bluuebunny/crossref_metadata_2025 huggingface dataset:
Course and origin of the Fennoscandian uplift: the case for two separate mechanisms
Authors: Mörner Nils‐Axel
Published: July 2007

The classical glacial isostatic uplift paradigm of Fennoscandia is in need of a thorough revision as to its course and origin. The total uplift amounts to 830 m (not 300 m). The centre of uplift started to rise 13,000 BP (not 9300 BP). The uplift appears to be composed of two separate mechanisms; one true glacial isostatic rebound, and one linear uplift factor possibly representing a phase boundary adjustment. Calculations and modelling must treat these two factors independently (which has not been the case).
SOME SECONDARY EFFECTS OF THE 1947 HEKLA ERUPTION: EXHALATIONS OF CARBON DIOXIDE
Authors: Kjartansson Guõmunder
Published: July 2007

In this, the eight in an occasional series of earth phenomena, the author fearlessly explores ‘death valleys’.
Human activities and environmental stress: some essentials revisited1
Authors: Schidlowski Manfred
Published: July 2007

Current pollution of the total environment is caused by waste products of the extrasomatic metabolism of Homo sapiens who, since the beginnings of the industrial revolution, has raised his energy consumption by a factor of 10–20 above the basic metabolic rate of the single individual. While the increased energy flow through the human ecosystem has brought about an improvement of the human condition unprecedented in the history of mankind (including a doubling of the average life expectancy), it is beset also with an intrinsic maladaptive potential for the possible emergence of an autotoxic effect. The future of high‐energy (industrial) societies will, accordingly depend on man's capability to maintain an adequate energy flow while hopefully minimizing the potential impact of autotoxicity on his environment by suitable technological fixes.
The chemistry of geothermal waters: its effects on exploitation
Authors: Czernichowski‐Lauriol I. , Fouillac C.
Published: July 2007

The aim of this paper is to demonstrate all aspects of the way in which chemistry affects exploitation of geothermal fluids: through scaling and corrosion and their treatment, through its influence on production characteristics, environmental considerations and also in the possible recovery of valuable by‐products. It is therefore essential that the chemical characteristics and behaviour of fluids are evaluated fully in order to optimize the design, operating conditions and management of a commercial geothermal system. Careful sampling and accurate measurements are thus indispensable. Chemical computer models are shown to be valuable tools for studying the chemical behaviour of a fluid in various situations; a brief illustration using the TPDEGAZ code is given.
Sulphur isotopic fractionation between sulphate and sulphide in hydrothermal ore deposits: disequilibrium vs equilibrium processes
Authors: Zheng Yong‐Fei
Published: July 2007

Correlative fractionation relationships of sulphur isotope data for coexisting sulphate and sulphide pairs from hydrothermal ore deposits on δ38S versus Δ34S diagrams are deciphered theoretically. Taking into account dissolved H2S and SO42‐ in hydrothermal fluids during precipitation of both sulphate and sulphide minerals, a 4‐species closed system is suggested for describing the conservation of mass among all sulphur‐bearing species on the δ‐Δ diagrams. The covariation in the δ34S values of both sulphate and sulphide is ascribed to isotopic exchange between oxidized and reduced sulphur species during mineral precipitation. The isotopic exchange could be a thermodynamic process due to simple cooling of high temperature fluids, which results in an equilibrium fractionation, or a kinetic process due to mixing of two sulphur reservoirs, which leads to a disequilibrium fractionation. The δ34S value of total sulphur in a hydrothermal system could change due to the precipitation of minerals, or due to the escape of H2S and/or SO42‐. Sulphur isotope data for anhydrite and pyrite pairs from the Luohe porphyrite iron deposit in the Yangtze River Valley is used to illustrate the mixing responsible for the disequilibrium fractionation.
Seismicity and volcanism of Jan Mayen Island
Authors: Havskov J. , Atakan K.
Published: July 2007

The small, arctic Jan Mayen Island, site of the World's northernmost active volcano, Beerenberg, is part of the mid‐Atlantic ridge system and located along the Jan Mayen Fracture Zone (JMFZ). Recent data from the local seismic network, and fault plane solutions from the global network, indicate that the island is located at a ridge‐crest intersection, which might explain the origin of the island and the associated volcanism. Moreover, the new data suggest a series of offset segments of the Mohn's Ridge, overlapping in an en echelon pattern.

In January 1985, a flank eruption was for the first time observed with the local seismic network. Volcanic tremors and low‐frequency events were observed on 5 January at 2230 h and 10 hours later the first large earthquake occurred. No visual confirmation of the eruption was made until 6 January at 1630 h. The seismic observations rule out the possibility that the large earthquake caused the eruption; it seems more likely that the changes in local stress conditions triggered the earthquake and that the eruption started before the first large earthquake. Recent observations show that the local network provides an efficient tool for monitoring and warning of volcanic activity. However, since there was no change in the local seismicity in the days or months before the 1985 eruption, it seems to be difficult to make long‐term predictions of Beerenberg flank eruptions without using other techniques such as observations of tilt.
Seismotectonic significance of the 29 January 1989 Etne earthquake, SW Norway
Authors: Karpuz M. Ridvan , Gabrielsen Roy H. , Engell‐Sørensen Lisbeth , Anundsen Karl
Published: July 2007

