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

cosmogenic 3 he in hematite and goethite from brazilian canga duricrust demonstrates the extreme stability of these surfaces helium isotopes were measured in hematite and goethite samples from several lateritiric duricrusts canga developed on banded iron formations these samples uniformly have high 3 he concentrations which must arise from long periods of cosmic ray exposure from coexisting phases from the quadrilatero ferrifero in east central brazil we determined the ratio of cosmogenic 3 he in hematite to that of 21 ne in quartz to be 3 96 0 19 combined with best current estimates of the 21 ne production rate in quartz this ratio implies a sea level high latitude slhl 3 he production rate in hematite of 68 1 8 1 atoms g yr from the chemical composition we estimate the 3 he production rate in goethite to be 5 higher we use these production rate estimates to interpret 3 he concentrations measured in goethite and hematite from a 10 m depth profile collected from a surface canga in carajas in the amazon basin of brazil we find that the carajas canga has experienced a very low rate of surface erosion 0 16 0 54 m myr over at least the last few millions of years this iron rich canga surface is remarkably resistant to erosion despite its location in a wet tropical environment details of the depth profile suggest that despite its stability the canga has also been internally dynamic translocation of material solution and reprecipitation over million year timescales

late mio pliocene chemical weathering of the yulong porphyry cu deposit in the eastern tibetan plateau constrained by goethite u th he dating implication for asian summer monsoon abstract chemical weathering has provided a potentially important feedback between tectonic forcing and climate evolution of the asian continent although precise constraints on the timing and history of weathering are only variably documented here we use goethite u th he and 4 he 3 he geochronology to constrain the timing and rates of chemical weathering at the yulong porphyry cu deposit on the eastern tibetan plateau goethite grains have u th he ages ranging from 6 73 0 51 to 0 53 0 04 ma that correlate with independent paleoclimatic proxies inferred from supergene mn oxides and loess deposits under variable tectonic regimes and vegetation zones over the southeastern asia this correlation indicates that regional climatic conditions especially monsoonal precipitation controlled chemical weathering and goethite precipitation in a vast area of southeastern asia the goethite ages suggest that the asian summer monsoon was relatively strong from 7 to 4 6 ma but weakened between 4 6 and 4 ma and then significantly intensified from 4 to 2 ma the precipitation ages of goethites collected along a 100 m thick weathering profile decrease with depth and indicate a downward propagation of the weathering front at rates of 53 5 10 8 and 4 8 0 6 m ma during the intervals of 7 4 4 2 and 2 0 7 ma respectively the rapid propagation of weathering front during 4 2 ma was caused by abrupt lowering of the water table which was possibly related to local surface uplift or reorganization of the river systems in southeastern tibet during this period

u th he dating of ferruginous duricrust insight into laterite formation at boddington wa abstract geochronological characterization of pisolites and nodules in ferruginous duricrust from laterite profiles exposed near the boddington gold mine bgm in western australia was undertaken by application of u th he dating optical microscopy raman spectroscopy x ray diffraction xrd analysis and tescan integrated mineral analyser tima mineral mapping identified areas in pisolites and nodules in pisolitic and fragmental duricrust suitable for u th he dating u th he dates of 5 8 1 3 ma for pisolites and fragmental duricrust nodules indicate late miocene pliocene to possible early pleistocene ages as a minimum age for the formation of pisolites and nodules and a maximum age for formation of the bgm duricrust averaged u th he ages suggest at least two main episodes in the evolution of pisolite formation the oldest occurring at 5 8 5 2 ma and a younger episode at 3 9 3 2 ma with indication of an even later episode of pisolite formation at 2 3 2 0 ma these results are comparable with u th he data for pisolitic duricrust approximately 50 km to the east of perth toodyay and are consistent with other age estimates for lateritization in western australia suggesting that processes of regolith formation and or modification in the darling range to the east and south west of perth were regionally synchronous the significant difference in age of the rim 2 0 0 2 ma compared to the core 3 9 0 5 ma of a single pisolite in conjunction with a difference in mineralogy and textural evidence suggest that ancient episodic bushfires may have affected or reset the u th he system of iron oxides despite this geochronological characterization can provide quantitative constraints on the age and relative timing of regolith formation

u th he chronology of the robe river channel iron deposits hamersley province western australia abstract channel iron deposits cid supply 40 of australia s iron ore but their genesis is still the subject of debate two well characterised samples of goethite hematite cid from a diamond drill core in mesa j of the robe river area in western australia were dated using u th he methods in order to constrain the timing of iron oxide formation and thereby provide a temporal context for cid genesis u th he ages he ages range from 25 7 0 6 to 7 0 0 8 ma and despite a high degree of scatter they corroborate relationships expected from the internal ooidal stratigraphy for individual ooids the hematitic core is older than or indistinguishable from the age of the surrounding goethitic cortex the goethitic cortices are in turn older than the ferruginised wood fragments recovered from the cementing goethitic matrix the data suggest the following paragenesis i hematitic cores in ooids formed in the early to middle miocene as documented by ages of 14 3 3 7 ma and 18 3 3 5 ma measured in the shallower 8 2 m deep and deeper 32 8 m sample respectively ii goethitic cortices of both samples formed in the late middle to early late miocene at 11 6 3 0 ma iii wood fragments form a prominent component of the matrix and were ferruginised during the late miocene he ages ranging from 9 4 0 5 to 8 2 0 4 ma in the deeper core and 8 4 0 9 to 7 0 0 8 ma in the shallower core the data suggest that the unique environmental conditions conducive to cid formation existed during the miocene and that a typical robe river cid sequence likely took 4 to 8 myr to accumulate a methodological implication of this study is that it confirms the previous observation of vasconcelos et al 2013 suggesting that the temperature utilised for he extraction from iron oxides has a critical impact on the mobility of parent nuclides the typical 1000 c laser heating used for crystalline minerals like apatite or zircon induces loss of u and th and results in erroneously old ages modest extraction temperature

quantitative mineralogy from infrared spectroscopic data ii three dimensional mineralogical characterization of the rocklea channel iron deposit western australia this study demonstrates how mineralogy generated from spectroscopic visible near and shortwave infrared reflectance data collected using rapid drill core logging systems can be used to build one two and three dimensional models of the architecture of ore systems with applications toward exploration and mining in particular this study examines both spectroscopic and traditional mining data laboratory geochemistry and field geologist logging from 180 drill holes through the rocklea channel iron deposit in the hamersley region of western australia valuable infrared reflectance spectroscopy based mineralogy includes the types and abundances of iron oxyhydr oxides hematite vitreous goethite and ochreous goethite clays well and poorly ordered kaolin al and fe smectite and carbonates calcite and dolomite algorithms to determine the abundance and composition of these minerals from infrared reflectance spectra were validated in an associated study by haest et al 2012 and were found to be accurate e g root mean square error rmse for fe oxyhydr oxide abundance prediction of 9 1 wt fe petrographic analysis and validated infrared reflectance spectroscopy based mineralogy constrained the stratigraphy in the paleochannel and the paragenetic history of each horizon the rocklea channel iron deposit developed over weathered basalt and metasedimentary rocks with an internal channel stratigraphy dominated from bottom to top by the following 1 well ordered in situ kaolinite and a partially denaturated channel iron deposit 2 poorly ordered transported kaolinite 3 ochreous goethite with scarce ooidal textures no clays and late stage vitreous goethite silica replacement 4 mostly poorly ordered kaolinite and 5 calcrete with associated fe smectite the mineral paragenesis of the rocklea deposit was compared against current models for channel iron deposit formation a key finding is the relationship between parent rock composition superimposed regolith cover and channel iron deposit ore quality which are linked through ground water interactions and the physicochemistries of both the parent rock and the deposit this has implications for both exploration and ore deposit characterization 1 ore grade channel iron deposits can develop several kilometers downstream 50 km in this case from the proposed source rock areas above mafic volcanics and metasediments 2 vitreous goethite calcrete al and fe smectite cover the rocklea deposit and are proposed as potential vectors to channel iron deposit mineralization at depth 3 improved mineralogy from hyperspectral data in terms of iron oxyhydr oxide and clay content composition can improve iron ore resource delineation iron ore processing separation of vitreous and ochreous goethite and pit design differentiating swelling smectite requiring pit walls with lower slopes from kaolin or white mica

environmental memory and a possible seasonal bias in the stable isotope composition of u th he dated goethite from the canadian arctic abstract goethite ax 2 from axel heiberg island 80 n on the margin of the arctic ocean is the dominant mineral in a sample of petrified eocene wood but u th and he measurements suggest that the goethite feooh crystallized in the latest miocene pliocene ca 5 5 to 2 8 ma measured d and 18 o values of ax 2 are 221 6 and 9 6 0 5 respectively the inferred d and 18 o values of the ancient water were about 139 and 18 6 respectively with a calculated temperature of crystallization of 3 5 c which compares with the modern summer j j a temperature of 3 c and contrasts with a modern mat of 19 c published results from various biological proxies on nearby ellesmere island indicate a pliocene 4 ma mat of either 6 or 0 4 c and corresponding seasonal amplitudes of about 18 or 13 c a conductive heat flow model suggests that a temperature of 3 c could represent goethite crystallization at depths of 100 200 cm for mat 6 c or 250 450 cm for mat 0 4 c over seasonally restricted intervals of time the 18 o value of the ax 2 water 18 6 is more positive than the modern j j a precipitation 22 in combination the paleotemperatures and 18 o values of ancient waters from ax 2 and published results from three eocene or pliocene proxy sites on axel heiberg and ellesmere islands are consistent with a warm season bias in those isotopic proxies the results are also consistent with higher proportions of j j a precipitation in the annual total if so this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates and suggests that the arctic hydrologic cycle as expressed in the seasonal distribution and isotopic composition of precipitation perhaps modified by a warmer arctic ocean differed from modern the 13 c value of the fe co 3 oh component in the ax 2 goethite is 6 6 which is much more positive than expected if crystallizing goethite incorporated co 2 derived primarily from oxidation of relict eocene wood with 13 c values of about 24 this apparent paradox may be resolved if the goethite is a product of oxidation of 13 c rich siderite which had previously replaced wood in an eocene methanogenic burial environment thus the goethite retains a carbon isotope memory of a diagenetic eocene event but a d and 18 o record of the latest miocene pliocene arctic climate

u loss associated with laser heating of hematite and goethite in vacuum during u th he dating and prevention using high o2 partial pressure abstract single aliquot u th he dating of hematite has been used to study iron oxide precipitation in various environments but we show there is an important challenge to the method highly retentive hematite samples require temperatures of 1000 c to be completely degassed whereas the temperature for major u loss is 980 c this leads to erroneously high u th he ages through the analysis of u th and sm of hematite and goethite samples we establish the degree of u loss at this temperature and demonstrate that prolonged heating at temperatures of 950 c can lead to u loss we show that loss of u in goethite and hematite samples is associated with phase change from hematite to magnetite as fe is reduced the onset temperature of vacuum reduction of hematite can be increased from about 800 900 c in vacuum to approximately 1250 c in an oxygen partial pressure of 100 mbar we demonstrate that samples can be outgassed to extract helium at 1150 c without u loss in an o2 rich atmosphere during heating which does not increase the analytical blanks we describe our implementation and automation of the procedure an average age calculated on a reference hematite sample from replicate aliquots n 12 which were analyzed using this procedure has a relative uncertainty of 2 1 and is within uncertainty of the previously measured two aliquot age we suggest this o2 degassing procedure as a way to precisely and reproducibly determine single aliquot hematite and goethite u th he ages

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

quantifying the diffusion kinetics and spatial distributions of radiogenic 4he in minerals containing proton induced 3he apatite titanite and olivine samples were bombarded with a 150 mev proton beam to produce 10 8 atoms mg of spallation 3he high precision stepped heating experiments were then performed in which the artificial 3he and for apatite and titanite the natural radiogenic 4he were measured to characterize the diffusive behavior of each isotope helium 3 diffusion coefficients are in excellent agreement with concurrently and or previously determined he diffusion coefficients for each mineral our results indicate that proton induced 3he is uniformly distributed and that radiation damage associated with a proton fluence of 5 x 10 14 protons cm 2 does not cause noticeable changes in 4he diffusion behavior in at least apatite and titanite proton induced 3he can therefore be used to establish he diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural 4he distribution is inhomogeneous in addition step heating 4he 3he analysis of a mineral with a uniform synthetic 3he concentration provides a means by which a natural 4he distribution can be determined

geochemistry unravels mis 3 2 paleoenvironmental dynamics at the loess paleosol sequence schwalbenberg ii germany abstract the schwalbenberg ii loess paleosol sequence lps denotes a key site for marine isotope stage mis 3 in western europe owing to eight succeeding cambisols which primarily constitute the ahrgau subformation therefore this lps qualifies as a test candidate for the potential of temporal high resolution geochemical data obtained by x ray fluorescence xrf scanning of discrete samples providing a fast and non destructive tool for determining the element composition the geochemical data is first contextualized to existing proxy data such as magnetic susceptibility ms and organic carbon corg and then aggregated to element log ratios characteristic for weathering intensity log ca sr log rb sr log ba sr log rb k and dust provenance log ti zr log ti al log si al generally an interpretation of rock magnetic particles is challenged in western europe where not only magnetic enhancement but also depletion plays a role our data indicates leaching and top soil erosion induced ms depletion at the schwalbenberg ii lps besides weathering log ca sr is susceptible for secondary calcification thus also log rb sr and log ba sr are shown to be influenced by calcification dynamics consequently log rb k seems to be the most suitable weathering index identifying the sinzig soils s1 and s2 as the most pronounced paleosols for this site sinzig soil s3 is enclosed by gelic gleysols and in contrast to s1 and s2 only initially weathered pointing to colder climate conditions also the remagen soils are characterized by subtle to moderate positive excursions in the weathering indices comparing the schwalbenberg ii lps with the nearby eifel lake sediment archive elsa and other more distant german austrian and czech lps while discussing time and climate as limiting factors for pedogenesis we suggest that the lithologically determined paleosols are in situ soil formations the provenance indices document a zr enrichment at the transition from the ahrgau to the hesbaye subformation this is explained by a conceptual model incorporating multiple sediment recycling and sorting effects in eolian and fluvial domains

fe oxides in jasperoids from two gold districts in nevada characterization geochemistry and u th he dating abstract this study examines the whole rock geochemistry fe oxide texture and crystal morphology and fe oxide u th he date variation of jasperoids as well as the relationships between these characteristics in order to evaluate jasperoids as an indicator for gold mineralization jasperoid samples with a range of textures appearances and expected gold concentrations were collected from two gold districts in nevada the northern carlin trend gold quarry mine and the battle mountain district marigold mine battle mountain prospect in our jasperoid samples whole rock concentrations of au are positively correlated with as ag pb sb u w and tl the following fe oxide textures are associated with anomalous gold concentrations disseminated submicron crystals feathery and acicular crystal morphologies concentric zonation from hematite to goethite and botryoidal textures calculated closure temperatures for the u th he system in observed jasperoid fe oxide morphologies within our dataset range from 26 to 136 c indicating variable susceptibility to he diffusion at near surface conditions fe oxide u th he dates range from 29 4 0 5 ma to 0 11 0 01 ma displaying intra and intersample variation we attribute the date variation to multiple factors including he implantation parent isotope exchange and he loss through closure temperature sensitivity and alpha ejection the intra and intersample variation within the fe oxide u th he dates limits our ability to make geologic interpretations our case study identifies important limitations of the u th he method in jasperoids and provides insight on how he date variation might be avoided in future studies

combined 40 ar 39 ar and u th he geochronological constraints on long term landscape evolution of the second parana plateau and its ruiniform surface features parana brazil regional correlation of dated weathered land surfaces provides the necessary constraints to test long term continental landscape evolution models but major challenges remain in properly dating these surfaces the geomorphological province of second parana plateau parana state brazil is a high elevation ca 800 m land surface characterized by widely distributed deep saprolites and scattered lateritic profiles e g vila velha and serra das almas prolonged exposure to weathering and erosion has promoted the pseudo karstic and ruiniform features that are characteristic of this landscape in this study 40 ar 39 ar laser incremental heating geochronology on 22 grains of supergene mn oxyhydroxides from lateritic profiles at vila velha yielded results ranging from 17 2 0 7 to 9 1 0 7 ma u th he geochronology on 28 goethite grains from the same profile yielded results ranging from 36 4 3 6 to 1 0 0 1 ma with an age cluster lying within the 17 2 0 7 to 7 9 0 8 ma interval u th he geochronology on 17 goethite grains from the serra das almas lateritic profile located 20 km from vila velha yield results ranging from 35 1 3 5 to 14 1 1 4 ma the combined results for the two sites reveal a common weathering history that started ca 35 ma suggesting that the second parana plateau results from regional fluvial incision and denudation before 35 ma followed by a decline in denudation rates and proportionally more intense weathering consistent with the laterite profile central ages weathering was particularly intense during the miocene 17 8 ma denudation intensified after the pliocene

hematite and mn oxide u th he dates from the buckskin rawhide detachment system western arizona gaining insights into hematite u th he systematics

goethite u th he geochronology and precipitation mechanisms during weathering of basalts u th he geochronology of 33 goethite grains from in situ ferruginous duricrusts overlying the parana flood basalt in the guarapuava region parana brazil reveals ages ranging from 3 6 0 4 to 0 4 0 1 ma thirty one grains from detrital fragments of ferruginous duricrust yield ages in the 6 2 0 6 to 0 7 0 1 ma range the results show that goethites from detrital blocks are generally older than those from the in situ ferruginous layers and that all the goethites from the guarapuava sites are relatively young 6 2 0 6 ma goethites show variable u and th contents depending on the mode of precipitation goethite that forms by progressive ferrugization and pseudomorphic replacement of basalts are rich in th u poor contain various mineral inclusions e g kaolinite rutile ilmenite and display a distinct checkered appearance colloform goethite precipitated within cavities and desiccation cracks contain higher u show low th u values and are free of mineral contaminants suggesting direct precipitation from solution the geochronological results reveal a dynamic evolution for the soils overlying the parana basalt where recurrent duricrust formation and dismantling lead to the evolution of regional colluvial soil profiles while simultaneously preventing the evolution of chemically stratified lateritic weathering profiles the modes of formation and u th and he contents of goethite at guarapuava provide useful constraints on the expected compositions and modes of formation of goethite formed on basaltic soils on mars

non magnetic indicators of pedogenesis related to loess magnetic enhancement and depletion examples from the czech republic and southern siberia abstract we carried out a multiparameter investigation for non magnetic proxies of the intensity of pedogenesis in loess paleosol sections from two different climate settings dolni v stonice central europe and krasnogorskoye southern siberia the work was performed in order to clarify the problem of two opposite scenarios of magnetic susceptibility ms patterns in these two profiles the chinese model with magnetically enhanced paleosols and the siberian alaskan model with magnetically depleted paleosols the age constraints on the krasnogorskoye section were inferred from an independent correlation with the well dated dolni v stonice section based on ms and sediment color cie l and with the ms log from lake baikal the pedologic description of the loess paleosol sections and their correlation was considerably improved by the use of vis spectral proxies cie l reflectance in the red band their weathering intensity can be effectively characterized by diffuse reflectance spectroscopy drs and geochemical cec and rb sr proxies whereas the ms is strongly dependent on the type of soil chernozems vs brown soils the geochemical proxies in particular cec proved to be relatively independent of the soil type these parameters are less affected by region specific conditions than the ms signal the non magnetic proxies indicate relatively dissimilar climatic trends at the two sites during the last glacial interglacial cycle a long distance correlation based solely on the ms signal can be adversely affected by switching between the chinese and the siberian alaskan magnetic modes this having been observed at the krasnogorskoye section in general no single universal proxy of weathering or pedogenesis intensity would be applicable across broad regions or considerable climatic gradients paleoclimatologic interpretations of large regions should always be based on a carefully designed multi proxy approach

dating paleochannel iron ore by u th he analysis of supergene goethite hamersley province australia comment comment despite their laudable efforts to date the channel iron deposits cid of the pilbara of western australia wa heim et al 2006 1 need to reassess their sampling and the statistical strategy behind their conclusions many details they report conflict with data from a major csiro industry

biogeographic impact of the leeuwin current in southern australia since the late middle eocene abstract the leeuwin current can be tracked from the western margin of the australian continent to the southern margin by the record of fossilized organisms typical of warm water marine environments this transport smudges the normal latitudinal asymmetry in the biotas of opposing oceanic and continental margins in which the eastern margins of oceans are cooler than the western margins and warmer biotas are restricted to lower latitudes in the east the most comprehensive record is in the large benthic foraminifera although fossils of benthic invertebrates nektonic nautiloids and planktonic protists are also informative in addition organic biomarker hydrocarbons in stranded bitumens and resins demonstrate that they have travelled the same route from their ultimate sources in cenozoic sedimentary basins and modern tropical rainforests of the indonesian archipelago the earliest spoor of the current is in the later middle eocene at which time the part deflection of counter gyral circulation in the indian ocean to the southeast was stimulated by the accelerated opening of the oceanic gap between australia and antarctica thus the origin of the leeuwin current is twice the age of the previously suggested origin in the miocene the current turns on and turns off in the great australian bight during the late quaternary in concert with the interglacials and the glacials at scales of 10 5 yr the switch can be seen in the faunal succession of planktonic foraminifera which are consistent with the neritic benthic faunas of the central gulfs both communities show that at the warm peak of the last interglacial the current transported biota across the bight more strongly than it has during the holocene the cenozoic record of the past 40 ma is in the same mode at 10 6 yr scales the relevant fossils are found concurrently at major marine transgressions and warming reversals of the overall fall in global temperature however the fossil pattern is due to transport on the activated leeuwin current not merely to general warming and the spread of friendly environments to higher latitudes

intracrystalline site preference of oxygen isotopes in goethite a single mineral paleothermometer abstract the crystal structure of goethite feo oh has two distinct oxygen sites one with exclusively fe o bonds the other with bonds to both iron and hydrogen we developed a method to assess the oxygen isotope contrast between these sites by measuring both the bulk goethite and the oxygen released in the conversion of goethite to hematite the method involves collecting the water released by dehydroxylation fluorinating that population of extracted atoms and measuring the resulting oxygen isotope composition extracted o 18 then on a separate aliquot all structural oxygen is fluorinated and measured bulk o 18 using synthetic goethite precipitates grown under controlled environmental conditions we found significant temperature dependent fractionation e bulk extracted 5 51 0 26 10 6 t 2 44 5 2 8 t in kelvin this intracrystalline fractionation forms the basis of a single phase paleothermometer with an estimated uncertainty of 2 3 c the temperature dependence appears to be independent of the isotopic composition of the parent fluid from which the goethite formed and the ph of that fluid this intracrystalline thermometer can be used to simultaneously determine the formation temperature of a goethite and the isotopic composition of the water from which it formed natural goethites analyzed with this technique yield geologically reasonable formation temperatures of between 15 and 41 c

a cenozoic terrestrial paleoclimate record from he dating and stable isotope geochemistry of goethites from western australia supergene goethites from the hamersley region of western australia were analyzed for 18 o and the results combined with both new and previously published u th he ages to assess the paleoenvironmental signal recorded by surficial goethite in a long term continental archive 18 o goe values increase monotonically by 3 between 71 ma and 5 ma and appear little affected by changes in temperature or other characteristics of depositional environment the temporal trend likely reflects the isotopic composition of meteoric water from which the goethite formed which varied as australia migrated 3000 km northward over the cenozoic translating age to paleolatitude reveals that the 18 o goe data are consistent with a latitudinal gradient in the 18 o precip that throughout the cenozoic remained largely unchanged from the modern gradient there is a 5 offset between the latitudinal trends of 18 o goe and modern precipitation approximately as expected from the water goethite fractionation factor temporal variation in the 18 o of local meteoric water arising from changes in moisture source or pathway are not evident in the goethites at least in part because topography is subdued and has evolved little in this tectonically quiescent landscape our results provide evidence that the efficiency of water transport from equator to pole that governs the latitudinal 18 o gradient of precipitation has been roughly constant over southern temperate latitudes for the entirety of the cenozoic

bromine counts from xrf scanning as an estimate of the marine organic carbon content of sediment cores 1 xrf sediment core scanning technology is increasingly used to quantify sediment composition the overall good correlation between biophilic halogen bromine br and sedimentary total organic carbon toc potentially allows the fast estimation of down core toc profiles by xrf scanning in order to test this approach we present data from the arabian sea and a mediterranean brine basin comparing xrf core scanning br data with discrete sample toc analyses overall br counts and toc show a clear correlation except when stable carbon isotope and c n data indicate intervals characterized by enhanced input of terrestrial organic matter hence solid phase br is exclusively associated with marine organic matter moc and can be used as a direct estimate of this parameter after a calibration is established high pore water br in the brine core steepens the br toc correlation but after salt correction shows a nearly identical gradient to that of the arabian sea core

gold and pathfinder elements in ferricrete gold deposits of the yilgarn craton of western australia a review with new concepts abstract secondary mineral deposits have played an important role in the global mineral resource economy for over 50 years with lateritic au al fe and ni deposits having a significant input to global metal production and reserves in the yilgarn craton of western australia a deeply weathered mantle is commonly capped with 2 10 m of lateritic residuum residual lateritic gravels and duricrust and or ferricrete fe oxide cemented sediment which formed under seasonally humid tropical and sub tropical climates during the cenozoic the principal constituents of these units are goethite hematite maghemite kaolinite and quartz they are commonly overlain by younger 2 10 m thick transported cover deposited under later semi arid conditions both ferricrete and lateritic residuum may host exploitable secondary gold deposits typically small

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

the origin of terrestrial pisoliths and pisolitic iron ore deposits raindrops and sheetwash in a semi arid environment abstract ooliths evidently form by chemical precipitation in limnic paralic fluvial and marine environments pisoliths however appear to be restricted to terrestrial environments typically composed of iron aluminium and manganese sesquioxides with minor admixtures of quartz and kaolinite they are widely distributed in tropical to subtropical regions overlying deeply weathered soil profiles although iron aluminium and manganese rich end members are important sources of these metals their genesis is still enigmatic their formation has never been observed or produced experimentally and current models for their origin are little more than guesses a new model is presented based on a unique personal observation in which pisoliths are formed by the action of charged raindrops during thunderstorms impacting on dry deeply weathered powdery soils the pisoliths are transported across pediments by sheetwash accumulating as thick deposits in the valley floors pisolites are characteristically unfossiliferous and typically clearly pedogenic the absence of fine depositional layering fossil seeds leaves and pollen in pisolites is explained by bioturbation and the action of soil organisms during extended pedogenesis while the major coarse bedding features derive from erosional and depositional events in the evolution of the pediment pisolitic iron ores aka channel iron deposits cid are a special case of transported pisolitic ferricrust that form an important resource of medium grade iron ore 57 60 wt fe in the pilbara region of western australia apart from minor deposits in the northern yilgarn province of western australia they have not been found elsewhere they differ from normal transported ferricrust and terrestrial pisolites not only in the exceptionally high iron and low alumina and silica content but also in containing abundant fossilised wood particles

dating constituent formation in soils to determine rates of soil processes a review abstract rates of soil processes are poorly known one approach to determine them could be through the radiogenic isotopic dating of soil constituents such methods have been recently used to date minerals in soils and weathering profiles thanks to the development of high resolution techniques such as 40ar 39ar u series of micro drilled samples u series by laser ablation and u th he and to the development of suitable methodology expanding application of the techniques to a variety of supergene minerals e g fe and mn oxihydroxides carbonates etc in this paper we identify i the main soil constituents that can be dated through these isotopic methods that are mainly fe oxides mn oxides pedogenic carbonates and organic matter ii the main pedogenic processes that leads to their formation in soils and iii the different soil settings that allow transforming soil constituent ages into rates of soil processes namely growth bands transformation fronts and chronosequences

pre quaternary landscape inheritance in australia palaeogeographic reconstructions indicate that parts of the australian continent have been subaerially exposed for hundreds of millions of years some landforms and regolith are demonstrated to be at least 300 million years old but their persistence at or near the surface is inconsistent with long term denudation rate estimates based on cosmogenic nuclides and apatite fission track thermochronology burial and exhumation are suggested as significant preservation factors in conjunction with prolonged tectonic stability and a shift to more arid climatic regimes in the cenozoic copyright 2007 john wiley sons ltd

40ar 39ar geochronology constraints on late miocene weathering rates in minas gerais brazil ar 40 ar 39 incremental heating ages for twenty one grains of cryptomelane collected at 0 42 45 and 60 in depths in the cachoeira mine weathering profile minas gerais permit calculating long term 10 ma time scale weathering rate saprolitization rate in se brazil pure well crystallized cryptomelane grains with high k contents 3 5 wt yield reliable geochronological results the ar 40 ar 39 plateau ages obtained decrease from the top to the bottom of the profile 12 7 0 1 to 7 6 0 1 ma at surface 7 6 0 2 to 6 1 0 2 ma at 42 m and 7 1 0 2 to 5 9 0 1 ma at 45 in 6 6 0 1 to 5 2 0 1 ma at 60 in yielding a weathering front propagation rate of 8 9 1 1 m m y from the geochronological results and the mineral transformations implicit by the current mineralogy in the weathering profiles it is possible to calculate the saprolitization rate for the cachoeira mine lithologies and for adjacent weathering profiles developed on granodiorites and scbists the measured weathering front propagation rate yields a saprolitization rate of 24 9 3 1 t km 2 yr this average long term 10 ma saprolitization rate is consistent with mass balance calculations results for present saprolitization rates in weathering watersheds these results are also consistent with longterm saprolitization rates estimated by combining cosmogenic isotope denudation rates with mass balance calculations c 2005 elsevier b v all rights reserved

40ar 39ar and u th he 4he 3he geochronology of landscape evolution and channel iron deposit genesis at lynn peak western australia u th he geochronology of authigenic goethite cements from the lynn peak channel iron deposit cid hamersley province western australia reveals a history of mineral precipitation ranging from ca 33 to 14 ma massive goethites from nearby weathering profiles at roy hill north a possible source of detrital material during the aggradation of the lynn peak channels yield u th he results as old as ca 64 ma the combination of u th he geochronology with incremental outgassing 4he 3he studies on proton irradiated samples reveals that lynn peak goethites host radiogenic 4he in low retentivity lrd and high retentivity hrd domains and that the hrds account for most of the sample mass and have lost very little of their original 4he over geologic time such high retentivity is especially notable given the goethites were collected from the surface where they were subject to significant heating by solar irradiation minor contamination by detrital fragments of potentially 4he rich primary phases e g rutile ilmenite zircon occurs in some samples fortunately the 4he 3he method permits characterization of this extraneous 4he component which is small 10 wt of the total 4he in the goethite and can be corrected out in estimating the goethite formation age these results indicate that the lynn peak channel was already aggraded and undergoing goethite cementation by ca 33 ma the history of aggradation and channel cementation independently measured through 40 ar 39 ar geochronology is consistent with that obtained from the u th he and 4he 3he record laser incremental heating 40 ar 39 ar geochronology of detrital and authigenic mn oxides primarily cryptomelane kmn 8o 16 xh 2o from the same locality in the lynn peak channel reveals that detrital oxides are older than ca 44 ma and as old as ca 65 ma and authigenic oxides are younger than ca 35 ma and as young as ca 16 ma authigenic cryptomelane precipitation and channel cementation occurred throughout the miocene with a particularly strong period at around 20 ma the 40 ar 39 ar geochronological results suggest that regional weathering profiles developed before 44 ma and possibly as early as ca 65 ma were incised and partially eroded in the 44 35 ma interval semi arid conditions promoted the transport of large volumes of sediments aggrading the regional drainage system metasomatic reactions in the aggraded channels caused the ferruginization and in some places manganese replacement of the cids goethite and k mn oxide cementation continued throughout the oligocene and miocene post miocene aridification contributed to the preservation of the cemented channel sediments forming some of the largest readily mineable iron ore deposits on earth

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

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

reply to comment by guedes et al on low temperature phanerozoic history of the northern yilgarn craton western australia by weber et al tectonophysics 400 2005 127 151

u th he geochronology of goethite and the origin and evolution of cangas abstract u th he geochronology of 147 grains of goethite cements extracted from ferruginous duricrusts cangas developed on banded iron formations from the quadrilatero ferrifero region minas gerais brazil records a history of protracted mineral dissolution reprecipitation that started at ca 48 1 4 8 ma and continues intermittently until the present a large majority of the samples more than 30 are younger than 2 ma revealing active mineral dissolution reprecipitation in the recent past within cangas goethite cements are younger near the surface and become progressively older towards the bottom of the weathering profile indicating that iron is more effectively cycled in the parts of the weathering profile more strongly affected by biogenic activity u th he geochronology of 14 goethite grains from saprolites in the same profiles yield results ranging from 55 3 5 5 to 25 7 2 6 ma for a single weathering profile goethite cements from cangas are invariably younger than goethite grains from the underlying saprolite indicating that the duricrust and the saprolite behave as independent and separate systems responding to different environmental controls thorium shows conservative behaviour during goethite dissolution reprecipitation and it is enriched towards the surface of the weathering profile uranium on the other hand is preferentially leached from the surface into the saprolite or out of the weathering profile recurrent goethite dissolution reprecipitation lends great textural complexities to cangas but it is also responsible for its capacity to reheal when physically disrupted this self healing property accounts for canga s role in armoring banded iron formation landscapes

revealing coseismic displacements and the deformation zones of the 1999 chi chi earthquake in the tsaotung area central taiwan using digital cadastral data 1 the 1999 chi chi taiwan earthquake mw 7 6 was the largest earthquake to strike taiwan in the twentieth century this earthquake is associated with a 100 km long surface rupture in order to reveal the details of displacement near the surface rupture we use a digital cadastral system to calculate coseismic displacement around the tsaotung area central taiwan the digital cadastral system was originally conceived to survey land and building boundaries in the tsaotung area taiwan authorities have taken digital cadastral measurements before and after the chi chi earthquake the cadastral system affords high density control points that reach 1421 points km2 a system denser than that of the gps accuracy is to within 11 cm a level that is higher than spot imaging and one that allows us to study surface deformation in detail coseismic displacement is 4 3 4 6 m at distance from the surface rupture and decreases to 3 4 m near the surface rupture the azimuth of horizontal displacements is 310 315 and rotates to 280 305 near the surface rupture this produced a compression left lateral deformation zone with 10 3 compression strain near the surface rupture coseismic displacement of the footwall is 1 1 2 m in 110 which is similar to that from using gps data in the tsaotung thrust slice we observed that the azimuth of horizontal displacement rotates from a nw trend to a south trend as a result of slip partitioning and gravity slide effect

a combined u th he and cosmogenic 3he record of landscape armoring by biogeochemical iron cycling u th he geochronology and cosmogenic 3he in iron oxides reveal mineral precipitation ages as old as 55 ma and exposure ages greater than 5 ma for canga cemented plateaus in the quadrilatero ferrifero brazil showing that lateritic profiles overlying banded iron formation bif landscapes in tropical regions have a long history of surface exposure the long term erosion history obtained from cosmogenic 3he on bif plateaus confirms that relic surfaces persist in the landscape for millions of years combined 3he and u th he dating shows that cangas are preferentially goethite cemented by biogeochemical reactions in the subsurface importantly pebbles of hematite magnetite in colluvia or shallow creeks draining the canga cemented plateaus record a much longer exposure history than in situ canga blocks showing that even older duricrusts now eroded once blanketed these plateaus physically stable but biogeochemically dynamic cangas armor the landscape by pervasive and recurrent iron cycling and cementation slowing down the delivery of weathered bif or friable hematite magnetite ore to erosion

dating paleochannel iron ore by u th he analysis of supergene goethite hamersley province australia u th he dating of late stage authigenic goethite combined with corrections for diffusive loss of he 4 by the he 4 he 3 methodology reveals strong correlation between a sample s age and its depth in ferruginized channel sediments from the yandicoogina deposit western australia corrected ages ranging from ca 18 ma near the surface to ca 5 ma at the bottom of the profile indicate that ferruginization of the aggraded channels becomes progressively younger with depth this trend is consistent with goethite precipitation at the groundwater atmosphere interface during water table drawdown driven by the aridification of western australia during the neogene the results demonstrate that the u th he system is ideal for dating goethite if diffusive loss corrections are applied the approach is suitable for dating weathering reactions on earth and should also be suitable for dating fe oxyhydroxides in the martian regolith

quantitative mineralogy from infrared spectroscopic data i validation of mineral abundance and composition scripts at the rocklea channel iron deposit in western australia visible near to shortwave infrared reflectance spectra vnir swir 400 2 500 nm wavelength region provide quantitative measurements of mineral abundances and mineral physicochemistries from drill core samples of channel iron ore the infrared spectral reflectance measurements of drill core samples from the rocklea channel iron deposit located in the hamersley basin of western australia were validated against x ray flouresence xrf and x ray diffraction xrd the reflectance data were collected using a csiro hy logging system from 180 reverse circulation and 14 diamond drill cores spanning a depth from surface to 55 m below surface intersecting the rocklea deposit the mineralogy of this channel iron deposit comprises chiefly goethite both vitreous and ochreous forms with lesser amounts of hematite and variable amounts of quartz kaolinite smectite both dioctahedral and trioctahedral varieties and carbonate both dolomite and calcite iron ore and waste rock mineralogy were extracted from the infrared spectroscopic reflectance data using the geometry depth wavelength of continuum removed reflectance spectra with depths of absorption features proportional to mineral abundance and wavelength positions proportional to chemical composition for any one mineral a number of its diagnostic spectral features are used to determine its mineral abundance and composition in order to avoid complications with minerals that spectrally overlap with part of the diagnostic spectral features of the mineral of interest this method that combines multiple spectral features to identify and quantify minerals is transferable to all types of infrared reflectance spectroscopic data collected from drill core to satellites final products include iron oxyhydr oxide content root mean square error rmse 9 1 wt fe al clay content rmse 3 9 wt al 2 o 3 hematite goethite ratio rmse 9 0 wt goethite vitreous versus ochreous goethite not easily measured using other analytical techniques clay mineral type kaolinite montmorillonite and nontronite and carbonate composition dolomite vs calcite the rocklea infrared reflectance spectroscopy based mineral abundance and composition results have been used in an associated study to characterize the architecture of the rocklea channel iron deposit with implications for exploration mining and ore genesis

the dynamics of gold in regolith change with differing environmental conditions over time significant au discoveries are becoming less common because the remaining prospective underexplored areas are obscured by transported cover at moolart well western australia secondary au deposits hosted in transported pisolitic ferricrete and saprolite are overlain by younger transported cover here we show how au has been and is being dispersed and concentrated in these deposits and the overlying younger transported cover and biota during the evolution of the landscape we identified coarse 400 m ag rich primary angular au accumulated residually along with some precipitated ag poor acacia aneura and termite mounds indicates active dispersion

protocols for in situ measurement of oxygen isotopes in goethite by ion microprobe abstract we present protocols for high spatial resolution measurement of oxygen isotope ratios of goethite feooh with the sensitive high mass resolution ion microprobe stable isotopes shrimp si and propose a natural sample as a potential goethite reference material rm for ion microprobe analysis we assess the effects of goethite chemical composition crystallographic orientation and texture on the accuracy and repeatability of shrimp si 18o 18osims results synthetic goethites evaluated as potential 18osims rm are powdery porous and finely crystalline they do not yield repeatable results a dense colloform goethite from the capao topaz mine minas gerais brazil fulfills major prerequisites it is stoichiometrically relatively pure yields repeatable oxygen isotope results and occurs in abundance to produce a rm for long term use we use an average laser fluorination 18olf vsmow value of 17 3 0 3 1sd obtained for five aliquots of this rm to normalize all 18osims measurements multiple 18osims analyses of a large fragment of the capao l4 cl4 rm analyzed in three different runs yield an overall repeatability of 17 3 0 5 2sd n 294 for all three runs combined natural variability and crystal orientation effects are the main reasons for the excess spread of the 18osims results compared to the spot internal precision ca 0 2 all 18osims analyses n 1027 in various aliquots of cl4 randomly oriented and analyzed in 26 sessions during eight distinct runs yield an overall repeatability of 17 3 0 7 2sd confirming that cl4 is a suitable sims rm after ascertaining its suitability as a rm we used cl4 to standardize analyses of other natural goethite samples with the shrimp si and compared 18osims and laser fluorination results to test the relationship between natural properties e g porosity minor elements substituting for fe preparation procedures e g polish and relief instrument conditions and the overall precision and accuracy of the sims analyses samples containing minor elements substituting for fe e g al mn cu zn etc or as contaminants e g si p require significant matrix corrections because we could not find homogenous natural goethite samples showing a large range in metal concentrations we extrapolate our calibration curves beyond the composition of our calibration goethite samples 18osims results corrected for instrument mass fractionation using cl4 and compositionally dependent matrix effects using several calibration goethites of known elemental composition are less precise but statistically indistinguishable from their laser fluorination results however porous samples are unsuitable for shrimp si 18o analysis dense colloform samples yield repeatable results for individual growth bands showing that the high spatial resolution moderate precision and speed of analysis of the shrimp si can resolve variations in oxygen isotope composition acquired during sample growth u th he geochronology of equivalent aliquots from the same goethite samples reveal that the combination of the two methods permits the extraction of temporal variation in the isotopic compositions of meteoric solutions in the geological past

age and evolution of diachronous erosion surfaces in the amazon combining u th he and cosmogenic 3he records u th he geochronology of two weathered plateaus in the carajas mountains para brazil reveals a history of weathering spanning from ca 80 ma to the present for this high elevation 720 m land surface cosmogenic 3he measurements of hematite pebbles and blocks cemented onto the plateaus at two sites n1 and s11d yield erosion rates as low as 0 09 and 0 08 m ma 1 respectively thus these results confirm that the plateau surfaces are nearly immune to physical erosion for tens of millions of years u th he geochronology of ferruginous duricrusts blanketing the low elevation 250 100 m plains surrounding the carajas mountains yield results consistently younger than 10 ma the geochronology results also reveal that the low elevation plain is diachronous becoming progressively younger towards the receding plateaus the spatial distribution of u th he ages permits reconstruction of the history of scarp retreat for the carajas landscape showing that scarp retreat along major river valleys may have been as fast as 20 km ma 1 during tectonically active and humid periods in the cenozoic the cessation of scarp retreat at some sites suggests that metamorphosed banded iron formations and quartzites provide effective barriers to retreating escarpments helping to preserve some of the oldest continuously exposed land surfaces on earth

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity