stable isotope stratigraphy of brachiopods from pennsylvanian shales in texas stable isotope stratigraphies have been generated for brachiopods from five late pennsylvanian sections upper winchell cycle finis shale colony creek shale necessity cycle and wayland shale in north central texas to examine the relationship between isotopic composition paleoenvironment and sea level change nonluminscent calcite from more than 300 specimens of 4 species of brachiopod composita subtilita crurithyris planoconvexa eridmatus texana neospirifer cameratus was analyzed sedimentological and paleontological data are used as evidence for paleoenvironmental change higher 18 o values of brachiopod shells occur in intervals of greatest paleodepth as indicated by fossil content and lithology these higher 18 o values reflect a decrease in bottom temperature with increased water depth normalized for paleodepth the 18 o values of the brachiopods are similar in all of the units except the wayland shale for which they are 0 5 higher this suggests either cooler temperatures or greater continental ice volume during the time of wayland deposition brachiopod 13 c values do not correlate with paleodepth the 13 c values of composita are consistently higher than those of crurithyris and eridmatus composita 13 c values are similar in the upper winchell cycle necessity cycle and wayland shale averaging 4 8 to 4 9 in contrast crurithyris 13 c values range from 2 5 in the necessity cycle to 4 4 in the wayland shale eridmatus values are also lowest in the necessity cycle 3 4 and greatest in the wayland shale 3 9 these differences between species do not correlate with susceptibility to diagenesis and appear to reflect a pore water influence on semi infaunal crurithyris forms the 13 c values of composita shells suggest that the late pennsylvanian ocean off eastern laurussia was enriched in 13 c by about 1 relative to the ocean off western laurussia

the influence of dataset decisions on paleocommunity results comparison of different categorizations of two datasets from devonian carbonate units abstract community paleoecology researchers have employed an array of methods for collecting counting and identifying fossils few studies have quantified the differences among results when employing various methods on a single stratigraphic series of paleocommunities here we examined fossils collected from the rapid member of the little cedar formation of coralville iowa usa and the waterways formation of northern alberta canada to compare the paleocommunity results between the use of abundance versus point counts as a counting method and between using all taxa in a paleocommunity versus only the brachiopod taxa comparisons between abundance and point count categorizations resulted in goodness of fit statistics ranging from 0 61 to 0 92 in addition we visually assessed each of the ordination comparisons and interpreted each categorization comparison as leading to different paleocommunity interpretations colonial and easily disarticulated taxa i e crinoids and bryozoans had a strong influence on the differences between abundance and point count categorizations when the colonial and easily disarticulated taxa were culled and the analyses rerun goodness of fit statistics increased when possible we recommend the use of both abundance and point counts when conducting paleocommunity analyses however because point counts allow the equal weighting of solitary non solitary and easily disarticulated taxa point counts may be a more accurate means of measuring taxonomic composition of paleocommunities furthermore because of the disparity between the paleocommunity results of brachiopods only versus all taxa we recommend the use of all taxa for environmental ecological or evolutionary research based on paleocommunities

geomagnetic field in the near east at the beginning of the 6th millennium bc evidence for alternating weak and strong intensity variations abstract this study presents new archeointensity results from the multilayered settlement yarim tepe i located today in northern iraq archeological evidences and new radiocarbon dates indicate that this site was occupied for about four centuries between the end of the 7th and the beginning of the 6th millennium bc leading to a 6 5 m thick sequence of archeological deposits a series of 16 groups of potsherds with a total of 76 fragments were collected from superimposed stratigraphic layers with thicknesses of 30 cm on average archeointensity measurements were carried out using the triaxe procedure which takes into account both anisotropy and cooling rate effects on thermoremanent magnetization acquisition in this study 114 specimens from 40 fragments have fulfilled our selection criteria and mean archeointensity results were derived from nine different groups of fragments with a minimum of three fragments per group according to an age model constructed using a bootstrap approach the new archeomagnetic record spans a time interval of 220 years between 6070 bce and 5850 bce no significant intensity variations were observed during this time interval with an overall mean intensity value of 42 0 1 6 t a comparison of the yarim tepe i data with other archeointensity results spanning the 7th and 6th millennia bc previously obtained from the near east as well as from eastern and western europe was conducted the yarim tepe i results enabled to constrain the short duration one century at most of an intensity peak evidenced around 5750 bce from the bulgarian database intensity variation rates associated with the ascending branch of the peak reached values as high as 0 12 0 15 t year summarizing the geomagnetic field intensity variations in the near east and eastern europe during the entire 6th millennium bc it appears that they were likely characterized by the occurrence of two short lasting intensity peaks at 5750 bce and 5500 bce with intensity variation rates similar or slightly higher than the maximum rates prevailing in the modern field finally it is worth mentioning that the four radiocarbon dates reported in our study provide new constraints for deciphering the temporal correlation between the cultural historical phases halaf and hassuna that were independently defined from excavations carried out in iraq and syria

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

multivariate hierarchical analyses of miocene mollusk assemblages of europe paleogeographic paleoecological and biostratigraphic implications mollusk dominated fossil assemblages from the marine miocene bioprovinces of europe the boreal province and the paratethys were analyzed by using bulk samples collected hierarchically across several spatiotemporal scales the study explores quantitative patterns recorded by benthic mollusk assemblages including implications for paleogeographic biostratigraphic and paleoenvironmental patterns and the relationship between spatiotemporal scale of analysis and levels of variability in paleontological data a total of 8455 specimens from 23 samples were collected from siliciclastic sediments clay and sand at 12 localities from france belgium the netherlands germany poland austria and hungary with the exception of one sample of serravallian age from the southeastern north atlantic all samples came from burdigalian and langhian deposits of the paratethys and the boreal province all specimens were identified to species level 297 species total classified in terms of ecology and analyzed by using multivariate and computer intensive methods the analyses focused on 1 bivalve gastropod ratios 2 diversity levels 3 multivariate taxonomic and ecological patterns and 4 multivariate euclidean distances between samples compared at five different scales within sites within localities within facies among facies among provinces the bivalve gastropod ratio is a highly volatile parameter thus its informative value is highly limited the estimates of alpha diversity sample species richness standardized by rarefaction indicate that fossil assemblages of the boreal province display higher diversity levels than those of the paratethys this result is consistent with the general tendency of isolated epicontinental basins to display impoverished fauna and may be due to geographic barriers limiting larval dispersal and to environmental instabilities inherent to marginal environments of epicontinental seaways rarefactions of pooled data indicate that for both provinces the taxonomic turnover among sites beta diversity accounts for 30 40 of species diversity multivariate analyses indicate that biogeographic variation between the provinces is the most important factor controlling differences among samples whereas facies type and stratigraphic position of samples play a secondary role the strong biogeographic signature is consistent with recent paleogeographic reconstructions that suggest a lack of a direct marine connection between the two provinces at that time the relatively poorer discrimination of mollusk assemblages across facies and biostratigraphic stages reflects the overriding role of the middle miocene biogeography in controlling the composition of mollusk assemblages the hierarchical multivariate analysis shows that with the increase in the scale of observation within sites within localities within facies among facies among provinces the average multivariate distance between samples increases continuously new heterogeneities that add notable amounts of new variation exist at each scale of observation the highest increase is observed for the among provinces comparison level again indicating the major role of geographic sources of variation in the data the hierarchical approach provides a rigorous way to quantify the effects of scale dependent sources of variability on paleontological patterns

archaeomagnetism of burnt cherts and hearths from middle palaeolithic amud cave israel tools for reconstructing site formation processes and occupation history abstract apart from magnetostratigraphy archaeomagnetism is rarely used in middle and late pleistocene sites here we present detailed palaeomagnetic analyses of cemented hearths and burnt chert items from amud cave israel 68 55 ka two types of materials common in levantine middle palaeolithic cave sites both materials are shown to be recorders of the geomagnetic field and were used to reconstruct either the ancient field direction for cemented hearths or intensity palaeointensity for chert at the time of the last burning or shortly after we test the utility of palaeomagnetic data to further our understanding of temporal aspects of occupations in the cave by comparing the dispersion of the palaeomagnetic data to the known characteristics of geomagnetic secular variation in the holocene we show that divergent palaeointensities can help identify diachronic burning events suggesting different activity patterns in two areas of the cave additionally we used palaeomagnetic directional vectors to distinguish between a well preserved hearth and one that had been mixed prior to cementation using rock magnetic investigations we demonstrate that magnetic methods can be used as a relatively fast and inexpensive method to identify burning of cherts in antiquity above 500 c the palaeomagnetic results are in agreement with results of previous studies at amud cave obtained by other independent methods this study shows that palaeomagnetic methods can serve as a powerful tool in the study of palaeolithic sites

high fidelity archeointensity results for the late neolithic period from central china author s cai s tauxe l wang w deng c pan y yang l qin h abstract 2020 american geophysical union all rights reserved archeomagnetism focuses on exploring high resolution variations of the geomagnetic field over hundreds to thousands of years in this study we carried out a comprehensive study of chronology absolute and relative paleointensity on a late neolithic site in central china ages of the samples are constrained to be 3 500 3 000 bce a period when available paleointensity data are sparse we present a total of 64 high fidelity absolute paleointensities demonstrating the field varied quickly from 55 to 90 zam2 between 3 500 3 000 bce our results record a new archeomagnetic jerk around 3 300 bce which is probably non dipolar origin the new results provide robust constraints on global geomagnetic models we calculated a revised chinese archeointensity reference curve for future application the variations of absolute and relative paleointensity versus depth show good consistency reinforcing the reliability of our results this new attempt of combining absolute and relative paleointenstiy provides a useful tool for future archeomagnetic research

searching for geomagnetic spikes in numerical dynamo simulations abstract we use numerical dynamo simulations to investigate rapid changes in geomagnetic field intensity the work is motivated by paleomagnetic observations of geomagnetic spikes events where the field intensity rose and then fell by a factor of 2 3 over decadal timescales and a confined spatial region no comparable events have been found in the historical record and so geomagnetic spikes may contain new and important information regarding the operation of the geodynamo however they are also controversial because uncertainties and resolution limitations in the available data hinder efforts to define their spatio temporal characteristics this has led to debate over whether such extreme events can originate in earth s liquid core geodynamo simulations produce high spatio temporal resolution intensity information but must be interpreted with care since they cannot yet run at the conditions of earth s liquid core we employ reversing and non reversing geodynamo simulations run at different physical conditions and consider various methods of scaling the results to allow comparison with earth in each simulation we search for extremal events defined as the maximum intensity difference between consecutive time points at each location on a 2 latitude longitude grid at earth s surface thereby making no assumptions regarding the spatio temporal character of the event extremal events display spike shaped time series in some simulations though they can often be asymmetric about the peak intensity maximum rates of change reach 0 75 t yr 1 in several simulations the lower end of estimates for spikes suggesting that such events can originate from the core the fastest changes generally occur at latitudes 50 which could be used to guide future data acquisitions extremal events in the simulations arise from rapid intensification of flux patches as they migrate across the core surface rather than emergence of flux from within the core the prospect of observing more spikes in the paleomagnetic record appears contingent on finding samples at the right location and time to sample this particular phase of flux patch evolution

on the suitability of baked clay for archaeomagnetic studies as deduced from detailed rock magnetic studies summary extensive rock magnetic investigations have been carried out on baked clays from four kilns two from bulgaria and two from switzerland found in archaeological sites of different age knowledge of the magnetic characteristics of the grains responsible for the archaeomagnetic signal enables us to determine which baked clays have the stablest magnetization and why this is so this is important in directional studies but even more so in painstaking palaeointensity studies that require a very careful evaluation of the suitability of the burnt clay material the proposed rock magnetic experiments enable the identification of the carriers responsible for the remanence and an adequate interpretation of the experimental results connected with the palaeointensity evaluation the experimental methods employed are illustrated with the particular results obtained from each of the four kilns studied the preliminary elucidation of the magnetic mineralogy of the archaeological samples helps first by obtaining a more reliable palaeointensity result and secondly by explaining some of the discrepancies in the palaeodirectional results examples of successful and failed palaeointensity experiments are given in relation to the magnetic properties previously established for each oven the burnt clay materials in this present study satisfy the essential condition of carrying a thermoremanence in spite of that it is shown that there are many factors that can produce undesirable magnetic properties and thus restrict the suitability of these materials for archaeomagnetic analysis the most important factors influencing the magnetic behaviour during magneto diagnostic experiments are the degree of heating in antiquity the initial composition of the unbaked material and the burial conditions the large difference in heating temperatures within a particular archaeological feature is a major cause of variation in magnetic behaviour amongst individual specimens and so preventing a successful pre selection of specimens for palaeointensity experiments nevertheless the study has shown a very good coincidence between the determined rock magnetic characteristics and the success rate in palaeointensity evaluation

late miocene turnover of molluscan faunas new zealand taxonomic and ecological reassessment of diversity changes at multiple spatial and temporal scales abstract previous estimates of molluscan biodiversity during the neogene in new zealand have revealed a pattern of significant diversity decline during the latest miocene this study uses an occurrence based dataset derived from published literature to examine this pattern in further detail with both traditional synoptic measures and subsequent sampling standardization synoptic analyses of regional scale data reveal diversity trajectories similar to those previously established and rarefaction techniques demonstrate that the inferred pattern of late miocene diversity decline and early pliocene rebound is only somewhat biased by variations in sampling intensity the pattern is also affected by temporal variations in the preservation of shelf paleoenvironments with representation of highly diverse shallow water facies varying considerably between biostratigraphic stages the sampling and corresponding synoptic genus richness of biogeographic areas within the new zealand region is also uneven within a single sedimentary basin sampled at high temporal resolution wanganui basin new data suggest that late miocene faunas were as diverse as those of the early pliocene contrasting with the pattern of diversity decrease and subsequent increase observed at the regional spatial scale in prior studies however an ecological analysis of the new data demonstrates that turnover and restructuring of benthic communities did take place at the end of the late miocene these findings suggest that spatial scale and temporal resolution are important considerations in determining the magnitude of diversity and ecological change observed in paleontologic studies contemporaneous biodiversity may not be similarly expressed at varying spatial or temporal scales in the fossil record rather regional patterns of diversity change are governed by a complex interplay of not only large scale environmental factors e g temperature control but also independent basin scale processes e g basin subsidence and local sampling intensity

on archeomagnetic secular variation curves and archeomagnetic dating abstract secular variation sv of the earth s magnetic field can be used for dating purposes by comparing archeomagnetic directions of unknown ages with a well dated reference curve in this study we propose a dating technique based on the statistics of mcfadden and mcelhinny geophys j int 103 1990 725 for testing the hypothesis that two fisherian distributions of individual directions share a common mean direction the statistics are adapted to test the degree of compatibility between one individual fisherian mean direction and a reference curve constructed using the bivariate extension of the fisher distribution furthermore as the density of the data which define the archeomagnetic reference curve varies in time we suggest that one computes the mean directions with moving windows of varying duration where both the window widths and the time shifts between successive mean directions are fixed when a minimum threshold density of data is reached within each time interval in our paper we apply this new procedure to the french archeomagnetic data set

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

the sensitivity of paleocommunity sampling strategy at different spatiotemporal scales abstract one of the primary differences between paleoecological and modern ecological research is the added dimension of deep geological time the temporal dimension of paleoecological research can create added difficulties when determining the appropriate spatiotemporal sampling procedures required for any particular study previous paleocommunity studies have found that the spatial extent of sampling can have a grave impact on the multivariate analytical results here we expand spatially on the previous paleocommunity study of forcino et al 2010 to determine the importance lateral variation may have on the paleocommunity signal within the pennsylvanian finis shale spatial and temporal community gradients of bulk sediment shale samples from six localities were examined using ordinations and anosim the expanded spatial examination of the finis shale reveals the same two distinct communities separated at the mid point of each sampled stratigraphic section thus lateral variation did not have an effect on the primary multivariate result for the finis shale communities at the temporal scale of the complete stratigraphic section a temporal factor has the greatest influence on the community result however based on separation of samples in ordination space with respect to location and based on a significant difference between locality based groupings using anosim the primary influence on the paleocommunity result at a finer temporal scale containing 19 samples from only the lower half of each stratigraphic section is a spatial factor this minor variation in scale leading to a major change in the primary factor affecting the multivariate paleocommunity result is evidence that the paleocommunity results are extremely sensitive to the temporal scale of sampling thus this differs from previous research there are cases in which fewer laterally equivalent samples are required per stratigraphic horizon bed or unit because the temporal signal overwhelmed the spatial signal

new late neolithic c 7000 5000 bc archeointensity data from syria reconstructing 9000years of archeomagnetic field intensity variations in the middle east we present new archeomagnetic intensity data from two late neolithic archeological sites tell halula and tell masaikh in syria these data from 24 groups of potsherds encompassing 15 different time levels are obtained using the triaxe experimental protocol which takes into account both the thermoremanent magnetization anisotropy and cooling rate effects on intensity determinations they allow us to recover the geomagnetic intensity variations in the middle east between 7000 bc and 5000 bc i e during the so called pre halaf proto halaf halaf and halaf ubaid transitional cultural phases the data are compared with previous archeointensity results of similar ages from northern iraq yarim tepe ii and tell sotto and bulgaria we find that previous dating of the iraqi material was in error when corrected all northern mesopotamian data show a relatively good consistency and also reasonably match with the bulgarian archeointensity dataset using a compilation of available data we construct a geomagnetic field intensity variation curve for the middle east encompassing the past 9000 years which makes it presently the longest known regional archeomagnetic intensity record we further use this compilation to constrain variations in dipole field moment over most of the holocene in particular we discuss the possibility that a significant dipole moment maximum occurred during the third millennium bc which cannot easily be identified in available time varying global geomagnetic field reconstructions

origin of the pennsylvanian coal bearing cyclothems of north america past controversy about the tectonic or eustatic origin of pennsylvanian cyclothems is resolved by regional basin subsidence analysis global paleoclimate paleogeography and plate tectonic evolution differences between marine carbonate kansas type cyclothems of the northern midcontinent and nonmarine clastic appalachian type cyclothems of the eastern united states are controlled by laterally changing flexural deformation during plate accretion into a supercontinent coupled with superposed glacial eustasy kansas type cyclothems accumulated on a relatively stable platform affected only moderately by collision tectonics of north american margins these cycles are eustatic characterized by a periodicity comparable to milankovitch orbital parameters appalachian type cyclothems accumulated in response to episodic thrust loading during plate collisions that developed a series of flexurally deformed wide and shallow resurgent foreland basins this resurgent foreland basin evolution during paleozoic time increased crustal rigidity in the appalachians thus yoking the appalachian and illinois basins during pennsylvanian time with each thrust load foreland basin deepening favored transgressive cyclothem facies which changed to a regressive facies because sediment yield increased as denudation rates increased off uplifted orogens illinois type cyclothems are intermediate between the two end member processes of flexural tectonics and glacial eustasy characterizing appalachian type and kansas type cyclothems respectively thus the pennsylvanian coal bearing cyclothems of north america owe their origin to the remarkable coincidence of supercontinent development concomitant glaciation and eustatic sea level change and associated episodic thrust loading and foreland basin subsidence of small magnitude on progressively more rigid crust

linear wavetrains in models of the stratosphere experiments with a primitive equation model of the stratosphere and mesosphere are described which investigate the effect on the stratosphere of the growth of localized stationary forcing in the troposphere two basic states are used which are representative of stratospheric flow in early and late winter in the southern hemisphere simple mechanistic models are then introduced to examine the wave phenomena which occur during the first 10 days of the experiments when the dynamics are known to be linear the localized forcing grows to a peak amplitude of 600 gpm and half width of 15 of latitude values typical of the mid latitude upper troposphere stratospheric travelling waves are excited with phase velocities which are sensitive to the zonal mean winds and to the speed of the switch on of the forcing and wave activity spreads quickly from the localized forcing with a typical vertical group velocity of 10 km d 1 strong horizontal curvature in the basic states can profoundly affect the vertical and horizontal structures of the wavetrains mid latitude regions of negative northward potential vorticity gradient in the stratosphere as seen in the southern hemisphere in late winter lead to the confinement and amplification of waves in high latitudes three dimensional diagnostics of wave activity propagation reveal wave reflections missed by zonally averaged ep flux diagnostics significant wave reflection and trapping occur on the flow from late winter eventually producing a steady linear wavetrain with an intense local centre of circulation in the upper stratosphere the maximum anomaly being 1000gpm at 1mb it is argued that such wavetrains are unrealistic because nonlinear ageostrophic winds drive the dynamics away from any linear steady state

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

new constraints on the most significant paleointensity change in western europe over the last two millennia a non dipolar origin over the last years new evidences of several short lived regional maxima of the geomagnetic field intensity at various times and locations have been defined these features have important implications both for geomagnetic field modeling and for earth s dynamo simulations however the nature extent and underlying causes of these variations are still poorly understood the major constraint for an adequate description of these important features is the absence of continuous detailed records and the current limited availability of precisely dated geomagnetic field recorders in this context archeological materials from superimposed strata covering long sequences of occupation provide a powerful tool to investigate the temporal variability of geomagnetic field strength at decadal and centennial time scales in this work we report the archeomagnetic study of 79 potteries from southeastern spain collected in 14 different stratigraphic units the chronological framework of the studied collection ranging from the 9th to the 12th centuries is based on historical archeological data such as written sources and well established typological and archeometric documentation on ceramics found on reference contexts in the area additionally two radiocarbon dates obtained from two different stratigraphic units confirm the proposed chronological intervals from classical thellier and thellier experiments including partial thermoremanent magnetization ptrm checks and trm anisotropy and cooling rate corrections height new high quality mean intensities were derived the new data provide an improved description of the sharp abrupt intensity decay that took place in western europe after the 800 ad intensity maximum the most significant geomagnetic field intensity feature observed in europe over the last two millennia the new results confirm that several rapid intensity changes with rates higher than 10 t century took place in western europe during the recent history of the earth the comparison between the regional curve of western europe and the sha dif 14k global field model predictions suggests that the 800 ad event observed in europe is probably controlled by non dipolar geomagnetic sources

archaeomagnetic knowledge of the neolithic in bulgaria with emphasis on intensity changes table s1 summarized archaeomagnetic determinations of the studied collections d magnetic declination after sun compass correction i magnetic declination fa archaeointensity value obtained with the corresponding standard deviation in a temperature interval tmin tmax using npi points nrm fraction f gap factor g quality factor q maximum angle of deviation mad are also given in the sample name the small letters indicate the specimens used for ai determination whereas each sample direction is calculated as an average of two or three specimen directions after the corresponding cleaning thermal or af specimens treated in rennes laboratory are marked in grey

two archaeomagnetic intensity maxima and rapid directional variation rates during the early iron age observed at iberian coordinates implications on the evolution of the levantine iron age anomaly abstract variations of geomagnetic field in the iberian peninsula prior to late iron age times are poorly constrained here we report 14 directional and 10 palaeointensity results from an archaeomagnetic study carried out on 17 combustion structures recovered from six archaeological sites in eastern spain the studied materials have been dated by archaeological evidences and supported by radiocarbon dates 8th 5th centuries bc rock magnetic experiments indicate that the characteristic remanent magnetization is carried by a low coercivity magnetic phase with curie temperatures of 500 575 c most likely titanomagnetite maghemite with low titanium content archaeointensity determinations were carried out by using the classical thellier thellier experiment including ptrm checks and magnetic anisotropy corrections a new full vector iberian paleosecular variation curve for the iron age is presented high fluctuation rates on both directions and intensities are observed during the early iron times that seems to be related with the levantine iron age anomaly liaa the most prominent anomaly of the geomagnetic field of the last three millennia two intensity maxima were observed at iberian coordinates the oldest around 750 bc associated with easterly declinations of around 23 and the second 275 yrs later 475 bc with northerly directions the related virtual axial dipole moment was up to 14 10 22 am2 for the oldest materials 750 bc and reaching 16 10 22 am2 for the materials corresponding to the end of the early iron age in order to investigate the origin of the unusually high fluctuations of the palaeofield we have developed a new global geomagnetic field reconstruction the shawq ironage model which is based on a critical revision of the global archeomagnetic and volcanic dataset the new model provides an improved description of the evolution of the liaa which is related to a normal flux patch at the core mantle boundary cmb below arabian peninsula clearly observed at around 950 bc this flux patch expanded towards the north west while decreasing in intensity reaching iberia at around 750 bc around 600 500 bc it underwent a revival below the european continent after that it seems to vanish in situ

further evidence of the levantine iron age geomagnetic anomaly from georgian pottery recent archaeomagnetic data from ancient israel revealed the existence of a so called levantine iron age geomagnetic anomaly liaa which spanned the first 350 years of the first millennium before the common era b c e and was characterized by a high averaged geomagnetic field virtual axial dipole moments vadm 140 z am2 nearly twice of today s field short decadal scale geomagnetic spikes vadm of 160 185 z am2 fast field variations and substantial deviation from dipole field direction the geographic constraints of the liaa have remained elusive due to limited high quality paleointensity data in surrounding locations here we report archaeointensity data from georgia showing high field values vadm 150 z am2 in the tenth or ninth century b c e low field values vadm 60 z am2 in the twelfth century b c e and fast field variation in the fifth and fourth centuries b c e high field values in the time frame of liaa have been observed so far only in three localities near the levant eastern anatolia turkmenistan and now georgia all located east of longitude 30 e west of this in the balkans field values in the same time are moderate to low these constraints put geographic limits on the extent of the liaa and support the hypothesis of an unusually intense regional geomagnetic anomaly during the beginning of the first half of the first millennium b c e comparable in area and magnitude but of opposite sign to the presently active south atlantic anomaly

investigating the expected archaeomagnetic dating precision in europe a temporal and spatial analysis based on the scha dif 3k geomagnetic field model abstract archaeomagnetic dating is a chronometric dating technique based on the ability of baked clay archaeological structures and artifacts to acquire a thermal remanent magnetization trm when heated at high temperatures and cooled in the presence of the earth s magnetic field the precision of archaeomagnetic dating depends on several factors among others the availability of a detailed reference secular variation sv curve for a given territory in this study we investigate the precision that archaeomagnetic dating can reach in europe we used the scha dif 3k european geomagnetic field model to calculate the dating uncertainties for the last 3000 years taking into consideration only the uncertainties depending on the change rate of the geomagnetic field in the past and the reference sv curve s uncertainty envelope such uncertainties were calculated both in time and space they are usually asymmetrically distributed around the considered year and it have been represented as dynamic maps of uncertainties the obtained results show that archaeomagnetic dating based solely on directional data declination and inclination can be very precise for the last four centuries with total uncertainties being almost always lower than 100 years all around europe inherent dating uncertainties are also low for the last millennium with values ranging from 50 to 300 years these results underline the great potential of archaeomagnetism on dating baked clays belonging to the last 1000 years for older periods the uncertainty maps show that the dating precision may importantly vary from place to place but with local non symmetric uncertainty ranges generally below 400 years the obtained maps also show that adding the intensity to the computation of the inherent uncertainties does not always reduce the uncertainty the temporal and spatial analysis presented here does not give the total dating imprecision of archaeomagnetic dating that definitely depends on numerous often uncontrollable factors but aims at offering a useful tool to archaeomagnetic and archaeological research to check the feasibility of archaeomagnetic dating for determining the age of an archaeological structure below a desired precision

gradient analysis of faunal distributions associated with rapid transgression and low accommodation space in a late pennsylvanian marine embayment biofacies of the ames member glenshaw formation conemaugh group in the northern appalachian basin usa abstract the ames sea situated in a shallow marine embayment in the appalachian basin was the result of the most extensive marine transgression of the pennsylvanian in this region gradient analysis of the proportional abundance of taxa reveals an environmental continuum across the ames embayment along which four biofacies were distributed biofacies distribution is interpreted to be controlled by salinity turbidity and oxygen gradients associated with the geometry of the ames depositional basin and relative sea level change the eastern portion of the ames sea resembled a foredeep trough located on the detrital slope of the recently uplifted appalachian highlands biofacies 1 and 2 occur exclusively in the eastern part of the ames depositional basin and are dominated by eurytopic molluscs tolerant of terrigenous influx biofacies 3 occurs in both the eastern and western portions of the ames depositional basin this biofacies is dominated by the opportunistic brachiopod neochonetes which would quickly colonize the seafloor in the wake of transgression d biofacies 4 occurs exclusively in the western part of the ames depositional basin and is composed primarily of stenotopic crinoids bryozoans brachiopods and epifaunal bivalves that inhabited a clear water cratonic ramp on the eastern flank of the cincinnati arch vertical variations of faunal assemblages in the ames member were the result of variations in relative sea level associated with glacio eustatic cycles biofacies 3 dominated by neochonetes was deposited at the base of the ames member during the initial rapid transgression in a mostly dysoxic environment with low turbidity and marine salinity during the first regression low density surface water from eastern sources restricted vertical circulation established a stratified water column and promoted estuarine conditions in the ames embayment well oxygenated surface waters were unable to circulate to the benthic habitat which led to periodically dysoxic conditions and the establishment of biofacies 1 and 2 composed of diminutive eurytopic molluscs a second stratigraphically higher occurrence of biofacies 3 is interpreted to represent a second transgression however unlike the first transgression lithologic and faunal data suggest that the benthic habitat was well oxygenated above the mid ames marine zone occurrence of biofacies 3 biofacies 1 and 2 were deposited in the final regressive phase as local terrigenous source areas brought increasing turbidity and fluctuating salinity to the ames embayment previous paleoecological research on the ames member cited freshwater and or clastic influx as the major controls on biotic distribution but the results of the present study suggest that oxygen availability was also a major control stratification of the water column during the ames sea level cycle promoted estuarine circulation that prevented well oxygenated surface waters from reaching the benthic habitat this led to the deposition of dark gray to black fissile shales that contain fossil assemblages dominated by diminutive molluscs and brachiopods that were tolerant of low oxygen conditions

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

palaeo and rock magnetic investigations on late quaternary sediments from low latitudes i geomagnetic palaeosecular variation and relative palaeointensity records from the tobago basin southeast caribbean

influence of the vertical and zonal propagation of stratospheric planetary waves on tropospheric blockings 1 case studies are used to elucidate the relationship between stratospheric planetary wave reflection and blocking formation in the troposphere the enhanced upward propagation of a planetary scale wave packet from the eurasian sector involving a euro atlantic blocking leads to a stratospheric sudden warming ssw following the weakening of the stratospheric westerly jet due to polar warming the stratospheric planetary wave packet then propagates downward over the american sector inducing a ridge over the north pacific as well as a trough over eastern canada in the upper troposphere the ridge promotes the formation of a pacific blocking this result explains why pacific blockings tend to form after ssw and why they are associated with suppressed upward propagation of planetary waves

glacial eustatic base level climatic model for late middle to late pennsylvanian coal bed formation in the appalachian basin abstract late middle late pennsylvanian middle allegheny and lower conemaugh marine units in the appalachian basin represent the distal edges of glacial eustatic marine incursions of the midcontinent sea onto the detrital apron of the appalachian highlands because these marine units typically overlie coal beds the main environment of formation of this type of coal bed appears to have been that of a coastal swamp migrating ahead of transgression as base level rose the water table continually rose and the swamp was further nourished and surrounding vegetation kept thick enough to inhibit detrital influx by rainfall from the expanding nearby source of moisture even in parts of the appalachian cyclic succession with no marine units upper allegheny monongahela dunkard the coal beds rep esent the wettest part of the climate cycle of cecil 1990 sandwiched between detrital units representing seasonal wet dry climates when sediment was most readily mobilized and antipodal to nonmarine limestones representing the driest climates throughout this time the appalachian basin was in the center of the tropical zone of a nearly accreted megacontinent quite distant 4000 km from permanent oceanic sources of moisture climate modeling without considering inland seas or orographic effects on winds shows that the tropical zone of such a large land mass would have suffered from a severe deficit in rainfall and soil moisture although further modeling shows that the appalachian orogenic highlands would have drawn in moisture to ncrease rainfall in their vicinity they also may have impeded the normal westward flow of moisture laden easterly winds the western source for enough moisture to form coal beds was most likely the north american midcontinent sea during major highstand this sea would have covered about 2 million km2 and provided both high base level and abundant nearby moisture for enough continual rainfall to keep the coastal peat swamps widespread fresh and relatively detritus free in the appalachian basin in contrast during major lowstand it would have covered only about 200 000 km2 with its shoreline about 1500 km away and it apparently provided less consistent moisture to the appalachian basin then because most nonmarine limestones and paleosols formed there during the e times contain evidence of drier climates therefore upper allegheny monongahela and dunkard coal beds most probably formed when the midcontinent sea was approaching highstand and stood just west of the presently preserved outcrop thus they likely represent the coastal lowland equivalent of a marine unit at highstand farther west this constrained time of peat formation and preservation in a variety of coastal environments prior to and during marine highstand is responsible for the discrete and widespread nature of the coal bed interval in a typical depositional cycle or cyclothem a pattern that stands in contrast to the complicated relations of overlying and underlying detrital units which reflect the segregation of sand and mud into a complex mosaic of local deltaic and ter estrial subenvironments that developed when sea level rainfall and the water table were lower

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

archaeomagnetic results on three early iron age salt kilns from moyenvic france variations of the earth fs magnetic field during the first millennium bc in western europe remain poorly constrained especially archaeointensity changes three salt kilns moa mob and moc sampled in moyenvic lorraine eastern france have been studied to provide new reference data each kiln has been dated by radiocarbon to originate from the early iron age or hallstatt period between viii and vth century bc rock magnetic experiments and hysteresis results suggest the predominance of pseudo single domain psd ti poor magnetite archaeomagnetic directions obtained by thermal and alternating field demagnetizations have high mean inclination close to 70 and declination between 19 and 31 a first set of classical thellier thellier experiments was conducted on 46 samples with a laboratory field almost parallel to the direction of the characteristic remanent magnetization chrm only 24 of these specimens present a linear nrm trm plot for other specimens nrm trm plots are concave up with positive ptrm checks the very large dispersion observed between the determined palaeointensity values suggests some artefacts have not been fully recognized a second set of thellier experiments was conducted on 34 sister specimens with the laboratory field applied quasi perpendicular to the chrm in these cases mineralogical evolutions during heating and chemical remanent magnetization acquisitions have been clearly recognized despite positive ptrm checks the concave up shapes of nrm trm plots appear mainly due to mineralogical alteration rather than to the presence of psd md grains for the entire set of samples the success rate of the palaeointensity determinations is very low with 80 per cent of the samples rejected nevertheless reliable mean archaeointensities have been obtained for two of the three kilns moa 80 1 14 5 et and mob 86 6 6 9 et at the latitude of paris the high field strength and the archaeomagnetic directions determined combined with previous published data provide further evidence for important changes of the earth magnetic field in europe during the first half of the first millennium bc these large variations of the geomagnetic field during the iron ages indicate that archaeomagnetism is highly suitable for dating of structures from this period

archaeomagnetic secular variation in germany during the past 2500 years summary the german archaeomagnetic data set was supplemented with 35 new directions from ger man sites mainly dating from the past 3000 yr together with archaeomagnetic data from the neighbouring countries of germany a database of 166 reliable archaeomagnetic directions has been compiled for the reference area which is defined by a 500 km radius circle around gottingen the retrieved directions come from well dated archaeological structures and about 40 per cent of the dating relay on natural science methods such as radiocarbon thermolumines cence dendrochronology dating or historical documents from this data set a secular variation sv reference curve has been calculated using a bivariate algorithm which fits a natural cubic spline based on roughness penalty to declination inclination and time simultaneously the error tube surrounding this curve was obtained from bayesian modelling of the experimental errors which can also take stratigraphic information into account the obtained sv reference curve for the past 2500 yr is similar to that from france but also significant differences are seen comparison of the curves does not show a simple westward drift of the sv pattern the german reference curve allows archaeomagnetic dating in the reference area and extends this dating technique to sites situated in middle europe

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

new high precision full vector archaeomagnetic data from a roman kiln in merida spain abstract this study presents new high precision age and full vector archaeomagnetic data from a kiln excavated in the roman archaeological site of mitreo s house merida badajoz spain the age of the kiln was obtained by the stratigraphic method and by the ceramological study of the italic and sigillata pottery found with a very precise age date of 55 15 years ad rock magnetic experiments pointed towards magnetite as the main carrier of remanence and highly reversible thermomagnetic curves suggested that the studied samples were suitable for archaeoeointensity determinations paleomagnetic experiments including thermal and stepwise alternating field demagnetization yielded the following mean direction for the kiln declination d 0 6 inclination i 54 0 k 481 95 2 5 archaeointensityexperiments with the thellier coe protocol on 28 samples yielded successful determinations in 27 cases anisotropy factors between 0 90 and 1 04 were obtained from anisotropy of thermoremanent magnetization atrm experiments a mean anisotropy corrected archaeointensity value f 56 3 5 5 t was obtained the geomagnetic model sha dif 14 k was used for an archaeomagnetic dating yielding a chronological interval between 40 bce and 150 ce this low age resolution when compared with the pottery based age data is related to the behavior of the geomagnetic field in the iberian peninsula during the roman period which does not allow to differentiate well between results corresponding to those centuries however it is also related to the fact that the iberian archaeomagnetic dataset in the analysed time range is highly scattered a high quality full vector data with a very precise age have been obtained which contribute to improve the iberian secular variation curve and geomagnetic databases

a regional archeomagnetic model for europe for the last 3000 years scha dif 3k applications to archeomagnetic dating 1 the available european database of archeomagnetic field values and instrumental data has been used to produce a regional model for the geomagnetic field in europe for the last 3000 years from 1000 b c to 1900 a d connecting with the epoch covered by the igrf models this new model scha dif 3k constitutes an improvement with respect to the previous regional archeomagnetic model scha di 00 f which used relocated values and was only valid for the last 2000 years the new model has been obtained by least sums of absolute deviation inversion of paleomagnetic data using spherical cap harmonics for the spatial representation of the field and sliding windows in time an algorithm has been developed to jointly model the three archeomagnetic elements declination inclination and intensity the resulting model provides the direction and intensity of the earth s magnetic field over the european continent northern africa and western asia for the last 3000 years the fit to the european archeomagnetic database is more accurate than that provided by global archeomagnetic models in addition this model represents a step forward in archeomagnetic dating studies since the relocation error is avoided and can also be used to study the rapid changes of the geomagnetic field archeomagnetic jerks that have been recently proposed

dead delta s former productivity two trillion shells at the mouth of the colorado river the diversion of the colorado river by dams and irrigation projects started in the 1930s triggered the collapse of the colorado delta ecosystem paleontological ecological geochronological stable isotope field and satellite image data provide estimates of the delta s benthic productivity during the 1 k y directly preceding the artificial shutdown of the river at least 2 1012 shells of bivalve mollusks make up the current beaches and islands of the delta the 125 individual valves dated using 14c calibrated amino acid racemization indicate that these shells range in age from a d 950 to 1950 seasonal intrashell cycles in 180 values indicate that average sized bivalves lived at least 3 yr the most conservative calculation based on these numbers indicates that during the time of natural river flow an average standing population of 6 109 bivalve mollusks population density 50 m2 thrived on the delta in contrast the present abundance of shelly benthic macroinvertebrates is 94 lower 3 m2 in 1999 2000 the dramatic decrease in abundance testifies to the severe loss of benthic productivity resulting from diversion of the river s flow and the inadequacy of its partial resumption 1981 to present an integration of paleontological records with geomorphological geochemical and geochronological data can provide quantitative insights into human impact on coastal ecosystems

large geomagnetic field anomalies revealed in bronze to iron age archeomagnetic data from tel megiddo and tel hazor israel abstract geomagnetic field measurements from the past few centuries show heightened secular variation activity in the southern hemisphere associated with the south atlantic anomaly saa it is uncertain whether geomagnetic anomalies at a similar scale have existed in the past owing to limited coverage and uncertainties in the paleomagnetic database here we provide new evidence from archaeological sources in the levant suggesting a large positive northern hemisphere anomaly similar in magnitude to the saa during the 9th 8th centuries bce called levantine iron age anomaly we also report an additional geomagnetic spike in the 8th century the new dataset comprises 73 high precision paleointensity estimates from ca 3000 bce to 732 bce and five directional measurements between the 14th and the 9th centuries bce well dated pottery and cooking ovens were collected from twenty archaeological strata in two large contemporaneous stratigraphical mounds tells in israel tel megiddo and tel hazor the new data are combined with previously published data and interpreted automatically using the pmagpy thellier gui program the tel megiddo and tel hazor data sets demonstrate excellent internal consistency and remarkable agreement with published data from mesopotamia syria the data illustrate the evolution of an extreme geomagnetic high that culminated in at least two spikes between the 11th and the 8th centuries bce iron age in the levant the paleomagnetic directional data of the 9th century bce show positive inclination anomalies and deviations of up to 22 from the averaged geocentric axial dipole gad direction from comparison of the levantine archaeomagnetic data with igrf model for 2015 we infer the levantine iron age anomaly between the 10th and the 8th centuries bce is a local positive anomaly the eastward extent of the anomaly is currently unknown

new archeointensity data from french early medieval pottery production 6th 10th century ad tracing 1500 years of geomagnetic field intensity variations in western europe nineteen new archeointensity results were obtained from the analysis of groups of french pottery fragments dated to the early middle ages 6th to 10th centuries ad they are from several medieval ceramic production sites excavated mainly in saran central france and their precise dating was established based on typo chronological characteristics intensity measurements were performed using the triaxe protocol which takes into account the effects on the intensity determinations of both thermoremanent magnetization anisotropy and cooling rate intensity analyses were also carried out on modern pottery produced at saran during an experimental firing the results show very good agreement with the geomagnetic field intensity directly measured inside and around the kiln thus reasserting the reliability of the triaxe protocol and the relevance of the quality criteria used they further demonstrate the potential of the saran pottery production for archeomagnetism the new archeointensity results allow a precise and coherent description of the geomagnetic field intensity variations in western europe during the early medieval period which was until now poorly documented they show a significant increase in intensity during the 6th century ad high intensity values from the 7th to the 9th century with a minimum of small amplitude at the transition between the 7th and the 8th centuries and finally an important decrease until the beginning of the 11th century together with published intensity results available within a radius of 700 km around paris the new data were used to compute a master curve of the western european geomagnetic intensity variations over the past 1500 years this curve clearly exhibits five intensity maxima at the transition between the 6th and 7th century ad at the middle of the 9th century during the 12th century in the second part of the 14th century and at the very beginning of the 17th century ad some of these peaks are smoothed or nearly absent when the selection of the data is extended to a 1250 km radius around paris the apparent regularity in the occurrence of intensity maxima with a recurrence of 250 years is particularly intriguing and might reflect a new characteristic of the secular variation at least in western europe it clearly requires further investigation and in particular the acquisition of new data from older periods

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

secular variation of the intensity of the geomagnetic field in mexico during the first millennium bce in western eurasia the first millennium bce is characterized by the fastest secular variation of the earth magnetic field observed over the last millennia and by a geomagnetic anomaly centered on the middle east on the global scale the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas here we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 bce and 200 ce from chalcatzingo archaeological site in central mexico archaeointensities were determined using the classical thellier thellier protocol with corrections for trm anisotropy and cooling rate effects our work doubles the number of high quality archaeointensity data in mexico during the considered period using a bayesian approach a new secular variation curve was calculated at mexico city between 1500 bce and 200 ce after selection of mexican archaeointensity data after a period of oscillations of the intensity between 20 and 40 t from 1500 to 300 bce the curve shows a large maximum 65 t in the second century bce the corresponding vadm varied between 4 0 and 11 0 1022 am2 which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought however this amplitude variation may be overestimated as it does not take into account the fast directional variation observed at this time

late quaternary secular variation data from mexican volcanoes abstract we present 32 new paleomagnetic directions and 21 absolute paleomagnetic intensities pi from 33 volcanoes sampled at 66 sites and covering the last 46 ka of these 29 were radiocarbon dated 3 by thermo luminescence and one is of historical age ad 1793 rock magnetic experiments show that the dominant minerals are magnetite and titanomagnetite of low to intermediate titanium content and of pseudo single domain size paleodirections were determined using stepwise demagnetization protocols and pi by the izzi or thellier coe protocols and strict selection criteria were applied to ensure the reliability of the data previously published data were evaluated to fulfill similar quality criteria as our data resulting in 65 directional data point 18 paleointensity entries from lavas 59 archeointensities are found to be acceptable all accepted data come from a region within an 860 km radius around mexico city paleosecular variation psv curves of the past geomagnetic full vector were established by using the bootstrap resampling algorithm combined with cubic p splines for smoothing and interpolation because of the uneven time distribution of the data this was done for two successive periods between ad 2000 1600 bc and 1600 bc 44000 bc the full vector psv curves are unique for the american continents because of their temporal extension end because they include both directions and absolute pi the recent psv curves the last 3600 years are of high resolutions which certainly have implication for both regional and global geomagnetic field models fast psv change centered around ad 700 and ad 900 separated by a period of much slower psv were observed and rapid pi changes were found around 400 bc and ad 1000 in the period between 1600 bc and 44000 bc psv curves are well defined only within some periods and otherwise only define general psv trends several intensity peaks with values up to 65 t vadm 15 1022 am2 were observed around 250 bc 12000 bc 15000 bc and 27000 bc and intensity lows around ad 700 1200 bc 24000 17000 bc and 34000 bc abnormal directions were found around 26000 bc with negative inclinations down to about 30 which may be related to the mono lake or rockall event a comparison with other psv curves is complicated by the large distance to europe and the hawaiian islands with longitude differences of 99 and 57 respectively lake sediment data from southern texas show more differences than agreements suggesting that either of the data may be affected by systematic errors

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

archaeomagnetic dating of archaeological sites from switzerland and bulgaria baked materials from three archaeological sites in switzerland and one in bulgaria have been examined and dated archaeomagnetically the detailed rock magnetic properties of the burnt clay collected have already been studied therefore and have been published elsewhere geophysical journal international 153 2003 146 the main aim of this paper is to determine the terminus ante quem for the last firing of the clay collected from pottery kilns or burnt layers the directional and intensity results of the ancient geomagnetic field corresponding to the time of the structure s last firing are given for each site these geomagnetic parameters are then compared with reference curves to provide archaeomagnetic dates for the last use of the kilns application of archaeomagnetism as a dating tool is only possible for those regions that already have reference curves bulgaria is fortunate in having established reference curves covering almost the last 8000 years two swiss sites were dated using only directional results on the basis of existing palaeodirectional results for switzerland as well as the french directional reference curves the archaeomagnetic dates of three of the sites were then compared to archaeological evidence and available radiocarbon dates the palaeointensity data obtained from this study will enrich the existing archaeomagnetic database for western europe

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

extreme geomagnetic field variability indicated by eastern mediterranean full vector archaeomagnetic records the magnetic field of the earth can exhibit considerable variations at short time scales even as short as decades the archaeomagnetic studies of middle eastern artefacts mainly from israel and jordan show evidence for an exceptionally high intensity period from 1050 700 bc which displays two distinct spikes over the levant the levantine iron age anomaly liaa its exact duration and geographical extent are still poorly known despite the wealth of ancient settlements the extensive cultural heritage and a long history of trade and immigration the archaeomagnetism of turkey and cyprus remains largely unexplored this study presents a large data set of ancient directions and intensities from seven archaeological sites in the eastern mediterranean covering a time span of 2000 yrs the recorded directions from thirteen sets of samples are coherent with our earlier findings yet show significantly larger swings than existing field models in particular we confirm the very large swing in inclination we found earlier from 1910 1850 bc that is also captured by the greek psv curve and shallower by more than 10 than predicted by existing field models consequently these models require substantial revision in this region we were able to determine the archaeointensity from five sets of mud bricks from the thirteen attempted allowing us to provide the full field vector furthermore we present thirty one new archaeointensity results from potsherds and mud bricks that considerably enhance existing data especially when a set of strict selection criteria is applied fourteen sets of potsherds from a single site tell atchana provide the longest sequence recorded so far in turkey from 2100 to 1350 bc we find exceptionally high intensities of 145 and 175 zam2 around 700 bc in well dated mud bricks and potsherds from two different locations tell tayinat and kilise tepe supporting extreme geomagnetic field variability in the region moreover these two high intensities confirm the younger spike of the liaa in turkey

paleoenvironments of the upper pennsylvanian ames limestone and associated rocks near pittsburgh pennsylvania paleoenvironmental analysis of the upper pennsylvanian ames limestone and associated rocks east of pittsburgh pennsylvania reveals a range of depositional environments from shallow marine to deltaic the depositional history began with paludal sedimentation followed by eastward transgression of a clastic lagoon dominated by abundant molluscs and mud lloater brachiopods especially thin shelled neochonetes this period was followed by the eastward transgression of a tidal belt and a shoreward low energy carbonate lagoon tidal belt sediments were derived from 1 shoreward transportation of offshore shelf sediments carbonate mud and fine sand fine crinoid debris and trilobites by tidal currents and 2 erosion and transportation of underlying clastic lagoon sediments molluscs neochonetes and clay minerals in tidal channels the carbonate lagoon contained abundant neochonetes in carbonate mud abandonment of the tidal belt allowed the eastward transgression of open circulation offshore shelf carbonate sediments the far offshore sediments were dominated by crinoids whereas near offshore shelf sediments had a sparse fauna of crurithyris and crinoids in the final stage of deposition deltaic progradation from the east established the following offshore to onshore sequence of environments offshore carbonate shelf near shore clay miner shelf prodelta and delta front nearshore clay mineral shelf deposits were dominated by crurithyris a robust thick shelled brachiopod indicative of higher energy conditions than were existent for the thin shelled neochonetes

unbiased analysis of geomagnetic data sets and comparison of historical data with paleomagnetic and archeomagnetic records reconstructions of the past geomagnetic field provide fundamental constraints for understanding the dynamics of the earth s interior as well as serving as basis for magnetostratigraphic and archeomagnetic dating tools such reconstructions when extending over epochs that precede the advent of instrumental measurements rely exclusively on magnetic records from archeological artifacts and farther in the past from rocks and sediments the most critical component of such indirect records is field intensity because of possible biases introduced by material properties and by laboratory protocols which do not reproduce exactly the original field recording conditions large biases are usually avoided by the use of appropriate checking procedures however smaller ones can remain undetected in individual studies and might significantly affect field reconstructions we introduce a new general approach for analyzing geomagnetic databases in order to investigate the reliability of indirect records this approach is based on the comparison of historical records with archeomagnetic and volcanic data considering temporal and spatial mismatches with adequate weighting functions and error estimation a good overall agreement is found between indirect records and historical measurements while for several subsets systematic bias is detected e g inclination shallowing of lava records we also demonstrate that simple approaches to analyzing highly inhomogeneous and internally correlated paleomagnetic datasets can lead to incorrect conclusions about the efficiency of quality checks and corrections consistent criteria for selecting and weighting data are presented in this review and can be used to improve current geomagnetic field modeling techniques

insights on the geomagnetic secular variation in the eastern mediterranean first directional data from cyprus abstract the first directional archaeomagnetic results from cyprus are presented based on the study of seven baked clay structures excavated at the copper smelting site of agia varvara almyras situated some 20 km south of nicosia this ancient copper working site represents a unique example of complete primary production of the copper metal in cyprus in total five furnaces one ore roasting pit and an oven were sampled in situ for an archaeomagnetic investigation all the studied structures are well dated based on pottery finds and radiocarbon dates with ages ranging from 600 bce to 50 bce several rock magnetic experiments were performed to determine the main magnetic carrier and to investigate the thermal stability of the studied material the direction of the characteristic remanent magnetization chrm for each structure has been determined by demagnetization of 7 15 specimens in alternating magnetic fields up to 100 120 mt mean directions were calculated assuming a fisherian distribution and are well defined for five out of the seven structures studied the new directions are compared with the directional data and the secular variation curves available from the surrounding area and with the predictions of global geomagnetic field models they are an important contribution to improving our knowledge of the geomagnetic field variations in the eastern mediterranean and offer new insights about fast geomagnetic directional changes during the first millennium bce that were not previously identified by the available geomagnetic field models predictions in this area

analyzing trends in tropical devonian brachiopod communities during environmental change in the waterways formation of northern alberta abstract brachiopods serve as important sources of marine paleoecological data in the paleozoic in this regard an ecological framework for much of north america during the devonian is well established however the brachiopod communities of the western canada sedimentary basin wcsb are understudied brachiopod communities of the late givetian and early frasnian waterways formation of northern alberta were analyzed to identify associations between community species composition basin topography architecture and environmental conditions during the givetian frasnian this region experienced a transition in basin architecture from a ramp to a carbonate shelf setting this transition is associated with an increase in energy and decrease in siliciclastic input a total of 5144 brachiopod specimens from 44 samples were collected identified to species level and ordinated using nmds recurring communities were defined based on taxonomic similarity as indicated by groupings in the ordination brachiopod species can be separated into two distinct fauna along the first axis of the ordination this faunal change co occurs with the change in basin topography from ramp to shelf this finding in combination with the presence of taxa in other stratigraphically younger formations within the wcsb suggests that faunal differences in the waterways are a result of environmental factors as opposed to biogeographic or evolutionary trends through time the ramp fauna and shelf fauna can be further subdivided into five reoccurring communities in comparison to other north american devonian brachiopod communities communities of the ramp fauna are similar to those of iowa from the same time which is consistent with the proximity of the two basins and the fact that both basins are carbonate dominated however shelf communities in the waterways include a unique combination of taxa including abundant productidines

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

statistical testing for paleocommunity recurrence are similar fossil assemblages ever the same abstract observations of the recurrence of similar fossil assemblages through long intervals of geologic time punctuated by rapid changes in both the composition and structure of fossil assemblages has recently resulted in the concept of coordinated stasis to describe this pattern in the behavior of paleocommunities through time coordinated stasis may imply the existence of ecological mechanisms that actively maintain particular community structures and thus have a significant impact on the process of macroevolution however before such mechanisms can be invoked it must be shown that ecological stasis as observed in the fossil record is more significant than the persistence of similar community types due to the repeated reinvasion of recurring habitats from a persistent species pool the null hypothesis for paleocommunity recurrence analysis of the relationship between communities and paleocommunities and an expansion of the ecological hierarchy at the community paleocommunity level allows the creation of a rigorous definition of the entities composing the local paleocommunity the samples collected within a stratigraphic horizon at a single locality paleocommunity groups of samples shown to be statistically identical and paleocommunity type groups of samples that are similar but can be shown to be statistically different these definitions permit the development of the null model for paleocommunity recurrence and establish a base level of variability within a local paleocommunity that permits rigorous statistical comparisons to be made between paleoecological samples at larger temporal and geographic scales paleoecological samples from four marine tongues in the middle pennsylvanian breathitt formation are used to analyze species abundance variability at several spatial and temporal scales and to test for paleocommunity recurrence although recurrence of statistically identical local paleocommunities occurs at single localities and between localities within individual marine units it is usually not detectable between marine tongues suggesting that paleocommunity recurrence in the marine strata of the breathitt formation is the recurrence of paleocommunity types and does not falsify the null hypothesis

geomagnetic field variations in western europe from 1500 bc to 200 ad part ii new intensity secular variation curve abstract in order to extend the secular variation curve svc of archaeointensity in western europe to the first millennium bc we studied 24 kilns and hearths in place two displaced hearths and six sets of pottery sherds from french archaeological sites archaeological artefacts radiocarbon and dendrochronology dated the acquisition of the thermoremanent magnetization trm carried by the studied objects rock magnetism experiments suggest that the main carrier of the magnetization is a ti poor titanomagnetite archaeointensity was determined by the thellier thellier classical protocol with ptrm checks a strict criteria set was applied to select only the most reliable results with linear nrm trm diagrams 55 of total specimens this study demonstrates that pottery sherds with two trms give reliable archaeointensities in the low temperature interval if the nrm trm diagram is adequately adjusted eighteen new mean archaeointensities 14 corrected from the anisotropy of trm and 16 from cooling rate were computed the comparison with previously published western europe paleointensities show a strong dispersion between data primarily due to their variable quality western europe data were weighted following the archaeointensity protocol the number of specimens per site and the type of studied materials in order to better highlight the secular variation of archaeointensity during the first millennium bc the svc built with sliding windows of 160 years shifted every 50 years presents at paris a maximum of 90 t around 800 bc and a minimum of 60 t around 250 bc these archaeointensity maximum and minimum correspond to cusps of the geomagnetic field direction in western europe this new curve is consistent with mesopotamian and eastern europe data the archaeointensity secular variation in western europe predicted by global geomagnetic models cals3k 4 arch3k 1 and arch3k cst 1 is smoother than our svc we used our directional dataset herve et al 2013 to build a new western europe vgps and vdms mean curves comparison with the predictions given by the global models points out a possible persistent non dipole fields effect over europe between 1000 bc and 600 500 bc finally we note that the strong variations of intensity of the geomagnetic field with a mean decrease rate per century close to 6 t will be useful for archaeomagnetic dating purposes

contribution of stratigraphic constraints of bulgarian prehistoric multilevel tells and a comparison with archaeomagnetic observations abstract the general aim of archaeomagnetism is to recover the behavior of the ancient geomagnetic field for a given territory using archaeological baked clay structures that have been well dated by other independent methods the sofia palaeomagnetic laboratory possesses a large data set for the three characteristic geomagnetic field parameters obtained from one and the same material and covering the last 8000 years the database accumulated by the authors has been updated several times and the greatest difficulty arose for the prehistoric collections most of which had no radiocarbon or other chronometric dates thus as well as methodological archaeomagnetism problems the main difficulty concerning the construction of reference curves of the variation of the geomagnetic field is related to the distribution of the experimental results over the absolute time scale this paper examines the similarity between the archaeomagnetic profiles obtained on multilevel tells from the same prehistoric epochs it would seem that when 14 c dates for multilayer tells are missing the comparison of such archaeomagnetic stratigraphic profiles with the corresponding chrono stratigraphic reference profile for the same epoch can be useful in verifying their assumed chronology however the described peculiarities connected with the multilevel sites results still show some difficulties for the overall estimation of geomagnetic field variations for a given territory

environmental controls on shallow subtidal molluscan death assemblages on san salvador island the bahamas abstract ecological studies that span multiple marine depositional environments frequently find that benthic invertebrate assemblages are correlated primarily with an onshore offshore gradient variability within the same depositional environment is inferred to not result from water depth differences but other parameters such as substrate consistency and shear stress modern studies focusing on assemblage variations within the same depositional environment can identify which variables affecting assemblage compositions are independent of water depth this study examines the environmental controls on the composition of molluscan death assemblages from the shallow subtidal environments of san salvador island molluscan assemblages were tabulated from twenty nine bulk samples collected from four locations around san salvador island representing seagrass meadows open sandflats and patch reef systems common in the shallow subtidal in addition quantitative environmental data for each sample was characterized including seagrass density water depth temperature ph dissolved oxygen and grain size as well as qualitative observations of wave energy and bioturbation cluster analysis and canonical correspondence analysis cca were performed to identify environmental gradients associated with molluscan assemblage composition cluster analysis and cca axis 1 identify seagrass coverage and substrate consistency as the primary environmental variables describing molluscan death assemblage compositions cca axis 2 identifies wave energy bioturbation and dissolved oxygen as the secondary environmental variables though the small range of dissolved oxygen values 17 21 mg l collected using single instantaneous measurements make it unclear whether the oxygen gradient is ecologically significant for our time averaged assemblages our analysis demonstrates the variability of assemblages within a single depositional environment as well as the utility of fine resolution studies for identifying secondary environmental variables that control the composition of marine invertebrate assemblages

factors determining magnetic enhancement of burnt clay from archaeological sites abstract the magnetic susceptibility of a collection of 212 archaeological samples of burnt clay of different origin burnt soil ovens and bricks taken from 60 archaeological sites from bulgaria were studied in order to determine factors which may have affected their magnetic enhancement the highest magentic susceptibility values were obtained for bricks and the lowest for burnt soils suggesting that the firing temperature and the duration of burning are important conditions for determining magnetic enhancement specific spatial pattern of the low field magnetic susceptibility was also observed characterized by separation of sites situated in northern and southern parts of the country divided by the west east trending mountain chain stara planina maximum susceptibility values are obtained for burnt soils in southern bulgaria and minima in northern bulgaria in contrast burnt clay plasters and bricks show the opposite picture it is supposed that the observed pattern is due to differences in the outcropped geological formations and variable climate conditions between the two regions which determine different iron supply during burning of initial clay material results from the thermomagnetic analyses show that the dominant ferrimagnetic mineral in all burnt clay materials studied is magnetite titanomagnetite with low ti content and different grain sizes high values of frequency dependent magnetic susceptibility indicate the presence of significant amount of fine grained d

identifying hierarchical spatial patterns within paleocommunities an example from the upper pennsylvanian ames limestone of the appalachian basin abstract identifying ecological mechanisms that produce hierarchically arrayed spatial variation in community structure can be difficult in the fossil record due to conflation of spatial and temporal patterns however this difficulty can be mediated by minimizing the temporal duration of deposition within the unit examined in this study the fauna of the upper pennsylvanian ames limestone conemaugh group was analyzed to explore whether ames paleocommunities exhibited hierarchical structure in a spatial dimension this widespread carbonate unit was deposited during the maximum flooding interval of a glacio eustatically influenced fifth order sea level cycle and preserved taxa are contemporaneous within only a few thousand years paleocommunity structure and variability was assessed at multiple spatial scales using samples collected from seven outcrops of the ames limestone throughout southeastern ohio which form a northeast to southwest trending transect parallel to the paleoshoreline abundance data were collected using quadrat sampling for brachiopods bivalves gastropods bryozoa corals crinoids echinoids trilobites and foraminifera paleocommunity structure was analyzed via cluster ordination guild and abundance analyses at multiple spatial scales within a single locality among localities and within the total study area to provide insight on geographic partitioning of paleocommunity variation multiple levels of paleocommunity organization were recovered within the ames fauna all levels exhibited spatial partitioning but the inferred proximate controls shifted from abiotic environmental controls at higher hierarchical levels to biotic controls at the lowest level at the highest level differentiation into a northern and southern regional paleocommunity was controlled primarily by substrate consistency and habitat heterogeneity related to variation in fluvial input within the basin local paleocommunity differentiation reflects biotic responses to topographic and environmental conditions that were geographically distributed within the region whereas within outcrop variation was due largely to biotic feedback mechanisms

the earth s magnetic field in italy during the neolithic period new data from the early neolithic site of portonovo marche italy we present new full geomagnetic field vector results from three neolithic ovens discovered at the archaeological site of portonovo marche italy the discovered structures are a rare example of very well preserved underground ovens from the early neolithic period standard thermal demagnetization procedures were used to isolate the direction of the characteristic remanent magnetization acquired by the baked clay during the ovens last firing the corresponding archaeointensities were determined by the multi specimen procedure msp dsc and show a clear intensity low during the neolithic period both directional and intensity results are of high quality offering the first contribution of full geomagnetic field vector data for this period in italy the new data are compared with other contemporaneous data from europe and with global geomagnetic field models independent archaeomagnetic dating of the three ovens was also performed by means of the scha dif 14k model the obtained results are in excellent agreement with available radiocarbon dates and confirm that all ovens belong to the neolithic these new data importantly enrich our knowledge of the geomagnetic field during the neolithic period that is poorly documented by data not only in italy but also in the whole of europe and show that archaeomagnetic dating can provide precise results even for prehistoric periods

vertical zonal propagation of a stationary planetary wave packet abstract in order to explain why the aleutian high stands out in the winter stratosphere a complex fourier analysis is made of simulated and observed stationary waves it is found that in the troposphere the envelope of the time mean geopotential height consisting of wavenumbers 1 3 attains its major and minor maxima in the pacific and atlantic respectively the major maximum is dominated by wavenumbers 1 2 and shifts eastward with height in the stratosphere in the approximate direction of the group velocity and strengthens the aleutian high the minor maximum is dominated by wavenumber 3 and is confined in the troposphere

rapid geomagnetic field intensity variations in the near east during the 6th millennium bc new archeointensity data from halafian site yarim tepe ii northern iraq abstract we present new archeointensity results from a series of groups of pottery fragments that were collected from the multi layered archeological site yarim tepe ii in northern iraq northern mesopotamia dated to the 6th millennium bc this site comprises a 7 m thick sequence of archeological deposits encompassing the middle halaf late halaf and the halaf ubaid transitional hut between 5750 and 5000 bc according to the chronology currently considered for the halafian archeological period three new radiocarbon dates obtained from bone fragments confirm that yarim tepe ii was likely not occupied before the middle halaf as was independently established from archeological constraints archeointensity determinations were carried out using the protocol developed for the triaxe magnetometer this procedure takes into account thermoremanent magnetization anisotropy and cooling rate effects 114 fragments fulfilled our set of archeointensity selection criteria with intensity data obtained from at least two but most often three specimens per fragment mean archeointensity values were estimated for 23 groups of fragments well distributed across the entire stratigraphic sequence from the averaging of the data obtained from a minimum of three fragments per group these values were dated using a bootstrap procedure relying on the stratigraphic position of the different groups of fragments and on the different age constraints available inside the yarim tepe ii sequence the new data show a significant decrease in geomagnetic field intensity by 12 t between the middle halaf and the late halaf hut time interval this decrease was accompanied by a short intensity peak which may have lasted only a few decades around the middle halaf late halaf boundary at 5500 bc this evolution is quite similar to that observed from syrian and bulgarian archeointensity data even though the precise duration of the intensity peak is presently questionable the bulgarian data set further suggests that the intensity secular variation in the near east and in eastern europe during the 6th millennium bc was in fact principally punctuated by two successive short lasting intensity peaks the first around 5800 bc and the second around 5500 bc the scarcity of the intensity data available worldwide however prevents us constraining the geomagnetic dipole or non dipole origin of these features the variation rates associated with the rapid intensity fluctuations observed in yarim tepe ii are of 0 15 0 25 t yr this range of values appears similar to that of rapid intensity variations that sporadically occurred in more recent times such as in western europe around 700 bc and 1000 ad in contrast it is lower than the variation rates that were proposed for geomagnetic spikes our results also have interesting implications on halafian archeology in particular they suggest that the late halaf hut boundary was older by one century than previously considered

tropospheric impact of reflected planetary waves from the stratosphere 1 a reflection of stratospheric planetary waves and its impact on the troposphere during a stratospheric sudden warming of march 2007 are investigated zonal propagation and reflection of the planetary waves is clearly seen in the longitude height sections of the eddy geopotential height and the vertical and zonal component of the three dimensional wave activity flux a wave packet propagating upward and eastward from eurasian continent was reflected by a negative wind shear in the upper stratospheric westerly jet caused by stratospheric warming waves then propagated downward to the american atlantic sector of the troposphere which led to the formation of a deep trough over the atlantic and brought cold weather to the northeastern part of the american continent

determination of domain structure in igneous rocks by alternating field and other methods abstract af alternating field demagnetization arm anhysteretic remanent magnetization and strong field hysteresis properties of a large collection of mostly continental igneous rocks are reported here the collection included rocks whose magnetic carriers were believed from previous work to be of one of three types md multidomain sd psd single domain pseudo single domain or a bimodal mixture of md grains e g discrete opaques and sd psd material e g silicate inclusions two series of subaerial basalts with a full range of deuteric oxidation classes included examples of all three classes of behaviour sd psd rocks have relatively hard inflected af decay curves decay rate initially increasing then decreasing md rocks have soft exponential like decay curves and bimodal rocks have a combination of these characteristics relative hardnesses of normalized decay curves of remanences acquired in weak intermediate and strong fields the lowrie fuller test are also distinctively different for the three classes and the results support the theory developed in an accompanying paper 1 that lowrie fuller characteristics are an expression of the shapes of decay curves the lowrie fuller test although its result can be expressed as a numerical parameter is not capable of fine scale classification of domain structure or grain size the shape of the arm induction curve does have a quasi continuous variation with grain size however the parameter ar j rs initial anhysteretic susceptibility normalized to saturation remanence which is easily measured with standard paleomagnetic instrumentation is potentially useful for magnetic granulometry although ar itself was not diagnostic of grain size

new archeomagnetic secular variation data from central europe ii intensities abstract variations of the geomagnetic field during the past millennia can be obtained by investigating archeological material the spatial distribution of the available data across europe is rather uneven and only about 15 of the sites provide a full vector record of the geomagnetic field here we report 39 new reliable paleointensity data for sites from austria germany and switzerland with ages ranging between 1500 bce and 1900 ce for 31 of them directional information is available too paleointensities were determined with thellier type techniques with the multiple specimen domain state corrected paleointensity protocol or with both techniques corrections for anisotropy of thermoremanent magnetization were carried out for the structures showing small variations of only a few per cent in most cases cooling rate dependence was tested for 16 structures often strong alteration during the experiments was observed seven successful cooling rate corrections were applied which lowered the paleointensity values by about 10 values obtained from the multiple specimen technique are generally somewhat lower than those from the thellier experiments rock magnetic measurements revealed magnetite type minerals mostly in pseudo single domain range as main magnetic carrier but also high coercive mineral components like hematite or epsilon iron oxide are present the new data are mostly in good agreement with published paleointensities they support the presence of strong intensity variations around 800 ce and in the millennium bce the new full vector data reveal that the deep paleointensity minimum observed from german data around 850 bce is accompanied by large variations in direction with declinations up to 50

permian marine paleoecology and its implications for large scale decoupling of brachiopod and bivalve abundance and diversity during the lopingian late permian abstract the transition during the permian triassic interval from brachiopod rich benthic marine assemblages to communities with diverse molluscs has been well constrained by measures of global taxonomic richness but its ecological context has not been studied using quantitative relative abundance data new relative abundance data from early middle and late permian silicified fossil assemblages from offshore shelf carbonate environments indicate that molluscs increased significantly in relative abundance from 0 8 in the middle permian guadalupian to 65 4 in the late permian lopingian these numerical changes are accompanied by increases in the abundance of infaunal bivalves and motile gastropods in the late permian although this ecological change was coincident with the end guadalupian extinction a new global diversity compilation indicates that the overall genus level severity of that biotic crisis was substantially lower than previous estimates the pronounced ecological shift was instead concurrent with the onset of deep marine anoxic or euxinic conditions around the guadalupian lopingian boundary suggesting that increased environmental variability in proximity to the deep water mass may have given eurytopic molluscs a competitive advantage over more stenotopic brachiopods however the lack of global changes in relative genus richness implies dramatic decoupling of global taxonomic and local ecological processes the pronounced increase in molluscan abundance and alpha diversity in the silicified assemblages contrasts with their unchanged global taxonomic richness and may also have resulted from increased environmental stress in offshore shelf environments these results demonstrate that the ecological transition from the brachiopods to molluscs was more complex than inferred from global measures of taxonomic richness and imply that initial stages of permo triassic environmental deterioration may have been responsible for the decoupling of local ecological from global taxonomic processes during the dramatic late permian rise of the modern fauna

rock magnetic and archaeomagnetic investigations on archaeological artefacts from maharashtra india figure s1 irm acquisition curves reveal the presence of soft magnetic mineral saturated between 100 and 300 mt a few samples reveal a dominant high coercivity anti ferromagnetic signal whereas the remaining samples irm curves indicate the occurrence of a low coercivity mineral perhaps magnetite and or titano magnetite