pronounced zonal heterogeneity in eocene southern high latitude sea surface temperatures paleoclimate studies suggest that increased global warmth during the eocene epoch was greatly amplified at high latitudes a state that climate models cannot fully reproduce however proxy estimates of eocene near antarctic sea surface temperatures ssts have produced widely divergent results at similar latitudes with ssts above 20 c in the southwest pacific contrasting with ssts between 5 and 15 c in the south atlantic validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites here we present multiproxy data from seymour island near the antarctic peninsula that provides well constrained evidence for annual ssts of 10 17 c 1 sd during the middle and late eocene comparison of the same paleotemperature proxy at seymour island and at the east tasman plateau indicate the presence of a large and consistent middle to late eocene sst gradient of 7 c between these two sites located at similar paleolatitudes intermediate complexity climate model simulations suggest that enhanced oceanic heat transport in the south pacific driven by deep water formation in the ross sea was largely responsible for the observed sst gradient these results indicate that very warm ssts in excess of 18 c did not extend uniformly across the eocene southern high latitudes and suggest that thermohaline circulation may partially control the distribution of high latitude ocean temperatures in greenhouse climates the pronounced zonal sst heterogeneity evident in the eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands

from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

seismic and geoelectric evidence for collisional and extensional events in the fennoscandian shield implications for precambrian crustal evolution extensive deep seismic and electromagnetic sounding programs have resulted in tens of deep refraction seismic profiles normal incidence reflection profiles several hundred magnetotelluric soundings and several magnetovariational array observations results are compiled into four maps 1 moho depth 2 thickness of the lower crustal high velocity layer vp 7 km s 3 depth to the upper interface of the high velocity layer and 4 distribution of upper and middle crustal electrical conductors the moho depth is approximately 40 km in the archaean domain and varies between 40 and 65 km in the svecofennian domain most of the thickness variation 0 24 km is concentrated in the lower crustal high velocity layer electrically the crust is formed of several rather homogeneous either resistive or conductive blocks that are bounded by upper and middle crustal conductive zones the cratonized archaean crust experienced an extensional phase during which a thin mafic lower crustal high velocity layer was produced in association with mafic dykes 2 2 2 1 ga and well conducting volcanogenic and metasedimentary belts 2 5 2 0 ga the moho of the archaean domain was consequently reformed in the early proterozoic major thickening of the crust 50 65 km occurred when a svecofennian island arc and the archaean craton collided the svecofennian orogeny 1 76 1 9 ga resulted in a collage of metasedimentary rocks squeezed between crustal blocks of the island arc the internal terrane boundaries are seen as good reflectors and or inclined or vertical conductors that extend at least to the middle crust the thick high velocity 7 km s lower crust is a combination of mafic lower crust of the island arc crustal blocks and mafic additions from either delamination of the lithosphere after the collision or from a period of late svecofennian subduction the collisional boundary is also preserved as a discontinuous conductive zone between the archaean and svecofennian domains the thickened crust was subsequently thinned to 42 km along e w striking zones during an extensional period characterized by the intrusion of anorogenic rapakivi granitoid batholiths coeval mafic dykes and gabbro anorthosite bodies 1 6 1 5 ga the crust of the central part of the shield has since remained virtually intact

late eocene southern ocean cooling and invigoration of circulation preconditioned antarctica for full scale glaciation during the eocene oligocene transition eot 34 33 5 ma antarctic ice sheets relatively rapidly expanded leading to the first continent scale glaciation of the cenozoic declining atmospheric co2 concentrations and associated feedbacks have been invoked as underlying mechanisms but the role of the quasi coeval opening of southern ocean gateways tasman gateway and drake passage and resulting changes in ocean circulation is as yet poorly understood definitive field evidence from eot sedimentary successions from the antarctic margin and the southern ocean is lacking also because the few available sequences are often incomplete and poorly dated hampering detailed paleoceanographic and paleoclimatic analysis here we use organic dinoflagellate cysts dinocysts to date and correlate critical southern ocean eot successions we demonstrate that widespread winnowed glauconite rich lithological units were deposited ubiquitously and simultaneously in relatively shallow marine environments at various southern ocean localities starting in the late eocene 35 7 ma based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns we analyze southern ocean paleoceanographic change across the eot we obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward flowing wind driven currents including a westward flowing antarctic countercurrent starting at about 35 7 ma the mechanism for this oceanographic invigoration remains poorly understood the circum antarctic expression of the phenomenon suggests that rather than triggered by tectonic deepening of the tasman gateway progressive pre eot atmospheric cooling played an important role at localities affected by the antarctic countercurrent sea surface productivity increased and simultaneously circum antarctic surface waters cooled we surmise that combined these processes contributed to preconditioning the antarctic continent for glaciation

numerical modelling of deep dipole dipole mhd sounding abstract distortion effects of surface geoelectrical inhomogeneities on deep mhd soundings must be taken into account in the interpretation of the measurements computer programs which calculate these effects for the steady state part of the mhd pulses using the thin sheet approximation and which present the results graphically are used to study the distribution of apparent resistivity for various kinds of models in which the mhd generator is located off the coast of the kola peninsula

late eocene to early oligocene dinoflagellate cysts from the priabonian type area northeast italy biostratigraphy and paleoenvironmental interpretation abstract marginal marine late eocene through early oligocene dinoflagellate cyst successions have been studied from the type area of the priabonian stage northeast italy the results allow the recognition of dinoflagellate zones previously defined in bio and magnetostratigraphically well calibrated pelagic sequences from central italy thus providing a first order correlation of the priabonian stage to the standard chronostratigraphic scale with unprecedented precision within this detailed biostratigraphic framework successive shifts in the composition of the dinoflagellate cyst assemblages are interpreted in terms of sea level and sea surface temperature sst fluctuations the evaluation of ecologically and sedimentary controlled changes in the composition of dinoflagellate cyst assemblages in combination with sequence stratigraphic analysis allows the reconstruction of third and fourth order sea level fluctuations the third order sea level fluctuations appear to correspond to exxon cycles ta4 1 4 5 the stratigraphically and palaeoenvironmentally important late eocene dinoflagellate cyst species glaphyrocysta priabonensis sp nov is formally described

late quaternary protoperidinium cysts as indicators of paleoproductivity in the northern arabian sea the reliability of organic walled cysts of the heterotrophic dinoflagellate protoperidinium as paleoproductivity indicators and the influence of bottom water oxygenation on cyst preservation is assessed by using arabian sea records of the past 125 kyr as a natural laboratory multidisciplinary geochemical micropaleontological and palynological datasets are integrated to analyze the relationship between protoperidinium cyst concentrations and other paleoproductivity proxies differential preservation potential is quantified in order to establish threshold oxidative degradation values for a possible application of quantitative protoperidinium cyst records in paleoenvironmental reconstructions results indicate that variations in protoperidinium cyst concentration closely correspond to other marine productivity and or upwelling proxies although oxygenation will lead to significant cyst degradation and thus decreased concentrations down core patterns in protoperidinium cyst concentration still primarily reflect changes in sea surface productivity in view of differential preservation among dinoflagellate cysts down core variations in relative abundance of protoperidinium should be treated with caution

foraminiferal mg ca evidence for southern ocean cooling across the eocene oligocene transition constraining the magnitude of high latitude temperature change across the eocene oligocene transition eot is essential for quantifying the magnitude of antarctic ice sheet expansion and understanding regional climate response to this event to this end we constructed high resolution stable oxygen isotope 18o and magnesium calcium mg ca records from planktic and benthic foraminifera at four ocean drilling program odp sites in the southern ocean planktic foraminiferal mg ca records from the kerguelen plateau odp sites 738 744 and 748 show a consistent pattern of temperature change indicating 2 3 c cooling in direct conjunction with the first step of a two step increase in benthic and planktic foraminiferal 18o values across the eot in contrast benthic mg ca records from maud rise odp site 689 and the kerguelen plateau odp site 748 do not exhibit significant temperature change the contrasting temperature histories derived from the planktic and benthic mg ca records are not reconcilable since vertical 18o gradients remained nearly constant at all sites between 35 0 and 32 5 ma based on the coherency of the planktic mg ca records from the kerguelen plateau sites and complications with benthic mg ca paleothermometry at low temperatures the planktic mg ca records are deemed the most reliable measure of southern ocean temperature change we therefore interpret a uniform cooling of 2 3 c in both deep surface thermocline waters and intermediate deep waters of the southern ocean across the eot cooling of southern ocean surface waters across the eot was likely propagated to the deep ocean since deep waters were primarily sourced on the antarctic margin throughout this time interval removal of the temperature component from the observed foraminiferal 18o shift indicates that seawater 18o values increased by 0 6 0 15 across the eot interval corresponding to an increase in global ice volume to a level equivalent with 60 130 modern east antarctic ice sheet volume

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

the tectonic history of drake passage and its possible impacts on global climate this study provides an integrated review of plate tectonic models of the evolution of the antarctica patagonia connection compared to geological records collected on land in patagonia and tierra del fuego and offshore along the northern edge of the scotia sea a temporal framework for the sedimentary and tectonic events of the north scotia ridge and tierra del fuego is constructed with additional data compiled from entire patagonia and the austral basin this review provides robust correlations of seaways and tectonic events along the scotia and south america plates and indicates that the opening of the drake passage was not steady state since ca 30 ma rather the regions forming the present day northern limit of this gateway experienced important paleogeographic changes from deep marine basins to shallow ridges and emerged regions during the late oligocene and early middle miocene time our compilation of geological data shows that emergence along the north scotia ridge and tierra del fuego was achieved at 23 22 ma and has been followed by elimination of the patagoniano sea in patagonia starting at 22 23 ma and achieved at 20 ma this transition towards more continental sedimentation in southern south america is correlated with more shallow marine conditions in the austral basin this succession of events had a strong influence on the general geometry of the drake passage corresponding to a constriction of its northern limit starting in the window 29 22 ma and achieved at 21 ma this period of active deformation in southern south america also corresponds to a period of the global climate having two anomalies well known from the isotopic records the late oligocene warming around 26 ma and the mid miocene climatic optimum which ended between 15 and 14 ma the possible effects of the post oligocene tectonic evolution of the drake passage region on general oceanic circulation are discussed causes for the synchronicity between tectonic events and these global warming events are examined

biogeographic gradients of middle eocene oligocene calcareous nannoplankton in the south atlantic ocean middle eocene oligocene calcareous nannoplankton have been analyzed quantitatively for eight dsdp and odp sites ranging from the equatorial zone to 65 s latitude in the south atlantic ocean there is a general decrease in calcareous nannoplankton species diversity from the middle eocene through the oligocene and species diversity also decreases towards the higher latitudes similar to findings of other studies the drop of the species diversity of calcareous nannoplankton across the eocene oligocene boundary is not drastic delineation of latitudinal distribution patterns of individual species or groups and r mode cluser analysis permit the classification of warm water taxa coccolithus formosus discoasters helicosphaerids and sphenoliths temperate water taxa coccoliths pelagicus cyclicargoliths floridanus group reticulofenestra bisecta reticulofenestra samodurovii reticulofenestra umbilica and cool water taxa chiasmoliths isthmolithus recurvus and reticulofenestra daviesii the abundance of warm water taxa plummets whereas the abundance of cool water taxa sharply increases across the eocene oligocene boundary at the middle and high latitude sites reflecting a profound cooling event in these areas polar ordination and similarity analyses reveal that steep latitudinal biogeographic gradients had been established at least by the middle eocene the gradient greatly increases near the eocene oligocene boundary indicating more severe and permanent cooling at the high latitudes the biogeographic gradient data of this study conflict with the widely accepted inference from the oxygen isotopic data that the thermal gradients between mid latitudes and high latitudes are low or nearly flat for the paleogene oceans lower surface water salinities in the high latitudes may have lowered the 18o values of the planktonic microfossils but apparently did not have significant effect on latitudinal distribution patterns of calcareous nannoplankton which offers an independent means for estimating latitudinal thermal gradients

magnetobiostratigraphic chronology and palaeoenvironmental history of cenozoic sequences from odp sites 1165 and 1166 prydz bay antarctica a transect of three sites was drilled during leg 188 of the ocean drilling program odp proximal to the east antarctic ice sheet eais across the prydz bay continental shelf site 1166 slope site 1167 and rise site 1165 we present results of a palaeomagnetic and rock magnetic study of sediments recovered at sites 1165 and 1166 magnetostratigraphic interpretations are presented for both holes and are mainly constrained by diatom and radiolarian biostratigraphies interpreted in the light of recent refinements to southern ocean zonal schemes and datum calibrations for these microfossil groups site 1165 records a history of sedimentation on the continental rise extending back to earliest miocene times about 22 ma several long term changes characterise this record including an overall trend of decreasing sedimentation rates from the bottom to the top of the hole there is a progressive decrease in the sedimentation rate above about 308 mbsf meters below sea floor which is marked by a transition from dark grey fissile claystones to greenish grey diatom bearing clays at this transition ice rafted debris sand grains and total clay content also increase the chronology presented here indicates a middle miocene age 14 3 ma for the lithological transition correlation to odp hole 747a from the kerguelen plateau suggests that this lithological transition coincides with the base of the mi 3 3a 18o event which suggests palaeoclimatic control on middle miocene sedimentation changes at site 1165 core recovery was poor at site 1166 consequently the magnetostratigraphic data are of limited value the deepest cores recovered at site 1166 record brief intervals in the early history of the eais for the prydz bay region extending back through the early stage of glaciation to pre glacial times an early cretaceous fluvio lacustrine unit lagoonal deposits and sandy fluvio deltaic units of mid late eocene age contain a sporadic record of the transition from humid and mild conditions to cool temperate conditions

source field problems in northern parts of the baltic shield abstract theoretical calculations using a stationary ionospheric electrojet model are presented for a resistivity model of interest in studies of the baltic shield the earth model includes the undistorted east european platform resistivity versus depth model and crustal and asthenospheric conducting layers the results show that close to the source region for periods 15 min the magnetic field depends only weakly on the earth s conductivity accordingly the resolution of apparent resistivity curves obtained by the horizontal spatial gradient hsg technique becomes poor at longer periods close to the source region a comparison with experimental hsg apparent resistivity from kiruna and kevo in northern scandinavia supports the existence of high conductivity in the lower crust the sharp decrease of apparent resistivity at periods 1 h may within the limits of experimental error be a result of the non uniform source rather than an indication of a good conductor in the upper mantle

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

description of the polar profile transect display abstract the polar profile transect display attempts to integrate all the existing aeromagnetic gravimetric geological and geochemical investigations with the results of the deep seismic and electromagnetic studies carried out along the polar profile our description is based on the stage of joint interpretation reached at the second earth science study centre the nearly 440 km long ne sw trending polar profile traverses archaean and early proterozoic parts of the baltic shield the thickness of the crust varies between 40 and 50 km and consists of three distinct crustal layers a geological interpretation based on the various geophysical results is given for the uppermost 10 14 km thick layer in the central part of the profile the overthrust early proterozoic lapland granulite belt forms a wedge shaped body reaching the middle crust the upper crust is underlain by a transparent layer 16 18 km thick with a smooth increase in velocity and density a reflective lowermost 10 21 km thick layer has a high velocity gradient the crust mantle has a pronounced topography

integrated biomagnetostratigraphy of the alano section ne italy a proposal for defining the middle late eocene boundary the alano section has been presented at the international subcommission on paleogene stratigraphy isps as a potential candidate for defi ning the global boundary stratotype section and point gssp of the late eocene priabonian stage the section is located in the venetian southern alps of the veneto region ne italy which is the type area of the priabonian being exposed along the banks of the calcino torrent near the village of alano di piave it consists of 120 130 m of bathyal gray marls interrupted in the lower part by an 8 m thick package of laminated dark to black marlstones intercalated in the section there are eight prominent marker beds six of which are crystal tuff layers whereas the other two are bioclastic rudites these distinctive layers are useful for regional correlation and for an easy recognition of the various intervals of the section the section is easily accessible crops out continuously is unaffected by any structural deformation is rich in calcareous plankton and contains an expanded record of the critical interval for defi ning the gssp of the priabonian in order to further check the stratigraphic completeness of the section and constrain in time the critical interval for defi ning the priabonian stage we performed a high resolution study of integrated calcareous plankton biostratigraphy and a detailed magnetostratigraphic analysis here we present the results of these studies to open a discussion on the criteria for driving the golden spike that should define the middle eocene late eocene boundary

middle eocene late oligocene climate variability calcareous nannofossil response at kerguelen plateau site 748 a major deterioration in global climate occurred through the eocene oligocene time interval characterized by long term cooling in both terrestrial and marine environments during this long term cooling trend however recent studies have documented several short lived warming and cooling phases in order to further investigate high latitude climate during these events we developed a high resolution calcareous nannofossil record from odp site 748 hole b for the interval spanning the late middle eocene to the late oligocene 42 to 26 ma the primary goals of this study were to construct a detailed biostratigraphic record and to use nannofossil assemblage variations to interpret short term changes in surface water temperature and nutrient conditions the principal nannofossil assemblage variations are identified using a temperate warm water taxa index twwt from which three warming and five cooling events are identified within the middle eocene to the earliest oligocene interval among these climatic trends the cooling event at 39 ma cooling event b is recorded here for the first time variations in fine fraction 18o values at site 748 are associated with changes in the twwt index supporting the idea that significant short term variability in surface water conditions occurred in the kerguelen plateau area during the middle and late eocene furthermore odp site 748 calcareous nannofossil paleoecology confirms the utility of these microfossils for biostratigraphic paleoclimatic and paleoceanographic reconstructions at southern ocean sites during the paleogene

paleogeographic controls on the onset of the antarctic circumpolar current development of the antarctic circumpolar current acc during the cenozoic is controversial in terms of timing and its role in major climate transitions some propose that the development of the acc was instrumental in the continental scale glaciation of antarctica and climate cooling at the eocene oligocene boundary here we present climate model results that show that a coherent acc was not possible during the oligocene due to australasian paleogeography despite deep water connections through the drake passage and tasman gateway and the initiation of antarctic glaciation the simulations of ocean currents compare well to paleoenvironmental records relating to the physical oceanography of the oligocene and provide a framework for understanding apparently contradictory dating of the initiation of the acc we conclude that the northward motion of the australasian land masses and the reconfiguration of the tasman seaway and drake passage are necessary preconditions for the formation of a strong coherent acc

large scale glaciation and deglaciation of antarctica during the late eocene approximately 34 m y ago earth s climate transitioned from a relatively warm ice free world to one characterized by cooler climates and a large permanent antarctic ice sheet understanding this major climate transition is important but determining its causes has been complicated by uncertainties in the basic patterns of global temperature and ice volume change here we use an unusually well exposed coastal incised river valley complex in the western desert of egypt to show that eustatic sea level fell and then rose by 40 m 2 m y prior to establishment of a permanent antarctic ice sheet this fall in sea level is associated with a positive oxygen isotope excursion that has been interpreted to reflect global cooling but instead records buildup of an antarctic ice sheet with a volume 70 of the present day east antarctic ice sheet both the sea level fall and subsequent rise were coincident with a transient oscillation in atmospheric co2 concentration down to 750 ppm which climate models indicate may be a threshold for southern hemisphere glaciation because many of the carbon emission scenarios for the coming century predict that atmospheric co2 will rise above this same 750 ppm threshold our results suggest that global climate could transition to a state like the late eocene when a large permanent antarctic ice sheet was not sustainable

interpretation of gravity anomalies along the polar profile in the northern baltic shield abstract the polar profile in the northern baltic shield was analyzed by two and three dimensional quantitative gravity modelling interpretation of fourier amplitude spectra qualitative interpretation using bouguer anomalies and second vertical derivative and horizontal gradient maps and reference to petrophysical data densities of outcropping crustal units show several distinct modes ranging from 2600 to 2990 kg m3 in relation to the mean background density of 2690 kg m3 used in the gravity modelling the granitic crustal units 2600 kg m3 produce well defined gravity lows of up to 20 mgals and the granulites 2750 kg m3 and greenstones 2940 kg m3 cause the most pronounced gravity highs of 30 and 45 mgal the estimated thickness of the kittila greenstone belt is about 6 km in the cross section along the polar profile the base of the lapland granulite belt dips to the northeast and reaches a maximum thickness of about 16 km the thickness of the vainospaa granite body is approximately 6 km evidence of buried anomaly sources also exists our interpretation predicts units of increased density in the basement under the varanger peninsula sedimentary rocks the general pattern of a gravity high near the barents sea coast coupled with a gravity low seawards implies a thick layer of sedimentary rocks under the sea which may be compensated by crustal thinning according to the seismic refraction interpretation there is a depression in the moho under the southwestern edge of the lapland granulite belt explaining together with other features of the seismic model the regional background on which the gravity anomaly of the granulite belt is superposed according to the fourier analysis of gravity anomalies there are two dominant depth clusters of density discontinuities in the southwestern karelian province and middle parts lapland granulite belt of the polar profile the shallower discontinuity varies between 6 and 10 km and the deeper one rises from about 20 km in the southwest to about 10 km in the middle area in the northwestern part inari and sorvaranger terrains and varanger peninsula there are many separate depth values and clusters exist only at depths between 13 and 15 km

a magneto and chemostratigraphically calibrated dinoflagellate cyst zonation of the early palaeogene south pacific ocean abstract investigation of the early palaeogene palaeoecological and palaeoclimatological evolution of the polar regions is hindered by the absence of calcite microfossils in sedimentary archives which are conventionally the main dating tool to overcome this problem we have generated large datasets of organic dinoflagellate cyst dinocyst assemblages from southern ocean shelf sediments over the past decade and we here calibrate these to the geomagnetic polarity time scale gpts using magnetostratigraphy and stable isotope stratigraphy this now for the first time allows a high resolution southern pacific ocean dinocyst zonation for the late palaeocene to late eocene 58 36 million years ago ma we compile published dinocyst chronologies from ocean drilling program odp hole 1171d on the south tasman rise hole 1172a d on the east tasman plateau and integrated ocean drilling program iodp hole u1356a on the wilkes land margin correlation to dinocyst zonations from new zealand lead to revisions of the magnetostratigraphic age model at holes 1171d and 1172a d stable carbon and oxygen isotope records reveal the stratigraphic location of the palaeocene eocene thermal maximum 56 ma and the middle eocene climatic optimum 40 ma respectively the resulting zonation consists of thirteen dinocyst zones calibrated to the geomagnetic polarity time scale gpts of vandenberghe et al 2012 which can likely be applied to the entire southern ocean finally we apply the revised stratigraphy to all published tex86 data a biomarker based proxy for sea surface temperature sst from odp site 1172 to assess long term climate evolution this shows that southwest pacific sst trends mimic the global compilation of benthic foraminiferal oxygen isotopes even better than previously appreciated

heat flow and thermal structure of the lithosphere across the baltic shield and northern tornquist zone abstract terrestrial heat flow data from archean and proterozoic provinces of the baltic shield its southwestern margin and the tectonic transition to the younger tectonic units of central europe northern segment of the european geotraverse are compiled and examined for local and regional variations a 2 d numerical lithospheric temperature and heat flux model is presented covering 1800 km of the deep seismic fennolora profile across the baltic shield and 500 km of eugeno s northern eugemi seismic lines across the northern tornquist zone and the danish and north german basins thermal lithosphere defined as the outer layer with relatively low temperatures t c in which heat transfer is dominantly by conduction is found to vary markedly in thickness from 85 110 km beneath basins and tornquist zone to about 150 km in central shield areas and 200 250 km in areas of low heat flow along the northern shield profile these results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction wide angle seismic interpretation of fennolora data the combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper relatively cold thermal layer which is interpreted to constitute shield lithosphere local and to some extent regional variations in surface heat flow are found to be closely related to variations in near surface radiogenic heat production for the southern baltic shield a heat flow heat production relationship of q 0 32 8 7 6 h 0 is derived regional increase in heat flow from northern and central shield provinces to the shield margin and the tornquist zone is interpreted to be related partly to differences in upper crustal heat generation partly and in southernmost areas mainly to an increased heat flux from the upper mantle upper mantle heat flux is estimated at 20 25 mw m 2 along the northern and central shield transect increasing to 30 40 mw m 2 beneath the shield margin basins and tornquist zone lithospheric thickness variations in this region of northern europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper mantle heat flux earthquake focal depth data and information on crustal strength show baltic shield seismicity to be limited generally to the upper 20 25 km brittle part of the crust at temperatures less than 300 400 c maximum source depth of magnetic anomalies at temperatures near 600 c is in the deepest part of the crust near the crust mantle boundary in the southern region about 25 km depth along the tornquist zone and about 35 40 km in southern shield areas and in the uppermost mantle 60 70 km depth in the northern shield areas some petrologic implications are discussed the present deep crust is supposed to be at lower temperature pressure conditions than at early stages of formation however also the present deepest parts of the shield crust 35 40 km are within the stability field of eclogites the general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high density eclogites to be present in significant amounts in the deep shield crust

the crustal structure along the polar profile from seismic refraction investigations abstract seismic refraction investigations along a 440 km long profije on the northern baltic shield have resolved the crustal structure in this area of archaean to early proterozoic lithosphere formation the profile called the polar profile extends approximately along a sw ne oriented line from the karelian province in northern finland across the lapland granulite belt and the kola peninsula province to the varanger peninsula in northeastern norway at six shotpoints large explosions 200 1680 kg and at three shotpoints small explosions 80 kg were detonated and recorded at an average station spacing of 2 km providing high quality record sections a two dimensional cross section of the crust was obtained by forward modelling using ray tracing techniques high velocity bodies are found in the upper crust related to the karasjok kittila greenstone belt and the lapland granulite belt they extend to a depth of 6 13 km in the karelian province in the southwest a low velocity zone was found between the depths of 8 and 14 km the middle crust shows a slight increase in the average velocities from the southwest to the northeast and a small velocity jump is found along a mid crustal boundary between 18 and 21 km the thickness of the middle crust varies between 16 and 18 km the lower crust and the crust mantle boundary moho show considerable lateral variation the top of the lower crust lies between 26 and 33 km while its thickness decreases from 21 km in the southwest to 10 14 km beneath the lapland granulite belt and the inari terrain reaching 20 km again in the extreme northeast the velocities also change laterally the thin lower crust is characterized by rather low velocities 6 8 6 9 km s whereas in the southwest and northeast the velocities 6 9 7 3 km s resemble more typical shield structures the moho is found at 47 km in the karelian province rises to 40 km beneath the lapland granulite belt and descends to 46 km in the northeastern part of the kola peninsula province the upper mantle velocities at the moho range from 8 1 km s in the region of the thin crust to 8 5 km s and more beneath the karelian province it is tempting to suggest that the anomalous lower crust underlying the lapland granulite belt and the inari terrain may represent the remnants of an early proterozoic back arc basin that was active prior to the 2 0 to 1 9 ga plate convergence event during which the lapland granulite belt was thrust onto the archaean basement of the karelian province another explanation is to assume that the velocity reduction in the anomalous lower crust was caused by a rather pronounced uplift of this region following the 1 9 ga collision event

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

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

reflection seismic measurements across the granulite belt of the polar profile in the northern baltic shield northern finland abstract reflection seismic measurements were carried out in 1985 on the central part of the polar refraction seismic profile in northern finland the survey was planned and executed jointly by the universities of helsinki uppsala and hamburg using digital equipment with a total of 144 channels by repeating the shots and moving the geophone spreads every day we were able to observe a 42 50 km recording spread referred to reflection elements a line of 84 km total length through the source receiver midpoints was recorded we processed the results up to normal moveout corrected time sections a number of reflectors dipping 8 15 to the northeast were recorded in the lapland granulite belt range these represent a system of sheared granulites which were observed on the surface in the southern part of the profile from gravity modelling the bottom of the dipping layers coincides with the lower boundary of the granulites between the depths of 22 and 35 km the crust in this area seems to be transparent to seismic signals this leads to the assumption that the middle part of the crust is characterized by gentle velocity and density gradients the crust mantle boundary seems to be a layered moho with good reflectors lying at depths between 40 and 44 km

stepwise transition from the eocene greenhouse to the oligocene icehouse the eocene oligocene transition is the largest global cooling in the cenozoic period a comparison of three independent proxies from the continental shelf and deep ocean reveals a three step transition to cold glacial conditions with ice sheets 25 larger than their present size

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

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

a marine geophysical study of the wilkes land rifted continental margin antarctica summary the wilkes land margin of east antarctica conjugate to the southern australian margin is a non volcanic rifted margin that formed during the late cretaceous during 2000 01 and 2001 02 geoscience australia acquired 10 000 line km of seismic reflection and refraction magnetic anomaly and gravity anomaly data over the margin we have used the seismic data to estimate the sediment thickness along the margin the data reveal a deep 11 km rift basin that contains over 9 km of sediments seaward of the totten glacier western wilkes land the limits of oceanic and continental crust that underlies the thick post rift and the significantly thinner pre and syn rift sediments are equivocal seismic reflection data suggest a 30 100 km wide continent ocean transition zone cotz along the margin the cotz extends over 400 km seaward of the shelf break off the eastern wilkes land terre ad elie sector

middle eocene to early oligocene paleoceanography from agulhas ridge southern ocean ocean drilling program leg 177 site 1090 1 the agulhas ridge off the tip of africa between the atlantic and indian oceans is ideally located to capture the evolution of paleogene early neogene circulation patterns associated with global cooling multiproxy records of productivity biogenic barium baex opal caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox state of deep waters u enrichment from ocean drilling program odp site 1090 reflect hydrographic shifts in this region between the middle eocene and early oligocene 39 33 ma several peaks in increased export productivity and burial of organic matter occurred within the late eocene 36 5 34 and 33 7 ma which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pco2 to a threshold level that facilitated large ice sheet development on antarctica in the earliest oligocene our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle eocene to early oligocene by facilitating increases in the relative or absolute burial of organic carbon

antarctic glaciation caused ocean circulation changes at the eocene oligocene transition a climate model is used to show that the growth of the antarctic ice sheet at about 34 myr ago drove changes in ocean circulation but the opening of ocean gateways had relatively little impact antarctica developed an ice sheet about 34 million years ago following a period of ice free conditions known as the super greenhouse climate previous research has suggested that ice sheet growth was driven by either the thermal isolation of antarctica arising from the opening of ocean gateways or by progressively lower atmospheric co2 content matt huber and colleagues now use a climate model to show that the growth of the ice sheet forced by changes in co2 drove the changes in ocean circulation in contrast the opening of the gateways had relatively little impact on ocean circulation two main hypotheses compete to explain global cooling and the abrupt growth of the antarctic ice sheet across the eocene oligocene transition about 34 million years ago thermal isolation of antarctica due to southern ocean gateway opening1 2 3 4 and declining atmospheric co2 refs 5 6 increases in ocean thermal stratification and circulation in proxies across the eocene oligocene transition have been interpreted as a unique signature of gateway opening2 4 but at present both mechanisms remain possible here using a coupled ocean atmosphere model we show that the rise of antarctic glaciation rather than altered palaeogeography is best able to explain the observed oceanographic changes we find that growth of the antarctic ice sheet caused enhanced northward transport of antarctic intermediate water and invigorated the formation of antarctic bottom water fundamentally reorganizing ocean circulation conversely gateway openings had much less impact on ocean thermal stratification and circulation our results support available evidence that co2 drawdown not gateway opening caused antarctic ice sheet growth and further show that these feedbacks in turn altered ocean circulation the precise timing and rate of glaciation and thus its impacts on ocean circulation reflect the balance between potentially positive feedbacks increases in sea ice extent and enhanced primary productivity and negative feedbacks stronger southward heat transport and localized high latitude warming the antarctic ice sheet had a complex dynamic role in ocean circulation and heat fluxes during its initiation and these processes are likely to operate in the future

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

magnetotellurics in southwestern sweden evidence for electrical anisotropy in the lower crust magnetotelluric data from measurements conducted on the southwestern part of the baltic shield are analyzed with respect to crustal and upper mantle structures the interpretations have been done using ordinary two dimensional and transverse anisotropic layered models in which distortions of the impedance tensors due to near surface electrical structures are included in the interpretation procedures the anisotropic model is able to explain the gross features of the data whereas the two dimensional model only displays features observed at long periods the two main results from the study with anisotropic models are the interpretation of a possible transverse anisotropic lower crust and a depth to the uppermost conductive layer within the mantle of more than 200 km the minimum depth to the conductive mantle layer is found from a most squares analysis

on induction effects at eiscat and image magnetometer stations summary when ground based magnetometer data are used for ionospheric magnetospheric studies it is important to know the external ionospheric magnetospheric and internal telluric contributions to the observed total variation to study them we calculate geomagnetic induction vectors and apply the siebert kertz separation method using data from the eiscat and image magnetometer stations in fennoscandia induction vectors in the period range 20 2560s show the expected and dominating ocean effect near the arctic ocean at masi a small scale inland anomaly is detected in addition to the ocean effect at hankasalmi a man made anomaly due to the nearby stare radar is present the source effect on induction vectors at high latitudes is briefly investigated by separating the magnetic variations of several bay events at image stations into external and internal parts we study the importance of the large scale induction in the recordings depending very much on the particular event the internal horizontal part is 10 30 per cent of the total field in the auroral electrojet region and its relative contribution increases in more distant regions the internal contribution of the vertical field at inland stations is 10 40 per cent having an opposite sign to the total field or 10 30 per cent having the same sign as the total field depending on the location with respect to the ionospheric currents and to the ocean results are also discussed using a thin sheet model

two stepping into the icehouse east antarctic weathering during progressive ice sheet expansion at the eocene oligocene transition in conjunction with increasing benthic foraminiferal 18 o values at the eocene oligocene transition eot ca 34 ma coarse grained ice rafted debris ird 425 m appears abruptly alongside fossil fish teeth with continentally derived neodymium nd isotope ratios e nd in kerguelen plateau southern ocean sediments increased antarctic weathering flux as inferred from two steps to less radiogenic e nd values coincides with two steps in benthic foraminiferal 18 o values these results indicate that two distinct surges of weathering were generated by east antarctic ice growth during the eot weathering by ice sheets during a precursor glaciation at 33 9 ma did not produce significant ird accumulation during the first e nd shift glacial weathering was sustained during a terrace interval between the two steps probably by small high elevation ice sheets a large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca 33 7 ma rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions parallel changes in antarctic weathering flux and deep sea carbonate accumulation suggest that ice sheet expansion during the eot had a direct impact on the global carbon cycle possible mechanisms include associated changes in silicate weathering on the east antarctic craton and enhanced fertilization of southern ocean waters both of which warrant further investigation

magnetotelluric array data analysis from north west fennoscandia abstract new magnetotelluric mt data in north west fennoscandia were acquired within the framework of the project magnetotellurics in the scandes masca the project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable precambrian cratonic interior to passive continental margin beneath the caledonian orogen and the scandinavian mountains in western fennoscandia an array of 59 synchronous long period and 220 broad band mt sites was occupied in the summers of 2011 to 2013 we estimated mt transfer functions in the period range from 0 003 to 10 5 s the q function multi site multi frequency analysis and the phase tensor were used to estimate strike and dimensionality of mt data dimensionality and strike analyses indicate generally 2 d behaviour of the data with 3 d effects at some sites and period bands in this paper we present 2 d inversion of the data 3 d inversion models are shown in the parallel paper we choose to invert the determinant of the impedance tensor to mitigate 3 d effects in the data on our 2 d models seven crustal scale and four lithospheric scale 2 d models are presented the resistive regions are images of the archaean and proterozoic basement in the east and thin caledonian nappes in the west the middle and lower crust of the svecofennian province is conductive the southern end of the kittila greenstone belt is seen in the models as a strong upper to middle crustal conductor in the caledonides the highly conductive alum shales are observed along the caledonian thrust front the thickest lithosphere is in the palaeoproterozioc svecofennian domain not in the archaean the thickness of the lithosphere is around 200 km in the north and 300 km in the south west

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

aspects of the geoelectric models of the baltic shield abstract the geoelectric structure of the baltic shield in finland has been studied since 1980 four types of geoelectric model have been considered so far numerical models for the galvanic distortions of the upper 10 km horizontal distribution of crustal inductive anomalies vertical cross sections above relevant crustal anomalies and vertical conductivity profiles on a regional scale the models are based on extensive on going measurements being conducted with magnetovariational magnetotelluric and frequency sounding methods geoelectric studies in finland are a part of both the international elas electrical conductivity of the asthenosphere and the egt european geotraverse projects in finland the most relevant crustal conductivity anomalies south of 67 n are a conductive band surrounding the central finland granite area in the west and south and the oulu mikkeli and outokumpu anomalies n s e w and n s respectively the anomalies are located in the middle crust typically from 6 12 km downwards several regional conductivity boundaries and the existence of a conductive layer in the lower crust at least in parts of central finland have also been noted a vertical cross section across the oulu anomaly shows a wide crustal conductor which seems to dip towards the west the anomaly has exceptionally good conductivity 0 5 5 m and cannot be attributed to the known sandstone formation or the schist zone on the surface along the sveka dss deep seismic sounding profile some increases in conductivity of the upper crust correlate with the kainuu and the kuhmo schist zones the upper crustal parts of the raahe ladoga zone has also a higher conductivity than the surroundings some local conductivity anisotropies seem to coincide with deep faults located by dss the area east of kuhmo seems to be more or less free of crustal conductivity anomalies allowing electric soundings down to the upper mantle a deep conductivity model based on the measurements in this area differs from earlier models for northern scandinavia where the presence of a good conductor at asthenospheric depths has been reported variations in the electrical conductivity of the earth s crust and upper mantle thus yield information about the structural composition and the tectonic development of the earth the results now presented are only preliminary and their detailed geological tectonic importance is not yet fully understood later the models will be completed with the results from work done in both the eastern and the western parts of the shield

depth and seasonality of alkenone production along the california margin inferred from a core top transect alkenone unsaturation indices uk 37 of marine sediment could prove particularly useful on organic rich continental margins where carbonate dissolution hampers the use of other paleoclimatic proxies mccaffrey et al 1990 kennedy and brassell 1992 forty core top samples of recent sediment from a latitudinal transect 23 40 n along the california margin yield uk 37 values that correlate linearly with modern mean annual sea surface temperatures ssts in the range of 12 23 c reproducibility of the unsaturation value in closely spaced cores is near analytical error uk 37 data define a relationship to temperature nearly identical to the prahl et al 1988 laboratory cultures of emiliania huxleyi the close agreement is particularly significant in light of the nannofossil composition of the sediments where the abundance of the coccolith taxon gephyrocapsa oceanica known to synthesize alkenones equals or exceeds that of e huxleyi comparison with seasonal temperature variations at different depths indicates that little if any alkenone production occurs at depths 30 m along the continental margin water depths 2 km sediments in more pelagic locations exhibit small but consistent biases toward winter and or subsurface production similar to previously reported sediment trap and core top data from the oregon margin prahl et al 1993 doose et al 1997

magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 ocean drilling program holes 744a and 748b represent key sections for calibration of southern ocean eocene oligocene biostratigraphic zonations sites 744 and 748 were above the carbonate compensation depth throughout this time interval and contain good planktonic foraminiferal calcareous nannofossil and diatom biostratigraphic records in particular the southern ocean diatom biostratigraphic zonation for the oligocene critically hinges on calibration of these two holes previous low resolution magnetostratigraphic studies at these sites were hampered by limited sampling and technical difficulties which prompted our high resolution reinvestigation of the magnetostratigraphy magnetic polarity zonations for holes 744a and 748b were constructed after inspection of vector component plots at 1 cm stratigraphic intervals from continuous u channel measurements the magnetizations are generally stable and a robust polarity stratigraphy has been obtained for both holes the increased resolution of our study and identification of persistent secondary overprints which were not recognised in previous studies suggests that the previously published interpretations need to be revised our magnetostratigraphic interpretations for both holes are constrained by foraminiferal and calcareous nannofossil datums as well as by sr isotope ages we have calibrated four diatom datums which are synchronous at the two studied sites to the geomagnetic polarity timescale including the first occurrence fo of lisitzinia ornata 27 8 ma the fo of rocella vigilans var b 27 8 ma the fo of cavitatus jouseanus 30 9 ma and the fo of rhizosolenia oligocaenica 33 8 ma the synchroneity of these datums suggests that diatom biostratigraphy has considerable potential for palaeogene biostratigraphic correlation in the southern ocean although the ages of some datums are obscured by an unconformity in hole 744a our age model from hole 748b suggests age estimates for the last common occurrence of rocella vigilans var a 29 0 ma the fo of rocella vigilans var a 30 0 ma and the fo of rhizosolenia antarctica 33 2 ma it should also be noted that the last occurrence of the calcareous nannofossil chiasmolithus altus occurs in chron c8r rather than c8n in our revised magnetostratigraphic interpretation which indicates that this datum is not diachronous between low and mid latitudes as had previously been suggested significant unconformities are documented in both holes in the middle oligocene and in the middle late oligocene respectively which probably resulted from periods of enhanced circumpolar deep water circulation

cyclicity in the middle eocene central arctic ocean sediment record orbital forcing and environmental response 1 continuous x ray fluorescence scanning of middle eocene 46 ma core m0002a 55x 236 241 m composite depth recovered during integrated ocean drilling program expedition 302 revealed a strong cyclical signal in some major and trace geochemical elements we performed a multiproxy study of the same core which included organic geochemical sedimentological and biological parameters and integrated our results with available geochemical and physical properties data the target was to look for cyclicity in the several proxies investigate their frequency and understand the environmental response to the potential forcing results indicate that a higher terrigenous component corresponds to lower organic carbon concentration smaller contributions by angiosperm pollen and spores organic walled dinoflagellate cysts and chrysophyte cysts lower productivity shorter growing season for flowering plants and lower stratification but higher contributions by bisaccate pollen and diatoms drier conditions on land more marine conditions and higher terrigenous sand ice rafted debris ird our investigation shows that physical proxy parameters hold cyclicity with periods of about 50 and 100 cm and that these frequency components are compatible with a milankovitchtype orbital forcing representing precession and obliquity respectively the longer 100 cm cyclicity is also present in the biological pollen dinoflagellate cysts and siliceous microfossils and in the sedimentological ird proxies the environmental signal derived from the integrated multiproxy analysis suggests that in an enclosed arctic ocean at time of ice sea ice and glacial ice initiation the biological proxies responded more strongly to growing season length darkness whereas the terrigenous components directly driven by sea ice and or glacial ice formation and extent responded more directly to seasonal insolation

geoelectric studies and conductivity structures of the eastern and northern parts of the baltic shield abstract large resistive regions ideally having a horizontal size of about 200 km are needed to study reliably the conductivity distribution of the lower crust of the baltic scandinavian shield by deep electromagnetic em methods the overburden of the shield consists of quaternary sediments and is thin with a low conductance this makes the shield favourable for em studies the numerous conductive zones e g schist belts in the uppermost crust however require careful two dimensional modelling in order to obtain reliable electrical cross sections of the earth s crust electromagnetic methods magnetometer array studies and magnetotelluric profiling have proven to be a useful tool in studies of the lithospheric geophysics of the shield the crust of the finnish and soviet baltic shield can be divided into geoelectrically different blocks in central finland the blocks are surrounded by narrow highly conductive band like formations they are located in the middle crust and their upper surface often occurs in the 6 10 km region the resisitivities are typically 5 10 m the greatest anomalous crustal regions have a conductance of more than 20 000 s the lower crust is very conductive in most parts of the shield two dimensional models of long magnetotelluric profiles indicate the great variety and complexity of the geoelectric structure of the crust

an introduction to the european geotraverse project first results and present plans abstract the european geotraverse egt is an international multidisciplinary project focused on a north south orientated lithospheric profile 4000 km long and of varying width extending from northernmost scandinavia to north africa this profile consists of three interlinking segments northern central and southern comprising a continuous succession of tectonic provinces ranging from the oldest precambrian areas of the baltic shield to the currently active area of the western mediterranean the broad aim of the egt project is to obtain a better three dimensional picture of the structure state and composition of the continental lithosphere to use as a basis for an understanding of its evolution and dynamics all of the 12 major projects that constitute the egt joint programme have now been initiated and several of these projects are nearing completion along the northern segment data from the fennoscandian long range project fennolora a 2000 km long seismic profile across the precambrian baltic shield show that except beneath southern sweden the shield is characterized by a high velocity 40 50 km thick crust including a 5 10 km thick crust mantle transition zone an alternating series of 4 6 high and low velocity zones is present in the subcrustal lithosphere the base of which increases in depth from ca 110 km to ca 230 km from south to north beneath the shield the top of the mantle transition zone lies at a depth of about 450 km the second major project along this segment the eugeno s european geotraverse northern segment southern part project is a multidisciplinary study of the fennoscandian border zone and was largely completed in 1984 with the realization of a large scale seismic experiment preliminary interpretation of the excellent data obtained indicate the presence of strong lateral variations in internal crustal structure beneath the danish basin field work for a third major project a multidisciplinary transect of the archaean and early proterozoic terrains in the northernmost part of the shield the polar profile was carried out in 1985 a series of deep seismic reflection lines has so far been realized in the area of the central segment in the context of german national programmes first interpretations of the seismic data from a 260 km long profile across the two main intra variscan hercynian lineaments have shown the presence of numerous horizons making up a highly reflective zone in the lowermost 10 km of the crustal section studied and distinct changes in reflectivity between the main variscan tectonic zones in 1986 the entire segment will be investigated in detail in an ambitious international programme of integrated geological and geophysical studies a series of seismic experiments termed egt s have been carried out across the southern segment in 1982 1983 and 1985 interpretation of data from the 1982 and 1983 experiments have led to several interesting results including 1 1 the suggestion that two crust mantle like interfaces exist beneath the po basin at depths of about 35 and 50 km and adjacent tectonic units these interfaces marking a deep contact zone between the adriatic and european plates 2 2 in the area between genoa and corsica the ligurian sea is underlain by a greatly thinned distinctly layered section of continental crust and 3 3 corsica and sardinia are underlain by bowl shaped typically variscan continental crusts the 1985 phase of seismic surveys focused on crustal structure beneath tunisia and the adjacent seas in addition two off traverse projects are being realized first a wide aperture network of autonomously recording seismic stations nars installed along the line gothenburg malaga between 1982 and 1984 is already yielding high quality data on the upper 600 700 km of the mantle second an investigation of lithospheric seismic anisotropy in the area of the iberian peninsula is being organized for 1987 1988 finally of great importance are the systematic compilation of existing data and where needed in critical regions collection of new geophysical and geological data presently being carried out for the entire area encompassed by the egt it is expected that these compilations will be completed by 1987 at about the same time that full results from the main large scale seismic experiments become available enabling the construction of an integrated lithospheric cross section along the egt requiring a final phase of intensive multidisciplinary collaboration

increased seasonality through the eocene to oligocene transition in northern high latitudes a profound global climate shift took place at the eocene oligocene transition approximately 33 5 million years ago when cretaceous early palaeogene greenhouse conditions gave way to icehouse conditions during this interval changes in the earth s orbit and a long term drop in atmospheric carbon dioxide concentrations resulted in both the growth of antarctic ice sheets to approximately their modern size and the appearance of northern hemisphere glacial ice however palaeoclimatic studies of this interval are contradictory although some analyses indicate no major climatic changes others imply cooler temperatures increased seasonality and or aridity climatic conditions in high northern latitudes over this interval are particularly poorly known here we present northern high latitude terrestrial climate estimates for the eocene to oligocene interval based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the norwegian greenland sea our data indicate a cooling of approximately 5 degrees c in cold month winter mean temperatures to 0 2 degrees c and a concomitant increased seasonality before the oi 1 glaciation event these data indicate that a cooling component is indeed incorporated in the delta 18 o isotope shift across the eocene oligocene transition however the relatively warm summer temperatures at that time mean that continental ice on east greenland was probably restricted to alpine outlet glaciers

electrical conductivity structure of north west fennoscandia from three dimensional inversion of magnetotelluric data abstract new magnetotelluric mt data in north west fennoscandia were acquired within the framework of the project magnetotellurics in the scandes masca the project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable precambrian cratonic interior to passive continental margin beneath the caledonian orogen and the scandinavian mountains in western fennoscandia an array of 59 simultaneous long period and 220 broad band mt sites were occupied in the summers of 2011 to 2013 the 3 d inversion of the masca data was obtained using the modem 3 d code the full impedance and tipper data were used for the inversion the rocks of archaean and proterozoic basement towards east and the caledonian nappes towards west are modelled as resistive structures in the central and southern parts the whole crust is resistive and reflects the trans scandinavian igneous belt granitoids the middle to lower crust of the svecofennian province is conductive an uppermost crustal conductor is revealed in the skelleftea ore district the south end of the kittila greenstone belt is seen in the models as a strong upper to middle crustal conductor in the caledonides the highly conductive alum shales are observed along the caledonian thrust front a map of the crustal conductance for the north west fennoscandian shield is presented

the polar profile revisited combined p and s wave interpretation abstract the polar profile project studied the crustal structure in a 440 km long swath extending across the northern baltic shield in a southwest northeasterly direction the obtained seismic data comprise p waves and very clear s waves the results of forward modelling using the raytracing technique together with synthetic seismograms for the s waves necessitated slight modification of a previously published velocity model obtained from p waves only the profile crosses the lapland granulite belt with granulite facies rocks at the surface the lapland granulite belt and a part of the karasjok kittila greenstone belt are recognized as high velocity bodies in the upper crust both for p and s waves the v p v s ratio and poisson ratio respectively seems to be slightly lower than that in the surrounding archaean gneisses which also prevail in the middle crust down to a depth of about 30 km the lower crust 30 45 km is marked by a pronounced velocity contrast of the p waves in respect to the middle crust but only a small velocity contrast for the s waves is seen in the southwestern part of the profile unusually high velocities 8 6 8 7 km s are found in the upper mantle at depths of 46 to 50 km

electrical conductivity distribution of the lithosphere in the central fennoscandian shield abstract geoelectric information on the crustal structures of the central fennoscandian shield consists of magnetovariational mv and magnetotelluric mt data mv data are obtained from magnetometer arrays devised to map lateral variations of subsurface resistivity mt data are obtained from soundings yielding knowledge on vertical resistivity distribution in the form of cross sections the electromagnetic data base for fennoscandia includes data from about 350 magnetometer sites and about 600 magnetotelluric soundings the results show that the crustal resistivity of the archaean and palaeoproterozoic crust varies greatly both laterally and vertically the model resistivities range from several tens of thousands of m to below 1 m which are extreme values amongst those normally observed in crustal rocks several large elongated and inclined crustal conductors which mark fossil tectonic boundaries have been discovered in the shield these include 1 the lake ladoga outokumpu kainuu schist belt and oulu conductors that form a discontinuous conductive boundary between the domains of archaean and palaeoproterozoic crust 2 the southern finland conductor caused partly by nearly vertical several kilometres deep graphite bearing metasedimentary layers that were tilted and deeply buried in a svecofennian collision 3 the kokkola bothnian skelleftea storavan and oulu conductors representing a collisional belt in a northwards accreted palaeoproterozoic terrain and 4 the lapland granulite belt conductors imaging a sequence of sheared thrust sheets that developed as the granulites were upthrusted southwestwards onto the archaean craton zones of enhanced electrical conductivity delimit more resistive and homogeneous crustal blocks including the archaean kuhmo block in eastern finland and the svecofennian central finland granitoid complex cfgc highly resistive upper crust 30 000 m in the cfgc coincides with the granitoid intrusions groundwater which fills the fractures and pores of the granitoids is non conductive 100 m and is thus not able to enhance the bulk conductivity therefore the resistivity of the upper crust approaches that of dry rocks at depths of 10 to 14 km a decrease in resistivity by one order of magnitude coincides with a seismic low velocity vp zone that appears related to a porous fractured zone filled with saline water a lower crustal conductor beneath the cfgc at depths of 30 to 40 km has a thickness of 10 to 15 km and a resistivity of 20 to 100 m it is most probably caused by graphite that can have been precipitated from co2 rich fluids during the peak metamorphism of the svecofennian orogeny and the subsequent cooling period free fluids trapped in the lower crust appear less plausible magnetotelluric soundings in the resistive cfgc in the central fennoscandian shield have not provided indications of a well developed electrical asthenosphere within the uppermost 300 km

the geoelectric model of the polar profile northern finland abstract electromagnetic soundings have been made in order to construct a geoelectrical conductivity model of the crust along the european geotraverse egt polar profile forty magnetotelluric mt soundings eighteen audiomagnetotelluric amt soundings and ten magnetohydrodynamic mhd soundings were made on the main polar profile polar i and ten more mt soundings on a parallel profile polar ii 40 km to the southeast of the main profile analysis of simultaneous recordings by the eiscat magnetometer chain and thin sheet modelling of the effect of the barents sea indicate that neither the source field effects nor the presence of the ocean are significant at periods below 200 s in the measurement area the magnetotelluric data have been modelled with two dimensional models representing the regional structure along the profiles in addition to the regional structure a thin inhomogeneous surface layer is included in the models in order to explain some local features of the measured response functions although details of the surface electrical structures are poorly resolved the gross features of the geoelectrical cross section are considered to be reliable the results divide the polar profile into three different blocks the better conducting karasjok kittila greenstone belt in the south has an average resistivity of less than 10 m the more resistant lapland granulite belt with a resistivity between 100 and 200 m is underlain by conductive the geoelectric cross section agrees in gross detail with the corresponding gravity refraction seismic and reflection seismic cross sections of the polar profile all methods indicated a similar shape for the southwestern part of the lapland granulite belt i e granulites have a gently ne dipping boundary against the underlying karelian province in the northeastern part of the granulite belt the geoelectric model and the gravimetric model show a rather steep s dipping boundary against the inari terrain northeast of the granulite belt

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

structure and composition of the precambrian crust along the polar profile in the northern baltic shield abstract along the 500 km long polar profile the continental crust of the northern baltic shield consists of several archaean and early proterozoic crustal segments in the south in the karelian province the upper crust consists of a 3 1 2 6 ga old archaean substratum with a 0 6 km thick low to medium grade volcanosedimentary cover here shallow basin facies rocks of the central lapland complex have been thrust northwards onto the karasjok kittila greenstone belt the repeatedly folded cover rocks form linear troughs between domes and culminations of granitoids the 47 48 km thick crust of the karelian province is of a shield type it is characterised by a low velocity layer interpreted as a horizon of decollement below the supracrustal and granitoid rocks in the lapland granulite belt early proterozoic high grade metapelites and metapsammites with minor metaigneous intercalations have been thrust to the southwest they are separated from the underlying karelian province by the tectonic mixture zone of the tanaelv belt in the interpretations two alternative models are given for the shape of the lapland granulite belt it is either a synformal nappe or a ne dipping body pinching out at depth and overthrust from the north by the archaean inari terrain both the lapland granulite belt and the inari terrain have a 42 44 km thick crust with a relatively thin lower crust marked by lower seismic velocities the early proterozoic polmak pasvik pechenga belt separates the archaean inari terrain from the archaean sorvaranger terrain in the north this belt is interpreted as a suture zone which continues to depth it may either dip steeply towards irregularities in the moho or form a sw dipping low angle plane below the lapland granulite belt the northernmost part of the baltic shield is concealed beneath a 0 7 km thick very low grade metamorphic late proterozoic cover this cover is divided into two parts by the trollfjord komagelv strike slip fault here the crust is again of a normal shield type with a thickness of 42 46 km

regional differences in pelagic productivity in the late eocene to early oligocene a comparison of southern high latitudes and lower latitudes paleoproductivity patterns at the eocene oligocene boundary in southern high latitudes and in the equatorial oceans were synthesized from the literature three odp dsdp sites from the southern ocean sites 689 748 and 511 were compared with three dsdp odp sites from the equatorial oceans sites 574 462 and 959 paleoproductivity was estimated by multiple sedimentological biological and geochemical proxies changes in paleoproductivity at the eocene oligocene boundary mainly took place in the southern high latitudes at site 689 the benthic foraminiferal fauna also indicates an increase in seasonality in equatorial oceans there are no indications for a shift to higher paleoproductivity at the eocene oligocene boundary on the contrary at site 959 sedimentology documents decreasing paleoproductivity in the oligocene major changes in temperature and ocean circulation in southern high latitudes versus only minor changes in the lower latitudes were probably responsible for the geographically different changes in paleoproductivity d 2004 elsevier b v all rights reserved

decomposition analysis of the bear magnetotelluric data implications for the upper mantle conductivity in the fennoscandian shield decomposition analysis of the bear magnetotelluric data implications for the upper mantle conductivity in the fennoscandian shield

reference events for regional seismic phases at ims stations in china seismic event location within the context of monitoring the compre hensive nuclear test ban treaty entails a priori knowledge of the travel time of seismic phases for a given source to stations of the international monitoring system ims such travel time information or ground truth gt is provided empirically by seismic reference events events that have well determined hypocenter locations epicenters typically known to 5 km with high confidence and origin times in this study we present new reference events for the calibration of six seismic stations of the ims in china a region with high seismic activity we use the annual bulletin of chinese earthquakes which lists about 1000 earthquakes in and near china each year with consistent phase picks at regional stations to determine precise relative earthquake locations from double difference cluster analysis the resulting high resolution image of active faulting at seismogenic depths in areas of dense seismicity is correlated with the tectonic structure derived from mapped fault information at the surface to validate the absolute locations we generated 59 reference events with m 3 5 distributed in six clusters in central and eastern china and recorded by at least one of the six ims stations the scatter in relative travel time residuals is reduced from 1 28 sec before to 0 61 sec after relocation consistent with the relocated po sitions of the events the degree of correlation between seismicity structure and well characterized fault data indicates that in four clusters the locations of the new ref erence events are accurate to within 5 km gt5 and in two clusters within 10 km gt10

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

crustal conductors along the sveka profile in the fennoscandian baltic shield finland summary electrical properties of the crust in the central fennoscandian baltic shield are examined along the 435 km magnetotelluric profile sveka a 2 d geoelectric model shows large variations in the crustal resistivity with the model resistivities ranging from 0 1 to 35 000 m the main geoelectrical features of the crust and upper mantle are 1 a resistive archaean lower crust conductance 30 s 2 a conductive palaeoproterozoic lower crust beneath the central finland granitoid complex 170 900s free h2o rich fluids trapped into the lower crust seem less plausible causes for enhanced conductivity as long retention times are required and no possible sources seem to be available to produce fluids into the dry lower crust most likely causes for permanent enhancement of lower crustal conductivity include the conductive fill of ductile shear zones conductive graphite bearing lamellae conduction in mafic rocks perhaps via conduction in magnetite or conductive solid remnants of an ancient shear zone between two crustal blocks thin graphitic grain boundary films precipitated from co2 rich fluids also seem less plausible 3 a very resistive 10 000 35 000 m upper crust of the palaeoproterozoic central finland granitoid complex and the archaean domain 4 narrow and elongated conductors 0 1 100 m beneath the palaeoproterozoic kainuu ksb and tampere tsb schist belts are caused by graphite bearing metasedimentary rocks buried deep into the crust in the collisions of crustal terranes during the formation of the palaeoproterozoic svecofennian crust the 500 km long tsb conductor represents an internal svecofennian terrane boundary whereas the ksb conductor is a part of a discontinuous archaean proterozoic boundary conductor 5 resistive upper mantle there are no indications of an upper mantle conducting layer within the uppermost 300 km in the central part of the fennoscandian shield

crustal structure beneath southern norway imaged by magnetotellurics abstract we use data from two magnetotelluric profiles tosca10 and tosca 09 over the scandinavian mountains to study the crustal structure in southern norway the profiles cross the major tectonic structures of the caledonian orogen as well as the western margin of the precambrian baltica dimensionality and strike analyses indicate generally 3 d behavior of the data however the majority of the used data distinguishes a preferable strike direction which is supported by the geology of the region hence we employ 2 d inversion and choose to invert the determinant of the impedance tensor to mitigate 3 d effects in the data on our 2 d models magnetotelluric data from both profiles are inverted using a damped least squares solution based on a singular value decomposition we improved the solution by defining the inverse model covariance matrix through gradient or laplacian smoothing operators the two dimensional inversion models of the tosca 09 and tosca 10 field data from southern norway derived from the damped least squares scheme with the laplacian inverse model covariance matrix are presented resistive rocks extending to the surface image the autochthonous southwest scandinavian domain and the allochthonous western gneiss region near surface conductors which are located between the resistive caledonian nappes and precambrian basement delineate highly conductive shallow sea sediments so called alum shales they exhibit a decollement along which the caledonian nappes were overthrust a deeper upper to mid crustal conducting layer in the southwest scandinavian domain may depict the remnants of closed ocean basins formed during the accretions and collisions of various sveconorwegian terranes in tosca 10 the caledonian nappes the conducting alum shales and the deeper conductor are terminated in the west by the faltungsgraben shear complex which represents a crustal scale boundary between the western gneiss region in the west and the southwest scandinavian domain in the east

multiproxy record of abrupt sea surface cooling across the eocene oligocene transition in the gulf of mexico the eocene oligocene transition eot ca 33 34 ma was a time of pronounced climatic change marked by the establishment of continental scale antarctic ice sheets the timing and extent of temperature change associated with the eot is controversial here we present multiproxy eot climate records 15 34 k y resolution from st stephens quarry alabama usa derived from foraminiferal mg ca d18o and tex86 we constrain sea surface temperatures ssts in the latest eocene and early oligocene and address the issue of climatic cooling during the eot paleotemperatures derived from planktic foraminifera mg ca and tex86 are remarkably consistent and indicate late eocene subtropical ssts of 28 c there was substantial and accelerated cooling of ssts 3 4 c through the latest eocene precursor d18o shift eot 1 prior to oligocene isotope 1 oi 1 our multispecies planktic foraminiferal d18o records diverge at the e o boundary 33 7 ma signifying enhanced seasonality in the earliest oligocene in the gulf of mexico

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

methane index a tetraether archaeal lipid biomarker indicator for detecting the instability of marine gas hydrates abstract gas hydrates represent one of the largest pools of readily exchangeable carbon on earth s surface releases of the greenhouse gas methane from hydrates are proposed to be responsible for climate change at numerous events in geological history many of these inferred events however were based on carbonate carbon isotopes which are susceptible to diagenetic alterations here we propose a molecular fossil proxy i e the methane index mi to detect and document the destabilization and dissociation of marine gas hydrates mi consists of the relative distribution of glycerol dibiphytanyl glycerol tetraethers gdgts the core membrane lipids of archaea the rational behind mi is that in hydrate impacted environments the pool of archaeal tetraether lipids is dominated by gdgt 1 2 and 3 due to the large contribution of signals from the methanotrophic archaeal community our study in the gulf of mexico cold seep sediments demonstrates a correlation between mi and the compound specific carbon isotope of gdgts which is strong evidence supporting the mi methane consumption relationship preliminary applications of mi in a number of hydrate impacted and or methane rich environments show diagnostic mi values corroborating the idea that mi may serve as a robust indicator for hydrate dissociation that is useful for studies of global carbon cycling and paleoclimate change

electromagnetic geophysics and global tectonics lateral variations of electrical conductivity in the lithosphere and below it can be informative concerning both contemporary and ancient global tectonics the methods of investigation include classical four electrode resistivity depth probing which is of special value in continental shields magnetotellurics long used on land and recently in the pacific to show that in electrical terms the lithosphere is thicker near an oceanic ridge than had been expected and magnetometer arrays which are useful primarily in mapping highly conductive structures examples of the use of all three methods will be reviewed with emphasis on the last in conjunction with other geophysical geological and geochemical data magnetometer arrays have been useful in mapping partial melt under the western united states in discovering an extension of the southern end of the african rift system to the atlantic coast in detecting a major fracture zone in central north america which may be a proterozoic interplate collision feature and in discovering a conductive belt under southernmost africa which may result from accumulation of serpentinized marine crustal rocks at the top of a subduction under proterozoic gondwanaland inherent difficulties of quantitative modeling limit the utility of magnetometer arrays largely to discovery and mapping of two and three dimensional conductive structures this remains valuable however particularly when other physical properties can be used to limit the range of possible interpretations of the conductive structures recent array studies now in progress in western canada have defined two new conductivity anomalies one of these may represent a local partial melt concentration under the rocky mountains trench the other a precambrian rift valley in the lower crust previously suggested by others on the basis of seismological gravity and static magnetic data both are being investigated by more concentrated arrays

effects of long term oxic degradation on the u37k tex86 and bit organic proxies abstract one of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis however studies have shown that oxic degradation of biomarker lipids can affect their relative distribution we tested the diagenetic stability of the u 37 k and tex86 palaeothermometers upon long term oxygen exposure for this purpose we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers gdgts in different sections of turbidites at the madeira abyssal plain map that experienced different degrees of oxygen exposure sediments were deposited anoxically on the shelf and then transported by turbidity currents to the map which has oxic bottom water this resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water concentrations of gdgts and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts indicating substantial degradation high resolution analysis of the pleistocene f turbidite showed that the u 37 k index of long chain alkenones increased only slightly 0 01 corresponding to u 37 k while for other pliocene miocene turbidites it either remained unchanged or decreased substantially up to 0 06 corresponding to 6 c previous observations showed that the bit index a proxy for the contribution of soil organic matter to total organic carbon was always substantially higher in the oxidized part in all the turbidites as a result of preferential degradation of marine derived gdgts this relative increase in soil derived gdgts affects tex86 as the isoprenoid gdgt distribution on the continent can be quite different from that in the marine environment our results indicate that the organic proxies are affected by long term oxic degradation to different extents this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation

structure of the scandes lithosphere from surface to depth abstract in this review we give an overview of geophysical data and models available for the scandinavian mountains and adjacent areas as they are of relevance to the debate about the existence and cause of neogene uplift emphasis is given to potential field and petrophysical data of which the earth science communities of norway and sweden have a long tradition of acquisition and interpretation this is reflected in the wealth and dense coverage of data available the topography of the scandes mountain chain correlates to a large degree with a bouguer gravity low which suggests isostatic compensation but comparison with magnetic and petrophysical data shows that the gravity low is partly influenced by the trans scandinavian igneous belt signals due to the effects of surface geology can be further eliminated by considering the near surface density distribution as provided by petrophysical sampling to illuminate the entire lithospheric structure active and passive seismic and magnetotelluric data can be used recent and ongoing experiments are aimed at improving the existing models of the lithosphere integration of these different geophysical data sets allows the structure of the lithosphere of the scandes and its surroundings to be addressed seismic models show no pronounced crustal root below the scandes which could provide isostatic compensation but instead an increase of crustal thickness towards the central fennoscandian shield from the integrated model isostatic compensation is inferred to be largely controlled by the density distribution of the crust and that a high density lower crust to the east of the scandes is necessary to achieve isostatic equilibrium on a regional scale we demonstrate the typical crustal structure with profiles crossing from the scandes into the shield and a combined onshore offshore basement map

lithospheric and upper mantle structures results of electromagnetic soundings in europe abstract information on electrical conductivity of the subsurface at a crustal scale is inferred mainly from magnetotelluric mt and magnetometer data the latter include both magnetometer array studies mv and geomagnetic depth soundings gds locally controlled source data e g data from d c and very low frequency vlf resistivity surveys frequency soundings and airborne electromagnetic mappings provide information on near surface structures e g on exposures of deeper conductors the variety of electromagnetic methods provides an efficient zooming ability for structures from a regional scale of hundreds of kilometres to small local details of some metres thus both the mapping of large scale crustal conductivity structures and a detail study of the anomalous structures are possible the electrical conductivity of the crust and upper mantle is described within the plate tectonic framework examples of structures which become electrically conductive at different phases of the process are shown using the results of electromagnetic soundings in various tectonic environments in europe it is shown how the crustal conductors can be interpreted as ancient and modern tectonic markers these include structures from the fennoscandian shield precambrian extensional basins and collisional zones the carpathians scotland and ireland suture zones and the pannonian basin extensional basin and thrust zones as well as conductors detected along the european geotraverse e g the terrain boundaries and the decollement of the variscan thrusting an example which considers the lower crustal conductivity from the fennoscandian shield shows rather large lateral variations in conductance of the lower crust varying from 1 s to several hundreds of siemens estimates of the depth of the asthenospheric conducting layer within the european territory also vary considerably shallowest depths are detected beneath extensional regions the pannonian basin and the rhinegraben 40 80 km whereas depths of 200 km or over or the absence of a conducting layer are detected beneath the alps and old precambrian cratons among the key areas where electromagnetic investigations should play an essential role are the deep structure of the east european platform boundaries of archaean and proterozoic terrains the structure of the teisseyre tornquist zone the nature of the present day continental lower crust and the characteristics of the electrical asthenosphere beneath europe

field petrophysical and carbon isotope studies on the lapland granulite belt implications for deep continental crust the palaeoproterozoic lapland granulite belt is a seismically reflective and electrically conductive sequence of deep crustal 6 9 kbar rocks in the northern fennoscandian shield it is composed of garnet sillimanite gneisses khondalites and pyroxene granulites enderbites which in certain thrust sheets form about 500 m thick interlayers the structure was formed by the intrusion of intermediate to basic magmas into turbiditic sedimentary rocks under granulite facies metamorphism accompanied by shearing of the deep crust about 1 93 1 90 gyr ago gal granulites were upthrust 1 90 1 87 ga and the belt was divided by crustal scale duplexing into four structural units whose layered structure was preserved the thrust structures are recognized by the repetition of lithological ensembles and by discordant structural patterns well distinguishable in airborne magnetic and electromagnetic data thrusting gave rise to clockwise pressure temperature evolution of the belt however some basic rocks possibly record an isobaric cooling path the low bulk resistivity of the belt 200 1000 m is caused by interconnected graphite and subordinate sulphides in shear zones on the basis of carbon isotope ratios this graphite is derived mostly from sedimentary organic carbon the seismic reflectivity of the belt may be caused by velocity and density differences between pyroxene granulites and khondalites as well as by shear zones

electromagnetic studies in the fennoscandian shield electrical conductivity of precambrian crust abstract electromagnetic em investigations of the 1980s in the fennoscandian baltic shield produced an unique and unified em data set studies include regional investigations by the magnetovariational mv method with large lateral sampling distance investigations of anomalous conductivity structures by magnetotelluric mt soundings and other em and electrical methods audio mt soundings d c dipole dipole and vlf resistivity profilings with shorter sampling distance and studies of the near surface conductivity by airborne em surveys the variety of methods provide an ability to map efficiently crustal conductivity structures from a regional scale of hundreds of kilometres down to local details of some metres in the anomalous structures the precambrian of the fennoscandian shield is characterized by roughly nw se directed elongated belts of conductors which separate more resistive crustal blocks the latter serve as transparent windows through which to probe deep electrical structure and belts of conductors as tectonic markers of ancient orogenic zones including 1 the kittila vetrenny poyas conductor 2 the lapland granulite belt and inari pechenga imandra varzuga conductors 3 the archaean proterozoic boundary conductor and 4 the southern finland conductor the conductive belts orogenic conductors indicate places where crustal masses collided and were finally sealed together enhanced conductivity in the orogenic conductors is caused primarily by an electronic conducting mechanism in graphite and sulphide bearing metasedimentary rocks estimations of the lower crustal conductivity indicate a laterally heterogeneous lower crust in the fennoscandian shield archaean lower crust seems to be in general more resistive than the early proterozoic lower crust of the karelian and svecofennian domains the lower crust in the southwestern part of the svecofennian domain and in the sveconorwegian domain seems to be more resistive than in the central part of the svecofennian domain

isotopic interrogation of a suspected late eocene glaciation ephemeral polar glaciations during the middle to late eocene 48 34 ma have been proposed based on far field ice volume proxy records and near field glacigenic sediments although the scale timing and duration of these events are poorly constrained here we confirm the existence of a transient cool event within a new high resolution benthic foraminiferal 18o record at ocean drilling program odp site 738 kerguelen plateau southern ocean this event named the priabonian oxygen isotope maximum prom event lasted 140 kyr and is tentatively placed within magnetochron c17n 1n 37 3 ma based on the correlation to odp site 689 maud rise southern ocean a contemporaneous change in the provenance of sediments delivered to the kerguelen plateau occurs at the study site determined from the 63 m fraction of decarbonated and reductively leached sediment samples changes in the mixture of bottom waters based on fossil fish tooth nd were less pronounced and slower relative to the benthic 18o and terrigenous nd changes terrigenous sediment nd values rapidly shifted to less radiogenic signatures at the onset of the prom event indicating an abrupt change in provenance favoring ancient sources such as the paleoproterozoic east antarctic craton bottom water nd reached a minimum value during the prom event although the shift begins much earlier than the terrigenous nd excursion the origin of the abrupt change in terrigenous sediment provenance is compatible with a change in antarctic terrigenous sediment flux and or source as opposed to a reorganization of ocean currents a change in terrigenous flux and or source of antarctic sediments during the oxygen isotope maximum suggests a combination of cooling and ice growth in east antarctica during the early late eocene