constraints on the deep structure and dynamic processes beneath the alps and adjacent regions from an analysis of gravity anomalies summary gravity anomalies including terrain corrections over the western alps and the molasse basin are within 30 mgal of those calculated assuming local airy isostatic equilibrium but isostatic anomalies over regions nw and se of the alps exceed 50 mgal therefore mass excesses and deficits that must be supported by the strength of the lithosphere or by dynamically induced stress in the asthenosphere appear to be greater beneath the areas surrounding the alps than beneath the alpine chain itself attempts to account for the gravity gradient over the molasse basin and sub alpine chains and the small bouguer anomalies measured over the elevated areas of the vosges and black forest by the flexure of an elastic plate require an absurd set of parameters the high elevations of the vosges and the black forest are presumably due to high temperature in the underlying uppermost mantle but the deviations from isostatic equilibrium as well as the high temperature probably result from active upwelling in the asthenosphere beneath this area the absence of large isostatic anomalies over the alps and the failure of an elastic model to account for the gravity anomalies over the molasse basin suggest that the dynamic processes that flexed the european plate down to form the molasse basin and that built the alpine chain have waned the late cenozoic uplift of the molasse basin and the alps might be a consequence of a diminution or termination of downwelling of mantle material beneath the alps

cadomian terranes wrench faulting and thrusting in the central europe variscides geophysical and geological evidence sixty five per cent of the paleozoic basement of western and central europe is hidden by a sedimen tary cover and or sea this work aims to remove that blanket to detect new structures which could used to build a more comprehensive model of the variscan or ogeny it is based on the interpretation of various forms of data a published gravity maps corrected for the ef fects of the crust mantle boundary topography and light sedimentary basins b aeromagnetic maps c measurements of densities and d induced and rema nent magnetizations on rocks from paleozoic outcrops of the upper rhenish area from the northern b ohem ian massif to the eastern paris basin the saxothurin gian is characterized by a 500 km long belt of gravity highs the most important being the kraichgau high most of the corresponding heavy bodies are buried un der a post early visdan cover they are interpreted as relics of late proterozoic terranes overlain by an early to middle paleozoic sequence equivalent to the bo hemian t errane in the bohemian massif the most probable continuation of these dense bohemian ter ranes toward the west is the southern channel north ern brittany cadomian terrane the gravity lows are correlated with variscan granites and pre and early variscan metagranites gravity and magnetic maps demonstrate large scale displacement in devonian early carboniferous times along the parallel and equidistant nw se striking vistula elbe bavarian bray and south armorican dextral wrench faults in the vosges schwarzwald and central massif the faults continue with the east west striking lalaye lubine ba den baden and marche faults and with south vergent thrusts the bavarian faults shift the kraichgau terrane by 150 km relative to the bohemian terrane whereas the offset of the north ern brittany cadomian relative to the northern vosges kraichgau terranes is estimated at 400km along the bray fault sinistral wrench faults are the ne sw striking sillon houiller rheingraben rodl vitis and diendorf faults the southern vosges schwarzwald devonian dinanti an basin is interpreted as a pull apart basin at the south easterly extremity of the bray fault the bohemian and kraichgau body form allochthonous terranes which were thrust over the saxothuringian crust thrusting to the north west was accompanied by back thrusting and led to the forma tion of pop up structures contemporaneous dextral and sinistral wrench faulting resulted in transpressive strain during collision the zonal structure of the varis cides in the sense of kossmat 1927 is relevant only to the rhenohercynian foreland belt kossmat 1927 al ready spoke of a moldanubian region because it dis plays no real zonal structure the saxothuringian zone was formed by terrane accretion their apparent zonal structure is not a pre collisional feature but only the result of accretion and collision

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

comparative tertiary stratigraphy of the rhine graben bresse graben and molasse basin correlation of alpine foreland events abstract comparative tectonostratigraphic analysis of the tertiary middle eocene pliocene of the rhine bresse graben system and the western molasse basin demonstrates the occurrence of eleven correlative sequences crf i xi these show a close relationship between intra basinal tectonics and depositional history their punctuated sediment accumulation can be related to phases of extra alpine taphrogenesis and alpine orogenesis and to coeval eustatic changes in sea level apparent simultaneity in rift and foredeep sequence development structural deformation and global change in sea level suggests a common causal control in which the development of the alps played an important role

deep structure of the european mediterranean area from seismological data abstract over the past 20 years the study of p and s wave velocities in the upper mantle of the european mediterranean area has been the subject of intensive research work we present a summary of results based on inversion of available surface wave dispersion data and p wave travel time observations in the european mediterranean area the correlation between the lithosphere and upper mantle structure obtained from the aforementioned analysis with other geophysical data is discussed

the rhinegraben extension subsidence and shoulder uplift abstract we apply a numerical model of the thermal evolution of a continental lithosphere undergoing extensional deformation to the rhinegraben using reasonable parameters the results of computations are in agreement with the present configuration of the rift and of its shoulders as well as with their evolution since the oligocene contrasting evolutions are reconstructed in the northern and southern rhinegraben whereas the northern history is accounted for by a simple model of homogeneous stretching of the lithosphere the history of the southern rhinegraben cannot be explained without introducing two main periods of heterogeneous stretching the results are locally supported by structural analyses of extensional patterns factors of extension average 1 2 in the axial portion of the rhinegraben and 1 15 for the whole rift section suggesting that the total amount of e w extension reaches 6 km

the structure and evolution of the wessex basin southern england an example of inversion tectonics abstract the wessex basin of southern england consists of four main sub basins each sub basin is thought to be fundamentally controlled by the normal reactivation of hercynian basement thrust and wrench or transfer faults post hercynian polyphase reactivation of both east west thrust and northwest southeast transfer faults tended to compartmentalise the basement thereby leading to the initiation of discrete permian cretaceous depocentres while rifting was confined to the western portions of the area during the permo triassic easterly migration in the mesozoic allowed the initiation of the weald and channel basins the sub basins represent therefore simple sinistral pull apart basins opening along northwest southeast faults this same fault direction is postulated to have also played a major role in controlling and or modifying the development of european basins in general major pre aptian uplift and erosion is largely attributed to the thermal effects and hence the isostatic uplift of the basin associated with continental rifting of the bay of biscay and the north atlantic margins major inversion and hence basin destruction began in the late cretaceous early tertiary with the uplift of the channel weald and vale of pewsey basins and culminated in the oligocene miocene synchronous with the helvetic phase of alpine deformation wessex basin inversion was facilitated by the thrust reactivation of variscan faults above an intracrustal detachment surface the same surface which allowed upper crustal extension and hence basin initiation in the permo triassic the structural development of the wessex basin both during extension basin formation phase and compression inversion phase was ultimately controlled by the plate motion of africa relative to europe such plate motions successfully predict the observed nw se sinistral motion from the stephanian to the aptian e w sinistral motion during the aptian cenomanian and largely nw se dextral motion from the cenomanian to the present day

a 2 d ray based depth migration method for deep seismic reflections summary although accurate depth migration is essential for the correct geometrical interpretation of deep reflection data migration by the standard numerical methods has generally not been satisfactory the alternative method presented in this paper provides an efficient migration for deep reflection profiles in the form of a digitized line drawing assuming a general 2 d velocity structure migration of a digitized line drawing reduces the effects of low signal noise ratios the calculation is rapid allowing migrations to be calculated for a large number of alternative velocity structures and iterative improvement of the velocity structure the migration has been applied to 3 d structures observed on intersecting profiles collected by birps british institutes reflection profiling syndicate

a deep reflection seismic line across the northern rhine graben abstract two reflection seismic lines across the tertiary rhine graben in central europe were recorded in 1988 as a joint venture of the french ecors and the german dekorp deep seismic reflection programs in this paper the line across the northern graben is presented the main results are the asymmetry of the graben as documented by the sedimentary fill is accompanied by asymmetric features throughout the entire deep crystalline crust a thin 3 7 s twt reflective lower crust in the east a thick 5 5 s twt relatively transparent lower crust in the west total crustal thicknesses of 8 7 s twt in the east vs 10 5 s twt in the west provided a laterally homogeneous crust existed prior to rifting significant differences in upper and lower crustal thinning must be postulated extension occurred along localized shear zones that are located in the upper crust and at the crust mantle boundary the entire lower crustal layer acts as a decoupling zone

crustal structure and dynamics in the rhine graben and the alpine foreland summary the rhine graben rift stretches for 300 km from basel to frankfurt the axis of maximum subsidence switches from west in the southern graben to east in the northern graben subsidence in the south began in the upper eocene and was interrupted in the mid miocene by a broad uplift of 1 1 5 km in the vosges schwarzwald black forest region whereas subsidence in the north proceeded continuously from the lower oligocene to the present a combined geophysical and geological interpretation of the rhine graben is presented in the form of a 3 d gravity model and 2 d flexural plate modelling from the alps across the alpine foreland to the rhenish massif modelling is based on crustal structure revealed by geologic gravity and seismic data including ecors dekorp and egt profiles the 3 d gravity modelling supports a modest density contrast of 0 3 g cm 3 at the crust mantle boundary since there is no evidence of a large scale upper mantle anomaly a dense lower crust 2 9 3 0 g cm 3 is proposed as the cause of this modest density contrast the presence of a dense mafic lower crust in south west germany is corroborated by lower crustal xenoliths elevated p wave velocities 6 7 7 2 km s 1 and high poisson s ratios 0 26 0 29 residual gravity and magnetic data reveal strong crustal heterogeneities particularly from the dense magnetic saxothuringian terrane to the light non magnetic moldanubian terrane the polarity of the asymmetric rhine graben reverses at this variscan tectonic boundary light graben fill can account for nearly the entire 20 40 mgal short wavelength gravity minimum but the presence of intrusive bodies ranging from granitic to mafic composition can also strongly influence the local gravity field 2 d modelling of the flexure of the european lithosphere along seven 1000 km long profiles indicates a flexural bulge of 1 1 5 km in the alpine foreland of southern germany which corresponds to an ene trending moho uplift of the same magnitude and to a band of free air gravity highs longer flexural wavelengths in the east indicate increasing lithospheric rigidity and increasing elastic thickness towards the bohemian massif the vosges schwarzwald dome is interpreted as the intersection of the oligocene rhine graben rift and associated rift flank uplift with the mid miocene flexural bulge

differential dissolution modification of late pleistocene oxygen isotope records in the western equatorial pacific deep sea records of the pacific ocean show dramatic variations in the dissolution intensity of calcium carbonate through the late pleistocene extremes are characterized by much depressed dissolution intensity during deglaciation preservation spikes and much enhanced dissolution intensity during ice growth dissolution spikes increased dissolution intensity at dissolution spikes distorts 18o records by preferential removal of 16o rich shells resulting in heavier 18o values at these sections the 18o values tend to remain unaltered at deglacial preservation spikes thus the fluctuations of carbonate dissolution intensity modify the late pleistocene oxygen isotope records in such a fashion that apparent climate optima as defined by the lightest 18o values tend to shift toward preservation spikes while apparent glacial maxima characterized by the heaviest 18o values shift toward dissolution spikes

wide angle vibroseis test across the rhine graben summary as a joint operation of ecors and dekorp a deep wide angle seismic experiment using vibrators was carried out in the autumn of 1984 the object was to get information on the deep crust under the rhine graben without crossing through sedimentary layers offsets were in the range of 50 to 89 km in the first phase two vibration points were executed in the vosges mountains a signal was received in the black forest from solely the farthest vp in the second phase fourteen vps were executed in the black forest no stacking or correlation was performed in the field in france the quality of the results is good only if an equalization is applied before vertical stacking and correlation in the computing centre

on the detectability of a highly conductive layer in the upper mantle beneath the black forest crystalline using magnetotelluric methods summary simultaneous geomagnetic and telluric variations 600 s 4 hr were observed at two stations on the rhine graben sediments and on the neighbouring black forest crystalline in order to extend the pulsation observations 10 600 s of former magnetotelluric mt surveys to longer periods these observations completely describe the anomalous magnetic and telluric fields in terms of a set of transfer functions using the black forest station as normal in the period range from 30 s to 4 hr the horizontal and vertical magnetic transfer functions of the rhine graben anomaly are characterized by continuously decreasing amplitudes the local schmucker induction arrows point uniformly 45 south east for all long period geomagnetic transfer functions and the nw se striking direction in the upper mantle derived from the induction arrows is also consistent with the preferred telluric direction in the black forest in both areas large offsets of apparent resistivity and phase curves for the e and b polarization directions are observed except that the phase curves converge above 400s in the long period range the interpretation of the period dependences of the observed magnetic and telluric transfer functions from 600 s to 4 hr by a 2 d conductivity model requires a highly conductive layer in the upper mantle at a depth of 120 km beneath the black forest this confirms bahr s 1992 model for a highly conductive layer in the upper mantle that has also been found south of the alps braitenberg et al 1994 and which is interrupted by low conductive alpine roots however no information about such a layer beneath the rhine graben can be derived 2 d model studies have shown that an improved depth resolution of highly conductive layers in the upper mantle is possible using telluric phases but the transfer functions for the vertical magnetic fields are not sensitive enough for the determination of the depth of an upper mantle conductive layer

gravity interpretation along seismic reflection profile dekorp 9 n northern rhine graben a 2 d gravity model incorporating geophysical and geological data is presented for a 110 km long transect across the northern rhine graben coinciding with the 92 km long dekorp 9 n seismic reflection profile the upper rhine graben is marked by a prominent nne striking negative anomaly of 30 40 mgal on bouguer gravity maps of sw germany surface geological contacts borehole data and the seismic reflection profile provide boundary constraints during forward modelling short wavelength 5 10 km gravity features can be correlated with geologic structures in the upper few km at deeper levels the model reflects the asymmetry visible in the seismic profile a thicker mostly transparent lower crust in the west and a thinner reflective lower crust in the east from west to east moho depth changes from 31 to 26 28 km the entire 40 mgal minimum can be accounted for by the 2 3 km of light sedimentary fdl in the graben which masks the gravitational effects of the elevated moho the thickened lower crust in the west partly compensates for the mass deficit from the depressed moho a further compensating feature is a relatively low density contrast at the crust mantle boundary of 0 25 g cm 3 the variscan must displays heterogeneity along the profile which cuts at an angle across the strike of variscan structures the asymmetry of the integrated crustal model both at the surface and at depth suggests an asymmetric mechanism of rift development

brunhes matuyama boundary 790 k y date consistent with odp leg 130 oxygen isotope records based on fit to milankovitch template the age of the brunhes matuyama boundary until recently taken as 730 k y in standard time scales for the quaternary e g imbrie et al 1984 prell et al 1986 and in ocean drilling program results kroenke et al 1991 shackleton et al 1992 has been revised to between 780 k y and 790 k y based on both orbital tuning of oxygen isotope data e g shackleton et al 1990 and on new 40ar 39ar dates on volcanic rocks e g baksi et al 1992 we apply the revised chronology to an oxygen isotope record for ontong java plateau odp leg 130 western equatorial pacific using this time scale we find excellent agreement between the record and a template based on orbital forcing the equation for the template is where the change in ice mass is given as the difference between constant ice growth igr and variable amounts of melting melting depends on summer insolation at 65 n ins the current ice mass present ice and the average ice mass mem over a given time interval l the memory base l and the exponents are adjusted for best fit the fit to the relevant portion of the record yields an age of 790 6 k y for the brunhes matuyama boundary the age assignment is robust relative to substantial changes in parameter settings

palaeoclimatic record from a loess soil profile in northeastern bulgaria ii correlation with global climatic events during the pleistocene summary magnetic susceptibility x variations and the behaviour of the ratio of susceptibility to saturation magnetization x j s along the loess palaeosol section at koriten ne bulgaria are used to deduce climatic changes during the pleistocene in southeastern europe a good correlation of susceptibility variations with the astronomically tuned oxygen isotope record from odp site 677 enables us to propose a more precise dating of the upper part of the bulgarian loess complex close correspondence between susceptibility and d18o records demonstrates the global significance of the palaeoclimatic signal recorded although diverences in relative amplitudes of x and x j s and d18o create diyculties in making quantitative estimates of the climatic humidity in the past the role of local factors avecting the palaeoclimatic mineral magnetic record deduced from the profile studied in bulgaria is discussed

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

crustal evolution of the rhinegraben area 1 exploring the lower crust in the rhinegraben rift by unified geophysical experiments abstract unified geophysical investigations of the lithosphere in the rhinegraben rift system have revealed new details of the lower crust and its role in the rifting process the new findings allow an assessment of the compatibility of four different geophysical notions and properties of the lower crust 1 1 the lower crust as the layer beneath the conrad discontinuity with a p wave velocity of about 6 5 km s or greater refraction seismics 2 2 the laminated band of reflections as seen in the near vertical reflection seismic experiments in many parts of the continents 3 3 the ductile part of the crust below the brittle ductile transition devoid of earthquakes in seismically active regions 4 4 the electrical conductivity of the lower crust indicative of dry or wet conditions or still unknown conduction phenomena in the rhinegraben area the lamination of the lower crust serves as an outstanding marker of deep tectonic activity during the rifting process in which the crust of the rhinegraben rift system has been subjected to three different natural dynamic processes 1 uplift by 2 to 3 km with subsequent erosion of the rhinegraben shoulders black forest and vosges mountains caused decompression possibly leading to the formation of a low velocity high electrical conductivity zone right on top of the laminated lower crust beneath the elevated shoulders of the black forest 2 the brittle crystalline wedge of the graben proper subsided nearly undeformed into the lower crust which became about 5 to 7 km thinner below the graben than below the shoulders 3 the deepest hypocentres in the black forest dinkelberg area if projected onto the neighbouring reflection profile would be located 7 to 8 km within the laminated lower crust beneath the southern black forest indicating a discrepancy between the top of the lower crust as defined by the brittle ductile transition as seen by the deepest earthquakes and by the top of the laminated reflection band the rhinegraben rift system reveals the properties and behaviour of the lower crust under a wide variety of tectonic situations

regional three dimensional gravity investigations in the black forest southwest germany abstract the gravimetric pre surveys of the continental deep drilling project ktb yielded results different to those hoped for at the beginning of the program firstly 2 d calculations based on a refraction seismic interpretation allowed a comparison of gravity effects on a 160 km long profile but despite the fact that in the 2 d model granitic bodies were added at the earth s surface we only obtained a regional gravitational fit with strong deviations on a local scale secondly a gravimetric field survey in the region around haslach yielded rather poor indications of the geological structures in the 5 15 km depth interval which is in the context of the ktb of significant interest therefore all available information derived from geological and tectonic hypotheses and from reflection and refraction seismic interpretation were combined in a regional 3 d density model for the local anomalies the distribution of granite and gneiss bodies known from surface geology was added model bodies from an earlier regional study in southern germany which combined gravimetric and seismic results the moho undulations and the density of the lower crust and upper mantle were taken as additional model parameters in order to discuss regional features the kraichgau anomaly in the north of the black forest is modelled from a 2 d hypothesis as a body with an unusually high density and with a considerable lateral extent this approach demonstrates that evidence concerning the density contrast of anomalous masses can be found if boundary conditions are considered in the construction of the model

the genesis and significance of hummocky moraine evidence from the isle of skye scotland abstract the range of genetic and climatic interpretations of scottish hummocky moraine is reviewed and new data are presented from the isle of skye western scotland which are used as the basis of a genetic classification hummocky moraine on skye is shown to consist of three principal sediment landform associations 1 recessional moraines 2 chaotic ice stagnation moraines and 3 drumlins and fluted moraines the recessional moraines consist of transverse moraine ridges and chains of mounds and were formed by a combination of glaciotectonics and debris accumulation at active ice margins second chaotic moraines consist of randomly distributed hummocks mounds and rim ridges and record deposition in contact with inactive ice finally drumlins and fluted moraines are longitudinally oriented subglacial bedforms formed by a combination of lodgement and sediment deformation individual occurrences of hummocky moraine may comprise one two or all of these associations the detailed study and differentiation of scottish hummocky moraine provides a valuable source of information on former glacier dynamics and landscape change

new insights on the post rift seismic stratigraphic architecture and sedimentary evolution of the antarctic peninsula margin central bransfield basin abstract a seismic stratigraphic study of the antarctic peninsula margin of the central bransfield basin was conducted using seismic and bathymetric data the study focused on seismic sequences and units deposited after the basin opened and yield a record of the evolution of the northern most antarctic peninsula ice sheet two seismic sequences compose the post rift stratigraphic succession on the central bransfield basin slope platforms both sequences are composed of seismic units that record glacial interglacial cycles and show evidence of the antarctic peninsula ice sheet having grounded on the continental shelf and slope platform on several occasions in the past this evidence includes glacial and glaciomarine related sedimentary and erosional features within the seismic units glacial unconformities glacial troughs till wedges prograded wedges trough mouth fans glaciomarine sheet deposits and moraines which are bounded by glacial unconformities the antarctic peninsula lower slope also registered in its eastern sector the deposition of gravity flow deposits during ice sheet retreat and interglacial stages the deposition of seismic units on the middle slope produced the present day step like profile of the margin composed of wide flat slope platforms and narrow and steep upper and lower slopes seismic units show changes in thickness and distribution that record the effect of the physiography and climatic changes on margin sedimentation these variations produced an overall change from more line sourced deposition to more point sourced deposition as ice streams evolved the stacking of units shows a change in the stratigraphic architecture through time from dominantly progradational s2 to progradational aggradational s1 this change is correlated with a change in the frequency of ice sheet grounding events which was probably driven by a higher rate of eustatic rise and fall in relation with the mid pleistocene global climatic change

40ar 39ar dating of the brunhes matuyama geomagnetic field reversal magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale gpts to date events in the range 0 to 5 million years ago a critical tie point on the gpts is the potassium argon age of the most recent brunhes matuyama geomagnetic field reversal astronomical values for the forcing frequencies observed in the oxygen isotope record in ocean drilling project site 677 suggest that the age of this last reversal is 780 ka thousand years ago whereas the potassium argon based estimate is 730 ka results from 4039 ar incremental heating studies on a series of lavas from maui that straddle the brunhes matuyama reversal give an age of 783 11 ka in agreement with the astronomically derived value the astronomically based technique appears to be a viable tool for dating young sedimentary sequences

history of the inflow of the warm tsushima current into the sea of japan between 3 5 and 0 8 ma abstract the stratigraphic distribution of warm water molluscs planktonic foraminifers and diatoms in plio pleistocene strata 3 5 0 8 ma of the sea of japan coast of japan is the basis for reconstructing the history of the tsushima current the results indicate 1 the tsushima current flowed at 3 5 3 2 2 9 2 4 and 1 9 ma in the 3 5 1 7 ma interval 2 the current flowed at every interglacial highstand except for mis 25 23 and 21 3 in the 1 71 0 8 ma interval 3 the salinity and volume of the tsushima current during the earlier interval may have been significantly lower and smaller respectively than in the latter interval 4 the late pliocene altitude of the southern part of the sea of japan was up to 50 m above present day sea level

structure of the southern rhine graben from gravity and reflection seismic data ecors dekorp program the southern rhine graben was investigated by the seismic reflection ecors dekorp program gravity data available in this region have been reprocessed in order to develop a coherent map along the seismic line the new map has been corrected for the gravity effects of tertiary sediment and crust mantle discontinuity the strong negative gradient towards the alps may be explained by a density contrast of 300 500 kg m3 at the crust mantle interface the residual map shows a negative long wavelength anomaly superimposed on the moldanubian domain of the variscan belt along a vosges black forest swabian jura axis this anomaly cannot be explained by the properties of the variscan crust but may result from a low density body within the upper mantle however its ene wsw direction rules out any connection with the formation of the tertiary grabens which trend north south the recent uplift of topography and the volcanic activity 20 ma of the southern rhine graben may partly be a consequence of an asthenospheric upwelling beneath this area the analysis of the residual short wavelength anomalies shows a fundamental difference between the light variscan terranes of the moldanubian zone and the dense barrandian saverne kraighau structures of the saxothuringian domain a density cross section along the ecors dekorp line confirms that the moho uplift extends beyond the graben whereas thinning of the lower crust affects the graben area only we interpret this crustal structure as an initially thin hercynian crust later deformed by asymmetric extension during oligocene rifting

a one dimensional model of continental ice volume fluctuations through the pleistocene implications for the origin of the mid pleistocene climate transition abstract a new one dimensional zonally averaged high resolution spherical model of the accumulation and flow of continental ice sheets in response to variations in insolation forcing has been constructed the model includes a detailed representation of the influence of the isostatic adjustment of the earth under the weight of the ice at a rate determined by the viscosity of the planetary mantle with this model we address the issue as to whether the combination of physical processes that it includes is sufficient to allow us to reconcile the variations of continental ice volume that are inferred to have dominated the pleistocene epoch on the basis of the analysis of 18o data from deep sea sedimentary cores we use high resolution data from the newly analyzed odp site 677 and from dsdp site 607 as principal observational constraints these datasets reveal a marked transition in climate to have occurred at mid pleistocene time about 900 000 years bp in order to understand this transition we find that we

the deep lithosphere in the alps a model inferred from p residuals abstract the tomographic studies of the alps and their surroundings based on the relative p residuals indicated two lithosphere roots attaining depths over 200 km separated by an upwelling of the lithosphere asthenosphere transition beneath the central part of this mountain range the directional dependence of relative p velocities indicates an anisotropic wave propagation in the subcrustal lithosphere beneath the alps and their surroundings the presented model of the deep lithosphere structure suggests several phases of the tectonic development of this region collision of a tip of the adriatic plate with europe in the eastern alps and dextral strike slip movement of the adriatic ending with underthrusting of europe beneath the western alps and counterclockwise rotation the latter contributes to a steep plunge of both plates beneath the eastern alps and to stress accumulation in the friuli region a model with delamination of the rigid upper crust and its rotation resolves some of the inconsistencies between the near surface and deep tectonics and also explains the distribution of seismicity

links between the onset of modern walker circulation and the mid pleistocene climate transition sea surface temperatures ssts reconstructed from ocean drilling program sites 806 and 849 in the western and eastern equatorial pacific provide a history of the strength of the walker circulation between 1 5 and 0 5 ma a progressive cooling in the eastern equatorial pacific is paralleled by intensification of the equatorial zonal sst gradient that began 1 17 ma prior to the expansion of global ice volume associated with the mid pleistocene climate transition the ssts in the eastern equatorial pacific and the zonal gradient reached modern values by 0 9 ma we propose that this onset and intensification of the modern walker circulation reduced heat flux but increased moisture transport to high latitudes leading to the development of more extensive ice sheets and the shift toward the 100 ka world

concordant sea floor spreading rates obtained from geochronology astrochronology and space geodesy reversals of the earth s magnetic field allied to sea floor spreading have left their imprint in the form of a magnetic tape recorder on the sea floor it is demonstrated that the geomagnetic polarity time scale for the past few million years derived utilizing a radiometric dates of magnetic field reversals trapped in subareal igneous rocks and b as derived from the milankovitch forcing frequencies and their imprint in the sedimentary environment are in good agreement further sea floor spreading rates calculated from these results are in substantial agreement with the rate of plate movement averaged over the last decade as obtained by space geodetic measurements since the principles underlying these dating techniques are entirely different it lends credence to the results obtained for sea floor spreading arguably the most fundamental process in plate tectonics

sedimentary record of the mid pleistocene climate transition in the southeastern south atlantic odp site 1090 abstract one important goal of leg 177 of the ocean drilling program odp was to explore the nature of the mid pleistocene climate transition mpt on the southern hemisphere a suitable mpt record was encountered at site 1090 in the southeastern south atlantic where a 44 m thick sequence of quaternary diatom bearing foraminiferal muds and oozes was recovered on the agulhas ridge environmental responses to the mpt comprised changes in terrestrial climate biological productivity and regional ocean circulation as inferred from compositional sediment data and clay mineralogy a shift towards more arid conditions occurred between 900 and 800 ka in southern africa changes in palaeoceanography already started earlier since 1150 ka northward displacements of the polar front appeared during glacial periods and shifted the area of dominant diatom deposition towards site 1090 likewise glacial interglacial contrasts in regional conveyor circulation strengthened after 1200 ka and became most severe after 650 ka however while changes in regional conveyor circulation likely responded in tune with global ice volume changes and show the onset of 100 kyr cycles after 1200 ka an unusual 130 kyr pattern characterises the pattern of frontal movements between 1200 ka and 650 ka probably in response to imperfect adaptation of regional climate to the global 100 kyr climate cycles

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

change in the thickness of the warm tsushima current at the initiation of its flow into the sea of japan abstract the initiation of flow of the warm tsushima current created significant changes in quaternary paleoceanography and ecosystems in the continental shelf of the japanese islands in the sea of japan in order to understand the behavior of the current at the initiation of its flow we reconstruct the change in the relative thickness of the current during the initiation of flow based on combining planktonic and shallow water molluscan fossil analyses of the early pleistocene omma formation in central japan the result indicates that warm water planktonic foraminifera and cold water molluscs coexisted during about 2300 2400 years just after the initiation of the intrusion of the tsushima current migration of a warm water molluscan fauna to the shelf occurred shortly after the local extinction of cold water molluscs this means that the rate of increase in thickness of the tsushima current during the initiation of flow was faster than that of the sea level rise using deep sea core records and modern biogeographic data the rates of the former and latter are calculated to be 17 2 8 9 m per 1000 years and 1 9 1 1 m per 1000 years respectively because bottom water change might lag behind surface water change during a rapid climatic change in all shallow water combining planktonic and benthic fossil analyses is necessary to reconstruct shallow paleoceanography

3 d structure of the lithosphere beneath the southern rhine graben area abstract the 3 d velocity structure of the lithosphere asthenosphere system beneath the southern rhine graben area is imaged by inverting p wave traveltime residuals of teleseismic events recorded by a dense network of short period stations the upper part of the lithosphere marked by velocity anomalies orientated along the graben strike can be related to the development of the graben these upper 50 km display stronger lateral heterogeneities than the weak anomalies observed at deeper levels which show roughly an e w orientation the teleseismic inversion models yield no indications for significantly reduced seismic p wave velocities in the upper mantle as could be expected from an actively upwelling mantle diapir located beneath the southern rhine graben area the observation of generally weak p wave velocity variations at greater depth indicates a rather smooth transition from the lower lithosphere to the upper asthenosphere the observed heterogeneities in the 25 50 km depth range may be related to partial melts which intruded the mantle lithosphere during the middle and late miocene these melts cooled and solidified since that intrusion the rifting and thermal doming stage of the rhine graben ceased at the end of the miocene

fourier stratigraphy spectral gain adjustment of orbital ice mass models as an aid in dating late neogene deep sea sediments orbital tuning has become an important means of dating deep sea sediments of pliocene pleistocene age one approach is to generate a template simulating ice mass history based on milankovitch forcing for comparison with a given 18o record to obtain a template that closely mimics a given 18o record we propose the following steps 1 generate a preliminary template based on a simple ice mass model 2 find the fourier matrix for this model 3 find the fourier matrix for the 18o record to be tuned if necessary adjust preliminary sedimentation rate so that maxima appear at the correct spectral lines 4 import the spectral power distribution from the matrix of the record into the matrix of the template while preserving phase of template and 5 generate the new template from the gain adjusted template matrix the record should now show optimum coherency with the template over the appropriate interval the efficiency of this method fourier matrix conjugation in producing hybrid templates is illustrated using four examples 1 testing the stacked record of prell et al 1986 for constant sedimentation rate 2 testing the date of 790 ka of the brunhes matuyama boundary in ontong java plateau ocean drilling program hole 805c berger et al 1993a 3 testing the age scale for a core from the norwegian sea containing meltwater events jansen 1989 and 4 checking the age model of ocean drilling program site 677 shackleton et al 1990 for internal consistency the template shows just where the given age models have optimum coherency with the selected orbital model and where in the record discrepancies arise

quaternary time scale for the ontong java plateau milankovitch template for ocean drilling program site 806 a 2 m y oxygen isotope record of globigerinoides sacculifer from the ontong java plateau based on cores from ocean drilling program leg 130 is dated by matching variations to an orbital template the procedure allows us to present the most complete quaternary record available for the western equatorial pacific the template generating algorithm describes a balance between growth and melting of ice following basic milankovitch theory ice growth is taken as constant while melting is taken to depend on summer insolation current ice mass and average past ice mass template settings must be changed once between 1 and 1 2 ma to reflect a major shift in climate template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances one result of template dating is an exact age for the brunhes matuyama magnetic reversal boundary at 790 5 ka as well as several other precise dates 900 ka for the middle pleistocene climate shift 1070 1240 and 1450 ka for isotope stages 31 37 and 47 respectively sedi mentation rates fluctuate between 18 and 28 m m y a ca 400 ka cycle being the most prominent major anomalies arise within the transitional regime 1 2 to 1 ma the origin of the cycles is unknown we propose productivity variations in the western equatorial pacific

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event

gravity modelling along the ecors crop vertical seismic reflection profile through the western alps abstract new gravity data from 500 stations and results from all previous surveys on the western alps are used to compile a detailed profile along the ecors crop vertical seismic profile the bouguer anomaly consists of two approximately two dimensional regional features namely a wide negative anomaly occurring on the central part of the belt and the pronounced positive anomaly of the geophysical ivrea zone at the border between the alps and the po plain the results of a wide angle seismic campaign and the preliminary line drawing from the vertical seismic have been the main constraints for the modelling of the anomaly two models are proposed their common feature is a piling up of the crust upper mantle units in the penninic zone of maximum crustal thickness as well as in the ivrea zone the contribution of the apulian lower crust to the positive anomaly is greater than formerly suggested several hypotheses are put forward for the zones where reasonable seismic information is available as an illustration of the uncertainties surrounding their geological interpretation the density models are consistent with the hypothesis of lithospheric accretionary processes for the collision between the european and apulian plates

stratigraphic and paleomagnetic evidence of mid pleistocene rapid deformation and uplift of the ne tibetan plateau abstract the ne tibetan plateau has become an important region for deciphering the cenozoic uplift of the plateau previous studies have verified that the quaternary uplift in this region had a multi stage character however geologists have not established which event constituted the main tectonic phase fortunately stratigraphic and paleomagnetic evidence from the jiuquan basin gansu province china now confirm that the laojunmiao movement represented as an angular unconformity occurred between 0 9 and 0 8 ma and an almost synchronous tectonic event has been well recorded within and around the plateau moreover many proxies indicate that the global climate changed more rapidly after 0 9 ma these proxies include eolian loess and vermiculated red soils caused by the asian monsoon the eolian sedimentation rate the stilostomella extinction changes in the global thermohaline circulation and the increased 13 c values recorded in the marine sediments based on the uplift driven climate change the mid pleistocene transition mpt could be the result of the laojunmiao movement certainly the laojunmiao movement and mpt had the significant impact on the quaternary earth we conclude that the laojunmiao movement was likely the main tectonic phase of the quaternary plateau uplift

deep seismic reflection and refraction profiling along the aquitaine shelf bay of biscay summary the 300 km ecors bay of biscay profile was carried out along the aquitaine shelf and comprised a complete set of experiments including zero offset and 7 5 km constant offset vertical seismic reflection and six expanding spread profiles large offset recordings were fundamental for the definition of the layered lower crust and the moho while esps provided decisive complementary information for the geological interpretation these data show a strong variation in crustal thickness from about 20 km beneath the rifted parentis basin a failed arm of the oceanic bay of biscay up to 35 km to the north below the armorican shelf in the hercynian domain and to the south below the cantabria shelf in the vicinity of the pyrenean deformation front the results have important implications for the behaviour of the crust during the formation of rifted sedimentary basins and during continental collision

the upper rhenish shield basement vosges upper rhinegraben and schwarzwald main structural features deduced from magnetic gravimetric and geological data abstract interpretation of magnetic and gravimetric data and correlations with geological observations on outcrops and in boreholes have enabled the construction of a geological sketch map of the pre westphalian basement in the area of the upper rhenish shield the map demonstrates the contrast between the heavy and magnetic saxothuringian characterized by palaeozoic units metamorphosed to varying degrees and intruded by early carboniferous basites and the lighter moldanubian consisting mainly of gneisses and granites geological structures and tectonic features are recorded beneath the mesozoic and cenozoic cover the present picture of the basement is mainly the result of late visean early namurian structural features represented by a linear arrangement of magmatic bodies and the distribution of strike slip and thrust faults the major structural features are the e w vittel lalaye lubine baden baden fault that marks the border between saxothuringian and moldanubian the n35 left lateral wrench fault system running along the present rhinegraben the n60 grain of the northern vosges and the saar basin and the s verging crustal thrusts of moldanubian

reconstruction of the thickness of the tsushima current in the sea of japan during the quaternary from molluscan fossils abstract the present distribution of the benthic fauna in the sea of japan reveals that the thickness of the warm tsushima current is about 150 m because cold water elements are found in bottom faunas in the underlying cold intermediate water below this depth identification of such cold water taxa from quaternary molluscan assemblages makes it possible to estimate the thickness of the tsushima current in the past in order to determine the depth and nature of the cold water fauna living below the warm surface current molluscan and planktonic faunas were analyzed from the omma formation which comprises at least 14 superposed cyclothems corresponding to oxygen isotope stages 50 to 22 based on faunal analyses one molluscan association that lived below the warm tsushima current was identified from the horizon equivalent to stage 47 about 1 45 ma the depth of the upper limit of the association that is the thickness of the tsushima current was estimated using sedimentary structures and oxygen isotope records from deep sea cores the result show that the thickness of the current was less than two thirds that of today

evolution and structure of the upper rhine graben insights from three dimensional thermomechanical modelling the evolution and geometry of the tertiary upper rhine graben were controlled by a continually changing stress field and the reactivation of pre existing crustal discontinuities a period of wnw ese extension in the late eocene and oligocene was followed by lateral translation from the early miocene onwards this study utilizes 3d finite element techniques to simulate extension and lateral translation on a lithospheric scale brittle and creep behaviour of lithospheric rocks are represented by elastoplasticity and thermally activated power law viscoplasticity respectively contact elements allocated with cohesion and frictional coefficients are used to describe pre existing zones of weakness in the elastic brittle field our results suggest that 1 extension is accommodated along listric border faults to midcrustal depth of 15 16 km beneath pure shear stretching occurs without a need for localized shear zones in lower crust and upper mantle 2 ductile flow at midcrustal depth across the graben accounts for the pronounced halfgraben morphology thereby the shape of the border faults their frictional coefficients and sedimentary loads have profound effects on the rate of ductile flow across the graben 3 horizontal extension of 8 8 5 km and sinistral displacement across the rift of 3 4 km are needed to accommodate the observed sediment thickness

characterising the extent of volcanism at the galapagos spreading centre using deep tow sediment profiler records abstract volcanism at the galapagos spreading centre consists of sheet flows and other distributed extrusives the surficial volcanics in the axial region should therefore be generally young over a finite area and those on the ridge flanks should be younger on average than would be predicted from simple seafloor spreading a method for determining an upper bound on the mean age anomaly of the flanks which is interpreted as equivalent to the mean extent of volcanism is demonstrated using sediment thicknesses digitised from deep tow profiler records of the galapagos spreading centre as found previously the sediments thicken linearly with distance from the ridge reflecting simple seafloor spreading up to 1 ma deviations from the linear trend are due to sediment redistribution short wavelength fluctuations and the age distribution of extrusives in particular due to large volcanic flows revealed by regions of uniform thickness the full width of the extrusion zone is obtained by regressing sediment thickness on across axis distance for both flanks and observing the separation of the two regression lines where they cross zero thickness since the method is quantitative and provides an average value for the length of the profile it is more representative than estimating the width from morphological observations of the spreading axis due to scattering from the basement which obscures sediment in depressions sediment thickness is generally under estimated and the measured axial width is an upper bound 10 12 km for the galapagos spreading centre the mean sediment thickness bias is calculated from high resolution topography data of lava flows and is 1 5 m suggesting that the true mean width of the extrusion zone is 8 10 km using this corrected value the surface of the crust is younger than predicted by seafloor spreading by 120 150 kyr on average this large value implies that the flanks of the galapagos spreading centre are covered with a series of large overlapping volcanic flows

new insight in the tectonics of the southern rhine graben jura region using local earthquake seismology 1 a new seismic data set was acquired using a dense temporary network of mobile seismic stations it is combined with existing seismological data for the southern rhine graben the data yielded some new focal mechanisms and allowed for a detailed local earthquake tomography these methods give new insight in the structure of the crust and stress conditions in the area by combining the tomography with the earthquake hypocenter locations and focal mechanisms some of the structures in the p wave velocity model are interpreted as active faults the eastern boundary fault zone of the graben is found to be activated in a left lateral strike slip sense the southern continuation of these faults is formed by variscan structures in the basement a change in orientation of the graben axis between the main graben and its southern end have played a role during the development of the system this difference in orientation caused the development of the dannemarie and allschwil subbasins during a late stage of the opening of the rhine graben this study shows evidence for active faulting in the basement underneath the detachment of the jura mountains these faults which are interpreted as reactivated permo carboniferous troughs coincide with the frontal thrusts of the jura mountains it might be that these structures in the basement have influence on the detachment tectonics in the region

seismic stratigraphy of the gulf of cadiz continental shelf a model for late quaternary very high resolution sequence stratigraphy and response to sea level fall

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

thermal structure of the low velocity zone derived from laboratory and seismic investigations laboratory measurements of seismic velocities in upper mantle peridotite can be used to constrain the thermal state in the low velocity zone the measurements carried out at high temperature and high confining pressure can be extrapolated to upper mantle conditions we compare laboratory velocities with seismic observations and estimate temperatures and partial melt fractions in the low velocity zone the comparison gives 1310 c and 7 vol partial melt at 45 km depth in 0 5 my asthenosphere beneath the iceland plateau and 1450 c and 3 vol partial melt at 85 km depth in 0 20 my asthenosphere beneath the pacific ocean the laboratory results show that up to a 6 velocity drop in the low velocity zone relative to the lithospheric velocity does not necessarily require the existence of partial melt this implies that partial melt may not exist in the low velocity zone older than 5 my and 50 my in the iceland plateau and the pacific ocean respectively

exposed coasts vs sheltered bays contrast between new zealand and japan in the molluscan record of temperature change in plio pleistocene cyclothems abstract cyclothems in the omma formation on the japan sea coast of central honshu each contains two ecostratigraphic datums the appearance and disappearance datums of warm water molluscs cold water molluscs occur both below in early tst and above in late hst and possibly rst warm water ones which occur in late tst and early hst in contrast no new zealand cyclothems in the main plio pleistocene basins contain both cold and warm water faunas in one cycle cyclothems in the petane group central hawke s bay and in the castlecliff section wanganui basin contain entirely eurythermal and warm water molluscs throughout cyclothems in south wairarapa have entirely eurythermal and cold water molluscs throughout the subantarctic zygochlamys delicatula fauna even in hsts of some cycles this contrast demonstrates the importance of exposure of the deposition site to strong coastal currents for the maximum faunal expression of temperature change the omma formation was deposited in an open site on the japan sea coast where currents transported larvae of a wide variety of molluscs northwards and southwards in response to temperature oscillations the main new zealand cyclothemic successions were deposited in large embayments sheltered from the influence of coastal currents the maximum faunal expression within one cyclothem of plio pleistocene temperature change can be expected in only those few deposition sites that satisfy the optimum requirements deposition of reasonably complete sequences at least tsts hsts and rsts preserved in an exposed coastal site influenced by strong currents from both the north and south on the inner shelf in the temperate regions between ca 30 and 60 north and south near the north south oriented coast of a large continent

evolution of sedimentary mode since pleistocene in the central south yellow sea china based on seismic stratigraphy analysis abstract in order to investigate the distribution development and evolution of the strata in the south yellow sea basin sysb seismic and core data were analyzed fourteen 14 reflecting interfaces and 13 seismic units are identified and a stratigraphic framework since 1 81 ma b p is established the deposition rate has changed since 126 ka b p the stratigraphic model shows that the sysb responded to sea level changes during the same period 126 ka b p which suggests a model change of the development of regional strata between 1 81 ma b p and 126 ka b p the zhejiang minnan uplift zmu obstructed the intrusion of seawater into the sysb which is the main factor responsible for the development of regional strata while the sea level fluctuation and fluvial material input have dominated the formation of the strata since 126 ka b p

astronomical theory of paleoclimates and the last glacial interglacial cycle in the 19th century croll and pilgrim stressed the importance of severe winters as a cause of quaternary ice ages later on mainly during the first half of the 20th century koppen spitaler and milankovitch regarded high winter and low summer insolation as favoring glaciation after koppen and wegener related the milankovitch new radiation curve to penck and bruckner s subdivision of the quaternary there was a long lasting debate whether or not such changes in the insolation can explain the quaternary glacial interglacial cycles in the 1970s with the improvements of radiometric dating and of acquiring and interpreting the long continuous geological records with the advent of computers and with the development of more sophisticated astronomical and climate models the astronomical theory and in particular its milankovitch version were revived over the last 5 years most geological astronomical and climatological obstacles have been overcome and the causal role of the orbital variations in long term variation of climate is taken almost universally for granted models of different categories of complexity from conceptual ones to 3 d atmospheric general circulation models and 2 d time dependent models of the whole climate system have now been astronomically forced in order to test the physical reality of the astronomical theory for example experiments with both low and high resolution gcms show that the increased seasonality at 9 000 bp leads to intensified summer monsoon circulation of africa and southern asia on the other hand seasonal models for simulating the transient response of the climate system to astronomical forcing are also developed and the output of these most recent modeling efforts compares favorably with data of the past 400 000 years accordingly the model predictions for the next 100 000 years are used as a basis for forecasting how climate would evolve when forced by orbital variations in the absence of anthropogenic disturbances the long term cooling trend which began some 6 000 years ago will continue for the next 5 000 years this first temperature minimum will be followed by an amelioration around 15 000 ap after present by a cold interval centered al 23 000 ap and by a major glaciation at around 60 000 ap

shallow water carbonates record marginal to open ocean quaternary paleoceanographic evolution 1 the oxygen and carbon isotopic composition of shallow water carbonates and their fossil components can be important tools for understanding quaternary paleoceanographic conditions of marginal seas including coral reef regions however most previous paleoceanographic studies using isotopes have been based on pelagic or hemipelagic sediments because the original 1 8 o and 1 3 c values of shallow water carbonates are normally altered by postdepositional diagenesis this study shows that marginal to open ocean isotopic signals can be preserved in carefully cleaned low mg calcitic planktic foraminifers of shallow water carbonates even when the isotopic values of the carbonate host rock have been altered by meteoric fluids and subaerial exposure the two studied core sections were collected from the mid quaternary ryukyu group southwestern japan which consists mainly of bioclastic grainstone packstone rhodolith floatstone rudstone and large foraminiferal floatstone corresponding to open shelf to shelf slope facies from the southwest ryukyu islands japan down core 1 8 o records of planktic foraminifers in the ryukyu group imply that sea surface temperatures sst in the northwestern pacific increased 2 0 c at the beginning of oxygen isotope stage 19 post mid pleistocene revolution mpr this warming may have triggered the expansion of reef complex deposits as large as those now in the ryukyu islands and was approximately coeval with the lower section of the australian great barrier reef sst warming due to the expansion of the western pacific warm pool wpwp toward the north and south subtropical regions is a possible mechanism for reef expansion and initiation of the coral reefs of the western pacific region

seismic refraction investigation of the black forest abstract within the framework of site surveys of the deep continental drilling program ktb deep seismic sounding experiments were carried out in the black forest southwest germany in august 1984 these site surveys comprised seismic refraction as well as seismic reflection measurements this paper will concentrate on the interpretation of the refraction data which were observed along a 240 km long line approximately following the morphological axis of the black forest in a n s direction and extending in the south into the swiss molasse basin from the available seismic refraction data a detailed velocity depth model of the crust and uppermost mantle was derived a clear phase refracted in the basement with a velocity of 5 9 km s is observed for all shots this phase is followed by a reflection from the upper boundary of a low velocity zone this zone is very accentuated under the northern and central black forest and is characterized by a velocity decrease from 6 2 to 5 4 km s between depths of about 8 and 14 km towards the south the velocity inversion gradually loses its intensity under the center of the southern black forest velocities of about 6 km s prevail throughout the upper crust the lower crust which starts at the lower boundary of the low velocity zone shows a very complicated response in the record sections due to long reverberations between travel times of 1 5 3 5 s reduced by 6 0 km s at an epicentral distance of approximately 30 70 km a classical phase correlation is not possible based on a combined interpretation of near angle and wide angle reflection data the lower crust is characterized by a stack of thin layers with alternating high and low velocities the average velocity of the laminated zone is 6 7 km s the reflection from the moho at a depth of 25 26 km is the most prominent phase at epicentral distances greater than 60 km

the gravity field along the central segment of the egt abstract we give an overview of the gravity field of central europe based on a compilation of bouguer maps available by mid 1989 a generalized gravity map corrected for moho effects is presented as well as several filtered maps of the second derivative additionally sediment stripped bouguer maps are used in the case of the northwest german basin and for northeastern franconia the north german line the erzgebirge minimum the kraichgau high and the regensburg gottingen low are treated in detail and a number of geologic interpretations are discussed

insight into the structure of the upper rhine graben and its basement from a new compilation of bouguer gravity abstract a compilation of gravity data from the upper rhine graben urg is presented that includes all the main data sources from its german and french parts this data is used to show that the urg consists of at least two arc shaped and asymmetric rift units that tectonically are the basic building blocks of the graben in this sense the urg does not differ from other continental rifts such as the african rifts this division should replace the now classical geomorphologic division of the urg into three segments based on their different trends moreover the gravity suggests that the faults in the central and southern segments are continuous and have the same trend appearing to respond as a single kinematic unit changes in the gravity field in the graben are shown to reflect not only the structure of the graben but also the highly variable composition of the basement in this respect the urg is quite different from some other tertiary continental rifts where possible changes in the composition of the basement are mostly masked in the gravity field by the effect of the overlying low density sediments this characteristic is used to study the extent of some of the main basement units that underlie the graben

a three dimensional crustal model of southwest germany derived from seismic refraction data abstract from densely covered seismic refraction data obtained in 1978 urach experiment and 1984 schwarzer zollern wald experiment and from seismic reflection data and results from previous refraction investigations a three dimensional crustal model of southwest germany was derived travel time and amplitude information of seismic refraction data were interpreted with two dimensional forward modeling ray tracing to calculate two crustal cross sections in southwest germany these results fill a gap in the existing data and enabled the construction of a detailed three dimensional crustal model while seismically the upper crust is laterally homogeneous 5 9 6 0 km s throughout the area the middle and lower crust show pronounced lateral variations in thickness velocity and reflectivity the moho is a flat surface at a relatively shallow depth 25 26 km we classify the middle and lower crust of southwest germany into two characteristic crustal types type i consists of a mid crustal low velocity zone 5 4 5 8 km s overlying a thick 10 km high velocity 6 6 6 8 km s lower crust type ii has no prominent mid crustal low velocity zone and a thin

geochemical evidence for efficient aquifer isolation over geological timeframes aquitards layers of rock having low permeability have been suggested as potential long term reservoirs for toxic materials such as nuclear or chemical waste but information about the isolation properties of aquitard layers is essential to evaluate whether they can indeed be used safely as reservoirs here we investigate the long term mobility of groundwaters between two aquifers surrounding an aquitard layer in the eastern recharge area of the paris basin france using helium isotopes as a geochemical tracer the deeper trias sandstone aquifer which lies above the crystalline basement accumulates radiogenic 4he and primordial 3he from large regions of the crust and mantle at rates comparable to the degassing of the whole crust1 and of mid ocean ridges2 we show that the overlying carbonate dogger aquifer which is separated from the trias aquifer by an aquitard layer consisting of a 600 m succession of shales and clays is stagnant and has been extremely well isolated from the trias over the past several million years this finding together with previous studies at the centre of the paris basin3 4 shows that diffusive mass transfer across aquitards is negligible and that cross formational flow in basins takes place preferentially in faulted areas

gravity and magnetic constraints on deep and intermediate crustal structure and evolution models for the rhine graben abstract the dekorp ecors project comprises two deep seismic reflection lines shot across the rhine graben in its southern part s of strasbourg and in its northern portion 30 km to the n of mannheim respectively in order to assist the geologic interpretation of the northern deep seismic line dekorp 9n an analysis of the gravity and magnetic data of the study area was undertaken in particular the removal stripping of the gravity effect of the tertiary and quaternary sedimentary infill enabled us to establish the existence of a gravity high over the graben proper this gravity high is asymmetrical with a steep gradient to the east and a gentler one to the west interpretation of a regional anomaly obtained by low pass filtering from a 400 km gravity profile incorporating the results from the stripping in terms of the moho topography indicates that the moho is shallower under the graben proper estimates of depths to the magnetic sources by spectral statistical analysis were conducted the mean depth to the magnetic sources ranges between 2 and 3 km the depth to the curie isotherm is estimated to be located between 15 and 18 km magnetic modelling indicates the existence of discontinuities in the crystalline basement that can be correlated with faults affecting the sedimentary infill a density model was produced that incorporated the image obtained by the deep seismic geotraverse constrained by the geology the known petrophysical parameters density magnetic properties results from seismic refraction studies and the information derived here this indicated the feasibility of an asymmetric heterogeneous extension related mechanism for the northern part of the rhine graben the lithosphere is characterized by a thicker lower crust to the west a mantle upwelling beneath the graben proper and a shear zone crossing the lithosphere

the variscan tectonic inheritance of the upper rhine graben evidence of reactivations in the lias late eocene oligocene up to the recent processing of gravity and magnetic maps shows that the basement of the upper rhine graben area is characterized by a series of ne sw trending discontinuities and elongated structures identified in outcrops in the vosges black forest and the odenwald mountains they form a 40 km wide n30 40 striking sinistral wrench zone that in the visean shifted the variscan and pre variscan structures by at least 43 km to the ne wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340 325 ma the sub vertical ne sw trending discontinuities in the basement acted as zones of weakness susceptible to reactivation by subsequent tectonism the first reactivation marked by mineralizations and palaeomagnetic overprinting along ne sw faults of the vosges mountains results from the liassic nw se extension contemporaneous with the break up of pangea the major reactivation occurred during the late eocene n s compression and the early middle oligocene e w extension the ne sw striking basement discontinuities were successively reactivated as sinistral strike slip faults and as oblique normal faults elongated depocenters appear to form in association with reactivated variscan wrench faults some of the recent earthquakes are located on ne sw striking variscan fault zones and show sinistral strike slip focal mechanisms with the same direction suggesting also present reactivation

a first deep seismic survey in the sea of marmara deep basins and whole crust architecture and evolution abstract increased source strength streamer length and dense spatial coverage of seismic reflection profiles of the seismarmara leg 1 allow to image the deep structure of the marine north marmara trough nmt on the strike slip north anatolian fault naf west of the destructive izmit 1999 earthquake a reflective lower crust and the moho boundary are detected they appear upwarped on an e w profile from the southern central basin eastwards towards more internal parts of the deformed region thinning of the upper crust could use a detachment suggested from an imaged dipping intracrustal reflector that would allow upper crustal material to be dragged from beneath it and above the lower crust accounting for the extensional component but also southwest motion of the southern margin of the nmt sections across the eastern half of the nmt crossing the cinarcik and imrali basins reveal several faults that are active reaching into the basement and have varying strike and proportions of normal and strike slip displacement they might be viewed as petals of a large scale negative flower structure that spreads over a width of 30 km at surface and is rooted deeper in the lithosphere under the central basin a very thick sediment infill is revealed and its extensional bounding faults are active and imaged as much as 8 km apart down to 6 km depth we interpret them as two deep rooted faults encompassing a foundering basement block rather than being merely pulled apart from a jog in a strike slip above a decollement the deep basin lengthening would account for only a modest part of the proposed 60 km finite motion since 4 myr along the same direction oblique to the nmt that sidesteps the shear motion from its two ends thus differential motion occurred much beyond the deep basins like subsidence involving the nmt bounding faults and the intracrustal detachments the complex partitioned motion localized on active faults with diverse natures and orientations is suggested to represent the overburden deformation induced from horizontal plane simple shear occurring in depth at lithospheric scale and in front of the north anatolian fault when it propagated through the region

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

a teleseismic and petrological study of the crust and upper mantle beneath the geothermal anomaly urach sw germany abstract teleseismic p wave travel time residuals recorded by a mobile shortperiod network are interpreted using the composition of crustal and upper mantle xenoliths a three dimensional inversion of the p residuals revealed a small scale anomalous domain with a velocity reduction of 3 in the crust and a broad low velocity anomaly of 4 beneath the moho down to a depth of 50 km xenoliths of the miocene urach volcanic field uvf 1300 km2 355 eruptive centres mostly diatremes comprise phlogopite bearing clinopyroxene rich mantle xenoliths evidence for large ion lithophile element lil metasomatism in an originally depleted harzburgitic mantle reflecting chemical modification of the upper mantle beneath the uvf the metasomatism caused partial melting in the spinel peridotite stability field indicated by glasses in xenoliths and a diapiric uprise of the partially molten metasomatized mantle the observed reduction of the p wave velocity of 4 in the lithospheric mantle can be explained by a local enrichment of phlogopite accompanied by increased temperatures the crustal low velocity body coincides very well with the postulated volume of an ancient intracrustal magma chamber or system of chambers required by the composition of xenoliths the magnetization of the diatremes and the spatial distribution of the volcanic eruption centres

subdividing the pleistocene using the matuyama brunhes boundary mbb an australasian perspective abstract the last major reversal of the earth s magnetic field the matuyama brunhes boundary mbb dated at 0 78 ma is widely identified in australian and new zealand pleistocene deposits in new zealand the mbb is precisely located in shallow marine sediments of wanganui basin where it corresponds with the base of the new zealand putikian substage a combination of marine biostratigraphy sequence stratigraphy and tephrostratigraphy permit correlation from wanganui basin to other on land sections and deep sea cores in australia the mbb is identified in many continental sequences particularly saline lake basins however chemical weathering has resulted in variable brunhes age normal overprints that are sometimes difficult to remove australasian tektites are a potential lithostratigraphic marker just prior to the mbb but have yet to be identified in the same on land section as the mbb in australia identification of reverse polarity magnetisation in weathered deposits including soils provides a minimum age of 0 78 ma for these materials a widespread arid shift in paleoclimate succeeded the mbb in australia placement of the lower middle pleistocene boundary at the mbb would constitute the most recognisable chronostratigraphic marker in weathered continental deposits

characterization and correlation of the hegawa kasamori 5 tephra a widespread tephra aged c 450 ka associated with large scale pyroclastic flows from southern kyushu sw japan

deformation and displacement of the jura cover on its basement abstract the sedimentary cover of the internal jura displaced over its basement conforms well with the model of a thin skinned thrust sheet the wedge shaped sheet which includes a thick sequence of molasse deposited ahead of the alpine front slid over the basement cover interface the alpine crustal thrust sheets created a load at the south east end of the overthrust european plate molasse was deposited on the bent plate and the internal part of the basin was progressively affected by thrusting this process also induced deformation and displacements in the foreland gravity spreading in the internal molasse and a forward motion by rigid slipping movement led to a horizontal push causing deformation by indentation in the internal jura in the plateaux of the external jura there is very little extension in the cover and minimal shortening in the basement this shortening induced a decollement under the plateaux over the bresse graben gravity sliding occurred in the form of huge landslides these contrasts in the origin of the jura structures along a median cross section from thonon to arbois are shown by geophysical data construction of a balanced cross section and calculations of realistic mechanical models for the bending of the foreland plate and for the motion of the cover sheet

tectonic inversion of an asymmetric graben insights from a combined field and gravity survey in the sorbas basin the formation of sedimentary basins in the alboran domain is associated with the exhumation of metamorphic core complexes over a ca 15 ma period through a transition from regional late orogenic extension to compression an integrated study coupling field analysis and gravity data acquisition was performed in the sorbas basin in the southeastern betic cordillera detailed field observations revealed for the first time that extensional tectonics occurred before shortening in this basin two extensional events were recorded with nw se to n s and ne sw kinematics respectively the first of which being likely responsible for the basin initiation tectonic inversion of the basin then occurred around 8 ma in an overall ca n s shortening context 2d gravity sections reveal that the basin acted as an active depocenter as the basin floor locally exceeding 2 km depth is characterized by a marked asymmetric architecture based on this integrated study we explore a new evolutionary scenario which can be used as a basis for interpretations of the neogene tectonic history of the southeastern betics

pinning down the brunhes matuyama and upper jaramillo boundaries a reconciliation of orbital and isotopic time scales until recently the temporal calibration of the plio pleistocene portion of the geomagnetic reversal time scale grts was based exclusively on kar isotopic ages of volcanic rocks the so called chronogram technique estimates the age that minimizes discrepancies between a given age assignment for a reversal boundary and the population of dates of known polarity the most widely quoted date 0 73 ma for the brunhes matuyama boundary was derived in such a manner 1 radioactive decay is not the only source of temporal information in the geologic record however variations in several of the orbital parameters of the earth e g precession obliquity eccentricity can be calculated for the last several million years and the climatic response approximated a recent analysis of the so called astronomical technique on oxygen isotopic data from deep sea sediments suggested an age of 0 78 ma for the brunhes matuyama boundary 2 some 50 000 years older than the chronogram estimate we reconcile the two estimates for the age of the last reversal by first presenting new magnetostratigraphic data tied to high quality40ar39ar dates our date for the upper jaramillo boundary is0 992 0 039 ma considerably older than the estimate of 0 91 ma in the standard chronogram based time scale 3 furthermore an age of0 746 0 009 ma was obtained for sediments immediately overlying the brunhes matuyama boundary these data are consistent with the astronomical estimates of 0 78 ma and 0 99 ma for the brunhes matuyama and upper jaramillo boundaries respectively finally we present a new method for estimating the uncertainties of ages calculated using the chronogram technique that employs a simple bootstrap resampling scheme the 95 confidence region for the chronogram estimate of the brunhes matuyama boundary using an updated compilation of date polarity pairs spans from 0 73 to 0 78 ma we find therefore that the discrepancies between the isotopic data set and the astronomical calibration of the brunhes matuyama boundary disappear when appropriate uncertainties are applied for the most recent compilation of isotopic data

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

ecological analysis of benthic ostracods in the northern japan sea based on water properties of modern habitats and late cenozoic fossil records abstract the ecology of ostracods in the northern japan sea is well documented these ostracods can be grouped in two assemblages 1 the tsushima warm current surface water assemblage twsa northern which lives in an environment where summer temperatures reach up to about 20 c winter temperatures up to about 5 c several species in this assemblage e g loxoconcha optima and pontocythere subjaponica tolerate seasonally low temperatures and lived in the region since the early pleistocene 2 the japan sea intermediate proper water assemblage jsi pa which lives at greater depths lower shelf to upper slope this assemblage lives under stable conditions with a small annual range in temperature 0 5 c the assemblage has a relatively low diversity contains species such as acanthocythereis dunelmensis and robertsonites spp and has been present in the area since the pliocene these data indicate that the presently living species either tolerate seasonally low temperatures twsa northern or tolerate stable but very low temperatures near 0 c and therefore they could survive the pleistocene environmental fluctuations in the japan sea caused by glacio eustatic changes in sea level our data document the survival of ostracod species during past climate change and thus can be used to speculate on the effect of possible future climate change on the faunas we predict that some of the cryophilic species in the japan sea cannot be expected to survive global warming for more than 2 centuries

a depth derived pleistocene age model uncertainty estimates sedimentation variability and nonlinear climate change 1 a new chronology of glaciation spanning the last 780 000 years is estimated from 21 marine sediment cores using depth as a proxy for time to avoid biasing this depth derived age estimate the depth scale is first corrected for the effects of sediment compaction to provide age uncertainty estimates the spatial and temporal variability of marine sediment accumulation rates are estimated and modeled as an autocorrelated stochastic process depth derived ages are estimated to be accurate to within 9000 years and within this uncertainty are consistent with the orbitally tuned age estimates nonetheless the remaining differences between the depth and orbitally tuned chronologies produce important differences in the spectral domain from the 18o record using the depth derived ages we infer that there are weak nonlinearities involving the 100 kyr and obliquity frequency bands which generate interaction bands at sum and difference frequencies if an orbitally tuned age model is instead applied these interactions are suppressed with the system appearing more nearly linear

the deep crust of the southern rhine graben reflectivity and seismicity as images of dynamic processes abstract the rhine graben part of the european cenozoic rift system deserves special attention because of its location in the foreland of the alpine orogen the phanerozoic evolution of the lithosphere in this region is defined by a set of major geodynamic events ranging from the variscan orogeny late orogenic crustal re equilibration to the interference of rifting and alpine orogeny in tertiary times the rhine graben is one of the most detailedly studied continental grabens prospecting for hydrocarbons in its sedimentary fill and intensive pre site studies for the continental deep drilling program ktb on its eastern crystalline flank black forest provided a comprehensive set of geoscience data seismic investigations ranging from a deep seismic network of near vertical reflection to concurrent wide angle refraction experiments were accompanied by seismological and geological surveys therefore a direct observational comparison between the two depth definitions of crustal subdivisions elastic vs strength rheological was possible in large parts of western europe deep seismic sounding dss investigation distinguishes between a crystalline upper crust of comparatively low p wave velocities 5 9 6 0 km s with little and discrete reflectivity and a strongly reflective lower crust with higher p wave velocities about 6 4 6 8 km s both are separated by the conrad discontinuity in contrast strength and rheological considerations define a brittle upper crust and a ductile lower crust the boundary between these two realms is usually referred to as the brittle ductile transition zone which in seismically active regions is imaged by the deepest crustal hypocentres the present brittle ductile transition in the rhine graben region as defined by the deepest hypocentres does not necessarily coincide with the structural separation in an upper and lower crust as seen in deep seismic studies this suggests that the laminated lower crust developed during the crustal re equilibration phase at the end of the variscan orogeny the second part of this paper concentrates on evidence of recent tectonic activities related to rifting processes impacting on the variscan lower crust a remarkable concentration of deep crustal earthquakes reaching to the top of an asymmetrical thinned lower crust is observed at or near the eastern border fault of the southern rhine graben and is possibly induced by the young rifting process we suggest that this asymmetry could be a consequence of the uppermost mantle detaching from the upper crust in collision with the alpine orogen this allows us to propose the distinction between the influence of compression extension continental subduction and intra crustal detachment during graben formation the dynamic interference of rifting and foreland compression shown by structural and seismological observations leads to the notion of small scale collisional escape tectonics associated with an intra continental transform fault at the southern end of the rhine graben the rhine sao ne transform zone

evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates new osmium os isotope and platinum group element pge concentration data are used in conjunction with published 3 he and th isotope data to determine the relative proportions of lithogenic extraterrestrial and hydrogenous iridium ir in a pacific pelagic carbonate sequence from the ocean drilling program odp site 806 on the ontong java plateau ojp these calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary ir budget are minor while hydrogenous ir accounts for roughly 85 of the total ir application of analogous partitioning calculations to previously reported data from a north pacific red clay sequence ll44gpc3 yields very similar results total ir burial fluxes at site 806 and ll44 gpc3 are also similar 45 and 30 pg cm 2 kyr 1 respectively average ir 3 he and ir xs 230 thinitial ratios calculated from the entire site 806 data set are similar to those reported earlier for pacific sites in general down core profiles of ir 3 he and xs 230 thinitial are not well correlated with one another however all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two while these results indicate that ir concentration has potential as a point paleoflux tracer in pelagic carbonates ir based paleoflux estimates are likely subject to uncertainties that are similar to those associated with co based paleoflux estimates consequently local calibration of ir flux in space and time will be required to fully assess the potential of ir as a point paleoflux tracer measured 187 os 188 os of the ojp sediments are systematically lower than the inferred 187 os 188 os of contemporaneous seawater and a clear glacial interglacial 187 os 188 os variation is lacking mixing calculations suggest os contributions from lithogenic sources are insufficient to explain the observed 187 os 188 os variations the difference between the 187 os 188 os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic os carried by particulate extraterrestrial material down core variations of 187 os 188 os with pt ir and os ir also point to contributions from extraterrestrial particles mixing calculations for each set of several triplicate analyses suggest that the unradiogenic os end member cannot be characterized by primary extraterrestrial particles of chondritic composition it is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions 187 os 188 os of pelagic carbonates has greater potential compared to abundances of pge an attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial os in the ojp samples and previously reported extraterrestrial os flux throughout most of the ojp record os isotope based paleoflux estimates are within a factor of two of those derived using other constant flux tracers meaningful flux estimates cannot be made during glacial maxima because the ojp sediments do not record the low 187 os 188 os reported previously we speculate that this discrepancy may be related to focusing of extraterrestrial particles at the ojp as has been suggested to explain down core 3 he variations

strike slip tectonics and quaternary basin formation along the vienna basin fault system inferred from bouguer gravity derivatives 1 the vienna basin at the transition between the alpine and carpathian belt hosts a number of large pleistocene sub basins forming along an active continental scale strike slip fault vienna basin strike slip fault we utilize first order derivatives from industrial bouguer gravity data to unravel the impacts of pleistocene kinematics on the vienna basin and to compensate for the lack of near surface fault data anomalies have been evaluated by independent geophysical and geological data and were integrated to build up a tectonic model factors influencing the wavelength and the amplitude of anomalies were additionally investigated by 2 d models to better interpret field data subsidence and related accumulation of quaternary sediments in the vienna basin produce significant gravity signals related to the activity of the strike slip fault the constrained fault patterns and structures highlight tight and elongated transtensional pull apart basins with typically associated features like separated depocenters and riedel fractured sidewalls in an en echelon alignment further pleistocene basins are highlighted as tectonic grabens developing along branches of the master fault the vienna basin is additionally affected by minor deformation represented by both subsidence along major miocene sidewalls and nw se faulting resulting in distinct topographic features which manifests kinematics on a regional scale the clear density contrasts between miocene marine and quaternary terrestrial sediments as well as the exceptional database provide a unique framework to demonstrate advantages of incorporating gravity derivatives for near surface fault analysis

operations and main results of the ecors project in france summary the ecors project was launched in 1983 with the aim of studying fundamental mechanisms of geodynamics in france the ecors deep seismic profiles have concentrated on a few structures of major significance outer zone of the variscan orogen in northern france the basin formed during the bay of biscay s opening and transects of recent orogenic ranges pyrenees and alps the seismic profiles have been carried out with all the available modern techniques of industry and completed wherever possible by additional geophysical surveys magnetism gravity mt wide angle and refraction seismics and geological surveys the first results already shed new light on major geodynamic phenomena such as variations in the frontal variscan detachment lower crust formation crustal behaviour during orogenesis and variations in the formation of cratonic basins

reconstruction of atmospheric co2 from ice core data and the deep sea record of ontong java plateau the milankovitch chron we provide a reconstruction of atmospheric co2 from deep sea sediments for the past 625000 years milankovitch chron our database consists of a milankovitch template of sea level variation in combination with a unique data set for the deep sea record for ontong java plateau in the western equatorial pacific we redate the vostok ice core data of barnola et al 1987 to make the reconstructions we employ multiple regression between deep sea data on one hand and ice core co2 data in antarctica on the other the patterns of correlation suggest that the main factors controlling atmospheric co2 can be described as a combination of sea level state and sea level change for best results squared values of state and change are used the square of sea level rule agrees with the concept that shelf processes are important modulators of atmospheric co2 e g budgets of shelf organic carbon and shelf carbonate nitrate reduction the square of change rule implies that on short timescales any major disturbance of the system results in a temporary rise in atmospheric co2

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression