palaeomagnetism of the late precambrian vadso and barents sea groups varanger peninsula norway abstract a palaeomagnetic study has been made on neoproterozoic rocks from the varanger peninsula northernmost norway several of the formations studied contain a stable magnetization of diagenetic origin two main groups of directions were obtained one a with a steep southeasterly positive direction the other b with a shallow northern direction the group a direction is not in accordance with the stratigraphic age of the rocks and the fennoscandian apparent polar wander path hence it may reflect a remagnetization the group b direction yields a late riphean early vendian palaeopole at 24 n 207 e dp 5 dm 11 n 11 in good agreement with data from contemporary rocks of the kola peninsula the varanger peninsula is transected by the trollfjord komagelv fault which divides the peninsula into the allochthonous barents sea region and the autochthonous varangerfjord region previous palaeomagnetic studies have suggested that the barents sea region has moved 500 to 1000 km to its present position this study indicates that the movement has been less than 250 km which is in better agreement with geological information

a spatially distributed model for the dynamic prediction of sediment erosion and transport in mountainous forested watersheds 1 erosion and sediment transport in a temperate forested watershed are predicted with a new sediment model that represents the main sources of sediment generation in forested environments mass wasting hillslope erosion and road surface erosion within the distributed hydrology soil vegetation model dhsvm environment the model produces slope failures on the basis of a factor of safety analysis with the infinite slope model through use of stochastically generated soil and vegetation parameters failed material is routed downslope with a rule based scheme that determines sediment delivery to streams sediment from hillslopes and road surfaces is also transported to the channel network a simple channel routing scheme is implemented to predict basin sediment yield we demonstrate through an initial application of this model to the rainy creek catchment a tributary of the wenatchee river which drains the east slopes of the cascade mountains that the model produces plausible sediment yield and ratios of landsliding and surface erosion when compared to published rates for similar catchments in the pacific northwest a road removal scenario and a basin wide fire scenario are both evaluated with the model

compression behaviour of minerogenic low energy intertidal sediments existing geotechnical approaches that describe volumetric changes in intertidal sediments in response to applied vertical effective stresses are limited by a lack of empirical research into their one dimensional compression behaviour in this paper we address this deficiency by presenting the results of an investigation into the compression behaviour of minerogenic low marsh and tidal flat sediments we have tested samples of these sediment types obtained from greatham creek cowpen marsh tees estuary uk analysis of physical properties and oedometer compression tests demonstrates that contrary to the implicit assumptions of existing models the surface sediments studied are overconsolidated structural variability between samples arises due to sedimentological factors notably variations in organic content we attribute overconsolidation to tidal exposure and falls in groundwater level that permit desiccation and cause capillary suction stresses greater rates of compression with respect to effective stress occur in sediments with higher initial voids ratios and more open unstable initial structures variability in structure decreases with application of higher effective stresses due to the destructuration of the sediments which also creates increased homogeneity of compression behaviour under higher effective stresses we subsequently develop a new conceptual framework to describe compression behaviour in minerogenic intertidal sediments that incorporates overconsolidation we advocate a statistical approach that accounts for structural variability and variations in compression behaviour at effective stresses less than and greater than the yield stress we argue that our conceptual framework is broadly applicable to minerogenic intertidal sediments at different locations and burial depths within holocene stratigraphic sequences providing site specific compression data are collected inter site transfer and application of measured material properties should not be undertaken due to local variations in compression behaviour resulting from varying ecological sedimentological geochemical climatic geomorphic and hydrographic conditions the individual characteristics of different field locations should be carefully considered before the suggested framework is routinely applied

