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

geomagnetic intensity variation during the last 4000 years abstract thellier type determinations of the ancient geomagnetic intensity are reported for a large number of samples from greece comprising ancient pottery and other archaeologically dated forms of baked clay comparison is made with results for other parts of the world of about the same latitude the near east china and the western u s a these data indicate that in the time range studied variation of the geomagnetic dipole moment is unlikely to have been the dominant influence it is suggested that the westward drift of a non dipole disturbance could have been responsible

two thousand years of archeointensity from west africa this study presents 17 archeointensity estimates from senegal and mali two neighboring countries in west africa for the period 1000 bce to 1000 ce the archeological artifacts used in this study were collected during the course of two separate projects together spanning 22 years and across 8 separate excavations a primary objective of this study was to get accurate dates hence only samples with independent age constraints from pottery style detailed stratigraphy and 14c dates were used a total of 236 specimens from 63 samples were subjected to a double heating paleointensity experiment izzi method from which 95 specimens were selected using a set of very strict selection criteria the paleointensity results were corrected for differential cooling rate effects and remanence anisotropy additionally we demonstrate the equivalence of using tensors derived from anhysteretic and thermal remanences for correcting remanent anisotropy of the specimens and use the former for the anisotropy correction our data show good agreement with the most recent paleosecular variation model but are lower than the pre existing data which are mostly from egypt and morocco the presence of substantial non axial dipolar contributions in the region is evident when virtual axial dipole moments vadms from the published literature are calculated for 20 latitudinal bands and compared with our data the average vadm values show a distinct latitudinal gradient a prominent feature of this dataset is an intensity high observed prior to 700 ce in both senegal and mali comparing this peak with existing records from regions further to the north suggests a small but significant temporal offset and is interpreted to be additional evidence for a geomagnetic field with a significant and rapidly changing non axial dipolar contribution

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

archeointensity in northeast brazil over the past five centuries abstract this study presents the first archeointensity results from northeast brazil obtained from 14 groups of architectural brick fragments sampled in the city of salvador bahia state 13 s 38 5 w and dated between the middle of the xvith century and the beginning of the xixth century the dating is ascertained by historical documents complemented by archeological constraints yielding in all cases age uncertainties of less than 50 years analyses were carried out using two experimental protocols 1 the zero field in field version of the classical thellier and thellier method as proposed by coe tt zi including partial thermoremanent magnetization ptrm and ptrm tail checks and 2 the triaxe procedure involving continuous high temperature magnetization measurements both trm anisotropy and cooling rate effects were taken into account for the intensity determinations the cooling rate effect was further explored for the tt zi protocol using three increasing slow cooling times 5 h 10 h and 25 h between 450 c and room temperature following archeological constraints the slowest cooling time was retained in our study yielding decreases of the raw intensity values by 4 to 14 for each fragment a mean intensity was computed and retained only when the data obtained from all specimens between 2 and 6 satisfied a coherence test at 5 a total of 57 fragments 183 specimens was considered for the computations of site mean intensity values with derived standard deviations of less than 8 of the corresponding means when separately computed using the two experimental techniques the site mean intensity values always agree to within 5 a good consistency is observed between intensity values of similar or close ages which strengthen their reliability our data principally show a significant and continuous decrease in geomagnetic field intensity in northeast brazil between the first half of the xviith century and the xxth century one result dated to the second half of the xvith century further suggests that the geomagnetic field intensity reached a maximum around 1600 ad this evolution is in good agreement with that expected in the city of salvador from the available global geomagnetic field models however the accuracy of these models appears less well constrained between 1550 ad and 1650 ad

pollen and non pollen palynomorph analyses of upper holocene sediments from dianshan yangtze coastal lowlands china hydrology vegetation history and human activity abstract the coastal deltaic plain of the yangtze river between taihu lake tai and shanghai in eastern china has been the scene of human settlement and agriculture since the early neolithic becoming increasingly intensive in the upper holocene when delta accretion and the establishment of a stable hydrological regime of freshwater lakes and wetlands allowed the development of extensive agriculture and complex society in late prehistoric and dynastic times during this period the area was significantly affected by changes in sea level climate and vegetation resulting in a dynamic and complex environmental history however little research has concentrated on environmental change and human impacts during the last few millennia this study focuses on this late period presenting the results of integrated sedimentary microfossil and radiocarbon analyses from a core near the eastern margin of lake dianshan to the east of taihu after the withdrawal of intertidal conditions and the conversion to freshwater lake at the core site about 2600 cal yr bp pollen and algal spore data show that increased sedimentation gradually reduced freshwater depth until a surface peat formed ca 1500 cal yr bp this also dates the start of a switch in woodlands from sub tropical and warm temperate trees to a mainly cool temperate and coniferous tree flora under climatic cooling and human impact after this time water depths at the site increased greatly partly due to climate change and flooding but also because of the establishment of deepwater paddy agriculture microcharcoal and pollen data show that a major episode of human impact using fire with deforestation and rice cultivation occurred between ca 1500 and 1200 cal yr bp these dates suggest it is one of the latest examples of flooded field paddy cultivation before more intensive agricultural techniques were adopted in the area after ca 800 cal yr bp

the time dependence of intense archeomagnetic flux patches 1 the long term temporal behavior of intense geomagnetic flux patches at the core mantle boundary and the relation with lower mantle lateral heterogeneity are under debate we apply an algorithm to detect centers of intense flux patches and track their time evolution in a recent archeomagnetic field model in order to study the kinematics of such intense magnetic flux patches on millennial timescale we find that most intense flux patches appear near the edge of the tangent cylinder quasi stationary periods with small oscillations of patches occur more than drifts detailed comparison of the archeomagnetic patches behavior with that seen in numerical dynamos with tomographic heat flux boundary conditions suggests that core mantle thermal coupling could be the cause of a statistical preference for some longitudes on the long term which does not exclude significant time spent away from the preferred longitudes this could explain the roughly coincident locations of high latitude patches in the historical geomagnetic field with that of the time average paleomagnetic field together with the much weaker patches intensity in the latter alternating eastward and westward drifts are also observed the drifts are more westward than eastward especially in the southern hemisphere indicating that the time average zonal core flow may also be driven by core mantle thermal coupling an average patch lifetime of 300 years is found which we hypothesize may indicate the vortex lifetime in the outer core

deltas radiocarbon dating and measurements of sediment storage and subsidence in holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling the nile and ganges brahmaputra deltas show remarkably similar radiocarbon age depth relationships 1 most radiocarbon dates by conventional and accelerator mass spectrometric ams analyses are older some by 4000 yr than reasonably expected 2 dates are commonly inverted i e older upcore and 3 sample dates at delta surfaces commonly exceed 2000 yr b p these anomalous age depth phenomena are in part a response to reservoir effects introduction of old carbon and emphasized herein influence of sediment storage and remobilization that prevail in fluvial and delta plains in fluvial systems sediment generally is not transported in a single episode from its original source area to the sea rather material transported from upland reaches and river valley to coast is subject to a repeated series of depositional burial and erosional events induced by episodic flooding overbank sedimentation and channel migration because sediment is likely to be temporarily stored in the delta plain it is difficult to determine the time of a sediment9s final deposition and burial at a delta site a successful strategy requires use of several independent dating methods including ams analyses of in situ basal peats and fossils and where possible archaeological evaluation of associated artifacts that are in place accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence information to help implement effective coastal protection measures

multi proxy evidence for late holocene anthropogenic environmental changes at bongpo marsh on the east coast of korea we present a multi proxy record pollen microscopic charcoal magnetic susceptibility carbon isotopic composition total organic carbon toc carbon nitrogen c n ratios and particle size of the late holocene environmental change and human activities from bongpo marsh on the east coast of korea mutual interaction between the environment and humans during the late holocene has not been properly investigated in korea due to the lack of undisturbed samples with high sedimentation rates in this study the history of human responses to late holocene environmental changes is clearly reconstructed using a multi proxy paleoenvironmental approach that has not previously been applied in korea the evidence from bongpo marsh indicates that 1 bongpo marsh began to develop ca 650 bc as a coastal lagoon was rapidly filled with organic matter 2 agricultural disturbance around the study site remained slight until ca ad 600 3 full scale intensive agriculture prevailed and the area of deforestation increased between ca ad 600 and ca ad 1870 and 4 the land use changed from lowland rice agriculture to upland cultivation when agricultural productivity declined after ad 1870 probably due to severe deforestation and the consequent heavy influx of clastic sediment on rice fields as described in various historical documents

neolithic settlement distributions as a function of sea level controlled topography in the yangtze delta china combined geological and archaeological data sets indicate that sea level controlled topography best explains the timing of neolithic settlement onto the southern yangtze delta plain almost 1500 yr later than inland china information on settlement patterns of the three major neolithic cultures ma jia bang song ze liang zhu dated from ca 5500 to 2200 b c is provided by petrologic study of habitat bases of sites and of sediment cores recovered near the sites in the early holocene rising sea level induced decreased relief and an aggrading silt mantle on the low lying delta surface changes of sea level and climate from early to mid holocene initiated a fertile delta plain at ca 6000 5500 b c and settlement and cultivation including rice began within only 500 yr of delta formation rate of sea level rise decelerated by mid holocene time resulting in rising ground water level and poor drainage and a reduced delta plain area suitable for human occupation and agriculture as a consequence neolithic settlements shifted progressively eastward toward higher more restricted areas of the yangtze delta chenier plain

agriculture and environmental change at qingpu yangtze delta region china a biomarker stable isotope and palynological approach rice oryza sp agriculture sustains vast numbers of people and despite great advancements made in recent years questions about its origins and spread throughout asia remain unanswered this study uses sedimentary biomarker stable carbon isotope and palynological analyses to investigate early rice agriculture in the yangtze delta a region where rice agriculture emerged at least 7000 years ago accelerator mass spectrometer ams 14c dating reveals the age of sedimentary section to be between c 6000 and 1800 cal bp widespread clearing of forest vegetation c 2400 cal bp is the earliest major human influence detected in the qingpu record following this rice agriculture probably dominated the qingpu area evidence supporting rice agriculture after c 2400 cal bp is provided by increased poaceae and cereal type taxa which occur with high concentrations of plant wax n alkanes with a dominant c3 plant origin c27 c31 with odd even preference 13c 29 8 to 36 3 also high concentrations of a

a holocene environmental record from the southern yangtze river delta eastern china abstract the holocene sedimentary record of core zx 1 recovered west of mid holocene chenier ridges on the monsoon controlled southern yangtze delta eastern china consists of lagoon salt marsh upper tidal flat and limnic facies reflecting low energy depositional environments holocene deposits mainly originated from the surrounding tai lake drainage basin the temporal variation of most geochemical element percentages corresponds with the climatic phases inferred from the pollen record i e the relatively low values of sio2 na2o cao and high values of al2o3 k2o mgo fe2o3 feo feo fe2o3 and tio2 generally concur with the warm and humid climate and vice versa three geochemical indices al2o3 na2o k2o na2o and cao k2o are found to be sensitive to past precipitation in the monsoon controlled southern yangtze river delta based on fine sediment analysis of core zx 1 the samples deposited under a dry climate with a mean annual precipitation map holocene climatic variation history is reconstructed for the southern yangtze delta from 8000 to 7000 yr bp regional climate demonstrated frequent fluctuations with warm and wet periods 8000 7700 7500 7200 yr bp alternating with cool and less humid periods 7700 7500 7200 7000 yr bp from 7000 to 6000 yr bp the climate was relatively warm and humid since then it had turned cool and dry climaxing in an intense cold event around 4000 yr bp after the cold event it became warm and humid until around 2500 yr bp

the effect of remanence anisotropy on paleointensity estimates a case study from the archean stillwater complex paleomagnetism of archean rocks potentially provides information about the early development of the earth and of the geodynamo precambrian layered intrusive rocks are good candidates for paleomagnetic studies such complexes are commonly relatively unaltered and may contain some single domain magnetite armored by silicate mineral grains however layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected here we examine the magnetic anisotropy of an anorthosite sample with a well developed magmatic foliation the effect of the sample s remanence fabric on paleointensity determinations is significant paleointensities estimated by the method of thellier and thellier range from 17 to 55 t for specimens magnetized in a field of 25 t we describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the stillwater complex mt usa of 32 t adjusted for the effects of slow cooling

a sediment based record of lateglacial and holocene environmental changes from guangfulin yangtze delta eastern china studies of the coastal sedimentary record have allowed both the reconstruction of relative sea level changes and the determination of local rates and magnitudes of tectonic deformation particularly in tectonically active areas despite their successful use elsewhere studies of this type are much less common for the mexican pacific coast which parallels the cocos north america subduction plate boundary stratigraphic geochemical and microfossil data from sediments in laguna mitla the pacific coast of guerrero mexico document late holocene sea level changes induced by tectonic activity in the mexican subduction zone three major events are identified first file formation of the lagoon by c 4630 yr bp as indicated by a freshwater to brackish peat second a relative sea level rise or land subsidence as indicated by a shift from a freshwater marginal lagoon environment to a marine setting preceded by a marine inundation represented by a sand unit possibly a tsunami deposit by c 3400 yr bp and finally a return to lagoonal conditions indicating a drop in relative sea level or coastal uplift by e 2300 yr bp the laguna mitla stratigraphy indicates general coastal subsidence or relative sea level rise of c 1 mm yr we argue that these relative sea level land level changes have been induced by tectonic activity associated with the mexican megathrust a plausible explanation for the 3400 yr bp marine inundation is probably a tsunami produced by a large seismic event accompanied by coastal subsidence discrete fining upward fine to coarse sand units with an erosional basal contact medium to poor sorting and clay mud rip up clasts all increase in na and sr elemental concentrations indicative of a marine origin and the landward extent of the sands support a tsunamigenic source for these deposits however these apparent tsunami deposits require further study to determine their lateral extent and to assess whether they call be correlated from one site to another this study demonstrates the applicability of a multiproxy sedimentary approach in interpreting relative sea level land level changes and to derive data on related earthquake and tsunami events in tropical coastal lagoons

quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the east china sea abstract paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the east china sea ecs undertaken in 1996 the geophysical data are correlated with a borehole situated on the outer shelf obtained by shanghai marine geology bureau indicating that six seismic units have been preserved since oxygen isotope stage 6 including four regressive transgressive cycles seismic units u2 u3 u4 u5 u6 and u7 are interpreted to correspond respectively to oxygen isotope stages 1 3 5 and 6 implying that sediment partitioning and sequence architecture in the ecs have been controlled by glacio eustasy and global climate changes alternating continental and marine strata corresponding to glaciation and interglaciation are well preserved on the outer shelf of the ecs most of the cold environment strata which formed on the outer shelf during oxygen isotope stages 2 and 4 are too thin to be recognized on sig 600j because of resolution but corresponding erosion surfaces exist seismic unit u7 is widespread over the shelf extending to the continental edge and showing little variation in thickness as the regression was pronounced and lasted a long time thus u7 can be used as a marker layer for correlation of quaternary strata on the shelf of the ecs post glacial transgression is obvious in the ecs marine strata with varied thickness were developed in the shallow sea of the inner shelf thinning toward the outer shelf the continental shelf of the ecs has been influenced by pacific tide wave systems for a long time forming tidal sand ridge sequences developed during transgressions corresponding to oxygen isotope stages 7 or 9 5 3 and 1

quaternary stratigraphy and trace element indices of the yangtze delta eastern china with special reference to marine transgressions the quaternary stratigraphy of the yangtze delta has been revealed by a deep 344 64 m continuous borehole the sediments of which are divided into four sections the early q1 middle q2 and late pleistocene q3 and the holocene q4 six lithofacies include lacustrine fluvial coastal drowned river channel deltaic and shallow marine in these time periods the fluvial and lacustrine lithofacies prevailed during q1and q2 coastal and drowned river channel lithofacies periodically appeared in q1 q2 and q3 shallow marine lithofacies dominated q3 and deltaic lithofacies occurred in q4 based on stratigraphy four transgressive events are inferred trace element sr ba b ga v content and ratios of sr ba and b ga are considered with regard to their distribution in the various lithofacies geochemical facies criteria are established based on combined diagnostic indices sr 160 ppm b 90 ppm sr ba 0 35 b ga 4 0 for the shallow marine lithofacies sr 90 ppm b 50 ppm sr ba 0 2 b ga 2 5 for the terrigenous lithofacies these indices correspond well to paleosalinity data obtained using the sedimentary phosphate method ca ca fe transgressive events identified by the geochemical indices are mostly the same as reflected by marine fossils nevertheless geochemical indices can indicate the occurrence of a weak transgression where marine fossils are rare

early mid holocene sea level change and coastal environmental response on the southern yangtze delta plain china implications for the rise of neolithic culture abstract we used a series of holocene sediment cores with ams 14c dated basal saltmarsh peat and supratidal sediment to reconstruct early mid holocene sea level change on the southern yangtze delta plain we also synthesized results for ca 150 late quaternary cores as well as archeological data to reveal the unique interplay between coastal evolution and neolithic cultural response relative sea level was ca 16 5 to 14 5 m from 8600 to 8500 cal bp and ca 6 to 4 m from 7400 to 7200 cal bp reflecting the rate of eustatic sea level rise but being ca 10 m higher possibly because of the effect of hydro istostasy three late pleistocene interfluve terraces t3 to t1 were revealed at burial depths of

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

re evaluation of greek archaeomagnitudes a new technique is used to determine the secular variation of the geomagnetic ancient field in athens the results indicate that published greek archaeomagnitudes were seriously affected by alteration it is shown that all intensities obtained using modifications of the thellier method may be affected by alteration and are therefore suspect

estimated solubility products and fields of stability for cryptomelane nsutite birnessite and lithiophorite based on natural lateritic weathering sequences

late quaternary evolution of the sub aqueous yangtze delta china sedimentation stratigraphy palynology and deformation abstract four sediment belts a d of the yangtze sub aqueous delta are defined from the sea bottom sediment distribution belt a delta front fine sand and silt with trough cross stratification belt b prodelta silty clay and clayey silt with abundant burrowing and rich in organic matter belt c prodelta to continental shelf sand silt clay with thin layers of sand and clay interbedded and belt d late pleistocene relict sands medium to fine grained mixed with shell fragments the late quaternary stratigraphy of the delta consists from bottom upward of late pleistocene terrigenous fluvial and lacustrine sand and mud holocene transgressive silt prodelta clay and delta front fine sand and silt in addition four pollen spore zones a d derived from these sediment sequences reveal a general trend of climate warming from early to late holocene the zone c distributed primarily within the prodelta muds provides evidence for a temperature maximum starting at ca 7000 years b p atlantic period this indicates that the delta initiation was essentially coeval with the climate optimum in early holocene sub bottom seismic surveys reveal three i iii acoustic facies facies i and ii are characterized by seaward remobilization of water saturated holocene prodelta muds facies iii is composed of highly contorted late pleistocene strata and mud diapirs that erupted from deep seated late pleistocene sediments in front of the estuarine depocenter gravity subsidence due to holocene sediment loading within the depocenter is the major factor in causing the deformation of underlying unconsolidated strata furthermore the sub aqueous yangtze delta proper is now obviously diverting to southeast owing to the long term tectonically induced southward shift of the river mouth and to the marine currents associated with the coriolis effect we thus predict that the large chongming island in river mouth area will have been coalesced with the northern yangtze coast in the recent future

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

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

holocene environmental change and its impacts on human settlement in the shanghai area east china abstract archaeological excavations and environmental archaeological studies over many years in the shanghai area have provided a wealth of information for holocene environmental changes growth and decline of human settlements and man land interaction distribution of archaeological sites between 7000 and 3000 cal yr bp indicates a regression process and a southward advance of the coastline in the study area temporal and spatial analyses of 14 c dates for archaeological sites shell ridges buried trees and peat suggest that holocene environmental changes may well have been a major cause of the rise and fall of human settlements and their civilization a relative sea level curve of the shanghai area was derived from dated shell ridges and peat and correlates well with the reconstructed sea level curves of the yangtze delta and east china the development of human settlements was interrupted at least four times in the shanghai area matching four periods of high sea level peat accumulation and increase in shell ridges after which neolithic communities moved onto the plain and reclaimed their lowlands for rice cultivation the chenier ridges played an important role in sheltering the neolithic settlers the collapse of liangzhu culture about 4000 cal yr bp was followed by the less developed maqiao culture these studies suggest that extreme environmental and hydrological conditions such as terrestrial inundation caused by sea level rise and heavy rainfall contributed to the cessation of paddy exploitation and to the social stress that led to the liangzhu culture demise

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

corrigendum for are systematic differences between thermal and microwave thellier type palaeointensity estimates a consequence of multidomain bias in the thermal results phys earth planet inter 180 2010 16 40

continuous global geomagnetic field models for the past 3000 years abstract several global geomagnetic field models exist for recent decades but due to limited data availability models for several centuries to millennia are rare we present a continuous spherical harmonic model for almost 3 millennia from 1000 b c to 1800 a d based on a dataset of directional archaeo and paleomagnetic data and axial dipole constraints the model named continuous archaeomagnetic and lake sediment geomagnetic model for the last 3k years cals3k 1 can be used to predict both the field and secular variation comparisons and tests with synthetic data lead to the conclusion that cals3k 1 gives a good general large scale representation of the geomagnetic field but lacks small scale structure due to the limited resolution of the sparse dataset in future applications the model can be used for comparisons with additional new data for that time span for better resolved regions the agreement of data with cals3k 1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world for poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data animations and additional snapshot plots of model predictions as well as the model coefficients and a fortran code to evaluate them for any time can be accessed under http www mahi ucsd edu cathy holocene holocene html the whole package is also stored in the earthref digital archive at http www earthref org

environmental change in the yangtze river delta since 12 000 years b p abstract a 52 m core from qidong at the tip of the yangtze river chang jiang delta provides a history of sea level change deltaic development and vegetational and climatic changes during the last 12 000 yr about 12 000 yr ago when sea level was about 60 m below the present level the coring site was situated in the innermost part of the exposed continental shelf the late pleistocene vegetation on the uplands of the lower yangtze river valley was a mixed forest of deciduous and broadleaved evergreen trees in which betula ulmus tsuga and cupressaceae were slightly more abundant than at present abies and picea were probably present as relict populations on mountains bordering the region rapidly rising sea level converted the qidong area to a coastal or estuarine environment between 11 000 and 10 800 yr b p leading to widespread development of wetlands dominated by gramineae and cyperaceae during the next 2500 yr coastal erosion due to marine transgression obliterated the sedimentary record deltaic sedimentation predominated from 8300 to 3800 yr b p as the yangtze river delta prograded by successively building a series of estuarine sand bars during the mid holocene the climate was slightly warmer and more humid than at present allowing the subtropical broadleaved evergreen trees to increase their populations pinus and quercus became more abundant after 3800 yr b p in response to climatic cooling the present deltaic plain in qidong formed less than 200 yr ago

widespread occurrence of a novel high coercivity thermally stable low unblocking temperature magnetic phase in heated archeological material 1 the widespread occurrence of a novel high coercivity magnetic phase in well heated archeological material is reported its properties are defined when it represents the dominant magnetic phase although it is nearly always found as part of a mixture of magnetic phases they are as follows very high coercivity remanence coercivity 600 mt low unblocking temperatures 200 c and high degree of thermal stability this last property distinguishing it from goethite the phase shows striking similarities to magnetic phases produced by thermal decomposition of nontronite an fe rich clay where decomposition occurs after prolonged heating in air to high temperatures conditions suffered by well heated archeomagnetic material preliminary results of mossbauer and x ray diffraction spectroscopy suggest that the phase is more likely to be a substituted hematite rather than fe cristobalite or a variant of fe2o3

holocene climate fluctuations in the yangtze delta of eastern china and the neolithic response six major pollen spore assemblage zones can be identified showing alternate warm and cool climate fluctuations on a millennial timescale the early holocene optimum at c 8000 7800 radiocarbon year

the secular variation of the geomagnetic field in egypt in the last 5000 years the palaeo intensities fa of the geomagnetic field in egypt at some ages are determined by archaeomagnetic measurements and found to be fa 36 2 t at 3100 b c fa 46 8 t at 3000 b c fa 36 5 t at 2780 b c 49 0 t at 2500 b c 36 4 t at 2200 b c 57 5 t at 1990 b c 62 1 t atca 1400 b c 61 5 t at 1400 b c 69 9 t at 600 b c 59 3 t at 550 b c 79 9 t at 460 b c 73 7 t at 450 b c 69 7 t at 320 b c 56 2 t at a d 50 64 9 t at a d 400 54 4 t at a d 300 57 5 t at a d 700 and 43 0 t at a d 1975

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

rising waters new geoarchaeological evidence of inundation and early agriculture from former settlement sites on the southern yangtze delta china new pollen phytolith charcoal and diatom data from 14c ams dated sediments from three clusters of former occupation sites on the southern yangtze delta liangzhu majiabang and chuodun reveal

a high resolution pollen record from east china reveals large climate variability near the northgrippian meghalayan boundary around 4200 years ago exerted societal influence abstract the large and rapid climate change event that occurred around 4200 years ago hereafter the 4 2 kyr event that marks the onset of the meghalayan stage is one of the most significant climatic anomalies in the holocene it may have exerted profound societal impact globally however its triggering mechanism remains uncertain here we present a high resolution well dated pollen record covering this interval from the tianluoshan archaeological site in east china our results show that the hydroclimatic conditions in the study area across this event strikingly resembled the regional expression of modern el nino southern oscillation enso and exhibited interdecadal enso like variability from ca 4 50 to 4 00 cal kyr bp also our pollen data indicate a marked shift toward an overall increased intensity and frequency of enso like climate variability from ca 4 50 to 4 30 cal kyr bp which was immediately followed by a decline of rice based agriculture providing direct evidence for the causal link between climate deterioration and the collapse of neolithic civilization in east china some 4200 years ago this observation is in accord with the enhanced enso variability reconstructed from proxy records in the tropical pacific ocean as enso is intimately coupled with the asian summer monsoon and the intertropical convergent zone itcz we suggest that the enhanced enso like climate variability may have triggered the 4 2 kyr event

high coercivity remanence in baked clay materials used in archeomagnetism a study of the high coercivity remanence in archeological baked clays has been carried out more than 150 specimens from 46 sites across europe have been analyzed selected on the basis of the presence of a fraction of their natural remanence that was resistant to alternating field demagnetization to 100 mt the study was based on the stability of isothermal remanence to alternating field and thermal demagnetization and its variation on cooling to liquid nitrogen temperature results indicate that the high coercivity remanence may be carried by magnetite hematite and in isolated cases partially oxidized magnetite and goethite in addition a high coercivity thermally stable low unblocking temperature phase has been identified the unblocking temperatures of both the isothermal remanence and the alternating field resistant natural remanence exhibit similar unblocking temperatures suggesting that the same phases carry both signals the high coercivity low unblocking temperature phase contributes to the natural remanence sometimes carrying a stable direction and behaving ideally during palaeointensity experiments and sometimes not an unambiguous mineralogical identification of this phase is lacking although likely candidates include hemoilmentite related to clay source lithology and substituted hematite or magnetic ferri cristabolite both possible products of thermal transformation of iron bearing clays

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

a unique middle pleistocene beech fagus rich deciduous broad leaved forest in the yangtze delta plain east china its climatic and stratigraphic implication abstract pollen analysis of middle pleistocene sediments from the yangtze delta plain provides a paleoecological reconstruction and has implications for stratigraphic correlation in east china the pollen assemblage is characterized by high values of fagus 16 8 on average which is unusual because fagus is generally present only sporadically in other lowland quaternary pollen records from the region in addition to fagus the assemblage has a rich diversity of broad leaved deciduous trees including quercus ulmus carpinus ostrya juglans betula and liquidambar as well as conifers including pinus picea abies larix and tsuga thus the pollen flora suggests a broad leaved deciduous forest mixed with abundant conifers which developed under cooler and more humid conditions than present the stable pollen sequence throughout the studied section suggests a stable environment beech forests also characterize the middle pleistocene of taiwan and japan and thus may be a stratigraphic indicator of the middle pleistocene in east asia the yangtze delta plain may have been an important refugium for the last survival of fagus in the lowlands