bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oceanic crust production and climate during the last 100 Myr
Authors: Kaiho Kunio , Saito Saneatsu 
Published: July 2007

ABSTRACTIn order to evaluate the possible influence of oceanic crust production on climatic changes during the past 100Myr variations in total oceanic crust for this period including production at mid‐ocean ridges, oceanic plateaus, and back‐arc basins were calculated using the most recent and accurate time‐scales. The rates presented here differ from those of Larson (1991a, b) on Cenozoic fluctuations and show that (1) maximum production values occurred during the Cenomanian, Palaeocene, and late Oligocene‐early Miocene and (2) minimum values occurred in Campanian‐Maastrichtian, late Eocene, and middle Miocene. Significantly, variations of oceanic crust production correspond with variations in the δ18O of deep‐water benthic foraminifera: maximum values of oceanic crust production correspond with minimum values of δ18O, and minimum production values with maximum values of δ18O. This latter synchronism suggests that changes in land‐sea relationships and atmospheric CO2 related to major fluctuations in oceanic crust production were the main cause of mid‐Cretaceous warming and Late Cretaceous cooling, and of climatic quasi‐cycles having a periodicity of 33–38 million years over the last 100 Myr. This is the first report showing variations of ocean crust production synchronized with the Cenozoic climate changes.
Very high18o enrichment in Archean cherts from South India: implications for Archean ocean temperature
Authors: Sharma S. Das , Patil D.J. , Srinivasan R. , Gopalan K. 
Published: July 2007

ABSTRACTStable carbon and oxygen isotopic compositions of essentially unmetamorphosed Archean (> 2.6 Gyr old) cherts and carbonates of the Dharwar Sequence of southern India, from the northernmost part of the Dharwar‐Shimoga supracrustal belt (Kalche and Nagargali), have been determined. The cherts from the Nagargali area, which preserve oolitic texture and cryptocrystalline silica, show highly enriched δ18O values ranging from 28 to 31.4%o relative to SMOW. Such values are the highest yet reported from Archean nondetrital sediments, but are similar to those of modern marine cherts. On the assumption of a seawater δ18O of 0%0, calculation of temperature based on the maximum δ18O value of 31.4%0yields a value of 40°C. This is significantly less than 70–80°C reported for the Archean oceans based on cherts and chert‐phosphate pairs. Diagenetically recrystallized microcrystalline chert‐dolomite pairs of Kalche area exhibit a range of oxygen isotopic ratios similar to those reported for Archean cherts and carbonates from other parts of the world. The temperature of diagenesis is estimated to be about 68°C.
Monitoring playa sedimentation using sequential radar images
Authors: Wadge G. , Archer D.J. , Millington A.C. 
Published: July 2007

ABSTRACTA series of ERS‐1 radar images of the Chott el Djerid playa in Tunisia obtained at intervals of 35 days demonstrates the ability to monitor geological change from space. The C‐band radar backscatter is shown from field measurements to be sensitive to changes in surface roughness at millimetric scale due to evaporative growth of halite and gypsum crystals. Backscatter increases gradually during the dry summer months and decreases rapidly in early winter as the rains begin. Episodic hydrogeological and sedimentological events including lake development, channel flow and aeolian deposition can also be detected in addition to the seasonal pattern. Multitemporal, spaceborne radar offers the prospect of being able to map the dynamics of evaporite sedimentation in continental playas.
On the interaction of geology, measurement, and statistical analysis of small‐scale permeability measurements
Authors: Jensen J.L. , Glasbey C.A. , Corbett P.W.M. 
Published: July 2007

ABSTRACTSedimentary rocks exhibit small‐scale (mm) permeability variations which can be detected with a probe permeameter. The structure of the laminations may provide evidence about the characteristics of the measurement device. The statistical interpretation of these measurements using averages and variograms is enhanced when the geological character of the rock is taken into consideration. The three aspects of rock characterization, namely geology, measurement, and statistical analysis, are best assessed in concert. This theme is illustrated using probe data taken from sections of the Rannoch and Etive Formations, Northern North Sea.
Late Cretaceous exhumation of the Oman blueschists and eclogites: a two‐stage extensional mechanism
Authors: Michard A. , Goffé B. , Saddiqi O. , Oberhänsli R. , Wendt A.S. 
Published: July 2007

ABSTRACTThe continental material of the Saih Hatat window has been affected by a Late Cretaceous, obduction‐related, HP‐LT metamorphism below the Oman ophiolite. A high‐rate exhumation process is witnessed by the Maastrichtian‐Palaeocene onlap onto the blueschist‐facies rocks. Drastic metamorphic omissions are documented between the lowest, eclogitic units and the overlying, blueschist‐facies ones. Widespread late‐metamorphic shear structures point to a top‐to‐the‐NNE detachment, in opposition to the sense of the Late Cretaceous obduction. The inversion of the shearing sense occurred under similar, low temperature conditions in both the blueschist and eclogite‐facies units. Admitting that these HP‐LT metamorphic rocks formed progressively at various depth in the subducting Arabian margin, a two‐stage extensional mechanism of exhumation is suggested: (i) early uplift of the eclogitic rocks up to the blueschists depth by ductile thinning or squeezing of a ‘blind extensional allochthon'; (ii) exhumation of the whole HP‐LT metamorphic core complex by inversion of the obduction sole‐thrust and isostatic rebound of the lower plate.
Structural evolution of the ‘41st parallel zone': Tyrrhenian Sea
Authors: Spadini Giacomo , Wezel Forese‐Carlo 
Published: July 2007

ABSTRACTThe present study is based on the interpretation of more than 1300 km of 16 kJ sparker seismic profiles recorded in July 1990, during the Cruise T‐41 of the Geological Institute of Urbino. The investigated area extends along the 41st parallel in the central Tyrrhenian Sea between the northern Sardinian margin to the west and the Latium–Campanian margin to the east. This zone, situated on continental crust, marks the boundary between the northern Tyrrhenian and the southern Tyrrhenian domains.A kinematic reconstruction is presented, based on the age‐dating of the recognized structures (i.e. normal faults, reverse faults, anticline and flower structures). The evolution of the ‘41st parallel zone’ can be described in terms of polyphase tectonics characterized by different orientations of the stress field during time. The direction of the normal fault‐trends, turned clockwise, striking NE–SW in the late Tortonian–Messinian, E–W in the early Pliocene, NNW–SSE in the late Pliocene and N–S during the Quaternary. The concurrence of compressional and strike‐slip deformations suggests oblique shear motions across the 41st parallel. The occurrence of late Pliocene–Quaternary tectonic activity in the northern Tyrrhenian Sea, locally characterized by inversion tectonics, suggests active mechanisms (intraplate compression?) superimposed on the post‐rift subsidence.
Kinematic evolution of thrust‐related structures in the Umbro‐Romagnan parautochthon (northern Apennines, Italy)
Authors: De Donatis Mauro , Mazzoli Stefano 
Published: July 2007

ABSTRACTIn the internal part of the Umbro‐Marchean‐Romagnan Apennines, the foredeep clastic wedge constituting the Neogene part of the sedimentary cover is completely detached from the underlying Mesozoic–Palaeogene succession. The resulting (Umbro‐Romagnan) parautochthon consists of tectonostratigraphic units with a general geometry of broad synclinal blocks separated by narrow faulted anticlines.Thrust‐related structures observed in the field require thrust ramp propagation to have occurred within already folded rocks; therefore, they cannot be restored using simple fault‐bend fold or fault‐propagation folding models. Evidence for a passive fold origin in the studied rocks suggests that an early detachment folding episode preceded ramp propagation. The latter was facilitated by the enhanced thickness of incompetent material in the cores of detachment anticlines, which became the preferential sites where thrust ramps cut up‐section. Depending on the trajectory of such thrust ramps, different types of fault‐related structures could develop. Hanging‐wall anticlines which give way to monoclinal structures higher up in the section are associated with listric thrust ramps, whereas hanging wall monoclines approximately parallel to the underlying fault surface are associated with straight‐trajectory ramps.This kinematic evolution, which occurred partly during syn‐depositional compression, also accounts for the observed lithofacies distribution. The latter reflects an early differentiation of the foredeep trough into sub‐basins that are progressively younger towards the foreland. The detachment anticlines that originally bounded such sub‐basins were the site of later thrust propagation, leading to a tectonic juxtaposition of different tectonostratigraphic units consisting of broad NW‐SE elongate synclinal blocks.
Strain measurements with the borehole slotter
Authors: Becker A. , Werner D. 
Published: July 2007

ABSTRACTIn the past, the doorstopper method has been used successfully for determining in situ tectonic stresses. Here an example is given about the application of the borehole slotter in the domain of tectonic stress determinations, which is an innovative strain relief technique without overcoring. Data are presented that test the reliability of the strain measurements by the borehole slotter under well‐known stress conditions, that indicate the reproducibility of borehole slotter strain data compared with those from doorstopper measurements, and that demonstrate the utility of the borehole slotter even for the determination of weak tectonic strains. In northern Switzerland the borehole slotter was used in a horizontal borehole under lithostatic loading conditions only, in a rock slope area with very heterogeneous stress conditions, and in a vertical borehole where tectonic stress should be dominant. The results show that the borehole slotter is a reliable technique, which allows precise determination of in situ strains. In addition, borehole slotter measurements are less time‐consuming and therefore less costly than most other stress‐measuring techniques—an important aspect in a future of reduced research budgets.SummaryThe borehole slotter is a strain relief technique, using a recoverable strain sensor that need not be glued to the rock surface and need not be overcored. It is quicker to use than most other stress or strain measuring techniques, especially in comparison to standard overcoring techniques (Fig. 14).The borehole slotter supplied convincing results with respect to principal stress orientations, in good agreement with:(i) principal stress orientations related to lithostatic stress conditions (Dittingen 2 site),(ii) palaeostress orientations during the main stage of Jura folding only 13 to 7 Ma (Laufen 1 site),(iii) the results of neighboring door‐stopper measurements (Dittingen 1 site).The borehole slotter tests do not supply stress magnitudes directly. Thus, the elastic properties of the rock mass have to be determined independently. Stress ratios from borehole dotter tests in Dittingen 2 are realistic.In conclusion, the borehole slotter is a fully developed probe to measure in situ strains in boreholes. It allows the reliable determination of a large number of data within a short time even in weakly stressed rocks. This makes the borehole slotter a powerful tool for the determination of contemporary regional tectonic stress fields.
Isotope palaeohydrology and the prediction of long‐term repository behaviour
Authors: Fontes Jean‐Charles 
Published: July 2007

ABSTRACTThere are considerable, well‐recognized difficulties involved in the investigation of very low permeability rocks by conventional measurements of water potentials and spatial distribution of hydrological parameters such as permeability and effective porosity. Therefore, most studies of predictive behaviour are based on models which, when unconstrained by data, are often worse than no model at all. Geochemistry and environmental isotope geochemistry are techniques well suited for hydrological investigations of potential sites of nuclear waste isolation and for constraining predictive models.Stable isotopes constitutive of the water molecule (2H and 18O) may give information on the origin of the water, especially 2H which is practically uninvolved in isotope exchange with rock‐forming minerals. Variations in stable isotope contents can be related to palaeohydrological and palaeoclimatic conditions whereas 3H is indicative of recent recharge.The 13C content of dissolved carbon is related to its origin(s) and the 14C activity gives a time‐scale. However, the initial carbon isotope contents can be modified by various diagenetic effects such as precipitation/dissolution of secondary calcite and oxidation of reduced carbon. The heavy isotope content of the Total Dissolved Inorganic Carbon (TDIC) cannot be interpreted without a detailed knowledge of the carbon chemistry and of the mineralogy and isotope contents of secondary carbonates. Species of Dissolved Organic Carbon (DOC), with high molecular weights (HMW) can generally be attributed to soil derived compounds. Their 14C content may be measured by AMS (Accelerator Mass Spectrometry) thus providing an estimate of the time elapsed since recharge took place.Chlorine‐36 is an interesting potential tool for dating old ground waters because of its long half‐life (301 kyr) and its hydrophilic behaviour. It can be also produced in situ in significant amount if the rocks are rich (some tens of ppm) in U and Th. In such cases, this time dependent build‐up provides a more systematic radiochronometer of CI‐ residence time in the rock than the decay of cosmic input 36CI, provided no Cl‐ is leached from the rock.The isotopic composition of aqueous sulphur compounds depends on their origin and on their diagenetic evolution. The redox reactions of SO2‐4 reduction or of S2‐ oxidation are marked by strong isotope effects especially when generated by bacteria. Sulphate reduction by organic matter is a potential source of dissolved inorganic carbon and may thus interfere with 14C age interpretations.After discussion of the possible age and origin of waters and solutes, some scenarios of evolution of local and regional palaeohydrological conditions are proposed.Examples are given with special emphasis on detailed results from the Fennoscanian shield (Stripa project), and from northern Switzerland.
The North Aegean region: a tectonic paradox?
Authors: Pavlides Spyros , Caputo Riccardo 
Published: July 2007

ABSTRACTIn the past two decades, several publications have been presented concerning the recent and active fault geometry, kinematics and geodynamics of the Aegean Region and particularly of the northern sector. Data and results are often contradictory and because of the complexity of the area most hypotheses and models should be considered carefully.The right‐lateral movement of the North Anatolia Fault continues into some branches of the North Aegean fault system. There, strike‐slip motion along NE–SW trending faults coexists with dip‐slip E–W trending faults in the frame of an extensional regime related to N–S crustal stretching.If we take into account the geodynamic environment of the region, several mechanical problems arise. To the east, the Aegean is compressed by the westward convergence of Anatolia, while to the south and west along the Hellenic Arc, a hemiradial compression occurs due to subduction. Although the North Anatolia–North Aegean Trough fault system resembles a restraining bend, the whole area is in fact affected by pure extension and local transtension, along NE–SW trending structures. Accordingly, the major paradox of the area and especially in the western sector (fault termination?) is the occurrence of extension where compression should regionally, or at least locally, predominate.
The Basel 1356 earthquake: which fault produced it?
Authors: Meyer Bertrand , Lacassin Robin , Brulhet Jacques , Mouroux Bernard 
Published: July 2007

ABSTRACTThe 1356 Basel earthquake was the strongest event to have shaken NW Europe in the last thousand years. The peculiar location of this historical event makes it possible to relate it to normal faulting along the edges of the Rhine Graben, as well as to reverse faulting along the Jura frontal thrust or to fault reactivation within the Hercynian basement. Alternate hypotheses are discussed and their implications compared taking into account available structural data and results of the morphotectonic study performed in the epicentral area. This study combines field observations with the analysis of SPOT satellite imagery, aerial photographs, and detailed topography. It is concluded that the Basel earthquake most probably reactivated a basement fault (reverse or wrench fault) beneath the shallow‐depth aseismic detachment that underlies the Jura Mountains.
The facies properties and depositional environments of nodular limestones and red marly limestones (Ammonitico Rosso) in the Ankara Jurassic sequence, central Turkey
Authors: Varol Baki , Gökten Ergun 
Published: July 2007

ABSTRACTThe nodular limestones and red marls of the Ankara region, deposited during the early to middle Jurassic, show similar palaeontological and sedimentological characteristics to those of the red nodular limestones form the Northern Alps (Adnet limestones) and from the Southern Alps (Ammonitico Rosso).The nodular limestones appear to be hardground breccias drowned into the red marly limestones due to the instability of the bottom. The association of sponge spicules, crinoid fragments, small ostracods, benthic foraminifers, shell debris and common micrite matrix suggests a subtidal environment. The subsequent formation of red marly limestones consists of the partial dissolution of the shells; this suggests that a low sedimentation rate and/or sedimentological breaks took place during the precipitation of the ammonite‐bearing marls.The nodular limestones (hardground breccias) and the Ammonitico Rosso‐type facies of the Ankara Jurassic succession were formed in a deeper subtidal environment and/or deeper shelf extending into the basin. The hardground layers drowned into the Ammonitico rosso were likely formed on a local carbonate shelf, that deepened increasingly through the early to middle Jurassic. Development of a local submarine clastic fan within the carbonate succession of the Ankara Jurassic basin indicates an irregular bottom topography induced by the syn‐sedimentary faults.
GPS surveys in eastern Nepal
Authors: Anzidei Marco 
Published: July 2007

ABSTRACTThe Nepal region, between the Ganges plain and the Tibetan Plateau, shows the great effects of the orogenetic deformation which started between 40 and 55 Ma, following the collision between the Indian and Asiatic continental plates. Today the Himalayan chain and the Tibetan plateau are some of the best manifestations of the collision process.Data from a geodetic network in Eastern Nepal were employed to study the motion of the crust in this recently evolved area. The data were collected by means of the Global Positioning System; this geodetic space technique can achieve a centimetric resolution in coordinate definition and baseline computation for observation sites, even those located at long distances away and it provides a powerful new tool for the comprehension of the dynamics of active tectonic regions.
Observation of sections of oceanic crust and mantle cropping out on the southern wall of Kane FZ (N. Atlantic)
Authors: Auzende Jean‐Marie , Cannat Mathilde , Gente Pascal , Henriet Jean‐Pierre , Juteau Thierry , Karson Jeffrey , Lagabrielle Yves , Mével Catherine , Tivey Maurice 
Published: July 2007

ABSTRACTThe objective of the 20 Nautile dives of the recent Kanaut cruise was to study the southern wall of the Kane Fracture Zone from its eastern intersection with the Mid‐Atlantic Ridge (MAR) to 5 Myr in age. The geological mapping shows four successive massifs, wrench faulted and slightly tilted. The transform‐facing walls of these massifs exhibit outcrops of fresh and serpentinized peridotites, gabbros and basalts. The entire crustal exposure is cataclased and metamorphosed to greenschist facies.
Foraminiferal changes and geochemical profiles across the Cenomanian/Turonian boundary in central and south‐east Poland
Authors: Peryt Danuta , Wyrwicka Krystyna , Orth Charles , Attrep Moses , Quintana Leonard R. 
Published: July 2007

ABSTRACTTwo sections of the Upper Cenomanian and Lower Turonian in central and south‐east Poland were investigated for foraminifers, CaCO3content, carbon content insoluble in HCl (Corg) and in the carbonates (Ccarb), carbon and oxygen isotopic composition of bulk‐rock carbonates and elemental abundances. The Cenomanian/Turonian boundary interval is characterized by the appearance of more marly facies, a δ13C and δ18O stable isotope anomaly, a considerable increase in Corg content and decrease in Ccarb content and substantial changes in the foraminiferal assemblages. A major carbon stable isotope excursion with a shift of +2 (PDB) occurs in the lowermost Whiteinella archaeocretacea Zone. The late Cenomanian δ13C anomaly is associated with heavy δ18O values. The peak value of δ13C corresponds to the minima in P/B ratio and in diversity of foraminiferal assemblages. A late Cenomanian anoxic event is thought to be responsible for changes in foraminiferal assemblages. However, elemental abundance analyses do not show changes in the concentrations of trace elements. This may be explained by the long distance between studied area and a source of enrichment which was probably located in the western hemisphere.
Ijolite versus carbonatite as sources of fenitization
Authors: Morogan Viorica 
Published: July 2007

ABSTRACTIjolite‐carbonatite complexes are ubiquitously surrounded of an aureole of metasomatically altered rocks. The process of alteration is termed fenitization and is generally caused by peralkaline fluids emanating from cooling alkaline, i.e. ijolite and carbonatite magmas. Ijolites and carbonatites normally occur together and attempts to determine the source of the fenitizing fluids may therefore lead to controversial, if not erroneous, conclusions.Mineralogical and chemical data of fenites from Oldoinyo Lengai (Tanzania), Fen (Norway), and Alnö (Sweden) are reviewed in the present paper in order to reveal the main factors controlling the fenitization around ijolite and carbonatite. Despite the overall alkaline nature of the process, variables such as XCO2 of the fluid, activity gradients of SiO2, Al2O3 and CaO, FeO/MgO ratio, fO2 and temperature gradients may differ, producing distinctive patterns of fenitization around the two magmatic sources. The ijolitic‐type fluid has low XCO2, high activities of alkalies, SiO2 and Al2O3, and low activity of CaO. The fO2 evolves along the hm‐mt buffer conditions and the temperature falls gradually with distance from the magmatic source. The carbonatitic‐type fluid has high XCO2, high activities of alkalies and CaO, and low activities of SiO2 and Al2O3. Temperatures and fO2 are initially high, but decrease sharply with distance from the source. Moreover, the CO2‐rich fluid may complex and transport the REE.