characteristics of the antarctic surface mass balance 1958 2002 using a regional atmospheric climate model temporal and spatial characteristics of the antarctic specific surface mass balance ssmb are presented including its components solid precipitation sublimation deposition and melt for this purpose we use the output of a regional atmospheric climate model racmo2 ant horizontal resolution of 55 km for the period 1958 2002 racmo2 ant uses european centre for medium range weather forecasts ecmwf 40 year re analysis era 40 fields as forcing at the lateral boundaries racmo2 ant underestimates ssmb in the high interior of east and west antarctica and overestimates ssmb on the steep coastal slopes otherwise the modeled spatial pattern of ssmb is in good qualitative agreement with recent compilations of in situ observations large scale patterns like the precipitation shadow effect of the antarctic peninsula are well reproduced and mesoscale ssmb patterns such as the strong precipitation gradients on law dome are well represented in the model the integrated ssmb over the grounded ice sheet is 153mmw e a 1 for the period 1958 2002 which agrees within 5 with the latest measurement compilations sublimation and melt remove 7 and

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

origin and depositional environment of ordovician stratiform iron mineralization from zamora nw iberian peninsula the ordovician stratiform iron deposits at zamora nw iberia are arranged in several levels ranging between 0 2 and 1 5 m in thickness which are interstratified in the upper member of the pielgo quartzites formation arenig the sandy nature and trace fossils corresponding to the ichnogenus cruziana and daedalus together with major and trace element contents of this formation suggest an inter and subtidal shallow marine depositional environment which on a global scale formed part of a broad shelf situated in the northern margin of the gondwana continent the iron mineralization displays a foliated and banded structure due to the alternation of quartzitic phosphatic apatite chamositic chamositic biotitic and ferriferous magnetite and hematite beds they have high tio2 ta sc v nb co zn and y contents the magnetite contains unusually large amounts of tio2 v cr and ni there is also a clear depletion in eu and the eu sm cn ratio is 1 the chamosite contains high concentrations of cr and v these results suggest that iron was supplied from the weathering of a continental source in combination with volcanic activity such as within basin basic volcanism or the presence of basic volcanic rocks in the exposed land the physicochemical conditions of iron mineral crystallization calculated from chamosite compositions are the following log f o2 38 8 to 30 7 log f s2 13 2 to 9 5 and t 200 to 330 c these results together with the 18o value 2 of the magnetite suggest that chamosite and magnetite were crystallized during later diagenesis and early low grade metamorphism under redox conditions below the magnetite hematite buffer

geochemistry of oolitic iron ores an electron microprobe study oolitic iron ores are made up of silicate oxide and carbonate minerals that are part of solid solution series the compositions of the minerals can depart from pure end members and show variation among deposits this variability can be quantified using electron microprobe techniques iron silicates are represented by chamositic clays both berthierine and chamosite glauconite was not seen in any of these samples berthierine predominates in younger deposits whereas the paleozoic ores studied contained only chamosite compositions of the chamositic clays however were independent of age iron oxides are mostly goethite in younger deposits or hematite in older deposits both minerals lack appreciable al in solid solution most analyses show small amounts of al but usually balanced by si in the same proportion as in chamosite indicating a slight admixture of clay iron carbonates are siderite with appreciable substitution of ca and mg but not of mn apatite is common but no iron phosphates were found the compositions of the silicates and carbonates are close to those reported for early diagenetic minerals from other types of sedimentary rocks indicating that ironstone formation does not require unusual chemical conditions other than a large supply of iron the analytical results can be used to argue against several hypotheses of ironstone genesis the lack of al in the goethitic and hematitic ooliths is inconsistent with an origin either by redeposition of soil ooliths or by oxidation and leaching of earlier chamositic ooliths the presence of high al contents in the chamositic ooliths shows that they cannot have formed from earlier aragonitic ooliths and the presence of small amounts of chamositic clay and apatite as discrete laminae in goethitic and hematitic ooliths suggests that this type of oolith could also not have formed by replacement of aragonite times of ironstone deposition show a correlation with climate and sea level stands that suggests a mechanism for generating locally high iron concentrations in seawater a combination of a warm humid climate and low average continental relief would intensify lateritic weathering and the formation of iron enriched detritus coincidence of this increased detrital iron supply with intensification and shallowing of the oxygen minimum layer in the ocean could lead to mobilization of iron from offshore shelf clastics to be redeposited near the shoreline in intertidal to shallow subtidal environments

preliminary firn densification model with 38 site dataset firn densification modeling based on hot isostatic pressing with power law creep is investigated using depth density data from 38 sites that collectively have mean annual temperatures ranging from 216 to 256 k and accumulation rates ranging from 0 022 to 1 2 m w e a 1 we use an inverse technique to obtain free parameters in a simple physical model for different stages of time dependent firn densification our model works as well as or slightly better than previous models interpolating within the data range but extrapolating would require additional physics

synsedimentary formation of ooidal ironstone an example from the jurassic deposits of se central iran abstract the study of the upper lower to middle jurassic badamu formation in se of central iran represents the first report of jurassic ooidal ironstone in iran and exhibits a record of ferruginous radial ooid dominated ironstone the studies showed that this chamosite or ferric oxide chamosite type ooidal ironstone is similar to minette type ironstones a shoreface zone in an epeiric or epicontinental sea is proposed for formation and accumulation of the ferruginous ooids and the ooidal ironstone fe derived from lateritic weathering has been transported into the shoreface zone via a fluvial current during the synsedimentary formation of the ooidal ironstone during the periods with moderate to lower energy or weakly agitated and quiet environmental conditions suspended ferruginous small radial ooids and fe were increased in the lower shoreface subzone higher environmental energy resulted in the development of large concentric ooids and limited distribution of fe in the upper shoreface subzone higher environmental energy also prevented the development of radial ooids and restricted fe precipitation on carbonate ooids variations in environmental energy in the middle shoreface subzone were unfavorable for increasing ferruginous ooids and fe in the environment although short term periods with weakly agitated and quiet or moderate to lower energy conditions could had been existed in the middle shoreface subzone but precipitation of fe on a few small radial ooids was allowed environmental energy in the shoreface zone was the major factor controlling precipitation of fe especially suspended river fe loads on the ooids however precipitation of dissolved fe could have been related to oxidizing conditions in the environment also the probable presence of fe oxidizing bacteria in the cortexes of the ferruginous small radial ooids indicates that bacteria could have possibly contributed to precipitation of fe on the ooids in a calm environment

facies analysis and palaeoclimatic significance of ironstones formed during the eocene greenhouse lower and middle eocene ironstone sequences of the naqb and qazzun formations from the north east bahariya depression western desert egypt represent a proxy for early palaeogene climate and sea level changes these sequences represent the only palaeogene economic ooidal ironstone record of the southern tethys these ironstone sequences rest unconformably on three structurally controlled cenomanian palaeohighs for example the gedida harra and ghorabi mines and formed on the inner ramp of a carbonate platform these palaeohighs were exposed and subjected to subaerial lateritic weathering from the cenomanian to early eocene the lower and middle eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies the distribution of low energy ironstone facies is controlled by depositional relief these deposits consist of lagoonal burrow mottled mud ironstone and laterally equivalent tidal flat stromatolitic ironstones the agitated water ironstone facies consist of shallow subtidal intertidal nummulitic ooidal oncoidal and back barrier storm generated fossiliferous ironstones the formation of these marginal marine sequences was associated with major marine transgressive regressive megacycles that separated by subaerial exposure and lateritic weathering the formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features such as colloform texture and alveolar voids implies periods of humid and warm climate followed major marine regressions the formation of the lower to middle eocene ironstone succession and the associated lateritic palaeosols can be linked to the early palaeogene global warming and eustatic sea level changes the reworking of the middle eocene palaeosol and the deposition of the upper eocene phosphate rich glauconitic sandstones of the overlying hamra formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions

origin of ooidal ironstones in relation to warming events cretaceous eocene bakchar deposit south east western siberia abstract an integrated study involving petrographical mineralogical and geochemical investigations proposes the origin of the bakchar ironstone deposit by upward migration of a mixture of fe rich brine and hydrothermal fluid through marine sediments trace element concentrations of the ironstone deposits rule out continental derivation of fe while high ree concentrations indicate mixed hydrogeneous and hydrothermal source three main types of ironstone within the bakchar deposit are characterized by distinct mineralogical assemblage of authigenic minerals corresponding to oxic methanic and weakly sulfidic dysoxic conditions changing redox conditions of the depositional environment methane seepage in warm seawater and availability of iron influx possibly determined the final mineralogy of three varieties of ironstones the association of siderite with ferrimagnetic sulfides like greigite and pyrrhotite in type 1 ore indicate anaerobic oxidation of methane with limited bacterial sulfate reduction the ironstone deposits of narym kolpashevo and bakchar are contemporaneous with geological events like ocean anoxic event 3 oae 3 cretaceous paleogene k pg boundary and palaeocene eocene thermal maximum petm respectively all corresponding to warm seawater conditions

dating the earliest pleistocene alluvial terrace of the alcanadre river ebro basin ne spain insights into the landscape evolution and involved processes abstract this work presents the results of a multi approach study of the extensive highest terrace qt1 of the alcanadre river system ebro basin spain the timing of the earliest morphosedimentary fluvial archives in the ebro basin ne spain under exorheic conditions is provided from esr dating techniques applied to optically bleached quartz grains and complemented by palaeomagnetic data and morphopedosedimentary features a mean esr age estimate of 1276 104 ka based on the ti centre provides the oldest numerical age obtained for a quaternary terrace in the iberian peninsula the polarity determined by palaeomagnetic analysis is normal although it must be contained within the matuyama reversed period therefore cobb mt is the more suitable chron although jaramillo cannot be fully ruled out this age is consistent with the last stretch of the matuyama reversed chron deduced from palaeomagnetism relevant consequences concerning the palaeogeographical setting palaeoclimatic context and fluvial incision rates are discussed to elucidate the landscape evolution of ne iberia

on the formation of blue ice on byrd glacier antarctica blue ice areas bias cover 1 of the east antarctic ice sheet and are visual evidence of persistent ablation in these regions more snow is sublimated and or eroded than is accumulated the physical processes driving the formation of bias are poorly understood here we combine a firndensification model with high resolution 5 5 km maps of surface mass balance and ice velocity to simulate the build up and removal of a firn layer along an ice flowline passing byrd glacier a bia is formed once the complete firn layer is removed feedback processes which enhance blue ice formation through the difference in surface characteristics of snow and ice are examined using sensitivity simulations the presence of blue ice on byrd glacier is found to be mainly determined by 1 ice velocity 2 surface mass balance and 3 the characteristics thickness mass of the firn layer prior to entering the ablation area with a moderate decrease of the surface mass balance the location and extent of the simulated bia on byrd glacier is found to be in good qualitative agreement with modis optical imagery

river incision and terrace formation in the late cenozoic of europe abstract late cenozoic environmental changes which affected european rivers are reviewed focusing especially on those of mid pleistocene times c 1 2 0 8 ma or around mis 22 and thereafter these involved dominating but fluctuating cold climate periglacial conditions shorter but major episodes of glaciation and brief interglacials there were also related sea level and tectonic responses the known history of european rivers in this period is individually varied but is predominantly marked by multiple stages of episodic incision the form of which changed in style at around the mid pleistocene transition it is suggested that the nature of climatic oscillations the dating of incision episodes and the processes that achieve this incision are as yet insufficiently understood fluvial process studies suggest that the onset of incision may broadly relate to changes in slope discharge sediment load and calibre and bedrock erodibility and these may all have been transformed as the direct or indirect result of mid pleistocene climatic changes common properties of basal sediments on strath terraces suggest that it was during the extended but variable cold stage episodes that both valley deepening and lateral widening occurred and that climatic change was the principal driver of episodic deep valley incision

dating the onset of lower tagus river terrace formation using electron spin resonance in the western iberian peninsula staircases of fluvial terraces have been the subject of several recent studies in particular many recent publications have focused on the quaternary fluvial chronostratigraphy of the lower tagus basin however there are still doubts with respect to the timing of the first incision into the late tertiary basin fill deposits their upper part already recording a fluvial environment basin inversion which was the start of terrace formation this is because most dating methods are ineffective for this type of deposit generally without organic and or volcanic materials in the last 10 years new dating methods such as electron spin resonance esr applied to sedimentary quartz now facilitate more accurate chronologies this paper presents the results of the esr dating of the older terraces of the lower tagus basin portugal with extrapolation on the age of early drainage network evolution according the results the oldest fluvial terrace was formed around 900 ka so the origination of the portuguese tagus river terrace system can be attributed to the final part of the early pleistocene

ironstones and green marine clays in the dongjeom formation early ordovician of korea abstract in the sino korean north china block the occurrence of ironstone is reported for the first time from the lower ordovician dongjeom formation korea the dongjeom formation comprises much quartzose sediment deposited on the extensive carbonate platform and is composed of three coarsening upward sequences ironstone beds are distributed on the tops of the lower two sequences suggesting that they mark approximately maximum flooding events during the relative lowstand of sea level when the dongjeom formation was deposited extensive weathering in the source areas coupled with higher order sea level rises resulted in the formation of the dongjeom ironstones the dongjeom ironstones include much green marine clays ironstones of the lowest sequence are characterized by glaucony facies and those of the middle sequence by chamosite facies chemical compositions of dongjeom glauconies reveal that they were originally nascent to slightly evolved 3 to 5 k 2 o wt and that they were affected by illitization after burial their immature compositions suggest that glauconies were formed in about 10 3 to 10 4 years or less on the seafloor the substrates for glauconitization are interpreted as detrital mineral grains regressions after glauconitization introduced iron oxides to the green grains eventually forming the iron oxide rich band under the most oxidizing conditions the distribution of glauconies in limited horizons suggests that the dongjeom glauconies are autochthonous in origin chamosites have granular shapes and are mixed with quartzose sand grains suggestive of reworking during storms the dongjeom chamosites were transformed from the precursor berthierines the occurrence of glauconies in correlative horizons in korea and north china may indicate that glauconitization in the host sediments which were deposited in far northern gondwana occurred under the influence of a coeval transgressive event

distribution and characteristics of a middle ordovician oolitic ironstone in northeastern kansas based on petrographic and petrophysical properties a laurasian ironstone case study abstract the margins of gondwana are generally considered to be the major sites of oolitic ironstone production during the ordovician and appear to be linked with global eustatic sea level rise occurrences of oolitic ironstones within the north american craton are less well documented but provide important supplementary data the low latitude of laurasia contrasted with gondwana allows useful comparisons of climatic and temporal patterns of ordovician ironstone formation middle ordovician ironstones occur in siliciclastic sequences in the american mid continent and appear to become progressively younger as the epicontinental sea advanced from the southwest across a predominantly carbonate terrain in northeastern kansas the regional distribution pattern of primary syndiagenetic goethite iron oolites within the st peter sandstone indicate deposition peripheral to a north northeast trending chain of islands underlain by predominantly granitic rocks located along an ancestral nemaha uplift detailed compositional mapping in the subsurface was made possible by the distinctive petrophysical properties of the goethite zone and the extensive regional control of wireline logged exploration wells petrographic data from ironstone core and drill cuttings both validate log analysis and give insights on possible modes of genesis we propose that eustatic changes in sea level were the primary factor governing the formation and observed distribution patterns of the oolite bed s the relationship of the observed occurrence patterns to major rift related faults of the central north american rift system suggests that synsedimentary tectonism also influenced this process the most likely source of iron appears to be by derivation from intensive humid weathering of granite exposed extensively on the ancestral nemaha uplift archipelago

nomenclature for iron formations abstract this paper explains the terminology and a classification scheme which are used in an accompanying paper about the genesis of iron formations an iron formation is considered to be a stratigraphic unit which consists mostly of iron rich chemical sedimentary rock specifically rock with more than 15 fe the rock is called ironstone iron formations may be classified into six groups on the basis of the sedimentary environment in which they accumulated some previous authors have used the terms ironstone and iron formation in more restricted ways for example ironstone has been used to name one of the six environmental types of iron formations and iron formation has been used exclusively for chert rich iron formations these restrictions are avoided herein because they are not consistent with the simplicity of the names by analogy with limestone ironstone is simply an iron rich chemical sedimentary rock the word formation clearly refers to a stratigraphic unit and so iron formation is applied to any stratigraphic unit which is composed predominantly of ironstone alternative usages of the terms ironstone and iron formation have been sufficiently varied that none of the usages can be defended on the grounds of overwhelming support independent of semantic arguments

blue ice areas in antarctica derived from noaa avhrr satellite data we have mapped antarctic blue ice areas using the u s national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr antarctica cloud free image mosaic established by the united states geological survey the mosaic consists of 38 scenes acquired from 1980 to 1994 our results show that approximately 60 000 km2 of blue ice exist for each of the two main types of blue ice melt induced and wind induced normally the former type is located on slopes in coastal areas where climate conditions i e persistent winds and temperature together with favourable surface orientation sustain conditions for surface and near surface melt the latter blue ice category occurs near mountains or on outlet glaciers often at higher elevations where persistent winds erode snow away year round and combined with sublimation creates areas of net ablation furthermore we have identified an additional area of 121 000 km2 as having potential for blue ice however in these areas features such as mixed pixels glazed snow surfaces crevasses and or shadows make interpretation more uncertain in conclusion a conservative estimate of antarctic blue ice area coverage by this method is found to be 120 000 km2 0 8 of the antarctic continent with a potential maximum of 241 000 km2 1 6 of the antarctic continent

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

geomorphological correlation of the tectonically displaced tejo river terraces gaviao chamusca area central portugal supported by luminescence dating abstract a suite of fluvial terraces t1 t6 from top to bottom of the staircase occur along a 70 km stretch of the tejo river in central portugal between the small towns of gaviao and chamusca terrace correlation was based upon the following a aerial photograph analysis geomorphological mapping and field topographic survey b sedimentology of the terrace deposits namely the maximum particle size clast composition and lithofacies identification and c k feldspar infrared stimulated luminescence irsl dating of the three lower terraces levels as quartz optically stimulated osl signal of the samples from these terraces was too close to saturation for all but two samples the two upper terraces t1 and t2 lack suitable materials for luminescence dating e g sands silts but also their probable ages are beyond the upper range of the dating method faults affecting terraces and older deposits have been reported the luminescence dating results suggest that some assignments of local terrace remnants were incorrect because of fault related vertical displacements the luminescence dating procedure also included a correction for anomalous fading in order to obtain more reliable estimates of the burial ages the fading rate was identical for all samples so for correlation of the terraces anomalous fading of the feldspar irsl signal is considered not to be a significant problem the t5 terrace has corrected ages of 42 99 ka the t4 from 107 to 222 ka and the t3 terrace has a minimal age of 300 ka fluvial incision appears to have been principally controlled by regional uplift but also by localised movements along fault structures using the corrected ages of the t4 surface a time averaged incision rate can be quantified as follows 1 0 29 m ka for reach iii 2 0 53 m ka in the chamusca area east side on reach iv and 3 0 13 m ka in the mato miranda area west side on reach iv the less uplifted block according to the geomorphic framework

depositional environments and iron ooid formation in condensed sections callovian oxfordian south eastern paris basin france carbonate platforms across western europe were superseded at the middle upper jurassic callovian oxfordian boundary either by alternating marl limestone and widespread marl deposits or by condensed sections containing iron ooids the characteristics of marine condensed sections in the south eastern part of the paris basin france and their distribution pattern are examined here and a model of iron ooid formation is developed iron ooids are found from the shoreface to the offshore zone they are most abundant in the median to distal offshore transition zone where they originally formed they also occur commonly albeit often as reworked grains in the proximal offshore zone to which they were transported the contemporaneous thick predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings distal offshore zone the iron ooids are composed of goethite typically they have a nucleus made up of a clump of goethite crystals and a laminated cortex three distinctive nanostructures are identified in the cortex laminae i a nanograined crystalline structure typical of primary goethite ii a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals and iii a coalesced structure acquired by subsequent diagenetic recrystallization the iron ooids formed successively i by lamina growth when goethite precipitated in the surface layer of the sediment nanograined structure and ii by interruption of growth when the ooids were remobilized by hydrodynamic agents as reflected by the flaked nanostructure iii these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried

influence of persistent wind scour on the surface mass balance of antarctica in the antarctic interior assessments of surface mass balance may overestimate accumulation because high winds remove some of the annual snowfall geophysical observations reveal localized zones of persistent wind scour where little or no snow accumulates that are predicted to occur across approximately 5 of the antarctic surface accurate quantification of surface snow accumulation over antarctica is a key constraint for estimates of the antarctic mass balance as well as climatic interpretations of ice core records1 2 over antarctica near surface winds accelerate down relatively steep surface slopes eroding and sublimating the snow this wind scour results in numerous localized regions 200 km2 with reduced surface accumulation3 4 5 6 7 estimates of antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes and overestimate the net mass input in wind scour zones3 here we combine airborne radar observations of unconformable stratigraphic layers with lidar derived surface roughness measurements to identify extensive wind scour zones over dome a in the interior of east antarctica the scour zones are persistent because they are controlled by bedrock topography on the basis of our dome a observations we develop an empirical model to predict wind scour zones across the antarctic continent and find that these zones are predominantly located in east antarctica we estimate that 2 7 6 6 of the surface area of antarctica has persistent negative net accumulation due to wind scour which suggests that across the continent the snow mass input is overestimated by 11 36 5 gt yr 1 in present surface mass balance calculations

impact of model resolution on simulated wind drifting snow and surface mass balance in terre adelie east antarctica this paper presents the impact of model resolution on the simulated wind speed drifting snow climate and surface mass balance smb of terre ad elie and its surroundings east antarctica we compare regional climate model simulations at 27 and 5 5 km resolution for the year 2009 the wind speed maxima in terre ad elie and the narrow glacial valleys of victoria land are better represented at 5 5 km resolution because the topography is better resolved drifting snow sublimation is 100mma 1 in regions with high wind speeds our results indicate a strong feedback between topography wind gradients and drifting snow erosion as a result smb shows much more local spatial variability at 5 5 km resolution that is controlled by drifting snow erosion whereas the large scale smb gradient is largely determined by precipitation drifting snow processes lead to ablation in the narrow glacial valleys of victoria land the integrated smb equals 86gt although wind climate drifting snow processes and smb variability are better represented at 5 5 km the area integrated smb is not significantly different between the simulations at 27 and 5 5km a horizontal resolution of 27 km is sufficient to realistically simulate ice sheet wide smb

spatial and temporal variation of sublimation on antarctica results of a high resolution general circulation model in this paper we use output of a high resolution general circulation model echam 3 t106 resolution 1 1 x 1 1 to study the spatial and temporal variation of sublimation on antarctica first we compare model results with available observations of sublimation rates the yearly cycle with small latent heat fluxes during the winter is well reproduced and the agreement with sparsely available spot observations is fair the model results suggest that a significant 10 15 of the annual precipitation over antarctica is lost through sublimation and that sublimation plays an important role in the formation of blue ice areas a preliminary analysis of the atmospheric boundary layer moisture budget shows that the spatial variation of sublimation in the coastal zone of east antarctica can be explained by variations of horizontal advection of dry air dry air advection and thus surface sublimation is enhanced in areas where katabatic winds are strong and have a large downslope component and where the antarctic topography drops suddenly from the plateau to the coastal zone in areas where horizontal advection is small like the plateau and the large ice shelves special conditions must be met to make significant sublimation at the surface possible

the ordovician iron ore of the anti atlas morocco environment and dynamics of depositional process abstract in morocco iron deposits of sedimentary origin are mainly developed in the ordovician where they are interbedded at different levels of the stratigraphic column a detailed analysis of the sedimentary facies shows that the iron ores are not randomly distributed but are concentrated at omission surfaces of the sequences thus raising the question of their sedimentological significance within the sequences that shelter them this study determines three morphological types of ore which provide a possible avenue for economic exploitation these morphological types are firstly from metric to decametric bodies of regional extension examples are caid rami and tachilla consisting of a set of detrital facies organized in two stratigraphic stages that cyclically recur to form genetic sequences within each sequence the maximum mineralization is at the top of the prograding basal stage and is expressed by diagenetic iron cement and at the base of the regressive stage in the form of strata of iron oolites or in massive beds secondly lenses with a thickness up to 30 m over a kilometer width example of imi n tourza field corresponding to incisions cut along the ravinement surfaces the maximum mineralization of this second type is within the median sandstone stage in connection with a large transgressive event thirdly there is a type of reworked material consisting of discontinuous layers of ferruginous conglomerates and bioclastics lining the ravinement surface that separates the higher order sequences it is this third type that has generated the most economic interest the iron bearing mineral phases identified are magnetite hematite iron chlorite maghemite iron hydroxides goethite lepidocrocite and siderite the ultimate source of iron would probably be the large reserves of banded iron formation of the west africa craton mauritania in particular intense tropical weathering would have leached the silica and left a highly enriched iron residuum that was carried as particulate iron to shallow marine shelf environments where fe3 was converted to fe2 during early diagenesis this reduced iron was recycled into the water column by tidal currents or storm waves where it precipitated as ferric oxide or ferrous silicate ooliths this depositional mechanism accounts for the positioning of ironstone beds at times of stasis and reworking

spatial and temporal variability of snow accumulation in east antarctica from traverse data recent snow accumulation rate is a key quantity for ice core and mass balance studies several accumulation measurement methods stake farm fin core snow radar profiling surface morphology remote sensing were used compared and integrated at eight sites along a transect from terra nova bay to dome c east antarctica to provide information about the spatial and temporal variability of snow accumulation thirty nine cores were dated by identifying tritium b marker levels 1965 66 and non sea salt nss so4 2 spikes of the tambora indonesia volcanic event 1816 in order to provide information on temporal variability cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation stake farm and ice core accumulation rates are observed to differ significantly but isochrones snow radar correlate well with ice core derived accumulation the accumulation ablation pattern from stake measurements suggests that the annual local noise metre scale in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation with no accumulation or ablation for a 5 year period in up to 40 of cases the spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi decadal secular scale stake measurements and firn cores at dome c confirm an approximate 30 increase in accumulation over the last two centuries with respect to the average over the last 5000 years

diagenesis of ferriferous phases in the northampton ironstone in the cowthick quarry near corby england berthierine siderite and pyrite are the major ferriferous phases in the northampton ironstone nis mineralogical and chemical data suggest a formation of these phases in a diagenetic marine environment changing from post oxic to sulphidic conditions berthierine was formed first when the fe 2 activity in the diagenetic system increased later this phase was partially replaced by siderite and or pyrite a second stage of the diagenetic development in the nis with increasing co 2 partial pressure p co 2 is documented by siderite the isotopic composition 18 o mean value 1 7 pdb 13 c mean value 8 6 pdb points to siderite precipitation from a marine porewater environment with a microbial co 2 source the shift from post oxic to sulphidic conditions is indicated by the occurrence of pyrite and can be considered as a final stage the diagenetic processes in the marine environment and the formation of the ferriferous phases were stopped by the influx of brackish or fresh water when the midland shelf turned estuarine

soil evolution over the quaternary period in a semiarid climate segre river terraces northeast spain abstract a macro and micromorphologic study was done on the soils from a stepped sequence of seven dated fluvial terraces in the lower segre river valley lleida northeast spain under a present day semiarid mediterranean climate the soils have evolved from the holocene through the early pleistocene providing an excellent morphostratigraphic framework for evaluating time dependent factors influencing soil formation in a dry and calcareous environment throughout the chronosequence some properties are regularly age related specially carbonatation in subsurface horizons the carbonates occur mainly as micrite and although microsparite and sparite also appear in the oldest soils they are replaced by fine grained calcite by dissolution reprecipitation processes micritization process which is active at present some pedological paleofeatures as the presence of sparite and recarbonated argillans in oldest terrace can be interpreted as the reflex of climatic changes during the quaternary in spite of this climate variability the soils display progressive and systematic patterns of carbonate accumulation on the lowest terraces the soils do not yet have secondary carbonates but in the beginning late pleistocene calcic horizons with carbonate pendents are developed these pendents increase its thickness with age although pendent growth rates decreases from late pleistocene to middle pleistocene in the middle of the late pleistocene calcic horizons evolved to petrocalcic horizons which increase its thickness in the middle and specially in early pleistocene the presence of calcic and petrocalcic horizons is the primary basis for soil classification this criterion is applicable not only to the soils of the lower segre river basin but also to many soils throughout the semiarid mediterranean region

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

ubiquitous occurrence of basaltic derived paleosols in the late archean fortescue group western australia abstract the 2 76 ga old mount roe basalt paleosols mr 1 and mr 2 recognized near the base of the 2 76 2 69 ga fortescue group in western australia represent some of the oldest definite examples of archean paleoweathering profiles the loss of fe and the absence of pedogenic carbonates in these reference paleosols have been considered as strong evidence for low oxygen and moderate carbon dioxide in the late archean atmosphere respectively however the robustness of such interpretations suffers both from the scarcity of paleosol exposures and the superposition of post weathering alteration over primary soil profiles here we report new exposures of the mr 1 paleosol as well as a number of new basalt derived paleosol occurrences distributed in the mount roe basalt and the 2 73 ga old kylena formations of the fortescue group we show that all these paleosols including mr 1 and mr 2 were strongly affected by post weathering reductive alteration nevertheless we discovered early lithologic units locally preserved within the hydrothermally altered paleosols which feature distinct chemical and mineralogic compositions these include i 13c depleted carbonaceous rich diaspore pyrophyllite boudins likely inherited from the hydrolysis and bauxitization of the parent basalt and ii green hard core material mostly composed of fe sericite associated with authigenic sphene and containing early relics of sulfate bearing iron rich smectite or berthierine we argue that smectite relics may constitute a part of the primary pedogenic mineral assemblage while berthierine and sphene formed during diagenesis through the circulation of reductive fluids because the depletion of iron observed in the fortescue paleosols is not solely due to pedogenesis but also to post weathering alteration particular care has to be taken when bulk chemical profiles of iron in such paleosols are used as atmospheric paleobarometer recognition of the regional scale syn depositional alteration of the fortescue subaerial basalts over the north pilbara suggests the onset of intense continental weathering associated with the uplift and emergence of the pilbara craton during continental break up and rifting such a regional onset of continental weathering may have provided large amounts of nutrients to nearby marine and or lacustrine systems favoring the development of microbial life in shallow waters

the iron ores and associated sediments of the chichali formation oxfordian to valanginian of the trans indus salt range pakistan a distinctive and widespread belemnite bearing shale of the tethyan region is well exposed in the trans indus salt range as the chichali formation where it contains two workable ironstone seams facies analysis indicates a pronounced deepening in the upper oxfordian and kimmeridgian followed by two regressive cycles marked by a transition from glauconitic phosphatic shales to glauconitic silts and sands and finally to winnowed and oxidized glauconitic sandy ironstones the first cycle ends in berriasian belemnite rich beds the second cycle which has few belemnites extends into the valanginian and is followed by deltaic sediments of the lumshiwal formation comparison with other areas indicates that the source area for the clastic components was the indian shield to the east and south the increased clastic supply in the upper jurassic lower cretaceous is thought to result from tectonic uplift in this source area rather than from climatic change the ironstone beds are distinctive in being pelletal glauconites compared with the oolitic chamosite and goethite so typical of the jurassic elsewhere enrichment of the glauconite to commercial grade was by winnowing and oxidation on the seafloor the absence of oolitic chamosite and goethite could be related to generally deeper water and an overall eh in the environment too high to allow iron to migrate in appreciable quantities as fe 2

review of cenozoic ooidal ironstones abstract cenozoic tertiary ooidal ironstones coi in 20 districts 39 deposits developed between the equatorial zone and 60 n except for one eocene district in mid southern latitude stratigraphic distribution paleocene oi occur in northern pakistan western siberia southern germany northwestern venezuela and northeastern colombia eocene oi in western siberia southern germany northwestern romania central north africa central west saudi arabia southwestern central africa northwestern venezuela northeastern colombia south central usa and northwestern australia oligocene oi in northwest and west central kazakhstan central denmark and north central iran miocene oi in northwestern venezuela northeastern colombia and southeastern malaysia pliocene oi in southeastern ukraine geotectonic framework ten districts developed in an interior or fractured craton five along the south trending uralian seaway and one along the east trending northern european seaway the south trending trans saharan seaway in or near an early red sea embayment in southeastern malaysia and in northwestern australia ten districts lay near a eratonic margin one along divergent margin and nine along the broad east trending caribbean and tethyan seaways almost all coi accumulated during the paleogene relatively high stand of sea level especially in early and middle eocene time as sea level fell gradually in neogene time coi developed in only three marginal districts including the giant pliocene kerch taman deposit in southeastern ukraine sedimentary environment almost all of the coi developed in deltaic to shallow marine facies these are commonly associated with shoaling upward siliciclastic sequences a few are in mixed siliciclastic carbonate sequences a few coi apparently occurred in fluvial and lacustrine facies some of these may have been reworked from laterite or from marine ironstones sedimentary petrology many coi are less than a few tens of centimeters thick and sporadic the ooids are entirely or predominantly ferric oxide a few contain a minor amount of berthierine 7a only the oldest one northern pakistan contains chamosite 14a more than half of the coi are associated directly or more remotely with glauconite nearly all the coi need much more rigorous examination for both their individual composition and their comparison with older ooidal ironstones

large scale karst subsidence and accelerated fluvial aggradation during mis6 in ne spain climatic and paleohydrological implications abstract fluvial systems crossing evaporitic bedrock are commonly affected by karstic subsidence which may result in river adjustments recorded by anomalous alluvial thickening a remarkable study case is the gallego river at the central ebro basin ne spain where dissolution of evaporite bedrock gave rise to a subsidence induced depositional basin 30 km long by 8 km wide infilled with alluvial sediments in excess of 110 m in thickness a detailed morpho sedimentary analysis of alluvial deposits supported with optically stimulated luminescence dating has revealed that paleokarst subsidence and accelerated fluvial aggradation occurred during discrete time periods the most recent one being at 140 155 kyr end of mis 6 subsequent alluvial terrace formation occurred at 110 kyr 63 48 kyr and 17 kyr linked to fluvio glacial activity at the pyrenean headwaters large scale bedrock dissolution and associated alluviation appear to be sensitive to 1 long lasting periods of glacial outwash discharges 2 high effective runoff from the extensive valley slopes and 3 increased surface groundwater exchange and groundwater circulation the last large scale subsidence episode 140 155 kyr correlates with hydrological proxies reflecting a prolonged 141 149 kyr salinity drop in the western mediterranean previously interpreted as linked to a heinrich event but which may instead represent an anomalous period of enhanced river discharge fed by extensively glaciated mountains

mineralogical and geochemical investigations of the middle eocene ironstones el bahariya depression western desert egypt abstract the middle eocene ironstone succession is located in the northeastern part of el bahariya depression western desert egypt this succession is subdivided into lower and upper sequences and consists of two main shallow marine ironstone facies associations the first is a lagoonal manganiferous mud and fossiliferous ironstone facies association and consists mainly of goethite and hematite detrital minerals quartz rutile and feldspars manganese minerals todorokite psilomelane pyrolusite birnessite aurorite and manjiroite and authigenic clay minerals kaolinite and illite the second is a peritidal microbially mediated stromatolitic and nummulitic ooidal oncoidal ironstone facies association consists of goethite apatite and secondary minerals that include quartz jarosite psilomelane and pyrolusite organic materials such as proteinaceous compounds lipids cellulose and carotenoids were detected in the cortices of the ferruginous ooids and oncoids the marine ironstone facies were exposed to subaerial weathering and subsurface alteration processes the weathering resulted in the formation of lateritic iron ores and paleosols during humid climatic periods the lateritic iron ores consist mainly of colloform goethite hematite and psilomelane the identification of cavity filling sulfate nitrate carbonate and silicate minerals in the marine ironstones and the lateritic iron ore may indicate more recent alteration under arid climatic conditions the subsurface alteration is attributed to the oxidation of sulfides primarily pyrite and weathering of glauconitic clastic rocks in the underlying cenomanian bahariya formation during the interaction with acidic heated groundwater the formation of ferrous and ferric sulfate and silicate minerals and mobilization of trace metals are the products of the alteration process enrichments in ba co k pb and sr are correlated with manganese oxides whereas anomalous p v cr ni zn as mo and u are correlated with iron oxyhydroxides

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

in situ measurements of antarctic snow compaction compared with predictions of models 1 we describe in situ measurements of the compaction of antarctic snow at three different sites in antarctica the rate of compaction was measured hourly over various depth intervals for up to two years these measurements show that compaction at each of the sites occurs through slow viscous deformation of the snowpack with no significant contribution from sudden collapse of weak layers the measured rates of compaction at the coldest site exhibit a strong seasonality consistent with a temperature dependent sintering mechanism having activation energy of 70 kj mol 1 at the two warmer sites activation energies of 80 and 120 kj mol 1 provide slightly better agreement with the observations published models of snow compaction underestimate the temperature sensitivity a good match to our observations is provided by a semi empirical model based on rate equations for lattice diffusion nabarro herring creep of material around pores combined with normal grain growth this model also provides a theoretical basis for a widely used empirical model of snow compaction the rate coefficient for lattice diffusion inferred from our measurements is considerably higher than published values however and other creep mechanisms cannot be ruled out

sea surface temperature during the quaternary at odp sites 976 and 975 western mediterranean abstract based on the relative abundances of the planktonic foraminifera species found in quaternary samples from odp sites 976 alboran sea and 975 menorca rise and using a modern analog technique winter and summer sea surface temperatures were estimated frequency distributions of temperatures are asymmetrical more so at odp site 976 where there is a greater abundance of samples from the warm part of the temperature range during the quaternary there is a general tendency for temperatures to fall with an overall diminution of 1 c for the winters and of more than 2 c for the summers overall mean temperatures and those of the biostratigraphic intervals identified are higher at odp site 975 than at 976 when differences are statistically significant the q1 interval i e the oldest in the quaternary is colder than the upl i e terminal pliocene and the q2 interval the q3 interval is also colder than the q2 interval and the q4 interval i e the most recent interval differences between intervals general trends and the asymmetries of frequency distributions cannot be explained as linear responses to insolation the stratigraphic series from odp site 976 was dated by correlating the relative maxima and minima of the summer temperature series with those of insolation during the month of july at 65 n it was found that 26 2 of the variance of the time series of temperatures was concentrated in the harmonics related to precession and obliquity while 19 was located in those related to eccentricity there are indications of the need to add lags and leads to the age of temperature spikes with respect to insolation but such delays and leads cannot be quantified precisely

multi storey calcrete profiles developed during the initial stages of the configuration of the ebro basin s exorrheic fluvial network abstract multi storey calcrete profiles developed in the quaternary on strath terraces of the cinca and alcanadre rivers tributaries of the ebro river in ne spain two calcrete profiles tor 1 and tor 2 near the village of el tormillo show horizons with an arrangement that differs from that of commonly described calcrete profiles significant lateral changes occur in these profiles within a distance of less than 200 m reflecting their pedofacies relationship the tor 1 profile on terrace qt1 the highest and oldest consists of six horizons from bottom to top 1 coarse fluvial gravels 2 mudstones with carbonate nodules 3 a chalky horizon 4 laminar horizons including one peloidal horizon 5 a multi storey horizon formed of at least six minor sequences each of which includes a lower detrital layer a pisolithic horizon and a thin discontinuous laminar horizon these sequences indicate several cycles of brecciation and or reworking and 6 a topmost laminar and brecciated horizon also including reworked pisoliths some 200 m to the north of tor 1 horizon 5 undergoes a lateral change to channel fill deposits the infill of the channels shows a fining upwards sequence ranging from clasts of about 10 cm in diameter to red silts with sparse pebbles all the clasts come from the underlying calcrete horizons laminar horizons are interbedded with the clastic channel deposits the youngest calcrete profiles developed on terrace qt3 of the cinca river and on the qp4 and qp6 mantled pediment levels all show relatively simple profiles composed mostly of lower horizons of coated gravels with thin laminar horizons at the top most of the horizons especially the laminar ones show biogenic features such as alveolar septal structures calcified filaments biofilms spherulites micropores and needle like calcite crystals these features indicate the important role of vegetation in the formation of all the above profiles the interbedding of clastic sediments and pisolithic horizons within the tor 2 profile indicates several stages of stabilisation during profile formation these sequences are an indication of the sedimentation soil formation and reworking processes operating on the soil surface the alternation of these processes is interpreted as the result of climate vegetation changes the channel fills of tor 2 indicate erosion and reworking of the hard laminar calcrete horizon both tor 1 and tor 2 are multi storey profiles reflecting the complex sedimentation erosion pedogenesis relationships at the final stages of the development of its corresponding fluvial terrace the study of these calcretes shows that these supposedly abandoned terraces continue to be active even though the fluvial network is entrenched both the pedofacies relationships and the complexity shown by tor 1 and tor 2 reflect the complex and unstable geomorphic setting in which these profiles developed after the establishment of the exorrheic network less complex calcrete profiles were produced in the lower terraces

vegetation response to obliquity and precession forcing during the mid pleistocene transition in western mediterranean region odp site 976 abstract the odp leg 161 site 976 alboran sea is a deep sea section sampled at a water depth of 1108 m in the western mediterranean sea pollen analysis provides a vegetation and climate record of the mid pleistocene transition mpt roughly one million years ago the age model tied to biostratigraphic events was revised by aligning the pollen climate index pci to mediterranean kc01b and global lr04 oxygen isotope records the studied time slice spans the interval 1 09 ma mis 31 to 0 90 ma mis 23 across this interval past phytogeography of nowadays extinct taxa which were rare allows a successful application of the modern analogues technique mat to quantitative climate reconstructions for the mpt five long term obliquity related vegetation successions o1 to o5 and eight short term precession related vegetation successions p1 to p8 are observed within the studied interval these vegetation successions regardless of their duration show the same pattern the progressive replacement of temperate trees by mountainous taxa and then by herbs and steppe maxima precession related successions correspond therefore to as dramatic vegetation changes as those driven by obliquity including a final steppe phase under deteriorated climate conditions wavelet analysis of the pci record shows that the western mediterranean experienced a shift at 1 01 ma from precession dominated frequencies 1 05 1 01 ma to obliquity dominated frequencies 1 01 0 9 ma there is therefore an apparent discrepancy between wavelet analysis results and vegetation dynamic analysis which suggests that obliquity and precession are recorded throughout the entire studied interval this discrepancy could result from the fact that the pci record sums somehow similar vegetation changes wet to dry occurring at different periodicities such a complex vegetation dynamics is mathematically rendered through a single parameter i e principal component which does not successfully catch the subtle combinations of variability occurring at two close periodicities furthermore the pollen inferred early pleistocene vegetation dynamic and climate of the western mediterranean region does not show a decrease of the obliquity response relative to the precession response at the onset of the mpt

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

a depositional model for the liassic minette ironstones luxemburg and france in comparison with other phanerozoic oolitic ironstones

debate about ironstone has solute supply been surficial weathering hydrothermal convection or exhalation of deep fluids ironstone is any chemical sedimentary rock with 15 fe an iron formation is a stratigraphic unit which is composed largely of ironstone the solutes which have precipitated to become ironstone have dissolved from the earth s surface from the upper crust e g the basaltic layer of oceanic crust or from deeper within the earth genetic modellers generally choose between surficial weathering e g soil formation and hydrothermal fluids which have convected through the upper kilometre of oceanic crust most genetic modellers attribute cherty laminated iron formations to hydrothermal convection and noncherty oolitic iron formations to surficial weathering however both types of iron formations are attributable to the exhalation of fluids from a source region too deep for convection of seawater evidence for a deep source of ferriferous fluids comes from a comparison of ancient ironstone with modern ferriferous sediment in coastal venezuela a deep source origin for ironstone has wide ranging implications for the origins of other chemical sedimentary ores e g phosphorite manganostone bedded magnesite sedimentary uranium ore various karst filling ores and even petroleum preliminary study of a modern oolitic iron deposit described herein suggests that the source of iron and silica to iron formations may have been even deeper than envisioned within most hydrothermal convection models

genesis of unusual lithologies associated with the late middle devonian taghanic biocrisis in the type taghanic succession of new york state and pennsylvania abstract the middle devonian late middle givetian tully formation in new york state is the type regional expression of the global taghanic biocrisis it is marked by anomalous development of massive to rhythmically bedded micritic limestone deposits within a vastly thicker acadian foreland basin clastic succession lower medial tully carbonates record the incursion of tropical old world realm owr taxa tully fauna and the outage of the long standing higher diversity cooler water endemic eastern americas realm ear biota hamilton fauna succeeding tully strata record a return of the hamilton fauna followed by its demise due both to replacement by the lower diversity cosmopolitan genesee fauna and by the overspread of widespread anoxic bottom conditions coupled with the onset of drastically increased sediment input following tully group deposition massive micritic limestones yielding modest diversity tully fauna assemblages are particularly characteristic of the lower medial tully succession on the western new york tully platform these are coeval with nearly barren ribbon limestone and siltstone deposits in the adjacent new berlin east central new york and central pennsylvania basins these depocenters trapped terrigenous sediment and helped to create sediment starved conditions on the platform anomalous tully carbonate deposition is believed to be coincident with strong super estuarine water mass stratification in offshore tully shelf and basin settings where a warmer denser more saline water mass flowed northward shoreward across the study area beneath a counter flow of oxygenated river influenced surface water dysoxic conditions would have developed below the pycnocline favoring the tully fauna incursion precipitation of carbonate mud and possibly promoting the formation of ooidal chamosite at least five thin 1 30 cm thick mappable beds of black ooidal chamosite are observed in taghanic shelf margin slope and basin deposits these beds are typically intensely bioturbated variably rich in associated siderite contain corroded low diversity fossil assemblages and are regionally associated with condensed lag deposits above unconformities work by others suggests that chamosite formation occurs under minimally reducing post oxic interstitial conditions which are followed in turn by more strongly reducing conditions which allow for variable siderite and pyrite formation terrestrial pedogenic alteration of silicates by evolving land plant communities under warm humid conditions led to an increased supply of kaolinite as well as iron oxides and hydroxides that served as precursors to chamosite formation in the new berlin basin the transgressive top hamilton base taghanic succession is marked by a succession of diastems associated with basin deepening and upward increasing chamosite occurrence in dysoxic facies occurrence of ooidal chamosite in upper medial tully platform deposits smyrna bed may reflect water mass stratification and extreme sediment starvation at the shelf margin eastward spectral transformation of sparsely fossiliferous smyrna ooidal chamosite in the western new berlin basin into richly fossiliferous non chamositic equivalent neritic deposits east of that basin suggests that the counter flow of oxygen and nutrient rich lower salinity water had blocked the denser restricted water layer from advancing over the eastern tully clastic shelf closer to shore

berthierine formation in reservoir rocks from the siri oilfield danish north sea as result of fluid rock interactions part i characterization abstract berthierine as the only authigenic fe rich clay mineral occurs in an oil bearing glauconite rich sandstone paleocene heimdal member of the lista formation danish north sea based on the results of thin section transmission and scanning electron microscopy five different morphological types of berthierine were identified 1 mainly as grain coatings partly together with authigenic quartz covering detrital grains 2 as pore filling clay in open pores 3 small crystals in transformed glauconite grains 4 small crystals associated with siderite in layers of mica micaceous glauconite and 5 as elongated crystals in siderite concretions although different in occurrence all berthierine types investigated by microprobe analysis are of similar chemical composition suggesting similar precipitation conditions investigations by transmission electron microscopy reveal that fine berthierine crystals display straight parallel layers with a typical lattice fringe spacing of 0 7 nm and that their occurrence is intimately connected to oil phases in pore space partly berthierine textures resemble mineralized oil water emulsions berthierine is more abundant in the oil leg than in the water leg but occurs especially abundant at the oil water contact the coexistence of berthierine together with quartz overgrowth but also its appearance in glauconite indicates that berthierine formed in situ and that it is a product of glauconite dissolution berthierine formation is coupled to the reduction of aqueous fe 3 into fe 2 derived from glauconite dissolution and is related to fluid rock interactions triggered by oil degradation which occurred in the oil filled zone and at the oil water contact the biomarker parameters pristane n c 17 and phytane n c 18 indicate an increased extent of oil degradation at the oil water contact on the one hand soluble oil degradation products methane carbon dioxide and hydrogen changed the hydrogeochemical conditions such as ph pe alkalinity etc and controlled dissolution of glauconite and feldspar on the other hand the changed hydrogeochemical conditions led to berthierine and quartz precipitation in water wet reservoir intervals

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

did the ebro basin connect to the mediterranean before the messinian salinity crisis the connection of the ebro basin via the ebro river to the mediterranean sea is supposed to have played a major role in the rejuvenation of relief of northern spain and especially of the south pyrenees from the neogene by lowering the initial base level of the ebro internal drainage area down to sea level however the timing and causes of this connection are still debated a fundamental issue is whether the ebro basin became connected to the mediterranean before or after the messinian salinity crisis morphological analysis and numerical modeling of landscape evolution show that this connection did not exist before the messinian salinity crisis but is effective from the pliocene because of progressive regressive erosion

the interaction of katabatic winds and the formation of blue ice areas in east antarctica blue ice areas bias are an extreme example of a local mass balance gradient and are furthermore reasonably stable in time and space owing to local feed back mechanisms a meteorological experiment performed in and around a blue ice area in dronning maud land east antarctica showed that during driftingsnow conditions surface wind speed over the blue ice behind the mountain barrier is equal to that away from the mountains when corrected for surface roughness and stability this implies that use of diagnostic katabatic wind models to estimate divergence of drifting snow can be extended to the situation where nunataks are involved in preventing the drifting snow from passing which is the case for most bias a diagnostic model is tested for a two dimensional profile in terre adelie after which it is applied to entire east antarctica the present order of magnitude estimate shows that areas sensitive to blue ice formation appear where precipitation is low and mean annual wind speed is high i e in dronning maud land and the drainage basin of lambert glacier the results appeared to be especially sensitive to a change in inversion strength a decrease in inversion strength weakens the katabatic flow and thus the amount of snowdrift transport reducing the area where bias can develop

identification of antarctic ablation areas using a regional atmospheric climate model the occurrence of antarctic ablation areas in dronning maud land the lambert glacier basin victoria land the transantarctic mountains and the antarctic peninsula is realistically predicted by the regional atmospheric climate model racmo2 ant with snowdrift related processes calculated offline antarctic ablation areas are characterized by a low solid precipitation flux in combination with strong sublimation snowdrift erosion and or melt the strong interaction between atmospheric circulation and topography plays a decisive role in the precipitation distribution and hence that of ablation areas three types of antarctic ablation areas can be distinguished all occurring in dry regions type 1 is the erosion driven ablation area caused by 1 d and or 2 d divergence in the katabatic wind field at high elevations 2000 3200 m asl type 2 is the sublimation driven ablation area this type occurs at lower elevations

fluvial networks of the iberian peninsula a chronological framework abstract knowledge of the evolution of spanish fluvial networks has improved during recent years as more river systems have been studied and more geochronological data has become available however the chronological framework is a major issue as the range of applications is limited by methodological constraints and spatial coverage is sparse integration of absolute dating methods with biostratigraphy and palaeomagnetism permits the recent evolution of these river systems to be reviewed the timing of incision from the late neogene to the present varies between the major iberian fluvial systems depending on the substrata and tectonic settings early pleistocene and older fluvial sequences in the core areas of the iberian peninsula provide a more extensive record of fluvial evolution and are better preserved than the terrace flights in the coastal lowlands middle pleistocene sequences are well developed in most of the major river systems in iberia particularly those of the tajo guadalquivir and aguas river and frequently represent the principal climatic cycles of that period although tectonic and sea level effects can also be seen for late pleistocene to holocene times the scheme becomes more complex our review suggests that each river system has responded differently to local and regional climate control glacial and periglacial processes in headwaters in high mountain areas glacio eustatic sea level changes and local and regional tectonic patterns

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure

dynamics and mass balance of four large east antarctic outlet glaciers this is the publisher s version also available electronically from http www ingentaconnect com

genetic and chemical relationships between berthierine chlorite and cordierite in nodules associated to granitic pegmatites of sierra albarrana iberian massif spain chlorite and berthierine occur through alteration of cordierite within enclaves of metamorphic rocks transformed by the sierra albarrana pegmatites the coexistence of both phyllosilicates allows us to study their stability relationships and to compare their chemical compositions samples showing incipient replacement of cordierite by small cryptocrystalline aggregates can be identified by x ray diffraction xrd as berthierine with small quantities of chlorite electron microprobe emp analyses give mixed compositions of berthierine and cordierite samples with extensive replacement of cordierite by aggregates show similar characteristics to those with incipient replacement but some small crystals are present the last type of sample shows complete replacement of cordierite by crystals showing optical properties of chlorite and empa compositions coherent with chlorite or berthierine their xrd pattern corresponds to chlorite and their high resolution transmission electron microscopy hrtem images only show perfect sequences of 14 a lattice fringes the cryptocrystalline aggregates of the samples with incipient and extensive replacement present coexistent areas of 14 a and 7 a lattice fringes that are intergrown at different levels 1 large areas 1 m of 7 a layers 2 packets of 7 a layers between 14 a layer areas with visible 7 a to 14 a lateral changes 3 random mixed layers 7 a 14 a chlorite is the final stable product of alteration of cordierite with berthierine as an intermediate metastable phase energy dispersive x ray spectrometry microanalyses of 14 a 7 a and 14 7 a areas show lack of systematic differences in chemical compositions between both phyllosilicates which may be considered as true polymorphs

petrography mineralogy and geochemistry of the late eocene oolitic ironstones of the jebel ank southern tunisian atlas abstract the oolitic ironstones ore deposit of jebel ank central tunisia is a simply folded stratiform ore body of about 2 5 8 m thickness located in the upper part of the epicontinental souar formation late eocene and is covered by the continental segui formation mio pliocene the deposit contains about 20 mt of ore with an average grade of 50 fe generally oolitic iron deposition occurs in shallow water lagoonal environments the jebel ank deposit lies between two regional disconformities late eocene and miocene and is evidence of a transitional stage at the end of regional regression before renewed transgression the footwall of the oolitic iron ore bearing bed consists of a fine grained sandstone bed 10 20 cm thick pinching out laterally westward into green clays the hanging wall is composed of thin bedded limestone and clay alternations 2 3 5 m thick iron occurs in the form of cryptocrystalline goethite with limited al fe substitution the goethite contains around 48 fe 5 al and up to 1 5 p jarosite alunite and manganese minerals cryptomelane psilomelane and manjiorite are supergene secondary minerals probably related to descending surface fluids these manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies local cement space filling and free centimeter sized nodules fe oolites in the deposit are similar to those documented in many other oolitic ironstone deposits the dominant fe oolite type 90 has a concentrically laminated cortex with no nucleus the nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains major elements in high grade samples fe 2 o 3 65 vary within a limited range and show higher concentrations of sio 2 average 7 85 and al 2 o 3 average 5 1 with minor tio 2 mno mgo na 2 o k 2 o and so 3 less than 1 paas normalized trace elements of bulk samples and fe oolite generally show similar behavior both are enriched in v co ni mo as zn and y and are depleted in cu rb zr nb ba and hf anomalous v cr ni zn and ree y are correlated with goethite paas normalized ree y patterns of both bulk samples and fe oolite show slight hree enrichment positive ce with negative y anomalies the mineralogy goethite and cryptomelane along with the geochemistry si vs al as cu mo pb v zn vs ni co binary plots zn ni co triangular diagram ree y content and patterns and ce ce vs nd and ce ce vs y n ho n binary plots of the studied oolitic ironstone are congruent with a hydrogenetic type while two possible sources of iron for jebel ank ironstone can be proposed i submarine weathering of glauconite rich sandstone and ii detrital iron from adjacent continental hinterland the later is the more plausible source of iron based on paleogeographic setting the occurrence of fine sandstone underlying the iron level occurrence of mn ores in the lower part of the fe ores succession high phosphorous zinc ree y concentrations and y ho ratios and low la ce ratios

extent of low accumulation wind glaze areas on the east antarctic plateau implications for continental ice mass balance persistent katabatic winds form widely distributed localized areas of near zero net surface accumulation on the east antarctic ice sheet eais plateau these areas have been called glaze surfaces due to their polished appearance they are typically 2 200km2 in area and are found on leeward slopes of ice sheet undulations and megadunes adjacent leeward high accumulation regions isolated dunes are generally smaller and do not compensate for the local low in surface mass balance smb we use a combination of satellite remote sensing and field gathered datasets to map the extent of wind glaze in the eais above 1500m elevation mapping criteria are derived from distinctive surface and subsurface characteristics of glaze areas resulting from many years of intense annual temperature cycling without significant burial our results show that 11 2 1 7 or 950 143 103 km2 of the eais above 1500m is wind glaze studies of smb interpolate values across glaze regions leading to overestimates of net mass input using our derived wind glaze extent we estimate this excess in three recent models of antarctic smb at 46 82 gt the lowest input model appears to best match the mean in regions of extensive wind glaze