late holocene erosion in upland britain climatic deterioration or human influence the evidence for enhanced erosion in upland britain during the late holocene is evaluated though there is widespread evidence for recent soil erosion on high plateaux this has not been precisely dated radiocarbon dating confirms the occurrence of late holocene solifluction on high ground but at only one site has evidence been found for recent accelerated activity several areas however have yielded evidence of late holocene debris cone accumulation and parts of the scottish highlands experienced a drastic increase in debris flow activity over the past few centuries climatic deterioration and vegetation degradation resulting from overgrazing or burning are frequently cited as the causes of enhanced erosion but cause and effect are often related only by coincidence of timing in consequence only circumstantial evidence links erosion with climatic deterioration though anthropogenic influences have been more firmly established at a few sites the role of extreme events in initiating phases of uplan

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

late quaternary soil erosion and landscape development in the apennine region central italy abstract this study on past soil erosion processes focuses on a catchment located in a mountainous sector of the central apennines 60 km northeast of rome humans are known to have interacted with the landscape in this region at least since the early iron age the area is highly sensitive to climatic changes and human intervention and thus is susceptible to soil erosion the environmental impact of past human activities has been examined by geomorphological and sedimentological investigations and supported by modelling operations percussion drillings in the floodplains reveal up to 10 m thick alluvial deposits combined sedimentological and geomorphological analysis suggests that the total sediment volume of the valley infill totals about 300 000 m3 of sediments radiocarbon dating documents that this alluvial sedimentation started during the sub atlantic period between the 1st and 2nd centuries bc and coincides with a shift from a flood quiescent to a flood prone phase according to historical sources the flood phase correlates chronologically with the roman occupation of the area when they practiced extensive logging in their territories gis modelling operations show a loss of soil surface of about 71 cm on average for the entire catchment 1 600 000 m3 loss of soil if long term land exploitation for wood supply is assumed the modeling showed that approximately 80 of the eroded soil has been fluvially transported out of the catchment so the present alluvial plains may represent only about 20 of the overall lost soil mass

iron partitioning in a pyrolite mantle and the nature of the 410 km seismic discontinuity pyrolite1 is a hypothetical mixture of distinct minerals which iswidely believed to represent the composition of the earth s mantle the main pressure induced phase transformations of the olivine component of pyrolite occur at about 13 5 gpa to and 24 gpa to mgsio3 rich perovskite magnesiowustite 2 3 which are thought to be responsible for the seismic discontinuities at 410 and 660 km depths in the mantle recent seismological studies however have demonstrated that the 410 km seismic discontinuity is sharper in some areas than that expected from the to transformation in mantle olivine with a fixed composition4 5 6 7 moreover some mineral physics studies suggest that the seismic velocity jump at the 410 km discontinuity is inconsistent with that associated with the to transformation in olivine8 9 here we present a phase equilibria study of a material having pyrolite composition at pressures of 6 16 gpa we found that the iron content in olivine changes significantly with increasing pressure as a result of the formation of a relatively iron rich majorite phase at these pressures this variation in iron content can overcome or at least reduce both of the above difficulties encountered with the pyrolite model of mantle composition by showing that the component mineral systems cannot be treated as separate

sediment sources and transport pathways in a rural catchment herefordshire uk the relative significance of primary and secondary suspended sediment sources has been identified in a small 15 km2 agricultural catchment through the application of a linear unmixing model using mineral magnetic geochemical and radionuclide signatures of fine sediments roads appear to be important as a secondary source of suspended sediment and in the conveyance of topsoils to the river channel roads also alter the source signatures of sediment in transport especially that derived from agricultural topsoils modelling suggests that c 30 of the suspended sediment collected from suspended sediment traps in the river leadon were derived from or transported via roads relative contributions from primary sources of c 43 and c 27 were estimated from a combined subsoil and channel bank subsurface source and a combined arable and grassland topsoil source respectively

evidence for mediaeval soil erosion in the south hams region of devon uk a major theme of research into the causes of past and present soil erosion has been to determine the relative importance of climate and land use change in influencing holocene erosion rates previous work suggests that land use change especially the conversion of woodlands into agricultural land is the main factor influencing long term increases in soil erosion a study of an extensive minerogenic sediment deposit in a wetland at slapton ley in devon suggests that agricultural intensification occurred before the onset of sedimentation a silty clay layer c 40 cm thick in the valley bottom wetland of the slapton sewage works marsh the base of the silty clay layer lies at an altitude of between 2 2 and 2 6 m aod and has been radiocarbon dated at two locations conventional radiocarbon ages 2 were 910 160 yr and 960 140 yr bp successful radiocarbon dating of the upper surface of this minerogenic layer at one location yielded a conventional radiocarbon age of 730 120 yr bp within the errors

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

high energy coastal sedimentary deposits an evaluation of depositional processes in southwest england sediments left by coastal flooding have been observed worldwide and have been variously ascribed to the action of storm surges and tsunami waves to date no study has attempted to unequivocally establish on stratigraphical sedimentological and palaeoecological grounds the means by which these two different processes might be distinguished in coastal sedimentary sequences this paper examines the evidence for historical storm surges and tsunamis and shows that both high magnitude events have been documented over the past 250 years in southwest england sand layers of varying thickness are present within holocene lagoonal and peat sequences of several shallow lakes of the scilly isles detailed analysis of big pool st agnes indicates that the basal peats date from around 1000 bp within the basal peats are numerous thin sand layers above the basal peat is an extensive sand layer 15 to 40 cm thick the base of this latter layer probably dates from the early to mid 18th century particle size grain surface morphology diatom and mineral magnetic studies are used to try and determine the most likely mode of deposition the results of all analyses are inconclusive but the weight of evidence suggests that the increasing frequency of thin sand layers in the upper part of the basal peat may be related to the increasing frequency and intensity of atlantic storms during the little ice age superimposed upon a rising sea level the thick sand layer may have been deposited by the tsunami wave generated by the lisbon earthquake of november 1 1755 due to the difficulties in distinguishing depositional processes in coastal environments known to have been affected by storm surges and tsunami waves it is suggested that generally accepted sedimentological techniques are inadequate for discriminating depositional processes in coastal environments

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

gcm sensitivity test using increased rotation rate reduced solar forcing and orography to examine low latitude glaciation in the neoproterozoic during the neoproterozoic period most landmasses were assembled into the super continent rodinia and parts experienced glaciation in low paleolatitudes we examine possible causes of glaciation by increasing rotation rate reducing the solar constant and carbon dioxide concentrations for an idealized super continent that is centered in the northern hemisphere tropics subtropics further we introduce a 2 km north south mountain chain in the western regions of this super continent a mixed layer ocean or prescribed time varying sea surface temperatures are used in these simulations our results show that neither an individual factor or a combination of these factors can cool temperatures enough to bring about glaciation on the tropical super continent we conclude that other factors would be needed to initiate glaciation

holocene alluvial fan and terrace formation in the bowland fells northwest england in the bowland fells lancashire northwest england in the headwater valleys of the hodder river system is a suite of holocene fluvial landforms debris cones and alluvial fans at tributary junctions and river terraces along the main valleys post date late pleistocene forms and pre date the modern valley floor alluvial forms eight 14c dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of holocene erosion to be identified with debris cone fan deposition taking place after c 5400 bp but before c 1900 bp and again at c 900 bp some of the fans and cones are complex with deposits attributable to both phases others are simple and attributable only to the later phase in the headwaters an upper terrace at c 5400 bp pre dates the cones and a lower terrace is contemporaneous with the first debris cone phase lower downvalley the youngest of three terraces date from c 5000 bp or earlier indicating that the sequence is less complex downstream

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

holocene alluvial fan development in the macgillycuddy s reeks southwest ireland holocene alluvial landforms in the macgillycuddy9s reeks southwest ireland were investigated to determine the controls and timing of postglacial geomorphic activity detailed geomorphologic analysis of three alluvial fan and debris cones within high level cirque basins demonstrates evidence of episodic phases of late holocene surface aggradation and incision radiocarbon dates from peat horizons above and below inorganic units show that phases of aggradation cluster into two distinct periods the first after 230 790 calibrated cal yr a d and the second from 1510 cal yr a d to the present an additional phase of fan aggradation at one site is dated after 1040 1280 cal yr a d all three phases coincide with episodes of enhanced late holocene valley floor alluviation and debris flow activity from upland britain alluvial fans and debris cones have developed primarily as a result of the resedimentation of late midlandian wisconsin drift and talus slopes and mobilization of materials involved flooding transitional flow and debris flow processes pollen analysis of peat horizons interbedded with alluvial fan and debris cone sediments indicates that land use changes were an important factor in lowering the threshold for local slope erosion phases of aggradation also coincide with well documented episodes of climate change and hence fan development is probably a function of both anthropogenic and climatic forcing a sequence of events may have involved initial slope destabilization due to overgrazing and removal of vegetation that was followed by debris mobilization and fan aggradation during intense rainstorms associated with climate change

holocene debris cone evolution in glen etive western grampian highlands scotland stratigraphic investigations radiocarbon dating of buried soils and pollen analyses were employed to reconstruct the history of development of a fluvially reworked debris cone in glen etive paraglacial aggradation of debris flow deposits resulted in cone formation between c 10000 yr b p and c 4000 yr b p until supplies of sediment from upslope were effectively exhausted and debris flow activity ceased there ensued a prolonged period of stability and soil development on the cone surface this ended sometime after c 550 yr b p when human interference including burning resulted in destruction of the natural vegetation cover and triggered fluvial incision and the development of an alluvial fan of reworked sediment that buried the lower part of the debris cone the wider implications of these findings are discussed

morava river floodplain development during the last millennium stražnicke pomoravi czech republic floodplain sediments deposited along the lower course of the morava river eastern czech 206 pb 207 pb and pop ddt pcb analysis and 137 cs activity data thecu trienmethodwasusedforstratigraphicallycorrelatingthesedepositsbasedonthevariationofexpand able clay minerals in the sediments the resulting stratigraphic pattern reveals the alluvial history of the cur rently active river channel system since the end of the first millennium ad fine overbank clayey sediments deposited during the mediaeval warm period were eroded from cultivated fields newly formed during mediaeval colonization between 1250 and 1450 these fine deposits are overlain by coarser floodplain sedi mentsofthe littleiceage indicatingachangeinthesedimentsourcesincethesixteenthcentury ad anda substantial increase in the sediment load in the second half of twentieth century the straunicke pomoravi floodplaindepositsrepresentavaluablepalaeoenvironmentalarchiveofthelastmillennium containingrecords offluvialprocessesconsiderablyalteredbyhumanactivities

agro industrial alluvium in the swale catchment northern england as an event marker for the anthropocene foulds s a macklin m g brewer p a 2013 agro industrial alluvium in the swale catchment northern england as an event marker for the anthropocene the holocene 23 4 587 602

soil erosion and sediment deposition in the belgian oess belt during the holocene establishing a sediment budget for a small agricultural catchment a method to establish a holocene sediment budget for a 103 ha agricultural catchment representative for the belgian loess belt is presented soil erosion and sediment deposition were determined based on 185 coring locations and a large excavation in the valley bottom results were integrated in a gis and interpolation techniques applied to derive spatial patterns of erosion and sedimentation total soil erosion sediment deposition and sediment export were calculated and the results show that volumes are highly dependent on the interpolation technique used sediment delivery ratios between 20 and 42 are derived and are consistent with data reported in previous studies this clearly shows that the majority of the sediments produced during the holocene have been stored near their source area and have not been delivered to the downstream rivers the spatial distribution of soil erosion and sediment deposition within the catchment is strongly dependent on slope gradient and position within the catchment which suggests that since human impact began topography has been the main factor determining long term soil erosion and sedimentation

the age of alluvial fan deposition at a site in the southern uplands of scotland the age of a large alluvial fan debouching onto the valley floor of the river tweed in southern scotland and the sequence of events relating to this are investigated using geomorphological sedimentological palynological archaeological and radiocarbon dating evidence prior to fan deposition the tweed valley floor seems to have been covered by a wooded peat at a time of low fluvial activity the fan commenced deposition in the 11th century ad and appears to have been a local event the tweed showing no response to this accelerated sedimentation later perhaps 200 years later the tweed commenced overbank deposition of the only flandrian terrace preserved local proxy data are examined in order to define the causes of these events but difficulties in temporal correlation despite the good resolution of the radiocarbon chronology mean that the causes of these events remain unknown

olivine emerges from isolation at a depth of around 410 km in the earth s mantle the speed of seismic waves rises sharply the reason is thought to be the high pressure transformation of the mineral olivine to wadsleyite at that depth seismological data have however been at odds with laboratory work with these minerals in which their behaviour is extrapolated to mantle conditions a study showing that manganese and iron can be exchanged between olivine and other mantle minerals is a step towards resolving these discrepancies

late holocene paleoecology and sedimentary history of a small lowland catchment in central england a variety of paleoecological and sedimentary techniques were used to investigate the storage of sediment within a small lowland catchment during the holocene radiocarbon dating of vertically accreted floodplain deposits allowed the calculation of inorganic accumulation rates these rates show a dramatic increase in sediment deposition during the late bronze age and early iron age 2900 2300 yr b p due to deforestation and cultivation of the catchment slopes and resultant soil erosion the soils within the catchment were susceptible to structural damage surface waterlogging and slope wash erosion from the calculated increases in sediment storage estimates of catchment erosion were made which vary from around 20 to 140 tons km 2 yr 1 the study of alluvial chronology at this scale can provide unique information on the source areas of holocene floodplain sediments and provide long term erosion rates

seismic evidence for olivine phase changes at the 410 and 660 kilometer discontinuities the view that the seismic discontinuities bounding the mantle transition zone at 410 and 660 kilometer depths are caused by isochemical phase transformations of the olivine structure is debated combining converted wave measurements in east asia and australia with seismic velocities from regional tomography studies we observe a correlation of the thickness of and wavespeed variations within the transition zone that is consistent with olivine structural transformations moreover the seismologically inferred clapeyron slopes are in agreement with the mineralogical clapeyron slopes of the mg fe 2sio4 spinel and postspinel transformations

mineral magnetic characterization of sediment sources from an analysis of lake and floodplain sediments in the catchments of the old mill reservoir and slapton ley south devon uk research on suspended sediment transport in the catchments of the old mill reservoir and slapton lower ley south devon has attempted to discriminate changing catchment sources on the basis of downcore variations in the mineral magnetic properties of lake reservoir and floodplain sediments here we examine these downcore variations and also explore the variability in catchment sources and the influence of topographic controls on mineral magnetic signatures of topsoils and subsoils particle size controls on the mineral magnetic signatures are explored by an analysis of a fractionated sediment sample whilst the possible impact of diagenesis is assessed by an examination of the mn profiles in the lake and reservoir sediments from this analysis it is evident that the mineral magnetic signatures of well sorted floodplain deposits are more likely to reflect the particle size composition of the transported material by contrast the mineral magnetic record in the sediment of slapton ley appears to be most strongly influenced by dissolution of magnetic minerals the sediment of the old mill reservoir provides the only suitable record for the application of a simple mixing model which is developed in order to quantify changes in the relative contribution of topsoil and subsoil through time the research has important implications for attempting to reconstruct sediment sources in highly eutrophic lakes and emphasizes the uncertainty in the application of simple mixing models 1998 john wiley sons ltd

modelling long term anthropogenic erosion of a loess cover south downs uk there is growing archaeological evidence that erosion induced by prehistoric agricultural activities has in many parts of europe greatly thinned an original thick loess cover the evidence for this is however almost entirely observational and qualitative whether in the time available anthropogenic activity could have produced modern thin loessial soils has not been quantitatively evaluated this study adopts a novel modelling approach in the estimation of long term rates of soil loss and textural modification under prehistoric and historic tillage practices the epic erosion productivity impact calculator model is used to simulate the effects of erosion on a hillslope in the uk south downs from 7000 bp to the present day results suggest that the major period of soil loss was between 4000 and 1800 bp under conditions of gradually intensifying agriculture following permanent clearance that land use rather than climate appears to be the main factor influencing past erosion rates and that a thin

linking forest cover soil erosion and mire hydrology to late holocene human activity and climate in nw spain this article is distributed under the terms of the creative commons attribution noncommercial 3 0 license http www creativecommons org licenses by nc 3 0 which permits non commercial use reproduction and distribution of the work without further permission provided the original work is attributed as specified on the sage and open access page http www uk sagepub com aboutus openaccess htm

diagenesis of magnetic minerals in the recent sediments of a eutrophic lake magnetic mineral assemblages in lake sediments are usulally interpreted as reflecting changing catchment erosion magnetic and chemical assemblages in a small eutrophic lake lough augher northern ireland suggest diagenetic dissolution of fine grained magnetite however probably as a result of changing redox conditions associated with eutrophication water column results show internal cycling of mn and fe from the sediments into the armxic hypolimnion calculations suggest that late summer hypolimnetic fe concentrations are controlled by formation of aulhigenic vivianite sedimentary pore water concentrations of total soluble fe and p suggest a similar process in the sediments the loss of mn from the lake by diffusion from the sediment and washout at overturn is indicated by mn budget calculations and by it marked decrease in its sedimentary concentration reflecting onset of eutrophication as indicated by diatom biostratigraph y the changes in the sediment mn profile are coincident with and in some cases identical to changes in several rnagnctic parameters the changes in magnetic stratigraphy suggest a coarsening of the magnetic grain size and reduction in the total concentration agreement with chemical profiles indicative of changing rcdox suggest that this coarsening results from dissolution of fine grained magnetite catchment stability together with other stratigraphic profiles of eutrophication and changing redox supports the conclusion that the magnetic profiles are reflecting in situ diagenetic changes rather than altered catchment processes with the data available it is not possible to identify the actual clissolution process involved or to determine whether it is chemically or bacterially controlled

late holocene channel changes of the middle trent channel response to a thousand year flood record this paper presents recent work on the floodplain sedimentology of the middle trent using data from gravel pits archaeological sites and documentary sources the middle trent has been unusually active during the holocene in comparison with other large lowland rivers in the british isles the holocene floodplain fill is dominated by sands and gravels with abundant structural evidence of changes in channel pattern and channel type a thousand year record of channel change has been reconstructed from palaeochannels and gravel units with radiocarbon dating of brushwood palaeomagnetic dating of fine channel fills dendrochronological dating of timber structures and dating via archaeological typologies the trent also has a reasonably well recorded flood history at least since the 11th century ad a comparison of the flood record and channel change indicates that the same degree of morphological and sedimentary response is not necessarily associated with floods of similar magnitudes i e there is no constant relationship between event magnitude and landform change instead the response seems dependent on the existing state of the channel and medium term trajectory of channel change there is evidence at both the hemington and colwick reaches of a cycle of channel change involving a change in channel typology and dating evidence that this may have migrated downstream the results of this work provide a medium term perspective on channel change which may be more appropriate for large british rivers than short term monitoring for both model validation and planning purposes

a calculation of ocean heat storage and effective ocean surface layer depths for the northern hemisphere abstract in the hierarchy of simple ocean formulations available for coupling to atmospheric gcms a scheme whereby ocean surface layer depths vary geographically and seasonally is deemed better than a fixed depth layer at all locations and seasons but still is less sophisticated than dynamic ocean models yet such simple ocean formulations are useful for basic sensitivity studies here a calculation of varying surface layer depths is done by first performing an ocean heat storage calculation using gridded long term mean mixed layer depths and sea surface temperatures with a parameterized temperature structure beneath the mixed layer derived from weather ship data heat storage values in the midlatitudes are larger in the atlantic than in the pacific which is in qualitative agreement with the weather ship data variants of the basic calculation show that neither mixed layer data nor sst data alone are sufficient to compute heat storage adequately using the results from the parameterized heat storage

archaeomagnetic dating and palaeochannels sediments data from the mediaeval channel fills at hemington leicestershire this paper illustrates how archaeomagnetic dating can be used for palaeochannel fills within floodplain sequences the sites investigated are palaeochannels associated with the mediaeval braided anastomosing channels of an unstable reach of the river trent at hemington north west leicestershire this reach has revealed abundant archaeological remains including fish weirs anchor stones a norman mill and three mediaeval bridges the studies used here show good agreement between archaeomagnetic dating and other evidence from archaeology dendrochronology and radiocarbon dating fabric and mineral analyses of the sediments are used to identify the source of the remanent magnetization and it is believed that this is predominantly the result of the biogenic synthesis of magnetic minerals in high ph but anoxic conditions this study illustrates the type of alluvial sediments that are most suitable for archaeomagnetic dating

land use change soil erosion and alluvial dynamic in the lower doubs valley over the 1st millenium ad neublans jura france abstract geochemical and particle size analyses surface scanning magnetic susceptibility microscopic charcoal counting and pollen analysis have been carried out on two cores from the lower doubs valley in order to reconstruct the land use history the interpretation of anthropogenic pollen indicators and micro charcoal deposits is discussed in relation to the lithological variation of sedimentary accumulation and evolution of the settlement the environmental changes which occurred during the 1st and the 6th century ad reflect the impact of human activities on the landscape in the immediate surroundings of the site multiproxy indicators indicate that soil erosion as a consequence of agricultural activities including fire practices a reactivation of hydrologic flow of the river recorded in the sedimentary sequences attests to a larger environmental perturbation between 1st 3rd and 7th 8th century ad

influence of climate change and human activities on the organic and inorganic composition of peat during the little ice age el payo mire w spain the study of environmental change during the little ice age lia offers a great potential to improve our current understanding of the climate system and human environment interactions here a

human impact on subatlantic slopewash processes and landform development at lake jasien northern poland abstract a survey of the lake jasien area northern poland demonstrates the relationship between human economic activity and the course of slopewash processes during the subatlantic in the catchment area of the erosional denudational valley affected by prolonged human economic activity in the early iron age the hallstatt period and the pre roman period deforestation may have led to activation of hillslope processes a manifestation of this activation is a fossil cut in the bottom of the valley and sediments of hillslope origin filling it lying on top of sediments dated to 450 bc 100 cal ad the intensity of the hillslope processes may have been modelled by climate changes involving cooling and humidification the most recent documented increase in the intensity of denudation occurred around the middle of the 17th century deposited on top of sediments dated to 1456 ad 1638 cal ad and 1453 ad 1797 cal ad is a sequence of hillslope sediments developed in the form of diluvium and tillage diamicton filling the bottom of the valley and the closed depression faster denudation in the landform catchments and accumulation on their bottoms were caused by deforestation of those areas and using them as farmland as indicated by old cartographic materials the cooling and humidification of the climate during the little ice age may also have contributed to the acceleration of the agrotechnical denudation in areas unaffected by deforestation no noticeable traces have been found of active denudation processes during the subatlantic this may suggest that hillslope processes did not play a major role in lowland forested areas of the temperate zone

gcm simulations of snowball earth conditions during the late proterozoic in order to simulate the snowball earth conditions that may have existed during the late proterozoic we have conducted a series of gcm simulations using a simple 50 meter slab ocean a reduced solar constant of 6 and varied co2 concentrations in this study we vary the co2 concentration from 100 to 3400 ppmv and use rotation rates corresponding to 18 and 24 hour day lengths we also examine the effects of increasing the poleward transport of heat by the oceans our results show that below a critical value of approximately 1700 ppmv of atmospheric co2 sea ice and sub freezing temperatures occur from the poles to the equator a global mean annual two meter air temperature of 221 k is found for boundary conditions of 100 ppmv atmospheric co2 6 reduction in solar forcing and a rotation rate corresponding to an 18 hour day these results confirm those of earlier studies suggesting or implying that low latitude glaciation occurred during the late proterozoic however since the ocean is the critical factor for low latitude glaciation the results should be view cautiously because of the simple slab ocean used in this study

gcm response to late precambrian 590 ma ice covered continents recent coupled energy balance ice sheet modeling studies indicate that ice covered continents can be simulated for the late precambrian with 6 solar constant reduction we examine the ocean mixed layer response to such an ice sheet with the genesis 2 general circulation model and co2 levels varying from 0 5 2 5 times present the ocean ices over completely at 0 5 1 0x present levels with the final phase of sea ice growth occurring within a single model year a qualitatively different 2 5x co2 solution is close to equilibrium and yields open water between 25 n and 25 s paleolatitude the prevailing wind patterns suggest that an equatorial pacific type circulation may have developed in part of the neoproterozoic ocean