modeling the tor dotted crests bedrock edges and parabolic profiles of high alpine surfaces of the wind river range wyoming abstract broad low curvature surfaces common to many alpine landscapes and particularly well expressed in the laramide ranges of the western usa appear to be roughly in steady state with respect to the current surface processes uniform thin order 1 m regolith covers the crystalline bedrock with the exception of occasional tors at ridgecrests the surfaces are commonly edged by bedrock lips at the tops of cliffs that bound the intervening glacial troughs regolith production is low order 10 m year on bare bedrock and reaches a maximum under tens of centimeters of regolith all of these characteristics may be accounted for with a numerical model that is faithful to the periglacial surface processes presently operating on these surfaces hillslope transport is modeled assuming the dominant process is frost creep transport efficiency depends linearly upon local slope and appropriately vanishes in the absence of regolith frost frequency scales the rate of motion while the ratio of frost penetration depth to regolith thickness dictates the degree to which the process is curtailed by available regolith initial conditions include initial mean slope and bedrock roughness and a uniform regolith cover boundary conditions are imposed by dictating that the edges of the calculation space be lowered at a rate appropriate for glacial incision broad convex surfaces emerge over time scales of order 1 million years all surfaces rapidly decouple from the bounding glacial troughs as the high negative curvature at the edges disallows accumulation of regolith these bedrock edges lower at a few microns per year while the troughs lower at many times this rate as the bedrock edges therefore serve as the effective boundary condition for the remaining surface the surfaces operate independently of both lowering and widening of the glacial troughs for a reasonable set of transport and weathering rates the final steady state landscape is sensitive to the initial condition in particular the steeper the initial landscape the more likely tors are to develop as the high curvature disallows accumulation of regolith these tors in turn limit the lowering rate of the crest and the landscape retains significant local relief low relief initial conditions more likely lead to parabolic surfaces that lack tors that tors are more likely on the crests reflects the high initial curvature at the crest tors on the side slopes are eliminated the present high surfaces in the laramide ranges of the western usa imply operation of periglacial surface processes over millions of years the occasional tors imply a steeper rather than flatter initial landscape the strong decoupling of surfaces from glacial troughs justifies their use as local geomorphic markers that allow calculation of relief production since glacial incision was initiated on the other hand their present low curvature does not require a landscape history in which these surfaces were once joined as an initially widespread erosion surface

development of slaty cleavage and degree of very low grade metamorphism a review illite crystallinity ic and other indicators of the grade of very low grade metamorphism associated with the appearance of various stages of slaty cleavage in phyllosilicate rich rocks have been compiled from a wide variety of terranes ic values have been converted to a kubler equivalent standard scale but the diverse characterizations of the cleavage fabrics in published descriptions do not always allow an unequivocal identification of equivalent stages of cleavage development nevertheless there exists a distinct relationship between grade and the appearance of various stages of cleavage development 1 indications of incipient slaty cleavage such as s0 s1 pencil structure appearance of primary s1 crenulation cleavage and of closely spaced cleavage without parallel fabric in the microlithons is associated with a wide range of mostly medium and high grade diagenetic ic values 2 the appearance of smooth cleavage with a strong parallel fabric in the microlithons and or quartz mica beards and the chlorite mica stacks shortened at a high angle to 001 and of irregular cleavage in sandy beds is associated with a much narrower range of predominantly low and medium grade anchimetamorphic grades rarely high grade diagenetic the first appearance of these stages of cleavage development with higher grades can often be related to post kinematic magmatic heating polymetamorphism pre cleavage metamorphism or static recrystallization without cleavage formation for example in low strain zones there exists a relationship between finite strain fabric and metamorphic grade in mudstones and slates in coarser clastic rocks the same finite strain fabric relationship occurs at appreciably higher grades a relationship between finite strain in carbonate rocks and ic in the nearby rocks has been reported from the helvetic zone of the swiss alps the earlier stages of cleavage formation are associated with little improvement in ic the narrow range of ic associated with smooth cleavage is concluded to represent recrystallization and grain growth concurrent with cleavage formation

a mechanism for the formation of overconsolidated horizons within estuarine floodplain alluvium implications for the interpretation of holocene sea level curves

the effect of calcium ions in pore water on the residual shear strength of kaolinite and sodium montmorillonite this paper reviews the literature concerning the effects of pore water chemistry on residual shear strength it presents the results of index limit and residual shear strength testing undertaken on kaolinite and sodium montmorillonite using concentrations of calcium chloride similar to the calcium levels measured in groundwaters obtained from landslipped calcareous mudrock of the fuller s earth formation the residual shear strength of the sodium montmorillonite increased markedly for the sample treated and tested with 80 mg 1 cat compared with that tested with deionized water greater concentra tions of ca2 resulted in only a marginal further increase in the residual shear strength these changes were also reflected in the interpreted parameters or and c the liquid limit of the montmorillonite decreased dramatically when the samples were treated with 80 mg 1 ca2 and this effect persisted and or was slightly enhanced when the concentration of ca2 was increased the residual shear strength

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

the structure and timing of lateral escape during the scandian orogeny a combined strain and geochronological investigation in finnmark arctic norwegian caledonides abstract determining the timing duration and mechanism of tectonic events within an orogenic cycle such as ocean subduction continent continent collision or gravitational collapse is challenging especially in ancient orogenic belts variations in the tectonic transport direction however can be used as a guide to these stages of orogeny while thrust sheets within the caledonian allochthon in north norway were emplaced broadly eastwards perpendicular to the trend of the orogen many features indicate material transport in other orientations one dominant feature of the mageroy nappe sitting above and infolded with the kalak nappe complex is the development of a strong n s lineation orthogonal to the main transport direction strain measurements in part determined by a new method are used in the context of the regional structural data to identify the critical stage in orogeny when compressional forces are balanced by orogen parallel lateral escape quantitative 3 d strain estimation in the mageroy nappe indicates prolate deformation with c 50 horizontal shortening parallel to the thrusting direction e w and c 200 extension along the orogenic strike n s with c 30 vertical shortening temporal constraint on this fabric is provided by ar ar isotopic analysis of undeformed white mica in cross cutting granitic pegmatites these data show that prolate deformation occurred before the white mica cooling age of 416 4 ma while the previously determined depositional age of the hellefjord schist indicates that it occurred after 438 4 ma a granitic pegmatite that intruded the hellefjord schist after an initial deformation phase but during or prior to a later deformation has been dated at 431 2 ma by u pb zircon a previous lower age constraint on this deformation of 428 5 ma is given by metamorphic zircon overgrowths on fractured grains these results constrain the continental collision between baltica and laurentia in finnmark to the interval c 431 428 ma placed in a regional context these results indicate that lateral escape was orthogonal to the thrusting direction and occurred during the continent continent collision stage in the scandian orogeny before gravitationally driven collapse

the engineering geology of the carse clay at the national soft clay research site bothkennar it is possible to subdivide the carse clay deposits above the bothkennar gravel into bedded laminated mottled and weathered facies the first is composed of silty clays which retain original sedi

40ar39ar whole rock dating and the age of cleavage in the finnmark autochthon northernmost scandinavian caledonides abstract four variably cleaved samples of red shale slate were collected from the nyborg formation vestertana group exposed in the finnmark autochthon northernmost scandinavian caledonides quartz normalized illite crystallinity values suggest metamorphism varied between upper diagenesis lower anchizone east and lower anchizone middle anchizone west the samples display similarly discordant 40 ar 39 ar whole rock age and k ca spectra with total gas ages ranging between 606 and 661 ma spectra complexity is a result of evolution of gas from relatively non retentive chlorite white mica and relatively refractory detrital plagioclase apparent ages defined by intermediate temperature increments are relatively constant within each sample but show marked intersample variations 550 575 to 635 650 ma three size fractions 1 2 2 4 and 4 8 m were separated from the sample containing the least chlorite the two coarser fractions contain numerous rock fragments and display 40 ar 39 ar age and k ca spectra similar to the whole rock the 1 2 m fraction is largely comprised of individual mineral grains gas increments evolved between 375 and 495 c record similar k ca ratios but systematically increasing apparent ages between 637 and 783 ma these results suggest that the 1 2 m fraction is composed of detrital white mica grains which were affected by a diagenetically related geologic disturbance at 635 ma although the affects of a late cambrian early ordovician orogenic event finnmarkian orogeny have been locally described from portions of the overlying caledonian allochthons no clear record of correlative tectonothermal activity has been documented within samples from the finnmark autochthon

fluvial erosion transport equation of landscape evolution models revisited we present a mesoscale erosion deposition model which differs from previous landscape evolution models equations by taking explicitly into account a mass balance equation for the streamflow the geological and hydrological complexity is lumped into two basic fluxes erosion and deposition and two averaged parameters unit width discharge q and stream slope s the model couples the dynamics of streamflow and topography through a sediment transport length function x q which is the average travel distance of a particle in the flow before being trapped on topography this property reflects a time lag between erosion and deposition which allows the streamflow not to be instantaneously at capacity the so called x q model may reduce either to transport limited or to detachment limited erosion modes depending on x but it also may not we show in particular how it does or does not for steady state topographies long term evolution and high frequency base level perturbations apart from the unit width discharge and the settling velocity the x q function depends on a dimensionless number encompassing the way sediment is transported within the streamflow using models of concentration profile through the water column we show the dependency of this dimensionless coefficient on the rouse number we discuss how consistent the x q model framework is with bed load scaling expressions and einstein s conception of sediment motion

a tectonic model for the metamorphic evolution of the basal gneiss complex western south norway a review of currently available information relevant to the basal gneiss complex bgc of western south norway combined with the authors own observations leads to the following conclusions 1 most of the bgc consists of proterozoic crystalline rocks and probably subordinate lower palaeozoic cover 2 the last major deformation of these rocks was during the caledonian orogeny and involved large scale thrusting recumbent folding and doming the structural development of the bgc is closely tied in with that of the caledonian allochthon 3 the whole eclogite bearing part of the bgc has suffered a high pressure metamorphism with conditions of between 550 c 12 5 kbar sunnfjord and about 750 c 20 kbar more og romsdal at the metamorphic climax 4 this metamorphism was of caledonian age probably rather early in the caledonian tectonic history of the bgc and is considered to have been a rather transient event by setting these conclusions in a framework provided by geophysical evidence for the deep structure of the crust in southern norway we have constructed a geotectonic model to explain the recorded metamorphic history of the bgc it is suggested that considerable crustal thickening was caused by imbrication of the baltic plate margin during continental collision with the greenland plate this resulted in high pressure metamorphism in the resulting nappe stack progradation of the suture caused underthrusting of the baltic foreland below the eclogite bearing terrain causing it to emerge at the earth s surface aided by tectonic stripping and erosion application of isostacy equations to the model shows that eclogites can be formed by in situ metamorphism in crustal rocks and reappear at the land surface above a normal thickness of crust in a single orogenic episode of approximately 65 70 ma duration

precise dating of low temperature deformation strain fringe analysis by 40ar 39ar laser microprobe pyritized graptolites from the welsh basin united kingdom slate belt acted as rigid bodies during cleavage formation and epizonal white micas formed within the resulting strain shadows orthogonal to the principal stress orientation although the quantities of mica are small they are a pure synkinematic mineral and have been dated by ar 40 ar 39 infrared laser microprobe as a means to dating cleavage four samples of strain fringe mica from different hand samples yielded ages ranging from 394 4 3 1 to 397 8 1 8 ma 2sigma with a mean age of 396 1 1 4 ma 2sigma by focusing on minerals that are unequivocally synkinematic this technique provides a novel solution to the problems of isotopically dating slaty cleavage previous studies have predominantly relied on dating whole rock slate samples or separated illite grains by ar 40 ar 39 techniques problems encountered included 1 separating the effects of isotopic contamination by detrital phases 2 ar 39 loss during the irradiation of illite mineral separates and 3 thermally induced ar 40 loss in nature from fine grained minerals by circumventing these problems this new method provides the first unequivocal and high precision age data for acadian deformation in the well characterized welsh basin slate belt with such precision the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent continent collision

evaluating late holocene relative sea level change in the somerset levels southwest britain holocene relative sea level rsl change is investigated at nyland hill somerset levels the lithostratigraphy comprises turfa peat underlying marine clay both onlapping a sloping upper palaeozoic basement the altitude of the peat clay contact ranges from 2 42 to 4 52 m od becoming lower down basement slope yet 14c dates of three samples taken laterally along the contact at different altitudes yield similar ages 3640 3330 3715 3460 3725 3465 cal yrs bp suggesting either very rapid instantaneous rsl rise or sediment compaction biostratigraphic data indicate a gradual transition to marine conditions across the peat clay contact therefore the height difference is interpreted as evidence for significant compaction we consider 4 64 m od the minimum pre compaction altitude indicating maximum observed compaction of 2 22 m the clay surface reclaimed during roman occupation represents an anthropogenically induced negative tendency and is dated chemostratigraphically to 1776 46 using a da

vegetation modulated landscape evolution effects of vegetation on landscape processes drainage density and topography 1 topography acts as a template for numerous landscape processes that include hydrologic ecologic and biologic phenomena these processes not only interact with each other but also contribute to shaping the landscape as they influence geomorphic processes we have investigated the effects of vegetation on thresholds for channel initiation and landform evolution using both analytical and numerical approaches vegetation is assumed to form a uniform ground cover runoff erosion is modeled based on a power function of excess shear stress in which shear stress efficiency is inversely proportional to vegetation cover this approach is validated using data plant effect on slope stability is represented by additional cohesion provided by plant roots vegetation cover is assumed to reduce sediment transport rates due to physical creep processes rainsplash dry ravel and expansion and contraction of sediments according to a negative exponential relationship vegetation grows as a function of both available cover and unoccupied space by plants and is killed by geomorphic disturbances runoff erosion and landsliding and wildfires analytical results suggest that in an equilibrium basin with a fixed vegetation cover plants may cause a transition in the dominant erosion process at the channel head a runoff erosion dominated landscape under none or poor vegetation cover may become landslide dominated under a denser vegetation cover the sign of the predicted relationship between drainage density and vegetation cover depends on the relative influence of vegetation on different erosion phenomena with model parameter values representative of the oregon coast range ocr numerical experiments conducted using the channel hillslope integrated landscape development child model confirm the findings based on the analytical theory a highly dissected fluvial landscape emerges when surface is assumed bare when vegetation cover is modeled landscape relief increases resulting in hollow erosion dominated by landsliding interestingly our simulations underscore the importance of vegetation disturbances by geomorphic events and wildfires on the landscape structure simulated landscapes resemble real world catchments in the ocr when such disturbances are considered

natural experiments in landscape evolution a natural experiment in landscape evolution is a case study of landform development in which only one element varies significantly and for which the driving forces initial conditions and or boundary conditions are well constrained natural experiments provide a means of testing landscape evolution theory on the large space and time scales to which that theory applies natural experiments can involve either steady or transient conditions cases with steady conditions allow one to test predictions about the relationships among topography erosion rates and various attributes related to climate and material properties transient cases are valuable for distinguishing between models whose predictions might be similar and therefore indistinguishable under steady conditions essential ingredients of a natural experiment include minimal variation in all but one factor good constraints on timing and or rates well characterized processes and high quality topographic data other useful ingredients include information about intermediate topographic states such as a former valley profile revealed by strath terraces and knowledge of the time history of erosion rates in order to deepen our understanding of the physics and chemistry of long term landscape evolution there is a pressing need to identify natural experiments and develop the necessary databases to take advantage of them copyright 2009 john wiley sons ltd

erosion quantification in the small marly experimental catchments of draix alpes de haute provence france calibration of the etc rainfall runoff erosion model abstract erosion rates measured for 15 years in the small ranging from 0 13 ha to nearly 1 km2 and steep 30 75 mountainous marly basins of draix south alps france are over 100 tons ha year in a badland area devoid of vegetation in a similar basin reforested at the end of the 19th century the sediment yield is considerably reduced less than 3 tons ha year the analysis of the sediment yield of these torrents reveals the importance of the erosion processes on slopes at the scale of the elementary gully and the influence of deposition transport and scouring processes as soon as the channel network of the basin is developed these processes were modelled by a hydrosedimentologic model developed by cemagref for flood torrent erosion and called etc etc is an integrated spatialized and global model working at the event scale the rainfall runoff component and the solid transport component which involves scouring deposition and armouring are well developed on the other hand the erosion component is not yet a physically based model as the knowledge on the elementary processes is not enough quantitative the etc model was used on a badland basin of 86 ha in area the laval and has shown its ability to simulate both water and sediment flows in mountainous and steep basins the erosion modelling highlighted the need for a better representation of the slope processes and for more information on the storing of sediments in the channel network observations carried out on the influence of the vegetation cover patterns and the links between slopes and channels should be taken into account to improve the model

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

palaeomagnetism of vendian early cambrian sedimentary rocks from e finnmark norway abstract a palaeomagnetic study has been made on vendian early cambrian rocks of the tanafjord and vestertana groups from the varanger peninsula northernmost norway magnetic components of probably primary origin were isolated at two sites apparently unaffected by the finnmarkian scandian events of the caledonian orogeny sites situated in the caledonian gaissa nappe or close to its front were remagnetized and comparison with a tentative ordovician to devonian apparent polar wander path indicates that the remagnetization occurred during these periods

excess argon 40are uptake during slate formation a 40ar 39ar uv laserprobe study of muscovite strain fringes from the palaeozoic welsh basin uk syn kinematic pure muscovite strain fringes grew around pyritized graptolites in response to the early devonian acadian closure and uplift of the peri gondwanan welsh basin they record ar isotope information on the timing of low temperature deformation and the mudrock to slate transition here we have applied three different 40ar 39ar laserprobe dating methods to strain fringes from the central welsh basin to test for variations in age and to explore the technical limitations of the method infrared laserprobe step heating analyses yielded only occasional plateau ages varying between ca 403 ma and 422 ma and strong evidence for discordance in the ar system likewise ages from infrared laserprobe total fusion analysis are scattered and range from ca 390 ma to 651 ma by contrast ultraviolet laserprobe intra fringe age profiles revealed a complex pattern of ages across individual strain fringes this is the highest spatial resolution technique available and the resulting age profiles consistently showed an oscillatory pattern comprising troughs or baseline ages that are all within error of ca 397 ma and peaks or apparent ages ranging up to ca 550 ma these apparent ages we interpret as the results of repeated periodic assimilation of excess 40ar 40are during deformation and the mudrock to slate transition here basinal fluids carrying 40are are driven through bulk mudrock during contractional phases of the acadian orogen and 40are is taken up by muscovite strain fringes the concentration of 40are varies with metamorphic grade and is inversely proportional to the temperature of metamorphism and we suggest is controlled by the solubility of ar in water which has potentially quite severe implications for 40ar 39ar dating of k bearing minerals in any mudrock these results provide a first record of ar isotope information in strain fringes and a first record of orogenically driven fluid flow through bulk deforming mudrock they also demonstrate how the high spatial resolution ultraviolet laserprobe 40ar 39ar method can access ar isotope information that is obscured by lower spatial resolution laser analysis or bulk sampling methods

exploring mechanisms of compaction in salt marsh sediments using common era relative sea level reconstructions salt marsh sediments provide precise and near continuous reconstructions of common era relative sea level rsl however organic and low density salt marsh sediments are prone to compaction processes that cause post depositional distortion of the stratigraphic column used to reconstruct rsl we compared two rsl reconstructions from east river marsh connecticut usa to assess the contribution of mechanical compression and biodegradation to compaction of salt marsh sediments and their subsequent influence on rsl reconstructions the first existing reconstruction trench was produced from a continuous sequence of basal salt marsh sediment and is unaffected by compaction the second new reconstruction is from a compaction susceptible core taken at the same location we highlight that sediment compaction is the only feasible mechanism for explaining the observed differences in rsl reconstructed from the trench and core both reconstructions display long term rsl rise of 1 mm yr followed by a 19th century acceleration to 3 mm yr a statistically significant difference between the records at 1100 to 1800 ce could not be explained by a compression only geotechnical model we suggest that the warmer and drier conditions of the medieval climate anomaly mca resulted in an increase in sediment compressibility during this time period we adapted the geotechnical model by reducing the compressive strength of mca sediments to simulate this softening of sediments decompaction of the core reconstruction with this modified model accounted for the difference between the two rsl reconstructions our results demonstrate that compression only geotechnical models may be inadequate for estimating compaction and post depositional lowering of susceptible organic salt marsh sediments in some settings this has important implications for our understanding of the drivers of sea level change further our results suggest that future climate changes may make salt marshes more susceptible to the impacts of rsl rise by enhancing sediment compressibility we stress however that the cause of the softening remains enigmatic until this is better constrained it is premature to widely extrapolate our findings to existing core based reconstructions of holocene rsl

the early caledonian finnmarkian event reassessed in finnmark 40ar 39ar cleavage age data from nw varangerhalvoya n norway abstract the relative significance of early finnmarkian and late scandian caledonian deformation in n norway is uncertain early studies suggested pervasive finnmarkian deformation whilst later results indicated a restricted finnmarkian domain the present work suggests it was more widespread than accepted and that inter finnmarkian scandian deformation occurred 40 ar 39 ar dating of 2 6 and 6 11 m pelitic fractions from the lower to mid greenschist facies tanahorn nappe five samples base middle allochthon and the epizone lokvikfjellet and barents sea groups three samples north varanger region in the north scandinavian caledonides show slightly discordant spectra most spectra from the tanahorn nappe preserve possible evidence of an early caledonian event in the high temperature steps with recoil excess ar effects in the low temperature steps no pre caledonian relict component has been recorded the results indicate finnmarkian deformation continued to 460 ma with scandian reactivation at 425 415 ma from the north varanger region a strongly crenulated sample yielded plateau ages 444 442 ma means of combined young steps from weakly to uncrenulated samples gave 470 450 ma suggesting penetrative strike slip deformation occurred in the late finnmarkian to inter finnmarkian scandian period no scandian ages were recorded in the north varanger region reassessment of published data from the laksefjord nappe and gaissa thrust belt suggests they were affected by finnmarkian deformation

physically based modelling of shallow landslide sediment yield at a catchment scale a shallow landslide erosion and sediment yield component applicable at the basin scale has been incorporated into the physically based spatially distributed hydrological and sediment transport modelling system shetran the component determines when and where landslides occur in a basin in response to time varying rainfall and snowmelt the volume of material eroded and released for onward transport and the impact on basin sediment yield derived relationships are used to link the shetran grid resolution up to 1 km at which the basin hydrology and final sediment yield is modelled to a subgrid resolution typically around 10 100 m at which landslide occurrence and erosion is modelled the subgrid discretization landslide susceptibility and potential landslide impact are determined in advance using a geographic information system gis with shetran then providing information on temporal variation in the factors controlling landsliding the ability to simulate landslide sediment yield is demonstrated by a hypothetical application based on a catchment in scotland

experimentally determined compositions of diopside jadeite pyroxene in equilibrium with albite and quartz at 1200 1350 c and 15 34 kbar abstract equilibrium compositions of diopside jadeite pyroxene coexisting with albite and quartz were experimentally determined at 25 different p t conditions using an electron microprobe for analysis the new data and the 600 c data of holland 1983 provided the following mixing properties of the diopside di jadeite jd solid solution j k g xs x jd x di 12600 9 45 t 12600 7 6 t x jd x di 21400 16 2 t x jd x di 2 the di jd solution is close to ideal above 1000 c but immiscible below 565 c the di jd solvus is slightly asymmetric with the crest at composition di 42 4 jd 57 6 excess enthalpy is positive but smaller than indicated by the enthalpy of solution measurements of wood et al 1980 disorder in the di jd solution is significantly smaller than complete disorder implied by the ionic two site model

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

hydrological behaviour of sub mediterranean alpine headwater streams in a badlands environment summary investigations of flash floods generation processes are very few compared with studies in humid areas the rapidity and intensity of these processes make difficult any data acquisition on the field the present study aims to improve our knowledge on these environments by using the facilities of the draix erbs southern french alps where well documented black marls show a typical badlands morphology with v shaped gullies time varying components of total flow and flow sources have been investigated from a long term isotopic and hydrochemical survey of rainwaters overland waters soil waters and streamwaters we present in greater detail two flood events which occurred in three adjacent basins and had contrasting antecedent soil moisture conditions isotopic data were used to apply time based hydrograph separations due to the very short transfer time of waters convolution of the rainfall isotopic signal with a two parameter transfer function dispersive transfer function proved the best way to assess the event isotopic concentration end members mixing analysis emma has been carried out using non reactive chemical species to get source areas of runoff new water participation by direct surface transfer was the main mechanism at the peak discharge this contribution was found to dominate irrespective of whether the antecedent soil moisture was dry or wet nevertheless up to 20 of subsurface water has been observed at peak discharge for dry pre event conditions during the flow recession phases this subsurface water contribution was greater for wet antecedent conditions in dry initial conditions subsurface water was mostly new water whereas in wet conditions pre event water could contribute to the flow a deep groundwater reservoir may take part in the pre event component in the larger basin but in the smaller basins pre event water was mostly made of short residence time water from previous rainfall events originating from sporadic highly transmissive shallow hillslope reservoirs loose detrital cover and upper regolith differences regarding the hierarchy of the processes were not found to be simply proportional to the basins area nor were they clearly related to the mean slope gradients or to the percentage of vegetal cover it is suggested that controls on streamflow generation occur at local scale and consist in the spatial organisation and the gradual accumulation downwards of first order basins with their respective physical specificities mostly orientation and slope gradient

holocene environmental change in the inner severn estuary uk an example of the response of estuarine sedimentation to relative sea level change holocene sediments of the wetlands around the inner severn estuary uk demonstrate a consistent stratigraphy of a single woody peat layer up to at least 4 5 m thick capped with a grey silty cla

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

petrology of a margarite bearing meta anorthosite from seljeneset nordfjord western norway implications for the p t history of the western gneiss region during caledonian uplift abstract the western gneiss region of norway contains relics of eclogite and high pressure granulite that have been extensively overprinted by amphibolite facies assemblages a meta anorthosite from seljeneset nordfjord contains fine grained margarite quartz plagioclase muscovite clots set in a zoisite quartz plagioclase clinozoisite matrix in some clots relict kyanite is preserved equilibria modeled in the cash system indicate a retrograde p t path that begins in the kyanite zoisite field p 8 2 kbar passes through reaction 1 kyanite zoisite quartz anorthite h2o between 610 c and about 800 c and finally through reaction 2 kyanite anorthite h2o margarite quartz the sodic composition of plagioclase in reaction 1 suggests that pressures in excess of 15 17 kbar at 750 800 c may have been experienced during silurian eclogite facies metamorphism the simplified cash reaction 2 occurs between invariant points at 4 3 kbar 520 c and 8 2 kbar 610 c but polyvariance due to variable na solid solution broadens the reaction into a band about 150 c wide cooling through 500 c occurred about 410 ma ago this study provides the first well defined p t path for caledonian retrograde metamorphism at amphibolite facies conditions

development of the thames drainage system in early and middle pleistocene times pre anglian terrace stages of the proto thames system are traced from the present middle thames area into essex and south east anglia gravel composition indicates that each of the main terrace stages is associated with an influx of far travelled material probably signifying at least three phases of pre anglian glaciation in the south midlands gravel composition also indicates the occurrence of major changes during early and middle pleistocene times in the extent of the thames catchment and in the disposition of the main drainage lines the important role of the goring gap in the development of the drainage system is noted and the nature and distribution of anglian fluvioglacial gravels are described

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press