dating loess up to 800 ka by thermoluminescence thermoluminescence tl ages agreeing with expected ages have been obtained for 13 loess samples spanning the age range from 20 to 800 ka our samples are from alaska and north island new zealand and are unusual in tl dating studies of loess older than 80 100 ka by having independent age assignments that are generally well constrained from ages of associated tephra beds with the polymineral fine silt sized 4 11 m grains the partial bleach tl technique yielded expected ages up to about 350 ka whereas the total bleach method gave accurate ages in the range 100 to 800 ka thus the much disputed upper age limit of 100 150 ka for the tl dating of loess now appears to be sample and worker dependent rather than a global property of the tl signals in the tl dominant feldspars

magnetospheric substorms and nighttime height changes of the f2 region at middle and low latitudes using the published plots of 15 min interval values of h f2 the minimum virtual height of the ionospheric f2 region at five japanese stations spread over 26 45 n 15 35 n geomagnetic and 128 142 e it is shown that there are frequent rapid increases and less frequent decreases of h f2 by 100 200 km in about 2 hours with near simultaneous start and end at all five stations in the postmidnight hours and at three to five stations in the premidnight hours in the months of september and december 1988 and march 1989 about 80 h f2 perturbations of the above type are identified the near simultaneity of the h f2 disturbances at the five stations suggests that an plasma drift due to an east west electric field is the cause of the h f2 disturbances this interpretation is validated by showing that there is a simultaneous presence of bay disturbances in auroral latitude magnetograms over a wide longitude range during almost all the h f2 increases it is shown that neutral wave disturbances propagating equatorward even with a speed of 750 m s cannot account for the h f2 disturbances the study reveals two categories of h f2 perturbations 1 h f2 increases starting near the beginning of the geomagnetic negative bays at auroral latitudes and 2 rapid h f2 increases starting near the maximum intensity phase of the auroral bays and preceded by h f2 decreases starting at the onset time of the bay disturbance or a little earlier using the vast amount of h f2 data collected all over the globe it is possible to quantify and characterize the substorm related electric fields and their variabilities such characterization is very useful in understanding the magnetospheric and the magnetosphere ionosphere interaction processes involved in the generation of magnetospheric substorms it is also pointed out that the understanding of f2 region changes during magnetic storms may improve greatly if the large f2 region changes caused by electric fields on the substorm time scale are taken into account the h f2 disturbances reported in this study are similar in time scale and appearance to the h f2 disturbances caused by long period atmospheric waves and this suggests the possibility of a mixup of the two effects and the consequent wrong identification on some occasions

the time averaged geomagnetic field global and regional biases for 0 5 ma summary palaeodirectional data from lava flows and marine sediments provide information about the long term structure and variability in the geomagnetic field we present a detailed analysis of the internal consistency and reliability of global compilations of sediment and lava flow data time averaged field models are constructed for normal and reverse polarity periods for the past 5 ma using the combined data sets nonzonal models are required to satisfy the lava flow data but not those from sediments alone this is in part because the sediment data are much noisier than those from lavas but is also a consequence of the site distributions and the way that inclination data sample the geomagnetic field generated in the earth s core different average field configurations for normal and reverse polarity periods are consistent with the palaeomagnetic directions however the differences are insignificant relative to the uncertainty in the average field models thus previous inferences of non antipodal normal and reverse polarity field geometries will need to be re examined using recently collected high quality palaeomagnetic data our new models indicate that current global sediment and lava flow data sets combined do not permit the unambiguous detection of northern hemisphere flux lobes in the 0 5 ma time averaged field highlighting the need for the collection of additional high latitude palaeomagnetic data anomalous time averaged field structure is seen in the pacific hemisphere centred just south of hawaii the location of the anomaly coincides with heterogeneities in the lower mantle inferred from seismological data the seismic observations can be partly explained by lateral temperature variations however they also suggest the presence of lateral compositional variations and or the presence of partial melt the role of such heterogeneities in influencing the geomagnetic field observed at the earth s surface remains an unresolved issue requiring higher resolution time averaged geomagnetic field models along with the integration of future results from seismology mineral physics and numerical simulations

thermoluminescence dating of the chelford interstadial abstract the sediments at chelford constitute one of the key devensian sequences in britain previous radiometric dating attempts using wood and peat from the interstadial deposits per se suggest its age is likely to be beyond the limits of resolution by radiocarbon using tl dating of feldspar and quartz mineral fractions from the host succesion of chelford sands a sequence of internally consistent dates is derived which accords with the existing litho and biostratigraphic evidence these suggest that the absolute age of the chelford interstadial is in the range 90 100 ka the chelford sands appear to be the product of at least two cold stages

shallow bias of paleomagnetic inclinations in the paleozoic and precambrian abstract an updated analysis of the global paleomagnetic database shows that the frequency distributions of paleomagnetic inclinations for the cenozoic and mesozoic eras younger than 250 ma are compatible with a random geographical sampling of a time averaged geomagnetic field that closely resembles that of a geocentric axial dipole in contrast the frequency distributions of paleomagnetic inclinations for the paleozoic and precambrian eras prior to 250 ma are over represented by shallow inclinations after discounting obvious secondary causes for the bias such as from data averaging sedimentary inclination error inhomogeneous lithological distributions and tropical remagnetization we show that the anomalous inclination distributions for the paleozoic and precambrian can be explained by a geomagnetic field source model which includes a relatively modest 25 contribution to the axial dipole from a zonal octupole field and an arbitrary zonal quadrupolar contribution the apparent change by around 250 ma to a much more axial dipolar field geometry might be due to the stabilization of the geodynamo from growth of the inner core to some critical threshold size a gross speculation which would imply that either the threshold size was rather large or the inner core nucleated rather late in earth history alternatively if a geocentric axial dipole model is assumed or can eventually be demonstrated independently the anomalous inclination distributions for the paleozoic and precambrian may reflect a tendency of continental lithosphere to be cycled into the equatorial belt perhaps because geoid highs associated with long term continental aggregates influence true polar wander

optical dating preliminary results on the anomalous fading of luminescence from feldspars abstract luminescence emitted from various beta dosed alkali feldspars and plagioclase feldspars has been measured under optical stimulation the luminescence sensitivities were compared as the initial stage of an on going study of short term anomalous fading of the optically stimulated luminescence osl signal anomalous fading was observed in the luminescence stimulated by both green light 514 5 nm and ir 880 80 nm from samples representing each of the major compositional regimes of the feldspar series means of alleviating the influence of this fading in luminescence dating applications are under investigation particularly the effect of isothermal storage at 100 c initial findings show that anomalous fading in these samples does not lead to a stable remanent level within the storage times used a practical consequence is that use of a fading monitoring procedure is strongly recommended in optical dating

late permian palaeomagnetism of northern eurasia data evaluation and a single plate test of the geocentric axial dipole model summary how the first order structure of the magnetic field changed through geological time is one of the most long living and hotly debated questions in geomagnetism for the last 5 ma the geomagnetic field is found to be essentially dipolar with about 5 per cent quadrupole term and possibly still smaller octupole term proving this became possible after accumulation of a large set of globally distributed reliable palaeomagnetic data and their analysis in the coordinates tied to the rotation axis for older times the data are less reliable scarce and unevenly distributed while tectonic motions destroyed the global coordinates in this paper a method to determine the geomagnetic field structure for a single plate is discussed it is suggested that the coordinate system for analysis can be derived from great circles each being drawn through a sampling point and the corresponding palaeomagnetic pole sp circle such circles are to intersect at a true i e pure dipole pole that is largely purified from the contributions of non dipole zonal terms and inclination shallowing the scrutiny of late permian 270 250 ma palaeomagnetic poles from northern eurasia revealed two distinct groups one includes several poles from a limited area in south france sf and the other consists of tightly clustered nine poles from locations spread over a large part of eurasia tentatively the former group can be explained by either rotation of sf with respect to main eurasia or less likely remagnetization in early triassic time irrespectively these poles cannot be used for calculation of the true dipole pole nor for computation of the apparent polar wander path of eurasia the poles from the main part of eurasia were used to find the position of the true dipole pole of this plate and for analysis of the field the minimum of residual dispersion of the observed data is found for the quadrupole and octupole terms of less than 10 per cent when each term is varied separately when both terms are varied together the best fit is observed for the quadrupole and octupole terms of 4 and 12 per cent respectively our analysis shows that the position of the true dipole pole is robust while the estimates of non dipole terms are not we argue that these estimates should be regarded as the upper limits on the non dipole contributions to the late permian geomagnetic field at the same time we are pretty sure that octupole term of 20 per cent or more are not permitted by the data

conditions for intense ionospheric storms expanding to lower midlatitudes 1 for studying conditions of intense ionospheric storms at lower midlatitudes several storms that occurred in march and april 2001 were compared in the two largest magnetic disturbances that occurred during this period the disturbance dst index reached 387 and 271 nt the two largest ionospheric storms occurred in response to other weaker magnetic disturbances in which dst reached 149 and 102 nt for the largest ionospheric storms on 21 march 2001 and 22 april 2001 a sequence of ionospheric and thermospheric disturbances was analyzed we found that a nighttime disturbance dynamo plays an important role in expanding ionospheric storms to lower latitudes when an eastward disturbance dynamo electric field forms after midnight the ionospheric layer is uplifted and the ion drag is reduced the storm time equatorward surge effectively reaches lower latitude regions without decaying under the condition of reduced ion drag the equatorward surge pushes up the ionosphere in turn and the ion drags might be further reduced the large event to event variation of ionospheric storms might be partly owing to such a positive feedback process in addition to the well known local time effect

paleomagnetism of the siberian traps new data and a new overall 250 ma pole for siberia the flood basalt province in siberia is one of the largest in the world but the number of reliable paleomagnetic data on these volcanics is still limited we studied lava flows and trap related intrusions from two areas in the north and west of the siberian platform a dual polarity characteristic component was isolated from most samples with the aid of stepwise thermal and alternating field demagnetization we then compiled all published paleomagnetic data on the siberian traps that have been obtained according to modern standards also included are presumably trap related overprint directions in paleozoic rocks although these overprints and trap results may locally differ the corresponding mean poles based on remagnetized sediments and volcanics show excellent overall agreement and justify pooling of both data types several ways of data grouping were attempted the trap mean pole proved to be rather insensitive to statistical treatment irrespective of the averaging procedure used the overall mean poles for the siberian traps nsp2 55 1 n 147 0 e n 8 k 123 a95 5 0 or nsp4 57 2 n 151 1 e n 8 k 192 a95 4 0 differ slightly but significantly from the coeval mean poles of baltica torsvik 2001 van der voo r and torsvik t h the quality of the european permo triassic paleopoles and its impact on pangea reconstructions in timescales of the paleomagnetic field j e t channell d v kent w lowrie and j g meert eds agu geophys monogr 2004 135 29 42 we consider possible causes for this difference and conclude that it could be explained either by persistent non dipole terms in the permo triassic geomagnetic field or widespread inclination shallowing in the european data

denisovan dna in late pleistocene sediments from baishiya karst cave on the tibetan plateau a late middle pleistocene mandible from baishiya karst cave bkc on the tibetan plateau has been inferred to be from a denisovan an asian hominin related to neanderthals on the basis of an amino acid substitution in its collagen here we describe the stratigraphy chronology and mitochondrial dna extracted from the sediments in bkc we recover denisovan mitochondrial dna from sediments deposited 100 thousand and 60 thousand years ago ka and possibly as recently as 45 ka the long term occupation of bkc by denisovans suggests that they may have adapted to life at high altitudes and may have contributed such adaptations to modern humans on the tibetan plateau

ionosphere disturbances observed throughout southeast asia of the superstorm of 20 22 november 2003 1 ionospheric disturbances in the southeast asian region during the super magnetic storm of 20 22 november 2003 were investigated through an ionosonde chain and a gps network assisted by the space borne instruments at early stage of the storm in the postsunset sector large enhancements in the critical frequency of f2 layer and total electron content were observed at northern crest region of the equatorial ionization anomaly eia which might be produced by both the storm meridional wind superimposed with traveling atmospheric disturbances and prompt penetration electric field ppe during the main phase of the storm when interplanetary magnetic field started a 12 h southward turning equatorial ionosphere was elevated to a very high level which should be most probably caused by a long duration ppe event meanwhile at mid low latitudes ionosphere witnessed an initial simultaneous decrease then followed by drastic increases which is very different from the past observations in this region reddy and nishida 1992 combined analysis of the data from the ionosonde and other space based measurement shows that for the present case the penetration efficiency of the interplanetary electric field ief to the equatorial ionosphere was larger at night than in the daytime which agrees with the results of fejer et al 2007 showing the ratios of ppe and ief changes were highly variable with the local time during the recovery phase eia was severely inhibited owing to a wind convergence and possibly because of the westward disturbance dynamo electric field

is 600 myr long enough for the random palaeogeographic test of the geomagnetic axial dipole assumption summary a simple analysis suggests that a time interval of more than about 5000 myr is needed for the random palaeogeographic test to be effective in assessing the geomagnetic axial dipole assumption this time is so long as to render the test ineffective consequently intervals of 600 myr should be recognized as providing only a small sample that is likely to be biased towards low inclination values

a strong positive phase of ionospheric storms observed by the millstone hill incoherent scatter radar and global gps network 1 during geomagnetic storms the ionospheric f region electron density may be greatly increased or decreased which are termed positive storms or negative storms it is generally accepted that negative storm phases are caused by neutral composition changes in contrast different mechanisms have been proposed to explain the generation of positive storm phases in this paper we present observations of a strong positive storm at middle latitudes the millstone hill incoherent scatter radar detected significant increases of the midlatitude ionospheric f region electron density during a magnetic storm on 3 april 2004 the positive phase of the ionospheric storm started to occur in the morning sector 0912 lt at millstone hill and lasted for more than 10 hours compared with the quiet time ionosphere the daytime f peak altitude over millstone hill during the storm was 80 km higher the f region electron density was increased by a factor of 2 4 and the f region electron temperature was decreased by 1000 k or 40 the radar also measured an enhanced eastward electric field and a slightly more equatorward neutral wind global gps measurements show that total electron content tec was increased at middle latitudes and decreased at lower latitudes and the large tec enhancements occurred primarily in the atlantic sector we suggest that electric fields may play an important role in the generation of the observed positive storm phase the eastward electric field will cause increases in the midlatitude ionospheric electron density by moving the plasma particles upward and decreases in the equatorial ionospheric electron density by strengthening the fountain effect the daytime poleward wind was reduced or even reversed during the storm which may also contribute to the occurrence of the positive storm

a middle palaeolithic site in the southern north sea investigating the archaeology and palaeogeography of area 240 the potential for middle palaeolithic sites to survive beneath the sea in northern latitudes has been established by intensive investigation within area 240 a marine aggregate licence area situated in the north sea 11 km off the coast of norfolk england the fortuitous discovery of bifacial handaxes and levallois flakes and cores led to a major programme of fieldwork and analysis between 2008 and 2013 the artefacts were primarily recovered from marine isotope stage 8 7 floodplain sediments deposited between 250 and 200 ka it is considered that the hand axes and levallois products are contemporaneous in geological terms with taphonomically complex sedimentary contexts as observed in several north west european sites the early middle palaeolithic emp lithics have survived multiple phases of glaciation and marine transgression the investigations confirm that the artefacts are not a chance find but indicate clear relationships to submerged and buried landscapes that although complex can be examined in detail using a variety of existing fieldwork and analytical methods the palaeogeographical context of the finds also offers expanded interpretations of the distribution of emp hominins in the southern north sea not predictable from onshore archaeological records

