crustal geomagnetic field two dimensional intermediate wavelength spatial power spectra abstract two dimensional fourier spatial power spectra of equivalent magnetization values are presented for a region that includes a large portion of the western united states the magnetization values were determined by inversion of pogo satellite data assuming a magnetic crust 40 km thick and were located on an 11 10 array with 300 km grid spacing the spectra appear to be in good agreement with values of the crustal geomagnetic field spatial power spectra given by mcleod and coleman 1980 and with the crustal field model given by serson and hannaford 1957 the spectra show evidence of noise at low frequencies in the direction along the satellite orbital track n s indicating that for this particular data set additional filtering would probably be desirable these findings illustrate the value of two dimensional spatial power spectra both for describing the geomagnetic field statistically and as a guide for diagnosing possible noise sources

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

stable isotopes of lake and fluid inclusion brines dabusun lake qaidam basin western china hydrology and paleoclimatology in arid environments the qaidam basin underlain by salt is the largest 120 000 km2 on the qinghai tibet plateau western china numerous shallow to ephemeral saline lakes and dry saline pans are present on the qarhan salt plain dabusun lake the largest about 200 km2 contains high salinity na mg cl brines whereas it precipitates halite it is fringed by a potash salt flat the dominant inflow to dabusun lake the golmud river contains dilute na hco 3 rich meteoric waters dabusun lake brines fall on an evaporation trend given by d 3 3 18o 43 both d and 18o values increase with salinity which in turn varies considerably with flooding and evaporation the isotope compositions of the fluid inclusion brines from modern halite formed along the lake s edge are intermediate to those of dabusun lake brines and those from the salt flat shallow sediments beneath qarhan consist of interbedded salts and mud a short core section 1 3 1 7 m depth from the northern edge of dabusun lake was found to contain three dissolution surfaces and three mud partings the 18o values for fluid inclusions in 22 primary halite samples from this section show a record of episodic flooding lower 18o values followed by evaporation gradual increase in 18o values primary fluid inclusions in halite crystallized initially at the surface provide a geochemical record of surface brines their major element compositions varied through time more concentrated fluids indicate more arid conditions in the basin whereas wetter conditions prevailed during intervals of non salt deposition when laminated muds accumulated the isotope compositions together with the activity of h2o of fluid inclusions in primary halite were used to determine isotope variations in regional precipitation and hence paleoclimatic changes on the qinghai tibet plateau during the past 50 000 years

the effects of orography on midlatitude northern hemisphere dry climates abstract the role of mountains in maintaining extensive midlatitude arid regions in the northern hemisphere was investigated using simulations from the gfdl global climate model with and without orography in the integration with mountains dry climates were simulated over central asia and the interior of north america in good agreement with the observed climate in contrast moist climates were simulated in the same regions in the integration without mountains during all season but summer large amplitude stationary waves occur in response to the tibetan plateau and rocky mountains the midlatitude dry regions are located upstream of the troughs of these waves where general subsidence and relatively infrequent storm development occur and precipitation is thus inhibited in summer this mechanism contributes to the dryness of interior north america as a stationary wave trough remains east of the rockies but is not effective in eurasia due to seasonal changes in the atmospheric circulation the dryness

cenozoic environmental evolution of the qaidam basin and its implications for the uplift of the tibetan plateau and the drying of central asia abstract a complete cenozoic pollen sequence of the qaidam basin has been constructed with absolute age control the cenozoic environmental evolution of the qaidam basin and its implications for the uplift of the tibetan plateau and the drying of central asia during the cenozoic era is discussed based on the interpretation of the pollen sequence the commencement of eolian deposition in central china and the change of climatic distribution pattern of china the results suggest that in the qaidam basin relatively dry climates prevailed in the eocene oligocene and pliocene pleistocene these dry periods resulted from the effects of a subtropical high pressure zone and the uplift of the surrounding mountains and the tibetan plateau respectively about a 600 km northward drift of western china has probably occurred during the late cenozoic resulting in the eocene oligocene arid climate belt twisting about six degrees of latitude the tibetan plateau reached probably 1500 m elevation by the latest miocene 8 5 ma not as high as it was thought previously the cenozoic environmental evolution of northwest china does not support the idea that the retreat of the paratethys sea played an important role in the late cenozoic drying of central asia at least not in northwest china

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

impact of early diagenesis and bulk particle grain size distribution on estimates of relative geomagnetic palaeointensity variations in sediments from lama lake northern central siberia summary high resolution analyses of rock magnetic and sedimentological parameters were conducted on an 11 m long sediment core from lama lake northern siberia which encompasses the late pleistocene and the holocene epochs the results reveal a strong link between the median grain size of the magnetic particles identified as magnetite and the oxidation state of the sediment reducing conditions associated with a relative high total organic carbon toc content of the sediment characterize the upper 7 m of the core holocene and these have led to a partial dissolution of detrital magnetite grains and a homogenization of grain size related rock magnetic parameters the anoxic sediments are characterized by significantly larger median magnetic grain sizes as indicated for example by lower median destructive fields of the natural remanent magnetization mdfnrm and lower ratios of saturation remanence to saturation magnetization msr ms consequently estimates of relative geomagnetic palaeointensity variations yielded large amplitude shifts associated with anoxic oxic boundaries despite the partial reductive dissolution of magnetic particles within the anoxic section and consequent minimal variations in magnetic concentration and grain size palaeointensity estimates for this part of the core were still lithologically distorted by the effects of particle size and subsidiary toc variations anomalously high values coincide with an interval of significantly more fine grained sediment which is also associated with a decrease in toc content which may thus imply a decreased level of magnetite dissolution in this interval calculation of relative palaeointensity estimates therefore seems to be compromised by a combined effect of shifts in the particle size distribution of the bulk sediment and by partial magnetite dissolution varying in association with the toc content of the sediment

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

mineral magnetic proxies of erosion oxidation cycles in tropical maar lake sediments lake tritrivakely madagascar paleoenvironmental implications abstract mineral magnetic measurements were performed on the upper 16 m of five piston cored sedimentary sequences from lake tritrivakely madagascar ams 14 c dating and correlation of the five magnetic susceptibility records allowed establishment of a composite sedimentary record of the last 46 kyr our data suggest that mineral magnetic changes result from changes in concentration of strongly ferrimagnetic terrigenous minerals and from preservation dissolution cycles of detrital iron oxides primarily high coercivity fe iii phases such as hematite in alternately oxic and anoxic depositional environments high coercivity iron oxide phases are restricted to stratigraphic intervals that are interpreted to represent dry periods with oxic conditions comparison with other paleoenvironmental proxies pollen total organic carbon lithology suggests that the sediments record relatively humid conditions before 22 kyr bp and relatively dry conditions during the last glacial maximum lgm and the early holocene such results contrast with the previous observations of relatively dry glacial conditions and humid mid holocene conditions in the summer rainfall area of east and se africa

geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism geochemical and mineral magnetic studies of lake sediments from the karsa valley in north sweden demonstrate that down core variations in magnetic properties have been determined by post depositional magnetite dissolution rather than by sediment source changes a low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss an increase in the sedimentation rate and a reduction in the organic carbon content primarily due to glacier reformation allowed magnetite preservation thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change this new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial stadial and interglacial interstadial episodes during the quaternary period

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

relative paleointensity across the last geomagnetic reversal from sediments of the atlantic indian and pacific oceans paleointensity records from marine sediments at three locations in the atlantic indian and pacific oceans show coherent and reproducible signals across the brunhes matuyama reversal the low field susceptibility signals are predominantly anticorrelated between the indo pacific and the atlantic sites while the normalization of the natural remanent magnetization by any rock magnetic parameter yield identical results we deduce that in these cases climatic components do not induce first order effects in the determination of relative paleointensity the results establish the worldwide character of the triangular pattern displayed by the decay and recovery phases of the field intensity variations across the brunhes matuyama reversal

late holocene vegetation and climate oscillations in the qaidam basin of the northeastern tibetan plateau abstract pollen evidence from sediment cores at hurleg and toson lakes in the qaidam basin was obtained to examine vegetation and climatic change in the northeastern qinghai tibetan plateau the chronologies were controlled by 210pb and 137cs analysis and ams 14c dating pollen assemblages from both lakes are dominated by chenopodiaceae 40 artemisia 30 35 and poaceae 20 25 with continued occurrence but low abundance of nitraria ephedra and cyperaceae artemisia chenopodiaceae a c pollen ratios from two lakes show coherent large oscillations at centennial timescale during the last 1000 yr a c ratios were high around ad 1170 1270 1450 1700 and 1920 suggesting that the vegetation was more steppe like under a relatively moist climate than that during the intervening periods wet dry climate shifts at the two lakes 2800 m asl are in opposite phases to precipitation changes derived from tree ring records in the surrounding mountains 3700 m asl and to pollen and snow accumulation records from dunde ice core 5300 m asl showing that a dry climate in the basin corresponds with a wet interval in the mountains especially around ad 1600 this contrasting pattern implies that topography might have played an important role in mediating moisture changes at regional scale in this topographically complex region

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

paleoclimatic implications of magnetic susceptibility in late pliocene quaternary sediments from deep drilling core sg 1 in the western qaidam basin ne tibetan plateau 1 lake sediments are important archives of paleoclimate change and erosion history a 938 5 m long core sg 1 of lacustrine sediments dated at 2 77 ma to 0 1 ma was obtained from the western qaidam basin in the northeastern tibetan plateau consisting of dark grayish mudstone and grayish siltstone intercalated with salts and fine sandstones in the upper part magnetic susceptibility data combined with detailed rock magnetic properties were analyzed for revealing the significance of ferro i magnetic concentration for past changes of climate and erosion mass specific susceptibility shows a striking cyclic and long term variation samples with high values are dominated by magnetite and maghemite with pseudo single domain properties in contrast samples with low values contain maghemite from single domain to multidomain and additionally a significant fraction of hematite the driving mechanism of variation can be explained by three alternative models 1 different source regions with alternations of wind and cryoclastic erosion in a wider hinterland dry cold climate and surface runoff erosion from a narrower area more humid climate and 2 and 3 low temperature oxidation occurring either in the lake sediments dry climate or in the catchment area during weathering more humid climate trends of match with changes in sedimention rates and are roughly synchronous with the deep sea 18o record on a glacial interglacial timescale therefore the concentration of magnetic minerals in the western qaidam basin sediments is likely controlled by both tectonic influence and paleoenvironmental changes but can be best interpreted by alternations and trends of dry cold and more humid periods due to asian drying and global cooling

late neogene rock magnetic record of climatic variation from chinese eolian sediments related to uplift of the tibetan plateau abstract the late cenozoic red clay loess sequence in the chinese loess plateau provides a high resolution record of paleoclimatic and tectonic changes related to the phased uplift of the tibetan plateau detailed magnetostratigraphy of a recently recovered 125 m thick sediment sequence from the central chinese loess plateau shows that the red clay began to accumulate at ca 8 1 ma implying a marked drying in the interior of asian as well as the initial establishment of the east asian paleomonsoon regime prior to 3 8 ma the ferromagnetic mineral concentrations as revealed by both magnetic susceptibility and s ratios exhibit a cyclic pattern superimposed upon a linear trend this pattern collapsed immediately after 3 8 ma suggesting a change in source area this in turn may have resulted from the reorganization of atmospheric circulation and the onset of the modern asian monsoon probably associated with the accelerated uplift of the tibetan plateau to a certain threshold elevation

eastward migration of the qaidam basin and its implications for cenozoic evolution of the altyn tagh fault and associated river systems the qaidam basin is the largest cenozoic intermontane basin within the tibetan plateau bounded by the qilian shan range to the north the east kunlun range to the south the altyn tagh range to the west and the ela shan range to the east its deposits consist of nonmarine sedimentary rocks with a maximum thickness exceeding 13 400 m modern sedimentation mainly takes place along the marginal areas of the basin where alluvial fans are formed along a series of rivers that originate from the surrounding mountains nevertheless drilling sedimentary and seismic data reveal that the depocenter of the basin during much of cenozoic time was not developed as foreland basins of the qilian shan belt to the north and the east kunlun belt to the south but instead the depocenter was in the center of the western part of the basin and had a northwest southeast trend that shifted eastward 380 km during oligocene to quaternary time this indicates that most of the basin sediments were not derived from the surrounding mountain ranges the results of the fi ssion track age dating reveal that the rapid uplift of the yousha shan anticline bounding the depocenter to the southwest initiated at ca 31 ma indicating that the southeastward shift of the depocenter began at that time yielding a migration rate for the depocenter of 10 2 mm yr the northwestern margin of the depocenter of the qaidam basin lies to the east of the westward prolongation of the qaidam basin the tula trough a 300 km long narrow trough fl anked by the altyn tagh range along the altyn tagh strikeslip fault on the north and the east kunlun thrust belt on the south the sedimentary and deformational evidence from this region indicates that the tula trough was formed as a syncline along which a paleoriver fl owed to the east into the qaidam basin to the southwest this river valley merges with the trace of the altyn tagh fault the latter and its westward continuation are interpreted to have extended to the northern margin of the pamir folded belt north of the western syntaxis of the himalaya we propose that most of the sediments within the depocenter of the qaidam basin were transported from the northern margin of the pamir folded belt along a progressively lengthening 2000 kmlong longitudinal river that developed along the left lateral altyn tagh fault and its western continuation as the eastward extrusion of the tibetan plateau took place in oligocene time both the crustal uplift and continuous southeastward aggradations of the sediments carried by the paleo kunlun river are interpreted to be the cause for southeastward migration of the depocenter of the qaidam basin the longitudinal river disappeared in late cenozoic time 2 4 ma due to stream capture and climate change

magnetic susceptibility variations in upper pleistocene deep sea sediments of the ne atlantic implications for ice rafting and paleocirculation at the last glacial maximum magnetic susceptibility ms variations are used to intercorrelate 17 upper pleistocene sediment cores taken from the ne atlantic between 40 degrees and 60 degrees n the ms based correlation depends on regionally consistent patterns of variation in the deposition of ice rafted detritus ird in response to pleistocene glaciations and especially to high frequency ice rafting episodes referred to in recent studies as heinrich events the sedimentological and rock magnetic basis for the apparent relationship between the ms signal and ird content of ne atlantic sediments is examined by 1 comparing the ms profiles of selected cores with their records of coarse fraction 150 mu m lithic fragment abundance and neogloboquadrina pachyderma sin percentages and 2 normalizing ms by expressing it both on a carbonate free basis and as a quotient with anhysteretic remanent magnetization a parameter sensitive to magnetic mineral grain size variations these comparisons show that variations in bulk sediment ms are only partly driven by simple carbonate dilution productivity and dissolution effects changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk ms values in particular horizons rich in ird are associated with significant increases in the relative proportion of coarse grained multidomain ferrimagnetic particles in the sediment this is because ice rafting in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments has a high potential for delivering large ferrimagnetic grains as components of sand sized polycrystalline lithic fragments this fundamental linkage between the ird content and ms signal of ne atlantic sediments is used to reconstruct the patterns of variation in ird deposition and by inference surface currents of the last glacial maximum lgm similar to 18 19 ka relative to the present day ne atlantic using the time slice mapping approach developed by the climap project group our lgm holocene ms ratio map based on sample pairs from over 80 deep sea cores confirms that there was a weak cyclonic gyre north of the polar front in the lgm north atlantic the gyre comprised a sluggish warm current in the ne atlantic flowing north between latitudes 47 degrees and 62 degrees n partly fed by subtropical waters from south of the polar front and carrying large numbers of icebergs derived from several sources most of which melted between latitudes 45 degrees and 52 degrees n the warm current probably continued its flow into the iceland basin where it fed into a south flowing current which transported melting icebergs from iceland and scandinavia along the western flank of the reykjanes ridge

geomagnetic excursions in the past 60 ka ephemeral secular variation features geomagnetic excursions have been reported for the past 25 years in both sedimentary and igneous rocks of brunhes age and from widespread geographic localities they comprise sequences of paleo magnetic directions that are anomalous in that they depart widely from the range of geomagnetic north directions recorded through historic time they have sometimes been interpreted as records of aborted reversals of polarity of the main geomagnetic dipole the search for excursions sought to provide a set of stratigraphic markers the case of the laschamp excursion described in lava flows from the chaine des puys massif central france is analyzed here through a new sequential record of paleosecular variation recovered from sedimentary cores collected in lac du bouchet a maar lake about 100 km from the laschamp site the absence of anomalous directions indicates that this excursion lasted for only a few centuries this constitutes a warning to stratigraphers who attempt to use excursions as marker events and it gives an insight on the behavior of earth s geodynamo on the scale of 102 to 103 yr

occurrence and distribution of high molecular weight hydrocarbons in selected non marine source rocks from the liaohe qaidam and tarim basins china abstract extracts of 18 potential source rocks from the qaidam liaohe and tarim basins china have been characterized by high temperature gas chromatography htgc and found to contain high molecular weight hydrocarbons hmwhcs above c40 these rocks were originally formed in freshwater lacustrine saline lacustrine and terrigenous bog environments with mudstone calcareous mudstone coaly shale and coal lithologies their ages range from triassic to miocene and maturities from immature to mature covering a vitrinite reflectance range ro for the liaohe and tarim samples of 0 54 0 84 the combined distributions of the n alkane and alkylcyclopentane homologues in the extracts can be used to characterize the nature of the original depositional environment in certain samples the carbon number predominance of the n alkanes changes from an odd even predominance to even odd predominance above c40 possibly suggesting different precursors for the n alkanes above and below c40 concentrations of the hmwhcs were also observed to increase with maturity of the source rocks this is the first comprehensive report on the occurrence of hmwhcs in source rocks and their discovery introduces the possibility of using these compounds for oil source rock correlation purposes in future studies along with the more conventional biomarkers

physical modelling of fault scarp degradation under freeze thaw cycles physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps data from 41 experimental freeze thaw cycles are presented they attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology i cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer ii combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer 0 3 cm cycle iii debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion iv quantification of the erosion rate gives values close to 1 cm3 cm 2 for 41 freeze thaw cycles these experimental results are consistent with field data acquired along the la hague fault scarp normandy france where an erosion rate of 4 6 1 m3 m 2 per glacial stage has been computed from the volume of natural slope deposits stored during the weichselian glacial stage these results show that moist periglacial erosion processes could lead to an underestimation of plio quaternary deformation in the mid latitudes copyright 2006 john wiley sons ltd

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

a 13 200 year history of century to millennial scale paleoenvironmental change magnetically recorded in the palmer deep western antarctic peninsula abstract a 13 200 yr record of magnetic parameters from the palmer deep western antarctic peninsula records a sequence of five distinct shifts in glacimarine sedimentation coupled with century scale variations in paleoproductivity the five major shifts are manifested as abrupt order of magnitude changes in low field magnetic susceptibility accompanied by changes in magnetic particle size and mineralogy the late holocene 3 4 0 ka the early holocene 11 5 9 ka and the last glacial maximum prior to 13 2 ka are intervals of strong low field magnetic susceptibility and are characterized by multi domain md magnetite md magnetite is associated with zones of abundant gravel grains and is interpreted here as an indicator of material transported as ice rafted debris deglaciation 13 2 11 5 ka and the middle holocene 9 3 4 ka were times of enhanced productivity the middle holocene marks the onset of century scale productivity cycles seen in high field magnetic susceptibility which is responding to variations in biogenic silica deglaciation and the middle holocene interval contain pseudo single domain magnetite and titanomagnetite respectively these observations are surprising given the abundance of coarse md magnetite available in local source rocks the magnetic mineral assemblage in the deglaciation interval however can be explained by density sorting in meltwater plumes during the middle holocene the magnetic mineral assemblage suggests the reduction or cessation of locally derived terrigenous sediment and by inference the reduction or cessation of iceberg generation the early holocene middle holocene shift in terrigenous sedimentation may be responding in part to sea level which controls the position of the grounding line the palmer deep late holocene interval coincides with the neoglacial period a time of glacier re advances worldwide

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

glass production for the silk road provenance and trade of islamic glasses using isotopic and chemical analyses in a geological context abstract we report the first nd and sr results for sands from inland locations in the middle east and new nd and sr results for coastal sand on the syro palestinian coast when the isotopic results for belus sands are combined with our seven new sand samples from the lebanon we have established the likely range of isotopic signatures for levantine sand that was used for the manufacture of hellenistic roman byzantine and some islamic glass in the area the combined isotopic results for sands and sr results for plants growing in syria and the lebanon provides an environmental base line which has allowed us to identify 5 separate isotopic production zones we have made direct comparisons with nd and sr signatures for raw furnace glasses from al raqqa syria and tyre the lebanon secondary furnace glasses from banias israel and with new results for four raw glass fragments from the early 11th century ce serce limani shipwreck excavated off the coast of turkey we have also compared the base line isotopic data with our new isotopic data for twenty one 9th 14th ce islamic plant ash glass vessel fragments from damascus and beirut and with published isotopic data for al raqqa vessel glass for the first time we have been able to provide a more secure provenance for the late 11th century ce serce limani raw glass it was made from levantine coastal sand or an equivalent source of geologically young sand and has a sr signature that suggests a production provenance in the palestinian area but not in established centres such as tyre as has been suggested we are able to suggest an inland isotopic provenance for 9th 12th century islamic vessel fragments from al raqqa beirut and damascus which probably coincides with an area in or near damascus two al raqqa vessel glasses with elevated potassium oxide levels and distinctive nd and sr signatures may have a central asian origin this environmental approach involving isotopic analysis of sands and plants has provided a more sensitive way of provenancing islamic plant ash glasses found in the syro palestinian area and in turkey than the use of trace elements has thus far the five separate production centres zones we have defined have provided more evidence for a decentralised system of islamic plant ash glass production also found across extensive areas of the silk road at least as far as northern iran

millennial scale climatic change during the last interglacial period superparamagnetic sediment proxy from paleosol s1 western chinese loess plateau detailed magnetic analyses of samples from the jiuzhoutai well section on the western chinese loess plateau reveal high resolution signals of summer monsoon change the last interglacial period is represented here by the 8 meter thick s1 paleosol complex we have used low temperature remanence studies to analyze variations in the concentration of superparamagnetic sp grains which previous studies have shown to be largely of pedogenic origin the sp concentration interpreted as a proxy for the extent of pedogenesis shows millennial scale variations within s1 we conclude that the last interglacial period in asia was characterized by rapid climate fluctuations with at least one brief return to near glacial conditions in the middle of oxygen isotope substage 5e

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals