new absolute time scale for the quaternary climate in the chinese loess region by grain size analysis continuous loess sequences in china provide not only information for paleoclimatic reconstructions but also permit the establishment of a reliable absolute time scale for the quaternary an empirical relationship is developed between the grain size of the loess and the sedimentation rate in a short well dated reference section step 1 this relationship is extrapolated to the complete quaternary section step 2 after derivation of the sedimentation rate by measuring the grain size in all the layers of the sequence the duration of deposition of each layer is obtained by dividing thickness by sedimentation rate and subsequently the age of each point in the sequence is calculated by adding together all the duration values of the overlying layers the chronology of the extrapolated part of the section obtained in this way is independent of dates provided by other methods and may also be checked by them

european glacial dust deposits geochemical constraints on atmospheric dust cycle modeling for a long time global paleodust numerical simulations have greatly underestimated dust sources other than modern deserts recent modeling experiments incorporating glaciogenic sources of dust have positively improved the agreement between model and paleodust data this highlights the importance of accurately representing all areas potentially subjected to deflation during an investigated interval geochemical results obtained from european loess sequences collected along a 50 n transect combined with dust emission simulations reveal the geographical distribution of the most important european dust sources between 34 ka and 18 ka we demonstrate that most european dust traveled only a few hundred kilometers or less within the boundary layer from its source before deposition we conclude that our results encourage acquisition of similar geochemical data for other relevant areas in the world further they could provide critical constraints to benchmark atmospheric models contributing to improve their performance in simulating dust cycle and associated climate feedbacks

young ores in old rocks proterozoic iron mineralisation in mesoarchean banded iron formation northern pilbara craton australia abstract the origin of bedded iron ore deposits developed in greenstone belt hosted algoma type banded iron formations of the archean pilbara craton has largely been overlooked during the last three decades two of the key problems in studying these deposits are a lack of information about the structural and stratigraphic setting of the ore bodies and an absence of geochronological data from the ores in this paper we present geological maps for nearly a dozen former mines in the shay gap and goldsworthy belts on the northeastern margin of the craton and the first u pb geochronology for xenotime intergrown with hematite ore iron ore mineralisation in the studied deposits is controlled by a combination of steeply dipping ne and se trending faults and associated dolerite dykes simultaneous dextral oblique slip movement on se trending faults and sinistral normal oblique slip movement on ne trending faults during initial ore formation are probably related to e w extension uranium lead dating of xenotime from the ores using the sensitive high resolution ion microprobe shrimp suggests that iron mineralisation was the cumulative result of several proterozoic hydrothermal events the first at c 2250 ma followed by others at c 2180 ma c 1670 ma and c 1000 ma the cause of the first growth event is not clear but the other age peaks coincide with well documented episodes of orogenic activity at 2210 2145 ma 1680 1620 ma and 1030 950 ma along the southern margin of the pilbara craton and the capricorn orogen farther south these results suggest that high grade hematite deposits are a product of protracted episodic reactivation of a structural architecture that developed during the mesoarchean the development of hematite mineralisation along major structures in mesoarchean bifs after 2250 ma implies that fluid infiltration and oxidative alteration commenced within 100 myr of the start of the great oxidation event at c 2350 ma

structures caused by repeated freezing and thawing in various loamy sediments a comparison of active fossil and experimental data in this paper the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments experimental data are compared with observations performed on active forms in high arctic and alpine mountain environments those observations are also compared with phenomena observed in fossil periglacial formations of western europe platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation when a long series of alternating freezing and thawing affects platy structures the fabric evolves also being influenced by slope and drainage conditions cryoturbations frostcreep and gelifluction can appear they are characterized by specific microfabrics which are better developed with an increasing number of cycles this is clear in experiments where hydraulic and thermal parameters are better controlled vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils the genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw

upper pleistocene loess palaeosol records from northern france in the european context environmental background and dating of the middle palaeolithic abstract in northern france the loess cover from the last glacial weichselian is represented by a semi continuous mantle up to 8 m in thickness in the best localities such as leeward slopes e ne exposures in this large area pedostratigraphic sequences from the last interglacial glacial cycle eemian weichselian have been intensively studied especially under the auspices of active rescue archaeological programmes that have provided hundreds of individual sequences from test pits or excavations in spite of variations in the thickness of the different stratigraphic units driven by differences in geomorphological contexts the pedostratigraphic sequences from the last interglacial glacial cycle exhibit a particularly constant pedosedimentary pattern including well identified pedological and periglacial marker horizons that can be followed towards the east in belgium in germany and even in central europe according to the newest data it is shown that northern france loess palaeosol sequences are well suited to record the response of western european environments to rapid climatic changes dansgaard oeschger cycles the main objective of this paper is to present a summary of the pedostratigraphic sequence from northern france supplemented by the data from the new reference sequence of havrincourt and a global correlation scheme with surrounding areas in northern france the synthesis of the observations carried out on ca 100 sequences during the last 20 years allows the establishment of a highly detailed pedostratigraphic and chronostratigraphic scheme that represents a unique database for the discussion of the relations between palaeolithic occupation and environment in this context a strong relationship between the intensity of human occupation and the climatic and environmental context is demonstrated this relationship appears to be conditioned by the relative abundance of large mammal fauna itself linked to vegetation density as indicated by the extremely sparse biomass and the hiatus in human occupation that characterise upper pleniglacial loess

high resolution record of the environmental response to climatic variations during the last interglacial glacial cycle in central europe the loess palaeosol sequence of dolni věstonice czech republic abstract high resolution multidisciplinary investigation of key european loess palaeosols profiles have demonstrated that loess sequences result from rapid and cyclic aeolian sedimentation which is reflected in variations of loess grain size indexes and correlated with greenland ice core dust records this correlation suggests a global connection between north atlantic and west european air masses herein we present a revised stratigraphy and a continuous high resolution record of grain size magnetic susceptibility and organic carbon 13c of the famous of dolni vestonice dv loess sequence in the moravian region of the czech republic a new set of quartz osl ages provides a reliable and accurate chronology of the sequence s main pedosedimentary events the grain size record shows strongly contrasting variations with numerous abrupt coarse grained events especially in the upper part of the sequence between ca 20 30 ka this time period is also characterised by a progressive coarsening of the loess deposits as already observed in other western european sequences the base of the dv sequence exhibits an exceptionally well preserved soil complex composed of three chernozem soil horizons and 5 aeolian silt layers marker silts this complex is at present the most complete record of environmental variations and dust deposition in the european loess belt for the weichselian early glacial period spanning about 110 to 70 ka allowing correlations with various global palaeoclimatic records osl ages combined with sedimentological and palaeopedological observations lead to the conclusion that this soil complex recorded all of the main climatic events expressed in the north grip record from greenland interstadials gis 25 to 19

short climatic oscillations in a western european loess sequence kesselt belgium this new study of the loess section at kesselt is focused mainly on the reconstruction of palaeoenvironments of the last glacial period in the belgian dutch region detailed grain size analyses in combination with the study of the palaeosols and periglacial structures indicate the occurrence of climatic cycles during loess deposition permafrost development coincided with enhanced deposition of relatively coarse loess and alternated with permafrost degradation decreased deposition of finer loess and tundra soil formation a newly designated palaeosol lafelt soil is described in detail particularly in terms of its micromorphological properties it is a luvisol and its chronostratigraphical position is still open to debate but radiocarbon dating places it in the weichselian middle pleniglacial 1998 john wiley sons ltd

an integrated rock magnetic and geochemical approach to loess paleosol sequences from bohemia and moravia czech republic implications for the upper pleistocene paleoenvironment in central europe abstract two central european loess paleosol sequences mis 6 2 from central bohemia zem chy and southern moravia dobsice situated in the important climatic transition zone between the oceanic atlantic and continental climate regimes were investigated for rock magnetism geochemistry grain size and micromorphology in both sites the magnetic profile shows good agreement with the standard model of magnetic enhancement in paleosols as established in the chinese loess the magnetic signal is dominated by the presence of fine grained magnetite and maghemite formed in situ and controlled by the intensity of soil formation magnetic proxies corresponded to proxies of chemical weathering and leaching intensity such as the chemical index of alteration cia the cation exchange capacity cec and the rb sr ratio correlation coefficient r 0 6 0 93 during the whole lower weichselian mis 5d 5a and in general also during the pleniglacial mis 4 2 nevertheless for the eemian period mis 5e this relationship was not always valid either due to weak magnetic enhancement at dobsice or even weak depletion of the magnetic minerals with soil formation at zem chy the presented data demonstrate that magnetic signals can be overprinted more easily than chemical proxies during later diagenetic events and are hence not in all cases reliable for deciphering paleoclimate changes during all periods of the studied time interval rock magnetic geochemical and micromorphological results suggest drier conditions in southern moravia compared to central bohemia during the weichselian glacial probably due to the more continental climate in southern moravia

links between bulk sediment particle size and magnetic grain size general observations and implications for chinese loess studies using a combination of particle size analysis magnetic measurements scanning electron microscopy and transmission electron microscopy imaging this study shows that in a wide range of depositional environments there is a strong link between particle size classes and magnetic response especially below the upper limit of stable single domain magnetic behaviour ferrimagnetic grain assemblages dominated by stable single domain magnetosomes regularly have peak susceptibility and remanence values in coarser grades than do those containing finer grained viscous and superparamagnetic secondary magnetic minerals formed during pedogenesis this effect is despite the fact that there is a one to two orders of magnitude size difference between the particle size boundaries at 1 or 2 m and key domain state transitions mostly below 0 05 m the implications of these results are explored using samples spanning 22 myr of loess accumulation on the chinese loess plateau the results from the loess sections complemented by data from low temperature magnetic experiments show that there are subtle distinctions in mean ferrimagnetic grain size between the pleistocene and miocene parts of the record thus allowing more refined rock magnetic interpretations of the fine grained ferrimagnetic mineral assemblages arising from the effects of weathering pedogenesis and possibly diagenesis in the sections studied

rapid and cyclic aeolian deposition during the last glacial in european loess a high resolution record from nussloch germany abstract this paper reports the results of an investigation of the weichselian upper pleniglacial loess sequences of nussloch rhine valley germany based on stratigraphy palaeopedology sedimentology palynology malacology and geochemistry 13 c supported by radiocarbon tl and osl dating grain size and magnetic susceptibility records are taken at 5 cm intervals from the upper pleniglacial upg loess the data indicate cyclic variations in loess deposition between ca 34 and 17 ka when the sedimentation rate is especially high 1 0 1 2 m per ka for more than 10 m the grain size index gsi ratio of coarse silt versus fine silt and clay shows variations which are assumed to be an indirect measurement of wind intensity the sedimentation rate interpreted from the profiles indicates high values in loess loess events le 1 to le 7 and low or negligible values in tundra gley horizons g1 to g8 osl ages from the loess and 14 c dates from organic matter in the loess show that loess deposition was rapid but was interrupted by shorter periods of reduced aeolian sedimentation comparison between the data from nussloch and other european sequences demonstrates a progressive coarsening of the loess deposits between ca 30 and 22 ka this coarsening trend ends with a short but major grain size decrease and is followed by an increase to a new maximum at 20 2 ka w shape correlation between the loess gsi and the greenland ice core dust records suggests a global connection between north atlantic and western european global atmospheric circulation and wind regimes in addition the typical upper pleniglacial loess deposition begins at ca 30 31 ka close to heinrich event he 3 and the main period of loess sedimentation at about 25 2 ka is coeval to he 2 correlation of magnetic susceptibility and grain size records shows that the periods characterised by high gsi coincide with an increase in the amount of ferromagnetic minerals reworked from the rhine alluvial plain they suggest enhancement in the frequency of the storms from n nw these results are integrated within a palaeogeographical model of dust transport and deposition in western europe for the weichselian upper pleniglacial or late pleniglacial

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

grain size of fine grained windblown sediment a powerful proxy for process identification abstract dust transport by the wind is not a uniform process but may occur in different modes according to source area conditions and transport height and distance subsequently these differences are expressed in terms of grain size and fluxes of the aeolian deposits transport distances may vary from several tens of meters to thousands of kilometers while the height accordingly may vary from meters to more than thousand meters a relation with grain size distributions may be established on the base of type occurrences of different loess facies three main loess populations and several subpopulations of primary windblown origin may be defined according to their grain size dominated by fine sand to very coarse silt silt and very fine silt to clay respectively each of them reflects a specific aeolian process and transport conditions it follows that the grain size distribution of a loess deposit is an excellent proxy for the reconstruction of aeolian processes and wind circulation patterns apart from primary pure wind deposition loess may also be affected by secondary post depositional processes examples are settling of loess particles in a lacustrine setting and reworking by rivers or surface runoff although the primary loess characteristics are maintained reworking processes leave also their imprint in the grain size distribution as a useful tool for secondary process identification

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

microstructures textures and deformation mechanisms in hematite abstract deformation and recrystallization of hematite in iron formations and high grade ore bodies of the caue formation from the quadrilatero ferrifero district minas gerais brazil resulted in several types of fabrics depending on the tectonic and metamorphic imprint the fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic mylonitic with local development of cataclastic features complete pole figures of the crystallographic planes 003 basal plane 110 prism and 104 rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types the configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore the analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active basal slip diffusion processes and anisotropic grain growth post tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation

loess in europe mass accumulation rates during the last glacial period abstract upper pleistocene loess palaeosol sequences provide excellent high resolution terrestrial archives of climate forcing due to improvements in numerical age determinations especially in luminescence dating methods a more reliable time based reconstruction of the past climate and environmental change has become available for the loess record in europe chronological information was collected from 43 sites along a northwest to southeast transect in europe thirty three of these sites had sufficient age information to allow estimation of mass accumulation rates and it was possible to isolate the mass accumulation rates of primary loess during the last glacial period 28 13 ka bp at 21 of these locations these sites fall along a coarse climatic gradient from the relatively coastal climate of belgium and france to the drier more continental climate of central europe interpreting mass accumulation rates of loess in terms of this climatic gradient is not straightforward as these deposits are dominated by sources in floodplains and large river systems thus accumulation rates are influenced strongly by regional wind and precipitation patterns but mostly by the availability of glacially derived material from the alps and the periglacial terrains that characterized european fluvial systems during and immediately following glaciation

introducing an improved multi proxy approach for paleoenvironmental reconstruction of loess paleosol archives applied on the late pleistocene nussloch sequence sw germany to study paleoenvironmental and paleoclimatic changes in loess paleosol sequences lps most proxies except for screening parameters have often been applied at low sampling density typically 1 2 per stratigraphic unit this might lead to results that overlook paleovegetation effects that were not only restricted to paleosols but also affected underlying loess material here a new profile was investigated in the loess paleosol sequence lps at nussloch sw germany using a high resolution multi proxy approach to improve our understanding of the late pleistocene record which serves as a standard sequence in central europe this approach included several geophysical and geochemical parameters as well as frequencies of root related features grain size distribution and osl dating enabled correlation of the new section with the nearby standard profile p4 revealing considerable variations of the thickness of stratigraphic units due to local small scale variations in depositional conditions and paleogeomorphology of longitudinal greda structures magnetic susceptibility revealed weathering of the entire lps under more humid conditions than those described for se european and chinese lps it further enabled a rough differentiation between an interval that was influenced by pedogenic processes lower pleniglacial to lower part of the upper pleniglacial and loess that was not markedly affected by soil formation color measurements confirmed these results and enabled the identification of several paleosols in the upper pleniglacial for the uppermost part of the lps low magnetic susceptibility and inorganic geochemical parameters such as low fe ti ratios indicated only weak or no pedogenic influence in contrast considerable variations e g in carbonatic carbon contents and organic carbon nitrogen c n ratio might be related to the high frequency of calcified root remains up to 200 rhizoliths m 2 and up to 12 500 microrhizoliths m 2 in certain depth intervals of the lps entailing incorporation and degradation of organic matter frequencies of biopores which are suggested to derive largely from former root growth and to a lesser extent from insect and earthworm bioturbation were related to paleosols and thus confirmed the pedostratigraphy an improved assessment of terrestrial sedimentary archives can be achieved by high resolution multi proxy analysis and three dimensional investigation of terrestrial sediments that are prone to bioturbation c 2014 elsevier b v all rights reserved

the upper pleistocene loess record at harmignies belgium high resolution terrestrial archive of climate forcing abstract the loess palaeosol sequence in a section at harmignies in belgium is one of the most important upper pleistocene sites in northwest europe an extensive luminescence dating study was carried out to get a reliable chronological framework and to understand the climate forcing in an area where continuous permafrost dominated during most of the last glaciations twenty eight samples were investigated by infrared optically stimulated luminescence irsl and thermoluminescence tl methods resulting in more than 100 luminescence age estimates the dating results on colluvial sediments are in good agreement with landscape destabilisation phases during ois 5 during the last glacial four major periods of loess accumulation were likely to have occurred in europe at the harmignies section the oldest loess was deposited between 67 000 to 60 000 yr the second one from 60 000 to 50 000 yr the third one from 50 000 to 40 000 yr and the youngest loess accumulation period started most likely after the heinrich 3 event and lasted until the heinrich 2 event 25 000 20 000 yr two main periods of permafrost occurred at approximately 60 000 and 28 000 yr bp

thermoluminescence dating of loess recent developments abstract thermoluminescence tl dating has developed into an important chronological method in loess research especially beyond the range of radiocarbon dating the principles and the present stage of the method applied to windborne sediments are summarized in this article advice to users is provided for appropriate sampling and handling of tl samples as well as for measuring the natural radioactivity in the field the potential and the limitation of loess tl dating are discussed in terms of various case studies from central europe in spite of the problem of age underestimation for old loess tl dating has already contributed greatly towards a better understanding of the loess stratigraphy and chronology thermoluminescence as a dating tool for archaeological samples has been established for 30 years but the application of tl dating to quaternary sediments is apart from some earlier attempts in the soviet union shelkoplyas and morozov 1965 dreimanis et al 1978 a more recent development essentially of the last decade wintle and huntley 1979 since several review papers have already appeared on this subject e g wintle and huntley 1982 mejdahl 1986 wintle 1987 singhvi and wagner 1986 berger 1988 the present contribution will only briefly mention the underlying tl principles and the dating techniques but will focus on the recent development in tl dating of loess

periglacial fluvial systems in northwest europe during marine isotope stages 4 and 3 comparison of fluvial successions in river valleys dating from marine isotope mi stages 4 and 3 in a west east transect from britain to poland shows the spatial and temporal variation in palaeohydrological characteristics of northwest european river valleys during these stages mi stage 4 has been a period of deep fluvial incision following this erosion most valleys were filled during mi stage 3 with successions of gravelly river deposits britain or sand silt peat successions northwest european lowlands the sedimentology of the deposits suggests strong discharge variations caused by a nival discharge regime with pronounced spring snowmelt discharges the mi stage 3 climate oscillations generally cannot be traced in the fluvial record an incision phase of hengelo interstadial age has been found in the netherlands but similar incision phases related to other warming events have not been proved convincingly the restricted reaction of the river systems is caused by the absence of geomorphologically effective vegetation changes and relatively minor variations in precipitation during mi stage 3 over longer time scales silt and peat beds gradually decrease in the younger post hengelo upton warren part of mi stage 3 corresponding with evidence of aeolian activity and permafrost this is related to the longer duration of the stadials in this part of mi stage 3

iron oxide mineralization at the contact zone between phyllite and itabirite of the pau branco deposit quadrilatero ferrifero brazil implications for fluid rock interaction during iron ore formation this study examines the whole rock geochemistry and laser ablation inductively coupled plasma mass spectrometry la icp ms iron oxide chemistry of itabirite and related iron ore as well as underlying phyllitic wall rock of the pau branco iron ore deposit quadrilatero ferrifero brazil the phyllite and iron ore of pau branco extend from hypogene deep seated into supergene weathered zones the phyllitic sequence that underlies the itabirite hosted iron ore along a sheared contact includes from the bottom to top carbonaceous and carbonate chlorite and fe rich zones which likely reflect distal to proximal alteration halos the fe rich phyllite and iron ore comprise a complex iron oxide mineralogy 1 magnetite martite is hosted in itabirite and related medium grade iron ore and present as disseminated minerals in phyllite 2 microplaty hematite replaces chlorite and carbonate in the phyllite 3 granoblastic hematite is a recrystallization precipitation product and the dominant iron oxide of the hard iron ore 4 schistose specular hematite overgrows earlier iron oxides and 5 goethite replaces earlier hematite and amphibole within the weathering horizon whole rock geochemistry and related mass balance calculations reveal that unlike the itabirite hosted iron ore interpreted to be the result of a solely residual iron enrichment via depletion of most major oxides and trace elements the iron enrichment of the phyllite is caused by addition of fe 2 o 3 the fe 2 o 3 is likely sourced from the overlying itabirite iron ore and is mineralogically reflected in the replacement of carbonate and chlorite by hematite the rare earth elements ree abundances of the different ore and phyllite zones reveal seawater like ree signatures and y ho ratios of the itabirite hypogene and supergene iron ore shale atypical ree patterns in the unaltered phyllite and eu fractionation trends this suggests a distinct input of hydrothermal fluids during the fe enrichment of the phyllite locally restricted ce fractionation is attributed to distinct e g mn rich lithostratigraphic intercalations within the itabirite laser ablation icp ms mineral chemistry of phyllite hosted martite and microplaty hematite suggests a strong chemical inheritance by the host rock and precursor mineral positive ce anomalies are restricted to phyllite and itabirite hosted martite only and therefore may reflect the highly oxidative conditions during martitization at pau branco the fluid rock interaction affected not only the itabirite but also the underlying phyllite resulting in distinct alteration halos that extend beyond the itabirite toward the footwall the significant chemical influence and importance of country rock lithologies as a possible elemental source for example must be taken into account when interpreting whole rock geochemical data and investigating an itabirite banded iron formation hosted iron ore system

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

geomorphological evolution of a lowland valley system during the weichselian weichselian geomorphological and fluvial evolution has been recorded in the valley fill of the reusel a small tributary of the lower maas river it has been studied by means of borehole sections a first deep incision into the substratum occurred during the early weichselian lower pleniglacial this was followed by aggradation at first by a braided river at a later date by a meandering river dating respectively from the lower and middle pleniglacial the upper pleniglacial aggradation again points to a braided river system the end of the pleniglacial is characterized by aeolian infilling of the valley and decreasing carrying capacity of the river

the late pleistocene loess palaeosol sequence of middle belgium abstract in belgium two areas show extended late pleistocene loess cover the hesbaye close to liege and the haine basin around mons for decades correlation between both areas remained problematic here we will show how by way of complementary approaches the records of the haine and the hesbaye could be inserted into a high resolution pedosedimentary sequence encompassing the major part of the late pleistocene and reproducible at the scale of the belgian loess belt based on the pedosedimentary and palaeoenvironmental signatures of the belgian sequence comparisons are proposed with high resolution loess sequences of eastern europe and central siberia they give access to well documented palynological data for the first part of the late pleistocene and to a strong climatic record on loess framed between 45 and 10 ka bp by long series of radiocarbon dates on charcoal and wood remains the conjunction of these complementary loess records has further given way to a consistent proxy correlation scheme linking a high resolution continental climatic record to the greenland ice sequence

magnetic susceptibility of loess in china abstract the low field susceptibility of the loess deposits in the chinese loess plateau is due to both paramagnetic and ferromagnetic minerals paramagnetism can be seen in the less to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles are not as strongly developed as in the heavily weathered palaeosols frequency dependent susceptibility and minimum unblocking temperatures of low temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds this grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau are considered as strong evidence that the ultrafine magnetite is not of detrital aeolian origin but was formedin situ the pedogenetic processes are clearly related to palaeoclimatic changes therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2 5 ma since the palaeomagnetically dated beginning of loess sedimentation in china

landscape instability at the end of mis 3 in western central europe evidence from a multi proxy study on a loess palaeosol sequence from the eastern lower rhine embayment germany abstract the lower rhine embayment hosts important loess palaeosol sequences lps within the western european loess belt yielding valuable information on landscape evolution and palaeoclimatic dynamics the study focusses on the palaeoenvironmental development based on a lps from the eastern shoulder of the lower rhine embayment dusseldorf grafenberg the palaeoenvironmental development within the study area is presented and discussed based on high resolution grain size analyses selected environmental magnetic parameters and geochemical analyses complemented by luminescence age estimates differences in grain size distribution gsd as well as the u ratio clearly reflect main stratigraphical units within the lps in addition the centered log ratio transformation of gsd gsd clr which is sensitive to post depositional grain size variations traces units of intensified soil formation despite no magnetic enhancement can be observed within the grafenberg lps environmental magnetic parameters combined with selected geochemical analyses sr rb provide direct information on the modification of silicates and magnetic minerals in the course of pedogenesis and diagenesis overall the grafenberg lps contributes to the understanding of environmental conditions within the lower rhine embayment particularly for the late mis 3 and the transition to mis 2 the lps reflects major shifts in the geomorphic system which are compared to palaeoenvironmental records from different archives and different geographic regions in north western europe indicating a direct relation to north atlantic climate oscillations during the last glacial period it is shown that the hesbaye unconformity at the mis 3 2 boundary is bound to an erosional event which can be traced over wide areas within the northern european loess belt

were last glacial climate events simultaneous between greenland and france a quantitative comparison using non tuned chronologies several large abrupt climate fluctuations during the last glacial have been recorded in greenland ice cores and archives from other regions often these dansgaard oeschger events are assumed to have been synchronous over wide areas and then used as tie points to link chronologies between the proxy archives however it has not yet been tested independently whether or not these events were indeed synchronous over large areas here we compare dansgaard oeschger type events in a well dated record from southeastern france with those in greenland ice cores instead of assuming simultaneous climate events between both archives we keep their age models independent even these well dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi centennial time scales if possible comparisons between proxy archives should be based on independent non tuned time scales copyright 2009 john wiley sons ltd

