dinoflagellate cyst assemblages as tracers of sea surface conditions in the northern north atlantic arctic and sub arctic seas the new n 677 data base and its application for quantitative palaeoceanographic reconstruction the distribution of dinoflagellate cyst dinocyst assemblages in surface sediment samples from 677 sites of the northern north atlantic arctic and sub arctic seas is discussed with emphasis on the relationships with sea surface parameters including sea ice cover salinity and temperature of the coldest and warmest months difficulties in developing a circum arctic data base include the morphological variation within taxa e g operculodinium centrocarpum islandinium cezare and polykrikos sp which probably relate to phenotypic adaptations to cold and or low salinity environments sparse hydrographical data together with large interannual variations of temperature and salinity in surface waters of arctic seas constitute additional limitations nevertheless the use of the best analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea surface conditions at the scale of the northern north atlantic and the arctic domain the error of prediction calculated from modern assemblages is 1 3 ca nd 1 8 c for the temperature of february and august respectively 1 8 for the salinity and 1 5 months yr 1 for the sea ice cover application to late quaternary sequences from the western and eastern subpolar north atlantic labrador sea and barents sea provide reconstructions compatible with those obtained using the previous dinocyst data base n 371 which mainly included modern data from the northern north atlantic copyright 2001 john wiley sons ltd journal of quaternary science

last interglacial eemian hydrographic conditions in the southeastern baltic sea ne europe based on dinoflagellate cysts abstract a rich organic walled dinoflagellate cyst and pollen record from the licze borehole in northern poland has been used to reconstruct the hydrographic history of the southeastern baltic sea during the last interglacial eemian stage late pleistocene warm saline waters ca 10 15 psu entered the site from the north sea within the first few hundred years of the eemian corresponding to the pinus betula e1 or pinus betula ulmus e2 regional pollen assemblage zones rpaz by about 300 years beginning of rpaz e3 dinoflagellate cyst assemblages were already indicating summer sea surface salinities in excess of about 15 psu and temperatures that perhaps exceeded 27 c warm and saline conditions of 15 20 psu or more at least twice present levels persisted throughout the early eemian a rise in sea level at licze appears to correlate with a similar event in eastern denmark as both coincide with the increase in corylus ca 750 years into the interglacial this sea level rise might therefore have a basinwide extent and appears to correspond to an opening of the danish belts there is little if any evidence of arctic waters throughout the sequence whereas dinoflagellate cysts reflect sustained high salinites within the upper water column a concomitant increase in abundance of the chlorococcalean alga pediastrum within the carpinus corylus alnus e5 rpaz indicates an escalating freshwater input presumably from the proto vistula whose mouth was nearby this suggests the development of a thin seasonal low salinity surface layer below which dinoflagellates lived in more saline waters increasing fluvial influence suggests shallowing through rpaz e5 this study is the first to document dinoflagellate cysts from the eemian of the southeastern baltic sea and reveals a flora with distinctive lusitanian mediterranean affinities

prograded holocene beach ridges with superimposed dunes in north east ireland mechanisms and timescales of fine and coarse beach sediment decoupling and deposition abstract two depositional models to account for holocene gravel dominated beach ridges covered by dunes occurring on the northern coast of ireland are considered in the light of infrared stimulated luminescence ages of sand units within beach ridges and 14 c ages from organic horizons in dunes a new chronostratigraphy obtained from prograded beach ridges with covering dunes at murlough north east ireland supports a model of mesoscale alternating sediment decoupling asd on the upper beach rather than macroscale sequential sediment sourcing to account for prograded beach ridges and covering dunes the asd model specifies storm or fair weather sand beach ridges forming at high tide positions on an annual basis at minimum which acted as deflationary sources for landward foredune development only a limited number of such late holocene beach ridges survive in the observed prograded series beach ridges only survive when capped by storm generated gravel beaches that are deposited on a mesoscale time spacing of 50 130 years the morphodynamic shift from a dissipative beach face for dune formation to a reflective beach face for gravel capping appears to be controlled by the beach sand volume falling to a level where reflective conditions can prevail sediment volume entering the beach is thought to have fluctuated as a function of a forced regression associated with the falling sea level from the mid holocene highstand ca 6000 cal yr bp identified in north east ireland the prograded beach ridges dated at ca 3000 to 2000 cal yr bp indicate that the holocene highstand s regressive phase may have lasted longer than previously specified

late and postglacial sea level change and paleoenvironments in the oder estuary southern baltic sea abstract knowledge of sea level change in the southern baltic sea region is important for understanding the variations in late pleistocene and holocene sea level change across northern europe these variations are a consequence of the response of the earth s crust to the deglaciation of fennoscandia and of the water added to the oceans from the melting of all pleistocene ice sheets the sedimentological and geochemical composition of five sediment cores from the lagoonal oder estuary offers new observational evidence for sea level change and coastal development in the southern baltic sea region the combined use of several geochemical proxies organic carbon nitrogen calcium carbonate and biogenic opal contents corg s and corg n ratios 13c values of organic matter and 15n values is a new approach for the study area the chemical evidence of this multiproxy approach allows clear identification of several stages in the development of the lagoonal environment postglacial lake stages with sandy sedimentation during the older dryas and the allerod stades lacustrine phases with high autochthonous productivity during the atlantic stade terrestrial stages with peat formation at the beginning of the subboreal stade sedimentation as a result of marine transgression and brackish sedimentation after the formation of sand spits and barrier islands during the subatlantic stade the stages are the result of regional sea level change owing to complex shoreline development they support the tentative sea level curve proposed nearly 20 years ago for the region in addition changes in oder river input in response to climate conditions is monitored whereas high terrigenous input of organic matter from the oder river occurred during periods of humid climate during the allerod atlantic and subatlantic stades oder river discharge decreased with drier and cooler climate conditions during the subboreal stade furthermore the geochemical evidence points to local anomalies such as the significance of river input and additional sulfate supply into the oder lagoon for the composition of the sediments overall the results provide a framework for future studies which would allow for a more detailed comparison with other similar environments

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

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

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

very fast exhumation of high pressure metamorphic rocks with excess 40ar and inherited 87sr betic cordilleras southern spain in order to attempt to further constrain the age of the early alpine tectonic evolution of the mulhacen complex and to explore the influence of inherited isotopes micas from a small number of well characterised rocks from the sierra de los filabres with a penetrative tectonic fabric related to the exhumation of eclogite facies metamorphic rocks were selected for 40 ar 39 ar and rb sr dating a single phengite grain from an amphibolite yielded an 40 ar 39 ar laser step heating plateau age of 86 9f1 2 ma 2r 70 39 ar released and an inverse isochron age of 86 2f2 4 ma with an 36 ar 40 ar intercept within error of the atmospheric value induction furnace step heating of a biotite separate from a gabbro relic in an eclogite yielded a weighted mean age of 173 2f6 3 ma 2r 95 39 ar released these ages are diagnostic of excess argon 40 arxs incorporation as they are older than independent age estimates for the timing of eclogite facies metamorphism and intrusion of the gabbros 40 arxs incorporation probably resulted from restricted fluid mobility in the magmatic rocks during their metamorphic recrystallisation rb sr whole rock phengite ages of graphite bearing mica schists from paleozoic rocks secano unit show a dramatic variation 66 1f3 2 40 6f2 6 and 14 1f2 2 ma an albite chlorite mica schist from the mesozoic series of the nevado lubro n unit has a whole rock mica albite age of 17 2f1 9 ma which is within error of an 40 ar 39 ar plateau age published previously and of the youngest rb sr age of the paleozoic series obtained in this study the significant spread in rb sr ages implies that progressive partial resetting of an older isotopic system has occurred the microstructure of the samples with pre miocene rb sr ages reveals incomplete recrystallisation of white mica and inhibited grain growth due to the presence of graphite particles this interpretation agrees with previously published disturbed and slightly dome shaped 40 ar 39 ar age spectra that may point similarly to the presence of an older isotope component the progressively reset rb sr system is a relic of variscan metamorphism of the paleozoic series of the mulhacen complex in contrast the origin of the ca 17 2 ma old sample from the mesozoic series precludes any isotopic inheritance in agreement with its pervasive tectono metamorphic recrystallisation during the miocene exhumation of the eclogite facies mulhacen complex occurred in two stages with contrasting rates of about 22 5 mm year during the early phase and 9 10 mm year during the late phase the latter with a cooling rate in the order of 330 jc ma d 2003 elsevier b v all rights reserved

39ar recoil artifacts in chloritized biotite biotite separates from the metamorphosed granitic rocks of eastern taiwan yield disturbed 40ar39ar age spectra their disturbed profiles become more pronounced with increasing degree of chloritization and are attributed to mixed release of argon from sub micron scale biotite and chlorite intercalations 39ar internal recoil best explains the discordance of the age spectra chlorite is randomly intercalated with biotite at scales ranging from 10 a to several tens of microns both 40ar and k were evidently lost during the chloritization reaction during the neutron irradiation 39ar atoms recoil into the chlorite from the adjacent biotite intercalations the recoil and chloritization combine to produce a variable 40ar39ar spatial distribution in the intercalated biotite chlorite during 40ar39ar step heating analyses argon in biotite is released in two pulses centered at 650 c and 950 1050 c which represent two stages of dehydroxylation of the biotite chlorite out gasses in two pulses centered at 550 c and 700 900 c during dehydroxylation and then decomposes this differential thermal release of argon from each mineral phase with variable 40ar39ar ratios yields discordant incremental heating age spectra

dating of deformation phases using k ar and 40ar 39ar techniques results from the northern apennines abstract paleozoic to oligocene metasedimentary rocks present in the alpi apuane region of the northern apennines italy have been sequentially deformed during a tertiary progressive deformation in an attempt to date the individual deformation episodes over 50 conventional k ar and 1140 ar 39ar incremental gas release analyses have been carried out on fine grained white micas separated from samples whose structural settings were well known mineralogy x ray diffractometry and thin section analyses indicate that the constituent muscovite and phengite formed under metamorphic conditions of 3 4 kbars and 300 400 c during all deformational phases pre existing micas were variably crenulated during each subsequent deformational phase both k ar and 40ar 39ar analyses were carried out on 0 6 2 m 2 6 m and 6 20 m size separates of the phengitic white mica although the k ar apparent ages range from 11 to 27 ma and are consistent with available stratigraphic constraints the 40ar 39ar age spectra display variable internal discordancy these isotopic data indicate that 1 both the k ar and 40ar 39ar total gas ages decrease as the degree of crenulation increases 2 the k ar and 40ar 39ar total gas ages decrease as grain size decreases 3 for each sample characteristics of the 40ar 39ar age spectra depend upon grain size with fine sizes yielding discordant patterns which systematically increase in apparent age from low to high temperature and 4 phengitic micas associated with earliest structures yield generally older ages than micas associated with later structures the isotopic results are interpreted to indicate that the major deformation phase d1 occurred at approximately 27 ma with subsequent pulses ending by c 10 ma these results may be combined with finite strain data to suggest that the region was deformed at strain rates between 10 15 and 10 14 s 1 a 27 ma age indicates mid oligocene initiation of plate tectonic activity in the western mediterranean and concomitant deformation in the northern apennines

a holocene coastal aeolian system vejers denmark landscape evolution and sequence stratigraphy stratigraphical studies of holocene aeolian strata formed at the inner margin of the vejers dunefield on the west coast of jutland have contributed to an understanding of aeolian landscape evolution in a storm influenced temperate climate belt the aeolian system was characterized by alternating periods of activity and stabilization intense inland sand transport occurred just after 4000 bc 2300 bc 600 bc and ad 300 500 periods of sand movement were apparently initiated during climatic shifts towards more stormy conditions and they may be linked to a millennial scale cycle in north atlantic holocene climate preservation of the accumulated aeolian sand records a long term rise in ground water level water table behaviour was initially controlled by sea level but after about 2300 bc water table rise was linked to coastal outbuilding and to an overall change towards a more humid climate

imprint of large scale atmospheric transport patterns on sea salt records in northern greenland ice cores the decadal to interannual variability of sea salt aerosol concentrations in northern greenland ice cores is investigated and contrasted to meteorological reanalysis data over the time span 1959 1993 correlation analysis with average data on sea level pressure and geopotential height at the 500 mbar level identifies the eastern and northeastern pacific region as the most important center of action responsible for variations in sea salt aerosol export onto the greenland ice sheet which is related to the pacific north american teleconnection pattern the atlantic region however appears to be of secondary importance only correlation coefficients are highest during the first quarter of the year but also significant for annual pressure data explaining 20 of the sea salt variance in the ice cores furthermore higher storm activity in the pacific center of action as well as in the northern atlantic leads to higher sea salt concentrations in northern greenland explaining about 40 and 17 of the ice core variance a 30 increase during the nineteenth century in a 600 year sea salt record from northeastern greenland may be interpreted at least in part as an enhancement of sea salt export from the pacific region during that time

quantifying orthoclase and albite muscovitisation sequences in fault zones abstract a new graphical method is described for assessing the degrees of alteration of orthoclase and albite feldspars to muscovite the method uses major element data from whole rock samples and given a range of samples of varying degrees of alteration pathways of the alteration sequences may be determined the method may be used quantitatively if likely starting compositions are known and aluminium immobility is assumed molar proportions of k na and al are plotted in the form of an na na k versus na k al graph modelled plots of muscovitisation of an orthoclase albite system are presented for comparison with actual data so that actual compositions may be assessed in terms of feldspar muscovitisation an example of the application of this technique to muscovitised granitic fault rocks in the external western alps is presented illustrating how the method is best used in conjunction with microstructural and field constraints on the fault rock evolution this yields an evolution pathway for muscovitisation of the feldspars during fault zone deformation and links specific alteration steps with particular microstructural changes within the fault zone we also apply this technique to a previously published data set on basement shear zone geochemical changes from the pyrenees where orthoclase albitisation provides an additional interest given that these reactions are fluid induced this work provides further information on the effects of fluid flow in such fault zones in terms of basement fault zone rheologies

late holocene north atlantic climate seesaws storminess changes and greenland ice sheet gisp2 palaeoclimates the oxygen isotope record of palaeotemperature from greenland ice cores has for many years been the kingpin of climate reconstructions for the north atlantic region and northern europe an air temperature seesaw between greenland and northern europe first described in ad 1765 is also well known and is related to the north atlantic oscillation nao whereas the nao index series is based on instrumental records of air pressure the north atlantic climate seesaw has conventionally been based on air temperature records here we describe relationships between this seesaw mechanism and the greenland gisp2 oxygen isotope chronology of air temperature variations as well as relationships between gisp2 na sea salt variations and instrumental records of north atlantic storminess the gisp2 proxy air temperature record is calibrated for the last 130 years with instrumental weather records for west greenland while the na series is compared with instrumental records of north atlantic storminess change reconstruction of an annual series of these climate parameters for the last 1000 years shows that during the mediaeval warm period there were no years characterized by high na extremes high north atlantic storminess but there were many years when there were extremes of temperature remarkably there were no years of exceptionally low air temperature and high na precipitation at gisp2 between ad 1650 and 1710 a period of time that in northern europe incorporates the period of maximum little ice age cooling it would appear also that for the last thousand years the most extreme seesaw winters when gisp2 temperatures were very low and na concentrations were high occurred in discrete clusters and pairs of years

comment on alpine thermal and structural evolution of the highest external crystalline massif the mont blanc by p h leloup n arnaud e r sobel and r lacassin in this comment we discuss the approach used and the significance of ar ar dating of synkinematic phengite within low grade alpine shear zones and we comment the geodynamic models that can be derived from this method the paper by leloup et al 2005 is a good step forward in the tectonic comprehension of the mont blanc area and provides a good synthesis of preexisting data leloup et al 2005 have proposed a polyphase alpine history for the mont blanc massif west alps based on a multidisciplinary approach ar ar on biotite for the higher pressure temperature events of the mont blanc and ar ar on k feldspar fission tracks ft on zircon and apatite for its later exhumation stages however at this point of our knowledge of alpine deformation in the mont blanc range the polyphased tectonic evolution in particular the timing of thrust and back thrust events are not in agreement with recently obtained ar ar data

holocene palaeoecology along the blekinge coast se sweden and implications for climate and sea level changes to investigate the holocene vegetation history and shoreline displacement along the southeastern swedish coast two radiocarbon dated pollen macrofossil and mineral magnetic sequences were studied in the western blekinge coast hunnemara lake and smygen bay both pollen records show mosaic vegetation with grasslands heaths and woodlands prior to 11 300 cal bp pinus dominated mixed forest was initially established by 11 000 cal bp by 10 000 cal bp mixed forest with higher species diversity was fully established expansion of broad leaved trees began at about 8600 cal bp indicating the onset of the mid holocene thermal maximum in scandinavia following the ulmus decline similar to 5800 cal bp the regional forest became much more open due to increased human disturbance both basins were isolated during the period of 11 300 11 000 cal bp and subsequently in contact with the ancylus lake between 10 700 and 9800 cal bp low abundance of brackish water diatoms at smygen suggests that this basin was connected with the baltic sea between 9800 and 8600 cal bp corresponding to the early littorina sea phase hunnemara was isolated during this period the two basins were in turn flooded at 8600 and 8300 cal bp as a result of global sea level rise a sedimentary hiatus 8300 7500 cal bp was present at hunnemara probably caused by a rapid sea level rise related to global meltwater pulse 3 aquatic macrofossil and mineral magnetic proxies reveal several minor transgressions at both sites probably regulated by centennial scale variations in regional storminess hunnemara was isolated from the baltic basin by 3100 cal bp concurrent with a lowering of the sea level at smygen less

teleseismic tomography of the loma prieta earthquake region california implications for strain partitioning from teleseismic travel times we derive three dimensional velocity models of the upper 71 km in the 1989 loma prieta earthquake region central california shallow crustal structure is consistent with local earthquake tomography horizontal velocity gradients at all depths suggest that the san andreas fault was a deep shear locus at least at one time a large low velocity feature near the moho beneath loma prieta probably is caused by a crustal root two low velocity features at about 45 70 km depth are offset right laterally along the san andreas by about 45 km cooling of this portion of the upper mantle furlong et al 1989 could have frozen in displacements in this region within a few million years after passage of the mendocino triple junction these results are consistent with furlong et al s model

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

precise dating of low temperature deformation strain fringe analysis by 40ar 39ar laser microprobe pyritized graptolites from the welsh basin united kingdom slate belt acted as rigid bodies during cleavage formation and epizonal white micas formed within the resulting strain shadows orthogonal to the principal stress orientation although the quantities of mica are small they are a pure synkinematic mineral and have been dated by ar 40 ar 39 infrared laser microprobe as a means to dating cleavage four samples of strain fringe mica from different hand samples yielded ages ranging from 394 4 3 1 to 397 8 1 8 ma 2sigma with a mean age of 396 1 1 4 ma 2sigma by focusing on minerals that are unequivocally synkinematic this technique provides a novel solution to the problems of isotopically dating slaty cleavage previous studies have predominantly relied on dating whole rock slate samples or separated illite grains by ar 40 ar 39 techniques problems encountered included 1 separating the effects of isotopic contamination by detrital phases 2 ar 39 loss during the irradiation of illite mineral separates and 3 thermally induced ar 40 loss in nature from fine grained minerals by circumventing these problems this new method provides the first unequivocal and high precision age data for acadian deformation in the well characterized welsh basin slate belt with such precision the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent continent collision

on the loss of 40ar from muscovite during polymetamorphism abstract recent laser studies have documented 40ar concentration gradients in micas that correspond to age variations of tens to hundreds of millions of years a fundamental problem to interpretation of such variations is to evaluate whether they represent loss via lattice diffusion or alternatively loss during chemical reactions and deformation new data of this study and comparisons with previous work suggest that muscovite is far less prone to lose accumulated 40ar via lattice diffusion during overprinting events than has been inferred previously kyanite muscovite assemblages in proterozoic schist along the eastern flank of the green mountain massif central vermont appalachians formed during proterozoic metamorphism at ca 1 1 ga and were remetamorphosed in the greenschist facies during both taconian ca 465 ma and acadian ca 390 ma events the overprinting events resulted in deformation of earlier kyanite and muscovite growth of chemically and isotopically distinct rims on earlier muscovite and growth of neoblastic muscovite and chloritoid with each event at inferred minimum temperatures of ca 425 c laser spot analyses of the grenville muscovite range from 988 11 ma in the centers of porphyroclasts to 397 7 ma along rims ages younger than 750 ma occur only on the deformed edges of porphyroclasts and in highly deformed areas within crystals parts of early formed muscovite that escaped late deformation and chemical reaction seem remarkably retentive of accumulated 40ar laser spot analyses along the outer 100 m of an undeformed growth face yield ages close to the timing of proterozoic metamorphism and cooling the present study suggests episodic heating events are ineffective for producing measurable diffusive argon loss along the edges of large muscovite crystals ca 1 mm in diameter particularly in comparison with deformation and reaction mechanisms and are unlikely to result in complete 40 ar 39 ar age resetting of such crystals the results of this study further emphasize that the argon diffusivity in muscovite is lower than commonly considered in previous work

rare earth and trace element mobility in mid crustal shear zones insights from the mont blanc massif western alps the behaviour of rare earth elements ree during fluid rock interaction in mid crustal shear zones has received little attention despite their potential for mass balance calculation and isotopic tracing during deformation in this study several cases of large ree mobility during alpine fluid driven shear zone development in the pre alpine granitic basement of the mont blanc massif are considered on a regional scale the undeformed granite compositions range within 5 wt sio2 70 5 75 3 wt and magmatic chemical variations are of the order of 10 20 ascribed to minor effects of crystal fractionation major and trace element mobility observed in shear zones largely exceeds these initial variations shear zones developed a range of mineral assemblages as a result of shearing at mid crustal depths at not vert similar0 5 gpa 400 c five main shear zone assemblages involve muscovite chlorite epidote actinolite and calcite respectively as major phases in most cases selective enrichments of light or heavy ree and y ta hf are observed ree mobility is unrelated to deformation style cataclastic mylonitic the intensity of strain and to the shear zone s major metamorphic mineral assemblages instead the changes in ree concentrations are ascribed to the alteration of pre existing magmatic ree bearing minerals during deformation related fluid rock interaction and to the syntectonic precipitation of metamorphic ree bearing minerals mainly monazite bastnasite aeschynite and tombarthite minor proportions 2 of these accessory phases with grain sizes mostly 20 m account for enrichments of up to 5 1 compared to the initial granite whole rock ree budget the stability of the ree phases appears to be largely dependent on the altering fluid composition ree mobility is ascribed to changes in ph and to the availability of co32 po42 and so42 ligands in the fluid such processes are likely to influence the mobility of ree y hf and ta in shear zones

excess argon in k ar and ar ar geochronology the k ar and ar ar dating techniques occasionally produce anomalously old ages attributed to excess argon and such data is often rejected as not offering any insight into the age thermal history or geochemistry of the rock however improvements in the quantification of argon geochemistry now provide a framework to model excess argon in both open and closed systems solubility data for argon in hydrous fluids melts and emerging data for minerals can be used to understand the behaviour of excess argon and provide valuable insights into the environment in which the samples cooled to their argon retention or closure temperature treating excess argon as a trace element also throws light on its behaviour in minerals above the closure temperature in deeply buried dry systems such as eclogites blueschists granulites and even in the lithospheric mantle extremely low partition coefficients between k feldspar and hydrous fluid phases predict lower excess argon susceptibility than micas and this is observed in fluid poor systems variation of partition coefficients can lead to excess argon in fluids being introduced into minerals or removed from minerals as grain boundary fluids change during flow through a rock however excess argon can also be introduced or removed from minerals by varying temperature without the need for fluid flow high mineral melt and mineral fluid partition coefficients are also the reason why excess argon is often concentrated in inclusions within minerals partition coefficients between minerals and hydrous fluids as low as 10 6 lead fluid inclusions to dominate the radiogenic argon budget particularly in low potassium minerals melt inclusions are less dominant but become critical in dating younger samples

patterns of faulting in the mont blanc granite abstract faults at the meso scale in the mont blanc granite have been analyzed considering their strike dip and pitch of the striae the resulting pattern is characterized by mainly sw ne striking strongly dipping faults with a pronounced dip slip character associated with oblique or transversal strike slip faults the dominant dip slip ne trending faults constitute a downward converging fan more or less concordant with the wedge shape of the granite mass reverse faults largely prevail over normal ones in some sections of the massif especially the nw section the fault pattern can be analyzed in terms of a plane strain model under compression with the nw azimuth towards the southeast two dimensional models of deformation become increasingly inadequate and the pattern needs being analyzed in three dimensions it can be simulated by a half cylindrical envelope of fault planes whose axis strongly dips towards nw dip slip movement characterizes the fault planes lying at the bottom of this half cylindrical gutter while the movement becomes strike slip in the faults whose planes lie at the gutter s flanks although this is only a geometrical simulation it may again be consistent with the hypothesis of a nw directed overall compression in all the examined sections of the massif the angle of dip of fault planes is much higher than expected by the mohr coulomb theory with horizontal maximum compression we suggest that this may be due to an association of faulting with bulk deformation which may have resulted in both a pattern of shearing stresses along very inclined planes different from that of perfectly elastic materials and some rotation of already formed fault planes the different patterns of nw and se dipping faults the bimodal distribution of the dip angles around the dominant ne strike and other features suggest that faulting occurred in more than one phase

possible solar influences on the dust profile of the gisp2 ice core from central greenland the greenland ice sheet project 2 gisp2 ice core dust profile in glacial wisconsinan ice from central greenland has been measured using laser light scattering lls from ice this data exhibits considerable high frequency variability by applying appropriate running averages to the data certain regularities emerge thus for example when the data was smoothed with rectangular 4 and 5 year running averages 11 year dust modulations of considerable amplitude were revealed in this paper we show how further smoothing of the data causes very large longer period dust modulations centered at 91 years in a gaussian distribution to emerge we believe that this corresponds to the 80 90 year modulation of the 11 year sunspot cycle first suggested by gleissberg we also show how adjacent 11 year dust periods can combine in a unique way to generate a 22 year hale period of dust modulation the way this occurs is similar to that by which a 22 year modulation of the measured terrestrial neutron flux is generated from two 11 year periods taken together with our observation of a 200 year suess dust modulation period these observations strengthen our claim that the dust modulations we measured in gisp2 ice are solar induced and suggest a mechanism for their production

a high resolution holocene sediment record from hunafloaall n iceland margin centuryto millennial scale varability since the vedde tephra md99 2269 is a 25 m long core from hunafloaall a deep trough which runs northward towards the shelf break from the narrow neck of land which joins the northwest peninsula of iceland with the main land the core was recovered from the thickest part of an elongate shelf sediment body underlain by glacial diainictons with ages 26 ka bp 3 5 khz profiles indicate the presence of a reflector ri which can be traced over long distances twelve ams radiocarbon dates and the presence of the saksunarvatn tephra which is the origin for the ri reflector at 21 m core depth define a linear depth age relation with an accumulation rate of 200 cm ky the date on the core top is modern x radiographs indicate that the sediments are principally massive bioturbated muds the data were measured at resolutions of between 5 and 40 yr sample our primary data represent aspects of a multisensor track measurements b colour c grain size d sediment properties and e sediment magnetic properties principal component analysis pca was used to simplify the analysis of these five data sets and resulted in nine significant axes compared to over 70 original variables the explained variance on the first axes varied between 47 and 96 these time series were reduced to a common 50 yr sample interval which were then also subject to pca using the resulting pc scores we present three primary axes of environmental variability in hunafloaall that have century scale quasi periodicities and demonstrate that these are highly correlated with specific raw variables we focus on variables linked to changes in grain size and productivity and show regional coherence cores b997 321 and 330 in the coercivity grain size measure armj 20 armj 0 which have a close similarity to the detrended 14 c series this provides a potential link to the vigour of the thermohaline circulation to the north of the iceland shelf in the iceland and greenland seas our data indicate increas

marine evidence for episodic holocene megafloods in north america and the northern gulf of mexico hemipelagic muds deposited during the past 5 3 cal kyr in the northern gulf of mexico orca basin contain seven intervals punctuated by relatively coarse siliciclastic grain size peaks planktonic faunal turnovers and negative 13c excursions we believe these episodes represent megaflood deposits reflecting historically unprecedented outfall of north american floodwater and terrigenous mud plumes into the gulf resulting in collapse of the open ocean pelagic ecosystem the deposits record multidecadal episodes of high continental precipitation and large mississippi river floods at 4 7 3 5 3 0 2 5 2 0 1 2 and 0 3 cal ka 500 1200 year recurrence interval variations in tropical plankton frequencies define submillenial warming intervals that culminate in these fluvial episodes strengthened tropical currents in the gulf at these times appear to have increased sea surface temperatures and associated flow of moist gulf air to the midwest terrestrial paleohydrologic records support the marine evidence for millennial scale changes in recurrence of large midwest flood episodes

lateral displacement during neogene convergence in the western and central alps although major deformation in the western alps is clearly the result of north northwest directed thrust tectonics there is evidence suggesting that orogen parallel deformation may have been important in the late tectonic history of the western alps the authors propose that this northeast trending deformation includes 1 southwest directed normal fault movement along the simplon line 2 a diffuse zone of northeast striking dextral strike slip deformation along the rhone valley in switzerland between the mont blanc and aiguilles rouges massifs and through the belledonne massif and 3 southwest directed thrusting in the embrunais ubaye and digne nappe systems of southeastern france the correlation of these three broad regions of deformation is based on similar amounts of minimum displacement consistent kinematics and timing of deformation

distribution of dinoflagellate cysts in surface sediments of the northern north atlantic in relation to nutrient content and productivity in surface waters abstract analyses of dinoflagellate cyst assemblages from the surface sediments of 371 sites from the north atlantic ocean were performed in order to define relationships with nitrate phosphate silica and productivity in the upper water layer statistical analyses reveal close links between dinocyst assemblages and nitrate content in february that provide a measurement of nitrate availability amongst the taxa in the assemblages nematosphaeropsis labyrinthus which positively correlates with nutrients shows an eutrophic relationship whereas impagidinium aculeatum impagidinium patulum spiniferites ramosus spiniferites mirabilis and lingulodinium machaerophorum have a rather oligotrophic relationship on these grounds transfer functions were tested using multiple regressions and the best analogue technique to reconstruct nitrate content both methods yielded reasonable estimates and allow the reconstruction of the nitrate concentrations in february with an accuracy better than 1 45 mol m 3 at the scale of the study area there are also tenuous links between the dinocyst assemblages and productivity transfer functions were tentatively tested for the reconstruction of annual productivity and yield estimates with an accuracy of about 26 5 gc m 2 year 1 these results demonstrate that dinocyst assemblages can be used for the reconstruction of productivity and nitrates

eemian and holocene sea surface conditions in the southern black sea organic walled dinoflagellate cyst record from core 22 gc3 in order to compare the sea surface conditions in the black sea during the holocene and eemian sapropelic parts of marine core 22 gc3 42 13 53 n 36 29 55 e 838 m water depth were studied for organic walled dinoflagellate cyst content the record shows a change from freshwater brackish assemblages pyxidinopsis psilata spiniferites cruciformis and caspidinium rugosum to more marine assemblages lingulodinium machaerophorum and spiniferites ramosus complex during each interglacial due to the inflow of saline mediterranean water the lacustrine marine transitions in 22 gc3 occurred at 8 3 cal kyr bp during the early holocene and 128 kyr bp during the early eemian slightly later compared to the onset of interglacial conditions on the adjacent land dinoflagellate cyst assemblages reveal higher sea surface salinity 28 30 e g spiniferites pachydermus bitectatodinium tepikiense and spiniferites mirabilis around 126 5 121 kyr bp in comparison to the holocene 15 20 as well as relatively high sea surface temperature e g tuberculodinium vancampoae s pachydermus and s mirabilis especially at 127 6 125 3 kyr bp establishment of high sea surface salinity during the eemian correlates very well with reconstructed relatively high global sea level and is explained as a combined effect of increased mediterranean supply and high temperatures at the beginning of the last interglacial the observed changes in the dinocyst record highlight the importance of nutrients for the composition of the eemian and holocene dinocyst assemblages

changes in holocene relative sea level and coastal morphology a study of a raised beach ridge system on samso southwest scandinavia changes in relative sea level rsl during the holocene are reconstructed based on ground penetrating radar gpr data collected across a raised beach ridge system on the island of samso denmark the internal architecture of the beach ridge and swale deposits is divided into characteristic radar facies we identify downlap points interpreted to mark the transition from the beachface to the upper shoreface and thus sea level at the time of deposition this new data set shows that beach steps can be preserved and resolved in gpr reflection data this is important as downlap points identified at the base of the beach steps should be corrected for beach step height in order to be used as a marker of sea level identification of beach steps in combination with observed changes in dips of the interpreted beachface reflections can give information about changes in the morphodynamic conditions of beach ridge progradation through time the vertical levels of identified downlap points are combined with an age m

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

holocene organic carbon burial rates in the southeastern swedish baltic sea to estimate holocene changes in organic carbon mass accumulation rates c org mars in the southeastern swedish baltic sea two sediment cores were studied in combination with biogeochemical modelling prior to 11300 cal bp c org mars were extremely low indicating low organic matter production on the catchment of the baltic ice lake following a brief regression the ancylus lake stage occurred between i i 100 and 9800 cal bp c org mars increased substantially during this period because of enhanced washing in of terrestrial organic matter when boreal forests were initially established the prominent marine stage known as the littorina transgression between 8500 and 3000 cal bp is marked by a minor increase in corg mars our modelling reveals a changing terrestrial organic carbon input between 100 and 1000 g m 2 per yr that accounts for 30 80 of total organic carbon in sediments of the southeastern swedish baltic sea with maximum values c 20 x 10 3 g m 2 per yr occurring during the bronze lron age transition at about 3000 cal bp c org mar in the entire baltic basin is estimated at 3 01 x 10 6 t yr during the pre industrial holocene comparable with other large inland water bodies regardless of the source of carbon our data indicate that the baltic basin is an important sedimentary reservoir for organic carbon storage and thus should be included in accounting for global terrestrial carbon cycling during the pre industrial holocene

evidence for excess argon during high pressure metamorphism in the dora maira massif western alps italy using an ultra violet laser ablation microprobe 40 ar 39 ar technique ultra high pressure eclogite amphibolite grade metamorphism of the dora maira massif in the western alps is a well established and intensively studied event however the age of peak metamorphism and early cooling remains controversial the 40ar 39 ar step heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 ma which have been interpreted as the time of early cooling after the high pressure event recent u pb and sm nd results challenge this assertion indicating a much younger age for the event around 45 ma and hence a radically different timing for the tectonic evolution of the western alps in a new approach to the problem samples from the undeformed hercynian metagranite brossasco were studied using an ultra violet laser ablation microprobe technique for 40ar 39 ar dating the new technique allowed selective in situ analysis at a spatial resolution of 50 urn of quartz phengite biotite and k feldspar the results demonstrate the frequent occurrence of excess argon with high 40ar 39 ar ratios 1000 10000 and a strong relationship between apparent ages and metamorphic textures the highest excess argon ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases the best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high pressure event then mixed with an atmospheric component during rapid cooling and retrogression producing a wide range of argon concentrations and 40ar 36ar ratios step heating analysis of minerals with this mixture would produce linear arrays on a40ar 36ar versus 40ar 36 ar correlation diagram leading to geologically meaningless plateau ages older than the true closure age in the present case some ages in the range 60 110 ma could be explained by the presence of excess argon incorporated around 40 50 ma ago similar results found in other high pressure terrains in the alps may reconcile the argon geochronometer with other systems such as rb sr u pb or sm nd this study therefore calls for an increasing use of high resolution in situ sampling techniques to clarify the meaning of 40ar 36 ar ages in many high pressure terrains

10 000 yr record of extreme hydrologic events well dated lacustrine sediments provide a hydrologic record indicating that the frequency and magnitude of runoff events and by inference storms have varied over the past 10 k y in northern new england we used five sediment cores and radiocarbon dating to develop a chronology of holocene hydrologic events for the ritterbush pond basin northern vermont chemical and physical analyses allow us to identify 52 distinct layers of predominately inorganic sediment that represent terrestrially derived material delivered to the pond by runoff events the thickness of some layers suggests hydrologic events at least equal in size to and probably much larger than any storm or flood recorded during nearly 300 yr of written regional history layer thickness and frequency and by analogy storm size and recurrence change through the holocene the largest events occurred 2620 6840 and 9440 calibrated 14c years before present cal 14c yr b p the most frequent hydrologic events occurred in three periods 1750 to 2620 6330 to 6840 and 8600 cal yr b p the recurrence interval of layer deposition during stormy periods averages 130 100 cal yr whereas the recurrence interval during less stormy periods is longer 270 170 cal yr the ritterbush pond event record illustrates the potential of inorganic lacustrine sediment to serve as a proxy record for estimating paleoflood frequency and deciphering climate change

holocene sea level changes and glacio isostasy in the gulf of finland baltic sea abstract shoreline displacement in the eastern part of the gulf of finland during the past 9000 radiocarbon years was reconstructed by studying a total of 10 isolated lake and mire basins located in virolahti in southeastern finland and on the karelian isthmus and in ingermanland in russia study methods were diatom analyses sediment lithostratigraphical interpretation and radiocarbon dating in southeastern finland the marine litorina transgression maximum occurred ca 6500 6200 14 c yr bp 7400 7100 cal yr bp in areas of the slower land uplift rate on the karelian isthmus and in ingermanland the transgression maximum occurred ca 6400 6000 14 c yr bp 7300 6800 cal yr bp the highest litorina shoreline is located at ca 23 m above present sea level in southeastern finland whereas in the eastern part of the karelian isthmus near st petersburg it is located at ca 8 m above present sea level the amplitude of the litorina transgression in virolahti area is ca 4 m whereas on the karelian isthmus and in ingermanland the amplitude has varied between 5 and 7 m the regional differences between areas are solely due to different glacio isostatic land uplift rates the seven basins studied in this research were connected to the baltic sea basin during the litorina sea stage and their diatom and lithostratigraphical records indicate a single smooth litorina transgression

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

centennial scale cycles in middle holocene sea level along the southeastern swedish baltic coast submerged sea grasses and stoneworts growing in the immediate nearshore of the baltic sea are sensitive indicators of sea level the alternating changes in concentrations of sea grass and stonewort macrofossils obtained from an ancient lagoon of the baltic sea are ascribed to middle holocene sea level fluctuations along the southeastern swedish coast abundances of stonewort and sea grass macrofossils between 7500 and 6000 cal calibrated yr b p were lower and less variable indicating high and relatively stable sea level low frequency fluctuations of sea level with a 1470 yr period during this time may have been forced by tidal action in the millennial band after 6000 cal yr b p sea level was lower and exhibited strong fluctuations at centennial time scales as evident in the stonewort and sea grass macrofossil records such a high frequency oscillatory mode of sea level may have been regulated by centennial scale solar activities or tidal actions or both the modest variation in solar irradiance is unlikely to have resulted in large scale oscillations of sea level by directly changing the steric component instead it governed sea level fluctuations by changing the regional storminess through a north atlantic oscillation nao like system storms embedded in the nao induced southwesterly winds played a major role in the centennial scale fluctuations of the baltic sea level by pushing saltwater from the north sea into the baltic basin less

postglacial water level changes of a small lake in southern quebec canada sediment stratigraphy and palaeobotanical data from five cores were used to reconstruct the postglacial water level changes of a small lake in southern quebec the cores were taken along two transects from the centre of the lake to the margins lake level was relatively high before 11 000 cal bp when sedimen tation was characterized by the deposition of silty gyttja 13 000 cal bp and marl 13 000 11 000 cal bp from 11 000 to 7000 cal bp a sediment hiatus was indicated by the lack of two regional pollen zones between the marl and the overlying gyttja suggesting either nondeposition or erosion of the previously deposited sedi ments due to a low lake level the lake level was approximately 2 m lower than present on the basis of macrofossil assemblages a rise in the water level of about 1 m occurred around 7000 cal bp which was interrupted by a second lowering between 6100 and 4400 cal bp as indicated by a hiatus in the pollen stratigra phy during this low period the water level was at leas

early holocene history of the baltic sea as reflected in coastal sediments in blekinge southeastern sweden integrated palaeoecological studies of two fiord sediment sequences in the province of blekinge se sweden covering the time span 11 000 5000 cal bp reveal the timing and the environment for the ancylus lake littorina sea transition 9800 8500 cal bp the first ingression of saline water into the baltic sea through the danish straits occurred earlier than formerly assumed new evidence particularly mineral magnetic and palaeobotanical analyses demonstrate that on the general trend of the eustatically caused littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years bp a distinct regression phase around 8 100 cal bp is correlated with the greenland ice core cold event dated to 8200 ice core years bp this is described as a regional climatic catastrophe for the baltic sea region the coastal stratigraphy is compared with the offshore stratigraphy earlier studied a tentative shore displacement curve for early and middle holocene is presented

multi stage thrusting at the penninic front in the western alps between mont blanc and pelvoux massifs the different segments of the tectonic boundary between external european and internal penninic units in the western alps the so called penninic front pf formed at different times and according to different kinematic scenarios during a first episode eocene the pf corresponds to a transpressive suture zone between penninic and european units north to nnw trending stretching lineations found along internal nappe contacts within the penninic units are related to this episode this subduction zone was sealed by the priabonian flysch of the aiguilles d arves a detrital trench formation that formed during the final stages of subduction during a second episode starting in mid oligocene times the pf imaged along the ecors crop profile acted as a wnw directed thrust this thrust the roselend thrust rt only partially coincides with the pf south of moutiers the rt propagates into the dauphinois units carrying the former eocene pf including the priabonian flysch passively in its hangingwall south of the pelvoux massif the rt finds its continuation along the brianconnais front an out of sequence thrust behind the embrunais ubaye nappes on a larger scale our findings indicate oblique sinistral collision within the future western alps during the eocene followed by westward indentation of the adriatic block

excess 40ar transport scale and mechanism in high pressure phengites a case study from an eclogitized metabasite of the dora maira nappe western alps application of the bulk separate furnace heating laser step heating and in situ laser agemapping 40ar 39ar techniques reveals that high pressure phengites from an alpine eclogite of the dora maira basement nappe western alps were pervasively contaminated with excess 40ar to yield ages 130 ma spot fusion dating of individual grains with the 40ar 39ar laserprobe reveals concentric radial patterns with core ages as high as 320 ma showing that this excess component was trapped at an early stage and subsequently remobilized by volume diffusion during a late greenschist thermal pulse the single grains and population from this hand sample retain major differences in apparent ages indicating that the extent of the excess 40ar contamination varies from grain to grain attempt to model these differences in terms of grain size dependent fractional loss falls short and demonstrates that strong cm scale argon isotopic gradients locally prevailed during syn kinematic high pressure metamorphism on petrostructural grounds a model of internal isotopic buffering is outlined whereby the excess 40ar is argued to have been internally derived from within the eclogite protolith itself low intergranular ar diffusion rates due to reduced water activity buffered below unity by the phengite assemblage resulted in the local segregation and partitioning of the excess 40ar along grain boundaries during ongoing ductile deformation supporting evidence for this model comes from the recent literature on fluid and stable isotope behaviour in alpine eclogites and very high pressure metasediments which shows that volatile recycling during high pressure metamorphism may occur on a very limited scale

constraining absolute deformation ages the relationship between deformation mechanisms and isotope systematics isotope diffusion in a mineral is strongly temperature dependent but is also a function of grain size deformation must therefore be an important consideration in the interpretation of isotopic data because it provides a means of modifying grain size and shape we illustrate the range of different deformation mechanisms common in micas and use simple models to investigate the relationship between these and isotope diffusion we consider three different thermal scenarios with deformation taking place during a the prograde heating path b at the closure temperature of the deforming mineral and c at temperatures significantly below the closure temperature we have modelled these simple systems using a finite difference algorithm that simulates argon diffusion profiles and bulk ages this modelling illustrates that obtaining deformation ages is critically dependent on an understanding and recognition of the different deformation mechanisms that have affected the sample in the cases where deformation causes a change in grain size it is important to characterise both the temperature at which deformation takes place and the closure temperature of grains formed during the deformation the development of grains with tc greater than the deformation temperature may record a deformation age examples of this condition include i neocrystallisation ii grain size reduction occurring at temperatures below tc of the reduced grain size where the deformation mechanism has reset the grains and iii deformation induced grain coarsening

nucleation and growth of retrograde shear zones an example from the needle mountains colorado u s a abstract brittle and ductile deformation features are heterogeneously developed in late proterozoic retrograde normal slip shear zones that cross cut amphibolites and quartzo feldspathic gneisses in the needle mountains replacement of amphibolite grade minerals by greenschist facies assemblages is spatially related to transgranular fractures that cross cut the older gneissosity steeply dipping chlorite lined slip surfaces are associated with chlorite quartz muscovite filled dilational jogs and narrow breccia zones arrays of slip surfaces are transitional into similarly oriented phyllonite zones within which the foliation locally overprints early cataclastic zones the nucleation of these shear zones under greenschist facies conditions involved fluid infiltration along early transgranular fractures and hydration of fe mg bearing minerals initial displacement occurred by slip along these fractures and local cataclasite development fluids were episodically drawn into dilatant sites along these slip surfaces a transition to plastic deformation resulted directly from the metamorphic breakdown of feldspars and amphiboles to phyllosilicates which allowed strain localization into narrow phyllonite zones thus dilatancy produced by early brittle deformation appears to be the main process by which fluids infiltrate into developing greenschist grade retrograde shear zones reaction softening via hydration reactions causes a brittle to plastic transition and results in strain localization

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

neogene kinematics of the central and western alps evidence from fission track dating zircon and apatite fission track analysis has established the continuation of a zone of rapid change in mineral ages extending from the simplon fault zone in the simplon alps through the rhone valley and along the southeastern side of the mont blanc and belledonne massifs apatite fission track ages to the northwest of this zone generally range from 1 4 to 6 ma whereas those to the southeast range from 6 to 13 ma corresponding values for zircon are 11 13 and 16 26 ma respectively the zone corresponds to the position of the frontal pennine thrust in the mont blanc belledonne region this structure a prominent feature on recent deep seismic profiles may have been reactivated in the neogene with an important normal fault component this is suggested by apatite and zircon fission track ages in the footwall that are younger than those in the hanging wall and by the observed elimination of the lower pennine or simplon nappes along this fault zone in the rhone valley mont blanc belledonne region resulting in the juxtaposition of north penninic and helvetic ultra helvetic nappes at the current erosion level the distribution of fission track ages reflects this movement and the related neogene exhumation of the mont blanc and belledonne external massifs which has continued until less than 1 4 m y ago i e it is almost certainly still active and has tilted the overlying nappe sequence

holocene history of the baltic sea as recorded in a sediment core from the gotland deep a 4 m long sediment core from the gotland deep baltic sea was investigated by means of biostratigraphical and chemical parameters and c 14 datings this multidisciplinary approach allows us to ev

alpine thermal and structural evolution of the highest external crystalline massif the mont blanc 1 the alpine structural evolution of the mont blanc highest point of the alps 4810 m and of the surrounding area has been reexamined the mont blanc and the aiguilles rouges external crystalline massifs are windows of variscan basement within the penninic and helvetic nappes new structural 40ar 39ar and fission track data combined with a compilation of earlier p t estimates and geochronological data give constraints on the amount and timing of the mont blanc and aiguilles rouges massifs exhumation alpine exhumation of the aiguilles rouges was limited to the thickness of the overlying nappes 10 km while rocks now outcropping in the mont blanc have been exhumed from 15 to 20 km depth uplift of the two massifs started 22 myr ago probably above an incipient thrust the alpine sole thrust at 12 ma the ne sw trending mont blanc shear zone mbsz initiated it is a major steep reverse fault with a dextral component whose existence has been overlooked by most authors that brings the mont blanc above the aiguilles rouges total vertical throw on the mbsz is estimated to be between 4 and 8 km fission track data suggest that relative motion between the aiguilles rouges and the mont blanc stopped 4 myr ago since that time uplift of the mont blanc has mostly taken place along the mont blanc back thrust a steep north dipping fault bounding the southern flank of the range the european roof is located where the back thrust intersects the mbsz uplift of the mont blanc and aiguilles rouges occurred toward the end of motion on the helvetic basal decollement hbd at the base of the helvetic nappes but is coeval with the jura thin skinned belt northwestward thrusting and uplift of the external crystalline massifs above the alpine sole thrust deformed the overlying helvetic nappes and formed a backstop inducing the formation of the jura arc in that part of the external alps nw se shortening with minor dextral ne sw motions appears to have been continuous from 22 ma until at least 4 ma but may be still active today a sequential history of the alpine structural evolution of the units now outcropping nw of the pennine thrust is proposed

holocene environmental history of the gotland basin baltic sea a micropalaeontological model organic microfossils of a well dated sediment core from gotland basin were analysed and used for the ecological interpretation of the holocene history of this area to avoid confusion with corrected and uncorrected 14c ages only calendar years bp are used in the lowermost part organic microfossils are rare but few marine dinoflagellate cysts between 11 300 and 11 000 years bp indicate the marine yoldia phase at 9800 years bp a significant environmental change is indicated by the rapid increase of freshwater dinoflagellates and pine pollen at the end of the freshwater stage an enormous abundance increase of cladoceran remains indicates an eutrophication event between 7600 and 7400 years bp first permanent brackish water conditions of the surface water were established at 7400 years bp and the increasing salinity reached its maximum between 6700 and 6400 years bp further changes in the brackish surface water ecosystem of the gotland basin can be found at 5500 4400 3000 1000 and 800 years bp which are thought to be mainly climatically induced

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

holocene changes in atmospheric circulation recorded in the oxygen isotope stratigraphy of lacustrine carbonates from northern sweden the oxygen isotope composition of local precipitation delta 18 o p is reconstructed from carbonate lake sediment components in a sediment core covering the last 10000 calendar years from lake tibetanus a small hydrologically open groundwater fed take in the abisko area northern sweden comparison of the delta 18 o p history with a pollen based palaeotemperature record from the same core clearly reveals pronounced deviations from the normally expected temporal delta 18 o p temperature relation so called dansgaard relation that may be a function of changing oceanicity the transition from relatively moist maritime conditions in the early holocene to a much drier climate after 6500 cal bp is reflected by major changes in forest extent and composition as recorded by pollen and plant macrofossil data at the time of maximum influence of westerly air mass circulation high zonal index c 9500 cal bp brought about by high summer insolation and enhanced meridional pressure gradients delta 18 o p at lake tibetanus was about 2 higher than would be predicted by the modem isotope temperature relation the occurrence of long term changes in delta 18 o p temperature relations which are more sensitive measures of palaeoclimate than either delta 18 o p or temperature alone needs to be taken into account when extracting palaeoclimatic information from continental oxygen isotope records less

rb sr microchrons of synkinematic mica in mylonites an example from the dav fault of the eastern alps abstract a technique for texturally controlled microsampling from rock thick sections and subsequent rb sr dating of g sized samples has been developed it allows direct dating of minerals unequivocally related to deformation the technique has been applied to strictly synkinematically grown white mica prepared from mylonites related to the defereggen antholz vals dav fault south of the tauern window eastern alps control of deformation ages is provided by field relationships with independently dated plutons and dykes dated here by single mineral rb sr the field observations and isotopic ages are fully consistent and demonstrate that this is a reliable method for sub mm scale geochronology the ages obtained establish that sinistral strike slip shearing associated with the dav fault lasted from at least 33 ma to 30 ma followed by an abrupt change to dextral transpression related to the adjacent periadriatic fault

on the causes for salinity variations in the baltic sea during the last 8500 years 1 the baltic sea became connected to the open sea about 8500 years b p and that marked the beginning of the still continuing litorina sea stage there have since been significant long term variations of the salinity from a maximum of some 10 15 to the present of 7 8 the salinity variations have been known since the beginning of the twentieth century and various mechanisms have been proposed to explain these however so far no one has actually tried to quantify and thereby rank the relative importance of the different proposed mechanisms in this paper we used a simple oceanographic model to quantify the impact of changes in cross sectional areas of the inlets to the baltic we found that such changes cannot explain the full variation of the salinity we propose that the remaining salinity variations 0 5 5 are explained by changes in net freshwater input in the range 15 60 the calculated variations in the freshwater supply are in large coherent with known variations of the northern european climate we show that other possible factors as increased mixing frontal displacements higher deep water salinity and larger depths in kattegat and larger oscillating flows across the sills due to increased sea level variability are less likely to have made substantial contributions to the salinity variations in the baltic sea

fine scale isotopic heterogeneities and fluids in the deep crust a40ar 39ar laser ablation and tem study of muscovites from a granulite eclogite transition zone spectacular exposures on holsnoy island western norway reveal that eclogites formed in situ from adjacent anhydrous granulites as a result of the localized infiltration of fluids stepwise and laser40ar 39ar experiments on muscovite from the eclogites have been used in conjunction with electron microprobe and transmission electron microscopy tem analysis to examine the behavior of argon under high pressure metamorphism and subsequent cooling muscovites with 0 10 0 17na na k yield40ar 39ar plateau and integrated ages in the range 450 465 ma 20 35 myr older than40ar 39ar muscovite plateau ages from adjacent eclogite samples laser40ar 39ar analyses on 75 m spots across two single muscovite grains from these samples are approximately uniform at 444 2 1 9 21 spots and 443 3 1 7 ma 26 spots however incremental heating of high sodic 0 18 0 32 na na k muscovite failed to yield a plateau laser40ar 39ar analyses of 100 areas from two single grains from this sample reveal complex two dimensional patterns with variable apparent ages in the range of 445 625 ma electron microprobe measurements obtained from one of the grains reveal that the paragonite content is also highly variable both parallel and perpendicular to 001 all the tem bright field images obtained from this mica yield information consistent with a single homogeneous phyllosilicate phase yet several of the selected area electron diffraction saed analyses document locally intergrown muscovite and sodic muscovite possibly in an exsolution relationship on a unit cell scale analytical electron microscopy aem analyses obtained over a 5 100 nm scale on the same sample reveal great range and heterogeneity inna k including pure muscovite although no separate paragonite domains were found in contrast muscovite grains with consistent laser spot fusion and plateau ages show little heterogeneity inna k at the microprobe level these data provide evidence of variable fluid mediated incorporation of excess40ar under high pressure eclogite facies conditions at the time of the development of the sodic muscovite compositions the data indicate that fine scale heterogeneities in argon isotopic compositions were generated during eclogite facies equilibration and were preserved as the rocks were cycled back to the surface despite the influx of free fluids in the rocks at high pressure the heterogeneities are best reconciled with local buffering and limited mobility of the fluids at least during the final stages of equilibration

effects of progressive mylonitization on ar retention in biotites from the santa rosa mylonite zone california and thermochronologic implications the santa rosa mylonite zone developed predominantly from a granodiorite protolith in the eastern margin of the peninsular ranges batholith a wide variation in k ar biotite dates within the zone is shown to reflect the times of cooling through closure temperatures whose variability is chiefly a result of deformation induced reduction in grain size we suggest that such variation generally may be exploited to place constraints on the timing of deformation episodes previous workers have shown that deformation in the santa rosa mylonite zone involved the formation of mylonites and an imbricate series of low angle faults which divide the area into structural units field work petrographic studies and tem analysis of deformation mechanisms in biotite show that the granodiorite mylonite the lowermost structural unit formed below the granodiorite solidus the granodiorite mylonite varies from protomylonite to ultramylonite with regions of high strain distributed heterogeneously within the zone previously reported biotite and hornblende k ar dates from the granodiorite protolith below 82 89 ma and the asbestos mountain granodiorite above 61 68 ma the mylonite zone indicate dramatically dissimilar thermal histories for the lowermost and uppermost structural units other workers fission track dates on sphene zircon and apatite from the granodiorite mylonite and the asbestos mountain granodiorite suggest thermal homogenization and rapid cooling to 100 c by ca 60 ma within and adjacent to the mylonite zone k ar dates on 5 samples of biotite from variably deformed granodiorite range from 62 76 ma dates are not correlated with structural depth but clearly decrease with degree of deformation and concomitant grain size reduction 40ar 39ar incremental heating analyses of biotite from the granodiorite protolith reveals no evidence of excess argon and produces a relatively flat age spectrum 40ar 39ar incremental heating analysis of biotite from the granodiorite mylonite discloses discordance consistent with 39ar recoil loss k analysis of samples allowing k ar dates to be calculated is therefore recommended as an adjunct to 40ar 39ar step heating analysis in rocks that have experienced similar deformation during mylonitization biotite grain size reduction through intracrystalline cataclasis results in estimated grain dimensions as small as 0 05 m locally within porphyroclasts as large as 1 mm because biotite compositions are relatively uniform fe fe mg mn ti alvi 0 47 0 52 and show no systematic variation with grain size compositional dependence of activation energy and diffusivity can be eliminated as sources of variation in ar retention ar closure temperatures calculated with appropriate diffusion parameters for the observed grain sizes are in the range 220 280 c and define a cooling curve consistent with a thermal history intermediate between those of the granodiorite protolith below and the asbestos mountain granodiorite above the mylonite zone changes in the slope of the cooling curve indicate that the main deformation episode initiated at or above ca 330 c 80 ma above the closure temperature for thermally activated diffusion of argon in biotite and continued to a minimum of ca 220 260 c 62 ma

a review of the history of the baltic sea 13 0 8 0 ka bp abstract the dynamic history of the baltic sea during the millennia following the last deglaciation has been one of the main topics for many generations of quaternary geologists around the baltic sea based on the present state of knowledge and certain hypotheses a model for the development during the baltic ice lake yoldia sea and ancylus lake stages are presented the oresund strait was the threshold of the initial stage of the baltic ice lake and was eroded down to bedrock as a result of the isostatic uplift the emerging threshold forced the baltic ice lake to rise above sea level at ca 12 0 ka bp this gradual up damming ended at ca 11 2 ka bp when the large glacial lake was lowered 5 10m by possible subglacial drainage at mt billingen a glacial readvance during the younger dryas ended a ca 400 year long land bridge between sweden and the continent by blocking the former drainage route once again the baltic ice lake had to rise above sea level to be drained over the oresund strait at ca 10 5 ka bp a gradual ice recession began and 200 years later when the receding ice sheet could not withhold the up dammed water masses the final drainage of the baltic ice lake occurred which rapidly lowered the water level within the baltic basin with ca 25 m and ended the baltic ice lake stage the next stage the yoldia sea was characterized by a complex pattern of relative sea level changes with large differences within the baltic basin a very restricted baltic sea in the south and thus an extensive landbridge at ca 9 9 ka bp a short 100 200 years saline ingression is seen in the baltic sediment records from stockholm in the north to the southernmost parts of the yoldia sea the gradually shallower strait in south central sweden the narke strait ended the saline influence 300 400 years later the two remaining outlets west of lake vanern gota alv and otteid steinselva had become too shallow to swallow the outflowing yoldia sea waters at this stage the baltic lake vanern level could thus not fall in pace with the relative sea level fall outside the outlet areas this was the isolation of lake vanern and the baltic from the sea and the beginning of the ancylus lake since the water depth of the larger gota alv outlet had to be more or less maintained the ancylus lake level had to rise in pace with the uplift of the outlet region this caused a significant and rapid transgression 10 30 m in ca 300 years in the southern baltic which flooded large areas with recently immigrated pine forests since the oresund strait during the yoldia sea stage had been uplifted more than southerly areas the ancylus transgression ended with a new drainage pathway at ca 9 2 ka bp through the darss sill area in the southern baltic and northwards through the store belt strait this so called dana river had cut off the former large land bridge the quaternary deposits of this new threshold were eroded and a fairly rapid regression set in at ca 9 0 ka bp the dana river had eroded down to the sea level which isolated lake vanern from the ancylus lake and created a land bridge between southern sweden and northwards ca 800 years later when the sea level rose above the oresund threshold marine water could enter the baltic and at ca 8 0 ka bp brackish water characterized the southern baltic this marks the end of the ancylus lake

millennial scale storminess variability in the northeastern united states during the holocene epoch for the purpose of detecting the effects of human activities on climate change it is important to document natural change in past climate1 in this context it has proved particularly difficult to study the variability in the occurrence of extreme climate events such as storms with exceptional rainfall1 previous investigations have established storm chronologies using sediment cores from single lakes2 3 4 5 6 7 8 but such studies can be susceptible to local environmental bias here we date terrigenous inwash layers in cores from 13 lakes which show that the frequency of storm related floods in the northeastern united states has varied in regular cycles during the past 13 000 years 13 kyr with a characteristic period of about 3 kyr our data show four peaks in storminess during the past 14 kyr approximately 2 6 5 8 9 1 and 11 9 kyr ago this pattern is consistent with long term changes in the average sign of the arctic oscillation9 suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of holocene climate variability in north america and europe

deep fluid circulation in alpine shear zones pyrenees france field and oxygen isotope studies a combined field stable isotope and whole rock chemical study was made on late cretaceous to tertiary metasomatic shear zones cutting hercynian gneisses in the aston massif pyrenees france mylonitisation occurred during the early stages of alpine compression under retrograde conditions at 400 450 c and about 10 km depth whole rock 18o values of 11 to 12 in the gneisses was lowered to 5 to 9 in the shear zones with the quartz muscovite 18o 16o fractionations of about 2 to 4 essentially unchanged these 18o 16o systematics together with d muscovite 40 to 50 indicate that large volumes of formation waters or d rich meteoric waters passed through the shear zones during deformation the same fluids also redistributed major elements as shown by the correlation of 18o shift with muscovitisation and albitisation reactions in granitic wall rocks however even though 18o was universally lowered within the shear zones the 18o 16o ratios were not homogenised nor do they correlate in detail with the presence or absence of muscovitisation suggesting that fluid flow was probably fracture controlled and episodic field mapping shows that along the length of a particular shear zone muscovitisation of granite gneiss dies out 150m above the contact with underlying sillimanite gneiss thus muscovitisation and albitisation of granite gneiss in shear zones and their wall rocks probably occurred during re equilibration of acidic chloride rich aqueous fluids that had previously moved upward within the shear zones through underlying sillimanite gneiss extremely high material balance fluid rock ratios 103 are required to explain the extent of muscovitisation along this shear zone implying integrated fluid mass fluxes of about 108 kg m2 this is probably close to the maximum value for other shear zones in the network similar volumes of a more chemically evolved fluid must have passed through the unmuscovitised mylonites showing that the absence of alteration cannot necessarily be used to infer low values of fluid flux for reasonable pressure gradients and time scales of fluid movement effective permeabilities of 10 15 to 10 17 m2 are required such values can be accounted for by short lived widely spaced cracks produced during seismic activity a model is presented in which formation waters were seismically pumped down an underlying shallow southward dipping decollement and then upward through the steeply dipping shear zone network

salinity changes in the central baltic sea nw europe over the last 10000 years we attempt a reconstruction of salinity levels of the central baltic sea based on diatom assemblages the isotopic composition of organic matter and sedimentological expression of anoxia over the last 10 000 years we use the data to investigate the dependence of salinity levels on climate evolution and isostasy changes in salinity of surface and deep waters were most pronounced from 8400 to approximately 5000 cal bp density stratification between salty deep and fresher surface waters caused the frequent development of anoxic conditions and deposition of laminated sediments on large parts of the sea floor in the central baltic sea and dramatic changes in organic carbon accumulation rates from 5000 to 3100 cal bp the salinity of the basin decreased oxygenation of deep sea floors was improved and fertility of the sea surface was significantly reduced this is reflected by low accumulation rates of organic carbon in bioturbated sediments since 2800 cal bp salinity rose again and anoxic periods were more common even though the major steps in environmental evolution in the baltic sea coincide with known patterns of climatic change of the north atlantic realm over the last 10 000 years we find no conclusive evidence for synchronous changes or linear responses on submillennial timescales however we note that major variations in our salinity records agree with temporal patterns of reconstructed summer warmth and winter precipitation in southern scandinavia both types of record suggest that climate in the mid holocene was far from stable our data also confirm that climate evolution over the late holocene had significant impact on environmental conditions in the baltic sea

staircase 40 ar39ar spectra of fine grained white mica timing and duration of deformation and empirical constraints on argon diffusion staircase 40 ar 39 ar spectra of 2 to 6 m white micas in ductile carbonate mylonites morcles doldenhorn nappe switzerland record ages between 32 and 13 ma these ages are within independent geochronologic and biostratigraphic time limits for the beginning and ending of deformation of this fold thrust nappe we interpret these data to record protracted white mica neocrystallization and growth during low temperature ductile deformation such that the differences between the maximum and minimum ages in the 40 ar 39 ar spectra record the time span over which mica formed and grew we have modeled the argon concentrations in these micas taking into account the thermal history of the nappe mica growth and diffusional loss of argon our results indicate that available experimental data underestimate the activation energy for argon diffusion in muscovite and that the retentivity of argon in white mica is greater than generally thought

a dinoflagellate cyst record of holocene climate and hydrological changes along the southeastern swedish baltic coast a high resolution well dated dinoflagellate cyst record from a lagoon of the southeastern swedish baltic sea reveals climate and hydrological changes during the holocene marine dinoflagellate cysts occurred initially at about 8600 cal yr bp indicating the onset of the littorina transgression in the southeastern swedish lowland associated with global sea level rise and thus the opening of the danish straits both the species diversity and the total accumulation rates of dinoflagellate cysts continued to increase by 7000 cal yr bp and then decreased progressively this pattern reveals the first order change in local sea level as a function of ice volume equivalent sea level rise versus isostatic land uplift superimposed upon this local sea level trend well defined fluctuations of the total accumulation rates of dinoflagellate cysts occurred on quasi 1000 and 500 yr frequency bands particularly between 7500 and 4000 cal yr bp when the connection between the baltic basin and the north atlantic was broader a close correlation of the total accumulation rates of dinoflagellate cysts with gisp2 ice core sea salt ions suggests that fluctuations of baltic surface conditions during the middle holocene might have been regulated by quasi periodic variations of the prevailing southwesterly winds most likely through a system similar to the dipole oscillation of the modern north atlantic atmosphere

40ar 39ar dating of synkinematic white mica insights from fluid rock reaction in low grade shear zones mont blanc massif and constraints on timing of deformation in the nw external alps this paper highlights the use of synkinematic white mica biotite and phlogopite for the dating of deformation in ductile shear zones within crystalline rocks under low grade metamorphic conditions the mont blanc shear zones range from 1 mm to 50 m in width and have localized intense fluid flow resulting in substantial differences in mineralogy and whole rock geochemistry on the basis of their synkinematic alteration assemblages and geographic distribution within the mont blanc massif three main metamorphic zones are distinguished within the network of shear zones these are i epidote white mica bearing assemblages ii chlorite phlogopite bearing assemblages and iii white mica biotite calcite actinolite epidote bearing assemblages 40ar 39ar age spectra of biotite and phlogopite are complex and reflect significant variations in chemical composition in biotite this is partly due to inheritance from precursor variscan magmatic biotite in contrast new white mica grew at the expense of feldspar during alpine deformation and its ar spectra do not show any excess 40ar on the se side of mont blanc ages of shear zone phengites have a narrow range of 15 8 16 0 0 2 ma which is in the same age range as 40ar 39ar ages of minerals from kinematically related veins the top to se sense of shear is consistent with initiation of a mont blanc flower structure within a dextral transpressional system by 16 ma on the nw side mini plateaux ages of 14 5 0 3 and 23 4 0 4 ma are preserved in the same sample suggesting the possibility of two phases of deformation this is also supported by partly preserved ages of 18 36 6 ma in biotites and phlogopites ages between 36 and 18 ma might reflect ongoing top to nw thrusting following penninic front activation in a context of nappe stacking and crustal thickening nw directed thrusting on the nw side of mont blanc continued after 18 ma synchronous with se directed thrusting on the se side of the massif these divergent movements produced the overall pop up geometry of the mont blanc massif which may correspond to a positive flower structure developed within a zone of regional dextral transpression extending sw from the rhone valley into the mont blanc area

holocene history of the baltic sea as a background for assessing records of human impact in the sediments of the gotland basin sediment cores from the gotland basin were studied for their siliceous microfossil assemblages and organic carbon content to compare recent environmental changes in the baltic sea with its natural

decadal to millennial scale periodicities in north iceland shelf sediments over the last 12 000 cal yr long term north atlantic oceanographic variability and solar forcing giant piston core md99 2269 recovered 25 m of sediment in hunafloaall a deep trough on the north iceland margin fronting the iceland sea and the site of a shelf sediment drift the rate of sediment accumulation is 2 m kyr 5 yr cm the core terminated in the vedde tephra v12 cal ka the sediment was sampled at between 5 and 50 yr sample including rock magnetic grain size and sediment properties data reduction was carried out using principal component analysis two pc axes for the 5 yr sample magnetic data are strongly correlated with measures of coercivity arm20 mt arm and magnetic concentrations karm in turn arm20 mt arm is highly correlated negatively with grain size and the mean size of the sortable silt fraction analyses of the two pc axes with mtm spectral methods indicate a series of significant s 99 periodicities at millennial to multidecadal scales including those at v200 125 and 88 yr which are associated with solar variability we also document a strong correlation between the sediment magnetic properties and the d 18 o on benthic foraminifera on the north iceland inner shelf we hypothesize that the links between variations in grain size magnetic concentrations and solar forcing are controlled by atmospheric and oceanographic changes linked to changes in the relative advection of atlantic and polar waters along the north iceland margin today these changes are associated with variations in the deep convection in the greenland and iceland seas the precise linkages are however presently elusive although a combination of coarser sediments and low d 18 o values define a holocene thermal maximum between v8 and 6 cal ka 2003 elsevier science b v all rights reserved

palaeo oceanography deepwater variability in the holocene epoch the conversion of surface water to deep water in the north atlantic results in the release of heat from the ocean to the atmosphere which may have amplified millennial scale climate variability during glacial times1 and could even have contributed to the past 11 700 years of relatively mild climate known as the holocene epoch 2 3 4 here we investigate changes in the carbon isotope composition of benthic foraminifera throughout the holocene and find that deep water production varied on a centennial millennial timescale these variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period

reconstructing salinity changes and environmental influence on dinoflagellate cysts in the central baltic sea since the late 19th century abstract we present a record of dinoflagellate cyst assemblage composition abundance and morphology from the central baltic sea spanning the late 19th to the early 21st centuries environmental time series were analyzed in relation to changes in community structure and diversity as inferred from the sediment record and average summer sea surface salinity sss was reconstructed based on the average process length of protoceratium reticulatum resting cysts the reconstructed summer sss was compared to instrumental data for a critical evaluation of this approach the most abundant species in this record were p reticulatum and biecheleria baltica and on average ten taxa were identified per sample the cyst record of b baltica indicated that although this species has been present in the gotland basin at least since the 1880s its concentrations have increased significantly since the 1980s possibly linked to eutrophication variations in assemblage composition and p reticulatum cyst morphology reflected patterns of major instrumentally recorded hydrographic and environmental changes in the baltic sea during the past century the variability in microfossil relative abundances was best explained by the average spring sss as well as by the average no3 concentrations during spring and by the combined effects of average summer sss and nao variability reconstructed summer sss and instrumental sss showed notable differences depending on the year and function applied for reconstruction although roughly reflecting the same patterns the reconstructed values are offset when compared to instrumental measurements we put forward suggestions for improvement of the process length method and recommend using the reconstructed values as an indication of relative changes in past summer sea surface salinity preferably as part of a multiproxy approach