tracking holocene glacial and high altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments lake blanc huez western french alps holocene palaeoenvironmental evolution and glacial fluctuations at high altitude in the western french alps are reconstructed based on a multiproxy approach within lake blanc huez 2550 m a s l drainage basin the combination of seismic profiling 3 5 khz piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the holocene over the last 9700 years the holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal bp during the early holocene the organic lacustrine facies reflects reduced glacial activity in the catchment this major glacial retreat seems to result from solar forcing and high summer insolation after 5400 cal bp lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion suggesting a progressive transition to wetter climatic conditions this climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations characterizing the beginning of the neoglacial period both colder temperature and humid climate induced significant glacier advance since 4700 cal bp over this global trend three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern westerlies regimes across the north atlantic and western europe they are dated from 8700 to 7000 4700 to 2500 and 1200 to 200 cal bp these wetter phases drastically contrast with periods of reduced glacial activities dated from the early bronze age ca 3870 3770 cal bp the iron age ca 2220 2150 cal bp the roman period ca ad115 330 and the medieval warm period ca ad760 1160 in addition these dryer periods are associated with mining activities at high altitude

medieval lead making on mont lozere massif cevennes france tracing ore sources using pb isotopes this study aims to document the origin of metallurgical activities on the mont lozere massif cevennes mountains south of massif central france which is the largest medieval site of pb ag metallurgical activities in france these activities are characterised by more than 70 sites comprising numerous dispersed slags related charcoal samples dated by 14c have yielded a medieval ca xi xii th c age numerous ore deposits now mostly old mine tailings surround the granitic massif and are possible candidates for suppliers of the old smelting activities in western europe pb ag mines were of primordial importance for the medieval monetary system mines were intensively coveted by lords bishops and kings and their exploitation was strictly regulated by each owner the scarcity of ancient manuscripts makes it impossible to use a historical approach to determine the ore source regions related to a given metallurgical activity the ore sources for this metallurgical activity were traced by comparing the pb isotopic composition of slags and that of galena deposits surrounding the mont lozere the range of pb isotopic compositions measured in slag samples is restricted and included in the field defined by galena from surrounding ores in pb pb isotope diagrams it is shown that although direct tracing of the ore supplies is not straightforward many ancient mine areas must be excluded whereas some others seem highly likely these old mines are not necessarily the closest to the smelting sites suggesting that the choice of metal making location was constrained by several factors including type of wood here beech and water proximity but more importantly land ownership

3d fold growth in transpression abstract geological folds in transpression are inherently 3d structures hence their growth and rotation behavior is studied using 3d numerical finite element simulations upright single layer buckle folds in newtonian materials are considered which grow from an initial point like perturbation due to a combination of in plane shortening and shearing i e transpression the resulting fold growth exhibits three components 1 fold amplification vertical 2 fold elongation parallel to fold axis and 3 sequential fold growth perpendicular to axial plane of new anti and synforms adjacent to the initial fold generally the fold growth rates are smaller for shearing dominated than for shortening dominated transpression in spite of the growth rate the folding behavior is very similar for the different convergence angles the two lateral directions always exhibit similar growth rates implying that the bulk fold structure occupies an increasing roughly circular area fold axes are always parallel to the major horizontal principal strain axis max i e long axis of the horizontal finite strain ellipse which is initially also parallel to the major horizontal instantaneous stretching axis isa max after initiation the fold axes rotate together with max sequential folds appearing later do not initiate parallel to isa max but parallel to max i e parallel to the already existing folds and also rotate with max therefore fold axes do not correspond to passive material lines and hinge migration takes place as a consequence the fold axis orientation parallel to max is independent of convergence angle and viscosity ratio therefore a triangular relationship between convergence angle amount of shortening and fold axis orientation exists if two of these values are known the third can be determined this relationship is applied to the zagros fold and thrust belt to estimate the degree of strain partitioning between the simply folded belt and the bordering strike slip fault system

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

impact of relative sea level and rapid climate changes on the architecture and lithofacies of the holocene rhone subaqueous delta western mediterranean sea abstract the modern rhone delta in the gulf of lions nw mediterranean is a typical wave dominated delta that developed after the stabilization of relative sea level following the last deglacial sea level rise similar to most other deltas worldwide it displays several stacked parasequences and lobes that reflect the complex interaction between accommodation sediment supply and autogenic processes on the architecture of a wave dominated delta the interpretation of a large set of newly acquired very high resolution seismic and sedimentological data well constrained by 14c dates provides a refined three dimensional image of the detailed architecture seismic bounding surfaces sedimentary facies of the rhone subaqueous delta and allows us to propose a scenario for delta evolution during the last deglaciation and holocene the subaqueous delta consists of parasequence like depositional wedges a few metres to 20 30 m in thickness these wedges first back stepped inland toward the nw in response to combined global sea level rise and overall westward oceanic circulation at a time when sediment supply could not keep pace with rapid absolute eustatic sea level rise at the younger dryas preboreal transition more rapid sea level rise led to the formation of a major flooding surface equivalent to a wave ravinement surface after stabilization of global sea level in the mid holocene accommodation became the leading factor in controlling delta architecture an eastward shift of depocentres occurred probably favoured by higher subsidence rate within the thick messinian rhone valley fill the transition between transgressive backstepping geometry and regressive prograding geometry para sequences resulted in creation of a maximum flooding surface mfs that differs from a classical mfs described in the literature it consists of a coarse grained interval incorporating reworked shoreface material within a silty clay matrix this distinct lithofacies results from condensation erosion which appears as an important process even within supply dominated deltaic systems due to avulsion of distributaries the age of the mfs varies along strike between ca 7 8 and 5 6 kyr cal bp in relation to the position of depocentres and climatically controlled sediment supply the last rapid climate change of the holocene the little ice age 1250 1850 ad had a distinct stratigraphic influence on the architecture and lithofacies of the rhone subaqueous delta through the progradation of two deltaic lobes in response to changes in sediment supply linked to rapid climate changes and to anthropic factors the rhone delta evolved from wave dominated to fluvial dominated and then wave dominated again

holocene climate variability and change a data based review the holocene thermal maximum with peak temperatures prior to 7 ka bp is mostly accentuated in the northern hemisphere still visible in the southern hemisphere and possibly did not exist in the tropics between this period and the modern warming a remarkable negative temperature trend occurred in the northern hemisphere which was probably the effect of a decreasing orbital induced insolation during the boreal summer on average the northern hemisphere humidity precipitation records do not show any significant trend a mechanistic explanation for the multi decadal to century scale holocene cold relapses which mainly occurred in the atlantic european regions exists for only the early holocene cooling events which are probably the result of a collapse of the meridional overturning circulation owing to freshwater outbursts from the laurentide ice sheet possibly the late holocene cold events after c 4 ka bp are influenced by the covarying influence of major tropical volcanic eruptions and grand solar minima

