fabric analysis application to paleolithic sites abstract this paper reviews data on the strike and dip fabric of clasts in slope deposits and stresses the usefulness of such investigations in regard to the study of prehistoric living floors particularly to test the occurrence of disturbance processes nine paleolithic sites have been studied for this purpose five of them located in rockshelters or cave entrances show a preferred orientation of the artefacts along the slope this pattern appears to be the result of periglacial mass movements so far such processes have been largely underestimated and may explain the absence of clear anthropogenic structures at these sites

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

the fezouata fossils of morocco an extraordinary record of marine life in the early ordovician the discovery of the fezouata biota in the latest tremadocian of southeastern morocco has significantly changed our understanding of the early phanerozoic radiation the shelly fossil record shows a well recognized pattern of macroevolutionary stasis between the cambrian explosion and the great ordovician biodiversification event but the rich soft bodied fezouata biota paints a different evolutionary picture the fezouata assemblage includes a considerable component of cambrian holdovers alongside a surprising number of crown group taxa previously unknown to have evolved by the early ordovician study of the fezouata biota is in its early stages and future discoveries will continue to enrich our view of the dynamics of the early phanerozoic radiation and of the nature of the fossil record supplementary material a complete faunal list is available at http www geolsoc org uk sup18843

the upper pleistocene loess record at harmignies belgium high resolution terrestrial archive of climate forcing abstract the loess palaeosol sequence in a section at harmignies in belgium is one of the most important upper pleistocene sites in northwest europe an extensive luminescence dating study was carried out to get a reliable chronological framework and to understand the climate forcing in an area where continuous permafrost dominated during most of the last glaciations twenty eight samples were investigated by infrared optically stimulated luminescence irsl and thermoluminescence tl methods resulting in more than 100 luminescence age estimates the dating results on colluvial sediments are in good agreement with landscape destabilisation phases during ois 5 during the last glacial four major periods of loess accumulation were likely to have occurred in europe at the harmignies section the oldest loess was deposited between 67 000 to 60 000 yr the second one from 60 000 to 50 000 yr the third one from 50 000 to 40 000 yr and the youngest loess accumulation period started most likely after the heinrich 3 event and lasted until the heinrich 2 event 25 000 20 000 yr two main periods of permafrost occurred at approximately 60 000 and 28 000 yr bp

evidence for ice clouds causing polar mesospheric summer echoes we compare 22 temperature height profiles derived from falling sphere experiments with simultaneous 50 mhz mesospheric radar echoes obtained during the middle atmosphere co operation summer in northern europe campaign in the summer of 1987 above andenes norway common features of these observations are as follows 1 more than 80 of the echoes occur at temperatures below 140 k and more than two thirds of the bottommost echo maxima appear at temperatures that deviate less than 5 from 140 k 2 we can find no significant correlation between the echo strength or the echo occurrence probability and the local temperature once it is below 140 k 3 the echoes are not symmetrically distributed around the mesospheric temperature minimum but there are clearly more echoes below than above the temperature minimum equivalently while the local temperature at the height of the bottommost echoes is about 140 k it is much lower at the height of the topmost echoes we compare the height range of the observed polar mesospheric summer echo returns with the height range that can be inferred for an ice cloud from the observed temperature profile by means of a simple stationary nucleation sedimentation model for reasonable values of the height integrated ice particle nucleation rate of about 3 107 m 2 s 1 and for a water molecule mixing ratio at the bottom of the ice cloud of 0 1 to 1 0 ppmv we find excellent agreement between the height range within which the ice particles may exist and the height range from which mesospheric echoes are seen for example in 17 out of the 22 individual observations reasonable values for the water vapor mixing ratio can be found such that the height of the strong bottommost echo corresponds to within the resolution of the radar to the bottom height of our model ice cloud if our height estimates are correct and the observations are representative our results yield a somewhat smaller water vapor mixing ratio in the summer mesosphere at high latitudes compared to what has been measured at midlatitudes

solifluction induced modifications of archaeological levels simulation based on experimental data from a modern periglacial slope and application to french palaeolithic sites the taphonomic study of petit bost croix de canard and cantalouette ii three palaeolithic sites that were recently discovered near perigueux and bergerac dordogne france in a colluvial context has enlightened the difficulty of adequately appreciating the relative role of cultural and natural processes in site spatial patterning periglacial solifluction was thought to have played a significant role in site formation because the nature of the modifications induced by solifluction was still poorly understood a simulation was made using data of soil movement recorded at la mortice french southern alps 3100 m in elevation in a modern periglacial environment the results show that for a knapping location the first steps of deformation are typified both by a downslope translation of the location center and by an anisotropic diffusion of the artifacts the knapping spot becomes elongated along the slope with a dense relic concentration of artifacts in the upslope portion this type of pattern has been obtained after 100 to 200 years of simulated displacement according to the climatic and soil conditions that characterise the la mortice site the ultimate stages of deformation show that the artifact distribution tends to homogenise on larger surfaces and resemble a random distribution the ability of the simulated patterns to closely fit those observed in archaeological contexts is evaluated at three sites from south western france at petit bost the hypothesis of limited solifluction explains accurately the association of both cultural artifact concentrations and natural artifact preferred orientation features at croix de canard long term solifluction can be proposed by contrast the simulated patterns do not describe the structures observed on the steeper slopes at cantalouette ii where the knapping spot transforms into distinct solifluction lobes

insect evidence for environmental and climate changes from younger dryas to sub boreal in a river floodplain at st momelin st omer basin northern france coleoptera and trichoptera the st omer area is a rapidly subsiding basin in which long sequences of weichselian and holocene sediments are preserved a core 21 m long extracted from near st momelin about ten km north of st omer has been analysed for insect fossils four faunal units smi 1 to smi 4 are described based on changes in both coleopteran and trichopteran assemblages the basal faunal unit smi 1 includes many cold adapted species and is attributed to the younger dryas chronozone the transition to holocene sedimentation was abrupt faunal units smi 2 to smi 4 are attributable to the holocene they lack all the cold adapted species found in the basal sediments and in their place are insect assemblages very similar to the present day fauna in this region this sequence spans the period from the pre boreal to the sub boreal faunal unit smi 2 includes insects from the pre boreal the boreal and most of the atlantic periods this fauna was fairly sparse and made up largely of species living in freshwater habitats the faunal unit smi 3 includes the insect assemblages from the late atlantic to sub boreal periods this fauna was much more diverse and indicated a river meandering across its floodplain and bordered by a mature forest at a time when the climate was warmer than that of the present day this chronostratigraphical sequence of events is supported by 14c dates and by lithological data thermal climatic conditions have been quantified using the mutual climatic range method during the younger dryas period smi 1 tmax the mean july temperature was in the region of 10 c and tmin the mean temperature of january february was close to 11 12 c after the sudden climatic amelioration at the start of the holocene smi 2 to smi 4 tmax probably fluctuated throughout the early holocene between 16 c to 19 c and tmin between 0 c to 5 c figures that are close to those of the present day this climatic history is compared with others in northern europe

surface temperature in nw europe during the younger dryas agcm simulation compared with temperature reconstructions during the younger dryas yd the climate in nw europe returned to near glacial conditions to improve our understanding of climate variability during this cold interval we compare an agcm simulation of this climate performed with the echam model with temperature reconstructions for nw europe based on geological and paleoecological records maps for the mean winter summer and annual temperature are presented the simulated winters are consistent with reconstructions in the northern part of the study area a strong deviation is noted in ireland and england where the simulation is too warm by at least 10 c it appears that the n atlantic was cooler than prescribed in the yd simulation including a southward expansion of the sea ice margin the comparison for the summer shows a too warm continental europe in the simulation supposedly these anomalously warm conditions are caused by the agcm s response to the prescribed increased summer insolation the region of maximum summer cooling is similar in both the simulation and reconstruction i e s sweden we suggest that this is due to the local cooling effect of the scandinavian ice sheet compared to the present climate a considerable increase of the annual temperature range is inferred especially for regions close to the atlantic ocean

the impact of periglacial processes on palaeolithic sites the case of sorted patterned grounds during the last glaciation western europe witnessed recurrent millennial scale episodes of periglacial climates that had significant impact on palaeolithic site preservation after a review on the genesis and climatic meaning of sorted patterned grounds examples of polygons stripes and stone banked solifluction lobes taken from archaeological contexts are described sorted features in palaeolithic sites imply that caution should be taken in site patterning analysis for reconstructing past human behaviours since spatial alteration of the original anthropogenic pattern took place on low gradients artefact movements remain limited but may increase dramatically on slopes when solifluction adds to sorting processes although these features are widespread in modern periglacial environments archaeological examples remain scarce multiple factors are probably involved including lack of knowledge of periglacial processes and landforms by archaeologists leading to misinterpretation but also more or less complete obliteration of surface features by sedimentary processes upon burial however it is assumed that scarcity of clear anthropogenic patterning in french palaeolithic sites before the late glacial is due for a large part to post depositional disturbance by periglacial processes

neandertal extinction and the millennial scale climatic variability of ois 3 population models seeking climate as a triggering factor for the extinction of neandertals and the colonisation of europe by anatomically modern humans are contradictory due to uncertainties in the dating methods in the cultural attribution of archaeological layers and to the lack of terrestrial continuous and well dated palaeoclimatic sequences this is particularly the case for the iberian peninsula where neandertal populations seem to have survived later than in other regions of europe a review of the available palaeoclimatic evidence for ois3 of iberia reveals that this mainly consists of low resolution fragmentary ill dated and often ill interpreted records correlation between palaeoenvironmental sequences from two images pollen rich deep sea cores and archaeological data from western europe the electronic archive of the radiocarbon dates is available at qsr website http www elsevier nl locate quascirev indicates that aurignacian moderns colonised france and the north of iberia at the onset of the h4 event during this cold episode a probable contraction of neandertal populations is recorded in southern iberia where no aurignacian settlements are detected such a decline in population density is correlated with the particular desert steppe like environments made up of artemisia chenopodiaceae and ephedra characterising the h4 of this area while reducing the size of neandertal populations this inhospitable environment may have favoured their persistence in this region mainly exploiting herds of herbivores adapted to graminees rich grasslands the aurignacian moderns were probably not interested in colonising these arid mediterranean biotopes and did that only after the h4 event

dynamics of periglacial sorted circles in western spitsbergen a working hypothesis for the development and maintenance of sorted circles which are finegrained soil domains delineated by borders of coarser material involves clast motion relative to soil and intermittent circulatory motion of soil in the active layer the hypothesis is compatible with the observed size regularity sorting microtopography surface soil motion vegetation cover and subsurface organic carbon content of soil patterns studied in spitsbergen theoretical considerations of buoyancy driven convection suggest that intermittent convection of thawed soils is plausible and that the requisite bulk density decrease with depth arises naturally from moisture gradients that develop during the thaw consolidation of ice rich soils these considerations also help in understanding the dependence of sorted circles on soil characteristics and on moisture moreover they point to the possible use of sorted patterns as paleoclimatic indicators based on the expected relation between pattern size and active layer depth

development of miniature sorted patterned ground following soil erosion in east falkland south atlantic miniature sorted patterned ground features nets and stripes occur at an elevation of ca 35 m in the l antioja valley east falkland the features have developed following recent soil erosion and display many of the characteristics associated with the operation of frost related processes in regolith materials the patterns are currently active and indicate that in cool oceanic climates the distribution of frost sorted patterns is controlled by the presence of bare ground on suitable regolith rather than by altitude

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

fabric of palaeolithic levels methods and implications for site formation processes fabric analysis in archaeological contexts i e the study of the orientation and dip of artefacts has been significantly improved during the last decade mainly with respect to the statistical treatment of data the development of a reference base for natural sedimentary processes as well as the increased number of data for palaeolithic levels these works show that fabrics are an efficient tool for assessing site formation processes fabrics allow discrimination between i undisturbed or minimally disturbed levels ii levels that have undergone strong pedoturbations due to biological activity or to shrinking and swelling of clayey sediments and iii levels that have been significantly reworked by slope processes such as periglacial solifluction or overland flow however in the present state of knowledge fabrics do not allow precise estimation of the degree of perturbation if not associated with other archaeological and geological criteria from the set of data on french palaeolithic sites used here it is demonstrated that slope dynamics and particularly solifluction for sites predating the late glacial may have played an important role in site formation

a model for sorted patterned ground regularity sorted patterned ground refers to polygons nets or stripes defined by rocky borders which are the result of sorting in soil subjected to frost action this paper presents a model in which convection cells driven by unstable density stratification in the aqueous phase result in uneven melting of the underlying ice front during thawing the resulting undulatory ice front with regularly spaced peaks and troughs provides the pattern which results in the regularity observed for certain types of patterned ground in addition the model predicts the width to depth of sorting ratio for both polygons and stripes and explains the characteristic hexagonal shape of sorted polygons the transition from sorted polygons to sorted stripes on sloped terrain and the formation of sorted polygons under water the predicted ratio of width to depth of sorting of 3 81 for sorted polygons is compared with the ratio of width to depth of sorting of 3 57 found from a linear regression analysis of 18 field study data

high resolution record of the last interglacial glacial cycle in the nussloch loess palaeosol sequences upper rhine area germany the nussloch loess sequences were sampled at close intervals 10 cm and documented in respect of their stratigraphy palaeopedology sedimentology palynology malacology and geochemistry and were dated using radiocarbon and osl methods for each stratigraphic unit the results of both the eld studies and the analytical and geochronological data obtained cast light upon the response of the loessic environment to global climatic variations during the last cycle the basal soil complex underwent a pedosedimentary evolution similar to those of the bordering area complex luvisol greyzem steppe soila which re ects the classic progression towards increased continentality of the environment between the end of the eemian 5d and the beginning of the full glacial stage pleniglacial the lower pleniglacial corresponds to an initially very arid phase dominated by the accumulation of loess followed by the deposition of strati ed niveo eolian sands the middle pleniglacial complex ca 55 30 is clearly characterised by the inhibited loessic sedimentation it is primarily marked by two phases of stabilisation recorded in the form of weathered horizons cambisols which are separated by a rather thin layer corresponding to loessic sedimentation with tundra gleys this intermediate phase brings together organic silt deposits which record an interstadial dated at 32 33 ka c bp the thick loessic accumulations of the upper pleniglacial 10 m which clearly began to accumulate before the oxygen isotope stage ois 3 2 boundary show evidence of vulnerability to considerable uctuations in response to variations in wind dynamics and the intensity of de ation in the rhine valley finally a proposed correlation of loess palaeosol stratigraphies from germany belgium and france spanning the entire last interglacial glacial cycle is presented 2001 elsevier science ltd and inqua all rights reserved

coversand and pleistocene palaeosols in the landes region southwestern france new sections in the coversand of the landes region southwestern france show at least two main depositional phases corresponding to the upper pleniglacial and the lateglacial which are separated by palaeosols the lower palaeosol a gleyic to histic cryosol overlying a net of sand wedges and dated to ca 23 14c ka bp testifies to a short occurrence of permafrost impeded drainage due to the frozen subsoil is assumed to be the main factor involved in lowered aeolian transport and soil formation pollen analysis indicates a shrub tundra type environment the overlying coversand unit is associated with small transverse ridges or sheet like deposits and corresponds to the maximal extension of the sands upper pleniglacial in age an incipient podzol developed on the dunes under a boreal pine forest and has been dated to 11 5 12 14c ka bp i e to the allerod period this has been buried by the second coversand unit during the younger dryas typified by abundant denivation features and root imprints although preliminary the chronology of sand deposition in the landes region appears thus to be roughly similar to that found for the other european coversands showing that all were the result of similar western european climatic changes i e repeated episodes of increasing aridity related to the upper pleniglacial and the younger dryas episode copyright 2008 john wiley sons ltd

differential frost heave and sorted patterned ground field measurements and a laboratory experiment abstract small scale sorted stripes and circles dominate over the alpine regions in the upper engadin swiss alps most of these features are spaced at less than 30 cm intervals by coarse margins shallower than 5 cm monitoring of sorted stripes indicates that shallow diurnal freezing often induces differences in amount and timing of frost heave by needle ice growth between fine and coarse stripes while deeper diurnal freezing and seasonal freezing rarely differentiate heave amounts of the two materials a laboratory simulation is designed to explore the contribution of differential frost heave to the sorting process at the monitoring site the device consists of a fine part loam and a coarse part a granule layer mounted on loam freeze thaw tests with a granule mantle of 0 5 2 5 and 5 cm thick demonstrate that the heave amount on the coarse part is greatly reduced by the 5 cm thick mantle and that the coarse part always heaves later but subsides earlier than the fine as a result of this time lag in frost heaving lateral soil movement towards the coarse part is generated within the surficial soil differential heave associated with diurnal freeze thaw cycles is capable of sorting of the top 5 cm of soil

self organization of sorted patterned ground striking circular labyrinthine polygonal and striped patterns of stones and soil self organize in many polar and high alpine environments these forms emerge because freeze thaw cycles drive an interplay between two feedback mechanisms first formation of ice lenses in freezing soil sorts stones and soil by displacing soil toward soil rich domains and stones toward stone rich domains second stones are transported along the axis of elongate stone domains which are squeezed and confined as freezing soil domains expand in a numerical model implementing these feedbacks circles labyrinths and islands form when sorting dominates polygonal networks form when stone domain squeezing and confinement dominate and stripes form as hillslope gradient is increased

european climatic response to millennial scale changes in the atmosphere ocean system during the last glacial period abstract pollen foraminifer dinocyst and coarse lithic high resolution analyses and 18 o measurements have been carried out for the last glacial section of marine core md95 2042 located near the southwestern margin of the iberian peninsula the pollen data indicate a high frequency of vegetational changes on the adjacent continent during this period suggesting a climatic variability very similar to that of the dansgaard oeschger cycles recorded by the greenland ice cores the detailed direct correlation of the terrestrial and marine proxy data from core md95 2042 indicates a three phase pattern of heinrich events in land and ocean environments the first and last phases of the h5 and h4 events are characterized by a mild and humid climate in southwestern europe probably associated with the european origin of the ice rafted detritus the middle phase exhibits a cold and dry climate in iberia linked with the maximum input of ice rafted detritus this phase seems to correspond with the laurentide ice sheet surges between the heinrich events several cold and dry periods on land are correlated with stades of the dansgaard oeschger cycles the impact of the dansgaard oeschger stades in southwestern europe seems to be preferentially connected to the cold winter air masses reaching this mid latitude region

physical modelling of gelifluction and frost creep some results of a large scale laboratory experiment an experimental slope was constructed in a 5 m 5 m square refrigerated tank the slope was formed of four sections each consisting of regolith soil collected from a distinct bedrock lithology the four lithologies utilized were granite limestone mudstone and slate the slope was subjected to freezing and thawing from the surface downwards water was supplied at the base of the soil during freezing frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle the experimental soils were non cohesive those derived from granite and limestone were respectively sandy and gravelly in texture while those derived from mudstone and slate were silt rich mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice in the mudstone and slate soils gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice mean per cycle rates of downslope soil transport for the granite limestone mudstone and slate soils were 5 8 cm3 cm 1 6 9 cm3 cm 1 21 2 cm3 cm 1 and 31 2 cm3 cm 1 respectively units referring to the volume of soil passing a unit width of slope per cycle mass movement rates were shown to be strongly related to the silt content of the soils