a theoretical treatment of paleointensity determination experiments on rocks containing pseudo single or multi domain magnetic particles a phenomenological theory of thermoremanent magnetization trm is applied to model the possible results of paleointensity determination experiments using the thellier method it is shown that intrinsic curvature of the arai plot for samples containing pseudo single or multi domain particles can be attributed exclusively to the presence of remanences which are unblocked below their blocking temperature thus the thermal demagnetization tail of partial trm ptrm is not a direct measure for a sample s tendency to yield a curved arai plot here it is proposed to use the advancing decay of a ptrm t1 t2 which during heating occurs already below the lower temperature t1 t2 as a more reliable pre selection criterion in addition the effect of an average magnetostatic interaction on the thellier experiment turns out to be negligible an extended thellier method which compares the thermal demagnetization of natural remanent magnetization with that of an artificial trm according to the applied trm theory should result in a perfectly linear modified arai plot even for pseudo single or multi domain samples if no alteration or viscous effects occur

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

improvements in procedure and paleointensity selection criteria picrit 03 for thellier and thellier determinations application to hawaiian basaltic long cores abstract in this paper we first describe the paleointensity furnaces and the procedures specifically designed to minimize oxidation of the samples during thellier and thellier paleointensity experiments routinely used at gif we also propose some improvements to the set of criteria commonly used to select the results of the thellier experiments in order to further increase the reliability of paleointensity determination finally to be included in databases the new set of paleointensity criteria picrit 03 paleointensity criteria in 2003 is discussed and the results obtained from two long hawaiian basaltic cores the scientific observation hole 4 soh 4 and the hawaiian scientific drilling project 1 hsdp1 are used to illustrate its effectiveness some of the results are re evaluated and a new composite record of absolute paleointensity and inclination spanning 420 kyr is presented the inclination values obtained from the two cores combined support the hypothesis of persistent shallow inclinations at hawaii in intensity the upper 100 kyr are covered by the data from soh 4 with 309 reliable determinations out of 766 examined obtained from 143 units which belong to the kilauea volcano at the top of this core the 341 reliable data covering the 100 420 kyr interval are from 149 units of core hsdp1 belonging to the mauna kea volcano the interval 320 to 420 kyr is particularly detailed because of high extrusion rate of the volcano the use of more stringent criteria decreases the number of determinations considered as reliable in previous publications but it improves their accuracy and robustness

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

long term trends in paleointensity the contribution of dsdp odp submarine basaltic glass collections abstract the deep sea drilling project and the ocean drilling program have been collecting fresh appearing submarine basaltic glass from the world s oceans for over three decades this glass has proved nearly ideal for estimating paleointensity variations of the earth s magnetic field we compile here data for 726 paleointensity experiments from six publications on paleointensity using dsdp odp glass we also include new data for an additional 225 specimens these were obtained through the so called izzi paleointensity experiment of tauxe l staudigel h 2004 strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite geochem geophys geosyst 5 2 q02h06 doi 10 1029 2003gc000635 whereby infield zerofield steps are alternated with the zerofield infield steps to enhance quality assessment of the resulting data the entire collection of data from 951 experiments was prepared for uploading to the magic data base http earthref org including original measurements interpretations and useful metadata excellent results were obtained throughout the depth 1400 mbsf and age 0 160 ma range sampled dsdp odp glass data are compared with published paleointensity data meeting minimal acceptance criteria from the time interval 1 160 ma paleolatitudes were estimated for all cooling units in a self consistent manner for use in calculating virtual axial dipole moments we conclude 1 there is about a 20 difference in mean values between the sbg and the lava flow data 48 36 and 57 29 zam2 respectively the difference is caused by the fact that there are more higher values in the lava flow data than in the sbg data set rather than a difference in the minimum values lava flows cooling over a periods of days to months can account for the discrepancy 2 the positive relationship between polarity interval length and average paleofield intensity first hypothesized by cox a v 1968 lengths of geomagnetic polarity intervals j geophys res 73 3247 3260 is supported by data compiled here the brunhes data for which we have only a minimum estimate for polarity interval length are consistent with a long polarity interval suggesting that instead of racing toward reversal hulot g eymin c langlais b mandea m olsen n 2002 small scale structure of the geodynamo inferred from oersted and magsat satellite data nature 416 620 623 we could instead be in the midst of a long stable polarity interval 3 because the average value appears to be a function of polarity interval length it is probably not useful to calculate a mean value nonetheless it appears that most of the time apart from the brunhes and the longest polarity intervals the average dipole moment is substantially less than the present day value as suggested by juarez t tauxe l gee j s pick t 1998 the intensity of the earth s magnetic field over the past 160 million years nature 394 878 881

toward an optimal geomagnetic field intensity determination technique 1 paleointensity determinations based on double heating techniques in field zero field cooling zero field in field cooling and two in field steps with opposite laboratory fields are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates to investigate this premise we have developed a simple mathematical model we find that both the zero field first and in field first methods have a strong angular dependence on the laboratory field parallel orthogonal and anti parallel while the two in field steps method is independent of the direction of the laboratory produced field contrary to common practice each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met even with marginal 10 tails of partial thermoremanence our calculations suggest that the zero field first method with the laboratory produced field anti parallel to the natural remanence nrm is the most robust paleointensity determination technique when the intensity of the lab induced field is smaller than ancient field however the zero field first method with the laboratory field parallel to the nrm is the optimum approach when the intensity of the lab induced field is larger than the ancient field by far the best approach however is to alternatethe infield zerofield iz steps with zerofield infield zi steps

a relative geomagnetic paleointensity stack from ontong java plateau sediments for the matuyama we present a stack of geomagnetic paleointensity estimates for the matuyama chron 0 778 2 582 ma sedimentary magnetizations from 4 ocean drilling program odp cores from the ontong java plateau ojp are analyzed with thermal techniques thellier thellier experiments are used to determine magnetic properties and indicate that a thermal treatment to 250 c can be used for paleointensity estimates the correlated records form a coherent ojp stack which is dated at reversal boundaries a coherent feature with two other data sets spanning the matuyama chron is the occurrence of a 150 kyr cyclicity however the time control of the ojp stack is not accurate except for the 10 tie points at the reversals this could at least in part explain why the three matuyama paleointensity records show no other coherent frequencies

paleomagnetic field intensity derived from non sd testing the thellier izzi technique on md slag and a new bootstrap procedure abstract experimental techniques to determine paleomagnetic field intensity are based on a theoretical framework that is valid only for single domain sd ferromagnetic particles yet most of the available materials exhibit distinctly non sd properties designing the optimal paleointensity methodology for non sd is therefore a fundamental challenge in paleomagnetism the objective of this study is to experimentally test the izzi thellier absolute paleointensity method on small md recorders the test has two purposes 1 to describe the characteristic non sd patterns occurring in arai plots and 2 to identify the optimal approach in interpreting non sd behavior we carried out paleointensity experiments on 40 specimens from 4 synthetic re melted slag samples with identical magnetic properties mineralogy texture and non sd state produced under different field intensities we ran three batches of izzi experiments using different conditions that allow for a detailed characterization of the non sd behavior we find that the curvature of the arai plot is systematically dependent on the angle and the proportion between the field used in the paleointensity experiment btrm and the field in which the nrm was acquired bnrm straight line arai plot occur when the two fields are parallel and equal and seems to always give the true slope convex curves occur when btrm is parallel and significantly stronger than bnrm concave curves occur in all the other cases and yield two end case slopes that are always different than the true slope in addition zigzagged patterns increase with the angle the proportion between btrm and bnrm we test the accuracy of the best fitting line approach and conclude that best fitting line in curved plots cannot provide robust paleointensity estimates yet the two end case slopes in concave curves provide adequate constraints for the true value we introduce a new procedure to calculate a 95 confidence interval of the paleointensity from curved plots using bootstrap statistics we substantiate the new procedure by conducting two independent tests the first uses synthetic re melted slag produced under known field intensities 3 sd samples and 4 non sd samples the second compares paleointensity determinations from archeological slag samples of the same age 34 sd samples and 10 non sd samples the two tests demonstrate that the bootstrap technique may be the optimal approach for non ideal dataset

comment on molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans arnold et al 1 1 reported mo isotope compositions of mid proterozoic black shale which were different from those of euxinic sediments in the black sea on the basis of a mass balance model calculation they claimed that the area of oxic sedimentation in the mid proterozoic oceans was

thellier paleointensity theory and experiments for multidomain grains 1 we extend theories of thermoremanent magnetization trm and partial trm ptrm in multidomain md grains to model thermal demagnetization and ptrm acquisition steps in thellier paleointensity determination because of the interleaving of zero field and in field heating cooling steps to increasing temperatures the initial state for any step is complex and theoretical modeling is more intricate than for ptrm production or thermal demagnetization separately at low to moderate temperature t trm lost exceeds ptrm regained causing convex down arai plots sagging below the ideal single domain sd line at moderate to high t ptrm acquisition outweighs trm loss as t approaches tcurie ptrm gain exactly equals trm loss and the arai plot becomes ideal when ptrms are produced perpendicular to the original trm and measured directly rather than by differencing field on and field off results there is less deviation from ideality at low to moderate t our theory agrees semiquantitatively with results for parallel and perpendicular ptrms for large md magnetites 135 m smaller md magnetites 6 and 20 m have less curved arai plots and the smallest magnetites 0 6 and 1 m have almost linear plots positive ptrm checks demonstrate that curved arai plots of md grains are reproducible unlike curved plots for rocks that alter physicochemically in the thellier experiment while negative ptrm tail checks indicate undemagnetized ptrm residuals low temperature demagnetization improves linearity only slightly practical applications of this work include using the predicted threshold t below which no net ptrm is produced in a parallel thellier experiment to screen data used for paleointensity fits straight line fits through low and medium t points in arai plots of md 135 m grains overestimated the paleofield by as much as 100 and for small pseudo single domain psd 0 6 and 1 m grains overestimated by about 25 however by using linear segments of medium to high t data with f values 0 5 it may be possible to obtain reasonable paleointensity estimates even for larger psd 6 and 20 m and md grains middle to high t fits for 0 6 m grains gave paleointensities within 4 of the correct value utilizing essentially the entire data set f 0 9 perpendicular data always gave superior linear fits orienting samples with their natural remanent magnetizations perpendicular to the laboratory field is therefore recommended for rocks containing psd and md grains however double heatings are preferable to single heatings because they allow ptrm tail checks to be carried out

cooling rate effects on paleointensity estimates in submarine basaltic glass and implications for dating young flows 1 cooling rate effects on the intensity of thermoremanent magnetization trm have been well documented in ceramics in that case laboratory cooling is generally more rapid than the initial cooling leading to an overestimate of the paleofield by 5 10 in thellier type paleointensity experiments the reverse scenario however has never been tested we examine the effects of cooling rate on paleointensity estimates from rapidly quenched submarine basaltic glass sbg samples from 13 sites at 17 30 18 30 s on the east pacific rise absolute cooling rates determined by relaxation geospeedometry at five of these sites range from 10 to 330 c min 1 at the glass transition 650 c over the dominant range of remanence blocking temperatures 200 400 c the natural cooling rates are approximately equal to or slightly slower than the laboratory cooling rates during the thellier experiment these results suggest that while the cooling rate effect might introduce some within site scatter it should not result in a systematic bias in paleointensity from sbg paleointensity estimates from the 15 sites range from 29 to 59 t with an average standard error of 1 t comparison with models of geomagnetic field intensity variations at the site indicate the youngest group of samples is very recent indistinguishable from present day and the oldest is at least 500 and probably several thousand years old these age estimates are consistent with available radiometric ages and geologic observations

testing the izzi protocol of geomagnetic field intensity determination 1 a new paleointensity determination protocol the izzi method was recently proposed the izzi technique combines the aitken in field zero field iz and coe zero field in field zi methods the izzi protocol of paleointensity method was experimentally tested showing a strong angular dependence resulting from the undemagnetized portions of partial thermoremanent magnetization ptrm tails the izzi method is better than the conventional techniques aitken coe and thellier in three respects 1 it can easily detect the angular dependence 2 it provides a quantitative estimate for the consistency of the outcome between iz and zi step and 3 it is quicker because the extra ptrm tail check step is unnecessary

application of copper slag in geomagnetic archaeointensity research 1 paleointensity and archaeointensity studies since the 1950s have produced numerous geomagnetic intensity data for the last seven millennia as a consequence of different experiments and materials there is a complex and internally inconsistent picture of the geomagnetic field behavior in this study we present data using a recently developed experimental design on a heretofore unexploited recording medium copper slag deposits our results based on hundreds of specimens from various archaeometallurgical sites of the southern levant demonstrate the applicability of copper slag material for archaeointensity studies in addition to frequently exhibiting good experimental behavior slag has further advantages such as dense multilayer deposits and in cases embedded charcoals which open the door to data sets with excellent age control and resolution the data presented here augment the high quality database from the middle east and support previously observed periods of rapid change of the intensity of the geomagnetic field

first order symmetry of weak field partial thermoremanence in multi domain md ferromagnetic grains 2 implications for thellier type palaeointensity determination two models derived in very different ways but both incorporating the symmetry constraints outlined in the previous paper are developed for use in simulating thellier type palaeointensity experiments these are then tested against experimental data which endorse them both as powerful tools they predict that non ideal behaviour due to md grain content is sensitive not only to the protocol employed and the vector difference between the partial thermoremanent magnetisations ptrms imparted in the laboratory and the natural remanent magnetisation nrm but also to the spacing of the temperature steps and the type of ptrm imparted during the remagnetisation stages consistent with experimental studies the models predict that ptrm checks may fail despite no alteration occurring and that any double stage experimental protocol will produce non ideal results to some degree provided that md grains are present a single heating perpendicular or high angle single heating protocol is predicted to remove non ideal effects provided that the grains obey the symmetry constraints perfectly however this remains to be experimentally tested and does not allow for the use of ptrm checks five straightforward recommendations for future palaeointensity studies to follow are outlined these are designed to minimise non ideal behaviour due to md grains as far as possible while retaining the capacity to detect and reject those samples which will nonetheless produce significant errors

low geomagnetic field intensity during the kiaman superchron thellier and microwave results from the great whin sill intrusive complex northern united kingdom 1 coe modified thellier cmt and microwave mw paleointensity experiments were conducted on samples from the multi phase late carboniferous ca 301 ma to early permian ca 270 ma great whin sill complex statistically comparable results were obtained with both techniques from high quality data forty three samples 25 with cmt and 18 with mw yielded mean paleointensity values of 12 0 5 8 t and 16 5 8 2 t for the early and late intrusive phases respectively corresponding to vdms of 1 6 0 8 1022 and 2 1 1 1 1022 am2 when combined with previous data the results suggest a generally low dipole moment during the krs reducing from 75 of the present value at 301 ma to 20 27 of the present value later in the superchron these data imply either a decoupling between processes controlling reversal rate and field strength or a more complex intriguing time lag relationship more absolute palaeointensity results are needed to further evaluate these alternatives

the superparamagnetism of yucca mountain tuff yucca mountain tuff contains small titanomagnetite grains with narrow size distributions in the superparamagnetic range schlinger et al 1988 magnetic measurements on three samples comprising hysteresis loops at low and ambient temperatures acquisition and demagnetization of isothermal remanent magnetization thermal demagnetization of the saturation remanence and of a low temperature thermoremanence and frequency and temperature dependent susceptibilities allow evaluation of the magnetic properties in terms of neel s 1949 single domain theory precise grain volume distributions have been obtained by applying the blocking volume concept to thermal demagnetization results in contrast an attempt to derive mean particle volumes by fitting a langevin curve to the room temperature magnetization curves fails probably because the precondition for the langevin function kv kt 1 is not met it is only for the sample with the smallest grains and in weak fields 20 mt that a langevin fit provides a reasonable volume estimate there is good agreement between the experimental results and the calculated frequency and temperature dependence of susceptibility thus verifying that neel s theory is sufficient for the magnetic description of single domain assemblages spanning the superparamagnetic stable single domain boundary however some deviations between modeled and measured susceptibilities exist and the physical causes may include size dependent anisotropy nonuniform magnetizations and also an uncertain preexponential time constant 0 while 0 10 11 s gives the best fit for the sample with the largest grains 0 10 9 s is more reasonable for the others thus 0 may indeed be size and temperature dependent as predicted by brown 1959 the commonly cited parameter fd frequency dependence of susceptibility reaches 30 at room temperature rt for one sample with a blocking temperatures just below rt while fd 0 at rt for a superparamagnetic sample with smaller grains these results thus exemplify that fd is not limited to 15 as a number of studies suggest and that fd 0 must not be taken to imply the absence of superparamagnetic grains

combined use of tracer approach and numerical simulation to estimate groundwater recharge in an alluvial aquifer system a case study of nasunogahara area central japan summary in this study we simulate the spatial and temporal distribution of groundwater recharge in an alluvial aquifer system in the nasunogahara area of japan natural stable isotopes 18 o d were considered as additional calibration targets in a numerical model the reliability of the model outputs was further validated by comparing the results from the numerical simulation and an independent tracer approach the results indicated that the calibrated model can effectively simulate the spatial and temporal characteristics of the contribution ratios of recharge sources to groundwater in the nasunogahara area however the tracer approach i e end member mixing analysis provided more reliable results at point scale particularly for the estimated contribution ratios of paddy field water the precipitation in the nasunogahara area is the major recharge source its mean contribution ratio is 58 for a one year period over the entire alluvial fan river seepage is significant in the upstream area of the alluvial fan and the contribution ratio of river waters along the river channels in the upstream area increases during the wet season paddy field water is a highly important recharge source in the midstream and downstream areas of the alluvial fan and the contribution ratio of paddy field water obviously increases from dry season to wet season because of irrigation this study demonstrates that combined use of the tracer approach and numerical simulation with stable isotopes as additional calibration targets can eliminate their respective limitations and can assist in better understanding the groundwater recharge mechanism in alluvial aquifer systems

multidomain behavior during thellier paleointensity experiments results from the 1915 mt lassen flow abstract paleointensity experiments using the thellier method on samples of the 1915 mt lassen dacite flow yielded concave and s shaped nrm trm curves on arai plots departure of these curves from the ideal straight line corresponding to the known geomagnetic intensity of 54 t for the region in 1915 is significant the magnetic properties of these rocks change very little during heating and hysteresis experiments that suggest pseudo single domain to multidomain md magnetic grains are confirmed by microscopic observations thus the curvature appears to be due to md like behavior rather than to irreversible alteration of magnetic minerals in support of this interpretation the slope of the line through just the initial and the final point yields an average value of 52 t that is in good agreement with the known field intensity using the slope of only the lower or higher temperature points which is never advisable for persistently curved arai plots such as these would lead to estimates that are 30 80 too high or too low s shaped nrm trm curves are atypical in paleointensity studies and the usual explanation in terms of md unblocking temperatures less than blocking temperatures cannot account for the convex curvature of the higher temperature part rather the convex curvature can be explained by the predominance of remanence with unblocking temperatures greater than blocking temperatures the so called tail of ptrm acquired in the higher temperature part of the ptrm spectrum during the thellier experiment

low temperature behavior of single domain through multidomain magnetite abstract we have investigated the low temperature behavior of a suite of grown synthetic and natural magnetites that span single domain sd and multidomain md behavior synthetic samples had been grown in the laboratory either in an aqueous medium or in glass natural samples included sd magnetites occurring in plagioclase and truly md magnetites in the form of large octahedra in all experiments a sample was first given a saturation remanence at room temperature next moment was measured continuously during cooling and warming between 230 k and 60 k similar to results reported earlier by other workers magnetic memory is large in sd samples whereas truly md samples are almost completely demagnetized by cycling between room temperature and 60 k pseudo single domain samples exhibit behavior that is intermediate with respect to that of the sd and truly md states when data from this study are combined with data obtained by hartstra 10 from sized natural magnetites it is found that the percentage of total remanence that survives cycling between room temperature and 60 k decreases linearly with the logarithm of grain size and thus with increasing number of domains this relation suggests that memory can provide a reasonable estimate of grain size in those magnetite bearing rocks for which these samples provide good analogues remarkably some of the large natural octahedra provide a magnified view of md response to low temperatures and thus reveal two surprising and intriguing types of behavior first below approximately 180 k these octahedra demagnetize through a series of large barkhausen jumps second near 117 k these same octahedra exhibit a wild zone where magnetic moment executes large random excursions we interpret these two phenomena as direct evidence for the unpinning and irreversible displacement of domain walls in response to the drop in coercivity and possibly the broadening of domain walls as temperatures drop toward the isotropic point one implication of this behavior is that cooling to progressively lower temperatures could provide an effective method for stepwise removal of paleomagnetic components carried by md grains even without passage through the isotropic point of magnetite

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

a new approach for geomagnetic archaeointensity research insights on ancient metallurgy in the southern levant we present results from an archaeointensity investigation based on a relatively unexploited recording medium copper slag deposits together with a recently improved experimental design for the archaeointensity experiment we demonstrate the applicability of this medium as well as other archaeometallurgical artifacts for the study of the ancient geomagnetic field intensity in addition to archaeointensity data from well dated archaeological contexts we obtained reliable archaeointensity results from poorly dated or contentious archaeometallurgical sites in the southern levant these results shed new light on the dating of these sites among them the copper smelting installation of timna 39b a site that has important implications for the beginning of metallurgy during the fifth millennium bce the paper also aims to introduce archaeointensity research to the archaeologist scholar and to encourage further collaboration between the disciplines in future research

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

physical interpretation of hysteresis loops micromagnetic modeling of fine particle magnetite 1 hysteresis measurements have become an important part of characterizing magnetic behavior of rocks in paleomagnetic studies theoretical interpretation is often difficult owing to the complexity of mineral magnetism and published data sets demonstrate remanence and coercivity behavior that is currently unexplained in the last decade numerical micromagnetic modeling has been used to simulate magnetic particles such simulations reveal the existence of nonuniform remanent states between single and multidomain known as the flower and vortex configurations these suggest plausible explanations for many hysteresis measurements yet fall short of explaining high saturation remanence high coercivity data such as those commonly observed in fine grained submarine basalts in this paper we review the theoretical and experimental progress to date in understanding hysteresis of geological materials we extend numerical simulations to a greater variety of shapes and sizes including random assemblages of particles and shapes more complex than simple rods and cubes our simulations provide plausible explanations for a wide range of hysteresis behavior

geomagnetic field intensity how high can it get how fast can it change constraints from iron age copper slag article the intensity of the geomagnetic field varies over different time scales yet constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record the purpose of this study is to place firm limits on these fundamental properties by constructing a high resolution archaeointensity record of the levant from the 11th century to the early 9th century bce a period over which the geomagnetic field reached its maximum intensity in eurasia over the past 50 000 years we investigate a 14 c dated sequence of ten layers of slag material which accumulated within an ancient industrial waste mound of an iron age copper smelting site in southern israel depositional stratigraphy constrains relative ages of samples analyzed for paleointensity and 14 c dates from different horizons of the mound constrain the age of the whole sequence the analysis yielded 35 paleointenisty data points with accuracy better than 94 and precision better than 6 covering a period of less than 350 years most probably 200 years we construct a new high resolution quasi continuous archaeointensity curve of the levant that displays two dramatic spikes in geomagnetic intensity each corresponding to virtual axial dipole moment vadm in excess of 200 zam 2