lake level and climate changes between 42 000 and 18 000 c 14 yr bp in the tengger desert northwestern china multiple lines of stratigraphic geochemical and fossil data suggest that fresh mesohaline paleolakes were widespread in the tengger desert of northwestern china and underwent major fluctuations during the late pleistocene the paleolakes started to develop at ca 42 000 c 14 yr b p the lake levels were the highest between 35 000 and 22 000 c 14 yr b p during which megalake tengger dominated the landscape the climatic conditions at this time were unique for this area and have no modem analogue after an episode of decline between 22 000 and 20 000 c 14 yr b p and an episode of rebound between 20 000 and 18 600 c 14 yr b p the paleolakes started to desiccate and completely disappeared around 18 000 c 14 yr b p the environmental proxy data indicate that the megalake tengger formed under warm humid climates the reconstructed climatic variations appear to be correlative with the abrupt climatic events reconstructed for the north atlantic c 2002 university of washington

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

fault reactivation and superimposed folding in a proterozoic sandstone volcanic sequence davenport province central australia abstract the davenport province is a fluvial to shallow marine sequence of weakly metamorphosed sandstone rhyolite and basalt deposited in an ensialic basin that was probably initiated by continental extension isopach ridges and cut offs suggest that synsedimentary normal and transfer faults controlled deposition these faults were reactivated as reverse faults and strike slip faults during deformation upright concentric folding took place in two episodes initially about nw trending axes and subsequently about generally ne trending axes balanced cross sections suggest that the folds die out downwards above the base of the sequence however units from well below the concentrically folded part of the sequence crop out in anticlinal cores indicating that there is no through going detachment horizon in the sequence this is consistent with the rarity of clayey silty and evaporitic sediments suitable for detachment hence the faults probably cut the entire sequence and enter the basement interference of the folds formed dome and saddle and crescentic patterns thrust sheets imbricate stacks and duplexes are not recognized in the province and layer parallel shortening is moderate about 28 these suggest a correspondingly low degree of earlier regional extension about 40 the folding may have been due to a sudden change in lithospheric plate velocity

the thermomechanical response of the greenland ice sheet to various climate scenarios using a three dimensional numerical model for land based ice sheets in the shallow ice approximation simulations are performed to determine the velocity and temperature distributions within the greenland ice sheet through time for various climate scenarios the ice is treated as a rheologically nonlinear heat conducting viscous fluid and the substrate is a heat conducting rigid solid this system is fed from above by prescribing as the climatic inputs the atmospheric temperature and the accumulation ablation rate functions at the free surface and from below by the geothermal heat we present the governing equations in the shallow ice approximation discuss the parameterizations used in the descriptions of the ice surface temperature and accumulation ablation functions briefly state how the complicated initial boundary value problem is numerically solved and how the input data that are available from measurements are implemented results of preliminary calculations disclose how the model performs and delimit its validity we study the role played by basal sliding and make clear that sliding should be accounted for where ever the basal ice is temperate and that the frictional heat generated in this sliding is thermomechanically significant we also study the reaction of the greenland ice sheet to various climate scenarios and make clear that today s thermal regime depends significantly upon the prior climate history moreover the thermomechanical properties of the ice are equally significant as is the thermal interaction of the ice sheet with the rockbed beneath

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

the structural development of the wessex basin the mesozoic and cenozoic structures of southern england form part of a system of disturbances which extends across the channel into northern france they are reviewed in the light of published data from south dorset basin development started with permo triassic rifting and is believed to have continued through the jurassic and early cretaceous with intermittent growth on deep seated listric normal faults probably associated with roll over anticlines this regime had ceased by the aptian and the basin passed through a period of relative stability in the late cretaceous followed by tectonic inversion and in the miocene by northwards compressive movement along the former normal faults this partially restored the earlier separative displacement at depth and probably accentuated pre existing roll over anticlines it was expressed in the surficial upper cretaceous palaeogene sequence as monoclinal flexuring the early rifting and the change from overall n s crustal stretching to compression may reflect plate tectonic events in the north atlantic region

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

use of vertical profiles of δ18o to constrain estimates of hydraulic conductivity in a thick unfractured aquitard vertical distributions of 18o were used to constrain hydraulic conductivity k in a thick unfractured aquitard previous investigations utilizing permeability tests at a variety of scales keller et al 1989 indicated that bulk k at the site ranges from 3 5 0 11 m s to 1 2 10 10 m s advective displacements calculated on the basis of these k values lead to a wide range of predicted distributions of natural tracers after 11 000 years comparison of 18o distributions and simulated advection diffusion profiles provide a more precise constraint on advective displacement and hence on k the simulations cast in terms of a peclet number p v2t d ranging in value from 0 to 12 indicate that transport is diffusion controlled and that k is actually less than 1 2 10 11 m s p greater than 0 1 k 1 2 10 11 m s overestimates transport this result indicates that conventional permeability tests in very tight media tend to overestimate k in practical terms advective transport at the site is negligible and transport can be simulated with diffusion only p o

two step deglaciation at the oxygen isotope stage 6 5e transition the zeifen kattegat climate oscillation comparison of marine lacustrine and terrestrial records from twenty four sites suggests the existence of a younger dryas type climate oscillation just prior to the oxygen isotope stage 6 5e boundary these records include results from biostratigraphic pedostratigraphic and speleothem studies as well as analyses of stable isotope compositions of marine records and ice cores the climate oscillation is named after the warm zeifen interstadial and the cold kattegat stadial the zeifen interstadial may be related to a major meltwater pulse in the baffin bay labrador sea norwegian sea region the climate oscillation is presumably in part a result of a variation in ocean circulation especially in the strength of the north atlantic drift but changes in the atmospheric circulation also played an important role the geographically widespread distribution of the oscillation suggests that the two step deglaciation influenced both the northern and southern hemispheres c 1996 elsevier science ltd

was there an abrupt cold climatic event in the middle eemian pollen record from a palaeolake at the hieronimowo site ne poland abstract seventy samples of lacustrine sediments from a palaeolake at the hieronimowo site ne poland were investigated by pollen analysis method the obtained results indicate that the examined sequence spans the whole eemian interglacial mis 5e the beginning of the early vistulian weichselian mis 5d and some undefined period of the plenivistulian middle weichselian mis 2 4 the specific feature of the studied profile is the great thickness of deposits representing the hornbeam phase of the eemian interglacial e5 r paz which was the younger part of the climatic optimum of this interglacial and the very well developed pollen record of this phase that is absent in other profiles in ne poland due to this our study allowed for the first time in ne poland the detailed reconstruction of changes in the vegetation and in the mean january and july temperature during the middle part of the eemian interglacial this reconstruction unequivocally rules out the existence of an abrupt short lasting cold event at that time only a gradual slight increase in temperature was apparent during the older part of the hornbeam phase to 21 c for july and to 0 c for january and gradual decrease during its younger part to 17 c for july and to 5 c and

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

holocene crustal movements and sea level changes in great britain crustal downwarping has occurred throughout southern and south eastern england and most of wales for at least the last 4000 years but the type of movement in some areas of southern and eastern england is more complicated than simple linear subsidence highest estimated rates of subsidence since 4000 bp are for the thames estuary and norfolk up to 2 mm yr glacio isostatic processes have resulted in uplift in northern england and mainland scotland the rates of uplift have decreased throughout the holocene estimates for the present range from zero in south lancashire and the tees estuary to over 1 mm yr though less than 2 mm yr in central scotland over 400 sea level index points from the databank of 904 cases collected for igcp project 200 are grouped into 15 main areas and used to investigate the nature of crustal movements in great britain since 8800 bp but there are significant deficiencies in available data which constrain the analysis

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

the proterozoic davenport province central australia regional geology and geochronology abstract the davenport province forms the southern part of the tennant creek inlier and lies to the north of the arunta inlier the oldest rocks exposed are turbidites and minor 1880 1870 ma old felsic volcanics of the warramunga group these were folded probably during the barramundi orogeny and intruded by granite before being overlain by the hatches creek group a sequence up to 10 000 m or more thick of fluvial to shallow marine sedimentary and bimodal volcanic rocks a rift sag model of basin development involving crustal extension in an intracratonic setting is suggested for this group interpretation of u pb zircon data for felsic volcanics in the lower part of the hatches creek group is hampered by problems of ancient pb inheritance but a preferred crystallization age of 1820 1810 ma is indicated two episodes of upright concentric folding about nw se and ne sw trending axes preceded emplacement of granite at 1660 ma or earlier rb sr whole rock data for felsic volcanics from the hatches creek group are tentatively interpreted to indicate a region wide hydrothermal alteration event at 1645 44 ma this alteration may have been associated locally with w cu bi and mo mineralization

a new greenland deep ice core the polar ice sheets are rich sources of information on past atmospheric conditions including paleoclimates a new deep ice core has been drilled in south greenland comparison of the oxygen isotopic profile with that from camp century and with a deep sea foraminifera record indicates that the new core reaches back to about 90 000 years before present in a continuous sequence the details in the wisconsin part of the ice core records seem to be climatically significant and the general trends reveal all of the relevant emiliani stages recorded in deep sea cores the redated camp century record suggests a dramatic termination of the eem sangamon interglacial

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

growth of an intermittent ice sheet in iceland during the late pliocene and early pleistocene abstract deep sea paleoclimatic records show that the quaternary climate around iceland was and probably still is very sensitive to rapid shifts in north atlantic oceanic circulation studies of several key sections in iceland indicate that similar oscillations are reflected in the late pliocene and early pleistocene terrestrial stratigraphy correlations between six rock sequences in western northern eastern and southern iceland show a fairly distinct trend during the pliocene pleistocene transition indicating the progressive growth of an ice sheet from southeast toward the north and west the correlations are based on k ar dates and paleomagnetic studies a total of 11 glacial horizons are recorded in a stratigraphic column from eastern iceland extending back 6 5 myr in western iceland 7 glacial horizons are preserved in a rock section dated from 7 0 to 1 8 myr and in northern iceland 14 glacial horizons are identified in a section that extends back to 9 0 myr well over 20 glacial horizons have been identified in the stratigraphic column in iceland full scale glacial interglacial cyclicity with regional ice cover is indicated at approximately 2 6 myr a further amplification leading to islandwide glaciations is identified at 2 2 2 1 myr these results show that changes in the ice cover in iceland correlate with the deep sea oxygen isotope records from benthic and planktonic foraminifera as well as ird studies from the north atlantic

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

the size distribution of microparticles from selected segments of the greenland ice core project ice core representing different climatic periods the size distribution of insoluble microparticles dust in the particle size interval 0 4 6 0 m radius has been measured in more than 1400 samples from the greenland ice core project grip deep ice core from summit greenland the samples were taken from ice core segments representing 32 climatic periods including ice from the eem interglacial and ice from below the eemian ice the mean dust volume distributions from the climatic periods are compared and the relationship of total dust mass to the concentration of ca2 and to the stable isotopic composition 18o is investigated the dust volume distributions are found to be lognormal in the size interval 0 4 2 0 m with nearly identical shapes changes of the lognormal part of the volume distributions are found to be connected to the total dust mass in a systematic way the total dust mass is correlated to the ca2 concentration and data do not show any enrichment in ca2 from exposed continental shelves due to lower sea levels during the last glacial maximum the total dust mass is strongly connected to 18o the volume distribution of the particles in the size interval 2 0 6 0 m is found to be almost the same in most periods the exceptions are the cold periods in the last part of the last glacial period where the volume of these particles is higher than in most periods and the periods from the eemian and just above the eemian where the volume of these particles is lower the volume distributions of both the eemian warm periods and the cold eemian events are different from the distributions in ice from both below and above the eemian ice climate changes appear to have modified the processes of production transport modification and deposition of the dust aerosol in the same way over the last 120 000 years or more

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

multifractal detrended fluctuation analysis of the δ 18 o record of ngrip ice core the multifractal properties and scaling behaviors of the long term and recent 2000 year 18o records of ngrip ice core are investigated by the multifractal detrended fluctuation analysis method the generalized hurst exponents multifractal scaling exponents and singularity spectrums of two 18o records are derived to verify the multifractiality of two records and the multifractal behaviors of two records are obviously different which may reflect the climate change of the recent 2000 year time is quite different from one of the long term time in addition the probability distribution analysis of two 18o records is presented to manifest the different multifractality between two 18o records of ngrip ice core our results will be helpful to research the climate change

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

long term palaeoenvironmental changes recorded in palynologically studied loess palaeosol and esr dated marine deposits of northern eurasia implications for sea land correlation abstract original materials of pollen analysis and esr chronostratigraphic studies provided a basis for reconstruction chronological subdivision and inter regional correlation of palaeoclimatic events and sediments of palaeo shelf glacial periglacial and extra glacial regions of northern eurasia within the scope of the brunhes epoch chronostratigraphic position of the identified palaeoenvironmental events and corresponding horizons in the composite chronostratigraphic column is established on the base of esr analyses of subfossil mollusc shells collected from marine freshwater and terrestrial deposits the palyno chronostratigraphic record displays a sequence of 8 intervals the holocene included of warm climate and high sea level stands when marine sedimentation occurred on palaeo shelves and 7 glacial epochs the alternating intervals are either fully recorded as complete glacial interglacial rhythms or represented by a large enough number of consecutive climatic phytocoenotic phases the rhythmic regularity in the sequence of glacial and interglacial events has been inferred from detailed palynological data on reference sections of loess palaeosol series in the centre of the east european plain arapovichi otkaznoe likhvin strelitsa sections a clear agreement between long pollen record directly dated warm climate related deposits and other records of palaeoenvironmental evolution known from literature has been established for the upper 15 oxygen isotope stages ois 15 to 1 finally we come to a conclusion that the integrated climate chronological sequence may be taken as a basis for inter regional correlations of palaeo shelf and terrestrial sediments within northern eurasia it may be used as an intermediate link in the continent ocean correlations

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

timing of palaeoproterozoic au cu bi and w mineralization in the tennant creek region northern australia improved constraints via intercalibration of 40ar 39ar and u pb ages abstract the magnitude of systematic uncertainties inherent in comparisons of proterozoic 40ar 39ar and u pb based ages is illustrated via a consideration of age constraints on two contrasting styles of palaeoproterozoic mineralization in northern australia published 40ar 39ar ages for au cu bi mineralization in the tennant creek region range from 1825 to 1829 ma apparently younger than the timing of deformation bracketed by 207pb 206pb zircon ages of igneous rocks at 1850 ma despite this apparent age offset propagation of systematic uncertainties in the 40ar 39ar ages shows that they are indistinguishable from the 1850 ma zircon ages recalculation using revised estimates of the 40k decay constant and age of the 40ar 39ar standard shifts the 40ar 39ar ages to 1847 1851 ma in excellent agreement with 207pb 206pb zircon ages from tennant supersuite igneous rocks and with local geological constraints to the south of tennant creek in the davenport ranges numerous small w prospects have been interpreted to be coeval with post tectonic granites of the devils suite at 1710 1720 ma new 40ar 39ar ages from muscovite selvages on wolframite bearing veins range from 1697 to 1703 ma these ages shift to 1711 to 1717 ma when recalculated using revised estimates for 40k decay constant and age of standard material bringing them into agreement with existing 207pb 206pb zircon ages for devils suite granitoids and consistent with field and geochemical interpretations these examples highlight the importance of considering systematic sources of uncertainty when comparing radiometric ages determined via different isotopic methods particularly in the proterozoic and archean parts of the timescale ongoing work to calibrate the 40ar 39ar and u pb based timescales will further enhance the application of multiple isotopic methods to constrain geological processes

multiple oscillations during the lateglacial as recorded in a multi proxy high resolution record of the moervaart palaeolake nw belgium this paper presents the results of multi disciplinary research carried out on the deposits of moervaart depression nw belgium one of the largest palaeolakes 25 km2 that existed during the lateglacial interstadial in nw europe the multi proxy study including physical organic matter and calcium carbonate magnetic susceptibility micromorphological botanical pollen macrofossils diatoms zoological ostracods molluscs chironomids and chemical analyses stable carbon and oxygen isotopes has resulted in a detailed reconstruction of the lateglacial landscape as well of the local conditions that prevailed in the lake itself a chronology of the record was provided by radiocarbon dating and comparison with radiocarbon dates of the nearby rieme site these yielded a good match with the regional biostratigraphy during the lateglacial vegetation and geomorphology of the landscape in general changed from a tundra landscape to a boreal forest the vegetation development however was interrupted by a number of cold reversals three centennial scale cold oscillations are present in the record 1 the so called older dryas corresponding to gi 1d in the greenland ice cores 2 a short and pronounced cold event during the early allerod which could be correlated to gi 1c2 and 3 a cooling event during the late allerod probably corresponding to the intra allerod cold period iacp or gi 1b the latter most likely was responsible for the disappearance of the moervaart palaeolake

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

glacier dynamics and paleoclimatic change during the last glaciation of eastern ellesmere island canada a 300 km transect along the east coast of ellesmere island fills a major gap in the late quaternary data base of the canadian high arctic the last glacial maximum lgm is marked by prominent moraines and meltwater channels that terminate within 30 km of modern ice margins shells in glaciomarine deposits collected beyond the lgm indicate deglaciation by more extensive ice prior to 35 ka bp more than 60 14c dates from glaciomarine sediments provide a chronology for past ice dynamics during the lgm to the north while many areas remained ice free due to severe aridity several glaciers remained in contact with the sea until 7 1 ka bp farther south most glaciers reached the coast and significantly infilled several fiords this southward increase in glacier extent is due to larger glacial catchment basins and increased precipitation towards storm tracks in northern baffin bay the earliest dates on deglaciation along the transect range from 8 1 to 7 7 ka bp initial retreat was controlled by the exten

magnetostratigraphic dating of river terraces rapid and intermittent incision by the yellow river of the northeastern margin of the tibetan plateau during the quaternary up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of huang he the yellow river and daxia he in the linxia basin at the northeastern margin of the tibetan plateau the magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire quaternary it includes evidence for the jaramillo and olduvai normal polarity subchrons within the matuyama chron as well as the cobb mountain and stage 54 formerly gilsa events age constraints within the brunhes are provided by 14c and thermoluminescence optical stimulated luminescence dating the magnetostratigraphic chronology of the quaternary sediments indicates that terraces were formed at about 1 66 1 4 1 1 0 6 0 12 0 055 and 0 01 ma the terraces may represent climatically induced pauses in long term tectonically induced incision by the rivers on the basis of terrace heights and ages incision rates were highest from 1 66 to 1 4 ma 1 m kyr decreased from 1 4 to 0 12 ma 0 1 m kyr and increased from 0 12 ma to present 0 75 m kyr if river incision is attributed solely to uplift of the tibetan plateau then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of huang he in this area at about 1 75 ma however the effects of uplift cannot be fully separated from incision caused by changes in climate copyright 1997 by the american geophysical union

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

holocene records of effective precipitation in west greenland holocene changes in effective precipitation precipitation evaporation p e were reconstructed for the sondre stromfjord region of southwest greenland using the sediment records of two neighbourin

pleistocene climatic stratigraphy and environments of the terek kuma lowland nw caspian sea region inferred from palynological paleomagnetic and rodent records of the long otkaznoye sediment sequence abstract the paper presents the results of a high resolution palynological paleomagnetic and microtheriological study of the pleistocene sediment sequence at otkaznoye in the eastern ciscaucasian foreland a sequence which is unique in its stratigraphic completeness and thickness 160 m the sequence includes loess paleosol alluvial and alluvial proluvial beds the detailed climatostratigraphic subdivision of the otkaznoye sequence allows a correlation of the established paleoclimatic record with the global marine isotope stages the past climatically induced variability in the landscape of the terek kuma lowland is reconstructed for all neopleistocene i e middle and late pleistocene interglacial and glacial periods and for some intervals during the later early pleistocene stages

rapid coastal change during the mid to late holocene the record of barrier estuary sedimentation in the romney marsh region southeast england a common problem facing sea level researchers lies in determining the cause of rapid changes observed in coastal stratigraphic sequences such changes are commonly ascribed to the interaction of processes that operate over differing temporal and spatial scales i e rapid local and regional sea level trends and storm magnitude frequency at least some of the difficulty in distinguishing between these processes lies in the often limited stratigraphic database upon which palaeoenvironmental reconstruction is based here we present the results of detailed morphostratigraphic and micropalaeontological investigations from a series of sites located at the interface between the protective gravel barrier complex of dungeness and the barrier estuary sediments of romney marsh england a period of rapid coastal regression is identified between c 4500 and 3000 cal yrs bp during which time the sea level continued to rise but was outpaced by sediment accretion and peat accumulation a subsequent acceleration in th

oxygen isotope record of sea level and climate variations in the sulu sea over the past 150 000 years the sulu sea is located in the warm pool of the western pacific ocean where mean annual temperatures are the highest of anywhere on earth because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change changes in the oxygen isotope composition of planktonic foraminifera from sulu sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial interglacial and millenial timeseales and such records have been obtained for the late pleistocene epoch and the last deglaciation1 3 here i present results that extend the millenial time resolution record back to 150 000 years before present on timescales of around 10 000 years the sulu sea oxygen isotope record matches changes in sea level deduced from coral terraces on the huon peninsula4 this is particularly the case during isotope stage 3 an interglacial period 23 000 to 58 000 years ago where the sulu sea oxygen isotope record deviates from the specmap deep ocean oxygen isotope record5 thus these results support the idea4 6 that there were higher sea levels and less continental ice during stage 3 than the specmap record implies and that sea level during this interglacial was just 40 50 metres below present levels the subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought

the late pleistocene palaeoenvironmental evolution in northern eurasia through the prism of the mollusc shell based esr dating evidence abstract long term investigations devoted mostly to the eurasian arctic sedimentary deposits have provided dated climatic sequence within the late pleistocene period most of the dates ca 315 were obtained by electron spin resonance esr method on marine mollusc remains taken directly from transgressive marine sedimentary deposits here it is shown that the climatic signature revealed in the studied sedimentary sequences can be compared by proxy and chronologic correlation with the climatic signals recorded in different parts of the continent from deposits of marine freshwater and terrestrial origin the resulting climate chronostratigraphic record allow the last interglacial to be placed approximately between 145 140 ka and 70 ka with concentration of overwhelming majority of the warm climate related dates ca 82 in the second half of marine isotope stage mis 5 in the time range between 110 and 70 ka this evidence coincides with integrative multidisciplinary results derived from the south eastern coast of the gulf of finland they show unambiguously that the second half of the mis 5 sequence at least between ca 94 ka and 71 ka reflects the fully interglacial character of the studied deposits the climate chronostratigraphic record within mis 3 displays a sequence of three successive palaeoenvironmental events 59 0 52 0 ka 47 5 40 0 ka and 32 4 24 8 ka which are interpreted as the consequence of large scale climate amelioration during which marine sedimentation occurred on palaeo shelves what is now dry land the consistency of the parallel comparative dating results obtained in this study by different methods both the numerical and relative exemplify the potential of palaeodosimetric dating methods mainly used in this study mollusc shell based electron spin resonance esr and feldspar based infrared optically stimulated luminescence ir osl to chronologically organize the sequence of the late pleistocene palaeoenvironmental events and to improve understanding of the palaeoenvironmental evolution during this period

non linear response of the golo river system corsica france to late quaternary climatic and sea level variations disentangling the impact of climatic and sea level variations on fluvio deltaic stratigraphy is still an outstanding question in sedimentary geology and geomorphology we used the golo river system corsica france as a natural laboratory to investigate the impact of late quaternary climate and sea level oscillations on sediment flux from a catchment and on fluvio deltaic stratigraphy we applied a numerical model pacmod which calculates catchment sediment production and transport and compared modeling output to the sedimentary record of the golo alluvial coastal plain whose chronology was reinterpreted using new optical stimulated luminescence osl ages on feldspars our modeling osl ages and geomorphological results indicate that the two main phases of braidplain development in the golo alluvial coastal plain occurred during the cold dry phases of mis5 and during the late mis4 early mis3 as a consequence of high catchment erosion rates and low water discharge incision and sediment reworking occurred during sea level low stand periods mis4 and late mis3 mis2 high sediment flux pulses from the catchment outlet were generated during the lateglacial and early holocene as a result of the release of sediments previously stored within the catchment and enhanced snowmelt our results suggest a non linear response of the golo river system to climatic and eustatic changes caused by sediment storage within the catchment and geomorphological thresholds this indicates that a direct comparison between palaeo climate and stratigraphy is not possible without considering catchment sediment storage and sediment transport delays out of the catchment

uranium series dating of fen peat horizons from pit nachtigall in northern germany abstract peat and other terrestrial sediments are important archives of climate forcing this study discusses the numerical age determination of stratigraphically important quaternary sequences from clay pit nachtigall near holzminden in northern germany which have been the subject of debate concerning their chronological classification since they were first described by grupe in 1929 uranium series dating 230 th u of different organic horizons as well as sedimentology including loss on ignition loi and palynology was carried out to set up a more reliable chronological framework for the weser river area 230 th u ages were calculated using an isochron approach with the leachate leachate method for chemical preparation open system requirements and specification of sample selection criteria for organic samples are investigated by determination of uranium and thorium composition of the rim layers different organic sediments are investigated the organic deposits from nachtigall show middle pleistocene 230 th u ages ranging from 227 9 8 ka to 201 15 13 ka and appear to represent a warm temperate phase preceding the eemian interglacial mis 5e and the drenthe stadial mis 6 indicating a correlation with marine isotope substage mis 7c these results are in good agreement with the investigation of the pollen spectra indicating a correlation with a warm stage within the lower saalian complex

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

eustatic sea level and climate changes over the last 600 ka as derived from mollusc based esr chronostratigraphy and pollen evidence in northern eurasia we reconstruct and correlate palaeoclimatic events and deposits from shelf glacial periglacial and extraglacial zones of northern eurasia over the last 600 000 years the chronostratigraphical correlation of identified palaeoenvironmental and sealevel events and corresponding horizons is based on electron spin resonance esr analysis of subfossil mollusc skeletal remains from marine freshwater and acheulian bearing cave site deposits over 230 shell samples from more than 40 sites along the continental margin of eurasian north in the black and caspian sea basins and terrestrial shells from a lower palaeolithic cavesite in the northern caucasus were dated via esr to produce a late quaternary geochronology the pleistocene composite section of the loess palaeosoil formation includes two reference sections likhvin and arapovichi from the centre of the easteuropean plain the palyno chronostratigraphic record is interpreted as the product of six warm climate high sea level events including the current interglacial and six glacial events they are presented either as complete climatic rhythms of glacial and interglacial rank or by considerable portions of climatic phytocoenotic phases constituents of the rhythm the full interglacial conditions are centred at about 580 400 310 220 and between 145 70 calendar ka a broad correspondence between long palynological sequence directly esr dated warm climate related events and other palaeoenvironmental records described in the literature has been noted for 11 upper oxygen isotope stages 11 to 1 the results obtained in this study exemplify the potential of integrated chrono climatostratigraphic sequences in linking marine and terrestrial palaeoclimate records that may eventually span the whole brunhes chron d 2002 elsevier science b v all rights reserved

integrated stratigraphic reconstruction for the last 80 kyr in a deep sector of the sardinia channel western mediterranean abstract a quantitative analysis of planktonic foraminifera coupled with petrophysical and paleomagnetic measurements and 14 c ams calibrations was carried out on a deep core recovered in the sardinia channel western mediterranean sea during the ciesm sub2 survey providing an integrated stratigraphic time framework over the last 80 kyr significant changes in the quantitative distribution of planktonic foraminifera allowed the identification of several eco bioevents useful to accurately mark the boundaries of the eco biozones widely recognized in the western mediterranean records and used for large scale correlations namely 10 eco biozones were identified based on the relative abundance of selected climate sensitive planktonic foraminiferal species sixteen codified eco bioevents were correlated with alboran sea planktonic foraminiferal data and several climatic global events sapropel s1 younger dryas greenland isotope interstadial 1 greenland isotope stadial 2 heinrich event h1 h6 were recognized the eco bioevents together with the 14 c ams calibrations allowed us to define an accurate age model spanning between 2 and 83 kyr the reliability of the age model was confirmed by comparing the colour reflectance 550 nm data of the studied record with the astronomically tuned record from the ionian sea odp site 964 a mean sedimentation rate of about 7 cm kyr included three turbidite event beds that were chronologically constrained within the relative low stand and regressive sea level phases of mis 4 and 3 the deep sea sedimentary record includes a distinct tephra occurring at the base of the core that dates 78 ka cal bp the paleomagnetic data provide a well defined record of the characteristic remanent magnetization that may be used to reconstruct the geomagnetic paleosecular variation for the mediterranean back to 83 kyr

temporal relationships of carbon cycling and ocean circulation at glacial boundaries evidence from high sedimentation rate south atlantic deep sea cores indicates that global and southern ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice sheet growth and retreat respectively no consistent lead lag relationships are observed during abrupt millennial warming events during the last ice age allowing for the possibility that ocean circulation triggered some millenial climate changes at the major glacial interglacial transitions the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets

role of the thermohaline circulation in the abrupt warming after heinrich events evidence of rapid climate oscillations during the last glacial period has been identified in climate records from greenland ice cores1 2 and ocean sediments in the north atlantic3 4 these records show that periods of gradual cooling are terminated by abrupt warming events5 with the coldest periods coinciding with the deposition of ice rafted debris so called heinrich events throughout the north atlantic heinrich events are thought to be a signature of massive iceberg discharges owing to collapse of the laurentide ice sheet bond et al 5 have proposed that the decrease in meltwater flux following collapse and retreat of the ice sheet enhanced the ocean s thermohaline circulation6 thereby increasing advection of heat from the tropics and giving rise to abrupt climate warming here we test this idea using a simple ocean model coupled to a model of a periodically surging ice sheet we find that massive discharges of icebergs first stop the thermohaline circulation because of the consequent freshwater influx cooling the north atlantic region this is followed by a rapid restart of the circulation leading to abrupt warming thus our model can reproduce the qualitative features of the climate oscillations seen in the ice core and ocean records

interglacial and glacial climate oscillations in a marine shelf sequence from northern denmark a multidisciplinary study abstract a 22 5 m long marine shelf sequence in northern denmark covers the climatic shifts from glacial environments through interglacial and into early glacial conditions the interglacial was interrupted by two cool intervals also the early glacial succession experienced oscillations of the climate and a period with ameliorated temperature conditions has been separated as an interstadial these results are based on a multidisciplinary high resolution study of lithology foraminifera ostracods macrofauna diatoms and stable isotopes in a silty clay sequence from a borehole at norre lyngby 70 5 48 0 m depth the lithostratigraphy and the variations in depositional environment in the area is supported by a reflection seismic profile across the core site the chronostratigraphy is discussed on the basis of biostratigraphical correlation and seismostratigraphy as well as optically stimulated luminescence osl dating and amino acid measurements the biostratigraphy and the osl dates suggest an eemian age for the interglacial while amino acid results point to an older age if the interglacial is confirmed as eemian we believe that the succeeding interstadial period is likely to be correlated with the brorup interstadial the climatic changes in this eastern part of the north sea region are closely linked with changes in the north atlantic circulation pattern and the environmental fluctuations at norre lyngby are therefore believed to reflect fluctuations in the past regional climatic and oceanic system

the response of northern hemisphere extratropical climate and vegetation to orbitally induced changes in insolation during the last interglaciation abstract the last interglaciation substage 5e provides an opportunity to examine the effects of extreme orbital changes on regional climates we have made two atmospheric general circulation model experiments p t approximated the northern hemisphere seasonality maximum near the beginning of 5e p t approximated the minimum near the end of 5e simulated regional climate changes have been translated into biome changes using a physiologically based model of global vegetation types major climatic and vegetational changes were simulated for the northern hemisphere extratropics due to radiational effects that were both amplified and modified by atmospheric circulation changes and sea ice feedback p t showed mid continental summers up to 8 c warmer than present mid latitude winters were 2 4 c cooler than present but in the arctic summer warmth reduced sea ice extent and thickness producing winters 2 8 c warmer than present the tundra and taiga biomes were displaced poleward while warm summer steppes expanded in the mid latitudes due to drought p t showed summers up to 5 c cooler than present especially in mid latitudes sea ice and snowpack were thicker and lasted longer polar desert tundra and taiga biomes were displaced equatorward while cool summer steppes and semideserts expanded due to the cooling a slight winter warming in mid latitudes however caused warm temperate evergreen forests and scrub to expand poleward such qualitative contrasts in the direction of climate and vegetation change during 5e should be identifiable in the paleorecord

the δ18o of atmospheric o2 from air inclusions in the vostok ice core timing of co2 and ice volume changes during the penultimate deglaciation one important question about the co2 climate connection is how increasing atmospheric pco2 levels affect climate and thereby the mass balance of continental ice sheets a record of atmospheric co2 variations over the last 160 000 years has recently been constructed by analyzing the trapped gas in the vostok ice core barnola et al 1987 the relationship between changes in atmospheric co2 and the size of the continental ice sheets has been difficult to ascertain because the co2 record is obtained from ice cores while the ice volume record has been constructed from the stable isotopic composition of biogenic caco3 in deep sea sediment cores in order to compare these two records in a more precise manner we present a record of the isotopic composition 18o of atmospheric o2 trapped in the vostok ice core and propose that it may be considered a proxy for the 18o of seawater and hence ice volume having a record of atmospheric co2 along with a continental ice volume proxy in trapped air in the same ice core allows us to compare the timing of changes in these two parameters with little uncertainty in the relative ages of important events our results suggest that during the penultimate glacial termination atmospheric co2 began to increase at least 3 kyr before the initial introduction of meltwater to the oceans possible errors in the relative age depth curve of the vostok ice core and uncertainties in the influence of biological and hydrologic processes on the 18o of atmospheric o2 introduce some uncertainty into our conclusions however our results are in general agreement with the observed phase relationship between atmospheric co2 and ice volume imbrie et al 1984 imbrie et al 1989 inferred from changes in the 13c difference between contemporaneous planktonic and benthic forams deposited in deep sea cores and the specmap ice volume record

millennial variability in an idealized ocean model predicting the amoc regime shifts abstracta salient feature of paleorecords of the last glacial interval in the north atlantic is pronounced millennial variability commonly known as dansgaard oeschger events it is believed that these events are related to variations in the atlantic meridional overturning circulation and heat transport here the authors formulate a new low order model based on the howard malkus loop representation of ocean circulation capable of reproducing millennial variability and its chaotic dynamics realistically it is shown that even in this chaotic model changes in the state of the meridional overturning circulation are predictable accordingly the authors define two predictive indices which give accurate predictions for the time the circulation should remain in the on phase and then stay in the subsequent off phase these indices depend mainly on ocean stratification and describe the linear growth of small perturbations in the system thus monitoring particular indices of the ocean state could help predict

glacial cold water coral growth in the gulf of cadiz implications of increased palaeo productivity a set of 40 uranium series datings obtained on the reef forming scleractinian cold water corals lophelia pertusa and madrepora oculata revealed that during the past 400 kyr their occurrence in the gulf of cadiz goc was almost exclusively restricted to glacial periods this result strengthens the outcomes of former studies that coral growth in the temperate ne atlantic encompassing the french iberian and moroccan margins dominated during glacial periods whereas in the higher latitudes irish and norwegian margins extended coral growth prevailed during interglacial periods thus it appears that the biogeographical limits for sustained cold water coral growth along the ne atlantic margin are strongly related to climate change by focussing on the last glacial interglacial cycle this study shows that palaeo productivity was increased during the last glacial this was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling after the younger dryas cold event the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the goc this primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems moreover these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern ne atlantic where more suitable environmental conditions established with the onset of the holocene

the esr age of portlandia arctica shells from glacial deposits of central latvia an answer to a controversy on the age and genesis of their enclosing sediments abstract the occurrence of portlandia arctica shells in glacigenic sediments of central latvia had created a controversy in many publications about 1 their age ranging from the holsteinian to the late weichselian and 2 the genesis of their enclosing sediments glacial glaciomarine or marine our reinvestigation of the main object of controversy the licupe site leads to a conclusion that the sedimentary package of diamictons clays and sands containing portlandia arctica shells and marine microfossils is a large glacial raft that had been transported and deposited by the riga lobe during the weichselian the electron spin resonance esr ages on five sets of portlandia arctica shells from the licupe and daugmales tom ni sites range from 86 0 6 8 to 105 0 9 2 ka bp these esr age determinations and the cool climate indicators of the associated microflora and microfauna suggest that their source sediments probably in the gulf of riga are marine clays of early weichselian age probably correlative to the brorup interstadial in central latvia portlandia arctica shells and their enclosing clay occur resedimented or translocated in glacial deposits during weichselian glacial advances

physical models of regional fold superposition the role of competence contrast abstract physical models of superposed folds demonstrate that rheologic contrast strongly controls the style of fold interference rheologic contrast affects strain partitioning between layer parallel shortening and buckling and affects the development of structural anisotropies parallel to first generation folds laminates with insignificant competence contrast are characterized by circular to elliptical domes and basins type 1 interference in addition to folding the layers accommodate shortening by layer parallel thickening preferentially in the fold culminations laminates with significant competence contrast are characterized by buckled fold hingelines and axial surfaces type 2 interference the less competent layers thicken in the hinges the more competent layers maintain their initial thickness in plan view the f 1 hingelines are refolded in a lobate cuspate to box style whose axial traces form conjugate pairs the models are dynamically scaled to represent folds with km scale wavelengths the evolution of surface structures map patterns at different depths and equal area projections synthesized from structure contour maps were used for analysis comparable to regional analysis common to field studies gravitational body forces effectively damp the vertical amplitudes of both the first and second generation folds thereby enhancing the formation of type 2 interference

particle size characterisation of holocene back barrier sequences from north atlantic coasts sw spain and se england abstract in this paper we present the results of bivariate plots of grain size parameters mean against sorting in the reconstruction of holocene environmental change in coastal environments where barrier formation has had an important control on sedimentation sites on the north atlantic coast with differing histories of climate sediment flux sea level change and barrier integrity are investigated to determine the general efficacy of this bivariate parameter model in distinguishing between open and closed basin conditions and in reviewing the significance of aperiodic high energy geomorphic events in controlling late stage back barrier sedimentation

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

late quaternary eolian deposition in central italy abstract records of eolian quartz from two continuous sediment sequences drilled in lagaccione and lago di vico volcanic lakes in central italy contribute to the knowledge of eolian deposition in the central mediterranean during the last 100 000 years the chronology is based on 14 c and 40 ar 39 ar dating and tephra analysis pollen data provide the paleoenvironmental framework and enable correlation between the cores eolian inputs were high during the steppe phases corresponding to oxygen isotope stages 4 and 2 low inputs correspond to the forest phases of the last interglacial and the middle holocene eolian inputs have increased in the late holocene patterns of eolian deposition in central italy resemble the antarctic dust record from the vostok ice core the italian patterns may also correspond with hydrological changes registered in north africa the main source of dust loading over the mediterranean now north africa may have played an important role in dust supply throughout the last climatic cycle

molecular record of secular sea surface temperature changes on 100 year timescales for glacial terminations i ii and iv high resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand year timescale1 3 little is known4 however about the variation of climate and of palaeoceanographic conditions throughout the quaternary on timescales of less than 1 000 years at frequencies far greater than those of the milankovitch orbital cycles here we show that such high time resolution is possible from molecular stratigraphic studies based on biomarker organic molecules alkenones we have sampled alkenone stratigraphic records at 70 to 200 yr intervals across glacial terminations i ii and iv in sediment cores from oop site 658 off northwest africa5 sea surface temperatures ssts derived from the alkenone uk37 index6 8vary rapidly beyond the range of analytical noise by up to 2 5 c in 300 yr showing hitherto unknown cycles with about 600 yr periodicities some of the changes parallel similar events in the oxygen isotope stratigraphy sst oscillations may be linked in part to abrupt breakdowns in atlantic deep water ventilation resulting from meltwater events of quaternary glacial terminations3 9 10

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

dielectric stratigraphy of ice a new technique for determining total ionic concentrations in polar ice cores a 133 m deep antarctic ice core from dolleman island antarctic peninsula has been profiled by dielectric measurements in the af lf 20 hz 100 khz frequency range this has revealed large variations in dielectric relaxation and conductivity down the core a comparison with the chemical stratigraphy along 45 m of the core demonstrates for the first time the decisive role played by acids and salts in determining the electrical behaviour of natural ice the total ionic concentration along the ice core can be deduced from the dielectric response this technique may be applied rapidly in the field and as it requires no contact between ice core and electrodes the core is maintained in pristine condition for later chemical analysis

the back barrier and barrier depositional history of romney marsh walland marsh and dungeness kent england previous stratigraphical investigations of romney marsh have tended to be local in scale and this has hindered efforts to establish a unifying stratigraphical framework for this area this paper addresses this problem by describing the results of a 12 km transect across romney marsh linking previously studied back and fore marsh sites horsemarsh sewer and broomhill respectively and presenting additional pollen diatom and radiocarbon data from an intermediate mid marsh site brookland one main organic unit is recorded across much of romney marsh although its age altitude and composition varies microfossil and radiocarbon data from brookland and elsewhere on romney marsh show that this organic unit accumulated under a general removal and return of marine conditions that took place between ca 5100 and 2000 yr bp a recently proposed model of barrier development is used to investigate the history of back barrier sedimentation in romney and walland marshes this model suggests a three phase life history for gravel barriers which consists of initiation stability and breakdown although there are problems in relating back barrier deposits directly to barrier dynamics nevertheless the romney marsh data do for the most part agree with the expected number and sequence of sea level tendencies predicted by this model the back barrier stratigraphical data suggest that initiation stability and breakdown of the dungeness foreland occurred between ca 6000 and 5000 yr bp 5000 and 2000 yr bp and 2000 yr bp and present respectively

rissian eemian and wurmian coleoptera assemblages from la grande pile vosges france abstract the grande pile peat bog sequence is one of the few west european sites that cover the entire time span of the last major climatic cycle 140 000 years a recent program of coring has provided material for insect analysis the aim of this palaeoentomological study is to interpret the environmental and climatic evolution from the end of the rissian glaciation to the holocene using subfossil coleoptera the studied samples yielded 394 taxa of coleoptera half of them identified to species level 19 of which do not belong to the present day french fauna the large number of taxa suggests a wide variety of habitats and provides much detailed palaeoecological evidence for the period studied the lowermost sediments of the sequence corresponding to the end of the rissian glaciation were deposited under very cold conditions in a tundra environment this is succeeded by a forest period in which two cool interludes of grassland environment occur although these periods are decidedly poor in tree dependent coleoptera they do not contain any really cold adapted taxa they divide the forest phase into three periods the first one corresponding to the eemian interglacial shows an early stage in which the beetle fauna is characterized by species dependent on deciduous trees a later stage in which this fauna is mixed with many conifer dependent elements some of which e g platypus oxyurus suggest warmer and perhaps wetter climatic condition than today the two later woodland periods yielded coleopteran assemblages rather similar to those recorded in the second part of the eemian i e with both deciduous and conifer dependent taxa there is some evidence to suggest that these two periods were slightly cooler than the eemian proper marked climatic deterioration becomes obvious in the upper half of the sedimentary sequence attributed to the last glacial period wurm with the reappearance of tundra beetle assemblages sediment and insect evidence suggest that the climate was extremely cold and continental at la grande pile at about 30 000 b p a comparison of the insect analysis with previous palynological works enables precise correlation between the results provided by these two independent approaches however large numbers of running water coleoptera in the forest periods replaced by standing water coleoptera in cold periods raise questions concerning the lacustrine origin of the sedimentation at la grande pile

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

the thrust and shear zones of the moine thrust zone and the nw scottish caledonides the caledonian thrust belts of nw scotland exhibit many features typical of foreland fold and thrust belts the major structures propagated westwards towards the foreland the thin carapace of cambro ordovician sediments being accreted in imbricate and duplex zones beneath the major thrust sheets on a broad scale the rules of thrust geometry are obeyed but many local anomalies are found particularly in the assynt region in assynt several large fault bounded gravity spreading structures surge zones have been identified extensional faults have been traced into strike slip and then contractional faults there are zones of extensional and contractional imbricate faults and extensional and contractional ductile flow similar structures have been found along the length of the moine thrust belt suggesting that gravity spreading was an important mechanism during the later stages of movement within the main caledonian fold belt there are several major tectonic slides which are recognized by a local increase in intensity of deformation the majority are nw verging and were originally gently dipping in the highlands se of the great glen there are early major se verging recumbent folds associated with considerable crustal thickening reflected in high pressure 12kbar metamorphism many of the major slides may have formed by spreading away from this thickened crust the caledonian deformation and metamorphism occurred later in the moines and moine thrust zone than in the dalradian and grampian moines to the se of the great glen this may reflect different levels of deformation alternatively it may argue for a large strike slip displacement on the great glen fault juxtaposing crustal blocks which had experienced different ages of caledonian deformation and metamorphism the late movement on the moine thrust involved spreading from an area of thickened caledonian crust formed either by the stair step trajectory of the basal thrust to the moines and or by thickening due to intrusion of large masses of late caledonian granites

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the late holocene evolution of denge marsh southeast england a stratigraphic sedimentological and micropalaeontological approach stratigraphic granulometric and micropalaeontological investigations of the sedimentary interface between the dungeness shingle complex and denge marsh have been carried out to establish the late holocene sedimentary evolution of the romney marsh region the arenaceous and argillaceous sediments overlying the buried shingle topography are of intertidal origin and indicate the gradual infilling of an initially deep tidal environment following an extensive period of peat deposition which affected the majority of the area the cause of this rather sudden marine inundation is considered to be storm breaching of the shingle complex although the timing of this event is difficult to determine without further chronological investigations

mid and late holocene evolution of the dungeness foreland uk abstract the dungeness foreland is located in the eastern part of the english channel and consists of over 500 gravel beaches which have accumulated since the mid holocene the south coast of the foreland between jury s gut and galloway s lookout is characterised by alternating areas of marsh sediments and gravel which have previously been interpreted as evidence for several oscillations in sea level stratigraphic and diatom data from the marsh sediments in this area indicate that they accumulated under marine brackish and brackish tidal channel conditions while pollen data from a peat bed recorded in the base of wickmaryholm pit show a removal and return of the marine influence at ca 2038 97 yrs b p and ca 1000 700 yrs b p respectively an established age altitude graph of sea level changes for the region shows that sea level changed little during the period of gravel deposition in the study area ca 4000 2000 yrs b p it is therefore argued that the alternating gravel and marsh sediments of the study area probably accumulated as a result of changes in storm incidence and gravel supply and not oscillations in long term sea level under periods of high storm incidence increased northward distal extension of the beach ridges in the study area has occurred while under calmer conditions reduced distal extension has taken place no clear relationship is apparent between long term time altitude changes in sea level and episodes of foreland development during the last ca 4000 years however evidence for a regional episode of increased storm incidence at ca 700 800 yrs b p may be recorded by the return of marine conditions to wickmaryholm pit breaching of the dungeness foreland at rye and a sudden increase in the altitude of the gravel beaches in denge beach identifying the importance of local and regional controls on foreland evolution is difficult though as the sensitivity of the foreland to processes operating at different spatial scales may well have changed through time

sedimentary record of rapid climatic variability in the north atlantic ocean during the last glacial cycle comparisons between a greenland ice core isotopic record and marine sediment grey level records of the north atlantic ocean show that rapid temperature variations witnessed by the ice core dansgaard oeschger events during the last glacial period can also be detected in marine sediments this shows that the resolution obtained in marine cores can be sufficiently high to record rapid climatic fluctuations several spectral analyses of those grey level marine records consistently indicate that significative fluctuations of the climatic response exist with periodicities of 5 to 1 kyr in addition to orbital forcing these high frequencies are close to those predicted by various dynamic ocean models

climatic signals in the chinese loess record for the last glacial the influence of northern high latitudes and the tropical pacific the high resolution shagou loess section near the northwest limit of the east asian summer monsoon northwest china was analyzed the timescale of this section was set up based on a grain size age model and age controls the record of the shagou section shows that the millennial scale oscillations are superimposed on an orbital scale trend which can be correlated with the variations found in greenland and the sulu sea differences in the corresponding dansgaard oeschger cycles between the records in greenland and the chinese loess sections including the orbital scale trend the timing and the amplitude suggest that the climatic signals in chinese loess might not be singularly regulated by the north atlantic the differences in trend and amplitude can be reasonably explained when compared with the sulu sea record this suggests that the western tropical pacific also exerted an important influence on climatic signals found in the chinese loess record possibly countering the impact of high latitude factors during the last glacial

relative variations in geomagnetic intensity from sedimentary records the past 200 000 years abstract eighteen records of relative paleointensity from marine sediments have been compiled in order to retrace the global changes in geomagnetic intensity during the past 200 kyr before dealing with any other source of noise we focused on problems inherent to the depth versus time correlations the accuracy and resolution of dating mostly deduced from isotopic stratigraphy were identified as significant factors of distortion we found also that different time scales have been used by authors after readjustment with respect to the same time scale the records were stacked together and the statistical significance of the results tested by a bootstrap technique seventeen records shown to be coherent were combined into a synthetic curve defined as sint 200 other stacks combining various subsets of data were found to be identical to sint 200 except for changes in dispersion in fact the dispersion around sint 200 could be reduced further by improving the correlations without violating the stratigraphy a procedure which at least for some records emphasizes the need for more detailed depth time correlations another characteristic emerging from the results is that paleointensity features as short as 10 kyr are observed between 120 200 ka and can thus in principle be resolved however subsequent refinement is still necessary for this period which is documented by fewer records than the following 120 kyr finally we compared sint 200 with the records from the labrador sea and the lac du bouchet ldb both of which rely mostly on 14c chronology the two records show satisfactory agreement with sint 200 when transferred with respect to the age model established by correlating their 18o labrador and susceptibility features ldb with the 18o reference record the offset of 7 kyr at 40 ka measured in both cases between the 14c and 18o ages is higher than the value deduced from a recent model of a geomagnetic field control of 14c production 1 but is not inconsistent with recent u th dates

esr dating evidence for early man at a lower palaeolithic cave site in the northern caucasus as derived from terrestrial mollusc shells eight terrestrial shell samples from recent excavations at treugolnaya triangular cave northern caucasus were analysed by electron spin resonance esr to produce a chronology for the most ancient acheulian bearing layers of the cave site the lifetime of the 2 0012 centre used for dating is about 3 108 at 53c that allows to date the multi level sequence of the cave site at least in the range of the last one million years the dating results obtained suggest that the rst from the bottom archaeological layer 7a is likely to be about 583 000a old and the next 5b is some 393 000 a old these layers can be correlated with oxygen isotope stages 15 and 11 respectively the estimates obtained imply that man presumably reached the northern caucasus at least as early as the beginning of stage 15 i e much earlier than generally recognised the leaving of the cave by ancient man due to development of glacial environment during the subsequent stage s can probably be linked with the penetration of man to the southern areas of the east european plain 2000 elsevier science ltd all rights reserved

climate change dynamics in northern eurasia over the last 200 ka evidence from mollusc based esr chronostratigraphy and vegetation successions of the loess palaeosol records abstract the time span of the past 200 ka has been marked by many large scale global and regional climate changes between warmer and cooler conditions as is usually the case when studying the past palaeoenvironmental data become scarcer with increasing age therefore every detailed palaeoenvironmental record may be of special interest to quaternary geologists in terms of palaeoenvironmental reconstructions correlations and general stratigraphy of the quaternary in this paper we present a long palynological record of terrestrial flora and an esr dated marine record of global scale climatic variation obtained from a loess palaeosol sequence in the east european plain and continental margin of northern eurasia for the time span starting from the penultimate glacial period correlating with marine isotope stage mis 6 these records show that in combination they have a potential of assigning warm cold climate related deposits to the chronostratigraphically organised sequence of the late pleistocene palaeoenvironmental events

modeling of the thermo hydro mechanical chemical response of sedimentary rocks to past glaciations abstract thermo hydro mechanical chemical thmc coupled processes that have resulted from long term past climate changes and glaciation cycles in the sedimentry rocks of southern ontario are investigated a conceptual numerical model has been developed to solve four coupled partial differential equations pdes which represent hydraulic thermal mechanical and chemical processes the finite element method is used to solve the pdes under transient surface boundary conditions imposed by past glaciation cycles to predict the hydraulic mechanical thermal and geochemical responses of the geological system the results show that past glaciations have a significant impact on the hydraulic gradient and pressure vertical effective stress and salinity profiles and a limited effect on the permafrost depth the predicted results show good agreement when compared with the field data for the total dissolved solid rock strength and quality the results show relatively good agreement with the anomalous pore water pressure profile in the field the modeling results indicate that the infiltration depth of glacial melted water is less than 300 m and are consistent with the field observation of total dissolved solids at the level of a deep geological repository dgr for low and intermediate level radioactive wastes being planned in these rock formations a safety factor of 6 9 is predicted against failure by using hoek brown failure envelopes while a low safety factor of 0 83 is predicted at the shallower level of the silurian salina formation it is found that solute transport at the middle and upper ordovician formations are diffusion dominated at depths of 300 m or more and controlled by diffusion advection above 300 m based on the results obtained the modeling of a past glaciation can be used with reasonable confidence in predicting the impact of future glaciations related to the long term safety and stability of the proposed dgr in the sedimentry formation however for site specific conditions thmc modeling is very sensitive to material properties and sensitivity analysis is required for future model development

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr