weichselian land sea interactions western norway norwegian sea abstract six major weichselian glacier expansions including the younger dryas are recorded in western norway three of the advances reached the continental shelf while the others were restricted to the coastal areas during the upper weichselian glacial maximum 18 20 ka there was an ice free corridor between the british and the scandinavian ice sheets in the northern north sea more or less complete deglaciation of southern norway seems to have happened some time around 90 and 70 ka large parts of the norwegian sea were at least seasonally open with influx of atlantic surface water in periods through isotope substage 5d to stage 4 possibly also during a short time interval close to the 2 3 boundary a small area in the southeastern norwegian sea was ice free all these influxes of atlantic water seem to correlate to periods with interstadial conditions in western norway during times with the most extensive continental glaciations there are no traces of any influx of atlantic surface water the western norwegian glacial record and the norwegian sea surface circulation record seem to vary with a ca 20 ka cycle during the weichselian this indicates a dominance of the precessional orbital forcing between the ca 100 ka interglacial glacial interglacial cycle

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

full traveltime inversion abstractmany previously published wave equation based methods which attempt to automatically invert traveltime or kinematic information in seismic data or migrated gathers for smooth velocities suffer a common and severe problem the inversions are involuntarily and unconsciously hijacked by amplitude information to overcome this problem we have developed a new wave equation based traveltime inversion methodology referred to as full traveltime i e fully dependent on traveltime inversion fti to automatically estimate a kinematically accurate velocity model from seismic data the key idea of fti is to make the inversion fully dependent on traveltime information and thus prevent amplitude interference during inversion under the assumption that velocity perturbations cause only traveltime changes we have derived the fti method in the data and image domains which are applicable to transmitted arrivals and reflected waves respectively fti does not require an accurate initial velocity model or

isotopic sm nd signatures of precambrian banded iron formation from the fennoscandian shield east european platform and bundelkhand craton india abstract in this communication we report geochemical and sm nd isotope data of banded iron formation bif from kola karelia fennoscandian shield east european platform and bundelkhand craton n e india the bifs from kola karelia algoma type and bundelkhand craton algoma type north central india and east european platform superior type characterized by alternate domains of quartz rich and iron rich layers except for magnetite and hematite orthopyroxene amphibole and garnet are the other dominant minerals present the bif s the shale normalized ree spectra of iron rich layers of bundelkhand kola karelia and east european bifs are similar the end t for silica rich layers is higher compared to the iron rich layers for all studied samples the higher end t values around 5 0 for silica rich layers from kola karelia bundelkhand bif and east european platform suggest a juvenile source for silica the lower end t values 5 to 2 for iron rich layers from the same samples implies continental source for the iron the present study suggests that the sedimentation mechanisms of silica and iron for algoma as well as superior types bifs are similar despite spatial diversity

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

late weichselian and early holocene shore displacement in the central baltic sea abstract the glacial unloading and resulting isostatic land uplift have together with hydro isostasy eustatic rise of sea level and geoidal changes ruled the shore displacement of fennoscandia within the baltic basin periods of damming and shifts of outlet further complicated the shore displacement during the period studied ca 12 2 8 4 ka bp information on the baltic history was derived from shoreline observations and studies on sediment cores from lakes formerly directly affected by the baltic these cores were analyzed with respect to pollen diatoms and lithology to determine sequences of baltic sediments and dated by a combination of radiocarbon dates and biostratigraphy the studied areas of southeastern sweden mainly central gotland and the oskarshamn area eastern smaland display a similar course of shore displacement the late weichselian period shows a regression of a slightly decreasing rate between ca 12 2 and 10 3 ka bp then followed a fast drop 25 m of the baltic s water level the final drainage of the baltic ice lake during the next ca 700 years the yoldia stage a regression of ca 17 m occurred this period is mainly characterized by freshwater diatoms in the baltic but at ca 10 ka bp there is evidence of a shortlasting 100 150 year period with brackish water the ancylus transgression of ca 11 m began ca 9 6 ka bp and culminated ca 9 3 ka bp it was followed by a fast regression of 8 10 m thereafter the rate of regression decreased shoreline gradients showed that the fastest shoreline tilting occurred around 10 ka bp thus ca 2 ka after deglaciation

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part i theoretical aspects we present a new method based on migration velocity analysis mva to estimate 2 d velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field classical approaches using picking on common image gathers cigs must consider continuous events over the whole panel this interpretive step may be difficult particularly for applications on real data sets we propose to overcome the limiting factor by considering locally coherent events a locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube in the prestack depth migrated volume obtained for an a priori velocity model locally coherent events are picked automatically without interpretation and are characterized by their positions and slopes tangent to the event even a single locally coherent event has information on the unknown velocity model carried by the value of the slope measured in the cig the velocity is e

viscosity and thickness of the asthenosphere detected from the fennoscandian uplift the earth s response to the deglaciation in fennoscandia is modelled using a layered viscous model with an elastic lithosphere the modelled tilting of palaeoshorelines at particular locations peripheral to the former ice load and the pattern of the present rate of uplift consistent with the observations strongly suggest a low viscosity asthenosphere earth models without a low viscosity asthenosphere give significant mismatch to the present rate of uplift and are unable to mimic the observed tilting of palaeoshorelines models with a viscosity of the lower mantle of 1 0 2 0 1021 pa s and a viscosity of the upper mantle of 0 7 1 0 1021 pa s overlain by low viscosity asthenosphere with a thickness ranging from 25 to 100 km fit equally well with the observations it is suggested strongly that the asthenosphere has a thickness of less than 150 km and a viscosity of less than 7 0 1019 pa s

wave equation reflection traveltime inversion with dynamic warping and full waveform inversion abstractin reflection seismology full waveform inversion fwi can generate high wavenumber subsurface velocity models but often suffers from an objective function with local minima caused mainly by the absence of low frequencies in seismograms these local minima cause cycle skipping when the low wavenumber component in the initial velocity model for fwi is far from the true model to avoid cycle skipping we discovered a new wave equation reflection traveltime inversion werti to update the low wavenumber component of the velocity model while using fwi to only update high wavenumber details of the model we implemented the low and high wavenumber inversions in an alternating way in werti we used dynamic image warping diw to estimate the time shifts between recorded data and synthetic data when compared with correlation based techniques often used in traveltime estimation diw can avoid cycle skipping and estimate the time shifts accurately even when shifts vary rapidly hence by minimizing tr

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

sensitivity kernel based tomographic migration velocity analysis using reverse time migration angle image gathers abstractsensitivity kernel based tomographic migration velocity analysis tmva provides a means to better update the migration velocity model in complex media for actual seismic data with finite frequency bandwidth migration velocity updated from wave equation based tomography is more suitable and robust than ray based tomography for images obtained from reverse time migration rtm depth residuals in the rtm extracted angle image gathers offer a reliable source of velocity information we have developed cost effective means of calculating the angle domain sensitivity kernel and incorporated it into the tmva approach using rtm angle image gathers the angle domain sensitivity kernels are used to convert the depth residuals from rtm angle image gathers into velocity perturbations which were then used to refine the velocity model we derived an approximate analytical residual moveout function for measuring depth residuals of the rtm angle image gather in isotropic media and also devised a workflow for

tomographic determination of three dimensional seismic velocity structure using well logs vertical seismic profiles and surface seismic data a tomographic technique traveltime inversion has been developed to obtain a two or three dimensional velocity structure of the subsurface from well logs vertical seismic profiles vsp and surface seismic measurements the earth was modeled by continuous curved interfaces polynomial or sinusoidal series separating regions of constant velocity or transversely isotropic velocity ray tracing for each seismic source receiver pair was performed by solving a system of nonlinear equations which satisfy the generalized snell s law surface to borehole and surface to surface rays were included a damped least squares formulation provided the updating of the earth model by minimizing the difference between the traveltimes picked from the real data and calculated traveltimes synthetic results indicated the following conclusions for noise free cases the inversion converged closely from the initial guess to the true model for either surface or vsp data adding random noise to the observations and performin

wave equation traveltime inversion this paper presents a new traveltime inversion method based on the wave equation in this new method designated as wave equation traveltime inversion wt seismograms are computed by any full wave forward modeling method we use a finite difference method the velocity model is perturbed until the traveltimes from the synthetic seismograms are best fitted to the observed traveltimes in a least squares sense a gradient optimization method is used and the formula for the frechet derivative perturbation of traveltimes with respect to velocity is derived directly from the wave equation no traveltime picking or ray tracing is necessary and there are no high frequency assumptions about the data body wave diffraction reflection and head wave traveltimes can be incorporated into the inversion in the high frequency limit wt inversion reduces to ray based traveltime tomography it can also be shown that wt inversion is approximately equivalent to full wave inversion when the starting velocity model is

the last interglacial glacial cycle in denmark abstract the stratigraphy of late pleistocene interglacial interstadial and stadial deposits in denmark shows radical alternation of marine and terrestrial environments within the last interglacial glacial cycle isotope stages 6 2 climatically dependent environmental changes eustatic and isostatic responses combined with the advance and retreat of glaciers are elements in a chronostratigraphic model for sw scandinavia the late saalian borglum margreteberg interstade isotope stage 6 was characterized by arctic to boreo arctic marine conditions and tundra vegetation the eemian interglaciation isotope substage 5e reflects high sea levels with boreo lusitanian marine faunas and dense temperate forests in the early weichselian brorup interstade isotope substage 5c boreal to boreo arctic seas with relatively low water level prevailed along with open forest vegetation the middle weichselian commenced with arctic seas accompanied by ice rafting and followed by major glacier cover possibly reaching eastern denmark karmoy ristinge goteborg i stade isotope stage 4 the bo older dosebacka hirtshals interstade isotope stage 3 witnessed boreo arctic conditions with ice rafting and the establishment of a park tundra vegetation during the later jaeren goteborg ii vennebjerg stade isotope stage 3 shelf ice appeared in high arctic kattegat and skagerrak along with surging glaciers in the baltic the middle weichselian isotope stage 3 ended with the sandnes mon gardslov interstade park tundra and boreo arctic seas prevailed the late weichselian jylland stade isotope stage 2 comprises complex stadial conditions with glacier advance and retreat the jylland stade peaked with the maximum extension of weichselian glaciers along the main stationary line equivalent to the frankfurt poznan glacial stage on the north european continent

the effect of spatially non uniform water loads on prediction of sea level change summary numerical modelling of postglacial rebound predics a spatially variable pattern of sea level change yet many previous models predicting late pleistocene sea level change either neglect the load of water added to the oceans or assume a spatially uniform time dependent load over the whole ocean this is a poor approximation of the load near the former ice sheet since sea level change varies geographically in addition the coastline goemetry changes through time a spectral technique has been used to solve the sea level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice ocean configuration the axisymmetric model is useful for demonstrating the fundamental physics involved in sea level changes caused by changes in surface loads in particular it can be seen that the elastic and gravitational response to the load is spread over a great distance whereas the viscous response is more localized a realistic ice ocean configuration has been used to demonstrate that neglect of the melt water load underestimates the amount of uplift in fennoscandia and other regions where rebound occurs in the ocean as previously noted by wu peltier 1983 in hudson bay and that movement of the coastlines and spatially varying water loads must both be included in calculations for the north sea and other near field regions with shallow seas sea level calculations including these effects and careful analysis of the sea level and ice melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

automatic velocity analysis via shot profile migration we described an implementation of differential semblance velocity analysis based on shot profile migration and illustrated its ability to estimate complex strongly refracting velocity fields the differential semblance approach to velocity analysis uses waveform data directly it does not require any sort of traveltime picking the objective function minimized by the differential semblance algorithm can measure either focusing of the image in offset or flatness of the image in scattering angle we showed that the offset variant of differential semblance yields somewhat more reliable migration velocity estimates than does the scattering angle variant and we explain why this is so we observed that inconsistency with the underlying model born scattering about a transparent background can lead to degraded velocity estimates from differential semblance and we showed how to augment the objective function with stack power to enhance ultimate accuracy a 2d marine survey over a target obscured by the lensing effects of a gas chimney provides an opportunity for direct comparison of differential semblance with reflection tomography the differential semblance estimate yields a more data consistent model flatter angle gathers than does reflection tomography in this application resulting in a more interpretable image below the gas cloud

holocene evolution of relative sea level and local mean high water spring tides in belgium a first assessment abstract holocene age depth data from the belgian coastal plain basal peat data particularly are assessed in terms of local water and tide levels basal peat formation was generally induced by sea level rise effects of local seepage were limited and significant river gradient effects were absent no relation was found between the timing of basal peat inception and substrate permeability in general edaphic moisture conditions were unfavourable for organic accumulation prior to sea level related rise of the groundwater table error envelopes for the minimum level of local mean high water spring tides and for upper and extreme lower relative mean sea level limits during the last 9400 solar years 8400 yrs b p are presented these indicate that the rate of relative sea level rise showed marked retardations at ca 7500 7000 yrs cal b p 6650 6100 yrs b p and ca 5500 5000 yrs cal b p 4400 yrs b p a eustatic explanation appears to be plausible particularly for the former prior to ca 4000 yrs cal b p ca 3600 yrs b p the relative sea level rise in belgium differs noticeably from that established for the western netherlands with both diverging progressively back in time this implies that considerable differential crustal movement occurred between the two areas in the early holocene

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

deep seismic expression of an ancient plate boundary in europe seismological results on the structure of the upper mantle below europe reveal a marked contrast in seismic properties between precambrian and younger parts of europe the precambrian craton in eastern europe is characterized by high shear wave velocities which can be explained by low temperatures the transition to low seismic velocities below phanerozoic europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers despite the long and complex tectonic history of the plate boundary zone the transition is remarkably sharp which rules out any significant lateral transport of asthenospheric material across the suture zone