early hydrothermal carbon uptake by the upper oceanic crust insight from in situ u pb dating it is widely thought that continental chemical weathering provides the key feedback that prevents large fluctuations in atmospheric co2 and hence surface temperature on geological time scales however low temperature alteration of the upper oceanic crust in off axis hydrothermal systems provides an alternative feedback mechanism testing the latter hypothesis requires understanding the timing of carbonate mineral formation within the oceanic crust here we report the first radiometric age determinations for calcite formed in the upper oceanic crust in eight locations globally via in situ u pb laser ablation inductively coupled plasma mass spectrometry analysis carbonate formation occurs soon after crustal accretion indicating that changes in global environmental conditions will be recorded in changing alteration characteristics of the upper oceanic crust this adds support to the interpretation that large differences between the hydrothermal carbonate content of late mesozoic and late cenozoic oceanic crust record changes in global environmental conditions in turn this supports a model in which alteration of the upper oceanic crust in off axis hydrothermal systems plays an important role in controlling ocean chemistry and the long term carbon cycle

genesis of tectonic inversion structures seismic evidence for the development of key structures along the purbeck isle of wight disturbance the interpretation of a densely spaced and well calibrated seismic grid sheds new light on the development and evolution of key regional and local structures in the wessex basin the results help to resolve long standing controversies concerning the tectonic significance of apparently anomalous outcrop patterns and the role of important local ancillary structures with respect to the major monoclinal folds with which they are associated although the structures are entirely consistent with the effects of contractional reactivation tectonic inversion of normal faults the subsurface data demonstrate the role that original extensional fault segmentation and associated relay ramps had on original depositional patterns subsequent inversion geometries and resultant outcrop patterns as well as illustrating regional controls on the formation of structures the new seismic based interpretations enable a reassessment of the lulworth crumple and the ballard down fault the lulworth crumple is interpreted as a parasitic fold complex generated by internal folding of the inverted incompetent syn rift fill in the immediate hanging wall to the purbeck fault a reactivated major normal fault the ballard down fault s origin is interpreted to result from the formation of a local late stage out of the syncline reverse fault which propagated southwards and upwards through a chalk succession as the chalk had already been rotated to form the northward dipping steep limb of the purbeck monocline at ballard down the structure cuts down stratigraphically the results stress the importance of understanding the nature of original extensional fault geometries and the competence of the sedimentary units incorporated in folds in gaining a full understanding of the genesis and evolution of structural styles in inverted basins

flow to horizontal drains in isotropic unconfined aquifers the laplace transform solution for the problem of flow to horizontal drains in an anisotropic unconfined aquifer is derived the solution for the constant flux horizontal well by zhan and zlotnik zhan h zlotnik v a 2002 groundwater flow to a horizontal and slanted well in an unconfined aquifer water resour res 38 7 13 1 13 11 is modified to obtain the solution for a constant head horizontal drain the laplace transform solution is converted to the real time domain and type curves for the drawdown around and the discharge to a horizontal drain are computed the solution is verified by a numerical simulation the type curves and derivative type curves of the drains are compared with type curves for horizontal wells the sensitivity of type curves on piezometer location specific storage horizontal drain elevation aquifer delay index and drain length is tested these type curves can be used for interpretation of drainage data

eocene sedimentation and tectonics in the hampshire basin sedimentary evidence in the eocene cuisian lutetian of the hampshire basin indicates important intra eocene movement on the isle of wight and purbeck monoclines and on the ridgeway fault evidence for syn depositional movement includes jurassic and cretaceous chert and flint pebbles in the eocene the distribution of which suggests derivation from both e and w at whitecliff bay two units of cross bedded sand have northward directed palaeocurrents and may have been deposited as localized fans of debris reworked from earlier tertiary sediments on the upwarped side of the monocline three units of laminated muds are intercalated with marine sediments in the eastern part of the basin and suggest periods of low salinity tideless conditions these episodes are attributed to the periodic isolation of the hampshire basin from the fully marine dieppe basin to the se this may have been the result of intermittent movement on a tectonic barrier to the se of selsey the onset of uplift and subsequent exposure of the chalk along the southern margin of the basin proceeded unevenly from early cuisian to late lutetian times movement on the portsdown anticline probably occurred over a similar period the isle of wight and purbeck monoclines are the superficial expressions of faults in the palaeozoic basement and not the result of lateral alpine pressures a minor series of syn depositional folds trend nw se across the basin and may reflect a component of sinistral strike slip on basement faults

vein calcite dating reveals pyrenean orogen as cause of paleogene deformation in southern england an improved method of u pb dating of vein calcite formed during deformation is used to determine the age and cause of folding along the south coast of england fractures arising from folding of late cretaceous chalk of southern england occurred 34 7 1 7 myr ago underlying jurassic strata have veins within fractures with ages of 55 48 42 39 37 34 31 and 25 ma with 34 31 ma being the tectonic culmination folding was slightly younger than the age of the youngest strata in the overlying solent group suggesting that folding terminated basin sedimentation this age of north south shortening is inconsistent with attribution to intraplate forces from the mainly younger alps but is plausibly a result of the pyrenean orogen which evolved from 50 to 28 myr ago with a late eocene culmination a modified method for carbonate laser ablation inductively coupled plasma mass spectrometry u pb dating is presented that uses measured 232 th and 208 pb as a better monitor of common pb and it has distinct advantages over existing methods initial common lead determined on samples conforms closely to model compositions calculated by earlier workers with free regressions giving the most robust dates the modified method is applicable to structural geology carbonate diagenesis and to dating of carbonate relevant to palaeo environmental and archaeological studies supplementary material details of sample locations and characteristics photographs of sample localities microscopic images of veins details of the experimental procedure and u pb data for all samples and reference materials are available at https doi org 10 6084 m9 figshare c 3997086

eocene inversion history of the sandown pericline isle of wight southern england study of the composition and distribution of derived lithoclast and fossil suites collected from the selsey barton and becton formations in whitecliff bay isle of wight has enabled a detailed reconstruction of mid late eocene uplift of 500 m on the northern limb of the sandown pericline the stratigraphical distribution of clasts and fossils derived from older formations demonstrates the erosion of progressively older eocene palaeocene and cretaceous sediments during growth of the structure the presence of delicate reworked fossils and clasts together with limited palaeocurrent data support very local derivation from the south the preservational state of the derived materials is used to identify the diverse processes of erosion and transport two phases of uplift lutetian bartonian separated by a period of quiescence and peneplanation have been identified rates of eocene uplift of about 100 m ma 1 are postulated to have taken place

the swiss alps and their peripheral foreland basin stratigraphic response to deep crustal processes 1 this paper gives a synoptic view of the cenozoic evolution of the swiss alps and their northern foreland basin in this orogen deep crustal processes subduction nappe stacking underplating and exhumation are intimately linked with surface processes surface uplift erosion basin formation and basin axis migration within the foreland basin the spatial pattern of subsidence and alluvial fan construction suggests that an increase in flexure of the foreland plate and the creation of relief in the orogen migrated from east to west in the course of collision in the orogen itself crustal thickening involved lower crust of the adriatic margin in the east and the european margin in the west exhumation of upper crustal units occurred earlier in the east as compared with the west an adriatic mantle wedge the ivrea body and its associated wedge of lower crustal material are identified as an extra lithospheric load which contributed to downward flexure of the european plate as a result of enhanced subsidence of the foreland plate relief was generated presumably in order to adjust to critical taper geometry it appears therefore that the westward motion of the adriatic wedge ultimately caused the contemporaneous westward propagation of the location of enhanced rates of alluvial fan construction coeval strike slip and n s convergence juxtaposed the adriatic wedge sequentially to different european upper crustal units which resulted in different styles of crustal structure and evolution along strike within the orogen

hydrological flowpaths and nitrate removal rates within a riparian floodplain along a fourth order stream in brittany france three main reservoirs were identified that contribute to the shallow subsurface flow regime of a valley drained by a fourth order stream in brittany western france i an upland flow that supplied a wetland area mainly during the high water period it has high n no3 and average cl concentrations ii a deep confined aquifer characterized by low nitrate and low chloride concentrations that supplied the floodplain via flow upwelling iii an unconfined aquifer under the riparian zone with high cl and low n no3 concentrations where biological processes removed groundwater nitrate this aquifer collected the upland flow and supplied a relict channel that controlled drainage from the whole riparian zone patterns of n no3 and cl concentrations along riparian transects together with calculated high nitrate removal indicate that removal occurred mainly at the hillslope riparian zone interface i e first few metres of wetland whereas dilution occurred in lower parts of the transects especially during low water periods and at the beginning of recharge periods stream flow was modelled as a mixture of water from the three reservoirs an estimation of these contributions revealed that the deep aquifer contribution to stream flow averaged 37 throughout the study period while the contribution of the unconfined reservoir below the riparian zone and hillslope flow was more variable from ca 6 to 85 relative to rainfall events and the level of the riparian water table at the entire riparian zone scale no3 removal probably from denitrification appeared most effective in winter despite higher estimated upland no3 fluxes entering the riparian zone during this period copyright 2003 john wiley sons ltd

extension tectonics in the wessex basin southern england the permian to cretaceous tectonic evolution of the wessex basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere the gross morphologies of its constituent structures were governed by the location of variscan thrust and wrench faults in the upper and middle crust which suffered extensional reactivation in tensional stress fields oriented approximately nw se several episodes of crustal extension can be resolved in early permian early triassic early jurassic and late jurassic early cretaceous times these were characterized by the rapid subsidence of fault bounded basins and commonly by erosion of adjacent upfaulted blocks superimposed upon the fault controlled subsidence dominant during periods of fault quiescence and becoming increasingly important with time a component of regional subsidence is considered to have a thermal origin this suggests that crustal extension was accompanied by some form of not necessarily uniform lithospheric thinning subsidence analyses assuming local airey isostasy give cumulative crustal extension factors of 20 28 beneath the grabens a more reasonable assumption of regional airey compensation indicates basinwide crustal extension of 13 17 which is consistent with birps offshore deep seismic reflection data

aspects of basin inversion in southern britain the wessex basin of southern england a permian to cretaceous extensional basin can be structurally divided into a set of constituent asymmetrical graben bounded by major e w trending zones of en echelon syn depositional normal faults the graben were inverted in late cretaceous and tertiary times by compressive stresses oriented roughly north south inversion structures fall into two related categories regional upwarps overlie earlier graben depocentres and were formed by bulk shortening of the graben fill superimposed upon and geographically delimiting the regional upwarps are roughly east west trending linear zones of en echelon inversion structures these coincide with the earlier graben bounding faults and typically have the form of monoclinal or periclinal flexures each underlain by a partially reversed normal fault the linear reverse fault monocline inversion structures were a relatively inefficient method of basin shortening because upper crustal faults in the region steepen upward markedly reversal of these faults under compression resulted in a shortening discrepancy at shallow depths locally particularly in south dorset this was overcome by bucklefolding and low angle reverse faulting which increased the amount of shortening attainable across the linear inversion structures elsewhere however the shortening discrepancy was accommodated by bulk shortening and regional upwarp of the graben sedimentary fill this occurred preferentially in those graben containing young poorly lithified and therefore weak sediments thus the early cretaceous depocentres of the weald and channel basins were strongly upwarped with axial uplifts of over 1000 m conversely graben having older more lithified sequences suffered little regional upwarp shortening primarily by fault reversal along the linear inversion structures the amount of crustal shortening which accompanied inversion was considerably less than the earlier crustal extension

a two dimensional transient analytical solution for a ponded ditch drainage system under the influence of source sink abstract an analytical solution is developed for predicting two dimensional transient seepage into ditch drainage network receiving water from a non uniform steady ponding field from the surface of the soil under the influence of source sink in the flow domain the flow domain is assumed to be saturated homogeneous and anisotropic in nature and have finite extends in horizontal and vertical directions the drains are assumed to be standing vertical and penetrating up to impervious layer the water levels in the drains are unequal and invariant with time the flow field is also assumed to be under the continuous influence of time space dependent arbitrary source sink term the correctness of the proposed model is checked by developing a numerical code and also with the existing analytical solution for the simplified case the study highlights the significance of source sink influence in the subsurface flow with the imposition of the source and sink term in the flow domain the pathline and travel time of water particles started deviating from their original position and above that the side and top discharge to the drains were also observed to have a strong influence of the source sink terms the travel time and pathline of water particles are also observed to have a dependency on the height of water in the ditches and on the location of source sink activation area

groundwater flow to a horizontal or slanted well in an unconfined aquifer 1 new semianalytical solutions for evaluation of the drawdown near horizontal and slanted wells with finite length screens in unconfined aquifers are presented these fully three dimensional solutions consider instantaneous drainage or delayed yield and aquifer anisotropy as a basis solution for the drawdown created by a point source in a uniform anisotropic unconfined aquifer is derived in laplace domain using superposition the point source solution is extended to the cases of the horizontal and slanted wells the previous solutions for vertical wells can be described as a special case of the new solutions numerical laplace inversion allows effective evaluation of the drawdown in real time examples illustrate the effects of well geometry and the aquifer parameters on drawdown results can be used to generate type curves from observations in piezometers and partially or fully penetrating observation wells the proposed solutions and software are useful for the parameter identification design of remediation systems drainage and mine dewatering

a late cenozoic regional mesofracture system in southern england and northern france the upper cretaceous and palaeogene rocks of s england and n france are cut by a nw trending system of fractures characterized by swarms of vertical extension joints accompanied by conjugate sets of hybrid and shear joints and normal mesofaults many major photolineaments exhibit the same nw trend as the fractures and are particularly conspicuous in n france where they are coincident with rectilinear drainage channels suggesting a relationship between fracture orientation and physiography in s england this relationship is absent possibly because of the influence of additional fracture systems related to major flexures trending obliquely to the nw se direction these major e w trending flexures and associated fracture systems were formed during the oligocene to early miocene 9helvetic9 phase of deformation and are cross cut obliquely by fractures in the nw trending system the nw trending fractures and lineaments are parallel to neotectonic normal faults in the lower rhine embayment and become less well developed to the west with increasing distance from these major structures the lower rhine faults were reactivated and propagated into the quaternary cover as a consequence of ne sw regional tension generated during the late neogene to recent 9jura9 phase of nw se alpine convergence the nw trending extensional structures in s england and n france are considered to be of about the same age and related to the same stress regime as the neotectonic normal faults of the lower rhine embayment however because fractures of the nw system cutting palaeogene sediments in se england are truncated by the erosion surface beneath the plio pleistocene red crag deposits it is possible that in england fracture initiation did not continue into quaternary times

crustal lithospheric structure and continental extrusion of tibet crustal shortening and thickening to c 70 85 km in the tibetan plateau occurred both before and mainly after the c 50 ma india asia collision potassic ultrapotassic shoshonitic and adakitic lavas erupted across the qiangtang c 50 29 ma and lhasa blocks c 30 10 ma indicate a hot mantle thick crust and eclogitic root during that period the progressive northward underthrusting of cold indian mantle lithosphere since collision shut off the source in the lhasa block at c 10 ma late miocene pleistocene shoshonitic volcanic rocks in northern tibet require hot mantle we review the major tectonic processes proposed for tibet including rigid block continuum and crustal flow as well as the geological history of the major strike slip faults we examine controversies concerning the cumulative geological offsets and the discrepancies between geological quaternary and geodetic slip rates low present day slip rates measured from global positioning system and insar along the karakoram and altyn tagh faults in addition to slow long term geological rates can only account for limited eastward extrusion of tibet since mid miocene time we conclude that despite being prominent geomorphological features sometimes with wide mylonite zones the faults cut earlier formed metamorphic and igneous rocks and show limited offsets concentrated strain at the surface is dissipated deeper into wide ductile shear zones

sidescan sonar images of mud volcanoes from the mediterranean ridge possible causes of variations in backscatter intensity abstract a survey of a large field of mud diapirs on the mediterranean ridge south of crete was carried out using both okean 9 5 khz and mak 1m 30 khz sidescan sonar systems during leg 2 of the third training through research cruise of r v gelendzhik in june and july 1993 high backscatter intensities were recorded by both systems to different degrees over the mud diapirs and their immediate surroundings causes of variations in the backscatter intensity are considered to be the spatial distribution of mud breccia associated with the mud domes both the burial depth of the mud breccia beneath hemipelagic drape and its areal extent and its physical properties along with contributions from seafloor roughness and the topography of the mud domes significant sources of volume scattering of the sidescan sonar sound signal are considered to be mud breccia inhomogeneities represented by millimetric centimetric clasts of various lithologies and free gas bubbles distributed through the mud matrix a good general relationship is established between these sources and the observed backscatter variations through analysis of ground truth data from core samples with 5 khz deep tow subbottom profiler records and seafloor video observations as well as the sidescan sonar records but a fully quantitative assessment of this relationship would require acoustic modelling and additional ground truth data

exhumation of the southern pyrenean fold thrust belt spain from orogenic growth to decay 1 the deformation and exhumation history of an orogen reflects the interactions between tectonic and surface processes we investigate orogenic wedge deformation erosion and sedimentation in the pyrenees by a quantifying the spatiotemporal patterns of exhumation across the southern fold thrust belt ftb with bedrock apatite fission track aft thermochronology and b comparing the results with existing deformation exhumation and sedimentation chronologies eighteen new samples record exhumation during and after orogenesis between 90 and 10 ma rocks from the range core axial zone record rapid exhumation that progresses east to west and north to south consistent with patterns of tectonically driven uplift synorogenic sediments shed into piggyback basins on the southern fold thrust belt during mountain building retain a detrital exhumation signal from the axial zone in contrast samples from other structural positions record exhumation of the thin skinned pyrenean thrust sheets suggesting sediment burial and heating of sufficient magnitudes to reset the aft system 3 km in some locations exhumation of these fold thrust structures is likely an erosional response to thrust driven rock uplift we identify an exhumation phase 25 20 ma that occurs along the central and eastern spanish pyrenees at the boundary between thick and thin skinned portions of the wedge we suggest that this distributed exhumation event records a a taper response in the southern orogenic wedge to sediment loading and or b a shift to wetter stormier climate conditions following convergence driven uplift and full topographic development a final exhumation phase between 20 and 10 ma may record the excavation of the southern fold thrust system following base level lowering in the ebro basin

tectonics of the new guinea region the new guinea region evolved within the obliquely and rapidly converging australian and pacific plate boundary zone it is arguably one of the most tectonically complex regions of the world and its geodynamic evolution involved microplate formation and rotation lithospheric rupture to form ocean basins arc continent collision subduction polarity reversal collisional orogenesis ophiolite obduction and exhumation of ultra high pressure metamorphic rocks we describe the major onshore and offshore tectonic and geologic components including plate boundaries seismicity faults and magmatism and we integrate these with emerging ideas about mantle dynamics to evaluate the cenozoic tectonic evolution of new guinea future research opportunities to resolve the mantle structure beneath new guinea will enable mantle dynamics to be linked to lithospheric and surface processes virtually all plate tectonic and mantle processes have been active in the new guinea region throughout the cenozoic and as such

a process based transfer function approach to model tile drain hydrographs tile drain response to rainfall events is determined by unsaturated vertical flow to the water table followed by horizontal saturated water movement in this study unsaturated vertical movement from the redistribution of water is modelled using a sharp front approximation and the saturated horizontal flow is modelled by an approximate solution to the boussinesq equation the unsaturated flow component models the fast response that is associated with the presence of preferential flow paths by convoluting the responses of the two components a transfer function is developed that predicts tile drain response to unit amounts of infiltrated water it is observed that the unsaturated flow component can be cast in a form that is linear in a power function of the infiltrated depth since the approach is process based model parameter definitions are easily identified with soil properties at the field scale furthermore it is demonstrated that the transfer function model parameters can be estimated from moment analysis using superposition the transient tile drain response to arbitrary amounts of infiltrated water can be constructed comparison with data measured from the water quality field station show that this approach provides a promising method for generating tile drain response to rainfall events copyright 2006 john wiley sons ltd

the chronology of the eocene tectonic and stratigraphic development of the eastern pyrenean foreland basin northeast spain abundant and clearly exposed relationships between structures and syntectonic sedimentary rocks in the southern pyrenees make this area particularly suitable for detailed studies of the sequential development of a collisional orogenic belt during the pyrenean orogeny major shortening occurred in the eastern pyrenees in eocene and early oligocene times until now individual tectonic and depositional events have been only loosely defined temporally by biostratigraphic data in order to provide a more precise chronological framework four new magnetostratigraphic sections spanning 8 km of eocene strata and encompassing 18 m y have been developed in the eastern pyrenees of northern spain the ages of nine major depositional sequences in the eastern pyrenean foreland have been specified within the context of these chronologic data beginning with the early eocene transgression that commenced at 58 ma the timing of numerous tectonic events that occurred during the subsequent 16 m y can also be delineated including the initial emplacement of the pedraforca thrust sheet 58 54 ma the development of the pedraforca breakback thrusts 47 5 40 ma at a mean shortening rate of 2 4 mm yr rotation of the pedraforca footwall three intervals of motion along the vallfogona thrust 42 5 44 0 40 5 41 5 and

analytical solutions for two dimensional groundwater flow with subsurface drainage tiles summary the tile drainage problem in an unconfined aquifer was investigated a mathematical model was established that describes two dimensional groundwater flow in an unconfined aquifer near a river with a linearized boussinesq equation time dependent sources and a sloped tile analytical solutions for groundwater level and discharge were derived and used to compare hydrologic conditions in a system with and without tile natural drainage we found that the spatial and temporal variations of groundwater level and discharge were significantly altered by the presence of drainage tile in an aquifer with tile drainage the groundwater level was lower and total groundwater discharge to the river increased compared to an aquifer with no tile application of the solutions to a synthetic case demonstrates that the analytical solutions derived can be used to quantify effect of tiles on nitrate loads in the baseflow of a river and assess the effectiveness of various conservation practices

a semi analytical model for transient flow to a subsurface tile drain the goal of this paper is to develop and test a semi analytical model for event based transient flow to a subsurface tile drain a sharp front theory was used to describe redistribution of infiltrated water in the vadose zone new approximate analytical solutions in terms of fourier series were sought for the boussinesq equation describing subsurface saturated flow subject to time dependent recharge both one and two term solutions of the series approximation were compared with observed tile hydrograph data from the purdue water quality field station wqfs in west lafayette indiana in general the models were able to capture the peaks of the tile drain hydrographs as well as the times to peak and the times of initial response to rainfall events the models performed particularly well for rainfall events with single burst hyetographs and in the prediction of the first hydrograph peak from multiple burst hyetographs though subsequent peaks could not be captured as well a further comparison of results from the one term model with those from hydrus 2d suggested that the one term model is adequate for estimating transient flow to a tile drain the solution developed here holds promise for extension to larger watersheds where the hydrology is governed by tile drains

a new analytical method for groundwater recharge and discharge estimation summary a new analytical method was proposed for groundwater recharge and discharge estimation in an unconfined aquifer the method is based on an analytical solution to the boussinesq equation linearized in terms of h2 where h is the water table elevation with a time dependent source term the solution derived was validated with numerical simulation and was shown to be a better approximation than an existing solution to the boussinesq equation linearized in terms of h by calibrating against the observed water levels in a monitoring well during a period of 100 days we shown that the method proposed in this study can be used to estimate daily recharge r and evapotranspiration et as well as the lateral drainage it was shown that the total r was reasonably estimated with a water table fluctuation wtf method if the water table measurements away from a fixed head boundary were used but the total et was overestimated and the total net recharge was underestimated because of the lack of consideration of lateral drainage and aquifer storage in the wtf method

u pb dating of cements in mesozoic ammonites dating sedimentary carbonates using the u pb method can help improve the phanerozoic timescale using a novel combination of laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms and thermal ionization multi collector mass spectrometry tims u pb numerical ages were obtained on early diagenetic calcite cements in jurassic ammonites in which concentrations of u range from 0 47 to 5 3 ppm the calcite cements of two ammonites is1 and is2 from the uppermost bifrons zone of the toarcian 179 180ma of the uk gave tims normalized la u pb dates of 164 9 5 3 ma and 166 7 4 8ma respectively normalizing la icp mc ms data to an in house calcite standard gave a more precise date of 165 5 3 3 ma for is1 cement an unzoned ammonite ss2 of bajocian age 168 170 ma yield a tims normalized la u pb age of 158 8 4 3 ma for its early diagenetic cement both the combined la mc icp ms and tims approach and the use of a calcite laser ablation standard can result in accurate ages of cements with uncertainties of 2 3 2 the later however is more efficient and precise these u pb dates of cements are 10 to 20 myr younger than the numerical ages of the biostratigraphic intervals from which the ammonites derive the u pb dates are taken to represent the time at which the aragonite shell of the ammonite inverted to calcite and released its u to precipitate in a late diagenetic alteration of early diagenetic fringing cements concentrations of u and pb in a range of other pristine biogenic carbonateswere found too low u b 0 01 ppm for meaningful dating using laser ablation method

asymmetric growth of the pyrenees revealed through measurement and modeling of orogenic fluxes orogenic asymmetry is ubiquitous in terms of topography structure and metamorphism but the relative influences of climate and tectonics in determining such asymmetry remain contentious this study demonstrates that for the case of the european pyrenees orogenic asymmetry is not defined by inherited structural asymmetry nor by orographic asymmetry of precipitation but is the simple consequence of the inherent tectonic growth of a doubly vergent orogen the pyrenees record approximately 60 myr of upper crustal accretion erosion and sedimentation that developed from late cretaceous to early miocene times approximately 165 km of plate convergence was accommodated by four phases of orogenic growth that can be summarized in terms of their generic orogenic development as follows 1 early inversion of passive margin extensional faults initiating the pro wedge 2 growth by a combination of frontal accretion and underplating to the pro wedge symmetrical and steady record of erosion and foreland basin sedimentation 3 cessation of pro wedge frontal accretion with propagation of the retro wedge deformation front 4 accelerated growth of pro wedge antiformal stack induced by underplating accelerated erosion over antiformal stack and increase in sediment discharge to pro foreland basin stabilization of outer pro wedge by sediment blanketing discrete element model experiments are used to explore the natural tendency of the system towards asymmetry model output demonstrates that during active frontal accretion to the pro wedge of an orogen the maxima in erosional denudation is offset towards the pro wedge relative to the maximum depths of exhumation this asymmetry is fundamentally driven by the progressive reduction in advection velocities of material within the orogen from the pro wedge into the retro wedge hence for an efficient erosional regime a dynamic coupling between erosion and structural uplift of the pro wedge will reduce activity of the retro wedge and hence drive asymmetry in terms of low temperature thermochronometry erosion and sedimentation the models also demonstrate the tendency for pro wedge growth through frontal accretion to slow however the cessation of frontal accretion as recorded by the south pyrenean thrust belt phases 3 and 4 requires additional forcing it is proposed that the thick wedge top sedimentation recorded at this time increased taper angles and hence stabilized the wedge accretionary influx into the orogen at this time was accomplished through underplating these processes governing asymmetry do not require a spatially variable climate or a laterally heterogeneous underthrust plate

field scale modeling of subsurface tile drained soils using an equivalent medium approach research conducted for the last 35 years has shown that subsurface drainage has a significant impact on hydrology and contaminant transport this can be observed at the field scale and also at the watershed scale impacts are always associated with modifying otherwise natural flow paths most computer model representations of drainage have been drawn at the field scale these models require relatively precise data that are usually unavailable when simulating hydrology and water quality in large watersheds we believe that in this case drainage representation should be simplified and yet closely match observations as a first step towards incorporating drainage systems into large scale hydrological models we propose an equivalent representation of drains buried in a soil profile by using a homogeneous anisotropic porous medium without drains this representation is based on a self consistent approach and on geometrical considerations simplification is such that calculating the equivalent hydraulic conductivity requires only information on the main length and spacing of the tile drains and not on their precise location this approach also provides a much simpler discretisation of the domain because of the absence of internal boundary conditions on the drainage pipes compared to other methods that have simplified drainage representation in existing watershed models it requires no parameter fitting two alternatives to the method are presented in the first one the soil profile equipped with the actual drain pipes is represented by an equivalent horizontally layered system with no pipes in the second the layered system has been replaced with an equivalent homogeneous profile the efficiency of these approaches was tested against a classical representation of tile drains using the swms 3d code which solves the richards equation for a typical drained plot configuration the equivalent medium approach appears to give satisfying results for global water outflow and mean water table elevation

pyrenean orogeny and plate kinematics 1 the evolution of the pyrenees a mountain range between iberia and eurasia has remained the subject of many debates between geologists and geophysicists for a long time by combining the identification of seafloor spreading anomalies a33o to m0 in the bay of biscay with those in the north atlantic we have derived a position of a mean pole of rotation for the entire opening of the bay of biscay four hundred kilometers of shortening took place between the iberian and eurasian plates in the pyrenean domain during the opening of the bay of biscay from chrons m0 to a33o time 118 to 80 ma the deep seismic etude continentale et oceanique par reflexion et refraction sismique ecors profile shot across the pyrenees and teleseismic data show the presence of two distinct slabs which dip to the north the southern slab is linked to the subduction of the neo tethys ocean which was created from late jurassic to early aptian simultaneously elongated back arc basins formed along the future pyrenean domain this slab was active from at least 118 ma early aptian to 100 ma late albian the northern slab active since 85 ma is linked to the subduction of the lower continental crust located south of the pyrenean domain in the upper crust normal faults as well as the north pyrenean fault became reverse faults and former back arc basins were inverted giving rise to the uplift of the pyrenees as a double asymmetrical wedge