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

the early holocene sea level rise the causes anatomy and consequences of the early holocene sea level rise ehslr are reviewed the rise of ca 60m took place over most of the earth as the volume of the oceans increased during deglaciation and is dated at 11 650 7000 cal bp the ehslr was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams the patterns of ice sheet decay and the evidence for meltwater pulses are reviewed and it is argued that the ehslr was a factor in the ca 8470 bp flood from lake agassiz ojibway patterns of relative sea level changes are examined and it is argued that in addition to regional variations temporal changes are indicated the impact of the ehslr on climate is reviewed and it is maintained that the event was a factor in the 8200 bp cooling event as well as in changes in ocean current patterns and their resultant effects the ehslr may also have enhanced volcanic activity but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated the rise probably influenced rates and patterns of human migrations and cultural changes it is concluded that the ehslr was a major event of global significance knowledge of which is relevant to an understanding of the impacts of global climate change in the future

tracking solitary waves below land fast ice 1 data from two acoustic doppler current profilers separated by 76 m and deployed through land fast ice in the canadian arctic archipelago in may 2002 are examined the three velocity components were sampled intermittently at 1 minute intervals over a 3 week period to 19 m below the ice water interface the vertical structure was resolved using empirical orthogonal functions eof while the shallow water korteweg de vries kdv and deep water benjamin ono bo theoretical solutions were used to guide a pseudo wavelet analysis of the horizontal structure numerous instances of near simultaneous spikes were detected in the empirical mode 1 time series a 3 5 hour period on 21 may 2002 containing two disturbances was examined in detail wavelet scalograms suggested that there was a 20 minute lag in the first disturbance and 16 minutes in the second the scalogram values indicated that kdv was more consistent with the waveshapewave shapes than bo theory the character of the two events was very different the first had a broader spatial distribution than the second and the measured translational speed was reasonably consistent with that of a mode 1 kdv solitary wave the second event had a much slower propagation speed and a near surface maximum in the vertical velocity eigenvector suggesting a mode 2 wave it is suggested that ice keels from a nearby pressure ridge could be the source

superimposed folding and w sn vein type mineralisation in the central iberian zone associated with late variscan oroclinal buckling a structural analysis from the regoufe area portugal abstract the cantabrian orocline is a major orocline that bends the variscan belt of western europe despite a wealth of studies its timing and relationship with the late variscan folding stages in the iberian massif are still debated this study provides an integrated structural analysis of the variscan fold generations and associated w sn bearing vein systems within the southern central iberian zone regoufe portugal giving insight into their kinematic relationship with oroclinal buckling two superimposed fold generations with mutually parallel steep to vertical fold axes have been identified isoclinal f 1 folds with e w striking axial planes formed during coaxial shortening and are spatially localised f 3 folds with nw se axial planes are associated with late variscan transpressional deformation and constrain the structural outline of the major folds temporal and kinematic considerations indicate that vertical axis asymmetric f 3 folding corresponds with the expected deformation style within the southern limb of the cantabrian orocline the regoufe area is characterised by two types of w sn vein type mineralisation granite hosted hydrothermal quartz veins show a concentric distribution and are associated with the stress regime during granite emplacement the vein system within the metasedimentary host rock however is emplaced along a regional subhorizontal cross fold joint system this cross fold joint system developed orthogonal to the subvertical f 3 fold axes and is interpreted to be coeval with oroclinal buckling these results impact the understanding of i the relative significance and geometry of the main deformation stages in the iberian massif reconciling the timing and kinematics of f 3 regional folding with oroclinal buckling and ii the kinematic relationship between late to postorogenic deformation and w sn vein type mineralisation

the senegal river mud belt a high resolution archive of paleoclimatic change and coastal evolution abstract fine grained sediment depocenters on continental shelves are of increased scientific interest since they record environmental changes sensitively a north south elongated mud depocenter extends along the senegalese coast in mid shelf position shallow acoustic profiling was carried out to determine extent geometry and internal structures of this sedimentary body in addition four sediment cores were retrieved with the main aim to identify how paleoclimatic signals and coastal changes have controlled the formation of this mud depocenter a general paleoclimatic pattern in terms of fluvial input appears to be recorded in this depositional archive intervals characterized by high terrigenous input high sedimentation rates and fine grain sizes occur roughly contemporaneously in all cores and are interpreted as corresponding to intensified river discharge related to more humid conditions in the hinterland from 2750 to 1900 and from 1000 to 700 cal a bp wetter conditions are recorded off senegal an observation which is in accordance with other records from nw africa nevertheless the three employed proxies sedimentation rate grain size and elemental distribution do not always display consistent inter core patterns major differences between the individual core records are attributed to sediment remobilization which was linked to local hydrographic variations as well as reorganizations of the coastal system the senegal mud belt is a layered inhomogeneous sedimentary body deposited on an irregular erosive surface early holocene deceleration in the rate of the sea level rise could have enabled initial mud deposition on the shelf these favorable conditions for mud deposition occur coevally with a humid period over nw africa thus high river discharge sedimentation started preferentially in the northern areas of the mud belt during mid holocene a marine incursion led to the formation of an embayment afterwards sedimentation in the north was interrupted in association with a remarkable southward shift in the location of the active depocenter as it is reflected by the sedimentary architecture and confirmed by radiocarbon dates these sub recent shifts in depocenters location are caused by migrations of the senegal river mouth during late holocene times the weakening of river discharge allowed the longshore currents to build up a chain of beach barriers which have forced the river mouth to shift southwards

fracture zones constrained by neutral surfaces in a fault related fold insights from the kelasu tectonic zone kuqa depression abstract stress variation associated with folding is one of the controlling factors in the development of tectonic fractures however little attention has been paid to the influence of neutral surfaces during folding on fracture distribution in a fault related fold in this study we take the cretaceous bashijiqike formation in the kuqa depression as an example and analyze the distribution of tectonic fractures in fault related folds by core observation and logging data analysis three fracture zones are identified in a fault related fold a tensile zone a transition zone and a compressive zone which may be constrained by two neutral surfaces of fold well correlation reveals that the tensile zone and the transition zone reach the maximum thickness at the fold hinge and get thinner in the fold limbs a 2d viscoelastic stress field model of a fault related fold was constructed to further investigate the mechanism of fracturing statistical and numerical analysis reveal that the tensile zone and the transition zone become thicker with decreasing interlimb angle stress variation associated with folding is the first level of control over the general pattern of fracture distribution while faulting is a secondary control over the development of local fractures in a fault related fold

internal tides observed by an acoustic doppler current profiler abstract previous studies of knight inlet british columbia revealed the presence of a strong internal m2 tide most of the energy was found to be in either the first or second dynamic modes due to difficulties in sampling of the surface layer objective estimates of the distribution of tidal energy and reflection coefficients until now have been impossible to obtain during june and july 1989 an intense acoustic doppler current profiler adcp sampling of the inlet was conducted these results are used to show the existence of a strong semidiurnal flow in the baroclinic field the authors propose that the horizontal phase information inherent in the spatial sampling by the adcp can be used to resolve the distribution of energy between dynamic modes through a least squares fit of the data to a simple free wave propagation model of the inlet the authors arrive at objective estimates of the distribution of m2 internal tide energy the fitting procedure is found to be sensitive to fluctuations in the

methods for determining deformation history for chocolate tablet boudinage with fibrous crystals abstract chocolate tablet boudinage with fibrous crystal growths between the boudinaged plates from two localities were studied in one from leytron valais switzerland the deformation history was found to be a succession of plane strain increments with the shortening direction perpendicular to the boudinaged sheet and the extension direction showing a progressive change in orientation within the sheet the incremental and finite strains were evaluated the other specimen from parys mountain anglesey great britain was found to have a more complex history with diachronous break up of the competent layer and flattening strain increments it was found that under these circumstances the direct graphical methods of determining finite and incremental strains gave inconsistent results a numerical model was developed which allowed the simulation of chocolate tablet structure with a complex deformation history the model was applied to the anglesey specimen and three possible strain histories for this structure were tried

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

sinking of a fragmented anhydrite layer in rock salt abstract two dimensional numerical models are used to study the gravity driven sinking of a dense boudinaged anhydrite layer within rock salt we analyze models with an infinite array of regularly spaced blocks two and three block clusters and irregularly spaced blocks we show that the mass of the blocks their shapes and spatial arrangement are the dominating factors that control sinking velocity variation of the block separation distance can modify the velocity by many orders of magnitude for the model with the regularly spaced cuboidal blocks we derive a new approximate formula for their terminal velocity the solution works best when the block separation distance to block width is smaller than 1 and the block height to block separation distance is larger than 1 the horizontally aligned and regularly spaced blocks sink vertically with a constant velocity for clustered blocks the velocity depends on the number of blocks in the cluster and their arrangement and it is larger than for the case of the regularly aligned blocks the blocks can exhibit swinging or rotational motions and can change their spatial arrangement which in turn affects their sinking velocity additionally we show examples of complex structures that develop during block sinking through a stratified salt in the case of two block clusters in the case of an irregularly spaced array the blocks sink faster up to few orders of magnitude than in the regularly spaced arrangement and the mean sinking velocity generally increases with the increasing irregularity of the blocks positions the blocks often tend to cluster initiating a locally fast downward flow that generates backflow which can lead to the upward motion of non clustered blocks the irregular spacing differentiates sinking velocities of individual blocks and promotes their vertical separation distance we show that the mechanical interaction between the blocks can explain low sinking rates of anhydrite blocks observed in zechstein basin

numerical simulations of parasitic folding in multilayers we use the finite element method to simulate slow viscous newtonian flow in two dimensions without gravity and to model asymmetric sand z shaped and symmetric m shaped parasitic folds during multilayer folding during multilayer folding the matrix between stiffer layers shows a deformation close to pure shear in the hinge area and a combination of pure and simple shear in the limb areas thinner layers placed between thicker layers develop symmetric parasitic folds in the hinge and eventually asymmetric parasitic folds in the limbs of the larger fold our results verify numerically the theory that asymmetric parasitic folds develop from symmetric buckle folds that are sheared by the hingeward relative displacement of the thick layers in the limbs of the first order fold to develop asymmetric shapes the amplitudes of the parasitic folds must exceed a critical value before the first order fold begins to amplify otherwise the parasitic folds are unfolded during flattening that takes place in the limb area between the thick layers more than five thin layers are necessary to generate distinct asymmetric parasitic folds for the applied model setting more layers generate higher amplification rates in the thin layers and hence higher amplitudes 2006 elsevier ltd all rights reserved

outcrop scale tomography insights into the 3d structure of multiphase boudins abstract we analyze the 3d geomorphology of a boudinaged amphibolite layer encased in marble using meter scale tomography by serial sectioning high resolution imaging and 3d reconstruction of a 2 m block from a quarry in the high grade core of the naxos core complex local uncertainties in the model are resolved by dissolution of marble in selected slabs yielding a large highly accurate 3d model results show five generations of brittle extension of the amphibolite in ductile marble although examination of the boudinaged layer on the outside of the block only suggested one generation most prominent are the rotated domino boudins where part of the dilatancy between domino boudins can be shown to be due to later reactivation shear fractures between domino boudins have relatively large throw gradients indicating ductile rupture layer parallel stretch as measured by reconstruction of domino boudins decreases with amphibolite layer thickness although the layer has undergone the same bulk stretch everywhere this suggests that with decreasing layer thickness deformation becomes delocalized offering tantalizing glimpses of rheology under metamorphic conditions

archaeological reconstruction of medieval lead production implications for ancient metal provenance studies and paleopollution tracing by pb isotopes abstract the identification of metal provenance is often based on chemical and pb isotope analyses of materials from the operating chain mainly ores and metallic artefacts such analyses however have their limits some studies are unable to trace metallic artefacts or ingots to their ore sources even in well constrained archaeological contexts possible reasons for this difficulty are to be found among a variety of limiting factors i problems of ore signatures ii mixing of different ores alloys iii the use of additives during the metallurgical process iv metal recycling and v possible pb isotopic fractionation during metal production this paper focuses on the issue of pb isotope fractionation during smelting to address the issue of metal provenance through an experimental reconstruction of argentiferous pb production in the medieval period an attempt was made to better understand and interpret the pb isotopic composition of ore smelting products it is shown that the measured differences outside the total external uncertainties of 0 005 2 sd for 206 pb 204 pb ratios in pb signatures measured between ores slag and smoke are not due to pb mass fractionation processes but to 1 ore heterogeneity 206 pb 204 pb slag ores 0 066 and 2 the use of additives during the metallurgical process 206 pb 204 pb slag ores 0 083 even if these differences are due to causes 1 and or 2 smoke from the ore reduction appears to reflect the ore mining area without a significant disturbance of its pb signature for all the isotopic ratios 206 pb 204 pb smokes ores 0 026 thus because the isotopic heterogeneity of the mining district and additives is averaged in slags slag appears as the most relevant product to identify ancient metal provenance whereas aiming at identifying a given mine seems beyond the possibilities provided by the method searching for the mining district through analysis of the smelting workshop materials should provide a more appropriate approach in cases where no archaeological evidence of ancient mining is available furthermore smoke pb isotopic composition does not seem to be significantly affected by the metallurgical process paleopollution recorded in peat deposits could help to detect ancient mining production and workshops integrated collaboration between mining archaeologists and geochemists appears crucial to achieve this goal

assessment of the precision and accuracy of lead isotope ratios measured by tims for geochemical applications example of massive sulphide deposits rio tinto spain the true reproducibility of lead isotope measurements by thermal ionization mass spectrometer tims was assessed on both the international standard nbs 982 and sulphide samples from the south iberian pyrite belt sipb lead isotope analyses were made on 21 pyrite and galena samples from rio tinto sulphide orebodies in the spanish part of the sipb independent lead isotope analyses were made in the um2 laboratory montpellier using a vg sector 54 mass spectrometer and at brgm orleans using a finnigan mat 262 mass spectrometer internal precision and reproducibility of the isotope measurements were calculated for lead isotope standards nbs 982 and for pyrite and galena samples the reproducibility 2 is 0 12 for 206pb 204pb 0 16 for 207pb 204pb and 0 22 for 208pb 204pb while the internal precision is on average 0 01 for each isotope ratio 2 m this indicates that the usually adopted errors of between 0 10 and 0 25 are appropriate for geological samples tims has been the most common method for measuring u pb ratios by isotopic dilution but since a few years icp ms has also been used for such determinations we thus checked the reproducibility of u pb ratio measurements by icp ms in order to apply this method to sulphide samples independent measurements 2 to 7 for each of 20 analysed samples showed that the measured average reproducibility for u pb ratios is better than 5 this method is thus suitable for determination of u pb ratios in sulphide samples and most other geological materials lead analyses for the rio tinto deposit were made of the pyritic and orebodies and the stringers this deposit one of the biggest massive sulphides in the world is remarkably homogeneous from a lead isotope viewpoint and no difference can be seen between pyritic and polymetallic orebodies the isotope composition of the deposit can be considered as the average composition of the south iberian crust during the devonian early carboniferous period of crustal fusion

transpressional folding and associated cross fold jointing controlling the geometry of post orogenic vein type w sn mineralization examples from minas da panasqueira portugal the world class w sn panasqueira deposit consists of an extensive subhorizontal vein swarm peripheral to a late orogenic greisen cupola the vein swarm consists of hundreds of co planar quartz veins that are overlapping and connected laterally over large distances various segmentation structures a local zigzag geometry and the occurrence of straight propagation paths indicate that they exploited a regional joint system a detailed orientation analysis of the systematic joints reveals a geometrical relationship with the subvertical f2 fold generation reflecting late variscan transpression the joints are consistently orthogonal to the steeply plunging s0 s2 intersection lineation both on the regional and the outcrop scale and are thus defined as cross fold or ac joints the joint system developed during the waning stages of the variscan orogeny when already uplifted to an upper crustal level veining reactivated these cross fold joints under the conditions of hydraulic overpressures and low differential stress the consistent subperpendicular orientation of the veins relative to the non cylindrical f2 hinge lines also when having an inclined attitude demonstrates that veining did not occur during far field horizontal compression vein orientation is determined by local stress states variable on a meter scale but with the minimum principal stress consistently subparallel to fold hinge lines the conspicuous subhorizontal attitude of the panasqueira vein swarm is thus dictated by the geometry of late orogenic folds which developed synchronous with oroclinal buckling of the ibero armorican arc

tablet boudinage of an anhydrite layer in rock salt matrix results from thermomechanical experiments abstract a single competent layer of anhydrite embedded in a matrix of incompetent rock salt was deformed in a flattening type of bulk deformation at temperature t 345 c strain rate 10 7 s 1 to a maximum finite strain e z 30 as the anhydrite layer was oriented perpendicular to the main shortening direction z the layer underwent equal layer parallel extension in all directions resulting in tablet shaped boudins boudinage results from tensile fracture of anhydrite the rock salt matrix on the other hand behaved viscously crystal plastic deformation of halite was accommodated by slip on 110 which led to formation and rotation of subgrains and a 001 maximum parallel to the principal shortening axis z an axisymmetric texture of halite however is present only in high strain domains at the contact to the anhydrite layer where the differential stress obtained from subgrain size of halite reaches maximum values of ca 6 mpa subgrains remote from the anhydrite layer yielded 2 3 mpa which is consistent with the flow stress recorded by the load cell of the machine the non isometric shape of the tablet boudins in plan view is indicated by the ratio between long and short axis r 1 2 1 9 and can be explained by the interaction of concentric and radial tensile fractures both the mean diameter of the tablet boudins in plan view w a and the number of boudins n show a linear relation to the layer thickness progressive finite strain results in a higher number and a smaller mean diameter of the boudins the thickness of the boudins h f is almost the same like the initial layer thickness h i while the aspect ratio w d w a h f decreases with finite strain the mean w d values obtained from all runs are ranging from ca 0 8 to ca 1 5 this range is much lower than the aspect ratio of boudins in viscous or brittle viscous layers but is similar to the aspect ratio expected from fracture saturation models the aspect ratio of the tablet shaped anhydrite boudins is further consistent with aspect ratios published so far for tensile fracture boudins which developed in a plane or constrictional type of bulk deformation

the pressure disturbance of a nonlinear internal wave train observations from a lander fixed to the seafloor over the continental shelf in 124 m of water provide highly resolved velocity measurements through nonlinear internal waves of elevation from these measurements we determine for the first time the non hydrostatic pressure disturbance p nh in nonlinear internal waves for near bottom waves of elevation ranging in amplitude a from 12 to 33 m the value of p nh evaluated at the seafloor changes sign from 0 to and back in accordance with weakly nonlinear theory peak values of vert p nh vert range from 25 to 90 n m 2 the external hydrostatic pressure disturbance due to the surface displacement eta h is inferred from horizontal accelerations for elevation waves eta h peak values range from 0 1 to 9 mm 1 to 90 n m 2 the internal hydrostatic pressure perturbation p wh caused by isopycnal displacement is inferred from measured streamlines and an ambient density profile its value at the seafloor is 0 for elevation waves peak values range from 100 to 300 n m 2 vert eta h vert and seafloor values of vert p nh vert p wh all increase monotonically with a since vert p nh vert and p wh increase at roughly the same rate with a no clear trend arises in the degree to which waves become more or less non hydrostatic as a changes a distinct bottom pressure signature is determined for bottom trapped nonlinear waves of elevation a wave train consisting of a sequence of positive pressure perturbations dominated by p wh by inference a train of surface trapped nonlinear internal waves of depression will consist of a sequence of negative pressure perturbations a result of this analysis is that significant properties of the waves can be discerned from a simple adequately resolved bottom pressure measurement

a new geodynamic interpretation for the south portuguese zone sw iberia and the iberian pyrite belt genesis 1 the south portuguese zone spz constitutes the southernmost segment of the variscan iberian massif it is bounded to the north by the beja acebuches ophiolitic complex and related accretionary wedge to the south lie the iberian pyrite belt ipb and flysch deposits forming the southern extent of the zone structural analysis within the spanish side of the spz supports continuous south propagating deformation evolving from early synmetamorphic thrusting in the internal zone to thin skinned tectonics in the southern external domain the accretion of the spz to the ossa morena zone is also witnessed by the presence of various melanges observed throughout the investigated area part of the melanges observed in the ipb are related to the volcanics and mineralizations setting a key point to understand the ipb mineralizations genesis is to constrain the volcanogenic model one underestimated feature is the large amount of submarine calc alkaline ignimbritic facies implying the presence of caldera structures within the province such correlation between caldera environment and ore deposits strongly suggests that the ipb developed in a continental arc our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south southward this episode is immediately followed by the development of the accretionary prism while farther south a second subduction zone responsible for the arc setting of the ipb initiates subsequent visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the spz

stress orientation and fracturing during three dimensional buckling numerical simulation and application to chocolate tablet structures in folded turbidites sw portugal abstract two orthogonal sets of veins both orthogonal to bedding form chocolate tablet structures on the limbs of folded quartzwackes of carboniferous turbidites in sw portugal structural observations suggest that 1 mode 1 fractures transverse to the fold axes formed while fold amplitudes were small and limbs were under layer subparallel compression and 2 mode 1 fractures parallel to the fold axes formed while fold amplitudes were large and limbs were brought to be under layer subparallel tension we performed two and three dimensional numerical simulations investigating the evolution of stress orientations during viscous folding to test whether and how these two successive sets of fractures were related to folding we employed ellipses and ellipsoids for the visualization and quantification of the local stress field the numerical simulations show a change in the orientation of the local 1 direction by almost 90 with respect to the bedding plane in the fold limbs the coeval 3 direction rotates from parallel to the fold axis at low fold amplitudes to orthogonal to the fold axis at high fold amplitudes the stress orientation changes faster in multilayers than in single layers the numerical simulations are consistent with observation and provide a mechanical interpretation for the formation of the chocolate tablet structures through consecutive sets of fractures on rotating limbs of folded competent layers

internal solitary waves in the warm pool of the western equatorial pacific abstract during the spring tides of late november 1992 early january and early february 1993 solitary internal wave packets were observed at 2 s 156 15 e in the western equatorial pacific apparently generated in the nuguria island group 3 s 153 e the waves propagate northeastward at 2 4 2 8 m s 1 appearing in fixed phase with the underlying semidiurnal baroclinic tide the initial solitary wave crests have downward displacements in excess of 60 m and peak velocities greater than 80 cm s 1 groups of 1 3 crests are observed with vertical structure resembling a first mode internal wave and horizontal variability consistent with third order comb kdv solitons many of the packets exhibit an overall organization reminiscent of undular bores this borelike behavior is confined primarily to the upper 70 m not sharing the mode one dependency of the crests the solitons displace the ambient equatorial currents including the equatorial undercurrent both vertically 80 m and laterally 1 2 km with l

the provenance of sediments in the gulf of lions western mediterranean sea in this study we undertook a reconnaissance study of sediments provenance in the gulf of lions focusing over the last 16 ka we used geochemical and isotopic tracers to determine the source of sediments and give insight into the weathering conditions prevailing sediments samples were selected both onshore and offshore from the western eastern and central part of the gulf of lions we analyzed bulk sediments coarse and fine silt and clay fractions elemental and nd isotope compositions appeared to differ from one grain size fraction to another one these are interpreted in terms of zircon addition in the coarse silt fraction for the elemental concentrations and variable sources influences for the nd isotope compositions our results indicate that sediments in the gulf of lions mainly originated from the rhone river watershed although a contribution of saharan dust is seen in one sample influence of pyrenean small rivers is minor in these samples some sr isotope compositions shifts are interpreted as reflecting variable amounts of chemical weathering that are consistent with published paleoclimatic reconstructions

carbon isotope evidence for sedimentary miliacin as a tracer of panicum miliaceum broomcorn millet in the sediments of lake le bourget french alps abstract we report the determination of the carbon isotopic composition of miliacin olean 18 en 3 ol methyl ether extracted from the sediments of lake le bourget french alps it is compared with the 13 c value of miliacin extracted from panicum miliaceum broomcorn millet a c 4 plant and chionochloa sp a c 3 plant the 13 c value of sedimentary miliacin 21 5 is very close to that of miliacin extracted from bran 23 and seeds 23 5 of p miliaceum and significantly different from that of chionochloa sp 33 these results provide additional support for the use of sedimentary miliacin as a tracer of broomcorn millet a c 4 cereal cultivated since the bronze age around lake le bourget these findings illustrate the potential of this compound to reconstruct past agriculture from lake sediment archives finally considering the high abundance of miliacin in the bran of p miliaceum the compound could have been wind transported to the sediment during threshing and winnowing on the lake shore

changes in erosion patterns during the holocene in a currently treeless subalpine catchment inferred from lake sediment geochemistry lake anterne 2063 m a s l nw french alps the role of climate and human activities a high resolution sedimentological and geochemical study was performed on a 20 m long core from the alpine lake anterne 2063 m a s l nw french alps spanning the last 10 ka sedimentation is mainly of minerogenic origin the organic matter quantity toc as well as its quality hydrogen hi and oxygen oi indices both indicate the progressive onset and subsequent stabilization of vegetation cover in the catchment from 9950 to 5550 cal bp during this phase the pedogenic process of carbonate dissolution is marked by a decrease in the calcium content in the sediment record between 7850 and 5550 cal bp very low manganese concentrations suggest anoxic conditions in the bottom water of lake anterne these are caused by a relatively high organic matter terrestrial and lacustrine content a low flood frequency and longer summer stratification triggered by warmer conditions from 5550 cal bp a decrease in toc stabilization of hi and higher sedimentation rates together reflect increased erosion rates of leptosols and developed soils probably due to a colder and wetter climate then three periods of important soil destabilization are marked by an increased frequency and thickness of flood deposits during the bronze age and by increases in topsoil erosion relative to leptosols hi increases during the late iron age roman period and the medieval periods these periods are also characterized by higher sedimentation rates according to palynological data human impact deforestation and or pasturing activity probably triggered these periods of increased soil erosion

land use changes and environmental dynamics in the upper rhone valley since neolithic times inferred from sediments in lac moras lac moras is a small lake located on a low elevation plateau in the upper rhone valley 304 m a s l the upper 5 m of accumulated sediment in the lake span 7500 years and offer a detailed record of environmental perturbations and land use history at a local scale a multiproxy analysis pollen charcoal and geochemical parameters led to the establishment of four periods of landscape dynamics the first evidence of human impacts was recorded during the neolithic and bronze age 6000 2700 cal bp these impacts were temporary and most likely affected small areas the second period in the iron age classical antiquity 2200 1900 cal bp appears to be a key period in which the intensification of anthropogenic pressure primarily grazing with localised areas of cultivation caused high intensity erosion events and deeply affected soil stability during the middle ages wheat rye and hemp cultures as well as tree farming walnut chestnut were intensively developed from 50 cal bp the 19th century on

evolution of the rhone delta plain in the holocene abstract the delta plain of the rhone shows many sandy beach ridges cropping out at the surface we propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form morphologies of the lobes depend on four principal factors 1 the variation of the relative sea level which constitutes the morphogenic base level 2 the fluvial input volume of water discharge and sedimentary input number and position of the mouths 3 marine dynamics volume and direction of the longshore drift dominant wave direction 4 the accommodation space created by the rise of relative sea level along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea our conclusions are the main holocene paleo delta lobes of ulmet and saint ferreol were contemporaneous being deposited from 4000 to 2000 yr bp however the fluvial style of their downstream channel meandering for ulmet channel and linear for saint ferreol and the lobe morphologies of both channels are contrasted rounded in the case of ulmet and elongated for saint ferreol the role of the accommodation space is confirmed by two recent drillholes traversing the entire holocene succession which reveal a prior stage of sedimentary filling in the case of the saint ferreol lobe thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe the decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of rhone however the high rate of progradation of saint ferreol lobe after 2900 bp is probably a consequence of the increase of human activity after this date the variation of relative sea level remains an important factor controlling the evolution of the rhone delta after 6000 bp the local stabilization of the relative sea level between 4585 bp and 3520 bp played an important role in the triggering of coastal progradation saint ferreol lobe eastern margin rhone delta

theory of chocolate tablet boudinage two dimensional boudinage in a flattening type of bulk deformation with equal layer parallel extensions in all directions leads to the development of roundish or polygonal outlines of boudins in plan view as combined experimental and theoretical studies show chocolate tablet boudinage with two sets of mutually perpendicular boudin axes may form in different ways 1 unequal layer parallel extension in the matrix results in one set of extension fractures forming perpendicular to the greatest principal stress in the matrix once these long narrow boudins are formed the greatest principal stress in the brittle layer becomes approximately parallel to the long axis of the boudin as a result a second set of fractures forms normal to the first set 2 in lineated rocks the anisotropy of tensile strength leads to the sequential formation of two sets of extension fractures parallel and perpendicular to the lineation depending on the orientation of the lineation the boudin axes may or may not be parallel to the principal stresses in the matrix 3 boudins with rectangular plan view may also form when two successive events of unidirectional boudinage are superposed on one another irrespective of the direction of principal extensional strain rate in the matrix the second generation extension fractures are likely to form approximately perpendicular to the first generation boudin axes

fluid assisted particulate flow of turbidites at very low temperature a key to tight folding in a submarine variscan foreland basin of sw europe 1 the problem addressed in this article is how sedimentary formations like turbidites in a foreland basin which include layers with apparently great competence contrast can be tightly folded in a regular manner under very low temperature and pressure this raises two major issues the rheological behavior of the rocks at the time of folding and the role played by fluids in order to understand very low temperature folding and the structural evolution of a submarine foreland basin we carried out detailed structural work in turbidites with alternating sandstone and shale for which estimated peak temperature conditions were top diagenetic to very low grade metamorphism folds are tight to isoclinal with local collapsed hinges which implies that the incompetent shale was mobile enough to flow away from strongly flattened areas we did not find evidence for cataclastic flow or crystal plasticity at mesoscopic and microscopic scales other structures mostly boudins foliations conjugate brittle faults and quartz veins associated with folds denote anisotropic compaction by fluid extraction during regional shortening this is possible if the folded rocks were unconsolidated fluid saturated sediments the estimated low peak temperature is consistent with the shale being unlithified poorly cemented grains are free to slide past one another under shallow burial or high pore pressure conditions following this line of thought we consider independent particulate flow assisted by fluids under very low confining pressure bean bag analogy as the rock deformation mechanism active during the described intense folding similar deformation is likely occurring and has occurred in other submarine accretionary wedges

stress evolution during 3d single layer visco elastic buckle folding implications for the initiation of fractures abstract buckle folds of sedimentary strata commonly feature a variety of different fracture sets some fracture sets including outer arc tensile fractures and inner arc shear fractures at the fold hinge zones are well understood by the extensional and compressional strain stress pattern however other commonly observed fracture sets including tensile fractures parallel to the fold axis tensile fractures cutting through the limb extensional faults at the fold hinge and other shear fractures of various orientations in the fold limb fail to be intuitively explained by the strain stress regimes during the buckling process to obtain a better understanding of the conditions for the initiation of the various fractures sets associated with single layer cylindrical buckle folds a 3d finite element modeling approach using a maxwell visco elastic rheology is utilized the influences of three model parameters with significant influence on fracture initiation are considered burial depth viscosity and permeability it is concluded that these parameters are critical for the initiation of major fracture sets at the hinge zone with varying degrees the numerical simulation results further show that the buckling process fails to explain most of the fracture sets occurring in the limb unless the process of erosional unloading as a post fold phenomenon is considered for fracture sets that only develop under unrealistic boundary conditions the results demonstrate that their development is realistic for a perclinal fold geometry in summary a more thorough understanding of fractures sets associated with buckle folds is obtained based on the simulation of in situ stress conditions during the structural development of buckle folds

records of holocene climatic fluctuations and anthropogenic lead input in elemental distribution and radiogenic isotopes nd and pb in sediments of the gulf of lions southern france marine mud belts represent potential continuous high resolution climatic environmental and anthropogenic archives in this study a geochemical record of the gulf of lions mud belt which receives

formation of chocolate tablet boudins results from scaled analogue models abstract we used power law viscous plasticine as a rock analogue to simulate chocolate tablet boudinage of rocks undergoing dislocation creep a competent plasticine layer oriented perpendicular to the main shortening direction z underwent two phases of plane strain in a weaker plasticine matrix with the principal stretching axis x and the axis of no change y replacing each other from the first to the second phase in each phase of plane strain boudinage was controlled by an initial phase of viscous necking followed by extension fracture along the neck domain increase in the magnitude of finite strain e and decrease in layer thickness h i result in a decrease in the boudin width w a and an increase in the number of boudins n given the viscosity ratio between layer and matrix m is higher than ca 5 the number of boudins decreases and the boudin width increases with increasing values of m an unexpected result of the present study is that in each experiment the number of boudins was significantly higher during the second phase of plane strain this difference should be related to additional drag of the matrix plasticine on the stiff layer in the neck domains formed during the first phase of boudinage the aspect ratio of the second generation of boudins w d w a h i is compatible with aspect ratios of natural boudins and with aspect ratios calculated using analytical solutions

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

late glacial to preboreal sea level rise recorded by the rhone deltaic system nw mediterranean abstract a unique late glacial preboreal record of changes in sea level and sediment fluxes originating from the alps is recorded in the rhone subaqueous delta in the western mediterranean sea the compilation of detailed bathymetric charts together with high resolution seismic profiles and long cores reveals the detailed architecture of several sediment lobes related to periods of decreased sea level rise and or increased sediment flux they are situated along the retreat path of the rhone distributaries from the shelf edge and canyon heads up to the modern coastline they form transgressive backstepping parasequences across the shelf the late holocene highstand deltas being confined to the inner shelf the most prominent feature is an elongated paleo shoreface deltaic system with an uppermost sandy fraction remolded into subaqueous dunes a long piston core into the bottomsets of this prograding unit allows precise dating of this ancient deltaic system in seismic data it displays aggradation starting at 15 cal kyr bp followed by progradation initiated during the first phase of the younger dryas a period of reduced sea level rise or stillstand the delta kept pace with resumed sea level rise during the preboreal which is estimated at about 1 cm yr as a result of increased sediment supply from the alps melting of glaciers and more humid climate flushing the sediment down to the sea abandonment of the delta occurred around 10 500 cal yr bp that is to say about 1000 yr after the end of the younger dryas probably because of decreased sediment flux

lead isotope systematics of the giant massive sulphide deposits in the iberian pyrite belt lead isotope analyses were performed on 26 polymetallic massive sulphide deposits of the iberian pyrite belt as well as on overlying gossans and associated volcanic rocks all the massive sulphide deposits except for neves corvo and nearly all the volcanic rocks show very similar isotopic compositions grouped around 18 183 206pb 204pb 15 622 207pb 204pb and 38 191 208pb 204pb indicating that most of the ore deposit lead was derived from the same continental crust environment as the associated volcanic rocks the isotopic compositions are representative of the average south iberian crust during the devonian to early carboniferous dinantian and their constancy implies a homogenization of the mineralizing fluids before the deposition of the massive sulphides from hydrothermal fluids circulating through interconnected regional fracture systems this isotopic constancy is incompatible with multiple small independent hydrothermal cells of the east pacific rise type and fits much better with a model of hydrothermal convections driven by magmatic floor heating neves corvo is the only south iberian massive sulphide deposit to have a heterogeneous isotopic composition with in particular a highly radiogenic stanniferous ore 206pb 204pb of the cassiterite is 18 40 a model of lead mixing with three components is proposed to explain these variations 1 one derived from the devonian to early carboniferous dinantian continental crust that generated all the other massive ores 2 an eohercynian stanniferous mineralization partly remobilized during the formation of the massive sulphides but independent of them and 3 a precambrian continental crust component the juxtaposition of three different sources places neves corvo in a specific paleogeographic situation that could also explain its mineralogical specificity the geodynamic context that best explains all the obtained isotopic results is one of an accretionary prism the fact that lead isotope signatures of the gossans are almost identical to those of the underlying massive sulphides means that this technique could be a useful exploration tool for the iberian pyrite belt

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

polyphase development of chocolate tablet boudins in the sat zone kumaun lesser himalaya india abstract a combination of two groups of boudins exposed in orthogonal sections is observed as chocolate tablet structures in the south almora thrust sat zone kumaun lesser himalaya evidence from boudin associated veins fractures folds and microstructures suggest that the chocolate tablet boudins were developed as a consequence of layer parallel stretching in two orthogonal directions during two successive phases of ductile shearing in the sat zone the early phase of top to nw shearing is speculated as a pre himalayan deformation during which the early boudins were developed this deformation was superposed by a late phase of top to sw himalayan shearing and development of the attendant late boudins it is concluded that the interference of two phases of successively developed boudins has resulted into development of the chocolate tablet structures in the sat fluid inclusion and microstructures indicate a low temperature about 300 c growth of the chocolate tablet boudins the finite strain analysis reveals that a maximum strain ratio rs of 1 7 was accumulated during the pre himalayan phase of deformation whereas rs was of the order of 2 1 in the himalayan phase of deformation

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

internal wave directional spectra using an acoustic doppler current profiler an acoustic doppler current profiler was deployed through land fast ice near resolute northwest territories it recorded a distinct train of high frequency periods 30 0 min horizontal flow without a corresponding coherent vertical velocity component attributed to a density driven along isopycnal flow created by salt rejection emanating from a broad shelf to the northeast

the origin of tablet boudinage results from experiments using power law rock analogs abstract we used power law viscous plasticine n ca 7 as a rock analog to simulate boudinage of rocks undergoing dislocation creep and brittle fracture a competent plasticine layer oriented perpendicular to the main shortening direction z underwent bulk pure flattening inside a less competent plasticine matrix computer tomographic analyses of the deformed samples revealed that boudinage results from an initial phase of viscous necking followed by tensile failure along the previously formed necks the resulting boudins display a polygonal shape in plan view and are referred to as tablet boudins in contrast to the square to rectangular shaped chocolate tablet boudins the ratio between the plan view long and short axis r ranges from 1 2 to 2 6 the polygonal non isometric shape of the tablet boudins can be explained by the strong interaction of concentric and radial tensile fractures with increasing layer thickness h i the mean diameter of the boudin tablets w a increases while the number of boudins n decreases progressive finite strain results in a higher number of the boudins and a smaller mean diameter the thickness of the boudins h f is almost the same as the initial layer thickness h i while the aspect ratio w d w a h f decreases with layer thickness and finite strain the mean w d values obtained from all experiments span from ca 4 to ca 11 tablet boudins described in the present paper have yet not been described from natural outcrops the reasons might be that pure flattening strain is not common in nature and the characterization and evaluation of tablet boudins requires geometrical analysis in three dimensions which is a difficult task when such structures occur in nature

3d numerical modeling of forward folding and reverse unfolding of a viscous single layer implications for the formation of folds and fold patterns abstract the main aims of this study are to show i that non cylindrical three dimensional 3d fold shapes and patterns can form during a single unidirectional shortening event and ii that numerical reverse modeling of 3d folding is a feasible method to reconstruct the formation of 3d buckle folds 3d viscous newtonian single layer folding is numerically simulated with the finite element method to investigate the formation of fold shapes during one shortening event an initially flat layer rests on a matrix with smaller viscosity and is shortened in one direction parallel to the layering forward modeling with different initial geometrical perturbations on the flat layer and different lateral boundary conditions generates non cylindrical 3d fold shapes and patterns the simulations show that in reality the initial layer geometry and the boundary conditions strongly control the final fold geometry fold geometries produced from the forward folding models are used as initial setting in numerical reverse folding models with parameters identical to those of forward models these reverse models accurately reconstruct the initial geometry of forward models with also only one extension event parallel to the previous shortening direction the starting geometry of the forward models is inaccurately reconstructed by the reverse models if a significantly different viscosity ratio than in the forward models is used this work demonstrates that reverse modeling has a high potential for reconstructing the deformation history of folded regions and rheological constraints such as viscosity ratio reverse models may be applied to natural 3d fold shapes and patterns in order to determine if they formed i during a single or multiple deformation events and ii as active buckle folds with a viscosity ratio 1 or as passive kinematic folds without buckling this approach may find much application to fold interference patterns in particular

late variscan deformation in the iberian peninsula a late feature in the laurentia gondwana dextral collision the late variscan deformation event in iberia is characterized by an intraplate deformation regime induced by the dextral oblique collision between laurentia and gondwana this episode in iberia is characterized by nne ssw brittle to brittle ductile strike slip faults which are considered by the classic works as sinistral strike slip faults however the absence of mesozoic formations constraining the age of this sinistral kinematics led some authors to consider it as the result of alpine reworking structural studies in almograve and ponta ruiva sectors sw portugal show that nne ssw faults have a sinistral kinematics and are occasionally associated with e w dextral shears moreover this kinematics is related to the late deformation episodes of variscan orogeny in almograve sector the late variscan structures are characterized by nne ssw sinistral kink bands spatially associated with e w dextral faults these structures are contemporaneous and affect the previously deformed carboniferous units the ponta ruiva sector constrains the age of deformation because the e w dextral shears affect the late carboniferous late moscovian units but not the overlying triassic series the new data show that the nne ssw and the e w faults are dynamically associated and result from the late variscan deformation episode the nne ssw sinistral faults could be considered as second order domino structures related to first order e w dextral shears linked to laurentia gondwana collision during late carboniferous permian times

fold thrust structures where have all the buckles gone special publication title folding and fracturing of rocks 50 years of research since the seminal text book of j g ramsay we dedicate the paper to the memory of martin casey 1948 2008 who did much through good humored argument to ensure that buckling ideas were not lost to what he called the ramping club the thrust belt community the fold thrust research group has been funded by interoil oilsearch and santos we thank paul griffiths and anonymous referee for comments together with hermann lebit for scientific editing the views expressed here of course remain those of the authors

structural evolution of the southernmost segment of the west european variscides the south portuguese zone sw iberia abstract the south portuguese zone spz represents the southernmost unit of the iberian massif it is mainly composed of three structural domains from north to south the beja acebuches ophiolitic complex baoc the pulo do lobo antiform pla and the iberian pyrite belt ipb this study proposes a structural analysis of the spanish part of the spz that allows us to point out two main kinds of deformation one accommodated by early top to the south and following sinistral strike slip tectonics in the northern part of the spz and the other by top to the south thrusting in a wide southern branch this transition underlining the strain partitioning is analysed by lattice preferred orientation of quartz using the texture goniometry method it shows that the deformation is accommodated in the pla at low to middle temperature by basal and prismatic a slip quartz textures suggest increasing thermal conditions of deformation from thrust to strike slip tectonics our work within the ipb allows us to present a sequence of deformation showing a primary south verging ductile thrusting and coeval crustal thickening in response to the thin skinned tectonics the progressive deformation generated backthrusts while it turns shallower southward these features are summarised in an interpretative cross section of the spz that underlines the main structural style of deformation the fore mentioned southward propagating thin skinned thrusts

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

metallogenic provinces and the remobilization process studied by lead isotopes lead zinc ore deposits from the southern massif central france the two main problems of ore genesis are the origin of metals and the process es of emplacement lead isotopes have proven to be a powerful tool for studying these questions we have studied pb zn mineralizations from montagne noire and cevennes southern massif central france by means of lead isotopes this study shows the existence of two populations of ore deposits defined by 17 76 206 pb 204 pb 17 94 and 18 25 206 pb 204 pb 18 63 a general model of lead evolution in these deposits is proposed after evolving in the earth s mantle until approximately 3 b y ago the lead became incorporated into a segment of continental crust then the less radiogenic population of ore deposits was emplaced contemporaneously with the formation of cambrian carbonate host rocks the second population is related to the emplacement of hercynian granitoids or in more general terms to fluid circulations associated with the hercynian orogeny it can also be shown that some of the deposits are remobilized from preexisting ore deposits

structure and generation of turbulence at interfaces strained by internal solitary waves propagating shoreward over the continental shelf abstract detailed observations of the structure within internal solitary waves propagating shoreward over oregon s continental shelf reveal the evolving nature of interfaces as they become unstable and break creating turbulent flow a persistent feature is high acoustic backscatter beginning in the vicinity of the wave trough and continuing through its trailing edge and wake this is demonstrated to be due to enhanced density microstructure increased small scale strain ahead of the wave trough compresses select density interfaces thereby locally increasing stratification this is followed by a sequence of overturning high density microstructure and turbulence at the interface which is coincident with the high acoustic backscatter the richardson number estimated from observations is larger than 1 4 indicating that the interface is stable however density profiles reveal these preturbulent interfaces to be o 10 cm thick much thinner than can be resolved with shipboard velocity measurements by as

three dimensional folding of an embedded viscous layer in pure shear a thick plate analysis is carried out to first order in interface slope for three dimensional folding of a single linear viscous layer of thickness h and viscosity embedded in a uniform viscous medium with viscosity 1 layer and medium are subject to a basic state of homogeneous pure shear with principal directions of strain rate x and y lying in the plane of the layer the solution is explicitly carried out for a fold perturbation in interface shape that is symmetric with respect to the principal strain rate axes f cos lx cos my but it is shown to apply to an arbitrary perturbation in the x y plane the growth rate of the perturbation is found to be are the principal strain rates of the basic state the wavenumber of the most rapidly growing perturbation d is the same as that obtained for a cylindrical perturbation m 0 in a basic state of plane strain yy 0 for maximum rate of shortening parallel to x the cylindrical fold form with axis normal to x m l 0 grows most rapidly for any ratio of yy xx 1 if yy xx all fold forms grow at the same rate and in particular an egg carton fold form is not preterentially amplified the velocity field for the perturbing flow consists of a poloidal field which solely determines the growth of the fold form and a toroidal field with non zero component of vorticity about the axis normal to the layer the latter is required to satisfy both of the two independent shear traction continuity conditions at interfaces there is no coupling between the two fields three dimensional fold forms in the appalachian plateau province in western pennsylvania are described

large scale mechanical buckle fold development and the initiation of tensile fractures tensile failure associated with buckle folding is commonly associated to the distribution of outer arc extension but has also been observed on fold limbs this study investigates whether tensile stresses and associated failure can be explained by the process of buckling under realistic in situ stress conditions a 2 d plane strain finite element modeling approach is used to study single layer buckle folds with a maxwell viscoelastic rheology a variety of material parameters are considered and their influence on the initiation of tensile stresses during the various stages of deformation is analyzed it is concluded that the buckling process determines the strain distribution within the fold layer but is not solely responsible for the initiation of tensile stresses the modeling results show that tensile stresses are most dependent on the permeability viscosity and overburden thickness low permeability 10 19 m2 high viscosity 1021 pa s and low overburden pressure can explain tensile failure at the fold hinge tensile stresses in the limb of the fold cannot in general be explained by buckling rather it develops due to a combination of compression and erosional unloading the modeling results show that erosion of high permeability rocks can explain the generation of tensile stresses at significant depths 2 km both at the hinge of the fold and throughout the limb of the fold this study shows that tensile stresses and associated failure within buckle folds is directly dependent on the distribution of material parameters but moreover to the strain history of the geologic system

flexural slip during visco elastic buckle folding abstract flexural slip is considered as an important mechanism during folding and a general conceptual and qualitative understanding has been provided by various field studies however quantitative evidence of the importance of the flexural slip mechanism during fold evolution is sparse due to the lack of suitable strain markers in this study 2d finite element analysis is used to overcome these disadvantages and to simulate flexural slip during visco elastic buckle folding variations of single and multilayer layer fold configurations are investigated showing that flexural slip is most likely to occur in effective single layer buckle folds where slip occurs between contacts of competent layers based on effective single layer buckle folds the influence of the number of slip surfaces the degree of mechanical coupling based on the friction coefficient and layer thickness on the resulting slip distribution are investigated the results are in agreement with the conceptual flexural slip model and show that slip is initiated sequentially during the deformation history and is maximum along the central slip surface of the fold limb the cumulative amount of slip increases as the number of slip surfaces is increased for a lower degree of mechanical coupling increased slip results in different fold shapes such as box folds during buckling in comparison with laboratory experiments geometrical relationships and field observations the numerical modeling results show similar slip magnitudes it is concluded that flexural slip should represent a significant contribution during buckle folding affecting the resulting fold shape for increased amounts of slip

holocene flood frequency across the central alps solar forcing and evidence for variations in north atlantic atmospheric circulation the frequency of large scale heavy precipitation events in the european alps is expected to undergo substantial changes with current climate change hence knowledge about the past natural variability of floods caused by heavy precipitation constitutes important input for climate projections we present a comprehensive holocene 10 000 years reconstruction of the flood frequency in the central european alps combining 15 lacustrine sediment records these records provide an extensive catalog of flood deposits which were generated by flood induced underflows delivering terrestrial material to the lake floors the multi archive approach allows suppressing local weather patterns such as thunderstorms from the obtained climate signal we reconstructed mainly late spring to fall events since ice cover and precipitation in form of snow in winter at high altitude study sites do inhibit the generation of flood layers we found that flood frequency was higher during cool periods coinciding with lows in solar activity in addition flood occurrence shows periodicities that are also observed in reconstructions of solar activity from 14 c and 10 be records 2500 3000 900 1200 as well as of about 710 500 350 208 suess cycle 150 104 and 87 gleissberg cycle years as atmospheric mechanism we propose an expansion shrinking of the hadley cell with increasing decreasing air temperature causing dry wet conditions in central europe during phases of high low solar activity furthermore differences between the flood patterns from the northern alps and the southern alps indicate changes in north atlantic circulation enhanced flood occurrence in the south compared to the north suggests a pronounced southward position of the westerlies and or blocking over the northern north atlantic hence resembling a negative nao state most distinct from 4 2 to 2 4 kyr bp and during the little ice age south alpine flood activity therefore provides a qualitative record of variations in a paleo nao pattern during the holocene additionally increased south alpine flood activity contrasts to low precipitation in tropical central america cariaco basin on the holocene and centennial time scale this observation is consistent with a holocene southward migration of the atlantic circulation system and hence of the itcz driven by decreasing summer insolation in the northern hemisphere as well as with shorter term fluctuations probably driven by solar activity

a 3 d lagrangian finite element algorithm with remeshing for simulating large strain hydrodynamic instabilities in power law viscoelastic fluids we present a three dimensional 3 d numerical algorithm pink 3d that is based on the finite element method the algorithm is designed to simulate hydrodynamic instabilities in power law viscoelastic fluids under gravity these instabilities are caused by large and sharp contrasts in mechanical strength and or density between different materials e g folding necking or rayleigh taylor diapirism the instabilities are controlled by the geometry of the material interfaces and the related intralayer stress distribution when amplitudes of the material interfaces are still low the presented algorithm combines a deformable lagrangian mesh with remeshing in order to accurately simulate the low amplitude stages of the emerging instabilities and also to simulate the large strain evolution of the structures emerging from these instabilities the remeshing is based on material interfaces that accurately track the boundaries between materials with strongly varying material properties e g effective viscosity or power law stress exponent we describe here the main technical details of the 3 d algorithm the accuracy of the 3 d algorithm is demonstrated with comparisons between the numerical results and 2 d and 3 d analytical solutions for folding necking rayleigh taylor diapirism and circular inclusions in viscous medium we also benchmark the 3 d algorithm with results of a different 2 d finite element algorithm to test the accuracy of the large strain results with remeshing furthermore two tests are presented that show the accuracy of the viscoelasticity implementation pink 3d is also used to study 3 d necking applied to lithospheric slab detachment and 2 d and 3 d folding applied to fold nappe formation in particular we apply the 3 d code to quantify and visualize the evolution of the 3 d finite strain ellipsoid for the developing 3 d structures

geomorphological evidence for fluvial change during the roman period in the lower rhone valley southern france abstract the hydrological and geomorphological dynamics of the lower rhone river southern france are studied during the roman period 2nd 1st centuries bc 2nd 3rd centuries ad the crossing of archaeological and radiocarbon dating methods allow to study events at a pluridecadal to centennial scale from the avignon town to the delta the 15 sites where roman fluvial dynamics were recorded show higher flooding frequencies higher energy levels during floods rises in the marshes or groundwater levels and or active morphological dynamics such as channel migrations from 1st century bc to 1st 2nd centuries ad with respect to the encircling periods although this fluvial change does not reach the amplitude of great climatic events such as the little ice age in the rhone valley we show that it is also perceived in other parts of the catchment and could have a climatic origin however this event is not recorded in the immediate mediterranean environment of the lower rhone so that the rhone appears to efficiently transmit a foreign climatic change

formation of chocolate tablet boudins in a foreland fold and thrust belt a case study from the external variscides almograve portugal abstract chocolate tablet boudins of quartzite are restricted to steep limbs of d 1 folds along the sw coast of portugal the chocolate tablet geometry results from older vertical and younger horizontal quartz veins both sets of veins developed during similar conditions by extension fracture in pre existing necked domains 1 both veins show stretched crystal fibers 2 the boudin aspect ratio is the same in vertical 3 0 1 4 and in horizontal sections 2 9 1 2 3 temperatures obtained from fluid inclusions are similar 200 20 for vertical and 230 22 c for horizontal veins and are compatible with temperatures obtained from illite crystallinity ca 200 ca 250 c given thermal equilibrium between the host rock and the precipitating fluid the chocolate tablet boudins formed close to the metamorphic peak we interpret that the vertical veins developed after the limbs of the d 1 folds had attained their steep attitude and the orientation of the greatest and intermediate principal strain axes had interchanged subsequently the initial strain field was restored and opening of horizontal veins led to the chocolate tablet geometry the direction of the main shortening direction was constant from the initial buckling stage via isoclinal folding and during all boudinage stages

how facies and diagenesis affect fracturing of limestone beds and reservoir permeability in limestone marl alternations abstract facies and diagenetic heterogeneities in carbonate reservoir rocks affect both fracture distribution and fracture permeability many studies focussed on fracture patterns in limestone marl alternations as e g fluid flow models are based on laterally continuous beds here we examine 4010 fractures in multiple layers of limestone marl alternations using a modified scan line method the studied successions belong to the blue lias formation hettangian sinemurian exposed on the coast of the bristol channel united kingdom we combine methods of sedimentology and structural geology with rock physics to gain a better understanding of the role of facies diagenesis and petrophysical properties tensile and compressive strength hardness porosity on the distribution of fractures fracture orientation density spacing and height fracture distribution varies significantly despite similar bed thicknesses indicating that planar bedding planes i e well bedded limestones wbl and beds with bedding plane irregularities i e semi nodular limestones snl must be distinguished snl show higher percentages of non stratabound fractures 67 while they are more stratabound in wbl 57 additionally beds with variable bed thicknesses in scale of 15 m long beds exhibit a wide range of fracture spacing whereas fractures in beds with more continuous bed thicknesses are more regularly spaced considering all lithologies the percentage of non stratabound fractures increases proportionally with caco 3 content three subsections studied in detail reveal different main sedimentological and diagenetic features from early lithified over differentially compacted to physically compacted all of them are characterised by dissimilar percentages of stratabound and non stratabound fractures in limestone beds and marl interbeds our findings demonstrate that the distribution of fractures in individual well bedded limestones is not necessarily representative for successions of limestone marl alternations multiple layers should therefore be studied in outcrop analogues as basis for fluid flow models of reservoirs composed of such lithologies

3d fold growth rates geological folds are inherently 3d structures therefore they also grow in three dimensions here fold growth in all three dimensions is quantified by numerically simulating upright single layer folds in 3d newtonian media horizontal uniaxial shortening leads to a buckling instability which grows from a point like initial perturbation in all three dimensions by fold amplification vertical fold elongation parallel to fold axis and sequential fold growth parallel to shortening direction of secondary and further folds adjacent to the initial isolated fold the two lateral directions exhibit similar averaged growth rates leading to bulk fold structures with aspect ratios in map view close to 1 however fold elongation is continuous with increasing bulk shortening while sequential fold growth exhibits jumps whenever a new sequential fold appears and the bulk fold structure therefore suddenly occupies more space compared with the two lateral growth directions fold amplification exhibits a slightly higher growth rate