present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

response of the chydorid faunas to rapid climatic changes in four alpine lakes at different altitudes abstract the subfossil assemblages of chydoridae from late glacial preboreal sediments of four sites from 603 m to 2290 m asl were analysed to trace the community response to rapid climatic warming that occurred at this period of time in each site distinct signals at the younger dryas preboreal boundary were recorded by density of remains species diversity or community composition however responses varied considerably among the sites this variation was attributed to the situation that the chydorid community structure is determined not only by temporal younger dryas preboreal boundary and spatial among the sites temperature gradients but also by the specific local ecological conditions at the sites in some species the classification with respect to cold tolerance should be reconsidered

snowball earth ocean chemistry driven by extensive ridge volcanism during rodinia breakup the cryogenian snowball earth glaciations were followed by the deposition of massive cap carbonates geochemical modelling suggests that shallow ridge volcanism supplied much of the alkalinity and cations that fuelled this deposition

integrated paleomagnetic and upb geochronologic studies of mafic intrusions in the southern canadian shield implications for the early proterozoic polar wander path abstract integrated paleomagnetic and u pb geochronologic studies are critical to establishing well dated apparent polar wander paths in the precambrian by collecting samples for both paleomagnetism and u pb geochronology at the same sampling sites and conducting rigorous paleomagnetic field tests to ensure that magnetizations are primary it is now possible to establish the age of paleomagnetic poles with uncertainties of no more than a few million years we have conducted such integrated studies on mafic intrusions of the southern superior province and adjacent portions of the southern province of the canadian shield these studies yield paleomagnetic tiepoints with high precision ages for use in polar wander path construction in the 2220 to 2110 ma period they indicate a direction of polar wander contrary to that of the most widely used paths for the superior province and for the canadian shield as a whole thus current interpretations of the movement of the superior province and the relative location and movement of the superior province and other structural elements of the canadian shield during this period are no longer valid

palaeomagnetism of red beds from the kimberley group western australia implications for the palaeogeography of the 1 8 ga king leopold glaciation abstract the 1 8 ga king leopold glaciation in northwestern australia is recorded in the kimberley basin by subglacial erosional forms cut in an unconformity surface at the top of the speewah group and buried by glaciofluvial deposits at the base of the king leopold sandstone the lowest formation of the kimberley group the glaciofluvial deposits are conformably overlain by texturally mature locally glauconitic quartzarenite of shallow marine origin implying that glaciation occurred near sea level palaeomagnetic data for five sites 29 specimens in the hematite bearing elgee siltstone of the upper kimberley group in the northeastern kimberley basin gave a dip corrected mean direction of declination d 95 4 inclination i 13 8 95 9 7 indicating a palaeolatitude 7 0 5 3 5 0 results for red beds from five sites 28 specimens in the conformably overlying pentecost sandstone gave a dip corrected mean direction of d 94 1 i 13 0 95 11 7 6 6 6 4 5 9 combining our data for the elgee siltstone and pentecost sandstone with results for the elgee siltstone in the southeastern kimberley basin li z x 2000 palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia geophysical journal international 142 173 180 yielded a dip corrected mean direction for 17 sites of d 93 5 i 15 1 95 4 4 palaeolatitude 7 7 2 3 and an overall pole position at latitude p 5 4 s longitude p 211 8 e with confidence semi axes dp 2 3 and dm 4 5 a positive fold test at 99 confidence was obtained for the combined data for the 17 sites the basinwide concordance of results for the elgee siltstone and the positive fold test argue for an early magnetisation acquired prior to late palaeoproterozoic initial folding of the kimberley group and close to the time of deposition our results imply a low palaeolatitude for the kimberley group and the king leopold glaciation palaeomagnetic data for the 1 822 ga plum tree creek volcanics in the pine creek orogen to the east of the kimberley basin are consistent with northwestern australia being in low palaeolatitudes during the late palaeoproterozoic hence the enigma of glaciation near sea level in low palaeolatitudes which marks the neoproterozoic and early palaeoproterozoic applies also to the late palaeoproterozoic red beds from the lansdowne arkose of the speewah group also were studied but only directions ascribable to tertiary regolith weathering processes were found similar findings for the late palaeoproterozoic mcarthur basin in northern australia suggest some units in that basin also record tertiary regolith processes

depositional controls on glacial facies associations in a basinal setting late proterozoic amadeus basin central australia abstract diamictites many established as being glacial in origin are globally distributed in late protezoic rocks their widespread occurrence is important in that it implies that significant climatic events occurred during the period between 900 and 600 ma however because of the age of the rocks correlations are poor and it is difficult to establish in a convincing manner whether these sediments were deposited synchronously during a major global ice age or if each occurrence of diamictite relates to local climatic or tectonic events since the biostratigraphy of these rocks is limited and only a small number of radiometric ages are available an alternative approach to correlation is necessary the most promising approach currently available appears to be the application of sequence stratigraphy and the careful evaluation of facies associations on a site by site basis before attempting global correlations late proterozoic diamictites occur in a number of intracratonic basins in a broad belt across the ancient australian craton two late proterozoic diamictite units both previously identified as glacial in origin are exposed in the intracratonic amadeus basin of central australia the areyonga formation the older of the two units forms the basis of this study the areyonga formation is contained within a major depositional sequence the areyonga sequence the bounds of which were determined by basin dynamics and eustatic sea level changes induced by an ice age of global dimensions during deposition of this sequence three major sedimentological systems were in operation along the northern margin of the basin glaciation dominated sedimentation in the south large volumes of sediment were deposited in a shallow marine setting whilst to the west braided streams supplied sediment to a major coastal plain and delta system all three systems operated within the same sea level and basinal constraints but each contributed sediment to the basin independently the glacial sediments of the areyonga sequence were deposited from a relatively small ice cap lying between the amadeus basin and the ngalia basin to the north sediments were deposited from two tongues of ice that extended about 100 km into the northeastern corner of the amadeus basin glacial sedimentation occurred in three stages determined by the initial fall and subsequent rise in eustatic sea level as the ice sheet grew and declined initially thick massive basal till units were deposited on an erosion surface intersected by subglacial and ice marginal channels they were then followed by thinner till units separated by channel like sandstone and conglomerate with associated boulder surfaces or concentrations that were deposited by an extensive subglacial drainage network finally the subglacial deposits grade into ice proximal and ice distal shallow marine sediments deposited in part by mass movement sedimentation appears to have been terminated by a major sea level fall in the ooraminna sub basin to the east rocks originally thought to have been deposited during a second glaciation appear to be part of a lowstand wedge formed during a sea level low following the areyonga glaciation a record of the second glaciation probably does not exist in the amadeus basin similarly diamictites in the inindia beds and originally correlated with the areyonga formation have been shown to belong to the non glacial lowstand wedge of the following sequence preservation of glacial sediments is most likely to occur in a basinal setting where depositional space is being actively created in the amadeus basin depositional space was created prior to deposition of the areyonga formation by subsidence following crustal extension that occurred approximately 150 m y previously the distribution of sequence boundaries and the succession of facies associations identified in the areyonga sequence provide the basis for a depositional model for glacial sedimentation during an ice age to be successful correlation of late proterozoic glacial sediments must be based on an understanding of these facies associations and their bounding depositional surfaces associations similar to those found in the amadeus basin have been documented in other proterozoic basins suggesting that the facies associations and relationships recorded in the areyonga sequence may form the basis for a generalized model for basinal sedimentation from an ice age of global significance if this is so it should be possible to determine if a sequence containing glacial sediments is part of a global climatic event or simply due to local conditions from a single site evaluation

central european vegetation response to abrupt climate change at 8 2 ka oxygen isotope records show a major climatic reversal at 8 2 ka in greenland and europe annually laminated sediments from two lakes in switzerland and germany were sampled contiguously to assess the response of european vegetation to climate change ca 8 2 ka with time resolution and precision comparable to those of the greenland ice cores the pollen assemblages show pronounced and immediate responses 0 20 yr of terrestrial vegetation to the climatic change at 8 2 ka a sudden collapse of corylus avellana hazel was accompanied by the rapid expansion of pinus pine betula birch and tilia linden and by the invasion of fagus silvatica beech and abies alba fir vegetational changes suggest that climatic cooling reduced drought stress allowing more drought sensitive and taller growing species to out compete corylus avellana by forming denser forest canopies climate cooling at 8 2 ka and the immediate reorganization of terrestrial ecosystems has gone unrecognized by previous pollen studies on the basis of our data we conclude that the early holocene high abundance of c avellana in europe was climatically caused and we question the conventional opinion that postglacial expansions of f silvatica and a alba were controlled by low migration rates rather than by climate the close connection between climatic change and vegetational response at a subcontinental scale implies that forecasted global warming may trigger rapid collapses expansions and invasions of tree species

combined effects of tectonics and glacial isostatic adjustment on intraplate deformation in central and northern europe applications to geodetic baseline analyses 6 1 we use a suite of spherical thin sheet finite element model calculations to investigate 7 the pattern of horizontal tectonic deformation within europe the calculations incorporate 8 the effects of africa eurasia convergence atlantic ridge push forces and changes 9 in the lithospheric strength of the east european and mediterranean subdomains these 10 predictions are compared to the deformation computed for the same region using a 11 spherically symmetric self gravitating viscoelastic earth model of glacial isostatic 12 adjustment the radial viscosity profile and ice history input into the gia model are taken 13 from a model that best fits three dimensional crustal velocities estimated from the 14 bifrost fennoscandian gps network the comparison of the tectonic and gia signals 15 includes predictions of both crustal velocity maps and baseline length changes associated 16 with sites within the permanent itrf2000 and bifrost gps networks our baseline 17 analysis includes reference sites in northern and central europe that are representative of 18 sites at the center edge and periphery of the gia induced deformation baseline length 19 change predictions associated with all three reference sites are significantly impacted 20 by both tectonic and gia effects albeit with distinct geometric sensitivities in this regard 21 several of our tectonic models yield baseline rates from vaas onsala and potsdam to sites 22 below 55 n which are consistent with observed trends we find that a best fit to the 23 itrf2000 data set is obtained by simultaneously considering the effects of gia plus 24 tectonics where the latter is modeled with a relatively weak mediterranean subdomain in 25 this case the tectonic model contributes to the observed shortening between onsala 26 potsdam and sites to the south without corrupting the extension observed for baselines 27 extending from these reference sites and sites to the north this extension is well reconciled 28 by the gia process alone index terms 1208 geodesy and gravity crustal movements 29 intraplate 8110 3210 mathematical geophysics modeling 8110 tectonophysics continental tectonics 30 general 0905 9335 information related to geographic region europe keywords tectonics gia 31 intraplate deformation

bolla bollana boulder beds a neoproterozoic trough mouth fan in south australia the bolla bollana formation is an exceptionally thick ca 1500 m rift related sedimentary succession cropping out in the northern flinders ranges south australia which was deposited during the sturtian mid cryogenian glaciation lithofacies analysis reveals three distinct facies associations which chart changing depositional styles on an ice sourced subaqueous fan system the diamictite facies association is dominant and comprises both massive and stratified varieties with a range of clast compositions and textures arranged into thick beds 1 to 20 m representing stacked ice proximal glaciogenic debris flow deposits a channel belt facies association most commonly consisting of normally graded conglomerates and sandstones displays scour and fill structure of ca 10 m width and 1 to 3 m depth these strata are interpreted as channelized turbidites rare mud filled channels in this facies association bear glacially striated lonestones finally a sheet heterolithics facies association contains a range of conglomerates through sandstones to silty shales arranged into clear normally graded cycles from the lamina to bed scale these record a variety of non channelized turbidites probably occupying distal and or inter channel locations on the subaqueous fan coarsening and thickening up cycles capped by dolomicrites or mudstones are indicative of lobe build out and abandonment potentially as a result of ice lobe advance and stagnation dropstones recognized by downwarped and punctured laminae beneath pebbles to boulders in shale or in delicate climbing ripple cross laminated siltstones are clearly indicative of ice rafting the co occurrence of ice rafted debris and striated lonestones strongly supports a glaciogenic sediment source for the diamictites comparison to pleistocene analogues enables an interpretation as a trough mouth fan most probably deposited leeward of a palaeo ice stream beyond emphasizing the highly dynamic nature of sturtian ice sheets these interpretations testify to the oldest trough mouth fan recorded to date

glacial isostatic adjustment observed using very long baseline interferometry and satellite laser ranging geodesy in global space geodetic solutions radial site motions are usually estimated relative to the geocenter the center of figure of the solid earth most geodesists estimate the motion of the geocenter assuming both that sites do not move radially and that sites move laterally as predicted by plate motion model nuvel 1a demets et al 1990 1994 here we estimate the motion of the geocenter assuming that the plate interiors deform radially and laterally as predicted by the postglacial rebound model of peltier 1994 or that of peltier 1996 without assuming a priori knowledge about relative plate motion radial site motions estimated relative to this rebound adjusted geocenter are in the same reference frame as the rebound model predictions whereas site motions estimated without adjusting for rebound are not we further constrain the motion of the rebound adjusted geocenter using satellite laser ranging s sensitivity to the center of mass of the solid earth the oceans and the atmosphere by assuming that the mean velocity between the rebound adjusted geocenter and the center of mass is negligible over the time period of geodetic measurement twenty years of observation with satellite laser ranging and very long baseline interferometry record the isostatic response of the solid earth to the unloading of the late pleistocene ice sheets the misfits of the postglacial rebound model of peltier 1994 and that of peltier 1996 are 34 and 16 less respectively than the misfit of the rigid plate model sites at onsala sweden and algonquin park ontario are observed to be rising at 3 mm yr and 2 mm yr respectively reflecting unloading of the fennoscandian and laurentide ice sheets sites along the east coast of the united states are subsiding at 2 mm yr indicating that the forebulge produced by the laurentide ice sheet is currently collapsing very slowly sites beneath the margins of the ice sheets during the last glacial maximum are currently moving laterally away from the ice sheet centers at 1 5 mm yr in disagreement with the moderately fast outward motion predicted by the model of peltier 1996

carbon and oxygen isotope systematics of a paleoproterozoic cap carbonate sequence from the sausar group central india abstract well preserved sedimentological features of the paleoproterozoic age sausar group of central india indicate glaciogenic origin for the diamictite in the lower part of the unit deglaciation was responsible for a marine transgression and the deposition of proximal glaciomarine facies and a cap carbonate followed by fine clastics with manganese ore analyses of 13 c and 18 o contents in the carbonate unit overlying the diamictite together with sr and ba contents and ree data indicate the preservation of primary geochemical signatures the average 13 c carb content ranges between 3 1 and 0 1 v pdb having peak negative 13 c excursions of up to 7 4 v pdb similar to paleoproterozoic and neoproterozoic cap carbonates elsewhere high sr and ba contents indicate the presence of aragonite and barite precursors similar to well studied neoproterozoic cap carbonates a single continuous carbonate unit shows 13 c excursions from 4 4 to 2 6 v pdb the lithological association and chemostratigraphy are comparable with the carbonate tillite association of the huronian supergroup of canada the snowy pass supergroup of the usa the transvaal supergroup of south africa and the turee creek group of australia

strain accumulation in the new madrid and wabash valley seismic zones from 14 years of continuous gps observation the mechanical behavior and hence earthquake potential of faults in continental interiors is an issue of critical importance for the resultant seismic hazard but no consensus has yet been reached on this controversial topic the debate has focused on the central and eastern united states in particular the new madrid seismic zone struck by four magnitude 7 or greater earthquakes in 1811 1812 and to a lesser extent the wabash valley seismic zone just to the north a key aspect of this issue is the rate at which strain is currently accruing on those plate interior faults a quantity that remains debated here we address this issue with an analysis of up to 14 6 years of continuous gps data from a network of 200 sites in the central united states centered on the new madrid and wabash valley seismic zones we find that the high quality sites in these regions show motions that are consistently within the 95 confidence limit of zero deformation these results place an upper bound on strain accrual on faults of 0 2 mm yr and 0 6 mm yr in the new madrid and wabash valley seismic zones respectively for the new madrid region where a paleoseismic record is available for the past 5000 years we argue that strain accrual if any does not permit the 500 900 year repeat time of paleo earthquakes observed in the upper mississippi embayment these results together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicate that either tectonic loading rates or fault properties vary with time in the new madrid seismic zone and possibly plate wide

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

late glacial fossil midge stratigraphies insecta diptera chironomidae from the swiss alps abstract chironomid midges insecta diptera chironomidae are sensitive indicators of environmental change but relatively few studies have been made of the response of european midge faunas to the high amplitude climatic oscillations of the late glacial in this study late glacial assemblages of chironomid midges from four swiss lakes or former lakes gerzensee 603 m leysin 1230 m regenmoos 1260 m and heremence 2300 m were compared and contrasted the study focused on the response of chironomid assemblages to the beginning and end of the younger dryas cold interval c 12 690 11 485 cal yr bp and to minor cold climatic fluctuations gerzensee oscillation c 13200 12800 cal yr bp and preboreal oscillation c 113 65 11 100 cal yr bp the durations of these climatic fluctuations were defined climato stratigraphically based on oxygen isotope boundaries and the chronology was derived by correlation with grip oxygen isotope records major differences in the composition of the four lakes chironomid assemblages reflected differences in altitude and local environmental conditions nevertheless each lake fauna showed a marked response to the major and minor climatic oscillations demonstrating that large scale temperature change had an overriding influence on the distribution of chironomid midges

a negative fold test on the lorrain formation of the huronian supergroup uncertainty on the paleolatitude of the paleoproterozoic gowganda glaciation and implications for the great oxygenation event previous paleomagnetic studies of the glaciogenic gowganda and lorrain formations have identified several low inclination magnetic components of high thermal stability which suggest low latitude glaciation during deposition of the huronian supergroup canada while extraordinary claims demand extraordinary proof prior authors have been unable to support their interpretations of these components conclusively with any of the classic field stability tests e g conglomerate fold and baked contact capable of demonstrating that the magnetization was acquired at or soon enough after the time of deposition to be used to constrain the paleolatitude of the gowganda or lorrain formations we report here the results of a fold test from the purple siltstone member of the lorrain formation near the town of desbarats ontario which indicate that none of the reported components dates to the time of deposition hence the paleolatitude of the gowganda glaciation is uncertain comparison of the lithostratigraphic paleomagnetic and radiometric constraints on the huronian sequence and the transvaal supergroup of southern africa implies that the one verified low latitude paleoproterozoic glacial event the makganyene glaciation transvaal supergroup south africa is younger than the three glacial units of canada with this correlation the physical rock record indicates that the great oxygenation event began in the time interval between the gowganda and makganyene glaciations these data are consistent with the sudden evolution of oxygenic photosynthesis destroying a methane greenhouse and thereby triggering the first snowball earth event in earth history

a comparison of strain rates and seismicity for fennoscandia depth dependency of deformation from glacial isostatic adjustment summary we investigate the influence of the glacial isostatic adjustment gia on the deformation at the surface and at seismogenic depths in fennoscandia the surface strain rate field derived from geodetic data is controlled by gia which causes nw se extension of up to 4 10 9 yr 1 in most of mainland fennoscandia surrounded by regions of radial shortening towards the centre of uplift the seismic deformation field derived from a new compilation of focal mechanisms shows consistent nw se compression on the norwegian continental margin and a tendency towards tension in mainland fennoscandia the seismic moment rate is at least two orders of magnitude smaller than the geodetic moment rate we propose that the low level of seismicity and the tendency towards tensional focal mechanisms in mainland fennoscandia may be explained by the destructive interference of the regional stress from ridge push with the flexural stress due to gia

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

a new velocity field for africa from combined gps and doris space geodetic solutions contribution to the definition of the african reference frame afref 1 we analyzed 16 years of gps and 17 years of doppler orbitography and radiopositioning integrated by satellite doris data at continuously operating geodetic sites in africa and surroundings to describe the present day kinematics of the nubian and somalian plates and constrain relative motions across the east african rift the resulting velocity field describes horizontal and vertical motion at 133 gps sites and 9 doris sites horizontal velocities at sites located on stable nubia fit a single plate model with a weighted root mean square residual of 0 6 mm yr maximum residual 1 mm yr an upper bound for plate wide motions and for regional scale deformation in the seismically active southern africa and cameroon volcanic line we confirm significant southward motion 1 5 mm yr in morocco with respect to nubia consistent with earlier findings we propose an updated angular velocity for the divergence between nubia and somalia which provides the kinematic boundary conditions to rifting in east africa we update a plate motion model for the east african rift and revise the counterclockwise rotation of the victoria plate and clockwise rotation of the rovuma plate with respect to nubia vertical velocities range from 2 to 2 mm yr close to their uncertainties with no clear geographic pattern this study provides the first continent wide position velocity solution for africa expressed in international terrestrial reference frame itrf2008 a contribution to the upcoming african reference frame afref except for a few regions the african continent remains largely under sampled by continuous space geodetic data efforts are needed to augment the geodetic infrastructure and openly share existing data sets so that the objectives of afref can be fully reached

the ongeluk basaltic andesite formation in griqualand west south africa submarine alteration in a 2222 ma proterozoic sea abstract the ongeluk lavas form part of the palaeoproterozoic transvaal griqualand west supracrustal sequence of the archaean kaapvaal craton of south africa they form a thick shallow marine volcanic sequence of pillow lava massive flows and hyaloclastite which together with their comagmatic subaerial hekpoort correlate once covered most of the craton in this study the magmatic composition and alteration features of ongeluk samples were distinguished using geochemistry and radiogenic isotopes the ongeluk hekpoort magma was a basaltic andesite derived from anomalous kaapvaal craton lithosphere with a long history of high u pb high rb sr and chur like sm nd ratios little evidence for magmatic fractionation was found although contamination of the lower lavas with cr rich material is evident in both hekpoort and ongeluk sequences the alteration of ongeluk lavas is characterised using diagrams which compare pillow core rim pairs hyaloclastite and massive lava samples with the estimated original magma composition alteration is ascribed to a shallow 87 sr 86 sr ratios decreased from magmatic 0 7071 towards seawater 0 7025 during submarine alteration the rb sr system also reveals a much later 1200 ma phase of ca and rb mobility in a few samples in contrast the submarine alteration affected pb isotope ratios so little that a 2222 13 ma isochron age is regarded as a refinement of earlier dates for the ongeluk hekpoort extrusion the ongeluk hyaloclastites acted as a sink for k and rb in the overlying sea while the mn and ca entering the sea could have contributed to the overlying kalahari manganese deposits

intraplate deformation in western europe deduced from an analysis of the international terrestrial reference frame 1997 itrf97 velocity field although tectonic deformation in western europe is essentially concentrated in the appenines and alpine alps pyrenees mountain ranges several large historical and instrumentally recorded earthquakes m 6 are known in the supposedly stable part of europe because of its accuracy and internal consistency at a global scale the international terrestrial reference frame 1997 itrf97 velocity field allows testing of intraplate rigidity in western europe at a millimeter per year level using the full statistical information available on the itrf97 velocities we identify a subset of sites located in central europe that satisfies a rigid cap rotation with residual velocities 1 mm yr and therefore provide a stable europe reference frame serf in this reference frame we find residual velocities at european itrf sites that are consistent with known active tectonic features we identify a northward motion at sites located in italy with internal deformation of the adriatic block rather than rigid plate motion and a westward motion of the westernmost part of europe of the order of 1 2 mm yr relative to central europe the relative motion of the adriatic block and western europe agrees with the current extension known in the tyrrhenian sea and the apennines in central europe we find active deformation 1 mm yr in the eastern alps and western carpathians in the alpine range our results indicate e w extension across the western alps and n s compression across the central and eastern alps in agreement with the strain regime deduced from seismotectonic observations in belgium and the netherlands we find residual velocities of 1 1 5 mm yr to the northwest at all the sites most likely accommodated along the upper and lower rhine graben structures an important outcome of this study is the identification of internal deformation of the order of 1 2 mm yr in an area usually interpreted as stable europe this result should be further checked as new denser and more accurate space geodetic data sets with longer observation time spans become available for europe

palaeomagnetism of the early palaeoproterozoic volcanic hekpoort formation transvaal supergroup of the kaapvaal craton south africa

deglaciation induced vertical motion of the north american continent and transient lower mantle rheology the last deglaciation event of the current ice age which began approximately 18 000 years ago and ended about 7000 years ago continues to exert a profound influence on the vertical motion of the solid earth in and surrounding the regions which were once ice covered observations of such vertical motions may be employed to constrain the radial viscoelastic structure of the planet and therefore to contribute in an important way to the understanding of geodynamic processes in general in this paper both present day rates of vertical motion as recorded on tide gauges and long time scale records of vertical motion as recorded in 14c controlled relative sea level histories are employed to refine previously constructed models of the radial viscoelastic structure an interesting sidelight to this analysis is the demonstration that the lower mantle viscosity inferred from the vertical motion data could represent a transient rather than the steady state value a fact which would help considerably to reconcile the small viscosity stratification required by the glacial rebound data with the large stratification which seems to be required by some recent analyses of the geoid height anomalies associated with internal density heterogeneity of the mantle which has been revealed by application of seismic tomographic techniques a further product of these new analyses is obtained by the application of the glacial isostatic adjustment model to filter this signal from the secular trends of relative sea level observed on tide gauges from both the east and west coasts of the north american continent these results may be important in the context of recently proposed scenarios of climatic change

transvaal supergroup carbonates implications for paleoproterozoic δ18o and δ13c records abstract the paleoproterozoic interval is characterized by the first evidence for incontrovertibly free oxygen in the ocean atmosphere system in this study carbonates from the transvaal group the silverton lucknow rooinekke and particularly the duitschland formations were analyzed for isotopes of carbon oxygen and strontium in order to constrain models dealing with the patterns of seawater evolution although the trace element data showed variable alteration of the carbonate samples selected samples with a lesser degree of alteration yielded interpretable results the best measured 87sr 86sr isotope value of 0 7031 at 2 35 ga ago fits well with the published curve for precambrian seawater confirming that paleoproterozoic budget of sr was dominated by input from continental sources during the paleoproterozoic times carbonates with 13c values of about 10 are known to have been present worldwide and they have been studied also during this research the observation that in the duitschland formation such high isotope values and normal marine values were both present within a single formation indeed within its single beds suggested that the large spread of 13c values reflects local or regional rather than global phenomena the oxygen isotope data show a large spread of values from 3 to 16 while their corresponding 13c signals are almost unchanged over this entire range with the lucknow and silverton formations clustering around 10 and the rooinekke formation around 2 the duitschland formation has a bimodal distribution with both 13c populations present the last formation also contains samples with 18o as low as 20 particularly in the vicinity of the bushveld intrusive body these highly 18o depleted samples show homogenization of 13c values towards 5 modelling suggests that the trends could have resulted from post depositional alteration by basinal fluids at near surface to about 50 c temperatures in a rock buffered system the duitschland formation samples particularly at duitschland farm the locality closest to the bushveld complex were then further altered at temperatures up to about 80 c in response to this intrusion

land motion estimates from gps at tide gauges a geophysical evaluation summary space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy monitoring vertical land motion is nonetheless of crucial interest in observations of long term sea level change or postglacial rebound measurements here we present a global vertical velocity field obtained with more than 200 permanent gps stations most of them colocated with tide gauges tgs we used a state of the art homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr we associate realistic uncertainties to our vertical rates taking into account the time correlation noise in the time series the results are compared with two independent geophysical vertical velocity fields 1 vertical velocity estimates using long term tg records and 2 postglacial model predictions from the ice 5g vm2 adjustment the quantitative agreement of the gps vertical velocities with the internal estimates of vertical displacements using the tg record is very good with a mean difference of 0 13 1 64 mm yr 1 on more than 100 sites for 84 per cent of the gps stations considered the vertical velocity is confirmed by the tg estimate to within 2 mm yr 1 the overall agreement with the glacial isostatic adjustment gia model is good with discrepancy patterns related either to a local misfit of the model or to active tectonics for 72 per cent of the sites considered the predictions of the gia model agree with the gps results to within two standard deviations most of the gps velocities showing discrepancies with respect to the predictions of the gia model are however consistent with previously published space geodesy results we in turn confirm the value of 1 8 0 5 mm yr 1 for the 20th century average global sea level rise and conclude that gps is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr 1

co2 drawdown and cooling at the onset of the great oxidation event recorded in 2 45 ga paleoweathering crust abstract the archean atmosphere is thought to have been devoid of oxygen but instead containing high concentrations of greenhouse gases such as co2 and possibly ch4 that were required to keep the earth surface environments warm enough for maintenance of liquid water under faint young sun conditions earlier studies have suggested that the co2 concentrations must have been as high as over 1000 times present atmospheric levels pal to overcome the effects of weaker solar luminosity however more recent studies of precambrian paleosols imply existence of at least tenfold lower but still high pco2 levels the appearance of minute amounts of atmospheric o2 at the transition of archean and proterozoic is well documented however the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated different paleoclimate proxies of the 2 45 ga kuksha paleoweathering crust suggest its formation in a cool temperate climate paleoatmospheric pco2 estimates by geochemical and isotopic mass balance models suggest remarkably low paleoatmospheric co2 levels with the best guess estimates of atmospheric co2 between 1 and 10 pal we speculate that the kuksha paleoweathering crust either predates or partly overlaps with the onset of huronian glaciation and corresponds to a time interval of low co2 level during the first recorded large glaciation in earth history

cyclostratigraphic constraints on the duration of the datangpo formation and the onset age of the nantuo marinoan glaciation in south china abstract constructing an accurate timeline is critical for reconstructing the earth systems through critical transitions in climate geochemistry and life existing dates constrain synchronous initiation ca 717 ma and termination ca 660 ma of the sturtian glaciation from multiple continents the termination of the younger marinoan glaciation is also well dated at ca 635 ma but the onset of this glaciation is only roughly constrained as ca 654 ma south china and ca 639 ma namibia to test if the marinoan glaciation started close to ca 654 ma or ca 639 ma we have conducted a cyclostratigraphic study on the cryogenian non glacial datangpo formation that conformably overlies and underlies sturtian and marinoan glacial diamictites respectively in a deep water basin section in south china a total of 28 765 magnetic susceptibility ms measurements from a drillcore of the 292 m thick muddy siltstone and shale dominated datangpo formation are used for cyclostratigraphic analysis the results reveal significant decameter to meter scale sedimentary cycles of 16 12 m 3 6 3 0 m 1 0 0 8 m and 0 6 0 4 m the ratios of these cycle wavelengths match well with those of the milankovitch cycles calibrated for the cryogenian period the established astrochronologic time scale suggests that the duration of the datangpo formation is about 9 8 million years together with the radiometric age of ca 660 ma for the termination of the sturtian glaciation the cyclostratigraphic data suggest that the nantuo marinoan glaciation in south china initiated at ca 650 ma which is slightly younger than but consistent with the ca 654 ma u pb age from the top of the datangpo formation in shelf sections this age however is significantly older than the ages obtained from marinoan age glacial diamictites in south china ca 636 ma and namibia ca 639 ma given that most of the shelf sections may have suffered from glacial erosion obtaining the onset age of the marinoan glaciation should focus on relatively complete deep water successions

investigation of glacial isostatic adjustment in the northeast u s using gps measurements 1 we have been observing three dimensional site velocities at over 60 permanent gps stations in the northeastern u s for the purpose of inferring mantle viscosity and thus improving current models of glacial isostatic adjustment gia we estimate the upper and lower mantle viscosity by comparing radial site velocities from a subset of continuous gps measurements with numerical gia predictions our inferences are consistent with previous esti mates obtained using different methods and data sets

vertical crustal motion determined by satellite altimetry and tide gauge data in fennoscandia 1 we present a new method of combining satellite altimetry and tide gauge data to obtain improved estimates of absolute or geocentric vertical crustal motion at tide gauges within a semi enclosed sea as an illustration we combine topex poseidon altimetry data 1992 2001 and 25 long term 40 years tide gauge records around the baltic sea region of fennoscandia an area where crustal deformation is dominated by glacial isostatic adjustment gia a comparison of the estimated vertical motion at 1 11 mm yr with independent solutions from 10 collocated bifrost gps sites shows a difference of 0 2 0 9 mm yr thus verifying the accuracy and robustness of the procedure the solution uncertainty is estimated at 0 4 mm yr which is significantly lower than previous analyses of this type we conclude that our technique can potentially provide accurate vertical motion observations globally where long term tide gauge records exist

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

tests of glacial rebound models for fennoscandinavia based on instrumented sea and lake level records summary evidence for changing sea levels in northwestern europe related to glacial rebound is found in both the geological record of the past millennia and in the instrumental records of the past two centuries the latter records are of two types records of sealevel change primarily from the baltic and the gulfs of finland and bothnia and records of the tilting of some of the larger lakes in both finland and sweden the sealevel records are particularly important because of their long duration and high quality their large number and good spatial distribution and the spatially coherent background noise the two instrumental data types are complementary and provide constraints on the upper mantle rheology and on the distribution of ice during the late glacial stage comparisons of the observed rates of change of the water levels with models for glacial rebound yield earth models with a lithospheric thickness of 80 100 km and an uppermantle viscosity of 4 5 1020 pa s evective parameters that are consistent with those obtained from the analysis of the geological evidence for the same region the mareograph results support ice sheet models in which the late weichselian ice thickness over the eastern and southern parts of fennoscandia is relatively thinner than that for the western region also consistent with the interpretation of the geological evidence for sea level change in addition the instrumental records provide constraints on the eustatic sea level change for about the past 100 years a satisfactory separation of the earth rheology parameters from this rate of change can be achieved by estimating the latter only from those records for which the predicted isostatic evects are small a check on these results is possible by using the lake level records to establish constraints on the earth model parameters and the sea level records to constrain also the eustatic change all approaches lead to an average eustatic sea level rise for the past century of about 1 1 0 2 mm yr 1

uncertainty in the velocity between the mass center and surface of earth 1 using spectral analysis and data decimation we estimate the uncertainty in the velocity between the cumulative mass center of earth cm and geodetic sites on earth s surface knowing this velocity is crucial for evaluating space geodetic observations of continental uplift and subsidence in terms of postglacial rebound and sea level rise we find slr observations of satellite lageos to constrain the x and y components of the velocity of cm to 0 4 mm yr and the z component to 0 9 mm yr 95 confidence limits x is in the direction of 0 n0 e y of 0 n9 0 e and z of 90 n the uncertainty in z is high so that the estimate includes the independent inference made jointly using site velocities the rigid plate hypothesis and models of postglacial rebound that the true velocity of cm has a z component of 0 5 1 0 mm yr relative to that in itrf2008 uncertainty in scale rate an intermediate parameter in the determination of an itrf is 0 36 mm yr for vlbi 0 52 mm yr for slr and 0 20 mm yr for gps the scale of gps depends on that of vlbi and slr but the low gps uncertainty indicates that gps results are for the first time unbiased by changing satellite block types evidently due to newly incorporated satellite phase center variations gps constrains the velocity of cm nearly as well as slr representing a technical advance given that a gps satellite is not a sphere and responds strongly to solar radiation pressure citation argus d f 2012 uncertainty in the velocity between the mass center and surface of earth j geophys res 117 b10405 doi 10 1029 2012jb009196

vertical gps ground motion rates in the euro mediterranean region new evidence of velocity gradients at different spatial scales along the nubia eurasia plate boundary we use 2 5 to 14 years long position time series from 800 continuous global positioning system gps stations to study vertical deformation rates in the euro mediterranean region we estimate and remove common mode errors in position time series using a principal component analysis obtaining a significant gain in the signal to noise ratio of the displacements data following the results of a maximum likelihood estimation analysis which gives a mean spectral index 0 7 we adopt a power law white noise stochastic model in estimating the final vertical rates and find 95 of the velocities within 2 mm yr with uncertainties from filtered time series 40 smaller than from the unfiltered ones we highlight the presence of statistically significant velocity gradients where the stations density is higher we find undulations of the vertical velocity field at different spatial scales both in tectonically active regions like eastern alps apennines and eastern mediterranean and in regions characterized by a low or negligible tectonic activity like central iberia and western alps a correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area glacial isostatic adjustment and weathering processes do not completely explain the measured rates and a combination of active tectonics and deep seated geodynamic processes must be invoked excluding areas where localized processes are likely or where subduction processes may be active mantle dynamics is the most likely process but regional mantle modeling is required for a better understanding

geodetic constraints on glacial isostatic adjustment in europe 1 direct measurements of surface deformation due to glacial isostatic adjustment gia in europe have been so far mostly limited to the present day uplift area here we use permanent gps networks results to investigate the significance of gia effects in europe south of fennoscandia we show that uplift in fennoscandia is surrounded by subsidence reaching as far south as the alps with a maximum vertical rate of 1 5 mm yr between 50 5 53 n horizontal velocity gradients show shortening between fennoscandia and north central europe with strain rates of 10 9 yr 1 and principal compressional strain axis pointing to the gulf of bothnia in a radial pattern we find a very good quantitative agreement with the 3d surface displacement predicted by milne et al 2001 although the increase of misfit in far field of fennoscandia suggests that geodetic data outside of the uplift area may bring additional constraints to the rheological parameters used in gia models

malley diabase dykes of the slave craton canadian shield u pb age paleomagnetism and implications for continental reconstructions in the early paleoproterozoic1geological survey of canada contribution 20110114 the ne trending malley dyke swarm dated herein at 2231 2 ma u pb baddeleyite extends from the central slave craton to the vicinity of the kilohigok basin and may continue farther to the nort

neoproterozoic glacial origin of the great unconformity the great unconformity a profound gap in earth s stratigraphic record often evident below the base of the cambrian system has remained among the most enigmatic field observations in earth science for over a century while long associated directly or indirectly with the occurrence of the earliest complex animal fossils a conclusive explanation for the formation and global extent of the great unconformity has remained elusive here we show that the great unconformity is associated with a set of large global oxygen and hafnium isotope excursions in magmatic zircon that suggest a late neoproterozoic crustal erosion and sediment subduction event of unprecedented scale these excursions the great unconformity preservational irregularities in the terrestrial bolide impact record and the first order pattern of phanerozoic sedimentation can together be explained by spatially heterogeneous neoproterozoic glacial erosion totaling a global average of 3 5 vertical kilometers along with the subsequent thermal and isostatic consequences of this erosion for global continental freeboard

a paleoproterozoic drowned carbonate platform on the southeastern margin of the wyoming craton a record of the kenorland breakup abstract the nash fork formation in the upper part of the early paleoproterozoic snowy pass supergroup medicine bow mountains of wyoming was deposited on a mature passive margin along the southern flank of the wyoming craton and straddles the end of the ca 2 2 2 1 ga carbon isotope excursion two drowning events marked by black shales subdivide the carbonate platform into three parts the lower nash fork formation consists of outer shelf to supratidal deposits represented by massive and stromatolitic dolomites heterolithic siliciclastics carbonates large silicified domal digitate stromatolites nodular dolomites and stromatolitic dolomites molds after evaporite crystals are pervasive in the heterolithic siliciclastics carbonates large silicified domal digitate stromatolites formed biostromes and bioherms following flooding events the middle nash fork formation comprises two intervals of black shale separated by inner shelf heterolithic siliciclastics nodular carbonates black shales are organic and pyrite rich contain turbidites and developed in response to drowning of the platform overlying massive dolomite of the upper nash fork formation was deposited in an unprotected intertidal setting and displays an upward shallowing trend terminated by a prominent karstic surface in the middle of the unit the nash fork formation is open marine with no evidence for restricted circulation on the carbonate platform the two drowning events on the carbonate platform are likely related to dissection of the mature passive margin associated with the breakup of kenorland the younger drowning event is associated with the end of the carbon isotope excursion the main building elements of the lower and middle nash fork carbonate platform are dolomitic mudstones and stromatolites macroscopic seafloor precipitates are volumetrically negligible with the exception of tufa deposits and domes in the massive and stromatolitic dolomites and possibly digitate stromatolites within domal digitate stromatolites the upper nash fork formation comprises dolomitic mudstones relatively rare stromatolites and inorganic precipitates that are more common than in the underlying carbonates styles of carbonate deposition on this early paleoproterozoic platform differ from those documented on late archean carbonate platforms there are fewer macroscopic seafloor precipitates and more dolomitic mudstones this pattern is considered to be related to a rise of the atmospheric oxygen level that led to a decrease in bicarbonate saturation in the ocean

vlbi baseline variations from the ice 4g model of postglacial rebound an analysis is presented of selected vlbi baseline variations expected as a consequence of the continuing process of glacial isostatic adjustment although these baseline variations are for the most part dominated by the radial component of the motion the tangential component can also be an important contributor to the net effect and is in fact dominant for short baselines the new calculations have been performed with the recently derived ice 4g model of the last deglaciation event of the current ice age peltier 1994 and the results demonstrate that those obtained with the previous ice 3g model are not reliable

continuous gps measurements of postglacial adjustment in fennoscandia 1 geodetic results 1 data collected under the auspices of the bifrost gps project yield a geographically dense suite of estimates of present day three dimensional 3 d crustal deformation rates in fennoscandia johansson et al 2002 a preliminary forward analysis of these estimates milne et al 2001 has indicated that models of ongoing glacial isostatic adjustment gia in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3 d velocity field in this study we revisit our previous gia analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the bifrost rate estimates to establish insight into the physics of the gia response in the region we begin by decomposing a forward prediction into the three contributions associated with the ice ocean and rotational forcings from this analysis we demonstrate that recent advances in postglacial sea level theory in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin involve peak signals that are larger than the observational uncertainties in the bifrost network the forward analysis is completed by presenting predictions for a pair of fennoscandian ice histories and an extensive suite of viscoelastic earth models the former indicates that the bifrost data set provides a powerful discriminant of such histories the latter yields bounds on the assumed constant upper and lower mantle viscosity nu um nu lm specifically we derive a 95 confidence interval of 5 x 10 20 less than or equal to nu um less than or equal to 10 21 pa s and 5 x 10 21 less than or equal to nu lm less than or equal to 5 x 10 22 pa s with some preference for elastic lithospheric thickness in excess of 100 km the main goal of the bayesian inverse analysis is to estimate the radial resolving power of the bifrost gps data as a function of depth in the mantle assuming a reasonably accurate ice history we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle we conclude that the bifrost data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer however these data provide little constraint on viscosity in the bottom half of the mantle finally elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity

multiple causes of earth s earliest global glaciation in the context of earth system evolution the causal factors driving the palaeoproterozoic huronian global glaciations occupy a central position the rise of o2 at 2320 ma which eliminated most of the methane was not apparently a single cause triggering the glaciation at c 2450 ma mantle plume driven continental uplifts led to the emplacement of voluminous continental flood basalts in low latitudes that were subsequently dissected by rifting major topographical features and continental drainage patterns were most likely similar to those in younger continental flood basalt provinces and would have enabled deep weathering and erosion of extensive basalt covered continental areas intense consumption of atmospheric co2 by silicate weathering of fresh basaltic surfaces would have been further amplified by a constant organic carbon burial rate these factors similar to those of younger glacial periods in combination with the diminished ch4 greenhouse led to an onset of global cooling at the million year timescale

holocene tree immigration and the chironomid fauna of a small swiss subalpine lake hinterburgsee 1515 m asl early holocene reforestation by stone pine pinus cembra and tree birch betula pubescens took place ca 500 years after the end of the younger dryas at hinterburgsee a small subalpine lake in the northern swiss alps during the next ca 3000 years the local vegetation consisted of open woodlands with many pioneer dwarf shrubs and herbs the expansion of silver fir abies alba at ca 7400 calibrated radiocarbon years before present cal bp and norway spruce picea abies at ca 6000 cal bp in hinterburgsee s catchment led to a closing of the local forests with a successive decrease in erosion and a distinct change in hinterburgsee s sediment composition first signs of probably human induced openings of the catchment forest are apparent at ca 2500 cal bp but it is not until the past ca 800 years that pollen analysis suggests strong local and regional anthropogenic activity the strongest and most abrupt changes in the holocene development of hinterburgsee s chironomid fauna took place at ca 11 500 cal bp and at ca 10 000 cal bp when parts of the alpine taxa that were dominant during the younger dryas disappeared from the lake the first change is most likely related to the increasing temperatures after the end of the younger dryas the second possibly to decreasing lake depth and increasing summer insolation in the early holocene that may have led to warmer bottom water temperatures in the lake no clear relationship between the changes in catchment vegetation and the development of the chironomid fauna was found possibly the increase in sediment organic matter associated with the denser catchment forests was responsible for a succession in the chironomid stratigraphy between 7000 and 4500 cal bp however due to the high sedimentation rates in hinterburgsee this trend could also be a consequence of or be promoted by the sediment infilling of the lake basin this conjecture is supported by the increasing importance of tanytarsus lugens type a chironomid taxon dominant in the extant chironomid assemblages of shallow mountain lakes in switzerland the only shift in the chironomid fauna that clearly parallels a change in catchment vegetation is found during the past ca 800 years we discuss possible reasons for the comparatively weak influence of catchment vegetation on the chironomid fauna of hinterburgsee and the implications of our results for multi proxy studies on past climate involving both palaeobotanical and chironomid based reconstructions 2002 elsevier science b v all rights reserved

rapid late miocene rise of the bolivian altiplano evidence for removal of mantle lithosphere abstract the oxygen isotopic compositions of carbonates deposited in the northern altiplano demonstrate a rapid change in late miocene time which we attribute to an increase in elevation rainfall samples over an elevation transect adjacent to the altiplano of northern bolivia display a systematic decrease in mean annual 18 o values and define a local 18 o vs altitude gradient r gonfiantini m a roche j c olivry j c fontes g m zuppi the altitude effect on the isotopic composition of tropical rains chem geol 181 2001 147 167 which we apply to paleo meteoric water values determined from carbonates age constraints from magnetostragraphy and paleoelevation estimates suggest surface uplift of 2 5 to 3 5 km occurred between 10 3 ma and 6 8 0 4 ma when the altiplano rose to its current elevation only the removal of dense eclogitic lower crust and mantle lithosphere can generate a change of this magnitude and rapidity this change coincides with an 30 decrease in the rate of convergence between the south america and nazca plates and the propagation of deformation into the eastern subandean zone which we infer to have resulted from the increase in the force per unit length applied by the elevated andean plateau to the surrounding lowlands

constraining models of postglacial rebound using space geodesy a detailed assessment of model ice 5g vm2 and its relatives summary using global positioning system very long baseline interferometry satellite laser ranging and doppler orbitography and radiopositioning integrated by satellite observations including the canadian base network and fennoscandian bifrost array we constrain in models of postglacial rebound the thickness of the ice sheets as a function of position and time and the viscosity of the mantle as a function of depth we test model ice 5g vm2 t90 rot which well fits many hundred holocene relative sea level histories in north america europe and worldwide ice 5g is the deglaciation history having more ice in western canada than ice 4g vm2 is the mantle viscosity profile having a mean upper mantle viscosity of 0 5 1021 pa s and a mean uppermost lower mantle viscosity of 1 6 1021 pa s t90 is an elastic lithosphere thickness of 90 km and rot designates that the model includes rotational feedback earth s response to the wander of the north pole of earth s spin axis towards canada at a speed of 1 myr 1 the vertical observations in north america show that relative to ice 5g the laurentide ice sheet at last glacial maximum lgm at 26 ka was 1 much thinner in southern manitoba 2 thinner near yellowknife northwest territories 3 thicker in eastern and southern quebec and 4 thicker along the northern british columbia alberta border or that ice was unloaded from these areas later thicker or earlier thinner than in ice 5g the data indicate that the western laurentide ice sheet was intermediate in mass between ice 5g and ice 4g the vertical observations and grace gravity data together suggest that the western laurentide ice sheet was nearly as massive as that in ice 5g but distributed more broadly across northwestern canada vm2 poorly fits the horizontal observations in north america predicting places along the margins of the laurentide ice sheet to be moving laterally away from the ice centre at 2 mm yr 1 in ice 4g and 3 mm yr 1 in ice 5g in disagreement with the observation that the interior of the north american plate is deforming more slowly than 1 mm yr 1 substituting vm5a t60 for vm2 t90 that is introducing into the lithosphere at its base a layer with a high viscosity of 10 1021 pa s greatly improves the fit of the horizontal observations in north america ice 4g vm5a t60 rot predicts most of the north american plate to be moving horizontally more slowly than 1 mm yr 1 in agreement with the data ice 5g vm5a t60 rot well fits both the vertical and horizontal observations in europe the space geodetic data cannot distinguish between models with and without rotational feedback in the vertical because the velocity of earth centre is uncertain and in the horizontal because the areas of the plate interiors having geodetic sites is not large enough to detect the small differences in the predictions of rotational feedback going across the plate interiors

crustal velocity field of western europe from permanent gps array solutions 1996 2001 we derive a new geodetic velocity field for western europe and the western mediterranean by rigorously combining 1 a selection of 36 itrf2000 sites 2 a solution from a subset of sites of the european permanent gps network euref epn 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy of the order of i mm yr 1 or better its analysis shows that central europe defined as east of the rhine graben and north of the alps and the carpathians behaves rigidly at a 0 4 mm yr 1 level and defines a stable europe reference frame in that reference frame we find no significant motion at sites located west of the rhine graben and on the iberian peninsula which sets an upper bound of 0 6 mm yr 1 on horizontal motion across the rhine graben and the pyrenees we find that the current strain pattern in the western alps combines e w extension and right lateral shear we confirm a counterclockwise rotation of the adriatic microplate which appears to control the strain pattern along its boundaries in the friuli area the alps and the apennines our results also suggest that the africa eurasia plate motion in the western mediterranean may be 40 50 per cent slower that the nuvel1a plate motion model and rotated 20 30 counterclockwise

u pb geochronology and paleomagnetism of the westerberg sill suite kaapvaal craton support for a coherent kaapvaal pilbara block vaalbara into the paleoproterozoic precise geochronology combined with paleomagnetism on mafic intrusions provides first order information for paleoreconstruction of crustal blocks revealing the history of supercontinental formation and break up these techniques are used here to further constrain the apparent polar wander path of the kaapvaal craton across the neoarchean paleoproterozoic boundary u pb baddeleyite ages of 2441 6 ma and 2426 1 ma for a suite of mafic sills located on the western kaapvaal craton in south africa herein named the westerberg sill suite manifests a new event of magmatism within the kaapvaal craton of southern africa these ages fall within a ca 450 myr temporal gap in the paleomagnetic record between 2 66 and 2 22 ga on the craton our older westerberg suite age is broadly coeval with the woongarra magmatic event on the pilbara craton in western australia in addition the westerberg suite on the kaapvaal craton intrudes a remarkably similar archean proterozoic sedimentary succession to that on the pilbara craton supporting a stratigraphic correlation between kaapvaal and pilbara i e vaalbara the broadly coeval westerberg woongarra igneous event may represent a large igneous province the paleomagnetic results are more ambiguous with several different possibilities existing a virtual geomagnetic pole obtained from four sites on the westerberg sills is 18 9 degrees n 285 0 degrees e a 95 14 1 degrees k 43 4 sample based vgp n 34 16 8 degrees n 2879 9 degrees e dp 4 4 degrees dm 7 7 degrees if primary i e 2441 2426 ma it would provide a further magmatic event within a large temporal gap in the kaapvaal craton s paleoproterozoic apparent polar wander path it would suggest a relatively stationary kaapvaal craton between 2 44 ga and 2 22 ga and ca 35 degrees of latitudinal drift of the craton between ca 2 66 ga and 2 44 ga this is not observed for the pilbara craton suggesting breakup of vaalbara before ca 2 44 ga however it is likely that the woongarra paleopole represents a magnetic overprint acquired during the ophtalmian or capricorn orogeny invalidating a paleomagnetic comparison with the westerberg sill suite alternatively our westerberg virtual geographic pole manifests a 2 22 ga magnetic overprint related to ongeluk volcanism the similarity between ongeluk and westerberg paleopoles however may also infer magmatic connections if both are primary directions despite the apparent 200 million year age this difference c 2015 elsevier b v all rights reserved less

defining the translational velocity of the reference frame of earth summary earth s centre is fundamental to geodesy and geoscience because motions of sites on the surface are estimated relative to it international terrestrial reference frames itrf2000 and itrf2005 are defined by the centre of mass of earth s system cm consisting of solid earth the ice sheets the oceans and the atmosphere satellite lageos rotates about cm satellite laser ranging slr is used to estimate the velocity of cm relative to sites on the surface however itrf2000 and itrf2005 differ by 1 8 mm yr 1 suggesting that the velocity of cm is constrained poorly by slr in this study we define earth s reference frame with the centre of mass of solid earth ce site velocities estimated using slr vlbi gps and doris are corrected for a postglacial rebound model and inverted for the rotational velocities of the plates and the rotational and translational velocities of the four space techniques because the postglacial rebound predictions are relative to ce the velocity of ce relative to sites on the surface is estimated because the input slr site velocities are relative to cm the output slr translational velocity is the velocity of cm relative to ce the estimated velocity of ce does not depend strongly on the postglacial rebound model corrected for equal within uncertainties and having a root mean square of 0 5 mm yr 1 are estimates of the velocity of ce determined assuming that plate interiors are deforming radially as predicted by three postglacial rebound models and an estimate of the velocity of ce determined assuming that parts of plate interiors neither beneath nor along the margins of the late pleistocene ice sheets are not deforming laterally the velocity of ce equals within uncertainties probability greater than 5 per cent the velocity of cm in itrf2000 the velocity of ce differs significantly 0 05 per cent probability from the velocity of cm in itrf2005 earth s reference frame and we believe itrf s should be defined with the tightly constrained velocity of ce not with the poorly constrained velocity of cm because ce is believed to be moving relative to cm no faster than 0 5 mm yr 1 the velocity of ce estimated in this study is likely to be nearer the true velocity of cm than is the velocity of cm estimated using slr

observation and interpretation of fault activity in the rochefort cave belgium abstract very recent fault movements have left their imprint on the karstic morphology in caves of the belgian ardenne western europe to quantify these movements and to understand their possible causes they have been measured since 1997 in the rochefort cave where this recent geological activity is clearly visible specific extensometers adapted to the underground conditions have been developed to measure very slow fault movements in the rochefort cave the movements correspond to a normal mechanism along n070 e striking faults with a small sinistral strike slip component ten years of measurements at the fontaine bagdad fault which shows the most significant displacement in the order of 0 3 m evidences continuous relative movements of 0 04 mm year and 0 01 mm year in the fault dip and strike direction respectively if the geological displacement has been continuous the total displacement could have occurred since the end of the last glacial period microtectonic analysis from the recent striated faults suggests that the maximal principal horizontal stress is oriented n030 e this direction is similar to that of the post last glacial period compressive stress resulting from the glacial isostatic adjustment in this part of europe but is perpendicular to the direction derived in western europe from earthquake fault plane solutions we provide evidence that the fault movements cannot be caused by gravity due to the surface topography or the vacuum in the cave we propose that these fault slips are an expression of the deformation of the lithosphere due to the compressive strain acting since the end of the last glacial period in the peripheral bulge of the flexure resulting from the unloading of the large ice sheet in fennoscandia

a chironomid based holocene summer air temperature reconstruction from the swiss alps we developed a quantitative chironomid july air temperature inference model based on surface sediments from 81 swiss lakes and applied it to the holocene subfossil chironomid record of hinterburgsee a small subalpine lake in the northern swiss alps present day mean july air temperature of 11 3 c after smoothing to reduce the high between sample variability of inferred temperatures the reconstruction indicates july air temperatures of 10 4 10 9 c at the end of the younger dryas of 11 9 12 8 c during the early and mid holocene 11500 4000 cal bp and slightly lower temperatures of 11 5 12 0 c during the late holocene 3500 1000 cal bp a warming trend inferred for the past millennium is most likely an artifact of human impact on hinterburgsee s chironomid fauna rather than a genuine temperature signal the most prominent climatological events during the holocene were two periods of lower temperatures at c 10700 10500 cal bp and 8200 7700 cal bp and an abrupt shift to a cooler late holocene cl

seismology tectonic strain in plate interiors arising from r smalley jr m a ellis j paul r b van arsdale nature 435 1088 1090 2005 r smalley et al reply it is not fully understood how or why the inner areas of tectonic plates deform leading to large although infrequent earthquakes smalley et al 1 offer a potential breakthrough by suggesting that surface deformation in the central united states accumulates at rates comparable to those across plate boundaries however we find no statistically significant deformation in three independent analyses of the data set used by smalley et al and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present

from bif to red beds sedimentology and sequence stratigraphy of the paleoproterozoic koegas subgroup south africa abstract the 2 4 ga old koegas subgroup of the transvaal supergroup contains siliciclastics and iron formations it occupies a transitional stratigraphic position between the major iron formations on the kaapvaal craton and strata with evidence for oxygenation of the environment koegas siliciclastics reflect a new phase of uplift and erosion on the craton after a period of chemical deposition paleocurrent data indicate transport to the west and northwest away from the craton however no precise source area can as yet be defined rocks were deposited in foreshore to offshore environments of a prograding delta or submarine fan system immature arkosic wackes and subarkoses occur in proximal parts and pass to terrigenous mudstones and chemical iron formations in offshore environments with low detrital input lateral facies transitions and the hierarchical stratigraphic stacking pattern of the koegas subgroup allow a sequence stratigraphic interpretation in which regressive coarse siliciclastics prograded repeatedly over transgressive units of chemical iron formations metals in the transgressive units have an intrabasinal hydrothermal source similar to underlying iron formations localized iron stained detrital units resemble red beds they reflect additional diagenetic fe remobilization from deeper water iron formations or possibly a continental fe source the second possibility would imply the presence of some free oxygen in the environment

two diamictites two cap carbonates two δ13c excursions two rifts the neoproterozoic kingston peak formation death valley california stratigraphic mapping of the neoproterozoic glaciogenic kingston peak formation death valley california provides evidence for two temporally discrete extensional deformation episodes these episodes are bracketed by the sourdough limestone and noonday dolomite the facies characteristics and 13 c data ranging between 2 15 and 2 56 and 1 88 and 4 86 respectively of which make them equivalent to sturtian and varangian age cap carbonates respectively this constrains the two extensional episodes along the southwestern margin of laurentia to ca 700 ma and ca 600 ma these observations and data show that the field evidence for mid neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest neoproterozoic breakup are both correct thus neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m y or more confining rifting to within the kingston peak formation thereby places the younger proterozoic rocks of the southwestern great basin in the rift to drift tectonic phase

slow net sediment accumulation sets snowball earth apart from all younger glacial episodes during the sturtian and marinoan snowball earth episodes ice cover is thought to have extended from polar to tropical latitudes we test the supposition that such an extreme glacial climate not repeated in the subsequent 635 m y of earth history would have reduced the vigor of the hydrologic cycle and thus diminished sediment flux to the oceans with 500 sediment accumulation rates to characterize sturtian and marinoan deposits we find median accumulation rates at least four to 15 times slower than expected for phanerozoic glaciomarine deposits as characterized by 10 000 rates our comparison is conservative with respect to time span latitude and distance from the ice margin phanerozoic accumulation rates decrease systematically when averaged over longer time spans comparisons were drawn therefore at 5 and 57 m y time spans to match minimum marinoan and sturtian durations respectively cenozoic glaciomarine accumulation also slows with increasing latitude from temperate to polar climates and with increasing distance from the ice margin after accounting for time span snowball earth deposits at low latitude are found to be thinner than would be expected either for high latitude cenozoic glacial deposits or for very distal glaciomarine abyssal muds with ice rafted debris the rate discrepancy is not readily attributed to overestimates of the total marinoan or sturtian durations if sediment fluxes during warm melt intervals did approach phanerozoic rates these intervals must have occupied a much smaller proportion of snowball earth episodes than in younger glacial climates

relation between continental rifting and uplifting evidence from the suez rift and northern red sea abstract the suez rift and the northern red sea are flanked by high standing shoulders with elevations often exceeding 2 km and with a structural relief reaching 4 5 km in this area pre rifting erosion was small not more than a few hundred meters there is no evidence that a precursory uplift formed along the site of future rifting uplifting and erosion began essentially at the same time as rift faulting and magmatism in late oligocene and early miocene limes in the gebel serbal area sinai where the uplifting history is resolved best the tectonic relief reached about 800 m by the end of the early miocene and a similar amount of tectonic uplifting developed in later times other parts of the rift shoulders probably had a similar uplifting history but the total uplifting was often less considerable erosion in places more than 3 km occurred mainly since middle miocene times and caused considerable isostatic rebound this magnified the uplifting and caused the structural and topographic relief to be considerably greater than the tectonic uplifting initial uplifting and contemporaneous magmatic activity were probably caused by rising of deep hot material which thinned the lithosphere and heated it such deep seated processes probably continued to operate also during the later stages of tectonic uplifting though igneous activity no longer occurred on the surface stretching of the lower lithosphere under the rift shoulders could have also contributed to their uplifting the features of uplifting history of the studied region may well be typical of other active rifts

present rate of uplift in fennoscandia from grace and absolute gravimetry abstract fennoscandia is a key region for studying effects of glacial isostatic adjustment the associated mass variations can be detected by the gravity recovery and climate experiment grace satellite mission which observes the earth s gravity field since april 2002 as well as by absolute gravimetry field campaigns since 2003 annual absolute gravity ag measurements have been performed in fennoscandia by the institut fur erdmessung ife institute of geodesy of the leibniz universitat hannover germany within a multi national cooperation this offers a unique opportunity for validation and evaluation of the grace results in this preliminary study the grace results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the fg5 220 gravimeter of the ife the results from grace monthly solutions provided by different analysis centres show temporal gravity variations in fennoscandia the included secular variations are in good agreement with former studies the uplift centre is located west of the bothnian bay the whole uplift area comprises northern europe nevertheless the differences between the grace solutions are larger than expected and the different centre specific processing techniques have a very strong effect on possible interpretations of grace results the comparison of grace to the ag measurements reveals that the determined trends fit well with results from grace at selected stations especially for the solution provided by the gfz variations of land hydrology clearly influence results from grace and the ag measurements

glacial isostatic adjustment and the anomalous tide gauge record of eastern north america sea level variations as recorded by the global network of tide gauges represent a rich data set for studying a wide range of natural and anthropogenic phenomena such as the sea level rise induced by possible global warming for this purpose long term sea level trends must be corrected for the contaminating effects of continuing glacial isostatic adjustment1 5 gia the numerical correction procedure has for sites on the east coast of north america yielded a set of highly anomalous sea level rates characterized by systematic geographical trends2 4 5 we demonstrate that these trends are a consequence of inadequacies in the previous standard numerical prediction for gia in particular we find that the well known trends in the gia corrected tide gauge rates are eliminated if the lower mantle viscosity of the earth model used in the gia prediction is increased this result obviates the need to explain the anomalous trend as a manifestation of gulf stream ocean circulation4 or neotectonic processes2

geology petrology and o and h isotope geochemistry of remarkably 18o depleted paleoproterozoic rocks of the belomorian belt karelia russia attributed to global glaciation 2 4 ga abstract this paper deals with strongly 18o depleted down to 27 3 vsmow 1 9ga paleoproterozoic mid grade metamorphic rocks found in the belomorian belt of karelia e baltic shield the protolith of these rocks is attributed to have been altered by glacial meltwaters during the world s first 2 4 2 3 ga paleoproterozoic slushball glaciation when karelia was located near equatorial latitudes we describe in detail three and report seven new localities with unusually depleted 18o signatures that now span 220 km across the belomorian belt hydrogen isotope ratios measured in amphibole biotite and staurolite also display remarkably low values of 212 to 235 isotope mapping in the three best exposed localities has allowed us to identify the world s most 18o depleted rock located at khitostrov with a 18o value 27 in khitostrov samples zircons have normal 18o detrital cores and low 18o metamorphic rims mapping demonstrates that zones of 18o depletion occur in a concentric pattern 100 400 m in dimension and each locality displays significant 18o and d heterogeneity on a meter to centimeter scale characteristic of meteoric hydrothermal systems worldwide the zone of maximum 18o depletions usually has the highest concentration of metamorphic corundum rutile and zircon and also display doubled concentrations of insoluble trace elements zr ti cr hree these results are explained by elemental enrichment upon mass loss during hydrothermal dissolution in ph neutral meteoric fluid remarkably low 18o and d values suggest that alteration could have only happened by glacial meltwaters in a subglacial rift zone many localities with 18o depletions occur inside metamorphozed 2 4 ga gabbro noritic intrusions or near their contact with belomorian gneisses implying that the intrusions were driving meteoric hydrothermal systems during the known 2 4 ga episode of belomorian rifting given that the isotopically depleted localities now spread over 200 km the extent of the karelian ice cap is estimated to be at least that large svecofennian 1 9 ga metamorphism is seen to cause metamorphic recrystallization of hydrothermally altered rocks into coarse grained assemblages and causing local metasomatism through devolatilization of the underlying hydrous low 18o protolith further depleting d via volatilization this process led to gem quality rubies and kyanites that preserve these remarkable 18o values in the geologic record

active tectonics of the adriatic region from gps and earthquake slip vectors 1 to investigate the kinematics of the adriatic region we integrate continuous and episodic gps measurements with mw 4 5 earthquake slip vectors selected from the regional centroid moment tensor catalogue coherent motion of gps sites in the po valley in apulia and in the hyblean plateau allows us to estimate geodetically constrained angular velocities for these regions the predictions of the gps inferred angular velocities are compared with the earthquake slip vectors showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion the remarkable consistency between geodetic seismological and geological evidence of active tectonics suggests that active deformation in the central adriatic is controlled by the relative motion between the adria and apulia microplates the microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses 1 that apulia forms a single microplate with the ionian sea and possibly with the hyblean region and 2 that adria and apulia rotate in such a way as to accommodate the eurasia nubia relative motion we suggest that the present day microplate configuration follows a recent fragmentation of the adriatic promontory that during the neogene rigidly transferred the africa motion to the orogenic belts that now surround the adriatic region

gps and tectonic evidence for a diffuse plate boundary at the azores triple junction abstract we use gps bathymetric structural and seismic data to define the pattern of present deformation along the northern half of the azores plateau where the nubia eurasia plate boundary terminates at the axis of the mid atlantic ridge mar new and existing campaign gps velocities from the azores islands reveal extension oblique to a series of en echelon volcanic ridges occupied by terceira s jorge pico and faial islands in a frame of reference defined by 69 continuous gps stations on the eurasia plate terceira island moves 2 1 mm yr away from eurasia consistent with the island s location within the terceira rift and plate boundary structure the volcanic ridges south of the terceira rift move toward wsw at progressively faster rates reaching a maximum of 3 5 0 5 mm yr 2 for the pico faial volcanic ridge the hypothesis that the terceira rift accommodates all nubia eurasia plate motion is rejected at high confidence level based on the motions of sites on s jorge island just west of terceira rift all of the islands move relative to the nubia plate with pico island exhibiting the slowest motion only 1 0 5 mm yr 2 detailed bathymetry from the interior of the hypothesized azores microplate reveals faults that crosscut young mar seafloor fabric these observations and the gps evidence for distributed deformation described above argue against the existence of a rigid or semi rigid azores microplate and instead suggest that nubia eurasia plate motion is accommodated by extension across a 140 km wide zone east of the mar axis most likely bounded to the north by the northern shoulder of the terceira rift the mar spreading rate along the western end of the azores deformation zone 38 5 n 39 5 n is intermediate between the eurasia north america rate measured at 39 5 n and the nubia north america rate measured at 38 5 n consistent with the joint conclusions that the nubia eurasia boundary is broad where it intersects the mar and the azores triple junction is diffuse rather than discrete

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

estimation of small surface displacements in the upper rhine graben area from a combined analysis of ps insar levelling and gnss data the intra plate deformation of the upper rhine graben urg located in central europe is investigated using geodetic measurement techniques we present a new approach to calculate a combined velocity field from insar levelling and gnss measurements as the expected tectonic movements in the urg area are small less than 1mma 1 the best possible solutions for linear velocity rates from single technique analyses are estimated in a first step second we combine the velocity rates obtained from insar line of sight velocity rates in ascending and descending image geometries levelling vertical velocity rates and gnss horizontal velocity rates using least squares adjustment lsa focusing on the northern urg area we analyse sar data on four different image stacks ers ascending ers descending envisat ascending envisat descending using the persistent scatterer ps approach the linear velocity rates in ascending and descending image geometries respectively are estimated in an lsa from joint time series analysis of ers and envisat data vertical velocity rates from levelling are obtained from a consistent adjustment of more than 40 000 measured height differences using a kinematic displacement model horizontal velocity rates in east and north direction are calculated from a time series analysis of daily coordinate estimates at 76 permanently operating gnss sites in the urg region as the locations at which the measurement data of ps insar levelling and gnss reside do not coincide spatial interpolation is needed during several steps of the rigorous processing we use ordinary kriging to interpolate from a given set of data points to the locations of interest with a special focus on the modeling and propagation of errors the final 3 d velocity field is calculated at a 200 m grid which carries values only close to the location of ps points resulting in a mean horizontal and vertical precision of 0 30 and 0 13 mm a 1 respectively the vertical component of the combined velocity field shows a significant subsidence of about 0 5 mm a 1 in the northern part of the graben coinciding with a well known quaternary basin structure horizontal displacement rates of up to 0 8 mm a 1 in southeast direction are observed outside the graben in reasonable alignment with the average direction of maximum horizontal stress within the graben the velocity directions rotate toward east in the non subsiding part while an opposite trend is observed in the subsiding part of the graben the complexities of the observed velocity field are compatible to the geomechanical situation in our investigation area which is characterized by a transition from a restraining to a releasing bend setting glacial isostatic adjustment is another potential source influencing the observed velocity field as well as anthropogenic signals due to mining oil exploration and groundwater usage that have been identified in some places

multiple sulfur isotopes of sulfides from sediments in the aftermath of paleoproterozoic glaciations geochemical evidence reported from paleoproterozoic sediments has long been used to evaluate the transition from the anoxic archean atmosphere to an oxygenated atmosphere sulfur isotopes 32s 33s 34s and 36s in sedimentary sulfides and sulfates are an especially sensitive means to monitor this transition such that the timing of the paleoproterozoic great oxidation event can be investigated using mass independently fractionated mif sulfur isotope systematics expressed as 33s here we report data from 83 individual analyses of pyrite pyrrhotite and chalcopyrite on a new suite of 30 different samples from finland south africa wyoming and ontario that span 600 my and follow one or several snowball earth events in the paleoproterozoic the samples were measured using a high resolution secondary ion mass spectrometry technique in multicollection mode that investigates multiple sulfur isotopes in microdomains 30 m within individual sulfide grains while preserving petrographic context we focused on sediments deposited in the aftermath of the paleoproterozoic glaciations between 1 9 and 2 2 ga to trace fluctuations in atmospheric o2 concentrations that were likely affected by an interplay of o2 sinks in the atmosphere and the upper ocean and continental crust and by the emergence and diversification of aerobic organisms our results demonstrate that mif sulfur isotopes are absent in sediments deposited after the period of protracted global cooling in the paleoproterozoic and independently confirm observations that mif ceased during this time we interpret our results by integrating 33s and 34s data in sulfides 13c data in carbonates and the estimated timing of glaciation events in the paleoproterozoic data strongly hint at the presence of microbial sulfate reduction and fluctuations in the concentration of dissolved seawater sulfate and or in 34ssulfate in the aftermath of glaciations and likely were affected by changing erosion rates and nutrient delivery to the oceans these changes modulated the population of primary producers especially oxygenic photosynthesizers and led to fluctuations in the abundance of atmospheric o2 co2 and ch4 our results support the interpretation that the world wide 13ccarb excursion observed between 2 25 and 2 05 ga karhu and holland 1996 was a period of significant accumulation of o2 in the atmosphere

repeated absolute gravity measurements for monitoring slow intraplate vertical deformation in western europe in continental plate interiors ground surface movements are at the limit of the noise level and close to or below the accuracy of current geodetic techniques absolute gravity measurements are valuable to quantify slow vertical movements as this instrument is drift free and unlike gps independent of the terrestrial reference frame repeated absolute gravity ag measurements have been performed in oostende belgian coastline and at 8 stations along a southwest northeast profile across the belgian ardennes and the roer valley graben germany in order to estimate the tectonic deformations in the area the ag measurements repeated once or twice a year can resolve elusive gravity changes with a precision better than 3 7 nm s yr 95 confidence interval after 11 years even in difficult conditions after 8 15 years depending on the station we find that the gravity rates of change lie in the 3 1 8 1 nm s yr interval and result from a combination of anthropogenic climatic tectonic and glacial isostatic adjustment gia effects after correcting for the gia the inferred gravity rates and consequently the vertical land movements reduce to zero within the uncertainty level at all stations except julich due to man induced subsidence and sohier possibly an artifact due to the shortness of the time series at that station

an exceptionally thick upper proterozoic sturtian glacial succession in the mount painter area south australia the yudnamutana subgroup is a thick succession of upper proterozoic sturtian glacigenic rocks preserved in the yudnamutana trough in the northeastern part of the adelaide geosyncline in ascending order the subgroup comprises the fitton bolla bollana and lyndhurst formations the name hamilton creek member is proposed for a locally developed conglomeratic facies at the base of the fitton formation these rocks are interpreted as the products of two glacial advances the first is evidenced by the hamilton creek member which includes sediment gravity flows derived from subaqueous glacial outwash the fitton formation is composed mainly of basinal siltstones and mudstones with associated coarser grained rocks that are largely sediment gravity flows diamictites in the upper part of the formation signify the onset of a second glacial advance thick diamictites of the bolla bollana formation are interpreted as rainout deposits from floating ice derived from ice streams debouching from a steep and high hinterland into a fault controlled basin the lyndhurst formation is mainly fine grained rocks dropstones and sparse diamictites attest to the presence of some floating ice but some of the diamictites are probably mass flow deposits paleocurrent data from the yudnamutana subgroup indicate transport to the west northwest the sturtian glacigenic rocks are overlain by a transgressive shale stratigraphic similarities exist between the yudnamutana subgroup and thinner successions to the west these stratigraphic similarities probably reflect paleoclimatic changes the twice repeated sequence of diamictite followed by mudstone is attributed to two glacial advance retreat cycles local variations in thickness and stratigraphic succession are probably related to contemporaneous faulting

a chronostratigraphic framework for the north central kaapvaal craton the bushveld complex and the vredefort structure abstract sufficient geochronological data are available pertaining to the north central part of the kaapvaal craton to construct a chronostratigraphic framework for the rock units involved in the vredefort event from the basement rocks at 3170 ma to the waterberg soutpansberg groups deposited between 2025 and 1425 ma the resulting framework forms a convenient chronological guide to the geological evolution of this area and the timing of events such as that at vredefort the basement on which the supracrustal rocks were deposited stabilised from 3170 to 3060 ma but metamorphism and metasomatism of these rocks occurred up to 2800 m y ago in different parts of the craton the first unit of the wits triad the volcaniclastic dominion group was deposited at 3060 ma on the stabilising basement this was followed by the dominantly clastic witwatersrand supergroup and the overlying ventersdorp supergroup the dominantly volcanic ventersdorp rocks are 2700 m y old and form the last unit of the wits triad a considerable time gap of 200 300 ma separates the triad from the lowermost units of the overlying transvaal sequence the age of these volcanic and clastic protobasinal rocks is poorly constrained between 2500 and 2300 ma they may in fact represent eroded remnants of a more extensive depositional cycle the mainly clastic sedimentary part of the transvaal sequence pretoria group has been dated at 2224 ma the upper part of the transvaal sequence rooiberg group is only constrained by the age of the intrusive bushveld complex the bushveld basic layered rocks are well dated at 2060 ma as are the subsequent granites at 2050 ma the vredefort event which post dates the bushveld complex is reasonably well constrained by the age of the bronzite granophyre at 2000 ma deposition of the waterberg and soutpansberg groups which post date the bushveld complex is poorly constrained between the age of the bushveld granites and younger alkaline intrusives at 1425 ma but these sediments and volcanics were probably formed between 2025 and 1752 ma the waterberg group may therefore contain debris from the vredefort structure

a spectral formalism for computing three dimensional deformations due to surface loads 2 present day glacial isostatic adjustment using a spherically symmetric self gravitating linear viscoelastic earth model we predict present day three dimensional surface deformation rates and baseline evolutions arising as a consequence of the late pleistocene glacial cycles in general we use realistic models for the space time geometry of the final late pleistocene deglaciation event and incorporate a gravitationally self consistent ocean meltwater redistribution the predictions of horizontal velocity presented herein differ significantly in both their amplitude and their spatial variation from those presented in an earlier analysis of others which adopted simplified models of both the late pleistocene ice history and the earth rheology an important characteristic of our predicted velocity fields is that the melting of the laurentide ice sheet over canada is capable of contributing appreciably to the adjustment in europe the sensitivity of the predictions to variations in mantle rheology is investigated by considering a number of different earth models and by computing appropriate frechet kernels these calculations suggest that the sensitivity of the deformations to the earth s rheology is significant and strongly dependent on the location of the site relative to the ancient ice sheet the effects on the predictions of three dimensional deformation rates of altering the ice history or adopting approximate models for the ocean meltwater redistribution have also been considered and found to be important the former especially so finally for a suite of earth models we provide predictions of the velocity of a number of baselines in north america and europe we find that in general both radial and tangential motions contribute significantly to baseline length changes and that these contributions are a strong function of the earth model we have furthermore found a set of earth models which together with the ice 3g deglaciation chronology produce predictions of baseline length changes that are consistent with very long baseline interferometry measurements of baselines within europe

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

global and continental scale glaciations on the precambrian earth abstract earth s climate during the proterozoic eon was marked by major glacial events with evidence for large continental ice sheets on many cratons and with sedimentological data indicating that glaciers had extended to sea level this paper emphasizes the sedimentological and sequence stratigraphic responses to glaciations and evaluates the major driving forces of glaciations during the precambrian first and second order sequences are recognized related to continental scale fragmentation and formation of marine rift basins wherein sedimentary rocks indicate glacial influences and pronounced tectonic climatic linkages coarse syn rift deposits are typically characterized by mass flow diamictites and conglomerates it is important to undertake sedimentological facies and sequence stratigraphic analysis of these syn rift and capping passive margin sequences as well as of slope turbidite deposits which formed if enhanced subsidence of the basins was occurring more generally latitude and syn rift tectonic uplift can cause formation of glacial ice and enhance distinctive glacial influences on extensional basin sedimentation thus supporting a causal relationship between thermal subsidence and the formation of glacier ice on inland areas during the precambrian however it is suggested that long lived marine terminated glaciers also situated at low paleolatitudes were related to an extensional tectonic setting in such settings glacial deposits associated with sedimentary sequences of distinctively different origin e g carbonate and chemically mature siliciclastic sequences can well be used to detect the prominent sequence boundaries to verify depositional systems tracts internal sediment stacking patterns in sequences are indicative of dynamic processes along glaciated continental margins and without always having the need for global synchroneity in glacially influenced rift basins and continental margins it is important to recognize the sequence boundaries of significant subaerial unconformities and their correlative conformities a sequence boundary is a chronostratigraphically significant surface always produced as a consequence of a change in relative sea level these can then be well related to initiation and decay of glaciations however on land glacial deposits in a very few cases are prevented from later erosion attenuation of continental crust during rifting and breakup of the continent raises relative sea level and also many of the shallow intra cratonic basins subsided below sea level in favourable conditions being affected by major continental glaciations paleoproterozoic and neoproterozoic glacial deposits are known in north and south america south africa india western australia and fennoscandia against this background continental scale to global glaciations in the precambrian appear to be possible however views on the causes and timing of these glaciations as well as on planetary extent of ice cover are still contradictory there is a need to continue detailed sedimentological studies of pre glacial and post glacial deposits as well as to interpret syn glacial lithofacies for their inferred transportation and depositional processes pre glacial deposits especially should provide a new target to help us understand the processes that initiated these precambrian glaciations the sequence stratigraphic approach with understanding of the stacking pattern of depositional systems could prevent oversimplification and use of just single events to explain the complexity of evolution of glacially influenced precambrian continental margin sediments

neoarchaean c 2 58 ga halite casts implications for palaeoceanic chemistry possibly the most extensive and best preserved archaean halite casts yet discovered occur in the c 2 58 ga upper black reef and basal oaktree formations transvaal supergroup in mpumalanga province south africa halite casts are isolated on bedding planes range in size from c 1 mm to 20 mm and have cubic dumbbell and triangular shapes as well as hopper like pyramidal hollows on cube faces some of the casts display distinct hopper shapes characteristic of halite crystals the halite cast bearing pavements are developed within silicified mudstone interbedded with siltstone or stromatolitic dolomite associated sedimentary structures pointing to subaerial exposure include adhesion ripples and warts desiccation and prism cracks rill marks and tepee structures halite cast bearing beds are interpreted as supratidal flat or sabkha deposits the presence of isolated casts and hopper shaped crystals suggests that halite resulted from displacive growth within the sediment from supersaturated residual brines after mudstone deposition absence of any indication of the former presence of gypsum or anhydrite supports previous contentions that the neoarchaean ocean was deficient in sulphate or contained a high bicarbonate to calcium ratio such that with progressive evaporation most calcium was consumed before the gypsum stability field was reached the association of halite and carbonate in the upper black reef and basal oaktree formations constrains the palaeolatitude of the transvaal basin at 2 58 ga to subequatorial 10 30

precambrian tidal and glacial clastic deposits implications for precambrian earth moon dynamics and palaeoclimate abstract over the past decade the study of precambrian clastic tidal rhythmites stacked laminae of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided accurate palaeotidal and palaeorotational data palaeotidal records obtained from tidal rhythmites may be systematically abbreviated however and derived periods and frequencies can be misleading the validity of such values including past length of day can be assessed by testing for internal self consistency through application of the laws of celestial mechanics such a test supports the estimated length of day of 21 9 0 4 h derived from the late neoproterozoic 620 ma elatina reynella rhythmites in south australia and the indicated mean rate of lunar retreat of 2 16 0 31 cm year since 620 ma the validity of estimated lengths of day obtained from other precambrian tidal rhythmites remain unverified because the data sets contain only one primary value directly determined from the rhythmites the elatina reynella data militate against significant earth expansion at least since 620 ma and suggest that the free nutation or tipping of the earth s fluid core has undergone a resonance with the earth s annual forced nutation since the neoproterozoic glaciogenic deposits are readily distinguishable from ejecta resulting from impacts with earth crossing bodies palaeomagnetic data based on the geocentric axial dipole model for the geomagnetic field indicate that neoproterozoic and palaeoproterozoic glaciation and cold climate near sea level occurred in low palaeolatitudes this enigmatic finding may imply global glaciation or an increased obliquity of the ecliptic and is relevant to modelling the effect of ice sheet formation on the earth s obliquity history by obliquity oblateness feedback mechanisms through multidisciplinary studies clastic sedimentology and geophysics together can make substantial contributions to understanding precambrian earth moon dynamics and global palaeoenvironments

effect of climatic and palaeoenvironmental changes on the occurrence of holocene bats in the swiss alps a large scale palaeozoological study compared 45 14c dated bat remains from the southern and northern swiss alps with palaeovegetational and palaeoclimatic data four thermophilous warm demanding and four psychrophilous cold tolerant bat species mainly forest dwellers were selected for the study myotis blythii is the oldest bat species recorded in the alps i e on the southern side going back to the early holocene at 10 500 cal bp our study showed that thermophilous species e g myotis bechsteinii and rhinolophus hipposideros were most abundant during the holocene climatic optimum in central europe 10 000 4000 cal bp when warm demanding mixed forests were dominant psychrophilous species such as myotis brandtii also occurred during the climatic optimum but most of the samples fall into the onset of the late holocene sub atlantic period when summer temperatures were already declining these species declined in the southern alps after 4000 cal bp when fire was intensively used by huma

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

magnetic properties related to hydrothermal alteration processes at the escondida porphyry copper deposit northern chile fluid rock interaction related to the circulation of hydrothermal fluids can strongly modify the physicochemical properties of wall rocks in porphyry cu deposits these processes can also produce compositional and textural changes in ferromagnetic minerals which can be quantified using magnetic methods in the escondida porphyry cu deposit of northern chile each hydrothermally altered lithology is characterized by a discrete assemblage of fe ti oxide minerals these minerals have distinctive bulk magnetic susceptibility k bulk temperature dependent magnetic susceptibility and magnetic hysteresis parameters selectively altered rocks i e potassic and chloritic alteration types exhibit the highest k bulk values 3 93 10 3 si units and their hysteresis parameters indicate multidomain magnetic mineral behavior this suggests that these rocks are composed of the coarsest magnetic grain sizes within the deposit optical analyses and susceptibility temperature curves confirm that the magnetic signals in selectively altered rocks are mainly carried by secondary magnetite in contrast pervasively altered rocks i e quartz sericite and argillic alteration types exhibit low k bulk values 1 93 10 4 si units and contain smaller pseudo single domain magnetic grain assemblages this is consistent with the destruction and or reduction in size of magnetite under acidic conditions the results therefore demonstrate a genetic relationship between the hydrothermal alteration processes fe ti oxide minerals and magnetic properties of the wall rock in the escondida deposit these magnetic methods can be considered a sensitive and efficient petrophysical tool for the identification and semi quantification of alteration assemblages and facilitating the recognition and mapping of discrete hydrothermal zones during exploration and operation of porphyry cu deposits

a cryogenian chronology two long lasting synchronous neoproterozoic glaciations the snowball earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons here we present four new re os geochronology age constraints on sturtian 717 660 ma and marinoan 635 ma termination glacial deposits from three different paleocontinents a 752 7 5 5 ma age from the base of the callison lake formation in yukon canada confirms nonglacial sedimentation on the western margin of laurentia between ca 753 and 717 ma coupled with a new 727 3 4 9 ma age directly below the glacigenic deposits of the grand conglomerate on the congo craton africa these data refute the notion of a global ca 740 ma kaigas glaciation a 659 0 4 5 ma age directly above the maikhan uul diamictite in mongolia confirms previous constraints on a long duration for the 717 660 ma sturtian glacial epoch and a relatively short nonglacial interlude in addition we provide the first direct radiometric age constraint for the termination of the marinoan glaciation in laurentia with an age of 632 3 5 9 ma from the basal sheepbed formation of northwest canada which is identical within uncertainty to u pb zircon ages from china australia and namibia together these data unite re os and u pb geochronological constraints and provide a refined temporal framework for cryogenian earth history

soft sediment deformation of late pleistocene sediments along the southwestern coast of the baltic sea ne germany a 1 460 m long profile of a late glacial subglacial glacio fluvial glacio limnic and glacio deltaic sequence exposed at a cliff section on usedom island sw baltic sea coast is described the sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting soft sediment deformation is encountered and is associated with changes in lithology these deformations include liquefaction slumping and faulting as the most plausible cause earthquake induced shaking is discussed the associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound as the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out no large earthquakes are anticipated for northern germany although in conclusion the lithosphere of the north german basin has to be regarded as weakened by repeated ice loading and deloading

effect of ice sheet growth and melting on the slip evolution of thrust faults abstract field investigations suggest that postglacial unloading and rebound led to the formation or re activation of reverse faults even in continental shields like scandinavia here we use finite element models including a thrust fault embedded in a rheologically layered lithosphere to investigate its slip evolution during glacial loading and subsequent postglacial unloading the model results show that the rate of thrusting decreases during the presence of an ice sheet and strongly increases during deglaciation the magnitude of the slip acceleration is primarily controlled by the thickness of the ice sheet the viscosity of the lithospheric layers and the long term shortening rate in contrast the width of the ice sheet the rate of deglaciation or the fault dip have an only minor influence on the slip evolution in all experiments the slip rate variations are caused by changes in the differential stress the modelled deglaciation induced slip acceleration agrees well with the occurrence of large earthquakes soon after the melting of the fennoscandian ice sheet which led to the formation of spectacular fault scarps in particular in the lapland fault province furthermore our model results support the idea that the low level of seismicity in currently glaciated regions like greenland and antarctica is caused by the presence of the ice sheets based on our models we expect that the decay of the greenland and antarctica ice sheets in the course of global warming will ultimately lead to an increase in earthquake frequency in these regions

new palaeomagnetic results from the northern bushveld complex of south africa abstract palaeomagnetic data have been acquired from seventeen sampling sites in the northern bushveld complex transvaal south africa twelve sites are situated in the main zone in the potgietersrus area while the remaining five are in the upper zone in the villa nora area specimens were subjected to alternating field and thermal demagnetization two mean directions were found one direction represents the main zone and yields a pole at 1 6 n and 22 3 e with associated polar errors d p and d m 14 7 and 15 9 the second direction represents the upper zone in the northern bushveld complex with a virtual geomagnetic pole at 7 9 n and 359 3 e with d p d m 44 4 and 54 6 the apparent polar wander path indicates a sequential emplacement process for the bushveld complex starting with the intrusion of the critical zone and ending with the emplacement of the upper zone