structural evolution of the texas orocline eastern australia the texas orocline with a half wavelength of similar to 120 km is the largest and most obvious orocline in the southern new england orogen and is clearly recognised in geological maps and geophysical images in the area of the orocline there is a major unconformity between devonian carboniferous metasedimentary rocks texas beds and the overlying early permian rift related basins detailed structural mapping shows that units both above and below the unconformity are folded around the orocline indicating that at least part of the oroclinal deformation has occurred after the deposition of the early permian rocks in addition early permian 298290 ma granitoids are aligned parallel to the oroclinal structure further indicating that deformation partly occurred during or after the early permian pre oroclinal isoclinal folds f 1 and related axial plane cleavage si are well developed in the texas beds and are curved around the oroclinal structure syn oroclinal structures are characterised by minor kink folds and disharmonic folding f 2 in the core of the orocline a later phase of kink folding corresponding to a similar to n s shortening direction does not seem to be related to the orocline and is interpreted as post oroclinal deformation a secondary penetrative fabric parallel to the axial plane of the orocline was not observed indicating low contractional shortening across the orocline 30 we demonstrate that the observed strain is too low to account for oroclinal bending during dextral transpression as previously proposed we suggest an alternative model involving an initial curved structure probably related to subduction rollback or a pre existing curvature in the palaeomargin of eastern australia which was amplified by dextral transpression and subsequent e w contraction c 2011 international association for gondwana research published by elsevier b v all rights reserved

effect of wind scouring on climatic records from ice core oxygen isotope profiles removal of winter snow by wind explains why the annual mean oxygen isotope ratio at an ice divide is 2 5 less negative than it is 1 2 km downslope cores from two sites on an ice cap ellesmere island canada show past variations in the difference depending on where the ice originated relative to the scoured zone some ice core climatic records may need correction for scouring

cone penetration test calibration for erksak beaufort sea sand interpretation of the cone penetration test in sands is generally based on empirical calibrations from tests in large diameter calibration chambers although interpretation of these calibration data for clean sands in terms of the state parameter is expected to be broadly applicable to other sands material specific correlations are desirable for many projects this paper describes a series of calibration chamber tests carried out on a sand dredged from the beaufort sea for construction of artificial islands this erksak sand is a uniformly graded subrounded medium grained sand with a fines content of 3 6 the testing chamber described is 1 4 m in diameter and allows independent control of vertical horizontal and back pressures on the sand sample samples of the sand were prepared by moist compaction to preserve the fines content and then back pressure saturated the chamber test data are presented and confirm that the erksak sand fits the general trends observed for other sands very well a method i

seasonal variability in the origin of recent atmospheric mineral dust at northgrip greenland abstract isotopic sr and nd and mineralogical analyses of dust extracted from snow deposits from the last decade at the northgrip greenland ice camp 75 1 n 042 3 w confirm the eastern asian source for greenland dust and extend it to the present day the 1998 and 1999 samples which represent a 2 4 month resolution of dust deposition show that there are at least two east asian sources for the greenland dust that vary seasonally the provenance of dust during the major spring summer deposition is the takla makan desert of northwest china

evidence for climate instability during the younger dryas interval in the hengduan mountains yunnan southwestern china abstract the younger dryas yd is the most recent abrupt climatic event recognized during the transition from the last glaciation to the holocene growing evidence from the middle and high latitudes of europe and north america shows that the climate within the yd event was highly unstable until recently however climate instability during this event has received little attention elsewhere in the world here we present evidence of a climatically unstable yd based on pollen climate transfer function and redfit spectral analysis of pollen data from haligu in the hengduan mountains of southwestern china a low latitude temperate biodiversity hotspot our data show that the climate fluctuated significantly during the yd with three warm peaks recognized at 11 5 11 7 and 12 3 cal kyr bp in particular we estimate a gradual rise in mean annual temperature by 3 7 c between the end of the yd and the early holocene 11 2 10 9 cal kyr bp in response to this the subalpine conifer forest dominated by picea and abies may have migrated about 610 m upwards we also detected that the climate fluctuations during the yd holocene transition show significant centennial periodicities of 76 yr 84 yr 91 yr 95 yr and 638 yr the former four cycles are possibly related to the gleissberg around 80 yr solar cycle which was also detected in the hongyuan peat the pc 6 core of the east china sea and the gisp2 ice core these new findings enhance our understanding of millennial scale abrupt climate events which may be of great significance in predicting the impact of future climate change on mountainous ecosystems in southwestern china the warming at the end of the yd may provide a potential analog for global warming in the near future during which the upward migration of vegetation zones will likely lead to the loss of habitat for threatened species we therefore should take action to restore habitats and provide protected areas for species at risk

high resolution ammonium ice core record covering a complete glacial interglacial cycle high resolution ammonium measurements were performed along the greenland ice core program grip deep ice core covering a complete climatic cycle no overall anthropogenic increase is observed over the last 300 years however springtime concentrations have roughly doubled since 1950 biomass burning is estimated to be a major source for ammonia emissions for preindustrial times it contributes between 10 to 40 to the total ammonium deposited on the central greenland ice sheet during the holocene no correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern north america which is considered to be the main source area for ammonium deposited on the central greenland ice sheet this suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core if unchanged meteorological conditions are assumed for the holocene as indicated by the 18o ice record a decreasing biomass burning activity toward present time can be derived from the ammonium ice record soil and vegetation emissions are responsible for the ammonium background concentrations in the ice the record therefore may be used to trace back the biomass history of the north american continent a pronounced decreasing trend in background ammonium is found during the holocene reflecting decreasing temperature and therefore lower nh3 emissions in the source region variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength which can be related to the extent of the laurentide ice sheet the data suggest that the laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

independence of geostatic stress from overconsolidation in some beaufort sea clays reply since 1982 extensive use has been made of the self bored pressuremeter in arctic offshore site investigations one finding of this work is that the in situ geostatic stress ratio k0 of beaufort sea clays is apparently unrelated to the overconsolidation ratio ocr the procedures and data to support this finding are documented and the finding is discussed in light of the present geological understanding for the area it is concluded that the independence of k0 from ocr may be quite widespread a finding that contradicts the widely held tenet regarding the existence of a single valued function relating k0 and ocr if k0 is regarded as important then it should be measured in situ key words self bored pressuremeter geostatic stress ratio k0 beaufort shelf geologic history overconsolidation ratio

timescales for dust variability in the greenland ice core project grip ice core in the last 100 000 years the calcium representing dust concentration record of the last 100 000 years from the greenland ice core project grip ice core shows a huge dynamic range factor 100 the relationship between dust concentrations and temperature represented by the oxygen isotope ratio is not a simple one as has often been assumed a rapid alternation factor of 5 10 between low concentrations during the dansgaard oeschger interstadial periods and high levels in colder periods is superimposed on a long term trend encompassing a further factor of 5 10 within climate periods there is only a very weak relationship between ca concentration and temperature previous authors biscaye et al 1997 have suggested that the most likely source for the increased dust is eastern asia for the first time we consider each possible cause of both rapid and slow increases from source to deposition we suggest that to account for the size and rapidity of the fast changes significantly higher wind speed in the source area is required although changes in atmospheric residence time could also play a role for the slower long term variability changes in transport speed or possibly route are probably also involved changes in the size of the source area could give some change on longer time periods the probable importance of changes in source area wind speed almost simultaneous with greenland temperature changes confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes this adds to evidence that the atmospheric circulation system underwent almost instantaneous large scale changes during the last glacial period

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

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

grip deuterium excess reveals rapid and orbital scale changes in greenland moisture origin the northern hemisphere hydrological cycle is a key factor coupling ice sheets ocean circulation and polar amplification of climate change here we present a northern hemisphere deuterium excess profile covering one climatic cycle constructed with the use of 18 o and d greenland ice core project grip records past changes in greenland source and site temperatures are quantified with precipitation seasonality taken into account the imprint of obliquity is evidenced in the site to source temperature gradient at orbital scale at the millennial time scale grip source temperature changes reflect southward shifts of the geographical locations of moisture sources during cold events and these rapid shifts are associated with large scale changes in atmospheric circulation

deconvolution based resolution enhancement of chemical ice core records obtained by continuous flow analysis continuous flow analysis cfa has become a popular measuring technique for obtaining high resolution chemical ice core records due to an attractive combination of measuring speed and resolution however when analyzing the deeper sections of ice cores or cores from low accumulation areas there is still need for further improvement of the resolution here a method for resolution enhancement of cfa data is presented it is demonstrated that it is possible to improve the resolution of cfa data by restoring some of the detail that was lost in the measuring process thus improving the usefulness of the data for high resolution studies such as annual layer counting the presented method uses deconvolution techniques and is robust to the presence of noise in the measurements if integrated into the data processing it requires no additional data collection the method is applied to selected ice core data sequences from greenland and antarctica and the results demonstrate that the data quality can be significantly improved

orbital and suborbital scale changes in the east asian summer monsoon since the last deglaciation the variability of the east asian summer monsoon easm has far reaching effects on the global climate system and the environment and full understanding of the variability and dynamics of the easm contributes to predictions of its future behavior here we present a well dated mineralogical and total organic carbon record from a saline inland lake in northern china which provides a robust archive of the easm evolution since 16 0 cal ka bp our record reveals a series of rapid and frequent millennial scale climatic fluctuations during the last deglaciation these fluctuations are documented by changes in the abundances of mirabilite bloedite and gypsum which appear to record the oldest dryas the bolling allerod warm period and the younger dryas the peak easm moisture occurred in the early and middle holocene which was punctuated by a prominent and abrupt weak monsoon interval that occurred synchronously with the 8 2 cal ka bp cold event this moisture maximum was terminated at 6 9 5 9 cal ka bp

nanodiamond rich layer across three continents consistent with major cosmic impact at 12 800 cal bp abstracta major cosmic impact event has been proposed at the onset of the younger dryas yd cooling episode at 12 800 150 years before present forming the yd boundary ydb layer distributed over 50 million km2 on four continents in 24 dated stratigraphic sections in 10 countries of the northern hemisphere the ydb layer contains a clearly defined abundance peak in nanodiamonds nds a major cosmic impact proxy observed nd polytypes include cubic diamonds lonsdaleite like crystals and diamond like carbon nanoparticles called n diamond and i carbon the nd abundances in bulk ydb sediments ranged up to 500 ppb mean 200 ppb and that in carbon spherules up to 3700 ppb mean 750 ppb 138 of 205 sediment samples 67 contained no detectable nds isotopic evidence indicates that ydb nds were produced from terrestrial carbon as with other impact diamonds and were not derived from the impactor itself the ydb layer is also marked by abundance peaks in other impact related proxies including

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

experience with measurement of horizontal geostatic stress in sand during cone penetration test profiling the incorporation of an additional transducer to cone penetrometers has recently been proposed at the university of california at berkeley the additional transducer is used to measure the horizontal stress on the friction sleeve this stress being related to the horizontal geostatic stress of the soil this type of cone is referred to as a horizontal stress cone hsc although it also incorporates a piezometric transducer the paper derives an algorithm for determination of horizontal geostatic stress from measurements made with an hsc in sand this step is a prerequisite to use of the data because of the disturbance caused by the cone during penetration some mathematical aspects of the algorithm and how these aspects constrain cone data evaluation are discussed it is possible at least in principle to determine the horizontal geostatic stress in sand by penetration testing with an hsc experience in applying the proposed algorithm to the data obtained in a hydraulically placed sand fill is described

tracing tectonic deformation using the sedimentary record an overview tectonic activity on a range of scales is a fundamental control on sedimentary activity the range of structural deformation within a region extends from the plate tectonic scale governing for example rift initiation to the basin scale with the formation of basin bounding faults internal basin configuration is also strongly influenced by tectonic activity however the relationship between tectonic activity and sedimentation is a complex one given the many additional factors which can also influence sedimentary activity including erosion sediment transport source area lithology groundwater chemistry range of depositional environments climate eustasy and the relative location of an area and its distality to marine influences in this paper we provide a selective overview of the issues associated with the interlinked themes of tectonics and sedimentation examining the main basin types forming in both extensional and compressional plate settings we then review the various models of sedimentation in the selected basins both on a local and a basinal scale finally we look to the future providing a series of possible research areas almost exclusively multidisciplinary which would help to improve existing models of interlinked sediment tectonics systems

a deep seismic profile of 800 km length recorded in southern queensland australia summary in 1984 the australian bureau of mineral resources and the geological survey of queensland recorded a regional seismic reflection profile of over 800 km length from the eastern part of the eromanga basin to the beenleigh block east of the clarence moreton basin a relatively transparent upper crustal basement with an underlying more reflective lower crust is characteristic of much of the region prominent westerly dipping reflectors occur well below the sediments of the eastern margin of the clarence moreton basin and the adjacent beenleigh block and provide some of the most interesting features of the entire survey a wide angle reflection refraction survey of 192 km length and an expanding reflection spread of 25 km length were recorded across the nebine ridge the only clear deep reflectors are interpreted as p to sv or sv to p converted reflections from a mid crustal boundary at a depth of about 17 km the combined nebine ridge data provide well constrained p and s wave velocity models of the upper crust and suggest a crustal structure quite different from that beneath the adjacent mesozoic basins

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

visual stratigraphy of the north greenland ice core project northgrip ice core during the last glacial period 1 a continuous high resolution record of digital images has been obtained from the north greenland ice core project northgrip ice core 75 1 n 42 3 w in the depth interval from 1330 m to the bedrock at 3085 m the ice core stratigraphy is clearly visible throughout the glacial period with the most frequent and brightest visible layers appearing during the coldest events down to a depth of 2600 m the horizontal layering is very regular below this depth small irregularities in the layering start to appear and below 2800 m the visual stratigraphy becomes more uncertain perhaps because of penetration into climatically warmer ice comparison of the visual stratigraphy with high resolution continuous records of chemical impurities and dust reveals a high degree of correlation which indicates that the visible layers are caused by these impurities a new approach is used to automatically determine annual layer thicknesses from the visual stratigraphy record by carrying out a frequency analysis of the most prominent visible layers in the profile the result gives strong support for the northgrip timescale model

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

fragmented reduction processes middle palaeolithic technical behaviour in the abri du maras shelter southeastern france new excavations at the abri du maras located in the southeast of france have yielded middle palaeolithic assemblages with evidence of rock shelter occupations in a cold climatic context contemporaneous with mis 4 few mis 4 sites are known in this part of france and especially in this state of preservation the paper is focused on one sedimentological layer divided into two archaeological levels sub levels 4 1 and 4 2 our goal was to examine the middle palaeolithic lithic assemblage of these two levels by interdisciplinary approaches technology origin of flint and functional analysis of stone tools in order to identify the technical strategies and the land use patterns in a specific environmental context the two occupations do not show differences in behaviours the technical strategies applied to flint and other stones indicate a fragmentation of the reduction processes in a local and semi local perimeter around the site the main core technology is levallois generally on flint cortical cores on flakes flint flakes blades and points are the main components of the series and the technological aims of the debitage due to the small size of the flakes used for flaking large flint flakes blades levallois or cortical and levallois points were produced elsewhere to the north and south of the site up to 20 30 km according to the geological study and then brought to the shelter flakes in other lithic materials quartz quartzite were also knapped elsewhere before being transported to the shelter some of the large flint flakes but also nodules and fragments of slabs were then used for onsite flaking flake tools are very rare evidence of impact fractures and tcsa tcsps values of the corpus of unretouched levallois points suggest that some points brought or prepared on the site could have been used as projectile tips the lithics attest to management of local and semi local stones in a perimeter of 30 km around the site possibly more due to some unidentified flint and an anticipation of domestic needs in relation to reindeer hunting the predominant activity imported artefacts and artefacts made on the site were used for the same diversity of activities and materials butchery plant and woodworking the technological strategies and the type of management differ slightly from those from cave assemblages in the same area located in valleys and on low plateaux near the rhone corridor possibly due to the type of the site a vast shelter data from the abri du maras are compared to data from the other middle palaeolithic sites of the region and the role of the topographic aspect of the site on the type of occupations is discussed

an oceanic origin for the increase of atmospheric radiocarbon during the younger dryas 1 variations in carbon 14 to carbon 12 ratio in the atmosphere 14catm provide a powerful diagnostic for elucidating the timing and nature of geophysical and anthropological change the atlantic marine archive suggests a rapid 14catm increase of 50 at the onset of the younger dryas yd cold reversal 12 9 11 7 kyr bp which has not yet been satisfactorily explained in terms of magnitude or causal mechanism as either a change in ocean ventilation or production rate using earth system model simulations and comparison of marine based radiocarbon records from different ocean basins we demonstrate that the yd 14catm increase is smaller than suggested by the marine archive this is due to changes in reservoir age predominantly caused by reduced ocean ventilation

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

electrical conductivity method ecm stratigraphic dating of the byrd station ice core antarctica a continuous ecm profile strong acid concentration has been measured along the 2191 m of ice core recovered at byrd station antarctica in 1968 the ecm profile reveals continuous and systematic seasonal changes which are used for dating the ice core back to 50 000 bp hammer and others ecm stratigraphic dating of byrd station ice core antarctica

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

greenland temperature response to climate forcing during the last deglaciation greenland ice core water isotopic composition 18 o provides detailed evidence for abrupt climate changes but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns we investigate greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean atmosphere climate model contrary to the traditional 18 o interpretation the younger dryas period was 4 5 2 c warmer than the oldest dryas due to increased carbon dioxide forcing and summer insolation the magnitude of abrupt temperature changes is larger in central greenland 9 to 14 c than in the northwest 5 to 9 c fingerprinting a north atlantic origin simulated changes in temperature seasonality closely track changes in the atlantic overturning strength and support the hypothesis that abrupt climate change is mostly a winter phenomenon

annual accumulation at two sites in northwest greenland during recent centuries during summer 1995 150 m firn and ice cores were drilled to determine annual accumulation rates at two greenland sites 73 84 n 49 49 w nasa u site and 78 53 n 56 83 w humboldt glacier site annual layers were identified in the cores using multiple parameters 18 o and concentrations of dust h 2 o 2 nh 4 ca 2 and no 3 using all parameters together to define annual layers resulted in a 350 year record for the nasa u core with no dating uncertainty for the lower accumulation humboldt core the dating uncertainty is about 5 years over the 852 year period of record with no uncertainty over the past 200 years annual accumulation over the periods of record at the two sites averaged about 0 34 and 0 14 m water equivalent respectively a set of 20 m firn cores drilled near the main 150 m cores showed that interannual variability of accumulation exceeded spatial variability at nasa u the humboldt cores showed equal spatial and interannual variability the accumulation rates at both sites showed a low frequency variation of about 100 years and both sites showed 200 year cumulative fluctuations of about 2 m from mean accumulation rates compared to central greenland and to nasa u the humboldt core showed higher annual accumulation rates around 1760 1810 possibly indicating a changed circulation pattern for the more northern part of greenland in that period

andean analogue for late carboniferous volcanic arc and arc flank environments of the western new england orogen new south wales australia abstract late carboniferous continental conglomerates interbedded with silicic ignimbrite sheets outcrop along more than 400 km of the western margin of the southern portion of the new england orogen farther east the coeval sedimentary facies are volcanogenic shallow marine and turbidite deposits the volcanic source terrain no longer exposed was located to the west of the existing conglomerate ignimbrite sequences and was underlain by continental crust which is in part represented by the northern lachlan fold belt the regional late carboniferous palaeogeography was similar to that of the present day western continental margin of south america the geology of the oceanward flank of the andean arc in northern chile and a section of the late carboniferous continental sequence near currabubula are comparable in detail the andean stratovolcanoes and ignimbrite centres thus provide the means of reconstruction of the late carboniferous volcanic source terrain the geological record of both of these continental margin volcanic arcs preserved in deposits of the arc flanks is shaped by volcanism especially the eruption of voluminous ignimbrites and by uplift deformation and glaciation centered on the arc for the arc sections considered diversity in the flank sequences arises because these controls vary in importance spatially and during the life of the arc 20 30 ma for the entire andean arc arc parallel variations in the sites of active volcanism and its character appear to be related to differences in the continental crust thickness and the circumstances of subduction of oceanic crust particularly the dip of the benioff zone by analogy variation in the age duration and style of volcanic activity along the late palaeozoic magmatic arc of the western new england orogen perhaps reflects the former existence of significant differences in crust thickness and in the angle of subduction

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

the cone penetration test in sands part ii general inference of state the state parameter concept provides a new method of characterizing sand behaviour but the utility of the concept relies on the ability to measure the state parameter in situ part i of this paper demonstrated a relationship between normalized cone resistance and state parameter for monterey sand in this paper the state parameter approach is applied to data from calibration chamber tests on several sands it is shown that this approach leads to a common relationship for all the data that includes the effects of material type quantified by the slope of the steady state line the state parameter for a sand can therefore be determined in situ with a reasonable precision using a general framework of interpretation which applies to all uncemented sands la notion de parametre d etat fournit une nouvelle methode pour caracteriser le comportement des sables mais son utilite depend de la possibilite de mesurer le parametre d etat in situ la premiere partie de cet article demontre une relation entre la resist

seismic imaging of late palaeozoic early mesozoic extensional and contractional structures in the bowen and surat basins eastern australia abstract the bowen and surat basins in eastern australia form part of a sedimentary basin system that was initiated in the latest carboniferous or earliest permian the basin system developed in a back arc plate tectonic setting and has had a complex evolutionary history with early phases of normal and oblique extension being followed by later phases of contraction and transpression the geometries of the phases are best observed in selected industry seismic data and in long regional bmr deep seismic reflection profiles recorded across the basins in 1984 and 1989 the denison trough along the western margin of the bowen basin was initiated as a series of extensional half grabens bounded by north to north northwest striking faults the polarity of the half grabens are relatively consistent along strike with the bounding faults being mainly on the western side of the haif grabens farther east the taroom trough is the main depositional centre in and around seismic line bmr 84 14 the taroom trough also displays a half graben geometry but only a very limited amount of horizontal extension 3 3 km maximum can be accommodated on the steep bounding fault at its eastern margin this trough developed by oblique extension with the bounding fault having a significant strike slip component reactivation of the bounding faults in the denison trough in the late permian to middle triassic led to tectonic inversion and the development of contractional structures at the same time to the east of the denison trough in the central bowen basin major shortening was accommodated by thin skinned thrusting on a series of listric thrust faults that dip to the east these thrusts root in a major east dipping detachment that appears to flatten in the middle crust in and around seismic line bmr 84 14 the zone of deformation is extremely localised confined to near the basin bounding faults and the structures are interpreted to result from transpression resulting from reactivation of the strike slip faults thus seismic data from the bowen and surat basins provide excellent images of early normal and oblique extensional structures and also of the later contractional structures in the denison trough and central bowen basin and the transpressional structures associated with the major bounding faults in the east

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

high resolution late glacial chronology for the gerzensee lake record switzerland δ18o correlation between a gerzensee stack and ngrip oxygen isotope variations were analyzed on bulk samples of shallow water lake marl from gerzensee switzerland in order to evaluate major and minor climatic oscillations during the late glacial to highlight the overall signature of the gerzensee 18o record 18o records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances then the records were stacked with a weighting depending on the differing sampling resolution to develop a precise chronology the 18o stack was then correlated with the ngrip 18o record applying a monte carlo simulation relying on the assumption that the shifts in 18o were climate driven and synchronous in both archives the established chronology on the gicc05 time scale is the basis for 1 comparing the 18o changes recorded in gerzensee with observed climatic and environmental fluctuations over the whole north atlantic region and 2 comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the bolling allerod period the 18o record of gerzensee is characterized by two major isotope shifts at the onset and at the termination of the bolling allerod warm period as well as four intervening negative shifts labeled gi 1e2 d c2 and b which show a shift of one third to one fourth of the major 18o shifts at the beginning and end of the bolling allerod despite some inconsistency in terminology these oscillations can be observed in various climatic proxies over wide regions in the north atlantic region especially in reconstructed colder temperatures and they seem to be caused by hemispheric climatic variations

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

holocene climatic variations in the western cordillera of colombia a multiproxy high resolution record unravels the dual influence of enso and itcz abstract the paramo de frontino 3460 m elevation in colombia is located approximately halfway between the pacific and atlantic oceans it contains a 17 kyr long stratigraphically continuous sedimentary sequence dated by 30 ams 14c ages our study covers the last 11 500 cal yr and focuses on the biotic pollen and abiotic microfluorescence x or xrf components of this high mountain ecosystem the pollen record provides a proxy for temperature and humidity with a resolution of 20 35 yr and xrf of ti and fe is a proxy for rainfall with a sub annual ca 6 month resolution temperature and humidity display rapid and significant changes over the holocene the rapid transition from a cold mean annual temperature mat 3 5 c lower than today and wet younger dryas to a warm and dry early holocene is dated at 11 410 cal yr bp during the holocene mat varied from ca 2 5 c below to 3 5 above present day temperature warm periods 11 410 10 700 9700 6900 4000 2400 cal yr bp were separated by colder intervals the last 2 4 kyr of the record is affected by human impact the holocene remained dry until 7500 cal yr bp then precipitations increased to reach a maximum between 5000 and 4500 cal yr bp a rapid decrease occurred until 3500 cal yr bp and the late holocene was dry spectral analysis of xrf data show rainfall cyclicity at millennial scale throughout the holocene and at centennial down to enso scale in more specific time intervals the highest rainfall intervals correlate with the highest activity of enso variability in solar output is possibly the main cause for this millennial to decadal cyclicity we interpret enso and itcz as the main climate change driving mechanisms in frontino comparison with high resolution xrf data from the caribbean cariaco basin a proxy for rainfall in the coastal venezuelian cordilleras demonstrates that climate in frontino was pacific driven enso dominated during the yd and early holocene whereas it was atlantic driven in cariaco itcz dominated from ca 8000 cal yr bp climate in both areas was under the dual influence of enso and itcz thereby showing existing teleconnections between the tropical pacific and atlantic oceans the frontino record is to date the highest resolution holocene study in nw colombia an implication of these results is that new records should be analyzed with multiproxy tools in particular those providing high resolution time series such as xrf

transferring radiometric dating of the last interglacial sea level high stand to marine and ice core records in order to derive a radiometric age marker for the end of the penultimate glacial interglacial transition we compiled published u series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial and computed the corresponding open system ages using thompson et al model thompson w g spiegelman m w goldstein s l speed r c an open system model for u series age determinations of fossil corals earth planet sci lett 210 2003 365 381 we obtain a global mean age of 126 calendar kyr bp ka 1 7kyr 2 for the beginning of the last interglacial sea level high stand after showing that the phase relationships observed between changes in sea level north atlantic benthic and planktonic foraminifera oxygen isotopic records and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation we derive an age of 131 2ka 2kyr 2 for the abrupt increase in atmospheric ch4 and north atlantic surface temperature marking the end of the penultimate glacial interglacial transition this age is consistent with u th dates of the penultimate glacial interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with north atlantic temperature records over the last deglaciation finally we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from termination ii to termination i implying that northern hemisphere summer insolation alone cannot explain the timing of terminations

the holocene younger dryas transition recorded at summit greenland analysis of ice from dye 3 greenland has demonstrated that the transition between the younger dryas and holocene climate periods occurred over a 40 year period a near annually resolved multiparameter record of the transition recorded in the gisp2 core from summit greenland shows that most of the transition occurred in a series of steps with durations of about 5 years some climate proxies associated with mid latitude sources appear to have changed about 15 years before climate proxies associated with more northern regions changes in atmospheric water vapor are likely to have played a large role in the climate transition

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

deglaciation of a major palaeo ice stream in disko trough west greenland recent work has confirmed that grounded ice reached the shelf break in central west greenland during the last glacial maximum lgm here we use a combination of marine sediment core data including glacimarine lithofacies and ird proxy records and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the greenland ice sheet gris across the shelf retreat of this outlet which contained the ancestral jakobshavns isbrae ice stream from the outer shelf in disko trough was rapid and progressed predominantly through iceberg calving however minor pauses in retreat tens of years occurred on the middle shelf at a trough narrowing forming subtle grounding zone wedges by 12 1 cal kyr bp ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf where it was pinned and stabilised for at least 100 years during this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice mass loss fine grained sediments muds were deposited alternately with ird rich sediments diamictons forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles high influxes of subglacial meltwater emanating from the nearby ice margins deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons this is the first example of this glacimarine lithofacies from a continental shelf setting and we suggest that the calving bay configuration of the ice margin plus the switching between calving and melting as ablation mechanisms facilitated its deposition by channelling meltwater and icebergs through the inner trough the occurrence of a major stillstand on the inner shelf in disko trough demonstrates that the ice dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the gris during retreat

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

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

episodic behavior of gondwanide deformation in eastern australia insights from the gympie terrane the mechanisms that drove permian triassic orogenesis in australia and throughout the cordilleran type gondwanan margin is a subject of debate here we present field based results on the structural evolution of the gympie terrane eastern australia with the aim of evaluating its possible role in triggering widespread orogenesis we document several deformation events d d in the gympie terrane and show that the earliest deformation d occurred only during the final pulse of orogenesis 235 230 ma within the broader gondwanide orogeny in addition we found no evidence for a crustal suture suggesting that terrane accretion was not the main mechanism behind deformation rather the similar spatiotemporal evolution of permian triassic orogenic belts in australia antarctica south africa and south america suggest that the gondwanide orogeny was more likely linked to large scale tectonic processes such as plate reorganization in the context of previous work our results highlight a number of spatial and temporal variations in pulses of deformation in eastern australia suggesting that shorter cycles of deformation occurred at a regional scale within the broader episode of the gondwanide orogeny similarly to the cenozoic evolution of the central and southern andes we suggest that plate coupling and orogenic cycles in the late paleozoic to early mesozoic gondwanide orogeny have resulted from the superposition of mechanisms acting at a range of scales perhaps contributing to the observed variations in the intensity timing and duration of deformation phases within the orogenic belt

geochronology of betula extensions in pollen diagrams of alpine late glacial lake deposits a case study of the late glacial deposits of the gasserplatz soil archives vorarlberg austria pollen diagrams of alpine late glacial calcareous lake deposits show several extensions of betula the geochronology of these extensions cannot be based on radiocarbon dating due to reservoir effects of such lakes on the radiocarbon ages a robust geochronology can be based on the oxygen isotope stratigraphy additionally recognition of 12 920 calbp lst in the sediment cores provides a secure time marker the combined results of pollen macro remains and stable isotope analyses of the gasserplatz cores point to a correlation of the betula extensions with the oscillations in the oxygen isotope curve and are related to global climatic oscillations this is sustained by the correlation of the gasserplatz isotope oscillations with the oscillations as registered in the greenland ice cores comparison of the results of the gasserplatz cores with the results of similar alpine lake deposits makes clear that the fluctuations in the betula curve are not a local but a regional phenomenon

tree rings and ice cores reveal c 14 calibration uncertainties during the younger dryas the younger dryas interval during the last glacial termination was an abrupt return to glacial like conditions punctuating the transition to a warmer interglacial climate despite recent advances in the layer counting of ice core records of the termination the timing and length of the younger dryas remain controversial also a steep rise in the concentration of atmospheric radiocarbon at the onset of the interval recorded primarily in the cariaco basin has been difficult to reconcile with simulations of the younger dryas carbon cycle here we discuss a radiocarbon chronology from a tree ring record covering the late glacial period that has not been absolutely dated we correlate the chronology to ice core timescales using the common cosmic production signal in tree ring 14c and ice core 10be concentrations the results of this correlation suggest that the cariaco record may be biased by changes in the concentration of radiocarbon in the upper ocean during the early phase of the younger dryas climate reversal in the cariaco basin this bias in the marine record may also affect the accuracy of a widely used radiocarbon calibration curve over this interval our tree ring based radiocarbon record is easily reconciled with simulated production rates and carbon cycle changes associated with reduced ocean ventilation during the younger dryas attaching a floating tree ring chronology to ice core records that cover the abrupt younger dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly the chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean which may affect the accuracy of a popular radiocarbon calibration program during this interval

holocene climatic changes in greenland different deuterium excess signals at greenland ice core project grip and northgrip 1 water stable isotope measurements d and 18o have been conducted on the holocene part of two deep greenland ice cores greenland ice core project grip and northgrip located 320 km apart these combined measurements provide the first two continuous greenland holocene deuterium excess profiles d d 8 18o a parameter strongly influenced by changes in moisture sources we discuss here temporal and regional fluctuations of the deuterium excess within central to north greenland with a mean temporal resolution of 4 years although grip and northgrip exhibit similar annual mean surface temperatures and 18o levels a significant offset of modern deuterium excess is observed between the two sites we attribute this offset to a different mix of modern moisture sources pointing to regional scale differences in moisture advection toward greenland the common long term deuterium excess holocene increasing trend is probably related to the increased relative contribution of low latitude moisture to greenland snowfall in response to the change in the earth obliquity as symmetrically observed in antarctica three abrupt declines punctuate the grip excess record 8 2 4 5 and 0 35 ka bp suggesting associated reorganizations of the northern high latitudes hydrological cycle the 8 2 ka bp event is characterized by 1 a rapid cooling followed by a progressive warming and 2 a deuterium excess cooling restricted to grip therefore totally different from rapid events during glacial times by contrast the northgrip deuterium excess record is more stable we propose that a slightly larger proportion of moisture supplied by local storm tracks to grip induces an isotopic compensation mechanism between simultaneous site and source temperature coolings resulting in a rather temperature insensitive 18o profile together with well marked deuterium excess amplitudes northgrip 18o seems less biased by isotopic processes and should provide a more reliable past temperature record

a multi proxy reconstruction of oceanographic conditions around the younger dryas holocene transition in placentia bay newfoundland abstract a marine sediment core from placentia bay off the south coast of newfoundland was studied to reconstruct past oceanographic conditions based on a multiproxy approach including diatoms benthic foraminifera grain size analysis ip25 x ray fluorescence calcium carbonate and total organic carbon content based on 6 radiocarbon dates the 513 5 cm long core spans the age interval from ca 13 to 10 cal kyrs bp and thus captures the transition from the younger dryas stadial into the holocene at sub decadal resolution the younger dryas was characterized by cold arctic water taxa of diatoms and benthic foraminifera and a stratified water column with high sea ice cover and low productivity due to strong influence of the labrador current during the second half of the younger dryas after ca 12 2 cal kyrs bp the influence of the labrador current gradually decreased and sea ice conditions became more variable the transition towards the holocene is characterized by a sequence of events starting with turnovers in the biogenic proxies followed by an abrupt retreat of sea ice and a rise in productivity these events are believed to be related to a northward migration of the gulf stream labrador current oceanic front the younger dryas termination is directly followed by a detrital carbonate layer associated with the final phase of the heinrich 0 event linked to laurentide ice sheet dynamics during the early holocene productivity remained high with minimal sea ice cover reduced stratification and stronger influence of warmer gulf stream derived waters

response of the lateglacial fauna to climatic change this study deals with faunal finds from the swiss paleolithic especially from the late glacial faunal assemblages from archeological sites as well as off site finds dated by scientific means are included in the middle of the oldest dryas the large glacial species mammoth rhinoceros cave bear musk ox become extinct during the early bolling the last arctic species disappear and are succeeded by animals like red deer and elk preferring a moderate climate from the middle of the allerod species typical of a denser forest roe deer and wild boar are very frequent