coastal resilience and late holocene tidal inlet history the evolution of dungeness foreland and the romney marsh depositional complex u k dungeness foreland is a large sand and gravel barrier located in the eastern english channel that during the last 5000 years has demonstrated remarkable geomorphological resilience in accommodating changes in relative sea level storm magnitude and frequency variations in sediment supply as well as significant changes in back barrier sedimentation in this paper we develop a new palaeogeographic model for this depositional complex using a large dataset of recently acquired litho bio and chrono stratigraphic data our analysis shows how over the last 2000 years three large tidal inlets have influenced the pattern of back barrier inundation and sedimentation and controlled the stability and evolution of the barrier by determining the location of cross shore sediment and water exchange thereby moderating sediment supply and its distribution the sheer size of the foreland has contributed in part to its resilience with an abundant supply of sediment always available for ready redistribution a second reason for the landform s resilience is the repeated ability of the tidal inlets to narrow and then close effectively healing successive breaches by back barrier sedimentation and ebb and or flood tidal delta development humans emerge as key agents of change especially through the process of reclamation which from the saxon period onwards has modified the back barrier tidal prism and promoted repeated episodes of fine grained sedimentation and channel inlet infill and closure our palaeogeographic reconstructions show that large barriers such as dungeness foreland can survive repeated catastrophic breaches especially where tidal inlets are able to assist the recovery process by raising the elevation of the back barrier area by intertidal sedimentation this research leads us to reflect on the concept of coastal resilience which we conclude means little without a clearly defined spatial and temporal framework at a macro scale the structure as a whole entered a phase of recycling and rapid progradation in response to changing sediment budget and coastal dynamics about 2000 years ago however at smaller spatial and temporal scales barrier inlet dynamics have been associated with the initiation stabilisation and breakdown of individual beaches and complexes of beaches we therefore envisage multiple scales of resilience operating simultaneously across the complex responding to different forcing agents with particular magnitudes and frequencies

modelling of estuarine response to sea level rise during the holocene application to the guadiana estuary sw iberia this paper focuses on simulations of the morphological evolution of an estuary during sedimentary infilling that accompanied holocene sea level rise the simulations were conducted using the estuarine sedimentation model which uses a behaviour oriented approach supported by the chronostratigraphy of the estuary s sedimentary sequence behaviour curves were computed to represent the relationship between the estuarine channel depth below maximum high tide and the net accretion at a given location relative to the average sedimentation rate of the estuary during the holocene the model was validated by comparing the observed present day bathymetry of the guadiana river estuary southeastern portugal with the corresponding simulated bathymetries for nine control sections across the estuary the best fit between simulated and actual sediment surface elevations was obtained along the cross sections in the sheltered low energy environments of the estuary the accuracy of the sedimentary stratigraphy of the best fit model was further established using 16 radiocarbon ages obtained from five boreholes in the estuary the present approach is particularly suitable for simulating long term morphological evolution in sheltered estuarine environments where tidally driven vertical aggradation dominates at centennial to millennium timescales however the accuracy of simulated sediment surface elevations and consequently the robustness of behaviour type models based on geographical information system platforms can be enhanced by incorporating i the impacts of nearshore hydrodynamic processes and episodic flood events in highly energetic channels and ii the impacts of cross currents in meandering channel sections

chemical weathering of a marine terrace chronosequence santa cruz california i interpreting rates and controls based on soil concentration depth profiles abstract the spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal california are interpreted in terms of chemical weathering rates and processes in regoliths up to 15 m deep and 226 kyrs old quartz normalized mass transfer coefficients indicate non stoichiometric preferential release of sr ca na from plagioclase along with lesser amounts of k rb and ba derived from k feldspar smectite weathering results in the loss of mg and concurrent incorporation of al and fe into secondary kaolinite and fe oxides in shallow argillic horizons elemental losses from weathering of the santa cruz terraces fall within the range of those for other marine terraces along the pacific coast of north america residual amounts of plagioclase and k feldspar decrease with terrace depth and increasing age the gradient of the weathering profile bs is defined by the ratio of the weathering rate r to the velocity at which the profile penetrates into the protolith a spreadsheet calculator further refines profile geometries demonstrating that the non linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface to volume ratios and at high residual feldspar concentrations at greater depth by the approach to thermodynamic saturation these parameters are of secondary importance to the fluid flux qh which in thermodynamically saturated pore water controls the weathering velocity and mineral losses from the profiles long term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute cl balances qh 0 025 0 17 m yr 1 during saturation controlled and solute limited weathering the greater loss of plagioclase relative to k feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics the steady state weathering rate under such conditions is defined as r q h m sol m total 1 s v b s the product of qh and the ratio of solubilized to solid state feldspar msat mtotal define the weathering velocity the weathering gradient bs reflects the kinetic rate of reaction where sv is the volumetric surface area of the residual feldspar both this rate expression and the spreadsheet calculations produce similar plagioclase weathering rates r 5 14 10 16 mol m 2 s 1 which agree with those reported for other environments of comparable climate and age weathering dependent concentration profiles are commonly described in literature the present paper provides methods by which these data can yield a more fundamental understanding of the weathering processes involved

application of the qda md method of environmental discrimination to particle size analyses of fine sediments by pipette and sedigraph methods a comparative study the results of particle size analyses by the low technology pipette method and by the modern sedigraph of a suite of fine lacustrine bottom sediment samples are compared good correlations between the two data sets are observed although the sedigraph consistently indicates finer grain sizes and better sorting of distributions the qda md method of environmental discrimination originally established on the basis of traditional methods of size analysis is found to be sufficiently versatile to accommodate the sedigraph data into the appropriate trend envelopes despite the considerable differences in derived grain size parameters

recognition of trench fill in orogenic flysch sequences ancient trench fill deposits within erogenic eugeosynclinal sequences are best recognized by their stratigraphic position above older hemipelagic and pelagic deposits such coarsening upward sequences reflect migration of an abyssal site toward and ultimately into the trench axial transport and continuity of turbidites may help to better define trench geometry and sedimentation patterns but alone are not strong evidence for trench sedimentation likewise sandstone petrography because it is influenced by such variables as tectonic and geologic peculiarities of the source area and transport of detritus from distant terrenes is not a useful tool for recognition of trench deposits melanges and broken formations are best considered as evidence for gravity transport of material onto the trench floor or tectonic deformation of trench fill when they are part of a coarsening upward sequence

kurosegawa zone and its bearing on the development of the japanese islands abstract the kurosegawa zone in southwest japan is a 600 km long serpentinite melange in the chichibu terrains it runs generally e w but is slightly oblique to the subparallel arrangement of the ryoke sanbagawa and chichibu belts of southwest japan a variety of geological units occurs in the kurosegawa zone 1 1 granodiorite gneiss and amphibolite of ca 400 ma 2 2 siluro devonian formations 3 3 upper carboniferous to jurassic formations 4 4 upper jurassic to lower cretaceous formations 5 5 serpentinite and 6 6 low to medium grade metamorphic rocks of various baric types ages 220 320 360 and 420 ma by k ar the most widespread is a high pressure intermediate group of metamorphic rocks serpentinite is emplaced along the faults between and within the constituent units rocks of the kurosegawa zone represent a mature orogenic belt along a continental margin or an island arc its original site as constrained by paleomagnetism was near the equatorial area here 400 ma old paired metamorphism and related magmatism took place the island arc or microcontinent migrated northward to collide with the eurasia plate during late jurassic thus consuming the intervening ocean

the impact of the 2009 10 el nino modoki on u s west coast beaches 1 high resolution beach morphology data collected along much of the u s west coast are synthesized to evaluate the coastal impacts of the 2009 10 el nino coastal change observations were collected as part of five beach monitoring programs that span between 5 and 13 years in duration in california regional wave and water level data show that the environmental forcing during the 2009 10 winter was similar to the last significant el nino of 1997 98 producing the largest seasonal shoreline retreat and or most landward shoreline position since monitoring began in contrast the 2009 10 el nino did not produce anomalously high mean winter wave energy in the pacific northwest oregon and washington although the highest 5 of the winter wave energy measurements were comparable to 1997 98 and two significant non el nino winters the increase in extreme waves in the 2009 10 winter was coupled with elevated water levels and a more southerly wave approach than the long term mean resulting in greater shoreline retreat than during 1997 98 including anomalously high shoreline retreat immediately north of jetties tidal inlets and rocky headlands the morphodynamic response observed throughout the u s west coast during the 2009 10 el nino is principally linked to the el nino modoki phenomena where the warm sea surface temperature sst anomaly is focused in the central equatorial pacific as opposed to the eastern pacific during a classic el nino featuring a more temporally persistent sst anomaly that results in longer periods of elevated wave energy but lower coastal water levels

macro and micro scale study and chronology of late weichselian aeolian sediments in estonia north eastern european sand belt patchy aeolian landforms representing the ne part of the european sand belt occur in ne estonia between the gulf of finland and lake peipsi the dunes are restricted to the former glacial lakebed thus lying directly in contact with glaciolacustrine sediments and have so far prompted different opinions regarding their genesis and age this study aims to answer these open questions regarding the age and origin of these landforms and to provide information on the associated past sedimentary processes to achieve this we combine macro scale sedimentary structures and ground penetrating radar survey and micro scale grain size shape and character of quartz grain surfaces and mineral composition studies with optically stimulated luminescence dating the glaciolacustrine fines in the study area are wavy stratified with the occurrence of mica horizons and prevalence of quartz sand grains with aeolian characteristics therefore these sediments argue for near standing low energy water conditions in the glacial lake where allochthonous material was delivered by wind a fall in the lake level and the occurrence of dry land on the northern coast of the regressive late weichselian lake peipsi favoured aeolian activity from ca 13 5 to 10 5 ka in the region the aeolian accumulation was brief as apparent from the results of the micro scale study and lacks evidence of sediment recycling only easily removable mica was deflated at the end of the aeolian depositional phase aeolian activity terminated ca 10 5 ka due to a rising groundwater level that is apparent from the onset of paludification in the region

molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans how much dissolved oxygen was present in the mid proterozoic oceans between 1 8 and 1 0 billion years ago is debated vigorously one model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen 2 3 billion years ago recent evidence for h 2 s in some mid proterozoic marine basins suggests however that the deep ocean remained anoxic until much later new molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid proterozoic compared to the present day ocean consequently oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years

denudation rates thermal evolution and preservation of blueschist terrains the erosion of low temperature high pressure blueschist facies metamorphic rocks presents a number of problems if their rate of erosion is not sufficiently rapid then the rise in temperature caused by thermal relaxation and radioactive self heating is great enough to obliterate the original low temperature mineral assemblages the problem has been investigated using a one dimensional two layer model to mimic an accretionary prism overlying oceanic lithosphere the results suggest that if no erosion takes place the maximum time that blueschist conditions may exist is about 26 m y if levels of radioactive self heating are high and approximately 100 m y if levels are very low if erosion takes place the maximum temperature reached by an element of rock is at a higher level in the earth s crust than its initial depth of burial rocks may re equilibrate at this temperature or be overprinted by incomplete reactions depending on the temperature rise and rocks involved this could result in the geotherm

chronology of sanbagawa metamorphism by collating age data based on the fossil age of the protoliths radiometric dating of the metamorphic minerals and sedimentary records of erosion at the earth s surface the history of the sanbagawa metamorphism can be summarized as follows 1 the pre metamorphic sedimentary rocks carboniferous jurassic early cretaceous became mixed and formed a thickened packet in the vicinity of an ancient trench through a variety of subduction related tectono sedimentary processes probably in early cretaceous time c 130 120 ma 2 the subducted protoliths underwent progressive metamorphism reaching a maximum depth of c 30 km in late early cretaceous time c 116 10 ma 3 the high p t metamorphic rocks began to rise toward the surface during the interval 110 50 ma with minimum estimates for the average cooling rate around 9 12 c ma and an average uplift rate around 0 4 0 5 mm year 4 finally at some stage after reaching the erosional surface the high p t metamorphic rocks were covered unconformably by the middle eocene c 50 42 ma kuma group on the basis of the present chronological summary of the sanbagawa metamorphism the areal extent of the sanbagawa metamorphism is also discussed with respect to the weakly metamorphosed subduction accretion complex of the next tectonic belt to the south the northern chichibu belt

the higher grade metamorphic zonation of the sambagawa metamorphic belt in central shikoku japan the higher grade metamorphic zonation of the sambagawa sanbagawa belt is established for the first time for the whole area of central shikoku as discontinuous reactions to define the isograd are absent the metamorphic grade is primarily determined by the mg fe partitioning between garnet and chlorite along representative traverses however for regional mapping mineralogical features of the pelitic schists such as using mineral assemblages of more than divariant equilibrium the modal garnet to chlorite ratio and the optical properties of chlorite are employed as auxiliary criteria the presence of the highest grade mineral zone in the middle of the structural level is confirmed but its spatial distribution is far more complex than hitherto accepted thermal axes are now confirmed at three different structural levels a model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re equilibrated local anomalies of metamorphic grade represented by mixing of schists of different metamorphic grade exist but they are due to a later stage event

seawater redox variations during the deposition of the kimmeridge clay formation united kingdom upper jurassic evidence from molybdenum isotopes and trace metal ratios 1 the kimmeridge clay formation kcf and its equivalents worldwide represent one of the most prolonged periods of organic carbon accumulation of the mesozoic in this study we use the molybdenum mo stable isotope system in conjunction with a range of trace metal paleoredox proxies to assess how seawater redox varied both locally and globally during the deposition of the kcf facies with lower organic carbon contents toc 1 7 wt were deposited under mildly reducing suboxic conditions while organic rich facies toc 7 wt accumulated under more strongly reducing anoxic or euxinic local conditions trace metal abundances are closely linked to toc content suggesting that the intensity of reducing conditions varied repeatedly during the deposition of the kcf and may have been related to orbitally controlled climate changes long term variations in 98 95mo are associated with the formation of organic rich intervals and are related to third order fluctuations in relative sea level differences in the mean 98 95mo composition of the organic rich intervals suggest that the global distribution of reducing conditions was more extensive during the deposition of the pectinatites wheatleyensis and lower pectinatites hudlestoni zones than during the deposition of the upper pectinatites hudlestoni and pectinatites pectinatus zones the global extent of reducing conditions during the kimmerigidan was greater than today but was less widespread than during the toarcian early jurassic oceanic anoxic event this study also demonstrates that the mo isotope system in jurassic seawater responded to changes in redox conditions in a manner consistent with its behavior in present day sedimentary environments

on bagnold s sediment transport equation in tidal marine environments and the practical definition of bedload bagnold s sediment transport equation has proved to be important in studying tidal marine environments this paper discusses three problems concerning bagnold s transport equation and its practical application 1bagnold s suspended load transport equation and the total load transport equation with are incorrect from the viewpoint of energy conservation in these equations the energy loss due to bedload transport has been counted twice the correct form should be for suspended load transport and for total load transport with 2the commonly used bagnold s transport coefficient k varies as a non linear function of the dimensionless excess shear stress which can be represented best by the power law where the coefficient a and exponent b depend on sediment grain size d the empirical values of a and b for fine to medium grained sands are determined using guy et al s 1966 flume experiment data 3the sediment transport rates predicted from this equation are compared with bedform migration measurements in the flume and the field this comparison shows that the sediment transport rates measured from bedform migrations are higher than the predicted bedload transport rates but comparable to the calculated total load bedload plus intermittent suspended load transport rates this indicates that bedform migration involves both bedload and intermittent suspended load transport as a logical conclusion bedform migration data should be compared with bagnold s total load transport equation rather than with his bedload transport equation in this respect the term bed material might be more appropriate than the term bedload for estimating sediment transport rate from bedform migration data the sediment transport rates predicted from this modified bagnold transport equation are in good agreement with field measurements of bedform migration rates in four individual tidal marine environments which cover a wide range of sediment grain size flow velocity and bedform conditions ranging from small ripples megaripples to sandwaves

clasts of high grade sanbagawa schist in middle eocene conglomerates from the kuma group central shikoku south west japan middle eocene conglomerates which overlie the sanbagawa metamorphic rocks contain clasts of metamorphic rock with isotope ages of 120 85 ma which fall within the age range reported from the sanbagawa metamorphic rocks they were derived from the chlorite to oligoclase zones of the sanbagawa metamorphic belt clasts of garnet amphibolite and oligoclase biotite schist show a mineral assemblage similar to the highest grade sanbagawa schists however the metamorphic temperatures estimated by various mineralogical thermometers show that some of the clasts were formed at higher temperatures than the in situ sanbagawa metamorphic rocks such higher grade rocks were at the surface by the middle eocene and for the most part they have been eroded away cretaceous and post cretaceous sediments overlie or are in fault contact with the sanbagawa metamorphic rocks which suggests that rocks in the belt were uplifted and eroded from the latest cretaceous to middle eocene time after strike slip movement along the median tectonic line since the middle eocene the belt has experienced relatively slow uplift which was locally around 2 km in central shikoku

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

comment on metamorphic p t time history of the sanbagawa belt in central shikoku japan and implications for retrograde metamorphism during exhumation by k aoki k kitajima h masago m nishizawa m terabayashi s omori t yokoyama n takahata y sano s maruyama lithos 113 2009 393 407 article history received 17 november 2009 accepted 24 january 2010 available online 6 february 2010 zones new zircon u pb age data presented by aoki et al 2009 of 85 6 3 0 ma are in good agreementwith relatively youngmetamorphism and rapid exhumation however aoki et al 2009 interpret these ages as recording the timing of retrograde metamorphism significantly later than the peak at around 120 ma in this comment we raise three points concerning the treatment of age data given by aoki et al 2009 we

mesoscale coastal behavior related to morphological self adjustment high energy events extratropical storms tsunamis and hurricanes sediment supply variability and sea level rise are regarded as major drivers of coastal geomorphic behavior in this paper we document a 170 yr record of cyclic coastal changes that occur independently of such external drivers in a geologically constrained situation with no external sediment input two end member morphological configurations attractors are identified between which the system alternates although neither configuration is stable the system as a whole exhibits century scale equilibrium our findings present a hitherto unreported form of decadal scale self adjustment in a coastal system that has occurred under a stable sea level with a consistent wave and tidal regime

sediment supply and barrier dynamics as driving mechanisms of holocene coastal change for the southern north sea basin the combined effects of climate change and human impact lead to regional and local coastal responses that pose major challenges for the future resilience of coastal landscapes increasing the vulnerability of communities infrastructure and nature conservation interests using the suffolk coast southeast england as a case study we investigate the importance of sediment supply and barrier dynamics as driving mechanisms of coastal change throughout the holocene litho bio and chronostratigraphic methods are used to decipher the mechanisms of coastal change from the record preserved within coastal stratigraphy results suggest that local coastal configuration and sediment supply were the most influential in determining coastal change during the mid and late holocene against a background control of sea level rise the importance of sedimentological and morphological factors in shaping holocene coastal changes in the southern north sea basin must therefore be considered when using the database of evidence from this region as an analogue for future change under accelerated sea level rise

heterogeneous oxygenation states in the atlantic and tethys oceans during oceanic anoxic event 2 abstract the cenomanian turonian boundary ca 93 5 ma is marked by an episode of profound environmental change including a major perturbation of the carbon cycle and an oceanic anoxic event oae 2 here we present molybdenum mo isotope variations within the oae 2 interval for four sections from the western tethys furlo and la contessa and the north atlantic odp site 1276 and dsdp site 367 the main target of this study is to investigate the extent of reducing conditions truly global in extent or restricted to poorly ventilated restricted deep basins with particular reference to the relationship between the change in the oxygenation state of the ocean and the link to global perturbations of the carbon cycle recorded in carbon isotopes all four sections show fluctuations in the redox sensitive trace metal rste distribution suggesting rapid variations in local redox conditions ranging from anoxic to euxinic the rste enrichment factors efs also suggest different depositional conditions and paleoceanographic processes in the western tethys versus the north atlantic whereas the north atlantic sites show evidence of weak watermass restriction associated with the action of a particulate shuttle within the water column the efs of the tethyan sections are characteristic of unrestricted marine systems mo isotopes show surprisingly negative values through the tethyan sections at the onset of oae 2 an increasing trend in mo 98 is observed with values ranging from 0 6 to 0 6 during the second half of oae 2 the mo 98 curve shows a progressive shift towards more negative values in the north atlantic mo 98 signatures from odp site 1276 show a similar behaviour as observed in the western tethys at dsdp site 367 mo isotopes are generally heavier during oae 2 fluctuating around an average value of 1 1 this is consistent with fully euxinic conditions and the black shales deposited may have recorded the seawater signature during oae 2 the mo isotope signature is lighter than the modern ocean value 2 3 and suggests a higher proportion of bottom water euxinia 10 although this estimate is greater than the euxinic fraction in the modern ocean our results challenge the suggestion of a globally euxinic deep waters during oae 2 the variations in mo toc ratios within the north atlantic and tethys oceans are in good agreement with a general drawdown of mo within the oae interval suggesting a general increase in anoxic conditions during oae 2 our results highlight the role of local parameters in the development of euxinia even during period of widespread anoxia such as oaes

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

response to comment on molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans relating changes in mo isotope signatures preserved in the geologic record to changes in the extent of seafloor anoxia is not a trivial exercise we previously presented and interpreted new mo isotope data as indicating expanded anoxia in mid proterozoic oceans potentially reaching global extent ling et al challenge our conclusions arguing that the data are not consistent with widespread anoxia we stand by our original interpretation but welcome the opportunity to clarify and expand on those conclusions particularly in view of the potential importance of ocean redox change for biological evolution

particle size evidence of estuary evolution a rapid and diagnostic tool for determining the nature of recent saltmarsh accretion abstract a conceptual model of saltmarsh sedimentation based on high resolution particle size analysis has been tested on short cores c 0 5 m of known age from the dee estuary nw england uk here two components of the particle size distribution psd are interpreted as the traction load deposited by the faster tidal flow velocities fast tide and the suspension load that settles during the turn of the tide slow tide the feasibility of this model for diagnosing the driving mechanism of estuary evolution in both time and space is tested with reference to historical evidence of saltmarsh accretion up core trends in dated saltmarsh cores and the psds of present day saltmarsh surface sediments cores that show an up core progression from very fine skewed to near symmetrical psds are interpreted in the context of estuary infilling due to a positive sediment budget sediment surplus whilst those that show a persistence of near symmetrical very poorly sorted mesokurtic particle size distributions in the fine to very fine silts size range are considered to be the result of slow tide sedimentation the influences of the two end member styles of saltmarsh accretion i e i infilling due to sediment surplus and ii slow tide settling linked to sea level exhibit spatial and temporal trends as predicted particularly in cores from mid and lower saltmarsh locations the upper saltmarsh cores also show evidence of estuary infilling due to slow tide sedimentation at rates in excess of sea level rise the results confirm that the diagnostic approach can be applied as a pre filtering method for assessing the suitability of saltmarsh sediments for reconstructing sea level trends and for providing input data for improved estuary morphological modelling

a 5000 year record of carbon sequestration from a coastal lagoon and wetland complex southern california usa abstract coastal wetlands have the potential to accumulate c at high rates over long time periods because they continuously accrete and bury organic rich sediments giving soils in coastal wetlands a distinct advantage over many other environments in the sequestration of organic c given that coastal wetlands are being lost worldwide it is important to understand their c sequestration potential sediments in a southern california usa coastal lagoon wetland complex were cored and depositional environments were interpreted suitable materials were radiocarbon dated bulk density and organic c were grouped by depositional environments and average mass of c per unit volume and c accumulation rates in each depositional environment were calculated the total organic c sequestered and rates of sequestration in each depositional environment were in the following order from most fastest to least slowest lagoon intertidal salt marsh freshwater marsh aeolian this study demonstrated that high levels of organic c are sequestered per unit volume of sediment 35 9 3 2 kg m 3 and the mean rate of c accumulation was high 0 033 0 0029 kg c m 2 year 1 over a long time period 5000 years results of this study strongly demonstrate the importance and necessary high priority for preserving and restoring coastal wetlands both in the usa and internationally however despite their excellent potential to sequester c significant losses of coastal wetlands are occurring in the united states and elsewhere in the world

molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the early jurassic relatively brief periods of severe paleoenvironmental change during the jurassic and cretaceous were associated with the widespread accumulation of organic rich marine deposits termed oceanic anoxic events oaes these intervals involved abrupt global warming of 5 10 c higher rates of continental weathering elevated extinction rates and large scale perturbations to the global carbon cycle the major oaes also overlapped temporally the emplacement of large igneous provinces however despite being known as oaes the extent of seawater anoxia at those times is undefined and the causative processes remain unclear here we show how changes in seawater molybdenum isotope ratios a proxy for seawater anoxia during the toarcian early jurassic oae define the onset and expansion of oxygen deficient conditions our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically broadly in line with precession driven changes in 13 corg despite their intermittent occurrence over geological history oaes have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day

re assessing the surface cycling of molybdenum and rhenium we re evaluate the cycling of molybdenum mo and rhenium re in the near surface environment world river average mo and re concentrations initially based on a handful of rivers are calculated using 38 rivers representing five continents and 11 of 19 large scale drainage regions our new river concentration estimates are 8 0 nmol kg 1 mo and 16 5 pmol kg 1 re natural anthropogenic the linear relationship of dissolved re and so 2 4 in global rivers r 2 0 76 indicates labile continental re is predominantly hosted within sulfide minerals and reduced sediments it also provides a means of correcting for the anthropogenic contribution of re to world rivers using independent estimates of anthropogenic sulfate approximately 30 of re in global rivers is anthropogenic yielding a pre anthropogenic world river average of 11 2 pmol re kg 1 the potential for anthropogenic contribution is also seen in the non negligible re concentrations in precipitation 0 03 5 9 pmol kg 1 and the nmol kg 1 level re concentrations of mine waters the linear mo so 2 4 relationship r 2 0 69 indicates that the predominant source of mo to rivers is the weathering of pyrite an anthropogenic mo correction was not done as anthropogenically influenced samples do not display the unambiguous metal enrichment observed for re metal concentrations in high temperature hydrothermal fluids from the manus basin indicate that calculated end member fluids i e mg free yield negative mo and re concentrations showing that mo and re can be removed more quickly than mg during recharge high temperature hydrothermal fluids are unimportant sinks relative to their river sources 0 4 mo and 0 1 pre anthropogenic re we calculate new seawater response times of 4 4 10 5 yr smo and 1 3 10 5 yr sre pre

the relationship between the rate of mesoscale sea level rise and the rate of retreat of swash aligned gravel dominated barriers abstract in theory a rise in sea level should force swash aligned gravel barriers to retreat landwards evidence from three single crested swash aligned gravel barriers from eastern canada and northwest europe indicates that barrier retreat rate correlates with the rate of sea level rise measured over the lower end of the mesoscale time spectrum subdecadal 10 0 yr 10 1 yr there is also a relationship between a barrier s rate of change in retreat rate and the decadal mesoscale mean rate of sea level rise specified by the duration of the tide gauge record 10 1 yr 10 2 yr specifically the higher the decadal mesoscale sea level rise rate the faster the rate of retreat of the swash aligned gravel barrier however this latter relationship may also be a function of the barrier s inertia as defined by the barrier s cross sectional volume in that barrier retreat rate correlates negatively with barrier inertia

sea cliff erosion as a function of beach changes and extreme wave runup during the 1997 1998 el nino abstract over time scales of hundreds to thousands of years the net longshore sand transport direction along the central california coast has been driven to the south by north pacific winter swell in contrast during the el nino winter of 1997 1998 comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches this resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends coincident with the south to north redistribution of sand shoreline morphology became prominently cuspate with longshore wavelengths of 400 700 m the width and elevation of beaches were least where maximum shoreline erosion occurred preferentially exposing cliffs to wave attack the resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches the observed magnitude of sea cliff retreat which reached 14 m varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the el nino winter a threshold representing the width of the beach performed better than a threshold representing the elevation of the beach the magnitude of cliff erosion can be scaled using a simple model based on the cross shore distance that extreme wave runup exceeded the pre winter cliff position cliff erosion appears to be a balance between terrestrial mass wasting processes which tend to decrease the cliff slope and wave attack which removes debris and erodes the cliff base increasing the cliff slope

holocene estuary development in the algarve region southern portugal a reconstruction of sedimentological and ecological evolution this paper presents a reconstruction of the former coastal estuaries of the quarteira and carcavai estuaries in southern portugal based on sedimentological geochemical and palynological analyses of holocene sediment cores the results show that each estuary developed differently depending on the morphology of the palaeovalley environmental conditions and especially the influence of the sea and the formation of barrier systems both estuaries were flooded between 7000 and 5500 cal bp by sea level rise and were almost completely filled by sediment by the beginning of the roman occupation 226 bc 2176 cal bp a clear change in sedimentological processes is evident in both estuaries between 5500 and 3000 cal bp and is interpreted as an erosion phase or evidence of high energy events such as storms or tsunamis

geomorphological variability among microtidal estuaries from the wave dominated south african coast abstract over 300 independent river outlets exist around the microtidal wave dominated south african coast most of these are located in drowned river valley settings and have acquired their present morphology during the holocene marine transgression a variety of geomorphological forms are identified in these estuaries that result from variation in antecedent topography fluvial sediment supply and marine sediment supply five distinctive estuary types are identified on the basis of contemporary morphodynamics these are categorised into three types of normally open estuary that maintain a semi permanent connection with the open sea and two types of normally closed estuary which are separated from the sea for long periods by a continuous supratidal barrier the contemporary morphodynamics and sedimentary environments of each estuary type are discussed open estuaries include barrier inlet systems maintained by fluvial discharge termed river dominated estuaries and tidal discharge termed tide dominated estuaries a third category of open estuary lacks a supratidal barrier due to inadequate marine sediment availability closed estuaries receive marine influence via barrier overwash and occasional breaching but are typically enclosed behind a continuous supratidal barrier two categories of closed estuary are identified perched and non perched perched estuaries develop behind high berms and maintain a water level above high tide level in the open sea they are often dominated by fresh to brackish water and breach and drain periodically non perched estuaries are developed behind low elevation barriers fronted by wide dissipative beach profiles high overwash frequency introduces marine water into such systems breaching of such estuaries does not produce dramatic draining as the water level may only drop according to the stage of the open sea tidal cycle the variety of estuary types suggests several potential pathways may exist in estuarine development and that the progressive infilling model is an over simplification

corrigendum to basin scale controls on the molybdenum isotope composition of seawater during oceanic anoxic event 2 late cretaceous geochim cosmochim acta 178 2016 291 306

variations in total organic carbon and acid volatile sulfide distribution in surface sediments from luan river estuary china the distribution of total organic carbon toc acid volatile sulfide avs and sediment grain sizes was studied in surface sediments collected from the coastal water near luan river estuary during spring and summer 2015 the aim was to examine the relationships between toc avs and sediment grain sizes the paired samples t test result revealed that seasonal variation had significant effects on the spatial distribution of toc and avs in the surface sediments p 0 05 the scatter plots indicated that avs concentration had significant positive correlations with toc content in both spring and summer spring r 0 475 p 0 05 summer r 0 689 p 0 01 the toc content had a good correlation with sediment grain size and for both seasons toc contents were relatively higher in fine grained sediments the relationship between avs concentration and sediment grain size was not significant in the spring but was significant in the summer cluster analysis further revealed that the spatial distribution of toc and avs in surface sediments was significantly affected by sediment grain size and these distributions varied slightly between the seasons according to avs concentrations in surface sediments the coastal water near luan river estuary during spring and summer 2015 was considered as the healthy area

pressure temperature trajectory of the sanbagawa metamorphism deduced from garnet zoning abstract most garnets in a small volume of the pelitic sanbagawa schists nucleated simultaneously grew and then ceased with their growth maintaining near equilibrium with coexisting minerals such as chlorite and biotite during the prograde metamorphism chemical trends of zoned garnets systematically shift from the pyrope poor to pyrope rich portions in a ternary mn fe mg system in order of ascending metamorphic grade a ternary mn fe mg model system suggests that the higher grade garnets started to grow at lower pressures and higher temperatures than the lower grade ones during prograde metamorphism it follows that high grade metamorphism took place at lower pressures in the garnet to oligoclase biotite zones of the sanbagawa metamorphic terrain in central shikoku

rapid coastal change during the mid to late holocene the record of barrier estuary sedimentation in the romney marsh region southeast england a common problem facing sea level researchers lies in determining the cause of rapid changes observed in coastal stratigraphic sequences such changes are commonly ascribed to the interaction of processes that operate over differing temporal and spatial scales i e rapid local and regional sea level trends and storm magnitude frequency at least some of the difficulty in distinguishing between these processes lies in the often limited stratigraphic database upon which palaeoenvironmental reconstruction is based here we present the results of detailed morphostratigraphic and micropalaeontological investigations from a series of sites located at the interface between the protective gravel barrier complex of dungeness and the barrier estuary sediments of romney marsh england a period of rapid coastal regression is identified between c 4500 and 3000 cal yrs bp during which time the sea level continued to rise but was outpaced by sediment accretion and peat accumulation a subsequent acceleration in th

basin scale controls on the molybdenum isotope composition of seawater during oceanic anoxic event 2 late cretaceous abstract it is well established that the burial of organic carbon in marine sediments increased dramatically at a global scale at the cenomanian turonian boundary oceanic anoxic event 2 oae 2 94 myr ago late cretaceous many localities containing chemostratigraphic expressions of this event are not however enriched in organic carbon and point to a heterogeneous set of oceanographic and environmental processes operating in different ocean basins these processes are difficult to reconstruct because of the uneven geographical distribution of sites recording oae 2 thus limiting our understanding of the causes and palaeoceanographic consequences of the environmental changes that occurred at this time a new highly resolved molybdenum isotope dataset is presented from the cape verde basin southern proto north atlantic ocean and a lower resolution record from the tarfaya basin morocco the new data reveal periodic oscillations in the mo isotope composition of proto north atlantic ocean sediments from which coupled changes in the dissolved sulphide concentration and mo inventories of the basin seawater can be inferred the cyclic variations in sedimentary mo isotope compositions can be hypothetically linked to regional changes in the depth of the chemocline and in the rate of seawater exchange between basinal waters and global seawater the new data suggest that a global seawater mo isotope composition of 1 2 was reached very soon after the onset of oae 2 implying a rapid expansion of marine deoxygenation coeval with or slightly preceding enhanced global rates of organic carbon burial during oae 2 the modelled flux of mo into anoxic sediments is likely to have been 60 125 times greater than at the present day although the spatial extent of anoxia is unlikely to have been greater than 10 of the total seafloor

modern sedimentary facies in a progradational barrier spit system goro lagoon po delta italy abstract barriers and spits connected to fluvial sedimentary sources represent environments which tend to evolve rapidly and experience sudden transformations mainly driven by changes in sediment supply and path as a consequence the variability of facies is significant even within small sedimentary records the 7 km long barrier spit system facing the goro lagoon and fed by the mouth of the po di goro is a typical example of an accretionary coastal morphotype suitable to describe adjacent nearshore depositional environments and their stratigraphic signatures variability and relationships thirteen short cores of sediment were sampled in order to represent the variable depositional sub environments from the shoreface prodelta delta front to the back barrier crossing the active barrier spit and the ancient spit arms and relative swales the description of the modern sedimentary records improved upon using core x rays has been coupled with information on the morphological changes which occurred during the period of maximum spit development 1955 2000 based on available aerial photos and a cartographic topographic dataset the results obtained allow for the description and interpretation of the depositional environments changing at the human scale sediments of the upper shoreface are quite uniform composed by evenly laminated sands the transition between delta front and prodelta at a depth of 6 m is marked by the alternation of sand and mud beds these reflect the periodic changes in sediment supply by the river as well as storm events the most recent spit branch and the relative back barrier swale environment are the results of the rapid progradation of the spit system which implies phases of rapid longshore growth hooked spit development cannibalization overwash and breaching morphodynamic changes have resulted in an overlap of short sedimentary records where stratigraphic signatures are linked either to phases of sediment transport and selection by waves and tidal currents cross bedding foreset and planar laminated sands shell imbrication massive beds or to phases of sedimentary stasis when biological activity is predominant algal mat and bioturbation human signature is also well marked inside the stratigraphic record clam harvesting is carried out within the lagoon causing the physical disturbance and winnowing of the superficial sediment thus inducing the local formation of graded beds and shell rehash

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

relationships between hydrodynamic parameters and grain size in two contrasting transitional environments the lagoons of venice and cabras italy abstract a comparison was made of shallow water sediments from the lagoon of venice lv and the lagoon of cabras lc comparing depositional environments and exploring the relationships between hydrodynamics and sedimentological parameters the two water bodies are very different in size lv 360 km2 lc 22 km2 and the sediments predominantly consist of silty clay lv mz 26 m lc mz 6 m however there are large differences between the two lagoons with respect to sand lv mean 19 lc mean 3 and clay lv mean 20 lc mean 45 contents the lagoon of venice mean depth 1 m can be considered a tidal basin whereas the lagoon of cabras mean depth 2 m has the character of a coastal lake in which wind is the main hydrodynamic forcing factor a comparison of sediment grain size distributions with water circulation patterns in different parts of the lagoons highlighted some interesting differences grain size analyses of samples reveal a deficiency of particles around 8 m in the lc which is interpreted as reflecting the transition between cohesive flocs aggregates and non cohesive coarser silt particles while the transition limit in the lv is 20 m thus particles are cohesive below 8 m in the lc and below 20 m in the lv this is probably because of the differences in the clay silt ratio which is much lower in the lv 0 3 than in lc 1 conferring a silt dominated network structure on most of the lv sediments the hydrographical data used were root mean square velocity rmsv and water residence time wrt computed under the main forcing conditions the results show a general correlation between rmsv and sortable silt in the lc and between rmsv and coarser sediments 63 105 m in the lv some significant differences between the lagoons were detected in the degree of correlation between wrt and grain size root mean square velocity 7 cm s 1 in the lv and 3 cm s 1 in the lc was a greater forcing factor in the lc than in the lv conversely wrt which is on average 16 days in the lv and 19 days in the lc has more influence in the lv this study highlights the usefulness of comparing environments with different hydrodynamic energies e g tidal and or wind driven currents to elucidate and thereby improve our understanding of the processes governing the spatial distribution of sedimentological features the transport mechanisms of sediments and the relationship between them the results demonstrate that the approach outlined in this study has the potential to provide a universal hydro sedimentological classification scheme

dynamic analysis and two types of kink bands in quartz veins deformed under subgreenschist conditions abstract in order to clarify deformation mechanisms and behaviours of quartz in a low temperature regime in the earth s crust microstructural analyses particularly on kink bands have been carried out for quartz veins moderately deformed under subgreenschist conditions both the dominance of subbasal deformation lamellae and geometry of kink bands suggest that basal 0001 slip was the sole active slip system in the deformed quartz on a morphological basis kink bands in the quartz were classified into two types type i is characterized by conjugate and narrow bands with angular hinge zones and type ii by a wide monoclinal band dynamic analyses using deformation lamellae and kink bands have revealed that type i kink bands were formed in grains with basal plane sub parallel to the compression axis whereas type ii kink bands were formed in grains with basal planes inclined to it using a numerical model of kinking of elastic multilayers modified after honea and johnson tectonophysics 30 197 239 1976 changes of the level of yielding stress for kinking and the width of kink bands as a function of the angle between the slip plane and the compression axis have been examined the theory predicts that type i kink bands were formed at a higher stress level than type ii kink bands and hence occurrence of type i kink bands suggests that a significant strain hardening occurred in the deformed quartz veins the theory also well explains the fact that the width of type i kink bands 0 to 10 is narrower by an order of magnitude than type ii kink bands 10 to 80

the role of extreme floods in estuary coastal behaviour contrasts between river and tide dominated microtidal estuaries abstract contrasting modes of sedimentation and facies arrangement in tide and river dominated microtidal estuaries arise from the degree to which river or tidal discharge and sediment supply influences an estuary a distinct facies gradation exists in tide dominated systems from sandy barrier tidal delta associated environments at the coast through deep mud dominated middle reaches to fluvial sediment in the upper reaches in river dominated systems fluvial sediment extends to the barrier and flood tidal deltas are poorly developed or absent from the estuary a number of independent observations during extreme floods on the south african coast indicate that these types of estuary respond differently to extreme river floods and that the mode of response corresponds to estuary type tide dominated systems exhibit preferential erosion of noncohesive barrier and tidal delta sediments during river floods while the middle reaches remain little modified river dominated systems experience consistent erosion throughout their channel length during extreme floods the increased cohesion of riverine sediments and stabilisation of bars by vegetation in river dominated channels means that higher magnitude floods are necessary to effect significant morphological change barrier erosion including the tidal delta results in deposition of an ephemeral delta composed almost entirely of sands from these deposits in tide dominated estuaries in river dominated systems eroded channel sediments and material from the river catchment may augment barrier sediments in the ephemeral delta deposit post flood wave reworking of ephemeral delta sediments acts to restore barriers to pre flood morphology within a few years however in river dominated systems the additional sediment volume may produce significant coastal progradation that requires several years or decades to redistribute these different modes of flood response mediated by the nature of the estuary have implications for coastal behaviour at the time scale of months to several decades estuary coastal behaviour at river dominated estuaries may be influenced for several decades by post flood morphological adjustment tide dominated estuaries however respond more rapidly in reworking flood eroded sediment and are typically fully adjusted to modal wave and tidal conditions within a few months to a few years in addition the facies arrangement within the two estuary types renders tide dominated estuaries more responsive to minor floods while river dominated estuaries by virtue of more cohesive channel sediments require greater discharges to effect significant morphological change

the influence of grain size analysis methods and sediment mixing on curve shapes and textural parameters implications for sediment trend analysis abstract to this day deterministic physical models capable of explaining the evolution of grain size distributions in the course of transport are still lacking for this reason various attributes of particle frequency distributions in particular curve shapes and textural parameters have for many decades been investigated for potential information about transport behaviour and size sorting processes of sediments in numerous environments such approaches are essentially conceptual and hence rely heavily on the validity of the assumptions on which they are based a factor which has to date been largely ignored in this context is the fact that different methods of grain size analysis e g sieving laser absorption and diffraction settling velocity measurements when applied to the same sample material produce variable curve shapes and hence incongruous textural data this is illustrated by selected examples showing the differences between sieving and settling results conversion of settling velocities into equivalent settling diameters psi phi transformations and the influences of particle shape particle density and water temperature it is demonstrated that particle size distributions are not only method dependent but also dependent on the adopted post processing procedure as a result only frequency curves generated by the same method and subsequently processed by identical computational procedures can be meaningfully compared furthermore the computation of textural parameters from bi or multimodal size distributions produces spurious results which are unrelated to the processes leading to the mixing of different size populations frequently observed in nature in such cases only the decomposition of such distributions into individual populations and the spatial comparison of such populations makes any sense because a physical explanation for the generation of size distributions is lacking a particular curve shape of a grain size population has no meaning on its own only a systematic comparison of progressively changing curve shapes and associated textural parameters of sediments collected on a closely spaced grid can yield data suitable for sediment trend analysis

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

metallogenic epochs in the inner zone of southwest japan abstract the principal metallogenic epochs in the inner zone of southwestern japan are classified by considering mainly radiometric and microfossil age data as follows 1 early cambrian epoch characterized by podiform type chromite deposits hosted in ophiolite complexes these are the earliest formed mineral deposits in the japanese islands and probably formed in the shallow mantle of island arc settings 2 carboniferous to permian epoch characterized by besshi type base metal sulfide deposits mainly associated with submarine lavas and tuffs of basaltic composition including their metamorphosed equivalents and by bedded cupriferous pyrite deposits associated with submarine acidic tuffs both types of deposits would have been formed in a back arc basin environment geochemically influenced by an island arc 3 middle triassic to jurassic epoch characterized by most of the bedded manganese deposits associated with bedded cherts including their metamorphosed equivalents which would have formed by hot spring activity in an ocean basin environment with a limited current circulation the manganese deposits and their host rocks are the result of seafloor accretion 4 late cretaceous to paleogene epoch characterized by extensive continental arc magmatism volcanic and plutonic resulting in formation of various mineral deposit types related mainly to ilmenite series late cretaceous or magnetite series paleogene granitic rocks related to the former are polymetallic skarns and veins containing cu sn and w also related to this metallogenic activity are stratabound hydrothermal clay deposits of kaolin pyrophyllite and sericite associated with pre ilmenite series granitoids subaerial felsic pyroclastic rocks molybdenite bearing veins and replacement type sericite deposits are characteristics of the magnetite series terranes with local skarns and vein occurrences as with ilmenite series granitoids occurring in southwestern japan eastward younging is also recognized in these mineral deposits regardless of ore type 5 neogene epoch characterized by intense submarine volcanism of acidic composition and associated kuroko deposits in the green tuff region a major tectonic division and a major metallogenic province of the neogene tertiary of japan these mineral deposits would be related to japan sea opening in the non green tuff region important mineralization events are represented by sedimentary uranium deposits and veins characterized by au sb or hg occurrences 6 plio pleistocene epoch characterized by epithermal au ag and au ag cu veins associated with subaerial andesitic to dacitic volcanic rocks of plio pleistocene age volcanism of this and following epochs is characteristic of an island arc setting and 7 quaternary epoch characterized by volcanic sulfur deposits and minor iron sand deposits

implications for sea level research of salt marsh and mudflat accretionary processes along paraglacial barrier coasts abstract paraglacial coastlines with dynamic coarse clastic barrier beaches are common in mid to high latitudes today and have been during the holocene sediments that have been deposited along these coastlines often in back barrier locations have been used to reconstruct relative sea level rsl movements and tendencies usually through the use of sea level index points derived frequently from salt marsh and mudflat deposits however the asymptotic relationship between minerogenic marsh mudflat accretion rates and time will produce regressive stratigraphies with a negative sea level tendency signature even within regimes of rising rsl the influence of gravel barriers on sedimentation will also tend to encourage regressive stratigraphies furthermore organogenic sediment production may release marsh accretion rates from the control of tidal inundation and result in succession to reed swamp despite rsl rise episodic minerogenic sediment supply to the marsh can trigger switches between marsh emergence and submergence which may result in stratigraphic sequences corresponding to negative and positive tendencies of rsl respectively although submergence may be prevented by organogenic sediment supply forcing by rsl rise may result in marsh emergence following initial submergence as a result of renewed accretion on the submerged marsh

granulometric characterization and evaluation of annually banded mid holocene estuarine silts welsh severn estuary uk coastal change sea level and climate abstract holocene silts salt marshes and highest intertidal supratidal peats are superbly exposed on a 15 km coastal transect which reveals two laterally extensive units of annually banded silts beds 3 7 associated with three transgressive regressive silt peat cycles early sixth early fourth millennium bc bed 3 in places is concordantly and gradationally related to peats above and below but in others transgresses older strata bed 7 also grades up into peat but everywhere overlies a discordance the banding in bed 3 at three main and two minor sites was resolved and characterized texturally at high resolution 2 5 5 mm contiguous slices using laser granulometry ls230 with pids and a comprehensive scheme of data assessment most of bed 3 formed very rapidly at peak values of several tens of millimetres annually in accordance with modelled effects of sea level fluctuations on mature marshes bed concordant and gradational and on marshes growing up after coastal erosion and retreat bed with discordant base using data from the modern severn estuary the textural contrast within bands and its variation between bands points to a variable but overall milder mid holocene climate than today the inter annual variability affected marsh dynamics as shown by the behaviour of the finely divided plant tissues present given local calibration the methodology is applicable to other tidal systems with banded silts in britain and mainland northwest europe

controls on coastal dune morphology shoreline erosion and barrier island response to extreme storms abstract the response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore while it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge the underlying causes of the alongshore variation remain poorly understood this study examines the alongshore variation in dune morphology along a 11 km stretch of santa rosa island in northwest florida and relates the variation in morphology to the response of the island during hurricane ivan and historic and storm related rates of shoreline erosion the morphology of the foredune and backbarrier dunes was characterized before and after hurricane ivan using empirical orthogonal function eof analysis and related through canonical correlation analysis cca the height and extent of the foredune and the presence and relative location of the backbarrier dunes varied alongshore at discrete length scales of 750 1450 and 4550 m that are statistically significant at the 95 confidence level cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner shelf the backbarrier cuspate headlands and the historical and storm related trends in shoreline change sections of the coast with little to no dune development before hurricane ivan were observed in the narrowest portions of the island between headlands west of the transverse ridges overwash penetration tended to be larger in these areas and island breaching was common leaving the surface close to the watertable and covered by a lag of shell and gravel in contrast large foredunes and the backbarrier dunes were observed at the widest sections of the island the cuspate headlands and at crest of the transverse ridges due to the large dunes and the presence of the backbarrier dunes these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper shoreface it is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively these findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during hurricane ivan

nd sr pb systematics and age of the kings river ophiolite california implications for depleted mantle evolution sm nd whole rock and mineral data for the kings river ophiolite define two isochrons of 485 21 ma and 285 45 ma age with end 483 10 7 0 5 and end 285 9 9 1 1 respectively the 483 ma isochron is defined by samples of the main igneous construct samples from crosscutting diabase dikes and flaser gabbro sheets within the peridotite unit yield the 285 ma isochron the 483 ma data provide the first evidence of lower paleozoic oceanic crust in the sierran ophiolite belt new u pb analyses of zircons from a plagiogranite lying on the 483 ma sm nd isochron yield upper and lower intercepts with the concordia of 430 60 200 and 183 15 ma published zircon ages have underestimated the primary age of the ophiolite by 200 300 m y due to the effects of polymetamorphism the 483 ma samples have initial 87sr 86sr 0 7023 0 7030 206pb 204pb 17 14 17 82 207pb 204pb 15 37 15 52 208pb 204pb 36 80 37 38 the 285 ma samples have similar initial 87sr 86sr but more radiogenic pb the range in sr and pb compositions is probably due to introduction of radiogenic sr and pb during multiple post emplacement metamorphic events the high end low 87sr 86sr 206pb 204pb 207pb 204pb 208pb 204pb of the least disturbed samples are clearly diagnostic of a midocean ridge origin for the 483 ma portion of the ophiolite igneous activity at 285 ma is thought to have occurred in an arc or back arc setting or perhaps along a leaky transform the initial end 483 10 7 is indistinguishable from that of the similar age trinity peridotite jacobsen et al 1984 this value is the highest yet reported for the mesozoic or paleozoic depleted mantle and requires either a mantle source that was depleted 850 m y earlier than average or a source more highly depleted than average alternatively if such values were more typical of the early paleozoic mantle than is currently thought then there has been little evolution of the depleted mantle over the last 500 m y this requires that the modern mantle has been refluxed by material with low end such as continental crust

hydrological changes and holocene climate variations in nw china inferred from lake sediments of juyanze palaeolake by factor analyses abstract the eastern juyanze palaeolake in hyperarid north western china 41 75 42 n 101 5 102 e provides evidence of a complex hydrological pattern during the holocene multivariate statistics based on lithological geochemical and mineral data from the reference site g36 in the centre of the lake were performed to reconstruct the interrelation between lake hydrology and climate variability of the last 11 000 yr principal component analyses pca analyses enabled us to extract the three system variables runoff lake level water budget and salinity as the major factors which have influenced the lake history during a highly variable holocene climate we can also demonstrate that the independent variable total organic carbon toc is not only a function of bio productivity in lakes under warm wet climate conditions but more frequently related to surface runoff processes which can result in over estimation of pollen types used for climate reconstructions a combined consideration of all system variables with lithological parameters catchment characteristics and the local groundwater situation show that lake formation and its persistence strongly depended on local rainfall runoff and the status of the underlying aquifer our results indicate remarkable differences between the early holocene and mid to late holocene lake formation owing to changes in the aquifer system beneath the lake at about 10 700 cal bp freshwater lake formation starts with extreme runoff events under a wet climate repeated dry climate spells of reduced runoff the overall climate during the early holocene points to wet conditions with frequent phases of very high runoff and highest lake levels until about 8900 cal bp extremely low runoff occurred between 8900 and 8100 cal bp indicating already dry climate conditions some hundred years prior to the worldwide recorded responses of the 8 2 ka cold dry event a second period of major dry climate conditions with generally low but fluctuating runoff unstable water budget and deposition of aeolian sand lasted for about 2100 yr between 7500 and 5400 cal bp these climate conditions corroborate previous assumptions of a mid holocene dry period in arid north western china increased runoff after 5400 cal bp under wet climate conditions led to a complete refill of the aquifer at about 5000 cal bp and favoured the development of a saline lake for about 3500 yr in terms of hydrology the time between 5400 and 4000 cal bp appears to be the climate optimum compared with the early holocene wet climate the mid to late holocene local rainfall was less pronounced and displays a general decreasing trend towards complete desiccation of the lake our results indicate an extremely variable moisture availability in arid regions of north western china during the entire holocene owing to the interplay of the east asian summer monsoon with the westerly waves at the boundary of the summer monsoon limit variations from dry to wet climate conditions seem to have been more pronounced than in other monsoon regions of china

geochronology and physical context of oldowan site formation at kanjera south kenya oldowan sites in primary geologic context are rare in the archaeological record here we describe the depositional environment of oldowan occurrences at kanjera south kenya based on field descriptions and granulometric analysis excavations there have recovered a large oldowan artefact sample as well as the oldest substantial sample of archaeological fauna the deposits at kanjera south consist of 30 m of fluvial colluvial and lacustrine sediments magneto and bio stratigraphy indicate the kanjera south member of the kanjera formation was deposited between 2 3 and 1 92 million years ago ma with 2 0 ma being a likely age for the archaeological occurrences oldowan artefacts and associated fauna were deposited in the colluvial and alluvial silts and sands of beds ks 1 to ks 3 in the margins of a lake basin field descriptions and granulometric analysis of the sediment fine fraction indicates sediments from within the main archaeological horizon were emplaced as a combination of tractional and hyperconcentrated flows with limited evidence of debris flow deposition this style of deposition is unlikely to significantly erode or disturb the underlying surface and therefore promotes preservation of surface archaeological accumulations hominins were repeatedly attracted to the site locale and rapid sedimentation minimal bone weathering and an absence of bone or artefact rounding further indicate that fossils and artefacts were quickly buried

comparison of the high pressure schist belts of new caledonia and sanbagawa japan the high pressure schist terranes of new caledonia and sanbagawa were developed along the oceanic sides of sialic forelands by tectonic burial metamorphism the parent rocks were chemically similar as volcanic sedimentary trough or trench sequences and metamorphic temperatures in both belts were 250 to 600 c from phase equilibria curves total pressures were higher for new caledonia 6 15 kb than for sanbagawa 5 11 kb and the estimated thermal gradients were 7 10 c km and 15 c km respectively pt paths identify the higher pressure in new caledonia p differences 2 kb at 300 c and 4 kb at 550 c with consequent contrast in progressive regional metamorphic zonation for pelites in the two areas lawsonite epidote omphacite new caledonia and chlorite garnet biotite sanbagawa in new caledonia the na amphibole is dominantly glaucophane and na pyroxenes associated with quartz are jadeite jd95 100 and omphacite in sanbagawa the amphibole is crossite or riebeckite and the pyroxene is omphacite jd50 for both areas garnet rims show increase in pyrope content with advancing grade but sanbagawa garnets are richer in almandine progressive assemblages within the two belts can be equated by such reactions as new caledonia sanbagawa glaucophane paragonite h2o albite chlorite quartz glaucophane epidote h2o albite chlorite actinolite and the lower pressure japanese associations appear as retrogressive phases in the new caledonia epidote and omphacite zones

particle size characterisation of holocene back barrier sequences from north atlantic coasts sw spain and se england abstract in this paper we present the results of bivariate plots of grain size parameters mean against sorting in the reconstruction of holocene environmental change in coastal environments where barrier formation has had an important control on sedimentation sites on the north atlantic coast with differing histories of climate sediment flux sea level change and barrier integrity are investigated to determine the general efficacy of this bivariate parameter model in distinguishing between open and closed basin conditions and in reviewing the significance of aperiodic high energy geomorphic events in controlling late stage back barrier sedimentation

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

the hyperbolic shape triangle as a tool for discriminating populations of sediment samples of closely connected origin this paper describes a new method for discriminating populations of sediment samples of closely connected origin it provides a dynamical interpretation to grain size data the descriptive modelling power of the hyperbolic distribution the hyperbolic shape triangle and the population concept have been applied to several hundred beach sand samples from the mediterranean coast of southern israel the investigated samples are from a 60 km stretch of beach from rafah to ashqelon and represent an autumn storm profile the domain of variation of the hyperbolic shape parameters y and 5 is a triangle referred to as the hyperbolic shape triangle the distribution of the estimated y shape positions in the hyperbolic shape triangle was studied graphically and statistically using the newly developed tools described here to present evaluate and compare hyperbolic shape position data for analysed grain size populations the graphical methods of contouring the scatter diagrams of the samples in the domain of the hyperbolic shape triangle and chi squared tests are demonstrated they were performed on two sedimentary environments normal to the beach namely inshore and mid swash zone the qualitative and quantitative estimated changes in the populations x 5 shape positions in the shape triangle suggest that they are subjected mainly to e erosion deposition processes their modes are located along one of the upper hammock curves in the shape triangle the location and scale invariant hyperbolic shape parameter p indicates a change of the grain size distribution across the left part of the hyperbolic shape triangle which is the domain of predominantly depositional processes however the mid swash zone sediments reflect that they are subjected more to depositional processes and the inshore sediments more to erosional ones

annual textural banding in holocene estuarine silts severn estuary levels sw britain patterns cause and implications a high resolution textural study has been made of laminated and banded estuarine silts exposed intertidally at representative localities and horizons in the holocene deposits of the severn estuary levels the laminae on a submillimetre to millimetre scale are sharp based graded couplets formed of a lower silty part overlain by a finer textured clayey element the centimetre to decimetre scale banding is formed of laminae in alternating gradually intergrading sets of relatively coarse and relative fine grained examples at outcrop in the field the banding is recognizable because the coarse sets prove to be recessive to varying degrees under the influence of weathering and current action independent evidence at two localities points toward an annual origin for the banding at a third it arose during part of what appears to have been a relatively short period quantified physical arguments suggest that the textural banding is a response of suspended fine sediment to marked seasonal changes in sea tempe

rb sr sm nd and k ar systematics of metamorphosed pillowed basalts and associated besshi type deposits in the sanbagawa belt japan samples from metamorphosed pillowed basalts and related besshi type deposits occurring in the sanbagawa belt of the shikoku island southwest japan have been analyzed for 87sr 86sr 143nd 144nd and 40 k 40ar this is to investigate the tectonic settings in which the original submarine volcanism and associated besshi type mineralization occurred as well as the age of metamorphism eight whole rock samples of the pillow lavas metamorphosed in pumpellyite actinolite facies conditions yield a rb sr isochron age of 107 15 ma with an initial ratio of 0 70401 0 00006 while they do not define a sm nd isochron we interpret the results as the metamorphic age an interpretation consistent with the previously reported rb sr whole rock age for the sanbagawa pelitic schists the overall ranges of the initial epsilon values at t 107 ma are nd t 7 8 to 4 3 sr t 2 2 to 7 0 suggesting that the most likely source for the pillowed basalts is depleted oceanic mantle a conclusion supported by the previous pb isotope studies the k ar ages determined for twelve mineral separates from the besshi type deposits range from about 60 to 112 ma with a mean age of about 80 ma in agreement with the previous k ar and ar ar data for the sanbagawa pelitic and basic schists the youngest age 60 ma was obtained for sericite from the hinooku deposit metamorphosed in pumpellyite actinolite facies conditions while the oldest one for hornblende from the spotted amphibolite in the immediate vicinity of the shiragayama deposit metamorphosed in albite biotite grade the oldest age 112 ma is interpreted to date the peak metamorphism consistent with the rb sr data though a possibility of excess ar cannot always be ruled out in view of the closure temperatures of muscovite 350 c in the biotite zone it is suggested that our k ar age data about 80 ma represent the age of the retrograde metamorphism or subsequent uplift datable microfossils found in the sanbagawa belt of shikoku suggest that the submarine basaltic volcanism and related besshi type mineralization occurred in an oceanic basin away from the trench region in late triassic conodont to late jurassic radiolarian times

morphodynamic evolution of a coastal lagoon entrance during swash overwash new field observations of beach berm growth resulting in the sub aerial closure of an intermittently closed and open lake or lagoon are presented these perched estuarine systems frequently exhibit ephemeral entrances that respond to process forcing almost instantaneously on a geomorphic timescale with closure by a supra tidal berm of depositional origin the observations were made following a mechanical opening of the entrance and show very rapid vertical growth of an initially low beach berm as a result of swash overtopping and sediment overwash very little simultaneous seaward progradation was observed sediment overwash volumes were obtained from survey data over a period of 12 days either side of spring tide and the observations also provide an accurate measure of swash sediment transport at the berm crest a process based parametric model is developed through robust parameterisations of wave run up wave run up distributions and sediment transport and is applied to predict the total overwash transport into and infilling the estuary entrance the model is tested against the field data and compares well with the observations while the field data are site specific the proposed modelling framework represents a first step in modelling the complex growth and recovery of natural beach berms in broad scale morphodynamic models

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

comparing spatial grain size trends inferred from textural parameters using percentile statistical parameters and those based on the log hyperbolic method abstract the folk ward f w and the log hyperbolic methods are applied to a small and easy to overlook number of typical sand sized grain size distributions from the danish wadden sea the sand originates from the same source and the pattern of change in the grain size distributions is therefore exclusively linked to dynamic sorting in general the f w parameters reflect the observed grain size trends far better than the corresponding log hyperbolic parameters the log hyperbolic typical log grain size is sensitive to changes in skewness and cannot replace mean grain size mz in grain size trend analysis the four log hyperbolic parameters describing dispersion 1 1 and are not able to give an unambiguous picture of spreading trends the f w sorting parameter sd can therefore not be replaced by any of the log hyperbolic parameters in grain size trend analysis in skewed grain size distributions there seems to be a general defect in the log hyperbolic approximation of the best represented tail this makes less sensitive to indicate the correct sign of slightly skewed grain size distributions than sk however when examining trends the relative change between and sk by and large seems to be the same the log hyperbolic peakedness parameter is preferable to the f w peakedness kurtosis parameter kg because the latter is hypersensitive to small insignificant variations in a grain size distribution by contrast the concept of peakedness as defined by seems to relate more directly to sedimentary environmental conditions in conclusion the log hyperbolic method has both advantages and disadvantages when compared with the f w method it is thus suggested that a sensible combination of the two methods could be advantageous to sediment trend analysis

holocene weak monsoon intervals indicated by low lake levels at hulun lake in the monsoonal margin region of northeastern inner mongolia china a 170 cm long sediment core spanning the last 10 000 years was recovered from hulun lake in the northeastern margin of the east asian summer monsoon the sediment core was analyzed at 1 cm intervals for grain size distribution and sedimentary component partition these data provide a proxy record of the monsoon variability on millennial to centennial scales during the holocene we used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions three coarse components representing nearshore suspension saltation and traction together with the sand fraction percentage and the median grain size of bulk samples indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation higher percentages of the nearshore components accompanied by more sand fraction proportions and coarser median grain sizes reflect lower lake stands resulting

exhumation of the sanbagawa blueschist belt sw japan by lateral flow and extrusion evidence from structural kinematics and retrograde p t t paths

comment on molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans arnold et al 1 1 reported mo isotope compositions of mid proterozoic black shale which were different from those of euxinic sediments in the black sea on the basis of a mass balance model calculation they claimed that the area of oxic sedimentation in the mid proterozoic oceans was

creation and preservation of subduction related inverted metamorphic gradients peak metamorphic temperatures and recrystallization increase structurally upward in the lower plate of several paleosubduction zones in the westernmost u s cordillera inverted metamorphic gradients are preserved in the pelona orocopia schist southern california the catalina schist california borderland the central metamorphic belt klamath province the south fork mountain schist northern california coast ranges and possibly the shuksan suite northern washington with the exception of the south fork mountain schist peak metamorphic temperatures increase structurally upward from 400 c to 650 c over 1 2 km indicating metamorphic gradients in excess of 100 c km 1 estimates of metamorphic gradients in some terranes such as the catalina schist depend critically on the effects of postmetamorphic faulting the tectonic settings and high metamorphic pressures 800 mpa suggest that the inverted metamorphic gradients formed in paleosubduction zones four out of five inverted metamorphic gradients lie structurally beneath ultramafic hanging walls whereas the pelona orocopia schist formed beneath granitic crystalline rocks the high temperatures recorded by the metamorphic rocks strongly suggest that inverted metamorphic gradients form during the early stages of subduction and thus provide insight into the early thermal history of subduction zones two separate two dimensional numerical models were constructed in order to constrain the thermal conditions under which inverted metamorphic gradients are created and preserved rapid subduction 10 cm yr 1 beneath young oceanic lithosphere 10 ma results in rapid heat conduction downward from the hanging wall and the creation of inverted thermal gradients in excess of 100 c km 1 in the top portion of the downgoing slab in order to be preserved in the geologic record the inverted metamorphic gradient must be accreted to the base of the hanging wall accretion of the upper portion of the subducting slab may occur because of declining temperatures that cause downward migration of the viscous slip zone and or greenschist facies devolatilization reactions that weaken the descending slab alternatively inverted metamorphic gradients may represent the continuous accretion of material at rates of 1 10 mm yr 1 under conditions of declining temperature continuously accreted inverted metamorphic gradients could form in oceanic lithosphere as old as 30 ma continued subduction of 1000 km of oceanic lithosphere effectively refrigerates the early accreted inverted metamorphic gradient synsubduction uplift and or moderately fast postsubduction uplift rates of 1 mm yr 1 are required to preserve the inverted metamorphic gradient the models predict that 1 the high grade metamorphic rocks in inverted metamorphic gradients form early in the subduction process and therefore effectively date the initiation of subduction and 2 inverted metamorphic gradients mark sites of major plate convergence in excess of 1000 km

seasonality of modern pollen and sediment deposition in an estuarine context the severn estuary levels southwest england recent sedimentological and palynological research on subfossil holocene banded sediments from the severn estuary levels suggested seasonality of deposition registered by variations in mineral grain size and pollen assemblages between different parts of the bands here we provide data that strengthen this interpretation from sampling of modern sediments and pollen deposition on an active mudflat and saltmarsh on the margin of the severn estuary and comparison with a vegetation survey and contemporary records of climate river and tidal regimes the results of grain size analysis indicate deposition of comparatively coarse grained silts during the relatively cool and windy conditions of winter and comparatively fine grained sediments during relatively warm and calm summer months pollen analysis demonstrates the significance of long term storage of pollen grains and fern spores in the estuarine waterbody superimposed on which seasonal variations in pollen inputs from local and regional vegetation remain detectable copyright c 2007 john wiley sons ltd

progressive grain size sorting along an intertidal energy gradient abstract along a 2 km nw se transect along the energy gradient of an intertidal sand body of the back barrier tidal flats of spiekeroog island german wadden sea southern north sea three sets of closely spaced surface sediment samples were taken at different times to investigate whether the effects of progressive size sorting could be identified in the textural parameters and size frequency curves of the sediments grain sizes analyses were carried out with a high resolution settling tube having an internal resolution of 1 50 psi intervals the settling velocity data were subsequently transformed numerically into equivalent settling diameters on the basis of a quartz sphere standard at this high resolution it was possible to visualize subtle changes in textural parameters which would not have been resolved by standard 0 25 phi sieve analyses the first two sample sets of 1992 and 1994 show similar trends of progressive fining in the sediment combined with a slight decrease in skewness and sorting in the direction of decreasing energy ten years later in 2003 the sediments were slightly coarser but still reflected the hydrodynamic energy gradient by a distinct fining trend along the transect however in contrast to the former data sets the skewness values now remained constant whereas the sorting values revealed the existence of two overlapping hydrodynamic energy regimes on the tidal flat the better sorting in the coarser size fractions and the general coarsening trend in the central part of the tidal flat are interpreted to reflect an increase in the hydrodynamic energy level since the first two sample sets were collected this observation suggests that some of the finer particles in the grain size spectrum on the tidal flat were winnowed out by wave action without however completely obliterating the former trend this interpretation is supported by an increase in the frequency and duration of strong winds as recorded by the national weather bureau since the early 1990s the results of the study demonstrate that the intertidal sediments of the wadden sea respond rapidly and sensitively to gradual changes in the hydrodynamic energy regime

