why are geomagnetic excursions not always recorded in sediments constraints from post depositional remanent magnetization lock in modelling abstract many geomagnetic excursions have been documented during the brunhes chron however high resolution paleomagnetic studies of sediments often provide evidence of few if any excursions we have investigated the reasons for this observation by modelling the post depositional remanent magnetization pdrm lock in process a cubic lock in function produces more rapid lock in compared to linear and exponential functions proposed in the literature we therefore used a cubic function to model best case scenarios for the quality of the paleomagnetic record when a high frequency geomagnetic input signal is convolved with the sediment lock in function for a wide range of sedimentation rates even for a lock in depth of 10 cm where 95 of the pdrm is locked in 5 cm below the surface mixed layer an input signal containing abundant excursions with 1 kyr duration is smoothed so drastically at low sedimentation rates 1 3 cm kyr that no excursions are recorded excursions are further attenuated by increasing the lock in depth as well as by sampling at discrete stratigraphic intervals the pdrm process acts as a low pass filter for high frequency secular variation signals even at moderate sedimentation rates 10 cm kyr we have also modelled the effects of modulation of sedimentation rate by a climatic forcing function e g insolation even though the average sedimentation rate might be substantial pdrm recording becomes much less reliable in intervals where sedimentation rates are lowest in these cases some excursions are reliably recorded in detail while others may not be recorded at all our modelling suggests that in order to consistently detect the presence of geomagnetic excursions it is ideal to work with sediments that maintain minimum sedimentation rates above 10 cm kyr if the normal spectrum of geomagnetic field behaviour contains abundant excursions failure to document excursions in many apparently high resolution analyses probably results from pdrm lock in within relatively slowly deposited sediments or to unrecognized intervals of slow sedimentation in environments with higher average sedimentation rates

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

enhancing weak magnetic fabrics using field impressed anisotropy application to the chinese loess summary the anisotropy of the low field magnetic susceptibility ams alternating field treated ams af ams and anisotropy of anhysteretic remanent magnetization aarm have been systematically examined for a sandwich sequence of loess palaeosols crossing the upper loess unit l2 marine oxygen isotope stage 6 mis6 to the last interglacial maximum palaeosol unit s1s3 mis5e from the yuanbao section northwestern china results show that a weak but detectable magnetic lineation is controlled by coarse grained aeolian fe3o4 magnetite because the long axes of the coarse grained magnetites are statistically parallel to the palaeowind directions the declination of the maximum susceptibility principal axis of ams can be used as an indicator of palaeowind direction in contrast fine grained pedogenic magnetic particles are responsible for the magnetic foliation we found that af ams can indicate the domain state of the magnetic particles which is consistent with potter stephenson s earlier model we also found that af demagnetization can significantly alter the ams in conclusion the angular dependence of af ams can enhance the weak ams fabrics

quaternary surface processes indicated by the magnetic fabric of undisturbed reworked and fine layered loess in hungary abstract statistical analytical methods were applied to classify the magnetic fabric of samples from different hungarian loess profiles a previous study of the anisotropy of magnetic susceptibility ams of hungarian loess suggested that typical wind blown or undisturbed and redeposited loess were well differentiated by known statistical methods the analyses of new samples require a review of previous results and the terms like typical wind blown reworked and redeposited loess the type of magnetic fabric of fine layered loess is classified by a new mathematical method in ams study of loess hierarchical cluster analysis the following quaternary surface processes were revealed by characteristics of the magnetic fabric of hungarian loess the primary magnetic fabric preserves the possible transport or accumulation direction of dust direction of maximum susceptibility ne sw axis and the structure of the fabric was affected by compaction in the case of loess the deviation of the inclination from vertical indicates the accumulation of dust on a sloping surface the secondary magnetic fabric fabric of the material after reworking or redeposition of loess shows the magnetic fabric characteristics of reworked or redeposited material scattered values of the principal susceptibilities indicate the effect of bioturbation redeposition fine layered loess samples is indicated by the alignment of the direction of maximum and intermediate susceptibilities on a stereographic plot and the degree of alignment possibly indicates the energy of the surface process lower or higher degree of energy connected to different kind of surface process can produce different kind of magnetic fabric the magnetic mineralogy of the pilot samples is determined by isothermal remanent magnetisation irm measurements no differences between loess samples with different sedimentary structure could be shown the dominant phase in the magnetic fabric that determined the magnetic character of samples was magnetite maghemite

magnetostratigraphy of chinese loess paleosol sequences abstract as one of the longest and most continuously deposited terrestrial sedimentary archives in the world chinese loess paleosol sequences record paleoclimatic and paleomagnetic variations at a range of time scales magnetostratigraphic studies provide a first order chronological framework for chinese loess sequences in this review we highlight recent developments in loess magnetostratigraphy including pedostratigraphy based on magnetic susceptibility variations we highlight progress in understanding the mechanisms by which the natural remanent magnetization nrm is acquired and discuss in detail the fidelity of paleomagnetic recording in loess records including the recording of magnetic polarity reversals excursions and relative paleointensity variations finally we discuss future prospects for studies of loess nrm

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

stratigraphic evidence for multiple holocene advances of lillooet glacier southern coast mountains british columbia holocene lateral moraines in the coast mountains of british columbia are commonly composed of multiple drift units related to several glacier advances in this paper we document lateral moraine stratigraphy at lillooet glacier in the southern coast mountains five tills separated by laterally extensive paleosols and layers of large woody debris were found in three cross sectional exposures through the northeast lateral moraine and two shallow gullies incised into its steep proximal face eighteen new radiocarbon ages constrain the timing of five separate advances of lillooet glacier 1 prior to 3000 14 c years bp 2 3000 14 c years bp 3 2500 14 c years bp 4 1700 to 1400 14 c years bp and 5 during the little ice age lia after 470 14 c years bp the lillooet glacier chronology is broadly synchronous with other glacier records from the coast mountains these records collectively demonstrate climate variability at higher frequencies during the late holocene than is apparent from many paleoecological reconstructions reconstructions of glacier fluctuations are often hampered by poor preservation of landforms that predate the extensive lia advances of the latest holocene our results highlight the potential of lateral moraine stratigraphy for reconstructing these earlier events

revisiting the stratigraphic position of the matuyama brunhes geomagnetic polarity boundary in chinese loess article i nfo it is commonly accepted that the climate records in chinese loess can be correlated well with that in marine sediments however discrepancies for the stratigraphic position of paleomagnetic polarity reversal boundary seriously restrict an accurate teleconnection between these two archives for example the exact stratigraphic position of the whole matuyama brunhes mb transitional polarity zone remains uncertain in chinese loess in this study an accurate transitional zone of the mb reversal from the mangshan profile southeast margin of the chinese loess plateau clp was statistically determined using multiple subsets of parallel samples by integrating results from the central clp the whole mb transitional zone is consistently located across the pedostratigraphic and climatostratigraphic transitional zones between s8 and l8 over a wide region of the clp this conclusion further supports that the paleosol unit s8 should be teleconnected to the marine oxygen isotope stage 19 rather than 21 and thus unambiguously supplies an accurate age control in constructing a new loess time scale

magnetic hysteresis parameters and day plot analysis to characterize diagenetic alteration in gas hydrate bearing sediments 1 the j meter coercivity spectrometer is a machine capable of rapid and simple measurement of magnetic hysteresis isothermal remanence acquisition and magnetic viscosity of rocks and sediments the j meter was used to study a suite of samples collected from strata in the gas hydrate bearing japex jnoc gsc mallik 5l 38 well 69 5 n 134 6 w in the mackenzie delta of the northwestern canadian arctic the day plot of magnetic hysteresis ratios for these samples is exotic in that the points do not plot along a hyperbola as is usually observed rather they plot as a scatter which is shown to contour into vertical slices using coercivity field hc or saturation magnetization js and horizontal slices using the relative quantity of superparamagnetism jspm js optical microscopy reveals that the magnetic minerals are detrital magnetite and authigenic greigite greigite is dominant in sands which in situ had 70 gas hydrate saturation and in silts in which gas hydrate growth was blocked by insufficient porosity we infer that the silts were the accumulation sites for solutes which had been excluded from the pore waters in neighboring coarser grained sediments during the course of gas hydrate formation consequently we conclude that magnetic properties are related to gas hydrate related processes and as such may have potential as a method of remote sensing for gas hydrate deposits

constraints on the acquisition of remanent magnetization in fine grained sediments imposed by redeposition experiments the magnetization of sediments is acquired through complex processes involving a large number of physical mineralogical and magnetic parameters despite many attempts the degree to which these processes distort the record of the geomagnetic field as it is archived as a natural remanent magnetization nrm remains poorly documented among many other parameters it is important to evaluate the amount of smoothing inherent to the signal its relation with the field intensity and its variability in the sediment column in order to address these problems we performed new redeposition experiments using carbonate rich ocean drilling program odp site 851 and clay rich odp site 854 sediments we used a dilute solution of gelatin which gels below 20 c thereby allowing mechanical blocking of the magnetic grains we observed two critical results 1 the efficiency of detrital remanent magnetization drm decreases with increasing sediment concentration for a given slurry sediment concentration is defined as c ms ms mh2o where ms and mh2o are the sediment and water mass respectively higher c would then reflect greater compaction lower water content and presumably greater depth in the sediment column this effect reduces drm efficiency nearly to zero for c 50 2 post depositional remanent magnetization pdrm is important for c 50 pdrm is carried by grains covering the entire coercivity spectrum by comparing the mean value of nrm divided by anhysteretic remanent magnetization from the previous magnetostratigraphic study at site 851 with the relevant ratio derived from our redeposition experiments we were able to estimate that pdrm was significant within the depth interval where 44 c 56 if the sediment concentration profile for the uppermost sediment was known at site 851 we could define the transfer function for the deconvolution of the field variations finally the dependence of drm efficiency on c suggests that changes in the thickness of the surface mixed layer would change drm efficiency thus fluctuations in maximum bioturbation depth could possibly cause drm intensity changes regardless of changes in earth s field

little ice age glacial activity in the mt waddington area british columbia coast mountains canada the establishment of fourteen little ice age lia glacier chronologies in the mt waddington area led to the development of an extended history of glacial activity in this portion of the southern british columbia coast mountains canada the glaciers were located within four different mountain ranges and were of varying size and aspect dendrochronological and lichenometric techniques were used to provide relative age estimates of moraines formed as glacier termini retreated from advanced positions evidence for pre lia glacial events is best preserved at tiedemann glacier where the oldest glacial advances date to a d 620 and 925 933 soil covered and well vegetated moraines built at cathedral pagoda and siva glaciers date to between a d 1203 and 1226 following this event moraines constructed at ragnarok siva and cathedral glaciers in the mid 14th century suggest glaciers in the region underwent a period of downwasting and retreat before readvancing the majority of moraines recorded in the mt waddington area describe late lia glacial events shown to have constructed moraines that date to a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 and 1942 1946 over the last 500 years these moraine building episodes were shown to occur on average every 65 years and suggest there has been prolonged synchronicity in the glaciological response to persistent climate forcing mechanisms nevertheless our analysis suggests that local factors such as aspect and size play an important role in individual glacial response notably ice termini of medium size glaciers facing eastwards showed a quicker response to climatically induced mass balance changes resume l historique de quatorze glaciers de vallee de la region du mont waddington sud de la chaine cotiere de colombie britannique canada durant le petit ge glaciaire pag fut evalue par l utilisation de techniques dendrochronologiques et lichenometriques procurant un ge minimum pour la formation des moraines laterales et frontales multiples les glaciers a l etude d aspect et de taille differents furent selectionnes a partir de quatre chaines de montagnes les evenements qui predatent le pag sont le mieux preserves sur le site du glacier tiedemann ou les plus vieilles avancees glaciaires date de a d 620 et 925 933 des moraines presentant une pedogenese avancee et recouvertes d une dense couverture vegetale furent datees entre a d 1203 et 1226 des moraines construites dans le milieu du 14 e siecle par les glaciers ragnarok siva et cathedral suggerent que les glaciers de la region se sont retires pour par la suite reavancer la majorite des moraines datees le furent vers la fin du pag soit en a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 et 1942 1946 au cours des 500 dernieres annees en moyenne 65 annees separent les differents episodes glaciaires ce qui suggerent un synchronisme des reponses glaciaires aux mecanismes climatiques des donnees preliminaires suggerent que l orientation et la taille des glaciers jouent un role important dans la reponse individualiste des glaciers en fait les terminus glaciaires des moyens glaciers d orientation est semblent repondre plus rapidement a un ajustement de volume interne glaciaire

lateglacial to holocene relative sea level changes in the bjarkarlundur area near reykholar north west iceland this paper presents results from seven isolation basins to investigate the relative sea level history from the lateglacial and the mid to late holocene from the bjarkarlundur area near reykholar on the reykjanes peninsula in north west iceland results presented help to constrain the timing and rate of relative sea level rsl change since deglaciation and also the timing of deglaciation itself in the bjarkarlundur area the marine limit is estimated to be approximately 80 m above sea level based on an isolation basin with sill altitude at 79 1 m the maximum age of this marine limit and hence local deglaciation is estimated at 12 2 14c ka bp relative sea level then fell rapidly during the late bolling early allerod at a rate of approximately 35 mm 14c a 1 to below 50 m by 11 4 14c ka bp after this the rate of rsl fall decreased significantly during the late allerod and younger dryas chronozones averaging 6 mm 14c a 1 between 11 4 and 9 7 14c ka bp based on isolation basins with sill altitudes of 51 1 and 41 1 m our data constrain any possible fluctuation in rsl produced by regrowth of ice during the younger dryas to below 10 m after 9 7 14c ka bp the rate of rsl fall increased significantly to approximately 23 mm 14c a 1 to at least 9 0 14c ka bp if eustatic sea level rise is taken into account and the calibrated timescale is used actual crustal uplift rates are estimated at 56 and 46 mm cal a 1 during lateglacial and early holocene times respectively during the mid to late holocene rsl then rose to at least 1 m above present day levels gradually falling to the present day level from 3 1 14c ka bp these results demonstrate the potential of isolation basin data for investigating the timing and rate of rsl change in iceland this can add important well constrained information on rsl when combined with data from raised beaches copyright 2009 john wiley sons ltd

depositional remanent magnetization toward an improved theoretical and experimental foundation the first theoretical predictions for the behavior of magnetic particles in water were that sedimentary magnetizations would be fully aligned with the ambient field yet redeposition experiments showed a strong and quasi linear dependence on the external field this empirically observed linearity has served as the fundamental assumption of sedimentary paleointensity studies for decades we present redeposition experiments which suggest instead that the relationship between depositional remanence drm and applied field may frequently be curved for magnetic fields in the range of the earth s numerical simulations using a flocculation model can explain the redeposition data and suggest that drm will be significantly non linear when the flocs are small several microns there is a strong dependence of floc size on salinity particularly in low salinity environments floc size has a profound influence on the efficiency of drm hence low salinity environment may give results with poor reproducibility the size of the floc in which magnetic particles are embedded is not accounted for in current methods of normalization yet is the most important parameter on the bright side however it now seems possible to quantitatively explain paleointensity in sedimentary systems opening the door to absolute paleointensity estimates from sediments whose key parameters of floc size distribution and settling times can be constrained

use of phosphorus mapping in assessing coastal activity zones of an icelandic multi period site of vatnsfjorður this paper presents the results of phosphorus mapping conducted on a number of coastal activity zones on the multi period archaeological farm site of vatnsfjor ur northwest iceland the aim of the study was to detect the exact levels and extents of shorelines contemporary with the archaeological site s activities and to use sea level change to establish a relative chronology of coastal activity zones absolute dating of the coastal zones and sea level changes was achieved by integrating an existing sea level curve with a novel tephrochronology based curve created for the purpose of this research results were projected onto a detailed digital terrain model of the area in order to reconstruct the extent of the coastline contemporary with human activity in the respective zones a significant component of the research was an attempt to develop the existing approach to phosphorus mapping results interpretation this has resulted in an improved methodology that can be applied to the dynamic and challenging environments of coastal sites worldwide

the chinese loess in xifeng ii a study of anisotropy of magnetic susceptibility of loess from xifeng summary measurements of specimens from the loess profile of xifeng gansu province china all show original magnetic fabric for sediments i e nearly horizontal foliation and the commonly oblate magnitude ellipsoid the degree of anisotropy always shows a strong correlation with the foliation f rather than with the lineation l specimens from wind blown loess redeposited water lain loess and red clay show their own distribution areas respectively in a diagram of l versus f magnetic fabric provides evidence for the suggestion that the red clay like the overlying wind blown loess is aeolian in origin the data points from the red clay all falling within the distribution area of the wind blown loess data points the magnetic fabric measured from present day palaeosols may still represent the features of the parent loess although the orientation of fabric has been slightly weakened through pedogenesis as shown in the present study

constraining the age of the last geomagnetic reversal from geochemical and magnetic analyses of atlantic indian and pacific ocean sediments we studied four marine sediment records of the matuyama brunhes geomagnetic reversal from four sites located in the indian atlantic and western pacific oceans the results combine paleomagnetic cosmogenic nuclide beryllium be 10 and oxygen isotope analyses that were performed on the same samples in order to avoid any stratigraphic bias the three records from the equatorial indian ocean and north atlantic ocean did not reveal any offset between the authigenic be 10 be 9 ratio be ratio peak and the interval of low relative paleointensity rpi that characterizes the reversal the lower and upper limits of transitional directions are also concomitant with the increased atmospheric be 10 production that accompanied the geomagnetic dipole intensity decrease in contrast the record from western equatorial pacific ocean sediments was found 18 cm below the be ratio changes as a result of late magnetization acquisition at all four sites maximum be 10 production occurred at the same period soon after the maximum of marine isotope stage 19 mis 19 and therefore indicates its synchronous worldwide character such features are effectively observed from the be ratio signals and their relationship with the magnetic transition interval which further confirms the synchronous character of the transition taking all dating uncertainties 1 6 ka between sites and 5 ka for the age model into consideration our records suggest a mean reversal age of 772 4 6 6 ka the age of the transition in the atlantic ocean record is closer to 774 ka but this difference is within the limit of significance

characteristics of residual and colluvial soils developed on granite and of the associated pre wisconsin landforms in north central new brunswick an area in north central new brunswick of approximately 20 km2 where tors are common was found to be undisrupted by glaciation the soils in this area are developed on grus and appear to be of pr

magnetic stratigraphy constraints on the matuyama brunhes boundary recorded in a loess section at the southern margin of chinese loess plateau although the matuyama brunhes boundary mbb in the chinese loess plateau clp is very important in reliably correlating quaternary loess with other sediments in the world particularly with marine and polar ice cores its exact stratigraphic position remains controversial previous investigations usually placed the mbb between paleosol unit s8 and loess unit l8 in various locations to better understand the spatial differences in the mbb position a high resolution paleomagnetic study was conducted in a loess section of the lantian basin at the southern margin of the clp the results show that the mbb is situated in the middle of the relatively weak paleosol unit s7 consistent with a recent report on the mbb based on a be 10 study from the xifeng and luochuan loess sections of the central clp however the regional anomalously low magnetic susceptibility in paleosols s7 and s8 indicates that it is more reliable to determine the paleoclimate boundaries between loess and paleosol horizons of this segment with median grain size then the mbb in the yushan section can be correlated with the bottom of paleosol s7 corresponding to the older part of interglacial marine isotope stage 19 this result temporally reconciles the striking discrepancy of the position of the mbb recorded in between loess and other typical sedimentary sequences and further confirms that the stratigraphic position of the mbb could spatially vary to a certain extent due to regional sedimentary or paleoclimatic conditions in the marginal areas of the clp in the yushan section the high frequency variations of paleomagnetic directions during a long period of similar to 31 ka before the mbb however could not be attributed to a genuine response to the true geomagnetic behaviour moreover the climate offset defined by the magnetic susceptibility and median grain size of the section can be preliminarily attributed to the regional geology and paleoenvironment background a multiproxy based stratigraphic division is considered very necessary when paleomagnetic and climatic boundaries are defined exactly in a specific area of the southern clp

reliability of the natural remanent magnetization recorded in chinese loess 1 chinese loess paleosol sequences undoubtedly have recorded geomagnetic events both polarity reversals and excursions however the fidelity of the rapid paleomagnetic field oscillations during a polarity reversal remains uncertain to test the reliability and consistency of the natural remanent magnetization records in chinese loess 10 subsets of parallel samples across the matuyama brunhes mb reversal boundary were obtained from the luochuan region in the hinterland of the chinese loess plateau our paleomagnetic results show diversified virtual geomagnetic poles vgps during the mb transition but consistent vgps outside of the transitional zone the anisotropy of magnetic susceptibility and rock magnetism results indicate that the sampled interval is rather uniform and undisturbed the discrepancies of the characteristic remanent magnetization within the mb transition are probably due to the low efficiency in aligning magnetic grains mainly pseudo single domain magnetite associated with the low field intensity nevertheless the stratigraphic location of the mb boundary can be confidently defined therefore we conclude that chinese loess paleosol sequences can record geomagnetic reversal events but the morphology within the polarity transition is rather questionable

late holocene vegetation and climate change at moraine bog tiedemann glacier southern coast mountains british columbia moraine bog lies just outside the outermost lateral moraine of tiedemann glacier in the southern coast mountains of british columbia a sediment core taken from the wetland was analyzed for pollen magnetic susceptibility and loss on ignition to reconstruct changes in vegetation and climate during the late holocene vegetation changed little between about 3500 and 2400 14 c years bp a period of local disturbance marked by deposition of a silty clay bed and increases in alnus pollen likely reflecting cooler moister conditions coincides with an extensive holocene advance of tiedemann glacier about 2400 14 c years bp warm dry conditions between about 1900 and 1500 14 c years bp are sug gested by peak values of pseudotsuga pollen and increasing nuphar sclereids the latter suggests lowered water levels this period coincides with a time of drought and increased fire frequency in the southernmost coast mountains about 1300 14 c years bp the forest became more coastal in composition with abundant tsuga heterophylla and abies a n increase in tsuga mertensiana pollen suggests the onset of cool and wet conditions by ca 500 14 c years bp coincident with the little ice age the record of inferred climate change at moraine bog is broadly synchronous with other paleoclimate records from the coast mountains and at the centennial scale with records elsewhere in the world

a magnetostratigraphic reassessment of correlation between chinese loess and marine oxygen isotope records over the last 1 1 ma abstract we present a magnetic polarity based paleoclimatic correlation between chinese loess and marine oxygen isotope stage mis records over the last 1 1 ma this revised land ocean comparison indicates that inconsistent occurrence of the matuyama brunhes boundary which lies in mis 19 in marine sediments and occurs either at the base lower part of loess l8 or the uppermost part of soil s8 in chinese loess is due to regional and or local climate variability across the chinese loess plateau and does not need to be attributed to lock in effects of loess remanence acquisition associated with pedogenesis this result implies that the geomagnetic polarity boundaries in chinese loess in general are reliable chronostratigraphic time markers therefore astronomically tuned timescales for chinese loess that presume a downward shift of polarity boundaries due to a time lag in remanence acquisition may have overestimated ages of certain loess paleosol units

dating of thaw depths in permafrost terrain by the palaeomagnetic method experimental acquisition of a freezing remanent magnetization summary the acquisition of a freezing remanent magnetization frm has been studied in controlled magnetic and thermal environments by successive freezing and thawing 18 to 20 c of samples of natural sediments from a frost polygon near ny alesund spitsbergen successive freeze thaw cycles cause a significant decrease in the intensity of the initially induced shock remanent magnetization srm associated with directional trends towards the ambient magnetic field direction during the freezing phase a slow increase in intensity commences after seven to 10 freeze thaw cycles the acquisition of a frm in samples carrying an isothermal remanent magnetization shows a significantly smaller reduction in intensity and only minor directional variations this result indicates that only a fraction of the magnetic grains in a natural sediment contributes to the natural remanent magnetization insignificant changes in lengths and directions of the principal susceptibility ellipsoid axes also indicate that magnetic fabric and remanent magnetization are carried by partly different populations of magnetic grains the acquisition of a frm in nature has yet to be explored if such a process is confirmed however it has the potential for obtaining age estimates of ancient thaw depths and for providing insights into material transport processes in frost polygons

magnetic fabric of loess and its significance in pleistocene environment reconstructions abstract a summary of approximately three decades and greater than thirty loess magnetic fabric studies is presented here the revised studies cover various loess regions from the chinese loess plateau across the european loess belt to alaska although there is still an ongoing argument about the feasibility of the magnetic fabric of loess in paleowind reconstructions the determination of prevailing wind direction during various periods of the pleistocene is the main goal of magnetic anisotropy analysis of the revised loess successions the magnetic fabric analysis of loess from chinese loess plateau provided significant information about the characteristics of paleomonsoon in east asia and the results from other loess regions such as alaska the european loess belt and siberia are also promising as it is shown in this review the synthesis of the paleowind direction results from the studied profiles may already provide a significant foundation for future climate models by the reconstruction of key climate centres and main continental level wind tracks besides the reconstruction of prevailing paleowind directions there are numerous loess magnetic fabric studies using magnetic anisotropy parameters in the reconstruction of the characteristics of long term climate trends climate transitions and glacial interglacial cycles there are some lesser known aspects contributing to magnetic fabric of loess such as the influence of various types of magnetic contributors on the overall fabric i e the study of sub fabrics and their role in environment reconstruction besides the identification of aeolian magnetic fabric not so many studies focus on the magnetic anisotropy characteristics of materials possibly developed by water lain sedimentation pedogenesis mass movements and permafrost activity novel results from hungarian loess especially from paks connected to some of the latter topics are also presented such topics includes the analysis of the nanofabric in paleosols developed by pedogenesis the comparison of magnetic fabric formed during high energy transportation by aeolian or aquatic agents and the periodicity analysis of magnetic parameters during the early middle pleistocene new research lines introduced in this review may inspire new researches and provide new perspectives for the next generation of magnetic anisotropy studies of loess successions

a lock in model for the complex matuyama brunhes boundary record of the loess palaeosol sequence at lingtai central chinese loess plateau summary in most marine sedimentary records the matuyama brunhes boundary mbb has been found in interglacial oxygen isotope stage 19 in the magnetostratigraphic records of most chinese loess palaeosol profiles the mbb is located in loess layer l8 which was deposited during a glacial period the mbb at lingtai central chinese loess plateau also occurs in l8 and is characterized by multiple polarity flips the natural remanent magnetization is mainly carried by two coexisting components the higher coercivity harder component dominates in loess layers and is thought to be of detrital origin the lower coercivity softer component prevails in palaeosols and was most probably formed in situ by bio chemical processes a lock in model for the lingtai mbb record has been developed by extending the lithologically controlled pdrm model of bleil von dobeneck 1999 it assumes two lock in zones the nrm of the magnetically harder component is physically locked by consolidation shortly after loess deposition whereas the softer component is formed at greater depth by pedogenesis and acquires a chemical remanent magnetization of younger age at polarity boundaries grains carrying reversed and normal directions may therefore occur together within a single horizon the model uses arm coercivity spectra to estimate the relative contributions of the two components it is able to explain the observed rapid multiple polarity flips and low magnetization intensities as well as the stratigraphic shift of the lingtai mbb with respect to the marine records

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

the matuyama brunhes polarity reversal in four chinese loess records high fidelity recording of geomagnetic field behavior or a less than reliable chronostratigraphic marker abstract the paleomagnetic recording fidelity of chinese loess has been a matter of long term dispute to help shed light on the acquisition retention mechanisms of natural remanent magnetization in loess we report on high sampling resolution paleomagnetic constraints on the position of the matuyama brunhes boundary mbb in four typical loess sections in different marginal areas of the chinese loess plateau clp each of which has experienced different east asian winter summer monsoon strengths and pedogenic intensities detailed thermal demagnetization experiments for 1850 specimens reveal that none of the high accumulation rate loess with the weakest pedogenesis at caotan western clp the massive pedogenesis loess characterized by extensive development of thick calcareous nodule layers at jixian se clp and the moderately pedogenized loess at fanshan ne clp have preserved high fidelity geomagnetic records across the mbbs jiuzhoutai western clp one of the thickest loess profiles in the world contains the thickest and hitherto the most complex mbb that is too extensive to be regarded as rapid fluctuations of geomagnetic field during the m b reversal at jixian a predominance of pedogenesis induced chemical remanent magnetization overprinting has heavily obscured the original remanence the significant downward displacement of the mbb at fanshan and even its total absence at caotan together with extensive remagnetization of the coarse grained upper sandy loess layer l9 in both sections further suggest that the processes of remanence acquisition retention of chinese loess in the marginal areas of the clp are rather complicated thus interpretations of the fine structure of geomagnetic transitional field behavior and excursions especially in the matuyama chron should be regarded with caution

high energy sedimentation creag aoil spean bridge scotland implications for meltwater movement and storage during loch lomond stadial younger dryas ice retreat this paper examines the origin and significance of loch lomond stadial younger dryas gravel deposits at creag aoil spean bridge scotland sedimentation into ice dammed lakes in glen roy and glen spean associated with shorelines at 260 m 325 m and 350 m is well documented yet little is known about later lower level lakes near spean bridge excavations on the northern flanks of the lundy channel revealed exposures into a 35 40 m thickness of sand and gravel these sediments reflect deposition in a subaqueous environment experiencing repeated short lived periods of high energy subaerial deposition deformation structures within subaqueous deposits are associated with at least two ice push events this study presents new evidence for the existence of ice dammed lakes at elevations between 260 m and 113 m and for periodic jokulhlaups draining southwest via the lundy channel active glacier ice associated with the deposits flowed northwest to southeast driving meltwater across the great glen to the lundy channel glacier retreat was punctuated by periodic minor readvances progressive ice retreat was accompanied by ice thinning and changes in ice flow direction and subglacial meltwater routing these findings add to knowledge of loch lomond stadial deglaciation around spean bridge and have implications for our understanding of lacustrine glacier margins during deglaciation copyright 2003 john wiley sons ltd keywords ice dammed lake subaqueous outwash jokulhlaups ice push structures scotland

timing of the brunhes matuyama magnetic polarity reversal in chinese loess using 10be in chinese loess the brunhes matuyama b m geomagnetic reversal occurs 25 k y prior to the age found in marine sediments this offset has been attributed by some to post depositional magnetic overprinting of loess while others have argued it is due to errors in the loess time scale here we solve this long standing debate by exploiting a new method to extract reproducible records of geomagnetic field intensity from loess with 10 be a proxy for global average geomagnetic field intensity and using it to show that a pronounced minimum in field intensity a requirement for dipole field reversal is recorded in two separate loess records at ca 780 3 kyr b p this timing is synchronous with the b m reversal timing seen in marine records verifying the standard loess time scale as correct but it is 25 k y younger than the age depth of the magnetic polarity reversal recorded in these same chinese loess sediments demonstrating that loess magnetic overprinting has occurred

geomagnetic episodes of the last 1 2 myr recorded in chinese loess 1 the matuyama brunhes m b boundary termination of jaramillo normal subchron j m as well as three young geomagnetic excursions has been revealed in the weinan loess section zhu et al 1994 1998 1999 recently we carried out further paleomagnetic directional studies on the same section and recovered the onset of the jaramillo normal subchron m j and four geomagnetic excursions two in the brunhes and two in the late matuyama the fact that all seven excursions found in this section are in loess units and expected excursions in paleosols are not found suggests that short lived geomagnetic signals could be only recorded in loess units and may have been fully smoothed or wiped out in paleosol units by strong pedogenesis constrained by a new astronomical timescale hld00 ages of the geomagnetic excursions and reversal boundaries have been estimated we tentatively correlated these excursions with previous results indicating that a large lock in model may not be correct for the whole loess profile although some apparently big positive age discrepancies were observed for the main boundaries

misleading positions of geomagnetic reversal boundaries in eurasian loess and implications for correlation between continental and marine sedimentary sequences abstract the matuyama brunhes boundary mbb where the earth s magnetic field changed to its present orientation is one of the most frequently used time markers in continental quaternary stratigraphy although magnetic signals have been successfully recovered from loess deposits and an apparently coherent magnetostratigraphy seems to be in place a close examination of the published loess records from northern mid latitudes reveals significant uncertainty and variability for the position of the mbb in asia and part of central europe the mbb has been found in loess a glacial deposit this is in contrast to the well established palaeomagnetic records in deep sea sediments where the mbb is located in the interglacial oxygen isotope stage 19 this discrepancy has caused serious confusion in stratigraphic correlation between loess and marine sequences here we examine the causes of the discrepancy between the two sedimentary environments in their records of the mbb our approach includes a comparison of the mbb in loess and other continental records and an evaluation of the stratigraphic significance of the microtektites found around the mbb based on the occurrence of the mbb in an interglacial stage in lake and continental margin sequences and the correlative stratigraphic positions of the microtektites in marine sediments and loess we demonstrate that the measured positions of the mbb in loess are erroneous and misleading and its true occurrence was during the time of formation of the palaeosol corresponding to oxygen isotope stage 19 the most plausible cause for the apparent offset i e the mbb being found in the underlying loess instead is that the acquisition of remanent magnetisation in loess occurs at a certain depth substantially below the land surface the degree of such displacement is dependent on the lithology and structure of the deposits formed prior to the reversal and the time delay is estimated to be in the order of 103 104 years we show that other geomagnetic boundaries such as those of jaramillo and cobb mountain in loess have been similarly displaced though to a varying extent we suggest that the remanence acquisition in loess is closely related to the post depositional evolution in the structure of loessic materials which is in part influenced by regional climate conditions our conclusions on the displaced remanence acquisition have implications for loess chronology magnetostratigraphy as well as the geomagnetic interpretation of detailed magnetic signatures from loess

loess magnetic fabric of the krems wachtberg archaeological site the loess sediment embedding the main gravettian layer at the krems wachtberg archaeological site facilitates exceptional preservation to gain insight in the sedimentation process before and after the palaeolithic settlement the magnetic fabric preferential orientation of magnetic particles of loess of the krems wachtberg site was investigated magnetic fabric properties clearly show an eolian origin of the loess but may indicate some relocation in the metre above the cultural layer the magnetic fabric properties can be divided into three intervals the top interval shows lowest foliation and inconsistent magnetic fabric directions the middle interval around the main cultural layer shows low foliation but a clear preferential nw se direction of the lineation this lineation is interpreted as preferential direction of the eolian loess accumulation from the southeast the interval below 0 5 m underneath the main find horizon shows a northeast southwest lineation but an imbrication suggesting that sediment accumulation occurred at 90 to this direction similar to the interval around the find horizon

sp grain production during thermal demagnetization of some chinese loess palaeosol summary progressive thermal demagnetization of natural samples to above 300 c may cause significant alterations of magnetic mineral phases such changes are commonly monitored by magnetic susceptibility ms determinations at every demagnetization step in an attempt to characterize in more detail alteration products created during thermal demagnetization of some chinese loess palaeosols l1 s1 ms was measured at both room temperature ms293k and at liquid nitrogen temperature ms77k between each demagnetization step we have used the difference between ms77k and ms293k temperature dependent susceptibility ktd ms293k ms77k to monitor production of superparamagnetic sp magnetic grains ktd is a function of 1 paramagnetic susceptibility according to the curie law k 1 t that predicts a theoretical 3 83 times increase in ms at 77k 2 sp grains at 293 k that passes into the single domain sd state on cooling to 77 k causing a dramatic reduction in ms77k 3 magnetite grains exhibiting magnetic changes when passing through the verwey transition at 120 k will also reduce ms77k we observe a linear relationship between frequency dependent ms kfd and temperature dependent susceptibility ktd indicating that sp sd blocking of magnetite may be the dominant factor of ms change during cooling high values of ktd indicates high sp concentrations and an increase of ktd with increasing demagnetization temperature is mainly attributed to the production of sp grains since the amount of magnetite exhibiting changes in ms at the verwey transition is unlikely to increase during heating of loess palaeosol to 600 c in air this interpretation is also based on results from zero field heating irm77k 1t zero field cooling of irm77k 1t and short time 100 s viscous decay of irm500mt our findings suggest that sp grains are produced continuously in both loess and palaeosol with thermal treatment and that sp production in palaeosol apparently commence at the surprisingly low temperature of around 200 c

timing and lock in effect of the laschamp geomagnetic excursion in chinese loess 1 the laschamp geomagnetic excursion lge at 41 ka is a critical age control for hemispherical comparison of paleoclimate records from various kinds of geological archives e g ice core marine and lake sediments the timing of the lge in chinese loess however remains poorly constrained due to the lack of a reliable chronology and the complex acquisition processes of natural remanent magnetization here we systematically compare the paleomagnetic results of three optically stimulated luminescence dated loess sequences on the chinese loess plateau our results indicate that the timing of the lge in the northwestern loess plateau is slightly older than the absolute radiometric age determination and the timing inferred from greenland ice core 10be flux and marine i e relative paleointensity and authogenic 10be 9be stack records but younger than the counterparts in the central loess plateau we attribute the different timing of the lge in the three loess sections to a progressive southeastward increase in the lock in depth caused by the combined effects of postdepositional processes e g surface mixing chemical weathering and lock in delay on the remanence acquisition process we conclude that caution is needed to use the lge in chinese loess as a reliable tie event for high resolution chronological correlation to marine and ice core records only if the potential lock in effect can be precisely determined

neoglacial lake alsek lowell glacier a large valley glacier in the st elias mountains of southwestern yukon territory advanced across alsek valley and blocked south flowing alsek river many times during the neoglacial interval the resulting lake termed neoglacial lake alsek extended east of the front of the st elias mountains and inundated parts of dezadeash valley that presently are populated lake alsek at its maximum was about 200 m deep at the glacier dam and over 100 km long staircase flights of beaches wave cut benches layers of driftwood and thin lacustrine sediments provide evidence of the former lake giant dunes and flood terraces on the floor of alsek valley indicate that the lake emptied catastrophically when the lowell glacier dam failed several phases of lake alsek have been identified each was preceded and followed by intervals during which the lake was empty and the present southward drainage pattern in alsek valley prevailed historical records radiocarbon and tree ring dates on driftwood and r

age and palaeoclimatic significance of the loess of lanzhou north china extending in a broad arc that abuts the sandy non gobi deserts the loess plateau of northern china1 3 is one of the most massive accumulations of loess in the world the loess sequence is typically characterized by an alternation of silty or sandy loess with more clay rich palaeosols these alternations in conjunction with their enclosed faunas and distinctive mineralogies have been interpreted as reflecting pleistocene glacial interglacial cycles3 8 because it holds implications for the climatic and anthropological history of china9 10 the definition of a reliable chronological framework for loess deposition is of great interest recent palaeomagnetic studies4 5 have indicated that loess deposition in shaanxi province commenced 2 4 myr ago to assess the synchrony of loess accumulation across the loess plateau we have dated a 330 m thick loess sequence near lanzhou gansu province the magnetostrati graphical results reported here indicate that the base of this loess succession dates from 1 3 my r ago this young age in comparison to the shaanxi sequence is attributed to uplift along the northern fringe of the tibetan plateau11 that precluded early pleistocene loess preservation in this mountainous region palaeosols in the basal loess occur on average once every 25 kyr suggesting that climates conducive to soil forming events may have been modulated by orbital precession in the early pleistocene

in situ remagnetization experiments of loess on the chinese loess plateau evidence for localized post depositional remanent magnetization 1 inconsistent stratigraphic positions of reversal boundaries and spurious paleomagnetic variations associated with polarity reversals recorded by loess paleosols on the chinese loess plateau clp have in general been attributed to inferred delayed acquisition of magnetization and high frequency variations of the geomagnetic field respectively these conclusions are partly based on an incomplete knowledge of the magnetization acquisition process of loess recent laboratory experiments which demonstrate that dry deposited loess acquires a stable remanent magnetization after its first wetting precipitation resulted in significant inclination errors that are not generally encountered in chinese loess laboratory experiments only remotely mimic natural conditions and we have therefore performed in situ experiments at two sites on the clp separated by some 650 km to elucidate whether variations in natural conditions can impose secondary remanent magnetization components in loess l1 the experiments were performed by relocating blocks volume 5 10 3 m3 of last interglacial loess after being turned upside down inside loess exposures inverted blocks were retrieved and analyzed after 8 and 17 months respectively thermal demagnetization reveals that partial remagnetization has occurred within different parts of the loess blocks this secondary magnetization which is characterized by blocking temperatures that overlap with those of the primary component to above 450 c cannot be attributed to a viscous remanent magnetization and is therefore proposed to represent local and partial realignment of magnetic grains we tentatively propose that physical unlocking and realignment of magnetic grains may be assisted by pressure release caused by differential thermal expansion of the different mineral grains in loess localized remagnetization may account for a number of reported spurious paleomagnetic results from clp

inconsistent palaeomagnetic recording of the blake event in chinese loess related to sedimentary environment three loess sequences located east of the liupan mountain region china were studied to obtain records of the blake polarity event palaeomagnetic records from the appropriate stratigraphic interval of these three sequences however record the blake event poorly in one case and not at all in the other two cases it is important to understand why these loess sequences miss the blake event whereas others record it quite well we conclude that regional variations in the sedimentary environment over the chinese loess plateau are responsible for the inconsistent recording of the blake event the palaeomagnetic records suggest a threefold subdivision of the chinese loess plateau into 1 the central and southern portions of the part of the plateau that lies east of the liupan mountains where the primary record of the blake event has been severely smoothed or wiped out by pedogenic processes during palaeosol s1 formation 2 the northern margin of the loess plateau to the east of the liupan mountains where frequent severe dust storms have resulted in discontinuous records with a high probability of missing the blake event and 3 the region west of the liupan mountains where loess sequences are deposited rapidly and nearly continuously with only minor pedogenesis and are thus capable of recording short events like the blake

draining and filling of ice dammed lakes at the terminus of surge type dan zhur donjek glacier yukon canada recent surges of dan zhur donjek glacier have formed lakes at the glacier terminus that have drained catastrophically resulting in hazards to people and infrastructure downstream here we use ai

evidence for magma heterogeneity in the white river ash yukon territory two recent plinian eruptions in the wrangell mountains southeast alaska gave rise to two distinct ash fall deposits that are collectively known as the white river ash and cover much of the yukon territory northwest canada analysis of the pumiceous glass indicates that the magma chamber was compositionally inhomogeneous prior to each eruption no compositional stratigraphy has been detected in the deposits indicating either thorough mixing in the eruption cloud or thorough reworking after deposition thus each individual sample of ash represents a large part of the magma chamber whereas larger pumice fragments are more homogeneous variations in temperature 950 990 and 995 1030 c respectively for the older and younger eruptions and log fo2 values 9 3 8 3 and 8 3 7 7 derived from the fe ti oxides support the conclusion that the magma chamber was inhomogeneous

a precursor to the matuyama brunhes reversal in chinese loess and its palaeomagnetic and stratigraphic significance summary we report high resolution palaeomagnetic results across the lower part of s8 in the luochuan area northwest of china using parallel subsets samples a palaeomagnetic anomaly with low palaeointensity and disordered magnetic direction was identified 21 ka prior to the matuyama brunhes mb polarity reversal and is consistent with the mb precursor observed from marine sediments and lava flows this is the first convincing report of the mb precursor in terrestrial material chinese loess which attests the global feature of the mb precursor constrained by the stratigraphic position of both the mb polarity reversal and the mb precursor the loess unit l8 and palaeosol unit s8 of the chinese loess sequence are undoubtedly tied to the marine isotope stages 18 and 19 respectively this correlation is critical for an accurate understanding of the correspondences of palaeomagnetic records between the chinese loess and marine sediments

pedogenic zonation in the well drained soils of the arctic regions abstract pedogenic zonation in the soils of the polar regions is a result of gradients in environmental factors and attendant chemical processes along a latitudinal transect it is best manifested at well drained sites and by soils developed on predominantly silicate rocks selected sites in arctic alaska in the canadian arctic greenland and svalbard adequately fulfill these prerequisites the processes of podzolization decarbonization carbonization pervection and salinization as models of arctic pedogenesis demonstrate that processes occurring in the temperate region also operate in the far north brunification melanization and oxidation are recognized for the first time as current geochemical and pedogenic mechanisms of the arctic region traditional genetic soil names have been retained because they represent a closer relationship to pedogenic processes than the more modern nomenclature the identification the chemical behavior the strength abundance and mobility of the proton donors and conjugate bases are keys to the genesis of soils and the distinction of contrasting soil processes this new approach to the understanding of arctic pedogenesis can be better fulfilled by collecting analyzing and interpreting soil solution obtained in situ

subaerial and subaqueous deposition of loess experimental assessment of detrital remanent magnetization in chinese loess abstract loess and intercalated paleosols on the chinese loess plateau clp are the most extensive and continuous terrestrial archive of geomagnetic and paleoclimate variations covering the last 2 6 ma a first order time frame has been established for these sequences using paleomagnetic polarity boundaries major inconsistencies between the positioning of the matuyama brunhes polarity boundary in chinese loess paleosol sequences and marine records previously accounted for by assuming magnetization lock in depths in loess of up to 2 3 m have recently been resolved using a paleoclimatic indicator insensitive to pedogenesis that does require any major post depositional acquisition of a remanent magnetization this resolved controversy accentuates the lack of an adequate understanding of how chinese loess acquires and retains a stable remanent magnetization we report on laboratory re deposition experiments with subaerial and subaqueous simulations of natural loess to elucidate factors controlling the acquisition of magnetization in loess our work complements and extends recently published results from comparable laboratory experiments by zhao and roberts 2010 our major finding is that a stable magnetization is acquired and retained after initial wetting of dry deposited loess with no significant time lag in general accord with recent findings

palaeowind directions and sources of detrital material archived in the roxolany loess section southern ukraine abstract measurements of the anisotropy of whole rock magnetic susceptibility ams and u pb ages of detrital zircons have been combined to define the palaeowind directions and sources of wind blown dust in the loess palaeosol key section at roxolany southern ukraine zircon dating has also been used to determine the age and provenance of the interbedded roxolany tephra the distribution of ams axes in the loess indicates that the prevailing wind during its accumulation blew from the north west the same as the mean present day summer wind direction measured in the nerby city of odessa the u pb isotopic ages of the detrital zircons mostly range between 0 25 and 2 ga with clusters at 0 28 0 32 0 45 0 58 1 0 and 1 5 ga single neoarchean grains ca 2 7 ga were also found these ages indicate that material from carpathian and podolian sources formed the roxolany loess this material initially was transported by the dniester river then was wind blown form the dniester liman and the lower dniester valley located nw of roxolany most of the pyroclastic zircons from the roxolany tephra gave ages of 470 840 ka with a peak between 500 and 750 ka this age range is consistent with their being derived from the ciomadul volcano in romania

a new correlation between chinese loess and deep sea δ18o records since the middle pleistocene abstract the quaternary chinese loess is one of the most continuous terrestrial sediments and preserves excellent palaeoclimate records at different timescales the conventional land ocean palaeoclimatic comparison has been established by correlation between magnetic susceptibility of the chinese loess and deep sea 18 o records during the 1980s however such a correlation results in long standing debates on the lock in depth of the palaeomagnetic polarity boundaries in chinese loess in this study the lock in depth of palaeomagnetic signals for loess

a record of the blake event during the last interglacial paleosol in the western loess plateau of china abstract a high resolution record of the blake event has been obtained from a 40 m well dug in a loess section at jiuzhoutai in the city of lanzhou in the western loess plateau of china the paleomagnetic signal is principally carried by magnetite both in loess and paleosols the blake event is located at the boundary between paleosol s1 c of the last interglacial equivalent to mis 5e in deep sea records and loess l2 2 mis 5d and is characterized by a triple feature consisting of two short reversed intervals separated by a short normal interval the directional changes are abrupt as previously revealed in other records and suggest geocentric dipole field behavior before after and during the event but not necessarily during n r or r n transitions the age and duration of the event are estimated as between 119 97 and 114 47 kyr bp and 5 5 kyr respectively from thermoluminescence dating and astronomically tuned climate stratigraphy based on high resolution magnetic susceptibility

volcanic soils of iceland abstract the parent materials of all icelandic soils are volcanic in origin and most of the soils are classified as andosols iceland has the largest area of andosols in europe and may have 5 of all andosols in the world a new classification scheme based on the world reference base world reference base for soil resources world soil resources reports 84 fao rome is used to provide an overview of icelandic volcanic soils the data were acquired as part of a recently initiated effort to build a database for icelandic soils but are also partly based on data from the eu cost 622 action a literature review and unpublished icelandic research the main soil types in iceland are histosols histic andosols gleyic andosols brown andosols vitrisols and leptosols in the icelandic language a single term is used to refer to each soil type this system reflects the dominant influence of eolian deposition and drainage conditions on the formation of histosols and andosols the parent materials of icelandic soils are mixtures of tephra layers and eolian sediments consisting mostly of volcanic glass the steady flux of eolian sediments from unstable sandy deserts constantly recharges the surface with basaltic tephra materials the histosols 20 c have appreciable amounts of andic materials because of the eolian deposition the andosols histic gleyic and brown andosols show characteristic properties of soils dominated by andic materials with allophane contents of up to 30 ferrihydrite commonly accounts for 5 15 of the soil the contents of both allophane and ferrihydrite generally decrease with increasing organic c content of soil horizons as organic matter inhibits allophane formation and iron tends to become reduced and lost in poorly drained locations the vitrisols are soils of desert surfaces with low organic content but they usually meet criteria for andic materials with 30 glass and al 1 2fe o 0 4 cryoturbation is intense in iceland resulting in a range of geomorphic surface features the cryoturbation is related to both climatic factors and the andic soil properties including high water retention and rapid hydraulic conductivity

inter profile correlation of the chinese loess paleosol sequences during marine oxygen isotope stage 5 and indications of pedogenesis abstract low field magnetic susceptibility has been widely used to determine the pedostratigraphy of the chinese loess paleosol sequences however uncertainties remain in correlating between the loess magnetic susceptibility and the marine oxygen isotope records because susceptibility variations are affected by both global and local paleoclimatic changes to provide a more sound paleoclimatic interpretation of magnetic susceptibility variations age models across marine oxygen isotope stage mis 5 for the jiuzhoutai jzt and yuanbao yb sections western chinese loess plateau were constructed through an integrated approach by linking the major pedostratigraphic boundaries of the loess profiles to the specmap oxygen isotope curve and by correlating relative magnetic paleointensity records with both the sint800 global paleointensity stack from marine sediments and 36cl records from the grip ice core results indicate good correlation of sirm60 mt a residual remanence of saturation isothermal remanent magnetization after a 60 mt alternating field demagnetization variations between these two sites which agree well with fluctuations in subtropical atlantic sea surface temperatures all cooling events recorded by ice core and atlantic marine sediments within mis5 have counterparts in sirm60 mt sirm60 mt is partially controlled by the degree of low temperature oxidation which is strongly temperature dependent however strong pedogenesis can decrease sirm60 mt due to further oxidation of partially oxidized magnetites above some critical points therefore we propose that sirm60 mt is best suited to record paleotemperature changes in loess profiles from the western chinese loess plateau where pedogenesis is the weakest furthermore by inter profile correlation between the yb and jzt sections we note that the seemingly uniform sub paleosol unit with a broad susceptibility peak previously assigned to mis5c between 34 4 and 37 4 m in the yb profile actually consists of two independent units lower part of s1l1 mis5b and s1s2 mis5c this indicates that susceptibility values can be strongly affected by local factors e g mainly precipitation therefore beside the simplistic traditional paleoclimatic interpretation of variations in loess susceptibility involving only cold dry and warm humid scenarios cold humid and warm dry scenarios should also be considered

application of anisotropy of magnetic susceptibility ams for the determination of paleo wind directions and paleo environment during the accumulation period of bag tephra hungary abstract this study provides the first application of anisotropy of magnetic susceptibility ams measurements for the study of pleistocene wind directions and the environment during the deposition of dust and lithifaction of loess in the carpathian basin a total of 67 samples were taken from seven loess paleosol outcrops to test this method on loess paleosol sequences the samples were collected from the loess overlying the bag tephra a characteristic marker horizon of the middle pleistocene age in the hungarian loess sequences statistical analysis of ams is a good tool to distinguish between redeposited and the undisturbed loess the first measurements indicated a n ne s sw direction dust transport in two outcrops when the principal susceptibilities were placed into a stereographic projection the effect of local slope proved to be important in determining the magnetic fabric the ams results were completed by isothermal remanent magnetization irm measurements to determine the main magnetic mineral components of the samples the dominant magnetic mineral which determines the ams character of the sample was magnetite or maghemite

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

geophysical prospection and soil chemistry at the early copper age settlement of veszto bikeri southeastern hungary abstract geophysical prospection and soil chemical analyses were conducted at the early copper age eca ca 4500 3900 cal bc antiquity 76 2002 619 journal of field archaeology 2004 in press site of veszto bikeri as part of the koros regional archaeological project investigations of the neolithic copper age transition on the great hungarian plain the goal of these investigations was to locate and map subsurface features and activity areas at the settlement vertical magnetic gradient measurements defined the extent and layout of the structures and features across the settlement and revealed that previously unidentified concentric ditches enclosed the site excavations confirmed the locations of most of the wall trenches postholes ditches and pits detected in the geophysical survey the soil chemical survey recorded high concentrations of phosphate around the perimeter of the site some of which were associated with a midden with the geophysical survey details of the plan and organization of the early copper age settlement were revealed that could not be discerned from surface artifact distribution patterns and test excavations the soil chemistry survey results showed a contrast between the cleaner center of the site near the structures and the ring of debris at the edge of the site near the circular enclosures the continuation of such nondestructive investigations at other eca sites will help improve models of settlement organization during the neolithic copper age transition

new aspects of the interpretation of the loess magnetic fabric cerna valley succession hungary abstract anisotropy of magnetic susceptibility ams is a frequently applied method in sedimentology especially in the determination of the orientation of transport processes we present an analysis of magnetic fabric mf studies on loess new aspects of fabric development reveal i the deposition of the aeolian sediments was controlled by gravity low energy transport and local geomorphology hence no clarified wind direction can be defined ii the influence of phyllosilicates is also significant among the magnetic components iii while the primary mf is relatively well defined the secondary mf is influenced by several processes the analysis of stereoplots combined with the q diagram and photostatistics showed encouraging results during the characterization of various secondary mf such as redeposited mf and pedogenic fabric iv changes in processes from aeolian to water lain deposition and the increasing transportation energy were reflected by the connection between ams and observed micro scale sedimentary features v a relationship was obvious between the degree of pedogenesis and the transformation of sedimentary mf into a vertical mf typical for paleosols vi the significant role of very fine grained magnetite on the formation of inverse mf could not be excluded

asynchronous records of brunhes matuyama reversal in marine sediments and chinese loess review and discussion abstract geomagnetic polarity reversals are generally considered to occur synchronously around the world and are commonly used as time markers to correlate events between different sediment archives they also play an indispensable role for understanding the mechanisms which generate the earth s geomagnetic field nevertheless in the case of the most recent reversal the brunhes matuyama b m reversal 780 ka comparison of paleomagnetic studies in chinese loess paleosol sequences versus marine cores reveal a marked discrepancy in timing of this event this timing offset has led to uncertainties in correlating the chinese loess paleosol sequences with other global climate records this paper briefly reviews the history of study on the b m reversal both in marine and chinese loess sediments and reviews several contentious explanations of the aforementioned b m boundary offset finally the most recent progress of paleogeomagnetic field variation studies using cosmogenic 10 be in chinese loess is introduced with the purpose of suggesting a potential way to address this b m boundary timing offset issue

deciphering records of geomagnetic reversals polarity reversals of the geomagnetic field are a major feature of the earth s dynamo questions remain regarding the dynamical processes that give rise to reversals and the properties of the geomagnetic field during a polarity transition a large number of paleomagnetic reversal records have been acquired during the past 50 years in order to better constrain the structure and geometry of the transitional field in addition over the past two decades numerical dynamo simulations have also provided insights into the reversal mechanism yet despite the large paleomagnetic database controversial interpretations of records of the transitional field persist they result from two characteristics inherent to all reversals both of which are detrimental to an ambiguous analysis on the one hand the reversal process is rapid and requires adequate temporal resolution on the other hand weak field intensities during a reversal can affect the fidelity of magnetic recording in sedimentary records this paper is aimed at reviewing critically the main reversal features derived from paleomagnetic records and at analyzing some of these features in light of numerical simulations we discuss in detail the fidelity of the signal extracted from paleomagnetic records and pay special attention to their resolution with respect to the timing and mechanisms involved in the magnetization process records from marine sediments dominate the database they give rise to transitional field models that often lead to overinterpret the data consequently we attempt to separate robust results and their subsequent interpretations from those that do not stand on a strong observational footing finally we discuss new avenues that should favor progress to better characterize and understand transitional field behavior

remagnetization mechanism and a new age model for l9 in chinese loess chinese loess during the quaternary is important for both paleomagnetic and paleoclimatic studies although magnetostratigraphy has been used for the initial loess timescale paleomagnetic records in loess still remain in debates such as magnetic polarity anomalies in l9 which is a thick and coarse sandy horizon as a typical marker bed to better understand the magnetization mechanism of these anomalies a new age model for l9 was first constructed based on a new correlation between loess and marine d 18 o which proposed that l9 should be correlated to marine oxygen stage mis 20 24 not 22 24 as previous suggested using combined grain size and environmental magnetism parameters an extended climatic optimum corresponding to mis 21 can be identified in middle of l9 a remagnetization mechanism of vis cous remanent magnetization overprinting on characteristic remanent magnetization chrm carriers mainly large pseudo single domain and multidomain magnetite particles associated with the chaotic detrital remanent magnetization caused by low efficiency alignment of chrm carriers along with the ambient field during deposition is proposed to interpret the magnetic anomalies this study provides new insights into the magnetization mechanism of the chinese loess and the new age model for l9 helps to accurately refine the finer scale correlation of paleoclimatic records between the chinese loess and marine sediments

paleoenvironmental significance of the magnetic fabrics in chinese loess paleosols since the last interglacial 130 ka abstract we compare new anisotropy of magnetic susceptibility ams data with previously determined paleoclimatically sensitive parameters for a loess profile at lingtai central loess plateau china to unravel factors that control loess ams magnetic lineations are clustered along ne sw and nw se orientations during cold and warm periods respectively which probably corresponded to paleowind directions of both winter and summer monsoons anomalously steep magnetic foliations coincidentally occur at the paleoclimatic stage boundaries indicating sediment disturbance lineation strength appears to be sensitive to millennial scale rapid paleoclimatic fluctuations generally the winter monsoon produces a lower degree of lineation than the summer monsoon furthermore by studying lineation subsets for the cold and warm periods we find that the cold interval lineation strengths co vary with grain size over the last 70 ka during the last interglacial about 74 128 ka the lineation and declination of the susceptibility maximum dec k max are sensitive to rapid fluctuations in winter and summer monsoons long term trends of magnetic foliation and anisotropy degree replicate grain size variations with superimposed short term peaks related to post depositional compaction as suggested by density the ams shape parameter t indicates oblate fabrics these new findings will not only improve our understandings of loess ams but also expand the possibilities of paleoclimatic studies in the chinese loess

palaeoclimatic and sedimentary history from magnetic susceptibility of loess in china the magnetostratigraphic age of the oldest loess sediments in the central chinese loess plateau investigated so far has recently been placed at ca 2 4 million years b p thus glaciations in central asia which are believed to provide the detritus for the formation of chinese loess commenced at the same time as the first ice rafted debris sank into the ocean basins of the northern hemisphere shackleton et al 1984 lithologic palaeontologic geochemical and especially rock magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition the variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen isotope record shackleton and opdyke 1976 and establish for the first time a continuous record of the pleistocene glacial and interglacial stages in a continental section spectral analysis of the rock magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils variable aeolic sediment influx as well as erosion and or polygenetic soil formation may also strongly influence the sedimentary history

how does chinese loess become magnetized despite nearly three decades of paleomagnetic research on the extensive chinese loess deposits a convincing explanation has yet to be developed for how chinese loess becomes magnetized to address this problem we conducted re deposition experiments using weakly consolidated holocene chinese loess that was disaggregated in the laboratory and compare our results with published paleomagnetic data we simulated a depositional remanent magnetization drm associated with dry deposition of eolian sediments and a post depositional remanent magnetization pdrm in which the sediment was water saturated after deposition the simulated drm faithfully records the declination of the applied field but with systematic inclination flattening addition of minor water slightly improves recording of the applied field but inclination flattening persists reliable recording of the applied field occurs for pdrm simulation in water saturated sediment our synthesis of paleomagnetic data from chinese loess indicates that time averaged paleomagnetic directions are often indistinguishable from the expected geocentric axial dipole gad field but in many cases inclinations are shallower than for a gad field we conclude that the chinese loess is magnetized by a combination of drm and pdrm mechanisms with water content providing the dominant control on which mechanism aligns the detrital mineral fraction where pedogenesis causes neoformation of magnetic minerals an additional chemical remanent magnetization crm will occur the magnetization of chinese loess therefore appears to be controlled by a complex time varying combination of drm pdrm and crm mechanisms

remanent magnetization of ash from the 18 may 1980 eruption of mount st helens ash from the may 1980 eruption of mount st helens deposited from air faithfully records the direction of the local geomagnetic field in eastern washington whereas ash settled from suspension in water in fluvial environments exhibits significant inclination and current rotation errors in magnetic direction similar to those reported in other subaqueously deposited sediments the current rotation errors are associated with partial alignment of the major axes of magnetic susceptibility in the direction of water currents subaerial deposition produces strong stable remanent magnetization in ash with or without postdepositional wetting by rain

apparent timing and duration of the matuyama brunhes geomagnetic reversal in chinese loess the matuyama brunhes mb geomagnetic reversal in chinese loess has been studied extensively as an important boundary for land ocean stratigraphic and paleoclimatic correlations however the apparent timing and duration of the mb boundary remain controversial in chinese loess deposits due to its inconsistent stratigraphic position and the uncertain chronologies here we synthesized high resolution paleomagnetic records from four loess sequences in the central chinese loess plateau and synchronized the loess paleosol chronology by matching the grain size variations to orbitally tuned grain size time series the synthesized paleomagnetic results reveal consistent features of the mb transition in chinese loess including the stratigraphic position l 8 s 8 transition timing 808 826 ka duration 14 16 ka and rapid directional oscillations compared with the mb transition in marine records 770 775 ka the timing of the mb transition is relatively older and longer in chinese loess due to a complex interplay between different remanence acquisition mechanisms which occurred during the course of postdepositional physical and chemical processes

geomagnetic excursions recorded in chinese loess in the last 70 000 years detailed paleomagnetic investigations conducted on the malan loess l1 at a well dated section weinan in the chinese loess plateau revealed two distinct anomalous directional intervals adi accompanied by lower relative paleointensity rock magnetic properties and anisotropy of magnetic susceptibility ams of samples taken from sedimentary horizons carrying the anomalous directions are similar to those taken from outside the anomalous directional intervals thus the anomalous directions are interpreted as geomagnetic excursions based on 14c and tl data the excursions occurred at 27 1 26 0 and 46 8 37 4 kyr b p the ages are consistent with the ages assigned to the mono lake excursion mle and laschamp excursion le respectively the result indicates that the mle and le were independent geomagnetic excursions the morphology of le at this section suggests that the le might be an aborted geomagnetic reversal

determination of magnetic carriers of the characteristic remanent magnetization of chinese loess by low temperature demagnetization abstract the chinese loess paleosol sequences can provide excellent paleomagnetic records for detailed studies on both magnetostratigraphy and secular variations of the earth s magnetic field however the nature of the loess paleosol characteristic remanent magnetization chrm isolated by thermal demagnetization from the natural remanent magnetization still remains in debate in this study we directly measure the thermal alternating field and low temperature demagnetization cooling warming cycle of remanence in zero field between 300 and 50 k spectra of chrm of the loess samples at touxiangdao xining pr china the results show that coarse grained pseudo single domain psd multi domain md magnetite and psd maghemite particles are the main magnetic carriers of the loess and paleosol chrms respectively by comparing the chrm characteristics across a loess paleosol transition zone we have found that during pedogenesis the thermally separable chrm original detrital remanent magnetization carried by the psd md magnetite in loess is gradually overprinted by the chemical remanent magnetization carried by psd maghemite even moderate pedogenesis e g for the pedogenically altered loess can strongly affect the loess chrm thus more attention has to be focused on the paleosol chrm separated solely by thermal demagnetization especially when constructing a continuous paleomagnetic record covering both loess and paleosol units