trace and rare earth element compositions of silurian conodonts from the vesiku bone bed histological and palaeoenvironmental implications abstract in situ minor trace and rare earth element ree compositions have been measured in conodonts from the lower silurian vesiku bone bed estonia with the aim to visualize and to quantify conodont apatite elemental geochemistry to evaluate compositional differences between conodont histologies and to evaluate the use of conodont chemistry as a palaeobiological or palaeoenvironmental proxy tissue selective analyses of minor trace and rare earth element compositions of albid hyaline and basal tissues demonstrated significant chemical offsets among these histologies the albid tissue had the lowest ree and trace element concentrations suggesting crystallinity determined better resilience to diagenetic alteration as documented in previous studies conversely the basal tissue had highest concentrations of rees and many trace elements except for sr that showed an opposite trend the higher concentrations in albid and hyaline tissues supports the in vivo sr incorporation by conodont crown nonetheless the obtained sn normalized ree patterns were uniform through all the analyzed conodont taxa and different tissues implying common diagenetic history absence of a ce anomaly and defined negative eu anomaly indicate reducing conditions during early burial these results validate current interpretations of the palaeoenvironmental conditions during the deposition of vesiku bone bed and bolsters the use of rees in palaeozoic marine vertebrates as an important palaeoenvironmental proxy

positive eu anomaly development during diagenesis of the k t boundary ejecta layer in the agost section se spain implications for trace element remobilization k t boundary geochemical anomalies have been used previously to support the impact event at the end of the cretaceous however impact models and assessment of the extraterrestrial contribution to the boundary sediments should also consider the diagenetic alteration of the impact signatures mineralogical and geochemical studies centring on redox proxies reveal differences in trace element concentrations at agost and caravaca se spain two of the most complete k t boundary sections these differences probably derive from variations in the diagenetic evolution of the ejecta layer several redox proxies such as extensive pyrite formation high authigenic uranium concentration and positive eu anomalies indicate very strong reducing conditions at agost positive eu anomalies are extremely unusual in sediments and in this case are interpreted to indicate a highly reducing environment in such conditions certain trace elements such as ir may have been remobilized thereby masking the original signature of the impact

post tectonic landscape evolution of a coupled basin and range pinaleno mountains and safford basin southeastern arizona the pinaleno mountains and adjacent safford basin are a landscape defined by the extensional tectonics of the basin and range physiographic province however over the last 4 m y this coupled basin and range have been actively degrading in the absence of widespread regional extension while rates of relief generation and upland erosion during active subsidence ca 12 5 ma are reflected in the geometry of the basin s structure and the stratigraphy it contains rates of post tectonic landscape evolution from the pliocene to the present have been heretofore unknown we combined topographic analyses of the pinaleno mountains with cosmogenic nuclide derived catchment averaged erosion rates and burial dates of axial and piedmont deposits to quantify rates of post tectonic landscape evolution and define a chronology for the last stages of deposition and subsequent incision in safford basin in addition to constraining the timing of a deposit s formation cosmogenic nuclide burial dates provide paleo upland erosion rates at the time of deposition erosion rates in the pinaleno mountains have been generally moderate over the past 4 m y ranging between 30 and 60 m m y with no strong relationship to the drainage basins modern topography a potential acceleration of erosion rates to 100 250 m m y between 3 5 and 2 ma correlates with an inferred period of enhanced precipitation as well as the arrival from upstream of the gila river in safford basin sometime shortly before 2 8 ma widespread incision of safford basin was under way by ca 2 ma as recorded by the dissection of piedmont basin highstand deposits frye mesa and two intermediate gila river terraces on the northeast margin of safford basin dated to 1 8 ma and 0 64 ma gila river incision rates have ranged from 30 to 60 m m y over the past 3 m y paleo upland erosion rates and modern millennial scale upland erosion rates fall within the same range as incision rates of the gila river in safford basin suggesting that upland erosion rates are predominantly a function of base level fall driven by axial incision however based on similarities between catchment averaged erosion rates and topography from basins draining into the integrated safford basin and the still internally drained sulphur springs basin to the south it appears that upland erosion rates during the quaternary are not being driven exclusively by regional incision rates

early diagenesis of bone and tooth apatite in fluvial and marine settings constraints from combined oxygen isotope nitrogen and ree analysis abstract fossil bones and teeth of late pleistocene terrestrial mammals from rhine river gravels rs and the north sea ns that have been exposed to chemically and isotopically distinct diagenetic fluids fresh water versus seawater were investigated to study the effects of early diagenesis on biogenic apatite changes in phosphate oxygen isotopic composition 18opo4 nitrogen content wt n and rare earth element ree concentrations were measured along profiles within bones that have not been completely fossilized and in skeletal tissues bone dentine enamel with different susceptibilities to diagenetic alteration early diagenetic changes of elemental and isotopic compositions of apatite in fossil bone are related to the loss of the stabilizing collagen matrix the ree concentration is negatively correlated with the nitrogen content and therefore the amount of collagen provides a sensitive proxy for early diagenetic alteration ree patterns of rs and ns bones indicate initial fossilization in a fresh water fluid with similar ree compositions bones from both settings have nearly collagen free ree u f and sr enriched altered outer rims while the collagen bearing bone compacta in the central part often display early diagenetic pyrite void fillings however ns bones exposed to holocene seawater have outer rim 18opo4 values that are 1 1 to 2 6 higher compared to the central part of the same bones 18opo4 18 2 0 9 n 19 surprisingly even the collagen rich bone compacta with low ree contents and apatite crystallinity seems altered as ns tooth enamel 18opo4 15 0 0 3 n 4 has about 3 lower 18opo4 values values that are also similar to those of enamel from rs teeth therefore ree concentration n content and apatite crystallinity are in this case only poor proxies for the alteration of 18opo4 values seawater exposure of a few years up to 8 kyr can change the 18opo4 values of the bone apatite by 3 therefore bones fossilized in marine settings must be treated with caution for palaeoclimatic reconstructions however enamel seems to preserve pristine 18opo4 values on this time scale using species specific calibrations for modern mammals a mean 18oh2o value can be reconstructed for late pleistocene mammalian drinking water of around 9 2 0 5 which is similar to that of late pleistocene groundwater from central europe

heterogeneous rare earth element ree patterns and concentrations in a fossil bone implications for the use of ree in vertebrate taphonomy and fossilization history abstract a bone fragment cgdq 3 of falcarius utahensis a therizinosaur from the early cretaceous cedar mountain formation utah contained within a carbonate nodule was analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms in order to investigate ree variability within a thin walled phalanx previous studies have found depth related ree pattern variations however in cgdq 3 variation occurs along the circumference of the bone nasc normalized ree patterns and concentrations vary between two apparent end members a light ree enriched lree pattern similar to solution icp ms analysis of this bone characterizes approximately two thirds of the bone fragment total ree concentrations are high and do not vary significantly from the periosteal surface to the medullar surface conversely the remaining one third of the bone has ree patterns that are mree depleted and low in total ree concentrations ree concentrations in this part of the bone do not vary significantly from the periosteal to the medullar surface a positive ce anomaly is found throughout the entire bone and is greatest within the lree enriched portion of the bone this in combination with the lree enrichment suggests that the bone fossilized under reducing conditions the distance between the lree enriched and mree depleted regions is less than 1 mm isotopic and petrographic analyses of the bone and surrounding carbonate matrix suggest the ree patterns in the bone were the result of partial fossilization incomplete filling of micro pore spaces around bone crystallites in an environment with changing redox conditions the lower mree depleted part of the bone fossilized contemporaneously with a pendant cement that formed on the underside of the bone in the vadose zone formation of the pendant cement restricted water flow through the bone isolating the lower portion which incorporated a mree depleted pattern the upper part of the bone lree enriched side fossilized under more reducing conditions than the lower part this resulted in reductive dissolution of minerals such as hydrous ferric oxides and manganese oxides which were lree enriched with positive ce anomalies these ree were then incorporated into the upper part of the bone this likely occurred after the bone entered the saturated zone below the water table the thinness of the bone and presence of a pendant cement helped facilitate partial fossilization of the bone preserving the ree signature of an earlier fluid as demonstrated by this case study differences in ree patterns within a fossil may record changes in geochemical conditions during fossilization particularly when bones are encased in a material that reduces fluid permeability such as micritic vadose calcite analysis of such bones may offer the opportunity to decipher complex fluid histories that occur during fossilization la icp ms should be utilized to confirm solution icp ms analysis if it yields high ree variability prior to an interpretation of reworking or time averaging

multistage collapse of eight western canary island landslides in the last 1 5 ma sedimentological and geochemical evidence from subunits in submarine flow deposits volcaniclastic turbidites in the madeira abyssal plain provide a record of major landslides from the western canary islands in the last 1 5 ma these volcaniclastic turbidites are composed of multiple fining upward turbidite sands known as subunits the subunits indicate that the landslides responsible for the sediment gravity flows occurred in multiple stages the subunits cannot result from flow reflection or splitting because the compositions of volcanic glasses from each individual subunit in an event bed are subtly different this indicates that each subunit represents a discrete failure as part of a multistage landslide this has significant implications for geohazard assessments as multistage failures reduce the magnitude of the associated tsunami the multistage failure mechanism reduces individual landslide volumes from up to 350 km3 to less than 100 km3 thus although multistage failure ultimately reduce the potential landslide and tsunami threat the landslide events may still generate significant tsunamis close to source

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

development of a positive eu anomaly during diagenesis diagenetic remobilization of eu is possible under conditions of reduction to eu2 at low oxidation potential and near neutral solution producing pore waters relatively enriched in eu2 as distinct from its trivalent ree neighbours eu is reprecipitated in the 3 state in environments of high oxidation potential these processes have produced positive eu anomalies in highly oxidized pleistocene muds of the amazon deep sea fan similar occurrences should be rare but where found they do provide valuable information on local diagenetic processes and conditions

rare earth element systematics of fossil bone revealed by la icpms analysis intra bone rare earth element ree fractionation trends were studied by la icpms analysis to put constraints on 1 the mechanisms controlling ree fractionation within fossil bones 2 the relative timing of ree uptake in various parts of fossil bone and 3 the origin of ree in fossil bones we have evaluated ree bone profiles across 54 fossil bones from a broad range of well characterised taphonomic settings ranging in age from triassic to early medieval ree patterns and concentration gradients are highly variable and intra bone fractionation trends in la yb n vs la sm n space of few specimens cover almost the entire range previously observed for bulk samples intra bone variability of ce anomalies as well as variable y ho and la la n is also observed sometimes diagenetic fluids with fractionated hree enriched compositions have entered the bone from the marrow cavity producing secondary ree uptake profiles theoretical intra bone fractionation trends modelled using lattice strain theory concur with most ree data but some trends cannot be modelled using realistic boundary conditions this fact as well as the occurence of positive and negative ce anomalies within the same fossil sample hint towards changing ree compositions of diagenetic fluids over the timescales of ree uptake because apparent ce anomalies frequently evolve over bone profiles and ce anomalies can be inherited from previous fractionation events ce anomalies are a highly ambiguous tracer for constraining ambient redox conditions in general bioapatite ree signatures may not always reliably reflect ambient taphonomic or redox conditions and diagenetic fluid compositions therefore ree patterns and ce anomalies of fossil bones must be interpreted cautiously as they vary spatially within skeletal remains and are affected by intra bone fractionation processes as well as changing compositions of the diagenetic fluid

isotopic composition of recent shark teeth as a proxy for environmental conditions abstract the o c and sr isotope compositions of teeth from ten species belonging to five families and three orders of sharks were measured to determine the influence of habitat diet and possible species specific fractionation effects on the isotopic composition of biogenic phosphate from fish the sharks were recently caught in subtropical waters off the kwazulu natal kzn coast of south africa as well as from cold waters in prince william sound pws alaska and victor bay vb nunavut canada 18 o values of tooth phosphate 18 o p range from 20 9 to 23 5 for the kzn sharks for most species the range in measured 18 o p values is about 0 6 but it may be as high as 1 1 for different teeth from a single shark dentine and enameloid within individual teeth have no apparent differences in 18 o p values the 18 o p values of the kzn shark teeth reflect the typical habitat of the studied species primarily the thermal structure of the water column off kzn at depths between 20 and 280 m the 18 o p values of teeth from different greenland sharks from vb and pacific sleeper sharks from pws are very homogeneous averaging 25 8 and 24 7 respectively these values appear to be in equilibrium with deep 500 m ocean waters in each case at temperatures of about 0 3 c or less there is little discernable evidence for species specific fractionation effects for the oxygen isotope composition of phosphate in the studied marine fish the oxygen isotope composition of carbonate in apatite averages about 9 1 higher than corresponding 18 o p values in agreement with equilibrium fractionation between carbonate and phosphate but with a large variance 1 1 5 18 o c values also vary by up to 1 between enameloid and dentine within single teeth but in a non systematic way differences in 13 c values between carbonate in enameloid and dentine is also large up to 8 but the 13 c values vary systematically enameloid is always enriched in 13 c compared to dentine and the 13 c content increases with developmental stage of the teeth 13 c values measured for enameloid 1 6 to 4 8 appear to approach equilibrium with dissolved inorganic carbon in seawater in contrast 13 c values for dentine range from 6 4 to 2 3 for kzn sharks and 9 0 to 10 8 for the cold water sleeper sharks and are compatible with a predominantly dietary carbon source the 87 sr 86 sr ratios of teeth from kzn sharks as well as those from pws and vb are uniform averaging 0 709167 sr content varies from 1270 to 2100 ppm a range that is similar to that in well preserved fossilized teeth seawater sr is thus clearly incorporated in vivo concentrations of sm and nd are in the ppb range and contrast the ppm range in fossilized teeth indicating a postmortem incorporation of rare earth elements in apatite of the teeth

paleoclimatic inferences from an isotopic investigation of groundwater in the central san juan basin new mexico groundwater from the ojo alamo and nacimiento aquifers in the central san juan basin new mexico has yielded 14c ages ranging from modern to 35 000 yr b p the pleistocene age samples are characterized by a stable isotope content about 25 lighter in d and 3 lighter in 18o than modern precipitation and groundwater we attribute this difference to a colder mean annual temperature and perhaps increased winter precipitation consideration of various factors controlling the stable isotope composition of the groundwater allows estimation of a 5 to 7 c temperature decrease during the late wisconsin accompanied by increased effective precipitation a similar estimate of the temperature change is obtained from noble gas paleothermometry these data support a model of moderately cooler late pleistocene climate in the american southwest characterized by summers with less precipitation than today but wetter winters

rare earth elements in solnhofen biogenic apatite geochemical clues to the palaeoenvironment rare earth element ree concentrations in biogenic apatite samples coprolite bone and soft tissue were used to investigate the environment of deposition of the celebrated solnhofen fossil lagerstatten the measured ree patterns are similar between different localities lithologies flinz faule and levels in the upper solnhofen plattenkalk suggestive of a stable ree supply during deposition the behaviour of cerium in the solnhofen samples implies that bottom water conditions were not anoxic and variations in the cerium anomaly can be explained by differences in burial rate these results provide further geochemical support for current depositional models barthel k w 1978 solnhofen ein blick in die erdgeschichte ott verlag thun barthel k w swinburne n h m conway morris s 1990 solnhofen a study in mesozoic palaeontology cambridge univ press cambridge that propose that extra basinal processes are responsible for the interbedded nature of the solnhofen deposits rather than intra basinal processes such as water turnover events

gold basin meteorite strewn field mojave desert northwestern arizona relic of a small late pleistocene impact event over 4450 meteorite specimens with a total mass of 168 760 g have been found in the gold basin l4 strewn field over an area of 225 km 2 the meteorite is a breccia composed only of fragments of l chondrite materials the parent meteoroid had a kinetic energy equivalent to 5 to 50 ktons when it hit the top of the atmosphere cosmogenic nuclide studies indicate the meteorite has a terrestrial age of 15 000 600 years corresponding to the late pinedale portion of the wisconsin glaciation conditions in the gold basin which is now part of the mojave desert were wetter and cooler at the time of the fall mossbauer analyses indicate the sample is 30 to 35 oxidized this is less than that in meteorites with similar ages found in eastern new mexico but comparable to that found in meteorites from the sahara and the nullarbor region oxidation is likely to have occurred soon after the fall when exposure to precipitation was at its maximum four other new meteorites were also found in the gold basin strewn field

seawater rare earth element patterns preserved in apatite of pennsylvanian conodonts past workers have used rare earth element patterns recorded in biogenic apatite as proxies for original seawater chemistry to explore the potency of this approach we analyzed pennsylvanian conodonts from limestones gray shales and black shales of the fort scott and pawnee formations desmoinesian and swope and dennis formations missourian in kansas missouri and iowa u s a analysis of individual platform conodonts from seven taxa using laser ablation inductively coupled plasma mass spectrometry la icp ms revealed a consistent enrichment in the middle rare earth elements mree analogous mree enrichment has been observed in authigenic apatite and bulk samples of phosphate rich black shales from the same formations importantly however phosphate depleted shales intimately associated with the p rich intervals are relatively depleted in mree these antithetic patterns argue convincingly for secondary migration from the bulk sediment into the phosphate and the extent of mree enrichment in the conodonts is correlated positively with the total ree content mree enrichment in conodonts does not vary systematically as a function of lithology stratigraphic level conodont genus geographic location or with independent estimates of paleoredox conditions in the bottom waters collectively these results argue for postmortem diagenetic ree uptake resulting in a pronounced and progressive mree enrichment any cerium anomalies if initially present were masked by diagenetic uptake of ree paleoenvironmental interpretations of conodont ree particularly for samples exhibiting mree enrichment should therefore be viewed with caution

rare earth element evolution of phanerozoic seawater recorded in biogenic apatites rare earth element ree contents of marine biogenic apatites have been shown to record seawater compositions a data base of available and newly acquired rare earth element ree contents of marine biogenic apatites has been created to assess the past seawater ree compositions to ensure that this data base contains only the pristine ree signals altered samples characterized by very low la sm n ratios where n stands for ree ratios normalized to the nasc composition gromet et al 1984 geochim cosmochim acta 48 1984 2469 acquired during apatite recrystallization are not included in the database these data reveal a change in the tethyan seawater composition between 110 and 80 ma after the end of the cretaceous the ree chemistry of seawater remains constant until present day this seawater composition change is likely due to concurrent changes in ree scavenging processes a strong correlation between decreasing sm yb n ratios and increasing ce anomalies for samples deposited during the 80 110 ma period is observed as ce anomalies are attributed to ocean water redox conditions changes in ree scavenging could reflect an evolution from stratified and poorly oxygenated waters towards well mixed and oxygenated waters this could have resulted from changing current patterns stemming from the contemporaneous opening of the atlantic ocean a major change in middle and late cretaceous oceanic circulation linked to plate tectonics would have favored the colonization of pelagic environments

a new helical trace fossil from the lower devonian of spitsbergen svalbard and its palaeoenvironmental significance abstract in devonian molasse deposits old red sandstone of spitsbergen vertical and regularly helical tubular trace fossils are found predominantely in pedogenically overprinted calcareous clay to siltstones host rocks are interpreted as alluvial plain deposits with lacustrine intercalations and marine ingressions skolithos helicoidalis isp nov generally occurs as tubes with a round to oval cross section continuously coiling downward from distinct bedding planes to a depth of 50 to 70 cm morphological variations with regard to cross sectional shapes amplitude of coiling and whorl distance are referred to primary trace heterogeneity sediment composition and secondary influences such as post sedimentary deformation diagenesis and lateral tectonic compression commonly occurring at the upper extent of fluvial lacustrine and marginal marine beds skolithos helicoidalis isp nov probably marks periods of slow or no sedimentation independent of facies its frequent association with pedogenic structures such as carbonate glaebules and slickensides suggests a plant origin rhizolith alternatively the extraordinary morphological regularity and wide distribution across facies could also point toward an animal possibly of euryecological arthropod origin

protracted diagenetic alteration of ree contents in fossil bioapatites direct evidence from lu hf isotope systematics abstract fossil bones and teeth are potentially important repository for geochemical proxy data and a target for radiometric dating the concentration of many trace elements in bones and teeth increases by orders of magnitude after death and it is this diagenetic incorporation that forms the basis for several areas of geochemical study the use of bones and teeth in this context relies on two assumptions first that target metal ions are incorporated rapidly after death reflecting a known environmental signal and second that after early incorporation the bone or tooth remains as an essentially closed system resistant to later diagenetic change a wide literature has developed exploring these assumptions but relatively little direct evidence has been used to assess the long term diagenetic stability of trace elements within bones and teeth in this study we use the lu hf isotope system to show that bones and teeth of cretaceous and triassic age from both terrestrial and marine settings experience continued long term diagenetic change most likely through gradual addition of trace elements modelling suggests that diagenetic addition after initial recrystallisation may account for 50 of the total ree content in the sampled bones the extent depending on initial uptake conditions tooth enamel and enameloid may be more resistant to late diagenetic changes but dentine is probably altered to the same extent as bone these results have significant implications for the use of bones and teeth as hosts of chronological palaeoceanographic palaeoenvironmental and taphonomic information particularly in mesozoic and palaeozoic contexts

impacts of climate change on the formation and stability of late quaternary sand sheets and falling dunes black mesa region southern colorado plateau usa abstract detailed geomorphic mapping and analysis of soil stratigraphy and optically stimulated luminescence osl dating of eolian sand dunes on black mesa arizona reveal eolian sediment deposition occurred from 30 to 16 ka followed by a period of widespread dune stabilization from 12 to 8 ka localized reactivation of the previously stabilized dune forms or local changes in sediment supply have occurred in the middle to late holocene in this region cooler wetter and more variable climatic conditions during mis 3 and 2 led to increased channel and floodplain sediment supply eolian sediment derived from these sources was transported up to 60 km deposition of this material has reduced regional topographic roughness by filling tributary canyon traps oriented perpendicular to the dominant wind and sediment transport direction topographically controlled falling dunes and sand ramps in this region are preserved because of their geomorphic position and provide evidence of the paleoenvironmental state of the fluvial and eolian systems before during and immediately after the last glacial maximum on the southern colorado plateau widely used predictive models of eolian system dynamics are typically based entirely on climatic variables and do not account for landscape complexity and geomorphic history climate only assumptions fail to give accurate predictions of the dynamics of this and many other dune fields a growing body of work suggests that eolian deposits in wind driven semiarid climates may be more strongly related to increases in sediment supply than to increases in aridity

paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite abstract rare earth element concentrations in biogenic apatite of conodonts fish debris and inarticulate brachiopods were determined in over 200 samples from cambrian to modern sediments tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory interexperiment or interspecies related variations clearly show that no resolvable fractionation of ree occurs incorporation of ree in biogenic apatite of recent fish debris occurs near the sediment water interface soon after deposition and reflects characteristics of seawater the original ree signature apparently survives subsequent burial and diagenesis cerium variations in fish debris from modern environments are controlled by redox potential ce is fractionated by co precipitation with metallic oxides under oxidizing conditions this fractionation produces a negative ce anomaly ce anom in seawater that is reflected in the sedimented fish debris conversely no fractionation of ce occurs under reducing conditions resulting in ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions extrapolation of observations of the redox control of ce anom in modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower paleozoic and lower triassic oceans whereas in the upper paleozoic the world ocean was generally oxidizing

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

an isotopic investigation of groundwater in the central san juan basin new mexico carbon 14 dating as a basis for numerical flow modeling carbon 14 dating of groundwater can be used to help determine the transmissivity distributions of aquifers this method may offer significant advantages in certain respects over traditional aquifer pumping test techniques we have applied 14c dating to a hydraulic analysis of a multilayer aquifer system in the central san juan basin of new mexico after corrections for geochemical evolution of the solutes the influence of dispersive processes on the 14c distribution was investigated a model incorporating stochastic dispersion theory indicated that macroscopic dispersion exerted only a small influence on the measured 14c activities the 14c derived transmis sivity distribution was used to construct a numerical flow model which was applied to an analysis of interaquifer leakage the model showed that even though vertical flow between aquifers was significant in this case it did not cause the 14c distribution to differ significantly from that predicted by a simple piston flow model carbon 14 can be used as a basis for detailed hydraulic evaluations of groundwater flow in areas where traditional well hydraulics methods are not practical

pulses of carbon dioxide emissions from intracrustal faults following climatic warming carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels an analysis of a 135 000 palaeorecord shows that pulses of carbon dioxide leakage from a natural reservoir in utah are associated with episodes of glacial unloading

recurrent large scale landsliding on the west flank of la palma canary islands a large area of debris avalanche deposits has been discovered on the western submarine flanks of the island of la palma multibeam bathymetry and its derivative backscatter data towed ocean bottom instrument tobi sidescan sonar images and 3 5 khz and airgun seismic reflection data have been used to identify at least two and possibly as many as four major landslide events the youngest of the events the cumbre nueva debris avalanche extends onshore into the valleys bounded by the caldera de taburiente and cumbre nueva ridge which mark the degraded collapse scars radiometric dating of the volcanic flows in the headwall indicate an age of between 536 and 125 ka for this landslide the debris avalanche covers an area of 780 km2 has a maximum thickness of 500 m and has an estimated volume of 95 km3 older deposits collectively referred to as the playa de la veta debris avalanche complex are probably as the name indicates an amalgamation of at least two or three events rather than the result of a single catastrophic failure the playa de la veta debris avalanche complex is associated onshore with an unconformity dated as late matuyama 1 ma to 800 ka it covers an area of 1200 km2 has a maximum thickness of 1300 m and may represent a total volume of up to 650 km3 the greater thicknesses and limited areas occupied by debris avalanches on the western flank of la palma compared to other landslides in the canary archipelago suggest that the la palma landslide masses have relatively low mobility the different debris avalanche lobes formed by each landslide event are separated by channels 2 2 5 km wide the clear relationship between channel position and the boundaries of each debris avalanche lobe indicates that debris avalanches control later channel formation and pathways the relief of the submarine flanks of the la palma volcanoes in the areas of island slope unaffected by landslides is mainly the result of constructional volcanic processes however the older submarine slopes such as in the northern taburiente volcano may also have been modified by smaller scale submarine mass wasting and sediment flows

aspect related microclimatic influences on slope forms and processes northeastern arizona 1 climate is a major control on geomorphology yet the effects of aspect related differences in microclimate have been little studied we examined several 60 100 m deep canyons in semiarid northeastern arizona where rock type and structure are essentially constant but where field data and a high resolution digital elevation model reveal consistent morphologic and microclimatic differences between asymmetric north and south facing sideslopes cliffs account for 29 of the vertical relief of south facing slopes but only 2 5 of north facing slopes excluding cliffs south facing slopes are 1 3 steeper than north facing slopes and have significantly less weathered bedrock we monitored air surface and subsurface temperatures and soil moisture at 0 5 h intervals at four locations over 1 year south facing slopes were 1 4 5 6 c warmer and soil moisture tension at 10 cm depth averages at least 78 kpa lower drier than on north facing slopes the dominant rock type in the study area morrison formation sandstone weathers primarily by clay hydration these sandstones form disaggregated mantles where weathering exceeds erosion but also maintain steep slopes and cliffs where little weathered south facing slopes were too dry during most of the instrumented year for significant clay expansion whereas the north facing bedrock slope was moist all year cliff growth thus occurs preferentially on warmer and drier slopes where weathering is reduced small north facing cliffs typically 3 m could have formed during the holocene but cliffs up to 70 m high on southerly aspects require more time to form and likely persisted or expanded under cooler and wetter late pleistocene climates

rare earth elements and stable isotope geochemistry δ13c and δ18o of phosphorite deposits in the gafsa basin tunisia rare earth elements ree and stable isotope compositions 13c and 18o of shark teeth and phosphatic coprolites were analyzed from the lower maastrichtian layers of the el haria formation and two sequences of the paleocene eocene p e chouabine formation in the gafsa basin south western of tunisia in order to trace the sedimentological climatic and oceanographic conditions the ree chemistry and their distribution in the two archives are the same for each of the studied layers indicating that the coprolites and shark teeth experienced the same early diagenetic environments however major differences occur between the maastrichtian and the p e reflecting changes in the depositional conditions the early maastrichtian burial environment tended to be more anoxic with ree derived from reduced feo while in the p e the ree patterns mimic the modern oxic suboxic seawater the ree source from remineralisation of organic coating could have more significance the oxygen isotope compositions of the structural phosphates 18opo4 indicate a stable and warm climate during both studied time intervals a small offset 0 4 in the 18o value between the coprolites and shark teeth show minor thermal gradient between bottom and surface water the pronounced negative shift of 3 4 in 13c values recorded in the upper part of the chouabine formation was ascribed to the paleocene eocene boundary at the same time the lack of negative change in the 18o is explained by the semi closed situation of the gafsa basin which situation also played an important role in the evolution of the organic matters in the sediment resulting in the exceptional low 13c values

sedimentological and geochemical evidence for multistage failure of volcanic island landslides a case study from icod landslide on north tenerife canary islands 1 volcanic island landslides can pose a significant geohazard through landslide generated tsunamis however a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained the study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process such as total event volume and whether landslides occurred as single or multiple events the northern flank of tenerife has undergone multiple landslide events the most recent being the icod landslide dated at 165 ka the icod landslide generated a turbidite with a deposit volume of 210 km3 covering 355 000 km2of seafloor off northwest africa the icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals named subunits sbu1 7 evidence from subunit bulk geochemistry volume basal grain size volcanic glass composition and sand mineralogy combined with petrophysical and geophysical data suggests that the subunit facies represents multistage retrogressive failure of the icod landslide the basal subunits sbu1 3 indicate that the first three stages of the landslide had a submarine component whereas the upper subunits sbu4 7 originated above sea level the presence of thin non bioturbated mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure these results have important implications for tsunamigenesis from such landslides as multistage retrogressive failures separated by several days and with both a submarine and subaerial component will have markedly lower tsunamigenic potential than a single block failure

δ18o and ree contents of phosphatic brachiopods a comparison between modern and lower paleozoic populations 18o values of both carbonate 18 7 25 1 and phosphate 15 1 16 7 components of the francolite from the fossil brachiopod shells are interpreted as the result of a partial resetting of pristine isotopic compositions the similarity of hat shape ree patterns of some lower ordovician linguloids with those of extant littoral specimens suggests the preservation of a 500 myr old record of ree marine chemistry in agreement with the known paleogeography the phosphatic brachiopods have been deposited in a coastal environment under shallow and oxygenated marine waters however the contents and distribution of ree in some strongly altered brachiopod shells reveal an alteration of the original negative ce anomalies and both nd and sm enrichments that transformed the initial hat shape patterns of linguloids into strongly convex or bell shape patterns

naturally weathered feldspar surfaces in the navajo sandstone aquifer black mesa arizona electron microscopic characterization abstract naturally weathered feldspar surfaces in the jurassic navajo sandstone at black mesa arizona was characterized with high resolution transmission and analytical electron microscope hrtem aem and field emission gun scanning electron microscope feg sem here we report the first hrtem observation of a 10 nm thick amorphous layer on naturally weathered k feldspar in currently slightly alkaline groundwater the amorphous layer is probably deficient in k and enriched in si in addition to the amorphous layer the feldspar surfaces are also partially coated with tightly adhered kaolin platelets outside of the kaolin coatings feldspar grains are covered with a continuous 3 5 m thick layer of authigenic smectite which also coats quartz and other sediment grains authigenic k feldspar overgrowth and etch pits were also found on feldspar grains these characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems and may partially contribute to the commonly observed apparent laboratory field dissolution rate discrepancy at black mesa feldspars in the navajo sandstone are dissolving at 10 5 times slower than laboratory rate at comparable temperature and ph under far from equilibrium condition the tightly adhered kaolin platelets reduce the feldspar reactive surface area and the authigenic k feldspar overgrowth reduces the feldspar reactivity however the continuous smectite coating layer does not appear to constitute a diffusion barrier the exact role of the amorphous layer on feldspar dissolution kinetics depends on the origin of the layer leached layer versus re precipitated silica which is uncertain at present however the nanometer thin layer can be detected only with hrtem and thus our study raises the possibility of its wide occurrence in geological systems rate laws and proposed mechanisms should consider the possibility of this amorphous layer on feldspar surface

responses of ground water in the black mesa basin northeastern arizona to paleoclimatic changes during the late pleistocene and holocene paleorecharge and paleo ground water flow patterns are reconstructed for the past 31 k y for the n aquifer in the black mesa basin northeastern arizona by 14 c dating of groundwater and numerical simulation of ground water flow and 14 c transport paleorecharge rates varied significantly and correlate with 18 o and d records of paleotemperatures in the n aquifer waters as well as other proxy records of regional paleoclimate and an atmospheric general circulation model recharge rates were two to three times higher than today during the late wisconsin when inferred temperatures were 5 6 c cooler but about 50 lower during early to mid holocene when inferred summer temperatures were 2 4 c warmer the pulse of the highest estimated recharge between 14 and 17 ka may be related to the northward migration of the southern branch of the split jet stream model simulations suggest that thousands of years are required for water levels to fully respond to the changes in recharge and that water levels fluctuated from 60 m higher to 6 m lower than today

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

rare earth element contents of jurassic fish and reptile teeth and their potential relation to seawater composition anglo paris basin france and england the rare earth element ree chemistry of jurassic shelf seawater from western europe anglo paris basin was investigated by analyzing the fish and reptile teeth deposited in shallow to deeper water 200 m environments ree patterns in apatites are controlled by the host sediments vertebrate teeth sampled from the siliciclastic sediments calcareous sandstones and shales show flat shale normalized ree patterns that reflect the dominant influence of the continental source from which the ree were derived carbonate deposits protected from the clastic sources contain fish and reptile teeth whose ree patterns reflect more accurately the ree composition of the overlying water column the ree patterns are similar through the bajocian to the oxfordian and are characterized by a depletion in heavy rare earth element dy ybn 1 8 5 0 compared to modern seawater compositions dy ybn 0 8 0 9 the fractionations among hree in the jurassic seawater are more efficient than in modern oceans and increases with depth instead of decreasing these hree removal processes operated as early as the paleozoic and disappeared during the late cretaceous the fractionation of hree relative to lree is correlated with the increasing depth of the basin as indicated by two independent criteria that are the sedimentary structures and the oxygen isotope composition of coexisting brachiopods the dy ybn ratio of the marine biogenic phosphates can be used as a proxy of paleo water depths at the scale of a water mass ce anomalies ce in biogenic apatite bearing limestones are variable and systematically negative relative to modern surface seawater and bathonian values mean ce 0 63 0 10 weak ce anomalies during the callovian mean ce 0 21 0 09 suggest the onset of more reducing conditions this redox change coincided with an increase of seawater temperatures as suggested by the oxygen isotope compositions measured on the same teeth we speculated that the callovian low ce could result from a decrease in the po2 due to the warming of seawater

the northwest african slope apron a modern analogue for deep water systems with complex seafloor topography the northwest african slope apron is an interesting modern analogue for deep water systems with complex seafloor topography a sediment process map of the northwest african continental margin illustrates the relative roles of different sedimentary processes acting across the entire margin fine grained pelagic and hemipelagic sedimentation is dominant across a large area of the margin and is considered to result from background sedimentary processes alongslope bottom currents smooth and mould the seafloor sediments and produce bedforms such as erosional furrows sediment waves and contourite drifts downslope gravity flows debris avalanches debris flows and turbidity currents are infrequent but important events on the margin and are the dominant processes shaping the morphology of the slope and rise the overall distribution of sedimentary facies and morphological elements on the northwest african margin is characteristic of a fine grained clastic slope apron however the presence of numerous volcanic islands and seamounts along the margin leads to a more complex distribution of sedimentary facies than is accounted for by slope apron models in particular the distribution and thickness of turbidite sands are controlled by the location of the break of slope which is itself controlled by the pre existing submarine topography

paleoenvironments revealed by rare earth element systematics in vertebrate bioapatite from the lower devonian of svalbard in situ rare earth element ree compositions have been measured in early vertebrate microremains from the lower devonian basin of andree land svalbard with the aim of obtaining information about their early depositional environment and potential reworking vertebrate microremains with different histology were used for the analyses sourced from two different localities of marginal marine to freshwater sediments from geographically distant parts of the grey h k formation skamdalen and tavlefjellet members we selected thelodont and undescribed chondrichthyan scales which allowed us to define potential taxonomic histological and taphonomic variables of the ree uptake results showed ree concentrations to be relatively uniform within the scales of each taxon but apparent discrepancies were visible between the studied localities and separate taxa the compilation of ree abundance patterns as well as ree ratios have revealed that thelodont and chondrichthyan originating from the same locality must have had different burial and early diagenetic histories the shapes of the ree profiles together with the presence and absence of the eu and ce anomalies equally suggested different depositional and diagenetic environments for these two sympatric taxa resulting from either stratigraphical or long distance reworking the ree concentrations appear to have visible differences between separate dental tissues particularly between enameloid and dentine of thelodonts emphasizing the importance of in situ measurements in microfossil biomineral geochemistry

removal of oceanic ree by authigenic precipitation of phosphatic minerals abstract early diagenetic phosphatic minerals containing rare earth elements ree are widespread in australian shallow marine sandstones of all ages most common is the aluminophosphate florencite ree al 3 po 4 2 oh 6 but the isomorphous and chemically intergrading phases crandallite gorceixite and goyazite all with up to several percent ree substituted for their major cation ca ba and sr respectively may also be present together they comprise up to 0 144 wt average 0 0134 wt of their host rocks the authigenic phosphates xenotime and apatite are also widespread but less common they all apparently precipitated within the diagenetic zones of sulphate reduction and methanogenesis as a result of reverse weathering reactions after the release of ree and po 4 by reduction of fe mn oxyhydroxides and the decomposition of organic material coating detrital particles as the aluminophosphates and apatite are enriched in light ree whereas xenotime concentrates heavy ree they collectively deposit light ree at a much greater rate la 129 10 9 g cm 2 yr 1 than heavy yb 0 40 10 9 g cm 2 yr 1 the total burial flux of light ree by shallow marine phosphatic precipitation is about 50 times greater than previously determined for deep sea sediments whereas heavy ree are buried at comparable rates this new sink produces a major imbalance in the marine ree budget requiring the existence of a substantial but currently unknown source to restore balance its size has important implications for the use of ree abundances distributions and isotopes as monitors of marine geochemical processes

fractionation of rare earth elements within bone mineral a natural cation exchange system the distribution of rare earth elements rees within fossil bones is controlled by their partition coefficients between apatite and pore waters and the rate of diffusion through the bone using simple theoretical models we show that rees are strongly fractionated from one another during diffusive transport and adsorption fractionation occurs due to the relative ease of substituting ree ions of differing ionic radius into the ca sites in the apatite lattice and the degree of fractionation is dependent on the rate of diffusion of ions within bone and therefore the rate of recrystallisation variations in bone thickness recrystallisation rate and potentially pore water composition may all influence the relative distribution of rees and thus ree ratios within bones increases in bone thickness and reductions in either diffusion coefficients or the duration of ree uptake lead to enhanced fractionation of rees in our model simulations interpretations of ree ratios in fossil bones either for palaeoenvironmental or taphonomic applications must consider how fractionation will influence ree ratios within bones particularly when interpreting spatially resolved analyses within single bones

paleoenvironmental interpretations of rare earth element signatures in mosasaurs reptilia from the upper cretaceous pierre shale central south dakota usa abstract rare earth elements were analyzed from fossil marine reptile mosasauridae bones collected from five superposed members sharon springs gregory crow creek degrey and verendrye of the upper cretaceous pierre shale at localities along the missouri river in brule buffalo hughes and hyde counties in central south dakota fossil bones from each member of the pierre shale have different rare earth element ree signatures that may be distinctive over wide geographic areas fossils from the sharon springs member have distinctive ree signatures that may be further subdivided into three superposed groups that correspond with the upper middle and lower sharon springs member ree signatures are distinctive from each stratigraphic unit therefore fossils eroded from their stratigraphic context may be assigned to their proper depositional unit based on ree signature comparisons differences in ree compositions of bones among members appear to result from differential mixing of oxygenated and anoxic seawaters if differences in mixing are interpreted as depth differences the lower sharon springs member was deposited in deep anoxic water water depths decrease in the middle and upper sharon springs and the overlying gregory and crow creek members were deposited in even more shallow water finally according to this interpretation the overlying degrey and verendrye members were deposited in progressively deeper marine waters but not as deep as the lower sharon springs these interpretations are generally consistent with those based on faunal diversity and eustatic sea level curves

geochemical taphonomy of shallow marine vertebrate assemblages abstract combined histological and geochemical analyses demonstrate complex processes leading to preservation of microbially altered bone in certain situations a chemical microenvironment distinct from surrounding pore waters is developed and maintained within the bone the bone acts as a closed system and hence palaeoenvironmental interpretations based on fossil bone apatite chemistry may not accurately reflect overall geochemical conditions of the sedimentary deposits where the bones were buried geochemical techniques based on variance in trace element compositions of bones from different assemblages can be used as a measure of the relative degree of mixing or taphonomic averaging within marine vertebrate assemblages

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

late pleistocene and holocene groundwater recharge from the chloride mass balance method and chlorine 36 data 1 the chloride mass balance cmb method for estimating groundwater recharge is economic and effective provided that the hydrological conditions for its applications are met and the modeling parameters are known however modeling parameters such as precipitation and cl deposition rates vary temporally most notably as a result of the climatic changes from late pleistocene to holocene the temporal variability of atmospheric cl input and annual precipitation were considered in this study by using a discrete steady state cmb model with different parameters for late pleistocene and holocene cl deposition rates estimated from 36cl data were lower in late pleistocene than holocene at yucca mountain nevada but higher in late pleistocene than holocene at black mesa arizona paleoclimate proxies at both yucca mountain and black mesa point to higher precipitation rates in late pleistocene than holocene the resulting average recharge estimates for black mesa are 9 5 mm yr for holocene and 35 22 mm yr for late pleistocene local recharge rates at yucca mountain were estimated from the 36cl cl ratios and cl concentrations in perched waters the estimated recharge for yucca mountain is 5 1 mm yr for holocene and 15 5 mm yr for late pleistocene these recharge rates are comparable to results of independent numerical groundwater flow models and watershed scale infiltration models at black mesa and yucca mountain respectively

reactions and reaction rates in the regional aquifer beneath the pajarito plateau north central new mexico usa reactions and reaction rates within aquifers are fundamental components of critical hydrological processes however reactions simulated in laboratory experiments typically demonstrate rates that are much faster than those observed in the field therefore it is necessary to conduct more reaction rate analyses in natural settings this study of geochemical reactions in the regional aquifer in the pajarito plateau near los alamos new mexico combines modeling with petro graphic assessment to further knowledge and under standing of complex natural hydrologic systems groundwater geochemistry shows marked evolution along assumed flow paths the flow path chosen for this study was evaluated using inverse mass balance mod eling to calculate the mass transfer x ray diffraction and field emission gun scanning electron microscopy were used to identify possible reactants and products considering the mineralogy of the aquifer and satura tion indices for the regional water refined initial inter pretations calculations yielded dissolution rates for plagioclase on the order of 10 15 mol s 1 m 2 and for k feldspar on the order of 10 17 mol s 1 m 2 orders of magnitude slower than laboratory rates while these rates agree with other aquifer studies they must be considered in the light of the uncertainty associated with geometric surface area estimates 14 c ages and

a new scenario for the mass transport deposits west canary volcanic province abstract a new temporal history of mass wasting processes for the west of the canary volcanic province is presented its onset has been estimated in the middle upper miocene 13 5 1 2 ma matching with a critical period of construction for this volcanic province seismic profiles show an emplacement longevity from the miocene to quaternary in multiple events defined by stacked lobes of debrites linked to the flank collapses and volcanic avalanches of the volcanic edifices islands and seamounts an evolution of pathways and source areas has been detected from east miocene to west quaternary as well as a migration of the activity to the northwest west of the canary islands e g el hierro and la palma six connected branches i vi three of them described for the first time here of quaternary seismic units of mass transport deposits mtds have been characterized the pleistocene makes up a huge buried mtds system until now unknown pointing a new mass transport sedimentological scenario finally the two southernmost branches v vi up to now unknown are a mainly buried system of stacked and terraced lobes of debrites sourced mainly from the flank collapses of the volcanic seamounts of the canary island seamount province apparently inactive from upper cretaceous

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

do archean chemical sediments record ancient seawater rare earth element patterns rare earth elements ree concentrations of archean and proterozoic chemical sediments are commonly used as proxies to study secular trends in the geochemistry of precambrian seawater in addition similarities in the ree signatures of archean chemical sediments and modern seawater have led researchers to argue that some archean rocks originated as biochemical precipitates i e microbial carbonates in shallow marine e g peritidal environments however terrestrial waters including river water and groundwater also commonly exhibit ree fractionation patterns that resemble modern seawater here we present the seawater like ree data for ground

geomagnetic field control of 14c production over the last 80 ky implications for the radiocarbon time scale we have used a recent estimate of the geomagnetic dipole field strength over the last 80 ky to examine the extent to which changes in geomagnetic field intensity have affected the radiocarbon time scale the magnetic record was converted into a 14c production signal which was then used to produce a synthetic atmospheric 14c record using a two box model for the carbon cycle this calibration suggests that the geomagnetic field has been the main factor governing the production of cosmogenic 14c atoms over the period of time considered and that 14c changes due to other causes such as climatic changes have been of lesser importance the results indicate that the radiocarbon ages are 2 to 3 ky younger than true age in the interval 18 40 ky b p in good agreement with recent u th and 14c age comparisons moreover the results predict that a negligible difference between true and 14c ages should be observed around 45 50 ky

lu hf isotope systematics of fossil biogenic apatite and their effects on geochronology abstract reliable methods for direct dating of biogenic apatite from pre pleistocene fossils are currently not available and recent attempts using the lu hf decay system yielded highly inaccurate ages for both bones and teeth the geological processes accounting for this poor accuracy of lu hf chronometry are not yet understood here we explore lu hf systematics in fossil bones and teeth in detail by applying five different sample digestion techniques that are tested on bones and composites of bone and sediment our current dataset implies that dissolution methods only slightly affect the resulting lu hf ages while clear differences between the individual digestion techniques became apparent for element concentrations by analysing the insoluble leftovers from incomplete sample dissolution four main reservoirs of hf in fossil bones were identified 1 a radiogenic end member associated with apatite 2 an unradiogenic end member represented by the authigenic minerals or the embedding sediment 3 a highly unradiogenic end member that can be attributed to detrital zircon and 4 a moderately soluble phase probably a zr hf phosphate that yielded very low lu hf but a highly radiogenic hf isotope composition at the same time this zr hf phase must have been precipitated within the fossil bone sample at a late stage of burial history thereby incorporating radiogenic 176 hf released from apatite surfaces over geological timescales a second focus of our study is the effect of different sediment matrices and of crystal size on the preservation of pristine lu hf isotope compositions in bioapatite because near depositional lu hf ages of phosphate fossils have previously been reported for the london clay england and a calcareous marl from tendaguru tanzania we herein investigate specimens fossilised in carbonate matrices calcareous marl from oker germany carbonate concretions from the santana formation brazil carbonate from the eifel germany and argillaceous matrices with low permeability oil shale of messel germany posidonienschiefer of holzmaden germany materials analysed from these localities include bones teeth conodonts as well as coproliths and diagenetic minerals siderite montgomeryite and messelite near depositional lu hf ages were obtained for a bony fish sample notelops brama encapsulated in an early diagenetic carbonate concretion from the early cretaceous santana formation brazil and for conodonts from a middle devonian carbonate from the eifel germany low 176 lu 177 hf ratios in all materials from the middle eocene messel oil shale e g bones fish scales sediment siderite result in poor age precision and an age that is near depositional due to this large analytical error in agreement with previous results all other ages determined here for both bones and teeth are by far younger than respective chronostratigraphic ages a model illustrating the behaviour of lu and hf over time with respect to the fossilisation process is presented which accounts both for the formation of a late diagenetic radiogenic zr hf phase and long term open system behaviour the continuous lu hf element exchange between the fossils and the embedding sediment is probably related to the nm scale crystal size of fossil bones dentine and also of enamel that generate large surface areas facilitating sorption desorption processes and open system behaviour

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

noble gas signatures of high recharge pulses and migrating jet stream in the late pleistocene over black mesa arizona united states many semiarid and arid regions of the world are almost entirely dependent on groundwater for water supply yet many of these aquifers were primarily recharged during the late pleistocene here we show that new noble gas data record the high pulses of recharge to the navajo sandstone aquifer at black mesa arizona between 14 and 17 ka which was associated with the passing of the southern branch of the jet stream higher excess neon coincided with high water levels independently deduced from numerical modeling of groundwater fl ow and 14 c data in previous studies this development allows the use of noble gases not only as a tool to reconstruct paleotemperatures but also as a new tool to reconstruct paleohydraulic conditions and to verify the conceptual and hydraulic assumptions of existing groundwater models