a high resolution pollen and geochemical analysis of late holocene human impact and vegetation history in southern cumbria england the historic era which in cumbria begins with the roman invasion of ad 71 is a frequently neglected period in palaeoecological research but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records pollen and geochemical data are presented for late holocene records from deer dyke and hulleter mosses in southern cumbria the records show initially low levels of anthropogenic impact followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries ad the timing of these clearances suggests that they were initially anglo saxon in origin rather than norse further clearances in the 16th century ad are interpreted as a response to monastic dissolution and late tudor population pressures the landscapes reached their contemporary form following extensive clearances in the 17th century ad silicon and titanium concentrations at deer dyke moss were used to reconstruct past levels of atmospheric dust loading which is broadly related to soil erosion geochemical influx was found to peak during periods of landscape transition rather than from established land use this relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region which changes as substantial woodland clearances during the 16th century ad and continuous land use pressure since then have greatly increased the supply of airborne dust

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research

crystal growth and disequilibrium distribution of oxygen isotopes in an igneous ca al rich inclusion from the allende carbonaceous chondrite abstract ts34 is a type b1 ca al rich inclusion cai from the allende cv3 chondrite consisting of spinel melilite ti al rich clinopyroxene fassaite and minor anorthite in an igneous texture oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in ts34 using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite the oxygen isotopic evolution of the cai melt was established oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line the spinel grains are uniformly 16o rich 17o 22 7 1 7 2sd while the melilite grains are uniformly 16o poor 17o 2 8 1 8 irrespective of their akermanite content and thus their relative time of crystallization the fassaite crystals exhibit growth zoning overprinting poorly developed sector zoning they generally grow from ti rich to ti poor compositions the fassaite crystals also show continuous variations in 17o along the inferred directions of crystal growth from 16o poor 17o 3 to 16o rich 17o 23 covering the full range of oxygen isotopic compositions observed in ts34 the early crystallized 16o poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously the correlation of oxygen isotopic compositions with ti content in the fassaite imply that the oxygen isotopic composition of the cai melt evolved from 16o poor to 16o rich during fassaite crystallization presumably due to oxygen isotope exchange with a surrounding 16o rich nebular gas formation of spinel the liquidus phase in melts of this composition predates crystallization of all other phases so its 16o rich composition is a relic of an earlier stage anorthite exhibits oxygen isotopic compositions between 17o 2 and 9 within the range of those of fassaite indicating co crystallization of these two minerals during the earliest to intermediate stage of fassaite growth the melilite and fassaite yield an 26al 26mg mineral isochron with an initial value of 26al 27al 0 5 003 0 075 10 5 corresponding to a relative age of 0 05 0 02 myr from the canonical al mg age of cais these data demonstrate that both 16o rich and 16o poor reservoirs existed in the solar nebula at least 0 05 myr after the birth of the solar system

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

microstructural analysis of wark lovering rims in the allende and axtell cv3 chondrites implications for high temperature nebular processes a coordinated electron backscatter diffraction ebsd and transmission electron microscope tem study was undertaken to obtain information on the origin of rims on refractory inclusions in the allende and axtell cv3 chondrites these measurements were supported by theoretical modeling using density functional theory crystal orientation analysis of wark lovering rims via ebsd revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions an epitaxial relationship between grains within the diopside and anorthite rim layers was observed in allende tem examination of the rims of both samples also revealed oriented crystals at depth the microstructural data on the rims suggest that grain clusters grew in the form of three dimensional islands density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature the results point toward condensation as the mode of origin for the rims studied here

a link between oxygen calcium and titanium isotopes in 26 al poor hibonite rich cais from murchison and implications for the heterogeneity of dust reservoirs in the solar nebula placs platy hibonite crystals and related hibonite rich calcium aluminum rich inclusions cais hereafter collectively referred to as plac like cais have the largest nucleosynthetic isotope anomalies of all materials believed to have formed in the solar system most plac like cais have low inferred initial 26al 27al ratios and could have formed prior to injection or widespread distribution of 26al in the solar nebula in this study we report 26al 26mg systematics combined with oxygen calcium and titanium isotopic compositions for a large number of newly separated plac like cais from the murchison cm2 chondrite 32 cais studied for oxygen 26 of these also for 26al 26mg calcium and titanium our results confirm 1 the large range of nucleosynthetic anomalies in 50ti and 48ca our data range from 70 to 170 and 60 to 80 respectively 2 the substantial range of 17o values 28 to 17 with 17o 17o 0 52 18o and 3 general 26al depletion in plac like cais the multielement approach reveals a relationship between 17o and the degree of variability in 50ti and 48ca plac like cais with the highest 17o 17 show large positive and negative 50ti and 48ca anomalies while those with the lowest 17o 28 have small to no anomalies in 50ti and 48ca these observations could suggest a physical link between anomalous 48ca and 50ti carriers and an 16o poor reservoir we suggest that the solar nebula was isotopically heterogeneous shortly after collapse of the protosolar molecular cloud and that the primordial dust reservoir in which anomalous carrier phases were heterogeneously distributed was 16o poor 17o 17 relative to the primordial gaseous co h2o reservoir 17o 35 however other models such as co self shielding in the protoplanetary disk are also considered to explain the link between oxygen and calcium and titanium isotopes in plac like cais

the possible role of magnetic measurements in the discrimination of sahara sahel dust sources the mineral magnetic properties of deposited dusts collected along a broadly north to south transect across niger have been investigated on both a bulk and particle size specific basis dusts display a general north to south gradient in fine grained ferrimagnetic mineral magnetite maghemite concentrations with samples south of the sahara sahel transition south of 15 5o n generally containing greater concentrations than dusts from further north where the climate is much drier this distinction is seen especially clearly in the clay 2 m fraction which harbours the products of weathering and pedogenesis this gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils sands across a similar latitudinal range we suggest that the regional distinction in both dust and surface soil sand magnetic properties can be related to differences in weathering regime between the arid saharan parts of the transect and the sahel sites where higher rainfall has permitted stronger weathering and pedogenesis given that the weathering related magnetic signatures in the clays dominate the magnetic properties of the 16 m fractions in these samples and that this particle size component is most likely to be involved in long range transport magnetic measurements hold out the potential of discriminating sahara and sahel dusts deposited in remote areas copyright 2011 john wiley sons ltd

grain sizes of susceptibility and anhysteretic remanent magnetization carriers in chinese loess paleosol sequences detailed rock magnetic studies show that susceptibility mass specific and anhysteretic remanent magnetization arm of the chinese loess paleosol sequences are carried by almost identical magnetic carriers therefore the ratio arm or equivalently arm where is defined as 0 and 0 is the intercept susceptibility of the plot of versus arm and arm is field normalized arm can be used to quantify the grain size of and arm carriers by determining this ratio for three chinese loess paleosol profiles jiuzhoutai yuanbao and yichuan characterized by different degrees of environmentally controlled pedogenesis and sedimentation rates we show that the lower grain size limit of aeolian magnetic particles in the less pedogenically altered loess units is about 100 300 nm in the finer grained pseudosingle domain psd grain size range in contrast the grain sizes of pedogenically produced magnetic particles for mature paleosols dominantly cover both the superparamagnetic sp and single domain sd ranges on the basis of plots of arm against samples can be divided into four regions i ii iii and iv region i corresponds to the least pedogenically altered primary loess samples with arm of 0 165 0 24 samples in region ii a transition zone between the least altered loess and the onset of development of paleosols have values identical to those in region i but have lower arm of 0 09 0 165 with increasing susceptibility in zone iii arm is positively correlated with indicating the gradually increasing influence of sp particles finally in zone iv with higher than 6 5 10 7 m3 kg 1 arm is independent of the variations in suggesting that arm is totally controlled by the pedogenic finest grained particles and the size distribution of these particles remains almost constant the development of soils in the chinese loess revealed by these three profiles from three sites can be clearly explained by a continuous process of pedogenesis increasing from zone i to zone iv the definition of the pedogenic zones can help to improve our understanding of the underlying mechanisms and variability of pedogenesis and thus could enable more successful and accurate separation of the authentic pedogenic signals from the background signal of the aeolian inputs at different loess sites worldwide

chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy type a cai from vigarano abstract fluffy type a ca al rich inclusions cais containing reversely zoned melilite crystals are suggested to be aggregates of direct condensates from solar nebular gas we conducted an investigation of 26 al 26 mg systematics of a fluffy type a cai from vigarano named v2 01 with known oxygen isotopic distributions of reversely zoned melilite crystals we also conducted oxygen isotope measurements of coexisting minerals two of six reversely zoned melilite crystals show continuous variations in magnesium isotopic composition with 25 mg decreasing along the inferred direction of crystal growth which supports the idea that they originated through condensation petrography suggests that the constituent minerals of v2 01 formed in the following order first spinel and fassaite enclosed by melilite then reversely zoned melilite crystals and spinel and diopside in the wark lovering rim the spinel enclosed by melilite has 16 o rich compositions 17 o 24 and on an al mg evolutionary diagram plots along model isochron with an initial value of 26 al 27 al 0 5 6 0 2 10 5 the fassaite enclosed by melilite crystals shows variable oxygen isotopic compositions 17 o 12 and 17 and plots on an isochron with 26 al 27 al 0 5 6 0 2 10 5 the oxygen isotopic compositions of reversely zoned melilite showed continuous variations in 17 o along the inferred direction of crystal growth suggesting that surrounding nebular gas during the formation of the reversely zoned melilite changed from 16 o poor 17 o values larger than 10 to 16 o rich 17 o 25 the six reversely zoned melilite crystals show indistinguishable initial 26 al 27 al values with an average 26 al 27 al 0 of 4 7 0 3 10 5 which is clearly distinguishable from the value of enclosed spinel and fassaite indicating a younger formation age than the enclosed spinel and fassaite the spinel and diopside from the wark lovering rim show 16 o rich compositions 17 o 23 with 26 al 27 al 0 4 5 0 4 10 5 the values of 26 al 27 al 0 are consistent with the formation sequence inferred from petrography the formation period for the v2 01 cai is estimated to be 0 18 0 07 myr from the difference in initial 26 al 27 al values these data suggest that the oxygen isotopic composition of solar nebular gas surrounding the cai changed from 16 o rich to 16 o poor and back to 16 o rich during the first 0 2 myr of solar system formation

high temperature rims around calcium aluminum rich inclusions from the cr cb and ch carbonaceous chondrites abstract we describe the mineralogy petrology and oxygen isotopic compositions of high temperature rims around mineralogically pristine calcium aluminum rich inclusions cais from the cr cb and ch carbonaceous chondrites in cr chondrites nearly all cais are surrounded by single or multi layered rims composed of cai like minerals relict cais inside chondrules in which the rims were resorbed by the host chondrule melt aleon et al 2002 makide et al 2009 are the only exception a complete multi layered rim sequence from inside outward spinel hibonite perovskite melilite anorthite replacing melilite al diopside forsterite is rarely observed al diopside forsterite rims are more common the cr cais and all rim layers are uniformly 16o rich 17o 24 indicating formation in a 16o rich gaseous reservoir the mineralogy petrology and 16o rich compositions of these rims suggest formation by evaporation condensation melting and thermal annealing in the formation region of the host cais we define such rims as the primordial wark lovering wl rims in ch chondrites most cais are uniformly 16o rich and surrounded by the primordial wl rims one of the 16o rich cais is surrounded by an anorthite al diopside wl rim showing a range of 17o values from 24 to 6 17o decreases towards the cai core we infer that this rim experienced incomplete melting and o isotope exchange in an 16o poor nebular gas most likely during chondrule formation most cais in cb chondrites and about 10 of cais in ch chondrites are uniformly 16o depleted igneous inclusions 17o values between individual cais vary from 12 to 5 these cais have diverse mineralogies grossite rich hibonite rich melilite rich spinel rich and al ti diopside forsterite rich but are surrounded by the mineralogically similar igneous rims composed of melilite al diopside and ca rich forsterite 0 5 1 4 wt cao the igneous rims and the host igneous cais have identical within uncertainties of our sims measurements o isotope compositions suggesting that they crystallized from isotopically similar but chemically distinct melts we suggest that the uniformly 16o depleted igneous rims around the uniformly 16o depleted igneous cais in cb and ch chondrites formed during melting of pre existing cais in an impact generated plume invoked for the origin of cb chondrites krot et al 2005 followed by o isotope exchange with an 16o poor plume gas 17o 2 condensation of gaseous sio and mg into cai melt and its subsequent crystallization we conclude that high temperature rims around cais from cr ch and cb chondrites recorded thermal processing in gaseous reservoirs with different oxygen isotopic compositions in contrast to the isotopically heterogeneous wl rims around cv cais our data provide no evidence that cais were transported between 16o rich and 16o poor gaseous reservoirs multiple times we suggest instead that oxygen isotope heterogeneity in the cv wl rims resulted from a fluid rock interaction on the cv parent asteroid

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

the mineral magnetic properties of an annually laminated holocene lake sediment sequence in northern sweden detailed mineral magnetic measurements were conducted on a 9000 year varved lake sediment sequence in northern sweden lake sarsjon the results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments which is controlled to a large extent by the intensity of the spring snow melt in contrast the concentration of ferrimagnetic magnetite reflected by initial magnetic susceptibility and magnetic hysteresis parameters is positively correlated to the concentration of organic carbon which is most likely of an autochthonous origin this magnetite has magnetic properties that are characteristic of stable single domain magnetite grains produced by magnetotactic bacteria the paramagnetic susceptibility record clearly points to a climatic excursion in the early holocene between 6100 174 bc and 5700 167 bc which can be correlated to an d18o excursion a cold event in the greenland ice cores and lake sediments in southern germany an

application of dynamic programming to the correlation of paleoclimate records 1 signal matching is a powerful tool frequently used in paleoclimate research but it is enormously time consuming when performed by hand previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records a new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate high resolution results with much less effort than hand tuning or preexisting automated correlation techniques

robust chronologies for landform development obtaining chronological control for geomorphological sequences can be problematic due to the fragmentary and non sequential nature of sediment and landform archives the robust analysis of 14c ages is often critical for the interpretation of these complicated sequences this paper demonstrates a robust methodology for the 14c dating of geomorphological sequences using a case study from the lower ribble valley northwest england the approach adopted incorporates using greater numbers of ages targeting plant macrofossils obtaining replicate measurements from single horizons to assess the extent of reworking and the use of bayesian approaches to test models of the relative order of events the extent of reworking of organic materials and space time dynamics of fluvial change means that it is critical that chronological control is sufficiently resourced with 14c measurements as a result bayesian approaches are increasingly important for the evaluation of large data sets assessing the conformability of relative order models informed by interpretation of the geomorphology can identify contexts or materials that are out of sequence and focuses attention on problem materials reworking and errors in interpretation outlier ages these relative order models provide a framework for the interrogation of sequences and a means for securing probability based age estimates for events that occur between dated contexts this approach has potential value in constraining the sequence of geomorphological development at scales that vary from individual sites to a catchment or region furthering understanding of forcing and change in geomorphological systems copyright 2008 john wiley sons ltd

26al 26mg chronology and oxygen isotope distributions of multiple melting for a type c cai from allende abstract disequilibrium oxygen isotopic distributions of ca al rich inclusions cais correspond to multiple melting events in the solar nebula 26al 26mg systematics may be applicable for age differences among such melting events we have carried out a coordinated study of detailed petrographic observations and in situ oxygen and magnesium isotope measurements for a type c cai ek1 04 2 from the allende cv3 meteorite to determine the melting events and their ages the cai consists mainly of spinel anorthite olivine and pyroxene and has a core and mantle structure petrography of the core suggests that the crystallization sequence of the core minerals is from spinel anorthite olivine and to pyroxene the mantle has the same mineral assemblage as the core and shows incomplete melting and solidification textures oxygen isotopic compositions of the minerals are distributed along the carbonaceous chondrite anhydrous mineral ccam line 18o 44 to 9 which indicates to preserve a chemical disequilibrium status in the cai spinel shows a 16o rich signature 18o 43 while anorthite is 16o poor 18o 8 olivine and pyroxene in the core have the same oxygen isotopic composition 18o 15 which indicates their equilibrium olivine and pyroxene in the mantle have variable oxygen isotopic compositions and are slightly depleted in 16o 18o 13 to 4 compared with the same minerals in the core the 26al 26mg systematics is consistent with the disequilibrium status observed according to the petrography and oxygen isotopes spinel is plotted on a line of 26al 27al 0 3 5 0 2 10 5 anorthite is plotted on a line of 1 5 10 7 and olivine and pyroxene in the core are plotted on a line of 1 7 10 6 plots of olivine and pyroxene in the mantle are scattered below the isochron of these minerals in the core this study indicates that the ek1 04 2 type c cai underwent multiple heating events after the formation of its cai precursor the precursor cai was formed 0 4 myr after the formation of the solar system defined by canonical cai formation at least 1 6 myr after the precursor cai formation the cai was partially melted and the melt exchanged oxygen isotopes with surrounding 16o poor nebular gas 16o poor olivine and pyroxene in the core crystallized from the melt subsequently al rich chondrules accreted onto the cai and the cai experienced partial melting again and recrystallized to form the mantle the oxygen and magnesium isotopes in anorthite were redistributed during thermal metamorphism in the allende parent body our study reveals that the cai had been retained in the solar nebula for at least 1 6 myr and underwent multiple melting events in the nebula and oxygen and 26al 26mg systematics has been partially disturbed depending on crystal sizes by metamorphism on the parent body

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

high precision al mg systematics of forsterite bearing type b cais from cv3 chondrites abstract in order to further elucidate possible temporal relationships between different varieties of calcium aluminum rich inclusions cais we measured the aluminum magnesium isotopic systematics of seven examples of the rare type known as forsterite bearing type b fob inclusions from four different cv3 carbonaceous chondrites allende efremovka nwa 3118 and vigarano the primary phases forsterite al ti rich diopside spinel melilite and anorthite in each inclusion were analyzed in situ using high precision secondary ion mass spectrometry sims in all cases minerals with low al mg ratios all except anorthite yield well defined internal al mg isochrons with a range of initial 26al 27al ratios 26al 27al 0 ranging from 5 30 0 22 10 5 down to 4 17 0 43 10 5 anorthite in all cases is significantly disturbed relative to the isochrons defined by the other phases in the same cais and in several cases contains no resolved excesses of radiogenic 26mg 26mg even at 27al 24mg ratios greater than 1000 the fact that some fobs preserve 26al 27al 0 of 5 2 10 5 close to the canonical value of 5 23 0 13 10 5 inferred from bulk magnesium isotope measurements of cv cais b jacobsen et al 2008 demonstrates that fobs began forming very early contemporaneous with other more refractory cais the range of 26al 27al 0 values further shows that fobs continued to be reprocessed over 200 000 years of nebular history consistent with results obtained for other types of igneous cais in cv chondrites the absence of any correlation between of cai fob formation or reprocessing times with bulk composition or cai type means that there is no temporal evolutionary sequence between the diverse cai types the initial 26mg value in the most primitive fob sj101 is significantly lower than the canonical solar system value of 0 040 0 029

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

magnetic susceptibility of loess in china abstract the low field susceptibility of the loess deposits in the chinese loess plateau is due to both paramagnetic and ferromagnetic minerals paramagnetism can be seen in the less to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles are not as strongly developed as in the heavily weathered palaeosols frequency dependent susceptibility and minimum unblocking temperatures of low temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds this grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau are considered as strong evidence that the ultrafine magnetite is not of detrital aeolian origin but was formedin situ the pedogenetic processes are clearly related to palaeoclimatic changes therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2 5 ma since the palaeomagnetically dated beginning of loess sedimentation in china

holocene alluvial fan and terrace formation in the bowland fells northwest england in the bowland fells lancashire northwest england in the headwater valleys of the hodder river system is a suite of holocene fluvial landforms debris cones and alluvial fans at tributary junctions and river terraces along the main valleys post date late pleistocene forms and pre date the modern valley floor alluvial forms eight 14c dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of holocene erosion to be identified with debris cone fan deposition taking place after c 5400 bp but before c 1900 bp and again at c 900 bp some of the fans and cones are complex with deposits attributable to both phases others are simple and attributable only to the later phase in the headwaters an upper terrace at c 5400 bp pre dates the cones and a lower terrace is contemporaneous with the first debris cone phase lower downvalley the youngest of three terraces date from c 5000 bp or earlier indicating that the sequence is less complex downstream

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

the nature and origin of type b1 and b2 caal rich inclusions in the allende meteorite abstract the type b ca al rich inclusions in the allende carbonaceous chondrite form a continuous range from the mineralogically concentrically zoned b1 subtype to the unzoned b2 subtype these subtypes differ in i structure texture grain size and shape ii mineralogical proportions and compositions iii accessory mineralogy iv relative abundance of spinel framboids v rim layering vi major element chemistry and vii degree of secondary alteration these differences together with observations on the crystallization of synthetic melts suggest that the b1 inclusions crystallised relatively rapidly from molten parental material while b2 types crystallised relatively slowly close to the solidus from material that had not been completely melted the same data are used to construct an evaporative residue model for the origin of the parental type b materials in the model dust in the protosolar nebula was heated with removal of more volatile elements leaving completely melted type b1 residues at the highest temperatures and incompletely melted less highly evaporated type b2 residues at lower temperatures

late holocene environmental change in the howgill fells northwest england abstract new data from chapel beck in the southwest howgill fells combined with existing data support the identification of three phases of extensive hillslope gullying after 2200 between 1250 700 and after 500 cal bp examination of cumulative probability density function cpdf plots of the distribution of calibrated radiocarbon dates confirms the identification of these phases there are differences in the spatial distribution of geomorphic activity between these phases with the c 2200 1800 cal bp episode limited to the western howgill fells in comparison the 1250 700 and post 500 cal bp episodes are more widespread cross region phenomena and affected the more remote central fells pollen and geochemical data reveal several phases of increased human activity in these uplands with small scale temporary clearances during the late bronze age early iron age and more substantial clearances during the late iron age and romano british times 2300 1500 cal bp and these were followed by woodland expansion and decline in human activity during both the mid to late iron age and the period after the roman withdrawal from britain after 1500 cal bp the final substantial woodland clearances occurred from c 1100 900 cal bp after which there has been little woodland recovery a range of pollen sites across the howgill fells indicate that there is spatial variability in the level of human activity and impact iron age romano british woodland clearances appear to have affected the west of the region more than the remote central valleys whereas the later 1100 900 cal bp woodland reduction affected the entire region this pattern is similar to that identified from the geomorphology and demonstrates the importance of pollen sites that record local palaeo vegetation information and the significance of using a series of sites to explore intra regional variability in the vegetation history we suggest that human activity is a critical factor in mediating the late holocene geomorphic record but climate and particularly individual storms are the trigger mechanism responsible for erosion and incision on hillslopes and within the wider fluvial system palaeoclimate data humification and plant macrofossil from peat deposits at archer moss identify shifts to wetter conditions c 3100 2700 2400 1700 1300 1100 and after 650 cal bp and probably reflect increases in summer wetness of these the 2400 1700 1300 1100 and post 650 cal bp wetter phases coincide with increased geomorphic activity and perhaps encouraged incision on hillslopes rendered more susceptible to erosion by the activities of people

