quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

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

climatic control of magnetic granulometry in the mircea vodă loess paleosol sequence dobrogea romania a detailed rock magnetic investigation of loess palaeosol samples from the section at mircea vod dobrogea plateau romania is presented investigation of climatic control on magnetic granulometry used several grain size and concentration dependent proxies magnetic susceptibility and its frequency dependence anhysteretic remanent magnetization isothermal remanent magnetization hysteresis properties and forc distributions and an unmixing model for isothermal remanent magnetization curves the paleosol layers in the mircea vod sequence experienced significant pedogenic alteration resulting in high amounts of ultrafine grained sp grains at sp sd threshold stable sd grains and psd magnetite maghemite grains the loess layers in the mircea vod sequence are dominated by md and or psd oxidized magnetite probably of aeolian origin the unmixing model for irm curves shows the presence of three components with different coercivities the soft 21 mt and medium 42 mt coercivity components are produced by pedogenesis during interglacial and interstadial periods the hard coercivity component 60 mt is of aeolian origin being dominant in loess layers

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

high resolution chronologies for loess comparing ams 14c and optical dating results the nuxloch loess section in south west germany is famous in central europe for its thick deposits from the last glacial maximum it has therefore been intensively studied during the past few years and offers an excellent opportunity to compare the performance of different dating techniques covering the period 15 45 ka here we present results fromoptical and ams 14 c dating the silt sized polymineral fraction of the clastic sediments and a multiple aliquot approach was used for ir osl dating 14 c dating was carried out on organic macro remnants and humin fractions extracted fromthe sedim ents with the exception of samples taken from the uppermost 1 5 m of the section ir osl and calibrated 14 c ams ages are consistent over the entire period the inconsistencies in the upper meters are thought to be due to disturbances during soil formation in the holocene the good agreement obtained on the remaining sequence demonstrates the high accuracy of both methods when studying loess sections for the ir osl ages no significant age underestimations are obvious the results clearly document that accurate chronologies can be developed for such continental sedimentary sequences this gives access to archives that can now be studied with a high temporal resolution and allows the establishment of new paleoclimatic proxies for the study of terrestrial responses to past climatic changes r 2003 elsevier science ltd all rights reserved

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

new insights into partial oxidation model of magnetites and thermal alteration of magnetic mineralogy of the chinese loess in air summary new rock magnetic data including low and high temperature thermomagnetic runs and hysteresis loops as well as x ray diffraction measurements are presented from the chinese loess palaeosols at jiuzhoutai on the northwestern margin of the chinese loess plateau to provide sound constraints on the partial oxidation model of magnetites and variations in magnetic mineralogy grain size and oxidation states of loess samples during thermal treatments from room temperature up to 700 c the results show that the partially oxidized magnetites in samples are first reduced probably as a result of the burning of organic matter below 300 c and then reoxidized above that however even after heating to 700 c the highly diminished in size magnetite core still remains stoichiometric as revealed by the 120 k verwey transition we conclude that the diffusion of fe2 from the magnetite core to the surrounding maghemite rim is confined to the oxidation front magnetite core maghemite rim boundary and has less effect on the stoichiometry of the magnetite core the new results also reveal that the absolute number of superparamagnetic grains magnetite maghemite remains relatively stable during heating furthermore the left downward shift in the data points of day plots mainly between 25 and 150 c is caused by a decrease in the oxidation gradient in contrast the right upward mainly between 500 and 650 c shift of the day plots corresponds to a much higher degree of oxidation resulting in the increase of a new oxidation gradient between the magnetite core or the residual maghemite mantle and the newly developed haematite outer rim which is transformed from maghemite by heating these new results place strong constraints on the fidelity of palaeomagnetic results from the chinese loess constructed by thermal demagnetization and provide a more accurate interpretation of the day plot and low temperature magnetic behaviours for these partially oxidized magnetites furthermore this study provides robust lines of evidence for the core rim coupling model between different magnetic phases magnetite maghemite and haematite

geodynamics seismicity and seismic hazards of the caucasus abstract being a part of ongoing continental collision between the arabian and eurasian plates the caucasus region is a remarkable site of moderate to strong seismicity where devastating earthquakes caused significant losses of lives and livelihood in this article we survey geology and geodynamics of the caucasus and its surroundings magmatism and heat flow active tectonics and tectonic stresses caused by the collision and shortening gravity and density models and overview recent geodetic studies related to regional movements the tectonic development of the caucasus region in the mesozoic cenozoic times as well as the underlying dynamics controlling its development are complicated processes it is clear that the collision is responsible for a topographic uplift inversion and for the formation of the fold and thrust belts of the greater and lesser caucasus tectonic deformations in the region is influenced by the wedge shaped rigid arabian block indenting into the relatively mobile region and producing near n s compressional stress and seismicity in the caucasus regional seismicity is analysed with an attention to sub crustal seismicity under the northern foothills of the greater caucasus which origin is unclear whether the seismicity associated with a descending oceanic crust or thinned continental crust recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the lesser and greater caucasus the knowledge of geodynamics seismicity and stress regime in the caucasus region assists in an assessment of seismic hazard and risk we look finally at existing gaps in the current knowledge and identify the problems which may improve our understanding of the regional evolution active tectonics geodynamics shallow and deeper seismicity and surface manifestations of the lithosphere dynamics among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution e g continental collision and associated shortening and exhumation lithosphere structure deformation and strain stress partitioning and to the lack of comprehensive datasets e g regional seismic catalogues seismic gravity and geodetic surveys

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

the regional and temporal significance of primary aeolian magnetic fabrics preserved in alaskan loess abstract the anisotropy of magnetic susceptibility ams data presented herein underscore the resolving power magnetic anisotropy has in non lithified poorly consolidated sediments we turn our attention to primary aeolian sedimentary magnetic fabrics preserved along two coeval loess profiles in central alaska at the halfway house hh3 and gold hill steps ghs2 sites we first demonstrate that published preliminary results along hh1 and hh2 are reproducible moreover the new sample suite the first ever at ghs collected at a higher temporal resolution and statistical confidence permits a better evaluation of the significance of the inferred paleowind directions and their temporal variability the data demonstrate that the resolvability of the magnetic lineation is independent of both the eccentricity of the ams ellipsoid and the strength of the magnetic foliation furthermore the orientations and temporal variability of the most significant magnetic lineations are not artifacts of the data filtering process developed to isolate them we conclude that the temporal variations of inferred paleowind directions along hh3 track paleoclimatic glacial interglacial cycles as well as provide additional constraints to the geochronology of the loess deposit along ghs2 the limited coeval primary magnetic fabrics suggest an influence from a local microclimate not present at the hh site complicating the interpretation of small scale variability in paleowind directions however the overall average paleowind directions are similar to those inferred along hh3 confirming a regional spatial consistency of past surface air circulation

an environmental magnetic fingerprint of periglacial loess records of late pleistocene loess palaeosol sequences from eastern germany a detailed rock magnetic analysis of the last glacial interglacial loess palaeosol sequences was carried out in the framework of a comprehensive stratigraphic study of loess in saxony eastern germany magnetic susceptibility and laboratory induced remanences have been determined to compare individual sections and to identify the specific rock magnetic characteristics of the saxonian loess province according to the model of pedogenic magnetic enhancement an increasing neoformation of ferrimagnetic minerals in the course of pedogenesis was observed only in the uppermost late weichselian lithological units consisting of pure aeolian loess and indicating dryer climatic conditions in contrast the rock magnetic characteristics of the lower middle and early weichselian units exhibit a significant destruction of primary magnetic minerals caused by such secondary processes as climatically controlled waterlogging and reworking this change in magnetic composition with stratigraphic depth was additionally proved by factor analysis in which the main observation an increasing fd with decreasing argues for a general magnetic depletion in conjunction with decreasing magnetic grain sizes caused by weathering of larger primary particles the magnetic fingerprint of the saxonian loess is characterised by prevailing magnetic depletion processes which effectively rules out the application of the wind vigour model moreover the magnetic characteristics differ significantly from that of other loess regions and support a new and independent model which explains the magnetic behaviour of strongly reworked and waterlogged gleyed loess palaeosol sequences in the relatively humid central european periglacial areas

abrupt millennial climatic changes from nussloch germany upper weichselian eolian records during the last glaciation abstract increasing attention has been focussed on the massive iceberg discharges in the north atlantic heinrich events during the last glaciation and their worldwide terrestrial counterparts however these events are particular episodes among more regular cyclic events named dansgaard oeschger events in ice cores or bond cycles in marine cores here we examine grain size 13c and magnetic susceptibility data from nussloch one of the most complete west european eolian sequence examined so far these indices indicate that during the 31 19 kyr interval using chronology provided by radiocarbon osl and tl dates millennial scale variations occurred affecting both precipitation and vegetation furthermore these are associated with oscillations in the wind strength matching the dust deposition rate in greenland as recorded in the grip ice core our study shows that the abrupt climatic changes the dansgaard oeschger events are also recorded in the west european loess sequences this implies an atmospheric mechanism linking dust deposition over greenland and europe which is probably connected to global climatic events during the last glaciation

a model of granitic melt formation by frictional heating on shear planes abstract based on geological data derived from structural investigations in the field a hypothesis of anatexite formation along shear planes by frictional heating is proposed the hypothesis involves a physico mathematical model which was tested for different mechanisms and by numerical calculations with different parameters the formation of frictionites melt rocks of small volumes m3 requires a depth of deformation in the crust of more than 5 km and a particular tectonic regime and should be possible on the assumption of a stick slip process in association with a trigger mechanism of source activation the thermodynamical model employed needs further verification from the mechanical and material points of view

lithospheric velocity structure of the anatolian plateau caucasus caspian region 1 the anatolian plateau caucasus caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities despite the complexity of the region little is known about the detailed lithospheric structure using data from 31 new permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region a 3 d velocity model is developed using joint inversion of teleseismic receiver functions and surface waves both group and phase dispersion curves love and rayleigh were derived from regional and teleseismic events additional rayleigh wave group dispersion curves were determined using ambient noise correlation receiver functions were calculated using p arrivals from 789 teleseismic 30 90 earthquakes the stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station the depths of major discontinuities sediment basement crust mantle and lithosphere asthenosphere were inferred from the velocity depth profiles at the location of each station distinct spatial variations in crustal and upper mantle shear velocities were observed the kura basin showed slow 2 7 2 9 km s upper crustal 0 11 km velocities but elevated 3 8 3 9 km s velocities in the lower crust the anatolian plateau varied from 3 1 3 2 in the upper crust to 3 5 3 7 in the lower crust while velocities in the arabian plate south of the bitlis suture were slightly faster upper crust between 3 3 and 3 4 km s and lower crust between 3 8 and 3 9 km s the depth of the moho which was estimated from the shear velocity profiles was 35 km in the arabian plate and increased northward to 54 km at the southern edge of the greater caucasus moho depths in the kura and at the edge of the caspian showed more spatial variability but ranged between 35 and 45 km upper mantle velocities were slow under the anatolian plateau but increased to the south under the arabian plate and to the east 4 3 4 4 km s under the kura basin and greater caucasus the areas of slow mantle coincided with the locations of holocene volcanoes differences between rayleigh and love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the anatolian plateau and the kura basin

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau magnetic susceptibility ms of surface sediment varies systematically across the loess plateau in central china decreasing exponentially from 200 10 8 m3 kg at the northern margin of the qinling shan to 30 10 8 m3 kg near the southern margin of the mu us desert ms correlates highly with loess median grain size r2 0 79 which decreases south southeastward across the plateau it also correlates with mean annual temperature mat and mean annual precipitation map r2 0 58 and 0 60 respectively and with their product mat map r2 0 83 which is considered a measure of potential pedogenic activity because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel it is difficult to determine their relative influence on ms a simple ms model based on the observed spatial variation in loess thickness permits quantitative assessment of the effect of the dust accumulation rate on the ms signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals the model suggests that 84 of the loess ms variance is dictated by the diluting effect of dust and 10 11 is associated with meteorological factors primarily precipitation the observed and modeled relationships support hypotheses that attribute variations in ms in the loess paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils both of which are controlled by monsoon climate

deep structures along the boundary of a collisional belt attenuation tomography of p and s waves in the greater caucasus summary seismic attenuation q 1 o fp and s waves shows a major discontinuity from the russian platform to the tectonically active greater caucasus broadband records show this boundary over paths 4 long as revealed by the decay of amplitude spectra from a digital seismic network flanking the greater caucasus we measure attenuation from individual spectra using a non linear least squares procedure to determine an attenuation parameter t simultaneously with source parameters at frequencies between 1 and 15 hz the t measurements are then inverted for spatial variations of q 1 with parametrizations of varying complexity model variance for heterogeneous structures improves by more than 30 per cent compared with homogeneous parametrizations site corrections also significantly improve the fit in these inversion results mountainous regions exhibit q values 2 3 times lower q s 775 75 than do the adjacent shields q s 2060 315 showing that the discontinuity is large for both regions q p is roughly equal to q s comparison of body wave to coda spectra indicates that intrinsic absorption rather than scattering dominates the q 1 measurements at least beneath the mountains hence q 1 variations may give a reasonable proxy for temperature if so then temperature beneath the mountains exceeds that beneath the shield by 70 400 c these temperature increases may not be high enough to generate widespread partial melting beneath the mountains but could produce regional metamorphism and could contribute substantially to isostatic compensation of the mountains whatever their origin the boundary in seismic attenuation is abrupt and large between stable craton and an adjacent mountain belt demonstrating that q 1 is a sensitive indicator of tectonic process

the cooling history of the late pliocene eldzhurtinskiy granite caucasus russia and the thermochronological potential of grain size age relationships abstract isotopic age investigations have been carried out on samples from the late pliocene eldzhurtinskiy granite great caucasus russia in order to elucidate the cooling history of this kilometere sized plutonic body the samples were taken from a horizontal profile from the edge to the centre of the granite and from a vertical profile from the top to a depth of 4570 m the 40ar 39ar results on biotites ranging from 2 5 to 1 2 ma indicate a vertical age zoning of the granite caused by regional uplift an uplift rate of 4 mm a is calculated from the age differences together with the results of fission track dating on apatite and zircon and the present day rock temperatures the biotite ages can be used to evaluate cooling rates below 400 c the cooling rates of about 180 c ma are relatively high and spatially and temporarily fairly uniform throughout the granite a geothermal gradient of 45 c km is derived from uplift and cooling rates this is identical to the present day borehole gradient the 40ar 39ar ages of distinct biotite grain fractions from one and the same sample specimen are discordant generally they show clear age grain size correlation as expected from ar diffusion theory for cooling systems thus the biotite results support the additional detailed thermochronological information the cooling rates in the temperature range of biotite closure based on the grain size age correlations of the biotites are close to 180 c ma they provide evidence that within a certain temperature interval the time temperature path of a rock may be determined exclusively by isotopic dating of different grain size fractions of only one type of mineral

pn tomographic imaging of mantle lid velocity and anisotropy at the junction of the arabian eurasian and african plates an edited version of this paper was published by blackwell publishing in geophysical journal international copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02355 x http atlas geo cornell edu middleeastnorthafrica publications al lazki2004 htm

sn attenuation in the anatolian and iranian plateau and surrounding regions an edited version of this paper was published in geophysical research letters by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018020 shtml http atlas geo cornell edu turkey publications gok et al 2003 htm

the chronological position of the lohne soil in the nussloch loess section re evaluation for a european loess marker horizon abstract the loess section of nussloch in southwestern germany is a key profile for the reconstruction of the terrestrial palaeo environment of central europe at the time of the last glacial and interglacial recently the significance of the site for palaeo environmental and geoarchaeological research increased additionally with the discovery of unique palaeolithic cultural remains from anatomically and culturally modern humans that invaded southwestern germany during the weichselian wurmian pleniglacial period at nussloch a chrono stratigraphical key position is taken by a middle pleniglacial cambisol remain which under the designation lohne soil serves as an important pedostratigraphic marker horizon for the greater area repeatedly greenland interstadial gis 8 was suggested as a likely period of soil formation for the lohne soil this interpretation is yet not justified on the basis of published chronometric data critical assessment of the data points to a later period of soil formation likely during gis7 to gis5 this conclusion is supported by a new set of radiocarbon ages for the nussloch site which are presented here for the first time consequences of a revised chronology for correlations of pleniglacial cryosols below and above the lohne soil with greenland interstadials are discussed the implications are important for european loess research as the nussloch section serves as a reference base for loess sections throughout europe

palaeoclimatic implications of the magnetic record from loess palaeosol sequence viatovo ne bulgaria summary loess palaeosol deposits in the lower danube area represent the southeastern edge of the loess cover in europe detailed rock magnetic investigations of the loess palaeosol sequence in viatovo in ne bulgaria reveal that magnetite and maghemite of very fine superparamagnetic grain size are responsible for the magnetic enhancement of palaeosol units a detailed palaeoclimatic record is obtained through high resolution measurements of magnetic susceptibility frequency dependent magnetic susceptibility and caco3 content magnetic proxies indicate a more warm and humid climate during the development of the older palaeosol units s4 s6

cenozoic recent tectonics and uplift in the greater caucasus a perspective from azerbaijan the greater caucasus is europe s highest mountain belt and results from the inversion of the greater caucasus back arc type basin due to the collision of arabia and eurasia the orogenic processes that led to the present mountain chain started in the early cenozoic accelerated during the plio pleistocene and are still active as shown from present gps studies and earthquake distribution the greater caucasus is a doubly verging fold and thrust belt with a pro and a retro wedge actively propagating into the foreland sedimentary basin of the kura to the south and the terek to the north respectively based on tectonic geomorphology active and abandoned thrust fronts the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning the central part of the mountain range defined by the main caucasus thrust to the south and backthrusts to the north forms a triangular shape zone showing the highest uplift and fastest rates and is due to thrusting over a steep tectonic ramp system at depth the meridional orogenic in front of the greater caucasus in azerbaijan lies at the foothills of the lesser caucasus to the south of the kura foreland basin

biopores and root features as new tools for improving paleoecological understanding of terrestrial sediment paleosol sequences abstract the important role of roots and rhizosphere processes is accepted for the top soil but still under debate for the deep subsoil including soil parent material especially for terrestrial sediments like loess and dune sands roots and root traces are mostly recognized in profile descriptions but not interpreted in the paleoenvironmental context further synchrony of sediment deposition and root trace formation is commonly assumed this is challenged by partially large maximum rooting depths of plants exceeding the soil depth and by frequent occurrence of secondary carbonates and biopores of potential root origin below recent soil and paleosols to improve understanding of paleoenvironmental records in terrestrial sediment paleosol sequences recent roots and root traces including calcified roots and root derived biopores were investigated in six soil loess and dune sand profiles across central and se europe visualization of small carbonate accumulations diameter 1 mm frequently called pseudomycelia by x ray microtomographic scanning and morphologic comparison with rhizoliths calcified roots diameter mostly 3 20 mm up to 100 mm possible indicate root origin of the former therefore requiring renaming to microrhizoliths quantification of roots biopores rhizoliths and microrhizoliths on horizontal levels yielded maximum frequencies of 2100 m 2 4100 m 2 196 m 2 and 12 800 m 2 respectively considering the pore volume remaining from former root growth this indicates their significant contribution to structural properties of the sediments and paleosols depth distribution of roots and root traces was frequently related to soil and paleosols respectively and mostly showed maximum frequencies within or immediately below these units root traces are therefore not necessarily of similar age like the surrounding sediment but are typically of younger age the time lag between root traces and the surrounding stratigraphic unit can vary between small time periods likely decades to centuries in case of microrhizoliths and several millenia in case of larger rhizoliths penetrating several stratigraphic units with assumed radii of former rhizosphere extension of 5 mm for microrhizoliths a frequency of 12 500 m 2 corresponded to 100 rhizosphere area in the respective depth interval these findings emphasize the meaning of root traces in sediment paleosol sequences potential temporal and spatial inhomogeneity of root growth on the one hand especially for shrub and tree vegetation and occurrence of root remains of different age and origin in identical depth intervals on the other hand hamper the assessment of the chronologic context of these with the surrounding sediment or paleosol nevertheless root traces in terrestrial archives provide valuable information with respect to paleovegetation and paleoenvironmental conditions if their chronological context is known

rock magnetic record of the last glacial interglacial cycle from the kurtak loess section southern siberia summary detailed rock magnetic investigations grain size determination and x ray diffraction were carried out on loess and buried soils of the last glacial interglacial cycle from kurtak southern siberia the susceptibility and the sand fraction of 63 m fluctuate in parallel suggesting that the higher susceptibility values in the loess horizons are mainly associated with the coarse size fraction the frequency dependence of the magnetic susceptibility of the loess and buried soils is very low and uniform indicating the absence of superparamagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility the magnetic assemblage is dominated by multidomain like magnetite grains maghemite and haematite are also present in the buried soils and loess horizons goethite may have been formed from gleying or waterlogging processes under a cooler and more humid climate the coarse magnetite grains which contribute significantly to magnetic susceptibility are probably carried by valley winds and derived from local sources thus the coarser magnetite grains with higher susceptibility values in the loess horizons could mainly reflect stronger wind intensity during cold and semi arid conditions and the consequent ease with which dense magnetite particles can be transported the lower susceptibility values in the buried soil horizons are mainly caused by weaker wind intensity during interglacial and interstadial periods although post depositional processes associated with gleying modifications are also partially responsible for the observations

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

mineral magnetic characterization of the upper pleniglacial nussloch loess sequence germany an insight into local environmental processes 1 first comprehensive environmental magnetism study of the nussloch rhine river valley germany loess palaeosol deposit 2 bulk ferrimagnetic concentration parameters are dominantly controlled by variations in coarse grained md ferrimagnetic particles of detrital aeolian origin 3 the imprint of waterlogging induced redoxomorphic processes on the magnetic record is observed by dissolution of fine grained magnetic minerals 4 the interpretation of magnetic susceptibility variations alone within loess and palaeosol deposits following the wind vigour or pedogenic enhancement models will be hindered by waterlogging induced redoxomorphic processes if present s u m m a r y presently most loess palaeosol magnetic susceptibility records are interpreted as following either the wind vigour model or the pedogenic enhancement model however redoxomorphic processes induced by waterlogging often referred to gleying in the loess literature are also known to alter loess deposits but their impact on loess palaeosol magnetic susceptibility records has received little attention the reported rock magnetic study aims to characterize the mineral magnetic response of loess to waterlogging induced redoxomorphic processes thus improving our understanding of mineral magnetic changes within loess deposits with respect to environmental and climate conditions the nussloch loess palaeosol deposit rhine valley germany was targeted because it is one of the best studied pleniglacial deposits for western europe in which numerous tundra gley intervals have been identified moreover a comprehensive high resolution environmental magnetism study has never been undertaken for this site various rock magnetism experiments were conducted at both room and low temperatures to characterise the composition concentration and relative magnetic grain size of the mineral magnetic assemblage the relative changes in magnetic parameters within the investigated loess interval are primarily controlled by 1 varying concentrations of coarse grained ferri magnetic particles of detrital aeolian origin and 2 dissolution of fine grained ferrimagnetic particles related to in situ post depositional alteration promoted by waterlogging induced re doxomorphic processes goethite is found to be ubiquitous throughout the studied interval and is argued to have both a primary aeolian and secondary in situ origin we conclude that redoxomorphic processes induced by waterlogging if present will hinder the interpretation of magnetic susceptibility variations within loess and palaeosol deposits following the expected relationships dictated by the wind vigour and the pedogenic enhancement magnetism models

cryptic post depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility abstract our anisotropy of magnetic susceptibility ams investigation of the gold hill steps ghs2 and halfway house hh3 loess and paleosol profiles in central alaska confirms that post depositional reworking of loess at gold hill steps has taken place and of greater importance identifies the reworked depth intervals in ghs2 the majority of the loess below 7 80 m depth has been reworked the loess at the halfway house site is as stated in the literature a predominantly undisturbed aeolian deposit however we have identified two intervals that have been reworked in hh3 we infer from the depth variation of the ams orientation distribution at ghs2 that the presence of permafrost in the past was the dominant active mechanism producing the observed deformations permafrost loess behaved 1 as impermeable layers focusing and channeling flow most likely that of groundwater and 2 as rigid bodies undergoing rotations and lateral translations a modern analogue of focused flow by an impermeable layer is identified at hh3

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

seismic structure of the crust and uppermost mantle beneath caucasus based on regional earthquake tomography abstract we present a new seismic model of the crust beneath the caucasus based on tomographic inversion of p and s arrival times from earthquakes occurred in the region recorded by regional seismic networks in the caucasian republics the resulting p and s velocity models clearly delineate major tectonic units of the study area a high velocity anomaly in transcaucasian separating the great and lesser caucasus possibly represents a rigid crustal block corresponding to the remnant oceanic lithosphere of tethys another high velocity pattern coincides with the southern edge of the scythian plate strongly deformed areas of great and lesser caucasus are mostly associated with low velocity patterns representing thickened felsic part of the crust and strong fracturing of rocks most cenozoic volcanic centers of caucasus match to the low velocity seismic anomalies in the crust for example the kazbegi volcano group is located above an elongated low velocity anomaly squeezed between high velocity segments of transcaucasian and scythian plate we propose that mantle part of the arabian and eurasian plates has been delaminated due to the continental collision in the caucasus region as a result overheated asthenosphere appeared nearly the bottom of the crust and facilitated melting of the crustal material that caused the origin of recent volcanism in great and lesser caucasus

middle and late pleistocene loess sequences at batajnica vojvodina serbia abstract loess sequences in the vojvodina region northern serbia reveal a continuous record of paleoclimatic variations during the middle and late pleistocene the most detailed stratigraphic information comes from remarkable exposures on the cliffs of the right danube bank from vukovar to belgrade the batajnica loess section has been recognized as one of the most complete middle and late pleistocene records in this region a more than 40 m thick loess paleosol succession represents environmental transition from relative thin loess layers and rubified soils in lower part of profile to thick loess and fossil chernozems characterizing the last three glacial interglacial cycles the proposed stratigraphic model is based on a detailed magnetic susceptibility ms record which is related to the deep sea isotope stratigraphy and on correlation with other eurasian loess records using the distinct ms pattern of selected loess paleosol couplets this new stratigraphic model suggests serious revision of previous chronological interpretations ms as function of depth shows a well known pattern of low values in loess and high values in paleosols indicating strong enhancement of magnetic minerals during soil formation with the exception of the recent soil v s0 which is strongly contaminated by archaeological artifacts the third paleosol v s3 reveals the highest values in ms and a very distinct double peak the rock magnetic signal at batajnica resembles the typical pattern of the enviromagnetic records determined from other eurasian loess sites the paleopedological interpretations rubification index values and rock magnetic record at batajnica yield valuable data for the reconstruction of paleoclimatic fluctuations for the last 5 glacial interglacial cycles at least moreover the record provides an important link between the classical central european loess sites and the central asian and chinese loess provinces

morin transition in hematite size dependence and thermal hysteresis 1 hematite is a frequently used mineral in paleomagnetic and environmental magnetic studies just below room temperature it undergoes a magnetic phase transition the morin transition whose nature is an important part of our basic understanding of hematite s magnetism and magnetic memory we have determined the temperature tm of the morin transition from saturation remanence warming curves to be 250 261 k for 0 5 6 mm hematite natural single crystals 257 260 k for 45 600 m sieved crystal fractions and 241 256 k for submicron synthetic hematites with grain sizes between 120 and 520 nm the variation must be due to differences in crystal morphology lattice strain and crystal defects common in both synthetic and natural crystals our results are compatible with published data for 100 nm to 10 mm hematites and show that tm is nearly size independent decreasing very gradually as particle size decreases over this broad range which includes both multidomain md and single domain sd structures however tm decreases sharply between 90 and 30 nm below 20 nm the transition disappears entirely as near surface spins deviate strongly from the antiferromagnetic easy axis our sd and md hematites exhibit a thermal hysteresis in the morin transition the values of tm in cooling and in heating are different for the same cooling warming rate tm is much greater for submicron hematites than for larger crystals we attribute the lag in the transition in both cooling and heating to crystal imperfections and resulting internal stresses and speculate that defects may serve to pin and stabilize surface spins preventing spin rotation in a region large enough to trigger the phase transition would inhibit destabilization of the weakly ferromagnetic phase in cooling and the antiferromagnetic phase in heating the wide distribution of particle sizes in our submicron samples may also play a role

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

climatic interpretation of the luochuan and lingtai loess sections china based on changing iron oxide mineralogy and magnetic susceptibility abstract hematite and goethite estimated from diffuse reflectance spectra and magnetic susceptibility ms have been determined from both the luochuan and lingtai loess sections of the loess plateau of central china changing concentrations of these iron oxides and ms were used to determine paleoclimatic change based on a model that relates pedogenic production of hematite and magnetite to precipitation we propose two precipitation phases on the loess plateau during the last 2 6 ma from the wucheng red clay boundary up to paleosol s5 mis 13 precipitation on the loess plateau was moderate probably not frequently exceeding 450 mm yr and highly seasonal from s5 to the present precipitation during interglacial times has gradually increased to the present levels of 600 650 mm yr for the localities examined throughout the pleistocene spanning both glacial and interglacial conditions hematite to goethite ratios display a consistent decrease this decrease suggests that precipitation on the loess plateau has been getting less seasonal and or has been occurring during times when temperature was lower in addition to these long term changes it also appears that iron oxide records from the loess plateau exhibit 400 500 ka cycles from the wucheng red clay boundary to s5 these 400 500 ka cycles may be analogous to similar length cycles recorded in 13 c marine records in the south china sea and may be linked through weathering and silica production as a result of the asian monsoon

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

iron mineralogical proxies and quaternary climate change in se european loess paleosol sequences abstract the loess paleosol sequences batajnica stari slankamen serbia and mircea voda romania represent key archives for the climate and landscape development of the middle and lower danube basin during the last 700 000 years for deciphering the quaternary climate evolution in these regions the batajnica stari slankamen and mircea voda sites are for the first time studied by a multi proxy approach based on iron mineralogical parameters changes in the iron mineralogical composition are identified and characterized by rock magnetic investigations diffuse reflectance spectroscopy drs and munsell color based proxies the results show that environmental conditions during mid and early middle pleistocene interglacials were more favorable for hematite formation suggesting a more oxidizing pedoclimate as in the more recent interglacials this is also reflected in a gradual increase of the anhysteretic remanent magnetization vs saturation isothermal remanent magnetization arm sirm ratio in the studied profiles changes in this ratio can be linked to a preferential hematitization of coarse grained ferrimagnetica and relates to warmer climate conditions and a more extended estival dry period at the same time rock magnetic parameters indicate a preferential destruction of fine grained magnetic particles in older paleosols resulting from seasonal excess moisture a progressive cooling and decrease of rainfall during the middle and late pleistocene is evidenced not only for interglacial pedocomplexes but also for glacial loess layers this finding is in line with previously published proxy records of silicate weathering and clay formation at these sites and similar trends reported from other sites in the european steppe belt relating iron mineralogical proxies to paleopedological characteristics and proxies of silicate weathering additionally a change in the seasonal pattern of the interglacial temperature and precipitation regime from a mediterranean type to a steppe type climate is revealed highlighting the potential of such a multi proxy approach possible triggers for this paleoenvironmental evolution are discussed as well finally highlighting a quaternary uplift hypothesis which best could explain the inferred trend of cooling aridification and increasing continentality accordingly changes in atmospheric circulation and rain shadow effects induced by small scale uplift of european mountain belts alps carpathians dinaric alps would provide a driving mechanism for the westward extension of the eurasian steppe belt into central and se europe during the quaternary

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

alteration and dissolution of fine grained magnetite and its effects on magnetization of the ocean floor abstract scanning and transmission electron microscopy stem of ocean floor pillow basalts with ages between 0 and 70 ma reveals progressive alteration of submicrometer titanomagnetite to phases such as goethite and clays in contrast larger titanomagnetite grains 1 m oxidize to titanomaghemite without apparent change in crystal morphology rock magnetic experiments are consistent with a selective removal of the submicrometer grains as the basalts age and show good correlations between the ranges of grain sizes observed by stem and those indicated by hysteresis properties remanence contributions from the larger pseudo single domain and multi domain titanium iron oxides are inferred to decrease only slightly as the ocean floor becomes older whereas the overall remanence decays with age as the substantial contribution from stable single domain titanomagnetite grains diminishes greatly due to their alteration to other phases although more work on many more samples is required to verify our conclusions the current data imply that this alteration is one of the reasons that amplitudes of marine magnetic anomalies diminish with age over time scales of tens of millions of years

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

iron oxide coatings on sand grains from the atlantic coastal plain high resolution transmission electron microscopy characterization nanoscale characterization of so called iron oxide coatings on aquifer sands is vital for understanding the fate and transport of naturally occurring and anthropogenic chemical species these coatings which typically have a strong reddish color are commonly assumed to consist primarily of iron oxides and oxyhydroxides this work shows that the yellowish red to strong brown coatings on sediments from an atlantic coastal plain aquifer in virginia are predominantly a mixture of si and al rich nanophases of variable crystallinity with interspersed smectite and agglomerates of goethite nanoparticles clusters of bacterial cells diatom fossils sponge spicules and other trace minerals are also observed

40ar 39ar and 18o 16o studies of the chegem ash flow caldera and the eldjurta granite cooling of two late pliocene igneous bodies in the greater caucasus mountains russia volcanic and intrusive rocks of the chegem caldera and the nearby eldjurta eldzhurtinskiy granite record a late pliocene episode of silicic magmatism in the north central caucasus mountains surface exposures created by the recent rapid uplift and erosion of the caucasus mountains span a 2 km vertical section of chegem caldera fill and 1150 m of the eldjurta granite cored mineral exploration drillholes in the eldjurta granite extend the sampling to a depth of 4 km the unique sampling range available in these two young igneous bodies affords an excellent opportunity to study their denudation and cooling histories which we examine by means of 40 ar 39 ar and 18 o 16 o measurements on an extensive sample suite total fusion biotite and sanidine ages from eight chegem tuff samples both intracaldera and outflow are analytically indistinguishable with a weighted mean of 2 82 0 02 ma a cross cutting granodiorite porphyry intrusion has a sanidine total fusion age of 2 84 0 03 ma and whole rock incremental heating of a post caldera andesite flow which caps the caldera fill yields an age of 2 82 0 02 ma thus caldera formation and post caldera resurgence and volcanism all occurred within a very short time 50 000 yr biotite total fusion ages of ten eldjurta granite samples including seven from 500 m intervals in the 4 km deep drillhole show a systematic linear decrease in age with depth from 1 90 ma near the roof contact of the granite to 1 56 ma at a depth of 3700 m assuming these ages were set at the same temperature this age depth gradient implies an isotherm migration rate of 13 mm yr between 1 90 and 1 56 ma this migration rate is due to a combination of rapid denudation and downward relaxation of isotherms with cooling rates between 200 and 500 c ma during this period oxygen isotopic compositions of quartz k feldspar plagioclase and biotite from the drillhole samples below the 800 m depth are fairly uniform and record primary igneous 18 o values with little evidence for subsolidus hydrothermal activity however in surface outcrop samples and in the shallowest drillhole sample mineral 18 o values have been lowered by up to 3 by interaction with an external meteoric hydrothermal fluid the primary mineral 18 o values of the eldjurta granite are distinctly higher than the corresponding phenocryst 18 o values in the chegem volcanic rocks indicating that the two bodies evolved as separxate magma batches

link between european and north atlantic abrupt climate changes over the last glaciation 1 sub millennial timescale climate variations correlated with those in the north atlantic area are identified in the loess sequence from nussloch germany exceptionally developed over the interval between about 38 000 and 18 000 years ago the dansgaard oeschger do events 8 to 2 as well as some less pronounced warming episodes recorded in the greenland ice have their counterpart in the nussloch loess stratigraphy and in the variations of the loess grain size index gsi the north atlantic heinrich events 3 and 2 are expressed at nussloch as maxima of the gsi record the similarity of the fine variations in the nussloch loess and the greenland ice records points to an intimate link of climate changes in western europe with those in the north atlantic

proxy records of climate change in the uk over the last two millennia documented change and sedimentary records from lakes and bogs this project of collaborative research project ha of the nerc tigger programme terrestrial initiative in global geological environmental research into the climatic history of the late holocene used a variety of techniques both tested and experimental on carefully chosen sites in lowland and upland environments to derive high quality proxy records of climatic change over the last 2000 years the methodology involved the use of high resolution analyses diatoms cladocera chironomids ostracods magnetics pollen macrofossils humification lipid biomarkers and stable isotopes of the stratigraphy of well dated ams and conventional 14 c 210 pb pollen tephra scp spheroidal carbonaceous particles cores from a remote montane lake and lowland lakes and from a montane blanket and a lowland raised bog linked to historical records of climate change this paper reviews some of the major results obtained both in the magnitude synchroneity and periodicity of change especially during the little ice age and in the evaluation of the various techniques used the fact that such techniques can be validated and calibrated against a known climatic signal in the recent past allows for better interpretation of changes in the more distant past