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

the tertiary structural and thermal evolution of the central alps compressional and extensional structures in an orogenic belt the western alpine arc has been created during the cretaceous and the tertiary orogenies the interference patterns of the tertiary structures suggest their formation during continental collision of the european and the adriatic plates with an accompanying anticlockwise rotation of the adriatic indenter extensional structures are mainly related to ductile deformation by simple shear these structures developed at a deep tectonic level in granitic crustal rocks at depths in excess of 10 km in the early palaeogene period of the tertiary orogeny the main tertiary nappe emplacement resulted from a nw thrusting of the austroalpine penninic and helvetic nappes heating of the deep zone of the upper cretaceous and tertiary nappe stack by geothermal heat flow is responsible for the tertiary regional metamorphism reaching amphibolite facies conditions in the lepontine gneiss dome geothermal gradient 25 c km the tertiary thrusting occurred mainly during prograde metamorphic conditions with creation of a penetrative nw se oriented stretching lineation xi finite extension parallel to the direction of simple shear earliest cooling after the culmination of the tertiary metamorphism some 38 ma ago is recorded by the cooling curves of the monte rosa and mischabel nappes to the west and the suretta nappe to the east of the lepontine gneiss dome the onset of dextral transpression with a strong extension parallel to the mountain belt and the oldest s vergent backfolding took place some 35 to 30 ma ago during retrograde amphibolite facies conditions and before the intrusion of the oligocene dikes north of the periadriatic line the main updoming of the lepontine gneiss dome started some 32 30 ma ago with the intrusion of the bergell tonalites and granodiorites concomitant with s vergent backfolding and backthrusting and dextral strike slip movements along the tonale and canavese lines argand s insubric phase subsequently the center of main updoming migrated slowly to the west reaching the simplon region some 20 ma ago this was contemporaneous with the westward migration of the adriatic indenter between 20 ma and the present the western aar massif toce culmination was the center of strong uplift the youngest s vergent backfolds the glishorn anticline and the berisal syncline fold the 12 ma rb sr biotite isochron and are cut by the 11 ma old rhone simplon line the discrete rhone simplon line represents a late retrograde manifestation in the preexisting ductile simplon shear zone this fault zone is still active today the oligocene neogene dextral transpression and extension in the simplon area were concurrent with thrusting to the northwest of the helvetic nappes the prealpes 35 15 ma and with the jura thin skinned thrust 11 3 ma it was also contemporaneous with thrusting to the south of the bergamasc 35 5 ma and milan thrusts 16 5 ma the oligocene neogene dextral transpression in the central alps is of the same age as the thrusting to the west and southwest in the external french part and to the east in the internal italian part of the alpine arc of the western alps

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

structure stability and transformation of contaminated lacustrine surface fine grained laminae an in situ annular flume sea carousel was deployed in hamilton harbour lake ontario to assess the structure stability and transformation of lacustrine surface fine grained laminae sfgl such laminae typify depositional lacustrine environments and occur at the sediment water interface the critical erosion thresholds erosion rates and internal friction coefficients were determined for natural undisturbed and physically disturbed sites in order to assess changes in bed stability sediment cores taken at each site were analyzed for bulk density using a ct scanner in order to provide an intercomparison of our results flocs and aggregates pumped from the flume during erosion experiments were analyzed for morphological characteristics using conventional optical microscopy and transmission electron microscopy to evaluate the mechanism and development of the sfgl and its structure a general three layer model is developed which depicts the organic flocs of the sfgl layer 1 compressing within a collapse zone layer 2 to form a consolidated bed layer 3 the sfgl was observed to be porous of low density and of high water content which possessed yield resistance due in part to binding by extracellular polymeric substances secreted by a colonized microbial population transmission electron microscopy observations showed an active biological community in the sediment promoting biostabilization time series of erosion thresholds and friction coefficients of the disturbed bed showed that the sfgl reconsolidated rapidly and increased in shear strength the artificial disturbance of the sediment resulted in incorporation of the sfgl and the collapse zone with the consolidated bed through mixing this stimulated the process of consolidation chiefly through removal of gas and breakdown of the organic fibril network reconsolidation began with the formation of a collapse zone at the surface of the disturbed sediment high friction coefficients and an increasing density with depth in the new surface layer indicated that rapid consolidation occurred after disturbance

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

role of flocculation and settling processes in development of the mangrove colonized amazon influenced mud bank coast of south america abstract the guianas coast downdrift northwestward of the amazon river mouth is characterized by the periodic migration of mud banks that originate from the amazon the characteristic sizes of these banks as well as their rates of alongshore migration have been estimated from remote sensing however the physical mechanisms leading to their displacement are not yet fully understood the present work is aimed at investigating a number of micro scale processes involved in the coastal and estuarine dynamics of fine sediments and expected to occur during the migration of mud banks the relative magnitudes of flocculation hindered settling and consolidation have been determined sampling of coastal mud was carried out during a field survey in 2001 that focussed on the fluid mud layer in the leading edge of a mud bank in french guiana settling column experiments were conducted under quiescent conditions for various mean sediment concentrations in the range of 2 5 110 g l 1 which is typical of mud bank concentrations the time dependent vertical profiles of suspended sediment concentration were monitored using an optical settling tank equipped with 32 pre calibrated optical sensors the corresponding settling velocities were deduced from the equation of the conservation of mass the results show that the timescales of hindered settling and consolidation processes are much larger than the timescales of mixing mechanisms such as tides or propagating waves the individual floc settling velocities are too small to counterbalance the turbulent mixing induced by breaking waves hindered settling favoured by wave action and by the high background suspended sediment concentrations is thus an overarching process in wave driven mud bank migration this pervasive hindered settling regime is characteristic of the wave exposed outer and leading edges of mud banks where active mobilization of mud assures mud bank migration as a result consolidation is theoretically precluded the experiments pointed out however that additional flocculation and differential settling should enhance sedimentation during slack water and under low wave conditions we deduce from this that enhanced settling in the inner subtidal intertidal parts of leading edges of banks during such conditions is important in the temporary sedimentation that generates gel like fluid mud patches and mud bars these low energy inner leading parts of banks form an accreted substrate colonized by mangroves which further contribute to enhanced settling and rapid sedimentation

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

tilting uplift volcanism and disintegration of the south german block abstract we present a large set of fault slip data together with six u pb ages on calcite vein fillings constraining the kinematics and timing of near surface uppermost 2 3 km of crust faulting of the uplifted south german block in the northern foreland of the nw ward advancing alps the structural data confirm earlier studies showing miocene subhorizontal ne directed extension with shortening mainly being subvertical but also subhorizontally nw oriented the u pb ages are between 15 3 0 2 and 2 3 1 1 ma 2 analytical uncertainty and date kinematically coordinated normal and strike slip faulting in the northern alpine foreland the faults in the south german block have limited strike lengths indicating that they do not cut deeply into the crust however the faults appear to control volcanic centers the melts of which originated at the base of the lithosphere we suggest that the miocene faults could tap the mantle because they reactivated formerly deep seated faults the ages for near surface faulting are coeval with eruption of the urach and hegau volcanics published data suggest that alpine shortening induced large wavelength lithospheric folding in the foreland since 18 16 ma volcanism in the south german block focussed along a lithospheric antiform which is in part superimposed on the foreland bulge of the alps we propose a close link between progressive southward tilting uplift and faulting of the south german block due to lithospheric scale folding and upward flow of the asthenosphere flexure of the lithosphere deep seated volcanism and the nw ward advancing alps

the northern coast of the ottnangian middle burdigalian early miocene molasse sea in germany sediments foraminiferal assemblages and biostratigraphy this study provides new data on the litho and biostratigraphy of the middle burdigalian ottnangian marine sediments at or close to the former northern coastline of the german molasse basin based on cores from three boreholes burgau hamlar 2 and lutzingen and two outcrops haunsheim and dattenhausen methods include quantitative analysis of benthic foraminiferal assemblages 90 samples studies of planktonic foraminifers and ostracods and investigations of lithofacies the data indicate that the transgressive regressive marine sediments of the upper marine molasse omm at burgau and hamlar 2 can be subdivided into the well known lower and middle ottnangian sedimentation cycles with the first cycle being represented by the omm basisschichten and kalkofen formation and the second by the baltringen and steinhofe formations we show for the first time that also the northernmost marginal marine omm facies lutzingen haunsheim and dattenhausen can be correlated with the lower and middle ottnangian sedimentation cycles consequently our results do not support the presence of a previously suggested third sedimentation cycle within the omm sediments our micropaleontological data reveal regionally diverse depositional environments reflecting different water depths and co varying environmental variables significant differences in abundance diversity and species composition of the benthic foraminiferal assemblages demonstrate marginal marine facies for lutzingen haunsheim and dattenhausen nearshore facies for hamlar 2 and shallow marine basin facies for burgau the characteristic lower ottnangian benthic foraminiferal species exhibit restricted ecological tolerances hence the absence or scarcity of these species in nearshore to marginal marine deposits has no stratigraphic significance the presence of two sedimentation cycles in the western german molasse basin alone may have resulted from the interplay of regional tectonics and basin development that have led to different rates of subsidence and sedimentation in the western and eastern sectors of the german molasse basin

retreat of northern margins of george vi and wilkins ice shelves antarctic peninsula the george vi and wilkins ice shelves are considered at risk of disinteg ration due to a regional atmospheric warming trend on the antarctic peninsula retreat of the northern margin of the george vi ice shelf has been observed previously but the wilkins ice shelf was thought to be stable we investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 landsat and 1992 and 1995 european remote sensing satellite ers synthetic aperture radar images our investigation shows that the northern george vi ice shelf lost a total of 906 km 2 between 1974 and 1992 and an additional 87 km2 by 1995 the northern margin of the wilkins ice shelf lost 796 km2 between 1990 and 1992 and another 564 km2 between 1992 and 1995 armadas of tabular icebergs were visible in front of this shelf in the ers images these two ice shelves mark the southern most documented conspicuous retreat of ice shelf margins

catastrophic ice shelf break up by an ice shelf fragment capsize mechanism two disintegration events leading to the loss of larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively proceeded with extreme rapidity order of several days and reduced an extensive seemingly integrated ice shelf to a jumble of small fragments these events strongly correlate with warming regional climate and accumulation of surface meltwater supporting a hypothesis that meltwater induced propagation of pre existing surface crevasses may have initiated ice shelf fragmentation we address here an additional subsequent mechanism that may sustain and accelerate the ice shelf break up once it begins the proposed mechanism involves the coherent capsize of narrow less than thickness ice shelf fragments by rolling 90 in a direction toward or away from the ice front fragment capsize liberates gravitational potential energy forces open ice shelf rifts and contributes to further fragmentation of the surrounding ice shelf

kinematic and geometric analysis of fault related folds in a rift setting the dannemarie basin upper rhine graben france abstract the upper rhine graben urg developed in the alpine foreland from mid eocene to pliocene as part of the west european rift system the dannemarie basin occupies the sw termination of the urg and is bordered by the vosges fault zone west and the illfurth fault zone east we constructed a 3d model of faults and principal pre and syn rift stratigraphic surfaces using all available subsurface and surface geological and geophysical data the model shows 1 syn rift strata thinning across kilometre scale fault parallel monoclinal flexures associated with basin margin faults and 2 major basin margin faults terminating laterally into major flexures sequential cross section restorations show that these flexures accommodated deposition of over 1300 m of syn rift strata salt series which is 42 63 of the basin fill these folds are interpreted as syn rift fault propagation folds that developed above normal faults their geometry is replicated in a trishear numerical model using reasonable parameter values fold development was controlled principally by 1 reactivation of favourably oriented basement faults 2 the presence of a thick viscous layer principally triassic evaporites allowing decoupling between crystalline basement and competent jurassic cover and 3 a relatively slow deformation rate

critical taper analysis reveals lithological control of variations in detachment strength an analysis of the alpine basal detachment swiss alps although evidence for weak detachments underlying foreland thrust belts exists very little is known about the lateral variations in effective strength as well as the geological nature of such variations using critical taper analysis we show that a detailed and systematic measurement of surface slope of the central european alps reveals variations in strength parameter f along the detachment based on the argument that the alps are close to the critical state we show that the basal detachment is very weak near the deformation front but strengthens toward the hinterland very low f effective coefficient of friction plus normalized cohesion values of 0 54 but may also require additional mechanisms of dynamic weakening

very low grade metamorphism of the taveyanne greywacke glarus alps switzerland detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic eocene oligocene taveyanne greywacke of the glarus alps eastern switzerland presented data indicate an increase of metamorphic grade from zeolite facies to prehnite pumpellyite and pumpellyite actinolite facies low grade outcrops contain laumontite minor corrensite and pumpellyite assemblage type 1 whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite type 2 prehnite pumpellyite al white mica type 3 a single outcrop shows pumpellyite actinolite facies type 4 from the zeolite to prehnite pumpellyite pumpellyite actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain 1 mm in type 1 to a few millimetres in type 2 and to a whole thin section in type 3 metamorphic p t conditions were determined by a combination of chlorite thermometry fluid inclusion and vitrinite reflectance data peak temperatures range from 170 190d c for zeolite facies to 270 310d c for prehnite pumpellyite and pumpellyite actinolite facies for the higher temperature range pressures of 2 3 kbar are derived indicating a geothermal gradient of 24 32d c km 1 the well constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed the best correspondence to the temperatures determined here is for the cathelineau calibration in addition in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites

thermo tectono stratigraphic forward modelling of the upper rhine graben in reference to geometric balancing brittle crustal extension on a highly viscous mantle abstract four structural cross sections through the central segment of the upper rhine graben urg were balanced by means of thermo tectono stratigraphic forward modelling ttsf modelling results were compared to geometric retro deformation of pre rift reference horizons applying line length and area balancing methods ttsf modelling with a deep necking level 20 km and or a high effective elastic thickness te 15 km yielded extension values similar to those of geometric balancing while modelling with shallower necking depths and or lower te yielded unrealistic high extension values a best fit of geometric balancing indicating 5 km rift orthogonal extension was reached by ttsf modelling with a te of 15 km and a pre rift necking depth of 29 km coinciding with the moho discontinuity this is compatible with a the geophysically mapped moho that does not shallow significantly beneath the central segment of the urg and its shoulders b seismicity indicating brittle elastic deformation of the entire crust and a seismic ductile deformation of the lithospheric mantle c compensation of crustal faults and shear zones in the crust mantle transition zone modelled time extension paths imply rifting during the middle eocene to early miocene a late miocene post rift stage and renewed rifting during the pliocene to recent apparent northward migration of extension in time is an effect of uplift processes which are not related to rifting correcting for these the extension history for the four cross sections becomes very similar suggesting plane strain deformation and rifting at very low strain rates of about 1 7 10 16 s 1 involving brittle elastic deformation of the crust and ductile deformation of the highly viscous high strength upper mantle that controls the position of the lithospheric necking level

three dimensional geological modeling supports a revised burdigalian chronostratigraphy in the north alpine foreland basin precise age data are a basic prerequisite for the correlation of a sedimentary succession with the global time scale which in turn allows one to place its biotic and other data in a global context in the north alpine foreland basin nafb a patchy distribution of outcrops and uncertainties in the correlation of strata have led to conflicting age models in particular for deposits of lower miocene burdigalian age here we present a new three dimensional geological model of the se german sector of the nafb covering an area of 13 200 km2 which helps to resolve the discrepancies the dataset comprises lithostratigraphic information from 150 boreholes supplemented by magnetostratigraphic data from six outcrops computer based 3d modeling was conducted with the open source software qgis for a 500 m thick succession comprising units of the upper marine molasse the brackish oncophora fm and the upper freshwater molasse the results provide new insights pertaining to 1 the isochrony of strata 2 subsidence and 3 synsedimentary tectonics the new data permit us to reliably place the outcrops within the regional lithostratigraphic scheme thus enabling a new correlation of their magnetic polarities with the global time scale on this basis we propose a revised age model for the middle and upper burdigalian strata in the eastern part of the nafb which is supported by previously reported 87sr 86sr age data the model indicates that the succession is substantially up to 0 8 ma younger than earlier publications have suggested furthermore it implies that the two synsedimentary tectonic events discerned may both be related to the large scale tectonic movements that affected the nafb during the late burdigalian

tectonics of the central swiss molasse basin post miocene transition to incipient thick skinned tectonics in this paper we investigate the tectonics of the central swiss molasse basin smb situated between the central european alps and the jura fold and thrust belt based on re interpreted 2d reflection seismic data and geological 3d modeling we present new insights into the structural configuration and evolution of the central smb during the thin skinned main deformation phase of the jura fold and thrust belt 12 4 ma the central smb was riding passively above a major detachment horizon within triassic evaporites which roots beneath the external crystalline massifs of the central alps in the smb low amplitude detachment folds and detachment rooted wsw ene striking thrust and reverse faults are related to this event younger major nne ssw and nnw sse trending strike slip fault zones cross the basin over a length of several kilometers affecting the cenozoic and mesozoic cover units and extending into the pre mesozoic crystalline basement in cases the fault zones apparently reactivate inherited permo carboniferous trough pct bounding paleozoic normal faults seismic data further reveals mild inversion of wsw ene striking pcts these structures clearly cut the basement cover contact thus postdating the main deformation phase of the jura fold and thrust belt present day earthquake focal mechanisms and epicenter distribution show strike slip faulting and basement seated seismicity respectively thus corroborating our observations from seismic interpretation our data suggests a change from late miocene thin skinned to pliocene to present day incipient thick skinned tectonics this major change reflects the establishment of a mid crustal detachment and may be related to changes in slab dynamics of the subducting european lithosphere

uplift and cooling pathways derived from fission track analysis and mica dating a review definition of time and temperature pathways for episodes of lithospheric movement provides not simply a chronological framework for crustal dynamism but also permits estimation of rates of crustal cooling and uplift important aspects of such pathways are the constraints provided for timing of both plate collision and lithospheric extension classically rb sr and k ar mica ages have been used to delineate rates of cooling and exhumation in the central alps by comparison of the measured ages with estimates of temperatures for the retention of daughter isotopes similar use of fission track apatite and zircon ages has provided data for lower temperature intervals 100 and 200 c respectively recent detailed studies of the annealing kinetics of fission tracks in apatite yield more precise estimates of cooling rate and permit predictive modelling of age and length parameters for given t t pathways in continental collision zones fast episodic uplift in the western alps can be contrasted with contemporaneous monotonic uplift in the central alps additional examples may be seen in the tibet himalayan orogenic belt in the southern alps of new zealand and in the bolivian andes in divergent teceonic regimes the record of uplift associated with rifting has been recorded by fission track ages in the southeastern australian margin and around the red sea in an intra plate tectonic setting our current fission track reconnaissance study in the british isles is revealing a hitherto unrecognised thermal history for crystalline and sediment alike

the rauenberg fossil lagerstatte baden wurttemberg germany a window into early oligocene marine and coastal ecosystems of central europe abstract the oligocene was a period of profound climatic and biotic changes coinciding with a shift from a mostly ice free warmhouse world at the eocene oligocene boundary to a globally cooler more seasonal climate the rauenberg locality baden wurttemberg germany is one of the most significant early oligocene fossil assemblages in europe containing both marine and terrestrial elements of fauna and flora preservation is often superb and comprises complete and articulated skeletons with soft tissue preservation the diverse assemblage provides critical insights into the paleoenvironment of the upper rhine valley we reassess diversity at the locality resulting in a list of 302 taxa found at the site 207 of which are marine 52 of taxa represented by macrofossils the rest are interpreted as originating from the coastal environment molluscan echinoderm and plant macrofossil diversity are assessed here for the first time based on these new results we interpret rauenberg as representing a fully marine assemblage deposited in a moderately shallow low energy tropical subtropical environment productivity was high and seafloor anoxia was intermittently developed there is no evidence for long term brackish influence or mangrove swamps and no direct evidence for the development of seagrass meadows on land warm frost free conditions permitted the development of prevailingly evergreen sclerophyllous broad leaved forests along with pine and palm rich coastal forests on sandy soils the marine invertebrate fauna shows more northerly affinities whereas the vertebrate fauna is distinctly paratethyan

hornblende k ar ages and the climax of tertiary metamorphism in the lepontine alps south central switzerland an old problem reassessed abstract twenty five new k ar ages for amphiboles from the tertiary barrovian type metamorphic terrain of the central alps were determined these results lead to the conclusion that the meso alpine metamorphism reached its peak condition and maximum expanse about 26 3 m y ago along a profile of increasing grade of alpine metamorphism in both basement and cover rocks the following observations can be made 1 pre alpine hornblendes in the zone of greenschist facies show ages ranging from 639 to 152 m y the implied open system behavior may be related to the observed mineralogical instability of these hornblendes during the alpine overprint in contrast two greenschist facies hornblendes which grew in pennine mesozoic rocks during the alpine metamorphism yield ages of 23 2 and 29 3 m y 2 on both sides of the boundary marking the first occurrence of alpine staurolite pre or early alpine hornblende k ar ages are not fully reset unless the rocks were completely recrystallized for one rock specimen which clearly exhibits two generations of hornblende an age two times greater was obtained for the smaller crystals oriented parallel to the foliation than for the structurally younger hornblende porphyroblasts which overgrew the preexisting texture 3 in the high grade area of alpine metamorphism only young alpine ages between 23 and 28 m y were found for hornblendes which grew syn to postkinematically with respect to the last penetrative deformation one amphibolitic inclusion not affected by this deformation yielded a significantly older hornblende age of 32 1 m y these results suggest that temperature controlled ar diffusion is not the main factor governing the k ar system of metamorphic hornblendes we conclude that these hornblende ages should not be interpreted as cooling ages from a structurally ill defined earlier event instead they indicate that the high grade metamorphism responsible for the well known isograd pattern in the lepontine area persisted until some 23 m y ago

a gastropod based biogeographic scheme for the european neogene freshwater systems abstract for the first time a palaeobiogeographic framework is proposed for european neogene freshwater systems the distribution of 2226 species group taxa of freshwater gastropods from over 2700 miocene and pliocene localities was evaluated the localities were grouped into palaeo freshwater systems based on latest palaeogeographic reconstructions cluster analyses were computed for four time slices i e early miocene middle miocene late miocene and pliocene the analyses demonstrate a generally high degree of provincialism for the neogene freshwater systems and allow the definition of biogeographic units the delimitations are based on the cluster analyses the degree of endemicity and geographical coherence the early miocene is characterised by a relatively low degree of provincialism suggesting the distinction of three regions coinciding with the development of many endemic systems on the dinarian anatolian island and in central europe the middle miocene demonstrates a higher degree of provincialism allowing the definition of six biogeographic regions with the onset of the late miocene the retreat of the central paratethys and development of the huge lake pannon massively shaped faunal evolution and palaeobiogeography in general the formation of the lago mare environment fringing the mediterranean basin as well as the development of several restricted freshwater systems in western europe additionally promoted biogeographic division the increasing provincialism allowed the delimitation of six biogeographic regions three of which could be subdivided into seven dominions with the disappearance of lake pannon and the decline of western european and mediterranean faunas at the miocene pliocene boundary biodiversity hotspots shifted towards eastern and southeastern europe for the pliocene four biogeographic regions five dominions and four provinces were defined most of the here proposed biogeographic units and faunal differences are governed by the varied existence of large long lived systems because of their prolonged duration they immensely influenced the community composition on the family level differences of the relative species richnesses per biogeographic region and the rising rate of endemicity the underlying mechanism for this pattern is the ongoing continentalization of europe triggered by the alpidic orogenesis and the simultaneous retreat of the paratethys sea the continuing restriction of this huge intracontinental sea from the mediterranean promoted the evolution of endemic freshwater faunas the arising long lived systems like lake pannon lake dacia or lake slavonia persisted over several millions of years and stimulated the evolution of highly diverse and endemic faunas

a mid miocene to early pleistocene multi level cave as a gauge for tectonic uplift of the swabian alb southwest germany a recently discovered deep cave laierhohle within a plateau of upper jurassic limestone is the deepest 126 m of the southwest german swabian alb providing a unique gauge for crustal tilting and isostatic uplift of the southwest german crust from late mid miocene to earliest pleistocene horizontal levels are considered a product of a stationary palaeo water table vertical shafts are related to base level fall which in turn may be the result of uplift and or incision we correlate speleogenetic with dated geomorphic features and thus come to a chronology of events the laierhohle records five episodes of long term stability of the karst water table covering the time span from late middle miocene until the pliocene pleistocene transition the first two stable episodes can be dated to the late middle miocene and late miocene horizontal levels 1 and 2a an episode responsible for the formation of level 2b falls within early pliocene time levels 3a and 3b are spatially well separated but must have formed within a relatively short time span towards the end of the pliocene in the working area total depth of penetrative karstification was in the order of 120 m this penetration has been accomplished over a period of approximately 12 ma resulting in an average uplift rate of 0 01 mm a

late miocene early pliocene climatic evolution of the granada basin southern spain deduced from the paleoecology of the micromammal associations this paper analyses the relationship between the evolution of the late miocene and early pliocene rodent and insectivore assemblages from the granada basin southern spain and climate changes these climatic changes in terms of humidity and temperature fluctuations are inferred from variations of the relative abundances of taxons with definite ecological preferences there is a general tendency towards a temperature increase from the latest tortonian middle turolian to the messinian late turolian and towards a decrease from the mio pliocene boundary latest turolian earliest ruscinian to the end of the zanclean late ruscinian dry conditions predominate in the latest tortonian middle turolian at the beginning of the messinian late turolian there was a significant increase in humidity followed by an aridification throughout the end of the messinian and zanclean late turolian and ruscinian these climatic variations are in accordance with the sedimentary evolution of the basin and agree with the climatic interpretations inferred from the shallow marine carbonate sediments temperate tropical deposited in the marine basins of southeastern spain during the studied time interval

radar measurements of melt zones on the greenland ice sheet surface based microwave radar measurements were performed at a location on the western flank of the greenland ice sheet here firn metamorphosis is dominated by seasonal melt which leads to marked contrasts in the vertical structure of winter and summer firn this snow regime is also one of the brightest radar targets on earth with an average backscatter coefficient of 0 db at 5 3 ghz and an incidence angle of 25 by combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter s snow pack this observation has important implications for monitoring and understanding changes in ice sheet volume using space borne microwave sensors

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

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

eocene pliocene time scale and stratigraphy of the upper rhine graben urg and the swiss molasse basin smb we present a general stratigraphic synthesis for the upper rhine graben urg and the swiss molasse basin smb from eocene to pliocene times the stratigraphic data were compiled both from literature and from research carried out by the authors during the past 6 years an index of the stratigraphically most important localitites is provided we distinguish 14 geographical areas from the helvetic domain in the south to the hanau basin in the north for each geographical area we give a synthesis of the biostratigraphy lithofacies and chronostratigraphic ranges the relationships between this stratigraphic record and the global sea level changes are generally disturbed by the geodynamic e g subsidence evolution of the basins however global sea level changes probably affected the dynamic of transgression regression in the urg e g middle pechelbronn beds and serie grise corresponding with sea level rise between ru1 ru2 and ru2 ru3 sequences respectively as well as in the molasse basin regression of the umm corresponding with the sea level drop at the ch1 sequence the urgent project upper rhine graben evolution and neotectonics provided an unique opportunity to carry out and present this synthesis discussions with scientists addressing sedimentology tectonics geophysics and geochemistry permitted the comparison of the sedimentary history and stratigraphy of the basin with processes controlling its geodynamic evolution data presented here back up the palaeogeographic reconstructions presented in a companion paper by the same authors see berger et al in int j earth sci 2005

geometry amount and sequence of thrusting in the subalpine molasse of western austria and southern germany european alps in this paper we review the structure of the most external thrust belt of the alps between the rhein valley and salzburg based on a new tectonic map and the re interpretation of seismic sections specifically we address the correlation between deformation in the subalpine molasse and the alpine thrust belt in general and focus on the control of sedimentary facies on the structural style a dramatic change in architecture from a ramp flat structure to buckle folding is related to a change from coarse grained fans to fine grained deposits within the subalpine molasse additionally the interaction of escape tectonics with postcollisional shortening controls the decrease of late early miocene and younger shortening within the subalpine molasse from 50 km near the rhine valley to almost zero near salzburg transfer of shortening into the hinterland which is the zone of lateral escape ended foreland propagation of the alpine thrusts and initiated a general break back sequence of thrusting throughout this time the thrusts remained active in such a scenario tectonic units on top of the subalpine molasse are expected to undergo clockwise rotation around vertical axes as thrusting in the subalpine molasse is closely related to contemporaneous transport and shortening within the tectonically higher helvetic thrust sheets amounts of miocene differential shortening and related clockwise vertical axis rotation are minimum amounts true clockwise vertical axis rotation is probably larger than the 12 deduced from the subalpine molasse thrust belt

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

the deep thermal field of the upper rhine graben abstract the upper rhine graben has a significant socioeconomic relevance as it provides a great potential for geothermal energy production the key for the utilisation of this energy resource is to understand the controlling factors of the thermal field in this area we have therefore built a data based lithospheric scale 3d structural model of the upper rhine graben and its adjacent areas in addition 3d gravity modelling was performed to constrain the internal structure of the crystalline crust consistent with seismic information based on this lithosphere scale 3d structural model the present day conductive thermal field was calculated and compared to measured temperatures our results show that the regional thermal field is mainly controlled by the configuration of the upper crust which has different thermal properties characteristic for the variscan and alpine domains temperature maxima are predicted for the upper rhine graben where thick insulating cenozoic sediments cause a thermal blanketing effect and where the underlying crustal units are characterised by high radiogenic heat production the comparison of calculated and measured temperatures overall shows a reasonable fit while locally occuring model deviations indicate where a larger influence of groundwater flow may be expected

enigmatic sedimentary structures in the lower old red sandstone south wales uk possible microbial influence on surface processes and early terrestrial food webs several enigmatic sedimentary structures are present in upper silurian and lower devonian terrestrial rocks of south wales these are millimetre ripples wrinkle structures cauliflower and molehill structures calcretized matgrounds pepper pots and fairy rings most of the structures occur on fine grained sandstone bedding surfaces in both inclined and non inclined red heterolithic deposits that form a large part of the lower old red sandstone in south wales these deposits consist of conspicuous units up to 3 m thick comprising millimetre to centimetre scale laminasets of alternating mudstone and fine grained sandstone interpreted as muddy point bars on ephemeral channel margins crevasse splay lobes or distal flood out deposits from ephemeral flow they are rich in trace fossils reflecting animal locomotion burrowing foraging ploughing and resting millimetre ripples and wrinkle structures are related to rapid growth of cyanobacterial mats on wet sediment surfaces especially in films of standing water that may have been a critical constituent of the food chain for terrestrial communities pustular cauliflower and molehill structures are preserved on tuffs and have been linked to algal blooms formed following an increase in nutrients due to ashfall into floodplain ponds the tuffs are associated with a diverse ichnofauna indicating that opportunist colonizers took advantage of an abundant food source

response of central european sst to atmospheric pco2 forcing during the oligocene a combined proxy data and numerical climate model approach abstract co 2 induced global warming will affect seasonal to decadal temperature patterns expected changes will be particularly strong in extratropical regions where temperatures will increase at faster rates than at lower latitudes despite that it is still poorly constrained how precisely short term climate dynamics will change in a generally warmer world particularly in nearshore surface waters in the extratropics i e the ecologically most productive regions of the ocean on which many human societies depend specifically a detailed knowledge of the relationship between p co 2 and seasonal sst is crucial to understand interactions between the ocean and the atmosphere in the present investigation we have studied for the first time how rising atmospheric p co 2 levels forced surface temperature changes in central europe paleolatitude 45 n during the mid oligocene from ca 31 to 25 ma a time interval of earth history during which global conditions were comparable to those predicted for the next few centuries for this purpose we computed numerical climate models for the oligocene winter summer annual average assuming an atmospheric carbon dioxide rise from 400 to 560 ppm current level to two times pre industrial levels pal and from 400 to 840 ppm three times pal respectively these models were compared to seasonally resolved sea surface temperatures sst reconstructed from 18 o values of fossil bivalve shells glycymeris planicostalis g obovata palliolum pictum arctica islandica and isognomon maxillata sandbergeri and shark teeth carcharias cuspidata c acutissima and physogaleus latus collected from the shallow water deposits of the mainz and kassel basins germany multi taxon oxygen isotope based reconstructions suggest a gradual rise of temperatures in surface waters upper 30 to 40 m on average by as much as 4 c during the rupelian stage followed by a 4 c cooling during the chattian stage seasonal temperature amplitudes increased by ca 2 c during the warmest time interval of the rupelian stage with warming being more pronounced during summer 5 c than during winter 3 c according to numerical climate simulations the warming of surface waters during the early oligocene required a co 2 increase by at least 160 ppm i e 400 ppm to 560 ppm given that atmospheric carbon dioxide levels predicted for the near future will likely exceed this value significantly the early oligocene warming gives a hint of the possible future climate in central europe under elevated co 2 levels

evidence for 5 ma paleo exposure of an eocene miocene paleosol of the bohnerz formation switzerland we obtained u th he formation ages and cosmogenic 3he concentrations for pisoliths from a paleosol of the bohnerz formation siderolithic of central europe the paleosol is exposed in the almenbuhl quarry near lohn canton schaffhausen switzerland the paleosol consists of red clay of 3 4 m thickness developed on deeply weathered jurassic limestone and overlain by early miocene conglomerates the u th he formation ages of the pisoliths are between 50 ma and 8 ma with most ages being older than 17 ma there is a sharp decline in the frequency of ages at the time of burial of the paleosol at 17 ma these ages are inconsistent with the previous assumption that the bohnerz formation formed in a cretaceous to early eocene laterite in a tropical climate we propose that the bohnerz formation more closely resembles terra rossa soils which do not require a tropical climate to form the 3he concentration in the pisoliths is roughly constant with depth throughout the paleosol at 300 matoms g we interpret this as the result of soil convection during cosmic ray exposure the minimum exposure duration at the surface of the paleosol is 5 ma a simple model of soil convection shows that the true exposure duration of the paleosol is approximately 10 20 ma these results indicate that the clay soils of the bohnerz formation were continuously exposed at the surface for millions of years since the paleosol was covered by conglomerate since 17 ma the 3he measured here was produced by cosmic ray exposure before burial cosmogenic 3he concentrations measured in fine grained soil iron oxides 1 m are similar to those measured in pisoliths this might indicate that fine grained iron oxides are retentive to helium and might be used for studying the formation and cosmic ray exposure of modern soils and paleosols

jakobshavn glacier west greenland 30 years of spaceborne observations early 1960 s reconnaissance satellite images are compared to more recent image and map data in an inter annual and seasonal study of west central greenland margin fluctuations from 1962 to 1992 ice sheet margins to the north and south of jakobshavn glacier retreated despite a decline in average summer temperatures the retreat may be reversing along the southern flank of the ice stream where regional mass balance estimates are positive from 1950 to fluctuated 2 5 km around its annual mean position the total calving flux during the summer is more than six times that during winter we identified that summer melting and the break up of sea ice and icebergs in the fjord are important in controlling the rate of iceberg production if correct calving rates may be expected to increase should climate become warmer in the near future

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

recognition of forebulge unconformities associated with early stage foreland basin development example from the north alpine foreland basin the peripheral upwarp forebulge associated with early foreland basin evolution may be recorded as an unconformity at the base of the foreland basin fill a forebulge unconformity represents a distinctive type of megasequence boundary forward modeling of foreland flexure illustrates the expected geometry of an unconformity cut by erosion of the forebulge during the early stages of foreland basin development internal conformity a zone of rapid increase in the depth of erosion and an external zone of steady state stratigraphic gap this geometry is modified by the preexisting bathymetry and by eustatic sea level changes which result in the formation of a composite unconformity however the geometry of the unconformity and the onlap of the overlying sediments are fund mentally different from those associated with a major eustatic sea level fall and represent a distinctive assemblage of petroleum play components producing hydrocarbon accumulations are associated with both forebulge arching and truncational unconformity traps modeling achieves an accurate simulation of the geometry and stratigraphic gap of the basal unconformity of the north alpine foreland basin switzerland further support for the flexural forebulge interpretation is provided by facies patterns in the overlying sediments suppression and smothering of forebulges during the late molasse stage of foreland basin development coupled with the cannibalization of the early flysch stage stratigraphy by the advancing orogenic wedge may limit the formation and recognition of forebulge unconformities model results may be helpful in predicting the timing duration and amount of uplift associated with flexural forebulges and thereby aid in assessing petroleum play potential particularly the formation of traps and the development of enhanced porosity

the fractal and multifractal dimension of volcanic ash particles contour a test study on the utility and volcanological relevance abstract image processing analysis is used to check the ability of the fractal dimension for quantitatively describing the shape of volcanic ash particles digitized scanning electron microscopy images of fine pyroclasts from the eruptions of monte pilato rocche rosse lipari italy are investigated to test the efficiency of the fractal dimension to discriminate between particles of different eruptive processes multivariate analysis of multiple fractal components allows distinction between magmatic particles and phreatomagmatic particles which however is less significant than the discrimination obtained in previous studies by the use of simple adimensional shape parameters approximation of the actual particle boundary and the not rotation invariant nature of the fractal data frequently result in a significant scatter of data points in the mandelbrot richardson plot such behavior obscures in some cases the actual information of particle shape and renders the discriminating power of fractal analysis less effective than classical shape descriptors data less affected by scatter reveal that phreatomagmatic particles of the monte pilato rocche rosse eruptions are true mono fractals whereas magmatic particles are multifractals the textural small scale fractal of magmatic particles is similar to the fractal dimension value of phreatomagmatic particles and is attributed to the rheological behavior of melt upon brittle fragmentation the structural large scale fractal of magmatic particles refers to the walls of ruptured vesicles that lay on the particle outline the high difference between the values of the textural and structural fractals of magmatic particles of the monte pilato rocche rosse eruptions suggests two distinct and independent processes in the formation of such pyroclasts at the scales corresponding to the textural fractal the fragmentation process is independent of vesicles magmatic fragmentation is not simply related to growth expansion interference and explosion of vesicles but to a brittle cracking of the highly viscous melt likely related to rapid decompression

graben width controlling syn rift sedimentation the palaeogene southern upper rhine graben as an example eocene to early oligocene syn rift deposits of the southern upper rhine graben urg accumulated in restricted environments sedimentation was controlled by local clastic supply from the graben flanks as well as by strong intra basinal variations in accommodation space due to differential tectonic subsidence that in turn led to pronounced lateral variations in depositional environment three large scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards brackish or freshwater conditions they form three major base level cycles that can be traced throughout the basin each of them representing a stratigraphic sub unit a relatively constant amount of horizontal extension l in the range of 4 5 km has been estimated for the urg from numerous cross sections the width of the rift lf however varies between 35 and more than 60 km resulting in a variable crustal stretching factor between the bounding masterfaults apart from block tilting tectonic subsidence was therefore largely controlled by changes in the initial rift width l0 the along strike variations of the graben width are responsible for the development of a deep trough like evaporite basin potash basin in the narrowest part of the southern urg adjacent to shallow areas in the wider parts of the rift such as the colmar swell in the north and the rhine bresse transfer zone that delimits the urg to the south under a constant amount of extension the along strike variation in rift width is the principal factor controlling depo centre development in extensional basins

fresh water carbonates from the lower freshwater molasse oligocene western switzerland sedimentology and stable isotopes abstract the lower freshwater molasse of western switzerland comprises a thick series of continental deposits of late oligocene early miocene age fresh water carbonates occur at two main horizons within this succession lower chattian palustrine carbonates calcaires inferieurs show a shallow fresh water fauna flora of ostracods and charophytes but display clear evidence of subaerial exposure in the form of glaebule pisoid formation circumgranular cracking rhizoliths and microkarstic cavities repeated desiccation led to locally intense modification by pedogenesis these horizons record the development of shallow ephemeral lakes at the northern margin of the swiss molasse basin stable isotope analyses were carried out on 46 calcite samples data from matrix and intraclasts reveal typical fresh water compositions 13c 5 to 7 5 18o 5 5 to 9 a weak co variant trend suggests deposition in hydrologically closed lakes although the range of 13c values recorded is also consistent with pedogenetic overprinting associated with subaerial exposure spar cements and vadose crystal silts display 13c compositions from 6 to 7 but show light 18o values from 10 to 11 recording formation from meteoric waters upper chattian carbonates calcaires d eau douce et dolomie include algal ostracodal laminites interpreted as profundal lake deposits as well as bioturbated shallow lake charophyte ostracod mudstones and wackestones sandy wackestones and white dolomite stable isotope analyses 20 calcites 2 dolomites show 13c values from 2 to 6 and 18o from 6 to 11 data for laminites and biomicrites plot in different fields variations in carbon isotopic composition may be attributable to higher organic productivity during high lake stands the laminites show heavier 13c values or to areal differences in the proportions of biogenic authigenic and detrital carbonate 13c values are generally higher in areas of greater detrital carbonate supply the heavier 18o values shown by the dolomites 13 c 3 18 o 0 to 1 suggest formation from evolved evaporitic lake waters these carbonates record deposition in an extensive possibly deeper lake complex subject to clastic input from the alps in the south

a structural glaciological analysis of the 2002 larsen b ice shelf collapse this study provides a detailed structural glaciological analysis of changes in surface structures on the larsen b ice shelf on the antarctic peninsula prior to its collapse in february march 2002 mapped features include the ice shelf front rifts crevasses longitudinal linear surface structures and meltwater features we define domains on the ice shelf related to glacier source areas and demonstrate that prior to collapse the central larsen b ice shelf consisted of four sutured flow units fed by crane jorum punchbowl and hektoria green evans glaciers between these flow units were suture zones of thinner ice where the feeder glaciers merged prior to collapse large open rift systems were present offshore of foyn point and cape disappointment these rifts became more pronounced in the years preceding break up and ice blocks in the rifts rotated because of the strong lateral shear in this zone velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago we suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units this we believe was the result of ice shelf front retreat during 1998 2000 reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units ice shelf thinning and pre shelf break up glacier acceleration

from soil aggregates to riverine flocs a laboratory experiment assessing the respective effects of soil type and flow shear stress on particles characteristics particles eroded from hillslopes and exported to rivers are recognized to be composite particles of high internal complexity their architecture and composition are known to influence their transport behaviour within the water column relative to discrete particles to date hillslope erosion studies consider aggregates to be stable once they are detached from the soil matrix however lowland rivers and estuaries studies often suggest that particle structure and dynamics are controlled by flocculation within the water column in order to improve the understanding of particle dynamics along the continuum from hillslopes to the lowland river environment soil particle behaviour was tested under controlled laboratory conditions seven flume erosion and deposition experiments designed to simulate a natural erosive event and five shear cell experiments were performed using three contrasting materials two of them were poorly developed and as such can not be considered as soils whilst the third one was a calcareous brown soil these experiments revealed that soil aggregates were prone to disaggregation within the water column and that flocculation may affect their size distribution during transport large differences in effective particle size were found between soil types during the rising limb of the bed shear stress sequence indeed at the maximum applied bed shear stress the aggregated particles median diameter was found to be three times larger for the well developed soil than for the two others differences were smaller in the falling limb suggesting that soil aggregates underwent structural changes however characterization of particles strength parameters showed that these changes did not fully turn soil aggregates into flocs but rather into hybrid soil aggregate floc particles copyright 2013 john wiley sons ltd

a lithospheric cross section through the swiss alps ii constraints on the mechanical structure of a continent continent collision zone summary the calculation of strength profiles along the european geotraverse egt through the swiss alps yields constraints on the large scale vertical and lateral mechanical structure through the alpine continent continent collision zone strength profiles are evaluated for different assumptions on petrological stratification and strain rate and are based on temperature depth profiles derived from transient thermo kinematic modelling of the neoalpine orogeny the main contribution to the total strength results from the mantle lithosphere which is strongly controlled by temperature in contrast the crustal contribution is mainly determined by variations in petrological stratification a direct correlation between surface heat flow and the total strength of the crust the mantle lithosphere and the entire lithosphere crust and mantle lithosphere is not observed our results demonstrate that in tectonically active areas a transient thermal model along with detailed knowledge of the deep structure and petrology is necessary to evaluate lithospheric strength envelopes inside the collision zone strain rate has a strong control on the bottom of the mechanically strong crust whereas outside the collision zone the effect is less significant the cut off depth of seismicity along the profile which correlates largely with the bottom of the mechanically strong crust deviates from the 300 400 c isotherm the inferred effective elastic thickness for the molasse basin north of the alps is in agreement with flexural modelling results whereas for the southern alps the predictions deviate

inssev an instrument to measure the size and settling velocity of flocs in situ abstract an instrument has been developed to observe the settling of individual flocs in turbid water in order to measure size and settling velocity spectra of estuarine cohesive suspended sediments inssev in situ settling velocity instrument is bed mounted and comprises a computer controlled decelerator chamber that collects a sample of water from which some of the suspended matter is allowed to enter the top of a settling column the settling flocs are viewed using a miniature video system subsequent analysis of video tapes can provide direct measurements of size and settling velocity of individual flocs down to 20 m from this information floc density can be estimated the main feature of the instrument is its ability to video flocs in situ irrespective of the concentration in the estuary with as little disturbance to their hydrodynamic environment as possible preliminary field testing in the tamar estuary has given useful results in flow velocities up to 0 4 m s 1 and in concentrations up to 200 mg 1 1 the video recordings show large numbers of low density flocs with multiple structures linked by fine organic fibres

the south western black forest and the upper rhine graben main border fault thermal history and hydrothermal fluid flow the thermal history of the south westernmost black forest germany and the adjacent upper rhine graben were constrained by a combination of apatite and zircon fission track ft and microstructural analyses after intrusion of palaeozoic granitic plutons in the black forest the thermal regime of the studied area re equilibrated during the late permian and the mesozoic interrupted by enhanced hydrothermal activity during the jurassic at the eastern flank of the upper rhine graben along the main border fault the analysed samples show microstructural characteristics related to repeated tectonic and hydrothermal activities the integration of microstructural observations of the cataclastic fault gouge with the ft data identifies the existence of repeated tectonic related fluid flow events characterised by different thermal conditions the older took place during the variscan and or mesozoic time at temperatures lower than 280 c whereas the younger was probably contemporary with the cenozoic rifting of the upper rhine graben at temperatures not higher than 150 c

surface structure and stability of the larsen c ice shelf antarctic peninsula a structural glaciological description and analysis of surface morphological features of the larsen c ice shelf antarctic peninsula is derived from satellite images spanning the period 1963 2007 the data are evaluated in two time ranges a comparison of a 1963 satellite image photomosaic with a modern digital mosaic compiled using 2003 04 austral summer data and an image series since 2003 showing recent evolution of the shelf we map the ice shelf edge rift swarms crevasses and crevasse traces and linear longitudinal structures called flow stripes or streak lines the latter are observed to be continuous over distances of up to 200 km from the grounding line to the ice shelf edge with little evidence of changes in pattern over that distance integrated velocity measurements along a flowline indicate that the shelf has been stable for 560 years in the mid shelf area linear longitudinal features may be grouped into 12 units each related to one or a small group of outlet feeder glaciers to the shelf we observe that the boundaries between these flow units often mark rift terminations the boundary zones originate upstream at capes islands or other suture areas between outlet glaciers in agreement with previous work our findings imply that rift terminations within such suture zones indicate that they contain anomalously soft ice we thus suggest that suture zones within the larsen c ice shelf and perhaps within ice shelves more generally may act to stabilize them by reducing regional stress intensities and thus rates of rift lengthening

migration of sharks into freshwater systems during the miocene and implications for alpine paleoelevation trace element and isotopic compositions of fossilized shark teeth sampled from miocene marine sediments of the north alpine molasse basin the vienna basin and the pannonian basin generally show evidence of formation in a marine environment under conditions geochemically equivalent to the open ocean in contrast two of eight shark teeth from the swiss upper marine molasse locality of la moliere have extremely low 18o values 10 3 and 11 3 and low 87sr 86sr ratios 0 707840 and 0 707812 compared to other teeth from this locality 21 1 22 4 and 0 708421 0 708630 the rare earth element ree abundances and patterns from la moliere not only differ between dentine and enameloid of the same tooth but also between different teeth supporting variable conditions of diagenesis at this site however the ree patterns of enameloid from the exotic teeth analyzed for o and sr isotopic compositions are similar to those of teeth that have o and sr isotopic compositions typical of a marine setting at this site collectively this suggests that the two exotic teeth were formed while the sharks frequented a freshwater environment with very low 18o content and sr isotopic composition controlled by mesozoic calcareous rocks this is consistent with a paleogeography of high elevation 2300 m miocene alps adjacent to a marginal sea

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

new geochemical results indicate a non alpine provenance for the alpine spectrum epidote garnet hornblende in quaternary upper rhine sediment abstract the heavy mineral assemblage of late pleistocene to modern rhine river sediment in the upper rhine graben is dominated by garnet green amphibole and epidote this so called alpine spectrum has been taken to indicate an exclusive derivation from the alps and has hitherto been investigated with optical methods only we present the first single grain geochemical data set of garnet and amphibole from the upper rhine river and some of its main tributaries we use the new data to test the alleged alpine provenance in the rhine our results show that the provenance of garnet mostly pyrope rich almandine is grain size dependent particularly the pyrope content indicates that the 0 063 0 25 mm size fraction has an alpine provenance whereas 0 25 0 5 mm grains derived from the black forest and the vosges which flank the upper rhine graben they mainly comprise of paleozoic metamorphic and igneous rocks supplying a suite of heavy minerals similar to the alpine spectrum to the rhine river amphibole mostly mg hornblende has an increasing tio2 content from the south to the north of the graben which also indicates an input from the graben shoulders the new data indicate that the so called alpine spectrum of heavy minerals in rhine river sediment of the upper rhine derived to significant degrees from non alpine sources furthermore our results indicate a relatively uniform provenance for the rhine river system during the past 1 ma

a synthetic stratigraphic model of foreland basin development the processes of erosion and deposition must be included in foreland basin models to predict correctly basin geometry and stratigraphy we present a synthetic stratigraphic model of the development of nonmarine foreland basins that predicts progressive geometry topography and facies patterns in the model steady crustal shortening occurs according to a wedgethickening model erosion and deposition follow a diffusive process and the lithosphere is compensated elastically erosion and deposition are controlled by the transport coefficients r of the diffusion equation for a range of thrust velocities and lithospheric rigidities transport coefficients are of order 102 103 m yr in the mountain belt these values are much higher than those derived from the study of scarp degradation in the sedimentary basin transport coefficients of order 104 m2 yr are appropriate and are compatible with previous studies of fluvial and deltaic deposition rapid thrusting results in a narrow underfilled basin while slow thrusting results in a wide overfilled basin in addition by varying the erosional and depositional transport coefficients while holding other parameters constant we generate both overfilled and underfilled basins these results suggest that changes in the rate of thrust loading the climate or the source rock lithology can create stratigraphic signatures that have been interpreted to record viscoelastic relaxation of the lithosphere clearly to understand either the long term behavior of the lithosphere or to interpret orogenic history from preserved foreland strata the manner in which a basin was filled must be considered we apply the model to the evolution of the modern sub andean foreland and find that an erosional transport coefficient of 3000 m2 yr and a depositional transport coefficient of 20 000 m2 yr successfully predict the observed basin geometry

can flocs and water stable soil aggregates be differentiated within fluvial systems abstract this paper uses a number of particle structural characterizations and behavioral assessments in an attempt to differentiate flocs formed in the water column from water stable soil aggregates formed in the terrestrial environment but transported to a river by overland flow using discrete populations of flocs and soil aggregates the study successfully illustrated differences in floc structure as defined by fractal dimension sphericity measures density and porosity and behavior as defined by settling velocity flocs were generally found to be porous and irregular in shape with high water content low density and low settling velocity whereas soil aggregates were found to be rounder more compact dense with lower porosity and a higher settling velocity the techniques were however inappropriate for differentiating the two particle forms from river storm samples which are collected at the time when both particle forms are believed to be in suspension results suggest that aggregates once within the river system undergo a quick transformation into hybrid particles aggregate floc combinations due to flocculation processes occurring on the river bed following quick settling or during suspended sediment transport it is also possible that the aggregates undergo flocculation processes during overland flow forming hybrid particles prior to entering the river system or never reach the river altogether ending up in long term depositional areas in the terrestrial environment

magnetostratigraphic constraints on relationships between evolution of the central swiss molasse basin and alpine orogenic events magnetostratigraphic chronologies together with lithostratigraphic sedimentological and petrological data enable detailed reconstruction of the oligocene to miocene history of the north alpine foreland basin in relation to specific orogenic events and exhumation of the alps the molasse of the study area was deposited by three major dispersal systems rigi hohronen napf distinguished by characteristic heavy mineral suites conglomerate clast populations and the presence of key clasts these systems record three major phases of denudation of the alpine edifice the rigi system eroded the austroalpine and penninic nappes of eastern switzerland from 30 to 25 5 ma as a result of backthrusting and uplift of these units along the insubric line subsequent uplift of the aar massif some 40 km to the north appears to have controlled the duration of the hohronen and napf dispersal systems spanning 24 22 ma and 21 5 15 ma respectively they record downcutting into the crystalline cores of the penninic and austroalpine nappes of eastern hohronen and western napf switzerland high resolution reconstruction of the structural and geometrical evolution of the proximal molasse reveals in sequence and out of sequence thrusting events at the alpine front and incorporation of the molasse into the orogenic wedge by in sequence thrusting and underplating furthermore it reveals close relationships between periods of rapid denudation in the central alps and phases of increased sediment accumulation rates at the proximal basin border an initial increase in molasse accumulation rates to 1 km m y occurred between 30 and 25 5 ma and coincides with the insubric phase of backthrusting along the eastern insubric line where 10 km of vertical displacement is interpreted during the same time span the alpine wedge propagated forward along the basal alpine thrust as indicated by the coarsening and thickening upward megasequence and by occurrence of bajada fans derived from the alpine border the end of this tectonic event is marked by a basinwide unconformity interpreted to have resulted from crustal rebound after initial loading a subsequent increase in accumulation rates to 1 km m y between 23 and 21 5 ma coincides with initial uplift of the eastern aar massif by at least 4 km this phase of high accumulation rates is associated with incorporation of early chattian conglomerates into the orogenic wedge the third advance of the alpine wedge between 21 and 15 5 ma caused underplating of molasse deposits resulting in synsedimentary backthrusting of previously deposited molasse sequences and in the development of a progressive unconformity a rapid increase in accumulation rates from 0 35 to 1 km m y between 15 5 and 15 ma marks the final loading event in the wedge which may be caused by further major displacement and loading of the aar massif this deformation is coeval with out of sequence thrusting of the helvetic border chain and of the piggyback stack of north penninic and ultrahelvetic flysch nappes along the basal alpine thrust

large scale stratigraphic architecture eustatic variation and unsteady tectonism a theoretical evaluation we incorporate a process based depositional model with basin subsidence models to predict stratigraphic records this allows us to investigate the importance of subsidence geometry on coastal stratigraphy and thus to characterize and compare the stratigraphic architecture of two categories of tectonic basins the models demonstrate that the correlation of stratigraphic sequences to eustatic cycles is not the same in passive margin basins as in foreland basins and that in a foreland basin the record of episodic tectonism is distinct from that of eustatic sea level change in the model sediment transport is approximated by slope controlled diffusion nonmarine transport is treated as more efficient diffusion than marine transport three different subsidence and sediment supply models are examined a simple passive margin basin a simple foreland basin and then a foreland basin for which vertical motions are driven by thrust shortening that is compensated flexurally and for which sediment supply is related to relief predicted passive margin stratigraphies for cases of varying eustatic sea level are similar to those of natural basins and include progradational packages and subaerial unconformities which are used to define sequence boundaries that form during sea level fall we explore the timing relationships between stratigraphic features and a sinusoidal sea level history showing that the phase relationship depends on subsidence sediment flux efficiency of sediment transport and period and amplitude of sea level when the basic geometry of the basin is inverted placing the sediment supply on the side with maximum subsidence as is the case in foreland basins the sequence character changes markedly subaerial erosion does not generate unconformities in the models of a dynamic foreland basin sediment supply and subsidence are linked to the structure of the flanking thrust belt and are not necessarily constant for steady thrusting and variable sea level unconformities that define sequence boundaries form only on the distal or forebulge side of the basin and the ages of the sequence boundaries correlate to limes of rising sea level in cases of constant sea level but variable thrusting subaerial unconformities are cut locally on both the proximal margin of the basin and the distal margin of the basin yet the ages of the proximal margin and distal margin unconformities are out of phase in the tectonic cycle erosion is most pronounced during quiescence on the proximal side and during thrusting on the distal side

history of the sevier orogenic wedge in terms of critical taper models northeast utah and southwest wyoming problems with applying critical taper models to ancient orogenic wedges are overcome in the late cretaceous late paleocene sevier orogenic wedge in utah and wyoming by a symptomatic approach in which wedge behavior is inferred from the time space distribution of thrust faulting erosion and synorogenic sediment accumulation in association with the orogenic wedge in turn the causes of wedge behavior are interpreted in terms of features that are known about the sevier wedge such as the locations of major decollements and the lithologic constituents of major thrust sheets from coniacian through late paleocene time 35 m y basement and cover rocks in the sevier wedge were shortened by 100 km in three major and one minor events an overall eastward progression of thrusting was punctuated by several episodes of out of sequence and hinterland vergent thrusting over the long term wedge taper was controlled by internal wedge strength initial taper and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge while the basal decollement was mainly in basement rocks the wedge was highly tapered and thrust spacing was relatively close 15 km beginning ca 75 ma the basal decollement ramped upward and eastward into weak cambrian shale and jurassic salt thrust spacing increased to 25 45 km and wedge taper decreased drastically the highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic decollements whereas the frontal lower taper part of the wedge carried sedimentary rocks above extremely weak salt and shale decollements through time internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal decollement of the wedge also became weaker through time both by strain softening beneath the rear of the wedge and by propagating along extremely weak rocks beneath the front of the wedge provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long term history of the sevier wedge as an increasing proportion of the erosional surface became occupied by resistant precambrian quartzite and basement rocks this would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope which would have helped the wedge to remain at critical to supercritical taper the sevier wedge also exhibits several shorter term 10 km and 3 was subjected to regional erosion marked by major unconformities that ultimately caught up with tectonic thickening and caused the wedge to stall this cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag time between wedge thickening and uplift and wedge erosion erosion eventually catches up to the rate of uplift the wedge stalls and the locus of deformation shifts to the rear of the wedge in order to rebuild taper this analysis suggests that orogenic wedges continually deform and find a way to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists the actual taper value may change substantially through time as lithostratigraphy internal strength upper surface durability and presence absence of weak potential stress guides conspire to maintain a critical taper

linking the northern alps with their foreland the latest exhumation history resolved by low temperature thermochronology the evolution of the central alpine deformation front subalpine molasse and its undeformed foreland is recently debated because of their role for deciphering the late orogenic evolution of the alps its latest exhumation history is poorly understood due to the lack of late miocene to pliocene sediments we constrain the late miocene to pliocene history of this transitional zone with apatite fission track and u th he data we used laser ablation inductively coupled mass spectrometry for apatite fission track dating and compare this method with previously published and unpublished external detector method fission track data two investigated sections across tectonic slices show that the subalpine molasse was tectonically active after the onset of folding of the jura mountains this is much younger than hitherto assumed thrusting occurred at 10 8 6 5 ma and potentially thereafter this is contemporaneous with reported exhumation of the external crystalline massifs in the central alps the jura mountains and the subalpine molasse used the same detachments as the external crystalline massifs and are therefore kinematically coupled estimates on the amount of shortening and thrust displacement corroborate this idea we argue that the tectonic signal is related to active shortening during the late stage of orogenesis

depositional and structural evolution of a foreland basin margin in a magnetostratigraphic framework the eastern swiss molasse basin this integrated study of the sedimentology magnetostratigraphic chronology and petrography of the mostly continental clastics of the oligocene to miocene swiss molasse basin underpins a reconstruction of facies architecture and delineates relationships between the depositional evolution of a foreland basin margin and exhumation phases and orogenic events in the adjacent orogen a biostratigraphically based high resolution magnetostratigraphy provides a detailed temporal framework and covers nearly the whole stratigraphic record of the molasse basin 31 5 13 ma three transverse alluvial fan systems evolved at the southern basin margin they are characterized by distinct petrographic compositions and document the exhumation and denudation history of the growing eastern swiss alps enhanced northward propagation of the orogenic wedge is interpreted to have occurred between 31 5 and 26 ma during the period 24 19 ma intense in sequence and out of sequence thrusting took place as molasse strata were accreted to the orogenic wedge a third active tectonic phase possibly caused by backthrusting of the plateau molasse probably occurred between ca 15 and 13 ma fan head migration between 31 5 and 13 ma is probably controlled by the structural evolution of the thrust front due to molasse accretion and backthrusting

settling speeds of floes in fresh water and seawater the settling speeds of floes of fine grained natural sediments approximately 10 200 m in diameter have been measured in both fresh water and seawater these floes were formed at fluid shears of 100 200 and 400 s 1 and at sediment concentrations of 10 100 and 400 mg l values typical of conditions in the near shore areas of lakes and oceans especially during storm conditions it is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe but it is a weak function of salinity for the same diameter and salinity floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations if the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored it is shown that the settling speed of a floe is a weak function of diameter and salinity

constraints on miocene oceanography and climate in the western and central paratethys o sr and nd isotope compositions of marine fish and mammal remains abstract the paratethys evolved as a marginal sea during the alpine himalayan orogeny in the oligo miocene sediments from the northern alpine molasse basin the vienna and the pannonian basins located in the western and central part of the paratethys thus provide unique information on regional changes in climate and oceanography during a period of active alpine uplift oxygen isotope compositions of well preserved phosphatic fossils recovered from the sediments support deposition under sub tropical to warm temperate climate with water temperatures of 14 to 28 c for the miocene 18o values of fossil shark teeth are similar to those reported for other miocene marine sections and using the best available estimates of their biostratigraphic age show a variation until the end of the badenian similar to that reported for composite global record the 87sr 86sr isotope ratios of the fossils follow the global miocene seawater trend albeit with a much larger scatter the deviations of 87sr 86sr in the samples from the well constrained seawater curve are interpreted as due to local input of terrestrially derived sr contribution of local sources is also reflected in the end values consistent with input from ancient crystalline rocks e g bohemian massif and or mesozoic sediments with end 7 excluding samples showing local influence on the water column an average end value of 7 9 0 5 may be inferred for the miocene paratethys this value is indistinguishable from the end value of the contemporaneous indian ocean supporting a dominant role of this ocean in the western and central paratethys

controls of erosional denudation in the orogen on foreland basin evolution the oligocene central swiss molasse basin as an example a high resolution three dimensional reconstruction of the 25 m y old central swiss molasse basin reveals two sedimentary domains separated by a 5 km wide flood plain the proximal domain of the basin attained a width of 20 km and its basement is steeply flexed 6 7 dip petrographic data indicate that it was filled by sediment from the rigi dispersal system derived from the central alps of eastern switzerland and by locally sourced bajadas in contrast the distal sedimentary domain located farther north was gently dipping 2 and was filled by the meandering lac leman and honegg dispersal systems chronological data reveal that sedimentation in the northern proximal part of the basin started at 27 ma when sediment supply to the basin started to increase deflection of the foreland plate at 25 ma is successfully simulated by flexural modeling of the thrust load and the sediment load the model reveals that the lac leman and honegg dispersal systems are located on a buried flexural bulge furthermore it shows that burial and suppression of the flexural bulge at 27 ma as well as an increase of the basin wavelength were controlled by the contemporaneous increase in the sediment supply rate of the rigi system the model presented suggests that the tectonic subsidence of the molasse basin was mainly controlled by tectonic events in the northern part of the orogen within 70 km distance from the tip of the orogenic wedge crustal thickening in this part of the orogen is reflected in the proximal molasse by sedimentary cycles characterized by an increase in the sediment accumulation rates up section and by the presence of locally sourced bajada fans at the top of each cycle although south vergent back thrusting along the insubric line 150 km south of the foreland basin contributed little to flexure it resulted in an increase of the sediment supply to the foreland basin this is reflected in the molasse by coarsening and thickening upward trends an increase of the basin wavelength basinward shifts of the depocenters of the dispersal systems and uplift and erosion of the proximal basin border

structure of southeastern antarctic peninsula ice shelves and ice tongues from synthetic aperture radar imagery examination of synthetic aperture radar data collected over the southeastern antarctic peninsula shows that features sometimes mapped as ice shelves are more likely composed of numerous ice tongues interspersed within a matrix of fast ice and icebergs the tongues are formed by the seaward extension of numerous small mountain glaciers that drain from the antarctic peninsula once afloat the tongues intermingle with a matrix of fast ice and brash examination of 1997 radarsat 1 image mosaics shows that southeastern antarctic peninsula composite ice shelves covered an area of about 3500 km 2 like ice tongues around the rest of antarctica these features are highly fragmented and likely to be susceptible to mechanical failure one such composite shelf located between new bedford and wright inlets was observed to decrease in area by 1200km 2 between 1997 and 2000

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

reworked microfossils as a paleogeographic tool the abundant occurrence of reworked microfossils within the paleogeographically restricted upper rhine graben of central europe represents a unique opportunity to investigate their inherent information allowing new insights into the paleogeographic framework and past sedimentary pathways in the late rupelian and early chattian a transgression regression cycle linked to the global ru2 ru3 sequences affected the entire upper rhine graben basin leading to the deposition of a thick marine to lacustrine series the occurrences of abundant reworked planktonic foraminifera are grouped into several events that are linked to intervals of increased clastic input during regressive phases the biostratigraphic ranges of the reworked taxa indicate late cretaceous ypresian lutetian and bartonian priabonian ages for the sediment sources the reworking originated from related west alpine source deposits via a northward draining fluviatile system a fast uplift of priabonian and older deposits within the alpine realm during the late rupelian is accordingly inferred confirming the increased rate of the mesoalpine orogeny at that time the careful analysis of reworked microfossil assemblages thus provides a valid tool for future paleogeographic tectonic and provenance studies

isotope systematics in minerals biotite rejuvenation and exchange during alpine metamorphism abstract the hercynian schists and granites of the helvetic basement aar massif in the central swiss alps are overprinted by low grade alpine metamorphism and associated deformation rb sr and k ar ages of biotites are systematically reset by the later greenschist facies event this rejuvenation is apparently controlled by temperature mineral chemistry and grain size and independent of deformation and exsolution thermally activated volume diffusion best explains this behaviour with ar and sr having similar activation energies and diffusion rates for sr showing a greater dependence on biotite composition feldspars and apatite also show increasing equilibration to the alpine event and together with alpine equilibria in the micas reveal important changes in the isotopic compositions of exchanging reservoirs these spatial and temporal variations must be assessed before true mineral ages can be calculated generally the higher grade equilibria show less radiogenic exchange reflecting increased dilution by external fluids of radiogenic components released at the main front of isotopic resetting rb sr ages of alpine muscovites in the granites suggest a maximum possible age of metamorphism of 25 ma in this low grade area this implies significant diachroneity in the timing of peak metamorphism in the central alps with the relatively delayed metamorphism in this area a reflection of the later initial thickening and delayed uplift of the helvetic basement

the last erosional stage of the molasse basin and the alps we present a synoptic overview of the miocene present development of the northern alpine foreland basin molasse basin with special attention to the pattern of surface erosion and sediment discharge in the alps erosion of the molasse basin started at the same time that the rivers originating in the central alps were deflected toward the bresse graben which formed part of the european cenozoic rift system this change in the drainage direction decreased the distance to the marine base level by approximately 1 000 km which in turn decreased the average topographic elevation in the molasse basin by at least 200 m isostatic adjustment to erosional unloading required ca 1 000 m of erosion to account for this inferred topographic lowering a further inference is that the resulting increase in the sediment discharge at the miocene pliocene boundary reflects the recycling of molasse units we consider that erosion of the molasse basin occurred in response to a shift in the drainage direction rather than because of a change in paleoclimate climate left an imprint on the alpine landscape but presumably not before the beginning of glaciation at the pliocene pleistocene boundary similar to the northern alpine foreland we do not see a strong climatic fingerprint on the pattern or rates of exhumation of the external massifs in particular the initiation and acceleration of imbrication and antiformal stacking of the foreland crust can be considered solely as a response to the convergence of adria and europe irrespective of erosion rates however the recycling of the molasse deposits since 5 ma and the associated reduction of the loads in the foreland could have activated basement thrusts beneath the molasse basin in order to restore a critical wedge in conclusion we see the need for a more careful consideration of both tectonic and climatic forcing on the development of the alps and the adjacent molasse basin

inter annual climate variability in europe during the oligocene icehouse abstract new sclerochronological data suggest that a variability comparable to the north atlantic oscillation nao was already present during the middle oligocene about 20 myr earlier than formerly assumed annual increment width data of long lived marine bivalves of oligocene 30 25 ma strata from central europe revealed a distinct quasi decadal climate variability modulated on 2 12 mainly 3 7 year cycles as in many other modern bivalves these periodic changes in shell growth were most likely related to changes in primary productivity which in turn were coupled to atmospheric circulation patterns stable carbon isotope values of the shells 13 c shell further corroborated the link between shell growth and food availability sub decal oscillations in the 3 7 year band in other annually resolved fossil archives were often interpreted as el nino southern oscillation enso cycles this possibility is discussed in the present study however combined shell derived proxy and numerical climate model data lend support to the interpretation of a nao like variability according to numerical climate models winter sea level pressure wslp and precipitation rate wpr across central europe during the oligocene exhibited a pattern similar to the modern nao the simulated nao index for the oligocene shows periodicities coherent with those revealed by the proxy data 2 5 6 years yet on shorter wavelengths than the modern nao biennial and 6 10 year cycles likely the different paleogeography and elevated atmospheric co 2 concentrations not only influenced the sea level pressure pattern but also the temporal variability of the nao precursor the present study represents the first attempt to characterize the inter annual climate variability in central europe during the oligocene and sets the basis for future studies on the early phase of the cenozoic icehouse climate state

flocculation a key process in the sediment flux of a large glacier fed lake this study investigates the consequences of flocculation for sediment flux in glacier fed lillooet lake british columbia based on density fractal dimension in situ profiles of sediment concentration and size distribution and settling velocity equations presented in the literature sediment flux attributed to macroflocs during the late spring and summer accounts for a significant portion of sediment flux in the lake equivalent to at least one quarter of the average annual sediment flux fine sediment is reaching the lake floor faster in flocs than occurs if settling as individual grains this flux varies both spatially and temporally over the observation period suggesting a link between deposition via flocculation and the properties of bottom sediments macrofloc flux increased through june reached a peak during july and then declined into august macrofloc flux was greatest in the distal end of the first basin approximately 10 km from the point of inflow relatively high excess densities 0 1 g cm 3 at 500 m for flocs in situ are consistent with a composition dominated by inorganic primary particles microlaminations within lillooet lake varves have been linked by earlier workers to discharge events and the action of turbidity currents emanating from the lillooet river while turbidity currents undoubtedly occur in lillooet lake these results demonstrate flocculation as an adjunct process linking discharge lake level macrofloc flux bulk density and microlaminations in situ measurements of sediment settling velocity in glacier fed lakes are required to better constrain flux rates and permit comparison between flocculation in lacustrine environments with existing studies of estuarine marine and fluvial flocculation copyright 2009 john wiley sons ltd

paleogeography of the upper rhine graben urg and the swiss molasse basin smb from eocene to pliocene twenty paleogeographic maps are presented for middle eocene lutetian to late pliocene times according to the stratigraphical data given in the companion paper by berger et al this volume following a first lacustrine continental sedimentation during the middle eocene two and locally three rupelian transgressive events were identified with the first corresponding with the early rupelian middle pechelbronn beds and the second and third with the late rupelian serie grise fischschiefer and equivalents during the early rupelian middle pechelbronn beds a connection between north sea and urg is clearly demonstrated but a general connection between north sea urg and paratethys via the alpine sea is proposed but not proved during the late rupelian whereas in the southern urg a major hiatus spans early aquitanian to pliocene times early and middle miocene marine brackish and freshwater facies occur in the northern urg and in the molasse basin omm osm however no marine connections between these basins could be demonstrated during this time after the deposition of the molasse series a very complex drainage pattern developed during the late miocene and pliocene with a clear connection to the bresse graben during the piacenzian sundgau gravels during the late miocene pliocene and quaternary sedimentation persisted in the northern urg with hardly any interruptions the present drainage pattern of the rhine river from alpine area to the lower rhine embayment was not established before the early pleistocene

in channel surficial fine grained sediment laminae part i physical characteristics and formational processes an in channel surficial depositional feature surficial fine grained laminae composed of loosely bound fine sediment deposited during low flow conditions has often been observed in river systems in south western ontario the physical characteristics of this feature have been determined by a direct observation image analysis system this sediment consists primarily of flocculated fine grained material the size distributions of surficial fine grained laminae and suspended sediment were not significantly different each distribution is bimodal in nature and shows a characteristic grain size deficiency in the 4 5 m size range this observation suggests that flocculation and not low discharge or low competence is the dominant mechanism for the formation of surficial fine grained laminae under conditions of low flow in fluvial systems of south western ontario a quantitative assessment of this feature shows its potential importance as a source of fine grained sediment and associated contaminants for downstream transport

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor