experimental reactions of amphibolite with boron bearing aqueous fluids at 200 mpa implications for tourmaline stability and partial melting in mafic rocks reactions between hornblende plagioclase amphibolite and acidic and alkaline b bearing aqueous fluids have been investigated by experiments at 475 600 c and 200 mpa at 600 c hornblende calcic plagioclase react to form tourmaline danburite clinopyroxene quartz in acidic fluids containing 0 5 1 0 wt b2o3 tourmaline is precipitated directly from acidic fluids and the reaction is driven by neutralization of fluids by na ca derived from the breakdown of reactant solids the concentration of b2o3 in fluids needed to stabilize tourmaline increases as ph increases above approximately 6 0 and tourmaline is unstable in alkaline fluids ph approximately 6 5 7 0 regardless of b concentration in addition to acid base relations tourmaline stability is favored by comparatively higher activity coefficients for al species in acidic fluids the concentrations of al and si in fluid increase with alkalinity with the eventual production of felsic borosilicate melts through partial melting of the plagioclase component of the amphibolite in seeded experiments tourmaline also contributes components to melt partial melting is evident in the range 500 525 c at 200 mpa in experiments with 8wt b2o3 in fluid as na2b4o7 the experimental results are applied primarily to metasomatic reactions between mafic rocks and borate fluids derived from granitic magmas but tourmaline stability and partial melting in mafic regional metamorphic systems are also discussed briefly

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

climatically driven sedimentary cycles in the late miocene sediments of the pannonian basin hungary abstract by detailed cycle analysis of marginal mostly delta plain facies successions of pannonian sediments the frequency of water level changes of the late miocene pannonian lake hungary can be identified cycle analysis is presented with the object of defining the orbital record preserved in the strata we use the bed thickness as input data for our cycle analysis statistical analysis revealed a slow upward increase of both the frequency and thickness of sand beds in the boreholes resulting from infilling of the lake by a basinward migration of the marginal facies cycles of different order were detected in the sediments the higher order cycles are very close to or are equivalent with the milankovitch climatic cycles 19 ka caused by precession 50 ka caused by obliquity and 400 ka is the longer period of eccentricity the longer 1 m y cycle is very poorly developed here it is probably the analogue of the 3rd order global climatic cycle cycle analysis suggests that one of the main controlling factors of the water level changes of the pannonian lake was high frequency climatic oscillations the long term climatic changes only had a faint impact on the sediments the record of the 3rd order water level changes is very subtle our results show that the water level changes followed the rhythm of that of the eustatic changes but being asynchronous to them i e at high sea level stage the pannonian lake level was low and vice versa

orbital forcing in a boreal cretaceous epeiric sea high resolution analysis of core and logging data upper albian of the kirchrode i drill core lower saxony basin nw germany abstract a 245 m 0 245 m subsurface core of upper albian marine sediments from north germany research well kirchrode i was studied to identify sequences and cycles of sedimentation and related forcing mechanisms on sedimentation in an epeiric sea of the sub boreal realm the core consists of monotonous gray marls with an exceptionally high sedimentation rate of 8 12 cm ka 1 in total it represents a period of approximately 2 5 4 ma a silty glauconite rich condensed layer marks a change in the succession at 132 m and is paralleled by the first occurrence of e turriseiffelii and g bentonensis the lower part of the core shows lenticular bedding siderite nodules average caco 3 content of ca 40 and an abundance of inoceramids inoceramus anglicus birostrina lissa actinoceramus sulcatus the upper part is characterised by plane bedding common siderite layers an average caco 3 content of ca 35 and an abundance of aucellinas aucellina gryphaeoides according to lithology and ichnofacies the succession represents a transgressive regressive cycle with distinct bimodality of lithology fossil and trace fossil content together with reworking and redeposition at the base and top we studied well log data sediment composition sediment color and carbonate content and applied various mathematical analysis techniques to these data principal component analysis spectral analysis fourier transform autocorrelation spectral analysis revealed well pronounced periodic cyclicity in the upper part of the upper albian 12 8 4 5 3 4 1 7 m the 12 m eccentricity cycles are the most intense cycles reflecting periodic changes in the terrigenous clastic supply chaotic transitional intervals occur around the middle upper albian upper albian and topmost albian parts of the core they are characterised by non cyclic changes in litho and biofacies mathematically these changes correspond to singularity points they are preceded by non orbital high frequency variations in carbonate content and in ray

hydrothermal water rock interaction and the redistribution of li b and cl in the taupo volcanic zone new zealand abstract lithium b and cl occur as trace elements in the dominant protoliths rhyolite andesite and greywacke underlying high temperature hydrothermal systems in the taupo volcanic zone tvz the fluid mobility of li decreases substantially at 200 c 20 c with the pervasive deposition of quartz chlorite regardless of protolith and altering fluid compositions boron and cl are more fluid mobile than li at all temperatures with mobility affected by the rock type composition of circulating aqueous solutions and to a limited extent by incorporation of the trace elements in hydrothermal minerals uptake of b by clays decreases its mobility at 320 c occur compared to volcanic rocks the mobility of b and cl in greywackes is very low and thus the b cl signature of greywacke in hydrothermal aqueous solutions of the tvz is overwhelmed by the effects of rhyolite and andesite dissolution temperature dependent transitions from mg fe clays and phyllosilicates to k bearing illitic clays tend to decrease the mg li ratios in aqueous solutions at 200 c

itqiy a study of noble gases and oxygen isotopes including its terrestrial age and a comparison with zaklodzie we report noble gas oxygen isotope 14c and 10be data of itqiy as well as noble gas 14c and 10be results for zaklodzie both samples have been recently classified as anomalous enstatite meteorites and have been compared in terms of their mineralogy and chemical composition the composition of enstatite and kamacite and the occurrence of specific sulfide phases in itqiy indicate it formed under similar reducing conditions to those postulated for enstatite chondrites the new results now seem to point at a direct spatial link the noble gas record of itqiy exhibits the presence of a trapped subsolar component which is diagnostic for petrologic types 4 6 among enstatite chondrites the concentration of radiogenic 4he is very low in itqiy and indicates a recent thermal event its 21ne cosmic ray exposure age is 30 1 3 0 ma and matches the most common age range of enstatite chondrites mostly el6 chondrites but not that of zaklodzie itqiy s isotopic composition of oxygen is in good agreement with that observed in zaklodzie as well as those found in enstatite meteorites suggesting an origin from a common oxygen pool the noble gas results on the other hand give reason to believe that the origin and evolution of itqiy and zaklodzie are not directly connected itqiy s terrestrial age of 5800 500 years sheds crucial light on the uncertain circumstances of its recovery and proves that itqiy is not a modern fall whereas the 14c results from zaklodzie suggest it hit earth only recently

experimental quantification of the fractionation of fe isotopes during metal segregation from a silicate melt abstract fractionation of fe isotopes between a silicate melt and metallic alloys has been quantified experimentally at 1500 c the effects of oxygen fugacity and run duration have been investigated to distinguish between kinetic and equilibrium fractionations a new experimental setup is presented in which metallic fe is produced by reduction of oxidized iron from a silicate melt due to a change of redox conditions this metallic fe is physically removed from the silicate and sequestered as a pt fe alloy bulk analyses of the silicate and metallic fractions using multi collector icp ms methods are coupled with in situ analyses using an ion microprobe experimental results indicate that significant isotopic fractionation of fe occurs during metal segregation during the early stages of the experiments we find evidence for kinetic fractionation caused by faster diffusion of 54 fe along concentration gradients in the alloy this process leads to the formation of a metallic phase which is isotopically light compared to the residual silicate metal silicate fractionation up to 2 35 a m u the data are used to quantify the difference in diffusion coefficient of each isotope of iron providing a means to predict fe isotope fractionation during fe diffusion in metallic alloys on the other hand this state of affairs is transient in nature and at superliquidus temperature the systems rapidly reach a state of isotopic equilibrium in which the metal is isotopically heavier than the silicate melt by about 0 2 0 15 a m u these results are consistent with the range of variation observed in natural samples these kinetic and equilibrium data provide an experimental framework to understand the observed variability among igneous and meteoritic materials formed at high temperature particularly for iron and pallasite meteorites

paleobathymetry in the backstripping procedure correction for oxygenation effects on depth estimates abstract this paper aims to provide a straightforward and easily applicable method for estimating the depositional depth evolution of marine basins vertical movements of the basin floor can be reconstructed from the sedimentary record and more accurately constrained when information from the sedimentary history is combined with palaeodepth estimates derived from fauna to this end we propose to extend an existing method based on the percentage of planktonic foraminifera with respect to the total planktonic and benthic foraminiferal association which is expressed as the percentage planktonics p the ratio between planktonic and benthic foraminifera is related to water depth and the p generally increases with increasing distance to shore however next to water depth the oxygen level of bottom waters has a profound effect on the abundance of benthic foraminifera and as such influences the p depending on basin configuration the oxygen level at the sea floor can vary on milankovitch time scales and is reflected by the fraction of benthic foraminiferal species that indicate an effect of oxygen stress on the biotic system these species can be used as stress markers and their percentage with respect to the total benthic population is here expressed as s to assess whether the effect of sea floor oxygenation impairs depth reconstructions we studied the percentage of planktonic foraminifera p in five well dated sedimentary successions from the lower pliocene of crete corfu and milos in greece additionally we assessed whether different foraminiferal size fractions and counting methods affect the determination of the percentage of planktonic foraminifera the palaeobathymetric evolution calculated for each basin was confirmed for all successions by an independent check on depth related occurrences of benthic foraminifera after correction for bathymetry changes of the basin due to sedimentation compaction and eustatic sea level variations the vertical movement history of the basin floor was inferred we propose a standard methodology for reconstructions of palaeobathymetry of marine sedimentary successions from foraminiferal associations

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

high temperature silicon isotope geochemistry abstract silicon si is the defining element of silicate reservoirs yet despite its dominance in major earth processes there is still no clear understanding of how much is hosted in earth s core how the enriched continental crust forms or even if the crust is isotopically different from the mantle because of a long history of weathering erosion and subduction with the advent of multiple collector inductively coupled plasma mass spectrometry it has become relatively straightforward to explore small 100 ppm level mass dependent variations in si isotopic composition resulting from high temperature fractionation and to develop new isotopic fingerprints of magmatic processes and source regions this paper reviews the technique developments the new data and the veracity of current interpretations only a small si isotopic effect is associated with basalt formation via mantle melting however there now is compelling evidence based on a considerable number of samples 100 that the silicate earth is isotopically fractionated by 100 200 ppm per amu to a heavy composition relative to that of chondrites and also all differentiated stony meteorites this could reflect variability in the circumstellar disc but this is not well supported by data for enstatite chondrites which are isotopically light the most plausible current explanation is that si is a light element in earth s core and that differences in the bond stiffness between silicate and metal hosted si resulted in substantial fractionation interestingly the moon has the same si isotope composition as earth s mantle which is hard to explain unless the moon s atoms were mainly derived from earth differentiated magmatic sequences such as those of hekla iceland display a systematic relationship between isotopic composition and si content more complex magmatic suites such as i and s type granites reveal a range of isotopic compositions not well correlated with chemical composition similar effects are found in lower crustal granulite facies xenoliths nonetheless the overall composition of the continental crust is only slightly heavy relative to the mantle in fact the effect is barely resolvable therefore the amounts of surface dissolved heavy si removed to the mantle via weathering over time have been small or these losses have been balanced by subduction of isotopically light clay

precession punctuated growth of a late miocene submarine fan lobe on gavdos greece sedimentary cycles in an upper miocene succession of hemipelagic sediments marls and laminites sapropels were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity individual marl laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr the lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences the turbidite sequences occur within or substitute entirely the laminite beds so that turbidite deposition is similarly precession punctuated the turbidite facies is characteristic for small prograding fan lobes fed by small volume turbidites the abundant plant remains the local palaeogeographic setting and the association with laminites related to wet climate suggest a river fed submarine fan lobe where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run off the onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief sea level changes seem least important for the triggering of turbidites which is in contrast with current beliefs

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

a multidisciplinary study of ecosystem evolution through early pleistocene climate change from the marine arda river section italy the arda river marine succession italy is an excellent site to apply an integrated approach to paleoenvironmental reconstructions combining the results of sedimentology body fossil paleontology and ichnology to unravel the sedimentary evolution of a complex marine setting in the frame of early pleistocene climate change and tectonic activity the succession represents a subaqueous extension of a fluvial system originated during phases of advance of fan deltas affected by high density flows triggered by river floods and overlain by continental conglomerates indicating a relative sea level fall and the establishment of a continental environment an overall regressive trend is observed through the section from prodelta to delta front and intertidal settings the hydrodynamic energy and the sedimentation rate are not constant through the section but they are influenced by hyperpycnal flows whose sediments were mainly supplied by an increase in apennine uplift and erosion especially after 1 80 ma the arda section documents the same evolutionary history of coeval successions in the paleo adriatic region as well as the climatic changes of the early pleistocene the different approaches used complement quite well one another giving strength and robustness to the obtained results

origin and transformation of organic matter in pliocene pleistocene mediterranean sapropels organic geochemical evidence reviewed abstract drilling of deep water post messinian sedimentary sequences by odp legs 160 and 161 in the mediterranean sea has shown that occurrence of organic carbon rich sapropels and sapropel like sediments extends from the levantine basin westward into the alboran basin in the eastern mediterranean sapropel deposition started in the early pliocene whereas in the western basin the onset of sapropel formation occurred later in the early pleistocene precessional cycles are apparently the primary external forcing for sapropel formation nevertheless the pattern of sapropel occurrence suggests that the precessional influence is modulated by the glaciation cycles large differences were observed in the organic carbon contents of sapropels recovered in the eastern and western mediterranean correspondence between organic carbon contents rock eval hydrogen index values and elemental c n ratios indicate that both variations in the production and preservation of marine organic matter have led to the accumulation of high amounts of organic matter in sapropels molecular organic geochemical compositions of sapropels from the eastern mediterranean further confirm that the major fraction of organic matter in sapropels is derived from marine algal sources and has undergone variable oxidation enhanced marine productivity and improved preservation of organic matter is central to sapropel formation accumulation of increased amounts of land derived material at times of sapropel formation is also evidenced supporting the hypothesis of significant periodic freshwater discharges

organic geochemistry of the upper miocene lower pliocene sedimentary rocks in the hellenic fold and thrust belt nw corfu island ionian sea nw greece abstract the northwestern margin of the hellenic fold and thrust belt situated along the southern edge of the dinarides albanides hellenides continental convergent zone has been studied in terms of its hydrocarbon generating potential more than a hundred 100 samples of the upper miocene lower pliocene sedimentary rocks from several sites in corfu island were analyzed using rock eval vi pyrolysis while a selected representative group was further analyzed using bitumen extraction open column chromatography and gas chromatography mass spectrometry results of this investigation revealed units with sufficient organic material of good enough quality and quantity to be considered as potential source rocks a general type iii kerogen was identified indicating terrestrial origin of the organic matter tmax and production index values further indicate that the most promising parts of the sediments are immature with respect to oil generation and have not experienced high temperature during burial n alkanes distribution for selected samples of the northern miocene to pliocene mudstones present dominance of the long chain components immaturity of the organic matter is also evident by the low pr ph and 20s 20s 20r steranes ratios

experimental determination of the si isotope fractionation factor between liquid metal and liquid silicate abstract the conditions of core formation and the abundances of the light elements in earth s core remain debated silicon isotope fractionation provides a tool contributing to this subject we present experimentally determined si isotope fractionation factors between liquid metal and liquid silicate at 1450 c and 1750 c which allow calibrating the temperature dependence of si isotope fractionation experiments were performed in a centrifuging piston cylinder at 1 gpa employing both graphite and mgo capsules tin was used to lower the melting temperature of the metal alloys for experiments performed at 1450 c tests reveal that neither sn nor c significantly affects si isotope fractionation an alkaline fusion technique was employed to dissolve silicate as well as metal phases prior to ion exchange chemistry and mass spectrometric analysis the results show that metal is consistently enriched in light isotopes relative to the silicate yielding average metal silicate fractionation factors of 1 48 0 08 and 1 11 0 14 at 1450 c and 1750 c respectively the temperature dependence of equilibrium si isotope fractionation between metal and silicate can thus be described as 30 si metal silicate 4 42 0 05 10 6 t 2 the si isotope equilibrium fractionation is thus about 1 7 times smaller than previously proposed on the basis of experiments a consequence of this smaller fractionation is that the calculated difference between the si isotope composition of the bulk earth and that of the bulk silicate earth generated by core formation is smaller than previously thought it is therefore increasingly difficult to match the si isotope composition of the bulk silicate earth with that of chondrites for metal silicate equilibration temperatures above 2500 k this suggests that si isotopes were more sensitive to the early stages of core formation when low oxygen fugacities allowed significant incorporation of si into metal

milankovitch cyclicity within the middle eocene deep marine guaso system ainsa basin spanish pyrenees abstract the guaso system is the youngest deep marine stratigraphic component in the middle eocene deep marine ainsa basin in common with the older systems in the ainsa basin it was mainly fed from the east southeast by a range of sediment gravity flow processes including turbidity currents debris flows and suspended sediment river derived plumes e g hyperpycnal flows a study of the guaso system interfan sediments provides a 44 m long geochemical stratigraphic series constructed from spectral gamma ray k u and th content and bulk sediment geochemical data caco 3 toc 18 o and 13 c spectral and average spectral misfit analyses of these data identify obliquity and precession orbital modes as present with respective periods of approximately 10 and 6 m these cycles are interpreted as reflecting carbonate dilution cycles linked to variation in siliciclastic sediment input into the ainsa basin the presence of such orbitally induced carbonate dilution cycles is consistent with the identification of orbitally forced waxing and waning of coarse grained sediment supply within the coeval up system sediment supply system in the fluvio deltaic montanyana group of the tremp graus basin the presence of orbitally controlled sediment input to basin during interfan marlstone accumulation supplements to the growing body of evidence for the orbital control of sedimentation within the ainsa basin

the impact of milankovitch scale climatic forcing on sediment supply abstract stratigraphy is the main technique to predict the occurrence of potential reservoirs and seals in the oil industry stratigraphic tools used are stratigraphic observations from drilled wells rock samples and wireline logs and seismic interpretation nowadays computer modelling allows scenario forecasting of the sequence to be expected application of these tools indicates that the key input parameters are initial basin topography subsidence eustasy and sediment supply the first three parameters are usually well constrained or can readily be deduced from well and seismic data however the fourth sediment supply is loosely defined and because of that it is used to calibrate the model in the present article the controls on sediment supply are reviewed and the impact of in particular milankovitch scale climatic forcing on sediment supply is tested on the neogene of the niger drainage and delta system sediment supply is controlled by a complex interplay of geographic and climatic factors such as 1 relief or mountain height 2 the size and temporal storage capacity of the drainage area 3 overall climate 4 amount and seasonality of precipitation and 5 vegetation cover studies in geomorphology have indicated that although complex computer models can be made to predict erosional product for the present a large scale sediment supply prediction should be based on the combination of palaeogeographical palaeoclimatological and erosion potential maps more detailed sediment supply predictions should include milankovitch scale variations the climatic impact of these variations is mainly felt when we are in a transition between two climates then the area will experience regular climatic changes from e g wet rainforest to dry monsoonal climate or low to high sediment supply respectively this concept was tested in the forward modelling package stratagem on the neogene of the niger delta four scenarios were evaluated using various combinations of large and milankovitch scale sediment supply curves combined with global or milankovitch scale eustatic sea level curves the results confirm the impact of both large scale and milankovitch scale climatic forcing on sediment supply however in an icehouse world the various scenarios also suggest that the effect of eustatic sea level fluctuations overshadows the impact of milankovitch scale sediment supply by contrast in a greenhouse world the impact of milankovitch scale sediment supply is expected to be more significant in the absence of significant sea level fluctuations

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

astronomically induced paleoclimatic oscillations reflected in pliocene turbidite deposits on corfu greece implications for the interpretation of higher order cyclicity in ancient turbidite systems the growth pattern of fan lobes in the early pliocene corfu turbidite system greece demonstrates that regional climatic fluctuations in the land locked mediterranean completely concealed global glacioeustatic effects the temporal evolution of the fan lobes studied closely matches the astronomical precession cycle in this time interval 23 ka strongly suggesting that regular waxing and waning of the sediment supply to the delta fed turbidite system were directly driven by changes of precipitation and continental runoff the common lack of high resolution time control in ancient turbidite systems may lead to mistaken interpretations of higher order cyclicity in ancient turbidite sequences produced by precession induced variations of sediment supply at low paleolatitudes

orbital forcing in turbidite accumulation during the eocene greenhouse interval the influence of astronomically driven short term climate change milankovitch cycles on deep marine turbidite systems is not well known particularly in the case of long term greenhouse intervals with no significant glacio eustatic sea level fluctuations this study carried out at the gorrondatxe section global stratotype section and point for the base of the lutetian stage in the western pyrenees demonstrates that the characteristics of lower middle eocene fan fringe basin plain turbiditic and pelagic deposits varied in line with orbitally forced fluctuations in seasonal rainfall runoff and terrigenous input to the sea reduced turbiditic activity during the formation of pelagic limy precessional hemicouplets indicates subdued seasonality and low terrigenous input conversely turbidity currents were more frequent had greater energy and were more voluminous during the formation of pelagic marly hemicouplets suggesting precessional hemicycles with strong seasonality and heavy summer rainfall these differences at precessional time scales were enhanced at maximum eccentricity because turbiditic activity was most intense when boreal summer occurred at perihelion i e maximum seasonality but declined when it occurred at aphelion at minimum eccentricity with relatively weak seasonality throughout one or more than one precessional cycle 21 kyr turbiditic activity remained relatively low the pattern observed at the gorrondatxe fan fringe basin plain succession implies that the orbitally forced environmental changes must also have affected the inner and middle parts of the submarine fan the astronomical influence on terrigenous sediment input also determined the changing characteristics of the pelagic sedimentation thus terrigenous sediment contribution to pelagic sedimentation fluctuated by a factor of five during opposite precessional situations at maximum eccentricity whereas there was almost no fluctuation at minimum eccentricity

redox state during core formation on asteroid 4 vesta abstract core formation is the main differentiation event in the history of a planet however the chemical composition of planetary cores and the physicochemical conditions prevailing during core formation remain poorly understood the asteroid 4 vesta is the smallest extant planetary body known to have differentiated a metallic core howardite eucrite diogenite hed meteorites which are thought to sample 4 vesta provide us with an opportunity to study core formation in planetary embryos partitioning of elements between the core and mantle of a planet fractionates their isotopes according to formation conditions one such element silicon shows large isotopic fractionation between metal and silicate and its partitioning into a metallic core is only possible under very distinctive conditions of pressure oxygen fugacity and temperature therefore the silicon isotope system is a powerful tracer with which to study core formation in planetary bodies here we show through high precision measurement of si stable isotopes that hed meteorites are significantly enriched in the heavier isotopes compared to chondrites this is consistent with the core of 4 vesta containing at least 1 wt of si which in turn suggests that 4 vesta s differentiation occurred under more reducing conditions iw 4 than those previously suggested from analysis of the distribution of moderately siderophile elements in heds

orbital forcing as principal driver for fine grained deep marine siliciclastic sedimentation middle eocene ainsa basin spanish pyrenees abstract the relative importance of climate tectonics and or autocyclicity in driving deposition of laminated deep marine fine grained siliciclastic sediments in tectonically active basins remains controversial consequently the recognition of milankovitch periodicities in such successions remains poorly documented this study evaluates the cyclostratigraphy and its likely drivers in the middle eocene ainsa basin spanish pyrenees a basin that is known to have been associated with major syndepositional tectonics this basin was infilled by a thick succession of siliciclastic sediments characterised by an alternation of coarse grained sandbodies interpreted as submarine fans and finer grained packages of interfan fan lateral margin and channel levee overbank sediments this study presents time series analysis of outcrop spectral gamma ray and cumulative sandstone turbidite abundance data from eight fine grained essentially interfan sections located between coarse grained sandbodies submarine fans the 1 4 km of cumulative stratigraphy studied show that milankovitch cyclicity can be recognised throughout the entire stratigraphic evolution of the ainsa basin even though the basin was tectonically active and suggest that the accumulation of the interfan deposits was orbitally controlled orbital parameters most likely paced the cyclic delivery of the fine grained sediments mainly by river and delta supplied turbidity currents from the non marine and shallow marine tremp basin immediately to the east sediment accumulation rates determined from spectral analysis show a gradual decrease throughout the deep marine stratigraphy from 57 to 24 cm kyr this study shows that orbitally induced climate change acted as a principal driver on deep marine terrigenous sediment accumulation within a tectonically active basin high frequency climate variability therefore should be considered when studying controls on siliciclastic sedimentation in tectonically active regions

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

a staurolite talc assemblage in tourmaline phlogopite chlorite schist from northern victoria land antarctica and its petrogenetic significance staurolite and corundum are found as inclusions in tourmaline in a talc phlogopite chlorite albite chist near mount bernstein 71 37 s 163 07 e northern victoria land antarctica these inclusions are interpreted as relics of a staurolite talc corundum chlorite assemblage that was stable during an early stage in the metamorphic cycle and subsequently armored by tourmaline probably during the middle stage pressures and temperatures during the middle stage are estimated to be 650 700 c and 5 5 6 4 kbar the transition from the early to the middle stage represents a roughly isothermal decrease in pressure of 2 3 kbar during a late retrograde stage t 300 370 c p 3 5 kbar staurolite was partly replaced by a muscovitic aggregate containing clinozoisite pumpellyite and margarite

hyperpycnites deposited 700 km away from river mouths in the central japan sea abstract relatively little is known about the characteristics of deposits and potential runout distances of hyperpycnal currents this study describes and discusses evidence of sediment deposition from sustained long duration quasi steady turbidity currents in the distal part of the toyama deep sea channel which extends ca 700 km from river mouths in the central japan sea the study is based on gravity cores and airgun seismic reflection profiles obtained from the channel distal reaches the silty turbidite beds of the channel s terminal fan show rhythmic layering that indicates sustained turbidity currents with distinct flow strength fluctuations some of the rhythmite beds show a fining upward internal trend net flow strength waning whereas others show an upward coarsening net flow strength waxing followed by fining seismic reflection profiles from the channel levees show large bedforms of climbing dune type attributed to the spillover of thick sustained turbidity currents the deposition of the terminal fan rhythmites and accretionary levee bedforms is attributed to turbidity currents generated by hyperpycnal river effluent a quantitative assessment of sediment concentrations in the coastal rivers indicates that their effluents could become hyperpycnal nearly every year or during every major seasonal flood the density of a river generated underflow would increase by the entrainment of saline water and seafloor sediment on the steep slope of the toyama bay resulting in robust long runout turbidity currents the estimated flow velocities of these currents were around 0 3 m s and their recurrence period for the last 1000 years was of the order of 70 years the estimated duration of hyperpycnal flows required for the deposition of rhythmite beds 700 km away from the river mouth is of the order of several days to 3 4 weeks the study provides new insights into the recognition and classification of hyperpycnites in distal zones of deep marine turbiditic systems

silicon isotope evidence against an enstatite chondrite earth the compositions of earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems although this suggests that earth largely accreted from enstatite chondrites definitive proof of this model has been lacking by comparing the silicon si isotope signatures of several extraterrestrial materials with terrestrial samples we show that they cannot be explained by core formation scenarios involving a bulk earth of enstatite chondrite composition si isotope similarities between the bulk silicate earth and the moon preclude the existence of a hidden reservoir in the lower mantle a necessary condition of the enstatite chondrite model and require an equilibrium process after the moon forming impact a three end member chondritic mixing model for earth reconciles the si isotope similarities between enstatite chondrites and earth

stochastic and deterministic controls on stratigraphic completeness and fidelity compilations of sedimentation rates determined across a large range of time spans and different sedimentary environments attest to the discontinuous nature of sedimentation and support the reasoning that hiatuses pervade sedimentary successions at multiple spatial and temporal scales the relationship between sedimentation rate and time span of observation also emphasises how stratigraphic completeness is a time span dependent concept the scaling of stratigraphic completeness with time span alludes to the likely stochastic and fractal nature of the stratigraphic record it also implies that the relationship between stratal thickness and time is inherently non linear and this has obvious implications for the way we should expect temporal processes to be recorded stratigraphically order within the stratigraphic record may arise from deterministic processes in stratigraphy most notably through astronomically influenced sedimentation intuitively a strongly ordered stratigraphic record due to the presence of cyclicity in sedimentation increases stratigraphic completeness at time spans equal to and longer than the time span of the cyclicity and minimises the non linearity between stratal thickness and time here geological data and simple modelling are used to support this supposition but these results also highlight how stochastic variability inherent in depositional processes may sensitise certain successions to missed cycles and incompleteness even in the presence of strong cyclicity this stochastic variability has the potential to mask evidence of astronomical forcing of sedimentation it is also shown how hiatuses affect the ability of a succession to faithfully record temporal processes and this is true regardless of whether hiatuses are deterministically controlled or random or indeed whether a succession is considered complete or not consequently stratigraphic completeness and stratigraphic fidelity are not synonymous terms

late quaternary terrestrial climatic variability recorded in deep sea turbidites along the toyama deep sea channel central japan sea abstract stratigraphic variations of coarse fraction and frequency and thickness of turbidites in three cores collected along the toyama deep sea channel tdsc in the central japan sea show consistent temporal trends with changes in terrestrial climatic records these temporal changes in turbidite deposition may reflect climatic forcing in the sediment source areas for the last 70 ka comparison of temporal changes in turbidite deposition with paleoclimatic and paleoceanographic records in the central japanese mainland and the japan sea revealed the following modes of climatic linkages 1 during the stadials and interstadials of the last glacial period 70 22 ka when the tsushima warm current twc periodically flowed into the japan sea the japanese mainland climate was cold and periodically wet resulting in occasional glacial advances in adjacent mountains turbidite flux increased in the tdsc system during the major glacial advances because of the increased production of coarse debris by glacial processes and high transport potential due to high precipitation 2 during the last glacial maximum 22 18 ka when the japan sea was capped by cold low salinity surface water the terrestrial climate was cold and dry due to low evaporation from the japan sea as a result of low precipitation less coarse debris was transported into deep basins and so during this period the turbidite flux along the tdsc was reduced 3 during the last deglaciation 18 8 ka precipitation in central japan increased due to intensified summer monsoons this resulted in destabilization of mountain slopes and increased transport of detritus to the lowlands and also to the tdsc system 4 after the twc flowed into the japan sea the land climate became warm wet and stable enhanced vegetation and re stabilized mountain slopes have reduced sediment input to the tdsc system since 8 ka

metal silicate silicon isotopic fractionation and the composition of the bulk earth abstract the difference in the si isotopic composition between the earth and primitive meteorites had been used to constrain the amount of si in the earth s core however there is presently a debate on the magnitude of the isotopic fractionation between metal and silicates as function of temperature based on experimental data here we use a natural sample an enstatite meteorite itqyi as a natural experiment to determine an independent si isotopic fractionation factor between metal and silicate we determined the temperature of equilibrium between metal and silicate as well as the si isotopic composition between the phases we find that the dependence of si isotopes with temperature to be 30 si silicate metal 7 6 0 7 10 6 1 s d t 2 using this dependence of the 30si with temperature we estimate the bulk earth 30si as a function of si content of the core for different plausible conditions even when using the most extreme parameters we show that the bulk earth must be isotopically heavier than any chondrites groups we therefore confirm that core formation alone cannot account for the isotopic difference between the earth and primitive meteorites we show that there is no correlation between 30si and the mg si ratio suggesting that forsterite fractionation in the solar nebula may have had only a limited effect if any our new results therefore confirm that volatility should have had a fundamental effect in shaping terrestrial planets chemical composition

ti poor hoegbomite in kornerupine cordierite sillimanite rocks from ellammankovilpatti tamil nadu india hoegbomite occurs sparingly in minute mostly 0 1 mm grains with fine grained hercynite magnetite and rutile in two coarse grained kornerupine cordierite sillimanite rocks from ellammankovilpatti tamil nadu india the hoegbomite is ti poor 2 5 wt tio2 fe rich 25 26 fe as feo and contains 6 2 6 8 mgo 59 8 60 1 al2o3 1 0 1 3 zno 0 3 0 7 cr2o3 and 0 02 li2o minor amounts estimated not to exceed 0 2 wt oxide of v co ni ga and sn were detected on the electron microprobe but be nb and zr were not detected with the ion microprobe mass analyser assuming the crystal structure refined by gatehouse and grey 1982 to be applicable to the ellammankovilpatti hoegbomite the analyses were recalculated on a basis of 22 cations 30 oxygens and two hydroxyls resulting in 49 to 53 of the iron being ferric identification of hoegbomite was confirmed by x ray powder diffraction associated cordierite fe fe mg 0 14 and kornerupine fe fe mg 0 27 contain 0 02 weight li2o and 0 05 0 07 beo while only the kornerupine contains b2o3 1 57 ion microprobe analyses hoegbomite and the other oxides may have crystallized at temperatures between 680 and 720 c p 6 5 kbar following attainment of peak conditions by the reaction kornerupine sillimanite rutile zno h2o o2 cordierite chlorite hercynite hoegbomite magnetite b2o3

experimental silicate mineral melt partition coefficients for beryllium and the crustal be cycle from migmatite to pegmatite partition coefficients dbemineral melt for beryllium between hydrous granitic melt and alkali feldspars plagioclase feldspars quartz dark mica and white mica were determined by experiment at 200 mpa h2o as a function of temperature 650 900 c activity of be in melt trace levels to beryl saturation bulk composition and thermal run direction at trace levels be is compatible in plagioclase of an31 1 84 at 700 c and muscovite 1 35 at 700 c but incompatible in biotite 0 39 0 54 from 650 800 c alkali feldspar 0 38 0 19 from 680 850 c quartz 0 24 at 800 c and albite 0 10 at 750 c the partition coefficients are different at saturation of the melt in beryl lower in the case of plagioclase of an31 0 89 at 700 c muscovite 0 87 at 700 c biotite 0 18 0 08 from 675 800 c alkali feldspar 0 18 0 14 from 680 700 c and quartz 0 17 0 08 from 750 800 c but higher in the case of albite 0 37 at 750 c with other data sources these new partition coefficients were utilized to track first the distribution of be between aluminous quartzofeldspathic source rocks and their anatectic melts and second the dispersion or concentration of be in melt through igneous crystal fractionation of different magma types e g s type i type up to beryl saturated granitic pegmatites and finally into their hydrothermal aureoles among the rock forming minerals cordierite calcic oligoclase and muscovite in this order control the fate of be because of the compatibility of be in these phases in general beryl bearing pegmatites can arise only after extended crystal fractionation of large magma batches to f fraction of melt remaining 0 05 granitic magmas that originate from cordierite bearing protoliths or that contain large modal quantities of calcic oligoclase will not achieve beryl saturation at any point in their evolution

sand composition changes across key boundaries of siliciclastic and hybrid depositional sequences abstract sand composition of arenite successions is sensitive to a suite of factors operating between initial grain production and final diagenesis on a variety of spatial and temporal scales seven allogenic factors the relative importance of which relies upon the complex interaction between tectonics eustasy and climate play a decisive role in dictating petrofacies distribution within siliciclastic to hybrid depositional sequences these factors include i tectonic exhumation ii physical and chemical rock breakdown iii change in sediment flux iv change in source basin physiography v shelf colonization by organisms vi generation of chemical grains and vii volcanism autogenic processes may locally have a considerable influence on the type and amount of sediment supplied to the basin thus interfering with the external control based upon literature data a conceptual framework of expected compositional changes across the key surfaces for sequence stratigraphic interpretation is outlined two case histories from the miocene shelf to turbidite deposits of the northern apennines and the quaternary alluvial to nearshore succession of the adriatic coast respectively are used as references to illustrate how arenite petrofacies changes can be framed into a sequence stratigraphic scheme on multiple timescales

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

an emp and tem aem study of margarite muscovite and paragonite in polymetamorphic metabauxites of naxos cyclades greece and the implications of fine scale mica interlayering and multiple mica generations

origin of the plio pleistocene vrica laminites organic geochemical evidence meyers p a 1993 origin of the plio pleistocene vrica laminites organic geochemical evidence mar geol 115 117 127 organic geochemical properties of samples from lower pleistocene laminite layer h at vrica calabria have been examined for evidence of the origin of these dark colored sediments the laminite samples are geochemically distinct from the surrounding gray marly clays they contain less caco 3 and more toc have higher c n ratios and lower 613c values and their hydrocarbon contents indicate larger proportions of land derived organic matter the vrica taminites appear to have originated principally as a consequence of enhanced runoff of land derived organic matter and clastic sediments from nearby land areas during episodes of wetter regional climate freshening of surface waters by the runoff created salinity stratification of the water column diminished availability of oxygen in near bottom waters and improved preservation of organic matter marine productivity was probably also enhanced but not as much as is evident for pelagic sapropels in the eastern mediterranean