aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

building of the amsterdam saint paul plateau a 10 myr history of a ridge hot spot interaction and variations in the strength of the hot spot source the amsterdam saint paul plateau results from a 10 myr interaction between the south east indian ridge and the amsterdam saint paul hot spot during this period of time the structure of the plateau changed as a consequence of changes in both the ridge hot spot relative distance and in the strength of the hot spot source the joint analysis of gravity derived crust thickness and bathymetry reveals that the plateau started to form at 10 ma by an increase of the crustal production at the ridge axis due to the nearby hot spot this phase which lasted 3 4 myr corresponds to a period of a strong hot spot source maybe due to a high temperature or material flux and decreasing ridge hot spot distance a second phase between 6 and 3 ma corresponds to a decrease in the ridge crustal production during this period the hot spot center was close to the ridge axis and this reduced magmatic activity suggests a weak hot spot source at 3 ma the ridge was located approximately above the hot spot center an increase in the hot spot source strength then resulted in the building of the shallower part of the plateau the variations of the melt production at the ridge axis through time resulted in variations in crustal thickness but also in changes in the ridge morphology the two periods of increased melt production correspond to smooth ridge morphology characterized by axial highs while the intermediate period corresponds to a rougher rift valley morphology these variations reveal changes in axial thermal structure due to higher melting production rates and temperatures

a diode laser system for heating minerals for u th he chronometry we have developed a diode laser 25 w 808 nm system for he extraction from minerals for u th he chronometry the laser beam is delivered via a 600 m fiber cable and focused using a binocular microscope temperatures necessary for he release from apatite 500 600 c and zircon 1100 1300 c encapsulated in pt foil tubes are attained by heating to 0 5 w for 30 s and 1 25 2 5 w for 20 min respectively using a defocused beam heating at these powers does not result in measurable u and or th loss from apatite as noted by the preservation of the distinct th u in multiple splits of two different durango apatite crystals analyses of durango and the california institute of technology internal standard apatite 97mr22 yield u th he ages of 32 8 1 8 ma 1 n 11 and 4 6 0 5 1 n 5 respectively well within accepted ages the u th he age and th u of five fish canyon tuff zircon aliquots yield 29 3 2 2 ma 1 and 0 6 0 03 respectively and are indistinguishable from ages produced by resistance furnace he extraction heating of unencapsulated minerals shows that the diode laser couples well with optically opaque minerals e g hornblende biotite muscovite garnet and basalt groundmass suggesting that diode lasers offer a cheap small low maintenance alternative to nd yag and ar ion lasers for 40ar 39ar cosmogenic noble gas and stable isotope studies

spatial and temporal variations in crustal production at the mid atlantic ridge 25 n 27 30 n and 0 27 ma we use high resolution multibeam bathymetry shipboard gravity side scan sonar images and magnetic anomaly data collected on conjugate flanks of the mid atlantic ridge at 25 n 27 30 n and out to 27 ma crust to investigate the crustal evolution of the ridge substantial variations in crustal structure and thickness are observed both along and across isochrons along isochrons within spreading segments there are distinct differences in seafloor morphology and gravity derived crustal thickness between inside and outside corners inside corners are associated with shallow depths thin crust and enhanced normal faulting while outside corners have greater depths thicker crust and more limited faulting across isochrons systematic variations in crustal thickness are observed at two different timescales one at 2 3 myr and another at 10 myr and these are attributed to temporal changes in melt supply at the ridge axis the shorter term variations mostly are in phase between conjugate ridge flanks although the actual crustal thickness can be significantly different on the two flanks at any given time we observe no correlation between crustal thickness and spreading rate thus during periods of low melt supply tectonic extension must increase to accommodate the full plate separation rate this extension commonly is concentrated in long lived faults on only one side of the axial valley resulting in strong across axis asymmetries in crustal thickness and seafloor morphology the thin crust flank has few volcanic features and exhibits elevated blocky topography with large offset often irregular faults while the conjugate thicker crust flank shows shorter offset regular faulting and common volcanic features the variations in melt supply at the ridge axis most likely are caused either by episodic convection in the subaxial mantle or by variable melting of chemically heterogeneous mantle

a plume model of transient diachronous uplift at the earth s surface convection in the earth s mantle appears to be strongly time dependent on geological time scales however we lack direct observations which would help constrain the temporal variation of convection on timescales of 1 10 ma recently it has been demonstrated that transient uplift events punctuated the otherwise uniform thermal subsidence of sedimentary basins which fringe the icelandic plume in the faroeshetland basin three dimensional seismic reflection surveys calibrated by well logs have been used to reconstruct a 55 million year old transient event the minimum amount of uplift is 490 m which grew and decayed within 2 ma this event has also been mapped 400 km further east in the north sea basin where peak uplift with an amplitude of 300 m occurred 0 3 1 6 ma later neither observation can be explained by glacio eustatic sea level changes or by crustal shortening we describe a simple fluid dynamical model which accounts for these transient and diachronous observations in this model we assume that the icelandic plume was already in existence and that it had an axisymmetric geometry in which hot e g 1400 c asthenospheric material flows away from a central conduit within a horizontal layer a transient temperature anomaly introduced at the plume center flows outward as an expanding annulus its geometry is calculated using radial flow between two parallel plates with a poiseuille cross stream velocity profile the expanding annulus of hot asthenosphere generates transient isostatic uplift at the earth s surface stratigraphic observations from both basins can be accounted for using a plume flux of 1 3 10 8 km 3 ma 1 for a layer thickness of 100 km plume flux is broadly consistent with that required to account for neogene 0 20 ma v shaped ridges south of iceland although our transient temperature anomalies are larger we suspect that the stratigraphic expression of transient convective behaviour is common and that a careful examination of appropriate records could yield important insights

lower crustal intrusion on the north atlantic continental margin near the faroe islands in the north atlantic the majority of basalt is intruded into the continent ocean transition rather than extruded onto the surface this melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 melt as has often been assumed when continents break apart the rifting is sometimes accompanied by the production of large volumes of molten rock1 2 3 the total melt volume however is uncertain because only part of it has erupted at the surface furthermore the cause of the magmatism is still disputed specifically whether or not it is due to increased mantle temperatures we recorded deep penetration normal incidence and wide angle seismic profiles across the faroe and hatton bank volcanic margins in the northeast atlantic here we show that near the faroe islands for every 1 km along strike 360 400 km3 of basalt is extruded while 540 600 km3 is intruded into the continent ocean transition we find that lower crustal intrusions are focused mainly into a narrow zone 50 km wide on the transition although extruded basalts flow more than 100 km from the rift seismic profiles show that the melt is intruded into the lower crust as sills which cross cut the continental fabric rather than as an underplate of 100 per cent melt as has often been assumed evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures with no requirement for either significant active small scale mantle convection under the rift or the presence of fertile mantle at the time of continental break up as has previously been suggested for the north atlantic ocean4 5 6

down slope variation in geotechnical parameters and pore fluid control on a large scale alpine landslide abstract a geotechnical investigation has been carried out on a large volume landslide in the stambach valley on the slopes above the town of bad goisern austria undrained loading has been considered as a means of triggering a large volume debris flow the initiation of this landslide has been linked with the collapse of rock pillars from the rock face of zwerchwand onto the head of the flow the concept of pore tensions resulting from stress relief has been used to account for the time delays of up to 10 months between the loading and the reactivation of the debris flow

testing the potential of geochemical techniques for identifying hydrological systems within landslides in partly weathered marls this paper s objective is to determine how useful geochemistry can be in landslide investigations more specifically what additional information can be gained by analysing the cation exchange capacity cec and cation composition in respect to the hydrological system of a landslide area in clayey material two cores from the boulc mondores landslide france and one core from the alvera landslide italy were analysed the nh4ac and nacl laboratory techniques are tested the geochemical results are compared with the core descriptions and interpreted with respect to their usefulness both analysis techniques give identical results for cec and are plausible on the basis of the available clay content information the determination of the exchangeable cations was more difficult since part of the marls dissolved with the ammonium acetate method more of the marls are dissolved than with the sodium chloride method the nacl method is preferred for the determination of the cation fractions at the complex be it that this method has the disadvantage that the sodium fraction cannot be determined to overcome this problem it is recommended to try other displacement fluids in the boulc mondores example the subsurface information that can be extracted from cec analyses was presented in the boulc mondores cores deviant intervals of cec could be identified these are interpreted as weathered layers and preferential flow paths that may develop or have already developed into slip surfaces the major problem of the cec analyses was to explain the origin of the differences found in the core samples both alvera and boulc mondores examples show transitions in cation composition with depth it was shown that the exchangeable caution fractions can be useful in locating boundaries between water types especially the boundary between the superficial rain fed hydrological system and the lower regional groundwater system this information may be important for landslide interventions since the hydrological system and the origin of the water need to be known in detail it is also plausible that long term predictions of slope stability may be improved by knowledge of the hydrogeochemical evolution of clayey landslides from the analysis it is concluded that geochemistry is a potentially valuable technique for landslide research but it is recognized that a lot of work still has to be done before the technique can be applied in engineering practice d 2003 elsevier b v all rights reserved

crustal structure of edoras bank continental margin and mantle thermal anomalies beneath the north atlantic we discuss the structure of the continent ocean transition of the edoras bank area of the ne atlantic margin and the influence of the iceland mantle plume during continental breakup edoras bank lies close to the present day limit of influence of the iceland plume sequences of seaward dipping reflectors imaged on multichannel seismic profiles are well developed over much of the margin they form aerially extensive dipping sheets with individual reflectors imaged on margin parallel profiles as laterally continuous and subhorizontal features we interpret them as basalt flows extruded from linear fissure vents close to sea level at the time of continental breakup a crustal velocity model for the margin was developed by travel time modeling of wide angle refractions and reflections recorded on digital ocean bottom hydrophones and the structure confirmed by gravity modeling oceanic crust formed immediately after breakup is 10 km thick and exhibits classic layer 2 and layer 3 seismic velocities the crustal thickness increases to the se reaching 17 km beneath the continental fragment of edoras bank the continent ocean transition is dominated in the lower crust by a lens up to 8 km thick of high velocity material 7 2 7 5 km s 1 which exhibits a very low velocity gradient it extends over a 60 km wide region beneath the seaward dipping reflectors the high velocities and densities of the lower crust are probably caused by igneous rock with a high mgo content that underplated the margin or heavily intruded pre existing crustal material during continental breakup both the addition of large quantities of melt to the margin and the subsidence curves inferred from postrift sediments sampled by deep sea drilling project dsdp boreholes on the margin indicate the presence of abnormally hot mantle beneath the area at the time of continental breakup comparison of the structure and subsidence history of the edoras bank margin with other areas of the nw european margin allows us to deduce the spatial extent and temporal variation of the thermal anomalies caused by the iceland mantle plume during and following continental breakup we find that at the time of breakup a thin layer of anomalously hot asthenospheric mantle 150 c hotter than normal lay beneath the 2000 km long rift extending from the lofoten margin off norway in the north to the edoras bank margin in the south over a period of 5 10 m y following the onset of rifting the mantle thermal anomaly decayed rapidly to only 50 c or so above normal as the thin layer of abnormally hot mantle decompressed beneath the rift and produced a large pulse of magmatism

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

geomorphic development of the escarpment of the eritrean margin southern red sea from combined apatite fission track and u th he thermochronometry apatite u th he and fission track thermochronometers are combined to constrain models of denudation and escarpment development of the high elevation eritrean margin along the southern red sea u th he ages have been determined for apatites from two coast perpendicular transects that were previously used for apatite fission track analysis e abbate m l balestrieri g bigazzi morphostructural development of the eritrean rift flank southern red sea inferred from apatite fission track analysis j geophys res 107 b11 doi 10 1029 2001jb001009 2002 in central eritrea near asmara he ages increase from c 7 ma at the coast to 152 ma on the plateau along a transect further south he ages from the margin border to the base of the escarpment span a narrower range 7 to 12 ma one sample from the top of a marginal high 2950 m yields older ages 22 43 ma forward modeling suggests that the he age distribution across the margin should allow scarp retreat and downwearing mechanisms to be distinguished in the case of a margin formed in the last twenty million years the distribution of he ages suggests that the escarpment evolved by downwearing and that post break up erosion of the escarpment was facilitated by in situ excavation rather than parallel retreat this implies the existence of an inland drainage divide located seaward of the present day escarpment rim we envisage that the inland divide formed during or immediately after continent break up and that the eastern marginal belt represents a remnant of the apex structure the short distance between the eastern marginal belt and the rim c 10 km represents the total retreat of the escarpment comparison of the measured he ages from the coastal plain with those predicted from forward modelling indicates that the main phase of post break up erosion started at about 15 ma closer to the initiation of seafloor spreading in the red sea than was thought previously

influence of the iceland mantle plume on oceanic crust generation in the north atlantic when a mantle plume with elevated temperature underlies an oceanic spreading centre it affects the generation of oceanic crust by creating thicker crust we map the variation in crustal thickness and seismic velocity along three long offset seismic profiles acquired over oceanic crust generated shortly after continental breakup in the north atlantic a 212 kmlong flowline from the faroes rifted continental margin across crust of 51 42 ma age where oceanic spreading developed close to the inferred centre of the iceland mantle plume a 256 km flowline extending from the hatton rifted continental margin across crust of 52 40 ma age about 800 km south of the presumed centre of the mantle plume and a 99 km strike line over oceanic crust formed at 43 ma in the iceland basin off the hatton continental margin the crustal velocity structure along each profile is constrained by multichannel seismic reflection data which is used primarily to map the sediments and by densely spaced ocean bottom seismometers which recorded wide angle reflections and refractions to offsets of more than 100 km over 56 000 crustal diving wave and moho wide angle reflection arrivals were used in joint crustal refraction and reflection tomographic inversions quantitative error analysis shows that the seismic velocity of the crust is mostly constrained to within 0 1 km s 1 and the depth of the moho to within 250 m we interpret the crustal thickness and velocity changes along the profiles as caused primarily by changes in the mantle temperature at the time of crustal formation if all the oceanic crustal thickness variations are ascribed to mantle temperature changes we infer that as mature seafloor spreading developed following continental breakup the mantle cooled by ca 75 c over a 10 myr period although it still remained hotter than the global average of normal oceanic crust the crust formed close to iceland is at all times thicker than that formed further away which we interpret as reflecting higher temperatures close to the centre of the thermal anomaly created by the mantle plume currently at the reykjanes ridge south of iceland we interpret thicker than normal oceanic crust as being caused by the presence of hotter mantle modulated by thickness variations of 1 5 2 0 km which are attributed to temporal variations in the mantle plume temperature of about 25 c on a 3 6 myr timescale a 1 5 km increase in thickness of oceanic crust generated between 48 and 45 ma on the faroes line is similar in magnitude and duration to those occurring on the present day reykjanes ridge which we suggest is due to a temperature pulse of 25 c gravity lineations in the northern north atlantic suggest that the oceanic crust has exhibited small thickness fluctuations of similar size throughout its history interpreted as due to small fluctuations in the temperature of the iceland mantle plume

imaging igneous rocks on the north atlantic rifted continental margin summary extruded basalt flows with thicknesses of several kilometres occur ubiquitously along the rifted continental margins of the northern north atlantic their total volume exceeds 1 million km 3 and may reach several million cubic kilometres intruded igneous rock comprising the complementary melt fraction to that extruded at the surface should exist in the lower crust with a volume at least as large as that of the extrusive basalts to image the extrusive and intrusive igneous rocks on the continental margin near the faroe islands in 2002 we shot a 375 km long deep penetration seismic profile across the margin using 85 ocean bottom seismometers for wide angle acquisition and shot a separate reflection profile using a 12 km streamer for optimal imaging by using large airgun sources tuned to produce low frequency energy we were able to constrain the seismic velocity structure of the whole crust we imaged not only layering and structure within the extrusive basalts but also lower crustal intrusions on the continent ocean transition cot combination of good velocity control on the lower crust together with direct imaging of the extrusive basalts enables us to constrain the volumes of extrusive and intrusive igneous rocks produced near the faroe islands to be 340 420 and 560 780 km 3 per kilometre along strike respectively the cot marked both by high velocity intrusions and lower crustal layering is surprisingly narrow with only 50 km separating unstretched continental crust from fully oceanic crust in contrast the extruded basalts flow up to 150 km landward at the paleo surface

slope instability mechanisms in dipping interbedded conglomerates and weathered marls the 1999 rufi landslide switzerland in may of 1999 melting snow cover combined with heavy rainfalls in the northeastern part of switzerland resulted in the occurrence of numerous shallow landslides many of these slides were located in the subalpine molasse a series of interbedded marls conglomerates and sandstones the subalpine molasse is highly prone to such sliding activity given the dip of bedding the surface topography and the weak nature of the marls that rapidly degrade when exposed to weathering historically the subalpine molasse has been the source of numerous slides of varying orders of magnitude and the surficial morphology is primarily dictated by previous rockslides which periodically reactivate as secondary soil slips given the conditions contributing to the slope failure and the history of previous sliding similar slides within the region are highly probable this paper presents the findings from a detailed investigation of one such slide the 1999 rufi slide results from a detailed engineering geological investigation show that the initial rockslide failure plane predominantly developed and passed through the marl beds as dictated by the penetration of the weathering front into the marls and not along reactivated shears or the bedding plane contact between the marls and overlying conglomerates numerical modelling results based on a coupled hydromechanical distinct element analysis were able to reproduce this mechanism by incorporating a progressive strength degradation procedure correlated to mapped weathering grades

density contrasts in the upper mantle and lower crust across the continent ocean transition constraints from 3 d gravity modelling at the norwegian margin summary 3 d gravity models that consider the highly complex density structure of the norwegian passive volcanic continental margin require a significantly lower density in the mantle below the ocean than below the continent this is especially pronounced on the crust free residual gravity anomalies obtained by 3 d gravity stripping this density contrast in the mantle indicates different physical properties either related to thermal or compositional conditions beneath the two domains we assess the gravity response of thermal differences and find that a hotter oceanic mantle compared to a colder continental mantle could cause the density contrast accordingly 3 d lithospheric scale gravity models considering temperature dependent mantle densities indicate that the transition between continental and oceanic lithosphere is rather sharp with a steep gradient in thickness beneath the continent ocean transition zone furthermore a mantle wedge of reduced density extends from the oceanic jan mayen fracture zone to the continental jan mayen lineament and points to increased mantle temperatures and or compositional changes beneath the lineament the models further indicate the presence of high density bodies within the lower crust at the continent ocean transition that are continuous with the lowermost oceanic layer 3b in terms of geometry and density this supports the concept of underplated lower crust beneath the western norwegian margin finally ne sw trending linear zones of increased density are required in the lower crust beneath the eastern voring and more basins to fit the short wavelength gravity signal

the effect of graben structures on the migration of groundwater contaminants at an industrial site industrial sites present a challenge to the hydrogeological delineation of pollution sources and their impacts when large scale geologic structures such as grabens exist on such sites these can have a significant impact on the hydrology and water quality distribution at the site investigated geophysical techniques standard hydrogeological approaches and hydrochemical characterisation with methods such as depth profiling and isotopes were used to determine the impact of a graben structure and the hydrogeological properties and consequent water quality distribution zones of high conductivity corresponding with available data were identified from the geophysical investigation and subsequent pumping tests in the area through hydrochemical characterisation including isotopes it was determined that the fault zone acts as a barrier for groundwater flow and is thus the reason for the lower levels of pollutants in groundwater beyond this feature however the surface water flow is not restricted by these zones and contributes significantly to the flow and salt loads at the discharge point the study showed that graben structures are important controls on the movement of contaminants and that the effect of such geological features on groundwater quality distribution must be investigated using multiple methodologies to construct a feasible conceptual model of the interactions

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

the slope movements within the mondores graben drome france the interaction between geology hydrology and typology the mondores graben in the south eastern french alps is an uncommon structural feature which originates in a complex polyphasic tectonic evolution in contrast with its immediate surroundings with hardly any huge landslides the mondores graben is characterised by various types of landslides a huge sagging caused part of the limestone cliff to subside some 50 m within 50 years two recent mud flows that occurred were considered a potential threat to some inhabited places downstream the hydrologic aspects of the boulc mondores landslide resemble the geology infiltration and karst input in the rock sliding zone and exfiltration in the marls resulting in slumps and mud flows the mass movement interactions could be explained by a structural geology analysis with geodetic monitoring using different techniques it is also shown that hydrochemistry as well as geophysical surveys are of importance in unravelling the hydrologic systems and the geological subsurface structures the present paper aims at explaining the geological control of the different slides in view of estimating their potential danger understanding the geological structure and its evolution therefore is a necessary prerequisite

kinematics and rheology of a major landslide based on signal analysis a detailed geodetic record which is over 23 years old and describes the kinematics of the mandria or left bank upstream landslide a major deep seated landslide close to the polyphyton dam greece was analysed on the basis of advanced signal analysis techniques without any geotechnical constraints it was found that all points share the same pattern of displacement which characterises both short and longer records the overall behaviour of the landslide can be described as viscoelastic and viscous or elastoviscous with multi annual periodic effects superimposed on the creep as the results of spectral analysis indicate the landslide seems insensitive to seasonal variations of precipitation and to annual fluctuations of the reservoir level although the first filling of the reservoir is likely to have had an important role in its movement there is a lack of subsurface information but the available data indicate that the landslide corresponds to a rigid mass dominated by brittle behaviour and int

geological discontinuities main flow path and chemical alteration in a marly hill prone to slope instability assessment from petrophysical measurements and borehole image analysis clay shale landscapes are sensitive to landslide erosion and re sedimentation processes in this context tectonized clay shales have peculiar hydrological and mechanical behaviours in order to improve our understanding of the processes involved in such systems an experimental site has been settled in the draix observatory ore draix on a black marl hill slope of the southern alps france in the framework of the ecou pref project the site is a natural laboratory to study the evolution of clay shale landscapes at several scales regional to m in this study we aim to characterize the internal structure and fissure patterns of a stable interfluve in order to locate preferential water flows within the system and anticipate its evolution this work is based on a series of mutli disciplinary approaches including petrophysical analyses well pulse injection tests and downhole geophysical measurements borehole geophysical results were combined with laboratory measurements on core plugs permeability density porosity and acoustic velocity optical and acoustical images have been used as an original tool for internal discontinuities characterisation and potential active flow path detection they allowed the identification of three main lithological units interpreted as several stages of shale alteration in addition several main structural plane discontinuities open fractures schistosity planes and fractures infilled with calcite or clays were identified from the images and their potential transmissivity discussed with regard to piezometric and tracer measurements in all the integration of measurements leads to propose a simple scenario of fluid circulation and chemical alteration of the interfluve copyright 2011 john wiley sons ltd

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

insights from the jan mayen system in the norwegian greenland sea ii architecture of a microcontinent summary we study the formation and evolution of the jan mayen microcontinent jmmc in the framework of conjugate margin evolution in the norwegian greenland sea the jmmc structural map and crustal architecture have been constrained by seismic mapping and potential field modelling supplemented by published seismic refraction transects the sedimentary and basement geometries have been further studied together with their conjugate to refine our knowledge on the less explored microcontinent structurally the jmmc main ridge is characterized by a platform and or terrace architecture flanked by sag type basins similar to those described on the mid norwegian conjugate margin while its southern part is marked by windows exposing crustal and or mantle material that was exhumed during higher degrees of extension the eastern side of the jmmc broke up in a magma rich fashion while the western side is magma poor the limited amount of magma involved in the jmmc formation suggests that changes in far field forces were the driving mechanism to initiate the isolation process and that a mantle plume had a lesser influence but might have helped the final mid ocean ridge establishment between the western jan mayen and greenland margin

eocene post rift tectonostratigraphy of the rockall plateau atlantic margin of nw britain linking early spreading tectonics and passive margin response a regional study of the eocene succession in the uk sector of the rockall plateau has yielded new insights into the early opening history of the ne atlantic continental margin data acquired from british geological survey borehole 94 3 on the rockall high provides a high resolution record of post rift early to mid eocene subaqueous fan delta development and sporadic volcanic activity represented by pillow lavas tuffs and subaerial lavas this sequence correlates with the east rockall wedge which is one of several prograding sediment wedges identified across the rockall plateau whose development was largely terminated in the mid lutetian linking the biostratigraphical data with the magnetic anomaly pattern in the adjacent ocean basin indicates that this switch off in fan delta sedimentation and volcanism was coincident with the change from a segmented transform margin to a continuously spreading margin during chron c21 however late stage easterly prograding sediment wedges developed on the hatton high during late mid to late eocene times these can only have been sourced from the hatton high which was developing as an anticline during this interval this deformation occurred in response to mid to late eocene compression along the ocean margin possibly associated with the reorganisation to oblique spreading in the iceland basin which culminated at the end of the eocene with the formation of the north hatton anticline and the deformation tilting of these wedges a series of intra eocene unconformities of which the mid lutetian unconformity is the best example has been traced from the rockall plateau to the faroe shetland region and onto the greenland conjugate margin bordering the early ocean basin whilst there appears to be some correlation with 3rd order changes in eustatic sea level it is clear from this study that tectonomagmatic processes related to changes in spreading directions between greenland and eurasia and or mantle thermal perturbations cannot be discounted

conjugate volcanic rifted margins seafloor spreading and microcontinent insights from new high resolution aeromagnetic surveys in the norway basin we have acquired and processed new aeromagnetic data that cover the entire oceanic norway basin located between the more volcanic rifted margin and the jan mayen microcontinent jmmc the new compilation allows us to revisit the structure of the conjugate volcanic rifted margins and the spreading evolution of the norway basin from the early eocene breakup time to the late oligocene when the aegir ridge became extinct the volcanic margins in a strict sense that formed before the opening of the norway basin have been disconnected with the previous jurassic mid cretaceous episode of crustal thinning we also show evidence of relationships between the margin architecture the breakup magmatism distribution along the continent oceanic transition and the subsequent oceanic segmentation the norway basin shows a complex system of asymmetric oceanic segments locally affected by episodic ridge jumps the new aeromagnetic compilation also confirms that a fan shaped spreading evolution of the norway basin was clearly active before the cessation of seafloor spreading and extinction of the aegir ridge an important mid eocene kinematic event at around magnetic chron c21r can be recognized in the norway basin this event coincides with the onset of diking and increasing rifting activity and possible oceanic accretion between the proto jmmc and the east greenland margin it led to a second phase of breakup and microcontinent formation in the norwegian greenland sea 26 myrs later in the oligocene

anomalous heat flow and geoid across the cape verde rise evidence for dynamic support from a thermal plume in the mantle summary we describe results from 200 heat flow measurements across the cape verde rise in the north atlantic they show that the heat flow through normal 125 myr old crust is 45 5 3 4mwm 2 close to the prediction for a lithospheric plate model heat flow increases towards the centre of the rise reaching a maximum of 16 4 mw m 2 above the normal oceanic value the concommitant geoid anomaly at the centre of the rise is 7 6 0 3 m and the depth anomaly is 1900 200 m the anomalous heat flow geoid and bathymetric values are used to constrain a variety of theoretical models of hot spot mechanisms lithospheric reheating models alone whether involving transient or sustained thinning of the lithosphere fail to model the broad heat flow anomaly and the long duration of uplift and volcanism observed on the cape verde rise axisymmetric convection models provide a better fit to the observed data and suggest that the swell is a consequence primarily of dynamic uplift generated by an ascending thermal plume in the underlying mantle uplift caused by expansion of the solid lithosphere is of smaller importance the observed geoid bathymetry and heat flow anomalies are reproduced well using convection models with upper mantle viscosities of 2 4 times 1020 pa s and a coefficient of thermal expansion in the range 2 0 2 5 times 10 5 k 1 the effect of melting in the ascending plume is to buffer the heat flow anomalies in the case of the cape verde rise partial melting is minimal but its effect on other hotspots will be to limit observed heat flow anomalies at the surface to less than 20 25 mw m 2

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

the norway basin revisited from continental breakup to spreading ridge extinction abstract we re evaluate the structure and spreading evolution of the southeastern norway basin nb based on a new high resolution aeromagnetic survey nb 07 the survey covers a complete oceanic spreading segment from the continental oceanic transition of the more margin off norway to the aborted aegir ridge the new survey documents a transform margin an orthogonally rifted segment and an oblique sheared volcanic margin formed during the onset of breakup observed from the east jan mayen fracture zone to the faroe platform the detailed fabric of the nb revealed by the new data indicates that two distinct tectonic phases have reshaped the basin before the cessation of seafloor spreading and abortion of the aegir ridge in the late oligocene after continental breakup phase i from c24 to c21r 52 to 49 ma marks the earliest phase of spreading probably initiated in the central and outer part of the more basin during this period competing oceanic segments led to the formation of overlapping systems and pseudo fault development we observe a significant change in the nb s oceanic spreading system in the late early eocene and based on observations from surrounding areas we suggest that this is a record of a major tectonic event in the norwegian greenland sea around c21r 49 47 9 ma during phase ii from c21r to c10 48 to 28 ma of nb s development spreading rates decreased spreading direction changed and the number of faulting with large displacement increased leading to the formation of unexpected n s oriented oceanic fracture zones the fan shaped development of the spreading system initiated around c21r 49 47 9 ma instead of c18 c17 40 38 ma or c24 53 3 52 3 ma as previously proposed these new observations were used to re evaluate the tectonic evolution of the norwegian greenland sea and discuss some implications on the syn and post breakup development of the surrounding continental margins and the evolution of the jan mayen microcontinent

seamounts and oceanic igneous features in the ne atlantic a link between plate motions and mantle dynamics a new regional compilation of seamount like oceanic igneous features soifs in the ne atlantic points to three distinct oceanic areas of abundant seamount clusters seamounts on oceanic crust dated 54 50 ma are formed on smooth oceanic basement which resulted from high spreading rates and magmatic productivity enhanced by higher than usual mantle plume activity late eocene early miocene soif clusters are located close to newly formed tectonic features on rough oceanic crust in the irminger iceland and norway basins reflecting an unstable tectonic regime prone to local readjustments of mid ocean ridge and fracture zone segments accompanied by extra igneous activity a soif population observed on mid miocene present rough oceanic basement in the greenland and lofoten basins and on conjugate kolbeinsey ridge flanks coincides with an increase in spreading rate and magmatic productivity we suggest that both tectonic kinematic and magmatic triggers produced mid miocene present soifs but the early miocene westwards ridge relocation may have played a role in delaying soif formation south of the jan mayen fracture zone we conclude that iceland plume episodic activity combined with regional changes in relative plate motion led to local mid ocean ridge readjustments which enhanced the likelihood of seamount formation

process identification at a slow moving landslide in the vorarlberg alps a fine grained slope that exhibits slow movement rates was investigated to understand how geohydrological processes contribute to a consecutive development of mass movements in the vorarlberg alps austria for that purpose intensive hydrometeorological hydrogeological and geotechnical observations as well as surveying of surface movement rates were conducted during 1998 2001 subsurface water dynamics at the creeping slope turned out to be dominated by a three dimensional pressure system the pressure reaction is triggered by fast infiltration of surface water and subsequent lateral water flow in the south western part of the hillslope the related pressure signal was shown to propagate further downhill causing fast reactions of the piezometric head at 5 5 m depth on a daily time scale the observed pressure reactions might belong to a temporary hillslope water body that extends further downhill the related buoyancy forces could be one of the driving forces for the mass movement a physically based hydrological model was adopted to model simultaneously surface and subsurface water dynamics including evapotranspiration and runoff production it was possible to reproduce surface runoff and observed pressure reactions in principle however as soil hydraulic functions were only estimated on pedotransfer functions a quantitative comparison between observed and simulated subsurface dynamics is not feasible nevertheless the results suggest that it is possible to reconstruct important spatial structures based on sparse observations in the field which allow reasonable simulations with a physically based hydrological model copyright 2004 john wiley sons ltd

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

remediation and analysis of kinematic behaviour of a roadway landslide in the upper minjiang river southwest china because of terrain geological structure river down incising and human activities the upriver minjiang valley in sichuan province southwest china constitutes a disaster area prone to frequent landslides during the roadway rebuilding periods the xiaozongqu landslide reactivated on the g213 roadway in maoxian district of sichuan province from the september to november in 2002 the landslide sped up reaching a maximum movement rate of 32 mm d the rapid slide seriously threatened the road to stabilize the landslide and eliminate the damage of landslide to the road remedying its damage and monitoring further developments are crucial based on its kinematic behaviour remediation was implemented in two phases from november 2002 to october 2003 systematic monitoring has been carried out since 18 june 2003 to determine kinematic variations of the landslide during the post remediation period and to assess the effects of remediation and the potential of the landslide for further destructive influences on the roadway

ridge plume interaction in the north atlantic and its influence on continental breakup and seafloor spreading development of the rifted continental margins and subsequent seafloor spreading in the north atlantic was dominated by interaction between the iceland mantle plume and the continental and oceanic rifts there is evidence that at breakup time a thin sheet of particularly hot asthenospheric mantle propagated beneath the lithosphere across a 2500 km diameter region this event caused transient uplift massive volcanism and intrusive magmatism and a rapid transition from continental stretching to seafloor spreading subsequently the initial plume instability developed to an axisymmetric shape with the 100 km diameter central core of the iceland plume generating 30 40 km thick crust along the greenland iceland faeroes ridge the surrounding 2000 km diameter region received the lateral outflow from the plume causing regional elevation and the generation of thicker and shallower than normal oceanic crust we document both long term 10 20 ma and short term 3 5 ma fluctuations in the temperature and or flow rate of the mantle plume by their prominent effects on the oceanic crust formed south of iceland lateral ridge jumps in the locus of rifting are frequent above the regions of hottest asthenospheric mantle occurring in both the early history of seafloor spreading when the mantle was particularly hot and throughout the generation of the greenland iceland faeroes ridge the northern north atlantic is a classic example of continental breakup above a thermal anomaly in the mantle created by a mantle plume the most obvious consequence of this was the generation of huge volumes of basaltic magmas by partial melting of the mantle at the time of continental breakup white mckenzie 1989 most of this magma bled up to the crust where the majority perhaps 60 80 was frozen in the lower crust while the rest was extruded as lava flows and pyroclastic deposits often after undergoing fractionation in crustal magma chambers if the extrusion rates are sufficiently high lava flows may form extensive sub horizontal flood basalts extending across the continental hinterland on rifted continental margins the extrusive lavas are typically expressed as seaward dipping reflector sdr sequences that are readily identifiable on seismic reflection profiles all these features have been found along more than 2 500 km of the rifted continental margins in the northern north atlantic on both the european and the greenland sides furthermore the mantle plume that gave rise to the thermal anomaly in the mantle is still going strong lying beneath iceland at the present day the northern north atlantic is therefore an excellent natural laboratory in which to investigate the interplay between rifting and magmatism because the history of rifting is well recorded from the time of continental breakup in the early tertiary to the seafloor spreading at the present day magnetic anomaly field reversals during the tertiary were frequent and south of iceland there are few large fracture zones in the oceanic crust so the seafloor spreading magnetic anomalies contain a clear record of the rifting history throughout the ocean basin there have also been several well constrained wide angle seismic surveys of the continental margins on both sides of the atlantic e g barton white 1997b smallwood et al 1999 korenaga et al 2000 often with coincident drilling penetrating the volcanic rocks so both the structure of the rifted margins and the timing of the igneous activity are well known in this paper we examine the interaction between the mantle plume and rifting first of the continental lithosphere to form the present continental margins and subsequently of the oceanic lithosphere to form the mid ocean ridge and the land mass of iceland smallwood white rift plume interaction 3

exhumation of the sierra de cameros iberian range spain constraints from low temperature thermochronology we present new fission track and u th he data from apatite and zircon in order to reconstruct the exhumation of the sierra de cameros in the northwestern part of iberian range spain zircon fission track ages from samples from the depocentre of the basin were reset during the metamorphic peak at approximately 100 ma detrital apatites from the uppermost sediments retain fission track age information that is older than the sediment deposition age indicating that these rocks have not exceeded 110 c apatites from deeper in the stratigraphic sequence of the central part of the basin have fission track ages of around 40 ma significantly younger than the stratigraphic age recording the time of cooling after peak metamorphic conditions apatite u th he ages in samples from these sediments are 31 40 ma and record the last period of cooling during alpine compression the modelled thermal history derived from the uppermost sediments indicates that the thermal pulse associated with peak metamorphism was rapid and that the region has cooled continuously to the present the estimated palaeogeothermal gradient is around 86 c km 1 and supports a tectonic model with a thick sedimentary fill c 8 km and explains the origin of the low grade metamorphism observed in the oldest sediments

the contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation in this study we reconstruct the timing of the onset of northern hemisphere glaciation this began in the late miocene with a significant build up of ice on southern greenland however progressive intensification of glaciation did not begin until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia were glaciated at approximately 2 74 ma 40 ka before the glaciation of alaska 2 70 ma and about 200 ka before significant glaciation of the north east american continent 2 54 ma we also review the suggested causes of northern hemisphere glaciation tectonic changes such as the uplift of the himalayan and tibetan plateau the deepening of the bering strait and the emergence of the panama isthmus are too gradual to account entirely for the speed of northern hemisphere glaciation we therefore postulate that tectonic changes may have brought global climate to a critical threshold but the relatively rapid variations in the earth s orbital parameters and thus insolation triggered the intensification of northern hemisphere glaciation this theory is supported by computer simulations which despite the relative simplicity of the model and the approximation of some factors e g using a linear carbon dioxide scenario neglecting the geographical difference between the pliocene and the present suggest that it is possible to build up northern hemisphere ice sheets between 2 75 and 2 55 ma by varying only the insolation controlled by the orbital parameters c 1998 elsevier science ltd all rights reserved

unraveling the mesozoic and cenozoic tectonothermal evolution of the eastern basque cantabrian zone western pyrenees by low temperature thermochronology this is a contribution of the geotec group idi 2018 000216 and projects misterios cgl2013 48601 c2 2 r consolider ingenio 2010 topo iberia csd2006 00041 and esf topoeurope project pyrtec sv pa 10 03 ip2 pyrtec we thank additional financial support by the university of oviedo banco santander the government of the principality of asturias through the science technology and innovation plan pcti the european union through feder funds and the spanish ministry of education culture and sport through the training programme for academic staff fpu grant for idf

testing the influence of the central american seaway on orbitally forced northern hemisphere glaciation 1 utilizing a climate model of intermediate complexity we test the hypothesis that the pliocene closure of the central american seaway was a necessary precondition for orbitally triggered northern hemisphere glaciation we conduct a series of sensitivity experiments in order to analyze the isolated and combined effects of panama closure and orbital forcing on northern hemisphere perennial snow cover while orbital forcing efficiently controls the extension of perennial snow cover the model results suggest that the closure of the central american seaway did not intensify orbitally forced glaciation in high northern latitudes

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

effect of lithostatic pressure and tectonic deformation on the magnetic fabric anisotropy of magnetic susceptibility in low grade metamorphic rocks the role of lithostatic pressure and strain in low grade metamorphic cover rocks is analyzed through the anisotropy of magnetic susceptibility ams of jurassic and cretaceous siltstones and limestones from the cameros basin north spain for rocks initially characterized by precleavage magnetic fabric the main change in the magnetic fabric produced by the increase of lithostatic pressure is the increment in the degree of anisotropy pj in rocks affected by syncleavage deformation the magnetic fabric depends on the mechanism of internal deformation involved in fabric development in siltstones where cleavage is correlated with synkinematic recrystallization of phyllosilicates and rigid body rotation of grains the magnetic fabric is coherent with the internal deformation determined by strain analysis on deformed nodules on the contrary in limestones we observe a complete reorganization of the magnetic fabric probably due to the discontinuous character of the cleavage formation mechanism detailed analysis of the parameter angle between the bedding pole and the minimum susceptibility axis parallel to the cleavage pole indicates that for rocks characterized by syncleavage magnetic fabric the different variation pattern of tj and pj parameters is closely related to the deformation mechanisms responsible for the fabric development

neogene overflow of northern component water at the greenland scotland ridge in the north atlantic ocean flow of north atlantic deep water nadw and of its ancient counterpart northern component water ncw across the greenland scotland ridge gsr is thought to have played an important role in ocean circulation over the last 60 ma the iceland plume has dynamically supported an area which encompasses the gsr consequently bathymetry of the gsr has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle here we reassess the importance of plate cooling and convective control on this northern gateway for ncw flow during the neogene period following wright and miller 1996 to tackle the problem benthic foraminiferal isotope data sets have been assembled to examine 13c gradients between the three major deep water masses i e northern component water southern ocean water and pacific ocean water composite records are reported on an astronomical timescale and a nonparametric curve fitting technique is used to produce regional estimates of 13c for each water mass confidence bands were calculated and error propagation techniques used to estimate ncw and its uncertainty despite obvious reservations about using long term variations of 13c from disparate analyses and settings and despite considerable uncertainties in our understanding of ancient oceanic transport pathways the variation of ncw through time is consistent with independent estimates of the temporal variation of dynamical support associated with the iceland plume prior to 12 ma 13c patterns overlap and ncw cannot be isolated significant long period variations are evident which are consistent with previously published work from 12 ma when lithospheric cooling probably caused the gsr to submerge completely long period 13c patterns diverge significantly and allow reasonable ncw estimates to be made our most robust result is a dramatic increase in ncw overflow between 6 and 2 ma when dynamical support generated by the iceland plume was weakest between 6 and 12 ma a series of variations in ncw overflow have been resolved

magnesian basalts from the hebrides scotland chemical composition and relationship to the iceland plume abstract the hebridean tertiary igneous province lay 700 900 km south of a presumed plume centre and 500 km landward of a rifted continental margin prior to opening of the northeast atlantic the province includes a small number of magnesian basalts containing olivine phenocrysts with core compositions equal to or in excess of fo 89 olivine liquid equilibrium calculations suggest that these phenocrysts formed from liquids with mgo contents of 14 15 wt and in rare instances 18 20 wt the liquidus temperatures of these magmas imply mantle potential temperatures of 1350 1460 c at distances up to 900 km from the axis of the iceland plume their emplacement at c 60 ma implies either a long established hotspot or active channeling of plume material along the base of the plate towards a region undergoing considerable lower crustal extension

slope instability mechanisms in dipping conglomerates over weathered marls bol landslide croatia in february 2005 a landslide of significant dimensions occurred at bol on the island of brac in croatia the location of the landslide was in a geological structure of weakly bounded conglomerates lying above a flysch in an area where numerous slides have been previously reported in the paper the results of a geological engineering investigation of the bol landslide are presented the investigation results show that the landslide was triggered by a combination of improperly started earthworks an increase in air temperature in days preceding landslide that caused snow melt and abundant rainfall but the primary cause of the landslide was weathering of the flysch in other words despite the fact that contact between the flysch and the conglomerates slopes is in approximate correspondence with the slope of the hillside the landslide surface was not in contact between the conglomerates and marl but deeper in the flysch provoked by the penetration of the weathering front into the flysch numerical modelling results were able to reproduce this mechanism by incorporating strength degradation into the weathered zone determined by field investigation the results of the research can be used to predict potential slides not only in the area under study

influence of daily surface temperature fluctuations on rock slope stability case study of the rochers de valabres slope france the present paper describes a rockfall that has affected the rochers de valabres slope france s southern alps region and discusses one possible mechanism for the occurrence of this rockfall along with the potential for future ones in the absence of an obvious explanatory trigger factor we set out to examine whether natural daily surface temperature changes could have played a role in this event in particular it is suspected that these slight yet repeated perturbations may be a preparatory factor for rockfalls with a day to day cumulative effect a numerical model strengthens this hypothesis by showing that thermally induced deformations can be sufficient to cause the gradual downward creep of a rock block located in an awkward position to investigate this notion more thoroughly a currently vulnerable part of the rochers de valabres slope has been instrumented with a high precision geodetic monitoring system total station it is believed that this device is able to capture thermally induced movements if specific precautions are taken the instrumented rock volume is used as a test site in the aim of better understanding the consequences of surface temperature changes on slope stability measured data with a precision level never before achieved on rock slopes are compared herein with numerical modelling results the initial conclusions of the long term study we are conducting indicate that surface temperature changes play an important while not easily quantifiable role in preparing rockfalls

nonlinear refraction traveltime tomography a few important issues for performing nonlinear refraction traveltime tomography have been identified they include the accuracy of the traveltime and raypath calculations for refraction the physical information in the refraction traveltime curves and the characteristics of the refraction traveltime errors consequently we develop a shortest path ray tracing method with an optimized node distribution that can calculate refraction traveltimes and raypaths accurately in any velocity model we find that structure ambiguity caused by short and long rays in the seismic refraction method may influence the inversion solution significantly therefore we pose a nonlinear inverse problem that explicitly minimizes the misfits of the average slownesses ratios of traveltimes to the corresponding ray lengths and the apparent slownesses derivatives of traveltimes with respect to distance as a result we enhance the resolution as well as the convergence speed to regularize our inverse problem we use the tikhon

comment on gonzalez acebron et al criteria for the recognition of localization and timing of multiple events of hydrothermal alteration in sandstones illustrated by petrographic fluid inclusion and isotopic analysis of the tera group northern spain int j earth sciences 2011 100 1811 1826 the paper by gonzalez acebron et al 2011 deals with both regional and methodological problems about the timing of thermal events in one of the best known and controversial basins in the iberian microplate the late jurassic early cretaceous cameros basin the aforementioned paper contains invaluable data about the thermal evolution of the basin and it is an important contribution to the understanding of the post sedimentary pre inversion processes in this strongly subsiding basin it will undoubtedly add new evidence to the knowledge of hydrothermal processes in general and particularly to the paleothermal evolution of the basin however in our opinion there are some problems involving important matters within the paper namely 1 the interpretation of the data obtained which are too constrained within a univocal line of thinking without considering other simpler and more viable options that in the discussed paper are aprioristically rejected 2 the second problem deals with referencing to previous papers and acknowledgement of previous works by other authors we must say that this aspect does not refer to this paper alone but it is recently becoming a commonplace for many scientific papers in this field on the side of the references to previous works it must be stated that

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

palaeogene continental to oceanic magmatism on the se greenland continental margin at 63 n a review of the results of ocean drilling program legs 152 and 163 mantle melting zone accompanied by an increase in the average drilling along a 63 n transect off se greenland during ocean degree of melting with time from 4 to 12 these modest drilling program odp legs 152 and 163 recovered a succession degrees of melting imply mantle temperatures only 100 c hotter of volcanic rocks representing all stages in the break up of the than normal upper mantle upwelling mantle must therefore have volcanic rifted margin the rocks range from pre break up continental been fed dynamically to the melt zone to generate the igneous crust tholeiitic flood basalt through syn break up picrite to truly oceanic of 18 km thickness deduced from seismic and gravity studies nbasalt forming the main part of the seaward dipping reflector morb like magmas dominated the earliest part of the succession sequence sdrs all the lava flows recovered from the transect although a few flows of icelandic basalt were erupted in the prewere erupted in a subaerial environment ar ar dating shows break up phase in contrast the post break up magmas had an that the earliest magmas were erupted at 61 ma and has icelandic mantle source this suggests that the developing head of confirmed that the main part of the sdrs was erupted during c24r the ancestral iceland plume was compositionally zoned with a core 56 53 ma following continental break up magma represented by of icelandic mantle surrounded by a thick outer zone of hot depleted the pre break up lava flows was stored in crustal reservoirs where upper mantle it evolved by fractional crystallization and assimilation of continental crust trace element and radiogenic isotope data show that the contaminant changed through time from lower crustal granulite to a mixture of granulite and amphibolite suggesting storage of magma at progressively shallower levels in the crust the degree of contamination declined rapidly as break up proceeded and the youngest rocks sampled in the transect are uncontaminated by continental basement variation of for example sc zr and sm

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

imaging the pulsing iceland mantle plume through the eocene the temperature of mantle plumes may vary on geologic time scales from a few million years to tens of millions of years in special circumstances such as near iceland in the north atlantic where the plume underlies an oceanic spreading center temporal variations in the oceanic crustal thickness provide a sensitive proxy for the mantle temperature if as is likely the crustal thickness is controlled primarily by passive decompression of mantle rising beneath the spreading center we show from both seismic reflection imaging and wide angle ocean bottom seismometer data from the norwegian sea that the temperature of the iceland mantle plume decreased by 50 c over the first 5 m y following continental breakup and then oscillated by 25 c over an 3 m y period similar temperature variations on a 3 6 m y time scale creating strong lineations in the gravity field are inferred from the regional north atlantic they occur both in the period immediately following breakup and at the present day reykjanes ridge south of iceland where they create v shaped ridges as the mantle thermal anomalies propagate away from the center of the plume beneath iceland we propose that mantle plume temperature variations of 25 c have occurred in the iceland plume with a similar amplitude and frequency since at least 49 ma and are likely to be a feature of all mantle plumes

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

tectonic and hydrodynamic control of landslides in the northern area of the central rif morocco the northern edge of the central rif morocco is subject to numerous landslides where mechanisms do not correspond to the classical models used by geomechanics specialists it is necessary to adopt a multidisciplinary approach that combines geomorphology geology hydrogeology and geotechnics in order to understand how such slope failures are generated especially in a region with a heterogeneous structure characterised by significant lithological differences severe fracturing and thrust sheets where tectonic contacts play a major role in groundwater circulation this report shows that these failures are essentially controlled by the tectonic contact separating the tisirene and chouamat thrust sheets and by subsurface hydrodynamic conditions a model of spatial and temporal variations in the factor of safety is proposed

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

dynamic earth system and ecological controls of rainfall initiated landslides abstract rainfall initiated landslides continue to inflict damages and loss of life throughout the world processes and mechanisms revealed from hydrological geomorphic geotechnical pedological geological hydrochemical and biological investigations have advanced our understanding of these effects on slope stability however the interactions amongst these processes and attributes as they affect the initiation and propagation of landslides are not as well understood too often landslide studies are conducted from only one or at most two of these perspectives moreover while precipitation and hydrology are recognized as dynamic influences the earth system and ecological effects are often assumed to be static we assess the interplay of these processes related to landslides triggered by positive pore water accretion and loss of soil suction each of these conditions arguably requires a different view on the processes that cause slope failure and predictive approaches this review starts from the perspective of dynamic adapting earth and ecological systems and discusses how these attributes relate to landslide initiation mode location and timing specifically the role that large and small scale preferential flow plays in both contributing to and mitigating instability is elucidated including effects of bedrock exfiltration we also examine how and under what conditions these pathways manifest in different soils lithology and landforms the multiple effects of rhizosphere processes on slope stability are discussed including root reinforcement evaporation from canopies and litter layers transpiration and the role of root structure affecting preferential flow paths rainfall initiated landslides involve highly dynamic hydrologic earth surface and ecological processes that persist over a range of spatial and temporal scales however guidance for overcoming these challenges has been elusive a conceptual framework is presented to shed light on these dynamic and interactive processes that should lend insights into why and when certain slopes fail during storms while other seemingly similar slopes do not fail such advances will benefit landslide hazard assessments and disaster responsiveness protocols

sedimentation in the venezuelan basin circulation in the caribbean sea and onset of northern hemisphere glaciation currents of the equatorial atlantic and tethys sea migrated westward through the caribbean sea and panama seaway from cretaceous to oligocene time at about 25 ma currents reversed direction allowing cool pacific waters peruvian current to enter the caribbean almost coincident with the reversal was a dramatic increase in central american explosive volcanism which resulted in development of large volcanic centers and an abundance of suspended volcanic detritus in pacific and southern caribbean waters the detritus was transported by pacific currents across the caribbean to be deposited as pelagic mud in the venezuelan basin during 25 to 15 ma these cool turbid pacific waters led to a dramatic reduction in the diversity of hermatypic corals at about 15 ma venezuelan basin pelagic sediments record a dramatic change in provenance with derivation of highly weathered detritus from the south american continent probably the result of renewed uplift of the northern andes exceptionally abundant kaolinit

the closing of a seaway ocean water masses and global climate change the late neogene witnessed various major paleoceanographic changes that culminated in intense northern hemisphere glaciation nhg the cause and effects of these changes are still debated we use a multiproxy approach to determine the relative timing of the closure of the panama gateway changes in atlantic circulation global cooling and ice sheet growth benthic foraminiferal mg ca records from a pacific and an atlantic site have been produced and are interpreted in terms of bottom water temperatures these mg temperature records are combined with published benthic 13c 18o and erosion records to reconstruct the flow of proto north atlantic deep water proto nadw over the past 12 ma the results suggest that between 12 5 and 10 5 ma and again between about 8 5 and 6 ma a nutrient depleted water mass that was colder by 1 2 c and fresher than the intervening deep water mass filled the atlantic basin this proto nadw became warmer by 1 c and saltier between 6 and 5 ma coincident with the restriction of surface water flow through the central american seaway the mg temperature records define a subsequent global cooling trend of 3 5 c between 5 ma and today early nhg in the late miocene was perhaps related to the formation of the relatively cold fresh proto nadw the formation of the warmer and saltier proto nadw in the early pliocene may have initially limited northern hemisphere ice growth however the increased moisture released at high northern latitudes associated with formation of warm proto nadw coupled with the global temperature decrease of deep and hence polar surface waters likely helped initiate the intense nhg of the plio pleistocene

gypsum scarps and asymmetric fluvial valleys in evaporitic terrains the role of river migration landslides karstification and lithology ebro river ne spain abstract most of the spanish fluvial systems excavated in tertiary evaporitic gypsum formations show asymmetric valleys characterized by a stepped sequence of fluvial terraces on one valley flank and kilometric long and 100 m high prominent river scarp on the opposite side of the valley scarp undermining by the continuous preferential lateral migration of the river channel toward the valley margin leads to vertical to overhanging unstable slopes affected by a large number of slope failures that become the main geological hazard for villages located at the toe of the scarps detailed mapping of the gypsum scarps along the ebro and huerva rivers gypsum scarps demonstrates that landslides and lateral spreading processes are predominant when claystones crop out at the base of the scarp while rockfalls and topples become the dominant movement in those reaches where the rock mass is mainly constituted by evaporites the dissolution of gypsum nodules seasonal swelling and shrinking and dispersion processes contribute to a decrease in the mechanical strength of claystones the existence of dissolution enlarged joints sinkholes and severely damaged buildings at the toe of the scarp from karstic subsidence demonstrates that the interstratal karstification of evaporites becomes a triggering factor in the instability of the rock mass the genesis of asymmetric valleys and river gypsum scarps in the study area seem to be caused by the random migration of the river channel in the absence of lateral tilting related to tectonics or dissolution induced subsidence once the scarp is developed its preservation depends on the physicochemical properties of the substratum the ratio between bedrock erosion and river incision rates and climatic conditions that favour runoff erosion versus dissolution

variation with spreading rate of oceanic crustal thickness and geochemistry abstract away from the influence of fracture zones hotspots and marginal basins oceanic crust exhibits remarkably uniform crustal thickness rare earth element concentrations and bulk composition at all but the most slowly spreading ridges at full spreading rates below 15 mm a however all these observed parameters show marked and abrupt changes the seismically determined crustal thicknesses decrease sharply from their average of 7 1 km as do melt thicknesses inferred from rare earth element inversions of basalts bulk element compositions of basalts show an increase in the percentage of na2o and decreases in the feo content and cao al2o3 ratio as the full spreading rate drops below 15 mm a we present a model of the melting beneath oceanic spreading centres which reproduces the observed variations with spreading rate of crustal thickness and the main geochemical changes observed in basalts changes in the volume and composition of melt generated at very slow spreading rates are caused by conductive heat loss from the mantle welling up beneath rifts we model the observed behaviour with normal mantle potential temperatures of 1300 20 c greater crustal thicknesses are generated at the north atlantic spreading centre adjacent to the iceland mantle plume suggesting mantle temperatures about 80 c hotter than normal in this area

timing of diagenesis and very low grade metamorphism in the eastern sector of the sierra de cameros iberian range spain a u pb shrimp study on monazite the sierra de cameros is an intracontinental orogen and represents the north western part of the iberian range in northern spain it comprises a thick sequence of syn rift continental sediments mainly sandstones and carbonates deposited during lower cretaceous times a unique characteristic of the sierra de cameros in relation to the rest of the iberian range is the presence of low grade metamorphism in certain parts of the basin an event that predates basin inversion this paper describes the presence textural relationships and geochemical aspects of authigenic and or metamorphic monazite within different lithologies from the deepest parts of the basin sensitive high resolution ion microprobe shrimp u pb dating of monazite records the presence of two age populations the first with 206 pb 238 u ages ranging from 122 to 116 ma which is considered as diagenetic in origin whilst the second is dated at 99 2 ma and postdates the metamorphic climax

rainfall induced landslides and debris flows in this preface we introduce the special issue on rainfall induced landslides and debris flows the topic is of high interest for many practical and scientific reasons in fact rainfall is the most relevant factor for the triggering of both shallow and deep seated landslides and rainfall analysis is the most frequently adopted approach for forecasting the occurrence of such phenomena the six papers of the special issue cover most of the key issues relative to rainfall induced landslides starting from the analysis of these contributions we identify and discuss in this paper several main topics that deserve further research in the field of rainfall induced landslide such as the uncertainty of the data the quality of geotechnical analysis the validation of the models and the applicability of results in the framework of natural hazards copyright 2007 john wiley sons ltd

crustal accretion at the reykjanes ridge 61 62 n we report results of a seismic gravity and magnetic survey of the reykjanes ridge spreading center at 61 62 n about 600 km from the center of the iceland mantle plume anomalously shallow water on the ridge crest enabled us to record seismic refractions on a 2 4 km hydrophone streamer the velocity within layer 2a is 2 4 0 3 km s 1 and its mean thickness is 400 100 m the velocity at the base of layer 2a is 3 3 0 3 km s 1 on the ridge axis increasing with crustal age to 4 0 km s 1 at 1 5 ma and 4 5 km s 1 at 5 ma assuming that seismic layer 2a on the ridge axis is also the extrusive layer i e the magnetic source layer we have successfully modeled the variations in amplitude of the magnetic field the best magnetic model includes enhanced magnetization within layer 2a at the sites of recent volcanic activity as independently recognized in side scan sonar data we also present a full crustal seismic model based on wide angle seismic recordings on digital ocean bottom hydrophones and disposable sonobuoys the seismic model is complemented by gravity modeling which further suggests that the ridge crest is in isostatic equilibrium the zero age crust is 10 0 km thick while crust of age 5 ma is 7 8 km thick these crustal thicknesses are greater than those of normal oceanic crust which we attribute to the presence of anomalously hot asthenospheric mantle beneath the spreading center we suggest that the variation in thickness between 0 ma and 5 ma crust is caused by temporal variation in the plume fed asthenospheric temperature beneath the reykjanes ridge

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

extensional subsidence contractional folding and thrust inversion of the eastern cameros basin northern spain tectonic analysis of the cameros massif northern spain demonstrates the need to integrate detailed structural analysis with stratigraphic studies in order to understand the development of inverted basins the cameros massif underwent three major tectonic events each characterized by different mechanisms of deformation the first event tithonian early albian manifested as continental rifting and formation of the cameros basin and was attended by normal faulting and related folding of pre and syn rift sedimentary sequences up to 9 km thick it corresponded to the beginning of rifting and opening of the bay of biscay to the north of the massif the second event occurred at the end of the early cretaceous the basin underwent contraction manifested as gentle folds containing axial plane cleavage this contraction was due to the migration of the center of rifting away from the basin and toward the northeast and correlates with the onset of oceanic spreading in the bay of biscay deformation happened during a low grade metamorphism period that reached its thermal peak after folding and cleavage formation 90 100 ma the final stage of deformation eocene miocene following a structurally quiescent period of approximately 40 ma occurred during the convergence collision between iberia and europe it formed contractional folds related to large e w striking overthrusts the mesozoic basin was inverted and transported 25 km toward the north during this stage both unfolding and tightening of the former folds occurred as determined from analysis of cleavage orientation associated with the previous shortening

benthic foraminiferal response to the emergence of the isthmus of panama and coincident paleoceanographic changes abstract late cenozoic benthic foraminiferal faunas from the caribbean deep sea drilling project dsdp site 502 3052 m and east pacific dsdp site 503 3572 m were analyzed to interpret bottom water masses and paleoceanographic changes occurring as the isthmus of panama emerged major changes during the past 7 myr occur at 6 7 6 2 3 4 2 0 and 1 1 ma in the caribbean and 6 7 6 4 4 0 3 2 2 1 1 4 and 0 7 ma in the pacific prior to 6 7 ma benthic foraminiferal faunas at both sites indicate the presence of antarctic bottom water aabw after 6 7 ma benthic foraminiferal faunas indicate a shift to warmer water masses north atlantic deep water nadw in the caribbean and pacific deep water pdw in the pacific flow of nadw may have continued across the rising sill between the caribbean and pacific until 5 6 ma when the pacific benthic foraminiferal faunas suggest a decrease in bottom water temperatures after 5 6 ma deep water to intermediate water flow across the sill appears to have stopped as the bottom water masses on either side of the sill diverge the second change recorded by benthic foraminiferal faunas occurs at 3 4 ma in the caribbean and 4 0 3 2 ma in the pacific at this time the caribbean is flooded with cold aabw which is either gradually warmed or is replaced by glacial bottom water gbw at 2 0 ma and by nadw at 1 1 ma these changes are related to global climatic events and to the depth of the sill between the caribbean and atlantic rather than the rising isthmus of panama benthic foraminiferal faunas at east pacific site 503 indicate a gradual change from cold pdw to warmer pdw between 4 0 and 3 2 ma the pdw is replaced by the warmer poorly oxygenated piw at 2 1 ma although the pdw affects the faunas during colder intervals between 1 4 and 0 7 ma the piw remains the principal bottom water mass in the guatemala basin of the east pacific

internal structure and deformation of an unstable crystalline rock mass above randa switzerland part ii three dimensional deformation patterns the monitoring of slope displacements over time provides the basis for most rockslide early warning systems yet the prediction of catastrophic failure from these records is highly problematic and tenuous especially if the underlying kinematics and instability mechanism are poorly understood an example is the moving slope above the town of randa in the swiss alps this slope is considered typical of those in crystalline rock that lacks a natural highly persistent weakness plane dipping towards the valley that can serve as a through going detachment surface for kinematic release in part i the companion paper to this the findings from a comprehensive geological and geophysical investigation to image the internal structures of the unstable rock mass were presented in this paper we develop a kinematic model that describes the pattern of displacement vectors for the rock mass along these structures both on surface and at depth the displacements were estimated from 5 years of data from an extensive monitoring system which included surface geodetic and crackmeter measurements borehole inclinometer and extensometer measurements up to 120 m depth and microseismicity the results showed that the displacement field is highly heterogeneous internal deformation is accommodated by both shear and opening mode dislocation of faults and fracture zones which dip moderately to steeply into the slope microseismicity is most intense near the front of the scarp where surface translation in large part reflects the toppling of blocks accommodated by slip along the steeper dipping fractures the small displacement rates at the study site of up to 2 cm year coupled with a modest deviation of up to 15 from vertical of the boreholes posed severe problems for the estimation of horizontal displacements from the inclinometer data we describe the error analysis of these data in some detail since it is relevant for similar installations elsewhere conclusions drawn from this work highlight the importance of integrating various types of data in order to better understand the complex block kinematic processes whose evolution governs the long term progressive failure of unstable rock slopes