transient features of the erosion of shales in the mackenzie basin canada evidences from boron isotopes abstract in order to refine our knowledge of the mechanisms that drive the weathering reactions and the rate at which elements are exported out of a shale basin we have analyzed the boron concentrations and isotopic compositions of 24 rivers contributing to the mackenzie basin canada boron has been chosen to conduct this study because of the relatively high sensitivity of its isotopic system to water rock interactions after examination of the chemical composition of the mackenzie river samples boron appears to be regulated in the largest part by reactions involving silicate rocks the other contributions of rainwaters and the dissolution of carbonate and evaporite rocks can locally control the b budget but they remain of second importance at the regional to continental scales it also appears that dissolved b in rivers is regulated by input of groundwaters the comparison between the isotopic composition of the b being exported by rivers soluble and particulates and of its bulk source indicates that it is behaving out of steady state in most of the mackenzie tributaries and particularly in rivers draining the plain a model of transport reaction is proposed in this study which demonstrates that b is controlled by rapid ion exchanges at the mineral water interface and by long term dissolution of shales the responses of the model to tested conditions reveal that the b isotopic ratio of river waters is highly sensitive to hydrological conditions and to changes of the weathering rate of shales of its partition coefficient with adsorbing surface and of the water velocity the departure of the b geochemical cycle from a steady state is interpreted as the record of changes in the weathering regime in the mackenzie basin the temporal evolution of the b cycle modeled here implies an increase of the weathering rate of shales in the mackenzie basin and or an increase of the partition coefficient between soluble b and adsorbing surfaces it also appears that these changes are consistent with timescales of the recent deglaciation of the basin this study demonstrates that the present b fluxes are actually responding to past changes of the water rock interactions and that the weathering history is a key parameter to interpret the modern geochemical fluxes this conclusion is valid for any other element that has similar chemical properties with solid surfaces

new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

early oligocene stratigraphic turnover on the west africa continental margin a signature of the tertiary greenhouse to icehouse transition the post rift stratigraphy on the west african margin is characterized by aggradation of a carbonate ramp during late cretaceous to eocene epochs and progradation of a terrigenous wedge from oligocene to the present such first order structure has been attributed in the past to geodynamic forcing however comparison of the stratigraphic record of the margin with eustasy 18o and 87sr 86sr curves shows a close temporal relationship with the tertiary climate cooling an increase of continental weathering and a long term lowering of sea level we suggest that the transition from low amplitude high frequency sea level changes during the greenhouse period to high amplitude high frequency sea level changes during the icehouse period may account for i the switch from an aggrading carbonate ramp to a prograding clastic wedge and ii the enhanced continental weathering and increased terrigenous influx to the margin

evidence for transform margin evolution from the ivory coast ghana continental margin the relative motions between lithospheric plates can be reduced to three major types convergence divergence and transform motion convergence leads to an active margin and eventual collision divergence results in the construction of a rifted passive margin transform motion generates a transform or sheared margin although passive margins have been extensively studied1 2 and many models have been proposed for their origin and subsequent evolution3 5 little is known about transform margins with the exception of a few studies of their morphologies6 7 shallow structures or crustal sections8 9 here we present the main conclusions derived from a recent study of the northern gulf of guinea margins particularly off the eastern ivory coast and ghana where the continental margin is one of the best preserved examples of an extinct transform margin10 12 our observations support a four stage model for transform margin evolution technically active transform contacts first between normal continental crusts and then between thinned margins induce characteristic structures such as pull apart grabens and shear folds the next stage in which thermal exchange between oceanic and continental lithos pheres controls a complex subsidence is followed by the transition to a true intra oceanic fracture zone

chemical multi isotopic li b sr u h o and thermal characterization of triassic formation waters from the paris basin this work reports chemical and isotope data and temperature estimates for seven water samples collected from triassic formations in the paris basin in france four samples were collected in the central part of the basin saline waters and three were collected at the edge of the basin near the recharge zone dilute waters the saline waters collected from the chaunoy and champotran boreholes have high salinities around 120 g l and very similar chemical and isotopic compositions the saline water sample from the la torche borehole has much higher salinity 168 g l and significantly different isotope characteristics the chemical geothermometers applied to these fluids from the centre of the basin give temperature values ranging between 80 and 100 c the fresh water samples collected at the edge of the basin have very different chemical and isotopic compositions these dilute water samples santenay and ch teauroux are shallow with colder temperatures of around 45 to 50 c the study of uranium activity ratios for these triassic formation waters allows us as a first approximation to estimate a mean apparent fluid circulation velocity of around 0 2 m yr which corresponds to a mean age slightly higher than 1 my for waters sampled in the chaunoy champotran and la torche fields in the centre of the basin the multi isotope characterization of triassic formation waters shows that our data are in agreement with literature values as concerns traditional isotope systematics delta18o deltad 87sr 86sr li and b isotope signatures in the centre of the paris basin are in a good agreement with a fluid signature derived mainly from water rock interactions involving clastic rocks with water essentially resulting from a seawater derived brine endmember diluted by meteoric waters the data reported in the present work for li and b isotopes could be used as a reference for future studies to characterize sandstone formation waters

crustal structure of the french guiana margin west equatorial atlantic summary geophysical data from the amazon cone experiment are used to determine the structure and evolution of the french guiana and northeast brazil continental margin and to better understand the origin and development of along margin segmentation a 427 km long combined multichannel reflection and wide angle refraction seismic profile acquired across the southern french guiana margin is interpreted where plate reconstructions suggest a rift type setting the resulting model shows a crustal structure in which 35 37 km thick pre rift continental crust is thinned by a factor of 6 4 over a distance of 70 km associated with continental breakup and the initiation and establishment of seafloor spreading the ocean continent boundary is a transition zone up to 45 km in width in which the two layered oceanic type crustal structure develops although relatively thin at 3 5 5 0 km such thin oceanic crust appears characteristic of the margin as a whole there is no evidence of rift related magmatism either as seaward dipping sequences in the reflection data or as a high velocity region in the lower crust in the p wave velocity model and as a such the margin is identified as non volcanic in type however there is also no evidence of the rotated fault block and graben structures characteristic of rifted margins consequently the thin oceanic crust the rapidity of continental crustal thinning and the absence of characteristic riftrelated structures leads to the conclusion that the southern french guiana margin has instead developed in an oblique rift setting in which transform motion also played a significant role in the evolution of the resulting crustal structure and along margin segmentation in structural style

groundwater surface waters interactions at slope and catchment scales implications for landsliding in clay rich slopes understanding water infiltration and transfer in soft clay shales slopes is an important scientific issue especially for landsliding geochemical investigations are carried out at the super sauze and draix laval landslides both developed in the callovo oxfordian black marls with the objective to define the origin of the groundwater in situ investigations soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems at super sauze the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations or at the landslide basement through a fault network such external origin of water is not observed at the local scale of the draix laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows hydrogeological conceptual models are proposed emphasizing the role of the interactions between local slope and regional catchment flow systems the observations suggest that this situation is a common case in the alpine area expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales

a three dimensional 3d structural model for an oil producing basin of the brazilian equatorial margin abstract hydrocarbon discoveries in regions such as the brazilian equatorial margin equatorial africa and french guiana have recently confirmed their importance as new exploration frontiers the mundau sub basin located on the brazilian equatorial margin is an oil and gas producing region with four producing fields in shallow water xareu atum espada e curima in order to understand the structural and seismic stratigraphic frameworks of an oil producing area of the brazilian equatorial margin this work addresses the 3d geometry and spatial distribution of main faults in the curima and espada fields the occurrence of hydrocarbons in the mundau sub basin is compared with fields in other parts of the brazilian equatorial basin and in equatorial africa data from 12 wells and a 3d post stack time migrated multichannel seismic volume are used to define nine 9 main seismic stratigraphic units the syn rift mundau formation units 1 2 3 and 4 the transitional paracuru formation unit 5 and the drift ubarana uruburetama and itapage members units 6 and 7 tibau and guamare formations units 8 and 9 the study area is dominated by nw se planar normal faults basinward dipping that formed multiple half grabens and tilted blocks with small anticlines and synclines genetically related to a transtensional system three types of plays are recognised in the mundau sub basins structural combined structural stratigraphic and stratigraphic turbiditic in the eastern part of the region where the basement is shallow no oil was found conversely oil was discovered in an anticlinal trap formed on a hanging wall block analogous to fields in cote d ivoire ghana transform margin this work shows that combined traps on footwall blocks are successful plays near the shelf break of the mundau sub basin in similarity with the espoir and baobab fields in ivory coast basin furthermore turbiditic reservoirs in drift units are analogous to the stabroek block in guyana and prospects in the gulf of guinea the structural and petroleum play analyses in this work are therefore crucial to understand the multiple geological processes leading to the trapping of hydrocarbons in the larger equatorial atlantic ocean

crustal structure beneath the southern grand banks seismic refraction results and their implications a seismic refraction profile was shot on the southern grand banks using large air gun sources and an array of ocean bottom seismograph receivers a sediment column 1 2 km thick directly overlies paleozoic basement with velocity structure similar to that of the meguma zone of nova scotia the main crustal layer is 27 km thick with seismic velocity of 6 3 km s increasing to about 6 5 km s in the lowest few kilometres complexity is apparent in the crust mantle transition around 32 km depth comparison with deep multichannel reflection data suggests that the increased velocity in the lower part of the crust may be associated with a reflective zone and shows the mohorovicic discontinuity to be delineated by a well defined reflection the absence of a major lower crustal layer of intermediate velocity 7 km s is consistent with observations elsewhere in the region

boron sources and transport mechanisms in river waters collected from southwestern taiwan isotopic evidence abstract boron b isotopes are sensitive tracers for constraining water rock interactions and pollution sources in river systems in this study we analyzed 11b using multi collector inductive coupled plasma mass spectrometry in addition to major and trace elements to delineate b sources and transport mechanisms in two river catchments the largest kao ping river and the most polluted erren river in southwestern taiwan dissolved 11b values vary more than 35 in kao ping river but keep relatively constant in erren river 12 2 26 7 four major b sources identified in these river waters are cyclic seasalt water rock interaction geothermal water and anthropogenic inputs all specimens collected near the estuaries were influenced strongly by the seawater b 4 5 mg l and 11b 39 5 the erren river results provide unique information on b and 11b compositions in anthropogenic sources in particular for fertilizer and hog manure characterized with high b up to 3 43 mg l and intermediate 11b average 13 the low 11b values in 2006 kao ping river are attributed to contributions from local geothermal inputs average 2 5 ppm and 2 prior to massive landslides caused by 2009 morakot typhoon mass balance calculations suggest that major contribution of b in river waters was derived from silicate weathering characterized by low b and intermediate 11b contributed approximately 49 97 in 2010 kao ping river the detected changes of 11b w rock reaches a maximum variation of 18 during chemical weathering in catchment and highlights the importance of water rock interaction enhancement after major climatic events

transform marginal plateaus abstract numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions due to their proximity to continents they have been frequently labelled marginal plateaus although this term has not been clearly defined or associated with a specific geology or geodynamic process until now these elevations have been interpreted as submerged thinned continental fragments detached from continents basaltic buildups formed by hotspots volcanic margins or oceanic plateaus many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages we propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting transform marginal plateaus tmps based on a compilation of 20 tmps around the world we show that most of them have a polyphased history and have undergone at least one major volcanic phase our review highlights in particular a hitherto unrecognized close link between hotspots volcanic activity and transform margins we also propose that due to their polyphased history tmps may contain several successive basins and overlooked long lived sedimentary archives we finally highlight that because these tmps were transform plate boundaries perpendicular or oblique to surrounding rifts many of them were close to last contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents therefore we discuss broader scientific issues such as the interest of tmps in recording and studying the onset and variations of oceanic currents or past biodiversity growth bio connectivity and lineage evolution

sinkhole monitoring and early warning an experimental and successful gb insar application abstract sinkholes represent a natural risk that may hit catastrophically without clearly detectible precursors however they are often overlooked by people and administrators therefore sinkhole monitoring and associated early warnings constitute important research topics but currently only a few papers about sinkhole prediction can be found in this paper an experience of sinkhole monitoring and early warning with gb insar is described the latter is a highly precise instrument that is able to produce displacement maps with metric spatial resolution the described activities were carried out on elba island central italy where karstified limestone set off the occurrence of nine sinkholes since 2008 all within less than 3000 m2 causing major damage to an important road and many indirect losses in 1 year of monitoring two deforming areas were detected and the point where a sinkhole was about to propagate to the street level was predicted thus permitting the preventive closure of the road the deformation area was larger than the hole generated by the sinkhole thus showing a subsidence that continued for a prolonged time even after the cavity was filled up the occurrence of a 1 5 m wide sinkhole undetected by the gb insar also showed the lower detection limit of the instrument

hydrogeological assessment of a deep seated coastal landslide based on a multi disciplinary approach abstract this study focuses on the understanding of the hydrogeological functioning of a complex landslide affecting the coastal municipality of villerville normandy france we wish to provide a conceptual model of functioning using a multi disciplinary approach a set of geomorphological geological and hydrological data as well as in situ observations were first used to understand the main landslides processes new acquisitions were then carried out to strengthen our hypotheses thanks to passive geophysics sp and the characterization of physicochemical parameters of surface waters the joint analysis of former ert surveys and sp results is of significant interest for correlating hydrokinetic information measured at the surface with resistivity tomograms which provide internal information this study highlights 1 a division of the behaviour into three parts from east to west 2 variable internal dynamics highlighted by geology and electric fields 3 a preferential discharge of the continental water table upstream of the central area of the landslide this work tends to demonstrate that on the basis of initial in situ knowledge available on many study areas the understanding of the hydrogeological functioning can be substantially improved by implementing light and inexpensive surveys also suitable for large and complex landslides

timing of post depositional events in the burano formation of the secchia valley upper triassic northern apennines clues from gypsum anhydrite transitions and carbonate metasomatism the burano evaporite formation from the secchia river valley is an up to 2200 m thick sequence composed of meter to decameter scale interbeds of gypsum anhydrite and dolostones with minor halite the deposit has been affected by a complex array of post depositional modifications thermal events and large scale evaporite dissolution preventing a satisfactory reconstruction of the environment of deposition the modifications are intense because these rocks were the main decollement horizon during the formation of the northern apennines chain the carbonate rocks are massive and or laminated dolomitic mudstone wackestone oolitic packstones and oolitic peloidal bioclastic grainstones which commonly appear as mega boudins within a sulfate groundmass the dolostones to 3 7 to 3 0 pdb have been affected by mg metasomatic replacement by magnesite to 2 6 to 1 4 pdb induced by hydrothermal circulation total homogenization temperatures of fluid inclusions in hydrothermal magnesite range from 275 to 310 c the anhydrite rocks are characterized by flow structures such as centimeter scale pseudo lamination composed of aligned prismatic crystals with transposed isoclinal folds outlined by dolostones fragments homogenization temperatures of fluid inclusions in authigenic quartz incorporated into sulfate rocks range from 260 to 305 c emilia and from 230 to 315 c tuscany the gypsum rocks are composed of xenotopic irregular cloudy crystals and more rarely by centimeter scale idiotopic crystals showing the same structures as the anhydrite rocks the origin of the gypsum rocks is due to late alteration of anhydrite by migration of sharp hydration fronts the hydration is a two step process and is revealed by the presence in the gypsum rocks of corroded anhydrite micro relics and authigenic quartz crystals which include anhydrite the role of the burano evaporites during the apennines tectogenesis can be depicted as follows a prevalent deposition of gypsum in the upper triassic b gypsum dehydration at burial conditions to form anhydrite cretaceous c syn tectonic flow of anhydrite rocks brecciation of dolostones syn tectonic growth stage of quartz euhedra at deep burial conditions possibly related to the development of the oligocene miocene greenschist facies apuane metamorphic complex d hydrothermal deposition of sparry magnesite and partial mg metasomatic replacement of dolostones by magnesite e sub surface dissolution of halite to form thick matrix supported residual caprock like anhydrite mega breccias f complete gypsification of anhydrite at sub surface conditions and g evaporite dissolution at surface exposure producing dolostone breccias with partial calcitization and removal of most clasts calcare cavernoso

development of the continent ocean transform boundary of the southern exmouth plateau a two stage model is proposed to explain the principal tectonic and magmatic features observed in multichannel seismic reflection and refraction data across the southern transform margin of the exmouth plateau northwestern australia 1 the rifting stage in which detachment surfaces developed under conditions of extension at a high angle to the future transform and were later sheared by right lateral strike slip faulting final transform rupture was attended by large fault block rotation and mafic intrusions in conditions of pure shear 2 in the drifting stage as the oceanic ridge abutted the continent the continental rim was underplated at this location resulting in a 10 km thick 7 3 km s 3 g cm3 layer resulting in a permanent isostatic uplift of the crust and tilting of synrift sedimentary deposits this wedge extends laterally forming a thickened oceanic layer 3 transient heating of the continental lithosphere induced thermal uplift and erosion of up to 3 5 km of sedimentary units over a 50 km distance from the continent ocean contact

thermal uplift and erosion across the continent ocean transform boundary of the southern exmouth plateau thermal evolution of the continental lithosphere at a continent ocean transform margin is examined using a two dimensional heat conduction model all heating is assumed to result from the emplacement of new oceanic ridge against the continent the assumed initial continental temperature gradient is probably best applied to regions having experienced finite duration periods of rifting lasting tens of millions of years a deep seismic reflection profile across the southern paleo transform margin of the exmouth plateau northwest australia tests the predictions of the model using this reflection profile it is estimated that up to 3 5 km of sediments have been eroded from the continental rim diminishing to almost no erosion at 60 km from the continent ocean transform boundary this trend and these values for erosion can be matched approximately using the model under the condition of local isostasy a finite difference scheme is employed where the surface elevation is the result of the competing 1 thermal uplift up 2 surficial erosion down and 3 local isostatic rebound up in response to the erosion the model predicts that most of the erosion ceases by 40 ma after ridge emplacement and that of the order of 1000 km3 eroded sediments are shed for every 10 km of transform length

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

do fracture zones define continental margin segmentation evidence from the french guiana margin abstract plate reconstructions suggest that the french guiana margin in the west equatorial atlantic is a highly segmented margin with both rift and transform style features we describe here the results of modelling coincident multi channel and wide angle seismic gravity and magnetic data acquired along two transects of this margin the resulting models not only highlight the degree of structural segmentation but also demonstrate the effect of trans tension on margin evolution as a whole the margin is characterised by 35 37 km thick pre rift continental crust which is separated from unusually thin oceanic crust 3 4 km by thinned continental and or transitional regions to the north the margin exhibits a 320 km wide zone of thinned continental crust adjacent to a narrow ocean continent transition and is interpreted as a transform margin where the wide zone of thinned crust is a result of profile orientation being highly oblique to the direction of rifting approximately 240 km to the south the margin is characterised by a 70 km wide zone of thinned continental crust which is wider than typical for transform and narrower than typical for rifted margins this crustal structure is interpreted to reflect a leaky transform formed by trans tensional extension these observations suggest that fracture zone influenced geometry of equatorial atlantic rifting did not produce a well defined margin crustal structure but instead resulted in margin segments which display characteristics of both rift and transform tectonic processes the associated abundance of fracture zones has likely also affected the post rift evolution of the margin and provided topographic basement highs which acted as sediment dams to the northwards flux of sediment from the amazon

evidence of deep water inflow in a tectonic window of the northern apennines italy water samples from the river network and from some shallow and brackish springs located in a tectonic window of the northern apennines of italy were studied in the frame of a comprehensive hydrogeological investigation in order to better understand the origin and the mixing processes between the two water types noticed also in previous studies ca hco3 and na cl a sampling campaign covering the drought period during year 2010 was planned to gather electric conductivity temperature and redox potential data along the river network and on groundwater occurrences located inside the tectonic structure additionally eight water samples were collected for hydrochemical major anions and cations na k ca2 mg2 hco3 cl so4 2 and trace ion btot and isotopic 18o 2h 3h analyses and compared with other eighteen samples from shallow and brackish springs collected near the study site during the period 2005 2012 moreover river discharge and water balance estimations were carried out results confirmed the presence of old na cl water with salinity progressively increasing up to 5 5 g l 1 at the northern termination of the tectonic window these values are in agreement with the ions contents of the most mineralized spring macognano spring salinity of 7 6 g l 1 which has been considered as having the deepest and longest flow path stable isotopes and trace ions contents are consistent with rainfall and snowmelt water mixed with brines associated with a hydrocarbon reservoir hosted at depth considering as end member the more mineralized na cl water a cumulate inflow in the range of 12 9 5 9 l s 1 has been estimated this aliquot is released into the river network with different mixing proportions by the groundwater occurrences discharging from the autochthonous flysch unit

a conceptual hydrogeological model of ophiolitic aquifers serpentinised peridotite the test example of mt prinzera northern italy the main aim of this study is the experimental analysis of the hydrogeological behaviour of the mt prinzera ultramafic massif in the northern apennines italy the analyzed multidisciplinary database has been acquired through i geologic and structural survey ii geomorphologic survey iii hydrogeological monitoring iv physico chemical analyses v isotopic analyses the ultramafic medium is made of several lithological units tectonically overlapped between them a low permeability discontinuous unit has been identified this unit behaves as an aquitard and causes a perched groundwater to temporary flow within the upper medium close to the surface this perched groundwater flows out along several structurally controlled depressions and then several high altitude temporary springs can be observed during recharge together with several perennial basal i e low altitude springs caused by the compartmentalisation of the system due to high angle tectonic discontinuities

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

early paleozoic transform margin structure beneath the mississippi coastal plain southeast united states a geophysical transect across the central gulf of mexico coastal plain shows that the early paleozoic continental margin of southern laurentia is preserved in a nearly pristine state beneath younger strata that were emplaced during the late paleozoic ouachita orogeny and formation of the modern gulf of mexico coastal plain the thickness of the crystalline crust decreases abruptly across the margin over a distance of 50 km from 35 km beneath the black warrior foreland basin to 10 km beneath the ouachita fold and thrust belt this abrupt decrease in crustal thickness is similar to modern transform margins but very different from most rifted margins which display much more gradual transitions in crustal thickness the geophysical data indicate an absence of synrift intrusive and volcanic rocks underplated mafic rocks at the base of the crust and abnormally thick oceanic crust adjacent to the margin the lack of these features is also characteristic of modern transform margins combined with transects across the margin farther west the data confirm previous suggestions that the central gulf of mexico coastal plain overlies an 800 km long transform segment of the late proterozoic early paleozoic southern laurentian continental margin that extends continuously from western arkansas to southeast alabama

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

structure and tectonics of the agulhas falkland fracture zone abstract the 1200 km long agulhas falkland transform developed during the early cretaceous break up of west gondwanaland on the african plate the continent bordering the agulhas fracture zone extends between the agulhas bank and the south tugela reentrant it is divided into four distinct parts mallory trough segment i diaz ridge segment ii east london segment iii and durban segment iv from southwest to northeast each segment differs from the ohters in its physiography and in the nature of the continent ocean crustal boundary in segment i a wedge like eastward narrowing deep water basin separates the steep continental slope from a marginal fracture ridge of probable volcanic origin along the transform fault trace along segment ii the south african continental slope is deeply embayed and a great thickness of sedimentary strata has been ponded behind a buried ridge along the northern side of the fracture zone trace above a probable fragment of oceanic crust representing a northerly extension of the jurassic falkland plateau basin in segment iii the continental margin is steep especially along the middle slope it lies directly along the transform trace but conspicuously rugged along the continental slope due to the effects of submarine canyoning and sediment slumping in segment iv the continent ocean boundary also lies directly along the transform fault trace and the margin shows evidence of seaward tilting above landward dipping faults along the middle or lower slope the segmentation is inherited from jurassic structural fabrics formed prior to early cretaceous transform motion when tectonic rotation of microplates caused rifting and partial oceanization along the future agulhas falkland megafault trajectory

evaporite karst and sinkholes a synthesis on the case of camaiore italy in 1995 a sinkhole suddenly formed at camaiore tuscany italy causing destruction or heavy damages to several houses and resulting in the evacuation of many people to understand the causes for the formation and evolution of the collapse surface and underground geologic features were investigated and reconstructed on the basis of geologic and geognostic surveys the sinkhole area is underlain by thick alluvial deposits that cover a bedrock consisting of the calcare cavernoso formation this formation results from hydration and dissolution of triassic evaporites and has a characteristic spongy and vacuolate texture the bedrock contains karst cavities generally filled by breccia and or alluvial materials thus the sinkhole disaster could be ascribed to deep collapse of a cave in the bedrock and might be considered a distant effect of ancient karst phenomena in evaporites

crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin implications for thermal exchanges across the palaeotransform boundary summary crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin is determined by 2 d modelling of wide angle seismic data and gravity data the resulting models together with geological data recently collected by drilling on the margin are compared with available thermomechanical models of transform margins in particular we test the predicted effects on the transform margin crust of continental heating by the adjacent oceanic lithosphere these effects include i ductile flow of the lower continental crust either parallel to the transform direction or perpendicular to it from the continent towards the ocean and ii thermal uplift of the transform margin in the region of the cote d ivoire ghana transform margin the seismic and gravity data indicate that the continental crust remains uniform in thickness as the continent ocean boundary is approached the interpreted models lack a transitional domain between continental and oceanic crusts and abnormally thin oceanic crust is found along the margin these results exclude large scale ductile flow of lower continental crust during the margin formation the geological data are moreover not consistent with thermal uplift of the margin during the period of contact between the transform margin and the spreading centre our geophysical and geological data thus infer only moderate heating of the transform continental margin by the adjacent oceanic lithosphere moderate heating of the cote d ivoire ghana transform margin during margin formation implies that the thermal exchange between the transform margin and the adjacent spreading centre were lower than predicted by available thermal models two main factors may have contributed to reduce thermal exchanges across the continent ocean boundary the first factor is that the oceanic edge may have been colder than assumed by thermal models an abnormally cold spreading axis along the transform margin when the oceanic crust was emplaced is supported by the atypical structure of the oceanic crust along the cote d ivoire ghana transform margin the oceanic crustal structure is similar to that found along oceanic fracture zones where oceanic crust is also emplaced near a ridge transform intersection in both cases abnormally low thermal gradients at the spreading centre along the transform margin may be explained by the cumulative effect of i a cold edge effect of the adjacent continental lithosphere ii accretion at the end of a ridge segment away from the main magma supply point along the spreading axis and iii an efficient upward cooling of the oceanic lithosphere owing to deep hydrothermal circulation within the faulted lithosphere the second factor causing moderate thermal exchanges is the possibility of large amounts of water in oceanic lithospheric faults which reduces the lateral thermal conduction in the lithosphere since water is much less conductive than rock during the margin formation the oceanic edge thus seems to have acted as a thermal buffer between the cold continental margin and the hot spreading centre we propose that this thermal buffer hypothesis may be generalized to most transform margins implying a lower amount of continental heating than assumed by the available thermomechanical models

contribution of water geochemistry and isotopes δ18o δ2h 3h 87sr 86sr and δ11b to the study of groundwater flow properties and underlying bedrock structures of a deep landslide a comprehensive understanding of bedrock lithology and groundwater circulation is necessary to identify areas prone to landslide initiation and reactivation this necessity is particularly required in the case of outcroppings of weak rocks such as gypsum that due to their high solubility and low mechanical strength can promote slope deformation with the development of caves and collapses in the upper secchia river valley where gypsum outcrops extensively and is covered by landslide deposits an accurate identification of the gypsum outcrops and their distribution is needed to reduce the damage to urbanized slopes in this paper a hydrologic and geochemical approach is used in the montecagno landslide to identify the origin flow paths and transit time of groundwater circulating inside the landslide body and to identify gypsum deposits and their distribution in the bedrock the results of groundwater level monitoring 18o 2h and 3h isotope analyses and flowpc modelling suggest a local and recent origin of the groundwater hosted in shallow flow paths inside the landslide chemical and isotope 87sr 86sr 11b analyses offer evidence of the presence inside the landslide of small blocks of gypsum that due to their dimensions probably have a minor influence on landslide stability this research demonstrates that the methodology used can provide satisfactory information about bedrock structures and their hydrological aspects

south atlantic fits and intraplate boundaries in africa and south america abstract the misfit problems raised by the pre drift reconstructions of the south and equatorial atlantic compel us to resort to intraplate deformations it is shown that acceptable deformations of the african plate in line with the benue trough and the transafrican rifts and shear zones provide a far from satisfactory solution to the geometrical misfit problems in the south atlantic these problems can instead be alleviated by considering a degree of deformation of the south american plate along an intraplate boundary in line with the parana province the rio grande rise and the walvis ridge in spite of the scarcity of field observations in this area of south america we show that such a deformation cannot be ruled out but it will have to be associated with deformations in the equatorial atlantic and in other areas of the african and south american plates

slope instabilities from echo character mapping along the french guiana transform margin and demerara abyssal plain the french guiana transform margin and demerara abyssal plain have been recently surveyed in the framework of the extraplac french program of extension of the continental shelf guyaplac survey ifremer ifp shom ipev based on the interpretation of some of the data collected during the guyaplac survey simrad em12 multibeam bathymetric data backscatter imagery and 3 5 khz profiles the area can be divided into three morphostructural domains 1 the western guiana margin including a part of the demerara plateau an important bathymetric relief prolonging the continental platform off guiana and surinam this domain is bounded by 1a the nw se trending northern border of the demerara plateau which appears quite steep and corresponds to a transform segment of the margin 1b the n s eastern border of the demerara plateau which corresponds to a divergent segment of the margin the demerara plateau shows a segmented morphology lowslope gradients and a very rough surface ripples perpendicular to the slope direction nnw sse structural steps seem to correspond to collapses of 100 km long blocs towards the east slumps initiate along these directions the observed rough bathymetry seems to be related to creeping processes at a greater scale seismic data this part of the margin has been totally destabilized numerous imbricate transparent masses rooted at about 0 5 s t w t t belowseafloor thenw se trending northern border of the demerara plateau corresponds to a cliff like continental slope probably slightly smoother than other transform margins ghana co te d ivoire margin the n s eastern border of demerara plateau is characterized by numerous small scale imbricate slumps some of these failures seem to be emplaced in the prolongation of the nnw sse structural steps identified on the demerara plateau 2 the eastern guiana margin corresponds to a nw se oriented gullied transform margin segment the associated continental slope is very steep and characterized by numerous imbricate slumps and related debris lows some undulated masses probably corresponding to creeping sediments or to older mass wasting events are still imprinted on bathymetry this transform margin segment is nearly entirely destabilized and eroded 3 the demerara abyssal plain this domain is characterized eastwards by channels belonging to the amazon turbidite system and westwards at the foot of demerara continental slope by sediment waves probably created by contour currents to conclude it seems that there is a strong relationship between the structure transform and divergent segments and the emplacement of recurrent slope instabilities these are probably related to the steepness of the slopes but also to subsidence histories generating in some cases huge deep seated collapses of the whole margin fluid ascents are common everywhere in the area probably enhancing slope instability their origin is not constrained but the black shales or cretaceous organic rich layers could be good candidates

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

sandwaves and other large scale bedforms as indicators of non tidal surge currents in the skagerrak off northern denmark abstract results from side scan sonar surveys made at two sites in the skagerrak off hanstholm and hirtshals show that transverse and longitudinal current induced bedforms are widespread in both areas down to a water depth of 70 m a maximum sandwave height of 7 m is found off hanstholm comet marks have a maximum length of near 50 m off hanstholm wave action markedly affects the seabed at depths of less than 25 m this can cause significant deformation of current induced bedforms the bedforms are not relict structures they demonstrate that maximum bottom flow velocities associated with the jutland current can locally reach a magnitude of at least 70 100 cm s bedform configuration and sediment distribution off hansholm indicate continuation of the jutland current bottom flow axis in a northeast direction diverging from the coastline this may favour sand transport in greater water depths than is usually found elsewhere in the area as an exception at one occasion at the site off hirtshals megaripples were found to have southwest facing leeside slopes and small comet marks were also directed towards the southwest this must have resulted from exceptional outflow conditions with bottom current speed in excess of 60 cm s

exploration for cretaceous stratigraphic traps in the gulf of guinea west africa and the discovery of the jubilee field a play opening discovery in the tano basin offshore ghana

structure and evolution of the demerara plateau offshore french guiana rifting tectonic inversion and post rift tilting at transform divergent margins intersection we present the structure and evolution of the eastern part of the demerara plateau offshore french guiana from the analysis of geophysical data collected during guyaplac cruise this area is located at the intersection of a transform segment and a divergent segment of a continental margin related to the early cretaceous opening of the equatorial atlantic the main structures are nne ssw to nnw sse trending normal faults on the eastern edge of the plateau and wnw ese to nw se trending acoustic basement ridges on its northern edge when replaced in their albian position these structures appear to be parallel to the coeval oceanic accretion axis and transform faults respectively the most striking structures are related to a post rift but syn transform tectonic inversion producing e w to wnw ese trending folds sealed by a regional unconformity this shortening can not be related to ridge push but is probably related to a plate kinematic change 105 my ago that modified the deformation in the vicinity of the transform fault late post rift evolution also includes a significant tertiary oceanward tilt of the edge of the demerara plateau the driving mechanism of this late tilt is unclear but may be related to a lithospheric flexure resulting from the loading of the abyssal plain by the orinoco and amazon deep sea fans

identifying the origin of groundwater and ﬂow processes in complex landslides affecting black marls insights from a hydrochemical survey the super sauze mudslide is a persistently active slow moving landslide occurring in the black marl outcrops of the french south alps it has been intensively studied since the early 1990s geotechnical geomorphological geophysical and hydrological investigations have led to a better understanding of the processes governing the landslide motion water ows inside the system have been proven to have a major impact to look closer at the processes involved and especially to gain a better idea of the origin and pathways of the waters a hydrochemical study was carried out from may 2003 to may 2004 the groundwater was sampled during ve eld campaigns spread uniformly over the year groundwater from a network of boreholes was collected as well as spring waters from the fractured bedrock in situ black marl and from the moraine aquifer above the landslide results showed that the groundwater chemistry could not be fully explained by rainfall recharge or simple water matrix equilibrium a contribution of saline waters coming from the bottom of a thrust sheet overhanging the landslide was required to get the observed high mineralization on a ow line the hydrochemical evolution was related to both soil matrix equilibrium and deep water sources coming up to the surface by means of major faults the bedding planes and the schistosity hydrochemical anomalies made it possible to point out such contributions locally it was shown that water chemistry and landslide activity were closely related this hydrochemical investigation also enabled us to better de ne the hydrosystem limits copyright 2006 john wiley sons ltd

the utilization of boron and strontium isotopes for the assessment of boron contamination of the cecina river alluvial aquifer central western tuscany italy abstract the groundwater b concentration in the alluvial aquifer of the upper cecina river basin in tuscany italy often exceeds the limit of 1 mg l 1 set by the european union for drinking water on the basis of hydrogeological and geochemical observations the main source of the b contamination of groundwater has been attributed to past releases into streams of exhausted b rich geothermal waters and or mud derived from boric acid manufacturing in larderello the releases were discontinued 25 30 years ago this study confirms that the b dissolved in groundwater is anthropogenic in fact the 11b values of groundwater b match the range 12 2 to 13 3 of the turkish b mineral colemanite processed in boric acid manufacturing in the course of which no significant isotopic effects have been observed this isotopic tracing of the cecina alluvial aquifer occurs just below the confluence of the possera creek which carries the b releases from larderello strontium isotope ratios support this conclusion at about 18 km from the possera creek confluence the groundwater 11b drops to much more negative values 22 to 27 which are believed to be produced by adsorption desorption interactions between dissolved b and the aquifer matrix the 11b of b fixed in well bottom sediments shows a similar variation at present desorption is prevailing over adsorption because the releases of b rich water have ceased a theoretical model is suggested to explain the isotopic trends observed thus b isotopes appear to be a powerful tool for identifying the origin of b contamination in natural waters although isotopic effects associated with adsorption desorption processes may complicate the picture to some extent

seismic evidence of current controlled sedimentation in the belgica mound province upper porcupine slope southwest of ireland the porcupine seabight is an embayment that takes a particular position in the ne atlantic slope sonographs a few current measurements and hydrodynamic modelling suggest the presence of a strong northward flowing bottom current locally enhanced by internal tides affecting the eastern slope of the seabight at this location a province of coral banks is described expressed as mounds lined up in along slope trending ridges in this paper very high resolution single channel seismic profiles are used to evaluate to what extent the bottom currents influenced the deposition of the sediments surrounding the mounds throughout the late cenozoic three seismostratigraphic units p1 p2 and p3 can be identified in the belgica mound area separated by two margin wide discontinuities rd2 and rd1 within unit p1 probably early to middle miocene upslope migrating sediment waves are observed suggesting strong bottom currents were already active in the miocene after an early middle miocene erosion event represented by reflector rd2 an acoustically transparent layer unit p2 of as yet unknown lithology was deposited in the studied area a second margin wide erosional event marked by the late pliocene rd1 reflector removed a large part of unit p2 and has cut deeply into unit p1 subsequently the belgica mounds were constructed spectacularly fast on topographic irregularities on the rd1 paleobathymetry the onlap within the quaternary unit p3 which surrounds these mounds suggests that the mounds were already present before the deposition of p3 and were big enough to affect the intensity of the currents around them furthermore the channels and the mounds are together with the complex oceanographic regime the key morphological elements responsible for the shaping of a contourite system in the belgica mound area during the quaternary one drift body is formed by an inferred south north directed current with a drift levee and associated channel located on its western side between this channel and the mounds large scale sediment waves suggest an intensified bottom current running along the foot of the steep flanks of the mounds the belgica mounds are embedded in another drift body here an interaction of bottom and turbidity currents is suggested creating short turbidite channels at the southern and northern flanks of the mounds locally small confined drifts can be observed where unit p3 is deposited in a narrow passage made by the paleobathymetry of rd1 and the mounds

geomorphology of the tertiary gypsum formations in the ebro depression spain abstract this paper reviews the current knowledge of the mainly karstic geomorphological features developed in the evaporitic formations of the ebro depression northern spain special emphasis is given to the recently published and unpublished scientific advances the gypsum formations of tertiary age have an extensive outcrop area within the ebro depression here their morphogenesis is controlled mainly by processes of surface and subsurface dissolution acting on the gypsum outstanding landforms in the gypsum terrain include saline lakes developed in flat bottom dolines saladas other characteristic morphologies include karren and gypsum domes which occur on a decimetre scale where the gypsum is covered by quaternary alluvial deposits the karstification processes are especially intense and cause subsidence phenomena karstic subsidence affects stream terraces mantled pediments and infilled valleys which in the region are called vales dissolution induced synsedimentary subsidence has produced interesting geological features which include significant thickening and deformation of the alluvial deposits in contrast to the rapid removal of gypsum by dissolution the amount of gypsum removed by erosion is low water erosion studies carried out on gypsiferous slopes of the ebro depression indicate that the sediment yield ranges from 0 59 to 7 82 t ha year this low yield results from the high infiltration capacity of the soils subsidence caused by gypsum dissolution has important socio economic consequences in the ebro depression the active alluvial karstification of the gypsum causes numerous sinkholes that are harmful to linear structures roads railway lines irrigation channels buildings and agricultural land unforeseen catastrophic subsidence also puts human lives at risk the benefits of such terrains include thickened alluvial deposits which act as valuable water reservoirs and which form excellent sources of aggregates fluvial valleys in this gypsiferous terrain commonly show an asymmetrical geometry with prominent gypsum scarps at one side these gypsum scarps are affected by numerous landslides these slope movements are hazardous may dam rivers and cause flooding of the alluvial plains

in situ geophysical and hydro geochemical monitoring to infer landslide dynamics pegairolles de l escalette landslide france the pegairolles de l escalette landslide is located in the central part of the languedoc region southern france it corresponds to a deep seated landslide 50 m of thickness with extremely slow slip displacement 3 4 mm year in this area the current landslide activity is associated with intense precipitation events 300 500 mm in a few days and the related dissolution of triassic evaporite layers at depth considering a relatively simple geological context and a landslide mainly controlled by slope hydrogeology this site constitutes a natural observatory to study the impact of large rain events on slope kinematics this work is based on complete and original instrumentation deployed in two nearby boreholes since 2012 the landslide is investigated down to 65 m depth by two in situ permanent observatories for geophysical electrical resistivity and deformation metric sensor spacing daily and seasonal data acquisition and hydrogeochemical monitoring pressure ph temperature electrical conductivity fluid sampling 4 depths monthly data acquisition the data recorded during the five years of investigations help us to characterize the active slip zones in the underground as well as the seasonal dynamics of the different hydrogeological units within the slope we also observe a heavy rainfall event characterized by both electrical resistivity and geochemical changes down hole which suggest different time responses of the system to the meteorological solicitations these first results point out the relevance of the downhole monitoring to progress towards a better understanding of internal landslide processes in relation to climate forcing

geochemical and boron oxygen and hydrogen isotopic constraints on the origin of salinity in groundwaters from the crystalline basement of the alpine foreland abstract the b isotopic composition in combination with o and h isotopes and hydrochemical tracers is utilized to constrain the evolution of basement hosted groundwaters via water rock interactions and fluid infiltration from external sedimentary reservoirs two distinct groundwater types have been identified in the central european crystalline basement n switzerland sw germany 1 fresh groundwaters characterized by low values of 11b 3 5 to 0 6 18o 12 0 to 10 0 and d 86 8 to 71 9 and 2 brackish groundwaters with distinctly heavier b o and h isotopic compositions 11b 6 4 to 17 6 18o 9 4 to 5 6 d 67 6 to 60 8 fresh groundwaters show a systematic decrease in 11b related to an increase in b concentrations and degree of total mineralization along the pathway of groundwater migration which can only be interpreted in terms of leaching of crystalline host rocks a 11b value of 3 3 is inferred for the crustal b source mainly hercynian granites involved in the leaching process in agreement with the known 11b range of granitic rocks the evolution of brackish groundwaters derived from crystalline basement reservoirs with little water circulation is more complex as indicated by b o h stable isotope and hydrochemical e g b cl na cl and br cl constraints brackish groundwaters from the study area are influenced by admixture of sediment derived fluids which infiltrated from late paleozoic permo carboniferous and early mesozoic lower triassic sedimentary strata the data presented show that b isotopes are sensitive to mixing processes of fluids derived from different crustal reservoirs and hence may be utilized as a tracer for constraining the internal autochthonous vs external allochthonous origin of salinity in basement hosted groundwaters

demerara plateau the structure and evolution of a transform passive margin summary the amazon cone experiment acquired two transects profile sd a across the demerara plateau part of the french guiana northeast brazil continental margin to better understand rift and transform style margin evolution profile a images an intermediate type margin formed as a result of trans tensional extension in this paper we describe the modelling of wide angle and multichannel seismic and gravity data from profile d to reveal whole crustal structure and features exhibiting transform characteristics combining these results with other studies in the region and comparing our results with young rift analogues we develop a model of along margin segmentation that explains the evolution of the west equatorial atlantic interpretation of the velocity depth model for profile d shows a 35 37 km thick continental crust which thins to 10 11 km over a distance of 320 km this thinning is accommodated in two regions the narrowest region associated with the ocean continent transition is interpreted to have formed by dextral shearing of the margin along major transform zones that accommodated the initial break up geometry of the central atlantic given the orientation of the margin relative to local fracture zone traces it is likely that the second region of thinning located 162 km landward of the ocean continent transition is a result of rifting suborthogonal to the profile orientation there is no evidence of rotated faulted blocks half graben structures or riftrelated magmatism manifest as either seaward dipping reflectors or as a high velocity region within the lower crust the demerara plateau is therefore interpreted as a margin segment comprising thinned continental crust bound to the north and south by transform type zones in which trans tensional extension is accommodated in contrast to profile a modelling suggests that the eastern margin exhibits a relatively broad region of crustal thinning associated with extension consistent with a rift type setting offshore unusually thin oceanic crust of 3 3 5 7 km thickness is identified which is consistent with similar observations further south in the absence of identifiable magnetic anomalies best estimates of the initial half spreading rate of 20 mm yr 1 suggest that the thin crust throughout the region is unlikely to be a result of ultra slow spreading but instead it is most likely due to a reduced magma supply at numerous long lived transform faults reflected by those presently offsetting the mid atlantic ridge in this equatorial setting

transform margins development controls and petroleum systems an introduction this paper provides an overview of the existing knowledge of transform margins including their dynamic development kinematic development structural architecture and thermal regime together with the factors controlling these this systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock seal rock and reservoir rock distribution expulsion timing trapping style and timing and migration patterns the paper then introduces individual contributions to this volume and their focus supplementary material location table and map of specific transform examples structural elements of the romanche transform margin and glossary of terms used in this article is available at https doi org 10 6084 m9 figshare c 3276407 gold open access this article is published under the terms of the cc by 3 0 license this volume shows dynamic linkage between new transform margin research and increasing transform margin exploration it offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors our introduction to this volume reviews the current knowledge of the transform margins focusing on their dynamic development kinematic development structural architecture thermal regimes and petroleum systems the last part of this paper introduces the contributions to this volume

cyclic variations of sulfate and boron concentrations and isotopes in deep groundwaters in the aquitaine basin france abstract concentrations and isotope contents of major and trace elements are principal factors in determining the origin of the chemical composition of groundwater this paper focuses specifically on the use of sulfur and boron isotopes to characterize the origin of cyclic variations in the deep eocene aquifer in the aquitaine sedimentary basin southwest of france it is part of a multi layer system mainly composed of sands and sandstone deposits groundwater contained in this deep reservoir is known to present stable chemical compositions allowing its use for various purposes like drinking water geothermal energy thermal activity and agricultural irrigation however among the dozens of wells exploiting this aquifer and despite the reservoir s substantial depth variations in sulfate concentration have been identified in a limited area of the reservoir these fluctuations are cyclic and they seem to be correlated with water level variations due to gas storage activities nearby in the same aquifer regular water samplings and analyses of major and trace elements and their isotopes have identified that bore concentration variations are correlated with sulfate variations a geochemical modelling approach based on water mixes elucidates the causes of these variations in chemical composition especially the boron and sulfate concentrations and their respective 11b and 34sso4 values from these numerical results we identify that different sources explain the variations of boron concentration one part coming from the silicates alteration present in sub layers of the exploited aquifer and the other part coming from the evaporites alteration present in the underlying molasse unit these results also confirm the existence of mass and potentially water transfers between the different sub layers of the reservoir and with the underlying molasse aquitard implying new constraints for the future hydrogeologic modelling

p and s wave delays beneath intraplate volcanic ridges and gravity lineations near the east pacific rise the gravity lineations intraplate melting petrology and seismic expedition glimpse explored the origin of two intraplate non hot spot ridge systems associated with gravity lineations in the south central pacific using the 11 month ocean bottom seismometer obs deployment of the glimpse experiment we determined the average p and s station delays for the region across the array station delays varied by 1 22 s for p waves and 2 13 s for s waves the presence of ultraslow shear velocity

mass transport deposits and fluid venting in a transform margin setting the eastern demerara plateau french guiana abstract the eastern demerara plateau offshore french guiana was surveyed in 2003 during the guyaplac cruise multibeam bathymetry and acoustic imagery 6 channel seismic reflection and 3 5 khz echo sounding the data show the post transform cenozoic that the series located on the outer part of the plateau below c 2000 m contain at least twelve stacked mass transport deposits mtds that have recorded a history of large scale slope failure as well as two main normal fault sets that provide possible pathways for upward fluid migration through the series reaching at high as the uppermost mtds seabed data show that the area above the failures is characterized by circular to elongate slope parallel depressions interpreted as fluid seeps pockmarks some of them have been modified by along slope currents we suggest that the development of the mtds to results from the combinaiton of the presence of fluid overpressure at depth the geometry of the margin s deep structure in particular the existence of a free borderlateral border on the outermost plateau our results also emphasise the role of stratigraphic decollements within the cenozoic series

erosion and flexural uplift along transform faults summary in all geodynamic settings intracontinental continent ocean intraoceanic the main morphological feature of transform plate boundaries is a narrow and elongated valley bounded on at least one side by an uplifted shoulder several mechanisms have been proposed to explain this uplift differential thermal subsidence lateral heat transfer extension perpendicular to the transform but none can be used in all settings we propose that the erosion of a lithospheric plate along the transform boundary may be an alternative mechanism that can be active in all geodynamic settings erosional unloading produces flexural uplift along the transform border which does not exceed 35 40 per cent of the difference in height between the lithospheric plate and the transform valley our model perfectly fits the morphology of several examples in the continental lithosphere the uplifted shoulder of the dead sea transform as well as marginal ridges in continental transform margins along an oceanic transform fault the erosion of the transform border only partially explains the uplift of the highest transverse ridges but may amplify other mechanisms

isotopic composition of precipitation in italy a first overall map abstract composite monthly samples of atmospheric precipitation were collected over different periods of time ranging from one to seven years at 77 different locations throughout italy these samples were measured for their oxygen and hydrogen isotopic composition to obtain basic information for hydrological and meteorological studies in this area on the basis of the results obtained a first map of the isotopic composition of precipitations in italy has been drawn up the main features of this map are the following 1 no isotopic latitudinal gradient has been found along the tyrrhenian coast from sicily to the italian french border despite the considerable range of latitude 2 a minor latitudinal gradient is found in the southeasternmost section of the country apulia partially favored by the local morphology 3 a marked shadow effect of the apennines is apparent along the southern section of the po valley and along the central section of the adriatic coast 4 the contribution of water vapor from the northernmost section of the adriatic sea affects the eastern and central sections of the po plain 5 the shadow effect of the alps is considerably smaller than expected 6 the isotopic vertical gradients calculated in nine different areas and based on groups of two to five different stations vary but are essentially close to about 0 2 100 m 7 when mean monthly temperature values were available their relationship with the isotopic composition of precipitation was found to be on average very poor 8 the relationship between mean 18o and mean d calculated for the collection locations shows shifts of both the slope and the deuterium excess when compared to the global meteoric water line these shifts are different for northern central and southern italy 9 in a few cases anomalously low monthly values suggest the existence of pronounced amount effects

structure of the demerara passive transform margin and associated sedimentary processes initial results from the iguanes cruise he iguanes cruise took place in may 2013 on the r v l atalante along the demerara passive transform margin off french guiana and surinam seismic multibeam and chirp acquisitions were made piston cores were collected for pore geochemistry and sedimentology a mooring was deployed on the sea bottom for 10 months temperature salinity turbidity and current measurements this new dataset highlights the lateral variability of the 350 km long guiana surinam transform margin due to the presence of a releasing bend between two transform segments the adjacent demerara plateau is affected by a 350 km long giant slide complex this complex initiated in cretaceous times and was regularly reactivated until recent times since the miocene contourite processes seem to be active due to the onset of the north atlantic deep water nadw bottom current a main nadw water vein flows towards se eroding slide headscarps and allowing the deposition of contourite drifts numerous depressions looking like comet tails or comet scours record this flow some of those were interpreted before the cruise as active pockmarks pore geochemistry and core analysis do not show any evidence of present day gas seepage

a strontium and sulfur isotopic study of permo triassic evaporites in the northern calcareous alps austria pervasively deformed permian and to a lesser extent triassic evaporites of the northern calcareous alps form a tectonic melange collectively known as alpine haselgebirge isotopic compositions of s and sr and trace element concentrations of sr and ba in ca sulfate minerals were investigated in terms of their stratigraphic and paleoenvironmental significance the majority of the samples yielded 34s values ranging from 9 8 to 13 8 indicating precipitation from late permian seawater with local modifications due to bacterial sulfate reduction bsr 87sr86sr ratios of these samples range widely from 0 7070 to 0 7098 but most samples show sr isotope values between 0 7070 and 0 7074 overlapping with the accepted late permian seawater values comparison of both s and sr isotopic compositions of individual samples reveals distinct trends of isotopic enrichment and depletion that can be linked to early diagenetic bsr mixing with continental surface or groundwaters and burial diagenesis concentrations of sr tend to be lower and ba values show a tendency toward values higher than those reported from marine evaporites implying variable diagenetic alteration triassic evaporites are volumetrically less important in the haselgebirge than their permian counterparts and are characterized by marine upper scythian to lower anisian s and sr isotope values in three localities hitherto unknown inclusions of these triassic evaporites were identified within the haselgebirge melange