compressive and tensile failure of inclined well bores and determination of in situ stress and rock strength in this paper we investigate the occurrence of compressive and tensile failures of arbitrarily inclined well bores under a wide variety of stress conditions the principal assumptions in this analysis are that the rock is isotropic and that it deforms elastically to the point of failure as has been shown by previous investigators for a given stress state and well bore orientation it is straightforward to predict the orientation of the failures around the well bore as well as whether failure is likely to occur depending on such parameters as rock strength and borehole fluid pressure however as the stress state is almost never known in situ we demonstrate how observations of compressive and tensile wall failures in inclined holes can be used to constrain in situ stress orientations and magnitudes if there are independent data on the magnitude of the least principal stress from either leak off or microfrac tests and on the formation pore pressure we further demonstrate how once the stress state is determined it is possible to assess both an upper bound on the effective in situ rock strength and the degree to which increasing the borehole fluid pressure or mud weight can reduce the likelihood of borehole failure through application of this methodology to an inclined well bore in an area of complex faulting in the gulf of mexico we illustrate how it is possible to utilize observations of borehole failures to determine the magnitude and orientation of the stress tensor in areas such as offshore sedimentary basins where drilling inclined well bores is quite common

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

high resolution record of environmental changes and tephrochronological markers of the last glacial holocene transition at lake lautrey jura france this paper presents the results of a multiproxy investigation including volume magnetic susceptibility mineral and pollen analyses of late glacial sediments from lake lautrey jura france small scale lithological variations have been identified with high stratigraphic resolution in order to establish lithostratigraphic correlations between cores measurements combined with mineralogical analyses provide information on past sedimentary processes this combined approach reflects major changes in terrestrial habitats and soil processes which may relate to the climatic events characterising the late glacial climatic warming and cooling phases during warm intervals the record indicates increased lake productivity via carbonate precipitation and decreased input of detrital material in contrast cooler intervals show reduced lake productivity catchment area instability and increased detrital inputs several short interruptions in reforestation and in soil stabilisation can be identified and linked with abrupt colder events occurring through the bolling a general trend of warming is recorded from the coldest part of the younger dryas three tephra layers were also detected the mineral composition analyses show that the upper tephra layer corresponds to the laacher see eruption eifel germany while the lower ones may relate to the volcanic activity of the chaine des puys massif central france around 13 000 cal yr bp these two events recognised for the first time outside the massif central region may provide additional chronostratigraphic markers for the late glacial sedimentary records of the jura mountains and northern alps copyright 2004 john wiley sons ltd

late glacial climatic changes in eastern france lake lautrey from pollen lake levels and chironomids high temporal resolution analyses of pollen chironomid and lake level records from lake lautrey provide multi proxy quantitative estimates of climatic change during the late glacial period in eastern france past temperature and moisture parameters were estimated using modern analogues and plant functional types transfer function methods for three pollen records obtained from different localities within the paleolake basin the comparison of these methods shows that they provide generally similar climate signals with the exception of the bolling comparison of pollen and chironomid based temperature of the warmest month reconstructions generally agree except during the bolling major abrupt changes associated with the oldest dryas bolling allerod younger dryas and the younger dryas preboreal transitions were quantified as well as other minor fluctuations related to the cold events e g preboreal oscillation the temperature of the warmest month increased by not vert similar5 c at the start of bolling and by 1 5 3 c at the onset of the holocene while it fell by ca 3 to 4 c at the beginning of younger dryas the comparative analysis of the results based on the three lautrey cores have highlighted significant differences in the climate reconstructions related to the location of each core underlining the caution that is needed when studying single cores not taken from deepest part of lake basins

climatic controls on holocene lake level changes in europe sensitivity experiments with a simple water balance model were used to constrain the possible climatic causes of distinct holocene patterns of lake level variation in different regions of europe lakes in s sweden were low at 9 ka high around 6 5 ka low again around 4 ka and are high now lakes in estonia show similar but weaker trends lakes in s france were highest around 9 ka lowest around 4 ka intermediate now lakes in greece were also high around 9 ka but continued rising until 7 5 ka then fell gradually from 5 ka with a brief high phase around 3 ka and are low now the model was forced with insolation anomalies deduced from orbital variations temperature anomalies inferred from the pollen record and cloudiness anomalies derived from changes in the position of the subtropical anticyclone inferred from reconstructed changes in the equator to pole temperature gradient in order to evaluate the effects of resultant evaporation changes on catchment water balance the resulting simulated changes in runoff precipitation minus actual evapotranspiration were slight and frequently opposite to the observed trends larger changes in precipitation are plausible and are required to explain the data the required precipitation increase in n europe from 9 ka low to 6 ka high is suggested by gcm experiments to have been a consequence of interacting insolation and residual ice sheet effects on the atmospheric circulation over the north atlantic the explanation of other observed changes including the drying trend during the holocene in s europe has not been provided by gcm experiments to date explanations may lie in changes in mesoscale circulation sea surface temperature patterns and the coupling between these phenomena that may not follow orbital changes in any simple way

true triaxial loading apparatus and its application to coal outburst prediction two generations of true triaxial loading ttal apparatuses are presented first generation apparatuses were intended primarily for true stress state imitation in rock or mineral specimens advanced second generation installations are designed to provide precise measurements in any stress and simulation of rock outburst at sudden relief of one sample face both ttal apparatuses can apply pressure up to 250 mpa corresponding to earth depth about 10 000 m independently along each of three axes experimental results are given on effect of absorbed water on ultimate state in coal as well as adsorbed methane influence on simulated coal outbursts

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

diamictic sediments within high arctic lake sediment cores evidence for lake ice rafting along the lateral glacial margin sediment cores from six small lake basins in the canadian high arctic reveal a gravel rich 30 by weight to gravel poor 2 diamict facies underlying massive post glacial clayey silt ten other lakes contain a second diamict facies within what are interpreted to be glaciolacustrine sedimentary assemblages the sedimentology clast fabrics and fossil remains diatoms ostracodes and chironomid head capsules within both diamict facies suggest that these deposits are not tills clast fabrics yielded low s1 0 41 0 57 and high s3 0 09 0 22 eigenvalues placing them within the range of ice rafted diamictons and glacigenic sediment flows the high percentage of clast dip angles 45 15 61 random clast azimuth and lower diamict contacts conformable to underlying current bedded sediment favours an origin as a rain out or settling deposit samples of the matrix and scrapings of clasts from the diamicts revealed a diatom assemblage dominated by littoral and planktonic forms such as are found in the littoral regions of the lakes today this contrasts sharply with the assemblages within the overlying clayey silt in which benthic forms predominate clasts are thus interpreted to have been rafted from the littoral areas of the lake the process proposed to explain this is rafting by the lake ice cover in a glacial marginal environment early season meltwater impounded along the lateral margin of retreating cold based glaciers would buoyantly lift the lake ice cover and any adfrozen lake sediment higher lake levels and increased areal extent of seasonal freeze on between the lake ice cover and the lake bed would allow the redeposition of littoral sediments to the benthic regions through greater lateral shifting of the ice cover as it broke up incision by meltwater streams into the lateral glacial margins would later isolate the lake allowing seasonal warming of lake water enough to support the growth and maturation of the ostracode and chironomid species found as fossils within the diamicts

spatial and temporal variability of ice dammed lake sediments in alpine environments abstract the stratigraphic record of ice dammed lakes is the product of a combination of daily intraseasonal seasonal and interseasonal fluctuations in sediment input combined with periods of drawdown or drainage of the lake sedimentation may take place on an ice cored bed which produces deformation structures on melting and eventually results in limited preservation during and after deglaciation the sediments of the contemporary and older ice dammed lakes in the kaskawulsh and dusty glacier basins of the southwest yukon reflect a number of hydrological regimes and lake histories and also demonstrate the complexity of the sedimentary environment the kaskawulsh glacier lake evolved from being semi permanent at the start of deglaciation from the little ice age maximum to annually draining at present the dusty glacier lake was impounded by glacier surges and had a duration of only a few years after each surge a model of the effects of variations in sediment source contrasting hydrological regimes and geomorphological events on sediment accumulation illustrates how spatial and temporal variability is the predominant characteristic of the sediments

contrasting patterns of hydrological changes in europe in response to holocene climate cooling phases the quantitative reconstruction of climatic parameters from pollen and lake level data obtained at saint jorioz lake annecy eastern france gives evidence for cooler and wetter conditions during the 8 2 ka cold event a comparison of these regional data with other hydrological records reconstructed in europe for the same period suggests as a working hypothesis that mid latitudes between ca 50 and 43 underwent wetter conditions in response to the cooling whereas northern and southern europe were marked by drier climate in the latter case leading to an interruption of the sapropel 1 formation in the mediterranean a similar hydrological tri partition of europe can be observed during other holocene cooling phases associated with north atlantic ird events data indicate that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8 2 ka event the differences in expansion of the wet mid european zone depending on holocene climate cooling phases could reflect variations in the strength of the atlantic westerly jet in relation with the thermal gradient between high and low latitudes

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

constraining the full stress tensor from observations of drilling induced tensile fractures and leak off tests application to borehole stability and sand production on the norwegian margin abstract understanding the interaction between rock strength in situ stress and engineering practice allows one to minimize wellbore failures by designing optimally stable borehole trajectories and appropriate mud weights we utilize an interactive software system stress and failure of inclined boreholes sfib peska zoback 1996 to illustrate how observations of drilling induced compressive and tensile wellbore failures in vertical and inclined wellbores can be integrated with other routinely available information to yield an estimate of the full stress tensor we further illustrate how such information allows one to place bounds on in situ effective rock strength we consider a deviated well in the visund oil field on the flanks of the viking graben along the norwegian margin a good quality electrical imaging log revealed drilling induced tensile wall fractures in an orientation consistent with other observations of stress orientation in the region interpretation of these fractures indicates that the maximum horizontal stress is 72 6 5 mpa at an azimuth of 100 10 no breakouts were detectable in the well indicating that the uniaxial compressive rock strength is greater than approximately 19 mpa we demonstrate how we utilized this information to design an optimally stable wellbore trajectory to minimize sand production

climatic changes in areas adjacent to the north atlantic during the last glacial interglacial transition 14 9 ka bp a contribution to igcp 253 this paper presents a summary of the evidence for climatic changes during the last glacial interglacial transition 14 9 ka bp in land areas adjacent to the north atlantic it is a synthesis of the results of the 12 regional summaries compiled by contributors to the north atlantic seaboard programme of igcp 253 that are published separately in this issue of journal of quaternary science eighteen palaeotemperature curves are compared and arranged in three transects one from southern europe to spitsbergen a second from ireland to poland and the third from southern new england to the labrador baffin shelf area ten maps are presented that summarise the synoptic climatic conditions of the region in 500 year time periods the purpose of the exercise is to examine the extent to which any emerging patterns support the ruddiman and mclntyre model of large scale shifts in the position of the oceanic polar front during the last glacial interglacial transition some broad agreement emerges although the influence of oceanic changes is diminished in areas that lay in close proximity to the laurentide and fennoscandian ice sheets attention is drawn to limitations in the compilations and to the potential for improved models in the future

the present day state of tectonic stress in the darling basin australia implications for exploration and production knowledge of the full present day stress tensor and pore pressure has significant applications in the exploration and production of conventional and unconventional hydrocarbon reservoirs the darling basin of new south wales australia is an old sedimentary basin late cambrian silurian to early carboniferous in which there was limited information about the present day stress field prior to this study in this paper we evaluate the contemporary stress field of the darling basin using a dataset from recent exploration wells and perform a geomechanical risk assessment with respect to borehole stability fracture fault generation and reactivation our interpretations of borehole failures in borehole image logs reveal a prevailing east west orientation of the maximum horizontal stress throughout the darling basin the estimates of the magnitudes for the vertical minimum and maximum horizontal stress in the studied wells indicate a transition between thrust and strike slip faulting stress regime at 600 700 m depths where the magnitude of vertical stress and minimum horizontal stress are close to each other however the presence of borehole breakouts and drilling induced tensile fractures that we observe in the image logs at greater depths 900 2100 m indicate a transition into a strike slip tectonic stress regime below a depth range of approximately 700 900 m these findings are in agreement with overcoring stress measurements east and west of the investigated wells furthermore there are several neogene to recent geological structures in the study area that indicate thrust faulting with an east west oriented maximum horizontal stress orientation around this old sedimentary basin the consistency between the orientation of maximum horizontal stress determined from wellbore data and neotectonic structures is significant and implies that horizontal stress orientations derived from very recent geological features may be valuable inputs to geomechanical models in the absence of wellbore or other data however the recent surface geological structures suggest a thrust faulting stress regime that is in slight contrast to the transition between thrust and strike slip stress regime sh sh similar to sv indicated by petroleum data and highlights a potential pitfall of using neotectonic structures in geomechanical models in particular careful attention and verification should be made when using neotectonic structures for input calibration or confirmation of geomechanical models especially in intraplate tectonic settings such as australia c 2016 elsevier ltd all rights reserved

a high resolution late glacial and early holocene diatom record from baffin island eastern canadian arctic an interval of late glacial to early holocene sedimentation spanning the period 12 9 8 4 ka bp 14c dated by accelerator mass spectrometry is contained within 15 cm of gyttja in a core from a small lake on southwestern cumberland peninsula baffin island this sediment was subsampled in continuous 2 5 mm increments for diatom analysis extremely low sediment accumulation rates 1 8 cm ka 1 are characteristic of the initial phase of organic sedimentation but they increase rapidly to 14 2 cm ka 1 after 9 ka bp the first 0 5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments thereafter and throughout the late glacial and earliest holocene diatom floras were dominated by alkaliphilous and circumneutral species of fragilaria around 9 ka bp shifts to acidophilous floras dominated by brachysira brebissonii and later eunotia rhomboidea and frustulia rhomboides vars saxonica and crassinervia suggest a period of natural lake acidification high dia

climatic and limnological changes associated with the younger dryas in atlantic canada pollen diatom and chironomid fossils from the sediments of a core from brier island bog lake nova scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in atlantic canada correlative with the european younger dryas ca 10 to 11 ka our paleolimnological data were then compared to similar types of data from splan pond new brunswick to determine if there were any significant differences between a coastal and a more inland site nonarboreal pollen was dominant throughout the brier island core and the interval 10 0 11 0 ka did not show the typical decline in picea and increases in tundra like vegetation characteristic of many sites in atlantic canada however the limnological indicators did undergo marked changes in taxon composition the chironomid assemblage was initially dominated by shallow water warm adapted chironomid taxa followed by abundant sergentia a cold stenotherm during 10 11 ka sergentia disappeared in the post younger dryas interval and the warm adapted genera resumed dominance chironomid inferred paleotemperature reconstructions revealed that at both brier island bog lake and splan pond summer surface water temperatures dropped abruptly to between 13 and 17 c during the 10 11 ka interval suggesting that a cooler climate was present in atlantic canada correlative with the european younger dryas diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations

the impact of the north atlantic ocean on the younger dryas climate in northwestern and central europe the main results of multiproxy climate reconstructions for the younger dryas and experiments carried out with an atmospheric general circulation model are discussed quantitative temperature inferences for northwestern and central europe show that winter conditions were remarkably extreme with values of 20 30 c below that of today annual temperature ranges with a continental signature 30 34 c were reconstructed for the entire study area compared with today the greatest cooling was experienced in the seaboard area the comparison of the climate reconstructions and simulation experiments indicates that sea ice in the north atlantic ocean played a decisive role in the climate of the study area by cooling the surface air temperatures and by controlling the position of the storm track surface air circulation was westerly even during younger dryas winters a slight northward shift of the mean atlantic sea ice margin during winter may explain the proposed subdivision of the younger drays into a phase of maximum cold and humidity succeeded by a less cold and relatively dry phase 1998 john wiley sons ltd

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

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

stress orientation on the norwegian continental shelf derived from borehole failures observed in high resolution borehole imaging logs abstract knowledge of stress orientation is crucial for the understanding of many processes in the earth s crust such as tectonic development earthquake occurrence and fluid transport along faults in the case of the norwegian continental shelf which is a prolific area for hydrocarbon production this knowledge also plays an important role for engineering decisions with respect to wellbore stability and reservoir management therefore data on stress orientation have been collected extensively over the past few years in this region however nearly all data published for the norwegian continental shelf for depths less than 6 km are based on the evaluation of four arm caliper data a method with intrinsic limitations for greater depths stress orientation is derived from earthquake focal plane mechanisms this article presents stress orientation data derived from an extensive set of image logs throughout the norwegian continental shelf the analysis is based on the identification of compressive and tensile failures of the borehole wall in electrical and acoustic borehole imaging logs this method for the determination of the stress orientation is found to be highly reliable and capable of delivering detailed and accurate results and thus is far superior to the analysis of breakouts from four arm caliper logs the analysis of image logs shows that the stress orientation is consistent both regionally and with depth strong variations in stress orientation which are often interpreted from earlier analyses of four arm caliper data are not observed this may indicate that some of the earlier four arm caliper analyses may have been biased by the misinterpretation of drilling induced artefacts as stress induced breakouts stress induced failures of the borehole wall are observed in only about 40 of the wells analysed in this paper this does not support the conclusion that the horizontal stresses are isotropic it just indicates that the stress difference in combination with the borehole conditions downhole pressure and temperature was insufficient to induce these failures

bacterial tetraether membrane lipids in peat and coal testing the mbt cbt temperature proxy for climate reconstruction abstract peatlands are widespread and important natural archives of environmental change here we explore the potential of the recently introduced mbt cbt proxy methylation index and cyclisation ratio of branched tetraethers to estimate past annual mean air temperature mat based on the distribution of bacterially derived branched glycerol dialkyl glycerol tetraether gdgt membrane lipids in peat and coal to this end branched gdgts in an ombrotrophic peat bog from switzerland and three coal deposits of increasing maturity were analysed for the surface of the bog reconstructed annual mat is higher than both measured annual mat and measured in situ pore water temperature changes in the cbt ratio considered a proxy for ph with depth in the bog do not match with present day in situ pore water ph but coincide with a peat stratigraphic boundary this indicates that gdgts down the bog profile are predominantly fossil and not derived from extant biomass the mbt cbt derived annual mat record also shows a large drop at this stratigraphic boundary which likely relates to past change in trophic status of the bog branched gdgts are abundant in an immature lignite vitrinite reflectance r o 0 25 but occur in low amount in a slightly more mature coal r o 0 32 annual mat could be reconstructed for the lignite alone and is higher than other proxy based estimates from approximately the same time and location our results indicate potential for the application of the mbt cbt proxy in peat and immature coals but improved constraints on the effects of different types of peat on branched gdgt distributions as well as improved calibration of mat estimates are needed before the method can be confidently applied

two terrestrial records of rapid climatic change during the glacial holocene transition 14 000 9 000 calendar years b p from europe two independent multidisciplinary studies of climatic change during the glacial holocene transition ca 14 000 9 000 calendar yr b p from norway and switzerland have assessed organism responses to the rapid climatic changes and made quantitative temperature reconstructions with modern calibration data sets transfer functions chronology at krakenes western norway was derived from calibration of a high resolution series of 14c dates chronologies at gerzensee and leysin switzerland were derived by comparison of 18o in lake carbonates with the 18o record from the greenland ice core project both studies demonstrate the sensitivity of terrestrial and aquatic organisms to rapid temperature changes and their value for quantitative reconstruction of the magnitudes and rates of the climatic changes the rates in these two terrestrial records are comparable to those in greenland ice cores but the actual temperatures inferred apply to the terrestrial environments of the two regions

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

late glacial climatic oscillations as recorded in swiss lake sediments regional pollen assemblage zones for the late glacial period of the swiss plateau are introduced and defined they include four major zones artemisia juniperus hippophae betula pinus paz with several subzones pollen and oxygen isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000 9500 yr bp the first oscillation termed the aegelsee fluctuation occurs shortly before 12 000 yr bp and varve counts suggest its duration was ca 100 yr it is characterised by a short decrease in the oxygen isotopes as well as a short increase in nap associated with a depression in birch pollen values the second oscillation which occurs in the 18o record shortly before the deposition of the laacher see tephra ca 11 000 yr bp is termed the gerzensee fluctuation it occurs during a pine dominated phase and its vegetational effects cannot be determined palynologically the most prominent regressive phase is the younger dryas biozone ca 10 700 10 000 yr bp characterised by an increase in heliophilous nap and low 18o values the younger dryas biozone can often be subdivided palynologically into two parts a first part rich in grasses and juniper and a second part with higher filipendula and birch values during the preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios comparison of the swiss oxygen isotope profiles with the greenland dye 3 record suggests that not only the three major shifts in the 18o curves but also the minor ones are closely comparable suggesting some common climatic control

glaciomarine sedimentation in disraeli fiord high arctic canada abstract disraeli fiord represents a glaciomarine environment unique to the north coast of ellesmere island featuring floating glacier tongues multi year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by ward hunt ice shelf it is a very low energy depositional environment even at sites proximal to glaciers sediment enters the fiord by interflow and is deposited through suspension settling ice rafting is precluded by the year round sea ice cover sedimentation rates in the inner fiord since about 7000 yrs b p are estimated to be 5 10 cm ka a reflection of the limited sediment influx from the cold based glaciers which contact the fiord changes in sediment structure through the holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation all of which relate to regional climate during deglaciation early holocene sedimentation rates were orders of magnitude greater than at present subglacial meltwater was the dominant source of inflow with sediment transported in turbid plumes as over or interflow and deposited through suspension settling this is supportive of other studies indicating that a pronounced climatic amelioration led to warm based glaciers at this time

land ice teleconnections of cold climatic periods during the last glacial interglacial transition independent calendar year chronologies are a basic requirement for the establishment of high resolution land ice teleconnections the annually laminated meerfelder maar record provides both an independent chronology established by varve counting and high resolution lithological proxy data for the period of the last glacial interglacial transition these data reveal a series of four periods of climatic deterioration coinciding with negative isotopic deviations in the grip record signal thus demonstrating the synchronicity of environment changes in western germany and temperature shifts in greenland the terrestrial data supports a further sub division of the event stratigraphy based on the grip core by introducing the cold event gi 1c2 between 13 500 and 13 400 calendar years bp multiproxy analyses reveal that the environmental response at meerfelder maar was not linear throughout the lateglacial but was modified by local processes a change in the response of the lake environment to climate deterioration was observed during sub stage gi 1b gerzensee oscillation the only event with gradual rather than abrupt transitions the two fold character of the younger dryas as seen in the grip record is more pronounced in the meerfelder maar record this lithological signal occurred with a delay of 60 years to the grip signal and has been linked to a shift in the catchment it is proposed that the trigger for this shift was a trend towards a more humid second half of the younger dryas

cosmogenic 10be and 26al ages for the last glacial maximum eastern baffin island arctic canada a chronology for the last glacial maximum based on cosmogenic exposure dating in the pangnirtung fjord area eastern baffin island arctic canada is at odds with many decades of land based glacial stratigraphic research most previous chronologies focused primarily on relative weathering criteria and suggested that ice extent was restricted during the late wisconsinan ca 24 8 ka in contrast by directly dating glacial features we conclude that late wisconsinan ice was far more extensive than previously believed there are 36 gneissic boulders and 8 samples of ice molded gneissic bedrock that yield late wisconsinan 10 be and 26 al exposure ages for the last glaciation of pangnirtung fjord the prominent duval moraines which were previously interpreted to represent a significant early wisconsinan 100 60 ka ice advance on southern cumberland peninsula were actually deposited between 24 and 9 ka two boulders from a raised glaciomarine delta stratigraphically related to the duval moraines date to about 10 ka two recessional moraines and striated bedrock along pangnirtung fjord as well as erratics on the floor of the kolik river valley a tributary to pangnirtung fjord indicate that deglaciation began between 12 and 9 ka in situ produced 10 be and 26 al abundances indicate that ice filled pangnirtung fjord for about 15 k y either continuously or intermittently prior to 10 ka which is compatible with 14 c chronologies for adjacent cumberland sound thus our data support other recent studies that suggest the northern and southern margins of the laurentide ice sheet were generally in phase during the latest wisconsinan contrary to earlier interpretations

catchment and lake controls over the formation of varves in monomictic nicolay lake cornwall island nunavut on the basis of thin section sedimentology 137cs and 210pb profiles and the pronounced seasonality of runoff and sediment delivery sediments from nicolay lake cornwall island nunavut 77 46 n

reconstruction and paleoclimatic interpretation of holocene lake level changes in lac de saint leger haute provence southeast france abstract lac de saint leger is located in the transitional region between central europe and the mediterranean the reconstruction of the past lake level changes was based on plant macrofossil and mollusc analyses of two stratigraphic transects correlated by pollen analysis past changes in lake level were quantitatively reconstructed from changes in the recorded level of overgrowth in the beginning of the holocene the lake level was high however a progressive lowering occurred from about 7500 b p between about 4500 b p and 4000 b p there was a moderate rise in lake level subsequently the lowering was continued and culminated between about 3300 b p and 2500 b p from the reconstruction there then occurred a progressive rise in lake level until the present the lake level changes recorded in lac de saint leger are compared with a compilation of lake level data from southern france the major long term changes can be supposed to be regionally significant and related to climatic changes to obtain a basis for paleoclimatic interpretation of the changes in lake level the reference pollen diagram from lac de saint leger was used for a quantitative reconstruction of paleoclimate during the middle and later part of the holocene there is a reasonable consistency between the recorded pattern of lake level changes and the paleoclimatic reconstruction during the earlier part of the holocene there are some disagreements which may be explained by the shortage in adequate modern pollen analogues the paleoclimatic reconstruction indicates that the major changes in lake level were mostly related to changes in precipitation

the climate of europe 6000 years ago palaeoclimates across europe for 6000 y bp were estimated from pollen data using the modern pollen analogue technique constrained with lake level data the constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration p e is consistent with the regional change in moisture balance as indicated by lakes an artificial neural network was used for the spatial interpolation of lake level changes to the pollen sites and for mapping palaeoclimate anomalies the climate variables reconstructed were mean temperature of the coldest month tc growing degree days above 5 c gdd moisture availability expressed as the ratio of actual to equilibrium evapotranspiration and p e the constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies especially for p e the reconstructions indicate clear spatial and seasonal patterns of holocene climate change which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations winter temperatures tc were 1 3 k greater than present in the far n and ne of europe but 2 4 k less than present in the mediterranean region summer warmth gdd was greater than present in nw europe by 400 800 k day at the highest elevations and in the alps but 400 k day less than present at lower elevations in s europe p e was 50 250 mm less than present in nw europe and the alps but was 10 15 greater than present in s europe and p e was 50 200 mm greater than present in s and e europe

reconstruction of climate and vegetation changes of lake bayanchagan inner mongolia holocene variability of the east asian monsoon a high resolution pollen and pediastrum record spanning 12 500 yr is presented for lake bayanchagan 115 21 e 41 65 n and 1355 m a s l southern inner mongolia individual pollen taxa pt mat and the pft affinity scores pft mat were used for quantitative climatic reconstruction from pollen and algal data both techniques indicate that a cold and dry climate similar to that of today prevailed before 10 500 cal yr b p the wettest climate occurred between 10 500 and 6500 cal yr b p at which time annual precipitation was up to 30 60 higher than today the early holocene increases in temperature and precipitation occurred simultaneously but mid holocene cooling started at approximately 8000 cal yr b p 1500 yr earlier than the drying vegetation reconstruction was based on the objective assignment of pollen taxa to the plant functional type the results suggest that this region was dominated by steppe vegetation throughout the holocene except for the period 9200 to 6700 cal yr b p when forest patches were relatively common inner mongolia is situated at the limit of the present east asian monsoon and patterns of vegetation and climate changes in that region during the holocene probably reflect fluctuations in the monsoon s response to solar insolation variations the early to middle holocene monsoon undoubtedly extended to more northern latitudes than at present

termination of the last glaciation in the iberian peninsula inferred from the pollen sequence of quintanar de la sierra abstract a 4 5 m thick late glacial pollen sequence supported by 17 ams14c dates has been investigated at the quintanar de la sierra marshland iberian cordillera north central spain pollen zones were defined that correspond to successive phases in vegetation history during the end of the late wurm late glacial interstade and younger dryas periods a transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data a first expansion ofjuniperusandhippophae about 13 50014c yr b p indicates the beginning of the late glacial interstade which is characterized by ajuniperus betula pinussuccession that suggests higher temperatures and moisture than during full glacial time the younger dryas interval is recorded by a 120 cm thick sediment unit that is dominated by herbaceous pollen transfer function estimates suggest that the climate during this period was cold with low precipitation during most of the year although not in summer the holocene arboreal recolonization in the area started about 10 00014c yr b p with a renewedjuniperus betula pinussuccession related to a strong increase in annual temperature and precipitation the start of this process was synchronous with mean sea surface temperature changes as recorded from the nearby su 81 18 marine core the strong affinity with other european late glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial interglacial transition was similar in both northwestern and southwestern europe

holocene cirque glacier activity in western spitsbergen svalbard sediment records from proglacial linnevatnet holocene glacial variations of a presently ice free cirque in western spitsbergen are inferred from sediment records from the proglacial lake linnevatnet glaciation is indicated in the core records by increased intensity of laminae derived from the cirque inflow and by increase in sediment accumulation rate radiocarbon ages on terrestrial plant macrofossils limit the onset of glaciation in the cirque to within the last six centuries no evidence for earlier glaciation is recognized in the core records indicating that the threshold for glaciation in the cirque was not reached during prior neoglacial advances local climate events favouring glacier expan sion were either of greater magnitude or of longer duration during the little ice age than at any other time during the holocene

holocene glacier fluctuations waskey lake northeastern ahklun mountains southwestern alaska lake sediments from waskey lake ahklun mountains southwestern alaska were studied to decipher the history of upvalley glacier e uctuations during the holocene several indicators of glacier activity were measured including magnetic susceptibility organic matter content grain size distribution bulk sediment mineralogy and diatom assemblages seven radiocarbon ages on macrofossils along with cross checks by tephrochronology provide the chronology of the cores the results from core wl 1 indicate that glaciers lingered near waskey lake until 9100 cal yr bp perhaps under conditions of high winter accumulation peak organic matter content occurs at 7400 cal yr bp when precipitation might have shifted to summer the onset of neoglaciation occurred 3100 cal yr bp and glaciers reached their maximum extent 700 cal yr bp this chronology is consistent with the lichenometrically dated moraines from the glacier foree elds although the ages are tentative the youngest and most widespread group of moraines was deposited sometime between 650 and 200 cal yr bp during the little ice age since then glaciers in the waskey lake area have shrunk by 50 and equilibrium line altitudes ela have risen by 35 6 22 m this rise in ela is much less than the 100 to 200 m rise observed elsewhere in alaska and indicates considerable spatial variability in late holocene climatic change

constraining the stress tensor in the visund field norwegian north sea application to wellbore stability and sand production abstract in this study we examine drilling induced tensile wellbore failures in five exploration wells in the visund oil field in the northern north sea we use observations of drilling induced wellbore failures as well as density pore pressure and leak off test measurements to estimate the magnitudes and orientations of all three principal stresses each well yields a very consistent azimuth of the maximum horizontal stress 100 10 both with depth and laterally across the field stress orientations are constrained at depths as shallow as 2500 m and as deep as 5300 m in these wells we show that the magnitudes of the three principal stresses s v s hmin and s hmax are also consistent with depth and reflect a strike slip to reverse faulting stress regime the magnitude of the maximum horizontal stress is shown to be significantly higher than the vertical and minimum horizontal stresses e g s v 55 mpa s hmin 53 mpa and s hmax 71 5 mpa at 2 8 km depth data from earthquake focal plane mechanisms lindholm et al 1995 proceedings of the workshop on rock stresses in the north sea trondheim norway 1 show similar stress orientations and relative magnitudes and thus indicate a stress field that is relatively consistent throughout the thickness of the brittle crust we illustrate how knowledge of the full stress tensor allows one to place bounds on in situ rock strength and determine optimally stable trajectories for wellbore stability and sand production during drilling after the completion of drilling and as pore pressure is reduced during oil and gas production

the climate in western europe during the last glacial interglacial cycle derived from pollen and insect remains using the pollen sequence of la grande pile xx france we review problems with the application of transfer functions in paleoclimatic reconstructions one of them is to find modern analogues for the herbaceous vegetation of the cold periods we propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods another method to solve these problems is based on constraining by insect remains the two methods provide coherent reconstructions the results are also compared with other paleodata there is a good correlation with the six cold heinrich events between 70 and 15 ka b p a cooling event during the eemian period marked by high percentages of taxas at about 125 ka b p needs still to be correlated with high resolution ocean and ice cores

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

the cold event 8200 years ago documented in oxygen isotope records of precipitation in europe and greenland stable oxygen isotope ratios of ostracod valves in late glacial and holocene sediments of core as 92 5 from deep lake ammersee southern germany reflect variations of mean oxygen isotope ratios in past atmospheric precipitation the record reconfirms the strong similarity of climate evolution in europe and greenland during the last deglaciation for the first time in europe we find a 200 year long negative 18o excursion which is contemporaneous with the strongest negative 18o excursion in the greenland ice around 8 2 ky before present the 8 2 ky isotopic event on both sides of the north atlantic ocean is interpreted as a cold period most probably induced by a perturbation of the north atlantic thermohaline circulation we discuss two possible triggering mechanisms 1 weak forcing as proposed by alley et al and 2 forcing by a strong and sudden freshwater pulse from the collapse of the hudson ice dome

mean july temperatures during the younger dryas in northwestern and central europe as inferred from climate indicator plant species abstract we estimated minimum mean july temperatures in northwestern and central europe during the younger dryas 10 950 10 15014c yr b p from distributions of climate indicator plant species which were reconstructed from 140 pollen and plant macrofossil diagrams paleobotanical records mainly from the central and eastern part of the study area show that the coldest conditions occurred early in the younger dryas before 10 55014c yr b p for this phase mean july temperatures at sea level of around 10 c are suggested for the northern part of the british isles and for ice free scandinavia we estimated a mean july temperature of 12 c for central england the netherlands and northern germany the 13 c mean july isotherm largely based on the modern distribution oftypha latifolia was most probably located in southern england belgium central germany and poland the reappearance of thermophilous elements in the records after 10 55014c yr b p suggests a summer warming at least temporarily of 1 to 2 c in the study area the reconstructed temperatures are comparable with temperature estimates based on beetle data however they appear rather high when compared with estimates based on glaciological evidence

holocene temperature variations at a high altitude site in the eastern alps a chironomid record from schwarzsee ob solden austria few well dated quantitative holocene temperature reconstructions exist from high altitude sites in the central eastern alps here we present a chironomid based quantitative reconstruction of mean july air temperatures tjuly throughout the holocene for a remote high mountain lake schwarzsee ob solden situated above the treeline at 2796 m a s l in the austrian alps applying a chironomid temperature inference model developed from lakes of the alpine region to a high resolution chironomid record from the lake provides evidence for early holocene ca 10000 8600 cal yr bp tjuly of up to 8 5 c i e 4 c above the modern 1977 2006 mean july temperature the reconstruction reveals the so called 8 2 ka cold event centered at ca 8250 8000 cal yr bp with temperatures ca 3 c below the early holocene thermal maximum rather warm ca 6 c and productive conditions prevailed during ca 7900 4500 cal yr bp the chironomid record suggests a climate transition between ca 5200 and 4500 cal yr bp to cooler tjuly a distinct cooling trend is evident from ca 4500 until ca 2500 cal yr bp thereafter the study site experienced its coldest conditions around 4 c or less throughout the rest of the holocene with the exception of the warming trend during the late 20th century beside other factors the northern hemisphere summer insolation seems to be the major driving force for the long term trends in tjuly at high altitudes in the eastern alps due to the extreme location of the lake and the limited temperature range represented by the applied calibration data set the chironomid based temperature reconstruction fails to track phases of the late holocene climatic history with tjuly cooler than 4 c further chironomid based palaeoclimate model and down core studies are required to address this problem provide more realistic tjuly estimates from undisturbed high altitude lakes in the alps and extract a reliable regional temperature signal

holocene sedimentation in glacial tasikutaaq lake baffin island tasikutaaq lake on cumberland peninsula baffin island receives inflow and fine sediment from a 448 km2 drainage basin 21 of which is glacier covered during the summer of 1983 the lake remained essentially isothermal between about 4 and 6 c the suspended sediment concentration of inflow never exceeded 100 mg l 1 with overflow and homopycnal flow dominant surface sediments are clearly laminated although varves are not apparent the sediments are very fine with less than 3 sand in all but the most proximal sites average sedimentation rates between 1976 and 1983 ranged from about 4 mm a 1 to 0 25 mm a 1 down lake from the point of inflow the absence of varves is a function of the low rates of sediment accumulation and the long residence time of the fine sediments in the water column three sediment cores up to 135 cm in length reveal marked changes in sediment characteristics and diatom assemblages through the holocene during the late foxe glaciation it is likely that glacier ice contacted the la

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

diatom shifts as evidence for recent subarctic warming in a remote tundra lake nwt canada abstract changes in diatom assemblage composition were examined from the sediments of slipper lake an isolated tundra lake located 50 km north of current treeline in canada s northwest territories diatom shifts over the last ca 5600 years were related to the response of this ecosystem to climatic and environmental change during the late holocene with particular emphasis on the last few hundred years to date a detailed diatom analysis for this recent time frame has not been undertaken for the central canadian subarctic the first ca 5400 years of the sediment record was marked by modest shifts between benthic alkaliphilous diatom taxa e g fragilaria achnanthes and navicula species and heavily silicified tychoplanktonic aulacoseira species in the 19th century abrupt changes were delineated by a marked shift to a diatom assemblage characteristic of more planktonic habitats consisting of the cyclotella stelligera complex c stelligera c pseudostelligera which was absent in earlier sediments several possible mechanisms for these recent changes are examined including atmospheric deposition of acidifying compounds and anthropogenically derived nutrient enrichment however we conclude that climatically induced limnological changes associated with shorter duration of ice cover and a longer growing season can best explain the direction and magnitude of changes in our diatom record

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

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

glacial history and landscape evolution of southern cumberland peninsula baffin island canada constrained by cosmogenic 10be and 26al since the first application of cosmogenic nuclides to the study of glacial history and processes in 1990 increasing numbers of studies have used a variety of cosmogenic isotopes to quantify the exposure age and erosion rate of glaciated landscapes however obtaining chronological data from glaciated landscapes once covered by cold based nonerosive ice is challenging because these surfaces violate assumptions associated with simple cosmogenic exposure dating nonerosive glacial ice fails to completely remove nuclides produced during previous periods of exposure leaving behind rock surfaces with complex multigenetic nuclide inventories here we constrain the glacial history landscape evolution and efficiency of subglacial erosion in the pangnirtung fiord region of southern baffin island using over 300 paired analyses of in situ cosmogenic 10be and 26al simple exposure ages are 6 3 160 ka for 10be n 152 and 4 3 124 ka for 26al n 153 paired bedrock boulder samples have discordant ages simple exposure ages generally increase with elevation 10be and 26al ages for the same sample disagree and both boulders and bedrock yield multimodal age distributions all patterns suggestive of limited subglacial erosion measured 26al 10be ratios indicate that about one third of the samples in the data set experienced at least one period of pre holocene exposure followed by burial with limited erosion modeled two isotope minimum limiting exposure durations are as high as hundreds of thousands of years and minimum limiting burial durations range up to millions of years implying that parts of southern baffin island have been preserved beneath nonerosive glacial ice for much if not all of the quaternary a subset of the samples contains few nuclides inherited from prior periods of exposure and is thus useful for constraining the chronology of the most recent deglaciation using these samples we infer that deglaciation of most of the landscape occurred ca 11 7 ka and that the duval moraines a prominent feature of the last deglaciation formed ca 11 2 ka

chironomidae insecta diptera succession in żabieniec bog and its palaeo lake central poland through the late weichselian and holocene abstract subfossil chironomidae assemblages were studied in a sediment sequence from abieniec bog in central poland the climate history and habitat changes in the palaeo lake were reconstructed from these assemblages currently no chironomid based climate calibration set is available from poland and so past mean july air temperatures were inferred from chironomid climate calibration data sets from norway russia and switzerland during the late weichselian the three calibration functions from these data sets provided similar temperature inferences but there was some divergence in the reconstructions for the younger dryas and holocene in the late pleniglacial inferred summer air temperature was relatively low 8 12 c and the lake was oligotrophic at about 16 5 ka bp temperature rapidly rose to 15 c and assemblage diversity substantially increased during the interstadial temperature stayed at this level in the younger dryas july air temperature was only 1 2 c lower than in the interstadial as inferred from the norwegian calibration data set whereas the russian and swiss calibration functions did not indicate any temperature decrease from the beginning of the holocene taxa typical of meso eutrophic conditions dominated there was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water level palaeotemperature reconstructions differed in their values from 8 0 to 8 7 ka bp inferences based on the swiss and russian data sets indicated a cold oscillation while reconstructions based on the norwegian data set did not show any temperature decrease after 2 5 ka bp assemblage diversity and head capsule concentrations decreased in the last millennium semi terrestrial taxa dominated except from late medieval to early modern times when shallow water species reappeared

when do faults in sedimentary basins leak stress and deformation in sedimentary basins examples from the north sea and haltenbanken offshore norway faults may be barriers or conduits for fluid flow in sedimentary basins the properties of faults however depend on stress conditions and rock properties at the time of deformation and subsequent diagenesis of the fault zone several recent publications have suggested that petroleum reservoirs in the north sea and at haltenbanken offshore mid norway have experienced leakage along faults caused by imposed stresses related to glacial loading during the quaternary the jurassic reservoirs in these areas are however bounded by faults produced during the upper jurassic rifting when the sediments were still soft and for the most part uncemented these faults do not represent zones of weakness because of strain hardening and later diagenesis in sandstones and cementation in mudstones the fault zones are commonly stronger than the adjacent rocks they are therefore not likely to be reactivated tectonically furthermore there is little evidence of glacial deformation in the quaternary sediments overlying these oil fields it has been proposed that very large horizontal stresses inferred to be related to periods of glacial loading caused shear failure at pore pressures below fracture pressure and subsequent leakage along these shear zones we argue that this is not a likely mechanism during progressive burial in sedimentary basins very high horizontal effective stresses up to 60 mpa at about 3 km 1 8 mi depth at haltenbanken would have caused more mechanical compaction and grain crushing than that observed in situ external stress i e plate tectonic stress from spreading ridges ridge push will be transmitted primarily through the basement and not through the much more compressible overlying sedimentary rocks during progressive basin subsidence chemical compaction i e caused by quartz cementation causes rock shrinkage which will relax differential stresses this makes brittle deformation shear failure resulting in open fractures less likely to occur at stresses below the fracture pressure in subsiding sedimentary basins with progressive compaction horizontal stress will normally not exceed the vertical stress except when there is significant shortening of the underlying basement

determination of optimal well trajectory during drilling and production based on borehole stability abstract several studies have been done about borehole stability and optimized wellbore direction however the majority of them focused on stability during drilling and there are only a few studies concerns with stability during drilling and production and its problems such as sanding simultaneously this paper presents an analytical model that estimates collapse pressure in stability analysis during drilling and in addition determines maximum drawdown pressure to prevent sand production using the mogi coulomb failure criterion the results show that in different in situ stress regimes the inclination and azimuth have a significant role in wellbore stability during both drilling and production furthermore the results show that the optimum direction for wellbore stability during drilling is also the best direction for stability of a production well the analytical model is applied to field data in order to verify the applicability of the developed model

diatom inferred climatic and environmental changes over the last 9000 years from a low arctic nunavut canada tundra lake abstract diatom assemblage changes over the holocene were examined from a 14c dated sediment core retrieved from lake tk 2 a small low arctic lake located ca 200 km north of the forest tundra ecotone in mainland nunavut canada notable changes in the diatom assemblages were recorded throughout the core suggesting that the holocene epoch in this region has been environmentally and climatically dynamic the earliest diatom assemblages ca 9000 cal yr bp were dominated by taxa that are atypical of post glacial assemblages commonly recorded throughout the arctic and may suggest that early holocene conditions at lake tk 2 were relatively warmer a shift to dominance by small benthic opportunistic fragilaria taxa followed after ca 8550 cal yr bp more typical of arctic assemblages during initial lake ontogeny suggesting the onset of cooler more alkaline conditions an abrupt and short lived marked decrease in diatoms between ca 8550 and 8500 cal yr bp with corresponding changes in physical and chemical indicators e g sedimentation rate siliciclastic content organic matter content provides potential evidence for the 8 2 k cooling anomaly an event rarely recognized from other paleolimnological studies in the canadian north following ca 7000 cal yr bp a substantial shift occurred to a more complex and diverse diatom assemblage that now included more acidophilic taxa this compositional change is likely indicative of a natural long term loss of alkalinity in the lake and marks the onset of the holocene thermal maximum consistent with the timing of this warm period for this region the relatively stable diatom assemblage composition during the neoglacial period was punctuated by fluctuations in key species potentially correlative with the so called medieval warm period and little ice age in the most recent sediments the post industrial expansion of the small planktonic cyclotella stelligera complex and a concurrent decline in the heavily silicified aulacoseira lirata complex are similar to shifts that are increasingly being recognized as geographically widespread diatom responses to recent climate warming the lake tk 2 diatom record provides important insights into the holocene environmental history of this understudied region of the canadian arctic furthermore it is one of the few arctic lakes in which the 8 2 k cold event is possibly expressed

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

novel insights from coleopteran and pollen evidence into the lateglacial holocene transition in aubrac french massif central the aim of this study is to describe the environmental and climate changes that occurred in the mountains of aubrac at the transition between the lateglacial and the holocene from a comparative analysis of fossil coleoptera and pollen and a series of 23 c 14 dates the changes affecting the ecological categories of coleoptera lead to a division of the sequence into 5 beetle assemblage zones baz the lowermost baz a is characterized by extremely poor assemblages periglacial environment baz b oldest dryas and lateglacial interstadial is marked by regular occurrences of taxa associated with open environments aquatic taxa associated with running and highly oxygenated water and cold adapted taxa with relatively low numbers baz c younger dryas corresponds to two important events a particular abundance of cold adapted taxa and a marked decrease of running water taxa beetles associated with herbaceous vegetation and open environments are also well represented baz d early holocene corresponds to the total disappearance of cold adapted taxa the transition baz c baz d is marked also by a dramatic peak of running water taxa the uppermost baz e early mid holocene is marked by a total absence of running water taxa which are replaced by standing water or taxa tolerant of a range of water conditions a particular abundance of wetland taxa and taxa associated with herbaceous vegetation and open environments beetle and pollen data suggest that the harsh climatic conditions prevailing in the aubrac mountains did not allow warm dependent fauna and trees to establish during the lateglacial interstadial at least in the roustieres region and that wide open landscapes occupied the plateau at that time the older dryas a cold spell previously recorded at la taphanel cantal is not visible in the roustieres record probably because of the higher altitude at roustieres whereas the younger dryas is strongly expressed during the holocene concordant beetles and pollen data enable to reconstruct the rapid recolonization of the plateau by mesophilous trees ulmus quercus suggesting the possible presence of refugia to the southern slopes of the aubrac plateau insect pollen comparisons provide evidence for hydrological changes in the former lake of roustieres and suggest that lacustrine water level changes often used as indicator of precipitation regime changes should be taken with caution c 2016 elsevier b v all rights reserved

quantifying the heterogeneity of the tectonic stress field using borehole data the heterogeneity of the tectonic stress field is a fundamental property which influences earthquake dynamics and subsurface engineering self similar scaling of stress heterogeneities is frequently assumed to explain characteristics of earthquakes such as the magnitude frequency relation however observational evidence for such scaling of the stress field heterogeneity is scarce we analyze the local stress orientations using image logs of two closely spaced boreholes in the coso geothermal field with sub vertical and deviated trajectories respectively each spanning about 2 km in depth both the mean and the standard deviation of stress orientation indicators borehole breakouts drilling induced fractures and petal centerline fractures determined from each borehole agree to the limit of the resolution of our method although measurements at specific depths may not we find that the standard deviation in these boreholes strongly depends on the interval length analyzed generally increasing up to a wellbore log length of about 600 m and constant for longer intervals we find the same behavior in global data from the world stress map this suggests that the standard deviation of stress indicators characterizes the heterogeneity of the tectonic stress field rather than the quality of the stress measurement a large standard deviation of a stress measurement might be an expression of strong crustal heterogeneity rather than of an unreliable stress determination robust characterization of stress heterogeneity requires logs that sample stress indicators along a representative sample volume of at least 1 km

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

reconstruction of holocene precipitation patterns in europe using pollen and lake level data abstract lake level data can be used to refine palaeoclimate reconstructions based on pollen data this approach is illustrated for the european holocene estimates of p pet precipitation minus potential evapotranspiration were first inferred from modern pollen analogues the pollen based estimates were then compared with the status of lakes within a 5 radius analogues with p pet anomalies inconsistent with the lake level changes were rejected the constrained sets of analogues were used to estimate continental scale patterns of annual mean temperature and annual precipitation at 3000 yr intervals estimated temperature anomalies differed only slightly from the unconstrained reconstructions estimated precipitation anomalies however showed improved spatial coherence and increased regional contrast and were occasionally reversed in sign the effect of the constraint was to impose a rational selection among almost equally similar modern pollen analogues with similar temperatures but widely varying moisture regimes the resulting maps showed clear spatially coherent patterns of change in precipitation as well as temperature suitable for comparison with climate model results further improvement of these maps will become possible as a more extensive coverage of lake level data is obtained

stress orientations from borehole wall fractures with examples from colorado east texas and northern canada azimuthally aligned breakouts in oil wells are explained as shear fractures in the zone of amplified stress difference near the borehole in a stress field having unequal horizontal principal stres

isotope signature of the younger dryas and two minor oscillations at gerzensee switzerland palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates oxygen and carbon isotope ratios in the carbonate of benthic ostracodes pseudocandona marchica and molluscs pisidium ssp were measured across the transitions bordering the younger dryas chronozone in littoral lacustrine cores from gerzensee switzerland the specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk carbonate oxygen isotope record 18occ if corrected for their vital offsets oxygen isotope ratios of pisidium and juvenile p marchica both formed in summer are almost identical to 18occ this bulk carbonate is mainly composed of encrustations of benthic macrophythes chara ssp also mainly produced during summer adult p marchica which calcify in winter show consistently higher 18o larger shifts across both transitions and short positive excursions compared with the summer forms especially during early preboreal despite such complexity the 18o of adult p marchica probably reflects more accurately the variations of the 18o of former lake water because during winter calcification temperatures are less variable and the water column isotopically uniform the difference between normalised 18o of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures in general the results indicate warmer summers during the late allerod and early preboreal compared with the younger dryas altogether the isotopic composition of lake water 18ol and of the dissolved inorganic carbonate 13cdic reconstructed from adult pseudocandona marchica as well as the seasonal water temperature contrasts indicate that the major shifts in the 18o of local precipitation at gerzensee were augmented by changes of the lake s water balance with relatively higher evaporative loss occurring during the allerod compared with the younger dryas it is possible that during the early preboreal the lake might even have been hydrologically closed for a short period we speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts

quantitative reconstruction of younger dryas to mid holocene paleoclimates at le locle swiss jura using pollen and lake level data abstract pollen and lake level data from le locle in the swiss jura were used to quantitatively reconstruct climatic parameters for the younger dryas event and the first half of the holocene period the younger dryas cold event at le locle was characterized by i a general trend toward a slight increase in summer temperature and a decrease in annual precipitation and ii a marked drying phase at ca 11 900 cal yr b p that occurred between two wetter ones further phases of major deficit in moisture occured at ca 11 500 cal yr b p younger dryas holocene transition 10 800 cal yr b p 8700 cal yr b p and 6500 cal yr b p climatic parameters reconstructed here suggest that phases of higher lake level developing at ca 12 500 12 000 11 750 11 600 11 200 10 900 synchronous with the preboreal oscillation 10 400 8900 8400 8300 possibly related to the 8200 yr event and 7800 7000 cal yr b p coincided with an increase in annual precipitation a decrease in summer temperature and a shorter growing season conversely periods of low lake level corresponded to a decrease in annual precipitation an increase in summer temperature and a longer growing season this general pattern could have resulted from alternate southward northward displacements of the atlantic westerly jet

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

holocene fluctuations of lake levels in the french jura and sub alpine ranges and their implications for past general circulation patterns temperature and precipitation variations reflected in lake level fluctuations in the french jura and pre alps during the last nine millennia are qualitatively assessed by reference to 1 climatic oscillations reconstructed in the alps and 2 modern processes behind alpine tree limit variations the summer season and mainly the late summer appears to have a deterministic impact on the holocene environment correlations between palaeoclimatic proxy data recorded in the north atlantic area from high and middle latitudes and climatic dynamics illustrated by the little ice age and the recent warming suggest 1 the existence of climatic oscillations due to varying solar activity superimposed on larger plurimillennial climatic trends and 2 that these minor climatic phases correspond with two main types of general circulation pattern alternating over western europe during the last six millennia the climatic deteriorations correspond with cooling at high latitudes inducing a stronger thermal grad

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

the stress pattern of iceland moritz ziegler mojtaba rajabi oliver heidbach gylfi pall hersir kristjan agustsson sigurveig arnadottir arno zang

vegetation changes and associated climatic changes in the southern altai mountains within china during the holocene the location of the altai mountains at the limits of both the pacific and atlantic influences implies that this mountain range is an important climatic boundary based on pollen data of 188 samples