paleomagnetism of the silurian volcanism at almaden southern spain the silurian volcanism of the almaden mining district southern spain has been the object of a very detailed paleomagnetic study the 175 cores 25 sites sampled all along the eastern termination of the almaden syncline were subjected to magnetic susceptibility measurements thermomagnetic cycles progressive alternating field and thermal demagnetizations as well as microscopic observations the magnetic mineralogy of these volcanics flows is dominated by magnetite in at least two very distinct forms including small cubic distributed grains and large elongated crystals the observed anisotropy of magnetic susceptibility varies according to the relative abundance of the two magnetite phases showing a complete inversion of the susceptibility tensors this anisotropy has been related to the emplacement of the flows on a gentle slope dipping 10 toward the southwest implying that their volcanic source was located to the northeast the paleomagnetic analysis has revealed two characteristic components of magnetization the first direction d 109 i 11 95 9 pole position at 11 s 69 e dp 5 dm 9 yields a negative fold test and is interpreted as a late paleozoic partial overprint its declination is 46 away of the expected late paleozoic field direction which confirms that rotations are still occurring after the main folding phases of the variscan orogeny the second direction d 62 i 36 95 14 pole position at 8 n 118 e dp 9 dm 13 is prefolding as evident from the significant clustering when applying appropriate tectonic corrections and we interprete it as the original magnetization of silurian age the compilation of all paleozoic paleomagnetic results from spain reveals that the iberian meseta has been moving along with gondwana at high drift rates throughout ordovician and silurian times

short paper terrane rotations in the irish caledonides palaeozoic palaeomagnetic data from scotland and ireland have been compared on a terrane model and early caledonide clockwise rotation of a terrane through 65o 30 connemara massif and later anticlockwise rotation of up to 50 in the vicinity of clew bay have been deduced these are the firfirst estimates of terrane rotations in the european part of the caledonian appalachian orogen terrane analysis of orogenic belts is currently a major field of study to a large extent this has been stimulated by studies in the north american cordillera where large rotations and translations have been determined palaeomagnetically see beck et al 1986 and references therein terrane analysis may be applied to older orogenic belts such as the caledonides which have been particularly intensively studied previously published palaeomagnetic data from connemara morris tanner 1977 and nw galway morris et al 1973 had indicated local block rotations but furnished few constraints on either their age and magnitude or on the identities of the blocks this paper relates the currently available palaeomagnetic dataseto a terrane model of w ireland hutton dewey 1986 see fig 1 new data new palaeomagnetic data from the irish caledonides comprise the following connemara gabbro robertson 1988 the dalradian rocks of the connemara massif are unique in the british caledonides in lying to the south of a caledonian ophiolite and also south of a thick sequence of ordovician shales and volcanics of low metamorphic grade in clew bay and the south mayo trough respectively the structural

limitation of fixed nitrogen and deepening of the carbonate compensation depth through the hirnantian at dob s linn scotland abstract the late ordovician is characterized by dramatic changes in global climate concurrent with a major mass extinction and possible changes in ocean redox to further refine our understanding of these events we present nitrogen and carbon isotope and abundance data from the ordovician silurian o s global boundary stratotype section and point at dob s linn scotland we show that this section experienced post depositional ammonium migration from the organic rich to the organic poor horizons however our data suggest that isotopic fractionations from ammonium substitution into illitic clay minerals are small and can be corrected reconstructed primary nitrogen isotope ratios indicate that unlike in tropical continental shelf sections that were transiently enriched in nitrate during the hirnantian glaciation the sub tropical continental slope setting at dob s linn experienced persistent limitation of fixed nitrogen across the o s boundary shallow subpolar settings appear to be the only environment that shows persistent nitrate availability at that time this pattern suggests that spatial trends in marine nitrate concentrations which are observed in the modern ocean as a result of latitudinal temperature gradients were already established during the paleozoic while the average marine o2 chemocline depth may have deepened during the hirnantian glaciation it probably did not lead to global ventilation of the deep ocean which may have been delayed until the carboniferous furthermore carbonate data from this and other sections suggest a deepening of the carbonate compensation depth ccd during the hirnantian this observation indicates that pacific style responses of the ccd to glacial interglacial periods were operational across the o s boundary and that the expansion of abiotic carbonate deposition and preservation beyond the shelf break could have in part mediated changes to surface co2 during these extreme changes in climate

the uplift magnetisation record in the central scandinavian caledonides results from basic igneous complexes abstract to identify the palaeomagnetic record acquired during slow post orogenic uplift and cooling in the central part of the scandinavian caledonides we have investigated four separated synorogenic basic complexes in the middle and upper allochthons a shallow n s axis of magnetisation is common to three of these bodies and therefore postdates all major tectonism it is defined in the mosjoen gabbro d i 7 3 n 23 samples 95 5 0 in the sulitjelma gabbro d i 20 9 n 22 samples 95 6 6 and the rana norite d i 9 16 n 19 samples 95 7 9 no vestige of this uplift remanence is recognised in the lyngen ophiolite where a characteristic remanence of d i 65 43 n 19 samples 95 10 6 is recorded the possibility that the n s shallow axis of magnetisation is of mid carboniferous age is considered and rejected instead it is attributed to the interval of post tectonic cooling of the caledonian nappe pile between synorogenic events dated ca 420 ma and the uplift to surface levels defined by later devonian events it corresponds closely to an axis of magnetisation extensively represented within the metamorphic caledonides and scotland and believed to record a post tectonic thermochemical event subordinate components record mesozoic overprinting events and relict caledonian magnetisations which have escaped replacement during this thermo tectonic event the latter collectively imply a rapid movement from high to low palaeolatitudes in late ordovician and early silurian times

palaeomagnetic and rock magnetic reliability criteria in ophiolitic rocks a case study from the palaeozoic ballantrae ophiolite scotland abstract palaeomagnetic studies of the ballantrae ophiolite southwest scotland are assessed in the light of palaeomagnetic and rock magnetic reliability criteria the remanence directions are palaeomagnetically reliable but have only limited significance for apparent polar wander path construction rock magnetic reliability criteria are found to be ambiguous when treated in isolation original grain size effects are detected in magnetic properties across three sections through pillow lavas we propose that a systematic study of spatial magnetic property variations within pillow lavas can provide an additional field test in the assessment of reliability thermomagnetic analyses and microscopic observations suggest three remanence carrying magnetic phases exist within the extrusive layer of the ophiolite these are almost pure magnetite hematite and titanomaghemite palaeomagnetic rock magnetic and geological observations are best satisfied by a pre obduction magnetisation age this study links the remagnetisation of an ultra oceanic conglomerate to local hydrothermal circulation rather than to a pervasive remagnetisation event as previously suggested

synthrusting deposition of the pennsylvanian and permian strathearn formation northern carlin trend nevada abstract the middle upper pennsylvanian and middle lower permian strathearn formation belongs to the overlap assemblage of the antler orogen in nevada at beaver peak near the carlin trend of gold deposits it contains synorogenic conglomerate deposits associated with emplacement of a regionally extensive 1 km thick tectonic wedge that is floored by the coyote thrust normal marine conodont biofacies throughout the strathearn formation suggest middle shelf or deeper depositional environments the allochthon floored by the coyote thrust has been thrust above a middle upper pennsylvanian lower conglomerate unit of the strathearn formation a middle lower permian upper conglomerate unit the highest unit recognized in the strathearn formation as well as similarly aged dolomitic siltstone onlap directly onto ordovician quartzarenite of the vinini formation that makes up most of the coyote allochthon quartz grains and quartzarenite fragments of variable roundness and shape in the conglomerate units were derived from the presently adjoining tectonic lobe of mostly quartzarenite that advanced southeast present geographic coordinates during the late paleozoic into the developing strathearn basin chert fragments in the conglomerates probably were derived mostly from devonian slaven chert including a widespread thick melange unit of the slaven chert in the footwall of the coyote thrust lithologic and shape ratio data from approximately 4200 clasts at 17 sites of the two major conglomerate units in the strathearn formation at beaver peak are roughly similar in that they contain only chert and quartzarenite clasts and chert clasts predominate in both units they differ in the relative proportion of the two lithologies whereby quartzarenite clasts increase sixfold in the upper unit middle lower permian versus its content in the lower conglomerate unit relations at the unconformity between the upper conglomerate unit and its underlying quartzarenite shows quartzarenite fragments actually breaking away from an immediately subjacent source ordovocian quartzarenite which forms a tectonically uplifted wedge with the coyote thrust at its base became a source region for much of the quartzarenite detritus deposited preferentially in the upper parts of the strathearn formation the conglomerate units of the strathearn formation temporally bracket emplacement of the coyote thrust thrusting related to contractional reactivation of the robert mountains thrust system largely was completed by middle early permian

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

amino acid epimerization implies rapid sedimentation rates in arctic ocean cores the palaeooceanography of the arctic ocean is less well known than any other ocean basin due to difficulties in obtaining cores and in providing a secure chronological framework for those cores that have been raised most recent investigators have suggested that low sedimentation rates 0 05 0 1 cm kyr 1 have characterized the deep basins over the past 5 myr refs 1 2 despite the glacial marine character of the sediment and proximity to major centres of shelf glaciation these calculations have been primarily based on the down core pattern in the inclination of magnetic minerals supported by uranium series 14c and micropalaeontological evidence here we analyse amino acid diagnesis in foraminifera from two gravity cores raised from the floor of the arctic ocean our results suggest that these cores span 200 kyr conflicting with the earlier estimate of 3 myr based on palaeomagnetic data the chronology of other arctic ocean cores and previous palaeoenvironmental interpretations need re evaluation

magnetostratigraphic data from late quaternary sediments from the yermak plateau arctic ocean evidence for four geomagnetic polarity events within the last 170 ka of the brunhes chron summary palaeomagnetic investigations of two sediment cores recovered from rv polarstern near the eastern slope of the yermak plateau sites ps 1533 and ps 2212 reveal convincing evidence for four polarity events of the earth s magnetic field during the last 170 ka a comprehensive rock magnetic study of the sediments proved that fine grained magnetite is the principal carrier of the remanent magnetization no changes in magneto mineralogy across the polarity transitions in the sediments investigated were found calcareous nannofossil biostratigraphy ams 14c accelerated mass spectrometry and oxygen isotope data and 10be and 230th stratigraphies yielded age ranges of 24 29 ka for the mono lake event 34 43 ka for the laschamp event 72 86 ka for the norwegian greenland sea event and 118 128 ka for the blake event two reverse polarity samples at the base of core ps 2212 3 kal are interpreted as the termination of the biwa i event 171 181 ka the events exhibit full inversion of inclination in both cores the data suggest that the transition process of the earth s magnetic field during such polarity events requires some 1 ka

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

palaeogeographic significance of mid silurian palaeomagnetic results from southern britain major revision of the apparent polar wander path for eastern avalonia summary wenlock c 430 ma lavas from the east mendips inlier southern briain are characterized by either single component magnetizations type 1 or a more complex system of three magnetization components type 2 during stepwise thermal demagnetization the type of demagnetization behaviour is related to changes in magnetic petrology within the lava pile the lower and intermediate unblocking temperature components of type 2 represent magnetic overprints of tertiary recent and hercynian mid carboniferous origin respectively the primary nature of the high unblocking temperature magnetization component types 1 and 2 dec 095 c inc 24 ag5 8 8 is demonstrated by positive agglomerate tests conversely an overlying upper old red sandstone sequence did not provide primary magnetizations the magnetic signature is governed by syn tectonic hercynian remagnetizations the primary silurian data demonstrate that the east mendips inlier experienced considerable clockwise rotation probably of the order of 80 prior to partial remagnetization during hercynian deformation and folding the silurian palaeopole vgp 13 n 271 e dp dm 5 9 cannot therefore be used for apparent polar wander path construction nevertheless the palaeolatitude estimate 13 f 5s suggests that southern britain eastern avalonia was at comparable mid silurian latitudes to baltica and northern britain 10 20 s both the iapetus ocean and tornquist sea therefore which separated southern britain from laurentia and baltica respectively in ordovician times were closed by wenlock time as ordovician and silurian palaeomagnetic data from baltica and eastern avalonia now record a comparable northwards translation from high southerly to near equatorial latitudes during this time we postulate pre wenlock collision of these blocks to form balonia baltica eastern avalonia a new apparent polar wander path for eastern avalonia constructed on the basis of this palaeogeographic model is presented

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

stable isotope data and depositional environments in the late quaternary arctic ocean there has been much speculation about the history of the arctic ocean particularly its response to the late quaternary climatic fluctuations1 8 as a result considerable data have been gathered from arctic ocean sediment cores to reconstruct glacial and interglacial arctic ocean palaeoenvironments8 9 but even with these data the reconstructions and the correlations with the quaternary chronostratigraphy have been unsatisfactory mainly because of the lack of detailed stratigraphical data such as those provided by stable oxygen isotope stratigraphy10 here we present stable isotope records from arctic ocean sediment cores which can be correlated convincingly with corresponding data from the north atlantic together with lithostratigraphical data they provide new evidence on arctic ocean history in relation to global late quaternary climatic fluctuations

multiphase magnetic overprints in the moine thrust zone palaeomagnetic studies from the southern part of the moine thrust zone mtz indicate a complex pattern of four major secondary remanence components a d their relative ages appear to vary from mid ordovician to recent tertiary the oldest remanence a is tentatively interpreted as associated with the formation of the lochalsh syncline dl and or d2 however the consistency between component a and the regional southeast plunging lineation makes it uncertain to what extent component a reflects the structural grain rather than a true palaeofield record component b appears to be associated with early devonian uplift along the mtz relating to localized shearing high level brittle thrusting and is almost synchronous with the emplacement of lamprophyre and felsic dykes in the inverted limb of the lochalsh syncline and beneath the balmacara thrust possible permian component c and recent tertiary magnetic overprints are recognized component c is partly of high magnetic stability and may indicate localized shears in the inverted limb usually considered as caledonian shearing it is uncertain to what extent the youngest component d essentially recorded in rocks close to the balmacara thrust in mylonites and fault breccias reflects important tectonic reactivation and magnetic resetting this component is governed by low stability magnetic phases with blocking temperatures below 200 c

the british siluro devonian palaeofield the great glen fault and analytical methods in palaeomagnetism comments on paper by k me storetvedt et al summary late silurian early devonian palaeomagnetic poles throughout the british isles lie in a coherent group about 1 s and 314 e a95 9 6 the clustering of these poles which are derived from 11 individual studies of siluro devonian rocks of all the major tectonic elements of britain carries two important tectonic implications 1 the british sector of the iapetus ocean recognizable from ordovician poles had closed by late silurian times and 2 any postulated mega shear whether related to acadian or hercynian deformation is below the limit of palaeomagnetic resolution the collective rejection of all siluro devonian results by storetvedt et al 1990a b is demonstrated to be unfounded

reworked jurassic neogene calcareous nannofossils in the central arctic abstract over 130 different reworked calcareous nannofossil taxa ranging from the lower jurassic to the neogene are recorded in quaternary sediments from the central arctic ocean species with mesozoic and tertiary stratigraphic ranges occur together this suggests that the reworked specimens are not primarily derived from the local bedrock but are transported to the central arctic ocean from the surrounding shelves and landmasses sea ice provides a possible means of transport the reworked nannofossil assemblages in the arctic are a result of geologic and climatic developments in the source areas both during the time of their deposition and during their subsequent erosion and transportation in the quaternary only two specimens restricted to the lower jurassic were observed and none restricted to the middle and upper jurassic the lower cretaceous is represented by at least four species restricted to that interval together with other long ranging taxa the presence of micrantholithus speetonensis perch nielsen is the first record of this species outside northwest europe the other lower cretaceous species observed are all typical of temperate to high latitude assemblages of both the southern and northern hemispheres the nannofossils reworked from the upper cretaceous strata are the dominant component of the assemblages nephrolithus corystus wind is recorded in the northern hemisphere for the first time some of the distinctive high latitude species present in the southern hemisphere have not been observed in the arctic helioliths discoasters and sphenoliths indicate relatively warm surface water conditions in the arctic subarctic areas during the paleocene and eocene

sediments of the lomonosov ridge and makarov basin a pleistocene stratigraphy for the north pole sediments of 16 short cores taken as part of the lomonosov ridge experiment lorex can be organized into the first pleistocene stratigraphy for the north polar region this stratigraphy can be correlated with stratigraphic units described from the alpha chukchi areas 300 km distant the lorex cores include at least 12 sedimentary subunits differentiated by texture color and carbonate content the units are silty and arenaceous lutites and are principally glacial marine benthic and planktonic foraminifera degree of bioturbation and fe mn micro nodule abundance generally are positively correlated foraminifera in core b 8 from 3 956 m in the makarov basin may have been affected by ccd fluctuations that did not affect fossils in core b 24 from 1 600 m on the crest of the lomonosov ridge the 12 stratigraphic units were deposited during the late pleistocene and represent the same major sedimentary events as those of stratigraphic units k l and m of the amerasian basin this correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial marine sediment times of major glacial ice transport reflect deglaciation events in the central arctic ocean surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50 of the arctic ocean even thin sedimentary units deposited during relatively long time intervals are correlated over 500 000 km 2

lithogeochemistry of carlin type gold mineralization in the gold bar district battle mountain eureka trend nevada abstract the gold bar district contains five carlin type gold deposits and four resources for a combined gold endowment of 1 6 m oz 50 t the gold deposits are hosted in devonian carbonate rocks below parautochthonous and allochthonous paleozoic siliciclastic rocks emplaced during the early mississippian antler orogeny the district is in the battle mountain eureka trend a long lived structural feature that localized intrusions and ore deposits of different types and ages the whole rock geochemistry of four different mineralized and unmineralized devonian carbonate rock units two favorable and two unfavorable were determined and interpreted in the context of the regional geology a combination of basic statistics r mode factor analysis isocon plots and alteration diagrams were utilized to 1 identify favorable geochemical attributes of the host rocks 2 characterize alteration and associated element enrichments and depletions and 3 identify the mechanism of gold precipitation this approach also led to the recognition of other types of alteration and mineralization in host rocks previously thought to be solely affected by carlin type mineralization unit 2 of the upper member of the denay formation with the highest al 2 o 3 fe 2 o 3 and sio 2 contents and the lowest cao content is the most favorable host rock based on the high regression coefficients of data arrays on x y plots that project toward the origin al 2 o 3 and tio 2 were immobile and k 2 o and fe 2 o 3 were relatively immobile during alteration and mineralization specific element associations identified by factor analysis are also prominent on isocon diagrams that compare the composition of fresh and altered equivalents of the same rock units the most prominent associations are au as sb sio 2 tl cao and loi the main gold mineralizing event and related silicification and decalcification cd zn ag p ni and tl an early base metal event and mgo early dolomitization alteration diagrams consisting of x y plots of sio 2 al 2 o 3 k 2 o al 2 o 3 co 2 al 2 o 3 s al 2 o 3 fe 2 o 3 al 2 o 3 provide evidence for progressive silicification decarbonation decalcification and dedolomitization argillization illite and sulfidation as a function of gold mineralization the latter process is identified as the principal mechanism of gold precipitation the lithogeochemistry of the ores in the gold bar district is typical of that documented in classic carlin type gold deposits in the region but the size of the deposits and the intensity of alteration and mineralization are less the presence of other types of mineralization in the gold bar district is also common to most of the other carlin type districts located in major mineral belts the approach used in this study is well suited to the interpretation of multi element geochemical data from other study areas with superimposed alteration and mineralization

climatic change during the lower carboniferous in euramerica based on multivariate statistical analysis of palynological data abstract lower carboniferous palynological assemblages show marked differences between north and south euramerica in order to assess these regional differences multivariate statistical analysis has been applied to percentage frequency data from palynological assemblages from twenty different localities of euramerica the principal components resulting have been related to climate sensitive rocks such as coal and evaporites this relationship has been interpreted in terms of humidity curves and climatic zones four climatic zones have been recognized a dry a moderately humid and a humid zone the latter zone may be subdivided into a humid and a very humid zone during the lower carboniferous the humid climatic zone and the related palaeoclimatic equator shifts southwards however the very humid conditions present in the uppermost tournaisian to middle visean of spitsbergen have not yet been reached in the lower namurian of western europe and the u s a the southward shift of the palaeoclimatic equator has been interpreted in terms of a northward drift of the euramerican continent the palaeomagnetic evidence available for this northward drift is briefly discussed

reappraisal of scottish ordovician palaeomagnetism summary critical re evaluation of scottish ordovician palaeomagnetism comprising data from the nw scotland syenites the aberdeenshire gabbros and the pre tectonic i e pre late ordovician silurian magnetic overprinting of dalradian tillites appears to provide a refined mid ordovician to silurian apparent polar wander path post closure magnetizations silurian across the great glen fault agree extremely well after correction for a 20d net clockwise rotation of the northern highlands the data emphasize a previous assumption that some of the existing discrepancies in british ordovician palaeomagnetism may disappear when the prevalence of multicomponent magnetizations is adequately considered the data also support the conclusion from an earlier analysis requiring an anticlockwise rotation of the british isles relative to the geomagnetic field during the ordovician however a recent suggestion that the aberdeenshire gabbros record the slow post orogenic cooling of the ne highlands is shown to rest on an inadequate palaeomagnetic basis

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

paleomagnetics of ringerike old red sandstone and related rocks southern norway implications for pre carboniferous separation of baltica and british terranes abstract paleomagnetic study of two stratigraphic sections of the upper silurian lower devonian ringerike sandstone oslo area norway indicate a straightforward multicomponent nrm for these rocks a lower temperature magnetization component gives a southwest and up reversed polarity in situ direction yields a negative fold test i e post folding at the 99 confidence level and is nearly identical to directions obtained from overlying permo carboniferous lavas a high temperature magnetization component exhibits both normal and reversed polarity directions passes a fold test at the 95 confidence level and is supported by a baked contact test which indicates a pre intrusion age of magnetization this characteristic high temperature component was successfully isolated in 79 samples from 19 sites within the ringerike succession results indicate a tilt corrected characteristic magnetic direction of declination 26 inclination 16 which is consistent with earlier work this direction corresponds to a time integrated paleopole position of 19 n latitude 164 longitude d p 4 8 d m 9 3 when compared to previous results from rocks of similar age from the british isles an approximately 20 latitudinal displacement between britain and baltica during late silurian early devonian time is suggested

pleistocene paleoceanographic correlations northern greenland sea to central arctic ocean abstract correlation of pleistocene paleoceanographic events across parts of the polar seas is accomplished with core mg 123 from the swedish ymer 80 cruise the 8 72 m sediment core one of the longest recovered from any part of the arctic ocean contains abundant microfossils and coarser grain sediment that are useful in interpretation and correlation of pleistocene events with shorter sediment cores in the central arctic ocean faunal and sediment correlations are constrained by 18 o correlations and a time series analysis that matches several possible sedimentation rates for mg 123 with central arctic ocean sedimentation rates and provides a best fit correlation of the cores the results of this study provide the first correlation of northern greenland sea southern arctic ocean sediment with that of the central arctic ocean more than 1000 km distant oceanic circulation patterns between the areas during the pleistocene involved increased circulation during interglacials with reduced circulation during glacials subpolar water was not present in the northern greenland sea during the past 600 000 years during this time alternating phases of the climate cycle show a strong relationship to the 100 000 year milankovitch cycle

central arctic ocean response to pleistocene earth orbital variations abstract three central arctic ocean sediment cores were sampled for percentage carbonate number of foraminifera and texture these three parameters were used in spectral analyses to test the idea that the ice covered arctic ocean may respond to orbital forcing in a different manner than has been indicated for lower latitude ice free oceans the record for two of the cores represents approximately 1 my and the record for the third approximately 400 000 yr the 100 000 yr frequency is well represented in all of the cores a 40 000 yr frequency may be present as well an unexpected 70 000 yr frequency occurs in most of the spectra and may reflect nonlinear sedimentation rates or the combined effect of obliquity and eccentricity the strong 100 000 yr signal confirms that in spite of ice feedback the arctic ocean has responded to orbital forcing in much the same manner as have ice free oceans

structure of a continental strike slip fault from deep seismic reflection walls boundary fault northern british caledonides reprocessing of four offshore deep reflection profiles across the walls boundary strike slip fault postulated as the northward continuation of the great glen fault over the shetland platform provides useful constraints on the lithospheric structure of a major continental transform and some insight into the manner in which strike slip faults deform the reprocessing was aimed at delineating complex structure and reducing noise contamination and consisted of analyses of diffractions and amplitude variations and experimentation with seismic migration the results demonstrate a highly variable crustal and uppermost mantle structure for the walls boundary fault along more than 150 km of its length six key observations can be made from this study 1 as middle and lower crustal reflections approach the fault they are truncated by and do not continue across the downward projection of the fault 2 trends in reflection structure of the crust and or uppermost mantle differ markedly from one side of the fault to the other 3 diffractions typically are concentrated at the level of the moho discontinuity directly beneath the fault 4 after seismic migration steeply dipping reflectors are imaged in places directly beneath the fault in the lower crust 5 in one location the moho reflection is deflected across the fault into a narrow synform or keel structure which is exactly bisected by the downward projection of the fault and 6 in a separate location a prominent upper mantle reflector is truncated across the fault a vertical or steeply dipping structure is deduced for the fault in much of the crust and perhaps parts of the uppermost mantle however more diverse reflecting structures are interpreted for the lower crust such as the moho deflection and steeply dipping reflectors directly beneath the fault that may have been related to a localized component of transpression and resultant crustal thickening the presence of diffractions at the level of the moho discontinuity where the downward projection of the fault intersects it suggests points of structural roughness that may be related to deformation of the moho by late motion along the fault integrating the interpretation of the reflection data with previous geological studies implies that the age of the moho deflection is post early cretaceous but that the dipping structure adjacent to and cut off by the fault is probably caledonian silurian early devonian although the disparate structure of the crust on opposite sides of the fault supports geologic interpretations of large scale displacement a major step in the moho discontinuity directly beneath the walls boundary fault cannot be substantiated from the seismic data

new faunal and isotopic evidence on the late weichselian holocene oceanographic changes in the norwegian sea downcore studies of planktonic and benthonic foraminifera and 18o and 13c in the planktonic foraminifer neogloboquadrina pachyderma sin in two piston cores from the southern part of the norwegian sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1 prior to oxygen isotope termination ia 16 000 13 000 yr b p an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice covered surface layer in the norwegian sea close to termination ia well oxygenated deep water probably with positive temperatures was introduced this deep water which must have had physical and or chemical parameters different from those of present deep water in the norwegian sea could have been introduced from the north atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the norwegian sea a seasonal ice cover in the southern part of the norwegian sea is proposed for the period between termination ia and the beginning of ib close to 10 000 yr b p the present situation with strong influx of warm atlantic surface water and deep water formation by surface cooling was established at termination ib

constraints on sst estimates for the northern north atlantic nordic seas during the lgm abstract a map of estimated calcification temperatures of the planktic foraminifer neogloboquadrina pachyderma sinistral tnps for the nordic seas and the northern north atlantic for the last glacial maximum was produced from oxygen isotopes with support of mg ca ratios to arrive at the reconstruction several constraints concerning the plausible salinity and 18 o fields were employed the reconstruction indicates inflow of temperate waters in a wedge along the eastern border of the nordic seas and at least seasonally ice free waters the reconstruction from oxygen isotopes shows similarities with mg ca based paleotemperatures in the southern and southeastern sector while unrealistically high mg ca values in the central nordic seas prevent the application of the method in this area the oxygen isotope based reconstruction shows some agreement with temperature reconstructions based on the modern analogue technique but with somewhat lower temperatures and a stronger internal gradient inside the nordic seas all told our results suggest a much more ice free and dynamic high latitude ocean than the climap reconstruction

early devonian pre acadian magnetization directions in lower old red sandstone of south wales uk summary two components of magnetization have been resolved from the lower old red sandstone of south wales all 39 sampled sites lie north of the variscan front and all but three are largely unaffected by variscan folding thirteen sites yield a high unblocking temperature magnetization component which pre dates acadian mid devonian folding the site mean direction for this component dec 232 2 inc 31 9 95 8 5 yields a pole position lat 7 3 s long 306 7 e which can be assigned an early devonian age a lower unblocking temperature component is present at 38 of the sampled sites this component post dates both the acadian and variscan folding has reversed polarity and a mean direction dec 193 8 inc 7 2 95 2 6 which corresponds to a pole position lat 40 4 s long 338 0 e consistent with a latest carboniferous or early permian age the early devonian pole position confirms the existence of a siluro devonian inflexion in the apparent polar wander path apwp for southern britain which coincides with an inflexion in the apwp for scotland britain north of the iapetus suture indicating the closure of the iapetus ocean by siluro devonian time the early devonian palaeolatitude 17 s 5 is consistent with an early devonian configuration in which gondwana laurentia baltica and avalonia were part of a single supercontinent

stable oxygen and carbon isotopes in planktic foraminifers from arctic ocean surface sediments reflection of the low salinity surface water layer planktic foraminifers neogloboquadrina pachyderma sin from 87 eastern and central arctic ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition additional results from 52 stations were taken from the literature the lateral distribution of 18o full size image 33 atlantic waters entering the arctic ocean through the fram strait 18o values decrease both to the barents shelf and to the north pole in accordance with the decreasing salinities of the halocline waters in the nansen basin a strong n s 18o gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources i e salinity reduction from sea ice meltwater in the south and from light isotope waters meteoric precipitation and river runoff in the northern part of the basin north of the gakkel ridge 18o and salinity gradients are in good accordance and suggest less influence of sea ice melting processes the 13c full size image 1 k values of n pachyderma sin from arctic ocean surface sediment samples are generally high 0 75 0 95 lower values in the southern eurasian basin appear to be related to the intrusion of atlantic waters the high 13c values are evidence for well ventilated surface waters because the perennial arctic sea ice cover largely prevents atmosphere ocean gas exchange ventilation on the seasonally open shelves must be of major importance lack of 13c gradients along the main routes of the ice drift from the siberian shelves to the fram strait suggests that primary production i e co2 consumption does probably not change the co2 budget of the arctic ocean significantly

roberts mountains allochthon and the western margin of the cordilleran miogeocline in the northern ritter range pendant eastern sierra nevada california the truncated southwestern edge of the roberts mountains allochthon is exposed in the northern ritter range pendant in the eastern sierra nevada structurally overlying parautochthonous rocks of the cordilleran miogeocline the northern ritter range pendant exposes units that have the same stratigraphic affinities and structural relationships as rocks of the antler orogenic belt in nevada paleozoic metasedimentary rocks exposed in the pendant consist of two major units 1 a structurally complex disrupted chert and argillite unit interpreted to be correlative with the roberts mountains allochthon and 2 a stratigraphically coherent siliceous and calcareous unit the rush creek sequence that is interpreted to be part of a transitional outer shelf and slope assemblage of the lower paleozoic cordilleran miogeocline in the northern ritter range pendant the roberts mountains allochthon structurally overlies the rush creek sequence along a north striking steeply dipping fault zone that may be a preserved remnant of the roberts mountains thrust which in north central nevada emplaced the allochthon over outer shelf and slope strata of the cordilleran miogeocline during the late devonian early mississippian antler orogeny these stratigraphic and structural belts are truncated on the southwest side of the pendant by the gem lake shear zone a northwest trending dextral strike slip fault associated with the cretaceous sierra nevada batholith the northern ritter range pendant thus defines both the southwestern limit of the antler orogenic belt and the westernmost exposures of parautochthonous miogeoclinal rocks in the central cordillera

palaeomagnetism and 40ar 39ar dating of the tregor dolerites armorican massif france abstract the tregor doleritic dike swarm intrudes the cadomian north tregor batholith armorican massif france alternating field a f and thermal demagnetization performed on 158 samples from 18 dolerite dikes and 37 samples from 4 baked contact sites reveal a multi component magnetization and a complex magnetic mineralogy which was thoroughly investigated with thermomagnetic experiments and polished thin section examinations three magnetization components were recognized in addition to a low temperature component with a viscous origin the most frequently observed component named b d 214 i 10 was isolated at 12 sites independent upon their magnetic mineralogy and appears to be a remagnetization negative baked contact test a carboniferous age of acquisition is inferred from comparison of the b component palaeopole 29 s 318 e with an armorican apwp at some sites after demagnetization of the b component higher temperature and coercivity components were isolated their directions fall into two groups named a and c positive baked contact tests were obtained for both the c component d 174 i 50 whose magnetic carrier is magnetite yields a palaeopole 11 s 2 e which is similar to some ordovician palaeopoles from the british isles south of the lapetus suture or eocambrian palaeopoles from the tregor area the a component d 191 i 33 whose magnetic carrier is magnetite partly transformed to leucoxene yields a palaeopole 58 s 336 e and a palaeolatitude 17 9 n not previously observed for the armorican massif in palaeozoic time comparison between this palaeolatitude and those for northern spain from ordovician to carboniferous time suggests a late silurian remanence age this interpretation supports the model of apparent polar wander for gondwana between ordovician and devonian time proposed by van der voo and bachtadse and briden 40 ar 39 ar dating of mineral separates from the dikes do not allow us to place constraints on the acquisition age of the a and c components

geologic and geophysical evidence for the influence of deep crustal structures on paleozoic tectonics and the alignment of world class gold deposits north central nevada usa abstract geologic data concur with geophysical and isotopic data that suggest the presence of deep crustal fault zones along the battle mountain eureka bme trend and elsewhere in nevada the fault zones may have originated during proterozoic rifting of the continent and were likely substantially reactivated and modified during paleozoic tectonism five distinct paleozoic structural and stratigraphic domains are defined that demonstrate the complexity of paleozoic tectonic events and also lead to hypotheses about ways in which the margin could have been modified the current locations of these domains adjacent to the geophysically and isotopically defined indicators of the buried continent edge corroborate their interactions with the continental margin during the tertiary preexisting crustal fault zones were intersected and reopened during episodes of extension and served as the conduits for deep sourced gold rich fluids which were disseminated into paleozoic slope facies sedimentary rocks forming sediment hosted carlin type and other deposits multiple factors including the locations of these deep seated structures the original configuration of the lower paleozoic continental margin of nevada and its subsequent reactivation during the paleozoic all were fundamental controls on the location of younger mineral deposits a clearer understanding of the original configuration of the margin and of the effects of subsequent paleozoic and mesozoic tectonic events on the margin would provide insight into the locations of these and other prospective mineral belts

palaeomagnetic argument for a stationary spitsbergen relative to the british isles western europe since late devonian and its bearing on north atlantic reconstruction abstract palaeomagnetic results from the devonian of central spitsbergen mimer valley formation billefjorden suggest an average palaeofield direction for the late devonian early carboniferous with declination 227 5 inclination 30 6 corresponding to a relative pole position at lat 24 s long 325 e this magnetization which is post tectonic is regarded as acquired chemically linked with the upper devonian svalbardian phase of deformation this result together with some recent data from central spitsbergen defines a devonian polar wander segment that accords extremely well with corresponding british data we interpret this in terms of no major displacement of central spitsbergen as compared with western europe since devonian time svalbard and the barents sea region have probably formed a fairly stable platform since the early devonian on the balance of available geological and palaeomagnetic evidence from spitsbergen the british isles and newfoundland the north atlantic region does not appear to have been subjected to strike slip motions in the order of thousands of kilometers in or since the late devonian

a palaeomagnetic study of the builth wells llandrindod wells ordovician inlier wales palaeogeographic and structural implications summary discrepancies exist in the southern british ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes although previous palaeomagnetic investigations from the builth inlier have delineated a three component remanence structure doubts have been raised concerning i the magnetization age of the supposed primary component p ii the structural setting of the sampling area llanelwedd quarry within a zone of strike slip deformation and iii whether detailed step wise demagnetization has fully separated the various magnetization components in addressing these problems we present new palaeomagnetic results as follows i a positive palaeomagnetic conglomerate test establishing a pre late llanvirn age for component p ii an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike slip tectonism are minor within the builth sampling area and iii evidence that component p is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35 s to be representative for the builth inlier we also present evidence for local syn volcanic deformation within llanvirn volcanics and for intrusion related deformation of llanvirn shales when the revised llanvirn pole from the inlier 3 s 4 e is combined with other data from southern britain in a statistical spline analysis a mean palaeolatitude of 44 5 s is calculated for builth in llanvirn times a palaeoreconstruction for 468 474 ma c mid llanvirn is presented utilizing this analysis

the ordovician history of the iapetus ocean in britain new palaeomagnetic constraints new late tremadoc early arenig palaeomagnetic results from sw wales imply that s britain part of eastern avalonia occupied a southerly latitude of c 60 s in early ordovician times when combined with scottish ordoviaan palaneomagnetic data which indicate a 15 s latitude the results indicate that the british sector of the iapetus ocean reached n latitudinal width of c 5000 km in tremadoc arenig times which was reduced to c 3000 km by llanvirn llandeilo mid ordovician times the new data resolve two previous controversies in palaeozoic palaeogeography first the high southerly palaeolatitude links avdonia to gondwana marginal to w africa thus reconciling codlicting reconstructions based upon either palaeomagnetic or faunal facies evidence alone second reliable llanvim palaeomagnetic data imply that avlonia had rifted northwards by arenig time whereas armorica remained proximal to northern africa throughout the ordovician the combined data therefore establish that avdonia and armorica formed separate micro continents when rifting from gondwana

geology and geochemistry of jasperoids from the gold bar district nevada gold bar is one of several carlin type gold mining districts located in the battle mountain eureka trend nevada it is composed of one main deposit gold bar five satellite deposits and four resources that contain 1 6 moz 50 t of gold all of the deposits and resources occur at the intersection of north northwest and northeast trending high angle faults in slope facies limestones of the devonian nevada group exposed in windows through ordovician basin facies siliciclastic rocks of the roberts mountains allochthon igneous intrusions and magnetic anomalies are notably absent the gold bar district contains a variety of discordant and stratabound jasperoid bodies especially along the wall fault zone that were mapped and studied in some detail to identify the attributes of those most closely associated with gold ore and to constrain genetic models four types of jasperoids j0 j1 j2 and j3 were distinguished on the basis of their geologic and structural settings and appearance field relations suggest that j0 formed during an early event petrographic observations geochemistry and 18o values of quartz suggest it was overprinted by the hydrothermal event that produced ore related j1 j2 and j3 jasperoids and associated gold deposits the greater amount of siliciclastic detritus present in j0 jasperoids caused them to have higher 18o values than j1 2 3 jasperoids hosted in underlying limestones ore related jasperoids are composed of main ore stage replacements and late ore stage open space filling quartz with variable geochemistry and an enormous range of 18o values 24 5 and 3 7 jasperoids hosted in limestones with the most anomalous au ag hg as sb tl concentrations and the highest 18o values are associated with the largest deposits the 28 range of jasperoid 18o values is best explained by mixing between an 18o enriched fluid and an 18o depleted fluid the positive correlation between the sizes of gold deposits and the 18o composition of jasperoids indicates that gold was introduced by the 18o enriched fluid the lowest calculated 18o value for water in equilibrium with late ore stage quartz at 200 c 15 and the measured d value of fluid inclusion water extracted from late ore stage orpiment and realgar 116 indicate that the 18o depleted fluid was composed of relatively unexchanged meteoric water the source of the 18o enriched ore fluid is not constrained the 34s values of late ore stage realgar orpiment and stibnite 5 7 15 5 and barite 31 5 40 9 suggest that h2s and sulfate were derived from sedimentary sources likewise the 13c and 18o values of late stage calcite 4 8 to 1 5 and 11 5 to 17 4 respectively suggest that co2 was derived from marine limestones based on these data and the apparent absence of any eocene intrusions in the district gold bar may be the product of a nonmagmatic hydrothermal system

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

reappraisal of scottish ordovician palaeomagnetism reply to storetvedt and deutsch summary storetvedt deutsch recommend refinements to the ordovician silurian apparent polar wander path for scotland which are not supported by the bulk of the palaeomagnetic evidence and are based on an arbitrary selection of data they seek to reinforce their interpretation by a geometrical adjustment which they invest with a tectonic significance viz large displace ment on the great glen fault since the mid devonian yet this adjustment is erratically applied is palaeomagnetically unjustified and is geometrically inconsistent with pure transcurrent motion along the length of that fault as part of their argument storetvedt deutsch attempt to reinterpret the palaeomagnetic data from aberdeenshire they do so on the basis of ill founded criticism of our previous data and wrong analysis of that of carniichael storetvedt the only substantial new point with which we sympathize see briden eta2 1986 is that the bulk of the nrm in most of the syn and pre tectonic rocks of the scottish caledonides is predominantly of crm rather than trm origin but in the case of the aberdeenshire gabbros again contrary to storetvedt deutsch we maintain this nrm acquisition was related to the waning of orogeny their alternative proposition of a distinct post orogenic event is not consistent with the regional geology and lacks the support of adequate experimental evidence likewise the assertions they have made regarding thermo chemical overprinting of the northwest highland syenites are unwarranted

pleistocene calcite lysocline and paleocurrents of the central arctic ocean and their paleoclimatic significance most previous references to the depth of the arctic ocean calcite lysocline have been based on comparison with the known north atlantic carbonate compensation depth foraminifera from cores taken at depths ranging from 2316 to 3956 m provide the first firm calcite lysocline constraints for the central arctic ocean these data suggest progressive lowering of the calcite lysocline to at least 3956 m during the past 1 5 m y interrupted by 300 m rises of the lysocline level that apparently correspond with interglacial and early glacial climate conditions most cores from less than 2450 m indicate variable foraminifera abundance but continual presence of foraminifera for the past 1 5 m y low abundances commonly occur in coarse textured sediment and are interpreted to represent low productivity during major deglaciations within certain equivalent lithostratigraphic units representing the past 1 5 m y there is an absence of foraminifera in cores from depths greater than 2450 m this absence of foraminifera is interpreted to be due to dissolution dissolution intervals are associated with fine grain sediments interpreted to represent interglacial and early glacial climate conditions the interpretation of a rise in the lysocline level during interglacials is in apparent disagreement with studies reported from lower latitudes in the atlantic ocean but is complementary with the hypothesis that formation of norwegian greenland sea deep water ngdw and cold canada basin deep water occurs during interglacials paleocurrent data from the lomonosov ridge and the adjacent makarov basin are interpreted to indicate that during periods of increased glacial ice influx into the arctic ocean system there was reduced current activity in the bottom and intermediate water masses relative to periods when little glacial ice was present this is in accord with the idea that ngdw affects intermediate and deep water circulation in the central arctic ocean and hence the calcite lysocline level

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

palaeomagnetic data from the borrowdale volcanic group volcano tectonics and late ordovician palaeolatitudes nineteen palaeomagnetic sampling sites from the borrowdale volcanic group between borrowdale and langdale english lake district yield high unblocking temperature magnetization components which postdate the structural tilt and therefore postdate the formation of the broad block faulted syncline which characterizes this part of the central lake district the mean magnetization direction before tilt correction dec 347 2 inc 61 9 95 6 9 corresponds to a palaeolatitude of 43 s 5 7 the magnetization is associated with pervasive late ordovician hydrothermal alteration and is certainly pre devonian based on comparison with available palaeomagnetic data from southern britain this implies that the block faulted synclinal structure of the borrowdale langdale region is pre acadian in age consistent with recent interpretations of late ordovician volcano tectonics based on mapping and volcanological studies

short paper palaeomagnetic constraints on the geological terrane models of the scottish caledonides a compilation of new and published palaeomagnetic data from the scottish caledonides allows construction of apparent polar wander paths apwps for the grampian highlands midland valley and southern uplands terranes geological incompatibilities between terranes are the result of predominantly palaeolongitudinal movements prior to late silurian times a common late silurian early devonian corner in each apwp suggests the terranes to have docked to within the errors of the individual determinations by this time

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

late pleistocene stratigraphy and micropaleontology of a part of the eurasian basin fram basin central arctic ocean during the 1979 lomonosov ridge experiment lorex 12 short gravity cores were collected from the fram basin part of the eurasian basin on the eastern flank of the lomonosov ridge sediments of these cores are organized into 11 lithologic units that constitute the first stratigraphy for any part of the deeper eurasian basin foraminifera are the same species that have been described elsewhere in the central arctic ocean but are abundant only in the uppermost part of the cores neogloboquadrina pachyderma is the most abundant species but the presence ofeponides tumidulus horvathi andstetsonia arctica in core ssk 2 provide a general chronologic framework for interpreting the fram basin sediment the stratigraphy a k is unique and is only partially correlated with other sediments of the north polar region including that of the adjacent lomonosov ridge and makarov basin amerasian basin differences in stratigraphies of the lomonosov area are interpreted to be at least in part the result of winnowing by turbidity currents and by currents crossing the ridge from the fram basin toward the makarov basin the sediment consists of silty lutites and sandy lutites as well as laminated lutites interpreted to have been deposited as a result of glacial marine and turbidite sedimentation these short cores document the same sedimentary processes in part of the arctic ocean east of the lomonosov ridge as have been previously reported for the western amerasian basin

palaeomagnetism of a caledonian ophiolite complex karmoy southwest norway abstract the palaeomagnetism of the karmoy ophiolite suite emplaced at the southwest extremity of the scandinavian caledonides in middle upper ordovician times is described low intensities of magnetisation and low q n values in the bulk of the constituent facies are linked to the effects of low grade metamorphism but ultramafic pods that have experienced serpentinisation yield well defined single component magnetisations a predominant a component of magnetisation isolated in 35 samples yields a mean of d i 51 58 95 5 this population is discrete from a subsidiary b component recognised in 17 samples with a mean direction of 145 63 95 8 a minor c component d i 330 60 95 8 is also identified and small numbers of anti parallel components are identified in each case an upper ordovician ignimbrite from kattnakken northeast of karmoy yields an in situ component of d i 270 38 together with similar components recognised elsewhere this mean d direction is most closely compatible with directions recognised in upper silurian lower devonian rocks from the scottish sector of the caledonides it is interpreted as an overprint of this age but may include a component of local rotation two interpretations are considered for the remanence record in the karmoy complex the a component could record the influence of a thermal event linked to uplift of the continental margin and development of the adjoining north sea basin in mesozoic times if this margin has been tilted seawards by 20 since magnetisation no plausible tectonic model can bring the b component into conformity with the post 300 ma apparent polar wander apw path and it is alternatively proposed that both the a and b components record upper ordovician post emplacement remanences with this interpretation the data complement a range of palaeomagnetic results from middle upper ordovician igneous and metamorphic rocks from north atlantic bordering terranes yielding intermediate to high palaeolatitudes and contrasting with older and younger data collectively they imply that the iapetus ocean had effectively closed by these times and that large apw movements took place between mid ordovician and mid silurian times

the palaeogeographic evolution of southern britain during early palaeozoic times a reconciliation of palaeomagnetic and biogeographic evidence abstract palaeomagnetic biogeographic and palaeoclimatic evidence together suggest that in the early ordovician southern britain lay off the west african margin of gondwana at around 60 s the combination of these disciplines reduces latitude uncertainties to around 5 to 10 degrees rifting of avalonia from gondwana was followed during most of the ordovician by northward drift as avalonia and baltica converged with subduction of tornquist sea crust both continents had similar moderate northward drift rates 3 6 cm yr so their convergence probably had a considerable longitudinal component silurian and early devonian data indicate that northward drift of avalonia and baltica continued after their collision and that southern britain reached a latitude of around 20 s by c 400 ma

a sequential back arc and foreland basin thrust duplex model for the southern uplands of scotland thrust imbrication of ordovician and silurian submarine fan sequences overlapping pelagic deposits in the southern uplands has been interpreted in terms of an accretionary prism formed above a nw directed subduction zone structural features invoked to support accretion are not definitive and could be explained in terms of a thin skinned thrusting model new palaeocurrent and compositional evidence from llandeilo to mid llandovery age turbidites in the northern part of the southern uplands proves interdigitation of sediments with strongly contrasting petrography turbidites derived from the south contain significant quantities of fresh andesitic detritus whereas those from the north form more mature quartz rich formations this implies a back arc situation the turbidites being deposited in a basin with a relatively mature continental landmass to the north and a rifted continental fragment containing an active volcanic arc to the south oblique collision of the opposing continental margins of the iapetus ocean during the llandovery caused the cessation of subduction underthrusting of the southern margin initiated a se propagating thrust stack which deformed the back arc basin sequence and may eventually have ramped over the eroded and faulted remains of the volcanic arc a southward migrating foreland basin formed ahead of the rising thrust stack and is now represented by the late llandovery hawick group and wenlock sequences mid to end silurian sinistral strike slip resulted from oblique collision and produced a transpressional regime during which reactivation of deep seated structures allowed the intrusion of lamprophyre dykes and granites

palaeomagnetism of silurian sediments in w ireland evidence for block rotation in the caledonides summary a palaeomagnetic study of mid silurian wenlock sediments of the salrock formation in nw galway yields a reliable silurian palaeomagnetic pole position for w ireland at latitude 1 6 s longitude 287 7 e dp 2 5 dm 4 6 n 27 sites a further 12 sampling sites were located in silurian redbeds on clare island s mayo where a palaeomagnetic remanence of silurian age was also identified both remanences pre date local late caledonian folding however the clare island result has an anomalous azimuth when compared with the salrock result and with published silurian results for britain the two irish results can be reconciled by anticlockwise block rotation of the clare island region through 40 50 the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment strike slip displacement across the clew bay fault zone producing a sinistral shear couple might have enabled such a rotation the timing and geographic extent of the proposed block rotation is as yet poorly defined however a younger age limit for rotation is provided by a late devonian or carboniferous partial magnetic overprint observed throughout both study areas and from geological evidence it seems likely that rotation is confined to the clew bay fault zone the dalradian rocks of the connemara massif located to the south of the salrock district have an e w structural grain some workers have proposed clockwise rotation of the connemara massif of ca 30 at between 500 and 390 ma which would bring the structural trends in w ireland into parallelism with caledonian trends in scotland because the silurian salrock succession which rests unconformably on the dalradian basement of connemara shows no such anomaly it provides a younger age limit for the possible rotation of connemara

stable isotope stratigraphy of the arctic ocean fram strait to central arctic abstract a comparison of stable isotope and textural records of sediment cores from the fram strait and central arctic ocean to isotopic records from low latitude oceans indicates that the arctic mediterranean responded dynamically to climatic change during the pleistocene core mg 123 from the fram strait shows at least four significant low 18 o intervals 5 high 13 c intervals and five intervals with a low amount of coarse sediment the association of high 18 o values with coarse sediment intervals indicates increased glacial ice in the fram strait during glacial phases of the climate cycle peaks within the low 18 o intervals increase in magnitude from oldest to youngest suggesting that glacial interglacial transitions are pulsed the magnitude of the different low 18 o intervals increases from oldest to youngest this is interpreted to indicate that there has been a progressive intensification of the oceanographic response to glacial interglacial transitions in the fram strait during the past 524 ky time series spectral analysis suggests an age of approximately 524 ky for the oldest sediment in core mg 123 yielding an average sedimentation rate of approximately 1 66 cm 1000 yr stable isotope records from the central arctic ocean indicate that sedimentation rates are on the order of 1 3 mm 1000 yr the isotope records support the established central arctic ocean lithostratigraphy coarse sediment deposition in the central arctic is not as clearly related to glacial conditions as it is in the fram strait the oxygen isotope range of central arctic ocean records is accentuated relative to the global ice volume signal recorded from lower latitude cores this may be caused by variations in salinity temperature and thickness of the arctic ocean s low salinity surface layer oceanographic responses to climatic change recorded in the fram strait are also recorded in the central arctic ocean but with decreased resolution due to the magnitude of difference in the sedimentation rates between the two areas

paleoenvironments in the fram strait during marine isotope stages 2 6 based on planktonic paleobiological and stable isotope proxies and ice rafted debris abstract two sediment cores from the knipovich ridge in the fram strait have been studied to examine paleoceanographic and climatic changes in the polar north atlantic during the late middle and late pleistocene as inferred from the data on foraminifers nannofossils diatoms ird oxygen isotope values and ams 14 c ages the recovered deposits span the interval of mis 2 6 several beds marked by a high productivity of microplankton and often by a great ird content are recorded in mis 2 mis 5a 5c 5e and mis 6 suggesting a repeated occurrence of seasonally ice free waters and strong meridional circulation in the eastern fram strait the planktonic foraminifers globigerinoides ruber globorotalia scitula g crassaformis and pink colored globigerina rubescens exotic for this latitude were identified in three points of the section a hiatus in one of the cores studied was revealed from comparison of ird variations and the occurrence of pullenia bulloides

the tectonic implications of solundian upper devonian magnetization of the devonian rocks of kvamshesten western norway the allochthonous old red sandstone of kvamshesten western norway records polyphase orogenic deformation and palaeomagnetic results from both the devonian sediments and mylonites associated with the basal thrust define a syn to post tectonic magnetization withd 218 i 3 and 95 9 7 the corresponding pole position lat 21 s long 324 e suggests a late devonian early carboniferous magnetization age solundian and probably dates the time of thrust movements

superimposed recent permo carboniferous and ordovician palaeomagnetic remanence in the builth volcanic series wales the builth volcanic series of llanvirnian age in llanelwedd quarries mid wales carries three components of natural remanent magnetisation component p regarded as primary is a thermochemical remanence directed at d 181 7 i 54 5 95 4 4 relative to bedding component s is a secondary component with in situ d 178 7 i 6 7 95 5 4 and is believed to be a low temperature chemical remanence crm of permo carboniferous age component r is directed close to the present geomagnetic field and is believed to be a recent viscous remanence vrm the results are of interest for three reasons first they are an unusually good example of multi component nrm analysis the three components being so clearly discriminated by thermal demagnetisation because they have almost completely separate blocking temperature ranges second they provide evidence of a permo carboniferous event possibly a mild thermal or hydrothermal pulse promoting crm acquisition some 40 km north of the hercynian orogenic front third they illustrate very clearly the importance of detailed demagnetisation this work revises the pole position for these rocks by 10 and removes an obstacle to the palaeomagnetic recognition of the 1000 km wide iapetus ocean cutting britain in ordovician time

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

a revised palaeozoic apparent polar wander path for southern britain eastern avalonia summary a revised apparent polar wander path apwp is presented for palaeozoic southern britain the new path based on a structural reinterpretation of existing data combined with new data from wales differs significantly from previous estimates in the following ways 1 the 1 ocus of the ordovician path segment is extended by approximately 25 degrees of arc 2 revised time calibration of the apwp suggests more ordovician apw than previously calculated and 3 the new path implies middle ordovician separation across the british sector of iapetus to be greater than previous palaeomagnetic estimates based on apwp analyses c 3300 km northern britain c 133 southern britain c 45s

depositional setting and paleogeography of ordovician vinini formation central nevada the eugeoclinal strata of the ordovician vinini formation composes most of the roberts mountains allochthon rma its stratigraphy reconstructed in the roberts mountains can be precisely correlated throughout much of the rma and into coeval strata of the autochthonous miogeocline by means of graptolite and conodont biostratigraphy the vinini is a mixture of clastic lithologies with some limestone and greenstone coarse clastics characterized by well rounded and well sorted sands derived from cratonic sources occur in two separate intervals and provide critical data on depositional and paleogeographic setting the lower interval hundreds of meters thick was deposited in the latest ibexian earliest whiterockian and can be closely correlated throughout central nevada it is a mixture of quartz sandstone siltstone limestone and calcareous sandstone deposited by turbidity flows during a lowstand of sea level both eastern and western sources have been interpreted for these sands the upper interval is a prominent pure quartzite up to 20 m thick deposited as a prograding blanket of sand in the latest whiterockian earliest mohawkian it occurs in the vinini in the northern toquima range and in a parautochthonous sequence of transitional strata in the southern toiyabe range this interval represents the most basinward edge of the eureka quartzite more which was also deposited across the miogeocline the presence of sand of the eureka quartzite in the rma indicates that the basin in which the rma strata were deposited was immediately adjacent to the margin of north america in the ordovician less

palaeomagnetic studies within the ballantrae ophiolite southwest scotland magnetotectonic and regional tectonic implications abstract the early arenig slockenray formation within the ballantrae ophiolite southwest scotland displays a multivectorial magnetisation structure two components s and m are identified delineated by differing blocking temperature coercivity spectra component s is removed around 200 c 10 mt and is regarded to be of recent viscous origin component m forms the characteristic formation magnetisation and resides in both magnetite and haematite extensive sampling of all exposed lithologies reveals an in situ non fisherian distribution of the characteristic magnetisation defining an envelope from se moderate positive to sw shallow negative directions a negative infra formation conglomerate test identifies this component as a pervasive overprint a second conglomerate test performed in the overlying benan conglomerate of llandeilo age reveals dispersely directed magnetisation with a stability range equivalent to that of component m this field test therefore defines a maximum remagnetisation window of 30 million years for the characteristic remanence hard viscous magnetisations are identified both in the benan conglomerate and at some sites within the slockenray formation structurally corrected site mean results from the slockenray formation define a non fisherian distribution and form a small circle partial arc centred on a vertical axis nw moderate positive to sw moderate positive directions a combined palaeomagnetic fold and fault test suggests that acquisition of component m pre dates both folding and faulting the resulting palaeolatitude of remanence acquisition 28 8 s implies a tectonic position close to the southern laurentian margin for the ballantrae ophiolite in arenig times

late pleistocene paleo oceanography of the norwegian greenland sea benthic foraminiferal evidence fluctuations in benthic foraminiferal faunas over the last 130 000 yr in four piston cores from the norwegian sea are correlated with the standard worldwide oxygen isotope stratigraphy one species cibicides wuellerstorfi dominates in the holocene section of each core but alternates downcore with oridorsalis tener a species dominant today only in the deepest part of the basin o tener is the most abundant species throughout the entire basin during periods of particularly cold climate when the norwegian sea presumably was ice covered year round and surface productivity lowered portions of isotope stages 6 3 and 2 are barren of benthic foraminifera this is probably due to lowered benthic productivity perhaps combined with dilution by ice rafted sediment there is no evidence that the norwegian sea became azoic the holocene and substage 5e the last interglacial are similar faunally this similarity combined with other evidence supports the presumption that the norwegian sea was a source of dense overflows into the north atlantic during substage 5e as it is today oxygen isotope analyses of benthic foraminifera indicate that norwegian sea bottom waters warmer than they are today from substage 5d to stage 2 with the possible exception of substage 5a these data show that the glacial norwegian sea was not a sink for dense surface water as it is now and thus it was not a source of deep water overflows the benthic foraminiferal populations of the deep norwegian sea seem at least as responsive to near surface conditions such as sea ice cover as they are to fluctuations in the hydrography of the deep water benthic foraminiferal evidence from the norwegian sea is insufficient in itself to establish whether or not the basin was a source of overflows into the north atlantic at any time between the substage 5e 5d boundary at 115 000 yr b p and the holocene

quaternary history of sea ice and paleoclimate in the amerasia basin arctic ocean as recorded in the cyclical strata of northwind ridge the 19 middle early pleistocene to holocene bipartite lithostratigraphic cycles observed in high resolution piston cores from northwind ridge in the amerasia basin of the arctic ocean provide a detailed record of alternating glacial and interglacial climatic and oceanographic conditions and of correlative changes in the character and thickness of the sea ice cover in the amerasia basin glacial conditions in each cycle are represented by gray pelagic muds that are suboxic laminated and essentially lacking in microfossils macrofossils trace fossils and generally in glacial erratics interglacial conditions are represented by ochre pelagic muds that are oxic and bioturbated and contain rare to abundant microfossils and abundant glacial erratics the synglacial laminated gray muds were deposited when the central amerasia basin was covered by a floating sheet of sea ice of sufficient thickness and continuity to reduce downwelling solar irradiance and oxygen to levels that precluded photosynthesis maintenance of a biota and strong oxidation of the pelagic sediment except during the early part of 3 of the 19 synglacial episodes when it was periodically breached by erratic bearing glacial icebergs the floating arctic ocean sea ice sheet was sufficiently thick to block the circulation of icebergs over northwind ridge and presumably other areas of the central arctic ocean interglacial conditions were initiated by abrupt thinning and breakup of the floating sea ice sheet at the close of glacial time which permitted surges of glacial erratic laden icebergs to reach northwind ridge and the central arctic ocean where they circulated freely and deposited numerous and relatively thick erratic clast rich beds breakup of the successive synglacial sea ice sheets initiated deposition of the interglacial ochre mud units under conditions that allowed sunlight and increased amounts of oxygen to enter the water column resulting in photosynthesis and biologic productivity and strong oxidization of the pelagic sediment the lithostratigraphy of northwind ridge suggests that during at least late pleistocene time glacial conditions in the arctic ocean were initiated abruptly and continued unabated until terminated also abruptly by onset of the succeeding interglacial warming variations in abundance of glacial erratics within the interglacial units of the late pleistocene indicate that during at least most interglacial episodes northern north america was glaciated but with generally diminishing severity until onset of the succeeding continental glaciation magnetostratigraphy suggests that the glacial interglacial cycles on northwind ridge had an average periodicity of approximately 93 5 k y during the brunhes normal and approximately 105 k y during the latter part of the matuyama reverse polarity zone these average periodicities are close to the 100 k y temperature cycles found in north atlantic deep water sediments of the brunhes normal polarity chron which have been ascribed to forcing by a milankovitch eccentricity cycle they are also close however to the average interval 101 k y between the aperiodic glacial terminations in the 500 k y pleistocene continental climate record from devil s hole nevada which have been ascribed to nonlinear feedbacks within the earth s atmosphere ice sheet ocean system

ice rafting history from the spitsbergen ice cap over the last 200 kyr abstract three piston cores taken from the mid to upper continental slope of the spitsbergen margin have been used to elucidate the calving history of the spitsbergen ice mass for the last 200 kyr the abundance of clasts larger than 2 mm was used as a measure of ice rafted detritus ird in the cores these clasts were counted from x ray photographs the fraction coarser than 63 m was also measured and compared to the clast counts to assess the validity of this parameter as a measure of ird content the correlation between clast counts and the fraction 63 m was poor and it was concluded that the fraction 63 m was a poor measure of ird in the spitsbergen cores in cores close to a major continental landmass or from an area of steep submarine relief the fraction 63 m is likely to be affected by factors other than ice rafting alone the ird peaks identified in this study were thought to be produced by the following advance of the spitsbergen ice cap during periods of increased moisture supply during interstadial periods mid stage 5 and stage 3 disintegration of a large ice mass on the continental shelf during deglaciations stages 6 5e 5b 5a and 2 1 boundaries summer melting of a large ice mass during glacial periods stage 6 a good correlation was found between interpreted ice advances from ird input to the spitsbergen margin and postulated ice advances from terrestrial evidence the ird peaks found from the spitsbergen margin appear to be produced by a different mechanism from that proposed for the production of the heinrich layers of the north atlantic these are thought to be produced by the collapse of the laurentide ice sheet once it reaches a threshold size correlation of heinrich layers produced from a mid latitude ice sheet with the ird events of the norwegian greenland sea is not possible due to their different mechanism of formation in fact there is possibly an antiphase relationship as heinrich layers are formed mainly during glacial periods whereas ird peaks in the greenland sea are produced during periods of rapid ice advance when moisture supply is high when relatively warm atlantic waters enter the norwegian greenland sea during interstadial periods as well as during melting events

late quaternary changes in surface water and deep water masses of the nordic seas and north eastern north atlantic a review quantitative and semiquantitative proxy data based on more than 200 core top samples and 100 deep sea cores lead to important new insights about late quaternary changes in paleo oceanography climate and microfaunal habitats in the north eastern north atlantic and nordic seas insights resulting from a detailed investigation by the kiel research project sfb 313 132 summarized in this paper planktonic foraminifera species provide reliable tracers of past sea surface temperatures and currents the genus beella in particular was found to trace subtropical water masses up to the far north benthic foraminifera species served as sensors of bottom currents and local flux rates of organic matter new orders of time resolution are reached via stable isotope stratigraphy and accelerator mass spectrometry carbon 14 dating allowing the identification of meltwater events lasting a few hundred years and shorter a time range where however the yet unquantified role of bioturbation presents a growing problem based on this high resolution stratigraphy a number of time slices synoptic time intervals are defined to reconstruct the incursion of atlantic water masses to map paleocurrent patterns within the nordic seas and the north eastern north atlantic and to test alternative circulation models for example for the last glacial maximum lgm and various meltwater episodes these are clearly coeval with dansgaard oeschger events found in greenland ice cores with the actual cause of the flickering climate as yet unknown likewise there is ongoing controversy about the extent of past sea ice cover and about possible changes from the present anti estuarine to estuarine mode of deep water exchange between the north atlantic and the nordic seas during the lgm south of iceland however the history of deep water renewal over the last glacial cycle covering the last 30000 years was largely deciphered

abrupt climatic change during the last interglacial glacial cycle in the polar north atlantic abstract we have investigated five sediment cores from the margin and abyssal plain off western svalbard barents sea in the polar north atlantic we discuss the palaeoceanography and its relationship to glacial history during the last interglacial glacial cycle based on detailed stratigraphic analyses of planktic and benthic foraminiferal fauna oxygen and carbon isotopes on foraminifera ice rafted debris grains 500 m and radiocarbon dates the sediment cores combined cover the last interglacial glacial cycle including marine isotope stage mis 5 1 sedimentation rates are generally high ranging from 3 to 100 cm 1000 years atlantic water repeatedly reached the polar north atlantic during the last interglacial glacial cycle and was present for at least 50 of the total time interval periods having atlantic water advection termed hp zones hp high productivity are characterised by high planktic foraminiferal production a small increase of benthic and subpolar planktic foraminifera benthic foraminiferal and stable isotope data indicate active deep water formation during the hp zones in substage 5e there are indications of sea surface temperatures similar to those of today the major glaciations on svalbard during the last interglacial glacial cycle are related to hp zones some hp zones correspond to an early build up phase of the ice sheets peak glacials all correspond to one hp zone that subsequently is terminated by a meltwater event however periods with advection of atlantic water during mid mis 3 do not correlate to a glacial phase on svalbard but rather to the western fennoscandian ice sheet the records in the present study are correlated to the northeast atlantic the arctic ocean and to the greenland ice core record and show parallel millennial scale variability

late neogene climate evolution of the central arctic ocean abstract because no sediment of post eocene to late miocene or pliocene age has been recovered from the central arctic ocean oceanographic conditions during the middle cenozoic are unknown the oldest late cenozoic sediment is glacial marine and contains agglutinated foraminifera a few calcareous organisms are present in the oldest late cenozoic sediment with an age of 2 4 ma but at approximately the time as deposition of lithostratigraphic unit f sometime between 2 0 and 1 5 ma there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central arctic ocean many of the newly introduced species are atlantic in origin preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the arctic ocean ccd level and this may be explained by increased circulation with the northern greenland sea details of the change in threshold values in the fram strait required for the introduction of relatively warmer and carbonate rich water into the central arctic ocean are unknown there is evidence that spreading rates along the north atlantic nansen ridge system increased during the pleistocene and this may have permitted increased circulation between the north atlantic and the central arctic ocean this important change in arctic ocean circulation corresponds to increased pleistocene seasonality in the northern hemisphere

paleomagnetic results from the peterhead granite scotland implication for regional late caledonian magnetic overprinting abstract palaeomagnetic results from the peterhead granite silurian ne grampian highlands define a characteristic magnetization with overall parameters of dec 180 4 inc 22 3 and a 95 5 2 these results agree with other newer granite data from north scotland an east west trending dyke cutting the peterhead granite shows an extremely well defined paleomagnetic direction with dec 192 5 inc 19 1 and a 95 1 3 suggesting a permo carboniferous age the peterhead granite results are seen in conjunction with other palaeozoic palaeomagnetic data from scotland it is concluded that the observed directional spread of characteristic remanence directions previously reported from the aberdeenshire gabbros are not related to slow post orogenic cooling watts and briden but is rather seen as the result of late caledonian magnetic overprinting

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

palaeozoic palaeomagnetic studies in the welsh basin recent advances in the last two years new palaeomagnetic data fro m wale s have resulted i n radical revision of the ordovician palaeogeography of eastern avalonia part of the southern margin of the iapetus ocean combined with palaeozoic palaeomagnetic data from laurentia and gondwana these data suggest that eastern avalonia was a peri gondwanide high latitude continental fragment during at least part of ordovician time with a palaeolatitude of about 62 s and 51 s in arenig and llanvirn time respectively this implies a latitudinal width of the early ordovician iapetus ocean between eastern avalonia and laurentia of at least 30 geological evidence for the proximity of eastern avalonia and laurentia suggests that the intervening iapetus ocean closed during silurian time from late llandovery to early ludlow recent palaeolatitude data from the iapetus bordering continents are consistent wit h closure b y middle to late silurian time new pre acadian early devonian palaeomagnetic data from the old red sandstone places the welsh basin at about 17 s consistent with a palaeogeography in which laurentia baltica avalonia armorica and possibly gondwana wer e part o f a singl e supercontinent pervasiv e lat e carboniferous early permia n remagnetization affect s the welsh basin the remagnetization i s probably associated with fluids emanating from th e variscan thrust front w e do not observe remagnetization associate d with acadian orogen y and the remagnetizations which have been studied in more detail in north america appear to be a unique feature of the variscan hercynian alleghenian orogeny

late quaternary sedimentation in the eastern arctic basin stratigraphy and depositional environment abstract the late quaternary history of the arctic basin is poorly known because most sediment cores seemed to have accumulated very slowly based on magnetostratigraphy on the order of one to a few millimeters per thousand years two short sediment cores from the eurasian basin of the arctic ocean have now been dated by means of o and c isotopic ratios the o isotope stratigraphy suggests that these sediments accumulated much faster on the order of one to four centimeters per thousand years than in the central arctic ocean the cores penetrated sediments belonging to isotope stages 1 3 and allow a detailed description of the depositional environment under the arctic ice cover during the last ice age and the ensuing climatic warm interval

arctic ocean chronology confirmed by accelerator 14c dating the role of the arctic ocean in earth s climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable arctic chronology the first arctic ocean chronology based on u th and 14c data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates new accelerator 14c data support the earlier u th magnetostratigraphic dates and confirm the reliability of the established arctic ocean chronology

magnetic properties of the lower old red sandstone lavas in the midland valley scotland palaeomagnetic and tectonic considerations abstract thermal demagnetization studies of lavas in the strathmore area of the midland valley scotland support overall palaeomagnetic data found in previous studies of these rocks reduced directional scatter as compared to some earlier studies is attributed to more effective demagnetization resolving some of the directional complexity of previous studies combined magnetic fabric and directional analysis suggest that at least some deviating directions may be explained by local tectonism the existence of almost antiparallel directional groups and field tests give supporting evidence for a primary deuteric origin of the main magnetization of these rocks additionally a second remanence component having shallow reverse directions of magnetization is attributed to later remagnetization in old red sandstone time the midland valley results are seen in conjunction with other palaeozoic palaeomagnetic results and possible geodynamic implications are discussed