provenance and transport of terrigenous sediment in the south atlantic ocean and their relations to glacial and interglacial cycles nd and sr isotopic evidence sr and nd isotopic compositions of late quaternary surface sediment and sediment cores from the south atlantic and southeast pacific sectors of the southern ocean are used to constrain the provenance and transport mechanisms of their terrigenous component we report isotopic and mineralogical data for core samples from three localities the mid atlantic ridge at 41 s and the northern and southern scotia sea in addition data for surface sediment samples from the south atlantic and southeast pacific sectors of the southern ocean are presented the variations of sr and nd isotopic compositions of the bulk sediment samples in all cores were correlated with the magnetic susceptibility of the sediment and with the inferred glacial interglacial stages the isotopic data indicate that during glacial periods sediment was delivered from continental crust with a shorter residence time than that supplying material during interglacial periods at the core site near the mid atlantic ridge nd isotopic combined with mineralogical evidence indicates interglacial period deposition of a relatively high amount of kaolinite and silt with low nd values 4 5 probably derived from southern south america was indicated the glacial interglacial shift in sources may be due to either a decreasing influence of north atlantic deep water during glacial times or by a larger contribution of glaciogenic detritus from southern south america at the core site in the northern scotia sea sediment of interglacial periods is dominated by smectite with nd 4 we suggest that smectite was derived from the falkland shelf and silt was derived from the argentinian shelf during glacial periods the argentinian shelf was an important source for silt and chlorite with nd 4 the contribution from the falkland shelf seems to have remained similar during glacial and interglacial periods hydrographic transport by bottom currents and turbidites could account for the high glacial detrital flux an evaluation of the significance of an aeolian contribution to deep sea sediment suggests that it plays only a minor role in the southern scotia sea the antarctic peninsula is considered an important source for young material with nd 4 in particular during glacial periods during interglacial periods sediment supply from the antarctic peninsula was lower than during glacial times resulting in a relatively high contribution of old material nd 8 from east antarctica deep water currents and icebergs could account for the transport of the old component to the southern scotia sea the accumulation rates of material from the various source regions for glacial times are in agreement with an increase in the strength of the antarctic circumpolar current the production rate and the circulation pattern of bottom water in the weddell sea appear to have remained similar over most of the last 150 kyr

sr and nd isotope composition of late pleistocene sapropels and nonsapropelic sediments from the eastern mediterranean sea implications for detrital influx and climatic conditions in the source areas isotopic ratios of sr and nd from lithogenic components of three isochronous core sections recovered from an east west transect in the eastern mediterranean sea ems have been analyzed the data are used for a quantitative estimate of the temporal and spatial variation of detrital flux to the ems assuming saharan dust and aegean nile particulate matter as dominant end members it was established that the carbonate free saharan dust flux during deposition of the nonsapropel layers of marine oxygen isotope stage 5 4 mis 5 4 was similar to the present flux during the deposition of sapropels s5 and s6 however the saharan dust input was drastically reduced and was not balanced by a change in the riverine influx at this time denser vegetation cover during more humid conditions may have reduced physical erosion and sediment removal in the source area during marine oxygen isotope stage 6 2 mis 6 2 a pronounced increase of saharan dust and detrital influx from the aegean region is evident and implies more arid conditions in the southern and northern catchment areas during this period intersite variations are interpreted in terms of their geographic location relative to the seaways connecting the aegean sea and ems the width of the straits and hence the amount of sediment entering the eastern basins may have been affected by a low sea level that impeded interbasin sediment dispersal

two high levels of continental waters in the southern tunisian chotts at about 90 and 150 ka uranium and thorium content and activity ratios were measured on 20 samples 19 molluscs and 1 calcareous concretion from the great chotts in southern tunisia results were studied by the isochron method and by age frequency histograms they suggest that two major flood episodes took place about 150 and 90 ka uranium activity ratios indicate a ground water supply of continental origin in agreement with biological indicators which show large variations in salinity from fresh to marine like conditions the existence of a lacustrine phase radiocarbon dated to 17 40 ka as previously suggested for the northern sahara is highly questionable

petrogenesis of early permian olivine bearing cumulates and associated basalt dykes from bocca di tenda northern corsica implications for post collisional variscan evolution abstract the early permian gabbroic sequence of bocca di tenda northern corsica intrudes a plutonic suite made of hornblende granitoids and is crosscut by basalt dykes with chilled margins the gabbroic sequence includes olivine gabbronorite cumulates that consist mainly of euhedral olivine fo78 72 and plagioclase an68 61 and poikilitic clinopyroxene mg 0 85 0 80 orthopyroxene and ti pargasite pyroxenes from the olivine gabbronorites have 18 o values of 6 3 to 6 7 which are evidence for the involvement of a crustal component in the petrogenesis of these rocks the basalts have mg values of 57 to 53 and chondrite normalised patterns characterised by a steady decrease from lree to hree relative to modern n morb they show also moderate enrichment of nb and ta over zr and hf which are in turn slightly enriched over y and hree the olivine gabbronorites and basalts show overlapping nd isotopic compositions initial nd of 2 4 to 1 4 and of 3 0 to 1 5 respectively and have clinopyroxenes with nearly parallel incompatible trace element patterns thus revealing that these two rock types formed by melts with similar compositions most likely the primary melts of bocca di tenda gabbroic sequence were slightly enriched in most incompatible elements and nd isotopic compositions relative to modern n morb

the mathematics of early diagenesis from worms to waves the changes that sediments undergo after deposition are collectively known as diagenesis diagenesis is not widely recognized as a source for mathematical ideas however the myriad processes responsible for these changes lead to a wide variety of mathematical models in fact most of the classical models and methods of applied mathematics emerge naturally from quantification of diagenesis for example small scale sediment mixing by bottom dwelling animals can be described by the diffusion equation the dissolution of biogenic opal in sediments leads to sets of coupled nonlinear ordinary differential equations and modeling organisms that eat at depth in the sediment and defecate at the surface suggests the one dimensional wave equation while the effect of waves on pore waters is governed by the two or three dimensional wave equation diagenetic modeling however is not restricted to classical methods diagenetic problems of concern to modern mathematics exist in abundance these include free boundary problems that predict the depth of biological mixing or the penetration of o2 into sediments algebraic differential equations that result from the fast reversible reactions that regulate ph in pore waters inverse calculations of input functions histories and the determination of the optimum choice in a hierarchy of possible diagenetic models this review highlights and explores these topics with the hope of encouraging further modeling and analysis of diagenetic phenomena

effects of benthic transport processes on abrupt climatic changes recorded in deep sea sediments a time dependent modeling approach 1 a one dimensional time dependent model is developed to characterize qualitatively and quantitatively the combined effects of bioturbation and burial on sedimentary signals related to abrupt climatic changes this model is based on the widely used advection diffusion equation and simulates rapid climatic transitions by representing the deposition flux at the sediment water interface by a steep ramp function of time this model is applied to both planktonic foraminifera abundance curves and 18o distributions output signals obtained at the bottom of the bioturbated layer for these rapid transitions have been generated for a broad range of sedimentation rates 5 50 cm kyr 1 biodiffusion coefficients 10 3 1 cm2 yr 1 and mixed layer thicknesses 2 15 cm numerical results clearly demonstrate the importance of a dynamic description of sediment mixed layers properties of the sedimentary response to fast transitions appear to be highly and nonlinearly dependent upon the sedimentation rate and the relative values of the original transition length and the time required to bury the signal below the mixed layer moreover for low sedimentation rates 10 cm kyr 1 we show that signals occurring over a 50 to a 250 year timescale are indistinguishable to quantify the distortion of sedimentary signals we determined the transition length of the bioturbated simulated signals and compare it to the initial transition length for given sets of bioturbation and sedimentation rates and mixed layer thicknesses comparison between model predictions and experimental results reveals a good agreement showing that transition timescales are compatible with ice core derived transitions 100 years for environments in which bioturbation can be approximated by a diffusive process tests performed on 18o distributions have illustrated the effect of bioturbation on the stratigraphic offsets between isotopic compositions of cold and warm species of foraminifera during climatic transitions

episodic deposition and 137cs immobility in skan bay sediments a ten year 210pb and 137cs time series abstract a geochronology time series provides a powerful tool for elucidating sedimentary processes such as episodic deposition and diffusive mobility of particle reactive constituents depth distributions of 210 pb and 137 cs from skan bay alaska were determined for sediment cores collected in 1980 1984 1987 and 1990 sediment x radiographs reveal distinct layers indicating that sediments were not continuously mixed by bioturbation however the geochronology time series is inconsistent with an undisturbed steady state sediment column profiles from 1980 1984 and 1990 reveal subsurface regions in which 210 pb activity is relatively constant in addition the depth of the primary 137 cs maximum reflecting the 1963 peak in atmospheric bomb testing does not increase in a regular fashion between 1980 and 1990 the 210 pb and 137 cs geochronologies can be reconciled by removing the effects of an instantaneous depositional event the average 210 pb sedimentation rate corrected for episodic deposition in cores that were collected over a ten year period 0 241 0 006 g cm 2 yr 1 is in excellent agreement with the average 137 cs sedimentation rate 0 258 0 008 g cm 2 yr 1 calculated from three stratigraphic markers peak fallout 1963 first appearance in the sediment record 1952 and the chernobyl accident 1986 the mobility of bomb derived 137 cs under in situ conditions was evaluated by a time dependent numerical model applied to the 137 cs time series the model indicates that bomb derived cesium is immobile in skan bay sediments with a solid liquid distribution coefficient k d of 10 5 ml g 1

from permo triassic lithospheric thinning to jurassic rifting at the adriatic margin petrological and geochronological record in valtournenche western italian alps abstract slices of polycyclic metasediments marbles and meta cherts are tectonically amalgamated with the polydeformed basement of the dent blanche tectonic system along a major alpine shear zone in the western alps becca di sale area valtournenche valley a combination of techniques structural analysis at various scales metamorphic petrology geochronology and trace element geochemistry was applied to determine the age and composition of accessory phases titanite allanite and zircon and their relation to major minerals the results are used to reconstruct the polyphase structural and metamorphic histories comprising both pre alpine and alpine cycles the pre alpine evolution is associated with low pressure high temperature metamorphism related to permo triassic lithospheric thinning in meta cherts microtextural relations indicate coeval growth of allanite and garnet during this stage at 300 ma textures of zircon also indicate crystallisation at ht conditions ages scatter from 263 to 294 ma with a major cluster of data at 276 ma in impure marble u pb analyses of titanite domains with variable al and f contents yield apparent 206pb 238u dates range from permian to jurassic chemical and isotopic data suggest that titanite formed at permian times and was then affected by extension related fluid circulation during the triassic and jurassic which redistributed major elements al and f and partially opened the u pb system the alpine cycle lead to early blueschist facies assemblages which were partly overprinted under greenschist facies conditions the strong alpine compressional overprint disrupted the pre alpine structural imprint and or reactivated earlier structures the pre alpine metamorphic record preserved in these slices of metasediments reflects the onset of the permo triassic lithospheric extension to jurassic rifting

chemical cycles in pliocene sapropel bearing and sapropel barren eastern mediterranean sediments abstract high resolution 3 4 cm investigations of major and minor elements were carried out on sediment cores from odp leg 160 sites 964 ionian basin 969 mediterranean ridge 967 and 966 northern slope and top of eratosthenes seamount south of cyprus at site 967 element al ratios display pronounced cyclic records that are related to astronomically forced climatic variations sediments from the top of eratosthenes seamount site 966 show a similar pattern to those from site 967 but they are more disturbed by bioturbation and also strongly influenced by long term variations in sediment dispersal sediments from site 969 display similar trends to those from site 964 i e they are characterized by higher mg al slightly higher k al and lower ti al ratios during sapropel formation higher ti al ratios at site 969 compared with sediments from site 964 may be explained by a westward transport of material from a source in the east where ti al ratios are highest sites 966 and 967 elevated mg al ratios at site 969 during sapropel intervals are due to river derived material transported through the kithira strait between peloponnesus and crete from the northwestern aegean sea which originates from ultramafic rocks a change in intermediate water currents current reversal during sapropel formation may explain the enhanced supply of mg rich and the relatively diminished supply of ti rich material we propose that during deposition of the reddish intervals at site 969 a change in circulation did not occur because a drastic decrease in ti al ratios is not evident in these sediments ba peaks indicative of former sapropels are not present ba enrichments in the same sapropel barren intervals at site 967 northern slope of eratosthenes seamount suggest that during such intervals the burn down process was more effective than during the sapropel bearing intervals mn contents in all investigated pliocene sediments correlate with the carbonate contents higher mn contents of the sapropel barren sediments suggest that during time intervals of sapropel formation either mn accumulation at the margins of the permanently oxic upper water column or mn export into the western mediterranean might have occured the latter could only be explained by sub or anoxic conditions in large parts of the water column

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

mixing sedimentation rates and age dating for sediment cores abstract analytic solutions to the advection diffusion equation useful as a guide for the interpretation of mixing sedimentation rate and age dating effects in sediment cores have been derived various simplified mixing models appropriate to 14 c and 210 pb measurements have been considered the emphasis has been on a discussion of the various interrelations and dependencies among the mixing coefficient sedimentation rate and radioactive decay constant parameters in determining the 14 c and 210 pb concentrations as a function of depth porosity variations within the sediment column are also considered and the transformed advection diffusion equation including porosity effects is derived

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

accumulation of anthropogenic and natural radionuclides in bottom sediments of the northwest pacific ocean abstract activities of anthropogenic radionuclides in bottom sediments of the northwest central and west caroline basins of the northwest pacific ocean are reported down core distributions of natural radionuclides were also investigated in order to elucidate the sedimentation processes of anthropogenic radionuclides in the seafloor in the northwest central basin the inventories of 239 240pu and 241am decrease from south to north while the opposite trend is observed for 137cs and 90sr this latitudinal gradient in the inventories of artificial radionuclides reflects higher fluxes of 239 240pu and 241am near the weapons test sites and transport of 137cs and 90sr over longer distances as well as the regional differences in sediment mixing and accumulation rates in the west caroline basin relatively low inventories of 239 240pu and 241am were observed due to the topographic isolation of deep water sediment mixing rates were calculated using down core distributions of 239 240pu 241am 137cs and 90sr based on two distinct models continuous and constant of tracer input and with a third model with pulsed input during the peak fallout period the continuous input model yielded mixing coefficients comparable to those derived from excess 210pb profiles within an order of magnitude

chemical evolution of a large mafic intrusion in the lower crust ivrea verbano zone northern italy the ivrea verbano and adjacent strona ceneri zones have been described collectively as a section through the continental crust while resident in the lower crust amphibolite to granulite facies paragneiss of the ivrea verbano zone was intruded by huge volumes of mafic to intermediate plutonic rocks grouped as the mafic complex growth of the mafic complex involved hypersolidus deformation in an extensional environment isotopic and trace element variations close to the axis of this structure indicate crystallization from mantle derived melts that were extensively contaminated by crustal material previous investigations determined that the contaminant was fingerprinted by 87sr 86sr 0 71 18o 10 12 5 and a positive eu anomaly in the present study the contaminant is also shown to have been enriched in ba with respect to rb and k charnockites associated with paragneiss septa in the lower part of the mafic complex have the appropriate chemistry to be samples of the contaminating material these chemical features can be explained by melting of granulite facies paragneiss which had previously been depleted in k and rb by an earlier melting event the ba enrichment in the core of the mafic complex can be modeled by a replenishment tapping fractional crystallization rtf process operating within a small magma chamber is repeatedly replenished by mantle melts and contaminated by ba rich charnockite very high ba k in the lower part of the complex are tentatively attributed to chemical exchange between the cumulate framework and infiltrating anatectic melts from underlying paragneiss septa in contrast to the mafic complex the chemistry of coeval granites in the adjacent strona ceneri zone reflect a component derived from crustal rocks that had not been significantly depleted by a previous melting event significantly the incompatible trace element abundances in the mafic complex and strona ceneri granites are similar to model compositions for the lower and upper crust respectively

a model for 137cs and other tracers in lake sediments considering particle size and the inverse solution abstract a numerical model for the time dependent behavior of particle associated tracers in sediments has been developed the model is based on the advection diffusion equation for a tracer and includes a sediment density that increases with depth as a modified power function and a diffusion coefficient that follows a half gaussian function versus depth with maximal diffusivity at the sediment water interface the solution procedure is based on finite elements or finite differences the density function is developed from soil mechanics concepts and includes mixing effects through a young s modulus that is increased in the top layer according to a half gaussian function the new density function provides a better fit to 15 out of 17 sediment cores from lake michigan than a frequently used exponential expression the tracer model provides an excellent fit for the 137cs distributions in all of the 17 lake michigan cores that were investigated our fit to the 137cs profile of a southern lake michigan core that has been examined by others is significantly better than previous fits particularly near the top of the core from two different forms of the governing equation for a tracer and the resultant fits to experimental data it appears that 137cs is associated with colloidal and 210pb with settling particles a previously developed time domain method to extract the historical input record of a tracer from its sedimentary profile influenced by mixing has been further improved by including m depth and n time intervals where m n and by fitting the influx to a polynomial the improved method is demonstrated for the cd input to a northern lake michigan core nlm84b although the time resolution obtained 5 yr is better than the previous resolution 15 yr it is clear that the method needs to undergo further development in order to decrease the error of the reconstructed influx and particularly to avoid negative fluxes

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

a synthetic pollen record of the eastern mediterranean sapropels of the last 1 ma implications for the time scale and formation of sapropels abstract the quaternary climate of southern europe south italy and greece is investigated by pollen analysis of the sapropels which were deposited in the deep eastern mediterranean sea during the last 1 million year ma the time scale of core kc01b in the ionian sea has been established by tuning its oxygen isotopic record to the ice volume model of imbrie and imbrie 1980 for the last 250 000 year 250 ka the previous pollen studies and astronomical tuning have been confirmed sapropels were deposited under a large range of mediterranean climates fully interglacial fully glacial and intermediary as revealed mainly by the balance between the respective pollen abundances of oak quercus and sage brush artemisia the high value of the oak reveals the warm and wet climate of an interglacial and the high value of the sage brush the dry and cold climate of a glacial whereas the mediterranean climate is directly related to the variation of the high latitude ice sheets the deposition of sapropels is not so in contrast with the wide climatic range sapropels were deposited only when summer insolation in the low latitudes reached its highest peaks however between 250 ka and 1 ma that stable pattern is not yet established only six sapropels are observed many expected ones do not appear even as ghosts signalled by peaks of barium abundance that remain after the post deposition oxidation of organic matter the pattern of sapropel formation in stable and direct relationship to highest insolation does not seem to apply for five of those sapropels neither climate extremes are observed they mainly formed during intermediary types of mediterranean climate in contrast one sapropel and one ghost relates to a relatively low peak of insolation and its climate is of a unique composite type not seen later this might suggest an unsuspected more complex pattern linking the formation of mediterranean sapropels to the astronomical configuration

the geochemistry of fallout plutonium in the north atlantic i a pore water study in shelf slope and deep sea sediments abstract the distribution of fallout plutonium between pore waters and sediments in the northwest atlantic is examined in order better to define the potential for pu migration from and within marine sediments along a transect of seven cores collected between woods hole and bermuda the solid phase 239 240pu 210pbex and 137cs results do not suggest that any of these tracers are preferentially mobile within the cores pore water pu activities appear to be controlled primarily by the distribution of pu in the solid phase with an operationally determined distribution coefficient kd in the range of 0 2 23 104 there is a trend in the kds along the transect with higher values in the 104 105 range on the shelf and slope to lower values 239 240 pu cm 2 year sediment mixing models are not significantly altered by the inclusion of pu diffusion terms since the pore water terms are so small relative to typical sediment mixing rates

interpretation procedures for the determination of sediment parameters from time dependent flux inputs abstract a formulation for the effects of a time dependent input flux to a sedimentation system consisting of a diffusive layer underlain by a non diffusive medium has been developed the intent is to provide interpretation procedures for the determination of sedimentation rate diffusion coefficient and mixed layer thickness from observed tracer concentrations they have been applied for illustrative purposes to published137cs and239 240pu measurements

modeling radiotracers in sediments comparison with observations in lakes huron and michigan a comprehensive model for the activity of radionuclides in sediments is presented the model is based on the advection diffusion equations for sediment solids and a radioactive tracer mixing caused by deposit feeders is taken into account by a half gaussian hg integrated gaussian ig or exponential ex diffusion coefficient with a maximum value d0 at the sediment water interface and an effective mixing depth m where m hg zm ig or a ex compaction is described by an exponential bulk sediment density the differential equations are solved by finite differences in particular the crank nicolson method for the time dependent case cs 137 estimation of the mixing parameters d0 and m is carried out efficiently by minimizing chi square for measured and calculated steady state pb 210 activities the derived mixing depths of zm 4 6 0 1 cm station 14 and a 0 8 0 1 cm station 18 for the cores from lake huron are in good agreement with the organism distributions the corresponding d0 values are 12 2 and 1 5 0 5 cm2 yr respectively where the latter number is lower than a previous lower limit estimate 3 3 cm2 yr based on 1974 data these diffusion coefficients are in excellent agreement with those inferred from the densities of pontoporeia and tubificid oligochaetes 9 3 and 1 6 cm2 yr respectively compared with southern lake michigan there appears to be less sediment focusing in northern lake michigan where the ratios of measured to atmospheric cs 137 inventories have an average value of 0 89 and range from 0 32 to 1 41 for six cores from the deep basin when these ratios are used to correct the pb 210 fluxes we obtain an atmospheric pb 210 flux of 0 99 0 06 dpm cm2 yr because of its more realistic activity profiles we consider the present model to be generally better than previous models

kinematics of syn and post exhumational shear zones at lago di cignana western alps italy constraints on the exhumation of zermatt saas ultra high pressure rocks and deformation along the combin fault and dent blanche basal thrust kinematic analyses of shear zones at lago di cignana in the italian western alps were used to constrain the structural evolution of units from the piemont ligurian oceanic realm zermatt saas and combin zones and the adriatic continental margin dent blanche nappe during palaeogene syn and post exhumational deformation exhumation of zermatt saas u hp rocks to approximately lower crustal levels at ca 39 ma occurred during normal sense top s e shearing under epidote amphibolite facies conditions juxtaposition with the overlying combin zone along the combin fault at mid crustal levels occurred during greenschist facies normal sense top se shearing at ca 38 ma the scarcity of top se kinematic indicators in the hanging wall of the combin fault probably resulted from strain localization along the uppermost zermatt saas zone and obliteration by subsequent deformation a phase of dominant pure shear deformation around 35 ma affected units in the direct footwall and hanging wall of the combin fault it is interpreted to reflect nw se crustal elongation during updoming of the nappe stack as a result of underthrusting of european continental margin units and the onset of continental collision this phase was partly accompanied and followed by ductile bulk top nw shearing especially at higher structural levels which transitioned into semi ductile to brittle normal sense top nw deformation due to vanzone phase folding from ca 32 ma onwards our structural observations suggest that syn exhumational deformation is partly preserved within units and shear zones exposed at lago di cignana but also that the combin fault and dent blanche basal thrust experienced significant post exhumational deformation reworking and overprinting earlier structures

nonlinear parameter estimation for sediment cores abstract nonlinear parameter estimation techniques are applied to three distinctly different sediment cores for which concentrations of tracers with steady and time dependent flux inputs are available the mathematical model employed consists of a diffusive upper layer of finite depth underlain by a semi infinite nondiffusive medium confidence regions and intervals are reported for sedimentation rate diffusion coefficient and mixed layer depth based on ordinary least squares criteria for each tracer conflicting estimates are resolved using a weighted least squares procedure which combines observations of the individual tracers and exploits their strengths and weaknesses

modeling of in situ crystallization processes in the permian mafic layered intrusion of mont collon dent blanche nappe western alps abstract the mont collon mafic complex is one of the best preserved examples of the early permian magmatism in the central alps related to the intra continental collapse of the variscan belt it mostly consists 95 vol of ol hy normative plagioclase wehrlites olivine and cpx gabbros with cumulitic structures crosscut by acid dikes pegmatitic gabbros troctolites and anorthosites outcrop locally a well preserved cumulative sequence is exposed in the dents de bertol area center of intrusion p t calculations indicate that this layered magma chamber emplaced at mid crustal levels at about 0 5 gpa and 1100 c the mont collon cumulitic rocks record little magmatic differentiation as illustrated by the restricted range of clinopyroxene mg number mg cpx 83 89 whole rock incompatible trace element contents e g nb zr ba vary largely and without correlation with major element composition these features are characteristic of an in situ crystallization process with variable amounts of interstitial liquid l trapped between the cumulus mineral phases la icpms measurements show that trace element distribution in the latter is homogeneous pointing to subsolidus re equilibration between crystals and interstitial melts a quantitative modeling based on langmuir s in situ crystallization equation successfully duplicated the ree concentrations in cumulitic minerals of all rock facies of the intrusion the calculated amounts of interstitial liquid l vary between 0 and 35 for degrees of differentiation f of 0 to 20 relative to the least evolved facies of the intrusion l values are well correlated with the modal proportions of interstitial amphibole and whole rock incompatible trace element concentrations e g zr nb of the tested samples however the in situ crystallization model reaches its limitations with rock containing high modal content of ree bearing minerals i e zircon such as pegmatitic gabbros dikes of anorthositic composition locally crosscutting the layered lithologies evidence that the mont collon rocks evolved in open system with mixing of intercumulus liquids of different origins and possibly contrasting compositions the proposed model is not able to resolve these complex open systems but migrating liquids could be partly responsible for the observed dispersion of points in some correlation diagrams absence of significant differentiation with recurrent lithologies in the cumulitic pile of dents de bertol points to an efficiently convective magma chamber with possible periodic replenishment

permian triassic high thermal regime in the alps result of late variscan collapse or continental rifting validation by numerical modeling 1 the permian triassic igneous activity associated with regional scale deformation developed under high temperature low pressure ht lp metamorphic conditions and widely recorded in the pre alpine crust of the european alps can result from late orogenic collapse of a collisional belt or from lithospheric thinning leading to a continental rifting process in order to reduce this ambiguity we use a two dimensional finite element model to give new insights on the sequence of mechanisms operating during active ocean continent convergence followed by continental collision and pure gravitational evolution and on the regional geodynamic interpretation of the paleozoic mesozoic evolution of the alpine area the modeling predictions are compared with the pt climax conditions of variscan and permian triassic metamorphism affecting the continental crust of the helvetic to southalpine domains the good agreement between model predictions and natural data realized for the early to neovariscan evolution indicates that during paleozoic the pre alpine crust of the alps was part of an active ocean continent convergence margin and an intracontinental suture zone furthermore modeling results support the interpretation envisaging a permian triassic lithospheric extension as responsible for the ht metamorphism and related intense igneous activity this evolution was precursor of the mesozoic oceanization during which the tectonic units coupled and accreted during the variscan subduction and collision were separated to form the two passive european and adriatic continental margins

interpreting the 137cs profiles observed in several small lakes and reservoirs in southern england abstract the depth distribution of bomb derived 137cs has been studied in cores collected from five small lakes and reservoirs with high sediment accumulation rates in southern england an empirical approach was employed to demonstrate the influence of the catchment derived 137cs input and the post depositional redistribution of 137cs on the 131cs profiles of the sediment cores by incorporating the remobilisation of 137cs and deposited sediment a catchment related 137cs lake deposition model has been used to interpret the 137cs inventories and concentrations in the lake and reservoir sediments in terms of sediment sources a clear linkage between the 137cs concentration in the lake sediment and that in catchment source soils has been established for the five water bodies estimates of the proportion of the total 137cs inventory of individual sediment cores derived from the catchments ranged between 57 and 97 these values emphasise the importance of the catchment derived contribution to the overall 137cs inventory of sediments in small lakes and reservoirs receiving significant sediment inputs from their catchments the estimates of sedimentation rates for the water bodies provided by the cores were also used to estimate the sediment yields from their respective catchments

modeling detailed sedimentary 210pb and fallout 239 240pu profiles to allow episodic events an application in chesapeake bay dependable sediment chronologies are essential to the interpretation of the sedimentary record of past environmental change in the present article we use high resolution chemical and radiochemical data as the basis for a numerical simulation of sediment accumulation bioturbation and episodic deposition or erosion in a dynamic estuary we simulate episodic events by employing a time dependent sedimentation rate that we solve by finding a set of model parameters that describes depth profiles of both excess 210pb and fallout 239 240pu we apply the model to depth distributions of these tracer nuclides in cores from upper mid and lower bay sites in chesapeake bay at the upper bay site combining chemical and radiochemical data permits us to recognize and to quantify the sediment deposition due to tropical storm agnes 1972 at the lower bay site we demonstrate nonsteady sedimentation and propose plausible scenarios to account for it given adequate data our model can provide information that is not available from steady state models