survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

rock magnetic properties and relative paleointensity stack between 13 and 24 kyr bp calibrated ages from sediment cores lake moreno patagonia argentina we conducted a detailed study of natural remanence and rock magnetic properties on three sediment cores from lake moreno patagonia argentina based on these measurements we constructed a relative paleointensity stack for the period 13 24 kyr bp calibrated ages rock magnetic properties of the sediment cores showed uniform magnetic mineralogy and grain size suggesting that they were suitable for relative paleointensity studies the remanent magnetisation at 20 mt nrm20 mt was normalised using the anhysteretic remanent magnetisation at 20 mt arm20 mt the saturation of the isothermal remanent magnetisation at 20 mt sirm20 mt and the low field magnetic susceptibility k spectral analysis showed that the normalised records were not affected by local environmental conditions the recorded pseudothellier paleointensity was compared with records obtained from conventional normalising methods comparing the paleointensity curves with others obtained previously in other lakes in the area has allowed us to reach reliable conclusions about centennial scale features 2008 elsevier b v all rights reserved

tajik basin and southwestern tian shan northwestern india asia collision zone 2 timing of basin inversion tian shan mountain building and relation to pamir plateau advance and deep india asia indentation the tajik basin and southwestern tian shan constitute the northwestern tip of the india asia collision zone basin inversion formed the thinskinned tajik fold thrust belt outlined by westward convex fold trains underlain by a decollement in jurassic evaporites the belt s leading edge the uzbek gissar and its transpressional northern lateral margin the tajik gissar constitute the thickskinned foreland buttresses apatite fission track data indicate 40 to 15 ma reheating by sediment burial in the tian shan in the gissar and the tajik fold thrust belt apatite fission track and u th he ages date the major phase of shortening erosion between 12 and 1 ma with exhumation to 2 to 3 km crustal depths within a few myr after onset of shortening shortening spread immediately across the fold thrust belt typical for belts floored by a detachment in ductile rocks and into the foreland buttresses reactivation concentrated in the internal eastern fold thrust belt with the thickest evaporates the youngest ages 6 6 1 6 ma occur along the vakhsh thrust the active erosional front of the fold thrust belt in the northeastern tajik basin where it narrows between the converging tian shan and pamir our study links major events in the pamir hinterland with the tajik basin and tian shan foreland in the late eocene early miocene the advancing pamir plateau crust loaded the foreland inducing subsidence reheating and early shortening basin inversion and major shortening transpression in the foreland buttresses from 12 ma onward were synchronous with the subcrustal indentation of indian lithosphere into the tajik tarim basin lithosphere and the onset of its rollback beneath the pamir

reconstructing holocene geomagnetic field variation new methods models and implications reconstructions of the holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long term solar terrestrial relationships and as relative dating tools for geological and archaeological archives here we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts igneous rocks and sediment records a new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data to reduce the influence of a few individual records all sedimentary data are resampled in 50 yr bins which also means that more weight is given to archaeomagnetic data during the inversion the sedimentary declination data are treated as relative values and adjusted iteratively based on prior information finally an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model as a result of the data adjustments power has been shifted from quadrupole and octupole to higher degrees compared with previous holocene geomagnetic field models we find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr the new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder possibly originating from the equator less

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

comment on experimental evidence for the pressure dependence of fission track annealing in apatite by a s wendt et al earth planet sci lett 201 2002 593 607 abstract the pressure experiments reported by wendt et al are cast in such a way as to question the fundamental basis underpinning apatite fission track thermochronology implying the possibility of a large systematic error in previous interpretations we find however that the study is severely compromised by fundamental errors in both experimental design and execution as well as lacking in consideration of a substantial body of previous work in the area of fission track annealing studies wendt et al have not attempted to extrapolate the results of their experiments to geologically relevant heating times and temperatures this has been the fundamental test that all previous annealing models have had to pass their study clearly fails this test moreover if significant pressure dependence does exist then it is implicit in existing deep borehole consistent annealing models whilst such models are interpolated in terms of temperature the borehole test means that they also accommodate any other factors which correlate with temperature including pressure the implications of the results reported by wendt et al have been overstated far from being intimidating we find that they have little relevance either to previous studies of apatite fission track annealing and extrapolations based on them or to the routine application of fission track analysis to elucidate thermal history information under geological conditions

thermal and exhumation history of sakhalin island russia constrained by apatite u pb and fission track thermochronology abstract sakhalin island represents a key locality to study the tectonic evolution of the western pacific the island is located at the amur okhotsk plate margin and records a complex thermotectonic history apatite double dating u pb and fission track and thermal history modelling were applied to three late eocene granitoid massifs within central and southern sakhalin the aniva okhotsk and langeri complexes apatite u pb results yield consistent late eocene 40 37 ma ages suggesting rapid post magmatic cooling apatite fission track results reveal bimodal age distributions with late eocene early oligocene 38 33 ma and early miocene 20 17 ma age populations that can be correlated with variations in uranium and chlorine concentrations thermal history modelling translates the aft age bimodality into two phase cooling histories the timing of the early cooling phase 38 33 ma corresponds with the apatite u pb ages indicating rapid cooling to at least 100 c during the late oligocene the second cooling phase at 20 17 ma cooled the samples to near surface temperatures both cooling phases correspond with regional unconformities and subsequent accelerations in sedimentation rate suggesting that cooling was a response to rapid exhumation in addition our data suggests that the studied terranes record differential exhumation with respect to the structural architecture the miocene exhumation pulse is coeval with the timing of transpressional fault displacement and the subsequent opening of the kuril basin

radiation enhanced fission track annealing revisited and consequences for apatite thermochronometry apatite fission track aft analyses for granitoid and metamorphic bedrock samples from the western superior province ontario the churchill rae province melville peninsula and southampton islan

did hot high heat producing granites determine the location of the oslo rift abstract the late carboniferous early permian oslo rift formed in apparently cold stable lithosphere of the fennoscandian shield in a tensional stress regime widely documented in northwest europe at that time the rift formed obliquely to older crustal structures that display only limited permian reactivation and although numerical modelling suggests that the present day lithospheric structure would serve to focus tensional stresses in the oslo region the assumption that no lithospheric evolution has occurred since the palaeozoic is by no means obvious here i show that up to 5 km thick regional scale late to post sveconorwegian granites in the vicinity of the oslo rift with heat production rates averaging ca 5 w m3 nearly three times higher than the surrounding sveconorwegian gneisses would have increased the temperature in the lower crust and lithospheric mantle by up to 100 c resulting in significant thermal weakening of the lithosphere in this area given a tensional stress regime weakening by these high heat producing element granites would have made the oslo area a favoured site for passive rifting and may have been a first order parameter locating rifting to this part of the fennoscandian shield the thermo rheological effects of such granites must be considered along with other factors in future models of initial rift mechanisms in the oslo rift and probably in other rifts elsewhere

on the use of calibrated relative paleointensity records to improve millennial scale geomagnetic field models current millennial scale time varying global geomagnetic field models suffer from a lack of intensity data compared to directional data because only thermoremanently magnetized material can provide absolute information about the past field strength the number of archeomagnetic artifacts that can provide such data diminishes rapidly prior to 3000 b c sediment cores provide time series of declination and inclination and of variations of magnetization the latter can reflect relative geomagnetic field variations if suitably normalized we propose a calibration technique based on predictions from global models and use the cals7k 2 model to calibrate relative paleointensity records from 22 globally distributed locations and assess whether they reflect actual field variations all except a few contain useful information for 0 to 7 ka and could be used to improve the existing models using synthetic data from a numerical dynamo simulation we show that with the existing directional data the distribution of intensity data has an important influence on model quality intensity data from a broad range of latitudes seem particularly important this study opens the possibility of extending global time varying geomagnetic field models further back in time than the current 7 kyr interval

why baltic shield zircons yield late paleozoic lower intercept ages on u pb concordia in the baltic shield the paleozoic is known as a period of regional pb mobilization that resulted in new lead deposits and the addition of radiogenic pb to older deposits in addition u pb data from zircons in the baltic shield commonly yield late paleozoic lower intercepts on the u pb concordia regarded as geologically insignificant results from fission track studies reveal that the rocks that form the present bedrock surface in sweden and finland were heated at the same time this fact is explained by upper paleozoic sedimentary deposits much thicker than hitherto known that covered the basement for at least 200 m y these erosion products of the caledonides formed terrestrial or shallow water old red deposits in a foreland basin that covered sweden and to a lesser extent finland hydrothermal solutions leached metamict zircons in the basement rocks for a long time resulting in pb loss and paleozoic lower intercept ages on u pb concordia the radiogenic pb was redistributed and preferentially concentrated into fractures and veins or was added to older sulfide deposits

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

post orogenic thermotectonic history of the mount buffalo region lachlan fold belt australia evidence for mesozoic to cenozoic wrench fault reactivation abstract the early devonian mount buffalo granite is exposed today as an inselberg at the dissected western margin of the southeastern highlands of victoria australia it dominates a block of deeply incised ordovician turbidites that appears structurally isolated from the surrounding highlands by treating these highlands as an elastic plate subject to flexure or warping previous workers have proposed that this region of the lachlan fold belt has experienced a relatively simple thermotectonic and landscape evolution history following shallow level intrusion of the granite however results of apatite and zircon fission track analyses from the granite indicate the occurrence of major previously unrecognized episodes of 1 heating burial prior to 246 ma early triassic and prior to 70 ma late cretaceous and 2 rapid cooling denudation at some time between 246 and 220 ma early to late triassic and between 70 and 50 ma late cretaceous to early tertiary while previous interpretations of the landscape history of the region suggest the prolonged subaerial exposure of the granite following shallow crustal residence our results clearly indicate this region of the lachlan fold belt has experienced a dynamic post paleozoic history thus this new dataset forces a radical re interpretation of the landscape evolution of the mount buffalo structural block which has significant implications for our understanding of the mesozoic and cenozoic geomorphic and structural development of southeastern australia we therefore propose a model incorporating reactivation of wrench faults that may explain the complex thermotectonic history while accommodating the detailed observations of previous workers in this area

paleointensities for 10 22 ka from volcanic rocks in japan and new zealand abstract eight volcanic rocks from japan and new zealand in the age range 10 50 ka b p were studied using the thellier method paleointensity experiment and yielded five successful results for 10 22 ka samples from the shikotsu kuttara and daisen volcanoes in japan were taken from pyroclastic flows both welded and non welded and a pumice fall deposit one of the two new zealand rocks is a rhyolite lava from the taupo volcanic zone four sites out of seven located on rocks that are not usually subjected to thellier s experiment yielded successful results which indicates that volcanic products such as pyroclastic flows and rhyolite lavas are as good a material as basalt and andesite lavas for application of the paleointensity experiment one paleointensity from new zealand at 9 9 ka is very large at about 100 t and provides support for the paleointensity high found in europe and japan 1 2 the other four paleointensities for 14 22 ka are smaller than the present day value and this agrees with the idea of a broad paleointensity minimum for the period 10 50 ka that was suggested by mcelhinny and senanayake 3 it is also noted that the variation curve of absolute paleointensity from the volcanic rocks is reasonably similar to the relative paleointensity curves from marine and lake sediments which were summarized by tauxe 4

paleozoic paleo cover of the southern part of the fennoscandian shield fission track constraints abstract granitic intrusions older than 1200 ma from an area west of lake vanern south sweden show fission track ages of 680 50 ma 2 late precambrian for sphene and 220 10 ma late triassic for apatite the samples were taken at the present post glacial erosion surface which is close to the sub cambrian peneplain the c 680 ma sphene fission track ages are thought to be related to the uplift of the area which led to the establishment of this erosion surface at c 600 ma ago the much younger apatite fission track ages and the confined spontaneous track length distributions along with regional stratigraphic constraints suggest that the basement was subsequently buried under 3 4 km of paleozoic supracrustals this induced in the basement a rise in temperature which obliterated the older apatite fission tracks but not those in sphene which has a higher closure temperature at the beginning of the mesozoic the area was uplifted again the cover rocks were removed and the basement rocks cooled slowly below the temperature range of fission track annealing in apatite

constraining long term denudation and faulting history in intraplate regions by multisystem thermochronology an example of the sudetic marginal fault bohemian massif central europe 1 the rychlebske hory mountain region in the sudetes ne bohemian massif provides a natural laboratory for studies of postorogenic landscape evolution this work reveals both the exhumation history of the region and the paleoactivity along the sudetic marginal fault smf using zircon u th he zhe apatite fission track aft and apatite u th he ahe dating of crystalline basement and postorogenic sedimentary samples most significantly and in direct contradiction of traditional paleogeographic reconstructions this work has found evidence of a large cretaceous sea and regional burial to 6 5 km of the carboniferous permian basement in the late cretaceous 95 80 ma during the burial by sediments of the bohemian cretaceous basin system the smf acted as a normal fault as documented by offset zhe ages across the fault at 85 70 ma the basin was inverted cretaceous strata eroded and basement blocks were exhumed to the near surface at a rate of 300 m ma as evidenced by late cretaceous paleocene aft ages and thermal modeling results there is no appreciable difference in aft and ahe ages across the fault suggesting that the smf acted as a reverse fault during exhumation in the late eocene oligocene the basement was locally heated to 70 c by magmatic activity related to opening of the eger rift system neogene or younger thermal activity was not recorded in the thermochronological data confirming that late cenozoic uplift and erosion of the basement blocks was limited to less than 1 5 km in the study area

combined apatite fission track and single grain apatite u th he ages from basement rocks of central dronning maud land east antarctica possible identification of thermally overprinted crustal segments abstract apatite fission track ft and single grain u th he ages from four vertical profiles in central dronning maud land east antarctica range from 312 20 ma to 135 11 ma and 304 28 ma to 104 8 ma respectively the combined age data allows to discriminate between undisturbed cooled due to exhumation and thermally overprinted crustal blocks profiles at the zwieselhohe and the conradgebirge revealed unusual apatite ft vs elevation relationships and u th he ages older than the corresponding central apatite ft ages possibly providing evidence for a jurassic thermal overprint most probably jurassic magmatism and associated advective heating led to total annealing of the apatite fission tracks but helium only partially diffused the model developed in this paper suggests that the u th he ages from the zwieselhohe and conradgebirge profiles are in part relicts of the pre jurassic cooling history two thermally undisturbed vertical profiles are used to record the long term cooling history of central dronning maud land time temperature paths derived from modelled apatite ft data of these profiles revealed two phases of accelerated cooling during the late carboniferous and the early jurassic both phases are followed by slow cooling which is also documented by the spread in apatite u th he single grain ages the cooling at the end of the carboniferous is most probably related to far field effects associated to the prevailing convergent tectonics during the initial separation between east antarctica and mozambique erosion along an evolving rift shoulder caused the jurassic cooling denudation of the basement was simultaneous with volcanism with both pre dating c 20 10 ma sea floor spreading in the riser larsen sea c 155 ma post jurassic cooling was restricted to the lowest temperature sensitivity of both methods combined inverse modelled apatite ft data and forward modelled u th he data suggest an eocene oligocene cooling step possibly related to the flexural isostatic response to the development of ice sheets

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

historic and paleomagnetic secular variation and the earth s core dynamo process this paper attempts to summarize briefly the recent and ongoing efforts of the geomagnetism and paleomagnetism community to understand both the earth s magnetic field secular variation and its implications for the core dynamo process secular variation is defined in this paper as the general spatio temporal variation of the field secular change will refer to the first time derivative of the spatial field strict geomagnetic definition of secular variation we will emphasize here the long term 10 year or longer behavior of the historic secular variation hsv for this is the variation that is comparable with the paleomagnetic secular variation psv two important related topics the 1969 1970 geomagnetic jerk in secular acceleration and the spatial geomagnetic field components due to crustal or mantle sources are treated more fully in other reviews

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

onset timing and slip history of the teton fault wyoming a multidisciplinary reevaluation the dramatic relief of the teton range in northwestern wyoming results from motion along the teton normal fault new apatite u th he ahe and fission track aft ages of samples collected in the footwall yield fundamental constraints on contrasting models of teton fault activity and consequent relative footwall uplift low elevation samples in the immediate footwall of the fault range from 12 5 to 6 5 ma ahe ages of samples from subvertical transects range from 57 8 to 6 5 ma rendezvous 54 0 to 6 8 ma grand and 20 5 to 7 1 ma moran with all three transects yielding an expected trend of decreasing age with decreasing elevation aft ages obtained from the three transects range from 55 4 to 45 7 ma rendezvous 43 2 to 13 3 ma grand and 38 0 to 11 7 ma moran inverse thermal history modeling indicates that the onset of relatively rapid cooling as a proxy for relative footwall uplift initiated first in the northern part of the range 15 13 ma and then migrated south as fault displacement continued 7 ma to present at rendezvous thus this work suggests that although the teton fault likely initiated due to basin and range extension this structure remains active normal fault displacement models also suggest a minimum of 6 km displacement for footwall uplift of 2 km if evaluated in the context of established normal fault length displacement relationships this yields a length of 180 km substantially longer than current estimates of teton fault length and putting the northern end of the fault well into and potentially beyond the bounds of yellowstone national park

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

a zero damage model for fission track annealing in zircon a zircon fission track annealing model is calculated on the basis of annealing experiments from the literature with induced tracks in decay event damage free zircon samples empirically derived parallel and fanning equations for this zero damage model yield an excellent fit to the data with the fanning model providing slightly better statistical parameters a comparison between annealing models with fanning iso annealing lines but different decay event damage densities reveals that annealing temperatures and closure temperatures for the estimated partial annealing zone are highest for the zero damage model compilations of existing geologic constraints on the zircon partial annealing zone on one hand and the zircon closure temperature on the other show that these constraints do not or only partly overlap with curves of proposed models for the zircon partial annealing zone and closure temperature this finding is consistent with the fact that the annealing behavior of zircon from long duration temperature evolutions is increasingly influenced by the accumulated decay event damage zircon samples of young age or low u content show a behavior closest to the predictions of the zero damage model and are in the predicted range of published models with low decay event damage density for thermal events of more than 10 myr duration however constraints from field studies show marked differences from proposed partial annealing zone boundaries of the zero or low damage models the applicability of the zero damage model is threefold 1 it predicts correct closure temperatures in the case of very rapid cooling across the partial annealing zone where basically no decay event damage is accumulated 2 it predicts an uppermost boundary for complete annealing of a mixture of zircon components of different age as found in sedimentary samples and in this case may be used as a thermometer 3 it represents an important reference for the establishment of a more comprehensive model of zircon fission track annealing that also includes the influence of decay event damage for such a model two different equations are discussed however additional detailed experimental and field data are needed for a more robust annealing model that includes the influence of decay event damage annealing

low temperature thermal history and landscape development of the eastern adirondack mountains new york constraints from apatite fission track thermochronology and apatite u th he dating the adirondack mountains in northern new york state form an elongate domal exposure of mainly high grade metamor phic tectonites in a mountainous setting with topographic relief of 1 km the origin of the adirondack mountains and this relief has long been enigmatic since the adirondacks presently lie within an intracratonic setting inboard of the north american passive mar gin and far from any active plate boundaries through the application of apatite fi ssion track aft thermochronology and apatite u th he ahe dating within the eastern adirondack mountains this study provides constraints on both the thermal and ero sional effects of mesozoic passage near a hot spot and the timing of relief development aft thermochronology and ahe dating record relatively stable thermal conditions within the eastern adirondacks from the middle jurassic into the early cretaceous during the early cretaceous ca 130 120 ma the region underwent heating as sociated with progressive movement near the great meteor hotspot resulting in the temporary establishment of an elevated geo thermal gradient following regional heat ing cooling rates increased considerably ca 105 95 ma likely due to both thermal doming producing an increase in erosion rate and the relaxation of isotherms after passage near the hotspot the regional distribution of aft ages across the eastern adirondacks reveals no systematic age gradient from core to periph ery which would be expected under con ditions of persistent high relief during the decay of a crustal root over many tens to hun dreds of millions of years instead thermo chronological data suggest that the present relief developed during the late cretaceous cenozoic through plateau dissection during periodic base level changes

early oligocene geomagnetic field behavior from deep sea drilling project site 522 hydraulic piston coring operations at deep sea drilling project site 522 in the south atlantic retrieved an unusually continuous section of late eocene to late oligocene pelagic sediments which we sampled at 3 4 cm intervals 3 5 kyr natural remanent magnetization demagnetization studies indicate a well behaved remanence various rock magnetic procedures strongly suggest the magnetic carrier is dominated by pseudo single domain magnetite appropriate for recording relative intensity variations of the paleomagnetic field nine zones of unusually low relative paleointensity were identified within the 2 my chron c12r interval seven can be typified by a 20 40 kyr interval of low field intensity accompanied by apparently random low amplitude short duration directional fluctuations the other two are of approximately equal duration and intensity but exhibit an orderly progression of directional changes that result in well defined virtual geomagnetic pole vgp paths confined along a preferred meridian of 70 90 w longitude we propose that both styles occur when the main dipole term diminishes significantly but that the former result when undiminished normal secular variation is continuous during the period of low axial dipole moment we propose that the other two lows in relative paleointensity along with one reversal record reflect a field structure of low axial dipole moment dominated by a low degree nonzonal spherical harmonic term alternatively the confined vgp paths could be an artifact of heavy remanence smoothing between nonantipodal semistable transitional geomagnetic pole positions geographical control of vgp paths particularly along 70 90 w longitude has recently been noted for much younger reversals the site 522 record may indicate that the underlying cause of this phenomenon was present at 32 ma we compare our c12r record of paleointensity lows with c12r marine magnetic anomaly tiny wiggles these data appear to indicate that c12r tiny wiggles resulted from periods of low geomagnetic field intensity that were sometimes accompanied by directional excursions

experimental evidence for the pressure dependence of fission track annealing in apatite abstract fission track analysis has seen a major expansion in application to general geological problems reflecting its advances in understanding the temperature dependence of track annealing and track length distributions however considerable uncertainties still persist in particular concerning the stability of fission tracks subjected to the interaction of environmental physical parameters e g pressure temperature stress and in extrapolation of laboratory data to geological time scales in this work we studied the fading behavior of spontaneous fission tracks in basic apatite hexagonal ca5 po4 3 oh f cl when exposed simultaneously to laboratory pressures temperatures and stress over varying time spans the experiments showed that track fading is a complex recovery mechanism which is extremely sensitive to the coupling of these three parameters in particular a strong decrease in the fission track fading rate was observed as a function of increasing pressure and a nearly temperature independent dramatic increase in fission track recovery was observed as a function of stress consequently 1 the stability field of fission tracks in apatite increases towards temperatures higher than 110 c depending on the absolute pressure 2 closure ages in apatite are underestimated 100 for an ideal geothermobarometric gradient 3 related exhumation and erosion rates are overestimated above the closure temperature and underestimated below the closure temperature and 4 since the widely applied statistical description of thermally induced fading kinetics does not account for the influences of either pressure or stress and is based on fission track annealing data produced at ambient pressure the accuracy in extrapolating fission track data to geological time scales and in their application to dynamical systems must be cast into doubt

sveconorwegian and caledonian foreland basins in the baltic shield revealed by fission track thermochronology fission track thermochronology has been applied to apatite zircon and titanite from various depths of the baltic shield burial due to sveconorwegian grenville and caledonian foreland sedimentation is revealed titanite and zircon fission track ages from surface samples from eastern sweden do not vary significantly and average 850 myr it is suggested that sveconorwegian sediments reached a thickness of at least 8 km in eastern sweden exhumation of these sediments was succeeded by deposition of lower palaeozoic cover rocks apatite fission track ages along a transect from sw to ne across the shield increase from 300 myr to 900 myr and yield the phanerozoic history of subsidence and exhumation apatite fission tracks in the basement of the thickest parts of the foreland basin were totally annealed these results suggest a 600 km wide caledonian foreland basin filled by devonian sediments that were 2 5 km thick in southern and western sweden thinning to the east in finland

brittle tectonothermal evolution in the forsmark area central fennoscandian shield recorded by paragenesis orientation and 40ar 39ar geochronology of fracture minerals in this paper we show how studies of fracture mineral paragenesis their orientation and ar 40 ar 39 geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area samples were selected from nearly 18 km of drill cores from the upper i km of the fennoscandian shield obtained during the site investigation for a repository of spent nuclear fuel in forsmark central sweden four major events of fracturing and or reactivation of fractures associated with fracture mineralisation have been distinguished the first event was characterised by precipitation of epidote quartz and chlorite along preferably sub horizontal and gently dipping fractures or steep wnw ese to nw se fractures precipitation occurred between 1 8 and 1 1 ga possibly during the late stage of the svecokarelian orogeny close to 1 8 1 7 ga the second event is associated with precipitation of hematite stained adularia and albite prehnite laumontite calcite and chlorite preferably along steep ene wsw to nne ssw and nnw sse fractures precipitation occurred around 1107 7 to 1034 3 ma probably due to effects from the sveconorwegian orogeny this event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite quartz pyrite and asphaltite during the palaeozoic the formation fluid emanated from an overlying organic rich sedimentary cover precipitation occurred during reactivation of proterozoic fractures but formation of new fractures is also inferred possibly due to far field effects of the caledonian orogeny or elevated hydrostatic pressure due to its foreland basin the latest event is dominated by clay minerals chlorite and calcite along hydraulically conductive fractures these minerals are prominent along sub horizontal and gently dipping fractures but also occur in sets of steeply dipping fractures it is inferred that the hydraulically conductive fractures are proterozoic structures in which mineral precipitation has occurred during a long period however some of the near surface sub horizontal fractures may be quaternary in age c 2009 elsevier b v all rights reserved less

thermochronological insights into the structural contact between the tian shan and pamirs tajikistan gilby jepson stijn glorie dmitry konopelko jack gillespie martin danisik noreen j evans yunus mamadjanov alan s collins

the importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow this paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics cfd model allowing the numerical prediction of flows around individual plants the morphological complexity which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning tls and is maintained in the numerical prediction of flow fields this is achieved where the post processed voxelised plant representation is incorporated into a cfd scheme through a mass flux scaling algorithm mfsa flow around prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves the complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields with velocity profiles that deviate significantly from the idealised inflected shape rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow with the point of reattachment extending up to seven plant lengths downstream the presence of leaves significantly modifies the flow field response with development of a second more pronounced wake structure around the dense foliage this approach provides a full flow numerical description of the pressure field enabling the vegetative drag force to be quantified for the example given here drag force is an order of magnitude greater for the foliated state the methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models and allows drag forces and coefficients to be calculated for specific plant species this article is protected by copyright all rights reserved

evaluating late holocene radiocarbon based chronologies by matching palaeomagnetic secular variations to geomagnetic field models an example from lake kalimpaa sulawesi indonesia palaeomagnetic and palaeoenvironmental data from indonesia and particularly from the island of sulawesi are scarce and exact dating has turned out to be a challenge in many archives from this region here we outline difficulties in radiocarbon dating of the palaeoenvironmental record from lake kalimpaa sulawesi indonesia these difficulties demand the integration of additional parameters to obtain a reliable chronology for this record thus we compare the palaeo magnetic secular variation data from this record with the cals3k 4 spherical harmonic geomag netic model of the 0 3 ka field korte constable 2011 the resulting age depth model for the lake kalimpaa sequence provides a profound basis for further multi proxy investigations on this record for the first time high resolution palaeomagnetic secular variation data continuously span ning the past 1300 years are presented for this region which complement existing records with lower temporal resolution or records missing the top most sections

spline analysis of holocene sediment magnetic records uncertainty estimates for field modeling 1 sediment and archeomagnetic data spanning the holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia in global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates uncertainties in sediment magnetic records arise from 1 imperfections in the paleomagnetic recording processes 2 coring and sub sampling methods 3 adopted averaging procedures and 4 uncertainties in the age depth models we take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of holocene magnetic records smoothing spline models that capture the robust aspects of individual records are derived this involves a cross validation approach based on an absolute deviation measure of misfit to determine the smoothing parameter for each spline model together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock in depth departures from the spline models provide information concerning the random variability in each record temporal resolution analysis reveals that 50 of the records have smoothing times between 80 and 250 years we also perform comparisons among the sediment magnetic records and archeomagnetic data as well as with predictions from the global historical and archeomagnetic field models combining these approaches we arrive at individual uncertainty estimates for each sediment record these range from 2 5 to 11 2 median 5 9 interquartile range 5 4 to 7 2 for inclination 4 1 to 46 9 median 13 4 interquartile range 11 4 to 18 9 for relative declination and 0 59 to 1 32 median 0 93 interquartile range 0 86 to 1 01 for standardized relative paleointensity these values suggest that uncertainties may have been underestimated in previous studies no compelling evidence for systematic inclination shallowing is obtained from the analysis of the available database of holocene sediment magnetic records the analysis highlights the importance of collecting oriented cores publishing and archiving unprocessed raw paleosecular variation determinations and presenting a detailed chronology so that changes in the sedimentation rate can be assessed with regard to future field models workers should consider rejection of anomalous cores through comparisons to other sources and ensure that realistically large uncertainties are allocated to high latitude declination records

full vector model for magnetization in sediments abstract sediments provide a continuous record of past geomagnetic field variations although it is theoretically possible to get both the direction and intensity of the geomagnetic field from sediment records the mechanism is not fully understood previous workers have postulated that flocculation plays an important role in detrital remanent magnetism drm flocs are porous loose and highly fragile aggregates of microscopic clay particles and their behavior in a viscous medium is likely to be different than single particles of magnetic minerals in order to understand the role of flocculation in sediment magnetization we carried out a set of redeposition experiments at different field intensities and a quasi constant field inclination of 45 we present here a simple numerical model of flocculation incorporating both magnetic and hydrodynamic torques to explain the experimental data at small floc sizes drm acquisition is likely to be non linear in field strengths comparable to the earth s but the sediments may be able to record the directions accurately with increasing floc sizes sediments may retain a record of the intensity that is linearly related to the applied field or a direction parallel to the applied field but are unlikely to do both at the same time also the majority of the magnetic particles in the sediments may not be contributing significantly towards the net drm and any bulk normalizing parameter may be unsuitable if the depositional environment has changed over the depositional period

towards absolute calibration of sedimentary paleointensity records abstract using relative paleointensity estimates derived from twelve globally distributed pelagic sediment cores we assess whether they record a signal consistent with that expected from a dominant geocentric axial dipole the cores span the matuyama brunhes boundary and we normalize the observations by supposing that at the time the direction reverses the intensity low reflects only the non axial dipole contribution to the field we further assume that this non axial dipole contribution to the field is invariant with geographic location from absolute paleointensity compilations we estimate its size to be about 7 5 t this supplies the calibration for the axial dipole signal away from the extreme low in intensity the data predict the dipole field variation with latitude with similar accuracy to that observed in absolute paleointensity records and show similar behavior when transformed to virtual axial dipole moments

eastern australian geomagnetic field intensity over the past 14000 yr summary two north eastern australian volcanic crater lake cores have been used to obtain relative intensity estimates for the geomagnetic field arm imparted in a low dc bias field has been used as a normalizing parameter the intensity fluctuations in the two lakes are in excellent agreement with each other and with south eastern australian archaeointensity data over their coeval time spans this strongly suggests that the same sources are influencing the geomagnetic secular variation throughout eastern australia at this time the relative intensity records go back to about 14000yr bp thereby extending currently available recent australian intensity records by some 7000 yr

thermal history of michigan basin and southern canadian shield from apatite fission track analysis apatite fission track ages and confined length distributions were collected from 38 basement outcrop and 5 basement drillcore samples in order to reconstruct the phanerozoic thermal history of the michigan basin and southern canadian shield the apatite data indicate two periods of thermal activity in the region triassic heating cooling that affected the basin and adjacent shield and cretaceous or post cretaceous heating cooling that primarily affected the basin the magnitude timing and cause of cretaceous thermal activity cannot be identified with the present data model calculations suggest that some of the shield samples and probably all of the basin samples were heated to temperatures of at least 90c just prior to relatively rapid cooling in the triassic available stratigraphic and geochemical constraints suggest that these elevated temperatures were the result of burial by an additional 2 5 km of late paleozoic probably pennsylvanian and permian sediments it is likely that the basin was buried during the alleghenian orogeny as observed for the adjacent appalachian basin

fission track thermochronology applied to phanerozoic thermotectonic events in central and southern sweden abstract central and southern sweden is characterized by a precambrian basement and a few lower palaeozoic sedimentary remnants with a probable initial thickness of less than 500 m upper palaeozoic deposits have not been documented in the swedish part of the fennoscandian shield regional deposition of upper palaeozoic sediments on the platform appears possible though since vast amounts of material must have been eroded from the caledonian mountain range during this period fission track thermochronology has been used in this study in order to validate the former existence of a post caledonian sedimentary load trace the variation in thickness and extent of the deposits and get an indication of the cooling history in the area samples from an east west trending profile from the caledonian border zone in the west to the aland archipelago in the east together with a few samples from surrounding areas have been analysed the obtained pooled apparent apatite fission track ages along the profile vary from 250 ma in the west to 500 ma in the east while the mean track lengths decrease from 14 m in the west to 11 m in the east in southern sweden ages between c 170 and 320 ma and a mean track length of 13 4 m were obtained the dating results show that all samples have experienced raised temperatures since the pre cambrian peneplanation temperatures leading to total annealing of fission tracks during the palaeozoic were reached in the western part of central sweden and in southern sweden while partial annealing is traced further east to the aland archipelago the obtained fission track results are interpreted by the former existence of a devonian foreland basin covering most of central and southern sweden an estimation of the upper palaeozoic sedimentary thickness yields 2 5 km of deposits in the ludvika area and at least 1 km in the aland archipelago inverse modelling of the fission track data resulted in several alternative modelled thermal histories one of these suggests that central sweden was covered by palaeozoic and mesozoic sediments until tertiary time in that case the surface relief of western central sweden has been chiselled out during the tertiary another possible thermal history includes denudation due to surface level conditions during the mesozoic in the west in that case reheating to 40 80 c during the late mesozoic cenozoic is required according to the present apatite annealing models none of the proposed modelled thermal histories can be rejected so far

establishing a first archaeointensity record for the sw pacific abstract the dearth of archaeomagnetic intensity data from the southern hemisphere is a limiting factor in evaluating models of global geomagnetic field evolution during the holocene here we present high quality microwave archaeointensity data obtained from 34 ceramic fragments 21 archaeological contexts from the duke of york islands fiji and vanuatu sw pacific complementary thellier type experiments corrected for anisotropy give good agreement with the microwave results the majority of the new data prior to 250 ad exhibit significantly lower intensity than predicted by current global field models cals3k 3 and arch3k for the region with an apparent intensity minimum at 250 bc reaching as low as 50 of the present day field strength between 400 ad and 1500 ad the data are broadly consistent with the global field models but with a 20 higher field between 1200 and 1400 ad these new results therefore imply that the geomagnetic field has a greater range of variability than predicted and that further data from the region are essential to better constrain the global field models the results also demonstrate that establishing an archaeomagnetic reference curve for dating sw pacific ceramic artefacts is feasible which has potentially significant implications for pacific archaeological research

the role of fault reactivation and growth in the uplift of western fennoscandia new structural data published aft data and topographic data suggest that the latest cretaceous cenozoic uplift of western norway was associated with normal reactivation of the more trondelag fault complex reactivation focused along the base of today9s topographic rise with maximum displacements in the order of 2 3 km structural and aft data indicate that reactivation occurred along a displacement gradient with least normal displacement in the ne and increasing displacements towards the sw reactivation commenced in connection with the triassic to earliest cretaceous phases of rifting on the norwegian margin and probably continued through most of the tertiary the late cretaceous to cenozoic topographic development of the scandes mountains followed structurally induced templates such as those described from other areas of active normal faulting a fault model for the cenozoic uplift of the norwegian mainland provides a framework for provenance erosion and transport of sediments eventually deposited in the offshore post rift basins in the latest cretaceous palaeogene and neogene the asymmetric topographic profile of fennoscandia is reflected in the aft data and suggests that lithospheric flexure places a first order control on the shape of the scandes mountains and the central fennoscandian craton

evidence of the contrasted fission track clock behavior of the apatites from in ouzzal carbonatites northwest hoggar the low temperature thermal history of an archean basement this fission track study is performed on the apatites from the in ouzzal northwest hoggar algeria carbonatite complex and permits us to present a complete thermal history of this archean core two types of apatites the pink ones early carbonatites and the green ones late carbonatites have been dated the temperature during the pan african orogeny would have reached 100 120 c in the in ouzzal core as both types of apatites from the carbonatites have recorded this event 500 630 m y a mild permian thermal event reset only the fission track clock of the green late apatites this permian thermal event is of quite a large extent in the hoggar shield it has also been detected in the pharusian belt and in central hoggar this event is related to the opening of the atlantic ocean the very high u th content of some of these apatites and consequently the amount of radiation damage in the mineral lattice has been shown to possibly influence the fission track clock behavior of these minerals the f cl content of the apatites does not show any correlation with the degree of age reductions

apatite fission track and u th he data from fennoscandia an example of underestimation of fission track annealing in apatite abstract apatite fission track aft data from cratons have commonly been interpreted in terms of major episodes of sedimentary burial and subsequent denudation often in the absence of any remnant sedimentary rocks or other supporting geological evidence reconciling these interpretations with geologically documented denudation events or outcropping regional stratigraphy can be problematic also u th he ages from cratonic igneous rocks that are older than paired aft data are commonly discarded as too old even when the former are repeatable at the 2 confidence level for example aft data from central fennoscandia have been interpreted to reflect first burial by a caledonian foreland basin several kilometres in thickness and subsequently its denudation however throughout fennoscandia there is no direct evidence that such a deep extensive foreland basin ever existed and indeed some geological evidence points to the contrary additionally a significant number of u th he ages from fennoscandia are older than their aft pairs but have been interpreted by their authors as too old relative to the aft ages and not geologically meaningful despite repeatable results here we propose a new interpretation of aft data from fennoscandia that closely reflects the observed data yet is compatible with the generally accepted geological history discarding the hypothesis of a thick caledonian foreland basin we suggest that 1 aft ages in finland are too young rather than that the u th he ages are too old 2 repeatable sequences of u th he ages are more likely to record the true denudation history of cratons 3 the importance of radiation enhanced annealing at low temperatures has been overlooked and 4 fennoscandian aft data may be divided into an eastern domain strongly affected by radiation enhanced annealing where current aft annealing models are invalid and a western domain much less affected by radiation enhanced annealing where current modelling methods may appropriately be used to extract thermal histories in principle radiation enhanced annealing is also pertinent to the interpretation of young aft ages from apatites rich in emitter actinides the construction of a properly calibrated annealing model that fully incorporates the effects of radiation enhanced annealing is fundamentally important

late cenozoic uplift of denali and its relation to relative plate motion and fault morphology apatite fission track analysis of samples that cover a 4 kilometer vertical section from the western flank of denali mount mckinley north america9s highest mountain suggests that the mountain massif was formed by rapid uplift 1 kilometer per million years beginning 6 million years ago ma uplift was a result of the morphology of the denali fault and a change in motion of the pacific plate with respect to north america at 5 ma which created opposing tangential vectors of relative movement along the fault and forced the intervening crustal blocks upward

normalized remanence in sediments of the western equatorial pacific relative paleointensity of the geomagnetic field piston cores from the ontong java plateau collected during the eurydice expedition have been used to estimate regional geomagnetic paleointensity rock magnetic measurements of the sediments show that 1 the remanence is carried by stable pseudo single domain magnetite 2 the grain sizes and concentrations are relatively uniform with respect to the normalization technique and 3 susceptibility is an adequate parameter for normalizing remanent intensity in order to determine relative variations in the intensity of the paleomagnetic field we therefore have measured the remanent intensity both natural and demagnetized to 15 mt and susceptibility of archive quarters of three cores at centimeter intervals using an automated through bore magnetometer a further test of the normalized intensity records is provided by the coherence function between the normalized remanence and the susceptibility of the cores one of our cores displays high coherence over a broad range of frequencies while for two others coherence is insignificantly different from zero at the 95 level of confidence oxygen isotopic records paleontological datum levels and the brunhes matuyama boundary provide an independent temporal framework for inter core comparison when the two cores which pass our acceptance criteria are placed on a common time scale the coherence between the normalized intensity records is significantly different from zero at well above the 95 level of confidence suggesting some common input signal over the same band of frequencies furthermore there is a great deal of similarity between the records from the ontong java plateau and a record from core rc10 167 taken some 3000 km to the north the distribution of intensities obtained from these sedimentary records has the same shape as the absolute virtual dipole moment data obtained from lava flows 0 5 ma with a slightly smaller standard deviation the inter core agreement within a single region the similarity of records from 3000 km apart and the general correspondence of statistical character of these sediments with lava flow data all argue that the normalized intensity records presented here reflect variations in the intensity of the ancient geomagnetic field spectral analysis of the paleointensity time series shows that there a is significant enhancement of variance concentrated in frequencies around 33 thousand years over the period 0 350 ka this feature is however lacking for the period 350 700 ka

absolute paleointensities between 60 and 160 kyear bp from mount etna sicily abstract paleointensity measurements were conducted on 17 distinct lava flows from mount etna sicily in order to obtain records of absolute paleointensities for the period covering the last 60 160 kyear a complementary aspect of this study was to improve and extend the calibration of relative paleointensities obtained for the same interval from sedimentary sequences based on absolute values of virtual axial dipole moments seventy three samples have been subjected to double heating thellier coe experiments under vacuum and care was taken to perform additional studies dealing with the magnetic mineralogy and to scrutinize the effects of heating upon magnetic minerals potassium argon k ar datings provided precise ages in most cases absolute paleointensities were obtained with success for ten lavas flows the succession of the virtual axial geomagnetic dipoles vadm oscillate between extrema centered around a mean value of 6 3 2 6 10 22 a m 2 this result is in good agreement with the sedimentary record published for the same period and confirms that there has been an appreciable decrease in geomagnetic field intensity between 80 and 150 kyear

paleointensity of the geomagnetic field during the last 80 000 years high resolution records of the relative paleointensity of the geomagnetic field have been obtained from five marine cores three duplicate records were used to estimate the regional coherency of the data within a single area tyrrhrenian sea while the two others document the field variations in the eastern mediterranean and the southern indian ocean careful investigations of distinct rock magnetic parameters have established the downcore uniformity of the sediments in terms of magnetic mineralogy and grain sizes the time depth control was provided by oxygen isotopes and small scale variations in the deposition rates were constrained by means of tephrachronology the synthetic curve calculated from the mediterranean records provides a continuous record of the intensity variations during the last 80 000 years 80 kyr which correlates well with the sparse volcanic data available for the period 0 40 kyr the fact that identical behavior is seen in both data sets and that they also compare quite well with results from a core collected in the pacific ocean establishes the truly dipolar character of these variations the dipole field moment is characterized by large scale changes as shown by the existence of pronounced drops at 39 and 60 kyr alternating with periods of higher intensity the record suggests a periodic nature for these intensity variations however the period studied is not sufficiently long to state this conclusively these results demonstrate the potential of sediments for such studies and constitute a first step towards obtaining a global paleointensity record over a long period of time

holocene geomagnetic secular variation records from north eastern australian lake sediments summary secular variation records have been obtained from cores from lakes barrine and eacham two north eastern australian volcanic crater lakes the results from several cores have been stratigraphically correlated and then stacked and smoothed the chronology provided by radiocarbon dating indicates that the lake eacham sequence spans the last 5700 calendar years the time scale for the lake barrine record is less weil constrained but it

paleomagnetism and petrophysics of the janisjarvi impact structure russian karelia paleomagnetic rock magnetic and petrophysical results are presented for impactites and target rocks from the lake janisjarvi impact structure russian karelia the impactites tagamites suevites and lithic breccias are characterized by increased porosity and magnetization which is in agreement with observations performed at other impact structures thermomagnetic hysteresis and scanning electron microscope sem analysis document the presence of primary multidomain titanomagnetite with additional secondary titanomaghemite and ilmenohematite the characteristic impact related remanent magnetization chrm direction d 101 5 i 73 1 95 6 2 yields a pole lat 45 0 n long 76 9 e dp 9 9 dm 11 0 additionally the same component is observed as an overprint on some rocks located in the vicinity of the structure which provides proofs of its primary origin an attempt was made to determine the ancient geomagnetic field intensity seven reliable results were obtained yielding an ancient intensity of 68 7 7 6 t corresponding to vdm of 10 3 1 1 x 10 22 am 2 the intensity however appears to be biased toward high values mainly because of the concave shape of the arai diagrams the new paleomagnetic data and published isotopic ages for the structure are in disagreement according to well defined paleomagnetic data two possible ages for magnetization of jnisjrvi rocks exist 1 late sveconorwegian age 900 850 myr or 2 late cambrian age 500 myr however published isotopic ages are 718 5 myr k ar and 698 22 myr 39ar 40ar but such isotopic dating methods are often ambiguous for the impactites

palaeointensities from sediments normalization by laboratory redepositions abstract deep sea sediments comprising small magnetic grains in coarse and fine fabrics were reconstituted and deposited in laboratory fields both the magnitude and the direction of the natural remanent magnetization nrm were accurately reproduced only the middle coercivity fraction however gave a faithful representation of the laboratory field this same fraction originally held the stable nrm component the results were interpreted on a model of post depositional realignment based on the physical characteristics of the sediment laboratory redeposition was found to be a closer analogue to the nrm than were anhysteretic or other laboratory induced magnetizations guidelines are given by which the techniques could be utilised to estimate the intensity of the ancient geomagnetic field

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

from orogen to passive margin constraints from fission track and u th he analyses on mesozoic uplift and fault reactivation in sw norway the post caledonian tectonic history and landscape evolution of southwestern norway are poorly understood primarily owing to the lack of onshore post devonian sediments to bridge this knowledge gap low temperature thermochronological techniques were applied to investigate vertical movements in the upper crust new apatite fission track and apatite and zircon u th he analyses on samples from southwestern norway yielded permian to jurassic triassic to cretac eous and carboniferous to triassic ages respectively thermal history modelling indicates rela tively high cooling rates 2 3 8 cm a 21 throughout permian to early jurassic times since the jurassic samples from coastal areas have remained close to the surface and were reheated to 30 50 8c during sedimentary burial in the cretaceous inland samples experienced lesser amounts of permo triassic exhumation continued to cool slowly 1 8 cm a 21 throughout the jurassic cretaceous and did not reach the surface until the cenozoic both fission track and u th he ages are offset across faults highlighting the importance of fault activity throughout the mesozoic in combination with previously published results the new data suggest that the geo morphological evolution of southwestern norway is closely connected to rift and post rift tec tonics related to north sea and north atlantic rifting the topographic relief was most likely repeatedly rejuvenated during periods of tectonic activity

exploiting radiation damage control on apatite u th he dates in cratonic regions abstract apatites from four pairs of samples of precambrian basement from the western canadian shield were analyzed by u th he thermochronometry to test for the influence of radiation damage on apatite u th he dates in this cratonic region recent studies have demonstrated that the accumulation of radiation damage increases the apatite he retentivity so that apatites with a span of effective u concentrations eu that experienced the same thermal history may be characterized by a range of closure temperatures in this investigation each sample pair consisted of a mafic dike cross cutting felsic gneisses from a single outcrop or nearby outcrops that contained apatites with a span of eu the apatites yielded u th he dates from 846 to 123 ma and were positively correlated with eu within each sample pair these results can be explained using a model that tracks the evolution of he mobility in response to the accumulation of radiation damage when coupled with regional geological constraints the data appear to require partial to complete he loss due to burial and reheating in phanerozoic time new apatite fission track dates and length data were obtained for five of these samples the apatite fission track dates are proterozoic regardless of apatite eu thermal history simulations indicate that the apatite fission track data are compatible with the u th he results although the thermal histories are not identical in detail and the fission track results alone do not require phanerozoic heating together the data are consistent with burial of this region by 1 km of phanerozoic strata that were subsequently denuded thus pointing toward significant phanerozoic deposition in the north american cratonic interior hundreds of kilometers east of where previously documented the results suggest that exploiting radiation damage control on apatite u th he dates through investigation of surface sample apatites with a span of closure temperatures can impose tighter restrictions on thermal histories in low relief cratonic landscapes than was previously possible

a 2000 year geomagnetic field record from the gulf of papua abstract a high resolution holocene record of geomagnetic field direction and intensity in the gulf of papua was constructed using paleomagnetic data from eight piston cores collected in the region the chronology of the cores was based largely on radiocarbon dates from benthic foraminifera correlation of seismic reflectors imaged in subbottom data between nearby cores was consistent with the chronostratigraphic framework based on radiocarbon dates and provided additional confidence of the age model in other regions where cores sampled different depositional settings associated with the three dimensional prograding lobes reflectors could not be confidently correlated between cores furthermore radiocarbon ages from the bottoms of trigger cores and tops of co located piston cores revealed varying amounts of overpenetration of the piston core below the seafloor the relative paleointensity and a general eastward trend in the declination and steepening of the inclination in our new record are generally compatible with the closest 4300 km existing records our record does not agree well with global field models cals3k and pfm9k likely reflecting the lack of existing data contributing to field models in the region

long term morphotectonic evolution in sweden abstract a morphotectonic interpretation of the relief of sweden is presented based on an analysis of the gross forms of the topography computer made topographic profiles covering 76 375 km have been examined together with contour maps new maps of relief and layers of height have also been used three main aspects considered are the relation between the surface of the precambrian basement and its cover rocks the erosional new surfaces developed in both caledonian basement and reexposed precambrian basement and the evolution of the valley pattern the analysis produced the following results the surface of the precambrian basement is a mosaic of old exhumed surfaces and new surfaces formed after erosion of the cover rocks the exhumed surfaces include 1 a sub jotnian surface mainly below cover rocks in downfaulted positions 2 the sub cambrian peneplain and 3 sub mesozoic etch surfaces block faulting was identified in relation to the different exhumed surfaces after the formation of the caledonides a post caledonian surface was cut across the caledonian basement and the precambrian basement with its cover the subsequent evolution of the swedish part of this surface has been traced through several new surfaces in stepped sequences and in relation to the exhumed surfaces five main denudation intervals are distinguished that result in characteristic relief they are preceded by intervals of orogeny uplift and faulting and followed by subsidence and or deposition of sedimentary strata the valley patterns the distribution of new and exhumed surfaces as well as remmants of cover rocks give some fundamental clues to where and when uplift and subsidence occurred historical geomorphology has mainly been based on theories of erosion cycles the relief of the cratons are difficult to fit exclusively into such a system the importance of long lasting covers and of exhumed surfaces have not been considered enough neither the movements of uplift and subsidence reconstruction of geomorphic events appears to be more important for understanding relief evolution than any model as every phase is unique the methods used in this study are worth testing within other cratons

low temperature thermochronology of the southern east greenland continental margin evidence from apatite u th he and fission track analysis and implications for intermethod calibration abstract the southern coast of east greenland is characterized by high topographic relief and deep fjords but the evolution of the landscape and the low temperature thermochronology of the region is not well understood here we present apatite fission track and u th he ages that suggest several important features of the long term geomorphic history of this region but which also illustrate an important discrepancy in the thermal histories derived from each technique apatite from bedrock of the southern coast of east greenland between 62 n and 67 n has fission track ages ranging from 60 to 840 ma and u th he ages ranging from 21 to 250 ma the ages generally increase with elevation and distance from the coast and fission track analyses show significant differences in thermal histories for the different regions in the kangertittivatsiaq area c 66 67 n apatite fission track data and models suggest two separate periods of slow cooling prior to c 200 ma and between c 160 ma and the late cenozoic more recently than c 20 ma each of which was followed by a period of rapid cooling and inferred exhumation apatite he data in the kangertittivatsiaq region including crystal size age correlations in low elevation samples are most simply interpreted as recording an incision event of at least 1 5 km later than 20 ma near the coast this may have been caused by glacial erosion the u th he data also indicate an earlier phase of rapid exhumation at c 250 ma in the skjoldungen kap mosting area c 62 64 n approximately 200 km south of the kangertittivatsiaq apatite fission track data suggest slow exhumation from c 200 ma into the neogene followed by fast exhumation the similarity of fission track ages 200 ma at sea level in the fjords in the skjoldungen area c 62 64 n do not suggest tilting in the hinterland related to the breakup of the east greenland continental margin furthermore the cenozoic fission track ages and modeling fission track data suggest that pre breakup basins may have covered the outer coast despite the broadly similar topographic implications of the fission track and u th he data the thermal histories derived from these systems are inconsistent fission track data require thermal histories that predict he ages younger than observed and he data require thermal histories that predict fission track ages older than observed similar discrepancies have also been observed in other settings characterized by long term low temperature thermal histories and may reflect changes in annealing or diffusion behavior or both that either develop or become more apparent in such cases

late vendian early palaeozoic tectonic evolution of the baltic basin regional tectonic implications from subsidence analysis abstract subsidence analysis was performed on 43 boreholes penetrating the upper vendian lower palaeozoic sedimentary succession of the baltic basin the results were related to lithofacial and structural data to elucidate subsidence mechanisms and the regional tectonic setting of basin development tectonic subsidence patterns are consistent throughout the basin for the time period studied an extensional tectonic subsidence event possibly of two phases is indicated from the late vendian to the beginning of the middle cambrian this event is seen in the southwestern part of the baltic basin peri tornquist zone until the earliest cambrian after which it is also observed in the sw ne trending baltic depression part of the basin basin development during this time is interpreted as recording the latest stages of break up of the precambrian super continent rodinia and ultimately the formation of the tornquist sea the late middle cambrian to middle ordovician tectonic subsidence pattern of the baltic basin is characteristic of post rift thermal subsidence of the newly formed passive continental margin of baltica developed along its southwestern edge a gradual increase in subsidence rate is observed from the middle late ordovician and throughout the silurian particularly for ludlow and pridoli times creating subsidence curves with convex shapes typical of foreland basin development the rate of late silurian tectonic subsidence increases significantly towards the southwest margin of the baltic basin adjacent to the present location of the north german polish caledonides the baltic basin therefore appears to have developed primarily as a flexural foreland basin during silurian oblique collision of baltica and eastern avalonia a foreland setting is supported by the influx of distal turbidites into the basin from southwest sources in the late silurian compressional deformation structures of early devonian lochkovian age are seen in seismic sections in the central part of the baltic basin lithuania these together with a change in subsidence pattern mark the end of the caledonian stage of basin development of the baltic basin

paleomagnetic secular variation records from holocene sediments of lake victoria 0 5 s 33 3 e we have conducted a paleomagnetic study of holocene sediments from lake victoria in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv

a preliminary magnetic study of soil samples from west central minnesota abstract various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west central minnesota there is a marked change in magnetic properties as a function of depth in the core x ray analysis and curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil the intensity of anhysteretic remanent magnetization arm decreases sharply as the depth increases in contrast the stability of arm was found to be higher for the subsoil the surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization vrm the vrm acquisition coefficient s a of the subsoil s a 3 18 10 6 emu g 1 3 18 10 6 a m 2 kg 1 was about ten times weaker than that of the top soil sample s a 3 868 10 7emu g 1 3 868 10 7 a m 2 kg 1 the magnetic domain state indicator the ratio of coercivity of remanence to coercive force h cr h c was 1 5 and 3 85 for the top soil and subsoil respectively it appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size we conclude that the magnetic grains in surface soil samples were more single domain sd like whereas the magnetite grains in the subsoil samples were more likely in pseudo single domain psd or small multidomain md range the observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs

experimental evidence for 234u 238u fractionation during granite weathering with implications for 234u 238u in natural waters abstract the daughter to parent 234u 238u activity ratio in natural waters is often out of secular radioactive equilibrium the major reason for this disequilibrium is related to the energetic decay of 238u and differential release of 234u relative to 238u this disequilibrium originates from 1 preferential release of more loosely bound 234u from damaged mineral lattice sites or 2 direct recoil of 234th into surrounding media from near mineral surface boundaries however it is unclear which of the two mechanisms is most important in nature to better quantify the effects of preferential release of 234u two continuous laboratory granite leaching experiments conducted over 1100 h were performed the leachates were characterized by declining u concentrations with time and 234u 238u initially greater than unity up to 1 15 which changed to below unity during leaching 0 95 the early elevated 234u 238u suggests that additional 234u is released into solution by preferential release of 234u from mineral phases however the excess 234u constitutes a finite pool of easy leachable 234u and the 234u 238u values become lower than unity when this pool is used up a model based on first order kinetics dissolution rates and preferential release of 234u from damaged lattice sites was developed and is able to quantitatively predict the observed pattern of 234u 238u values and u concentrations for the two granite leaching experiments extending the modeling to longer time scales more comparable to natural systems shows that the production of waters with high 234u 238u ratios can be achieved in two distinct regimes 1 slow weathering where the rate of directly recoiled 234u near mineral surfaces into waters is high 2 fast weathering where the role of incipient chemical weathering and preferential release of loosely bound 234u are important the model is able to explain apparent opposite correlations between physical erosion rates and 234u 238u in waters and it provides a new framework that will be useful for examining weathering regimes their timescales and their coupling with physical erosion

quantitative resolution of the debate over antiquity of the central australian landscape implications for the tectonic and geomorphic stability of cratonic interiors we report the first measure of long 100 myr and short 1 myr term denudation rates from key geologically stable landforms in the davenport range central australia these landforms have previously been assigned a cambrian age which arguably places them amongst the oldest persistent landforms on the continent if not on earth our results from combined apatite fission track thermochronology and in situ cosmogenic radionuclide analyses using 10 be and 26 al show that while average exhumation rates are low the denudation history for this cratonic region is incompatible with extreme sub aerial longevity and long term tectonic and geomorphic stability our revised model for the landscape evolution of this region is consistent with one of maximum burial prior to and during the mesozoic followed by a phase of kilometre scale exhumation that was largely complete by the beginning of the cainozoic we suggest that a similar process of burial and exhumation has probably been responsible for the sub aerial preservation of seemingly ancient landforms elsewhere in australia

low temperature thermal evolution of the azov massif ukrainian shield ukraine implications for interpreting u th he and fission track ages from cratons abstract the low temperature thermal evolution of the azov massif eastern part of the ukrainian shield ukraine is investigated by combined zircon fission track zft apatite fission track aft and apatite u th he ahe thermochronology the data help to better understand the geodynamic evolution of the azov massif and the adjacent intra cratonic rift basin dniepr donets basin as follows zft data reveal that the precambrian crystalline basement of the azov massif was heated to temperatures close to 240 c during the late palaeozoic the heating event is interpreted in terms of burial of the basement beneath a several kilometres thick pile of devonian and carboniferous sedimentary deposits of the adjacent dniepr donets basin during permo triassic times large parts of the basement were affected by a thermal event related to mantle upwelling associated magmatic activity and increased heat flow in the adjacent rift the major part of the basement cooled to near surface conditions in the early to middle triassic and since then was thermally stable as suggested by aft and ahe data further aft data confirm late triassic magmatic activity in the azov massif which however did not influence regional thermal pattern the northern part of the basement and its sedimentary cover record a cooling event in the jurassic which was probably related to erosion however although ar ar data of jurassic magmatic activity in the donbas foldbelt are about 20 my younger than the aft data thermal relaxation after elevated heat flow associated with this magmatic event cannot be completely ruled out our results reveal apparent inconsistencies between aft and ahe data the ahe ages corrected for alpha ejection according to the standard procedure farley k a wolf r a silver l t 1996 the effect of long alpha stopping distances on u th he ages geochim cosmochim acta 60 21 4223 4229 farley k a 2002 u th he dating techniques calibrations and applications mineral soc am rev mineral geochem 47 819 844 are older than corresponding aft ages in order to test the relevance of alpha ejection correction mechanical abrasion of several apatite grains was applied we found that in case of relatively slow cooling alpha ejection correction of raw u th he ages leads to erroneously high ages this shows that alpha ejection correction should be used with caution we propose that this correction should only be applied to samples with a fast cooling history whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means

heat flow map of northern and central parts of the fennoscandian shield based on geochemical surveys of heat producing elements abstract the heat flow heat production q a relationship is a useful tool in geothermal research and it has been widely used for delineating geothermal provinces and determining characteristic parameters of heat production in the continental crust in this study a simple but rarely used technique of utilizing the heat flow heat production relationship is discussed in central and northern parts of the fennoscandian shield extensive geochemical surveys have produced 1483 samples taken from glacial till with a sampling density of 1 sample 300 km 2 heat production values determined from u th and k concentrations in these samples were used to calculate a map of heat flow density a previously determined q a relationship q 15 8 10 8 a was applied the compiled map covers all finland northern sweden and northern norway about 35 of the exposed shield area in fennoscandia heat flow density and heat production increase with decreasing geological age and correlate with granitoid types the calculated heat flow density values on the map were controlled with 12 drill hole measurements not used in calculating the applied q a regression line nine of them are from previously unpublished data from the finnish part of the shield the agreement with drill hole measurements and the geochemical estimate is reasonable although not perfect in all cases the differences can be attributed to anomalous vertical variation in heat production reliability of the applied q a plot reliability of till geochemistry in bedrock studies convective groundwater disturbances or local structural effects the calculated heat flow map can be used as a data set supplementing drill hole measurements to determine representative values of heat flow density in areas with low numbers of drill hole measurements

relative paleointensity of the earth s magnetic field from marine sedimentary records a global perspective abstract to assess the potential of marine sediments as a source of relative paleointensity information we have undertaken an investigation of selected box cores stored in the scripps core repository we present here new results from two north atlantic box cores magnetic remanence in the sediments is carried by magnetite and is univectorial during alternating field and thermal demagnetization the median destructive field is 25 30 mt normalization by anhysteretic remanent magnetization yields relative paleointensity data that are highly concordant within and between cores age control provided by oxygen isotope data from both cores allows comparison of these relative paleointensity data with contemporaneous archeomagnetic data from czechoslavakia both data sets indicate a peak in paleofield intensity at around 8 10 ka this peak is less prominent in box core data from the western pacific and global averages of archeomagnetic and lava flow data however the peak is evident in data estimating changes in production of radiocarbon which is controlled in part by changes in the dipole moment of the geomagnetic field the excellent agreement between production variations predicted by the changes in dipole moment and those observed suggests that long term variations in atmospheric radiocarbon are dominated by geomagnetic field variations

palaeointensity in the pelagic realm marine sediment data compared with archaeomagnetic and lake sediment records summary four box cores collected from the ontong java plateau during the eurydice expedition have been used to make relative geomagnetic palaeointensity measurements rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy and that they are suitable for relative intensity estimates these are obtained by normalizing the nrm by an arm imparted in a low dc bias field the palaeoceanographic event known as the preservation spike is used to establish a crude time scale for the record so that it may be compared with other data from the same region and also with global palaeointensity estimates the marine sediment data are quite similar to australian intensity data from lake sediments and archaeomagnetic sources but as might be expected exhibit some obvious differences from the global record