active tectonics and quaternary basin formation along the vienna basin transform fault abstract the vienna basin transform fault is an active fault system extending over a distance of some 300 km from the eastern alps through the vienna basin into the west carpathians active sinistral movement is indicated by moderate seismic activity in a ne striking zone paralleling the fault focal plane solutions and recent stress measurements by analogy to the miocene kinematics we propose that the sinistral strike slip fault terminates in the carpathians where horizontal offset is transformed into thin skinned thrust type deformation hypocenter depths mostly well above 12 km are in line with the inferred thin skinned style of deformation with active faults restricted to the overthrust alpine carpathian units mapping of active fault segments in the vienna basin using subcrop data thickness maps of quaternary deposits seismological data and geomorphological features seen in the digital elevation model shows that virtually all active faults are reactivated miocene structures in the southern part of the basin active faulting defines a small scale pull apart structure with an actively subsiding quaternary basin which is filled with up to 140 m fluvial gravel sand and paleosoils for this basin quaternary sinistral displacement was quantified by adopting a geometrical model for thin skinned extensional strike slip duplexes accordingly 1 5 2 km sinistral slip accumulated during deposition of the basin fill in the last 400 ky corresponding to a slip rate of 1 6 2 5 mm y results are in good agreement with published gps data indicating 2 mm slip per year a second group of quaternary basins is related to listric normal faulting rollover and crestal collapse of the reactivated normal faults at the nw basin margin rollover also resulted in tilting and dissecting late pleistocene river terraces of the danube

palynological analyses of eocene to oligocene sediments from dsdp site 338 outer voring plateau article i nfo against the background of the profound global climatic shift from greenhouse to icehouse conditions during the eocene oligocene transition major geographic and oceanographic changes were taking place in the norwegian greenland sea region the voring plateau was a prominent structural feature which influenced the evolution of water mass circulation in the nordic seas and we present detailed palaeoenvironmental reconstructions of this structure new palynological results suggest that shallow water inner neritic environments were developed across parts of the voring plateau during early eocene times with terrestrial and brackish water palynomorphs indicating that both basement highs to the north and the crestal part of the voring escarpment may have been emergent a transition from marginal marine to open marine conditions occurred around 44 ma ago with the complete subsidence of the voring plateau below sea level facilitating inter basinal surface water circulation and promoted a significant increase in photic zone fertility carbon sequestration associated with such enhanced productivity in the late eocene nordic seas may have contributed to declining cenozoic atmospheric carbon dioxide levels thence to declining global temperatures and the development of limited northern hemisphere continental ice on greenland in the latest eocene

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

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

polyphase tectonic subsidence evolution of the vienna basin inferred from quantitative subsidence analysis of the northern and central parts the vienna basin is a tectonically complex neogene basin situated at the alpine carpathian transition this study analyzes a detailed quantification of subsidence in the northern and central parts of the vienna basin to understand its tectonic subsidence evolution about 200 wells were used to arrange stratigraphic setting and wells reaching the pre neogene basement were analyzed for subsidence to enhance the understanding of the regional subsidences the wells were sorted into ten groups based on their position on major fault blocks in the early miocene subsidence was slow and along e w to ne sw trending axis indicating the development of thrust controlled piggyback basins during the late early miocene data show abruptly increasing subsidence making the initiation of the vienna pull apart basin system from the middle miocene the tectonic subsidence curves show regionally different patterns the tectonic subsidence during the middle miocene varies laterally across the vienna basin and the differential subsidence can be related to the changing tensional regime of weakening transtension and strengthening extension toward the late middle miocene from the late middle miocene to the late miocene the tectonic subsidence occurred dominantly along the regional active faults and corresponds to the axis of e w trending extension of the western parts of the pannonian basin system in the quaternary the vienna basin has been reactivated and resulted in subsidence along the ne sw trending vienna basin transfer fault system

palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

the stress field in the frontal part of the eastern alps austria from borehole image log data abstract stress orientations in the frontal part of the eastern alps are inferred from borehole breakouts and drilling induced tensile fractures depicted in image logs from 62 vertical or slightly deviated wellbores with up to 5 km depth borehole breakouts 2463 individual features with 1673 9 m cumulative length are observed in all the wells except one whereas drilling induced fractures only occur in four wells microresistivity image log data from the alpine foreland the external thrust sheets allochthonous molasse helvetic and flysch nappes and the autochthonous units in the footwall of the alpine units reveal consistent in situ stress orientations with approximately n s directed maximum horizontal stresses shmax indications for stress partitioning across thrusts including the alpine floor thrust are not observed in the western sector of the study area the mean shmax is oriented 002 with a standard deviation sd of 11 1 in the central and eastern sector the mean shmax is oriented 177 sd 14 and 173 sd 14 3 respectively indicating a counterclockwise rotation of shmax of about 10 from west to east the observed stress indicators and the analysis of deviated wells suggest a strike slip regime for the western and central sector whereas a thrust regime is probable in the east of the study area the thrust regime there coincides with the occurrence of middle pleistocene conglomerates which were previously described to be displaced by alpine thrust faults the orientations of shmax fit into the general observation that shmax directions at the alpine front are oriented about perpendicular to the strike of the mountain belt and rotate along the alpine arc our stress orientations including those derived from the autochthonous basement are however markedly different from the nw se directed maximum horizontal stresses reported from the variscan units in the european foreland north of the study area

the eocene oligocene preglacial glacial transition in the atlantic sector of the southern ocean odp site 690 abstract high resolution interdisciplinary analyses of the clay and coarse 40 m fractions of odp leg 113 site 690 eocene oligocene sediments on the flank of the maud rise provide information on paleoproductivity water masses paleoclimate and erosion in the antarctic range as well as on the cyclicity of these processes three time intervals are distinguished 1 1 the middle eocene characterized by a nearly pure smectites b productivity varying between relatively high values in the 42 44 ma interval to very low values after 42 ma and c cyclic variations which correspond to changes in clay mineral associations a warm saline deep water mass is inferred to have protected carbonate shells against dissolution at site 690 we interpret the abundant mica in the coarse fraction as distributed by intermediate currents 2 2 the latest middle eocene late eocene characterized by low productivity values increasing with time kaolinite and illite concentrations also increase since the middle late eocene boundary mixing in the water column which starts during a cooling event causes similar clay mineral assemblages at site 690 and at site 689 on top of maud rise 3 3 the oligocene separated from the eocene by a hiatus is characterized by high productivity highly increased amounts of illite and other minerals originating from erosion and physical weathering of antarctica and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400 450 kyr cyclicity six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a proto aabw type

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

changes in upwelling mechanisms drove the evolution of marine organisms abstract long term evolution is thought to take opportunities that arise as a consequence of mass extinction as argued for example by gould 2002 and the following biotic recovery but there is absolutely no evidence for this being the case however our study shows that eutrophication by oceanic mixing also played a part in the enhancement of several evolutionary events amongst marine organisms and these results could indicate that the rates of oceanic biodiversification may be slowed if upwelling becomes weakened by future global warming this paper defines three distinct evolutionary events of resting spores of the marine diatom genus chaetoceros to reconstruct past upwelling through the analysis of several dsdp odp and land based successions from the north south and equatorial pacific as well as the atlantic ocean during the past 40 million years the atlantic chaetoceros explosion ace event occurred across the e o boundary in the north atlantic and is characterized by resting spore diversification that occurred as a consequence of the onset of upwelling following changes in thermohaline circulation through global cooling in the early oligocene pacific chaetoceros explosion events 1 and 2 pace 1 and pace 2 are characterized by relatively higher occurrences of iron input following the himalayan uplift and aridification at 8 5 ma and ca 2 5 ma in the north pacific region these events not only enhanced the diversification and increased abundance of primary producers including that of chaetoceros other diatoms and seaweeds but also stimulated the evolution of zooplankton and larger predators such as copepods and marine mammals which ate these phytoplankton and plants current thinking suggests new evolutionary niches open up after a mass extinction but our study finds that eutrophication can also stimulate evolutionary diversification moreover in the opposite fashion our results show that as thermohaline circulation abates global warming progresses and the ocean surface becomes warmer many marine organisms will be affected by the environmental degradation

the explosive diversification of the diatom genus chaetoceros across the eocene oligocene and oligocene miocene boundaries in the norwegian sea abstract eocene to middle miocene stratigraphic changes in species richness abundance and valve size of chaetoceros resting spores in the norwegian sea dsdp site 338 were investigated in order to understand past productivity and paleoenvironmental changes in upwelling regions as a result drastic resting spore events were recognized in a 6 myr interval across the eocene oligocene boundary eo event the oligocene miocene boundary om event and in the early middle miocene emm event the eo event was characterized by explosive diversification at both the morpho generic and specific levels an increase in abundance and a decrease in valve size from the upper eocene through the lowest oligocene the om event was defined by a two fold increase in species richness during the emm event spore abundance decreased rapidly and species richness and valve size decreased gradually these changes may indicate changes in the nutrient supply especially in upwelling regions the increased species richness suggests a change from a stable water column with a constant nutrient supply in the eocene to an unstable one with a sporadic nutrient supply by increased vertical mixing in the oligocene based on evaluation of the ecologic differences between dinoflagellate cysts and chaetoceros resting spores the role of main primary producer might have switched from dinoflagellates and or nannoplankton in the eocene to diatoms especially chaetoceros in the oligocene in the norwegian sea increased resting spore species richness during the om event may show that environmental changes such as global cooling and nutrient mixing led to a diversification of the spore producing genus chaetoceros the emm event might have been affected by changes in paleoceanographic conditions perhaps a decrease in nutrient supply this study presents the first paleoceanographic analysis using not only the total resting spore abundance but also the abundances of individual species and establishes the value of spore taxonomy and diatom analysis including spores

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

lateral extrusion in the eastern alps part 1 boundary conditions and experiments scaled for gravity lateral extrusion encompasses extensional collapse gravitational spreading away from a topographic high in an orogenic belt and tectonic escape plane strain horizontal motion of wedges driven by forces applied to their boundaries in the eastern alps it resulted from 1 an overall northerly compression apulia against eurasia 2 a strong foreland bohemian massif 3 lack of constraint along a lateral boundary carpathian region and 4 a previously thickened gravitationally unstable thermally weakened crust eastern alpine orogenic belt six indentation experiments reproduce lateral extrusion at lithospheric scale the models have two to four lithospheric layers with a mohr coulomb rheology for the upper and a viscous rheology for the lower crust the lithosphere rests upon a low viscosity asthenosphere a broad indenter a narrow deformable area and a weakly constrained eastern margin fullfill as closely as possible conditions in the eastern alps indentation produces both thickening in front of the indenter and escape of triangular wedges lateral variations in crustal thickness become attenuated by gravitational spreading the overall fault pattern includes domains of reverse strike slip oblique normal and pure normal faults strike slip faults in conjugate sets develop serially the narrow width of the deformable area and the strength of the foreland determine the angles between the sets gravitational spreading produces a rhombohedral pattern of oblique and pure normal faults along the unconstrained margin opposite the unconstrained margin the indenter front shows thrusts and folds intersecting with the conjugate strike slip sets a triangular indenter favors spreading high velocity of indentation favors escape high confinement limits lateral motion inhibits spreading and favors thickening lateral extrusion in the eastern alps is best modeled by 1 a weak lateral confinement 2 a broad and straight indenter 3 a narrow width of the deformable area and 4 a rigid foreland crustal thickening lateral escape and gravitational spreading all contribute to the overall deformation

the tertiary dynamics of the northern eastern alps austria changing palaeostresses in a collisional plate boundary abstract six tertiary deviatoric palaeostress tensor groups from 165 stations in the calcareous alps describe the upper crustal dynamics of the leading edge of the adriatic plate during protracted continental collision with the european lower plate palaeostress changes are correlated to the kinematic evolution of the plate boundary and to independently derived plate kinematic data of the alpine carpathian pannonian area each palaeostress direction is defined by 32 to 89 individual tensors which constrain 1 late eocene to oligocene nw directed compression during thrusting and dextral shearing on wnw striking faults nw directed compression along the northern margin of the adriatic plate is correlated to its n directed translation combined with a counterclockwise rotation 2a late eocene to early miocene n directed compression during n directed thrusting of penninic and helvetic units and the molasse 2b early to middle miocene n directed strike slip compression during the onset of eastward lateral extrusion the change from nw to n directed compression is interpreted to result from strain partitioning at the periadriatic fault which has formed the new adriatic plate boundary since the oligocene dextral shearing on this fault accommodated continued anticlockwise rotation and decoupled the northern eastern alps from the rotational component n directed compression in the calcareous alps paralleled the n directed translation of the adriatic plate 3 middle miocene ne directed compression of thrust and strike slip type during lateral extrusion ne directed compression in the calcareous alps resulted from the drag of the eastward extruding central eastern alps sinistral shear stress was transmitted across the ene trending salzach ennstal fault ne oriented 1 axes include 45 with the e w striking zone of distributed sinistral shear in the calcareous alps 4 middle miocene e directed extension associated with orogen parallel normal faulting of the central eastern alps e directed extension paralleled the direction of mass transfer towards the pannonian basin during lateral extrusion normal faulting was induced by reduced lateral confinement due to removal of material east of the alps on the large scale eastward motion was enabled by the e directed retreat of the eastern carpathian subduction zone 5 late miocene e directed compression orogen parallel compression obstructed lateral extrusion the stress change from extension to e directed compression was caused by the end of subduction retreat in the eastern carpathians due to dynamic changes in the subduction zone 6 n directed extension late to post miocene extension paralleled recent topographic slopes in the foothill of the eastern alps palaeostresses changes correspond to distinct phases in the kinematic evolution of the northern eastern alps and to the systematic formation and reactivation of major fault zones wnw striking faults changed deformation styles from dextral shear to dextral transpression reverse faulting and finally to sinistral shear the early to middle miocene salzach ennstal fault which formed the northern boundary of the extruded central eastern alps changed from sinistral transpression to sinistral shear sinistral transtension and finally to dextral shear

earliest oligocene increase in south atlantic productivity as interpreted from rock magnetics at deep sea drilling project site 522 the magnetic properties of the sediments rock magnetics at dsdp site 522 in the south atlantic exhibit clear differences between the latest eocene and earliest oligocene based on low temperature behavior of saturation remanence and hysteresis loops we attribute the difference to a slightly greater proportion of the finest grained so called superparamagnetic magnetite in the eocene sediments we believe that the lower proportion of very fine grained magnetite in the oligocene sediments is a result of incipient reduction diagenesis caused by increased productivity and hence increased labile organic carbon transport to the sediments due to an early oligocene increase in thermohaline circulation the eocene to oligocene transition at site 522 is also expressed by changes in microfossil assemblages increased carbonate content decreased insoluble residue and decreased foraminiferal shell fragmentation the increase in carbonate is synchronous with and parallels a change in the ratio of two of the rock magnetic parameters a ratio that tracks the decrease in the very fine grained magnetite component also parallel to these is a trend toward heavier 13c values in foraminiferal tests the increase in organic carbon transport to the sediments led to chemical dissolution of the finest grain size fraction of magnetite in the oligocene sediments hence a reduction in the superparamagnetic component and the change in the rock magnetic ratio in this way rock magnetics can be sensitive indicators of environmental changes such as fluctuations in organic carbon transport which may leave little other trace in the sedimentary record

genes diversity and geologic process on the pacific coast abstract we examine the genetics of marine diversification along the west coast of north america in relation to the late neogene geology and climate of the region trophically important components of the diverse west coast fauna including kelp alcid birds e g auks puffins salmon rockfish abalone and cancer crabs appear to have radiated during peaks of upwelling primarily in the late miocene and in some cases secondarily in the pleistocene phylogeographic barriers associated with mio pliocene estuaries of the mid california coast the pliocene opening of the gulf of california tectonic and eustatic evolution of the california bight as well as the influence of pleistocene and holocene climate change on genetic structure are assessed in a geologic context comparisons to east coast and western freshwater systems as well as upwelling systems around the globe provide perspective for the survey

the early origins of terrestrial c4 photosynthesis abstractthe c4 photosynthetic pathway is a series of structural and biochemical modifications around the more primitive c3 pathway that improve the photosynthetic efficiency under specific climatic conditions hence the origin and subsequent geographical expansion of the c4 plants likely reflects a record of climate change multiple paleoatmospheric pco2 proxies indicate a critical co2 threshold was breached 30 ma that potentially selected for co2 concentrating mechanisms to overcome photorespiratory stresses imposed on the basic c3 pathway details of the c4 pathway s earliest origins remain enigmatic given the paucity of the geologic record nonetheless 13c proxy records from paleosol carbonates ungulate teeth and plant derived compounds indicate c4 plants likely represented an important component of plant biomass by the early miocene low co2 levels appear to be a precondition for the development of the c4 photosynthetic pathway however comparisons of 13c proxy records indicate that the timin

on late oligocene to pliocene depocentre migrations and the evolution of the carpathian pannonian system abstract the late oligocene to pliocene evolution of foredeep basins of the eastern alps carpathians fold and thrust belt is marked by pronounced internal to external and lateral depocentre shifts the latter shifts covering a present along arc distance of 1700 km portray accelerating rates of foredeep depocentre migration particularly so in the late early and in the middle miocene from about 7 to about 45 cm yr lateral depocentre migration came to a close at the beginning of the late miocene the subsequent late miocene to pliocene foredeep infill history was characterized by exponentially increasing accumulation rates in the intersection area of the east european ukrainian and moesian platforms successive steps in the evolution of the foredeep basins had pronounced counterparts in the intra carpathian area the beginning of acceleration of foredeep depocentre migration in latest early miocene times was coeval with the inception of intra carpathian extensional tectonics the extremely rapid middle miocene depocentre shift coupled with a change in direction of foredeep depocentre migration corresponded with maximum extension in the intra carpathian area the ensuing end of foredeep depocentre migration around the middle late miocene transition was coeval with the end of extension of the intra carpathian area which in turn was followed by the inception of overall thermal subsidence at about 11 5 ma the timing of and spatial relationships between discrete coeval events in arc and intra arc evolution put unambiguous geological constraints on geodynamic modelling of the evolution of the carpathian pannonian system it is speculated that the geological observations may best be understood in terms of the surficial effects of lateral migration of slab detachment such effects would mirror the dominant role of a concentrating slab pull taken to result in e g a time progressive acceleration of foredeep depocentre migration

challenges in constraining ages of fluvial terraces in the vienna basin austria using combined isochron burial and pirir225 luminescence dating abstract burial dating with terrestrial cosmogenic nuclides and luminescence dating techniques have become two powerful tools to temporally constrain quaternary deposits a combination of both methods at the same geological setting has rarely been realized to date although their viable time frames overlap by several tens of thousands of years when middle pleistocene sediments with depositional ages ranging around ca 120 ka to ca 300 ka are targeted both methods are employed but come towards their lower and upper limits respectively a combined dating approach can be worthwhile at this age range and allows not only exploring the edges of both methods but holds the opportunity to do a cross check of results at an age spectrum where both dating techniques are at risk to become fuzzy here we present a case study where numerical ages of two middle pleistocene terraces located in the vienna basin were generated by combining burial and luminescence dating a variety of processes such as changing sediment input rates erosion and tectonics controlled the formation of fluvial terraces in the basin and shaped its complex modern surface age correlation of the evolved mosaic of blocks and dislocated sediment bodies is challenging and requires quantitative geochronological information in order to establish a coherent terrace stratigraphy luminescence and burial samples originating from two fluvial terraces the lower gaenserndorf terrace gdt and the higher schlosshof terrace sht were analyzed and evaluated luminescence and burial ages at the gdt site are in good agreement and suggest a depositional age of 140 170 ka bracketed by pirir225 luminescence ages ranging from 120 10 ka to 260 30 ka luminescence samples at the sht site are in saturation but provide minimum ages which are coherent with the burial dating result of 340 170 ka the new numerical ages indicate that the vertical offset between the gdt site and the sht site was not purely caused by fault activity but suggest two independent episodes of sediment accumulation besides providing new insights into the stratigraphic and morphological configuration of the central vienna basin area the cosmogenic nuclide data set is compelling from a methodological point of view at the gdt site several samples exhibited 26al 10be nuclide ratios exceeding the surface production ratio of 6 75 even though affected samples were excluded from burial age calculations a detailed investigation on possible scenarios which could have caused an upwards shift of 26al 10be ratios was carried out

drake passage and cenozoic climate an open and shut case drake passage opening has often been viewed as a single discrete event possibly associated with abrupt changes in global circulation and climate at or near the eocene oligocene boundary a new plate tectonic model based on recent reinterpretations of the opening history of basins in the scotia sea suggests that an effective ocean gateway may have developed even earlier during the middle eocene this is consistent with a growing body of evidence from sediment core proxy data for eocene changes in southern ocean circulation and biological productivity the period between earliest opening after 50 ma and the latest eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins this shallow opening may have caused important changes in southern ocean circulation contributing to eocene cooling and the growth of antarctic ice sheets

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

build up and dismembering of the eastern northern calcareous alps the structural geometry and kinematics of a segment of the classical fold and thrust belt of the northern calcareous alps nca is analyzed by map mesoscale fault slip and calcite twin data the most distinct feature of the eastern nca is the miocene semp salzachtal ennstal mariazell puchberg lineament which extends 400 km wsw ene from the northern tauern window in the west to the vienna basin in the east it forms an orogen parallel strike slip zone constitutes the major left lateral wrench corridor accommodating eastward lateral extrusion of crustal wedges along the central eastern alps and crosses the nca as an anastomosing zone of distributed shear the semp line and related structures dismember a fold and thrust belt formed during early transpressional and subsequent orthogonal contraction most early miocene structures are reversed in the late miocene accommodating little strain distinct strain fields are calculated based on fault slip and calcite deformation twin data they are regionally consistent in orientation and relative age and correlate with the following deformation stages 1 late cretaceous to early tertiary top to nw nappe stacking and right lateral wrenching along nw trending tear transfer faults as an expression of the build up of the austroalpine orogenic wedge e3 317 17 e1 058 28 e1 e2 e3 principal strains 2 early tertiary top to n stacking and conjugate strike slip faulting reflecting the change from transpressional to frontal contraction within the nca e3 356 12 e1 088 10 3 early to middle miocene large scale left lateral wrenching including early transpression and late transtension as expression of eastward displacement of the southern part of the nca e3 019 22 e1 109 27 4 post middle miocene e w contraction reactivating strike slip and normal faults e3 092 10 e1 004 12 the distributed nature of the lateral extrusion deformation and the anastomosing faulting along the semp line reflect the rheological heterogeneity inherited by the lithology and multiple deformations of the nca a combined extension and stress deflection model possibly accounts best for the pattern of northward concave faults branching off the semp line

opal sedimentation shifts in the world ocean over the last 15 myr biogenic silica opal accumulation records were used to trace mechanisms consequence and geographic pattern of shifts in the main locus of opal deposition of the world ocean over the last 15 myr over this time interval the main opal sink seems to have moved from the north atlantic to the pacific equatorial pacific eastern equatorial pacific eastern boundary current upwelling systems california namibia peru and finally to the southern ocean the interplay between opal deposition and a series of climatic tectonic oceanographic and biologic events has been analyzed and discussed these events include the cenozoic global cooling trend intensified glaciation in antarctica late miocene early pliocene biogenic bloom development of northern hemisphere glaciation nhg closing of the panama seaway transition of the climate system from a monopolarto a bipolar glaciated world mid pleistocene revolution mpr nutrient availability evolution of diatoms and c4 plants and changes in continental weathering rates while the observed shifts are mostly traceable to oceanic reorganizations and global climatic evolution conditions favorable to opal deposition involve the above mentioned complex mix of processes for this reason the interpretation of opal deposition records might not always be straightforward we however believe that it can still provide clear indications of large scale oceanographic reorganizations in the geological past d 2004 elsevier b v all rights reserved

post collisional orogen parallel large scale extension in the eastern alps abstract large scale extension affected the eastern alps during post collisional lateral tectonic extrusion in early and middle miocene times the tauern window was mainly tectonically exhumed by the 160 km pullapart of the rigidly behaving austroalpine basement blocks forming the tectonic lid of the penninic contents of the window an evaluation of the syn extrusion fault pattern reveals displacements of several tens of kilometers along the low angle extensional shear zones at the western and eastern margins of the window and along the important strike slip fault zones north and south of the window large scale shear is reflected by discontinuities in mineral cooling patterns across important shear zones the cooling histories of the tectonic blocks show that the window boundaries during exhumation coincide only partly with the classical boundaries of the window defined by thrust units reconstruction of the exhumation history shows an asymmetric evolution of the tauern window we argue that the eastern and western low angle extensional shear zones formed in sequence which is reflected by different evolutions of the fragmentation and uplift history of the austraolpine tectonic blocks to the east and west of the window in the central and eastern alps three structural domes the lepontin dome in the central alps and the tauern and rechnitz domes in the eastern alps were formed by large scale extension in miocene times total e w stretch amounts to more than 300 km and results in 70 extension we propose that the central and eastern alps are part of an extensional province that also includes the pannonian basin and has a counterpart separated by the moesian indenter in the rhodope mountains the aegean sea and the menderes massif in asia minor in these regions a number of mainly tectonically exhumed domes or deep sedimentary basins formed by miocene large scale extension

intensification of the asian monsoon and a chemical weathering event in the late miocene early pliocene implications for late neogene climate change several sedimentary geochemical and isotopic records indicate that the hypothesized intensification of the asian monsoon at about 8 ma triggered a physical and chemical weathering event in the himalayan tibetan plateau records of sediment input and clay composition from the northern indian ocean reveal clear weathering changes in the plateau at this time and ge si ratios of opaline silica as well as biogenic sedimentation rates indicate that increased dissolved element fluxes from this weathering event had an oceanwide effect it is likely that weathering intensity also increased in the andes and amazon basin in this interval as well perhaps the most important impact of this weathering event was to increase the net flux of the biolimiting nutrient phosphorus to the ocean as evidenced by a peak in phosphorus accumulation rates at this time the temporary increase in nutrient inputs to the ocean triggered increased oceanic productivity and organic carbon burial recorded in carbon isotopic records and paleooxygen concentrations the net result of this weathering event may have been an increase in the rate of drawdown of atmospheric co2 through the late miocene early pliocene via direct silicate weathering reactions and increased burial of organic carbon in the ocean this increased rate of atmospheric co2 drawdown may have destabilized the climate system by the late pliocene thus initiating a period of intense cooling and ice buildup leading to the present

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

origin signature and palaeoclimatic influence of the antarctic circumpolar current the antarctic circumpolar current acc is today the strongest current in the world s ocean with a significant influence on global climate its assumed history and influence on palaeoclimate while almost certainly equally profound are here called into question in this paper we review 30 years of accumulated data interpretation and speculation about the acc deriving mainly from dsdp and odp drilling in the southern ocean for most of this time a conventional view of acc development signature and influence has held sway among palaeoceanographers and marine geologists in this view the acc began at about 34 ma close to the eocene oligocene boundary the time of onset of significant antarctic glaciation and the time of creation of a deep water gap tasmanian seaway between australia and antarctica as the south tasman rise separated from north victoria land this is the smoking gun of synchroneity the southern ocean sediment record shows a latest eocene development and subsequent geographic expansion of a siliceous biofacies its northern limit taken to indicate the palaeoposition of the acc axis in addition the acc was considered to have caused antarctic glaciation by isolating the continent within a cold water annulus reducing north south heat transport a different and later date for antarctic south american opening drake passage was proposed but the timing of acc onset there was disputed and the simple story survived recent developments however call it into question modern physical oceanography shows that all or most of present day acc transport is confined to narrow jets within deep reaching circumpolar fronts and numerical modelling has suggested that a steady reduction in greenhouse gas concentration through the cenozoic could cause antarctic glaciation with or without a contribution from ocean circulation change the rapidity of antarctic glacial onset at the eocene oligocene boundary and coeval creation of a deep water gap south of tasmania both survive but in light of the new information the presence of a siliceous biofacies cannot be claimed as evidence of the existence of a continuous deep reaching oceanic front and therefore of an acc and the possibility arises that cool and cold sea surface temperatures were effects of antarctic glaciation rather than evidence of a major contributor to its cause in considering future work we emphasise the importance of additional information from ancillary fields better definition of the necessary and sufficient properties of oceanic fronts additional determinations of cenozoic atmospheric pco2 and further developments in models of antarctic glaciation but also suggest the way forward in marine geology our knowledge of the development and palaeoclimatic significance of the acc will be best served by grainsize studies of bottom current strength at selected locations and geochemical or mineralogical studies of clays and ird as a way of examining provenance and therefore surface and bottom current directions and the existence of interocean connections

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

magnetostratigraphic calibration of eocene oligocene dinoflagellate cyst biostratigraphy from the norwegian greenland sea the presence of abundant age diagnostic dinoflagellate cysts in ocean drilling program odp hole 913b leg 151 deep sea drilling project hole 338 leg 38 and odp hole 643a leg 104 has enabled the development of a new biostratigraphy for the eocene oligocene interval in the norwegian greenland sea this development is important because the calcareous microfossils usually used for biostratigraphy in this age interval are generally absent in high latitude sediments as a result of dissolution in parallel with this biostratigraphic analysis we developed a magnetic reversal stratigraphy for these norwegian greenland sea sequences this has allowed independent age determination and has enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic polarity timescale gpts the relatively high resolution of this study has enabled identification of dinoflagellate cyst assemblages that have affinities with those from the north sea and the north atlantic which allows regional correlation correlation of each site with the gpts has also allowed comparison of the stratigraphic record preserved in each drill hole hole 913b is the most complete and is the best preserved record of the eocene and oligocene in the northern hemisphere high latitudes and can serve as a reference section for palaeoenvironmental reconstructions of this age interval

3d geometry and kinematics of the lassee flower structure implications for segmentation and seismotectonics of the vienna basin strike slip fault austria abstract the active vienna basin strike slip fault consists of several segments which differ both in their kinematic and seismotectonic properties mapping of industrial 2d seismic geomorphological data and quaternary basin analysis proves that active deformation uses miocene faults this is shown in detail for the negative flower structure of the lassee fault segment which developed during the miocene and was reactivated in the quaternary the flower structure consists of riedel type splay faults which merge in a major branch line at the top of the principle displacement zone pdz in approximately 3 5 5 5 km depth mapping the pdz of the vienna basin strike slip fault in the continuations of the lassee segment reveals several fault segments which differ by the orientation of the pdz ne and nne striking segments with releasing bend geometries are associated with quaternary basins these segments are delimited by fault bends where the strike of the pdz changes by angles of 20 35 and are connected by ene striking segments orientated parallel to the displacement vector among the releasing bends the lassee segment is subject to increased extension due to the high angle ca 35 between the general slip vector and the orientation of the segment resulting extension seems to be accommodated by both the negative flower structure and normal faults which branch off from the pdz south of the lassee releasing bend the significant fault bends of 20 35 delimiting the geometrical fault segments are regarded to act as impediments during dynamic rupture propagation hence fault segment dimensions can be used for constraining the maximum fault surfaces which can break during single earthquakes the data on active kinematics and fault segmentation of the vienna basin strike slip fault system therefore may serve as a basic input for future assessments of maximum credible earthquake estimates

coeval high pressure metamorphism thrusting strike slip and extensional shearing in the tauern window eastern alps 1 recent findings for a young 31 5 0 7 ma age of high pressure metamorphism at 90 km depths in the eclogite zone of the tauern window eastern alps prompt the question about the timing of the structural development of the tauern window and its relation to high pressure metamorphism we show that all major structures in the tauern window resulting from strong n s lithospheric shortening and simultaneous minor e w extension began developing coevally with high pressure metamorphism in the eclogite zone large scale strike slip shear zones started to form at 32 30 ma and facilitated the spatial accommodation of simultaneous shortening and extension at least some of the strike slip and extensional shear zones operated into the middle miocene either continuously or intermittently with pronounced activity at 21 15 ma the considerable exhumation of the eclogite zone from 90 km depths into the middle crust and the tectonic development of its framework occurred within only 1 2 ma after eclogitization this is evidenced by almost identical ages for eclogite facies metamorphism and for the development of the major structures that bound the eclogite zone under blueschist and greenschist facies metamorphic conditions we discuss a tectonic model in which considerable transpressional shortening and thickening took place in the present central southern part of the tauern window we propose that the tauern window nucleated here and that most of the regional deformation at 32 30 ma is today found at the periphery of the window and in the adjacent austroalpine units afterward transpression continued the window grew to the e w and n and deformation progressed to those parts of the window ductile deformation in the present day surface level ceased at 15 ma

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

tertiary evolution of the intra carpathian area a model abstract the outer carpathian flysch nappes encircle an intra carpathian domain which can be divided into two megatectonic units north pannonian and tisza mostly on the basis of contrasting mesozoic and palaeogene facies development we see two major kinematic problems to be solved 1 1 the present distribution of the mesozoic and palaeogene facies is mosaic like and some belts form exotic bodies within realms of austroalpine affinity 2 2 late eocene palinspastic reconstruction of the outer carpathian flysch nappes suggest that the entire intra carpathian area must have been located several hundreds of kilometres to the south and to the west of its present position neogene extension can account for shortening in the external carpathian nappes but is unable to explain mesozoic facies anomalies and offsets of palaeogene formations we suggest that evolution of the intra carpathian area involved first late palaeogene early miocene juxtaposition of the north pannonian and tisza megatectonic units accompanied by the closure of the external carpathian flysch troughs thereafter extension of this amalgamated unit occurred which was compensated by thrusting of flysch nappes onto the european foreland and formation of molasse foredeeps eastward escape of the north pannonian unit from the alpine collisional belt involved left lateral shear along the pieniny klippen belt and right lateral shear along the mid hungarian zone parts of the late palaeogene basin and an early miocene volcanic edifice were dissected offset and elongated by several 100 kms the driving mechanism of the eastward escape of the intra carpathian area can be related to the collision of apulia and europe and the subduction of the external carpathian crust under the pannonian units the escape ceased gradually in the early miocene when oblique collision between the north pannonian unit and european continent occurred neogene extension of the pannonian region was an areal deformation the extension at locally variable rate resulted in the break up of the heterogenous floor of the neogene basin the driving mechanism of basin extension and contemporaneous compressional deformation of the external carpathians is thought to be related to ongoing subduction involving the marginal part of the attenuated european continental crust tectonic activity in the carpathians and basin subsidence and volcanism shifted in time and in unison from the west toward the east southeast

basement involved reactivation in foreland fold and thrust belts the alpine carpathian junction austria the late eocene early miocene alpine carpathian fold and thrust belt ftb lies in the transition between the eastern alps and the western carpathians se of the bohemian crystalline massif our study shows the involvement of crystalline basement from the former european jurassic continental margin in two distinct events a first extensional event coeval with eggerian karpatian c 28 16 ma thin skinned thrusting reactivated the rift basement fault array and resulted from the large degree of lower plate bending promoted by high lateral gradients of lithospheric strength and slab pull forces slab break off during the final stages of collision around karpatian times c 17 16 ma promoted large wavelength uplift and an excessive topographic load this load was reduced by broadening the orogenic wedge through the reactivation of the lower plate deep detachment beneath and ahead of the thin skinned thrust front with the accompanying positive inversion of the basement fault array and ultimately by the collapse of the hinterland summits enhanced by transtensional faulting although this work specifically deals with the involvement of the basement in the alpine carpathian junction the main conclusions are of general interest to the understanding of orogenic systems

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

fault slip analysis along the northern margin of the eastern alps molasse helvetic nappes north and south penninic flysch and the northern calcareous alps fault slip data are analyzed and paleostress tensors computed from 84 stations along the northern margin of the eastern alps between liechtenstein and vienna most fault sets resulted from more than one deformation heterogenous sets are divided into homogenous subsets by cross cutting relationships observed in the field and stress tensors are calculated separately for each subset the deviatoric stress tensors fall into six distinct groups that are regionally consistent in orientation stress ratio and relative age throughout the northern margin of the eastern alps from oldest to youngest the tensor groups are as follows 1 1 subhorizontal e w 3 subvertical thrusting related e w compression this group is only encountered in the south penninic flysch and the northern calcareous alps 2 1 subhorizontal n s 3 subvertical thrusting related n s directed compression 3 1 subhorizontal n s 3 subhorizonal e w strike slip faulting conjugate to n s compression 4 1 subvertical 3 subhorizontal e w e w directed subhorizontal extension 5 1 subhorizontal e w 3 subhorizontal n s strike slip faulting during e w compression and 6 1 subvertical 3 subhorizontal about n s 3 trajectories are oriented perpendicular to the general strike of the eastern alps and parallel topographic gradients the six trensor groups correlate with distinct steps in the cretaceous and the post eocene tectonic evolution of the northern units of the eastern alps 1 1 thrusting related e w compressional structures in the south penninic flysch and the northern calcareous alps are correlated to cretaceous top to w directed thrusting in the south penninic and austroalpine domains 2 2 thrusting related n s compressional structures encompass large scale folds with e w trending axes rare e w oriented thrust branch lines and cut off lines and s dipping ramps in the rhenodanubian flysch tensors reflect the stresses during northward thrusting in the late eocene early miocene 3 3 4 strike slip faults and extensional structures depicting n s compression and e w extension formed during the eastward lateral extrusion of the eastern alps prominent reactivations of strike slip faults during subhorizontal extension in the east and permutation between 1 and 2 reflecting periodic superposition of strike slip and normal faulting in the western eastern alps during overall e w extension suggest a close relationship of both tensor groups deformation resulted in the eastward lateral motion of the northern units of the eastern alps that started during the miocene 4 5 the significance of late miocene e w directed compression reactivating pre existing fractures and faults is presently not well understood we tentatively relate this event to a major change of boundary conditions within the miocene 5 6 the youngest deformation recorded is caused by surface uplift and gravitational collapse of the eastern alps

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

dating the longevity of ductile shear zones insight from 40ar 39ar in situ analyses we attempt to improve temporal constraints on the longevity and the termination of ductile shear zones by performing texturally controlled in situ 40ar 39ar analyses of pre kinematic muscovite biotite and k feldspars of syn kinematic phengite and k feldspar and of post kinematic phengite within the same samples of sinistral shear zones from the western tauern window eastern alps additionally two samples were dated by the rb sr method microsampling relative sequences of mineral formation based on microstructural cross cutting relationships were confirmed by in situ 40ar 39ar analyses showing that syn kinematic minerals are in general younger than pre kinematic minerals and older or of equal age than the post kinematic minerals of the same sample from the rim to the core of the western tauern window syn kinematic phengite and k feldspar reveal a set of formation ages varying between 33 and 15 ma for the northernmost and peripheral shear zone ahorn shear zone between 24 and 12 ma for the intermediate shear zone network tuxer shear zones and between 20 and 7 ma for the southernmost and central shear zone greiner shear zone the age variation of syn kinematic phengite and k feldspar analyses is larger than the analytical error of each age obtained in addition isochron calculations of the syn kinematic minerals reveal atmospheric like 40ar 36ar intercepts therefore the obtained age values of the syn kinematic minerals are interpreted as formation ages which date increments of a long lasting deformation period the time range of deformation of each shear zone system is bracketed by the oldest and youngest formation ages of syn kinematic phengite and k feldspar post kinematic phengite laths show the youngest formation ages and overlap with the youngest syn kinematic formation ages this relationship indicates that post kinematic growth occurred immediately after syn kinematic mineral formation at the end of ductile sinistral shear hence the termination of deformation is dated by the ages of these post kinematic phengite blasts pre kinematic minerals are characterized by break down and exsolution reactions and their age values are heterogeneous and often affected by the presence of extraneous ar these age values are usually older than but sometimes overlapping with ages of the syn kinematic minerals using the temporal constraints obtained by the ages of pre syn and post kinematic minerals we could assess partly overlapping time intervals of syn kinematic mineral formation of 19 myr 33 15 ma in the ahorn shear zone 13 myr 24 12 ma in the tuxer shear zones and 14 myr 20 7 ma in the greiner shear zone this indicates successive localization and propagation of ductile shear zones in the western tauern window from lower metamorphic sites at the rim towards higher metamorphic sites in the center

lower miocene structural evolution of the central vienna basin austria abstract the tectonic evolution of the vienna basin overlying the alpine carpathian fold and thrust belt includes two stages of distinct basin subsidence and deformation the earlier phase contemporaneous with thrusting of the alpine carpathian floor thrust is related to the formation of a wedge top basin piggy back which was connected to the evolving foreland basin lower miocene c 18 5 16 ma this stage is followed by the formation of a pull apart basin middle to upper miocene c 16 8 ma sediments of the latter unconformably overly wedge top basin strata and protected them against erosion analyses of subcrop data from the central part of the basin focus on the complex stratal geometries and tectonics of the lower miocene wedge top basin during that period the overriding allochthon is characterised by syntectonic subsidence and sedimentation out of sequence fold thrusting normal faulting and sinistral wrenching all types of faults are dated as lower miocene by the occurrence of growth strata and the age of overlying post tectonic sediments related to the pull apart basin stage faults mapped in 3d seismic are compared to faults along the sw margin of the vienna basin they prove that complex lower miocene deformation occurred in large parts of the austroalpine overriding nappes concurrent with thrusting at the alpine floor thrust and in the molasse unit the structural analysis of 3d seismic data shows that lower miocene sediments of the ottnangian and karpatian stage unconformable overly the alpine carpathian thrust nappes with a thickness of up to 1500 m geometries include onlaps to the basin floor internal unconformities and toplaps to the overlying middle miocene sediments these toplaps are the results of tilting and subsequent erosion of the sediment pile by out of sequence thrusting in the central part at the karpatian badenian transition c 16 3 ma prior to the onset of pull apart deformation

evidence for late oligocene establishment of the antarctic circumpolar current removal of the last impediment to circum antarctic flow opening of the drake passage between antarctica and south america is essential to establishment of the acc and has been placed in both the earliest oligocene and earliest miocene on the basis of paleomagnetic reconstructions the tasman gateway between antarctica and tasmania notably deepened following 33 5 ma completion of the acc circuit has been seen as the key to major growth of the east antarctic ice sheet by thermal isolation of the continent an alternative argument attributes ice sheet growth to changes in atmospheric pco2 we present evidence on current strength and water mass properties suggesting a clear increase in flow speed and homogeneity of southern ocean water masses in the latest oligocene after about 23 95 ma marking establishment of the acc attributable to deep opening of drake passage the mi 1 glaciation may be a consequence establishment of a permanent low altitude ice sheet does not appear to take place prior to mid miocene cooling

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

late oligocene initiation of the antarctic circumpolar current evidence from the south pacific the antarctic circumpolar current acc is a key feature of the southern ocean its development may have helped cool antarctica and initiate southern hemisphere glaciation the deep circulation of the acc must have been established after both the tasman gateway between antarctica and australia and the drake passage between south america and antarctica opened however estimates for acc initiation range over 20 m y from the middle eocene to early miocene a new piston core of upper oligocene to holocene sediments from the south pacific has allowed us to delimit the formation of the acc to the late oligocene ca 25 23 ma upper oligocene current worked sediments and a hiatus to the upper miocene result from the beginning of the modern acc flow i e when strong currents and mixing throughout the water column were established previously published nd isotope data date the first intrusion of pacific water into the atlantic much earlier the discrepancy with our results can be reconciled by the different methods measuring different flow regimes tracer methods such as nd are sensitive to relatively small and shallow incursions of water whereas pelagic erosional regimes require vigorous deep flow

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

chronostratigraphic distribution of cetaceans in the pliocene of northern apennines italy palaeoecological implications abstract a large number of cetacean fossils have been recovered through the time from the pliocene deposits in northern apennines thrust belt on both the padan adriatic and the tyrrhenian side in this work the cetaceans of castell arquato basin padan adriatic side have been placed within a high resolution chronostratigraphic framework available for this area this results in a better assessment of their evolutionary history and of the palaeoecologic factors controlling their diversity and abundance through the time our results document a greater diversity between 3 1 and 2 7 ma time interval likely due to the development of eutrophic conditions during precessionally driven insolation maxima at 400 ka eccentricity maxima which are recorded in deeper depositional settings by sapropel clusters eutrophic conditions kept a complex trophic chain as currently observed in the ligurian sea corsican ligurian provencal basin an area characterized also by upwelling a reduction in both number and ecological diversity of cetacean taxa is observed along the pliocene pleistocene transition this trend related to the onset of the quaternary icehouse conditions appears in good agreement with the recently recognized extinction event that affecting the marine megafauna at the end of the pliocene

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

simulating the impact of the panamanian seaway closure on ocean circulation marine productivity and nutrient cycling abstract the closure of the panama isthmus 14 3 ma caused large reorganizations of ocean circulation here we use a global climate ocean ecosystem model to investigate the effects of the closing gateway on ocean circulation marine productivity and nutrient distributions several sensitivity experiments with different sill depths and vertical diffusivities are performed consistent with previous model studies we find constricted throughflow due to shallowing of the sill leads to intensification of the north atlantic thermohaline overturning we demonstrate a strong coupling between the flows through the tropical gateways of panama and indonesia in a way that reduced outflow of upper ocean pacific waters via the panama gateway into the atlantic is compensated by increased flow through the indonesian archipelago the simulated rates of north atlantic deep water formation strongly depend on the vertical diffusion in the model particularly for a deep sill for the first time we document by model results shifts in nutrient distributions associated with reorganizations of ocean circulation with repercussions on marine productivity patterns reduced flow of nutrient rich sub surface waters from the pacific into the atlantic reduces biological productivity in the north atlantic in the eastern tropical pacific restriction of the nutrient rich outflow leads to nutrient accumulation which in turn maintains a strong increase in productivity these results seem to be largely consistent with the paleoproductivity proxy record a massive drop of opal accumulation rates however as found in north pacific sediments for the time of the final closure 2 75 ma cannot be simulated generally global marine net primary productivity npp is found to increase with proceeding gateway closure

mesozoic and tertiary evolution of the alpine carpathian foreland in eastern austria abstract the bohemian massif partly covered by mesozoic sediments extends southward some 50 km under the alpine carpathian nappe complex a major basement spur devoid of mesozoic sediments and referred to as the south bohemian basement spur separates the jurassic cretaceous upper austrian basin from the lower austrian basin the latter came into evidence during the middle jurassic under a tensional setting late jurassic shelf carbonates and basinal shales were deposited under a tectonically quiet regime early cretaceous uplift of the south bohemian basement spur induced the truncation of jurassic strata along its margins transgressive late cretaceous elastics overlap the truncated jurassic series and locally onlap on basement upper austria latest cretaceous to paleocene foreland deformations may have caused a renewed uplift of the south bohemian basement spur the eocene to late miocene evolution of the molasse foredeep went hand in hand with the emplacement of the alpine carpathian nappe system differential movements between the eastern alpine nappes and the carpathian nappes combined with tensional stresses in the basement caused the subsidence of the vienna basin

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

cooling and vertical motions of crustal wedges prior to during and after lateral extrusion in the eastern alps new field kinematic and fission track data from the mur murz fault system new structural and thermochronological zircon and apatite fission track data from the eastern most alps highlight distinct deformation phases affecting the austroalpine unit along a major sinistral strike slip fault system the mur murz fault mmf the data link deformation to vertical motions prior to during and after the main phase of lateral extrusion of the orogen zircon fission track ages document rapid ca 15 c myr and diachronous eastward younging cooling and rock exhumation during the latest cretaceous to paleocene subsequent regional eocene to early miocene cooling below the closure temperature of the apatite fission track system occurred at slow rates ca 2 c myr suggesting that the region was not subject to major surface uplift and erosion during that period fault kinematic analysis along the mmf document pre extrusion nnw sse contraction middle miocene syn extrusion ne sw to nne ssw directed shortening and late miocene e w contraction all phases are characterized by strike slip fault regimes formation of the complex mmf zone triggered the exhumation of small fault bound crustal blocks within the fault zone as documented by middle miocene apatite fission track ages overall ages are similar on both sides of the fault suggesting that lateral extrusion along the mmf was not associated with significant differential vertical motions local pliocene rock cooling and exhumation was probably related to the buttressing effect of the underthrust bohemian basement spur whereas large scale post extrusion surface uplift of the extruding crustal wedges such as the styrian block must have been related to long wavelength deformation processes affecting the easternmost alps

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

paleogene and neogene kinematics of the alpine carpathian fold thrust belt at the alpine carpathian transition abstract in this study we analyze a 300 km long segment of the alpine carpathian orogen using novel outcrop data and regional seismic profiles from the west carpathians to unravel the kinematics and timing of eocene to late miocene deformation of the fold thrust belt comparison with data from the eastern alps and the vienna basin leads to an updated tectonic model for the paleogene and neogene of the alpine carpathian transition which includes three stages 1 eocene to early oligocene nnw directed foreland propagating thrusting thrusts are directed perpendicular to the strike of the european foreland in the outer west carpathians owc and sub parallel to thrusts observed in the eastern alps west of the vienna basin 2 continued late oligocene to early miocene nnw directed foreland propagating thrusting simultaneous with sinistral strike slip reactivation of former nappe boundaries in the hinterland of the active thrusts this deformation corresponds to the early stage of eastward lateral extrusion of the eastern alps the ene striking sinistral faults in the owc are kinematic equivalents of the semp fault system in the eastern alps which was active at the same time the latest stage of thrusting is characterized by sse directed out of sequence thrusts in the hinterland of the owc and the reactivation of variscan basement thrusts in the european foreland as sse directed backthrusts 3 formation of n ne striking sinistral strike slip faults which are kinematically linked to n ne directed out of sequence thrusts post dating nnw directed thrusting the sinistral faults formed coeval with the opening of the vienna pull apart basin during the middle to late miocene stage of lateral extrusion unlike proposed in previous studies the west carpathians do not appear to be affected by oligocene to early miocene crustal scale wrenching of the pieniny klippen belt our data show that the deformation of the pkb is in line with the eocene to late miocene tectonic evolution reconstructed for the owc

new calibration of neogene radiolarian events in the north pacific abstract new age models for twelve deep sea drilling project sites in the north pacific have been produced based on in order of importance in our dataset a recompilation of previously published diatom calcareous nannofossil and foraminifer first and last occurrences and magnetostratigraphy the projected ages of radiolarian first and last occurrences derived from the line of correlation of the age depth plots have been computed from these sites and 28 radiolarian events have thereby been newly cross calibrated to north pacific diatom and other stratigraphy several of the north pacific radiolarian events are older than in previously published equatorial pacific calibrations and some may be diachronous within the north pacific these patterns may be due to complex latitudinal patterns of clinal variation in morphotypes within lineages or to migration events from the north pacific towards the equator

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

far field effects of late miocene subduction in the eastern carpathians e w compression and inversion of structures in the alpine carpathian pannonian region kinematic and paleostress data constrain a late miocene e w compressional event that affected the entire alpine carpathian pannonian system after 9 ma and prior to 5 3 ma the maximum horizontal compression directions obtained from 110 stations show a mean 1 orientation of 083 deformation is mainly strike slip e w directed compression followed early to middle miocene upper plate extension in the pannonian basin which was caused by the retreating subduction boundary in the outer carpathians this compressional event terminated early to middle miocene eastward lateral extrusion of the eastern alps and reverted strike slip faults which bounded earlier extruded wedges such as the salzachtal ennstal fault the periadriatic fault the mur murz vienna basin fault system and strike slip faults in the western carpathians e w compression caused the reorientation of the extension direction of the alpine crustal stack east directed tectonic unroofing of the metamorphic domes in the central eastern alps terminated between 9 and 6 ma and early to middle miocene orogen parallel e w extension switched to late miocene n s extension which parallels modern topographic slopes in the pannonian basin the change from synrift extension to late miocene compression during the postrift phase caused the pronounced postrift subsidence by stress induced downward flexure of the loaded lithosphere we relate late miocene e w compression to coeval late stage west directed subduction of the european plate below the eastern carpathians slab pull of the subducted plate caused subduction roll back and upper plate extension of the pannonian area up to the middle miocene subduction slowed down and ceased when up to 60 km thick buoyant continental crust entered the subduction zone during the short period of continued convergence e w directed compressive stress was transmitted across the subduction boundary into the upper plate compressive stress was transferred through the uppermost brittle crust of the earlier extended pannonian region into the eastern alps up to 1400 km behind the subduction zone e w compression terminated during the pliocene when the pliocene to recent nnw sse compressive stress field was established in central europe

basin inversion in tectonic wedges insights from analogue modelling and the alpine carpathian fold and thrust belt abstract this work simulates the inversion and incorporation of sub thrust segmented half graben basins into tectonic wedges by means of sandbox analogue models segmented half graben basins striking at 90 45 and 15 to the extension direction were created first and then shortened using different angles for the basal detachment and topographic slope a shallow viscous polymer layer located above the half graben basin was included in one of the models the experiments were analysed using time lapse photography topography laser scans and image based 3d voxels the results indicate a deformation sequence characterised by layer parallel compaction fault reactivation thrust propagation and related folding fault reactivation was associated with the layer parallel compaction accomplished by slip along the basal detachment prior to and in between pulses of thrusting results reveal the fundamental control imposed by the vertical load of the tectonic wedge and its integrated strength profile in the inversion of sub thrust basins results are compared to the alpine carpathian fold and thrust belt

present state of tectonic stress of the friuli area eastern southern alps stress orientations are determined for the friuli area from focal mechanisms using the inversion technique of gephart and forsyth 1984 the data consist of 244 fault plane solutions selected for the period 1988 1995 where the data coverage was poor this period was extended to 1978 1996 local magnitude ranges from 2 0 to 4 3 and the depths extend from 4 to 16 km the friuli area is subdivided into five seismotectonic zones on the basis of tectonic characteristics seismic activity and focal mechanisms and for each zone a stress tensor is determined the results show that the active tectonic stress in the friuli area is heterogeneous and conditioned by the complex structural pattern which is characterized by two indented tectonic wedges the western and central parts of the area are mainly affected by a compressional state of stress while in the eastern part a strike slip state of stress prevails the orientation of the principal stresses varies from the western to the eastern part of the area and differences are also noticeable with depth in the central part of the friuli area the maximum compressional stress is n s trending at shallow depths 10 km changing to nw se at deeper levels the maximum compressional stress is nw se oriented in the western part while in the eastern part it is n s oriented

balancing lateral orogenic float of the eastern alps abstract oligocene to miocene post collisional shortening between the adriatic and european plates was compensated by frontal thrusting onto the molasse foreland basin and by contemporaneous lateral wedging of the austroalpine upper plate balancing of the upper plate shortening by horizontal retrodeformation of lateral escaping and extruding wedges of the austroalpine lid enables an evaluation of the total post collisional deformation of the hangingwall plate quantification of the north south shortening and east west extension of the upper plate is derived from displacement data of major faults that dissect the austroalpine wedges indentation of the south alpine unit corresponds to 64 km north south shortening and a minimum of 120 km of east west extension lateral wedging affected the eastern alps east of the giudicarie fault west of the giudicarie fault north south shortening was compensated by 50 to 80 km of backthrusting in the lombardian thrust system of the southern alps the main structures that bound the escaping wedges to the north are the inntal fault system ca 50 km sinistral offset the konigsee lammertal traunsee klt fault 10 km and the salzach ennstal mariazell puchberg semp fault system 60 km these faults as well as a number of minor faults with displacements less than 10 km root in the basal detachment of the alps the thin skinned nature of lateral escape related structures north of the semp line is documented by industry reflection seismic lines crossing the northern calcareous alps nca and the frontal thrust of the eastern alps complex triangle zones with passive roof backthrusts of middle miocene molasse sediments formed in front of the laterally escaping wedges of the northern eastern alps the aim of this paper is a semiquantitative reconstruction of the upper plate of the eastern alps most of the data is published elsewhere

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

relating collisional kinematics to exhumation processes in the eastern alps abstract based on a review of the surface and deep structure of the eastern alps we link the timing and the inferred displacement fields to exhumation of upper and lower crustal units of the orogenic nappe stack during collision the discussion focuses mainly on the tauern window and its country rocks the only area of the eastern alps where the orogenic wedge from its uppermost austroalpine nappes down to its deepest european basement nappes is continuously exposed we summarize and discuss the long standing controversy on the mechanisms of exhumation of this nappe stack on the base of a synthesis of structural and geochronological data and restorations of collisional displacements both in cross sections and map views we conclude that the large amounts of exhumation assessed for the western eastern alps resulted from large amounts of thickening and erosion not observed in the eastern part of the eastern alps extensional faults laterally bounding the area of major thickening and exhumation are inferred to nucleate in order to accommodate displacement around the indenter corner in the west and in order to reduce a large gradient of crustal thickness and surface elevation in the east restorations to the pre indentation stage document an amount of northward increasing orogen parallel extension varying 45 km to 85 km corresponding to 15 of extension that is partly accommodated along normal faults n s shortening between the northern calcareous alps and the dolomites indenter attained 75 km in the west and decreased to 30 km in the east 55 km out of these 75 were accommodated in the area of the tauern window our kinematic model shows that lateral extrusion accommodated along conjugate strike slip faults requires large amounts of north south shortening in the western part of the eastern alps such shortening is consistent with the reconstructed upright folding and erosion of the tauern window thus explaining the largest amount of its exhumation in contrast the eastern termination of the eastern alps represents an area where collisional convergence was barely accommodated by crustal thickening this transition from a highly shortened thickened and exhumed wedge in the west mainly affected by orogen perpendicular displacements to a barely shortened and exhumed wedge in the east mainly characterised by orogen parallel displacements spatially coincides with a change in the deep structure of the european slab indeed the inferred continental european slab imaged in the west disappears into a low velocity anomaly where no slab is detected in the east an inherited step in the geometry in map view of the european passive margin causing its crust to enter the subduction zone earlier than the area east of the tauern window may explain the rapid decrease of shortening of thickening the different syn collisional p t gradients and the disappearance of the continental slab east of the katschberg fault

quantifying early miocene in sequence and out of sequence thrusting at the alpine carpathian junction a detailed reconstruction of late oligocene and early miocene thrusting at the leading edge of the east alpine fold thrust belt is achieved from well data seismic and interpretative cross sections data are used for constraining the paleogeographic positions of the alpine thrusts quantifying in sequence out of sequence thrust distances assessing the timing of thrust propagation from structurally higher units into more external ones and estimating thrust velocities results are depicted in five palinspastic maps for time slices between 26 ma and 16 ma the termination of foreland propagating thrusting at the alpine front is apparently controlled by the subcrop topography of the european basement which includes a major recess in the east leading to a diachronic along strike termination of foreland propagating thrusting with younger thrust ages and higher in sequence thrust distances in the east early locking of foreland propagating thrusting in the west causes prominent out of sequence thrusts which add to the in sequence thrust distances there continuing consecutive detachment of foreland units in the east occurs at rather fast propagation velocities with time intervals between foreland thrust propagations ranging between 0 1 and 0 7 ma the resulting increase of in sequence thrust distances from west to east is balanced by out of sequence thrusts in the west the total amount of late oligocene to early miocene thrusting is quantified with a minimum of 51 km average thrust velocities range between 4 6 and 5 2 mm yr this rate refers to the movement of the basal thrust at the leading edge of the fold thrust belt which occurs contemporaneous with the eastward lateral extrusion of the eastern alps in the hinterland

constraints on the active tectonics of the friuli nw slovenia area from cgps measurements and three dimensional kinematic modeling we use site velocities from continuous gps cgps observations and kinematic modeling to investigate the active tectonics of the friuli nw slovenia area data from 42 cgps stations around the adriatic indicate an oblique collision with southern friuli moving nnw toward northern friuli at the relative speed of 1 6 to 2 2 mm a we investigate the active tectonics using 3dmove a three dimensional kinematic model tool the model consists of one indenter shaped fault plane that approximates the adriatic plate boundary using the fault parallel flow deformation algorithm we move the hanging wall along the fault plane in the direction indicated by the gps velocities the resulting strain field is used for structural interpretation we identify a pattern of coincident strain maxima and high vorticity that correlates well with groups of hypocenters of major earthquakes including their aftershocks and indicates the orientation of secondary active faults the pattern reveals structures both parallel and perpendicular to the strike of the primary fault in the eastern sector which shows more complex tectonics these two sets of faults probably form an interacting strike slip system

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher

origin of the joya honda maar san luis potosi mexico abstract joya honda is a quaternary maar of unusual type from the mexican basin and range province its 300 m deep crater is excavated in cretaceous limestones the surrounding tephra deposit which in places is 100 m thick begins with a series of weakly indurated pyroclastic surge and fall layers that we interpret as dry surge deposits these are overlain by the main sequence of strongly indurated massive tuff breccias that we interpret as wet surge deposits joya honda formed subaerially from the interaction of groundwater with rapidly ascending intraplate type basanitic magma carrying peridotitic mantle xenoliths local aquifer characteristics controlled the style of eruption and the nature of the deposits groundwater in the limestone hosted aquifer beneath joya honda was apparently contained within solution enhanced fractures at the onset of the eruption magma began to interact with a moderate amount of groundwater producing the dry surge deposits which are typical of deposits found at many maars and tuff rings as the eruption continued the crater grew and the hydromagmatic blasts fractured the limestones around the explosion foci a marked increase in the water magma ratio of the system followed when a large fracture or a portion of the limestone with enhanced secondary permeability was intersected by the expanding crater subsequent phreatomagmatic explosions occurred in a system with groundwater flow rates several orders of magnitude larger than in the initial dry surge stage at the maar rim these wet eruptions led to the emplacement of massive tuff breccias through a combination of fallout surges and mudflows these steeply dipping tuff breccias are similar to deposits found at many tuff cones juvenile clasts in the near vent deposits show marked upward increases in both hydration palagonitization and vesicularity the increased palagonitization with height in the section appears to be a consequence of the overall increased wetness of the eruption with time correlating with greater carbonate cementation and lithification in the upper part of the deposit the transition toward higher vesicularity is interpreted as evidence of a gradual reduction in the confining pressure for the ascending magma prior to explosive fragmentation perhaps related to unroofing during progressive excavation of the overlying maar crater thus joya honda does not support maar formation models that invoke downward displacement of explosion foci caused by formation of a cone of depression in the aquifer in order to maintain the confining pressure for the hydromagmatic blasts