phases of PlioQuaternary subsidence. The observed acceleration in tectonic subsidence occurs after a phase of general quiescence in subsidence in these basins and deviates from predictions of stretching models. The latter indicate a decay of subsidence with time after Mesozoic‐Tertiary basin formatioh and a slow tectonic subsidence in Plio‐Quaternary times. A possible explanation for the observed patterns of anomalous subsidence could be an increase in the level of intraplate compression in the northern Atlantic region. Intraplate stress changes in the Plio‐Quaternary are related to the dynamics of African/ Eurasian collision processes and a reorganization of spreading directions in the AtlAntic, possibly reflecting a plate reorganization of global nature.

It seems that the Plio‐Quaternary record reflects a period of increased levels of neotectonic activity, interplaying with periods of (de)glaciation. Stress‐induced topography in the onshore parts of continental margins, coupled with the stress‐induced subsidence in the offshore deeper parts of the basins, could have contributed to recent phases of uplift in Fennoscandia, augmenting the uplift induced by glacial unloading. Estimates of ice thicknesses are directly inferred from the observed uplift ignoring other driving mechanisms whereas topography plays a crucial role in the dynamics of glaciation. It is, therefore, important to quantdy the interplay of rapid tectonic uplift and subsidence phases with climatic effects during the Plio‐Quaternary.