oxygen isotopic and chemical zoning of melilite crystals in a type a ca al rich inclusion of efremovka cv3 chondrite abstract different oxygen isotopic reservoirs have been recognized in the early solar system fluffy type a ca al rich inclusions cais are believed to be direct condensates from a solar nebular gas and therefore have acquired oxygen from the solar nebula oxygen isotopic and chemical compositions of melilite crystals in a type a cai from efremovka cv3 chondrite were measured to reveal the temporal variation in oxygen isotopic composition of surrounding nebular gas during cai formation the cai is constructed of two domains each of which has a core mantle structure reversely zoned melilite crystals were observed in both domains melilite crystals in one domain have a homogeneous 16o poor composition on the carbonaceous chondrite anhydrous mineral ccam line of 18o 5 10 which suggests that the domain was formed in a 16o poor oxygen isotope reservoir of the solar nebula in contrast melilite crystals in the other domain have continuous variations in oxygen isotopic composition from 16o rich 18o 40 to 16o poor 18o 0 along the ccam line the oxygen isotopic composition tends to be more 16o rich toward the domain rim which suggests that the domain was formed in a variable oxygen isotope reservoir of the solar nebula each domain of the type a cai has grown in distinct oxygen isotope reservoir of the solar nebula after the domain formation domains were accumulated together in the solar nebula to form a type a cai

heterogeneous distribution of 26al at the birth of the solar system evidence from refractory grains and inclusions we review recent results on o and mg isotope compositions of refractory grains corundum hibonite and calcium aluminum rich inclusions cais from unequilibrated ordinary and carbonaceous chondrites we show that these refractory objects originated in the presence of nebular gas enriched in 16o to varying degrees relative to the standard mean ocean water value the 17osmow value ranges from approximately 16 to 35 and recorded heterogeneous distribution of 26al in their formation region the inferred 26al 27al 0 ranges from approximately 6 5 10 5 to 2 10 6 there is no correlation between o and mg isotope compositions of the refractory objects 26al rich and 26al poor refractory objects have similar o isotope compositions we suggest that 26al was injected into the 26al poor collapsing protosolar molecular cloud core possibly by a wind from a neighboring massive star and was later homogenized in the protoplanetary disk by radial mixing possibly at the canonical value of 26al 27al ratio approximately 5 10 5 the 26al rich and 26al poor refractory grains and inclusions represent different generations of refractory objects which formed prior to and during the injection and homogenization of 26al thus the duration of formation of refractory grains and cais cannot be inferred from their 26al 26mg systematics and the canonical 26al 27al 0 does not represent the initial abundance of 26al in the solar system instead it may or may not represent the average abundance of 26al in the fully formed disk the latter depends on the formation time of cais with the canonical 26al 27al ratio relative to the timing of complete delivery of stellar 26al to the solar system and the degree of its subsequent homogenization in the disk the injection of material containing 26al resulted in no observable changes in o isotope composition of the solar system instead the variations in o isotope compositions between individual cais indicate that o isotope composition of the cai forming region varied because of coexisting of 16o rich and 16o poor nebular reservoirs gaseous and or solid at the birth of the solar system or because of rapid changes in the o isotope compositions of these reservoirs with time e g due to co self shielding in the disk

quantifying grain size distribution of pedogenic magnetic particles in chinese loess and its significance for pedogenesis quaternary glacial interglacial cycles have been imprinted on the chinese loess paleosol sequences through pedogenesis in order to accurately decode the paleoclimatic signals carried by these pedogenic particles it is essential to quantify the pedogenically produced magnetic particles in terms of mineralogy as well as grain size distribution gsd to date the gsd has not been accurately determined because of the dearth of available means for analyzing extremely fine grained nanometer scale pedogenic magnetic particles using low temperature techniques we systematically investigated the temperature dependency of fd defined as 1hz 10hz where 1hz and 10hz are ac magnetic susceptibility measured at 1 and 10 hz respectively from two characteristic loess profiles one located at the western chinese loess plateau and the other in the central plateau on the basis of neel theory for a shape anisotropy dominant grain and experimental analysis at low temperatures a quantitative gsd for pedogenic particles in chinese loess paleosols was constructed we found that the dominant magnetic grain size lies just above the superparamagnetic single domain threshold 20 25 nm and that the gsd is almost independent of the degree of pedogenesis this observation agrees well with other constraints from previous studies this new gsd model improves our understanding of the pedogenic processes in chinese loess enabling further explicit linkage of environmental magnetism to paleoclimate changes

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

age limit and age underestimation using different osl signals from lacustrine quartz and polymineral fine grains as part of a systematic palaeohydrological reconstruction of lake level fluctuations during the last glacial maximum a transect of cores from ancient lake xinias in centra greece has already been studied with respect to pollen sediment and mineral magnetic analyses the chronology was based on c 14 ams dating of terrestrial plant macrofossil remains from peat and clayey peat palaeogeog palaeoclimatol palaeoecol 158 2000 65 this site thus provides an opportunity for the comparison of fine grain optically stimulated luminescence osl ages of water lain sediments with an independent chronology we present here infrared ir post ir blue and blue osl characteristics of the fine grain sediments from lake xinias and a preliminary comparison with independent ages the equivalent doses based on the ir results are about 40 of those based on post ir blue stimulation which in turn are 10 15 below those based on quartz osl we discuss the ages derived from the 3 signals in terms of the independent chronology and draw conclusions about initial bleaching of the quartz and feldspar components and the reliability of the post ir blue signal as a chronometer c 2003 elsevier science ltd all rights reserved less

holocene environmental reconstruction of sediment source linkages at crummock water english lake district based on magnetic measurements to reconstruct lateglacial and holocene environmental changes in the british uplands two c 5 8 m long sediment cores from crummock water nw england together with several hundred soil samples from the crummock water catchment were studied using magnetic techniques optically stimulated luminescence osl dating using fine silt quartz and 14c dating of terrestrial plant macrofossils were used to establish a chronology for the lake sediments a good agreement between optical and 14c ages indicates first that the osl dating method can be used to date lake sediments in the british isles second that macrofossil based 14c dating can be used to avoid the problem of old carbon error associated with bulk sample 14c dating of lake sediments and third that the established chronology is robust the lake sediment magnetic properties indicate a series of changes in sediment composition during the holocene which correlate well with sediment lithology water content and weight loss on ignition the first change corresponds to the lateglacial postglacial climatic shift at around 11400 years ago the subsequent suite of changes corresponds to a probable regional onset of human activity at 2000 bc and particularly to the intensification of human activity at around ad 900 a comparison of the lake sediment magnetic properties and those of the catchment soils shows a clear linkage for the lateglacial period and for the period after ad 900 in contrast detailed magnetic measurements of the early through mid holocene sediments suggest that their magnetic properties are dominated by bacterial magnetosomes

26al 26mg isotope systematics of the first solids in the early solar system high precision bulk aluminum magnesium isotope measurements of calcium aluminum rich inclusions cais from cv carbonaceous chondrites in several laboratories define a bulk 26al 26mg isochron with an inferred initial 26al 27al ratio of approximately 5 25 10 5 named the canonical ratio nonigneous cv cais yield well defined internal 26al 26mg isochrons consistent with the canonical value these observations indicate that the canonical 26al 27al ratio records initial al mg fractionation by evaporation and condensation in the cv cai forming region the internal isochrons of igneous cv cais show a range of inferred initial 26al 27al ratios 4 2 5 2 10 5 indicating that cai melting continued for at least 0 2 ma after formation of their precursors a similar range of initial 26al 27al ratios is also obtained from the internal isochrons of many cais igneous and nonigneous in other groups of carbonaceous chondrites some cais and refractory grains corundum and hibonite from unmetamorphosed or weakly metamorphosed chondrites including cvs are significantly depleted in 26al at least some of these refractory objects may have formed prior to injection of 26al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk bulk aluminum and magnesium isotope measurements of various types of chondrites plot along the bulk cv cai isochron suggesting homogeneous distribution of 26al and magnesium isotopes in the protoplanetary disk after an epoch of cai formation the inferred initial 26al 27al ratios of chondrules indicate that most chondrules formed 1 3 ma after cais with the canonical 26al 27al ratio

infra red stimulated luminescence dating of holocene reworked silty sediments abstract infra red stimulated luminescence irsl ages are reported for holocene colluvial lacustrine and alluvial sediments and late glacial loess for colluvial sediments irsl ages concur with independent ages age overestimation occur in the case of very poorly bleached sediments such as young less than 2000 years floodloams for which a high suspended sediment load was deduced from sedimentation rates and actually observed floods age underestimates are observed for late glacial loess probably due to inadequate preheat procedures

bacterial magnetite in swedish varved lake sediments a potential bio marker of environmental change abstract detailed mineral magnetic measurements were carried out on three varved lake sediment sequences in sweden which extend to ca 7000 bc the comparison of the magnetic properties of the organic rich varved lake sediments with their respective catchment materials indicates that the magnetic properties of the sediments are dominated by relatively high concentrations of single domain magnetite magnetosomes produced by magnetotactic bacteria the dimictic nature of the lakes which help form and preserve the varves due to the weakly oxic or suboxic environment also appear to be suitable for a high degree of magnetosome preservation the concentration of the magnetosomes in two of the sequences as determined by mass specific magnetic measurements exhibits a positive linear relationship with the total organic carbon content and suggests that magnetic remanence measurements reflect lake productivity via processes of organic matter accumulation and decomposition further research should focus on the potential to use the fossil magnetosomes as proxy climate environmental change indicators and as recorders of geomagnetic field variations and behaviour

catchment hydro geomorphological responses to environmental change in the southern uplands of scotland lake sediment and geomorphic evidence from the loch of the lowes st mary s loch basin in the central southern uplands of scotland provide a multiproxy reconstruction of changing sediment availability and transmission through the catchment interrogation of magnetic geochemical and grain size parameters for lake and catchment materials suggests it is possible to identify independent proxies that reflect both supply availability and discharge capacity controls on the sediment signal chronological control for the lake sediment record is proposed by linking a 210pb 137cs chronology for the last c 120 yr to an age depth profile based on proposed temporal correlations between cyclic hirm lf variability and the north atlantic oscillation geochronological studies on debris cones and alluvial fans yield evidence for episodic hillslope gullying 2000 0 bc with more extensive region wide slope instability ad 700 900 1100 1300 and after ad 1450 1550 and gully stabilization over the last 150 years the latter two episodes coincide with the lake sediment evidence for increased sediment supply from ad 1600 declining after ad 1870 the capacity related lake proxies appear to identify phases of increased flooding ad 1625 1650 1680 1700 1730 1760 1800 1815 1850 1880 1910 1930 1960 1970 and possibly the 1990s close correspondence between the sediment flood archive and historical records of flooding in scotland suggests that lake catchment systems of this type have the potential to yield valuable information on past hydrological response

testing a cellular modelling approach to simulating late holocene sediment and water transfer from catchment to lake in the french alps since 1826 this paper describes the application of a hydrogeomorphological numerical model caesar to simulate at hourly time steps changes in the hydrological and sediment regime of the petit lac d annecy catch ment the outputs of the model were validated in three ways in the short term 5 years water discharge out puts were compared against observed instrumental data over the longer term modelled sediment discharge ad 1825 2005 was compared with proxies for detrital sediment influx environmental magnetism and accumu lation rates discerned from a 210 pb chronology for the lake sediments finally spatial validation of the modelled erosion and deposition of sediment was undertaken by comparison with a field and remotely sensed survey of catchment geomorphology the results suggest that while minor perturbations in forest cover during the last 180 years have partially conditioned the response of the sediment system the bulk of modelled sediment discharge and particularly the peaks in sediment discharge were controlled by flood duration and magnitude which in turn is driven by precipitation storms floods and snowmelt basin geometry and geomorphology of each sub catchment ire and tamie were also important in producing differences in the modelled sediment discharge in essence these differences were a function of sediment accommodation space and the ability of each system to store and release sediments modelled sediment discharge and para lake sediments display similar histories and thus are both interpreted as reflecting variations in detrital sediment supply intriguingly the style of mod elled sediment discharge from the ire a confined mountain torrent displays a greater similarity to and perhaps dominates the lake sediment record these results provide partial validation of the caesar model and indi cate that perhaps in the future it may be used as an exploratory and predictive tool in determining the impact of changes in climate meteorology and land use on lake catchment systems

fluffy type a ca al rich inclusions in the allende meteorite abstract allende fluffy type a s fta s are a distinct sub group of ca al rich inclusions whose primary mineral assemblage consists of al rich melilite ak 0 33 spinel that is commonly very v rich perovskite and frequently hibonite some contain relatively coarse grained melilite up to 1 5 mm that is intensely kink banded and commonly reversely zoned hibonite and v rich spinel others contain much finer grained and strain free melilite 50 m and have not been found to contain hibonite or v rich spinel some fta s contain both coarser and finer grained melilite and textural relationships indicate that the latter is replacing the former fta s are characterized by extremely irregular shapes and 60 75 volume per cent of fine grained secondary alteration products many are aggregates of innumerable nodules each of which is surrounded by a wark lovering type rim sequence these nodules are frequently separated from one another by matrix like clastic rim material other fta s do not have nodular structure structural and mineralogical characteristics of their wark lovering rims suggest that fta s did not achieve their shapes by deformation of a liquid or a hot plastic solid in contrast to those in type b inclusions formation of reverse zoning in the coarser grained melilite crystals in fta s cannot be understood in terms of crystallization from a liquid but are readily explainable by condensation from a solar nebular gas during a period of falling pressure further evidence against a liquid origin is the wide range of spinel compositions within individual coarser grained fta s the fact that the reversely zoned melilite crystals cannot have been produced in any kind of sublimation or distillation process precludes formation of these inclusions as volatilization residues fta s are aggregates in some of which are preserved vapor solid condensate grains that formed at high temperature in the solar nebula

the detection of bacterial magnetite in recent sediments of lake chiemsee southern germany the sediments of lake chiemsee located in the alpine foreland in southern germany host a variety of magnetotactic bacteria mtb which contain intracellular crystals of magnetite arranged in linear chains to detect bacterial magnetite in the carbonate dominated surface sediments and further quantify its contribution to the magnetic signal of the sediments we conducted detailed rock magnetic measurements as well as complimentary non magnetic analyses electron microscopy powder x ray diffraction and sediment pore water analysis our results demonstrate that biogenic single domain magnetite characterized by bullet and truncated hexagonal prismatic shapes is the dominant ferrimagnetic component in the topmost few centimetres of the sediment the changes of magnetic properties with depth are due to the occurrence of live mtb and the downward increasing dissolution of biogenic magnetite moreover the ratios of remanence loss on warming through the verwey transition after field cooling and zero field cooling of saturation isothermal remanence dfc dzfc were determined as 1 47 and 1 25 for freeze dried and air dried sediment samples containing mtb respectively these low ratios suggest that the bacterial magnetite chains were disrupted to a large extent and or that the bacterial magnetosomes might have undergone partial

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

plagioclase rich inclusions in carbonaceous chondrite meteorites liquid condensates plagioclase rich inclusions in carbonaceous chondrites are of two types 1 mm cm sized ca al rich inclusions cais with 30 60 vol anorthite and up to 35 vol each of ti al pyroxene tpx melilite and spinel and 2 smaller 3 mm ca chondrules similar to those found in ordinary chondrites containing more sodic plagioclase pyroxene olivine and spinel the cais which were formerly named type i and thought to be intermediate between type a and type b cais are shown to be an independent type renamed type c with distinctive chemical and mineralogical compositions type c cais have group i or group ii trace element patterns low initial 26al27al ratios of 5 10 6 typical ak 35 55 melilite tpx with 2 12 tio2 and opaque grains osirrumopt alloy nuggets and fremdlinge smaller than 10 m the textures sequence of crystallization and concentric zonation indicate that they crystallized from melt droplets the texture of the anorthite ranges from coarse laths to a fine grained groundmass reflecting increasing retardation of its nucleation the few cais with the coarse laths cooled slowly 2 5 h from below the liquidus but the majority cooled faster from completely molten material as the elemental abundances in type c s are dominated by volatility the melts were not formed by planetary magmatic processes evaporative residues and remelted solid condensates are also ruled out because the compositions of naturally occurring experimentally produced and thermodynamically calculated residues and solid condensates differ from those of type c cais type c cais have compositions similar to those calculated for liquid condensates under high solar gas pressure 1 atm or in dust rich environments and are probably liquid condensates the few type c cais that crystallized from incompletely molten materials may have been reheated liquid condensates or mixed liquidsolid condensates

internal 26al 26mg isotope systematics of a type b cai remelting of refractory precursor solids high precision sims 26 al 26 mg isotope analyses were performed for a pristine type b1 cai leoville 3535 1 on multiple mineral phases that include aluminum rich zoned melilite mantle ak20 ak60 magnesium rich melilite ak70 fassaite spinel and anorthite in the core the data yield a well defined internal isochron with an inferred initial 26 al 27 al ratio of 5 002 0 065 10 5 which is lower than those of bulk cais and pristine fine grained cais assuming homogeneous dis tribution of 26 al in the early solar system leoville 3535 1 formed 50 ka after the time corresponding to the bulk cai iso chron one anorthite analysis near the grain boundary adjacent to melilite shows sub lm scale heterogeneous magnesium distribution though the 26 al 26 mg data plot on the isochron regression thus the internal 26 al 26 mg system of the cai remained closed since the last melting event that crystallized anorthite high precision magnesium isotope analyses of magnesium rich minerals fassaite magnesium rich melilite and spinel show a small amount of scatter from the regression line 0 1 beyond analytical uncertainties most spinel and some fassa ite data are systematically displaced below and above the regression line respectively it is likely that spinel remained unmelted at the time of the last melting event while fassaite and anorthite crystallized from a partial melt the regression line made by fassaite and anorthite data shows an initial 26 al 27 al ratio indistinguishable from that using all data mass dependent fractionation of magnesium isotopes in spinel is the same as those in melilite and fassaite d 25 mg 5 indicating that magnesium isotope fractionation presumably from evaporative magnesium loss predated the last melting event thus a majority of the cai appears to have escaped magnesium isotope exchange with nebular gas during the last melting event except for the outer rim of the melilite mantle that shows slightly lower d 25 mg values the 26 al 26 mg systematics of this leoville type b cai suggest it experienced a final melting event at 50 ka after the initial al mg fractionation event this may correspond to melting during the active protostar stage known as class i during which sporadic high temperature heating events repeatedly affected refractory solids in the solar nebula 2012 elsevier ltd all rights reserved

the superparamagnetism of yucca mountain tuff yucca mountain tuff contains small titanomagnetite grains with narrow size distributions in the superparamagnetic range schlinger et al 1988 magnetic measurements on three samples comprising hysteresis loops at low and ambient temperatures acquisition and demagnetization of isothermal remanent magnetization thermal demagnetization of the saturation remanence and of a low temperature thermoremanence and frequency and temperature dependent susceptibilities allow evaluation of the magnetic properties in terms of neel s 1949 single domain theory precise grain volume distributions have been obtained by applying the blocking volume concept to thermal demagnetization results in contrast an attempt to derive mean particle volumes by fitting a langevin curve to the room temperature magnetization curves fails probably because the precondition for the langevin function kv kt 1 is not met it is only for the sample with the smallest grains and in weak fields 20 mt that a langevin fit provides a reasonable volume estimate there is good agreement between the experimental results and the calculated frequency and temperature dependence of susceptibility thus verifying that neel s theory is sufficient for the magnetic description of single domain assemblages spanning the superparamagnetic stable single domain boundary however some deviations between modeled and measured susceptibilities exist and the physical causes may include size dependent anisotropy nonuniform magnetizations and also an uncertain preexponential time constant 0 while 0 10 11 s gives the best fit for the sample with the largest grains 0 10 9 s is more reasonable for the others thus 0 may indeed be size and temperature dependent as predicted by brown 1959 the commonly cited parameter fd frequency dependence of susceptibility reaches 30 at room temperature rt for one sample with a blocking temperatures just below rt while fd 0 at rt for a superparamagnetic sample with smaller grains these results thus exemplify that fd is not limited to 15 as a number of studies suggest and that fd 0 must not be taken to imply the absence of superparamagnetic grains

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

high resolution seismic imaging of a younger dryas and holocene mass movement complex in glacial lake windermere uk the stratigraphy and sedimentological processes operating over the last 15 000 years within glacial lake windermere uk at the mouth of cunsey beck were imaged by a decimetre resolution seismic reflection survey a complex of fifteen mass movement deposits was identified as contemporaneous with the younger dryas and two within the overlying holocene drape the high vertical resolution and dense grid of profiles allowed pseudo three dimensional mapping of individual events along with the determination of their relative temporal relationships the size of the mass wasting deposits has been estimated to range between 2100 and 100 000 m3 the geometry structure and relationship to the existing stratigraphy suggest a rapid emplacement of the younger dryas mass movement deposits facilitated by climatic changes making subaqueous slopes unstable with possible triggering by seismic activity morphometric parameters such as volume and planar surface area indicate a greater mobility of the younger dryas mass movement deposits compared to the holocene events the sediments of all imaged mass movement deposits are believed to originate from the slope deposits of the lake the age of two holocene mass movement deposits triggered by flooding or terrestrial debris flows is estimated to be 2400 and 4400 years bp

the formation of rims on calcium aluminum rich inclusions step i flash heating abstract wark lovering rims of six calcium aluminum rich inclusions cais representing the main cai types and groups in allende efremovka and vigarano were microsurgically separated and analysed by neutron activation analysis naa all the rims have similar 4x enrichments relative to the interiors of highly refractory lithophile and siderophile elements the naa results are confirmed by ion microprobe and scanning electron microscope sem analyses of rim perovskites and rim metal grains less refractory eu yb v sr ca and ni are less enriched in the rims the refractory element patterns in the rims parallel the patterns in the outer parts of the cais in particular the rims on type b1 cais have the igneously fractionated rare earth element ree pattern of the melilite mantle below the rim and not the ree pattern of the bulk cai proving that the refractory elements in the rims were derived from the outer mantle and were not condensates onto the cais the refractory elements were enriched in an al2o3 rich residue 50 m thick after the most volatile 80 of the outermost 200 m of each cai had been volatilized including much mg si and ca some volatilization occurred below the rim and created refractory partial melts that crystallized hibonite and gehlenitic melilite the required flash heating probably exceeded 2000 c but for only a few seconds in order to melt only the outer cai and to unselectively volatilize slow diffusing o isotopes which show no mass fractionation in the rim the volatilization did however produce heavy mass fractionated mg in rims in some cais this was later obscured when normal mg diffused in from accreted olivine grains at relatively high temperature not the lower temperature meteorite metamorphism and created the 50 m set of monomineralic rim layers of pyroxene melilite and spinel

hillslope gullying in the solway firth morecambe bay region great britain responses to human impact and or climatic deterioration abstract in the solway firth morecambe bay region of great britain there is evidence for heightened hillslope instability during the late holocene after 3000 cal bp little or no hillslope geomorphic activity has been identified occurring during the early holocene but there is abundant evidence for late holocene hillslope erosion gullying and associated alluvial fan and valley floor deposition interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500 2200 1300 1000 1000 800 and 500 cal bp both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds and palaeoecological data on climatic change bog surface wetness and human impact pollen together with archaeological and documentary evidence of landscape history provide a context for addressing the causes of late holocene geomorphic instability high magnitude storm events are the primary agent responsible for gully incision but neither such events nor cooler wetter climatic episodes appear to have produced gully systems in the region before 3000 cal bp increased gullying after 2500 2200 cal bp coincides with population expansion during iron age and romano british times the widespread and extensive gullying after 1300 1000 cal bp and after 1000 800 cal bp coincides with periods of population expansion and a growing rural economy identified during norse times 9 10th centuries ad and during the medieval period 12 13th centuries ad these periods were separated by a downturn associated with the harrying of the north ad 1069 to 1070 the gullying episode after 500 cal bp also coincides with increased anthropogenic pressure on the uplands with population growth and agricultural expansion after ad 1500 following 150 years of malaise caused by livestock and human the black death plagues poor harvests and conflicts on the scottish english border the increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late holocene and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events in particular the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion and the hillslope gullying record in the region therefore contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape

evidence for changes in holocene sediment flux in semer water and raydale north yorkshire uk article i nfo we present preliminary results from studies carried out in the lake and extensively gullied drainage basin of semer water in north yorkshire england the results obtained so far are limited by physical problems encountered during coring at the present day lake the complex nature of the sedimentary infill upstream in raydale and difficulties experienced in establishing a continuous holocene chronology for the site both magnetic measurements and organic geochemical analyses show that the bulk of the sediment sampled in semer water and in the alluvial area of raydale just upstream is derived from the catchment although in some cases the allochthonous magnetic signature is overprinted by contributions from bacterial magnetosomes growing in the lake or surface sediments significant traces of polyaromatic hydrocarbons pahs in sediments contemporary with the mesolithic occupation of the pennines reinforce evidence from elsewhere for the use of fire at this time several lines of evidence identify a mid holocene period of reduced allochthonous input rapid sediment accumulation during the period between 4200 and 3500 cal bp points to the likelihood of increased erosion during the bronze age geomorphological studies point to periods of alternating dissection and aggradation in the catchment during the last 2000 years the record presented gives some indication of the potential for uniting geomorphological palaeolimnological and organic geochemical research in an effort to trace the holocene evolution of a complex highly eroded system 2008 elsevier b v all rights reserved

oxygen isotopic composition of the solar nebula gas inferred from high precision isotope imaging of melilite crystals in an allende cai high precision isotope imaging analyses of reversely zoned melilite crystals in the gehlenitic mantle of type a cai on01 of the allende carbonaceous chondrite reveal that there are four types of oxygen isotopic distributions within melilite single crystals 1 uniform depletion of 16o 18o 10 2 uniform enrichment of 16o 18o 40 3 variations in isotopic composition from 16o poor core to 16o rich rim 18o 10 to 30 20 to 45 and 10 to 35 with decreasing akermanite content and 4 16o poor composition 18o 10 along the crystal rim hibonite spinel and perovskite grains are 16o rich 18o 45 and adjoin 16o poor melilites gas solid or gas melt isotope exchange in the nebula is inconsistent with both the distinct oxygen isotopic compositions among the minerals and the reverse zoning of melilite fluid rock interaction on the parent body resulted in 16o poor compositions of limited areas near holes cracks or secondary phases such as anorthite or grossular we conclude that reversely zoned melilites mostly preserve the primary oxygen isotopic composition of either 16o enriched or 16o depleted gas from which they were condensed the correlation between oxygen isotopic composition and akermanite content may indicate that oxygen isotopes of the solar nebula gas changed from 16o poor to 16o rich during melilite crystal growth we suggest that the radial excursions of the inner edge of the protoplanetary disk gas simultaneously resulted in both the reverse zoning and oxygen isotopic variation of melilite due to mixing of 16o poor disk gas and 16o rich coronal gas gas condensates aggregated to form the gehlenite mantle of the type a cai on01

the geomorphological impact of loch lomond younger dryas stadial plateau icefields in the central lake district northwest england detailed geomorphological mapping has revealed evidence for the development of plateau icefields in the central fells of the english lake district during the loch lomond younger dryas stadial ca 12 9 11 5 ka the largest plateau icefield system which covered an area of approximately 55 km2 including outlet glaciers was centred on high raise to the west smaller plateau icefields developed on grey knotts brandreth and dale head covering areas of 7 km2 and 3 km2 respectively the geomorphological impact of these plateau icefields appears to have been minimal on the summits where the survival of blockfields and other frost weathered debris mostly peat covered implies the existence of at least patches of protective cold based ice ice moulded bedrock at some plateau edges however documents a transition to wet based erosive conditions prominent moraine systems were produced by outlet glaciers which descended into the surrounding valleys where their margins became sediment traps for supraglacial debris and inwash in some valleys ice marginal moraines record successive positions of outlet glaciers which actively back wasted towards their plateau source this interpretation differs from that of previous workers who assumed an alpine style of glaciation with reconstructed glaciers emanating from corries and valley heads it is likely that plateau icefields were more common at this time in upland britain than hitherto has been appreciated

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

oxygen isotopic zoning of reversely zoned melilite crystals in a fluffy type a ca al rich inclusions from the vigarano meteorite the oxygen isotopic microdistributions within melilite measured using in situ secondary ion mass spectrometry correspond to the chemical zoning profiles in single melilite crystals of a fluffy type a ca al rich inclusions cais of reduced cv3 vigarano meteorite the melilite crystals show chemical reverse zoning within an individual single crystal from the akermanite rich core to the akermanite poor rim the composition changes continuously with the crystal growth the zoning structures suggest that the melilite grew in a hot nebular gas by condensation with decreasing pressure the oxygen isotopic composition of melilite also changes continuously from 16o poor to 16o rich with the crystal growth these observations suggest that the melilite condensation proceeded with change consistent with an astrophysical setting around the inner edge of a protoplanetary disk where both 16o rich solar coronal gas and 16o poor dense protoplanetary disk gas could coexist fluffy type a cais could have been formed around the inner edge of the protoplanetary disk surrounding the early sun

well resolved variations in the formation ages for ca al rich inclusions in the early solar system recent whole rock magnesium isotopic data for calcium aluminum rich inclusions cais in chondrite meteorites indicate that the primary nebular fractionation of aluminum from magnesium probably by condensation occurred within 20 000 years at 4 567 ga however high precision multicollector ion microprobe data for diverse cais from vigarano cv3 yield internal isochrons with a clearly resolved spread in initial 26al 27al meaning that cais formed and were reprocessed over a much longer time span primitive unmelted cais have a consistent value of 5 2 0 1 10 5 melted cais range from 5 17 10 5 to 4 24 10 5 and one single object with a complex multistage history has an internal range of 26al 27al 4 77 2 77 10 5 the entire range corresponds to an age span of 0 7 ma thus not all cais formed at time zero and only the most primitive cais should be used as benchmarks for earliest solar system chronology

the viscosity of shoshonitic melts vulcanello peninsula aeolian islands italy insight on the magma ascent in dikes abstract the viscosity of shoshonitic melts and glasses from vulcanello peninsula vulcano island italy was experimentally determined at temperatures between 733 k and 1673 k the water content of the melts varies from 0 03 to 4 75 wt h 2 o the micropenetration technique was employed at ambient pressure in the high viscosity range 10 9 10 12 pa s falling sphere s experiments were performed at 500 and 2000 mpa in the low viscosity range 10 0 5 10 3 pa s results show a decrease of about 2 orders of magnitude in viscosity if 3 wt of water is added to the dry melt at 1300 k at high temperature the viscosity of vulcanello melts is intermediate between that of andesitic and basaltic melts in contrast at low temperatures 1050 k the shoshonitic melt is characterized by a lower viscosity with respect to the two previous melts the general viscosity models of giordano et al giordano d mangiacapra a potuzak m russell j k romano c dingwell d b di muro a 2006 an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids chemical geology 229 42 56 for dry silicate melts is in good agreement with the experimental data in the high temperature range less than 0 3 log units but shows significant differences in the low temperature range up to 1 1 log units the calculation model for hydrous silicate melts from huy and zhang huy h zhang y 2007 toward a general viscosity equation for natural anhydrous and hydrous silicate melts geochimica et cosmochimica acta 71 403 416 reproduces the new viscosity data in the high temperature range within 0 6 log units but shows as well large discrepancies in the low t range for hydrous melts deviations up to 2 log units thus we propose a specific calculation model to predict the viscosity of the shoshonitic melts as a function of temperature and water content this model reproduces the experimental data 24 measurements with a 1 standard deviation of 0 17 log units the viscosity data are used to constrain the ascent velocity of shoshonitic magmas from vulcanello within dikes using petrological data temperature and crystal content of the magma and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate the time scale for the ascent of magma from the main reservoir to the surface results show time scales in the order of hours to few days we conclude that the rapid ascent of poorly evolved melts from moho depths should be taken into account for the hazard assessment of vulcano island

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

optical dating of annually laminated lake sediments a test case from holzmaar germany abstract we present results of an optical dating feasibility study for annually laminated varved lake sediments the fine silt sized clastic fraction of the sediments was extracted stimulated with infrared and the 410 nm emission was detected a multiple aliquot additive dose protocol in combination with a subtraction technique was used for the equivalent dose determinations results are promising only for sediments with high amounts of clastic components for sediments with a high organic component results are inaccurate perhaps due to problems in dose rate calculation we speculate that besides the low concentrations of radio nuclides and disequilibria in the u series dose rate determination procedures are inaccurate for sediments with high contents of biogenic silica sediment compaction seems to account for minor effects only

a once molten coarse grained ca rich inclusion in allende a compact spheroidal type b inclusion in allende contains melilite laths that project radially inward from the inclusion edge which show interference growth textures the combined textural and chemical features of this object cannot be explained by independent vapor solid condensation of grains in space followed by random aggregation of these grains into an inclusion rather it probably formed from a once molten droplet that crystallized in response to radiative cooling from its outer surface the crystallization sequence in this and another similar inclusion in which oxygen isotopes have been measured is melilite spinel anorthite fassaite this sequence supports the idea that oxygen isotopic heterogeneities in coarse grained inclusions were formed after complete solidification of these objects by partial exchange with a less16o rich gas and not during or before a melting event

182hf 182w age dating of a 26al poor inclusion and implications for the origin of short lived radioisotopes in the early solar system refractory inclusions calcium aluminum rich inclusions cais represent the oldest solar system solids and provide information regarding the formation of the sun and its protoplanetary disk cais contain evidence of now extinct short lived radioisotopes e g 26al 41ca and 182hf synthesized in one or multiple stars and added to the protosolar molecular cloud before or during its collapse understanding how and when short lived radioisotopes were added to the solar system is necessary to assess their validity as chronometers and constrain the birthplace of the sun whereas most cais formed with the canonical abundance of 26al corresponding to 26al 27al of 5 10 5 rare cais with fractionation and unidentified nuclear isotope effects fun cais record nucleosynthetic isotopic heterogeneity and 26al 27al of 5 10 6 possibly reflecting their formation before canonical cais thus fun cais may provide a unique window into the earliest solar system including the origin of short lived radioisotopes however their chronology is unknown using the 182hf 182w chronometer we show that a fun cai recording a condensation origin from a solar gas formed coevally with canonical cais but with 26al 27al of 3 10 6 the decoupling between 182hf and 26al requires distinct stellar origins steady state galactic stellar nucleosynthesis for 182hf and late stage contamination of the protosolar molecular cloud by a massive star s for 26al admixing of stellar derived 26al to the protoplanetary disk occurred during the epoch of cai formation and therefore the 26al 26mg systematics of cais cannot be used to define their formation interval in contrast our results support 182hf homogeneity and chronological significance of the 182hf 182w clock

flood stratigraphies in lake sediments a review abstract records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer term context than is available from gauged river flow and historical records recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high magnitude floods over these longer timescales abyssal lake sediments can record past floods in the form of coarser grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake this paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection the processes of sediment movement from watershed to lake bed are complex meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear stratigraphical palaeoflood records are all affected to some degree by catchment conditioning fluvial connectivity sequencing of high flows delta dynamics as well as within lake processes including river plume dispersal sediment focussing re suspension and trapping efficiency with regard to analytical techniques the potential for direct e g laser granulometry and indirect e g geochemical elemental ratios measurements of particle size to reflect variations in river discharge is confirmed we recommend care when interpreting fine resolution geochemical data acquired via micro scale x ray fluorescence xrf core scanning due to variable down core water and organic matter content altering x ray attenuation we also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and or geochemistry with stream power where these processes are considered and suitable dating control is obtained discrete historical floods can be identified and characterised using palaeolimnological evidence we outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records we also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers to demonstrate their utility we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records these were achieved by consistently applying site validated direct and proxy grain size measurements well established chronologies validation of the proxy process interpretation and calibration of the palaeoflood record against instrumental or historical records

variations in initial 26al 27al ratios among fluffy type a ca al rich inclusions from reduced cv chondrites abstract al mg mineral isochrons of three ca al rich inclusions cais that formed primarily by condensation one fine grained spinel rich inclusion and two fluffy type a cais from the reduced cv chondrites efremovka and vigarano were obtained by in situ al mg isotope measurements using secondary ion mass spectrometry the slope of the isochron obtained for the fine grained spinel rich inclusion gives an initial 26al 27al value 26al 27al 0 of 5 19 0 17 10 5 this is essentially identical to the solar system initial 26al 27al determined by whole rock al mg isochron studies for cais in cv chondrites in contrast the isochron slopes for the two fluffy type a cais from their al mg mineral isochrons 4 703 0 082 10 5 and 4 393 0 084 10 5 are significantly lower than the solar system initial value the range of 26al 27al 0 values of the three cais from 5 19 0 17 to 4 393 0 084 10 5 corresponds to a formation age spread of 0 17 0 04 myr this formation age spread is similar to that of igneous cais from cv chondrites the data suggest that condensation and melting of minerals occurred in the hot nebular gas contemporaneously for 0 2 myr at the very beginning of our solar system if 26al was distributed homogeneously in the cai forming region alternatively the observed variations in 26al 27al 0 among fluffy type a cais would also raise a possibility of heterogeneous distributions of 26al in the forming region