observations of temperature inversions over central arctic sea ice in summer we analysed high resolution tethersonde sounding data from the drifting ice station tara in the arctic ocean in april to august 2007 to a better understand the multiple processes affecting the generation and properties of arctic air temperature inversions and b to obtain insight into the vertical structure of the atmospheric boundary layer during the exceptional spring and summer 2007 which resulted in a historically low sea ice extent a total of 95 profiles up to the height of 2 km were measured on 39 days inversions were present in 88 of the data 13 of them being surface based compared to winter the occurrence and properties of summer inversions depended much less on surface net radiation and were mainly controlled by the surface melt and warm air advection inversions occuring during snow ice melt were located at low altitudes frequently based at the surface and were often as strong as winter inversions reported in previous studies in general the tara inversions were shallow and the deepest ones were observed when clouds occurred inside or partly above the inversion layer inversions were strongest under clear skies or in cases when the cloud top was above the inversion base related to cases of strong warm air advection up to 35 k day 1 in july exceptionally high temperatures around the inversion top caused maximum inversion strengths up to 13 k inversions of this magnitude at this time of the year have been rarely documented previously

a multivariate mixing model for identifying sediment source from magnetic measurements a sequential method for quantitative identification of sediment source components based on magnetic measurements has been developed and tested for sediments from the rhode river maryland simulated mixing tests and multiple regression were employed to establish numerical relationships between source component proportions and the magnetic measurements of mixtures on the basis of these multivariate mixing models source components of three estuarine sediment cores were estimated by linear programming the results strongly support the previous studies on this catchment which indicated a dramatic change in sediment source some 150 to 200 yr ago quantitative calculations are more useful and informative than purely qualitative descriptions

sediment yields and sources in a welsh upland lake catchment during the past 800 years estimates of suspended sediment yield over the past 800 years have been derived from a whole basin study of lake sediments in llyn geirionydd north wales magnetic and physical sediment properties were used to correlate a suite of cores to a master chronology based on 210pb and 14c dates the sources of sediment within the catchment were identified by comparing the magnetic and heavy metal properties of sediments soils and stream sediments mean suspended sediment yields range from 6 to 18 t km 2 yr 1 with high yields in the periods 1765 1830 and 1903 1985 corresponding to mining activities in the catchment the impact of earlier deforestation agricultural expansion or climatic change on sediment yields is low although there is evidence that agricultural activities increased levels of peak stream discharge afforestation in the 20th century does not appear to have significantly increased sediment yield sediment sources have remained fairly constant through time they appear to be widespread and dominated by stream channel sides rather than point sources except during the mining phases when spoil material has dominated the sediment load sediment loads to the lake today are still dominated by sediment derived from unvegetated spoil heaps

modular construction of early ediacaran complex life forms newly discovered exceptionally preserved soft bodied fossils near spaniard9s bay in eastern newfoundland exhibit features not previously described from ediacaran terminal neoproterozoic fossils all of the spaniard9s bay taxa were composed of similar architectural elements centimeter scale frondlets exhibiting three orders of fracticality in branching frondlets were combined as modules atop semi rigid organic skeletons to form a wide array of larger constructions including frondose and plumose structures this architecture and construction define the rangeomorphs a biological clade that dominated the mistaken point assemblage 575 to 560 million years ago but does not appear to be ancestral to any phanerozoic or modern organisms

ediacaran δ13c chemostratigraphy of south china abstract we report new 13 c chemostratigraphic data of the ediacaran system in south china using litho and biostratigraphic markers as independent calibrators we combine new and previously published 13 c data to construct a composite 13 c profile for the ediacaran system in south china the composite curve shows in chronostratigraphic order 1 a negative 13 c excursion en1 in the doushantuo cap carbonate that overlies the ghaub age nantuo diamictite 2 a pronounced positive 13 c excursion ep1 in the lower doushantuo formation where doushantuo type acanthomorphic acritarchs red algae and animal embryos first appear 3 a mild negative 13 c excursion en2 in the middle doushantuo formation 4 a positive 13 c excursion ep2 in the upper doushantuo formation where doushantuo type acanthomorphic acritarchs micrometazoans and stem group florideophyte red algae become abundant and diverse 5 a pronounced negative 13 c excursion en3 near the uppermost doushantuo formation 6 a strongly positive 13 c excursion up to 6 3 pdb ep3 in the lower dengying formation 7 a stable 13 c plateau ca 2 5 pdb ei in the middle and upper dengying formation where abundant vendotaenid algae macroscopic ediacaran fossils biomineralized animal tubes and mostly horizontal animal traces occur and 8 a 10 negative 13 c excursion en4 immediately below the ediacaran cambrian boundary the general pattern of this composite 13 c curve is robust despite a considerable amount of variation among the 13 c profiles of different sections this composite 13 c curve provides a first order chemostratigraphic framework for the subdivision and correlation of the ediacaran system in south china

using sims to decode noisy stratigraphic δ13c variations in ediacaran carbonates abstract carbonate carbon isotope 13ccarb chemostratigraphy is a valuable tool in precambrian stratigraphic correlation the effectiveness of this tool rests on the assumption that 13ccarb data record global seawater signals however in some cases 13ccarb data exhibit rapid and noisy stratigraphic variations that may have been influenced by authigenic or diagenetic carbonate minerals to assess the contribution of non primary minerals towards bulk carbonate carbon isotope values we acquired sims secondary ion mass spectrometry 13ccarb data electron microscopic data and cl cathodoluminescence microscopic data from two ediacaran successions the lower member ii of the doushantuo formation in south china and the mooifontein member of the zaris formation in southern namibia the doushantuo samples came from a stratigraphic interval with noisy meter scale 13ccarb variations of up to 10 whereas the mooifontein member is characterized by consistent 13ccarb values with limited meter scale variations of less than 4 our data show that the meter scale stratigraphic variations in 13ccarb are also mirrored in the sims data at m mm scales in both doushantuo and mooifontein samples in the doushantuo samples sims 13ccarb values of authigenic calcite vary by up to 10 over m mm scales and can be either higher or lower than those of the co existing dolomite matrix which also appears to be affected by authigenic carbonate on the basis of petrographic observation bulk sample 13ccarb values measured on powders microdrilled from the same sims specimens are within the range of sims 13ccarb values thus we infer that bulk sample 13ccarb values of doushantuo samples represent mixtures of different carbonate components the doushantuo and mooifontein sims 13ccarb data validate the traditional method of using chemostratigraphic consistency to evaluate authigenic diagenetic alteration but given that secondary phases may be 13c enriched relative to matrix carbonate caution is warranted when taking maximum values to approximate primary chemostratigraphic trends

diagnosis of the record minimum in arctic sea ice area during 1990 and associated snow cover extremes the arctic sea ice cover exhibited its record minimum area during 1990 characterized by extensive ice free conditions during august along the siberian coast these reductions are consistent with warm windy conditions in may and continued warmth in june promoting early melt and reductions in ice concentration followed in august by strong coastal winds forcing a final breakup and retreat of the pack ice the unusually warm arctic conditions in 1990 are part of a larger scale temperature anomaly pattern linking the sea ice anomaly to accompanying record minima in eurasian snow cover

influence of sediment source and type on the magnetic susceptibility of fiord and shelf deposits baffin island and baffin bay n w t volume and mass magnetic susceptibility are measured on recent and late quaternary sediments from the fiords and shelf of eastern baffin island baffin bay and the northern labrador sea major changes in hinterland bedrock geology are associated with order of magnitude changes in magnetic susceptibility the fiords that head into the proterozoic foxe fold belt have mass magnetic susceptibilities ms of 2 4 10 7 m3 kg compared with 25 60 10 7 m3 kg in sediments derived from archean gneisses and granites another low ms region is the middle reach of frobisher bay ms studies in cambridge mcbeth and itirbilung fiords included analyses of surface samples and samples from lehigh 3 m and piston 11 m cores lehigh cores had higher ms values on average than the piston cores suggesting a coarsening in texture or an increase in the flux of magnetic minerals during the last 0 3 3 ka an analysis of the ms logs of 17 piston cores indicated that six broad patterns of ms can be recognized based on a

did glacials start with global warming abstract correlation of paleoclimatic evidence with orbital changes shows that the build up of polar ice accelerated when low obliquity coincided with perihelion in northern hemisphere winter under low obliquity the insolation was channeled to the tropics at the expense of both polar caps as perihelion moved from winter solstice toward spring equinox the solar beam in astronomic winter and spring became stronger than in summer and autumn this orbital configuration under climate conditions like today would lead to warming of tropical oceans but cooling of the polar regions the areally weighted global mean surface temperature which is dominated by the low latitudes would increase consequently during the first millennia the early glacial ice build up was most likely accompanied by global warming it was the associated increase of meridional insolation and temperature gradients which were instrumental in the transition to a glacial a significant part of the current global warming is due to the gradual temperature increase of the tropical oceans as the changing orbital configuration today resembles that of the last interglacial glacial transition the warming is likely to have a natural component

acritarchs from the doushantuo formation at liujing section in songlin area of guizhou province south china implications for early middle ediacaran biostratigraphy abstract a taxonomically diverse and morphologically disparate microfossil assemblage is recovered from the upper doushantuo formation in the liujing section of songlin area guizhou province including acanthomorphic and sphaeromorphic acritarchs multicellular algae and filamentous cyanobacteria acritarch mengeosphaera membranifera sp nov is newly erected and genus cymatiosphaeroides and several species c forabilatus c kullingii bacatisphaera baokangensis are emended in the systematics the acanthomorphic species are dominated by cymatiosphaeroides forabilatus and mengeosphaera membranifera sp nov the liujing assemblage shares many species with other ediacaran coeval assemblages from south china australia siberia the east european platform india mongolia and svalbard and indicates a significant taxonomic similarity to the global age diagnostic assemblages new occurrence of those known taxa in the liujing succession documents the biodiversity of the ediacaran acritarchs in south china the liujing assemblage extends the palaeogeographic distribution of the ediacaran acritarchs and may be assigned to the tanarium conoideum cavaspina basiconica assemblage zone that was recognized in the yangtze gorges area of south china alternatively it could be partially correlated with the barren interval between t conoideum c basiconica assemblage zone and the overlying tanarium pycnacanthum ceratosphaeridium glaberosum assemblage zone

weathering and abrasion of fe ti oxides during rock degradation and fluvial transport implications for sedimentary provenance studies physical and chemical degradation of individual grains of titanomagnetite and ilmenite during rock weathering and fluvial transport processes in the river eden catchment eastern scotland have been traced using backscattered electron images and electron probe microanalysis magnetic characteristics have been used to detect differences in magnetic mineralogy concentration paragenesis and grain size between rock samples showing different stages of weathering and between different sources and sediment samples results have shown higher physical and chemical durability of ilmenite during this segment of the geological cycle than titanomagnetite which is rapidly altered during progressive subaerial weathering of a dolerite the increasingly intensive and extensive oxidation and development of internal fractures in titanomagnetite are observed however under subaqueous conditions titanomagnetite was found to be progressively replaced by titanite and ti impoverished magnetite due to hydrocirculation neither the total physical nor the total compositional degradation of titanomagnetite is achieved under rock weathering and fluvial transport processes thus the importance of titanomagnetite as a provenance indicator remains despite its degradation during the geological processes studied in the river eden catchment

geochemical tracing and spatial evolution of the sediment bed load of the romaine river quebec canada abstract a four reservoir hydroelectric complex which is projected on the romaine river in eastern quebec canada will likely lead to the complete settling of the sand size bed load of the river in order to characterise the present river bed load sources sediment transport and sedimentary connectivity a study was conducted to document the compositional continuum of the lower 300 km portion of the river bed load samples were collected during the late summer low water period and icp ms geochemical analyses of the light and heavy mineral portions were conducted principal component analysis of the results successfully identified a series of distinctive geochemical domains multivariate euclidean distance coefficients were also calculated between consecutive samples along the river revealing major bed load compositional breaks these results indicate a longitudinal fractionation of the bed load along the 300 km course of the river this is further supported by the sedimentary budget calculated from the annual sedimentary input derived from erosion rates of the river banks from sediment bed load measurements at three gauging stations and from calculated bed load transport capacity at these three locations it appears that significant sediment accommodation space is available on the upper course 250 km of the romaine river in spite of the fact that this river has drained highly sediment laden meltwaters from the receding laurentide ice sheet some 10 ka ago this accommodation space leads to the renewal of the bed load due to recurrent partial to complete sedimentation the major part of the bed load reaching the romaine river mouth originates from the lower 50 km of the river course

observation of perennial arctic sea ice melt and freeze up using passive microwave data the onset of spring melt and autumn freeze up of arctic sea ice are shown through comparison with coincident ers 1 synthetic aperture radar sar and surface air temperature data to produce significant and detectable changes in the passive microwave signature melt onset is marked by a sharp rise in brightness temperatures resulting from the increased emissivity of moisture in the snow cover freeze up is accompanied by a sharp drop in brightness temperatures because of volume scattering by bubbles in the upper ice layer an algorithm is developed to detect melt and freeze up from passive microwave data and is applied to the scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data from 1979 to 1996 the mean accuracy of melt and freeze up dates determined from the ssm i is estimated to be 2 and 3 days respectively the reduced temporal sampling of the smmr degrades the accuracy by 1 day on average melt onset varies from late may in the southern beaufort sea to mid june in the central arctic north of the canadian archipelago while freeze up varies between mid september and mid august the shortest melt season appears to occur north of the canadian archipelago rather than at the north pole which is consistent with the fact that minimum summer air temperatures are centered over greenland the mean standard deviations of the interannual variability of melt and freeze up are 6 8 and 11 4 days respectively

lake catchment based studies of erosion and denudation in the merevale catchment warwickshire u k sediment yields estimated from contemporary stream monitoring of suspended sediment in the merevale forested catchment north warwickshire were compared with the sediment yield record obtained from analysis of lake sediment in the downstream reservoir total sediment volume and mass for nine periods since 1861 were calculated by extrapolation of synchronous levels in 54 cores identified from magnetic susceptibility and other magnetic measurements and by using 210pb and 137cs analysis to provide an absolute sediment chronology sediment yield estimated from the two methods show comparable but low 50 200 kg ha 1 yr 1 levels of sediment loss while suggesting that lake sediments can be a useful means for extending the period over which contemporary monitoring exists the study stresses the need for detailed historical records of land use and climate against which long term sediment yield records can be evaluated

magnetic and chemical parameters of andic soils and their relation to selected pedogenesis factors in the case of andic soils developed on volcanic rocks permanently humid conditions are essential for andosolisation processes although volcanic rocks are usually rich in highly magnetic iron oxides knowledge about these minerals in andic soils with respect to the soil development is missing the aim of this contribution is to investigate the relationship between magnetic and basic chemical properties of soils developed on volcanic basement and parameters related to the pedogenesis factors the studied sites are located on basaltic lava flows in the eastern part of the french massif central investigated pedons with alu andic sil andic and vitric properties were pedologically described and analysed by a set of magnetic and soil chemical methods magnetic parameters include low field volume specific and mass specific magnetic susceptibility frequency dependent magnetic susceptibility remanent properties including s ratio and coercivities chemical parameters included the phh2o soil organic matter total cation exchange capacity base saturation and content of fe and al extracted in dithionite citrate acid ammonium oxalate and pyrophosphate solutions micro morphology of andosols and parent material was observed by scanning electron microscopy completed with energy dispersive spectrometry the pedogenesis factors are represented by parent rock age annual precipitation and soil thickness our findings suggest that 1 precipitation is the most important pedogenesis factor with a strong relationship to the relative magnetic grain size concentration of ferrimagnetic minerals aluminium dissolved in pyrophosphate and acid ammonium oxalate and content of organic matter 2 parent material age shows a well pronounced relationship with magnetic grain size parameters represented by the frequency dependent susceptibility and ratio of saturation remanent to saturation induced magnetisation mrs ms selective dissolution parameters and phh2o 3 thickness of soil profile shows a link to mrs ms phh2o and content of organic matter

land use history and sediment flux in a lowland lake catchment groby pool leicestershire uk whole basin sediment records have been used to investigate the impact of land use change and catchment processes on sediment flux to groby pool leicestershire uk over the past c 200 years estimates of sediment yields for the period ad 1945 1989 were calculated using dry mineral mass data from multiple cores up core changes in loss on ignition values were used to correlate cores and these were tied to a master chronology based on 2 10 pb and 137 cs profiles sediment sources within the catchment were identified by comparing the magnetic properties of lake sediment soil and stream samples in addition documentary records were used to establish the pattern of land use change and other activities which might affect material flux to the lake a lakewide change in sediment type is recorded after parliamentary enclosure in 1789 as the focus of arable activity shifted from outside to inside the lake s drainage catchment trends in lake sediment mineral magnetic properties also indicate a slight shift in the source of allochthonous inputs from subsoil to topsoil derived material at that time recent changes in mineral magnetics are thought to reflect the changing supply of subsoil flux resulting from modifications to inlet streams coupled with increased inputs of atmospheric pollutants sediment yield estimates of is t km 2 yr 1 obtained for the period 1945 1989 are similar to other lowland uk sites with similar lake catchment ratios activities such as quarrying road construction and agricultural intensitication appear to have had little or no impact on sediment yields to the lake in recent times this is thought to be due to the interplay between catchment and instream storage a low drainage density and the buffering effect of riparian vegetation

apatite glaucony association in the ediacaran doushantuo formation south china and implications for marine redox conditions abstract major phosphogenic events took place in the late paleoproterozoic and the ediacaran both of which followed an episode of atmospheric oxygenation these apparent coincidences have led to suggestions that the precambrian phosphorus cycle was partly regulated by oceanic redox conditions although direct evidence is lacking in this paper we report the discovery of glaucony in drill cores from the phosphorite rich ediacaran doushantuo formation at weng an south china which provides new insights into redox conditions and geochemical cycles during the deposition and early diagenesis of the lower doushantuo formation the presence of flaser and lenticular bedding in the sandstones suggests deposition in a tidally influenced shallow water environment apatite is present as millimeter scale flasers in sandstones but more commonly as intraclastic grains glaucony typically occurs as interstitial aggregates cementing and replacing detrital minerals and phosphatic grains with an upsection decrease in abundance the doushantuo glauconies have consistently high k2o 7 6 9 6 wt in particular phosphorite hosted glaucony has generally higher total iron tfe2o3 than sandstone hosted glaucony consistent with al3 fe3 substitution in the octahedral site as supported by raman peaks slightly shifted towards lower wavenumbers for higher fe content a decrease in detrital input probably resulted in limited al availability during early diagenesis which in turn led to the waning of glaucony upsection the phosphate grains do not show any negative ce anomalies consistent with precipitation of authigenic apatite in suboxic environments with insignificant preferential remobilisation of ce during deposition and early diagenesis ree y features show variable diagenetic ree enrichment in phosphorites but identical concave down patterns the wide occurrence of glaucony cement further documents the presence of a generally suboxic early diagenetic environment on the seafloor which was in active exchange with bottom seawater slight fluctuations of redox states in the porewater and bottom water would have promoted the cycling of fe enrichment of phosphate and ree and extensive glaucony authigenesis therefore the glaucony bearing phosphorites in the doushantuo formation are a direct result of fe redox driven diagenesis apatite glaucony association likely forms in suboxic environments and is considered as a useful mineralogical proxy for paleoredox conditions on the precambrian ocean floors

the contribution of throughflow to storm runoff an evaluation of a chemical mixing model the contribution of throughflow to storm runoff is examined using a chemical mixing model the results predict that throughflow is an important component of storm runoff particularly during the period of stream recession supporting hydrological data suggests that a major throughflow input occurs coincident with the stream discharge peak the two sets of results therefore conflict in the predicted timing of the throughflow response

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

introduction from snowball earth to the cambrian explosion evidence from china the neoproterozoic palaeozoic transition npt around 600 ma ago was a critical time interval when the earth experienced fundamental change manifested as climatic extremes snowball earth followed by the emergence and rapid diversification of animals cambrian explosion how animals and environments co evolved and what caused these fundamental changes to the earth system during the npt is a great scientific puzzle which has been a rapidly developing frontier of interdisciplinary research between bio and geosciences south china preserves a complete stratigraphic succession of the npt developed in various facies ranging from shallow to deep marine realms with extraordinarily well preserved successive fossil biotas in various taphonomic settings zhu 2010 fig 1 making it a key area and global focus of studies in the field over recent decades indeed the current narrative of early animal evolution has largely been based on the fossil biotas from south china these include 1 the world9s oldest microscopic animal fossils with cellular details from the early ediacaran weng9an biota doushantuo formation 2 putative macroscopic animal fossils preserved as carbonaceous imprints from the early ediacaran lantian wenghui and miaohe biotas also doushantuo formation 3 typical late ediacaran faunas preserved in dark limestone shibantan biota and as large and poorly mineralized tubular animal fossils gaojiashan biota both from the dengying formation 4 phosphatized small shelly and soft bodied animal fossils from the early cambrian meishucun and kuanchuanpu faunas and 5 cambrian fossil lagerstatten chengjiang guanshan and kaili faunas with typical burgess shale type soft bodied preservation

climate change and human occupations in the lake daihai basin north central china over the last 4500 years a geo archeological perspective abstract high resolution climate variations since the last 4500 years in the monsoonal arid transition zone of north central china were revealed through the integration of proxies from sediment cores in the lake daihai basin human occupations in the lake basin deduced from archeological findings and historical literatures were then incorporated into the climate sequence to demonstrate the patterns of human responses to the climate changes and the recent anthropogenic effects it indicated that 1 climate dominated human environment adaptations prevailed prior to 2700 cal yr bp an amicable climate setting before 4100 cal yr bp would facilitate the growth of the laohushan culture lc in the lake basin while a pronounced deterioration of water thermal condition after that had led to human exodus and the collapse of the lc the reduced human activity in the lake basin indicated at 3800 3500 cal yr bp and a subsequent cultural blank at 3500 2700 cal yr bp were both in response to the climate and lake level fluctuations during 3800 2800 cal yr bp 2 transition to a positive human adaptation was seen at 2700 1100 cal yr bp represented by the exploitation of arable land for cultivation and animal husbandry as the lake contracted 3 an increasing human presence that affected environmental processes became more severe over the last 1100 cal yr bp this was basically due to the ongoing lake shore reclamation for cropping and more recently heavy metals emissions from fossil fuel combustion and local industries

magnetic studies of erosion in a scottish lake catchment 1 core chronology and correlation1 magnetic susceptibility opb 137cs 14c and paleomagnetic secular variation are used to establish the chronology of sedimentation in a set of cores from loch frisa in western scotland the 14c dates obtained are not compatible with the chronology derived from all the other techniques and this is ascribed to inwash of old particulate carbon from the watershed central cores show little evidence of changes in sedimentation rate over the last 150 years whereas marginal cores contain evidence of major increases arising from ploughing and from drainage associated with catchment afforestation since 1935 the results illustrate the value of a multiple core approach to sedimentation and erosion studies even where complex lake morphometry precludes calculation of sediment budgets

50 myr recovery from the largest negative δ13c excursion in the ediacaran ocean sedimentary rocks deposited during the ediacaran period 630 542 ma contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from 5 to 12 followed by a sub linear recovery to positive 13c values isotopic ages u pb and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at 600 ma and duration of recovery of approximately 50 myr the excursion is widely recognized in oman and has potential correlatives in ediacaran strata elsewhere and may thus represent a characteristic feature of the ediacaran period the amplitude of this carbon isotope excursion far exceeds those of other neoproterozoic anomalies the isotopic trend of negative excursion and long term recovery spanned at least one short lived glacial episode at 580 ma but appears unrelated to glaciation which indicates that negative anomalies in the neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages

a 13 000 year record of environmental magnetic variations in the lake and peat deposits from the chandra valley lahaul implications to holocene monsoonal variability in the nw himalaya abstract an 13 000 year old record of in situ peat bog and lacustrine sediments from a post glacial lake in the chandra valley of the lahaul himalaya is studied to generate the record of environmental magnetic signatures in response to indian summer monsoon ism variability in the nw himalaya the chronology of studied chandra peat trench cpt profile is based on 9 ams 14c calibrated dates cal yr bp the piece wise linear regression analysis of age depth model indicates non linear sedimentation with higher rates from 4142 cal yr bp to the present and lower accumulation during 12 880 4142 cal yr bp the mineral magnetism showed three dominant assemblages of magnetic minerals with varying concentrations in peat lake sediment sequence i e 1 mixed ferri and antiferromagnetic minerals between 12 880 and 11 019 cal yr bp 2 dominant antiferromagnetic mineralogy from 11 019 to 3172 cal yr bp and 3 significantly increased concentrations of mixed ferri and antiferromagnetic minerals from 3172 cal yr bp to the present with characteristically increased ferrimagnetic concentrations after 2032 cal yr bp the characteristic increase in antiferromagnetic mineral concentration accompanied by decreased ferrimagnetic concentration from 10 398 to 5770 cal yr bp suggest possible oxidation of magnetite to hematite under warmer climate conditions and corresponds to increased ism intensity during early to mid holocene warm wet climate in the nw himalaya the distinctly increased concentration of antiferromagnetic minerals from 6732 to 5770 cal yr bp indicates mid holocene climate optimum hco in the lahaul himalaya the strengthening and weakening of ism recorded in environmental magnetic signatures during 1260 852 cal yr bp 690 1098 ad and between 852 and 239 cal yr bp 1098 1711 ad corresponds to medieval warm period mwp and little ice age lia events respectively

the effects of particle breakage and abrasion on the magnetic properties of two soils as mineral magnetism is used as a tracer for sourcing river and dam sediments changes in the magnetic properties that may occur during transport between the source and sink must be considered abrasion and breakage of particles will occur during transport these processes were examined in simulation experiments with a granitic and a sedimentary soil the effects of these processes on the magnetic properties of a granitic and a sedimentary soil were examined using a simulated breakage abrasion experiment breakage and or abrasion had substantial effects on the magnetic properties of both soils all particle sizes were affected but the magnitude varied through the size range of derived particles the major effect was on the concentration of magnetic minerals with differences between the concentrations in particle sizes of the original material and those generated by the experiments being as much as 20 times the effect on the granite soil was to reduce the concentrations i e derived material was less than original material whereas for the sedimentary soil the derived particles had higher concentrations the effect on magnetic grain size as indicated by the magnetic ratios was less than the effect on the mass magnetic properties but still substantial for some ratios for some sizes 1998 john wiley sons ltd

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

magnetism of the huguangyan maar lake sediments southeast china and its paleoenvironmental implications abstract the huguangyan hgy lake a typical maar lake in the southeast of china is sensitive to the evolution of the asian monsoon system including the east asian summer monsoon easm and the indian summer monsoon ism so far the mechanism of how magnetic properties of the hgy lake sediments respond to climate changes has not been well determined in this study we performed a detailed mineral magnetic analysis on the high resolution hgy sediments results revealed that finer grained magnetite superparamagnetic and single domain magnetite mixed with a small amount of goethite and hematite is the dominant magnetic mineral which is consistent with the magnetic properties of the red weathered soils collected from the catchments but differs greatly from that of the aeolian inputs therefore magnetic minerals of the hgy sediments were originated mainly from the lake catchment rather than the wind blown dust inputs considering the high tephra wall relative elevation of 10 20 m and great precipitation surface runoff by rainfall is interpreted as the main process to transport red soils into the lake the magnetic records of hgy sediments revealed that the summer monsoon was enhanced at the early holocene and then declined abruptly at the mid late holocene 5 5 kyr cal bp this pattern strongly mimics the evolution pattern of ism but is inconsistent with the easm thus we suggest that the magnetic records from hgy have the great potential to investigate the evolution of ism

the significance of various sediment magnetic mineral fractions for tracing sediment sources in killimicat creek abstract the mineral magnetic properties of sediment are increasingly being used to determine the sources of sediment and associated nutrients and contaminants in drainage basins this study was undertaken to measure the relative contributions of the magnetic mineral components in sediment i e components associated with surface bound fe the heavy mineral fraction and as inclusions in particles to determine the extent to which they represent the bulk of the sediment deposited channel sediment samples from the tributaries and downstream reach at the first major confluence in the headwaters of killimicat creek new south wales were sieved to separate 6 particle size fractions and the mineral magnetic properties measured to determine the relative contribution of sediment from the smaller tributary basin the finest sand component 63 125 m was then separated into light and heavy mineral fractions and magnetic measurements made on each fraction magnetic parameter data from the 63 125 m fraction measured before density separation show a dominance of sediment 70 12 derived from the smaller tributary basin measurements of the light sediment fraction give a similar result 73 13 the proportion of the heavy mineral fraction delivered from the smaller tributary is 78 38 the light mineral fraction of all of the samples were treated with hcl to remove surface bound fe and subsequent magnetic measurements show that 41 94 of the mass specific magnetic susceptibility is attributable to magnetic minerals associated with surface bound fe the heavy mineral component while 60 is associated with sediment particles rather than the discrete heavy mineral component

recent sediment flux and erosional processes in a welsh upland lake catchment based on magnetic susceptibility measurements abstract single sample magnetic susceptibility measurements are used to correlate synchronous levels in 16 cores of dated 210 pb 137 cs recent sediment taken from the deep and oligotrophic llyn peris n wales in order to provide a basis for calculating total sediment and chemical influx through time results show that sediment influx has steadily increased since c 1750 a d to reach peak levels in the period 1966 1976 a d equivalent to a rise in erosion in the catchment from c 5 t km 2 yr 1 to c 42 t km 2 yr 1 comparison of down core susceptibility fluctuations with sediment pollen and organic pigment data indicates that maximum susceptibility values relate to periods of channel erosion and minimum susceptibility values relate to periods of slate debris inwash from spoil tips in the catchment a study of historical records reveals that pre twentieth century peak levels of erosion were due to the effects of extractive industries while twentieth century erosion has been caused by overgrazing increased trampling pressure and heavy construction works in the catchment

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

nanosims u pb dating of fossil associated apatite crystals from ediacaran 570 ma doushantuo formation abstract sedimentary rocks record a wealth of information on the evolution of lithosphere hydrosphere atmosphere and biosphere however uncertainty about the age of many precambrian sequences makes it very difficult to establish the accurate temporal framework which can dramatically improve our understanding of the scale and duration of geological and biological events the neoproterozoic doushantuo formation south china preserve unique assemblages of early multicellular fossils and records valuable paleoenvironmental information the age of these formations is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon in this study we used nanosims to date samples from the doushantuo formations by apatite u pb geochronology fossil associated precipitated apatite grains were identified using optical microscope and raman spectrometer the resultant age is 305 26 ma high common pb and low u concentration in those apatite specimens limit the precision of age determination while the yielded age suggests that the doushantuo formation may have experience a post depositional hydrothermal event

historic and contemporary sediment transfer in an upland pennine catchment uk a sediment budget for an upland catchment reservoir system at burnhope reservoir north pennines uk has been developed this provides a framework for quantifying historic and contemporary sediment yields and drainage basin response to disturbance from climate change and human activities in the recent past bathymetric survey core sampling 137cs dating and aerial photographs have been used to assess sediment accumulation in the reservoir the average reservoir sedimentation rate is 1 24 cm yr 1 annual sediment yield 33 3 t km 2 yr 1 10 trap efficiency 92 mean annual reservoir sedimentation over the 67 year period has been estimated at 592 t 10 inputs of suspended sediment from direct catchwater streams account for 54 of sediment supply to the budget best estimate yield of 318 t yr 1 129 while those from actively eroding reservoir shorelines contribute 328 t yr 1 92 sediment yield estimates from stream monitoring and reservoir sedimentation are an order of magnitude lower than those reported from south pennine reservoirs of comparable drainage basin area analysis of historical rainfall series for the catchment shows fluctuations in winter and summer rainfall patterns over the past 62 years from 1976 to 1998 there has been a diverging trend between winter and summer rainfall with a large increase in winter and a gradual decrease in summer totals periods of maximum variation occur during the summer drought events of the late 1970s early 1980s and mid 1990s analysis of the particle size of core sediments highlights abrupt increases in sand sized particles in the top 20 cm of the core based on the 137cs chronology these layers were deposited from the late 1970s onwards and relate to these diverging rainfall records and rapidly fluctuating reservoir levels this provides evidence of potential sediment reworking within the reservoir by rapid water level rise after drought copyright 2008 john wiley sons ltd

palaeoenvironmental reconstruction of the alluvial landscape of neolithic catalhoyuk central southern turkey the implications for early agriculture and responses to environmental change archaeological discussions of early agriculture have often used the neolithic village of catalhoyuk in central southern turkey as a key example of the restricting effect of environment on agricultural production and organization central to these discussions is the palaeoenvironmental reconstruction of the landscape surrounding the site this paper presents an important new dataset from an intensive coring programme undertaken between 2007 and 2013 in the immediate environs of the site designed to improve significantly the spatial resolution of palaeoenvironmental data using sediment analyses including organic content magnetic susceptibility particle size total carbon and nitrogen contents and carbon isotope analysis coupled with 3d modelling we are able to present a new reconstruction of the palaeotopography and sedimentary environments of the site our findings have major implications for our understanding of neolithic agricultural production and social practice we present four phases of environmental development phase 1 consists of the final phases of regression of palaeolake konya in the later parts of the pleistocene dominated by erosion due to wind and water that created an undulating surface of the marl deposited in the palaeolake phase 2 occurs in the latest pleistocene and early holocene and indicates increased wetness probably characteristic of a humid anabranching channel system in which there are localized pockets of wetter conditions in phase 3a this infilling continues producing a flatter surface and there are fewer pockets being occupied by wetter conditions the fluvial regime shifts from humid to dryland anabranching conditions the earliest period of occupation of the neolithic east mound coincides with this phase phase 3b coincides with the shift of occupation to the west mound in the chalcolithic when there is evidence for a very localized wetter area to the southeast of the west mound but otherwise a continuation of the dryland anabranching system finally phase 4 shows a shift to the pre modern style of fluvial environment modified by channelization this reanalysis demonstrates the importance of extensive spatial sampling as part of geoarchaeological investigations with this new evidence we demonstrate that the landscape was highly variable in time and space with increasingly dry conditions developing from the early holocene onwards in contrast to earlier landscape reconstructions that have presented marshy conditions during the early holocene that impacted agriculture we argue that localized areas of the floodplain would have afforded significant opportunities for agriculture closer to the site in this way the results have important implications for how we understand agricultural practices in the early neolithic

magnetic fingerprint of the sediment load in a meander bend section of the seine river france abstract this study aims to evaluate the potential of magnetic methods to determine the composition of the sediment load in a cross section of an unmanaged meander in the upstream stretch of the seine river marnay sur seine suspended particulate matter spm was collected based on a regular sampling scheme along a cross section of the river at two different depth levels during a low water stage may 2014 and a high water stage february 2015 riverbed sediments rbs were collected during the low water stage and supplementary samples were taken from the outer and inner banks magnetic properties of the dry bulk spm and sieved rbs and bank sediments were analysed after characterizing the main magnetic carrier as magnetite hysteresis parameters were measured giving access to the grain size and the concentration of these magnetite particles the results combined with sedimentary grain size data were compared to the three dimensional velocity profile of the river flow in the rbs where the magnetic grain size is rather uniform the concentration of magnetite is inversely proportional to the mean grain size of the total sediment indicating that magnetite is strongly associated with the fine sedimentary fraction the same pattern is observed in the samples from the outer and inner banks during the low water stage the uniformly fine spm grain size distribution characterizes the wash load the magnetic fraction is also relatively fine within the pseudo single domain range with concentration similar to that of the fine rbs fraction during the high water stage spm samples correspond to mixtures of wash load and resuspended sediment from the bedload and riverbanks here the grain size distribution is heterogeneous across the section showing coarser particles compared to those in the low water stage and more varying magnetite concentrations while the magnetic grain size is like that of the low water stage the magnetite concentration in the high water spm can be modelled based on a mixing of the magnetite concentrations of the different grain size fractions thus quantifying the impact of resuspension in the cross section

medium term effects of afforestation on sediment dynamics in a water supply catchment a mineral magnetic interpretation of reservoir deposits in the macclesfield forest n w england short term increases in stream sediment loads during pre afforestation ground preparation have often been followed by a return to low sediment loads however in the macclesfield forest in the southern pennines comparison of the magnetic characteristics of soils and downstream reservoir deposits suggest that significant changes in the processes of soil erosion occur later in the cycle of forest management at the time of canopy closure a preliminary magnetic mixing model indicates that the proportion of reservoir sediments derived from the subsoil below 0 3 m depth has increased from 30 to 70 per cent between 1929 and 1981 changes in hydraulic stresses subsequent to road construction and forest development in association with unstable pleistocene deposits may provide an explanation for these events

quantitative sediment source ascription using magnetic measurements in a reservoir catchment system near nijar s e spain the magnetic properties of sediments from a dried out reservoir and its inflowing streams were measured to provide a basis for sediment source determination quantitative estimates of source component proportions in the reservoir sediments were made using linear programming procedures the study confirms that this type of research must be based on a detailed knowledge of the relationship between magnetic properties and particle size in both the sediments and the potential sources in the case of the site studied the isabel ii reservoir near nijar s e spain the sediments generated by contemporary surface processes within the reservoir catchment fail to reflect fully the 19th century material largely responsible for the rapid infill of the reservoir an additional source type namely unweathered schist derived material not represented in the fine sediments sampled within channels upstream from the reservoir has to be included in the model before calculations of source component contributions can be made it is inferred that one or more high magnitude low frequency event outside the amplitude of the most recently operating processes was largely responsible for the infilling of the reservoir

in situ u pb dating of monazite xenotime and zircon from the lantian black shales time constraints on provenances deposition and fluid flow events abstract the lantian formation located in eastern south china block scb forms the lower sequence of the ediacaran period at the transition from proterozoic to paleozoic the fossils of lantian formation have been proposed to predate the avalon biota about 579 565 ma the earliest known fossil assemblages with complex morphologies based largely on stratigraphy mineral chemistry and in situ u pb dating of monazites xenotimes and zircons from the black shale in fossil rich zone are studied for the first time to provide critical age constraints for provenance early diagenesis and fluid flow events detrital zircons and monazites give age populations similar to that of the doushantuo formation indicative of the same provenances for ediacaran basins throughout the scb the low y monazites formed during early diagenesis yield a weighted mean age of 612 29 ma n 9 mswd 3 1 age spectrum of analyzed monazites demonstrated that the sedimentation started from at least around 645 ma subsequently the overprinting events could be recorded by xenotimes and zircons precipitated from fluids during late diagenesis age results from xenotimes ranging from 441 ma and 585 ma were contemporaneous with the timing of collision of scb with gondwanaland and a weighted mean age of 394 8 3 7 ma n 23 mswd 2 8 obtained from diagenetic zircons could be correlated to the post tectonic granites widespread on the scb the pre existing monazites generally remain pristine and the multi staged fluids were locally interacted with the samples to form th rich domains in monazites

iron phosphate in the ediacaran doushantuo formation of south china a previously undocumented marine phosphate sink abstract ediacaran phosphorites capture the dynamics of the ultimate biolimiting nutrient phosphorus during perhaps the most critical transition of earth s climatic and ecological history concomitant with the neoproterozoic oxygenation event was the deposition of the first extensive phosphorites across marine shelves typically interpreted as a basinward shift in the locus of phosphogenesis facilitated by deep ocean oxygenation petrographic and spectroscopic analyses of proximal phosphorites from the ediacaran doushantuo formation near the yangtze gorges area of south china reveal the presence of interlaminated pristine muddy and granular phosphorites that were cemented by early diagenetic iron phosphate an additional previously undocumented seafloor p sink transmitted and reflected light microscopy cathodoluminescence microscopy and back scattered electron scanning electron microscopy were used to reconstruct the paragenesis of phosphorites at the wanjiagou section near zhangcunping hubei province and demonstrate that pristine phosphorite precipitated authigenically as francolite via microbially mediated phosphogenesis as evidenced by preserved microbial laminations along with filamentous and coccoidal microfossils subsequent tidal reworking of pristine hardgrounds and phosphatic mudstones produced minimally coated intraclasts and peloidal phosphatic grains that were cemented by iron phosphate soon after deposition but before compaction raman spectroscopy bulk sample and micro x ray diffractometry indicate the iron phosphate cement is composed of phosphosiderite strengite fe 3po4 2h2o the presence of phosphosiderite can be attributed to either syndepositional oxidation of phosphorites or thermal stabilization of vivianite fe2 3 po4 2 8h2o in both cases the occurrence of phosphosiderite represents the first direct evidence for iron phosphate minerals as a p sink during the ediacaran and suggests phosphogenesis may have partially proceeded in ferruginous porewaters in contrast to the redox independent process of francolite precipitation integration of petrographic and geochemical techniques such as those employed in this study offers the ability to corroborate p speciation analyses and provides an independent determination of p phase partitioning ultimately this approach is paramount in testing hypotheses that suggest ferrous iron phosphate minerals played a regulatory role in global proterozoic oxygenation

a mineral magnetic study of holocene sediment yields and deposition patterns in the llyn geirionydd catchment north wales mineral magnetic investigations of sediment cores and catchment materials from llyn geirionydd north wales form the basis of a study of holocene sediment yields and deposition patterns catchment soils and bedrock materials are highly variable in magnetic concentration in contrast the lake sediments are more homogenous in magnetic concentration magnetic hysteresis properties of catchment materials bulk sediments and magnetic extracts demonstrate that the occurrence of authigenic greigite fe3s4 in early holocene sediments is responsible for differences between the magnetic characteristics of sediments older than 5000 bp and the more recent sediments and catchment materials a whole lake stratigraphy based on core correlation using magnetic measurements pollen stratigraphy and 14c age determinations indicates sediment yields which increase almost threefold from the early holocene to the period from c ad 500 1850

variation of chemical index of alteration cia in the ediacaran doushantuo formation and its environmental implications abstract the ediacaran period 635 541 ma witnessed rapid turnovers of marine organisms that eventually led to the early cambrian radiation the ediacaran doushantuo formation ca 635 551 ma serves as one of the most important and intensively studied stratigraphic units for understanding the co evolution of life and environment during this critical time interval to better understand the early middle ediacaran climate change we reconstruct a temporal variation curve of chemical index of alteration cia from a drill core and an outcrop of the doushantuo formation in combination with previously published cia data from segments of time equivalent strata the results show three distinct decreases in cia values that correlate well with the positive carbon isotope 13c excursion at the low doushantuo formation ep1 and the negative 13c excursion at the middle en2 and upper en3 doushantuo formation the decline of cia in ep1 is consistent with occurrence of glendonites at the same stratigraphic interval that suggests a cooling event the low cia values in en2 and en3 also suggest relatively colder periods that are consistent with evidence from strontium isotope 87sr 86sr and oxygen isotope 18o data with existing bio and chemostratigraphic constraints the cooling event associated with en2 might be synchronous with the gaskiers glaciation the other two cold periods associated with ep1 and en3 however have not been documented from other successions globally which needs to be tested in future studies

silicified glendonites in the ediacaran doushantuo formation south china and their potential paleoclimatic implications the ediacaran period is punctuated by the ca 580 ma gaskiers glaciation in newfoundland however paleoclimatic data are scarce in ediacaran successions in south china where abundant geochemical and paleobiological data are shaping current understanding of ediacaran evolutionary and environmental history here we report the occurrence of silicified glendonites in the ediacaran doushantuo formation deposited in an inner shelf environment on the south china block petrographic evidence suggests that these silicified glendonites are pseudomorphs after syndepositional or early authigenic ikaites formed at near freezing temperatures the glendonite bearing stratigraphic interval is characterized by positive 13c values it predates both the negative 13c excursion en3 widely believed to be an equivalent of the shuram negative excursion and excursion en2 although alternative interpretations may be possible these glendonites may be related to and correlated with the gaskiers glaciation if confirmed this correlation suggests that the shuram event postdates the gaskiers glaciation thus having important implications for ediacaran climate changes carbon cycles and biological evolution

investigating contemporary and historical sediment inputs to slapton higher ley an analysis of the robustness of source ascription methods when applied to lake sediment data this paper reports the results of a quantitative source analysis of the contemporary and historical sediments delivered to slapton higher ley devon uk contemporary suspended and bedload sediment inputs to the higher ley were apportioned successfully using r and q mode analysis and an unmixing model pasture topsoil was responsible for 80 of the suspended sediment load during stormflow but only 50 under baseflow conditions channel bank material dominated bedload 70 80 dating by 137cs of three cores from the higher ley indicates that rapid sedimentation has occurred since the 1950s and that pasture topsoil has been the dominant source of sediment deposited in the higher ley since the early 1980s both the unmixing model and r and q mode analysis support this interpretation however the robustness and validity of applying such source ascription techniques to the sediment cores of the higher ley is debatable as chemical and mineral magnetic signatures in the cores are diluted in comparison with sediment sources from the slapton catchment particles size effects selective transport and post depositional physical and chemical processes are examined as possible causes of this dilution effect post depositional alteration of the sediment was identified as the most probable explanation but further analysis of the process was not possible within the scope of this study

holocene environmental change in the west african sahel sedimentological and mineral magnetic analyses of lake sediments from jikariya lake northeastern nigeria previous studies have demonstrated long term changes in effective moisture in sub saharan africa here we reconstruct holocene environments using a similar to 7 m lake sediment sequence recovered from the northeastern nigerian sahel and attempt to distinguish basin specific changes from regional climatic variations the sequence was analysed for sedimentological properties mineral magnetism and pollen and dated by cs 137 pb 210 excess and c 14 extremely arid conditions of the terminal pleistocene ended ca 11 500 cal bp calendar years when climate ameliorated and a lake developed until the occurrence of an arid event leading to lake desiccation at similar to 11 200 cal bp following this climate ameliorated and a water body re emerged very wet conditions predominated 11 200 5600 cal bp followed by drought between 5600 and 5500 cal bp and a return to moderate humidity from 5500 to 4000 cal bp after 4000 cal bp a marked deterioration occurred culminating in lake desiccation at ca 800 cal bp after this time the climate remained generally dry and the re emerging lake was shallow comparison of these results with other well dated sequences in the region demonstrates the importance of basin specific influences on the palaeolimnological records in addition to regional climatic controls disentangling these different controls as well as the reconstruction of holocene climate therefore requires a multiple basin approach copyright c 2008 john wiley sons ltd

evidence for cirque glaciation in the colorado front range during the younger dryas chronozone abstract late pleistocene glacial chronologies developed for the front range mountains of colorado include two or more cirque glacier advances locally known as the satanta peak advances sediment cores were recovered from sky pond an alpine lake 3320 m located less than 100 m downvalley from a moraine that exhibits late pleistocene to early holocene relative age features and appears to correlate to the satanta peak deposits one of the cores penetrated 0 5 m of basal diamict and recovered 3 3 m of overlying sediments that are predominantly gyttja an accelerator mass spectrometry ams age of 12 040 60 yr14c b p was obtained from directly above the basal diamict and is similar to other reported ages for cirque deglaciation in the front range mountains the lower portion of the gyttja contains an interval of clastic sediments that show characteristics consistent with glacial activity in alpine catchments radiocarbon ages obtained from below and near the upper contact of this clastic interval are 11 070 50 and 9970 8014c yr b p respectively an additional ams age of 10 410 9014c yr b p was obtained from within the clastic interval in a second core the most likely source for this interval of clastic sediments is a moraine situated directly upvalley from sky pond and consequently it appears that the deposition of this moraine was coeval with the european younger dryas event 11 000 10 00014c yr b p similarities in soil development weathering features and altitude between this moraine and the type satanta peak moraines suggest that the moraines are correlative these findings are in agreement with a growing body of evidence that suggests a relatively minor advance of alpine glaciers occurred in the north american rockies during the younger dryas chron

estimating the time of melt onset and freeze onset over arctic sea ice area using active and passive microwave data abstract accurate calculation of the time of melt onset freeze onset and melt duration over arctic sea ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates this comparative study evaluates several methods used to estimate sea ice melt and freeze onset dates 1 the melt onset database derived from ssm i passive microwave brightness temperatures t b s using drobot and anderson s j geophys res 106 2001 24033 advanced horizontal range algorithm ahra and distributed by the national snow and ice data center nsidc 2 the international arctic buoy program polar exchange at the sea iabp poles surface air temperatures sats 3 an elaborated version of the ahra that uses iabp poles to avoid anomalous results passive microwave and surface temperature analysis pmsta 4 another elaborated version of the ahra that uses t b variance to avoid anomalous results mean differences and standard deviation analysis mdsda 5 smith s j geophys res 103 1998 27753 vertically polarized t b algorithm for estimating melt onset in multiyear my ice ssm i 19v 37v and 6 analyses of concurrent backscattering cross section and brightness temperature t b from okean 01 satellite series melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different arctic sea ice regions comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the t b calibration coefficients and algorithm threshold values compared to the pmsta method the ahra method tended to estimate significantly earlier melt dates likely caused by the ahra s susceptibility to prematurely identify melt onset conditions in contrast the iabp poles surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice the mdsda method was least sensitive to small adjustments of the smmr ssm i inter satellite calibration coefficients differences among methods varied by latitude freeze onset dates among methods were most disparate in southern latitudes and tended to converge northward surface air temperatures iabp poles indicated freeze onset well before the mdsda method especially in southern peripheral seas while pmsta freeze estimates were generally intermediate surface air temperature data estimated latest melt onset dates in southern latitudes but earliest melt onset in northern latitudes the pmsta estimated earliest melt onset dates in southern regions and converged with the mdsda northward because sea ice melt and freeze are dynamical transitional processes differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development these studies contribute to the growing body of documentation about the levels of disparity obtained when arctic seasonal transition parameters are estimated using various types of microwave data and algorithms

further paleomagnetic results from pleistocene sediments in northern canada supporting the existence of stationary secular variation sources abstract our recently published results from pleistocene sediments in northwestern canada provided no compelling evidence for the so called blake event but did yield an interesting secular variation pattern interpreted as the signature of one or more stationary sources near the core mantle boundary new data from a site about 1 km away confirm this interpretation and thus support the division of the non dipole field into drifting and standing parts in the geological as well as the bistoric past measurements of the initial susceptibility of all 694 samples in this study and the previous one greatly facilitated stratigraphic correlation between the four 6 m sections involved

a new sims zircon u pb date from the ediacaran doushantuo formation age constraint on the weng an biota as a well known phosphatized lagerstatte the ediacaran weng9an biota in central guizhou province of south china contains diverse acanthomorphic acritarchs algal thalli tubular microfossils as well as various spheroidal fossils these fossils provide crucial palaeontological evidence for the radiation of multicellular eukaryotes after the termination of the neoproterozoic global glaciation while the weng9an biota is generally considered as early ediacaran in age on the basis of phosphorite pb pb isochron ages ranging from 572 ma to 599 ma the reliability and accuracy of these age data have been questioned and some geologists have proposed that the weng9an biota may be younger than 580 ma instead here we report a sims zircon u pb age of 609 5 ma for a tuffaceous bed immediately above the upper phosphorite unit in the doushantuo formation at zhangcunping yichang south china litho bio and chemostratigraphic correlations suggest that the upper phosphorite unit at zhangcunping can be well correlated with the upper phosphorite unit at weng9an which is the main horizon of the weng9an biota we therefore conclude that the weng9an biota could be as old as 609 5 ma

mechanisms responsible for streamflow generation on a small salt affected and deeply weathered hillslope this paper considers the contributions of overland flow throughflow and deep seepage to the generation of streamflow in a salt affected deeply weathered landscape runoff mechanisms on a small hillslope in south western australia were dependent on the extent and development of variable source areas in winter streamflow generation was controlled by returnflow saturation overland flow and throughflow in summer post ponding infiltration excess and saturation overland flow dominated the extent of the variable source area and the magnitude of streamflow were due to antecedent soil moisture rainfall and slope morphology concave hillslope sections accumulated soil moisture due to both saturated and unsaturated lateral flow processes throughflow provided the mechanism and vehicle for solute movement from the groundwater discharge area to the stream however discharge from the deep aquifer was the primary mechanism responsible for soil salinity and maintaining the core of the variable source area estimates of throughflow which only take account of soil water movement and disregard returnflow will underestimate the magnitude of throughflow

sediment tracing in a reservoir catchment system using a magnetic mixing model magnetic mixing models are developed for specific susceptibility and a demagnetisation parameter which demonstrate how the magnetic properties of soils are altered by mixing these phenomena are used to interpret the composition of reservoir sediments in terms of the relative proportions of two types of source materials top soil and sub soil which are eroded from the catchment area and deposited in the reservoir the model provides a black box approach to the reservoir catchment system dependent on four simplifying assumptions which are the subject of current research application of the model to an afforested catchment suggests a marked change in the types of erosion processes associated with the maturation of the forestry plantation over a period of 50 yr

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

soil magnetism an approach for examining archaeological landscapes to investigate archaeological landscapes and the extent to which humans have influenced them we have developed an innovative approach that employs complementary geophysical methods drawn from the fields of exploration geophysics and soil magnetism integrating soil magnetic techniques with exploration surveys and more standard archaeological procedures i e topographic mapping excavation coring and soil chemical studies at the cahokia mounds site has helped us to better understand the formation of this premier north american mound center and has also demonstrated a scientific methodology of great potential for subsurface investigations of archaeological terrains

comparative taphonomy and phylogenetic signal of phosphatized weng an and kuanchuanpu biotas abstract the ediacaran cambrian is a time with globally enhanced production of phosphorites this includes perhaps the two most famous deposits with variable cell and soft tissue phosphatization in microfossils the ediacaran doushantuo formation which contains the weng an biota and the lower cambrian kuanchuanpu formation and equivalents found in china a wide range of variables is responsible for phosphatization during this interval including depositional and geochemical conditions and microbial activity degree of microfossil phosphatization is widely dependant upon original cell and tissue types microfossils with non diagenetic morphologies that are iconic for modern crown group metazoans have had the highest level of acceptance for their interpreted phylogenetic affinity microfossils with these iconic morphologies are rare from the weng an biota but relatively common from the kuanchuanpu biota thus metazoan affinity for doushantuo microfossils has commonly relied on relatively simple and less well known morphologic features of embryonic organisms for which there is not a concensus on the nature of their phylogenetic signal differences in the phosphatized microfossil record between the weng an and kuanchuanpu biotas are due to the combination of a primary signal reflecting the initiation of the cambrian explosion and a secondary signal driven by a multitude of taphonomic processes operating at different levels of effectiveness during deposition of these two units

the onset of spring melt in first year ice regions of the arctic as determined from scanning multichannel microwave radiometer data for 1979 and 1980 sea ice ablation is an important physical process affecting the global climate system during the arctic melt season rapid changes occur in both sea ice surface conditions and the extent of ice these changes alter the albedo and vary the surface energy budget understanding variations in arctic sea ice is critical for global climate studies this paper investigates the spring onset of melt in the arctic seasonal sea ice zone through analysis of melt signatures derived from nimbus 7 scanning multichannel microwave radiometer data satellite derived melt signatures determined by 18 and 37 ghz vertical brightness temperatures are associated with the initial melt of the snow pack on the sea ice surface sea ice melt events vary spatially and temporally within the arctic basin the melt signature is observed first in the chukchi sea and the kara and barents seas as melting progresses the melt signature moves westward from the chukchi sea and eastward from the kara and barents seas to the laptev sea region the initial location of the melt signal also varies with year in 1979 the melt signature occurs first in the chukchi sea and in 1980 in the kara sea the date for the initial melt varies between 1979 and 1980 by an average of 7 10 days with a maximum of 25 days in the chukchi sea region monitoring the occurrence of melt signatures can be used as an indicator of climate variability in the arctic s seasonal sea ice zones

a combined radiometric and mineral magnetic approach to recent geochronology in lakes affected by catchment disturbance and sediment redistribution abstract as a result of empirical testing of 210 pb dating models in a wide variety of lakes we conclude that there are many situations where despite major changes in sedimentation rates as a result of lake or catchment disturbance the crs constant flux model provides a sound basis for establishing recent chronology factors which may complicate or vitiate the assumptions of the model include short water residence time bioturbation for which we propose a modified dating model discontinuous or disturbed sedimentation sediment resuspension and shifts in sediment source in the case of the last three processes we illustrate ways in which the problems can be identified and evaluated using mineral magnetic measurements we propose an evaluative approach to 210 pb dating projects with emphasis on independent dating evidence on tests of internal consistency and on the use of data from several correlatable cores

june cloud cover over the arctic ocean june cloud cover over the beaufort sea west ward to the east siberian sea and up to approximately 85 n is manually charted using 12 years of satellite imagery

high resolution biostratigraphic and chemostratigraphic data from the chenjiayuanzi section of the doushantuo formation in the yangtze gorges area south china implication for subdivision and global correlation of the ediacaran system intensive investigations on the doushantuo formation of south china have greatly advanced our understanding of the evolution of multicellular life and the atmospheric oceanic system during the ediacaran period particularly the well established carbon isotope profile and rich acritarch microfossils from the composite carbonate and shale successions of the yangtze gorges area provide potential for chronostratigraphic subdivision and global correlation of the ediacaran system here we present high resolution biostratigraphic and carbon isotope data from a well exposed section the chenjiayuanzi section in the yangtze gorges area the bio and chemostratigraphic data confirm the presence of three distinct negative and two positive 13c excursions and two characteristic assemblages of acanthomorphic acritarchs the lower tianzhushania spinosa assemblage and upper hocosphaeridium scaberfacium hocosphaeridium anozos tanarium conoideum tanarium anozos in liu et al 2013 assemblage within the doushantuo formation the results demonstrate the clear stratigraphic relationship between the acritarch assemblages and carbon isotope excursions of the doushantuo formation and that the last occurrence of acanthomorphic acritarchs in the chenjiayuanzi section represents the last occurrence datum found so far in the yangtze gorges of south china four stratigraphic markers are suggested here for defining chronostratigraphic boundaries of the ediacaran system based on bio and chemostratigraphy combined with intra and interbasinal correlation in particular the base of the most significant and distinctive carbon isotope excursion dounce at the top of the doushantuo formation which is equivalent to the shuram wonoka event elsewhere shows potential to be a marker to define the series lower and upper boundary of the ediacaran system because it also marks the extinction of the ediacaran acanthomorphic acritarchs

wide but not ubiquitous distribution of glendonite in the doushantuo formation south china implications for ediacaran climate abstract glendonites are pseudomorphs of syndepositional or early authigenic ikaite caco3 6h2o that often forms at near freezing temperatures silicified glendonite has been reported from inner shelf deposits of the lower ediacaran doushantuo formation at a single stratigraphic section in south china where they are stratigraphically associated with the positive 13c excursion ep1 but predate the negative 13c excursion en3 shuram excursion indicating a period of cool climate somewhere between 609 ma and 551 ma this interpretation predicts a wider geographic distribution of ediacaran glendonites in equivalent strata in the yangtze block of south china to test this prediction we conducted a regional survey of doushantuo formation and found that although glendonites are not universally present they occur in expected stratigraphic intervals and in association with ep1 at two new sections representing inner shelf and intrashelf basin facies the wide but not ubiquitous distribution of doushantuo glendonites indicates that ikaite precipitation and glendonite formation was controlled by both regional climatic and local geochemical factors glendonites at the new localities are stellate clusters pseudomorphed by calcite spar and sometimes are rimmed with silica the calcite spar is characterized by highly variable and mostly negative 13c values as low as 37 indicating that diagenetic transformation of precursor ikaite to calcitic glendonite may be related to anaerobic oxidation of organic matter or methane in sediment the new data suggest an early ediacaran cold period prior to en3 or the shuram excursion and facilitation of glendonite ikaite formation by both climatic and local geochemical conditions such as redox conditions and phosphate concentrations

blanket peat erosion in a mid wales catchment during two drought years the rate of blanket peat erosion was measured at an upland site in central wales during the 1983 1984 drought years erosion pins a peat surface sediment trap and sediment sampling in the effluent stream were used to estimate the rate of peat surface recession and the rate of organic sediment loss from the catchment an overall rate of surface recession of 16 mm y 1 on exposed peat faces was recorded this differed between faces of different aspects with the greatest recession on southwest faces eroding peat surfaces exhibited maximum recession during the summer but the peat surface sediment trap indicated that the highest rates of sediment loss from peat faces due to rain wash occurred during the autumn and early winter stream sediment sampling showed that the yield of organic sediment from the catchment was 34 4 t km 2 yr 1 with greatest losses also during the autumn and early winter the evidence suggested that the surface recession as measured on erosion pins included a wastage or shrinkage component which possibly accounted for as much as 80 per cent of the apparent loss direct and circumstantial evidence suggested that peat wastage during the summer months was the most important agent of surface recession in the study period which encompassed the two dry summers desiccation provided available sediment during the autumn but organic sediment supply became limited as the winter progressed despite the occurrence of frost heave

misinterpreting proxy data for paleoclimate signals a comment on shukla et al 2020 shukla et al explored paleoclimatic signals from a 8 m thick profile of a moraine dammed lake in the central himalaya exposed due to lake burst from a flash flood in 2013 the main objective of t

pb pb ages of neoproterozoic doushantuo phosphorites in south china constraints on early metazoan evolution and glaciation events the pb pb isochron ages of 576 14 ma for the upper part of the upper phosphorite bed upb this study and 599 4 ma for the lower part of the upb earth planet sci lett 201 2002 203 in the doushantuo formation in the weng an area south china suggest that the deposition of the upb lasted at least 5 ma and indicate that the observed microfossil assemblage animal remains multicellular algae and giant process bearing acritarchs in the doushantuo formation predates all well dated diverse ediacaran assemblages and represents the earlier paleontological record of eukaryotes radiation on earth the 576 14 ma age in the upper part of the upb approximates the age of a negative delta 13 c excursion near the boundary between the doushantuo and the overlying dengying formation if the doushantuo dengying boundary at the weng an area is equivalent to that in the yangtze gorges area this negative excursion might correlate to a post marinoan glaciation in south china suggesting that the ice age following doushantuo sediment deposition is younger than 590 ma the 599 4 ma age in the lower part of the upb earth planet sci lett 201 2002 203 represents the minimum age of the nantuo diamictites which are generally correlated with the marinoan glaciation c 2004 elsevier b v all rights reserved

magnetic separation and evaluation of magnetization of brazilian soils from different parent materials abstract ten selected brazilian soils representative of oxisols ultisols alfisols and inceptisols and derived from gneiss basalt sandstone diabase and itabirite were sampled and examined to provide insight into the behavior of their magnetic minerals the objective was to measure the magnetization of the sand silt and clay fractions and to submit the clay fraction to variable magnetic fields to obtain the magnetization curves and to study their magnetic behavior as related to their parent material lithology the separation procedure using a magnetic separator was done in two different ways dry separation for the sand and wet separation for the silt and clay fractions x ray diffraction patterns of magnetic and nonmagnetic fractions were obtained and the segregation of ferrimagnetic minerals were shown the magnetization s of the total and the magnetic and nonmagnetic soil fractions was evaluated using a special analytical balance the s values obtained varied from 0 03 to 17 72 j t 1 kg 1 for sand 0 05 to 8 91 j t 1 kg 1 for silt and 0 05 to 2 54 j t 1 kg 1 for the clay fractions the results from the magnetically concentrated fractions varied in the same fashion but reached higher values magnetization curves showed spontaneous magnetization ms values of 0 6 to 3 35 j t 1 kg 1 high field slopes ranging from 0 17 to 0 77 j t 2 kg 1 and clearly the influence of the parent material lithology on the nature of the soil magnetic behavior magnetic measurements suggested pathways for ferrimagnetic minerals transformations in soil systems

quantitative evaluation of the biostratigraphic distribution of acanthomorphic acritarchs in the ediacaran doushantuo formation in the yangtze gorges area south china abstract doushantuo acanthomorphic acritarchs are large morphologically complex organic walled microfossils broadly constrained between the 635 ma nantuo glaciation and the 551 ma miaohe biota they are potential biostratigraphic tools for subdivision and correlation of the ediacaran system in south china however major variations in sedimentary facies and stratigraphic thickness present challenges in understanding the spatial and temporal distribution of these acritarchs further the distribution of acritarchs in the doushantuo formation is associated with the presence of early diagenetic chert and phosphate implying a certain degree of preservational bias and or environmental control the purpose of this paper is to document the stratigraphic distribution of doushantuo acritarchs and to quantitatively evaluate their biostratigraphic significance and possible taphonomic environmental biases based on high resolution paleontological data from six sections over 100 km in the yangtze gorges area south china a total of 1082 acritarch fossils were recorded from 84 chert horizons in the six sections of the study area these chert horizons are not uniformly distributed throughout the doushantuo formation thus the presence absence of early diagenetic chert does play a role in controlling the distribution of acritarchs the sampled chert horizons can be grouped into two stratigraphic intervals in the lower and upper doushantuo formation respectively based on regional stratigraphic correlation quantitative analysis shows that the two intervals are distinct taxonomically and largely independent of taphonomic or facies controls thus the two intervals can be regarded as assemblage biozones the lower biozone biozone 1 is numerically dominated by tianzhushania spinosa n 587 68 3 and meghystrichosphaeridium magnificum n 74 8 6 whereas the upper biozone biozone 2 is dominated by ericiasphaera rigida n 104 47 1 and tianzhushania spinosa n 34 14 1 the three most common genera meghystrichosphaeridium tianzhushania and ericiasphaera have been identified in all sections correspondence analysis ca detrended correspondence analysis dca discriminant analysis da and pairwise comparisons of samples spearman rank coefficient and jaccard chao index all consistently support biostratigraphic zonations thus the distribution of the doushantuo acanthomorphs is primarily controlled by biostratigraphic position of samples with facies and taphonomic differences playing a secondary role our case study suggests that acanthomorphic acritarchs can offer a viable tool for regional correlation of the ediacaran system

acanthomorphic acritarchs from the ediacaran doushantuo formation at zhangcunping in south china with implications for the evolution of early ediacaran eukaryotes abstract microfossil assemblages preserved in the ediacaran doushantuo formation phosphorites i e the weng an biota and chert nodules in south china provide key evidence for the diversification of marine eukaryotes in the aftermath of cryogenian global glaciation two biozones i e the lower tianzhushania spinosa biozone and the upper hocosphaeridium anozos biozone have been proposed on the basis of acanthomorphic acritarchs preserved in the doushantuo formation chert nodules in the yangtze gorges area strata containing the weng an biota at weng an have been correlated either with the upper acritarch biozone based mainly on chemostratigraphic data or with the lower acritarch biozone according to the occurrence of tianzhushania spinosa in both assemblages these alternative correlations need to be resolved in order to improve our understanding of the evolutionary pattern of microscopic eukaryotes after the marinoan glaciation to address this problem we carried out an integrated litho bio and chemostratigraphic study of the doushantuo formation in the zhangcunping area where the microfossil assemblage resembles the weng an biota at weng an in both taxonomic composition and biostratigraphic ranges our study supports the litho and chemostratigraphic correlation of the doushantuo formation between the zhangcunping and yangtze gorges areas thus the doushantuo formation at zhangcunping provides a link between the weng an and yangtze gorges areas together with published paleontological and stratigraphic data the present study favors a correlation between the fossiliferous strata at zhangcunping and the upper part of the t spinosa biozone recognized in the yangtze gorges area the strata yielding the weng an biota at weng an can be at least partially correlated with the t spinosa biozone supporting the idea that the weng an microfossil assemblage is biostratigraphically transitional between the lower and upper acanthomorphic assemblages this correlation is consistent with the fact that several taxa that used to be regarded characteristic of the h anozos biozone may actually range downsection into the t spinosa biozone thus supporting an earlier diversification of doushantuo acanthomorphs these results call for more detailed investigation on the taxonomic composition and biostratigraphic ranges of acanthomorphs in the t spinosa biozone and re consideration of acanthomorphic biozonation of the doushantuo formation in the yangtze gorges area

new lu hf and pb pb age constraints on the earliest animal fossils abstract the neoproterozoic doushantuo formation south china preserves a unique assemblage of early multicellular fossils and overlies rocks which are thought to have formed during an ice age of global extent the age of this formation is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon until now direct dating of sedimentary formations such as the doushantuo has been difficult and associated with large uncertainties here we show that dating of doushantuo phosphorites by a novel lu hf dating method and conventional pb pb geochronometry independently yield ages of 584 26 ma and 599 3 4 2 ma respectively these ages are in agreement with bio and chemostratigraphical observations and show that the doushantuo animal remains predate diverse ediacaran fossil assemblages making them the oldest unambiguous remains of metazoans currently known furthermore the pb pb age for the post glacial doushantuo rocks suggests that the neoproterozoic glaciation in china might predate glacial rocks in eastern north america commonly associated with the younger marinoan of two major neoproterozoic glaciations the combination of lu hf and pb pb dating shows considerable potential for dating other phosphorite successions and future application of these methods could therefore provide further constraints on proterozoic biological and environmental history

sediment source tracing using environmental magnetism a new approach with examples from australia environmental magnetism can be used for sediment source tracing in situations such as stream junctions where two catchments deliver magnetically distinguishable well combined average source mixes to a trunk stream consistent mineral magnetic parameter relationships show that spatially and temporally constant magnetic mineral assemblages occur along reaches of natural streams for most of the confluence mixing situations examined it is possible to distinguish between tributaries using magnetic parameter relationships using these relationships relative tributary contributions to the resultant downstream mix can be quantified the method can be used for tracing suspended and bedload sediments so that the principal source catchments can be determined by a sequence of measurements at stream junctions along a drainage network there is considerable potential for using this new and easily applied method for studies of sediment delivery processes and sediment movement in fluvial environments

strontium isotopes a tracer for river suspended iron aggregates abstract the kalix river shows distinct temporal variations in the sr isotope ratio in filtered water 0 726 0 732 during base flow in winter the 87 sr 86 sr ratio is on average 0 730 when discharge increases and peaks during spring flood the 87 sr 86 sr ratio shows the most radiogenic 0 732 values the temporal variations in the 87 sr 86 sr ratio in the kalix river can be explained by mixing of water from the woodlands and the mountain areas during high water discharge in may the 87 sr 86 sr ratios are more radiogenic in the suspended phase 1 kda 70 m compared to the truly dissolved phase 87 sr 86 sr ratio between the two phases 87 sr 86 sr is linearly correlated with the suspended iron concentration during spring flood sr and fe derived from an additional source reach the river deep groundwater has a more radiogenic 87 sr 86 sr isotope ratio than the kalix river during spring flood and thus represents a possible source for the suspended fe and the associated sr strontium can be coprecipitated with and adsorbed to different types of fe aggregates we propose that the sr isotope ratio in the suspended phase reflects the isotopic composition of the water at the interface between anoxic groundwater and oxic stream water in the riparian zone where the fe aggregates are formed these particles dominate the suspended phase in the river and the mixing with mountain waters poor in fe produces the difference in the isotopic signature the different signatures in suspended and truly dissolved fraction indicate that these aggregates are relatively stable during stream river transport as such the 87 sr 86 sr can be used to trace the origin of the non detrital suspended phase