the stranded beach dune sequence of south east south australia a test of thermoluminescence dating 0 800 ka the remarkable sequence of stranded beach dunes in south east south australia deposited during the past 800 ka has provided us with a rare set of samples for testing thermoluminescence sediment dating methods here we report thermoluminescence ages obtained from quartz separated from the dunes and compare them with accepted ages for the high sea levels responsible for the dunes the independent ages of the dunes were obtained from earlier work by schwebel which has been extended and refined by modelling the dune formation using sea level variations derived from the oceanic 18o record the work is unusual in extending thermoluminescence dating to an 800 ka sequence with modest geological control of the age the agreement between thermoluminescence and geological ages is satisfactory for eight dunes with ages in the range 120 800 ka quartz is not usually thought to be useful for thermoluminescence dating in this time span two factors contribute to our success the first is that the dose rates are low about 0 5 gy ka 1 or one quarter of that typical of sediments the second is that the thermoluminescence vs dose response continues to rise monotonically above the saturation region at doses above 300 gy

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

positive and negative ionospheric disturbances at middle latitudes during geomagnetic storms the morphology of middle latitude ionospheric disturbances in response to geomagnetic storms has been investigated to determine the phenomenological differences between positive and negative ionospheric storm effects using fof2 observations from azimuthal chain of stations to better organize the disturbance signatures two ionospheric indices were introduced to describe the maximum positive dfu index and negative dfl index deviation observed during an ionospheric storm a systematic appearance of nighttime positive effects was determined with a 24 hour recurrence the thermospheric ionospheric view associated with positive and negative storm effects proposed by prolss 1993 was extended to encompass our observations this test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms nevertheless the prominent feature of large nighttime enhancements in the ionization density have yet to be explained

non dipole fields and inclination bias insights from a random walk analysis abstract the paleomagnetic assumption that the earth s magnetic field is reduced to a geocentric axial dipole gad when sufficiently sampled has been called into question for mesozoic and earlier times it has been suggested for example that modest contributions from axial quadrupolar 10 and octupolar 25 fields are resolvable using inclination only data from paleomagnetic studies the underlying assumption in inclination only studies is that considerable continental drift has occurred over a sufficiently long period of time to render paleomagnetic sampling random in a paleogeographic sense this assumption was stated in all previous studies dating back to 1976 but was never tested we have developed a random walk model designed to test this assumption our model uses three different configurations for the continents in the random walk and allows the user to vary parameters such as maximum velocity sampling distribution sampling frequency and frequency of directional change the model generates large sample sizes that cannot be adequately evaluated using the standard 2 statistical test and therefore we introduce two statistical parameters used in structural equation models our models indicate that the random paleogeographic sampling assumption used in the previous studies is not valid due primarily to the lack of an adequate sample size and temporal distribution we show for example that even the most robust dataset compiled in 1998 is severely undersampled a series of model runs on a gad earth with sampling over a 600 myr period demonstrates that detailed sampling will on average produce a gad like distribution only 30 of the time other model runs demonstrate that inadequate sampling can produce false quadrupolar and octupolar effects it is our conclusion that time averaged inclination only studies using the extant paleomagnetic database should be viewed with extreme caution

geodynamo reversal frequency and heterogeneous core mantle boundary heat flow abstract we analyze more than two hundred and forty magnetic polarity reversals and excursions over forty million years of time from numerical dynamos with heterogeneous boundary heat flux comparisons between a dynamo with uniform boundary heat flux dynamos with boundary heat flux patterns consisting of a single spherical harmonic and dynamos with tomographic heat flux patterns proportional to the large scale lateral variation of seismic shear wave velocity in the lower mantle reveal that boundary heat flux heterogeneity tends to increase the average frequency of polarity reversals relative to uniform boundary conditions particularly if the heterogeneity increases the average equatorial heat flux non axisymmetric spherical harmonic degree l 1 and 2 boundary heterogeneity and the seismically derived tomographic heterogeneity produce comparable reversal and excursion frequencies in our models suggesting that geomagnetic polarity reversal rates may be relatively insensitive to the non axisymmetric planform of core mantle boundary heat flux in contrast the average polarity reversal frequency in our models is quite sensitive to the total boundary heat flow and to the total heat flow at the equator with non reversing behavior at low heat flow and frequent reversals at high heat flow conditions reversal frequency also increases with the amplitude of the boundary heterogeneity although it is less sensitive to this parameter our results suggest that geomagnetic superchrons may correspond to times with reduced core mantle boundary heat flow either globally or equatorially and conversely periods with high paleomagnetic reversal frequency may correspond to times with increased heat flow at the core mantle boundary

incompatible ediacaran paleomagnetic directions suggest an equatorial geomagnetic dipole hypothesis abstract paleomagnetic results obtained from rocks of ediacaran age in several localities in laurentia and baltica persistently display co existence of two magnetization components one shallowly and the other steeply inclined both components pass criteria for a primary magnetization while geological considerations and radiometric age dating indicate that these magnetizations are surprisingly close in age the conventional interpretation of these results translating the inclination into paleolatitudes using the geocentric axial dipole hypothesis would imply that rocks acquired magnetizations in positions switching back and forth between equatorial and near polar latitudes in a geographic reference frame such large scale and fast 45 cm yr migrations of a continent have been rejected as dynamically implausible neither plate tectonics nor true polar wander are thought to be able to attain the required velocities a highly irregular behavior of the geomagnetic field during the ediacaran possibly an alternation of the geomagnetic dipole axis between a co axial and an equatorial alignment remains the only viable explanation for the paleomagnetic data such a behavior entails specific outer core conditions which in turn impose strong constraints on the possible models for the thermal evolution of the earth s interior

possible links between long term geomagnetic variations and whole mantle convection processes the earth s internal magnetic field varies on timescales of months to billions of years the field is generated by convection in the liquid outer core which in turn is influenced by the heat flowing from the core into the base of the overlying mantle much of the magnetic field s variation is thought to be stochastic but over very long timescales this variability may be related to changes in heat flow associated with mantle convection processes over the past 500 myr correlations between palaeomagnetic behaviour and surface processes were particularly striking during the middle to late mesozoic era beginning about 180 myr ago simulations of the geodynamo suggest that transitions from periods of rapid polarity reversals to periods of prolonged stability such as occurred between the middle jurassic and middle cretaceous periods may have been triggered by a decrease in core mantle boundary heat flow either globally or in equatorial regions this decrease in heat flow could have been linked to reduced mantle plume head production at the core mantle boundary an episode of true polar wander or a combination of the two

linking lowermost mantle structure core mantle boundary heat flux and mantle plume formation abstract the dynamics of earth s lowermost mantle exert significant control on the formation of mantle plumes and the core mantle boundary cmb heat flux however it is not clear if and how the variation of cmb heat flux and mantle plume activity are related here we perform geodynamic model experiments that show how temporal variations in cmb heat flux and pulses of mantle plumes are related to morphologic changes of the thermochemical piles of large scale compositional heterogeneities in earth s lowermost mantle represented by the large low shear velocity provinces llsvps we find good correlation between the morphologic changes of the thermochemical piles and the time variation of cmb heat flux the morphology of the thermochemical piles is significantly altered during the initiation and ascent of strong mantle plumes and the changes in pile morphology cause variations in the local and the total cmb heat flux our modeling results indicate that plume induced episodic variations of cmb heat flux link geomagnetic superchrons to pulses of surface volcanism although the relative timing of these two phenomena remains problematic we also find that the density distribution in thermochemical piles is heterogeneous and that the piles are denser on average than the surrounding mantle when both thermal and chemical effects are included

thermoluminescence dating applied to glaciolacustrine sediments from central british columbia glaciolacustrine and lacustrine sediments are important indicators of deglacial interglacial and nonglacial intervals within the quaternary of canada yet there are no techniques for measuring their absolute deposition ages beyond the last 50 000 years in an attempt to develop an absolute dating tool for such sediments we applied the partial bleach thermoluminescence tl dating technique to glaciolacustrine sediments of known age from central british columbia samples were selected to represent both ice proximal and ice distal deposition and different modes of sedimentation the results show clearly that both tl procedures and sedimentation processes as reflected in the particle size and sedimentary structures of the samples critically affected the accuracy of tl apparent ages specifically care was required to isolate the effects of laboratory overbleaching apparent glow curve shifts and inappropriate regression analysis clay dominant layers lacking silt or sand interlayers produced expected

testing the geomagnetic dipole and reversing dynamo models over earth s cooling history abstract we use the inclination test of the geocentric axial dipole hypothesis to interpret observational magnetic field models and earthlike polarity reversing numerical dynamo models with uniform and latitudinally variable buoyancy flux boundary conditions dynamo models with uniform buoyancy flux represent three convective states of the mantle and core 1 present era earth driven thermochemically at the inner core boundary 2 mantle overturn with elevated heat flux at the core mantle boundary and 3 ancient earth prior to inner core nucleation with buoyancy production solely at the core mantle boundary by verifying the effect of latitudinal heat flux variation on reversal frequency we show that polar cooling at the core mantle boundary is likely to yield only small inclination anomalies instead we find that radial heat flow structure can explain magnetic field morphologies over broad eras of earth s cooling history consistent with earth s present magnetic field dynamos driven by buoyancy due to inner core growth are nearly dipolar in contrast elevated core mantle boundary heat flow yields small to moderate inclination flattening due to a persistent octupole that reverses synchronously with the dipole we find that reversal frequency and inclination anomalies can indicate the convective state of the mantle core system in particular our results along with evidence of a young inner core are consistent with a previous suggestion that an entirely liquid core contributed to shallow inclinations in precambrian time

effectiveness of natural zeroing of the thermoluminescence in sediments the last exposure to sunlight of detrital feldspars and quartz grains in quaternary sediments can be dated directly by thermoluminescence tl methods but the effectiveness of zeroing of the light sensitive tl signal by daylight varies widely depending upon details of the sedimentation processes to document this variability and to help develop objective criteria useful for future sample selection and laboratory procedures i have collected and analyzed several eolian fluvial marine deltaic and lacustrine samples from less than 100 year old deposits as well as suspensions from sediment plumes also underwater spectral irradiance was measured during recovery of suspensions tl properties of polyrnineralic feldspar dominated 2 4 m and 4 11 m size fractions were measured in the laboratory unexpectedly some light sensitive tl was found to remain in all samples however the light sensitive tl was more effectively zeroed in some samples a proximal loess a sandy braided channel deposit tidal flat and upper delta front muds and thin clayey lacustrine laminae than in others a silty braided channel deposit submarine fan muds and silt bearing lacustrine laminae for the first group the minimum relict paleodose obtained with the partial bleach technique is about 0 4 0 3 gy corresponding to a relict tl age estimate of about 200 years for these sediments thus similar sediments excluding fluvial deposits as young as about 2 ka can be accurately and routinely dated without significant correction for a zero point error if one uses the partial bleach technique coupled with integrated optical bleaching energy fluences of less than 1 j cm 2 and wavelengths only above about 550 nm also some simple optical bleaching tests are reported that have a potential use in sample selection and in provenance studies of some surficial detrital sediments finally a simple mathematical model is presented that helps account for the gross features of the observed bleaching response curves

a review of current research on tl dating of loess abstract the thick loess deposits of china central europe and north america are particularly suitable for the application of the thermoluminescence tl dating method because individual grains are likely to have travelled large distances and thus been well exposed to light before deposition wind blown silt grains collected close to glacial rivers in alaska have been shown to give a zero age of not more than 2 ka demonstrating the efficiency of the zeroing mechanism differences in laboratory procedures can cause differences in the tl ages reported particularly for loess over 100 ka tl ages for interstadial soils in europe are in agreement with the very few radiocarbon dates on reliable material such as charcoal on the other hand tl dates from sites in belgium and north western germany indicate that the previously accepted chronology which was based on two radiocarbon dates on humic rich sediments is incorrect the use of the last interglacial palaeosol for assessing the tl dates on loess above and below it is limited by the uncertainty in the timing of termination of soil forming processes 107 and 71 ka are the limits suggested by the astronomically derived time scale results on deposits from china north america alaska and europe are discussed in this context

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

optical dating studies of quartz and feldspar sediment extracts abstract continuing developmental work into optical dating has led to some clarification of the optical behaviour of quartz and feldspar sediment extracts we have verified the key assumption intrinsic to the method that the optical signal is zeroed completely upon exposure to daylight we also show that the rate of zeroing in optical dating is much more rapid than it is in tl dating studies concerned with the extraction of the thermally stable signal from laboratory irradiated samples showed that problems may arise from medium to high temperature preheating of young samples optical alternatives to thermal stabilization were tested using dye and krypton lasers using a krypton laser we have succeeded in obtaining an equivalent dose of 0 0 0 7 gy for the quartz from a modern intertidal sand and an average dose of 120 22 gy for the feldspar extract of a 70 ka sand unit both were obtained using six wavelengths from the infrared to the violet and no dependence on wavelength was found we found that the photon energies of infrared and deep red light can stimulate luminescence in unirradiated quartz and feldspar extracts of sediments this was not expected and suggests that the process of trap emptying is more complex than we had envisioned but implies a far greater than expected degree of technical flexibility for the optical dating method

the age of the inner core abstract the energy conservation law when applied to the earth s core and integrated between the onset of the crystallization of the inner core and the present time gives an equation for the age of the inner core in this equation all the terms can be expressed theoretically and given values and uncertainties of all relevant physical parameters the age of the inner core can be obtained as a function of the heat flux at the core mantle boundary and the concentrations in radioactive elements it is found that in absence of radioactive elements in the core the age of the inner core cannot exceed 2 5 ga and is most likely around 1 ga in addition to have an inner core as old as the earth concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds

thermoluminescence chronology of toronto area quaternary sediments and implications for the extent of the midcontinent ice sheet s we report direct dating by thermoluminescence tl methods of key quaternary stratigraphic horizons in the toronto area tl ages indicate that 1 most of the exposed sediments of the don formation at the sampled site were probably deposited during the closing phase of the sangamon interglacial 80 ka oxygen isotope stage 5a not the climatic optimum substage 5e 120 130 ka as generally supposed 2 overlying deltaic strata of the scarborough formation which accumulated in an ice dammed ancestral lake ontario were deposited between 60 and 50 ka early wisconsin oxygen isotope stage 4 3 the sunnybrook diamict overlying the scarborough formation was deposited in the middle wisconsin at 40 45 ka oxygen isotope stage 3 likely by glaciolacustrine processes rather than before 65 ka as previously supposed 4 sediments of the upper thorncliffe formation lying stratigraphically just beneath the last glacial maximum hallton till were deposited at 23 ka consistent with reliable 14 c dating thus the earliest wisconsin incursion of the proto laurentide ice sheet into the lake ontario basin as recorded by the scarborough formation probably did not take place until at least 60 ka and did not extend south and southwest of the toronto area until after 25 ka ice free conditions probably persisted over large areas of midcontinent north america from the end of the illinoian glaciation at 130 ka to the late wisconsin glacial maximum at 20 ka

limitations of thermoluminescence to date waterlain sediments from glaciated fiord environments of western spitsbergen svalbard abstract a fundamental problem in the tl dating of waterlain sediments particularly in the arctic is the accurate determination of the level of solar resetting prior to deposition this study determined the effect of wavelength on the solar resetting of the tl signal and concomitant effects on the accuracy of tl age estimates for late glacial and modern glacial and nearshore marine sediments from fiords on spitsbergen the reduction in tl level decreases with filtering of wavelengths above 400 nm modern and late weichselian tills have tl levels at saturation probably received no light exposure prior to deposition and thus cannot be dated by tl glacial marine sediments deposited within 0 5 km of a glacier terminus yielded tl age estimates 10 times the known age presumably because these sediments received limited light exposure prior to deposition modern sublittoral sediments and fiord muds yielded tl apparent ages between

chronological separation of interglacial raised beaches from northwestern europe using thermoluminescence thermoluminescence tl age estimates have been obtained on coarse grained detrital feldspar from eemian beach sand substage 5e early weichselian dune sands substages 5d and 5b and pre eemian beach sand the past radiation dose is obtained using the additive dose method even for the oldest samples which date to 300 000 yr b p by other methods the tl signal is not in saturation and can be doubled by the addition of laboratory radiation doses without saturation being achieved this is contrasted with the behavior of polymineral silt sized grains from loess in the adjacent area the tl age estimates are systematically underestimated by about 40 when compared with the expected geological ages however they are in correct stratigraphic order and demonstrate that stage 5 beach deposits can be distinguished from those resulting from earlier high sea levels using tl signals from potassium feldspars

interpretation of holocene sea level tendency and intertidal sedimentation in the tees estuary using sediment luminescence techniques a viability study it is demonstrated that detailed examination of the photo and thermoluminescence pl tl of holocene intertidal sediments can reveal important information regarding their depositional history in the context of sea level tendency and storm surge activity the technique is particularly applicable to thick deposits of relatively uniform composition and is demonstrated with a 1 7 m core of marine to brackish water silty clay taken from cowpen marsh in the tees estuary north east england this sedimentary unit is intercalated with an upper and a lower terrestrial peat bed which have been radiocarbon dated to 5250 45 and 7065 45 14c years bp respectively an investigation of the mineral composition and diatom assemblage of the silty clay facies reveals a marked hiatus in deposition towards the top of the minerogenic unit analysis of the luminescence profiles of the sediment illustrates that below this hiatus sedimentation was slow and continuous with approximately 1 0 m of sediment being deposited in 1800 400 years whilst above sedimentation was rapid with 0 7 m of sediment being deposited in 0 200 years it is shown that variations in the luminescence of the sediments can be interpreted in terms of the onset of a positive sea level tendency period coupled with the occurrence of a low frequency extreme water level event

a mu radar based study of mid latitude f region response to a geomagnetic disturbance during the night of january 20 21 1989 ionospheric incoherent scatter power measurements were made with the mu middle and upper atmosphere radar at shigaraki geographic latitude 34 85 n longitude 136 10 e geomagnetic latitude 24 9 longitude 204 3 japan and the electron density profiles in the 180 to 1000 km height range were derived at 8 min intervals the observations showed the presence of three f region disturbances during the night during the very large first disturbance which lasted from 2300 to 0240 lt approximately the height of maximum electron density nm increased by 220 km in 2 hours to reach an altitude of 600 km the other two smaller disturbances occurred during 0300 0500 lt and 0530 0700 lt approximately a detailed interpretation of the above f region disturbances is given examination of some high and middle latitude magnetograms showed the beginning of an intense geomagnetic substorm at auroral latitudes at the start of the first f region disturbance and a less intense substorm around the starting time of the second f region disturbance on the basis of this evidence the first two f region disturbances are interpreted as the result of large vertical drifts of f region ionization due to the substorm generated east west electric fields appearing at mid latitudes the patterns of h f variations during this night at five ionospheric stations in japan support the above interpretation additionally during the second disturbance the possible presence of a wind perturbation due to the equatorward propagation of a wave disturbance generated probably by the first major substorm is indicated by the mu radar data and the ionosonde data the third f region disturbance is attributed to a neutral wind perturbation associated with a gravity wave traveling equatorward the wave being generated most plausibly by the joule heating during the first major substorm the brief unusual distortions of the f layer shape as revealed by mu radar observations are also interpreted as the consequence of an unusually large convergence of ionization in the bottomside of the f layer due to the unusually large electric field and wind perturbations theoretical calculations are made using the mu radar data and f region continuity equation and the east west electric field values during the disturbances are quantified during the first major rise of the f layer during 2300 0115 lt the inferred eastward electric field in the ionosphere at shigaraki is found to be as large as 6 1 mv m and after this disturbance a westward electric field and or a poleward meridional wind is found to occur for some time an eastward electric field of about 3 0 mv m is found to occur during the second f region disturbance along with a possible meridional wind perturbation the large eastward electric field around local midnight is most unusual in both magnitude and direction because the theoretical models of disturbance electric fields predict a strong westward electric field in this lt sector this result has important implications for understanding the physics of disturbance electric fields at middle and low latitudes during substorms

the signature of inner core nucleation on the geodynamo abstract energy considerations indicate that the power delivered to the present day geodynamo comes mainly from the growth of the solid inner core through light element and latent heat releases the nucleation of the inner core was therefore a major transition for the geodynamo here we use numerical dynamo simulations linked by thermochemical evolution of the core to investigate the effects of inner core nucleation icn on the geodynamo and identify possible icn footprints in the palaeomagnetic field our results suggest that a strong field dipole dominated dynamo prior and after icn the uniformitarian scenario is most likely we predict little footprint of icn on the surface field intensity consistent with the observed lack of a long term trend in paleointensity data instead we find that the best proxy for inner core growth is an increase in axial octupole strength with age from present day to icn which might be resolvable in the palaeomagnetic record we confirm the existence of weak field multipolar dynamos prior to icn suggesting the dynamo might have transiently reached a weak field state the catastrophic scenario the narrow stability domain of these weak field dynamos implies that the catastrophic scenario is less probable than the uniformitarian scenario

thermoluminescence dating and geochemistry of loessic deposits in southeast england the results of a thermoluminescence tl dating and geochemical survey of loessic deposits in southeast england involving sampling at 26 localities demonstrate that the loessic deposits appear to be the product of at least three depositional phases of aeolian silt during the late pleistocene namely 10 25 ka bp 50 125 ka bp and 170 ka bp the majority of localities sampled date to the late devensian but isolated pockets of older material were found throughout the area the majority of the samples analysed were of decalcified material the results of geochemical analyses of major oxide and trace element concentrations indicate the uniformity of material and suggest a common provenance

two step development of geomagnetic storms using the dst index more than 1200 geomagnetic storms from weak to intense spanning over three solar cycles have been examined statistically interplanetary magnetic field imf and solar wind data have also been used in the study it is found that for more than 50 of intense magnetic storms the main phase undergoes a two step growth in the ring current that is before the ring current has decayed significantly to the prestorm level anew major particle injection occurs leading to a further development of the ring current and making dst decrease a second time thus intense magnetic storms may often be the result of two closely spaced moderate storms the corresponding signature in the interplanetary medium is the arrival of double structured southward imf at the magnetosphere

the blue emission of k feldspar coarse grains and its potential for overcoming tl age underestimation abstract this paper presents preliminary tl ages on k feldspar coarse grains from raised shallow marine sediments of nw europe and southern italy comparisons between tl ages using different optical filters suggest the use of the blue transmitting corning 7 59 filter allows measurement of an apparently stable tl component in k feldspar which could overcome the problem of age underestimation in the 75 300 ka range

thermoluminescence dating applied to paleosols abstract thermoluminescence tl dating of quaternary sediments has developed rapidly in the last few years as paleosols often prove to be useful stratigraphic marker horizons it is of great interest to obtain absolute ages for them a technique is proposed which increases the range of tl dating of loess to some 300 ka special problems associated with paleosol tl dating such as sampling and dose rate evaluation are discussed three examples for paleosols from west german loess regions are presented the intra wurmian lohner boden soil 28 30 ka lower wurmian chernozem like soils ca 70 ka and the penultimate interglacial soil karlich interglacial between 230 and 170 ka

optical dating using inclusions within quartz grains a sequence of stranded beach dunes in the southeast of south australia which resulted from the advance and retreat of the sea over a tectonically rising land surface during the past 800 ka has been securely dated by geological means and successfully used to test thermoluminescence dating based on quartz we have now obtained a series of promising results from the same sequence with a test of optical dating on inclusions within the quartz grains the innovative aspect of the measurements is the use of infrared irradiation to stimulate emission from the inclusions rather than conventional stimulation of the quartz itself by light of shorter wavelength satisfactory ages were found for seven dunes covering the time span 0 400 ka

a comparison of tl age estimates from different mineral fractions of sands abstract although tl dating of sediments aims to produce accurate dates some recent attempts to date both fine grain polymineral mixtures and large grain feldspars have resulted in age estimates that appear to underestimate the true geological age of the material tl age estimates reported for different mineral fractions quartz and feldspar from the same large grain sand samples have also proved unexpectedly different the possible reasons for underestimation of large grain feldspar ages are reviewed in the context of an exercise designed to look for internal consistency in tl age estimates from quartz and feldspar fractions of sand samples from chelford u k the analyses of the chelford material show internally consistent age estimates over the range 20 100 ka bp that are also in agreement with the independent age control that is available for the site

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

mantle plumes link magnetic superchrons to phanerozoic mass depletion events abstract the four most recent large mass extinction events in the phanerozoic the cretaceous tertiary kt the triassic jurassic tj and the permo triassic pt and guadalupian tatarian gt doublet are associated with a major flood basalt eruption with the timing of peak volcanic activity corresponding within measurement uncertainties to the extinction event three magnetic superchrons precede the four largest phanerozoic extinctions the cretaceous long normal superchron duration 35 myr precedes the kt and the permian kiaman long reversed superchron 50 myr precedes the pt gt doublet in addition the newly recognized ordovician moyero long reversed superchron 30 myr precedes the end ordovician extinction event there is a 10 20 myr delay between the end of each superchron and the subsequent mass depletion event both of which represent distant outliers from their respective populations we propose that deep mantle plumes link these seemingly unrelated phenomena long term 200 myr variations in mantle convection possibly associated with the wilson cycle induce temporal and spatial variations in heat flow at the core mantle boundary polarity reversals are frequent when core heat flow is high and infrequent when it is low thermal instabilities in the d layer of the mantle increase core heat flow end the magnetic superchron and generate deep mantle plumes the plumes ascend through the mantle on a 20 myr time scale producing continental flood basalt trap eruptions rapid climatic change and massive faunal depletions

testing the geomagnetic dipole hypothesis palaeolatitudes sampled by large continents summary an analysis is presented of the way in which a continental spherical cap samples geographic latitude bands as it drifts over the earth s surface this is necessary to establish the likely success of the random palaeogeographic test of the geocentric axial dipole hypothesis and to gauge how much geological time is required it appears that a few hundred million years may suffice

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined