the chronology of holocene alluvial sediments from the wetterau germany provided by optical and 14c dating holocene floodplain chronologies are often hard to establish the principal limitation being the scarc ity of organic remains in the present study optical dating of flood loam was carried out in

phases of soil erosion derived colluviation in the loess hills of south germany in south germany soil erosion is as old as farming and dates back to early neolithic times its sedimentary products form thick colluvial and alluvial sediment bodies in all drainage basins numerous local studies exist but the extrapolation of findings from local case studies to a regional scale has been problematic here a graphical approach is used for frequency analysis of existing data a frequency distribution for optical dates on colluvial sediments from the beginning of agriculture until 1200 ad was constructed by 1 representing the optical ages by gaussian distributions and 2 summing all the single curves the resulting graph clearly shows phases of increased colluviation during periods of stronger human impact a first significant increase occurred during the bronze age during the iron age roman period and at around 800 ad distinct maxima appear in the distribution and highest frequencies are present towards the end of the analysed period at around 1100 ad conclusions that can be drawn from such an approach are limited by sampling bias and other factors but for the analysed period and on a regional and long term scale colluviation seems to have been mainly triggered by intensity of land use climatic fluctuations are of only secondary importance rainfall events that were sufficiently erosive to produce colluvial sediments occurred throughout the agricultural periods the limiting factor for colluvium production was sensitivity of the landscape to erosion and this is a result of land use d 2002 elsevier science b v all rights reserved

thermal stresses differential subsidence and flexure at oceanic fracture zones geosat geoid undulations over four pacific fracture zones have been analyzed after correcting for the isostatic thermal edge effect the amplitudes of the residuals are shown to be proportional to the age offset the shape of the residuals seems to broaden with increasing age both geoid anomalies and available ship bathymetry data suggest that slip must sometimes occur on the main fracture zone or secondary faults existing models for flexure at fracture zones cannot explain the observed anomalies a combination model accounting for slip and including flexure from thermal stresses and differential subsidence is presented our model accounts for lateral variations in flexural rigidity from brittle and ductile yielding due to both thermal and flexural stresses and explains both the amplitudes and the shape of the anomalies along each fracture zone the best fitting models have mechanical plate thicknesses that are described by the depth to the 600 700 c isotherms

determining the burial time of single grains of quartz using optically stimulated luminescence abstract in the optical dating of sediments it is usually assumed that the optically stimulated luminescence osl signal has been completely reset by light exposure prior to burial this assumption is often not valid one approach to testing and perhaps circumventing this assumption is to examine the apparent date of last exposure to daylight of individual sediment grains this paper reports on the application for the first time of 2 new measurement protocols to the estimation of the radiation dose received during burial for individual quartz grains from an aeolian deposit of known age 10 000 year old which is considered likely to have been completely reset by sunlight at deposition additive dose laboratory doses added to the burial dose before osl measurement and regenerative dose doses added after measurement of osl from burial dose single aliquot protocols are applied to 28 and 25 individual grains respectively each grain provides an independent estimate d e of the burial dose the average d e from the additive dose protocol 21 8 1 1 gy is in good agreement with the average from the regenerative dose protocol 23 8 1 0 gy both agree well with 1 13 multiple grain regenerative dose single aliquot measurements each on 1 mg sub samples of 23 9 0 3 gy 2 9 multiple grain additive dose single aliquot measurements also on 1 mg sub samples of 22 4 0 7 gy and 3 one previously published multiple aliquot additive dose estimate of 23 5 0 6 gy using 52 sub samples each of 5 mg the resulting optical ages are in good accord with 14 c and thermoluminescence age determinations the distribution of equivalent doses in the single grains is however unexpectedly large 23 of mean d e given the very likely complete resetting of the osl signal at deposition possible reasons are discussed and it is concluded that heterogeneity in beta dosimetry is the most likely explanation the single grain optical dating protocols reported here allow a detailed examination of the dose distribution in very small samples thus they should enable accurate dates to be obtained for sediments and soils that contain poorly bleached or mixed age components as well as deposits in which quartz grains are present in extremely low abundance

holocene alluvial sediment storage in a small river catchment in the loess area of central belgium abstract soil erosion and sediment deposition widely affect landscape development particularly in erosion prone areas with loess derived soils nevertheless until now few attempts were made to quantify soil losses and sediment storage over long centennial or millennial timescales in this study the holocene alluvial sediment storage in a small river catchment 52 km2 of the belgian loess belt is estimated and a preliminary sediment budget for the catchment is presented in the valley of the nethen river c 13 km long a detailed survey of the alluvial sediment archive was conducted hand augerings and percussion drillings were made along cross valley transects at 12 locations in the catchment ams 14c dating of peat samples provided a temporal framework for the interpretation of the cores results show that the thickness of holocene sediment deposits in the nethen valley is 4 to 6 m which corresponds to a total clastic sediment mass of 14 106 t stored in the valley bottom three alluvial units could be distinguished and associated with deposition phases from 9600 to 2900 b c 2900 b c to a d 1000 and a d 1000 to present in contrast to the older sediments units 1 and 2 deposits from the last 1000 year unit 3 contain little organic matter they are seldom intercalated with peat layers and devoid of tufa unit 3 reaches a thickness of c 2 m thereby representing 50 of the holocene sediment mass stored in the alluvial plain the mean sedimentation rate in the alluvial plain for this last phase is 26 t ha 1 a 1 which is about tenfold larger than the sedimentation rates calculated for the older holocene sediment units sediment supply towards the alluvial plain has therefore increased tremendously since medieval times these results are in contrast to dating results obtained for colluvial sediments in a nearby dry valley within the catchment of the nethen where soil erosion and sediment deposition started in the early iron age and was already substantial during the roman age this means that there is a time lag of about one millennium between the onset of high sedimentation rates in the upstream area and high deposition rates in the alluvial plain this is probably caused by a change in coupling sediment connectivity between the plateau slopes and rivers as soil erosion proceeds first the dry zero order valleys in the catchment act as sediment traps and only after these are filled sediment reaches the floodplains the preliminary sediment budget for the nethen catchment illustrates that 50 of the sediment that was eroded during the holocene was stored in colluvial deposits which are mainly located on footslopes and in dry valley bottoms another 29 of the sediment mass is stored in the alluvial plain

optical dating using infrared diodes young samples abstract ages are reported for unburnt sediment samples from 9 archaeological sites in england spanning 1000 5000 years samples from two modern contexts have also been measured

spatio temporally variable response of fluvial systems to late pleistocene climate change a case study from central germany abstract the change of the earth s climate and anthropogenic forcing challenge catchment management as the deliberate use of the fluvial system s natural resources depends to some extent on the predictability of the system s variable sensitivity to external impacts the alluvial history of the wetter valley in central germany provides an example of the occurrence of a spatio temporally variable catchment sensitivity to the late pleistocene climate change empirical models that are based on sediment flux controls such as sediment supply transport capacity and gradient serve to explain differential floodplain construction during the early younger dryas the large scale basin upland morphology caused localised divergent cooling impacts and vegetation changes which generated reach scale variable sediment transport system states in the wetter valley the spatial arrangement of reach scale variable response is ascribed to the tectonically driven morphological configuration of the wetter catchment the crucial amplification of differential floodplain construction can be assigned to the spatially variable availability of a surplus of laacher see tephra particles in manner of a pulsed sediment input the ubiquitous tephra cover was previously deposited by the laacher see volcano event in the upper allerod thus the reach scale variable response during the early younger dryas can be deemed to have been climatically triggered but superimposed by an internally driven specific upstream catchment response the documented processes of late quaternary alluviation in the wetter valley imply the need for whole catchment approaches the latter are a prerequisite to reveal the occurrence and causalities of variable fluvial response in relation to external impacts that interact with internal morphological controls this is seen to be crucial to achieve an improved predictability of future environmental change in fluvial landscapes

rheology of the lower mantle abstract the rheology of the lower mantle of the earth is examined from the viewpoint of solid state physics recent developments in high pressure research suggest that the lower mantle contains a considerable amount of mg fe o with fe mg fe 0 2 0 3 the pressure and temperature dependences of diffusion in mg fe o are estimated by the theory of diffusion in ionic solids of the materials composing the lower mantle mg fe o may be the softest and therefore the rheology of the lower mantle may be that of mg fe o unless the framework effect is important temperatures in the lower mantle are inferred from the depths of phase transitions and the melting temperatures of the core materials a thermal boundary layer at the base of the mantle is suggested the physical mechanisms of creep are examined based on a grain size stress relation and non newtonian flow is shown to be the dominant flow mechanism in the earth s mantle the effective viscosity for the temperature models with and without the thermal boundary layer is calculated for constant stress and constant strain rate with depth for constant strain rate which may be appropriate for discussing the mechanics of descending slabs the increase in effective viscosity with depth is smaller than for the constant stress case which may be appropriate for discussing the flow induced by the surface motion of plates the relatively small depth gradient of viscosity for constant strain rate suggests that the lower mantle could also participate in convection the effective viscosity increases with depth however by at least 10 2 to 10 3 from the top to the bottom of the lower mantle for a reasonable range of activation volumes and temperatures there will be a low viscosity layer at the base of the mantle in contrast to the high viscosity layer at the top of the mantle plates if a thermal boundary layer is present the constant newtonian viscosity inferred from rebound data may be an apparent feature resulting from the difference in deformation mechanisms between isostatic rebound and large scale flow

lateglacial to holocene pedogenesis and formation of colluvial deposits in a loess landscape of central europe wetterau germany abstract loess areas in central europe have been settled since ancient times and are therefore predestined to archive information about both the paleoenvironment with and without human activities in gentle rolling loess landscapes distinct short and shallow valleys so called dells are prominent landscape elements that act as sediment traps the loess paleosol colluvium lpc sequence of gambach wetterau germany can be regarded as an exceptional sequence for lateglacial holocene pedogenesis and human impact in dry loess landscapes with the lpc sequence of gambach reflects climate controlled pedogenesis from ca 15 ka to 4 7 ka with the formation of a cambisol having some properties related to chernozem soil forming processes during the lateglacial a chernozem is developed in the deposits of the laacher see tephra which still show the influence of periglacial climate in their lowermost part the upper part of these deposits was relocated by colluvial processes at around 6 7 ka chernozem soil forming processes were still ongoing until 4 7 ka when these shifted to luvisol formation which is still active today since 4 7 ka extended land use with indications of agricultural fire use since at least 2 3 ka led to the formation of colluvial deposits combined with a topographic leveling of upland positions on a landscape scale the results of the formative element of humans on loess landscapes from the wetterau can also be taken as representative for around 9400 km2 of dry loess landscapes in central europe

trace metal storage in recent floodplain sediments along the dill river central germany abstract trace metals are stored in near channel floodplain sediments along many rivers in industrial and mined watersheds of western european countries such as germany in this paper i document the distribution of cu pb and zn in 13 cores collected from near channel floodplain sediments along a 25 km reach of the dill river in central germany mean concentrations of the three trace metals exceed background concentrations an indication of anthropogenic enrichment along the study reach many individual samples have concentrations several times the background levels and exceed standards for trace metals contained in the german federal soil protection act metal concentrations generally peak at depths of 0 2 to 0 7 m below the floodplain surface and are assumed to represent the period of maximum metal releases to the environment through upstream industrial activity ore mining or both in eight of the cores radiocarbon ages obtained below the depth of peak metal concentrations provide maximum dates for sediment accumulation of between 90 and 1700 years ago with most ages clustering in the period of 90 to 300 years ago the ages and depth to peak metal concentrations indicate 0 6 to 1 0 m of floodplain sedimentation over the last 150 to 300 years 0 3 0 4 cm y 1 which exceed sedimentation amounts and rates found in surrounding watersheds surface sediments contain lower metal concentrations suggesting deposition recently of cleaner sediments trace metals stored along the dill river serve as a reminder that stores of contaminants exist in geomorphically sensitive locations of the fluvial system these legacy sediments bear the chemical imprint of industrial or mining activities that no longer occur in the watershed

a temporarily changing holocene sediment budget for a loess covered catchment central belgium abstract this study presents a holocene sediment budget for the nethen catchment a typical river catchment 55 km 2 in the belgian loess belt soil erosion and hillslope sediment storage are quantified by extrapolating detailed data obtained from soil profile truncation studies in three representative zero order sub catchments floodplain sediment storage is estimated by augerings along several transects across the main river and some of its tributaries the sediment budget shows that ca 38 of the soil eroded during the holocene is redeposited as colluvium on hillslopes and in dry valley bottoms another 23 of the eroded sediment is now stored as alluvium in the floodplain the remaining 39 or 21 10 6 mg is exported from the catchment dating of both colluvial and alluvial sediment deposits reveals that sediment dynamics between the hillslopes the dry valley bottoms and the floodplain behave highly non linearly before 500 bc sediment delivery from the hillslopes to the river channels was near maximum however since the onset of significant agriculture in the late bronze age early iron age increased rates of soil erosion are only reflected in the colluvium but not in the floodplain resulting in very low hillslope sediment delivery ratios from the medieval period onwards soil erosion increased even further mainly as a result of a further increase in agricultural land use but now also accelerated floodplain sedimentation took place due to an improved slope channel coupling and the management of floodplains

asynchronous holocene colluvial and alluvial aggradation a matter of hydrosedimentary connectivity based on optically stimulated luminescence osl and radiocarbon dating we establish chronologies of colluviation and alluviation in different floodplain sections of the northwestern wetterau loess basin germany similar to some other european valley floors holocene floodplain aggradation is marked by two important breaks 1 a millennial scale delay between the neolithic agricultural colluviation and floodplain aggradation in loess catchments agricultural colluviation started at about 7000 cal bp and anthropogenic floodplain aggradation only at about 2200 200 cal bp 2 a centennial scale variability in a temporary rise in rates of anthropogenic floodplain aggradation up to 3 6 1 7 mm yr during the high middle ages in directly neighbouring reaches independent archaeologic historic and vegetation records document distinct agricultural histories of hillsides and floodplains and highlight the importance of hydrosedimentary connectivity as compared with land use intensity the late iron age

changes in sediment flux and storage within a fluvial system some examples from the rhine catchment the rhine river system can look back on a long history of human impact whereas significant anthropogenic changes to the river channel started only 200 years ago the impacts of land use have been felt for more than 7500 years here we review results from several case studies and show how land use change and climate impacts have transformed the fluvial system we focus on changes in sediment delivery pathways and slope channel coupling and show that these vary in time and depend on the magnitude of a rainfall event these changes must be accounted for when trying to use sediments as archives of land use change and climatic impacts on fluvial systems for example human impact is recorded in slope deposits only as long as rainfall intensity and runoff generation do not exceed the threshold for gullying similarly climatic impacts are only recorded in alluvium when both the landscape is rendered sensitive by human activities e g deforestation and rainfall thresholds for gullying are exceeded copyright 2003 john wiley sons ltd

viscosity of the earth s mantle inference from dynamic support by flow stress abstract in this study the viscosity is estimated from a new and different point of view the plates with various dip angles and penetration depths are descending into the mantle at many locations around the world since these descending slabs are affected by viscous flow negative buoyancy forces in the slabs and other effects some information about the viscosity can be obtained through the balance of torques exerted on the slabs a model is constructed on the basis of the corner flow treatment for a given viscosity model the stress exerted normal to the slab by the flow is calculated from the balance of torques by this stress the negative buoyancy force and the bending moment the dip angles of the descending slabs are calculated by the comparison between these calculated angles and the observed angles better viscosity models are selected the viscosity distribution obtained here consists of a low viscosity layer with a thickness of about 100 km and a viscosity of about 10 20 p poises an intermediate viscosity layer with about 10 22 p viscosity and either a highly viscous 10 24 p or more layer around 700 km depth or the highly viscous lower mantle

a numerical model of coupled subcontinental and oceanic convection abstract at least two different types of convection should exist in the earth s mantle a large scale flow which is revealed by the creation and subduction of oceanic crust and a circulation of unknown scale under the continents which does not approach the surface the effects of these coexisting and interacting modes on mantle dynamics and thermal regime are investigated by means of a finite element model system of two adjacent cells which are coupled thermally and mechanically at their interface an a priori viscosity distribution is applied in such a way that the surface layer of the longer cell can move with almost uniform velocity while it is immobile on the shorter cell the results suggest that the pattern of sub oceanic convection is stabilized to some extent by the frame of the highly viscous but moving lithosphere whereas convection under continents is more complex and less stable most of the sub continental heat is transferred into the oceanic cell this causes an imbalance of surface heat flow which is well in accordance with recent determinations of global heat loss distribution furthermore the model reflects at least semiquantitatively the continent ocean differences in lithospheric thickness mean topographic level and upper mantle temperatures while the average geotherms below ocean and continent diverge by up to 400 k at moderate depth they nearly coincide below 250 km depth thus giving no support for deep reaching continent ocean differences these results refer to convection penetrating the lower mantle if the circulation is confined to moderate depth the continental upper mantle is too hot compared with the oceanic however this may be due to the strict separation of the flow on either side the model results stimulate some speculations on the possible form of whole mantle convection

secondary convection and the growth of the oceanic lithosphere abstract this paper presents a study of the evolution of the oceanic lithosphere from a thermomechanical approach we have investigated the finite amplitude development of secondary convection cells beneath the oceanic plates by means of the single mode mean field equations and the fully 2 dimensional convection equations using finite element techniques both newtonian and non newtonian rheologies with highly temperature and pressure dependences and an activation energy of 100 kcal mol 1 have been employed the temperature at the base of the convecting medium governs the final thickness of the lithosphere the mean interior temperature varies only slightly during the temporal evolution non newtonian rheology has the tendency to induce oscillatory time dependent behavior of the flow heat flow topography and gravity are influenced by secondary convection in two ways small scale perturbations with wavelengths of around 600 km arise from the lateral thermal differences between the uprising and descending convective limbs large scale features are also produced as a consequence of lithospheric growth the calculated quantities of the heat flow topography and gravity associated with small scale convection are typically in the range of o hfu o 102m and o 10 mgal the horizontal mean temperature profiles from the convection model are used to calculate long wavelength geophysical observables as a function of age convective processes are found to reduce the rate of lithospheric thickening predictions from our model can fit well the observed data of heat flow ocean floor topography and geoid offsets along fracture zones the last data base exhibiting the most sensitivity to thermal perturbations below the lithosphere our calculations show that the oceanic lithosphere is able to grow continuously up to o 109 y long past the flattening of the seafloor we report here that the thickness of a thermally equilibrated lithosphere could reach 250 km which lies within the appropriate range of values for the continental lithosphere as inferred from studies in seismology flexure observations and secular polar motions

alternative chronologies for late quaternary last interglacial holocene deep sea sediments via optical dating of silt sized quartz abstract we summarize the results of a test on the potential of optical dating for the age assessment of late quaternary deep sea sediments our approach combines a single aliquot regeneration sar protocol for equivalent dose d e estimation on fine silt sized quartz with a time dependent evaluation of supported and unsupported long lived radioisotopes within the deposited sediment matrix for this purpose nine samples from two independently dated deep sea cores from the indian ocean were obtained the sar analysis resulted in mean d e estimates with precisions ranging from 0 9 to 3 7 combination of these data with measured radioisotope concentrations resulted in stratigraphically sensible ages ranging from ca 7 to 120 ka these ages exhibit good agreement with existing chronologies for the cores based on radiocarbon age determinations and correlation of key volcanic palaeoecological and isotopic events optical dating may provide an important additional dating method for late quaternary deep sea sediments

on the existence of a second scale of convection in the upper mantle summary this paper is concerned with an examination of the possibility that there might exist a small scale of convective circulation beneath the oceanic lithosphere recent suggestions that this might be the case have been made in an effort to understand why the bathymetry of the sea floor deviates from the prediction of boundary layer theory for ages in excess of about 100 ma the energy source which sustains the secondary motion is supposed to be found in the steep temperature gradient near the planetary surface which is itself presumably maintained by the large scale convective circulation associated with plate creation and destruction here we investigate the extent to which the temperature dependence of viscosity may act so as to stabilize the upper boundary layer against disruption by such secondary instability if the viscosity profile is monotonie and the asymptotic upper mantle viscosity is about 1022poise as suggested by post glacial rebound data then the existence of the second scale is extremely unlikely on the other hand if a sufficiently pronounced low viscosity zone does exist under old sea floor then the development of such a second scale cannot be ruled out completely some recently obtained geophysical evidence is reviewed which suggests that this is unlikely to be the case

infrared stimulated luminescence dating of holocene colluvial sediments using the 410 nm emission abstract infrared stimulated luminescence irsl ages are reported for loessic colluvial sediments from wiesenbach south germany the samples were collected by boring and the polymineral fine grain fraction t4 1 i m was used for irsl investigations irsl spectra were measured prior to dating they show two major emissions at approx 560 and 410 nm the advantages of the subtraction dating technique aitken and xie 1992 using the 410 run emission are demonstrated the ages obtained are used for the reconstruction of the landscape development at the studied site subsequent to an erosion phase the deposition of a colluvium started prior to the roman period and increased to a maximum accumulation rate during the middle ages

shear modulus and q of forsterite and dunite near partial melting from forced oscillation experiments an apparatus designed to determine the complex shear modulus of rock samples by forced torsion oscillations at high temperature and in the seismic frequency band 0 003 30 hz is briefly described measurements were performed on natural dunite from aheim norway up to 1400 c and on polycrystalline forsterite up to 1500 c at 1 atm pressure the two materials were chosen to study by comparison the effect of melt on the elasticity and anelasticity of mantle rocks between 1000 and 1200 c the absolute values of the shear modulus g are almost equal for both materials above 1200 c g for natural dunite decreases progressively with temperature and at 1400 c and 1 hz reaches 13 of its value at 1100 c in contrast g of pure forsterite depends little on temperature for petrological reasons supported by simultaneous measurements of the electric resistivity there is strong evidence that the decrease of g in dunite above 1200 c is due to melt from the lower melting components of the dunite based on different models estimates of the melt fraction are made at high temperature in both materials q 1 is characterized by a monotonic decrease with frequency according to with 0 25 an apparent activation energy of 38 5 kcal mol 1 for forsterite and 48 8 kcal mol 1 for dunite was found with no significant change in the regime of partial melting from this it is concluded that q 1 even at partial melting is dominated by solid state high temperature background absorption there is no indication from these experiments for a constant q band at low seismic frequencies or an increase of q proportional to frequency as suggested by some seismologists the present results are in good qualitative agreement with those for young s modulus obtained previously by strain retardation experiments

stress and flow beneath island arcs summary the flow pattern stress distribution topography and gravity anomalies were computed from numerical models having density and viscosity distributions resemblant to the aleutian arc the results were compatible with the hypothesis that the excess density of the slab drives its descent and that hydrodynamic forces are responsible for topographic and gravity highs over the outer rise seaward of the trench and the frontal arc and lows over the trench in models with simple distributions of rheological parameters the force from the slab was transmitted directly upward producing a negative gravity anomaly over the arc material with low resistance to flow was needed along the fault plane above the slab or within the crust of the frontal arc and within the wedge of asthenosphere above the slab to reduce that force and to allow the horizontal lithosphere to move with the slab models with the resistance to flow thus reduced had outer rises deep trenches horizontal tension seaward of the trench horizontal compression under the trench and downdip tension in the slab free air gravity anomalies which are the sum of between deflections of the free surface due to hydrodynamic forces and direct attractions from the masses driving the flow were not fit excellently by any of the models in part because the coarse grid used precluded accurate representation of the fault zone above the slab and the frontal arc an alternate to the hypothesis that about 5 kb of stress on the fault plane is needed to produce an outer rise is offered by these models shear stress between the slab and the island arc was always below 700 bars in the more successful models if the density distribution was scaled to match the topography of the trench this is much less than the 2000 bars stresses needed if frictional heating causes island arc volcanism

geoarchaeological records in temperate european river valleys quantifying the resource assessing its potential and managing its future throughout the quaternary episodes of glaciation and associated low sea level have resulted in the connection of the terrestrial landmasses of britain and mainland europe the river systems that established themselves across these newly emergent land surfaces of the coastal plain would have created important migration corridors for both animals and humans a point corroborated by the affinity of palaeolithic remains across britain and europe technological developments within the last decade have allowed these now submerged valley floors and adjacent terrestrial landscapes associated with the last cold stage and early and middle parts of the current holocene interglacial to be explored and their archaeological legacies unravelled providing geoarchaeologists with an opportunity to contribute to major cultural debates however in order to maximize knowledge it is essential that geoarchaeologists working within river valleys across both britain and the european continent are addressing similar research questions by collecting data using comparable methodologies this paper reviews the approach taken in different regions and provides a baseline assessment to allow the development of a coherent european wide framework for alluvial geoarchaeology and geoprospection particularly with respect to the holocene record

sensitivity of west and central european river systems to environmental changes during the holocene a review abstract sediment deposition in floodplains is an essential part of the sediment dynamics of a catchment these sediment dynamics can vary largely on a holocene time scale under the influence of driving forces such as land use and climatic variations in this paper we review the holocene floodplain sediment deposition history of rivers in west and central europe with special attention to the influence of climate and land use variability during the early holocene preboreal to atlantic period most floodplains were rather stable with limited floodplain aggradation after this initial phase of relative stability sedimentation rates increase during the middle and late holocene with often the most important deposition phase during the last 1000 to 2000 a the start of the increase in sedimentation varies spatially with an earlier start in the west france germany then in the east poland belarus ukraine while there are also local differences between regions which are settled early e g loess regions compared to later settled regions the sedimentation history of most floodplains can be linked to the local land use history while influence of climatic variations on floodplain aggradation is often reported to be of minor importance processes related to bedload are often reported to be more influenced by climatic events relationships between the driving forces and the sediment history are mainly based on synchronicity and there is seldom proof for a direct causal relationship future research should focus on a system based approach integrating the floodplain deposition in the entire sediment dynamics which includes also erosion colluvial deposition and export main research questions that need further attention include integration of system based concepts like landscape connectivity and buffering effects and also the assessment of the individual contribution of land use changes and climatologic variations on the sediment dynamics detailed sediment budget studies combined with modeling studies can make an important contribution to the understanding of floodplain sediment dynamics

topography and geoid undulations caused by small scale convection beneath continental lithosphere of variable elastic thickness summary the effect of subcontinental upper mantle convection on topography gravity and geoid undulation is studied with special regard to the effective elastic thickness of the continental lithosphere hel we designed a numerical model of the upper mantle lithosphere system consisting of a constant viscosity fluid overlayed by a partly elastic plate the boundary tractions stresses at the top of the convecting mantle model were applied to the lithosphere model for which we used the thin plate approximation the total thickness of the lithosphere was kept constant to 150 km while the elastic thickness was varied between 0 and 150 km the aspect ratio of the convecting mantle was varied between 0 7 and 3 and the rayleigh number between 104 and 106 our calculations demonstrate the effect of a thick elastic lithosphere on the surface observables peak to peak averaged amplitude of topography geoid undulation and gravity are strongly reduced and their spectra are low pass filtered for an aspect ratio less than 1 and a very thick elastic lithosphere topography tends to zero and while geoid undulation and gravity may even become negative above the up welling plume the spectral relation of geoid or gravity to topography admittance is nearly unaffected for hie 70km for aie 70km admittance values for all wavelengths generally decrease with increasing elastic thickness of the plate and may become negative geoid admittance for the basic mode increases with larger aspect ratio while gravity admittance for hie 100 km slightly decreases associating higher rayleigh numbers of the convecting fluid with lower viscosity an increase in rayleigh number leads to considerable decrease of the surface observables however admittance values are only slightly affected and decrease approximately linearly with increasing rayleigh number comparison of our results with observations of the topography spectrum and the free air gravity admittance for north america suggests that large aspect ratio cells beneath continents are unlikely however convection cells of aspect ratio 1 or less underlying an elastic lithosphere of at least 100 km thickness is in agreement with data the rayleigh number should be as high as 106

geochemical tools for the stratigraphic correlation of floodplain deposits of the morava river in stražnicke pomoravi czech republic from the last millennium article i nfo the floodplain of the morava river in stra nicke pomoravi south east moravia czech republic contains a very valuable record of regional environmental change which goes back to several thousand years its interpretation has been limited by poor stratigraphic correlation and dating of the sediments we present a geochemical solution to this challenge we studied 8 outcrops of floodplain deposits from 4 localities along a 6 km long part of the current meander belt of the morava river in stra nicke pomoravi using geochemical proxy analyses magnetic susceptibility measurements 14 c dating of wood remnants and sediment micromorphology the proxy methods are based on elemental analysis edxrf and analysis of the cation exchange capacity of clay minerals granulometric analyses provided the basis for lithological and facies assignment of the sediments our geochemical and mineralogical interpretations have further been tested by microstratigraphically studying the optical properties of the fine fraction horizons older than about 3 centuries were 14

fluvial terrace formation in the northern upper rhine graben during the last 20 000 years as a result of allogenic controls and autogenic evolution abstract the northern upper rhine graben hosts a well preserved late weichselian and holocene fluvial terrace sequence terraces differ in elevation morphology and overbank sediment characteristics the purpose of this study was to determine the relative importance of allogenic controlling factors versus autogenic evolution on the successive formation of these terraces for a representative valley segment the gernsheim region results from previous research were integrated with newly obtained borehole data and digitized elevation maps to construct palaeogeographic maps and cross sections coarse grained channel deposits below terrace surfaces were dated using optically stimulated luminescence and fine grained abandoned channel fill deposits were dated using pollen stratigraphy and radiocarbon analysis initiation of terrace formation was caused by climatic change in the late pleniglacial after 20 ka but fluvial response was complex and slow and continued locally until the middle boreal 9 ka early to middle holocene 6 ka changes in fluvial style and associated overbank lithofacies are not necessarily controlled by climatic change as was previously proposed instead autogenic processes combined with river reach specific factors explain the observed terrace development continuous incision autogenic evolution and high preservation potential provide an alternative explanation for the presence of a terrace sequence in this subsiding area

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

osl dating of coarse grain fluvial quartz using single aliquot protocols on sediments from ne peloponnese greece abstract optical ages of quartz extracts in holocene sediments from the north eastern peloponnese greece are reported the single aliquot regenerative dose protocol proposed by murray and wintle 2000 radiation measurements 32 57 73 was used to estimate the equivalent dose in these samples a large inter aliquot scatter in d e values was observed for all samples this is ascribed to heterogeneous bleaching of the samples at deposition to estimate a d e for age calculation a technique is suggested based on the analysis of the d e scatter obtained from nine different quartz samples which were artificially bleached and irradiated this procedure is especially useful when the sample quantity is limited the optical age estimates increase with sampling depth an average aggradation rate of 1 5 mm yr is derived using the osl ages this value is consistent with the known uplift rate of 1 2 mm yr

transient magmatic convection prolonged by solidification magma chambers cool from all sides with expected vigorous convection strong changes in viscosity with crystallization however lock up within an inwardly propagating crust a great deal of buoyancy otherwise available to drive convection with sufficiently small degrees of superheat the rayleigh number re is small and convection is transient and never becomes fully developed in order to understand this transient stage of convection we have performed some fluid dynamic experintents on the solidification of a paraffin layer except in the growing crust and its thin forward boundary layer the interior remains isothermal and the temperature decreases uniformly until it is locked at the convective liquidus the crystals are fine and hair like dendrites and no major differentiation of the fluid composition is observed the time scale of the convective stage is predictable and is very short relative to the time of complete solidification we also report measurements over time of crust thickness convective velocity and heat transfer when the interior temperature reaches the convective liquidus convection wanes although the calculated re based on an arbitr ary small temperature contrast of 0 2oc is still large 107 a small 0 2oc uncertainty in at i e 0 at 0 2oc produces a large uncertainty in ra i e 0 ra 107 this uncertainty in nature may preclude an accurate determination of ra in a magma chamber residing at a temperature very close to the convective liquidus htroduction in 1905 l v pirsson described in some detail how crystallization induced convection at the margins of a magma chamber could greatly facilitate crystal settling fractionation and differentiation ordinarily slowly settling crystals could be swiftly carried downward by descending convective currents to be deposited as the current approaches and spreads across the chamber floor later f f grout 1918 again clearly enunciated the process with the additional concept of a strongly variable magmatic viscosity due to large changes in crystallinity at the margins this form of convection and crystal transfer has many times since been invoked to explain magmatic differentiation e g wager and deer 1939 brandeis and jaupart 1986 marsh 1989 these considerations and results often suggest that most any body of basaltic magma will reveal the effects of this process through a systematic variation in composition downward through a sheetlike body the overall process involving actual crystallization and convection in aqueous solutions has been experimentally modelled by kerr et el 1989 they observe strong differentiation and suggest that this might explain the large compositional change observed in sills such as the palisades sill shirley 1987 however there are also numerous thick sills and lava flows that show no or very little effect of internal differentiation e g stott

infra red stimulated luminescence dating of holocene reworked silty sediments abstract infra red stimulated luminescence irsl ages are reported for holocene colluvial lacustrine and alluvial sediments and late glacial loess for colluvial sediments irsl ages concur with independent ages age overestimation occur in the case of very poorly bleached sediments such as young less than 2000 years floodloams for which a high suspended sediment load was deduced from sedimentation rates and actually observed floods age underestimates are observed for late glacial loess probably due to inadequate preheat procedures

sensitivity of the eastern mediterranean geomorphic system towards environmental change during the late holocene a chronological perspective alluvial and colluvial sediment deposition provide a vital record of environmental change during the holocene firm chronological control on these archives is necessary to enable us to relate sediment dynamics to human activity and climate variability in the eastern mediterranean such relationships are hard to establish due to the lack of spatially well distributed sediment archives with good chronological control this scarcity is problematic with respect to regional scale reconstructions of the temporal variation of sediment dynamics here we present a radiocarbon database n 178 of geomorphological activity collected from multiple distinct sediment archives within the territory of sagalassos in south western turkey the data were grouped according to their sedimentary facies for analysis using cumulative probability distributions cpds and sedimentation rate sr modelling two small scale colluvial valleys where chronological information was abundant were investigated in more detail results show that sedimentation chronology differs between individual nearby cores as it depends strongly on the local geomorphic situation a generalizing approach combining multiple core results yields more widely valid conclusions high sedimentation rates coincided with the initial major anthropogenic disturbance of the landscape and decreased afterwards probably due to hillslope soil depletion cpd and sr analysis indicates that in general colluvial sedimentation rates did not change much from 2000 bc onwards river floodplain sedimentation in contrast increased markedly during the first millennium bc and during recent times and a significant time lag in enhanced sediment deposition between the upper and lower reaches of the river valleys was observed copyright 2012 john wiley sons ltd

fluvial history of the northern upper rhine river southwestern germany during the lateglacial and holocene times abstract three time slices were focused on reconstruction of the lateglacial and holocene landscape evolution in the northern upper rhine rift valley the fluvial history of the northern upper rhine river during the last 15 000 years is characterised by repeated rapid changes of fluvial morphodynamics and sedimentation conditions in consequence the floodplain of the rhine river may be subdivided into three different meander generations which differ mainly on morphological lithological and pedogenetical criteria using complementary dating techniques pollen irsl ams 14c a detailed chronology was obtained for the floodplain sediments e g overbank deposits peat bogs aeolian dune sands of the rhine river and its tributary the neckar river bergstrasen necker while the latter became completely abandoned during the younger dryas period the rhine river probably started meandering at the onset of the allerod period and most likely continued its meandering pattern since the lateglacial the change from the oldest meander generation to the older meander generation occurred during the late phase of the atlantic period however the timing of the onset of the younger meander generation is not known in detail at present probably it started to develop in the late subboreal period or at the transition from the subboreal to the subatlantic period

phase boundaries in finite amplitude mantle convection summary phase boundaries are included in dynamical finite element models of mantle convection they are represented by point chains which act as additional sources of buoyancy forces when distorted and as additional source or sink of heat the influence of the exothermic olivine spinel transition is studied in both shallow and deep convection models the flow is only slightly enhanced by the transition the increase of temperature due to latent heat release is step like in the deep model in the case of shallow convection it is more diffuse other quantities like ocean floor topography gravity anomalies and stress distribution are no more than moderately affected in a further investigation the effect of spinel post spinel transition whether endothermic or exothermic on deep convection is examined the effect on the flow is negligibly small in both cases

non uniform and diachronous holocene floodplain evolution a case study from the dijle catchment belgium fluvial architecture changed under the influence of increasing human impact throughout the holocene in many north west european catchments typically peat formation in a marshy environment during the early and middle holocene is replaced by clastic overbank deposition in this study we show the importance of a detailed chronology of floodplain changes with an example from the belgian dijle catchment in total 45 radiocarbon ages from 15 alluvial sites were used cumulative probability functions were made of the radiocarbon ages from the base 16 samples and top 29 samples of the peat layer two alluvial sites were studied in detail the results indicate that the end of peat growth and the transition towards clastic overbank deposition is diachronous at the catchment scale ranging between 6500 and 500 cal a bp this diachronous pattern can be attributed to differences in timing and intensity of agricultural activities at the catchment scale or to differences in hillslope floodplain connectivity moreover in the broad floodplain of the main valley the top of the peat layer is even diachronous at cross section scale these results indicate that inferences on changes in sedimentation rate and floodplain changes should be based on a multi transect and multi core dating approach copyright 2014 john wiley sons ltd

effectiveness of natural zeroing of the thermoluminescence in sediments the last exposure to sunlight of detrital feldspars and quartz grains in quaternary sediments can be dated directly by thermoluminescence tl methods but the effectiveness of zeroing of the light sensitive tl signal by daylight varies widely depending upon details of the sedimentation processes to document this variability and to help develop objective criteria useful for future sample selection and laboratory procedures i have collected and analyzed several eolian fluvial marine deltaic and lacustrine samples from less than 100 year old deposits as well as suspensions from sediment plumes also underwater spectral irradiance was measured during recovery of suspensions tl properties of polyrnineralic feldspar dominated 2 4 m and 4 11 m size fractions were measured in the laboratory unexpectedly some light sensitive tl was found to remain in all samples however the light sensitive tl was more effectively zeroed in some samples a proximal loess a sandy braided channel deposit tidal flat and upper delta front muds and thin clayey lacustrine laminae than in others a silty braided channel deposit submarine fan muds and silt bearing lacustrine laminae for the first group the minimum relict paleodose obtained with the partial bleach technique is about 0 4 0 3 gy corresponding to a relict tl age estimate of about 200 years for these sediments thus similar sediments excluding fluvial deposits as young as about 2 ka can be accurately and routinely dated without significant correction for a zero point error if one uses the partial bleach technique coupled with integrated optical bleaching energy fluences of less than 1 j cm 2 and wavelengths only above about 550 nm also some simple optical bleaching tests are reported that have a potential use in sample selection and in provenance studies of some surficial detrital sediments finally a simple mathematical model is presented that helps account for the gross features of the observed bleaching response curves

historical soil erosion by water in germany scales and archives chronology research perspectives abstract the published record of historical soil erosion by water in germany as deduced from dated slope deposits n 306 alluvial sediments n 120 and lake sediments is summarized in this paper the number of sediments investigated reflects the state of knowledge chronology of historical soil erosion and to a certain degree the intensity of the human impact on german landscapes during the holocene even though few data of calculated historical soil erosion intensities exist an estimation of historical soil erosion in germany combining the available data has been calculated soil erosion in germany occurred first locally during the early holocene probably triggered by climatic variability from the neolithic onward the record reflects the human impact according to agricultural land use the observed variability indicates phases of weaker and regained intensity of agricultural land use in germany few records characterise the early and middle bronze age ca 2000 1600 bc and the migration period and the early medieval times ca 400 1000 ad surprisingly for the roman emperor times ca 1 400 ad a decreasing number of soil sediments is recorded even when the data from southern germany is examined separately phases characterised by an increase in soil erosion were the late bronze age and pre roman iron age ca 1600 bc 1 ad the high and late medieval times ca 1000 1350 ad and the modern times ca 1500 ad until today some extraordinary heavy precipitation events late 18th early 19th first half of 14th century pre roman iron age topped the even high soil erosion intensities research gaps as well as potential for future research as derived from the available data are outlined

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

stratigraphy and age of colluvial deposits indicating late holocene soil erosion in northeastern germany abstract in the focus of this study are the sedimentary characteristics chronology magnitude and causes of past soil erosion dynamics of an agriculturally intensively used glacial lowland landscape from the mesoscale quillow river catchment sedimentary sections bearing colluvial sediments from different landforms were analysed to explore their geoarchive potential and to establish a local chronology of late holocene soil erosion sections from footslopes contain a rather simple stratigraphy with one topping colluvial horizon of up to 1 m thickness burying a palaeosol in contrast glacial kettle holes preserve more complex sequences partly having several colluvial layers with intercalating palaeosols the most complex stratigraphy is associated with a kettle hole being the ultimate sediment trap for a dendritic gully system forming a 4 m thick sequence of alternating peat and colluvial layers thirty osl ages and 13 radiocarbon ages are used to reconstruct phases of soil erosion potentially human induced soil erosion which is corroborated by local archaeological and palynological data can be traced back to the last c 4000 years the oldest colluvial deposits date back to the late bronze age most datings however cluster within the last 600 years with a peak in the last 200 years ascribing the main phase of local soil erosion to the recent past thus although numerous archaeological finds are detected in the catchment since the neolithic considerable agricultural soil erosion does not occur before the last millennium a compilation of osl chronologies based on colluvial sediments from other regions in central europe shows a more complex erosion history there with a pronounced two or three phased distribution of ages primarily dating into the last c 4000 5000 years this study underlines that in northeastern central europe human impact on landscapes was effective apparently at a later stage as compared to some adjacent regions

on some consequences and possible causes of layered mantle convection laboratory and numerical experiments are used to study convection confined to discrete layers the laboratory experiments which use the water content of a predominantly glycerine solution as a way of establishing chemical density variations show that convection will remain confined to superimposed layers when the chemical density contrast between layers is greater than the density change associated with the greatest temperature difference within the convecting system the numerical experiments show a double thermal boundary layer at the interface between layers a feature that would result in an average temperature increase of about 500 c in the mantle near 700 km depth if the lower mantle is isolated as suggested by recent geochemical models the possible causes of a layered mantle convection system include major element chemistry variations the combined effect of major element chemistry and a phase change or a phase change alone if it has a sufficiently negative clapeyron slope

laboratory convection experiments effect of lateral cooling and generation of instabilities in the horizontal boundary layers convection experiments are carried out in a tank with two isothermal heat sinks the top plate and one of the sidewalls heating is supplied either by an isothermal bottom plate or by generation within the fluid this situation is similar to that of the earth s subcontinental mantle in the presence of a neighboring subducting oceanic lithosphere there the mantle material loses heat not only to the base of the continental lithosphere but also to the cold dipping oceanic slab the thermal structure of the convective fluid is observed by a variety of techniques including differential interferometry and strioscopy two parameters characterize the observations the usual vertical rayleigh number and a newly defined lateral rayleigh number the lateral cooling induces a large roll with axis parallel to the cold wall the variation of its width relative to the values of the two rayleigh numbers has been determined an application to the earth s upper mantle would predict rolls 5 times wider than high the circulation in the large roll remains two dimensional for rayleigh numbers up to about 3 104 beyond this value boundary layer instabilities are observed within the persisting large roll their period has been determined the interferometric method is shown to be very useful for visualizing other time dependent processes such as the growth of the induced large rolls this growth is rapid enough to allow us to propose the existence of such large rolls in the earth and argue that their action could have led to continental break up

budgeting soil erosion from floodplain sediments of the central rhenish slate mountains westerwald germany the distribution thickness and composition of the floodplain sediments in the valleys of the gelbach lower westerwald and grose nister upper westerwald depend on the occurrence of loessic periglacial cover beds in their catchments as well as on historical land use the budget of floodplain sedimentation was derived from a study of the floodloams underlying the monastery garden of marienstatt a village in the grose nister valley from the study of two occupation levels pottery shards and radiocarbon dating 55 of the floodloam can be attributed to the modern period younger than c ad 1450 from the radiocarbon age of a charcoal fragment extracted from the base of the floodloam at another site in the nister valley it can be concluded that the floodloams were almost exclusively deposited by human impact since the time of high medieval expansion of settlement into the uplands the fine grained loamy sediments blanket a rather irregular floodplain of channels and gravel bars similar results as to t

steady propagation of delamination events delamination of the lithospheric thermal boundary from overlying continental crust propagates laterally from the line of initiation accelerating as the sinking slab of detached lithosphere grows longer this propagation has been numerically modeled with steady state equations in a moving reference frame by matching an interior finite element solution to flexible boundary conditions which represent the mechanical and thermal response of the surroundings the form of the solution depends on the shear coupling of intruding asthenosphere to the top of the sinking slab across a thin layer of crustal material without coupling the tip of the intrusion cools and stiffens to form a wedge dividing the crust cold mode with coupling the intrusion is forced to convect and remains ductile hot mode the cold mode can propagate at all velocities the hot mode has a lower limiting velocity of 1 2 cm year but offers less resistance at higher speeds resistance to delamination includes a constant term from the buoyant crustal downwarp plus a velocity proportional term representing viscous deformation however the proportionality constant of the latter term is only weakly dependent on crust and lithosphere viscosities matching this resistance to loading lines of 100 to 800 km slabs sinking in a mantle of 1022 p velocities of 0 3 8 0 cm year are obtained changes in viscosity affect this rate but cold mode delamination is unstoppable except at continental margins or by failure in the sinking slab the surface expression of delamination is a leading outer rise followed by a submarine trough with a large negative free air anomaly which finally evolves into a 1 km plateau if crustal viscosity and velocity are both low however there is a montonic crustal uplift with no trough thus the present lack of linear supracontinental oceans does not preclude delamination at up to 4 cm year driven by slabs up to 400 km in length

the interaction of a subducting lithospheric slab with a chemical or phase boundary we have used a finite element model of time dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle a temperature dependent and non newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection the 650 km discontinuity is taken as either a chemical or phase boundary or as a combination of both it is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position when the compositional density contrast is greater than about 5 the descending slab is deflected sidewards at the boundary and two layer convection prevails a resulting depression of the boundary in the range of 50 200 km should be detectable with seismic methods below 5 density difference the slab plunges several hundred kilometers into the lower mantle and below 2 it will probably not stop before reaching the core mantle boundary and extensive mixing would be expected with a pure phase change a negative clapeyron slope of about 6 mpa k 60 bar k is required to establish a type of leaky double layer convection a more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle with the present uncertainties about the physical nature of the 650 km discontinuity a variety of convective styles appears possible on dynamical grounds

the formation of alluvial fans and young floodplain deposits in the lieser catchment eifel mountains western german uplands a study of soil erosion budgeting this study deals with the exploration and spatiotemporal quantification of the young holocene nearly skeleton free floodplain sediments of the lieser river a tributary of the mosel river in the eifel mts the deposits are primarily a consequence of anthropogenic triggered soil erosion in the catchment to observe the phenomenon of corresponding soil erosion on multiple levels two small alluvial fans of tributary catchments were investigated for comparison one location in the neighboring salm valley was described the results were compared with those of other streams with extensive fieldwork more than 100 drillings and pits were made at 12 locations for dating the sediments osl dating 14c dating of organic contents and archaeological artifacts were used in the floodplains of the lieser and its tributaries 35 1 106 t of overbank fines are stored to achieve this an average soil erosion of 61 4 mm in the whole catchment would have been necessary about 28 of young floodplain sediments in upper a

holocene relief and soil changes in loess covered areas of south western germany the pedosedimentary archives of bretten bauerbach kraichgau based on infrared stimulated luminescence irsl dating of loess borne sediments a chronometry of holocene landscape evolution is established for a representative study site in the early settled kraichgau area in south western germany the results show that the gently rolling relief is due essentially to soil erosion and colluvial deposition triggered by humans cultivating the loess soils since the onset of agriculture in the neolithic period levelling of relief is accompanied by alterations in soil type patterns from haplic luvisols before the impact of humans over variably truncated luvisols with bt horizons prevailing at the slope surfaces in the middle ages to calcaric regosols characterizing both sites of erosion and accumulation since then the tremendous changes show that the effects of human activities have been recorded over thousands of years indicating an early anthropocene in a geomorphological and pedological sense most landscapes are probably more modified by humans than thought at first sight as the results show this recognition requires considering that current geomorphological and soil forming processes might work at different frequencies or magnitudes e g by changes of internal system thresholds such as increased erodibility following the complete erosion of a more resistant bt horizon and or in a different direction e g accumulation instead of erosion or sediment transport due to slope angles decreased by former deposition of colluvium than they would in the absence of a human controlled pre history

reconstruction of holocene glacier history from distal sources glaciofluvial stream bank mires and a glaciolacustrine sediment core near sota saeter breheimen southern norway this study attempts to reconstruct the holocene glacier history of breheimen southern norway from four stream bank mire sites and a downstream lake sediment core near sota saeter based on lithostr

on the effects of the lithosphere on mantle convection and evolution abstract an idealized model is discussed for plate motion and mantle convection it consists of a numerical square box filled with a newtonian boussinesq fluid heated from below at the surface the fluid has a high viscosity i e it contains a stiff lid which may or may not be laterally decoupled by weakness zones lid stiffness and coupling were varied systematically only if the lid is effectively decoupled laterally does it move as a quasi rigid plate it is then driven by the lateral pressure differential from the rising and descending plumes in the fluid and it moves against viscous shear at its bottom gravitational sliding and sinking may also drive the plate if allowed for in the model a decoupled freely moving stiff plate effectively removes heat from the interior a strongly coupled stiff lid on the other hand or one with a very large aspect ratio inhibits heat transfer through the convecting layer if heating occurs by a given flux through the bottom or internal heat generation the internal cell temperatures become very high because the stagnant surface lid can only conduct the heat by assuming the required temperature gradient throughout its thickness since the earth is partly covered by conducting continental lids which in addition contain much of the heat sources the thermal history may be affected caution must be exercised in parameterized convection modelling in this respect the overall effect cannot easily be predicted because mantle flow and continental plates will interact the importance of mechanical decoupling for plate motion strongly calls for thorough studies of the decoupling mechanisms particularly at convergent plate boundaries bending stick slip processes and the role of volatiles

two layer mantle convection and the depletion of radioactive elements in the lower mantle only a small percentage of the mantle s total content of radioactive elements can be in the lower mantle if this region convects steadily and separately from the upper mantle recent geochemical models of a depleted upper mantle and an undepleted lower mantle are thus inconsistent with a steady thermal model involving distinct upper and lower mantle convection cells steady two layer mantle convection requires a depleted lower mantle and an undepleted upper mantle to match the observations of surface heat flow and mantle viscosity the constraint on the abundance of radioactive elements in the lower mantle depends on the existence of at least one thermal boundary layer at the upper mantle lower mantle interface with thickness comparable to that of the surface thermal boundary layer since the temperature drop across an interface boundary layer is limited by the relatively small difference between the solidus temperature and the upper mantle temperature the amount of heat which can be transferred across this layer is small compared with the surface heat flow the upper limit on the concentration of radioactive elements in the lower mantle can be relaxed only if both the lower boundary layer of the upper mantle cell and the upper boundary layer of the lower mantle cell are extremely thin or absent altogether which we consider however highly unlikely

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

holocene river activity analysing 14c dated fluvial and colluvial sediments from germany records of fluvial dynamics in response to long term changes of climate and land use impacts are rare therefore cumulative probability functions cpfs of 401 14c ages originating from german rivers and hillslopes were compiled to reconstruct phases of increased geomorphic activity and stability during the holocene an improved analytical method is suggested to normalise cpfs and eliminated the effects of wiggles of the calibration curve and the young age bias nine periods of activity are identified peaking at 7050 6250 5525 3690 2250 1350 820 325 bc and since 875 ad and are compared with climatic palaeohydrological and human impact proxy data until 2250 bc events of geomorphic activity are mainly coupled to wetter and or cooler climatic phases due to growing population and intensive agricultural activities during the bronze age the increased geomorphologic activity between 1300 and 820 bc cannot unequivocally be related to climate since 875 ad the growing population density is considered as the major external forcing differential geomorphic activity of hillslopes and floodplains suggest that the hillslope channel coupling during the holocene is mainly controlled by human impact with a strong increased coupling after 1500 bc

human and climate impact on catchment development during the holocene geul river the netherlands interest in the holocene development of small to medium sized river catchments in western and central europe in relation to changes in land use and climate has increased over the past years in this study we reconstruct the holocene landscape development and fluvial dynamics of the geul river the netherlands and the main forcing mechanisms of environmental change field studies were carried out and we used osl and 14c dating methods to reconstruct the holocene valley development our study shows that 2 periods of deforestation during the roman period and the high middle ages led to severe soil erosion and increased floodplain sedimentation in the catchment of the geul river possibly combined with periods of increased wetness during the high middle ages alluvial fans have been active since the roman deforestation phase our results show that the geul catchment is highly sensitive to changes in land use

surprisingly small increase of the sedimentation rate in the floodplain of morava river in the stražnice area czech republic in the last 1300 years abstract sediment profiles from the floodplain of morava river in the czech republic have been collected from exposed river banks 4 6 m long sections and cores 2 4 m deep and investigated using a set of geochemical proxies validated by granulometry and conventional geochemical analysis outlined in our previous paper the work was conducted to evaluate the increase in sedimentation rate during medieval and modern time periods correlation of sediments along the current channel belt allows identification of two most important synchronous changes in the channel structure over the past 1300 years in the 13th century and at the end of the 16th century these changes could be related to central european climatic extremes rather than to land cover land use practises analysis of the pollen record in peaty deposits at the floodplain edge allows excluded dramatic deforestation in medieval times maps of the area from the last five centuries revealed direct and indirect signs of past avulsions and clearly show how the original multichannel system was transformed into a single meandering channel in the early 20th century the extrapolated aggradation rate net vertical accretion of floodplain fines except for levee sediments increased from 0 2 0 3 cm year in 700 ad to 0 3 0 4 cm year in 2000 ad depending on the grain size of the sediment this is the smallest yet reported enhancement of siliclastic deposition although morava river watershed has been intensively used for agriculture and its land cover has changed in a manner similar to west and central european rivers