permo carboniferous magmatism of the northeast german basin abstract variscan continent continent collision in central europe was followed by a period of syn to late tectonic magmatism involving the extrusion of large volumes of permosilesian age volcanic rocks particularly in the northeast german basin the volcanic suite up to ca 2000 m thick comprises rhyolites acid and basic andesites and tholeiitic and alkali basalts tectono geochemical analysis in conjunction with volume calculations and petrography reveals changes in volcanic activity over time a total of five eruptive stages are recognised beginning in the stephanian and extending up into the upper rotliegend permian these include the stephanian late carboniferous andesite pre ignimbrite stage i lower rotliegend permian age explosive ignimbrite stage ii post ignimbrite stage iii late rhyolite stage iv and upper rotliegend permian age late basalt stage v in addition several volcanic centres including at least two large caldera like structures are recognised the total calculated volume for the northeast german basin volcanics is ca 48 000 km3 comprising rhyolitic rocks and ignimbrites ca 70 andesitic rocks ca 26 and basalts with cogenetic dolerites ca 4 regional variations in composition and geochemistry are related to diverse crust mantle regimes which correlate with differing positions relative to the heterogeneous basement of the variscan foredeep or within the rhenohercynian orogenic zone the crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre existing subduction influenced basaltic magma source

crustal memory and basin evolution in the central european basin system new insights from a 3d structural model abstract the central european basin system cebs is composed of a series of subbasins the largest of which are 1 the norwegian danish basin 2 the north german basin extending westward into the southern north sea and 3 the polish basin a 3d structural model of the cebs is presented which integrates the thickness of the crust below the permian and five layers representing the permian cenozoic sediments structural interpretations derived from the 3d model and from backstripping are discussed with respect to published seismic data the analysis of structural relationships across the cebs suggests that basin evolution was controlled to a large degree by the presence of major zones of crustal weakness the nw se striking tornquist zone the ringkobing fyn high rfh and the elbe fault system efs provided the borders for the large permo mesozoic basins which developed along axes parallel to these fault systems the tornquist zone as the most prominent of these zones limited the area affected by permian cenozoic subsidence to the north movements along the tornquist zone the margins of the ringkobing fyn high and the elbe fault system could have influenced basin initiation thermal destabilization of the crust between the major nw se striking fault systems however was a second factor controlling the initiation and subsidence in the permo mesozoic basins in the triassic a change of the regional stress field caused the formation of large grabens central graben horn graben gluckstadt graben perpendicular to the tornquist zone the ringkobing fyn high and the elbe fault system the resulting subsidence pattern can be explained by a superposition of declining thermal subsidence and regional extension this led to a dissection of the ringkobing fyn high resulting in offsets of the older nw se elements by the younger n s elements in the late cretaceous the nw se elements were reactivated during compression the direction of which was such that it did not favour inversion of n s elements a distinct change in subsidence controlling factors led to a shift of the main depocentre to the central north sea in the cenozoic in this last phase n s striking structures in the north sea and nw se striking structures in the netherlands are reactivated as subsidence areas which are in line with the direction of present maximum compression the moho topography below the cebs varies over a wide range below the n s trending cenozoic depocentre in the north sea the crust is only 20 km thick compared to about 30 km below the largest part of the cebs the crust is up to 40 km thick below the ringkobing fyn high and up to 45 km along the teisseyre tornquist zone crustal thickness gradients are present across the tornquist zone and across the borders of the ringkobing fyn high but not across the elbe fault system the n s striking structural elements are generally underlain by a thinner crust than the other parts of the cebs the main fault systems in the permian to cenozoic sediment fill of the cebs are located above zones in the deeper crust across which a change in geophysical properties as p wave velocities or gravimetric response is observed this indicates that these structures served as templates in the crustal memory and that the prerift configuration of the continental crust is a major controlling factor for the subsequent basin evolution

structure and quantification of processes controlling the evolution of the inverted ne german basin abstract a ne sw reflection seismic transect crossing the entire ne german basin negb was investigated in detail to study the interaction between tectonics and sedimentation during the multiphase evolution of the region by restoring a geological section across the post rotliegend the kinematic evolution was reconstructed and rates of important geological processes such as erosion or basin shortening were quantified the present day structural style of the negb is the result of several major deformation events 1 regional subsidence accompanied by local thin skinned e w extension during the permo triassic jurassic was followed by basin inversions at the 2 jurassic cretaceous and at the 3 cretaceous tertiary boundary zechstein salt played an important role since mobile zechstein evaporites decoupled the supra salt from the sub salt succession and allowed the transmission of deformation over a large distance of major significance to the late cretaceous structural development was the crustal scale upthrusting of the calfoerde block along the gardelegen fault at the southern basin margin the accompanying horizontal shortening has a minimum value of 9 km and led to the development of thrusts and folds within the post zechstein succession

summary of project tor delineation of a stepwise sharp deep lithosphere transition across germany denmark sweden project tor teleseismic tomography across the tornquist zone in germany denmark sweden is now producing results we are able to detect very significant deep lithosphere differences and we can now discuss the sharpness laterally in 1996 1997 our 120 seismographs constituted the largest seismic antenna ever in europe the tor area was chosen along a well studied crustal profile of an earlier project and the inversion efforts are concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km the tor investigation can be called two and a half dimensional as it has a 900 km profile length with 100 km width plus a few seismographs off the profile the tor data have been subjected to p wave travel time tomography surface wave and receiver function analysis as well as anisotropy and scattering measurements through ray tracing in a compiled crustal model and subtraction of the modelled travel time anomalies the influence of the lower lithosphere asthenosphere on the seismic rays from distant earthquakes is being established travel time tomography results confirm very large lateral lithosphere differences of 4 6 in p wave velocity for several events of the large data base it is demonstrated that the observed p wave travel time anomalies of 1 2 s can be divided almost equally between known crustal effects and lower lithosphere asthenosphere differences which then must account for about 1 s of the travel time differences the transition is interpreted to be sharp and steep in two places it goes all the way through the lithosphere at the northern rim of the tornquist zone near the border between sweden and denmark and here the lithosphere difference is large a smaller lithosphere difference is found near the southern edge of the ringkobing fyn high just north of the border between denmark and germany also this transition is sharp and steep and goes all through the lithosphere these two sharp transitions divide the tor region into three different lithosphere structures distinguishable in p wave travel time tomography surface wave dispersion p and s wave anisotropy and partly in p wave scattering

evolution of the northeast german basin inferences from a 3d structural model and subsidence analysis abstract a 3d structural model of the northeast german basin was evaluated with special emphasis on its evolution as an intracontinental depression the study includes investigations on subsidence history and structural setting of the basin thickness evolution and calculated tectonic subsidence volumes of permian to quaternary sediments in the northeast german basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms for the initial rift phase in the late carboniferous to early permian a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence the main part of basin subsidence occurred in a nw se oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from early permian rotliegend to middle triassic muschelkalk from middle triassic the thermal subsidence pattern was superposed by further tectonic events in the middle triassic regional extension led to a reconfiguration of the southern part of the basin where new nne ssw trending troughs rheinsberg and gifhorn troughs developed in the jurassic the northwestern part of the basin was uplifted while in the south the keuper subsiding areas continued to sink and nw se trending depressions related to salt margins became important differentiation continued into cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins a final subsidence phase occurred in the cenozoic this was accompanied by intensive salt movement recent basin configuration reflects the superposition of structural elements resulting from different evolution stages the main structural characteristics of the basin are 1 a vertical tectonic zonation in a pre zechstein succession which lacks significant internal structures and a strongly deformed post zechstein succession which was decoupled due to the thick zechstein salt and 2 a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin elbe fault system the northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation in contrast initial structures in the southeastern part are strongly overprinted by younger tectonic events including middle triassic to jurassic extension late cretaceous inversion and late to post cretaceous salt movements tectonic elements that deform the whole sedimentary succession are restricted to the basin s southern eastern and northeastern margins where salt thickness decreases combined volumetric and backstripping investigations show that 2 3 of the total subsidence was induced by the sediment load and 1 3 was caused by tectonics the tectonic subsidence history varies laterally across the basin while tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the permian and early triassic decreasing exponentially with time subsidence curves in the southeastern part indicate repeated tectonic activity however the tectonic subsidence volume created during permian to late triassic is significantly higher than the tectonic subsidence during younger phases of basin history

basin evolution of the northern part of the northeast german basin insights from a 3d structural model abstract a 3d structural model for the entire southwestern baltic sea and the adjacent onshore areas was created with the purpose to analyse the structural framework and the sediment distribution in the area the model was compiled with information from several geological time isochore maps and digital depth maps from the area and consists of six post rotliegend successions the upper permian zechstein lower triassic middle triassic upper triassic jurassic cretaceous and cenozoic this structural model was the basis for a 3d backstripping approach considering salt flow as a consequence of spatially changing overburden load distribution isostatic rebound and sedimentary compaction for each backstripping step in order to reconstruct the subsidence history in the region this method allows determination of the amount of tectonic subsidence or uplifting as a consequence of the regional stress field acting on the basin and was followed by a correlation with periods of active salt movement in general the successions above the highly deformed zechstein evaporites reveal a thickening trend towards the gluckstadt graben which also experienced the highest amount of tectonic subsidence during the mesozoic and cenozoic two periods of accelerating salt movement in the area has been correlated with the e w directed extension during the late triassic early jurassic and later by the late cretaceous early cenozoic inversion suggesting that the regional stress field plays a key role in halokinesis the final part of this work dealt with a neotectonic forward modelling in an attempt to predict the future topography when the system is in a tectonic equilibrium the result reveals that many of the salt structures in the region are still active and that future coastline will run with a wnw ese trend arguing that the compressional stresses related to the alpine collision are the prime factor for the present day landscape evolution

observed and modeled pathways of the iceland scotland overflow water in the eastern north atlantic abstract the spreading of iceland scotland overflow water isow in the eastern north atlantic has largely been studied in an eulerian frame using numerical models or with observations limited to a few locations no study to date has provided a comprehensive description of the isow spreading pathways from both eulerian and lagrangian perspectives in this paper we use a combination of previously unreported current meter data hydrographic data rafos float data and a high resolution 1 12 numerical ocean model to study the spreading pathways of isow from both of these perspectives we identify three isow transport cores in the central iceland basin 59 n with the major core along the eastern boundary of the reykjanes ridge rr and the other two in the basin interior based on trajectories of observed and or numerical floats seeded along 59 n we also describe the isow spreading pathways and quantify their relative importance within 10 years 7 11 of isow from 59 n escapes into the irminger sea via gaps in the rr north of the charlie gibbs fracture zone cgfz the water that moves through these gaps principally originates from the shallower isow layer along the rr eastern boundary 10 13 travels further southward until the cgfz where it crosses westward into the western subpolar gyre 18 21 of isow spreads southward along the eastern flank of the mid atlantic ridge into the western european basin web most of the remaining water stays in the iceland basin over the 10 year period a model based investigation provides a first look at the temporal variability of these isow pathways we find that the fraction of southward water exported into the web is anti correlated with the export through the cgfz a result assumed to reflect these pathways interactions with the north atlantic current in magnitude and or position shift

late cretaceous cenozoic evolution of the north german basin results from 3 d geodynamic modelling abstract the late cretaceous cenozoic evolution of the north german basin has been investigated by 3 d thermomechanical finite element modelling the model solves the equations of motion of an elasto visco plastic continuum representing the continental lithosphere it includes the variations of stress in time and space the thermal evolution surface processes and variations in global sea level the north german basin became inverted in the late cretaceous early cenozoic the inversion was most intense in the southern part of the basin i e in the lower saxony basin the flechtingen high and the harz the lower crustal properties vary across the north german basin north of the elbe line the lower crust is dense and has high seismic velocity compared to the lower crust south of the elbe line the lower crust with high density and high velocity is assumed to be strong lateral variations in lithospheric strength also arise from lateral variations in moho depth in areas where the moho is deep the upper mantle is warm and the lithosphere is thereby relatively weak compression of the lithosphere causes shortening thickening and surface uplift of relatively weak areas tectonic inversion occurs as zones of preexisting weakness are shortened and thickened in compression contemporaneously the margins of the weak zone subside cenozoic subsidence of the northern part of the north german basin is explained as a combination of thermal subsidence and a small amount of deformation and surface uplift during compression of the stronger crust in the north the modelled deformation patterns and resulting sediment isopachs correlate with observations from the area this verifies the usefulness and importance of thermomechanical models in the investigation of intraplate sedimentary basin formation

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

structure and evolution of the glueckstadt graben due to salt movements the salt tectonics of the glueckstadt graben has been investigated in relation to major tectonic events within the basin the lithologic features of salt sections from rotliegend zechstein and keuper show that almost pure salt is prominent in the zechstein dominating diapiric movements that have influenced the regional evolution of the glueckstadt graben three main phases of growth of the salt structures have been identified from the analysis of the seismic pattern the strongest salt movements occurred at the beginning of the keuper when the area was affected by extension this activation of salt tectonics was followed by a jurassic extensional event in the pompeckj block and lower saxony basin and possibly in the glueckstadt graben the paleogene neogene tectonic event caused significant growth and amplification of the salt structures mainly at the margins of the basin this event was extensional with a possible horizontal component of the tectonic movements 3d modelling shows that the distribution of the initial thickness of the permian salt controls the structural style of the basin regionally where salt was thick salt diapirs and walls formed and where salt was relatively thin simple salt pillows and shallow anticlines developed

the mesozoic cenozoic structural framework of the bay of kiel area western baltic sea a dense grid of multichannel high resolution seismic sections from the bay of kiel in the western baltic sea has been interpreted in order to reveal the mesozoic and cenozoic geological evolution of the northern part of the north german basin the overall geological evolution of the study area can be separated into four distinct periods during the triassic and the early jurassic e w extension and the deposition of clastic sediments initiated the movement of the underlying zechstein evaporites the deposition ceased during the middle jurassic when the entire area was uplifted as a result of the mid north sea doming the uplift resulted in a pronounced erosion of upper triassic and lower jurassic strata this event is marked by a clear angular unconformity on all the seismic sections the region remained an area of non deposition until the end of the early cretaceous when the sedimentation resumed in the area throughout the late cretaceous the sedimentation took place under tectonic quiescence reactivated salt movement is observed at the cretaceous cenozoic transition as a result of the change from an extensional to compressional regional stress field the vertical salt movement influenced the cenozoic sedimentation and resulted in thin skinned faulting

crustal structure of the mid polish trough beneath the teisseyre tornquist zone seismic profile abstract a new seismic refraction and wide angle reflection experiment in the teisseyre tornquist zone ttz in poland was conducting during july 1993 as an international polish finnish german and swedish co operation the ttz profile running in an se nw direction was exactly located in the central part of the mid polish trough in the zone of maximum subsidence from upper permian to upper cretaceous 19 shot points were placed along the 450 km profile the interval between the shot points was about 25 km 31 explosions 90 to 1000 kg of dynamite were recorded in two deployments using 135 modern three component seismic stations with spacing of the recording sites of about 1 7 km in this area the depth of the consolidated basement with a velocity of about 5 7 5 8 km s is 5 to 12 km deep nevertheless the p wave velocity is very low vp

salt redistribution during extension and inversion inferred from 3d backstripping abstract a 3d backstripping approach considering salt flow as a consequence of spatially changing overburden load distribution isostatic rebound and sedimentary compaction for each backstripping step is used to reconstruct the subsidence history in the northeast german basin the method allows to determine basin subsidence and the salt related deformation during late cretaceous early cenozoic inversion and during late triassic jurassic extension in the northeast german basin the deformation is thin skinned in the basinal part but thick skinned at the basin margins the salt cover is deformed due to late triassic jurassic extension and late cretaceous early cenozoic inversion whereas the salt basement remained largely stable in the basin area in contrast the basin margins suffered strong deformation especially during late cretaceous early cenozoic inversion as a main question we address the role of salt during the thin skinned extension and inversion of the basin in our modelling approach we assume that the salt behaves like a viscous fluid on the geological time scale that salt and overburden are in hydrostatical near equilibrium at all times and that the volume of salt is constant because the basement of the salt is not deformed due to decoupling in the basin area we consider the base of the salt as a reference surface where the load pressure must be equilibrated our results indicate that major salt movements took place during late triassic to jurassic e w directed extension and during late cretaceous early cenozoic nne ssw directed compression moreover the study outcome suggests that horizontal strain propagation in the salt cover could have triggered passive salt movements which balanced the cover deformation by viscous flow in the late triassic strain transfer from the large graben systems in west central europe to the east could have caused the subsidence of the rheinsberg trough above the salt layer in this context the effective regional stress did not exceed the yield strength of the basement below the rheinsberg trough but was high enough to provoke deformation of the viscous salt layer and its cover during the late cretaceous early cenozoic phase of inversion horizontal strain propagation from the southern basin margin into the basin can explain the intensive thin skinned compressive deformation of the salt cover in the basin the thick skinned compressive deformation along the southern basin margin may have propagated into the salt cover of the basin where the resulting folding again was balanced by viscous salt flow into the anticlines of folds the huge vertical offset of the pre zechstein basement along the southern basin margin and the amount of shortening in the folded salt cover of the basin indicate that the tectonic forces responsible for this inversion event have been of a considerable magnitude

reflection seismic constraints on paleozoic crustal structure and moho beneath the ne german basin abstract a 330 km long ne sw trending seismic transect across the ne german basin combined with a 75 km long perpendicular cross line in the basin centre reveals the structure of this intracontinental basin between the stable precambrian baltic shield and the weaker mid european variscides the combination of high fold vibroseis and low fold explosive seismic profiling images both upper and lower crustal structures in detail distinct faults related to a rift stage are not observed below the permian sedimentary basin but there is evidence of lower crustal thinning a moho pattern less reflective below the basin centre than at the margins may be related to magmatic underplating the rather flat lying moho dips slightly towards the basin margins structures further north suggest a southern extent of baltica below the ne german basin the caledonian accretionary wedge may be outlined by sw dipping mid crustal reflectors beneath the basin

the glueckstadt graben a sedimentary record between the north and baltic sea in north central europe abstract the glueckstadt graben is one of the deepest post permian structures within the central european basin system and is located right at its heart at the transition from the north sea to the baltic sea and from the lower saxony basin to the rynkoebing fyn high the mesozoic to recent evolution is investigated by use of selected seismic lines seismic flattening and a 3d structural model a major tectonic event in the latest middle late triassic keuper was accompanied by strong salt tectonics within the glueckstadt graben at that time a rapid subsidence took place within the central part which provides the core of the glueckstadt graben the post triassic tectonic evolution of the area does not follow the typical scheme of thermal subsidence in contrast it seems that there is a slow progressive activation of salt movements triggered by the initial triassic event starting with the jurassic the subsidence centre partitioned into two parts located adjacent to the triassic core in comparison with other areas of the central european basin system the glueckstadt graben was not strongly affected by additional jurassic and cretaceous events during the late jurassic to early cretaceous the area around the glueckstadt graben was affected by relative uplift with regional erosion of the elevated relief however subsidence was reactivated and accelerated during the cenozoic when a strong subsidence centre developed in the north sea during paleogene and quaternary neogene the two centres of sedimentation moved gradually towards the flanks of the basin the data indeed point toward a control of post permian evolution by gradual withdrawal of salt triggered by the initial exhaustion along the triassic subsidence centre in this sense the glueckstadt graben was formed at least partially as basin scale rim syncline during post permian times the present day hamburger east and westholstein troughs are the actual final state of this long term process which still may continue and may play a role in terms of young processes and e g for coastal protection

deep seismic survey images crustal structure of tornquist zone beneath southern baltic sea the tornquist zone is europe s longest tectonic lineament and bisects the continent in a nw se direction from the north sea off nw denmark to the black sea new deep seismic reflection and coinci

seismic anisotropy of the lithosphere around the trans european suture zone tesz based on teleseismic body wave data of the tor experiment abstract a passive teleseismic experiment tor traversing the northern part of the trans european suture zone tesz in germany denmark and sweden recorded data for tomography of the upper mantle with a lateral resolution of few tens of kilometers as well as for a detailed study of seismic anisotropy a joint inversion of teleseismic p residual spheres and shear wave splitting parameters allows us to retrieve the 3d orientation of dipping anisotropic structures in different domains of the sub crustal lithosphere we distinguish three major domains of different large scale fabric divided by first order sutures cutting the whole lithosphere thickness the baltic shield north of the sorgenfrei tornquist zone stz is characterised by lithosphere thickness around 175 km and the anisotropy is modelled by olivine aggregate of hexagonal symmetry with the high velocity ac foliation plane striking nw se and dipping to ne southward of the stz beneath the norwegian danish basin the lithosphere thins abruptly to about 75 km in this domain between the stz and the so called caledonian deformation front cdf the anisotropic structures strike ne sw and the high velocity ac foliation dips to nw to the south of the cdf beneath northern germany we observe a heterogeneous lithosphere with variable thickness and anisotropic structures with high velocity dipping predominantly to sw most of the anisotropy observed at tor stations can be explained by a preferred olivine orientation frozen in the sub crustal lithosphere beneath northern germany a part of the shear wave splitting is probably caused by a present day flow in the asthenosphere

structure and evolution of the northeastern german basin and its transition onto the baltic shield abstract the post permian sequence stratigraphical and structural evolution of the northeastern german basin and its transition onto the baltic shield has been studied in the bay of mecklenburg sw baltic sea by means of seismic interpretation five major sequences have been identified middle triassic upper triassic jurassic cretaceous and cenozoic time isochore maps allowed the identification of several phases of salt pillow growth the contemporaneity of active salt tectonics and the well studied tectonic evolution of the northeastern german basin suggest a causative correlation the e w directed extension during the triassic early jurassic marking the beginning break up of pangaea is seen as the trigger process for the first period of salt movement a fault system outside the limit of the zechstein evaporates is understood as the consequence of thin skinned faulting and brittle thick skinned deformation that accompanied this extension the observed pronounced erosion of upper triassic and lower jurassic strata is considered to result from the uplift due to the mid north sea doming event in middle jurassic times the seismic data show an undisturbed late cretaceous succession which reflects a period of rising sea level tectonic quiescence and no salt movement in contrast to the salt pillows which emerged above triassic fault systems in the westernmost baltic and western north german basin the cenozoic salt movement activity is the most pronounced this period of reactivated salt pillow growth started coevally with the onset of the alpine orogeny at the cretaceous cenozoic transition when the africa arabian plate collided with eurasia generally no significant faults were identified in the overburden of the salt floored southern bay of mecklenburg where ductile zechstein salt decouples deep rooted faulting from supra salt deformation

caledonian and proterozoic terrane accretion in the southwest baltic sea abstract a marine seismic reflection survey was carried out in 1996 by dekorp potsdam and bgr hannover in the sw baltic sea several tectonic lineaments were crossed nearly perpendicularly for example the caledonian deformation front which is assumed to mark the northern boundary of the terrane avalonia which accreted to baltica ca 400 ma here a bivergent collision is clearly observed confirming early ideas from the babel survey the ne dipping reflections in the uppermost mantle are interpreted as signs of the subducted tornquist ocean a similar tectonic style of compression and indentation is observed in the proterozoic crust northeast of bornholm where in addition a remarkable crustal thickening and a strong increase of reflection power is observed the three dekorp lines in this area provide a certain three dimensional control and allows extension of similar observations from the babel line a southward this proterozoic terrane accretion seems to be connected to major tectonic lineaments in southern sweden either to the gothian thrust or the sveconorwegian front

hydrographic variability in the bottom layer of the iceland basin abstract the variability of the lowest 400 dbar in the deep iceland basin has been studied for the years 1988 1991 it appears that hydrographic parameters of the iceland scotland overflow water in the lowest 100 dbar mainly vary on longer timescales interannual centered around 140 dbar from the bottom at a more or less constant density level salinity dissolved silica oxygen and potential vorticity show a maximum in variability this is attributed to the isopycnal advection of lenses of water with distinct coherent hydrographic properties these lenses are assumed to form a mechanism for lateral isopycnal advection of deep water enriched with either lower deep water or subpolar mode water the vertical extent of the lenses is determined by a density window between labrador sea water and iceland scotland overflow water centered around 2 5 39 27 kg m 3 the lateral isopycnal advection followed by subsequent diapycnal mixing is proposed as the mechanism to incorporate lower deep water into t

correcting for the influence of ice rafted detritus on grain size based paleocurrent speed estimates the grain size of deep sea sediments provides an apparently simple proxy for current speed however grain size based proxies may be ambiguous when the size distribution reflects a combination of processes with current sorting only one of them in particular such sediment mixing hinders reconstruction of deep circulation changes associated with ice rafting events in the glacial north atlantic because variable ice rafted detritus ird input may falsely suggest current speed changes inverse modelling has been suggested as a way to overcome this problem however this approach requires high precision size measurements that register small changes in the size distribution here we show that such data can be obtained using electro sensing and laser diffraction techniques despite issues previously raised on the low precision of electro sensing methods and potential grain shape effects on laser diffraction down core size patterns obtained from a sediment core from the north atlantic are similar for both techniques reinforcing the conclusion that both techniques yield comparable results however ird input leads to a coarsening that spuriously suggests faster current speed we show that this ird influence can be accounted for using inverse modelling as long as wide size spectra are taken into account this yields current speed variations that are in agreement with other proxies our experiments thus show that for current speed reconstruction the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modelling meaningful current speed reconstructions can be obtained from mixed sediments

an integrated study of the ne german basin abstract the ne german basin is part of the southern permian basin south of the transeuropean suture zone tesz here we report an attempt to integrate a variety of geological and geophysical data in order to reveal the present day deep crustal structure of the ne german basin special focus is taken on detailed geological information available reflection seismic data wide angle refraction seismic data and gravity data based on this integrative approach a concise crustal model is developed which can be subject to further evaluation furthermore it is shown that the ne german basin is an outstanding feature quite different from classical basin types as the moho is flat below the basin neither a simple shear nor a pure shear extension model can be applied instead a thick high velocity lower crustal layer is present below the basin centre this high velocity lower crust is also observed in the western part of the basin and can be taken as characteristic for east avalonia results of gravity modelling indicate the presence of a high density lower crust thus supporting the wide angle data furthermore changes in crustal structure can be derived from changes in reflectivity pattern and from the gravimetric signature along the elbe fault system indicating the presence of different crustal domains north and south of the fault system an elastic plate model where the forces applied are the sediment load a vertical load at the southern margin accounting for the harz moutains and a nne ssw directed compression indicates a buckling of the crust during late cretaceous to tertiary inversion however the correlation between the observed crustal structure and the tectonic events that have affected the area remains a subject of discussion a permian thermal event affected the upper mantle and the lower crust and therefore may have modified the crustal memory with regard to caledonian and variscan events additional tectonic events affected the area during the mesozoic in conclusion it remains an open question whether the high velocity and high density lower crustal structure represents a remnant of east avalonia whether it is related to the formation of the permo triassic basin or is the cumulative result of a series of events during the palaeozoic and mesozoic

late vendian early palaeozoic tectonic evolution of the baltic basin regional tectonic implications from subsidence analysis abstract subsidence analysis was performed on 43 boreholes penetrating the upper vendian lower palaeozoic sedimentary succession of the baltic basin the results were related to lithofacial and structural data to elucidate subsidence mechanisms and the regional tectonic setting of basin development tectonic subsidence patterns are consistent throughout the basin for the time period studied an extensional tectonic subsidence event possibly of two phases is indicated from the late vendian to the beginning of the middle cambrian this event is seen in the southwestern part of the baltic basin peri tornquist zone until the earliest cambrian after which it is also observed in the sw ne trending baltic depression part of the basin basin development during this time is interpreted as recording the latest stages of break up of the precambrian super continent rodinia and ultimately the formation of the tornquist sea the late middle cambrian to middle ordovician tectonic subsidence pattern of the baltic basin is characteristic of post rift thermal subsidence of the newly formed passive continental margin of baltica developed along its southwestern edge a gradual increase in subsidence rate is observed from the middle late ordovician and throughout the silurian particularly for ludlow and pridoli times creating subsidence curves with convex shapes typical of foreland basin development the rate of late silurian tectonic subsidence increases significantly towards the southwest margin of the baltic basin adjacent to the present location of the north german polish caledonides the baltic basin therefore appears to have developed primarily as a flexural foreland basin during silurian oblique collision of baltica and eastern avalonia a foreland setting is supported by the influx of distal turbidites into the basin from southwest sources in the late silurian compressional deformation structures of early devonian lochkovian age are seen in seismic sections in the central part of the baltic basin lithuania these together with a change in subsidence pattern mark the end of the caledonian stage of basin development of the baltic basin

polonaise 97 an international seismic experiment between precambrian and variscan europe in poland abstract the trans european suture zone tesz comprises a series of sutures that developed by palaeozoic amalgamation of the phanerozoic central europe onto the proterozoic baltica and east european plate during the formation of pangea within tesz the permian basin in poland forms the easternmost part of the permian central european basin which is bordered on the east by the east european craton eec and on the southwest by the bohemian massif the axis of the basin the mid polish trough parallels the edge of the eec the teisseyre tornquist zone ttz is a geological inversion zone in the polish trough a large seismic experiment the polonaise 97 project was conducted in poland during may of 1997 and targeted the deep structure of the tesz and the complex series of upper crustal features associated with it it included contributions from the geophysical communities in poland denmark the usa lithuania germany finland sweden and canada this large lithospheric seismic experiment deployed 613 instruments to record 64 shots along five profiles with a total length of about 2000 km moreover five multichannel seismic reflection stations 90 and 120 channels recorded all signals from shots two dimensional velocity models were derived by p wave tomographic inversion these models provide an initial interpretation of this massive data set and allow us to present a few significant seismic and tectonic observations one of the most important is a very distinct asymmetry between the maximum thickness of the sedimentary cover in the polish trough 16 20 km and the crustal root 50 km associated with tesz ttz

changes in the strength of the nordic seas overflows over the past 3000 years the nordic seas overflows constitute the densest component of the deep limb of the atlantic meridional overturning circulation amoc changes in the vigour of the overflows may have had important climatic effects in the past and may also have in the future yet evidence for multidecadal to millennial changes in the deep limb of the amoc and their potential relationship to north atlantic climate variability during the holocene remains weakly constrained here we present grain size data as a proxy for near bottom current speed from sub decadal to decadally resolved sediment cores located in the direct pathway of the two nordic overflows east and west of iceland the iceland scotland overflow water isow and the denmark strait overflow water dsow respectively the results show no clear relationship between reconstructed changes in the vigour of the nordic overflows and the well known periods of centennial scale climate variability recorded in the north atlantic region however well defined millennial scale trends are found in both of the overflow strength records over the last 3000 years which were possibly related to hydrographic reorganizations in the nordic seas driven by the decrease in northern hemisphere summer insolation over the neoglacial period a comparison between the near bottom flow speed reconstructions from isow and dsow suggests an anti phased relationship between the nordic seas overflows east and west of iceland over the last 3000 years this feature has been observed in climate models potentially as a result of shifts in the deep water formation sites as a response to changes in atmospheric patterns over the nordic seas

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope