paleomagnetic secular variation at the azores during the last 3 ka 1 we report on 33 new paleomagnetic directions obtained from 16 lava flows emplaced in the last 3 ka on sao miguel the largest island of the azores the data provide 27 well dated directions from historical or 14c dated flows which together with 6 directions previously gathered from the same flows by johnson et al 1998 yield the first paleomagnetic directional record of the last 3 ka from the atlantic ocean within flow directions are consistent suggesting that inclination swings from 60 to 25 and declination changes between 10 to 20 reflect variations in the geomagnetic field over the last 3 ka to a first approximation the declination record is consistent with predictions from cals3k 4 and gufm1 global field models conversely inclination values are lower than model predictions at two different ages 1 four sites from the 1652 ad flow yield i 48 instead of i 63 predicted by gufm1 2 data from several flows nicely mimic the inclination minimum of 800 1400 ad but inclination values are lower by 10 than cals3k 4 model predictions by interpolating a cubic spline fit on declination inclination versus age data we tentatively infer the directional evolution of the geomagnetic field at the azores from 1000 bc to 1600 ad the obtained curve shows three tracks in virtual overlap during the 1000 800 bc 800 500 bc and 400 700 ad time spans

archeomagnetic study of seven contemporaneous kilns from murcia spain new archeointensity values have been determined from seven spanish kilns sampled at the same archeological site and dated by archeological constraints as between 1100 and 1200 a d the directions of the characteristic remanent magnetization and paleointensities have been obtained from classical thellier experiments conducted on 69 samples collected from the walls of the kilns thermoremanent magnetization trm anisotropy and the cooling rate effect upon trm intensity acquisition have been investigated in all the samples differences between mean archeointensities per site before and after corrections for cooling rate are between 3 and 17 the study of these seven contemporaneous kilns coming from the same archeological site and treated in the same way in the laboratory allows us to discuss the different factors that can cause the dispersion between sites generally observed in archeointensity studies the results confirm on one hand the need for cooling rate corrections in this kind of study and on the other hand the need to obtain several archeointensity determinations per century in order to construct a reliable archeointensity curve finally the new data provide a robust mean intensity 60 3 3 3 t at the latitude of paris for the middle of the xii century in western europe and constrain better the evolution of the geomagnetic field intensity during medieval times in this area

intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

paleomagnetism of trap intrusions east siberia implications to flood basalt emplacement and the permo triassic crisis of biosphere article history despite decades of concentrated studies large igneous provinces lips are still among the most enigmatic phenomena of the earth evolution among the myriad questions facing researchers the duration of eruptive magmatic activity and its distribution through time are probably the most mysterious ones although the accuracy of modern dating techniques offers relatively high resolution it is impossible to discriminate whether magmatic activity was more or less uniform or concentrated in few powerful outbursts consequently many trap related questions from their origin to possible impact on the biosphere still cannot be answered some of the above questions can be addressed with paleomagnetic data as have been effectively done in the case of the end cretaceous deccan traps the siberian traps are one of the largest lips in the phanerozoic and are thought by some to be the triggering event for the end permian mass extinction we conducted a paleomagnetic study of trap intrusions along two long profiles in the eastern part of the province and found that most site mean directions are grouped several times tighter than is common for the data on thick lava series and dyke swarms similar over grouping is found in other parts of the siberian trap province too we argue that this phenomenon is the most likely related to nearly simultaneous emplacement of trap intrusions over areas of several ten to few hundred kilometers in dimension for few millenniums or even faster moreover such brief events account for all or nearly all magmatism in each area how such events correlate over the entire siberian lip however remains an open question still our data together with paleomagnetic results on thick lava series in siberia strongly indicate that magmatic activity consisted of a number of brief pulses in comparison to the other lips the siberian one is underlain by the thickest succession of carbonates evaporites and coal bearing clastics that are capable of producing huge amount of green house and poisonous gases we hypothesize that these very fast injections of magma into thick underlying sediments and the unique geological setting of the siberian lip are the major reasons for the permo triassic mass extinction being

first archaeomagnetic secular variation curve for the iberian peninsula comparison with other data from western europe and with global geomagnetic field models 1 a first secular variation sv curve for the iberian peninsula was computed by hierarchical bayesian method using a total of 134 archaeomagnetic directions with ages ranging from 775 to 1959 a d a general agreement is observed between the iberian curve and the french and german sv curves although some interesting differences were found such as the occurrence of lower inclinations between the 11th and 14th centuries in the iberian curve the analysis of these three reference curves indicates that sv in western europe is characterized by three major directional changes at 125 200 and 1350 a d it is suggested that these cusps are regional features of the geomagnetic field the iberian curve has been compared with the predictions of the jackson calsk7k 2 and hongre global models despite large differences recognized between these models even for the dipolar terms they predict reasonably well the iberian archaeomagnetic sv

determination of rapid deccan eruptions across the cretaceous tertiary boundary using paleomagnetic secular variation 2 constraints from analysis of eight new sections and synthesis for a 3500 m thick composite section 1 the present paper completes a restudy of the main lava pile in the deccan flood basalt province trap of india chenet et al 2008 reported results from the upper third and this paper reports the lower two thirds of the 3500 m thick composite section the methods employed are the same i e combined use of petrology volcanology chemostratigraphy morphology k ar absolute dating study of sedimentary alteration horizons and as the main correlation tool analysis of detailed paleomagnetic remanence directions the thickness and volume of the flood basalt province studied in this way are therefore tripled a total of 169 sites from eight new sections are reported in this paper together with the results of chenet et al 2008 these data represent in total 70 of the 3500 m combined section of the main deccan traps province this lava pile was erupted in some 30 major eruptive periods or single eruptive events see each with volumes ranging from 1000 to 20 000 km3 and 41 individual lava units with a typical volume of 1300 km3 paleomagnetic analysis shows that some sees with thicknesses attaining 200 m were emplaced over distances in excess of 100 km both likely underestimates due to outcrop conditions and up to 800 km the total time of emission of all combined sees could have been much less than 10 ka with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence so called big red boles the number of boles thickness of the pulses and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end on the basis of geochronologic results published by chenet et al 2007 and paleontological results from keller et al 2008 we propose that volcanism occurred in three rather short discrete phases or megapulses an early one at 67 5 1 ma near the c30r c30n transition and the two largest around 65 1 ma one entirely within c29r just before the k t boundary the other shortly afterward spanning the c29r c29n reversal we next estimate sulfur dioxide likely a major agent of environmental stress amounts and fluxes released by sees they would have ranged from 5 to 100 gt and 0 1 to 1 gt a respectively over durations possibly as short as 100 years for each see the chemical input of the chicxulub impact would have been on the same order as that of a very large single pulse the impact therefore appears as important but incremental neither the sole nor main cause of the cretaceous tertiary mass extinctions

palaeomagnetic dating of two recent lava flows from ceboruco volcano western mexico ing j escalante supported studies with the micromag agfm and the curie balance and e nava warranted the functionality of the laboratory computers and the network this work was supported by unam project in 112712 hb and fjpc and conacyt grant no 180032 hb and anm fjpc has received funding from the european union s horizon 2020 research and innovation programme under the marie sklodowskacurie grant agreement no 659901

detransformation of the british geomagnetic secular variation record for holocene times in this note we replot the british post glacial secular variation curve in terms of actual values of declination and inclination rather than the transformed declination and inclination system used in our original paper turner thompson 1981 this should facilitate the comparison of our record with contemporaneous european archaeomagnetic data our composite record was obtained by averaging the dated records from 10 cores of lake sediment the sequence of unit vectors describing the magnetic direction record of each core was rotated so as to place its mean direction the mean over the section of core dated between 0 and 7000 bp the time span of the shortest core at zero transformed declination and inclination dt o it 0 the transformed coordinate frame of each core is thus derived from its mean direction assumed to represent the mean geomagnetic field direction over the 7000 yr period rather than from the core tube and its orientation during coring hence the problem of not knowing the azimuthal orientation and inclination of the corer during core collection is avoided and the 10 records can be averaged in this coordinate system transformed coordinates then provide a convenient generalised method of plotting averaged sediment records however in the archaeomagnetic method sample orientation is straightforward and the results can readily be plotted as absolute declination and inclination values so for consistency when comparing the two we have attempted here to detransform our record the following procedures assumptions and approximations were taken to produce the detransformed magnetograms and bauer type plots of figs 1 and 2 1 amplitude correction although the combination of 10 data sets produces a good estimate of the signature of the geomagnetic variations the following factors contribute to an overall loss of amplitude in both declination and inclination a the quality of magnetic recording varies widely between different sediments depending on the porosity of the sediment the size and shape distributions and the nature of the magnetic carrier verosub 1979 the loch lomond sediments carry a good high amplitude pattern of remanent directions of which the most recent closely follow the london observatory records the much wetter and less compacted sediments of llyn geirionydd on the

first archaeomagnetic field intensity data from ethiopia africa 1615 12 ad abstract first archaeointensity determinations have been obtained from ethiopia seven bricks 34 specimens from the dabsan archaeological remains were subjected to archaeointensity determination by means of classical thellier thellier experiment including tests for magnetic anisotropy and magnetic cooling rate dependency the age of the dabsan palace is well controlled by historical information between 1603 when land grants were conceded to the jesuits and the catholicism was established as the official religion in ethiopia and the age of the palace foundation in 1626 27 successful archaeointensity determinations were obtained in 27 specimens from five individual bricks revealing an average field value of 33 5 1 1 t which is 11 26 lower than expected values from global geomagnetic models based on historical and archaeomagnetic data global models for 1615 ad predict a low in central southern africa related to past location of the present southern atlantic anomaly saa our results suggest that the field intensity in central africa may have been slightly lower than global model predictions this would indicate that the low could be probably more extended towards central eastern africa or more intense than previously considered further data from this region are especially welcome to delineate the evolution of the saa

first directional archaeomagnetic results from syria evidence from tell mishrifeh qatna summary we report on the first archaeomagnetic directional data obtained from syria reliable palaeomagnetic directions were collected from four pyrotechnological archaeological structures dated by type of pottery and radiocarbon from the 19th to 8th century bc middle bronze to iron age in tell mishrifeh qatna syria fairly constant northward declination values within confidence limits were obtained whereas inclination values increased from 42 3 to 73 0 from the middle bronze to iron age at first approximation these new data are consistent with coeval archaeomagnetic directions from western europe and bulgaria the high inclination 73 0 2 8 documented for the iron age translating to a vgp latitude of 65 9 n suggests that very strong secular variation was occurring during the 8th century bc

secular variation of the earth s magnetic field in the balkan region during the last eight millennia based on archaeomagnetic data summary the first archaeomagnetic secular variation sv curves for the whole southern balkan peninsula are presented these are based on all data within a 700 km circle centred at thessaloniki 40 60on 23 00oe this data set consists of 325 directional and 625 intensity data mainly from greece bulgaria serbia and southern hungary some data from southern italy are also included the sliding moving window technique was used to calculate a continuous sv curve for intensity while the directional sv curves were calculated using the bivariate extension of the fisher statistics these curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia comparisons with the predictions of the scha dif 3k and scha dif 8k regional and the cals7k 2 and arch3k 1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times the balkan sv curves identify several rapid changes of the geomagnetic field in eastern europe and can be used as reference curves for archaeomagnetic dating in the balkan peninsula

a german catalogue of archaeomagnetic data summary a catalogue has been compiled of existing published and unpublished archaeomagnetic directional data from sites in germany the data comprise 125 results dated mainly in the past two millennia the stability of the natural remanent magnetization was proven for most structures with at least a thellier viscosity test although for the majority of the data the direction is based on the characteristic remanent magnetization obtained from demagnetization experiments rock magnetic experiments carried out on the samples from many of the sites reveal that the dominant magnetic carrier is magnetite often oxidized or with impurities for many sites the archaeological age estimate is supported by physical dating methods while the roman epoch 0 400 ad and the period from medieval to modern times 800 1700 ad are reasonably well covered with data the time interval in between and the first millennium bc are only poorly covered the geographical distribution of data throughout germany shows a concentration along the rhine valley during roman times with in general a better coverage to the north nevertheless this data set clearly shows the secular variation during the past three millennia and it extends the european archaeomagnetic data set considerably

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

high resolution fluvial record of late holocene geomorphic change in northern tunisia climatic or human impact abstract in northern tunisia the late holocene alluvial record of medjerda floodplain sediments indicates geomorphic changes due to fluctuations of past climate superimposed by the effects of human activity geomorphic activity occurred several times interrupting stable conditions enhanced fluvial dynamics occurred around 4 7 3 0 1 7 1 0 and 0 7 ka cal bp a peak of activity took place about 0 4 ka cal bp some periods of fluvial activity show event like phenomena in particular when an anthropogenic impact intensifies climatic aridification this has been the case around 1 7 1 0 0 7 and 0 4 ka cal bp with severe floods in the medjerda valley during antiquity as well as around 1 3 0 8 and 0 5 ka cal bp immature alluvial soils have developed the first one being the most distinct late holocene medjerda alluvial history shows that fluvial dynamics in northern tunisia were predominantly climate driven anthropogenic impact only intensified or weakened these processes

archaeomagnetic results from southern italy and their bearing on geomagnetic secular variation archaeodirectional results from kilns and other baked structures in southern italy are presented they are generally compatible with the much larger data sets from france and bulgaria in particular a summary of all the results associated with the well known eruption of vesuvius that destroyed pompeii n 9 d 355 i 5 8 95 1 5 provides a reliable archaeomagnetic anchor point supporting the french and bulgarian master curves it is extremely well constrained in time and it comprises independent studies carried out in four different countries furthermore it is derived from a diverse set of features agreement amongst which argues strongly against significant perturbations due to magnetic refraction structural disturbance or depositional shallowing in terms of geomagnetic secular variation we interpret the western european archaeomagnetic data summarized here in terms of an open loop caused by westward drift followed by an inclination low spanning the first few centuries ce representing the signal of a static flux pulse that reaches a maximum magnetic moment of a few percent of the earth s main central dipole 2005 elsevier b v all rights reserved

new archeointensity data from novgorod north western russia between c 1100 and 1700 ad implications for the european intensity secular variation abstract reconstructing the secular variation of europe s geomagnetic field over the past millennium is challenging because of the lack of recently acquired archeomagnetic data from western russia in this paper we report on nine new archeointensity values obtained from groups of brick fragments sampled in novgorod north western russia and its vicinities these fragments were collected from churches whose precise ages range from the beginning of the 12th century to the end of the 17th century ad all the archeointensity measurements were carried out using the triaxe experimental protocol which takes into account the thermoremanent magnetization trm anisotropy effect intensity determinations were performed using fast and slow cooling rates for laboratory trm acquisition the results confirm that the triaxe protocol overcomes the trm cooling rate dependence the new data shows that geomagnetic field intensities in north western russia have decreased in the past millennium comparisons were made with other data previously obtained in western europe the balkans and russia as well as with intensity values expected in novgorod from global geomagnetic field models these comparisons yielded three main results 1 the new archeointensity data do not show the occurrence of large intensity variations in north western russia as those observed in the balkan dataset conversely they appear more compatible with western european results which suggests a limited non dipole field effect across europe during the past millennium 2 our data are weaker than the intensity values expected in novgorod from the available global geomagnetic field models this suggests that the field models are inaccurate for the novgorod area 3 a constant linear decrease of the geocentric axial dipole moment since 1600 ad does not appear compatible with our younger data

geomagnetic secular variation as recorded in british lake sediments and its application to archaeomagnetic studies abstract lake sediments can play an important role in understanding and reconstructing temporal characteristics of the geomagnetic field as they potentially offer near continuous high resolution archives of magnetic information extending throughout the holocene to date lake sediment geomagnetic data has typically been excluded from british archaeomagnetic secular variation curves svc due to uncertainties with the acquisition of magnetisation by lake sediments this paper presents the argument that with regards to british datasets the real problem lies with poor chronological control and sets out to illustrate that with british archaeomagnetic data some progress has been made the results indicate that it is not currently possible to resolve secular variation on a time scale of 100 years from published british lake sediment data but more success has been made with data from archaeological sediments this level of detail has been considered necessary for the incorporation of lake sediment data into the british archaeomagnetic dataset as the ability to resolve short term geomagnetic changes is critical for the integration of any dataset into the british svc as the latter is predominantly employed to date archaeological architecture and artefacts requires that it has the ability to resolve changes over timescales relevant to human lifetimes using currently available data this retrospective critique confirms that in archaeological sediments depositional and thermoremanent magnetisation can record the same direction over the same time interval

recent achievements in archaeomagnetic dating in the iberian peninsula application to roman and mediaeval spanish structures archaeomagnetic studies in spain have undergone a significant progress during the last few years and a reference curve of the directional variation of the geomagnetic field over the past two millennia is now available for the iberian peninsula these recent developments have made archaeomagnetism a straightforward dating tool for spain and portugal the aim of this work is to illustrate how this secular variation curve can be used to date the last use of several burnt structures from spain four combustion structures from three archaeological sites with ages ranging from roman to mediaeval times have been studied and archaeomagnetically dated the directions of the characteristic remanent magnetization of each structure have been obtained from classical thermal and alternating field af demagnetization procedures and a mean direction for each combustion structure has been obtained these directional results have been compared with the new reference curve for iberia providing archaeomagnetic dates for the last use of the kilns the inferred ages obtained from this study are consistent with the archaeological evidence available

lakes as paleoseismic records in a seismically active low relief area rieti basin central italy abstract small lakes in low relief areas are atypical candidates for studies on paleoseismicity but their sediments can contain seismically induced event layers seismites generated through strong ground shaking sediment transport hydrological reorganization and or changes in groundwater chemistry and flow lakes lungo and ripasottile are shallow lakes

estimate of the magnetic anisotropy effect on the archaeomagnetic inclination of ancient bricks abstract the magnetic fabric of 59 bricks coming from 5 ancient kilns has been studied by measuring the anisotropy of magnetic susceptibility ams and the anisotropy of isothermal airm anhysteretic aarm and thermal atrm remanent magnetization the bricks are characterized by a well developed magnetic fabric that matches their flat shape the shape of the anisotropy ellipsoids is in almost all cases oblate with the maximum and intermediate axes lying parallel to the large face of the brick and the minimum axis perpendicular to it the directions of the principal axes are almost the same irrespectively of the type of anisotropy measured whereas the degree of anisotropy of the airm aarm and atrm is much higher than the ams as the bricks lie horizontally within the kiln the planar magnetic fabric results in an inclination shallowing of the archaeomagnetic direction with respect to that of the earth s magnetic field at the time of their last cooling estimation of this effect on the grounds of atrm measurements yields a shallowing that varies from 4 to 10 for individual samples such inclination difference may significantly bias archeomagnetic dating for the case of the canosa late roman kiln it leads to a dating error of more than two centuries

is it possible to identify temporal differences among combustion features in middle palaeolithic palimpsests the archaeomagnetic evidence a case study from level o at the abric romani rock shelter capellades spain abstract archaeomagnetic dating is probably one of the most known applications of magnetic methods to archaeology but there are others still underutilized and of particular interest to palaeolithic archaeology here we report a novel application of archaeomagnetism as a technique to determine temporal diachronies among combustion features from the same surface within palaeolithic palimpsests the approach is based on the subtle directional changes of the earth s magnetic field through time secular variation sv and on the ability of burned materials to record such variations under certain conditions three middle palaeolithic hearths from level o ca 55 ka bp at the abric romani rock shelter ne spain were archaeomagnetically investigated the studied surface black homogeneous carbonaceous facies recorded the magnetic enhancement produced by fire with a tenfold increase in concentration dependent magnetic parameters in the uppermost centimetre with respect to its unburned or deeper counterparts pseudo single domain psd ti low titanomagnetite was identified as the main remanence carrier the irreversibility of thermomagnetic curves suggests that these samples did not undergo enough high temperatures as to record a full thermoremanence trm additionally the occasional occurrence of maghaemitized magnetite is interpreted as an indication of a thermochemical remanent magnetization tcrm making these samples unsuitable for absolute palaeointensity determinations two well defined 95

late devonian palaeomagnetism of the north tien shan kyrgyzstan can secular variation vary on a short timescale summary we studied more than 80 lava flows from a 600 m thick pile of upper devonian frasnian basalts and andesites of the aral formation in the north tien shan kyrgyzstan central asia with the aid of stepwise thermal demagnetization a high temperature dual polarity component was reliably isolated from most flows the primary origin of the high temperature component is demonstrated by positive reversal conglomerate and fold tests the most prominent and intriguing feature of this late devonian data set involves a clear distinction in angular dispersion between the lower and upper parts of the studied section a rather low concentration parameter k 13 and several directional anomalies characterize the lower section in contrast a much better grouping k 46 and a lack of directional outliers is observed for the dual polarity vectors from the upper flow sequence of the formation we analysed different mechanisms to account for this directional pattern and found that it is possible in just two ways one is to assume that secular variation sv in the upper sequence is strongly underrepresented and it is a coincidence that the mean directions of both polarities are statistically antipodal and the corresponding concentration parameters are statistically equal the other explanation is to hypothesize that the magnitude of sv can vary several fold at the same palaeolatitude and over time intervals estimated as 10 5 10 6 yr this is in sharp contrast with other models of sv where this magnitude has been assumed to be rather time independent for a givenlatitude ourhypothesisaccountsfortheobservedirregularitiesinpalaeomagneticdata but makes attempts to establish a correlation between sv and other parameters geographic latitude reversal frequency age etc more difficult we are aware however that more data are needed to refute or confirm it

abnormal shallow palaeomagnetic inclinations from the 1950 and 1972 lava flows hawaii summary high precision palaeomagnetic sampling and measurements of 1950 mauna loa lava flows hawaii show as noted by other workers a significantly low inclination compared to the geomagnetic direction expected from available observatory data such shallow inclinations appear related to the unusually high intensity of magnetization of the 1950 basalt resulting in a high magnetic refraction for the lava flows considered other altered palaeomagnetic directions both inclination and declination on kilauea 1972 flows possibly result from displacements during and or after cooling erroneous palaeomagnetic direction imprints do not appear to be the rule

high fidelity paleointensity determination from historic volcanoes in japan 1 providing high fidelity paleointensity estimates is pivotal to identify temporal fluctuation of ancient geomagnetic field despite abundance of available paleointensity data in japan only dozen of them satisfy modern standards with systematic alteration checks high fidelity paleointensity estimates were obtained from historic andesitic lavas collected from mt aso ojodake 700 bc mt kirishima iwoyama ad 1768 ohachi ad 1235 and mt sakurajima an ei ad 1779 nabeyama ad 764 766 variation of geomagnetic field intensity is distinctively different from the prediction of global models arch3k 1 cals3k 3 cals3k 4 cals7k 2 and cals10k 1b for the past 4000 years in japan the compilation of high fidelity thellier data set in japan showed two obvious high intensities at ad 590 765 and ad 1330 1435 and one low intensity at 700 bc these time intervals with anomalous high low intensities are nearly identical to three of the four potential archeomagnetic jerks recognized from the european archeomagnetic data implying that the archeomagnetic jerks were global or at least northern hemispheric features to improve the poor representation of regional geomagnetic field variation with respect to the global model prediction more high fidelity paleointensity determinations are required in east asia

global geomagnetic field models for the past 3000 years transient or permanent flux lobes psvmod1 0 is a compilation of globally distributed palaeodirectional data from archaeomagnetic artefacts lava flows and lake sediments at 24 sites evaluated at 100 year intervals from 1000 bc to ad 1800 we estimate uncertainty in these measures of declination and inclination by comparison with predictions from standard historical models in time intervals of overlap and use the 100 year samples and their associated uncertainties to construct a sequence of minimum structure global geomagnetic field models global predictions of radial magnetic field at the coremantle boundary cmb as well as inclination and declination anomalies at the earth9s surface provide an unprecedented view of geomagnetic secular variations over the past 3000 years and demonstrate a consistent evolution of the field with time resolution of the models is poorest in the southern hemisphere where only six of the 24 sites are located several with incomplete temporal coverage low flux regions seen in the historical field near the north pole are poorly resolved but the northern hemisphere flux lobes are clearly visible in the models these lobes are not fixed in position and intensity but they only rarely venture into the pacific hemisphere the pacific region is seen to have experienced significant secular variation a strong negative inclination anomaly in the region like that seen in 0 5 ma models persists from 1000 bc until ad 1000 and then gradually evolves into the smaller positive anomaly seen today on average between 1000 bc and ad 1800 the non axial dipole contribution to the radial magnetic field at the core mantle boundary is largest in the north central pacific and beneath central asia with clear non zonal contributions at the earth9s surface average inclination anomalies are large and negative in the central pacific and most positive slightly to the east of central africa inclination anomalies decrease with increasing latitude average declinations are smallest in equatorial regions again with strong longitudinal variations largest negative departures are centred over australia and eastern asia secular variation at the earth9s surface is quantified by standard deviation of inclination and declination about their average values and at the cmb by standard deviation in radial magnetic field all three show significant geographical variations but appear incompatible with the idea that secular variation in the pacific hemisphere is permanently attenuated by greatly enhanced conductivity in d 00 beneath the region

archeomagnetic secular variation from korea implication for the occurrence of global archeomagnetic jerks abstract an archeomagnetic paleosecular variation psv was first defined in korea using baked materials collected from 26 kilns or hearths with ages ranging from 1100 bc to ad 1790 variations of geomagnetic declination and inclination from the korean peninsula are distinctively different from the prediction of a global model cals3k 3 or cals7k 2 for the past 3500 yr in particular a distinctive offset in magnitude and phase is noticeable between the observations and predictions at 745 bc ad 300 and ad 1400 1700 a bi plot of magnetic declination versus inclination displays three cusps at the corresponding time intervals these time intervals are nearly identical to or at least overlap with three of the four potential archeomagnetic jerks suggested by gallet et al 2003 from the european archeomagnetic data a comparison of the psv curves for neighboring countries regions revealed that european archeomagnetic jerks at 800 bc ad 200 ad 800 and ad 1400 were all preserved in east asia suggesting that the archeomagnetic jerks were global or at least northern hemispheric features

three archaeomagnetic applications of archaeological interest to the study of burnt anthropogenic cave sediments abstract recent archaeomagnetic studies carried out on mid to late holocene burnt anthropogenic cave sediments have shown that under certain conditions these materials are suitable geomagnetic field recorders archaeomagnetic analyses carried out on these contexts constitute a rich source of information not only for geophysical purposes in terms of reconstructing the variation of earth s magnetic field in the past but also from the archaeological point of view for example by archaeomagnetic dating here we report three different archaeomagnetic applications to the study of burnt cave sediments i archaeomagnetic dating ii determining palaeotemperatures and iii assessing post depositional processes the first case study is a dating attempt carried out on a late holocene bronze age burnt level from el mirador cave burgos spain using the directional european secular variation curve several dating intervals were obtained for the last burning of this combustion feature considering the archaeological evidence and the independent radiometric 14 c dating available the possible ages obtained are discussed this is the first archaeomagnetic dating obtained in these contexts so far the second case study is an application of the method to determine the last heating temperatures reached by the carbonaceous facies of these fires stepwise thermal demagnetization of oriented samples can be used to quantitatively estimate heating temperatures an intermediate normal polarity component interpreted as a partial thermo remanence ptrm with maximum unblocking temperatures of 400 450 c was systematically identified revealing the last heating temperatures experienced by this facies these temperatures were confirmed with partial thermomagnetic curve experiments finally archaeomagnetic analyses on a partially bioturbated burning event were performed in order to evaluate until what spatial extent the burnt sediments were affected by post depositional mechanical alteration processes for each case study the archaeological implications are discussed highlighting the potential of archaeomagnetic methods to retrieve archaeological information

ensembles of low degree archeomagnetic field models for the past three millennia abstract we introduce ensembles of time varying archeomagnetic field models consisting of a reference model a mean model and a thousand individual models we present a set of three such ensembles built from archeomagnetic volcanic and sedimentary data sets that cover the past three millennia these ensembles can be used to describe the field at any location from the core surface to the magnetosphere and assess the way uncertainties due to the limited distribution and quality of the data affect any of its component or parameter such as individual gauss coefficients they provide alternative and we argue more complete descriptions of the archeomagnetic field to those provided by previously published archeomagnetic field models being better suited to existing and emerging needs such as those of geomagnetic data assimilation we present the data sets we rely on essentially the same as those used by other recent archeomagnetic field models and describe how errors affecting the data and errors due to non modelled small spatial scales of the field are taken into account we next explain our modeling strategy and motivation for building low degree spherical harmonic degree ensembles of models we carry on a number of end to end simulations to both illustrate the usefulness of such ensembles and point at the type of errors one should expect practical illustrations of what can be done with these three ensembles of models with examples of geomagnetic inferences are also described northern high latitude flux patches for instance appear to be the most robust features of all these patches tend to fluctuate but clearly have some favored locations resulting in the same clear signature with three tongues over northern america europe and asia in the time averaged field at the core mantle boundary similar to what had been found in earlier models inferences about the field behavior in the southern hemisphere are more difficult to draw still some suggestions that the well known present south atlantic reversed patch could have arisen as early as in 1500 a d are found in some of the ensembles we otherwise confirm that most of the current archeomagnetic field model limitations are related to a number of sediment cores identified as producing frequent outliers in the modeling process we provide evidence that such cores are likely affected by timing errors and timing delays between magnetization lock in and sediment deposition that future more advanced treatment should be able to handle all source files for the three ensembles of models together with appropriate matlab applications can be downloaded from http geomag ipgp fr download archeo fm zip

on the resolution of regional archaeomagnetism untangling directional geomagnetic oscillations and data uncertainties using the french archaeomagnetic database for between 1000 and 1500 ad as a guide a complexity is emphasised in the distribution of the french archaeomagnetic directions during the 13th and the 14th centuries ad data uncertainties and the smoothing introduced when estimating an average secular variation curve prevent scrutiny of the very nature of this complexity it might correspond to a directional yaw the nature of which would be compatible with the recent geomagnetic field evolution as traced by the gufm1 model in order to emphasise this indeterminacy a reference secular variation curve was constructed for between 1000 and 1500 ad including the yaw in question and synthetic databases that mimic the accuracy and density characteristics of the true french archaeomagnetic database were considered for some of these the synthetic curves hence obtained show that the dating accuracy of archaeomagnetic data is the crucial parameter for constructing a detailed secular variation path the significant impact of the experimental data accuracy is also illustrated even more crucial is the fact that precision of the data dating required to describe the directional variability over the century timescale largely exceeds the precision of the archaeological dates available for the structures generally studied this highlights the intrinsic limitation of archaeomagnetism for regional reconstruction of century scale geomagnetic field variations

an updated and homogeneous world secular variation data base 1 smoothing of the archaeomagnetic results the available original archaeomagnetic world data on intensity and direction have been compiled and sorted according to geographical region then after correcting them to correspond to a single site associated with each region called a world site they have been processed using the gaussian statistic for the intensity f data and bivariate statistic for the declination d and inclination i data to obtain smoothed values at regular time intervals we include a discussion of the statistical methods used we have limited the data to the last 20 centuries because the archaeomagnetic data alone do not allow us to go back further in the past we have also excluded archaeomagnetic studies at world sites where the number of data is not sufficient to perform a statistical analysis we obtained results at nine world sites for which the values of at least two of the three above quoted parameters have been calculated at 25 year intervals from the beginning of our era the results for each world site with their associated errors are given and discussed the potential of this new set of world data for improving our knowledge of the global terrestrial magnetic field tmf during the past 20 centuries is sketched these results will be completed in a second paper by analysing in the same way the data supplied for volcanic rocks and lake sediments

paleomagnetism and dating of a thick lava pile in the permian bakaly formation of eastern kazakhstan regularities and singularities of the paleomagnetic record in thick lava series abstract paleomagnetic results on thick lava series are among the most important sources of information on the characteristics of ancient geomagnetic fields most paleo secular variation data from lavas psvl are of late cenozoic age there are far fewer results from lavas older than 5 ma the central asia orogenic belt that occupies several million square kilometers in asia is probably the world s largest area of paleozoic volcanism and is thus an attractive target for psvl studies we studied a ca 1700 m thick lava pile in eastern kazakhstan of early permian age magmatic zircons successfully separated from an acid flow in this predominantly basaltic sequence yielded an early permian age of 286 3 3 5 ma oriented samples were collected from 125 flows resulting in 88 acceptable quality flow means n 4 samples radius of confidence circle 95 15 of the high temperature magnetization component the uniformly reversed component is pre tilting and arguably of a primary origin the overall mean direction has a declination 242 0 and an inclination 56 2 k 71 5 95 1 8 n 88 sites pole at 44 1 n 160 6 e a95 2 2 our pole agrees well with the early permian reference data for baltica in accord with the radiometric age of the lava pile and geological views on evolution of the western part of the central asia orogenic belt the new early permian result indicates a comparatively low level of secular variation especially when compared to psvl data from intervals with frequent reversals still the overall scatter of dispersion estimates that are used as proxies for sv magnitudes elongation values and elongation orientations for psvl data is high and cannot be fitted into any particular field model with fixed parameters both observed values and numerical simulations indicate that the main cause for the scatter of form parameters elongation values and elongation orientations is the too small size of collections dispersion estimates concentration parameter and standard angular deviation are more robust and their scatter stems from other sources which may include non stochastic features of datasets like clusters loops etc or non stationary behavior of secular variation magnitude over time intervals of many million years

paleoseismic evidence for the 21 april 1918 mw 6 9 surface rupture of the northern clark strand of the central san jacinto fault california abstract in this study we present the results of a new paleoseismic investigation in the south fork wilderness 7 km southeast of blackburn canyon 5 km northwest of hog lake near anza california that demonstrate that the northern clark fault has ruptured twice in the past 300 yrs these new results corroborate previously made interpretations that were based solely on surficial geomorphology that the northern clark fault with a recurrence interval of 100 yrs ruptured in both the november 1800 and april 1918 earthquakes and has a more frequent recurrence interval than the central and southern clark fault

a catalogue of spanish archaeomagnetic data a total of 58 new archaeomagnetic directions has been determined from archaeological structures in spain together with five previous results they allow the compilation of the first archaeomagnetic catalogue for spain which includes 63 directions with ages ranging between the 2nd century bc and the 20th century ad characteristic remanence directions have been obtained from stepwise thermal and alternating field demagnetization the hierarchical structure has been respected in the calculation of the mean site directions rock magnetic experiments reveal that the main magnetic carrier is magnetite or titanomagnetite with different titanium contents the age estimate of the studied structures is generally well justified by archaeological constraints for six structures the proposed date is also supported by physical methods the data are in close agreement with the french secular variation sv curve this catalogue represents the first step in the construction of a sv curve for the iberian peninsula which will be of much use in archaeomagnetic dating and in modelling of the earth s magnetic field in western europe

reply to the comment on chronology of vesuvius activity from a d 79 to 1631 based on archeomagnetism of lavas and historical sources by r lanza and e zanella

a preliminary secular variation reference curve for archaeomagnetic dating in austria the construction of a secular variation sv reference curve for a region for which little or no archaeomagnetic directions are available is presented here a sv curve is illustrated for austria centred on radstadt 47 38 n 13 45 e and based on data from sites in other countries less than 500 km away the published data were selected on site characteristics of n 3 and k 50 and dated within 400 yr this yielded 170 directions from which a sv curve was derived using bayesian techniques the obtained reference curve represents the past 2300 yr new data mainly from austria substantiate this curve and confirm the validity of the techniques employed which can therefore be applied for similar situations another test has been made using the german reference curve for dating the austrian archaeological sites here a systematic shift to older times in the order 30 110 yr occurs

paleointensity determination from sao miguel azores archipelago over the last 3 ka elsevier editorial system tm for physics of the earth and planetary interiors manuscript draft manuscript number pepi d 14 00015 title paleointensity determination from sao miguel azores archipelago over the last 3 ka article type research paper keywords paleomagnetism paleointensity azores atlantic ocean global spike corresponding author dr anita di chiara corresponding author s institution usp first author anita di chiara order of authors anita di chiara lisa tauxe prof fabio speranza dr abstract paleointensity data from the atlantic ocean are rare we present new paleointensity data from sao miguel azores islands portugal based on 20 paleomagnetic sites from 13 lava flows emplaced over the last 3 000 years ten lava flows are radiocarbon dated moore 1990 1991 moore and rubin 1991 whereas three flows were archeomagnetically dated by di chiara et al 2012 and one site was dated using stratigraphic relations all the samples previously investigated to recover paleodirections di chiara et al 2012 were subjected to izzi experiments importantly the new data are internally consistent agree with moroccan and european datasets and offer new constraints for cals style models e g korte and constable 2011 the inferred virtual axial dipole moments vadms range from 68 2 zam2 and 163 5 zam2 a peak in field strength with an estimated age of around 600 bce is well supported by two sites from the same flow furna and is comparable to the spike of intensity found in portugal of the same age nachasova et al 2009 and at about 1000 bce in the levant ben yosef et al 2009 shaar et al 2011 a gradient in vadm values with latitude observed by mitra et al 2013 between 100 to 1000 ad is confirmed as well as its absence from between 0 to 100 ad

geomagnetic field hemispheric asymmetry and archeomagnetic jerks abstract we investigate the origin of the so called archeomagnetic jerks detected in the french archeomagnetic record over the past three millennia although only very large scale global archeomagnetic field models are currently available we show that the occurrence of archeomagnetic jerks is intimately linked to what we define as most eccentric events i e periods of time when a simple description of the geomagnetic field in terms of an eccentric dipole reveals the center of this eccentric dipole to strongly move away from the earth s center from the behavior of the much better known historical field we interpret the evolution of the center of the eccentric dipole as reflecting the production and gathering of flux patches at the core mantle boundary within preferential hemispheres archeomagnetic jerks would thus correspond to episodes of maximum geomagnetic field hemispheric asymmetry such most eccentric events could also provide an explanation for some of the properties previously reported in the long term paleomagnetic field

2700 years of mediterranean environmental change in central italy a synthesis of sedimentary and cultural records to interpret past impacts of climate on society abstract abrupt climate change in the past is thought to have disrupted societies by accelerating environmental degradation potentially leading to cultural collapse linking climate change directly to societal disruption is challenging because socioeconomic factors also play a large role with climate being secondary or sometimes inconsequential combining paleolimnologic historical and archaeological methods provides for a more secure basis for interpreting the past impacts of climate on society we present pollen non pollen palynomorph geochemical paleomagnetic and sedimentary data from a high resolution 2700 yr lake sediment core from central italy and compare these data with local historical documents and archeological surveys to reconstruct a record of environmental change in relation to socioeconomic history and climatic fluctuations here we document cases in which environmental change is strongly linked to changes in local land management practices in the absence of clear climatic change as well as examples when climate change appears to have been a strong catalyst that resulted in significant environmental change that impacted local communities during the imperial roman period despite a long period of stable mild climate and a large urban population in nearby rome our site shows only limited evidence for environmental degradation warm and mild climate during the medieval warm period on the other hand led to widespread deforestation and erosion the ability of the romans to utilize imported resources through an extensive trade network may have allowed for preservation of the environment near the roman capital whereas during medieval time the need to rely on local resources led to environmental degradation cool wet climate during the little ice age led to a breakdown in local land use practices widespread land abandonment and rapid reforestation our results present a high resolution regional case study that explores the effect of climate change on society for an under documented region of europe

archeomagnetism of piton de la fournaise bearing on volcanic activity at la reunion island and geomagnetic secular variation in southern indian ocean historical and other recent lavas from piton de la fournaise la reunion island are studied using the large sample archeomagnetic method which provides here paleodirections of the earth magnetic field with confidence cones between 0 9 and 2 5 thus offering a precise record of the geomagnetic field and potential dating constraints ages of the lavas are known thanks to historical chronicles from 1708 or 14c dating and their analysis give information about the directional secular variation sv in a region where observatory measurements are scarce and not available before the end of the 19th century for the past 250 yr we find a high value of inclination 50 to 55 with respect to the geographic latitude 21 s connected with a very restricted directional sv conversely the older volcanic units present a larger sv with magnetic inclinations of between 31 and 46 and declinations from 16 w to 10 e these results which are in reasonable agreement with instrumental measurements made on ships in the vicinity of la reunion allow us to infer that undated lavas of the northern part of the caldera emanated from eruptions during the second half of the 1700s other volcanic products e g mare longue flow piton chisny cone and flows and pointe langevin despite their fresh morphology are necessarily older than about 1500 ad further knowledge of the path of the sv in the more distant past and therefore further archeomagnetic dating is hampered by the lack of a precise chronology through radiometric or other similar methods available models of the geomagnetic field during the last millennium which suffer from the scarcity of data in the southern hemisphere are discussed in the light of our results

intensity of the earth s magnetic field in greece during the last five millennia new data from greek pottery abstract new archaeointensity results have been obtained from the study of four ceramic collections coming from four different archaeological sites in greece the ages of the ceramic fragments based on archaeological constrains and radiocarbon analysis range from 2200 bc to 565 ad low field magnetic susceptibility versus temperature reveals a good thermal stability for most of the samples however for some samples the thermomagnetic curves are not reversible indicating mineralogical changes during heating isothermal remanent magnetisation irm acquisition curves and thermal demagnetisation of three orthogonal irm components have also been performed the rock magnetic results identify magnetite and or ti magnetite as the main magnetic carriers in the studied samples classical thellier experiments with regular partial thermoremanent magnetisation ptrm checks have been conducted on 125 specimens belonging to 34 independent ceramic fragments only 61 archaeointensity determinations at specimen level that correspond to linear nrm trm plots were used for the calculation of the site mean archaeointensities the effect of the anisotropy of the thermoremanent magnetisation trm and cooling rate upon trm intensity acquisition have been investigated in all specimens the maximum difference between the trm anisotropy corrected and uncorrected intensities is around 30 at specimen level confirming that the trm effect can be very important in ceramic samples cooling rate correction factors determined per specimen are up to 10 with only one exception that reaches 35 despite the moderate success rate of archaeointensity determination around 50 reliable mean site intensities have been obtained with in situ intensities ranging from 53 6 4 1 to 69 3 3 9 t corresponding to virtual axial dipole moments from 9 2 0 7 to 11 9 0 7 10 22 am 2 the new data are reasonably consistent with other available data for the studied region as well as with the sv reference curves for greece and the south balkan peninsula and the regional and global geomagnetic field models combined with previously published data from the area they confirm that important changes of the earth s magnetic field intensity occurred in greece during the last five millennia for some periods the available archaeointensity data for the balkan area show a large dispersion even for data corresponding to high quality intensity standards whereas for other periods their limited number prevents an accurate description of geomagnetic field intensity changes this evidences the need of new reliable and well dated archaeointensity data in order to obtain a robust description of geomagnetic field intensity changes during the last five millennia in this area

interpreting drivers of change in fluvial archives of the western mediterranean a critical view abstract fluvial archives in particular late glacial to holocene floodplain records may provide valuable information regarding past environmental conditions and stages of landscape evolution in view of the high significance of floodplain dynamics for the development of entire landscapes the number of studies that have been performed on floodplain sediments remains comparatively low especially regarding the western mediterranean region however one of the reasons could be seen in the high complexity and diversity of processes and factors that control and influence fluvial activity that often hampers a straightforward interpretation of floodplain dynamics therefore a basic demand on fluvial archive research is to address the complexity of the factors that control the characteristics of fluvial sequences in order to provide a robust basis for their interpretation as a starting point for discussion this paper aims to give an overview of fluvial dynamic patterns in the western mediterranean for the last 15 ka in order to examine their relevance for palaeoenvironmental reconstructions the basis for this is provided by previous investigations on four different river systems in spain and northern africa the results of which are herein synthesized in order to propose a regional late pleistocene and holocene fluvial history for the western mediterranean realm basic results are related to alluvial floodplain deposits and visible features within them such as alluvial soils incision marks and aggradation phenomena since fluvial systems are open systems we discuss our findings against the background of different influencing factors that could modify fluvial architecture and may restrict palaeoenvironmental reconstructions a more comprehensive interpretation focuses on signals that are common to each of the studied river systems in this respect we critically discuss the customary nature of cumulative probability functions for the identification of regional flooding episodes and point out the benefits of a stratigraphy supported approach for characterizing regional floodplain dynamics finally three alluvial soil formation periods were found in all settings a first phase after 15 ka ending with the younger dryas event a second one from 7 to 5 ka with a break between 6 5 and 5 5 ka and a third phase between 3 and 2 ka these soil formation periods were interrupted and framed by fluvial dynamic phases accompanied by channel aggradation floodplain deposition floodplain erosion and or river incision in particular after 5 ka around 1 6 and at 1 ka and during the little ice age lia floodplain aggradation affected river systems in iberia and northern africa as well a cautious assessment of these results and extensive comparisons with secondary archive information prompts us to relate the aggradation periods with climate forcing by means of a supra regional aridification that effected large areas of the western mediterranean in contrast the three mentioned soil formation periods can be linked with landscape stability most probably triggered by favorable climate conditions in the western mediterranean apart from these large scale patterns we discuss the reliability of information emerging from floodplain records against the background of individualistic river behavior and self organization regarding future work we want to emphasize the great potential of yet rarely applied system oriented approaches that also attach importance to sub catchment dynamics as a link between catchment slopes and the main river floodplain

high resolution paleomagnetic secular variation and relative paleointensity records from the western canadian arctic implication for holocene stratigraphy and geomagnetic field behaviourthis article is one of a series of papers published in this special issue on the theme polar climate stability network geotop contribution 2008 0024 two piston cores recovered from the chukchi and the beaufort seas document arctic holocene geomagnetic field behaviour and highlight the potential of secular variation and relative paleointensity as a regional chronostratigraphic tool several centennial to millennial scale holocene declination and inclination features can be correlated in both cores with other high resolution western north american lacustrine and volcanic paleomagnetic records and with records of changes in earth s dipole moment supporting the geomagnetic origin of these features and implying that they are associ ated with changes in earth s dipole moment resume deux carottes sedimentaires prelevees dans les mers de beaufort et de chukchi ont permis de reconstruire les variations d intensiteet d orientation de haute resolution du champ magnetique terrestre au cours de l holocene afin de caracteriser le comportement du champ geomagnetique dans l arctique ainsi que d explorer la possibilited utiliser les variations du champ geomagnetique comme outil chronostratigraphique au cours de l holocene la declinaison et l incli naison magnetique des deux sequences etudiees peuvent etre correlees entre elles avec des enregistrements paleomagne tiques lacustres ou volcaniques de l ouest de l amerique du nord a des echelles de temps au moins seculaires les variations de paleointensiterelative des deux carottes analysees sont egalement coherentes avec des enregistrements des variations du dipole geomagnetique confirmant ainsi l origine geomagnetique de ces variations et suggerant leur nature di polaire

advances in archaeomagnetic dating in britain new data new approaches and a new calibration curve abstract archaeomagnetic dating offers a valuable chronological tool for archaeological investigations particularly for dating fired material the method depends on the establishment of a dated record of secular variation of the earth s magnetic field and this paper presents new and updated archaeomagnetic directional data from the uk and geomagnetic secular variation curves arising from them the data are taken from publications from the 1950 s to the present day 422 dated entries derived from existing archaeo and geomagnetic databases are re evaluated and 487 new directions added resulting in 909 entries with corresponding dates the largest collection of dated archaeomagnetic directions from a single country an approach to improving the largest source of uncertainty the independent dating is proposed and applied to the british iron age resulting in 145 directions from currently available databases being updated with revised ages and or uncertainties and a large scale reassessment of age assignments prior to inclusion into the magnetic moments of the past and geomagia50 databases from the significantly improved dataset a new archaeomagnetic dating curve for the uk is derived through the development of a temporally continuous geomagnetic field model and is compared with previous uk archaeomagnetic dating curves and global field models the new model arch uk 1 allows model predictions for any location in the uk with associated uncertainties it is shown to improve precision and accuracy in archaeomagnetic dating and to provide new insight into past geomagnetic field changes

two thousand years of geomagnetic field direction over central europe revealed by indirect measurements summary supplemented by 32 new directions the hungarian archaeomagnetic data set now consists of 217 archaeologically dated directions ranging in age from 300 bc to 1800 ad from this data set reference curves of secular variation of the geomagnetic field direction were computed using hierarchical modelling and curve estimation by moving average technique thanks to some of the new data the gap in the earlier reference curves around 500 ad has now been filled up for comparison s sake directional records of comparable length from central europe were also processed by the same curve building method for this purpose all dated directional data declination and inclination with statistics were drawn from the geomagia50 database for france germany the ukraine and moldavia bulgaria and italy and transferred via their virtual geomagnetic poles to a reference point of their respective countries the resulting reference curves including those for hungary show more or less similar temporal behaviour to the corresponding cals7k 2 model curves also available from the geomagia50 database but significant deviations from the low order cals7k 2 predictions are also discernible owing to the likely presence of additional higher order complications in the regional field therefore the regional field and its secular variation are suggested to be approximated by the reference rather than the predicted curves at any other location within the study area the direction of the regional field can be obtained by spatial interpolation from the reference curves as illustrated by isogonic and isoclinic maps shown for selected times local time series of interpolated directions for other central european countries lacking reference curves might serve as master curves for magnetic dating

extended and revised archaeomagnetic database and secular variation curves from bulgaria for the last eight millennia the efforts of geophysicists to describe geomagnetic field behaviour in the past lead to creation of different geomagnetic field models on the other hand the established regional palaeosecular variations of geomagnetic elements are increasingly used for dating purposes in archaeology both of these goals can be achieved if sufficient amounts of long archaeomagnetic data sets exist for different geographical regions the accumulation of archaeomagnetic determinations began at the middle of the last century parallel with the progressive development of experimental methodology and acceptance criteria the presence of great number of old determinations requires their critical assessment the important question about the reliability of the associated dating intervals should be also re assessed all this requires the continuous refinement and extension of the accumulated databases this paper presents the last synthesis of bulgarian archaeomagnetic database and the local palaeosecular variation curves obtained using a statistical treatment based on bayesian approach rencurve software the rock magnetic characteristics of the newly included non published results are summarized

first archeointensity determinations on maya incense burners from palenque temples mexico new data to constrain the mesoamerica secular variation curve we present archeointensity data carried out on pieces of incense burners from the ancient maya city of palenque chiapas mexico covering much of the mesoamerican classic period from a d 400 to a d 850 we worked on pieces from 24 incense burners encompassing the five classic ceramic phases of palenque motiepa a d 400 500 cascadas a d 500 600 otulum a d 600 700 murcielagos a d 700 770 and balunte a d 770 850 all the samples come from highly elaborate flanged pedestal of incense burners that are undoubtedly assigned to a ceramic phase by means of their iconographic morphological and stylistic analyses archeointensity measurements were performed with the thellier thellier s method on pre selected samples by means of their magnetic properties we obtained archeointensities of very good technical quality from 19 of 24 pieces allowing the determination of a precise mean value for each ceramic phase between 29 17 0 9 mt and 32 57 1 2 mt the firing

on the possible occurrence of archaeomagnetic jerks in the geomagnetic field over the past three millennia abstract archaeomagnetism can provide a high resolution full vector description of the earth s magnetic field for the past several thousand years we analyse the bulk of archaeomagnetic data both direction and intensity obtained recently in western europe and the eastern mediterranean covering the past three millennia we demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima two clear ones at ad 200 and 1400 two presently less well constrained at 800 bc and ad 800 these sharp changes may constitute a new feature of geomagnetic secular variation archaeomagnetic jerks with time characteristics intermediate between geomagnetic jerks and magnetic excursions

a matlab tool for archaeomagnetic dating a matlab tool for archaeomagnetic dating has been developed in this work well dated palaeosecular variation curves psvcs can be used to date archaeological artefacts with unknown ages the archaeomagnetic direction declination and or inclination and the archaeointensity obtained from the archaeological artefact are compared with a master psvc in addition historical lava flows with controversial ages can be dated using this methodology the dating process follows the descriptions given by lanos 2004 which is based on the combination of temporal probability density functions of the three geomagnetic field elements here we develop an interactive tool in matlab code to carry out archaeomagnetic dating by comparing the undated archaeomagnetic or lava flow data with a master psvc the master psvcs included with the matlab tool are the different european bayesian curves and those generated using both regional and global geomagnetic field models a case study using all the psvcs available in europe and some undated archaeomagnetic data has been carried out to analyze how the different psvcs affect the dating process in addition the dating uncertainty and the relocation error have been analyzed in the european region results show that some regional bayesian psvcs and the regional scha dif 3k archaeomagnetic model are the best choices to obtain an accurate date in europe moreover when it is available the full geomagnetic field vector must be used for archaeomagnetic dating

transpressive tectonics along a major e w crustal structure on the algerian continental margin blocks rotations revealed by a paleomagnetic analysis abstract the present paleomagnetic study has been conducted on volcanic rocks of miocene age outcropping on the northern border of the neogene chelif basin northwest algeria the results show the existence of numerous small tectonic blocks of probable size around 0 5 to 0 6 km which underwent clockwise rotations the magnitude of these rotations is often important and of different strengths according to the studied sites that evidences the effect of a major narrow dextral e w crustal shear structure the location of this structure on the northern border of chelif basin is coherent with the geodynamical context of this basin which corresponds to a wide zone affected by clockwise rotations of large blocks limited by such major faults the present paleomagnetic results confirm that the relative convergence motion between the africa and eurasia plates could be interpreted as a transpressional tectonic deformation model with block rotations along the algerian continental margin

first directional european palaeosecular variation curve for the neolithic based on archaeomagnetic data neolithic cha1colithic and bronze age anthropogenic cave sediments from three caves from northern spain have been palaeomagnetically investigated 662 oriented specimens corresponding to 39 burning events ash carbonaceous couplets from the three sites with an average of 16 samples per fire were collected 26 new archaeomagnetic directions have been obtained for the time period ranging from 5500 to 2000 yr ca bc these results represent the oldest archaeomagnetic directions obtained from burnt archaeological materials throughout all western europe magnetisation is carried by pseudo singie domain low coercivity ferromagnetic minerals magnetite magnetite with no significant isomorphous substitution and or maghaemite rock magnetic experiments indicate a thermoremanent origin of the magnetisation although a thermochemical magnetisation cannot be excluded combination of the new data presented here and the recent updated bulgarian database allows us to propose the first european palaeosecular variation psv curve for the neolithic a bootstrap method was applied for the curve construction using penalised cubic b splines in time the new palaeosecular variation curve is well constrained from 6000 bc to 3700 bc the period with the highest density of data showing a declination maximum around 4700 bc and a minimum in inclination at 4300 bc which are not recorded by the recent global calslok 1 b and regional scha dif 8k models due to the use of lake sediment data dating resolution by using the proposed psv curve oscillates from approximately 30 yr to 200 yr for the period 6000 to 1000 yr bc reaching similar resolution as radiocarbon dating considering the good preservation age control and widespread occurrence of burnt archaeological materials across southern europe they represent a new source of data for geomagnetic field modelling as well as for archaeomagnetic dating

a regional archaeomagnetic model for the palaeointensity in europe for the last 2000 years and its implications for climatic change the scha di 00 directional model for the geomagnetic field in europe for the last 2000 years pavo n carrasco et al 2008 has been updated by modelling the palaeointensity this model scha di 00 was developed from available bayesian european palaeosecular variation curves using the regional spherical cap harmonic analysis technique the comparison of the palaeosecular variation curves given by the regional model with available archaeomagnetic data not used in its development showed an improvement with respect to the fit obtained by global archaeomagnetic models in this paper advantage is taken of recently published palaeointensity databases to develop a complete direction and intensity regional archaeomagnetic model for the last 2000 years valid for the european region the scha di 00 f model not only does this complete model provide an improvement for example for archaeomagnetic data studies but it is also shown that this new regional model can be used to study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change the pattern of the archaeosecular variation of the field intensity obtained by scha di 00 f seems to verify the hypothesis presented by gallet et al 2005 about a possible causal connection between changes in the geomagnetic field intensity and in climate parameters opening the door for more discussions on this challenging subject

improving our knowledge of rapid geomagnetic field intensity changes observed in europe between 200 and 1400 ad vailable archaeomagnetic data indicate that during the past 2500 yr there have been periods of rapid geomagnetic field intensity fluctuations interspersed with periods of almost constant field strength despite europe being the most widely covered region in terms of archaeomagnetic data the occurrence and the behaviour of these rapid geomagnetic field intensity changes is under discussion and the challenge now is to precisely describe them the aim of this study is to obtain an improved description of the sharp intensity change that took place in western europe around 800 ad as well as to investigate if this peak is observed at the continental scale for this purpose 13 precisely dated early medieval spanish pottery fragments four archaeological french kilns and three collections of bricks used for the construction of different french historical buildings with ages ranging between 335 and 1260 ad have been studied classical thellier experiments performed on 164 specimens and including anisotropy of thermoremanent magnetisation and cooling rate corrections gave 119 reliable results the 10 new high quality mean archaeointensities obtained confirm the existence of an intensity maximum of 85 t at the latitude of paris centred at 800 ad and suggest that a previous abrupt intensity change occurred around 600 ad together with previously published data from western europe that we deem to be the most reliable the new data also suggest the existence of two other abrupt geomagnetic field intensity variations during the 12th century and around the second half of the 13th century ad high quality archaeointensities available from eastern europe indicate that very similar geomagnetic field intensity changes occurred in this region european data indicate that very rapid intensity changes of at least 20 t century took place in the recent history of the earth s magnetic field the results call for additional high quality archaeointensities obtained from precisely dated samples and for a selection of the previously published data if a refined description of geomagnetic field intensity changes at regional scales is to be obtained

distribution analysis of errors due to relocation of geomagnetic data using the conversion via pole cvp method implications on archaeomagnetic data summary secular variation master curves are built up using geomagnetic historical observations or archaeomagnetic data from a limited area and their use is usually restricted to regions of around 1000 km radius relocation of data within this distance is a common practice to enable comparison of data although the errors due to such process are rarely taken into account a detailed analysis of the distribution of relocating geomagnetic data has been done using three popular sets of geomagnetic models igrf 9 gufm and cals7k 2 this study improves the error analysis of relocating geomagnetic directions made up to date and expands it to geomagnetic intensities maximum errors correlate with the non dipole to dipole field ratio archaeomagnetists could use this analysis to valuate the error introduced by reducing data

three millennia of directional variation of the earth s magnetic field in western europe as revealed by archeological artefacts directional secular variation of the geomagnetic field over the last 2000 years has been defined in western europe from numerous archeomagnetic studies however the number of archeomagnetic results for older periods is much more limited for this reason we present new data obtained from fired archeological structures found in two french sites loupiac and aspiran dated within the first millennium b c latest bronze earliest iron age transition 850 700 b c and iron age 525 475 b c respectively from a compilation of archeomagnetic results from western europe great britain italy and france and northern africa tunisia we propose a directional secular variation curve for western europe that covers the entire first millennium b c this curve exhibits a large clockwise motion with rapid changes during the first half of the millennium while the last four centuries b c are characterized by weak variations

archaeointensity determinations from italy new data and the earth s magnetic field strength variation over the past three millennia summary three kilns and a collection of baked bricks from italian archaeological sites have been studied for archaeointensity determination using the thellier method as modified by coe all sites are dated based on archaeological information and their ages range from 500 to 800 ad and 1500 to 1700 ad rock magnetic studies identify magnetite ti magnetite and hematite as the main magnetic minerals and magnetic susceptibility versus temperature shows a good thermal stability of the samples the intensity results have been corrected for anisotropy of the thermoremanent magnetization and cooling rate effects the new data together with 136 previously published results are used to estimate the variation of the earth s magnetic field over the past three millennia the time distribution of the italian absolute intensity data is irregular with the majority of determinations concentrated during the last four centuries while older periods are very poorly covered most of the data come from volcanic rocks and show significant discrepancies all data have been compared with archaeointensity results from europe and regional and global models predictions this work indicates the need to obtain more high quality archaeointensity results in particular for the periods older than 200 bc and between 200 and 1000 ad in order to determine a robust italian intensity secular variation curve that in combination with directional data could be used for archaeomagnetic dating

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

an updated archeomagnetic directional variation curve for france over the past two millennia following 25 years of additional data acquisition abstract nearly 40 years ago emile thellier published an article summarizing the archeomagnetic data he had obtained during his career which had allowed him to recover the main features of the directional variations of the geomagnetic field in france for the last two millennia this database went on to be significantly completed 25 years ago by ileana bucur who had taken over thellier s work on archeomagnetism this forms the current basis of our knowledge of the directional evolution of the geomagnetic field in france since then archeomagnetic studies have been continued at thellier s historical laboratory in saint maur this article presents the directional archeomagnetic data obtained in france over the past 25 years in this same laboratory a total of 528 new data are presented which together with the 170 results obtained on the french territory previously listed in bucur 1994 constitute the french directional database 698 data in all all but two of these data were obtained using the experimental protocol developed by e thellier based on the analysis of large samples and on a magnetic viscosity test that has proved its reliability on numerous occasions the directions from the entire french database have been precisely defined with 95 of the 95 values being less than 1 9 and 50 being less than 0 8 the selection of 286 data with dating uncertainties of 50 years allowed us to compute a new reference directional variation curve for france since the first century bc using sliding windows the variable durations and shifts of which were adapted to the time distribution of the available data and the bivariate extension of the fisher statistics this shows ample and smooth variations fairly similar to those previously determined from a much smaller database the resulting secular variation curve is particularly well suited for use in archeomagnetic dating

does earth s magnetic field secular variation control centennial climate change abstract we obtained new archeointensity data from french faience potsherds dated from the 17th to 19th century these results further document the occurrence of sharp changes in geomagnetic field secular variation in western europe over the past three millennia the intensity variation curve shows several maxima whose rising parts appear to coincide in time with the occurrence of cooling events documented in this region from natural and historical data this coincidence suggests a causal link between enhanced secular variation of the geomagnetic field and climate change over centennial time scales challenging the role of solar forcing as the sole factor provoking these climatic variations we propose that the archeomagnetic jerks described by gallet et al 1 y gallet a genevey v courtillot on the possible occurrence of archeomagnetic jerks in the geomagnetic field over the past three millennia earth planet sci lett 214 2003 237 242 may engage the mechanism for centennial climate change

statistical analysis of palaeomagnetic data from the last four centuries evidence of systematic inclination shallowing in lava flow records the main objective of this work is to compare directional declination and inclination volcanic and archaeomagnetic data for the last four centuries 1600 1990 with the historical geomagnetic predictions given by the gufm1 model which spans from 1590 to 1990 the results show statistical agreement between archaeomagnetic data and directions given by the geomagnetic field model however when comparing the volcanic data with the model predictions marked inclination shallowing is observed this systematically lower inclination has already been observed in local palaeomagnetic studies italy mexico and hawaii for the 20th century by comparing recent lava flows with the international reference geomagnetic field igrf model here we show how this inclination shallowing is statistically present at worldwide scale for the last 400 years with mean inclination deviation around 3 lower than the historical geomagnetic field model predictions

the influence of high latitude flux lobes on the holocene paleomagnetic record of iodp site u1305 and the northern north atlantic 1 paleomagnetic analysis and radiocarbon dating of an expanded holocene deep sea sediment sequence recovered by integrated ocean drilling program iodp expedition 303 from labrador sea site u1305 lat 57 28 5 n long 48 31 8 w water depth 3459 m provides insights into mechanisms that drive both paleomagnetic secular variation psv and magnetization acquisition in deep sea sediments seventeen radiocarbon dates on planktonic foraminifera define postglacial ca 8 ka sedimentation rates as ranging from 35 to 90 cm kyr alternating field af demagnetization of u channel samples show that these homogeneous sediments preserve a strong stable and consistently well defined component magnetization normalized remanence records pass reliability criteria for relative paleointensity rpi estimates assuming that the age of magnetization is most accurately defined by well dated psv records with the highest sedimentation rates allows us to estimate and correct for temporal offsets at site u1305 interpreted to result from postdepositional remanence acquisition at a depth of 20 cm comparisons indicate that the northern north atlantic psv and rpi records are more consistent with european than north american records and the evolution of virtual geomagnetic poles vgp are temporally and longitudinally similar to global reconstructions though with much larger latitudinal variation the largest deviations from a geocentric axial dipole gad are observed during times of the highest intensities in contrast to the usual assumption these observations are consistent with the idea that psv in the north atlantic and elsewhere during the holocene results from temporal oscillations of high latitude flux concentrations at a few recurrent locations

new archaeomagnetic data recovered from the study of roman and visigothic remains from central spain 3rd 7th centuries summary new archaeomagnetic results from four heated combustion structures recovered from two archaeological sites in central spain are reported they have been dated by archaeological evidence and in two cases by radiocarbon dating rock magnetic experiments indicate low coercivity magnetic phases such as magnetite and thermally stable maghaemite as the main carriers of the remanent magnetization haematite has been observed in poorly heated baked clays archaeomagnetic directions have been obtained from either alternating field or thermal demagnetization experiments performed on 57 specimens coming from 46 independently oriented samples the four well defined archaeomagnetic directions obtained are in good agreement with previous archaeomagnetic data and with recent regional and global field models they define the beginning of easterly declination drift that was initiated around 350 400 ad and culminated around 800 850 ad and delineate the maximum in inclination that took place around 600 650 ad in addition classical thellier thellier experiments including thermal remanent magnetization anisotropy and cooling rate corrections were conducted on 23 specimens only 13 specimens corresponding to well defined single component behaviour gave reliable results new mean archaeointensities have been obtained for two of the four studied structures vbk1 64 2 5 0 t and vbt1 62 4 2 6 t the new data suggest that two relative intensity maxima occurred in western europe around 320 and 630 ad being of lower magnitude that observed in eastern europe

new archeointensity data from spain and the geomagnetic dipole moment in western europe over the past 2000 years archeomagnetic studies on 14 kilns a group of jar fragments and a collection of baked bricks dated between 1000 and 1959 ad plus one roman pottery kiln have been conducted in order to obtain high quality archeointensity data to enhance the western european database the thellier method with corrections for anisotropy of thermoremanent magnetization trm and for cooling rate dependence upon trm acquisition was used the effect of trm anisotropy is only important for the bricks where the corrected and uncorrected mean intensities differ by more than 5 cooling rate correction factors determined per sample are up to 15 and per site up to 7 7 our 17 new data together with 62 previously published results were used to obtain by bayesian modeling the geomagnetic field intensity over the past two millennia for western europe our results indicate that geomagnetic intensity remained more or less constant between the 1st and 4th centuries and between the 14th and 16th centuries mean values at paris around 65 and 57 t respectively whereas an important decrease occurs between 1600 and 1800 ad the detailed evolution of geomagnetic field intensity during the high middle ages is not yet well established despite their differences geomagnetic global models predict our results reasonably well this work indicates the need to obtain a number of archeointensity data for each time interval in order to reliably record variations of the geomagnetic field and to test whether any relationship exists between field intensity and climate

a refined age calibrated paleosecular variation and relative paleointensity stack for the nw barents sea implication for geomagnetic field behavior during the holocene abstract reconstruction of paleomagnetic secular variation psv of the geomagnetic field is fundamental both to assess geodynamo models and to obtain age constraints for rocks sediments and archaeological material we present refined age calibrated holocene psv and relative paleointensity rpi stack curves derived from arctic marine sediments northwestern barents sea the holocene sections of four sedimentary cores were correlated on the basis of paleomagnetic trends and age models and stacked the resultant composite psv and rpi holocene records nbs stack and the reconstructed holocene virtual geomagnetic pole vgp path were evaluated in comparison with the most recent paleomagnetic stack curves and geomagnetic field models the data indicate that during the holocene time the vgps moved within the superficial projection of the inner core tangent cylinder with the exception of short time intervals around 5600 and 3200 cal yr bp when vgps extended to lower latitudes these deviations might reflect regional geomagnetic features such as persistent geomagnetic flux lobes at core mantle boundary our data confirm that the large vgp shift observed around 5600 cal yr bp is the result of an increased radial magnetic field at the core mantle boundary over north america whilst the vgp shift around 3200 cal yr bp represents a major swing to middle latitudes toward the middle east and might be associated to a regional high paleointensity peak known as levantine iron age anomaly liaa

hydrogeochemical properties of a salinity affected coastal aquifer in western japan coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion in many cases however the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea other salinity increasing processes may also significantly contribute to the total salt content of the groundwater this paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the motooka coastal area in fukuoka japan a strong increase in electrical conductivity at 15 20 m depth was observed corresponding to the freshwater and saltwater interface oxidation reduction potentials observed in deeper groundwater were low indicating long residence time for the groundwater these results together with hydrogen oxygen isotope ratio analysis indicated that the deeper groundwater is affected by seawater consequently observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system and a c 14 isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years the overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater the deeper groundwater is therefore mainly affected by old seawater in other words modern saltwater intrusion has not yet occurred even if some wells contain saline water the study shows that even though coastal aquifers are heavily pumped the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms copyright c 2006 john wiley sons ltd less

recent eruptive history of stromboli aeolian islands italy determined from high accuracy archeomagnetic dating 1 the large sample method of archeomagnetic dating was applied to stromboli 127 samples 10 sites yielded paleofield directions with 95 confidence intervals less than 2 coupled with a reference curve for secular variation in western europe these allow accurate dating of volcanic events a lava flow underlying san bartolo village gave a minimum age of ad 100 100 a lava overflow predating the last sector collapse was dated from 1350 60 suggesting the recent occurrence of highly hazardous events lava spatters and a hot avalanche high on the northern flank were emplaced during the xxth century lava spatters on the lower flanks could date the onset of the still ongoing phase from ad 550 50 these results are different from those obtained in a recent study probably because traditional paleomagnetic sampling cannot yield sufficient precision considering the characteristics of the archeomagnetic secular variation curve

evidence for rapid geomagnetic field intensity variations in western europe over the past 800 years from new french archeointensity data abstract the number of reliable archeointensity determinations obtained from western europe for the past millennium remains limited moreover the large scatter between different datasets available is puzzling the present study analyzed 31 new groups of baked clay ceramic or brick fragments sampled in france 29 groups and in belgium 2 groups these groups contain several fragments collected from different artefacts and are precisely dated principally from historical constraints between the xiiith and the xixth centuries additionally we re evaluated 14 intensity values that we previously obtained from the same time period the fragments were analyzed using two different thermal methods 1 the in field zero field iz or the izzi version of the classical thellier and thellier method and 2 the triaxe protocol that involves high temperature magnetization measurements data were corrected for the anisotropy of thermoremanent magnetization trm and the dependence of trm acquisition on the cooling rate was taken into account in the different protocols archeointensity data obtained on twin specimens sampled from the same fragment and using both experimental techniques generally show a good agreement i e within 5 at the fragment and at the site level all retained site level averaged intensity results 43 of 45 groups have standard deviations of less than 5 t furthermore groups of approximately the same age have very consistent archeointensity altogether the data presented herein recover a detailed and smoothed geomagnetic field intensity variation curve characterized by two peaks in intensity the first during the second half of the xivth century and the second around ad 1600 followed by a significant decreasing trend in intensity during most the xviith and xviiith centuries this evolution does not satisfactorily fit with the expected intensity values for france derived from geomagnetic field models relying on a different evolution of the axial dipole moment our results lead us to propose that the axial dipole moment decreased from ad 1600 to the end of the xviiith century then slightly increased up to ad 1850 before decreasing again to present day

palaeomagnetic and rock magnetic analysis of holocene deposits from the adriatic sea detecting and dating short term fluctuations in sediment supply we present palaeomagnetic and rock magnetic results from five cores collected in the basin of the adriatic sea four cores prad2 4 ks02 246 css00 23 and css00 07 were collected along a shore parallel transect whereas the fifth core amc99 01 was retrieved in the central adriatic in 250 m water depth on the floor of the meso adriatic depression after alternating field demagnetization the natural remanent magnetization nrm directions show a characteristic and primary magnetization of the sediments that is representative of secular variation of the geomagnetic field by combining 14c dating and the ages of magnetic inclination features it has been possible to establish an age depth model for all of the cores precise identification of the secular variation features provides a refined chronology that allows us to quantify short term changes in sediment flux from the adriatic catchment as well as changes in sediment routing within the basin rock magnetic parameters indicate a homogeneous magnetic mineralogy dominated by fine grained magnetite variations in both concentration and grain size related magnetic parameters reflect changes in sediment supply between glacial and interglacial stages as well as changes in environmental conditions selective dissolution of magnetic grains is associated with the formation of sapropel s1 during the first part of the holocene although the duration of the anoxic interval varies between cores a significant modification in sediment supply characterizes the late holocene deposits with a marked increase in sedimentation rate occurring during the last few centuries we interpret this as a far reaching response to the rapid construction of the modern po delta under increasing anthropogenic impact