Showing papers in "Bulletin De La Societe Geologique De France in 2007"
TL;DR: In this article, the authors present a current state-of-the-art on the application of surface geophysical methods to landslide characterization and focus on recent papers published in peer-reviewed international journals.
Abstract: In the last two decades, shallow geophysics has considerably evolved with the emergence of 2D spatial imaging, then 3D spatial imaging and now 4D time and space imaging. These techniques allow the study of the spatial and temporal variations of geological structures. This paper aims at presenting a current state-of-the-art on the application of surface geophysical methods to landslide characterization and focuses on recent papers (after 1990) published in peer-reviewed international journals. Until recently, geophysical techniques have been relatively little used for the reconnaissance of landslides for at least two main reasons. The first one is that geophysical methods provide images in terms of physical parameters, which are not directly linked to the geological and mechanical properties required by geologists and engineers. The second reason shown through this study probably comes from a tendency among a part of the geophysicists to overestimate the quality and reliability of the results. This paper gave the opportunity to review recent applications of the main geophysical techniques to landslide characterisation, showing both their interest and their limits. We also emphasized the geophysical image characteristics (resolution, penetration depth), which have to be provided for assessing their reliability, as well as the absolute requirements to combine geophysical methods and to calibrate them with existing geological and geotechnical data. We hope that this paper will contribute to fill the gaps between communities and to strength of using appropriate geophysical methods for landslide investigation.
322 citations
TL;DR: In this paper, the authors reviewed the techniques of image analysis (interferometry and optical data correlation) to measure displacements and examined the performance of each type of platforms in French South Alps are shown.
Abstract: Surface displacement field of landslides is a key parameter to access to their geometries and mechanical properties. Surface displacements can be calculated using remote-sensing methods such as interferometry for radar data and image correlation for optical data. These methods have been elaborated this last decade and successfully applied on sensors (radar, cameras, terrestrial 3D laser scanner imaging) either attached to space or aerial platforms such as satellites, planes, and unmanned radio-controlled platforms (drones and helicopters) or settled at fixed positions emplaced in the front of landslides. This paper reviews the techniques of image analysis (interferometry and optical data correlation) to measure displacements and examines the performance of each type of platforms. Examples of applications of these techniques in French South Alps are shown. Depending on the landslide characteristics (exposure conditions, size, velocity) as well as the goal of the study (operational or scientific purpose), one or a combination of several techniques and data (characterized by several resolution, accuracy, covered surface, revisiting time) have to be used. Radar satellite data processed with differential interferometric or PS methods are mainly suitable for scientific purposes due to various application limitations in mountainous area. Optical satellite and aerial images can be used for scientific studies at fairly high resolution but are strongly dependant on atmospheric conditions. Platforms and sensors such as drone, fixed camera, fixed radar and Lidar have the advantage of high adaptability. They can be used to obtain very high resolution and precise 3D data (of centimetric accuracy) suitable for both scientific and operational purposes.
161 citations
TL;DR: In this article, the authors review the state-of-the-art in the understanding of landslide processes and identify some pressing challenges for the development of our modelling capabilities in the forthcoming years for hazard assessment.
Abstract: Slope movements (e.g. landslides) are dynamic systems that are complex in time and space and closely linked to both inherited and current preparatory and triggering controls. It is not yet possible to assess in all cases conditions for failure, reactivation and rapid surges and successfully simulate their transient and multi-dimensional behaviour and development, although considerable progress has been made in isolating many of the key variables and elementary mechanisms and to include them in physically-based models for landslide hazard assessments. Therefore, the objective of this paper is to review the state-of-the-art in the understanding of landslide processes and to identify some pressing challenges for the development of our modelling capabilities in the forthcoming years for hazard assessment. This paper focuses on the special nature of slope movements and the difficulties related to simulating their complex time-dependent behaviour in mathematical, physically-based models. It analyses successively the research frontiers in the recognition of first-time failures (pre-failure and failure stages), reactivation and the catastrophic transition to rapid gravitational processes (post-failure stage). Subsequently, the paper discusses avenues to transfer local knowledge on landslide activity to landslide hazard forecasts on regional scales and ends with an outline how geomorphological investigations and supporting monitoring techniques could be applied to improve the theoretical concepts and the modelling performance of physically-based landslide models at different spatial and temporal scales.
95 citations
TL;DR: In this article, the authors present seismic noise investigations carried out on two different sites, the "Super Sauze" mudslide and the "Saint Guillaume" translational clayey landslide (France), where independent measurements (geotechnical and geophysical tests) were performed earlier.