The integrated analysis of geological, seismological and field observations with lineament data derived from satellite images allows the identification of a possible seismogenic fault zone for an earthquake which occurred near Etne in southwestern Norway, on 29 February 1989. The hypocentre of the earthquake was located at the mid‐crust at a depth of 13.8±0.9 km which is typical of small intraplate earthquakes. The Etne earthquake occurred as a result of normal faulting with a dextral strike‐slip component on a NW–SE trending fault. Available geological and lineament data indicate correlation of the inferred seismogenic fault with the NW–SE trending Etne fault zone. An aeromagnetic anomaly related to the Etne fault zone forms a regional feature intersecting both Precambrian basement and allochthonous Caledonian rocks. Based on these associations the occurrence of the Etne event is ascribed to the reactivation of a zone of weakness along the Etne fault zone. Slope‐instabilities developed in the superficial deposits during the Etne event demonstrate the existence of potentially hazardous secondary‐effects of such earthquakes even in low seismicity areas such as southwestern Norway.
PETROLEUM GEOLOGY OF THE SOUTHEASTERN PART OF THE PANNONIAN BASIN
Authors: Šarković Miodrag , Stanković Srboljub , Miloslavljević Stanislav
Published: July 2007

The large Pannonian Basin is one of the most prospective European regions for petroleum. This paper considers the geological framework and tectonic relations of the southeastern part of the basin, its generative potential for oil and gas, and some physico‐chemical descriptions of the oil and gas fields so far identified.
GEO‐GIANTS OF THE PAST
Authors: Selby Jonathan
Published: July 2007

The occasional series continues, laying bare the trials and tribulations of our geological forebears.
Hydrogen in petroleum geochemistry
Authors: Levshounova S.P.
Published: July 2007

950 samples were analysed to study the possibility of using information on hydrogen in the evaluation of regional, zonal and local hydrocarbon potential. The main method for identifying that hydrogen is of natural origin is by comparison with the δD of hydrogen of technical origin that is −792‰. As an added criterion for recognizing the origin of hydrogen in wells the investigation of changes in gas composition within the borehole section is proposed. The distribution of hydrogen in the free and adsorbed states and the role of hydrogen in hydrocarbon gas formation have been evaluated. These data combined with tests on hydrogen absorption establish a difference between oil and gas generation in terrigenous and carbonate rocks caused by different types of organic matter and by the ability of hydrogen to be preserved in the crystal lattice of carbonate minerals. This absorbed hydrogen promotes HC generation and also changes the physical properties of limestones producing fundamentally different styles of fracture genesis.
Neptunian dykes along a drowned carbonate platform margin: an indication for recurrent extensional tectonic activity?
Authors: Lehner Benedikt L.
Published: July 2007

Three successive Mesozoic neptunian dyke generations and related unconformities suggest recurrent extensional fracturing and periods of relative sea‐level rise along the NW Trento Plateau margin in the Southern Alps, Italy. The first neptunian dyke generation was induced by NNW–SSE directed extension of Early Jurassic skeletal oolitic periplatform deposits generating micritic early Middle Liassic neptunian dykes with orthogonal orientation. The second generation of neptunian dykes was possibly caused by marginal extension at the drowned platform edge penetrating Late Jurassic, red pelagic limestones with a pelagic matrix of Albian/Cenomanian age and nearly orthogonal fracture orientation. The third generation of neptunian dykes occurred after a prolonged period of submarine exposure and erosion (Aptian/Albian to Late Maastrichtian) during the rapid burial of the submarine Trento Plateau margin relief. The Late Maastrichtian neptunian dykes were caused by extension of Early to Middle Jurassic oolitic periplatform limestones along steep (inclination > 10°) submarine slopes.

Generally successive neptunian dyke generations along drowned carbonate platform margins could be caused by repeated extensional brittle fracturing of lithified periplatform deposits and the filling of micritic matrix derived from overlying pelagic sediment sequences under substantial hydrostatic pressure. This would suggest that recurrent extensional fracturing is continuously recorded by neptunian dyke formation which could be used to indicate extensional tectonic activity at a foundering deep‐marine carbonate platform edge.
Strike‐slip faults parallel to crustal spreading axes: data from Iceland and the Afar Depression
Authors: Passerini Pietro , Marcucci Marta , Sguazzoni Giovanni , Zan Leonardo , Haga Abdourahman Omar
Published: July 2007

Slickenside studies in regions of crustal spreading such as Iceland and the Afar Depression, East Africa, reveal that a significant number of faults parallel and close to rift axes are strike‐slip rather than normal. Therefore, the pattern of brittle deformation in these regions does not conform to the classic two‐dimensional schemes of oceanic tectonics and pre‐oceanic rifting. Dip‐slip and strike‐slip faulting presumably alternated along or in the vicinity of spreading axes, indicate a varying stress field and a combination of transverse and longitudinal movements.

In Iceland, strike‐slip faults parallel to rifts are observed both west and east of the rift system as well as in a median area between overlapping rifts; the mechanisms proposed for their origin include accommodation of oblique convergence or divergence of crustal sections due to variations of spreading directions along axis and the interaction of overlapping rifts. In the Afar Depression this kind of fault is recorded west of the rift of Asal and can be imputed to reflect an interaction among rifts in the vicinity of the Afar triple junction.

Rift‐parallel strike‐slip faults cannot however be assumed to be a feature of all crustal spreading axes due to the peculiarity of the examined regions: both of them are hot‐spot areas and the Afar Depression lies at a triple junction.
Debris‐flow phenomena in the Central Apennines of Italy
Authors: Guzzetti Fausto , Cardinali Mauro
Published: July 2007

The results of a research project on the extent of debris‐flow processes in the Monti Sibillini area (Central Italy) are presented. Debris flows have greatly contributed in shaping the landscape of the Monti Sibillini territory. Based on the dominant active process they can be subdivided into three sections: a source area, a transport area and a depositional area. Four environments can be identified as source areas: landslide deposits, highly fractured rocks, scree or talus deposits, and glacial deposits. The evolution of some of the largest features present in the area is examined. These may have developed from an initial stage of mostly gully erosion and minor landsliding, through an intermediate stage characterized by extensive mass‐movement, to a final stage dominated by fluvial processes. Lastly, generalizations on the debris‐flow hazard in the study area are made.
Chaotic fault interactions: implications for seismic hazard in New Zealand
Authors: Hodder A.P.W.
Published: July 2007

A chaotic fault interaction model previously developed for the San Andreas Fault System and the Nankai Trough (examples of transform fault and subduction dominated tectonic regimes, respectively) is here applied to the large‐event seismicity in the New Zealand region, where the interacting blocks of the model are taken to be those parts of the Indo‐Australian plate boundary that are, from north‐east to southwest, subduction dominated, ‘transpressional’, and transform‐fault dominated. The model suggests a shorter term recurrence of large events than do simple seismic cycle approaches.
A facies geological test of stable isotope interpretation of the Upper Permian depositional environment in West Spitsbergen
Authors: Malkowski Krzysztof , Gruszczyński Michal , Hoffman Antoni
Published: July 2007

Lithofacies analysis of two transgressive sequences within the Kapp Starostin Formation (Upper Permian, West Spitsbergen), indicates considerable differences in seawater chemistry between their depositional environments. The onshore part of the sequence represented in the Vøringen and Svenskeegga Members is largely calcareous, with allochthonous and corroded siliceous materials. In contrast, in the equivalent sequence within the Hovtinden Member, silica is ubiquitous whereas carbonate materials include mainly corroded bioclasts. These differences are consistent with predictions of the oceanographic model of ‘overfed’ and ‘hungry’ oceans proposed previously on the basis of carbon and oxygen stable isotope analysis.
Oversized U‐shaped canyon development at the edge of rotating blocks due to wrench faulting on margins of the Dead Sea graben
Authors: Gilat Arieh
Published: July 2007

Strike‐slip fault systems on the western margin of the Dead Sea active pull‐apart basin (central part of the Dead Sea Transform) have been mapped in detail in the vicinity of the Ya'elim Valley, in the southeastern Judean Desert.

Compressional, tensional and strike‐slip shearing features are described and the geomorphology of the valley (which changes over a 6 km long segment from a mature meandering valley to a deep and narrow canyon, and then to an oversized, very deep and very wide U‐shaped canyon), is elucidated using profiles and superimposed cross‐sections.

A kinematic model for the Formation of the Ya'elim Valley is proposed, reflecting dextral shearing on the margins of counterclockwise rotating blocks. In the same area Subrecent‐Recent spreading of tensional fractures has occurred, separating sections of blocks which protrude eastward into the deepest on‐land depression.

The large‐width of shear zones sub‐perpendicular to the Transform may relate to repeated reversals in the sense of rotation of second‐order (rigid block) domains, caused by rotations of neighbouring first order domains due to earthquake ruptures on individual parallel faults of the Transform.
Seismotectonic evidence of an active normal fault beneath Thessaloniki (Greece)
Authors: Hatzidimitriou P.M. , Hatzfeld D. , Scordills E.M. , Papadimitriou E.E. , Christodoulou A.A.
Published: July 2007

During 3 weeks in 1985, we operated a dense network of portable seismological stations around the city of Thessaloniki, in Northern Greece, where a destructive earthquake had occurred in 1978. We recorded 282 microearthquakes, with magnitudes ranging between ‐0.2 to 3.0, and we computed 22 Fault Plane Solutions.

The experiment was designed to map the stress pattern west of the 1978 shock, and to study the Asvestohorio fault. Around this fault, located near Thessaloniki, Mercier et al. (1983) observed a few cracks during the 1978 shock.

The seismicity shows the same scattered pattern seen through the whole Chalkidiki region. We observe also a dense cluster around Asvestohorio, but this cluster is probably related to explosions in nearby mines. After filtering the data from possible explosions we found evidence of seismic activity. The earthquakes are dipping toward the NE, suggesting that the Asvestohorion fault is active. The Fault Plane Solutions do not help in defining the geometry of the fault but the P and T‐axes are consistent with the regional stress pattern.
Seismic image of undercrusted serpentinite beneath a rifted margin
Authors: Boillot Gilbert , Beslier Marie‐Odile , Comas Maria
Published: July 2007

During the continental rifting the upper mantle was unroofed, and the mantle rocks were transformed into serpentinite at the ocean‐continent transition of the west Galicia margin (Spain). The serpentinite layer, several km thick, extends probably eastwards, beneath the highly thinned continental crust of the margin.

The serpentinite layer was recently imaged by seismic reflection. It is discontinuously and deeply layered. As serpentinized peridotite can have densities and seismic velocities comparable to those of the lower continental crust, we suggest that undercrusting by serpentinite can play a part in building the lower seismic crust in highly stretched continental rifted areas.
Generation and metamorphism of new crust in magmatic arcs: a case study from northern Chile
Authors: Lucassen F. , Franz G.
Published: July 2007

In a deep section of the Jurassic Andean arc, coastal Cordillera of northern Chile, south of Antofagasta, basic magmas from a mantle source accreted large masses of crust in an early stage of arc development. These gabbroic intrusions were isochemically metamorphosed at moderate pressures (≤ 5 kbar) and high temperatures (∼ 800°C) into uniform garnet‐absent dino+ortho‐pyroxene gneisses (granulites). Subsequently they were partly transformed into amphibolites (T≤ 700°C) during tectonically controlled access of fluid without major changes in whole rock chemistry. Locally migmatization occurs in the amphibolites. The metamorphic unit was diversified by enduring magmatic activity in the form of chemically distinct gabbroic and quartz dioritic intrusions. Formation and composition of continental crust might be a typical example for the deeper plutonic sections of this continental magmatic arc.
The nature and geological history of the deep crust under the Eifel, Germany
Authors: Stosch H.‐G. , Schmucker A. , Reys Ch.
Published: July 2007

The crust ≈ 10–20 km under the Eifel is composed of amphibolite‐facies metasediments and meta‐igneous rocks of tonalitic to granodioritic composition; mafic granulites occupy the base of the crust down to a Moho depth between about 29 and 34 km. The meta‐granodiorites and meta‐tonalites have I‐type chemical characteristics and appear to have formed approximately 400 Myr ago by partial melting of a lower crustal source. Amphibolite‐facies metamorphism probably followed within the same orogeny. During the Quaternary, many amphibolite‐facies rocks were subjected to contact heating in crustal magma chambers and/or during transport to the earth's surface. Contact heating is also recorded in radiogenic isotope compositions of minerals from one xenolith. A genetic link between meta‐igneous amphibolites and the deeper crustal mafic granulites can neither be proven nor discounted by the isotope data. If there is a genetic relationship, it requires fractionation of a mafic magma in the lower crust and assimilation of metasediments and separation of a highly evolved melt.
3D seismic study of a ductile shear zone from laboratory and petrofabric data (Saint Barthélémy Massif, Northern Pyrenees, France)
Authors: Barruol Guilhem , Mainprice David , Kern Hartmut , de Saint Blanquat Michel , Compte Patrick
Published: July 2007

In order to constrain interpretations of seismic reflection records more effectively, the seismic properties of a middle crustal section exposed in the Saint Barthélémy Massif have been determined. The massif, transected by a 200 m thick shear zone has been systematically sampled for density measurements and modal analysis has been performed in order to define the spatial variations of physical properties. Seismic velocities (Vp, VS, shear wave birefringence), have been measured on five representative samples to 600 MPa and 600°C simultaneously in the three structural directions (X, Y and Z). For two samples, the experimental data have been compared with calculated values, based on petrofabric analyses. The Lattice Preferred Orientation (LPO) is determined using universal stage, electron channelling microscopy and neutron diffraction goniometry. Using the experimental and calculated velocity data, we establish a lateral homogeneous anisotropic model.
A seismic reflection‐refraction experiment across the exposed lower crust in Calabria (southern Italy): first results
Authors: Lüschen E. , Nicolich R. , Cernobori L. , Fuchs K. , Kern H. , Kruhl J.H. , Persoglia S. , Romanelli M. , Schenk V. , Siegesmund S. , Tortorici L. ,   (Italian‐German Lower Crust Group)
Published: July 2007

Exposed crystalline basement of the Serre Mountains in Calabria presents a tilted block of a nearly complete section of the Hercynian continental lower crust (HCLC). In addition to petrological and structural data from surface mapping, and petrophysical data from the laboratory, a seismic reflection‐refraction experiment was conducted in May 1990. This consisted of a 40 km long N‐S profile crossing the HCLC and of four short transverse profiles, each recorded using 3‐component receivers with an 80 m spacing and explosive sources.

The reflectivity of the outcropping lower crustal units is lower than theoretically predicted from the observed compositional layering. A low‐velocity zone, outcropping in the north, and dipping to the south, marks the contact between the HCLC and the underlying Alpine metamorphic units. Below this zone, the deeper crust appears well‐structured by strong and continuous, discrete reflections down to 6.5–8 s t.w.t. (presumably the crust‐mantle boundary at 19–24 km depth) with a dominant dip toward the south.

Analysis of refracted‐wave velocities reveals values systematically lower by up to 30% than laboratory data on rock samples or calculated data from modal analysis. This discrepancy can only partly be explained by the effect of microcracks (10%), the underestimation of the amount of leucosomes (2–5%) and the effect of seismic anisotropy (0–5%). The remaining discrepancy must be attributed to large scale alteration of the rocks due to Apennine tectogenetic events.
Evolution of the petrological and seismic Moho‐implications for the continental crust‐mantle boundary
Authors: Mengel K. , Kern H.
Published: July 2007

The chemical and petrological composition of mafic rocks from the lower continental crust are discussed by comparing mafic granulites and meta‐gabbroic rocks from the Ivrea Zone and the Northern Hessian Depression (NHD) xenolith suite. Both regions contain contrasting types of meta‐mafic lithologies (i) former basaltic rocks with trace element patterns ranging from MORB‐Iike to subduction‐related or intra‐plate tholeütes and (ü) Ca‐and Al‐enriched, plagiodase‐dominated gabbroic rocks showing positive Eu‐anomalies generated by complex deep crustal magmatic processes such as fractionation, accumulation of plagiodase and pyroxene, and crustal contamination. The absence of typical garnet‐omphadte parageneses in these rocks indicates that the eclogite stability field was not reached during Palaeozoic orogenic processes.

A compilation of experimentally determined P‐wave velocities and densities for mafic granulites, gabbroic rocks, eclogites and peridotites is used to evaluate key physical properties of lower crustal mafic rocks during crystal thickening caused by continent‐continent collision. In a step‐by‐step scenario it is demonstrated that the position of the seismic Moho (defined as a first‐order velocity discontinuity) and the petrological Moho (defined as the boundary between non‐peridotitic crustal rocks and olivine‐dominated rocks) is not identical for the case that mafic rocks are transformed into edogites at the base of orogenically thickened crust. P‐wave velocities of eclogites largely overlap with those of peridotites, although their densities are significantly higher than common upper mantle rocks.

As a consequence, refraction seismic field studies may not detect edogites as crustal rocks. This means that the seismic Moho detected by refraction seismic field studies appears at the upper boundary between edogites and overlying crustal units. Since edogites generally have higher densities than peridotites, they might be recycled into the deeper lithosphere thereby transferring excess Eu into the upper mantle. This process could be a due for understanding the negative Euanomaly in the upper continental crust which is apparently not balanced quantitatively by the abundance of common mafic crustal rocks.
The Kola Superdeep Drillhole and the nature of seismic boundaries
Authors: Pavlenkova N.I.
Published: July 2007

The Kola Superdeep Drillhole was drilled through 7 km of Proterozoic rocks of the Pechenga structure and 5 km of the Archean basement in the Baltic Shield to 12 km depth. The results of drilling revealed a significant heterogeneity of physical properties of the crystalline rocks and a surprisingly high porosity and water content throughout the section. Seismic wide‐angle reflection data, obtained in the region of the hole, were used to delineate the volcanic‐sedimentary layers of the Pechenga structure and the intersecting faults. These studies revealed also a subhorizontal boundary at a depth of 7 km of uncertain origin. Core sampling implies that this boundary is associated with a change in core pressure, with higher porosity and with velocity anisotropy. A change in rock fissuring and in the fluid regime correlates with a velocity inversion zone reached by the hole at a depth of 4.5 km.
The Helice Fault?
Authors: Mouyaris N. , Papastamatiou D. , Vita‐Finzi C.
Published: July 2007

The site of the ancient Greek city of Helice, which was destroyed by an earthquake in 373 bc, has never been found. We propose that it was submerged as the result of seismic slip on a normal fault traceable SE of Egion and that the fault was reactivated in 1881, when Schmidt reported a fresh scarp 2 m high and 13 km in length at the same locality. Earlier movements on the fault are inferred from Lithophaga borings on coastal Sectors of the footwall which yield 14C ages representing over 6.5 m of uplift in the last 4880 years.
En echelon fractures in a dextral shear zone ‐ tectonic heritage for a hydrothermal cave (Budapest, Hungary)
Authors: Fodor L. , Leél‐Össy SZ. , Tari G.
Published: July 2007

Microtectonic study of brittle structures in the József Hill Cave, Budapest, highlights the connection between different phases of fracturing and cave formation. E‐W trending dextral faults (second order Riedels) and NW‐SE oriented tension fractures developed in a ENE‐WSW trending dextral shear zone as a result of WNW‐ESE directed compression. Ascending thermal water dissolved cave galleries and created barite veins along these fractures. The first stage of cave formation as inferred from timing of fracturation from the regional stress field was Oligocene‐Early Miocene. Between the Middle Miocene and Quaternary new N‐S to NE‐SW trending normal faults were formed by ESE‐WNW extension. Pleistocene differential uplift resulted in the reactivation and enlarging of fault zones, dominantly the E‐W trending older Riedels. These recent tectonic events enhanced the original en echelon geometry of the older cave corridors.
The massive stibnite veins of the French Palaeozoic basement: a metallogenic marker of Late Variscan brittle extension
Authors: Munoz Marguerite , Courjault‐Radé Pierre , Tollon Francis
Published: July 2007

The stibnite ore deposits of the French Palaeozoic basement are spatially related to major Late Variscan strike‐slip faults. They occur as small discontinuous veins mostly hosted in epizonal or catazonal siliciclastics. Stibnite crystallizes in the final stage of a polymetallic paragenesis from an antimony‐bearing solution, which deposits a first discrete Fe‐As assemblage at 300–400°C and 0.5–0.8 Kbar. Experimental data have shown that antimony solubility drastically decreases on cooling. Characterization of the Late Variscan antimony‐bearing fluids enables us to predict the temperature range ‐ 270/150°C ‐ under which stibnite was precipitated. Since the latter coincides with the fluid inclusion homogenization temperature range, the pressure at which stibnite crystallized can be estimated from vapour pressure data to have been around 0.1 Kbar.

Extensional brittle shear zones, developed at the end of the Late Variscan orogeny (probably at the Westphalian/Stephanian boundary), drained the hydrothermal fluids near to the surface (c. 1000 m ?) reaching the critical P‐T conditions for stibnite crystallization.
Palaeontological and facial features of the Upper Jurassic Hochstegen Marble (Tauern Window, Eastern Alps)
Authors: Kiessling Wolfgang
Published: July 2007

Micropalaeontological, microscopic and mineralogical investigations of the ductily deformed and greenschist‐facies metamorphic Hochstegen Marble in the Tauern Window shed new light on its stratigraphy and fades.

New radiolarian and sponge spicule discoveries have been made in cherty limestone marbles. They confirm previous age assignments and permit for the first time a more exact micropalaeontological age determination of early Tithonian for the upper parts of the marble. Forty morphotypes of radiolarians could be distinguished; in one sample a Fisher diversity index of 6 is reached indicating deeper marine conditions. The spicule fauna is also diverse and shows affinity to the S‐German Malm. In respect to all the data it can be presumed that carbonate sedimentation of the Hochstegen Marble took place in a deeper marine environment at the southern margin of the European continent (Helvetic realm) during the whole Late Jurassic.
Palynological evidence for Lower Ordovician rocks (Tremadoc and Àrenig) in the Northern Greywacke Zone (Eastern Alps)
Authors: Reitz Erhard , Höll Rudolf
Published: July 2007

Until recently, only fossils of Caradoc to Carboniferous age have been reported from the Northern Greywacke Zone/Eastern Alps. New medium‐preserved and diversified acritarch assemblages from the Lower Wildschönau Formation indicate a Lower Ordovician (Tremadoc and Arenig) age. These fossil spectra define a well‐constrained time interval for a lower section of the Northern Greywacke Zone for the first time.
Ordovician faunas in mass‐flow deposits, Southern Scotland
Authors: Clarkson Euan N.K. , Harper David A.T. , Owen Alan W. , Taylor Cecilia M.
Published: July 2007

In the Ordovician Northern Belt of the Southern Uplands, basal volcanics (Arenig) are followed by cherts (Llanvirn‐?Llandeilo), then by graptolite shales (Llandelio‐Lower Caradoc), and finally by Caradoc greywackes. Within the greywackes (Kirkcolm Formation) are a number of occurrences of fossiliferous conglomerate and overlying mudstone; these can be traced along‐strike for some 30 km.

The conglomerates, and especially the mudstones, yield rich mid‐ Caradoc shelly assemblages; brachiopods (20 spp.)/ trilobites (14 spp.), gastropods, bivalves, bryozoans, and the first known Palaeozoic scleractiniamorph coral.

These occurrences are interpreted as mass‐flow deposits derived by downslope movement from a now‐vanished shelf to the North, and may belong either to a single gigantic debris flow event, or to a series of smaller, but roughly contemporaneous flows.

Strong faunal similarities to faunas at Girvan (western Scotland), and Tyrone (Northern Ireland), lying North of the Southern Upland Fault may suggest sinistral strike‐slip movement of no more than a few hundred kilometres.
The earthquake of 1546 in the Holy Landz
Authors: Ambraseys N. , Karcz I.
Published: July 2007

The earthquake of 1546 is considered to be one of the largest shocks in the Middle East associated with surface faulting and great loss of life. The examination of contemporary documents shows that this seismic event was a medium magnitude earthquake of Ms about 6.0, in many respects similar to that of the earthquake of 1927, that is, one of those early and grossly exaggerated events which excited widespread interest rather on account of the geographical location than because of their size or special violence. We cpud find no evidence of faulting or excessive damage and no justification to regard this earthquake as one of the most destructive in the Jordan Rift Valley.
Oceanographic and climatic implications of the Palaeocene carbon isotope maximum
Authors: Corfield Richard M. , Cartlidge Julie E.
Published: July 2007

We have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the Palaeocene and early Eocene successions at DSDP Site 577 (Shatsky Rise, North Pacific), a composite section derived from DSDP Leg 74 sites (Walvis Ridge, South Atlantic) and a composite section from ODP Leg 113 sites (Maud Rise, Weddell Sea). The δ13C records of Palaeocene and early Eocene Foraminifera at Site 577 and the Leg 74 sites show that an increase in δ13C values in surface waters at 64 Ma (end of Zone P1) resulted in increased vertical carbon isotope gradients (δ13C) between surface and deeper dwelling planktonic foraminifera, and between surface‐dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle Late Palaeocene (Zone P4). This steepening also occurs in the latest Palaeocene of the composite Leg 113 section and can be explained by an increase in surface ocean productivity. This increase in productivity probably resulted in an expansion of the oxygen minimum zone (OMZ).

Benthonic δ13C values increased during the late Palaeocene in Site 577 and the composite Leg 74 section, suggesting that the Palaeocene carbon isotope maximum was composed of both within‐ocean reservoir (increased surface water productivity) and between‐reservoir (organic carbon burial) ftactionation effects. The benthonic δ13C increase lags the surface ocean δ13C increase in the early Palaeocene (63–64 Ma) suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation. Moreover, inter‐site δ13C comparisons suggest that the locus of deep to intermediate water formation for the majority of the Palaeocene and the earliest Eocene was more likely to have been in the high southern latitudes than in the lower latitudes.

Oxygen isotope data show a decline in deeper water temperatures in the early and early late Palaeocene, followed by a temperature increase in the late Palaeocene and across the PalaeoceneEocene boundary. We speculate that these changes in deeper water temperatures were related to the flux of CO2 between the oceans and the atmosphere through a mechanism operating at the high southern latitudes.
Formation and growth of normal faults at the divergent plate boundary in Iceland
Authors: Gudmundsson Agust
Published: July 2007

The divergent plate boundary in Iceland is characterized by 40–80 km long and 5–10 km wide swarms of tension fractures (∼102 m long) and normal faults (∼103 m long). The upper part of the crust is mainly composed of lava flows, with abundant columnar joints that are mostly perpendicular to the lava contacts. The lava flows are horizontal at the surface of the rift zone but become tilted at the rate of 1° for every 150 m depth in the crust. At the surface of the rift zone the joints are vertical and parallel to the vertical principal stress. Because of tilting of the lava pile, the columnar joints become oblique to this stress, hence becoming potential shear fractures, and form echelon sets at greater depths in the crust. Theoretical considerations suggest that normal faults start to nucleate on sets of en echelon columnar joints and/or large‐scale tension fractures at crustal depths of 0.5–1.5 km. The width (depth) must be the smallest (controlling) dimension of many faults. Nevertheless, there is a positive linear relation (r = 0.91) between maximum throw and length of the Holocene faults. If the faults grow as self‐similar structures, the throw‐length relationship can be explained by a similar relation between fault length and width.
Stable isotope geochemistry and structural elements of the Sabina region (Central Apennines, Italy)
Authors: Maiorani† A. , Funiciello R. , Mattei M. , Turi B.
Published: July 2007

Various tectonic features are present in the Meso‐Cenozoic basin units of the Sabina region (Central Apennines, Italy): Mio‐Pliocene northeasterly verging thrusts are followed by Plio‐Pleistocene, N‐S oriented right‐lateral strike‐slip faults. Stable isotope geochemistry and examination of meso‐ and microstructures show that strain conditions differed through the course of tectonic history. Carbon and oxygen isotope analyses of the calate‐filled extensional fractures, the sigmoidal veins present between stylolitic cleavage surfaces, and fault plane surfaces with differing motion, demonstrate those different geneses.

The “C/'” C of the older calcite‐filling fractures (present both in the thrust and the strike‐slip systems) suggests a deposition from shallow, fresh water circulation. Furthermore, the calcite fill of en echelon systems, that occur in the southernmost Plio‐Pleistocene units, is clearly the result of a more recent, right‐lateral strike‐slip movement, connected with shallow water circulation within Mesozoic limestones.

The sigmoidal vein fills are derived from solid‐state pressure solution processes which were the result of strike‐slip movement. The deformation pattern related to the older thrust system is similar, but less intense; this also demonstrates general recrystallization processes in a closed system.

This suggests that the total shortening of the deformed sections is lower than that obtained on the basis of solution on stylolitic planes, because a sigruficant volume of dissolved carbonates remained in the system.

Stable isotope analysis also confirms that the deformational history of strongly cleaved rocks in the Sabina region took place in two phases and that extensional fractures formed before stylolithic planes, as suggested by structural and field observations.
On the mechanical properties of synthetic kaolinite/quartz fault gouge
Authors: Rutter E.H. , Maddock R.H.
Published: July 2007

The mechanical properties and microstructures of mixed kaolinite/ quartz fault gouge have been studied by means of triaxial tests, wherein a 1 mm thickness of fault gouge was sheared between rigid, sintered alumina sliders. Test conditions ranged up to 200 MPa confining pressure, 175 MPa pore water pressure and temperatures to 600°C. Constant displacement rate tests were carried out at 5×10‐4 mm s‐1, and the stress relaxation technique was used to access a wide range of lower displacement rates down to 10‐10 mm s‐1. The effects of different ratios of clay: quartz were studied, and some experiments were cafried out using crushed Tennessee sandstone gouge and pre‐faulted cylinders of Tennessee sandstone. Deformation‐induced microstructures were studied by optical, scanning and transmission electron microscopy, and mineral chemistry changes were identified using EDS analysis in the STEM.

The most important factor determining the strength of these gouges is effective confining pressure, and the effective stress law was obeyed at all test conditions. Increasing the proportion of quartz in the gouge slightly increases the strength, as does increase of temperature. Under all test conditions the gouges deformed by strain‐hardening stable sliding. At 2 mm displacement the friction coefficient is similar to that for rock and rock sliding (μ= 0.85).

Over wide ranges of strain‐rate and temperature the strength of these gouges is little affected if the effective pressure is high, but strength drops rapidly with decreasing strain‐rate if effective pressure is low (or if pore water pressure is high).

Reloading of the gouge after stress relaxation at high temperatures demonstrated hardening arising from hydrothermal cementation during stress relaxation, which led to sudden rupture of the cemented gouge. This phenomenon may be responsible for cyclic rupture of natural faults.

New mineral phases were produced in these experiments only at 600°C. At 400°C, anticipated production of pyrophyllite from kaolinite plus quartz was not found, but recrystallization of kaolinite is believed to have occurred and evidence of healing of cracks in quartz was seen. Microstructural studies revealed the ubiquitous development of P and R1 foliations and other features, which are identical to those found in natural clay‐bearing fault zones. Microstructural evolution is associated with the strain‐hardening, and apparent hardening is strongly associated with the stress path during loading.
Earthquake premonitory processes: Evolution of stresses and electric current generation
Authors: Teisseyre R.
Published: July 2007

The principles and assumptions of the Earthquake Premonitory and Rebound Theory are reviewed. The Theory based on a continuum model of fracturing processes; the stress evolution equations describe the dynamic processes governing a continuous distribution of dislocations.

Special attention is paid to the problem of electric current generation in a seismic source zone. Electric current is considered as reflecting the rate of polarization, which is influenced by motion of the charge‐bearing dislocations; the relationship between the current density and stress accumulation rate is derived.
The geological history of insect‐related plant damage
Authors: Stephenson Jonathan , Scott Andrew C.
Published: July 2007

Biological damage to plants is commonly found from the Devonian but occurs most commonly from the Cretaceous. Damage inflicted on plants whilst they were alive may trigger a pathological response involving the growth of abnormal tissues. Much of the damage is caused by arthropods, particularly insects. Whilst some damage is non‐taxon specific, such as simple feeding traces, other damage, such as leaf mines, galls or bark boring, may reveal the co‐evolution of host specific taxa and the timing of such interactions. Damaged plants, particularly from the Cretaceous and Tertiary are described and illustrated. The geological history of the evolution of insect‐related plant damage is briefly reviewed. Increased variety in the pathological response of plants is seen from the Cretaceous with the evolution of the angiosperms and diversification of numerous insect groups.
Milankovitch cyclicity recorded from Devonian non‐marine sediments
Authors: Kelly S.B.
Published: July 2007

Hydrographically closed basins are sensitive to environmental change at all scales, the influence of climate being particularly strong. Some Devonian basins contain non‐marine successions which appear to represent the deposits of such basins. Climatic fluctuations may be recorded by sediments in the form of Milankovitch band cyclicity. Two novel records of climatically related cyclicity are discussed.

Well 12/13‐1 in the North Sea penetrates a fine‐grained Old Red Sandstone succession which is thought to be comparable to the largely lacustrine Middle Devonian deposits of the Orcadian Basin which outcrop onshore. The gamma ray log through the Devonian interval reveals periodic large peaks which correlate with U‐rich, fine‐grained intervals deposited during periods of greatest lake expansion. The peaks are cyclical; power spectrum of the gamma ray data reveal periodicities of c. 8 and 40 m, which are thought to correlate with the 21,000 yr (precession) and 100,000 yr (eccentricity) Milankovitch cycles.

The Sherkin Sandstone Formation of the Munster Basin, SW Ireland, is a thick (> 1000 m) succession of largely alluvial deposits which were deposited by a terminal fan network. Detailed analysis of channel body sandstones and sedimentary structures contained within them reveals a cyclical variation in the dimensions of the bedforms camed by the channels. The same cyclicity is evident in the proportion of channel deposits. This variation reflects fluctuations in palaeodischarge, probably related to climatic variation. The main cycles are approximately 130 m thick; spectral analysis reveals two further strong periodicities at approximately 36 and 55 m. Estimated sediment accumulation rates suggest that the cycles represent periods of the order of lo4 years. It is proposed that the longer cycles reflect the 412,000 yr orbital eccentricity cycle and that the shorter cycles are either harmonics or components of the 100,000 yr eccentricity cycle.
High‐resolution profile of stable isotopes and iridium across a K/T boundary section from Koshak Hill, Mangyshlak, Kazakhstan
Authors: Sarkar A. , Bhattacharya S.K. , Shukla P.N. , Bhandari N. , Naidin D.P.
Published: July 2007

Oxygen and carbon isotopes were measured to a high depth resolution in a nannoplankton carbonate sequence spanning the Cretaceous‐Tertiary boundary at Koshak Hill, Mangyshlak Peninsula, Kazakhstan. The boundary is characterized by the presence of a ∼ 1 cm thick clay layer having a sharp peak in iridium concentration with a maximum value of 3.7 ng g‐1. The δ18O data reveal rapid (∼103years) excursion of sea‐surface temperature at the boundary where an initial cold pulse is followed by a persistent warm period. The δ13C data, in contrast, indicate only a gradual change in productivity across the boundary. The observations suggest a biogeochemical scenario for the boundary event pertaining to shallow epicontinental seas.
Fracture in a heterogeneous medium: a network approach
Authors: Reuschié Thierry
Published: July 2007

Fracture in a heterogeneous medium is simulated by a network model. Heterogeneity is introduced by randomly distributing an initial population of cracks on a triangular network of bonds. Each ruptured bond represents a crack. External stresses are applied onto the network and the evolution of the crack population is analysed when the stresses are increased. A crack will propagate to an intact bond if the critical crack extension force is reached. This propagation leads to the coalescence of bonds: crack clusters are formed. When their shapes are complex we approximate them by simpler ones to compute a crack extension force. Crack interactions are introduced by adding for a given bond the contributions of all adjacent dusters. By using this kind of approach combining fracture mechanics and network modelling, we are able to simulate the rupture of a rock specimen under compression/ traction or shear stresses and to give some characteristics of the macroscopic fracture.