rare element mineralization related to precambrian alkali granites in the arabian shield five examples of disseminated rare element mineralization with sufficient resource potential to warrant exploration all are characterized by enrichment in a suite of granitophile elements which typically includes nb ta sn rare earth elements y th u and zr but they differ in size geometry mode of occurrence and lithology two types of mineralization the jabal sa id type is characterized by high total iron to total alkali ratios and high k 2 o na 2 o ratios the ghurayyah type is characterized by major oxide abundances approximating those of typical alkali granites both types evolved from alkali granite magmas formed by high temperature dry melting of late proterozoic island arc crust indicated resources range from 6 million metric tons jabal tawlah and umm al birak through or 20 million metric tons jabal sa id and jabal hamra to 440 million metric tons ghurayyah the highest average grades from nb 3 400 ppm sn 380 ppm y 5 200 ppm and zr 37 000 ppm occur at jabal tawlah the highest ta grades 200 ppm at ghurayyah and the highest u 130 ppm and th 830 ppm grades at jabal sa id modified journal abstract

charcoal and wood remains for radiocarbon dating upper pleistocene loess sequences in eastern europe and central siberia abstract the present paper concerns long upper pleistocene loess sequences from eastern europe with multiple upper palaeolithic occupations rich in charcoal as well as loess sequences from central siberia with abundant wood remains these complementary records have allowed establishing a high resolution climatic sequence integrating 24 interstadial episodes between ca 42 5 and 10 kyr bp here we discuss the methodology of dating used to fix the chronological framework of this climatic sequence based on a set of 240 available radiocarbon dates mainly produced on charcoal and wood remains special attention is paid to the strategy of sampling charcoal and wood material in strict accordance with stratigraphy as well as to the preparation process in the laboratory for extraction cleaning identification and selection of the best fragments to date careful stratigraphic drawing and detailed positioning of the samples for each geological layer are also considered in order to clarify the relationship of the obtained dates with respect to any sedimentary pedological or archaeological event to be dated the reliability and accuracy of the dates obtained from loess sequences are further controlled by the internal consistency with regard to stratigraphy palaeoenvironmental implications are also discussed

influence of hcl pretreatment and organo mineral complexes on laser diffraction measurement of loess paleosol sequences abstract the influence of different sample pretreatment methods on grain size distributions in particle size analysis has been subject to controversial discussions standard sample preparation typically comprises the disaggregation of aggregated and agglomerated particles into single primary particles i e the organic binding material is oxidized by hydrogen peroxide h2o2 and the contained carbonates are dissolved by hydrochloric acid hcl the aim of this study is to evaluate the effects of hcl treatment on grain size analyses of late pleistocene and holocene loess paleosol sequences investigated by a beckman coulter ls 13320 laser particle analyzer for this purpose samples from two different sections with different weathering degrees and sedimentary genesis were measured 1 the suohuoduo section on the northeastern fringe of the tibetan plateau china containing loess and paleosols and 2 a vibracore from dusseldorf grafenberg germany containing calcareous loess and intercalated interglacial interstadial and periglacial soils and soil sediments all samples were pretreated with hydrogen peroxide and sodium pyrophosphate subsequently the samples were prepared with and without the addition of hcl there is no significant association of the hcl induced grain size modifications after the hcl treatment with the calcium carbonate content conversely a distinct dependence of the modification of grain size distributions on the content of organic matter the weathering degree of the sediment and the presence of stable aggregates as well as organo mineral complexes was observed consequently pretreating post depositionally modified aeolian sediments with hcl may result in misleading grain size distributions and should be avoided in standard analyses of loess paleosol sequences however the hcl induced modification of grain size distributions provides an indication of the existence of stable aggregates or organo mineral complexes

relaxation time effects of wave ripples on tidal beaches 1 seabed roughness due to wave ripples is a key factor in controlling sediment transport processes in the nearshore zone roughness is commonly considered a function of the ripple geometry which in turn can be predicted from sediment and hydrodynamic parameters existing ripple predictors consider the bed morphology to be in equilibrium with the hydrodynamics whereas recent laboratory measurements show that the time scale for ripple development is of the order of tens of minutes to hours here we show that wave ripples on tidal beaches are significantly affected by relaxation time effects with ripple height and length progressively increasing during the rising tide and remaining constant during the falling tide moreover we examine the ripples in the context of existing empirical models and suggest how the temporal evolution over a tidal cycle may be predicted

paleoenvironment and stratigraphy during the last glacial in the belgian dutch border region the weichselian deposits of the flat dutch belgian coversand area are characterized by highly varying facies types the geomorphological location and the role of water during the deposition and the transportation of the original eolian sediments may fully explain the texture and sedimentary structures of the lithostratigraphic units directly deposited eolian loams and sands on the dry interfluves contrast with the same but reworked sediments in wet valleys and depressions the formation of periglacial phenomena is also dependent on the geomorphologic lithologic and hydrologic conditions the occurrence of peaty beds is restricted to wet environments without precise climatic significance the pleniglacial sequence is subdivided into early and late pleniglacial stades both characterized by partial permafrost conditions interrupted by a middle pleniglacial interstadial complex with clearly milder conditions

geochemical evolution of the banded iron formation hosted high grade iron ore system in the koolyanobbing greenstone belt western australia the banded iron formation bif hosted iron ore deposits in the lower greenstone succession of the koolyanobbing greenstone belt 50 km north of southern cross in western australia are a 200 mt high grade fe 58 pre mining resource and represents one of the most important iron ore districts in the yilgarn craton four hypogene alteration ore forming stages and one supergene upgrading event took place 1 during ore stage 1 lree depleted transition metal enriched mg fe ca carbonates replaced quartz in bifs the deposit scale alteration was most likely induced by devolatilization of sea floor altered ca si depleted mafic rocks in the vicinity of the bif during early regional syn d 1 very low to low grade metamorphism and was most strongly developed on reactivated bif basalt contacts 2 ore stage 2 involved the formation of patchy magnetite ore by a syn d 2 to d 4 dissolution of early carbonate enrichment of fe 2o 3total in magnetite iron ore was by a factor of 2 to 2 4 and compatible trace elements in magnetite such as ga v and al were immobile a subdeposit scale ferroan talc footprint proximal to magnetite iron ore in the largest deposit k deposit was associated with ore stage 2 and resulted from dissolution of magnesite due to reaction with silica in the bif under greenschist facies conditions and potentially high fluid rock ratio 3 magnetite growth during ore stage 3 forming granular magnetite martite ore is related to a subsequent hydrothermal event occurring locally throughout the belt especially in d 2b faults 4 ore stage 4 was associated with fe ca p l ree y enriched hydrothermal fluids possibly from a magmatic source such as the postmetamorphic lake seabrook granite that crops out about 10 km west of the koolyanobbing deposits and at the southern margin of the greenstone belt these ca enriched fluids interacted with distal metamorphosed mafic rock and influenced the bif ore system in a small number of deposits they were channelled through regional d 4 faults and caused specularitedolomite quartz alteration resulting in fe grades of up to 68 5 supergene upgrade ore stage 5 by further gangue leaching in the weathering zone was most effective in carbonate altered bifs and magnetite ore this process together with supergene martitization and goethite replacement of magnetite led to the formation of high grade locally at k deposit high p goethite martite ore at koolyanobbing the two geochemically distinct stages of archean carbonate alteration clearly controlled the formation of hypogene magnetite specularite martite rich ore and recent supergene modification including the further upgrade of fe ore 2012 by economic geology

uranium bearing hematite from the olympic dam cu u au deposit south australia a geochemical tracer and reconnaissance pb pb geochronometer abstract uranium bearing hematite containing up to several wt u also containing al mo w and radiogenic pb is described from olympic dam south australia these elements are present in grains that display both oscillatory zonation and porous structures laser ablation inductively coupled mass spectrometry la icp ms element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238u and 206pb and are distinct from those of w and mo the crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope focused ion beam technique satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long range superstructure ordering that is inferred to assist metal incorporation via the substitution 2fe3 me6 vacancy where me u w mo the suitability of u bearing hematite for pb pb geochronology as a first pass was tested on both zoned and porous hematite grains via la icp ms using the gj 1 zircon as the primary external standard only pb pb ages were considered and resulted in 207pb 206pb ages of 1590 8 ma and 1577 5 ma for oscillatory and sector zoned hematite from two samples although reconnaissance in nature these ages potentially support the supposition that mineralization is coeval with emplacement of the gawler range volcanics and associated hiltaba intrusive suite the geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron bearing ores

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

palaeomagnetism of the cordillera de la costa northern chile evidence for local forearc rotation abstract palaeomagnetic studies of lower jurassic to lower cretaceous volcanic plutonic and sedimentary rocks from the cordillera de la costa of northern chile indicate that there has been no significant latitudinal movement of northern chile since early cretaceous times a palaeomagnetic pole for the cordillera de la costa 63 s 187 e 95 7 7 was derived from combining the results of three studied units the la negra formation jurassic volcanics jurassic lower cretaceous granodioritic plutons and the e1 way formation hauterivian marine carbonates together with the coloso formation lower cretaceous red beds comparison with a cretaceous reference pole for the stable shield area of south america 87 s 235 e 95 2 4 indicates that 24 7 of clockwise rotation has taken place possible mechanisms for the rotation of the andean forearc in this area have been examined in relation to the kinetics of the subducting nazca and over riding south american plates the cordillera de la costa has been subjected to both compressional and extensional tectonics since the lower cretaceous major eastwardly directed thrusting in mid cretaceous and early tertiary times possibly associated with a period of oblique subduction of the nazca plate contributed to the accretion of the cordillera to the main forearc rotation may have occurred during this process in oligo miocene and later tertiary times extensional faulting possibly associated with roll back of the nazca plate led to the reactivation of the atacama fault zone and the formation of oblique extension faults in the cordillera de la costa structural rotation associated with this phase of extension could equally explain the observed palaeomagnetic results

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

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

1760 ma magnetite bearing protoliths in the olympic dam deposit south australia implications for ore genesis and regional metallogeny spatial associations between banded iron formation and iron oxide cu au iocg style mineralization are well documented in the gawler craton south australia but the possible genetic relationships between these two distinct types of mineralization are hitherto unclear a texturally conspicuous generation of coarse grained silician magnetite intergrown with carbonates and quartz is observed in drillholes intersecting the outer shell of the olympic dam iocg type deposit this magnetite is characterised by high u content 50 ppm siliceous chemistry and unusual zonal textures with respect to si fe nanoprecipitates direct dating of this magnetite by laser ablation inductively coupled plasma mass spectrometry yields reproducible 207pb 206pb dates 1761 16 ma that are significantly older than the granite hosting the deposit 1593 ma or the mineralized breccias constituting the cu u au ag resource 1592 1589 ma the older fe rich crustal material can be correlated with the 1 76 1 74 ga meta sedimentary wallaroo group host to fe rich horizons across the gawler craton including locations 15 km nw of olympic dam a generation of granitic rocks which intruded bedrock at 1 75 ga are present 30 km ne of olympic dam and likely exsolved hydrothermal fluids that enriched pre existing magnetite bearing protoliths in both u and ree such material was physically and likely chemically incorporated into the outer shell at olympic dam some 150 ma later during granite uplift along faults the coincidence between fe rich horizons bif and 1750 ma granitoids may have provided iocg systems with an additional source of both fe and u that predates the 1 59 ga craton scale metallogenic event the uranium concentrations in some south australian iocg systems represent major global anomalies in the element a combination of the fortuitous geological circumstances outlined here may help explain the highly anomalous accumulation of uranium found at olympic dam

high grade iron ore at windarling yilgarn craton a product of syn orogenic deformation hypogene hydrothermal alteration and supergene modification in an archean bif basalt lithostratigraphy banded iron formation bif hosted iron ore deposits in the windarling range are located in the lower greenstone succession of the marda diemals greenstone belt southern cross domain yilgarn craton and constitute a total hematite martite goethite ore resource of minimum 52 mt at 60 wt fe 0 07 p banded iron formation is interlayered with high mg basalts at windarling and precipitated during episodes of volcanic quiescence trace element content and the rare earth element ree ratios y ho 42 to 45 sm yb 1 5 together with positive la and gd anomalies in least altered hematite magnetite metachert bif indicate the precipitation from archean seawater that was fertilised by hydrothermal vent fluids with a basaltic hree y signature hypogene iron ore in sub greenschist facies metamorphosed bif formed during three distinct stages ore stage 1 was a syn to post metamorphic syn d1 fe ca mg ni co p ree metasomatism that produced local ni ree rich fe dolomite magnetite alteration in bif hydrothermal alteration was induced by hot fluid flow controlled by brittle ductile reactivation of bif basalt margins and crosscutting d1 faults the ni co rich content of dolomite and a shift in ree ratios in carbonate altered bif towards archean mafic rock signature y ho to 31 to 40 sm yb to 1 to 2 and gd gd to 1 2 to 1 4 suggest that high mg basalts in the windarling range were the primary source of introduced metals during ore stage 2 a syn deformational and likely acidic and oxidised fluid flow along bif basalt margins and within d1 faults leached carbonate and precipitated lepidoblastic and anhedral granoblastic hematite high grade magnetite hematite ore is formed during this stage ore stage 3 hydrothermal specular hematite spch fe dolomite quartz alteration was controlled by a late orogenic brittle compressional transpressional stage d4 the regional scale shear zone related d3 is not preserved in windarling this minor event remobilised iron oxides carbonate and quartz to form veins and breccia but did not generate significant volumes of iron ore ore stage 4 involved mesozoic to recent supergene oxidation and hydration in a weathering environment reaching down to depths of 100 to maximum 200 m below surface supergene ore formation involved goethite replacement of dolomite and quartz as well as martitisation important ground preparation for supergene modification and upgrade were mainly the formation of steep d1 to d4 structures steep bif basalt margins and particularly the syn d1 to syn d2 carbonate alteration of bif that is most susceptible to supergene dissolution the windarling deposits are structurally controlled supergene modified hydrothermal iron ore systems that share comparable physical chemical and ore forming characteristics to other iron ore deposits in the yilgarn craton e g koolyanobbing beebyn in the weld range mt gibson however the remarkable variety in pre syn and post deformational ore textures relative to d1 and d2 has not been described elsewhere in the yilgarn and are similar to the ore deposits in high strain zones such as of brazil quadrilatero ferrifero or iron quadrangle and nigeria the overall similarity of alteration stages i e the sequence of hydrothermal carbonate introduction and hypogene leaching with other greenstone belt hosted iron ore deposits supports the interpretation that syn orogenic bif alteration and upgrade was crucial in the formation of hypogene supergene iron ore deposits in the yilgarn craton and possibly in other archean paleoproterozoic greenstone belt settings worldwide

a comparison of different tl techniques on loess samples from rheindahlen f r g abstract 9 tl samples of the loess profile rheindahlen lower rhine area germany covering the time span of the last 300 ka were studied systematic investigation was carried out using different filters and preheating procedures ed determinations were done by the additive dose and the regeneration method the annual dose was determined by aas alpha counting naa and gamma spectrometry in the laboratory and in the field the results show that the weichselian loess is datable whereas no tl age differentiation between loesses of stage 6 and stage 8 is possible if the accumulated dose ed is in the 600 gy region every apparent tl age between 100 and 300 ka can be obtained this leads to the conclusion that in rheindahlen no reliable tl ages are available for loess deposits underneath the eemian soil stage 5e

iron oxides constrain bif evolution in terranes with protracted geological histories the iron count prospect middleback ranges south australia abstract when studied at appropriate scales of observation and using complementary methods the intrinsic textural and geochemical complexity of iron oxides can provide unparalleled insights into the evolution of iron ore resources from banded iron formation deposition to ore formation iron count is one of 20 deposits and prospects within the archean middleback ranges iron ore belt south australia in which iron oxides from bifs and ores display variable textural and trace element signatures integrated petrography iron oxide laser ablation mapping and geochemistry and in situ dating of bif derived ores was undertaken to assess whether features observed in samples from this representative prospect might be attributed to localized and superimposed overprint processes the prospect consists of a west and east ridge each characterized by a sequence of overprints expressed as interconversions between iron hydr oxides and accompanying variation in trace element concentrations pseudomorphic replacement of early magnetite by hematite martite followed by replacement by iron hydroxides is recognized in samples from the east ridge further overprints are expressed as veining brecciation and crystallization of micro platy hematite rich in granitophile elements sn mo w u martitization of early magnetite in the west ridge is accompanied by enrichment in zn co and ni in martite subsequent recrystallization of martite iron hydroxides by granoblastic hematite is marked by enrichment in ti ta nb ree and granitophile elements and co crystallization of ree minerals this is followed by crystallization of micro platy hematite similarly rich in these elements enrichment in ti and granitophile elements in granoblastic hematite is interpreted to infer crystallization from highly saline fluids generated by interaction between evaporite bearing sedimentary rocks and granite derived fluids post archean australian shale normalized rey fractionation trends of iron oxides from the east ridge are consistent with precipitation of iron rich minerals from a mixture of anoxic seawater and hydrothermal vent fluids analogous trends from the west ridge lack a seawater signature contrasts in rey fractionation trends between the two ridges is interpreted as a combination of the loss of primary seawater signature due to severe overprinting in the west ridge and to lateral variation in the marine depositional environment results validate the hypothesis that variation in iron oxide trace element signatures seen throughout the middleback ranges iron ore belt results from overprinting due to superimposed tectono magmatic events that have locally affected each deposit despite undergoing different sequences of ore forming stages as well as possibly distinct depositional environments the two ridges share a common overprint dated here at 1790 ma using in situ u pb geochronology of co existing hematite monazite and xenotime this age is considered to represent the timing of interaction between granite derived fluids with ore hosting rock such interpretation is supported by the geochemical signatures of the dated iron oxides showing enrichment in granitophile elements and coincident ages for the wertigo granite and myola volcanics which occur proximal to the prospect and were emplaced erupted during intracontinental rifting the approach undertaken here combining petrography iron oxide geochemistry and in situ dating of bif derived ores is generically applicable to other iron resources within the middleback ranges or analogous terranes elsewhere

late pleistocene landscape dynamics in saxony germany paleoenvironmental reconstruction using loess paleosol sequences abstract loess archives are of paramount importance for reconstructing regional paleoenvironmental conditions of past glacial periods the saxonian loess region is an area of transition between the western and the eastern european loess belt with this contribution a documented loess paleosol composite profile for the saxonian loess region is extended and a new chronostratigraphy established by high resolution osl dating of two profiles is described in addition for the first time osl age estimates for the loess paleosol sequence at seilitz are presented for the quartz and polymineral fine grain fraction based on the presented composite profile climatic and environmental conditions e g wind speed temperature are deduced based on high resolution osl dating it is possible to identify a hiatus spanning ca 30 ka this gap is located in the gleina complex where an underlying layer shows an age of ca 60 ka and the upper layer an age of ca 30 ka additionally two periods of strong loess accumulation with ages of ca 70 60 ka and 30 18 ka could be identified there is a general trend of grain size coarsening up towards the late glacial which shows a maximum at ca 21 ka correlations with french western german and polish loess sections are discussed

improved constraints on the estimated size and volatile content of the mount st helens magma system from the 2004 2008 history of dome growth and deformation 1 the history of dome growth and geodetic deflation during the 2004 2008 mount st helens eruption can be fit to theoretical curves with parameters such as reservoir volume bubble content initial overpressure and magma rheology here assumed to be newtonian viscous with or without a solid plug in the conduit center data from 2004 2008 are consistent with eruption from a 10 25 km3 reservoir containing 0 5 2 bubbles an initial overpressure of 10 20 mpa and no significant sustained recharge during the eruption we used curve fits to project the eruption s final duration and volume early projections predicted a final volume only about half of the actual value but projections increased with each measurement implying a temporal increase in reservoir volume or compressibility a simple interpretation is that early effusion was driven by a 5 10 km3 integrated core of fluid magma this core expanded with time through creep of semi solid magma and host rock

a multi technique evaluation of hydrothermal hematite u pb isotope systematics implications for ore deposit geochronology abstract hematite fe2o3 is a common iron oxide mineral known to incorporate u into its crystal lattice at up to wt concentrations and has been previously used to date ore formation within iron oxide copper gold and banded iron formation deposits however there has been no detailed evaluation of the potential challenges this novel mineral geochronometer may present for accurate temporal interpretation we report a multi technique u pb geochronological study comprising laser ablation inductively coupled plasma mass spectrometry la icp ms sensitive high resolution ion microprobe shrimp and the first isotope dilution thermal ionization mass spectrometry id tims procedure and analyses using an in situ grain micro sampling technique we assess intra and inter sample data reproducibility and examine the compatibility of spatial and analytical resolutions to texturally and compositionally diverse samples five samples of hydrothermal primary oscillatory zoned hematite were analysed from distinct lithologies throughout the 1 59 ga olympic dam cu u au ag deposit with typical u concentrations ranging between 20 and 1000 ppm la icp ms mapping of isotope distributions across mm sized grains allows pinpointing of u rich and relatively u pb isotopically homogeneous domains micro domains were extracted via laser cut square shaped trenches 100 100 m u pb datum range in complexity with concordant age domains measured by id tims indicating that hematite can retain a near closed u pb system over 1 6 ga while also demonstrating that younger pb loss events may be recorded significant reverse discordance is common in the data likely to be a real feature due to both internal decoupling and mobility of pb within a single grain and u pb fractionation during microbeam analysis these effects will obscure the interpretation of real ages for proterozoic samples where non zero age pb loss events occur and restricts the evaluation of common pb mixing components as a result microbeam analyses may be biased younger or older in terms of 207pb 206pb dates in samples with complex histories microbeam datum compare favourably with high precision id tims ages although reproducible id tims u pb dates were generally not obtained in the best case example a 207pb 206pb weighted mean age of 1589 91 0 91 ma mswd 1 3 n 5 within 0 2 of the olympic dam granite host rock age 1593 87 0 21 ma was generated all five hematite samples dated by la icp ms and shrimp yield weighted mean 207pb 206pb dates within 2 of the host granite age after small degrees of data rejection the results demonstrate that with careful sample petrography screening and data interpretation hematite can be considered a very useful u pb mineral geochronometer with potential application to all u bearing fe oxide rich mineral systems

paleoenvironmental fluctuations as recorded in the loess paleosol sequence of the upper paleolithic site krems wachtberg abstract the loess paleosol sequence of krems wachtberg is famous for its archeological findings above all its gravettian infant burials it represents a complex system of paleoclimatic fluctuations which is nearly complete and thus enables the correlation with global paleoclimatic records this sequence comprises activity phases with dominant eolian and partly erosional processes as well as stable short periods of weak pedogenesis periglacial environment with drier climate conditions and high eolian sedimentation rates characterize the upper part of the sequence and in periods with lower sedimentation rates cryosols and permafrost induced structures are developed although the krems wachtberg site is situated at a slope position intensive erosional phases events can be excluded the basal parts of the sequence show signs of decalcification bioturbation organic inclusions as well as changes in element distribution pedogenic horizons are partly overprinted by permafrost related structures and are disturbed by redepositional processes to a minor degree remarkably the archeological horizon is not affected by permafrost in contrast to the layers below and above the focus of this study is deciphering stratigraphy by a combination of paleopedological sedimentological analyses with rock magnetic analyses on the chronological scale the sequence records a timespan from 35 ka to 20 ka altogether there is evidence of five pedogenic units and one archeological layer which are correlated with the greenland interstadials gi 7 to gi 2 however an equivalent of a mis 3 interstadial soil comparable with the lohne soil or stillfried b soil could not be detected

geochemical characterization and origin of southeastern and eastern european loesses serbia romania ukraine abstract the loess paleosol sections of batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine were geochemically characterized based on discriminant analysis of major and trace elements the ratios of al ti fe ti and al fe the a cn k ternary plot and element enrichment depletion relative to the average composition of the upper continental crust the origin of the loess material in the southern pannonian basin vojvodina the lower danube basin dobrudja and the dnieper area was evaluated by comparison with the representative element composition of possible source areas and by considering the geomorphodynamic setting also the background values of the initial magnetic susceptibility of the loesses were taken into account for the lower danube basin dobrudja and the ukraine paleowind direction was reconstructed based on the geographic distribution of sandy soil texture and dunes related to river systems finally loesses were evaluated as possible samples of the average upper continental crust our results show that danube and dnieper loess areas can be clearly distinguished the former reveal higher al and fe contents the latter higher si zr hf content and indications of effective mineral and grain size sorting we can confirm that vojvodina loess originated from danube alluvial material and loess of the dnieper area from glaciofluvial sediments of the fennoscandinavian ice sheet the dobrudja loess derived also predominantly from danube alluvium but shows significant contribution of a second loess source probably the glaciofluvial sediments of the ukraine this was forced by northerly katabatic winds from the fennoscandinavian ice sheet whereas wnw winds prevailed in the western walachian plain the studied loesses reflect the average composition of the upper continental crust yet biases exist due to selective mineral element enrichment and depletion in the course of previous sedimentary recycling phases respectively material of all studied loess deposits seems to derive originally from sedimentary rocks

thermoluminescence dating of late devensian loesses in southern england scattered across southern england are many isolated deposits of loess like material1 a few such as that at pegwell bay in kent are highly calcareous and unweathered but most have been reworked by fluvial or colluvial processes there is good stratigraphical evidence for a few pre devensian loesses also in kent but dating of more recent loess has so far been based on indirect evidence much work has been done on the pegwell bay loess as it is the most extensive truly aeolian loessic deposit in britain kerney2 compared the late devensian deposits in the isle of thanet and at pegwell bay with similar deposits in holland and belgium where radiocarbon dates have been obtained for interstadial deposits correlation of the east kent deposits with these in northern europe indicates that the loesses in kent were formed between 30 000 and 14 000 yr ago i report here dates for six of the more recent deposits in southern britain from the scilly isles to kent the dates have been obtained on the loess itself using a recently developed thermoluminescence tl dating technique3 4 and confirm the ages as being late devensian

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

petrographic and geochronological constraints on the granitic basement to the middleback ranges south australia abstract the middleback ranges is a 60 km long bif endowed iron ore belt located in the southeastern gawler craton and is the largest exploited iron resource in south australia the belt is hosted within an archean to paleoproterozoic aged granitic gneissic basement terrane petrographic and geochronological constraints are given for a suite of granites associated with deposits throughout the middleback ranges and compared with other regional granites granites from the middleback ranges show complex mineralogical and geochemical features indicating multiple overprinting events sensitive high resolution ion microprobe u pb zircon ages from all granites across the middleback ranges yield archean ages suggesting the existence and a more extensive distribution of mesoarchean crust than previously recognized beneath the entire middleback ranges bif sequence grey and pink granites from the central middleback ranges sultan prospect produced the oldest 207pb 206pb weighted mean ages within the sample suite 3241 6 and 3238 9 ma respectively zircon in the latter granite also features overgrowths dated at 2 6 ga and interpreted to be metamorphic a second group of younger granites from the iron monarch deposit and a sample of cooyerdoo granite northern middleback ranges have a minimum crystallization age of 3165 8 ma and a 207pb 206pb weighted mean magmatic age of 3134 18 ma respectively the youngest granites analyzed here derive from the iron baron deposit in the central part of the belt which display strong deformation and have a minimum crystallization age of 3089 9 ma and from the iron magnet deposit in the southern part of the belt 207pb 206pb weighted mean age of 3023 33 ma petrographic and geochemical features observed within the sample suite indicate that post archean overprinting events led to alteration of the granitic basement and may infer that fluid rock interaction and granite leaching were important for bif upgrading processes and iron oxide formation

micromorphology of loess paleosol sequences a record of paleoenvironmental change abstract the record of paleoenvironmental change retained within thin sections from loess paleosol sequences is discussed with reference to case studies from western europe china and northwestern usa the paleoenvironmental significance of individual micromorphological features such as calcitic concentrations clay coatings and cryogenic structures are first evaluated and the value of recognising and interpreting microstratigraphic relationships of features in terms of paleoenvironmental change is illustrated recent developments have seen a greater emphasis on using micromorphology within a pedosedimentary approach whereby both pedogenic and sedimentary processes are taken into account when interpreting loess paleosol sequences this has led not only to the acquisition of important information on conditions during phases of enhanced loess accretion and periods of climatic transition but also to an increased awareness of spatial changes in processes and environmental controls during particular time periods micromorphologically based reconstructions have enabled the isolation of key stages of pedosedimentary development although absolute dating of stages is often limited by lack of age controls a novel approach aimed at addressing this limitation afforded by presence of datable tephra in microstratigraphic association with key micromorphological features is discussed

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

late pleistocene loess of the lower rhine abstract from the lower rhine a compiled 25 7 m thick late pleistocene loess paleosol sequence is differentiated into five lithostratigraphic units the rheingau member mis 5 the keldach member weichselian early pleniglacial gs 21 1 18 mis 4 the ahrgau member weichselian middle pleniglacial mis 3 and the hesbaye and brabant members weichselian late pleniglacial mis 2 it correlates well with climate fluctuations known from ice cores and deep sea cores the sequence was continuously sampled by 335 samples it cuts through all essential layers and soils of the late pleistocene upper loess formation a continuous coarse silt index csi curve shows a maximum in the hesbaye member 31 24 ka b2k indicating the strongest wind conditions during the early late pleistocene further csi highs lie in the keldach and early brabant members csi lows are found the early and middle rheingau member gi 25 gi 22 the jackerath spenrath soils within the deeper keldach member gi 20 19 the early ahrgau member gi 17 gi 12 and finally in the elfgen soil gi 2 at the base of the brabant member the organic carbon culminates in the titz humus zone presumably at the end of gi 21 indicating scanty oxidation during the following cold lower weichselian pleniglacial period the garzweiler solcomplex forming a prevailing period of soil formation between 130 and 78 ka bp mis 5e a is considered as interglacial complex rhine interglacial complex continuing the style of the older interglacial complexes of mis 7 9 etc the ahr interstadial complex mis 3 is seen as immature complex of warm phases with fabric of the interglacial complexes author s suggestion the rhine interglacial complex covers mis 5e a and restricts the weichselian glacial to mis 4 through mis 2 this procedure follows the style of the older interglacial complexes

high resolution record of the last interglacial glacial cycle in the nussloch loess palaeosol sequences upper rhine area germany the nussloch loess sequences were sampled at close intervals 10 cm and documented in respect of their stratigraphy palaeopedology sedimentology palynology malacology and geochemistry and were dated using radiocarbon and osl methods for each stratigraphic unit the results of both the eld studies and the analytical and geochronological data obtained cast light upon the response of the loessic environment to global climatic variations during the last cycle the basal soil complex underwent a pedosedimentary evolution similar to those of the bordering area complex luvisol greyzem steppe soila which re ects the classic progression towards increased continentality of the environment between the end of the eemian 5d and the beginning of the full glacial stage pleniglacial the lower pleniglacial corresponds to an initially very arid phase dominated by the accumulation of loess followed by the deposition of strati ed niveo eolian sands the middle pleniglacial complex ca 55 30 is clearly characterised by the inhibited loessic sedimentation it is primarily marked by two phases of stabilisation recorded in the form of weathered horizons cambisols which are separated by a rather thin layer corresponding to loessic sedimentation with tundra gleys this intermediate phase brings together organic silt deposits which record an interstadial dated at 32 33 ka c bp the thick loessic accumulations of the upper pleniglacial 10 m which clearly began to accumulate before the oxygen isotope stage ois 3 2 boundary show evidence of vulnerability to considerable uctuations in response to variations in wind dynamics and the intensity of de ation in the rhine valley finally a proposed correlation of loess palaeosol stratigraphies from germany belgium and france spanning the entire last interglacial glacial cycle is presented 2001 elsevier science ltd and inqua all rights reserved

radiometric dating and temperature history of banded iron formation associated hematite gogebic iron range michigan usa newly developed techniques were used to characterize the age origin and temperature history of coarse hematite contained in high grade iron ore three botryoidal specimens from two different mines in the gogebic iron range near ironwood michigan usa yielded u th 21 ne ages concordant with plateau 4he 3he ages these data reveal that while two of the specimens grew at ca 772 41 ma the third formed 300 m y later 453 14 ma 4he 3he polydomain thermochronometry indicates hematite formation at 80 c for the older specimens and 60 c for the younger fe mobilization and recrystallization in open cavities at 3 5 km subsurface has occurred episodically or possibly continuously over hundreds of millions of years despite a quiescent tectonic setting throughout this interval while the analyzed specimens are distinct from typical fe ore their ages along with structural relationships constrain the onset of iron enrichment to between 1060 and 770 ma cooling of 0 5 c m y ensued between ca 800 and ca 550 ma declining to 0 1 c m y for the last 550 m y these data suggest an erosion rate of 6 m m y and 5 km of total erosion of the superior upland province through the phanerozoic and limit unroofing associated with pleistocene glaciation to 1 km

refined proterozoic evolution of the gawler craton south australia through u pb zircon geochronology abstract through the application of both conventional u pb zircon analyses and small sample u pb isotopic analyses the nature and timing of tectonic events leading to the formation of the gawler craton have been defined more precisely constraints on deposition of early proterozoic iron formation bearing sediments have been narrowed down to the period 1960 1847 ma deformed acid volcanics including the economically important moonta porphyry have zircon ages of 1790 and 1740 ma the voluminous acid gawler range volcanics and correlatives to the east were erupted over a short interval at 1592 2 ma and were intruded by anorogenic granites at 1575 ma small sample zircon analyses proved to be an extremely valuable adjunct to conventional analyses generally yielding more concordant data which forced a curved discordia through an upper intercept slightly younger than from a conventional straight line discordia

pedo chemical climate proxies in late pleistocene serbian ukranian loess sequences abstract the last glacial interglacial loess paleosol sequences of serbia and ukraine provide a good climate reconstruction potential for this part of europe four loess sections distributed over an area with present day moist to semi arid climates were studied in addition to traditional paleoclimate proxies such as grain size distribution as proxy for wind strength and source aridity and magnetic susceptibility as proxy for precipitation and temperature pedo chemical elemental ratios obtained by selective sediment leaching procedures function as sensitive recorders of variations in weathering intensity due to changes in precipitation and temperature especially the earth alkaline element ratios of ba sr and sr ca are subject to strong variations as a result of carbonate dissolution precipitation and variable cation exchange capacity on clay minerals along the elemental sequence of ca sr ba as shown by the close similarity to the magnetic susceptibility records in the different loess sections these ratios reflect the effects of weathering intensity as a result of precipitation changes the fact that ba sr unequivocally shows higher values in both soils and paleosols in the four studied sections over the present day climate gradient singles this elemental ratio out as an interesting paleoclimate proxy

a continuous high resolution dust record for the reconstruction of wind systems in central europe eifel western germany over the past 133 ka 1 the last glacial cycle in central europe is dominated by processes of aeolian dust transport and accumulation these dust deposits are preserved in soils and lake sediments and provide detailed information about the climate variability during cold and dry periods especially the transitions from warm into cold periods are characterized by turbulent climate conditions the main problems of terrestrial paleoclimate reconstructions are the completeness of the core material and a sampling resolution to detect single dust storms we use a particle detection method which allows high resolution sub annual analyses of sediment structures in undisturbed samples the elsa eifel laminated sediment archive stack is a compilation of four different lake sediment cores of the eifel region western germany and comprise the period of the last 133 ka the results of our analyses show high frequencies of dust storm events during the first cold events c24 and c23 after the last warm stage in opposition the coldest periods of the last glacial cycle ois 4 70 60 ka bp and ois 2 35 14 ka bp are characterized by stable climate conditions that provide the accumulation of homogenous dust sediments

prolonged history of episodic fluid flow in giant hematite ore bodies evidence from in situ u pb geochronology of hydrothermal xenotime abstract absolute ages for hydrothermal mineralization and fluid flow are critical for understanding the geological processes that concentrate metals in the earth s crust yet many ore deposits remain undated because suitable mineral chronometers have not been found the origin of giant hematite ore deposits which are hosted in precambrian banded iron formations bifs remains contentious several models have been formulated based on different sources and timing for the mineralizing fluids supergene metamorphic syn orogenic late orogenic extensional collapse and syn extensional precise geochronology of the ore offers a means of discriminating between these models in this study two u pb chronometers xenotime and monazite have been identified in high grade hematite ore bodies from the mount tom price mine in the hamersley province northwestern australia both phosphate minerals occur as inclusions within the hematite ore and as coarser crystals intergrown with martite hematite pseudomorph after magnetite and microplaty hematite indicating that the xenotime and monazite precipitated during mineralization in situ u pb dating by ion microprobe indicates that both phosphate minerals grew during multiple discrete events our results suggest that ore genesis may have commenced as early as 2 15 ga with subsequent hydrothermal remobilization and or mineralization at 2 05 ga 1 84 ga 1 67 ga 1 59 ga 1 54 ga 1 48 ga and 0 85 ga the location of the ore bodies along ancient fault systems and the coincidence of at least some of the u pb phosphate dates with episodes of tectonothermal activity in the adjacent proterozoic capricorn orogen implies that fluids were channelled through major structures in the southern pilbara craton during discrete phases of tectonic compression and extension our results show that the hematite ore bodies formed at sites of repeated focussed hydrothermal fluid flow in contrast to the aforementioned models our results imply that iron ore formation was probably a long lived multi stage process spanning more than one billion years

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

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

multiple episodes of hematite mineralization indicated by u pb dating of iron ore deposits marquette range michigan usa high grade hematite ore so called hard ore was first mined in the lake superior region of north america in a d 1848 the development of ore deposit models from the region has strongly influenced research on the origin of this deposit type worldwide the inability to date high grade hematite ores has hindered the testing of competing genetic models in the marquette range northern michigan usa high grade hematite ore is hosted by the 1 9 1 85 ga negaunee iron formation and unconformably overlying goodrich quartzite field relations and new in situ u pb geochronology of monazite and xenotime intergrown with hematite from six mines across the marquette range michigan indicate that the formation of high grade hematite ore bodies involved up to three events the presence of pebbles of hematite ore in basal conglomerate of the goodrich quartzite indicates that the first episode of iron oxide mineralization occurred after deposition and deformation of the negaunee iron formation but before the ca 1 85 ga sudbury impact monazite in iron ore deposits within the hinges of penokean aged folds yields an age of ca 1 8 ga which is interpreted to record a second phase of hematite enrichment monazite and xenotime in iron ore deposits along the limbs of regional folds give ages of ca 1 77 ga and are interpreted to record a later episode of hematite upgrading the ca 1 8 ga and ca 1 77 ga phosphate ages coincide with the timing of regional tectonic events suggesting hematite mineralization was coeval with the penokean orogeny and yavapai interval accretion our results support the proposal that the formation of high grade hematite ore bodies is a multistage process linked to discrete orogenic events

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

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

the ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

opening the magmatic hydrothermal window high precision u pb geochronology of the mesoproterozoic olympic dam cu u au ag deposit south australia

tectonic framework and evolution of the gawler craton southern australia the gawler craton is the major crustal province in the southern australian proterozoic and is pivotal in models seeking to describe the evolution of proterozoic australia the craton is host to the olympic dam iron oxide cu au u ree deposit as well as a number of other iron oxide copper gold iocg au and iron ore deposits the evolution of the gawler craton is dominated by two major phases of tectonic activity late archean and late paleoproterozoic early mesoproterozoic in total spanning ca 1 billion years the late archean 2560 2500 ma basin development was coeval with arclike felsic magmatism and mafic ultramafic magmas including komatiites collisional deformation between 2480 and 2420 ma led to ca 400 m y of tectonic quiescence conceivably within an early paleoproterozoic continental interior the second major phase of tectonic activity was in the middle to late paleoproterozoic and early mesoproterozoic 2000 1450 ma paleoproterozoic tectonism was initially dominated by rift related events which produced a series of basins over the interval ca 1900 to 1730 ma some of which contain significant iron ore reserves transient contractional deformation at ca 1850 ma led to batholith scale granitic magmatism in part derived from melting of the late archean basement major basin development was finally terminated by the 1730 to 1690 ma kimban orogeny the effects of which are widespread and include the formation of crustal scale shear systems granitic magmatism and low to high grade metamorphism the kimban orogeny was followed by a renewed period of extension between ca 1680 and 1640 ma leading to local magmatism and sedimentation which appears in part to have been coeval with the high grade ca 1650 ma ooldean event in the western gawler craton at ca 1620 to 1615 ma the generation of the arc related st peter suite in the southern gawler craton implies that craton components were located at an active plate margin the arc environment was superseded by a transition to a continental interior regime which coincided with the voluminous gawler range volcanics 1595 1590 ma and hiltaba suite granitoids 1595 1575 ma the hiltaba suite is dominated by high t fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement emplacement of the hiltaba suite coincided with the major mineralizing interval in the gawler craton regionally two distinct mineral systems have been recognized the olympic iocg province in the eastern part of the craton and the gold dominated systems within the central gawler gold province the spatial distribution of iocg versus au dominated mineral systems appears to reflect regional variations in crustal composition and hiltaba suite petrogeneses hiltaba aged granites in the olympic iocg province are isotopically more evolved richer in u and th and oxidized compared to similar aged granites in the au dominated province modern day heat flow in the iocg province is significantly higher 90 10 mwm 2 compared to the au dominated province 54 5 mwm 2 suggesting there are important lithospheric compositional differences between the two metallogenic provinces which may reflect an older phase of craton assembly widespread northwest southeast contractional deformation coeval with the emplacement of the hiltaba suite is expressed by the formation and or reactivation of shear zones ranging up to crustal scale within this regime northwest trending structures such as those in the vicinity of the olympic dam deposit are likely to have accommodated dilation associated with strike slip movements intersection between these structures and northeast trending contractional faults may have formed suitable structural traps for 1590 to 1580 ma mineralization the timing of syn hiltaba deformation overlaps with transpression and medium to high grade metamorphism associated with the ca 1570 to 1540 ma kararan orogeny which dominates the geophysical architecture of the central northern part of the craton the youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca 1470 and 1450 ma and regional cooling

in situ la icp ms trace elemental analyses of magnetite the late palaeoproterozoic sokoman iron formation in the labrador trough canada abstract the sokoman iron formation in the labrador trough canada a typical granular iron formation gif is coeval with the 1 88 ga nimish volcanic suites in the same region it is composed of the lower middle and upper iron formations in addition to primary and altered magnetite in iron formations of the hayot lake rainy lake and wishart lake areas magnetite in volcanic breccia associated with the iron formation is identified for the first time in the stratigraphy trace elemental compositions of the most primary altered and volcanic brecciated magnetite of the sokoman iron formation were obtained by la icp ms commonly detected trace elements of magnetite include ti al mg mn v cr co and zn these three types of magnetite have different trace elemental compositions primary magnetite in the iron formation has a relatively narrow range of compositions with the depletion of ti pb mg and al magnetite from volcanic breccia is rich in ti al v mn mg zn cu and pb indicative of crystallization from mantle derived magmas altered magnetite in the iron formation shows a relatively wide range of trace elemental compositions mineralizing fluids associated with magmas that generated the 1 88 ga nimish volcanic suites circulated through the sedimentary piles to further enrich the iron formations and to form magnetite with variable compositions the comparisons of different types of primary and altered magnetite in the iron formation in the region show distinct provenance discrimination our findings also support the origin of iron formations in association with multiple stages of exhalative volcanic and hydrothermal processes

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

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

oxygen isotope stage 3 fluvial and eolian successions in europe compared with climate model results abstract fluvial and eolian successions of oxygen isotope stage 3 are compared with global gcm and regional climate rcm modeling experiments of the stage 3 and last glacial maximum climate in europe differences in precipitation between stage 3 stades and interstades were minor which is confirmed by the fluvial successions the fluvial response to climate variation is non uniform and in southern europe more pronounced than in northern europe the model simulations indicate a strong western winter circulation over europe during stage 3 which is supported by the eolian deposits data wind speeds in the last glacial maximum simulation appear modest compared with those of stage 3 which contrasts with the abundance of eolian deposits this suggests that during glacial climates the stabilizing effect of vegetation determines eolian sedimentation rates rather than wind speed stage 3 can be divided into an older part 45 000 cal yr b p with a relatively stable landscape and moist climate and a younger part with more frequent climate change and decreasing landscape stability