Abstract: In order to better understand the mechanics and dynamic of landslides, it is of primary interest to image correctly their internal structure and their slip surface. Several active geophysical methods are able to provide the geometry of a given landslide, but were rarely applied in 3 dimensions in the past. The main disadvantages of methods like seismic reflection and electrical tomography are that there are heavy to set up and/or to process, and they consequently are expensive and time consuming. Moreover, in the particular case of soft-rock landslides, their respective sensitivity and resolution are not always adequate to locate the potential slip surfaces. Passive methods may represent an interesting alternative particularly for landslides difficult to access, as they require lighter instrumentation and easier processing tools. Among them, the seismic noise based methods have shown increasing applications and developments, in particular for seismic hazard mapping in urban environment. In this paper, we present seismic noise investigations carried out on two different sites, the "Super Sauze" mudslide and the "Saint Guillaume" translational clayey landslide (France), where independent measurements (geotechnical and geophysical tests) were performed earlier. Our investigations were composed of electrical tomography profiles, seismic profiles for surface-wave inversions, H/V measurements, which are fast and easy to perform in the field, in order to image shear wave contrasts (slip surfaces), and seismic noise array method, which is heavier to apply and interpret, but provides (S)-waves velocity profile versus depth. For both sites, landslide bodies are characterized by lower S wave velocity (Vs 550 m.s-1; {rho} > 150 ohm.m). Their thickness vary from a few m to 50 m. Comparison between geophysical investigations and geotechnical data proved the applicability of such passive methods in 3D complex structures, with however some limitations.
86 citations
TL;DR: Magmatic charnockitic rocks and TTG plutons intruded successively the Archaean greenstone belts of the Ntem Complex, at the northwestern margin of the Congo Craton.
Abstract: Magmatic charnockitic rocks and TTG (tonalite-trondhjemite-granodiorite) plutons intruded successively the Archaean greenstone belts of the Ntem Complex, at the northwestern margin of the Congo Craton. Geochemical data, zircon Pb-Pb ages, and Sr-Nd isotope studies, constrain the magmatic features, the genetical timing, and the geodynamic settings of these different suites. Charnockites and TTGs are characterized by high Al2O3 contents, high Na/K ratio, low Th content, LREE enrichment, HREE depletion, negative anomalies in Nb, Ta, and Ti, and positive anomalies in Sr. The Pb-Pb zircon ages indicate that charnockites were emplaced at ca. 2900 Ma and TTGs, which cross-cut the charnockites, at ca. 2830 Ma. TDM Nd mean crustal residence ages of both suites range between 3.10 and 2.93 Ga. The charnockites show slightly positive initial {varepsilon}Nd2.9Ga (+0.3 to +1.3), whereas the TTGs have slightly negative values (+0.1 to -1.5). The charnockitic and TTG magmas may have resulted from different partial melting processes of the primitive Archaean basaltic crust and contaminated mantle, possibly in a hot slab subduction convergent regime. They contribute to a two-stage crustal growth of the Archaean craton.
69 citations
TL;DR: In this paper, a review of the potential hydrogeochemical information can have for landslide research and analyses the use of hydrogelogical information to unravel the hydrological processes in landslide triggering.
Abstract: This review aims to give an overview of the potential hydrogeochemical information can have for landslide research and analyses the use of hydrogeochemical information to unravel the hydrological processes in landslide triggering. Landslides are well known for their data shortage; especially in case the hydrogeology is heterogeneous and difficult to measure. In this article we analyse the impact hydrogeochemical processes has on physical properties of the soil material and rock slopes, i.e. the relation with deformation rate and the relation of pore fluid composition and residual shear strength of soil material. Furthermore, the paper looks at the subsurface information that can be gained, i.e. the geological information of subsurface architecture and the hydrological information on origin of water, flow paths and travel times (using isotope analyses). Hydrochemical information used in both hard and soft rocks enables the display of clusters of water types, which is useful to identify contribution of different aquifers to the landslide area. Moreover, it can demonstrate the existence of lithologies and structures that are not visible with surface based geological investigations. Kinetic-based modelling is shown to be very useful in the interpretation of hydrogeochemical information. Lastly, it is shown that chemical information such as cation exchange properties coming from cored drilling is worthwhile for hydrological interpretations of landslides.
57 citations
TL;DR: In this paper, the syn-rift evolution of the central part of the southern coast of the Corinth rift is revisited, based on new sedimentological and paleontological data.
Abstract: The southern coast of the gulf of Corinth exhibits syn-rift deposits, giving insights into the first stages of continental extension as well as the geodynamic evolution of the surrounding Aegean region. The stratigraphy (relative position, 3D geometry, dating) of these deposits is still subject to controversies. The syn-rift evolution of the central part of the southern coast of the Corinth rift is revisited, based on new sedimentological and paleontological data. While ostracods analysis provides precise information about the paleoenvironments, recent advances in palynology supply a more accurate chronology. For the first time, we document marine evidences and Pleistocene evidences below the well-known giant Gilbert-type fan deltas of the Corinth rift. The syn-rift fill records a three-phase history: (1) the Lower Group corresponds to continental to lacustrine environments passing up progressively to brackish environments with occasionally marine incursions from before 1.8 Ma to some time after 1.5 Ma, (2) the Middle Group corresponds to giant alluvial fans and to Gilbert-type fan deltas prograding in an alternating marine and lacustrine environment from around 1.5 Ma to some time after 0.7 Ma, and (3) the Upper Group corresponds to slope deposits, Gilbert-type fan deltas and marine terraces indicating the emergence of syn-rift sediments along the southern coast from at least 0.4 Ma to the present day, with alternating marine and lacustrine deposition controlled by the position of the Mediterranean sea level relative to the Rion Strait sill.
49 citations
TL;DR: In this paper, the authors presented seismic monitoring data acquired on a mudslide located in the South French Alps and showed that recordable seismicity exists in the frequency range of 0.01 Hz to 10 Hz associated with landslide deformation.
Abstract: The macroscopic deformation of rocks, at scales ranging from laboratory samples (cm) to rock hillslopes and earth crust (hm to km), is associated with local irreversible processes (cracks/faults propagation and shearing). These movements involve propagation of acoustic wave's which can be observed by remote sensing. Seismic monitoring during strain progression can help our understanding of rock behaviour and lead to the recognition of failure precursors. Although of significant potential, this observational tool has had only limited application in the study of gravitational instabilities such as landslides. This paper presents seismic monitoring data acquired on a mudslide located in the South French Alps. Results show that recordable seismicity exists in the frequency range of 0.01 Hz to 10 Hz associated with landslide deformation. Acceleration of landslide movement is controlled by rainfall and appears to be well correlated with seismic activity. The origin of the seismicity is attributed to shearing of the moving mass at the interface with the in-situ stable bedrock. Spectral analysis of the seismic wave reveals that the range 0.1-1 Hz is the most sensitive to the variations in landslide velocity. The results emphasize the strong potential of seismic monitoring for improving our understanding of mechanisms controlling rock mass deformation and gravitational instability. The determination of operational failure precursors based on seismic monitoring has yet to be achieved but remains a major target of future research.
48 citations
TL;DR: In this paper, a data fusion strategy based on fuzzy subsets theory is developed for the interpretation of the geomechanical behavior of the mudslide from geophysical data.
Abstract: Geophysical methods such as seismic surveying or electrical resistivity imaging appear to be well adapted to investigate landslide structure and understand related mechanisms They allow direct and non-intrusive measurements of acoustic (P), shear (S) waves velocity and electrical resistivity, three physical parameters considered as essential to define the properties of reworked moving materials Both methods were applied at the "Super-Sauze" site, in the French South Alps, where a typical example of an intra-material mudslide can be observed Measurements were taken simultaneously along a profile of 325 m in length, perpendicularly to the axis of the mudslide The P and S-wave velocity fields, as well as the electrical resistivity field, were inverted from recorded data according to suitable algorithms P and S-wave velocities as well as resistivity tomographies are presented and discussed in term of reliability Preliminary interpreted results show a correlation between the seismic velocities and electrical resistivity data, confirming that the simultaneous use of both methods gives complementary information on the geomechanical behaviour of the landslide The seismic data provide information on the variations of fissure density and on the presence of deformed material whereas the electrical resistivity data provide information on the variations of water content within the mudslide In order to go deeper into the interpretation of the geomechanical behaviour of the mudslide from geophysical data, a data fusion strategy based on fuzzy subsets theory is developed The computed fuzzy cross-sections show the possibility of geomechanical hypotheses to be realized in specific areas of the tomographic cross-sections highlighting the places where plastic or solid-body deformations could occur This information is consistent with the geotechnical data and the borehole inclinometer measurements available for the mudslide
40 citations
TL;DR: A phylogenetic analysis using 101 characters for 29 mesoeucrocodylian taxa and 3 outgroup taxa supports the monophyly of the family Goniopholididae and the Thai specimen forms a clade with the European Goniaopholis.
Abstract: A new taxon of a broad-snouted goniopholidid, Siamosuchus phuphokensis , gen. et sp. nov., was discovered in the Sao Khua Formation (ante-Aptian), northeastern Thailand. The specimen is described on the basis of an incomplete skeleton showing the premaxillae, maxillae, nasals, left lacrimal, frontal, left jugal, right postorbital, caudal part of the cranial table, most of the right part of the postcranial skeleton, and several heavily sculptured osteoderms. S. phuphokensis is distinguished from the other broad-snouted goniopholidids on the basis of the following characters: penetration of the nasals in the narial border; presence of a robust and high median ridge on the interorbital surface; lateral margin of the frontal forming the medial edge of the orbit; supraoccipital exhibiting a wide pentagonal shape. A phylogenetic analysis using 101 characters for 29 mesoeucrocodylian taxa and 3 outgroup taxa supports the monophyly of the family Goniopholididae. In addition, the Thai specimen forms a clade with the European Goniopholis . Based on our strict consensus tree, the generic name Goniopholis should be restricted to the European forms only.
35 citations
TL;DR: A partial crocodilian skeleton, including a well-preserved skull and mandible, from the marine Lower Cenomanian of Normandy (northwestern France) is described as a new genus and species of the family Pholidosauridae (Mesosuchia), Oceanosuchus boecensis.
Abstract: A partial crocodilian skeleton, including a well-preserved skull and mandible, from the marine Lower Cenomanian of Normandy (northwestern France) is described as a new genus and species of the family Pholidosauridae (Mesosuchia), Oceanosuchus boecensis. Diagnosis for genus and species: Mesorostrine pholidosaurid (rostral index 66% as compared with 74% for Terminonaris robusta and 75% for Sarcosuchus imperator , hitherto the least longirostrine species in that family), relatively short mandibular symphysis (11 post-symphysial alveoli), no external mandibular fenestra, prearticular present, paired tuberosities at the base of the cervical vertebral centra.
TL;DR: In this article, the authors investigate the cover-basement relations in eastern Anti-Atlas south of the Ougnat culmination, based on mapping at scale 1:50,000.
Abstract: Keywords. - Foreland fold belts, Variscan, Paleofaults, Inversion tectonics, Anti-Atlas, Morocco Abstract. - North of the Saharan cratonic domain, the Anti-Atlas mountains correspond to the foreland, external fold belt of the Variscan orogen which extends in the Meseta block to the north, and Mauritanides to the southwest. The Anti-Atlas was uplifted during the Mesozoic-Cenozoic, and display several basement culminations ("boutonnieres") amidst the folded Palaeozoic cover. Recent studies in western Anti-Atlas emphasized the basement implication in the shortening process (thick skinned structure). Hereafter we investigate the cover-basement relations in eastern Anti-Atlas south of the Ougnat culmination, based on mapping at scale 1:50,000. The Palaeozoic sequence is much thinner than in the west, and the decollement levels are less important. Flexural slip folds are concentrated along the faults (en echelon folds) and within some rhombic domains crushed between major faults (e.g. Angal-Gherghiz Lozenge), whereas other areas are monoclinal. The main shortening direction deduced from the fold axes trend is directed ~N045 o Ea s in the Ou- garta range further to SE. At a regional scale, this shortening direction interferes with a N-S trending one. A sketch map of the top of the basement makes visible a mosaic of S- to SE-ward tilted blocks. The faults between these blocks are in- herited from paleofaults which formed during extensional events during the Cambrian, late Ordovician, and (mainly) Middle-Late Devonian. The paleofault array is indicative of a proximal passive margin setting at the northern border of the metacratonic domain. The fault inversion and their dominant strike-slip throw occurred during a late Variscan (Ste- phanian-Permian) compression event, postdating the NNW-SSE collision of the Meseta block.
SIDI1
TL;DR: In this paper, a new genetic model based on fluid inclusion (FI) microthermometry and REE geochemistry was proposed for the deposition of celestite in Jebel Doghra.
Abstract: The celestite ore of Jebel Doghra occurs as stratabound deposits within the cap-rock of a diapiric structure of Triassic salt-rocks. The celestite deposits result mainly from the late diagenetic to epigenetic replacement of the carbonated host-rocks giving rise to a dolomite-celestite "banded ore". Celestite is locally observed within fractures. This study proposes a new genetic model based on fluid inclusion (FI) microthermometry and REE geochemistry. FI show that celestite, occurring either as stratabound bodies or lodes, was deposited from a highly saline (20.7 ± 1.3 wt%NaCl equivalents) and warm (174 ± 3oC) basinal fluid, which contains hydrocarbon droplets and CO2. The geochemistry of the REE shows that the deposition of celestite is due to the mixing between a deep-sourced fluid which has acquired high Sr concentrations by leaching feldspar-rich series in depth and a sulfate-rich solution associated with the Triassic evaporites.
TL;DR: A theropod tibia from the Phu Kradung Formation of Mukdahan Province, northeastern Thailand was described and referred to the family Sinraptoridae, previously known only from the Jurassic of China (Xinjiang and Sichuan).
Abstract: A theropod tibia from the Phu Kradung Formation of Mukdahan Province, northeastern Thailand, is described and referred to the family Sinraptoridae, previously known only from the Jurassic of China (Xinjiang and Sichuan). This find confirms the affinities of the vertebrate assemblage from the Phu Kradung Formation with Late Jurassic faunas from China. The Late Jurassic age suggested by fossil vertebrates for the Phu Kradung Formation is not in good agreement with an attribution to the Early Cretaceous based on palynomorphs.
TL;DR: The specific biodiversity of stromatoporoids, tabulates and brachiopods from the Ardennes (707 taxa) has been analyzed stage-by-stage from the Lochkovian up to the Famennian.
Abstract: The specific biodiversity of stromatoporoids, tabulates and brachiopods from the Ardennes (707 taxa) has been analyzed stage-by-stage from the Lochkovian up to the Famennian. The diversity of each group may be correlated with external factors (e.g. facies), but it varied individually (e.g. decline of brachiopods in the Givetian). The faunas are discussed at the order level, however some more diversified orders are analyzed at family level. Biodiversity shows a single peak centered on the Givetian for the bioconstructors, and two major peaks (Emsian-Eifelian and Frasnian) for the brachiopods. The most diversified orders are Stromatoporellida (stromatoporoids), Favositida (tabulate corals) and Spiriferida (brachiopods). Stromatoporoids display two, tabulate corals four and brachiopods five stages of renewal of fauna.
TL;DR: Trilobite occurrences and biodiversity from Devonian sections of the Ardennes Massif are presented in this article, where the distribution of these associations is correlated with the deposition environments and age of the strata.
Abstract: Trilobite occurrences and biodiversity from Devonian sections of the Ardennes Massif are presented. Fluctuations in diversity reflect environmental changes and event-stratigraphic turnovers throughout the Devonian. Peak diversity is attained during the Eifelian (Middle Devonian) when the carbonate system is developed. Six trilobite associations have been delineated based on cluster analysis. Distribution of these associations is correlated with the deposition environments and age of the strata.
TL;DR: In this paper, a sequence stratigraphic analysis for the Permo-Triassic facies was performed from outcrops in the Aragonian branch of the Iberian range (Zaragoza, Spain) using an integrated analysis of sedimentological and palynological data.
Abstract: The Permo-Triassic ‘Buntsandstein' facies was studied from outcrops in the Aragonian branch of the Iberian range (Zaragoza, Spain). Using an integrated analysis of sedimentological and palynological data, we propose a sequence stratigraphic analysis for the Permo-Triassic deposits in this area. A comparison with the stratigraphical cycles of other parts of the Iberian domain and other peri-Tethyan basins enables us to specify the stratigraphic context of the Lower Triassic in the western European domain and characterize the importance of the Lower Triassic hiatus. The ‘Buntsandstein' deposits studied here from the Aragonian branch occur in three outcrop areas: Tabuenca-Rodanas, Morata de Jalon and Fombuena. The Permo-Triassic deposits lie unconformably on the Hercynian (Variscan) basement. The ‘Buntsandstein' facies were attributed to the ‘Detrital Group' by Arribas [1984], who recognized four informal formations: the Araviana, Tierga, Calcena and Trasobares formations, in ascending stratigraphic order. Based on sedimentological criteria indicating fluvio-lacustrine environments for the Araviana cycle, the basal ‘Buntsandstein' facies of this area can be attributed to the Permian. The discontinuity observed between the Araviana and Tierga formations, and the palaeobotanical evidence indicating an Anisian age (i.e. Middle Triassic) for the Tierga, suggests a hiatus during the Lower Triassic in this area. The Lower Triassic in Spain and many other parts of western Europe is characterized by fluvial sediments preserved in arid palaeoenvironments, associated with occasional aeolian deposits, and lacking any palaeoflora. At the scale of the western European domain, the onset of Triassic sedimentation would appear mainly in the Olenekian. Stratigraphic continuity between Permian and Triassic non-marine deposits, with sediments attributable to the Induan (lower part of the Lower Triassic), is only observed in the central Germanic Basin. In the Aragonian branch, the first Triassic sediments are dated as Anisian and characterize the retrogradational trend of a major cycle (Tierga – Calcareous Group major cycle) showing the vertical evolution from braided rivers to marine Muschelkalk deposits. At the scale of the west-European domain, the Anisian is always characterized by fluvial and fluvio-lacustrine deposits, with palaeosols, passing upward into marine deposits. Thus, the connection with the open sea was established during the Anisian. In this western Peritethyan domain, the diachronous nature of the Muschelkalk transgression is evident: the onset of Muschelkalk facies occurs during the lower Anisian in the Germanic Basin, the middle Anisian in the eastern part of the Paris Basin and the late Anisian in the Iberian Peninsula.
TL;DR: Mauremys thanhinensis and Hardella siamensis n. sp. as discussed by the authors were two early representatives of testudinoid turtles from South-east Asia, which shed light on the early evolution of geoemydids.
Abstract: Two new species of geoemydid turtles from the late Eocene -- early Oligocene of Krabi Basin in southern peninsula of Thailand are described on the basis of shells and other postcranial material: Mauremys thanhinensis n. sp. and Hardella siamensis n. sp. These early representatives of testudinoid turtles from South-East Asia shed light on the early evolution of extant geoemydids.
TL;DR: In this paper, a regional diversity curve of the Ordovician organic-walled microphytoplankton (acritarchs) from the Yangtze Platform at species level is presented using all literature data at the generic level.
Abstract: Following the publication of a regional diversity curve of the Ordovician organic-walled microphytoplankton (acritarchs) from the Yangtze Platform at the species level (Servais et al., 2004), a diversity curve for China is here presented using all literature data at the generic level. The Chinese curve is a compilation of three separate curves from the three major continental blocks that constituted China in the Ordovician: South China (including the Yangtze Platform), Tarim and North China. The diversity changes can partly be related to sea level changes, both at a regional (South Chinese sea level curve) and at a global level (global curve). The totalised curve for all Chinese localities indicates peaks in diversity that apparently correspond to three sea level highstands at a global level at the early-middle Ordovician boundary (middle "Arenigian"), at the Sandbian-Katian boundary (middle "Caradocian") and during the upper Katian (pre-Hirnantian "Ashgillian") Boda Event (Fortey and Cocks, 2005).
TL;DR: In this paper, it is suggested that the exhumation history is mostly controlled by a D2+D3 crustal-scale vertical shortening resulting in the thinning of the previous tectonic pile formed during D1.
Abstract: The basement domes of the central part of western Alps may result either from a multistage tectonic evolution with a dominant horizontal shortening component, an extensional behaviour, or both. The Ambin massif belongs to the "Brianconnais" domain and is located within the HP metamorphic zone. It was chosen for a reappraisal of the tectonic evolution of the Internal Alps in its western segment. Structural investigations have shown that Alpine HP rocks were exhumed in three successive stages. The D1 stage was roughly coeval with the observed peak metamorphic conditions and corresponds to a non-coaxial regime with dominant horizontal shortening and north movement direction. Petrological observations and P-T estimates show that the exhumation process was initiated during D1, the corresponding mechanism being still poorly understood. The D2 stage took place under low-blueschist facies conditions and culminated under greenschist facies conditions. It developed a retrogressive foliation and pervasive shear-zones at all scales that locally define major tectonic contacts. D2 shear zones show a top-to-east movement direction and correspond actually to large-scale detachment faults responsible for the juxtaposition of less metamorphic units above the Ambin basement and thus to a large part of the exhumation of HP rocks toward the surface. D2 shear zones were subsequently deformed by D3 open folds, large antiforms (e.g. the Ambin dome) and associated brittle-ductile D3 shear-bands. The D1 to D3 P-T conditions and P-T path of the blueschists occurring in the deepest part of the Ambin dome, was estimated by using the multi-equilibrium thermobarometric method of the Tweeq and Thermocalc softwares. Peak pressure conditions, estimated at about 14--16 Kb, 500oC, are followed by a nearly-isothermal decompression that occurred concurrently with the major D1--D2 change in the ductile deformation regime. Eastwards, the Schistes Lustres units exhibit a similar geometry on top of the Gran Paradiso dome but exhibit opposite D2 movement direction. Lower-grade units are lying above higher-grade units, the shear zones occurring in between being similar to Ambin's D2 detachments. Thus at regional scale, the D2 detachments seem to form together with the Ambin shear-zones, a network of conjugate detachments. Such a pattern suggests that the exhumation history is mostly controlled by a D2+D3 crustal-scale vertical shortening resulting in the thinning of the previous tectonic pile formed during D1. The slab-break off hypothesis may explain such an extensional behaviour within the western Pennine domain. It is suggested that the thermo-mechanical rebound of the residual European slab initiated between 35 and 32 Ma the fast exhumation of the previously thickened orogenic wedge (stack of D1 HP slices). It was immediately followed by a collapse of the wedge that may correspond to the E-W Oligocene extensional event responsible for the opening of rifts in the West European platform.
TL;DR: In this paper, the evolution of continental climates and oceanic productivity in the westernmost Mediterranean over the past 50,000 years were reconstructed using ODP Site 976, Alboran Sea.
Abstract: Records of calcium carbonate, organic matter (organic carbon content, palynology) and planktonic foraminiferal oxygen isotopes from ODP Site 976, Alboran Sea, are used to reconstruct the evolution of continental climates and oceanic productivity in the westernmost Mediterranean over the past 50,000 years. The records mimic the Greenland ice core records in that they display the Heinrich events and the rapid Dansgaard/Oeschger-type stadial-interstadial oscillations. Warm interstadials correlate with an expansion of deciduous forests on the adjacent continents and enhanced river runoff and organic matter flux from terrestrial sources. In contrast, cold stadials are characterized by an expansion of semi-desert vegetation, reduced river runoff and limited terrestrial organic matter flux. The organic carbon record displays a longer-term cyclicity that correlates with the North Atlantic ’Bond’ cooling cycles. The records enable the documentation of rapid changes of continental climates in the western Mediterranean borderlands that caused changes in river runoff and in oceanic productivity that were driven by rapid fluctuations of the Atlantic inflow into the Mediterranean Sea. The combined terrestrial-marine patterns demonstrate the close linking of western Mediterranean climate with the climatic evolution in the North Atlantic region.
TL;DR: In this paper, an inventory of unstable hillslopes, hydrogeological mapping and hydrochemical characteristics of natural spring waters were used to determine the long-term relationships between groundwater and gravitational instabilities in the Upper Tinee Valley (South-East French Alps).
Abstract: Inventory of unstable hillslopes, hydrogeological mapping and hydrochemical characteristics of natural spring waters were used to determine the long-term relationships between groundwater and gravitational instabilities in the Upper Tinee Valley (South-East French Alps). Water chemistry and flow records allow to propose a conceptual model of water flow within unstable rocky slopes and to back-calculate the volume of infiltrated water and the flow velocity in the aquifers for different deformation states of the slopes. An increase in infiltrated yield, flow velocity and porosity is observed and linked to collapsed and toppled structures in the upper parts of the hillslopes. In these areas, perched aquifers take place in the reworked media. When a large landslide occurs, it modifies the geometry of the slope and bypasses the perched flows down to the foot of the slope. With long-term continuous slope deformation, the associated effect between water flows and slope destabilization changes. In the fractured rock, the coupled effect corresponds to rising water pressures with limited volumes of infiltrated water; in the more fractured and permeable collapsed and toppled areas, the volumes of infiltrated water increase with a lower variation of water pressures.
TL;DR: The genus C. australis is a huge hunting hyena, a little bigger than the extant species Crocuta crocuta, the spotted hyena as mentioned in this paper, which was described from North America, Asia, Euro- pa and South Africa but it was recorded for the first time in central Africa.
Abstract: Late Miocene localities of Toros Menalla (Chad) have yielded many bones of fossil vertebrates with a lot of mammalian remains. Among the mammals, there are several Carnivora taxa, especially hyenids. The family Hyaenidae is very well developed during this period with classical bone crusher species but also with flesh eater taxa which are cal- led hunting hyenas. The genus Chasmaporthetes is one of these taxa. It was described from North America, Asia, Euro- pa and South Africa but it is recorded for the first time in central Africa. The Chadian specimens are close to the South African species C. australis (HENDEY, 1974) but differs through some morphological and metrical details. C. australis is a huge hunting hyena, a little bigger than the extant species Crocuta crocuta, the spotted hyena. An isolated premolar recorded in the locality Sahabi (Libya) belongs probably to the same group. The spreading of this large hunting species is probably correlated with the abundance of large ungulates in the local faunas.
TL;DR: The Tan-Lu Fault Zone (TLFZ) is a sinistral strike-slip fault that extends in a NE to NNE direction for more than 2,000 km in eastern China as mentioned in this paper.
Abstract: The Tan-Lu Fault zone (TLFZ), often considered as a major sinistral strike-slip fault, extends in a NE to NNE direction for more than 2,000 km in eastern China. A structural analysis of the southern segment of the TLFZ (STLFZ) and surrounding areas enables us to propose the following evolution of this area during the Mesozoic-Palaeocene. The mid-Triassic NNW-SSE and late Triassic SSW-NNE to SSE-NNW strikes of the stretching lineations in the Zhangbaling massif favour ductile shears in a Zhangbaling metamorphic formation located along a ~NNE-SSW orientated "Tan-Lu margin"; this margin connected two margin segments situated north of the Dabie and Sulu belts. During the Mid-Late Triassic, the continental crust of the South China block (SCB) has been obliquely subducted along this margin below the North China block (NCB). We confirm that the SCB continental crust has been sliced and thrust toward the SSE and propose that the ductile thrusts have merged into the decollements of the sedimentary cover of the platform, forming the thrust-and-fold belt which has acted as a sinistral compressional transfer zone between the Dabie and Sulu collision belts. Thrusting and folding, under a N to NNE compression, affecting Jurassic deposits north and south of the Dabie Shan, indicate that the SCB/NCB collision has continued during the Jurassic. We show that a strike-slip tectonic regime occurred at that time, east of the STLFZ, which initiated as a sinistral continental transform fault between the Dabie and Sulu collisional belts. Dikes and strike-slip faults confirm that a ~NW-SE stretching was active during the basal early Cretaceous (~135--130 Ma), in and around metamorphic domes intruded by plutons. We show that strike-slip faulting, under a NW-SE compression-NE-SW tension, has been active subsequently, until the Aptian-? Early Albian (110/105 Ma), possibly until the Cenomanian (~95 Ma); at that time, the TLFZ has acted as a sinistral continental trans-current fault zone in eastern Asia. Subsequently, normal faulting, under a WNW-ESE extension, indicates that the TLFZ has been a normal fault zone during the Campanian-Palaeocene (~83--55 Ma), possibly until the Early Ypresian (~50 Ma). Sinistral offsets, in the order of several 100 of kilometres, on both sides of the TLFZ have been proposed; the present study does not support such large offset magnitudes.
TL;DR: In this article, a vertebrate association consisting of chondrichtyan teeth and scales of the genus Phoebodus is documented for the first time from the Aragonian Pyrenees of Spain.
Abstract: Keywords .-L owervarcus Zone, Middle varcus Zone, Teeth, Scales, Squamation pattern, Phoebodus fastigatus. Abstract .-AL ower andbasal Middle varcus Zone (Givetian, Middle Devonian) vertebrate association consisting of chondrichtyan teeth and scales of the genus Phoebodus is documented for the first time from the Aragonian Pyrenees of Spain. This record suggests that different teeth morphologies that were previously treated as separate taxa could be grouped in Phoebodus fastigatus. Moreover, the teeth and scales association is in agreement with the previously recons- tructed squamation pattern of this taxon.
TL;DR: In this paper, the authors discuss ostracods and their environmental setting close to the Givetian/Frasnian boundary in the Puech de la Suque Global Stratotype Section and Point.
Abstract: This paper discusses ostracods and their environmental setting close to the Givetian/Frasnian boundary in the Puech de la Suque Global Stratotype Section and Point. The ostracod fauna belongs exclusively to the Eifelian mega-assemblage and is largely dominated by Podocopina instars. Consequently, the majority of the 33 species recognised and illustrated is described in open nomenclature. The abundance of instars also indicates that most of beds are related to storm deposition. The composition of the fauna suggests a regression in the late Givetian followed by a transgression at the beginning of the Frasnian. Only one ostracod assemblage collected in the upper part of the section indicates a deeper setting below the storm wave base. Eight taxa disappeared in two steps near the Givetian / Frasnian boundary, probably in relation to the Frasnes Event.
The sedimentological analysis confirms that the section is constituted principally of storm deposits and reveals in addition the presence of numerous reddish hardgrounds highlighting an important condensation of the sequence.
TL;DR: In this paper, the authors reinterpreted the deformations observed within Quaternary alluvium in the Champagne region (Paris Basin) as karst subsidence features or/and soil displacements due to periglacial processes.
Abstract: Deformations observed within Quaternary alluvium in the Champagne region (Paris Basin) comprise faults, folds and soft-sediment deformation structures. Their occurrence is linked to the subjacent weathered chalk. Previously interpreted as neotectonic features, the deformations are reinterpreted as karst subsidence features or/and soil displacements due to periglacial processes. Dissolution of chalk has produced superficial subsidence, explaining the geometry of some faults and their large offsets within surface deposits. The freezing-thawing cycles in the porous superficial layers have also favoured gravity instability and deformations, and this can explain local small-scale deformations but also mass movement (sliding). The seismotectonic hypothesis is rejected, because of the absence of regional faults able to generate such large co-seismic offsets. The fault directions and the apparent vertical offsets are not homogeneous at regional scale and they are often inconsistent with the Quaternary stress field. Moreover, the rooting of faults into the basement is not documented and therefore, the neotectonic origin is very doubtful.
TL;DR: The approche synthetique a pris en compte les donnees paleoenvironnementales obtenues par les etudes sedimentologiques et paleontologiques anterieures.
Abstract: Comme tous les elements du benthos, les ostreides sont particulierement sensibles aux variations de leur environnement. Lanalyse de leur distribution au sein de plus de dix coupes levees dans le Cenomanien de la bordure nord du Bassin aquitain a ainsi permis dapprehender la repartition paleoenvironnementale des neuf especes recensees. Chacun des paleoenvironnements represente par un facies a huitres particulier dans le Cenomanien charentais a ete positionne sur deux profils de depot, lun barre, lautre ouvert. Cette approche synthetique a pris en compte les donnees paleoenvironnementales obtenues par les etudes sedimentologiques et paleontologiques anterieures. Les domaines preferentiels de distribution des differentes huitres identifiees ont ete decrits au travers de sept parametres majeurs, a savoir loxygenation, lagitation, la salinite, la turbidite, la bathymetrie, la nature et linduration du substratum. Les huitres fossiles apparaissent ainsi comme dexcellents marqueurs paleoecologiques benthiques susceptibles dapporter, a limage de nombreux groupes dinvertebres, des criteres edaphiques et oceanographiques precis utiles dans les reconstitutions paleoenvironnementales du Mesozoique.
TL;DR: In this paper, the authors show that the reaction sequence of the last ice maximum is autocyclic, which is the same as that of the entire Cenozoic of a whole glaciation or of much shorter events.
Abstract: The maximum extent of a glaciation is often confused with the coldest part of a glaciation. During the Last Glaciation, the date of the Last Ice Maximum Extent (LIME) is diachronous very early at high latitudes close to the traditional date in the intertropical mountains. The classical Last Glacial Maximum (LGM) never corresponds to the LIME with the exception of intertropical regions. At middle and high latitudes advances of the LGM only correspond to surges of a lately thickened ice sheet. The same structure also exists at the level of the entire Cenozoic of a whole glaciation or of much shorter events as the scale of a whole Bond’s cycle. For each type of event the reactional sequence is autocyclic: a rapid warming ends a slowly cooling trend due to the higher susceptibility of lower latitudes to external forcing (orbital and solar activity). Moisture supply from an ice-free ocean is the sine qua non to build glaciers. The syngenetic extent of the cold desert toward the equator is the limiting factor for ice volume: when glaciations develop in intertropical mountains with the development of sea ice in the polar zones, glaciers recede by precipitation starvation with restricted sedimentation. During a glacial era in parallel with ice cap building, the progressive sea level lowering and the subsequent enhanced aridity counterbalance the generalization of a world-scale glaciation. This concept could be also valid for the Neoproterozoic Glacial era and should probably invalidate the snowball hypothesis.