bluuebunny/crossref_metadata_2025_split huggingface dataset:
The present rate of uplift of Fennoscandia implies a low‐viscosity asthenosphere
Authors: Fjeldskaar W. , Cathles L. 
Published: July 2007

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTIn 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

ABSTRACTField 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

ABSTRACTA 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

ABSTRACTWe 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTSome 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

ABSTRACTSince 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTDeep 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

ABSTRACTA 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

ABSTRACTIt 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

ABSTRACTStatistical 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

ABSTRACTDifferent 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.