tidally discontinuous ocean forcing in bar built estuaries the interaction of tides infragravity motions and frictional control shallow bar built estuaries on wave dominated coasts in mediterranean climates experience an intermittent connection to the ocean in the presence of low streamflow their inlets may completely close as a result of nearshore sand transport but even in the open condition these inlets remain constricted extensive field measurements in the highly salt stratified pescadero estuary in northern california show that the shallow mouth causes these estuaries to experience discontinuous tidal forcing while the ocean and estuary are fully connected with near equal water levels tidal velocities are slow but infragravity motions in the nearshore induce large velocity oscillations within the estuary as the ocean tide falls infragravity forcing is cut off because the estuarine mouth is perched above the low tide ocean water level and ebbing velocities are set by bed friction observations reveal this oscillation between ocean forced and frictionally controlled conditions characterizes and sets estuarine hydrodynamics additional wave setup of the lagoon emphasizes the dependence of these estuaries on nearshore ocean conditions but the diurnal or semidiurnal retreat of the ocean below the mouth cuts off this nearshore influence so it too is tidally varying here we present detailed observations and a framework for understanding hydrodynamics in small shallow bar built estuaries

isotopic constraints on the origin of appalachian mafic complexes isotopic analyses of modern oceanic basalts and ophiolites have shown that both modern and ancient oceanic crust have a characteristic nd and sr isotopic signature indicative of derivation from a depleted mantle reservoir it also appears that the nd isotopic system is not appreciably disturbed by metamorphism these isotopic characteristics have been extended to the pt sal kings kaweah and josephine ophiolites of california we have used these characteristics in an attempt to identify pieces of proto atlantic oceanic crust among the mafic and ultramafic rocks of the appalachians sm nd mineral isochrons for the baltimore mafic complex maryland bmc yield an age of 490 20 my which we interpret as the igneous crystallization age bmc whole rock samples do not define isochrons and have initial isotopic compositions of 6 4 nd t 2 2 51 sr t ll5 nd t and sr t are anti correlated this is not the signature of depleted mantle and oceanic crust hut is similar to old continental crust we propose that the bmc is a mafic continental intrusion possibly subduction related which was contaminated with old continental crust during emplacement whole rock samples from the thetford mines complex qe tmc do not define isochrons and have 1 5 nd t 4 2 2 6 sr t 114 these data do not in any way reflect the signature of normal oceanic crust these results are in contrast with geologic relationships that show the tmc to have the characteristics of an ophiolite complex the tmc is chemically and isotopically similar to a class of other ophiolites that have affinities to modern honinites the chunky gal amphibolite north carolina lake chatuge complex north carolina and hazen s notch amphibolite vermont were found to have a depleted mantle signature with 5 nd t 8 and may he fragments of oceanic crust the webster addie body north carolina has nd t 1 sr t 30 and is not isotopically similar to oceanic crust or the other north carolina mafic bodies analyzed from these isotopic results we infer that appalachian mafic rocks have diverse origins some are continental intrusives bmc others are probably fragments of oceanic crust vermont and north carolina amphiholites future models for the development of the appalachians must allow for these various origins the possibility that some onhiolites are not normal oceanic crust but have an origin in a partially continental setting or as anomalous oceanic crust may require further attention

on using the log hyperbolic distribution to describe the textural characteristics of eolian sediments abstract following the early work of bagnold 1941 it has recently been suggested that the log hyperbolic distribution offers a better description of grain size distribution than the log normal distribution this paper undertakes a comparison of the suitability of the log hyperbolic and log normal distributions in describing the textural characteristics of desert dune sediments a statistical analysis of the results shows that no apparent gain is obtained when using the parameters of the log hyperbolic distribution to describe such sediments

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

the isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans despite important biological and biogeochemical consequences of extensive ocean anoxic events their identification is controversial the marine isotope geochemistry of molybdenum can help quantify the past oxygenation state of the ocean if the riverine input of mo isotopes is known analysis of a set of rivers that account for 28 of global river runoff suggests more variable mo isotopic ratios in rivers that are also isotopically enriched in the heavy isotopes suggesting near total anoxia in the proterozoic ocean and during mesozoic ocean anoxic events despite its important biological and biogeochemical consequences1 2 3 the identification of extensive oceanic anoxia in the geological record is controversial in particular global anoxia is difficult to distinguish from spatially restricted anoxia in the deep ocean or in tectonically isolated basins such as the modern black sea the marine isotope geochemistry of molybdenum mo can help quantify the past oxygenation state of the ocean4 5 6 7 8 9 10 11 12 13 14 because to first approximation under oxic conditions lighter isotopes of mo are preferentially removed to sediments whereas in euxinic conditions quantitative removal leads to no fractionation however the isotopic composition of the mo input from rivers the main contributor of mo to the oceans is poorly constrained and had been assumed to be isotopically comparable to the narrow range found in a small dataset of continental rocks4 5 6 7 8 9 10 11 12 13 14 here we present an isotopic analysis of mo in a set of rivers that together account for 22 of the global riverine water discharge we find a broad range of variability in the mo isotopic composition of these rivers with almost all samples enriched in the heavy isotopes compared with continental rocks our data remove key uncertainties associated with the marine mo isotope budget14 and strongly suggest near total anoxia in the mid proterozoic ocean8 as well as during mesozoic ocean anoxic events13

buried salt marsh edges and tide level cycles in the mid holocene of the caldicot level gwent south wales uk combining stratigraphical sedimentological and biofacial foraminifera approaches a high resolution time constrained study has been made of a mid holocene c 5800 4900 14c yrs bp estuarine su

a sediment record of barrier estuary behaviour at the mesoscale interpreting high resolution particle size analysis abstract at present limited understanding of mesoscale years decades centuries back barrier lagoon barrier estuary behaviour is a critical shortcoming for resource managers and decision makers in this paper high resolution particle size analysis of a sediment core from an intermittently open and closed barrier estuary is utilised to reconstruct a history of back barrier environmental change at mesoscale temporal resolution sediments from pescadero marsh california were analysed for their particle size distribution at consecutive 2 mm intervals down core site selection informed by a time series of maps and aerial photographs coupled with a robust core chronology ensured that the particle size data primarily reflect changing hydrodynamics of the back barrier area over the european american era 1850 to the present following more traditional plotting of particle size data and summary statistics and statistical analysis of particle size end members visual analysis and categorisation of particle size distribution curves psdcs provide an effective basis for the identification of recurring modal sizes and subpopulations these particle size windows psws are interpreted as reflecting different modes of sediment transport and deposition i e suspension and saltation loads the varying prominence of which is interpreted as being modified by barrier integrity when considered together the down core mean particle size mps trend and individual psdcs offer considerable insight into mesoscale system behaviour at subannual resolution over multiple years this behaviour is expressed in the recurrence of characteristic barrier estuarine environments closed lagoon tidal lagoon tidal marsh and open estuary and the overall barrier regime and their persistence over the last c 150 years subannual and multiannual fluctuations in back barrier environmental configuration are seen to be superimposed on a longer term quasi stable barrier regime demonstrating the value of the applied methodology with regard to bridging the estuarine evolution long term stratigraphic and process short term geomorphic knowledge bases the documented behaviour suggests a level of innate morphological resilience in the system over the long term despite episodic disturbance by high energy storms such empirical demonstrations of resilient behaviour in coastal environments are rare at the mesoscale

muscovite k ar ages of the sanbagawa schists japan and argon depletion during cooling and deformation seventy muscovites from schists in the sanbagawa terrain in central shikoku were dated by the k ar method the muscovite ages are consistently older with increasing metamorphic grade within the same zone the ages are significantly younger in schists which have been more severely deformed these k ar age variations could be due to systematic argon depletion during deformation i e to the dynamic recrystallization of muscovites during ductile deformation that formed a large scale recumbent fold during the uplift and cooling argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low temperature deformation than the higher grade zone the relationships between age and grain size in a pelitic schist suggest that coarse grained muscovites lost more argon than the finegrained ones there was no significant resetting of ages in the vicinity of major strike slip faults such as the median tecotonic line or near thrust faults the combination of geochronological and geological data constrains the cooling rate of the sanbagawa schists to 9 12 c ma in the oligoclase biotite zone in central shikoku japan

evolution of a foredune and backshore river complex on a high energy drift aligned beach abstract this paper examines the multi decadal evolution of a foredune and backshore river complex on a wave dominated drift aligned coast at wickaninnish bay on southwestern vancouver island british columbia canada local shoreline positions are generally prograding seaward as fast as 1 46 m a 1 in response to rapid regional tectonic uplift and positive onshore sediment budgets the northern end of the foredune system has extended rapidly alongshore in response to net northward littoral drift despite these net accretional responses the beach dune system experiences relatively frequent return interval 1 53 years erosive events when total water levels exceed a local erosional threshold elevation of 5 5 m above regional chart datum geomorphic recovery of the beach dune system from erosive events is usually rapid i e within a year by way of high onshore sand transport and aeolian delivery to the upper beach this response is complicated locally however by the influence of a backshore river that alters spatial temporal patterns of both intertidal and supratidal erosion and deposition historic landscape changes and rates of shoreline positional change are derived from several years of aerial photography 1973 1996 2007 2009 2012 using the usgs digital shoreline analysis system dsas significant volumetric changes are also estimated from aerial lidar derived dems in 2005 2009 and 2012 and related morphodynamics are interpreted using a statistically constrained geomorphic change detection method results suggest that supratidal bar development overwash deposition and aeolian deposition on a low lying supratidal platform combined with alongshore extension of the foredune complex is forcing sandhill creek to migrate northward in the direction of beach drift in response the river actively erodes 1 24 m a 1 a bluff system landward of the channel which generates substantial sediment volumes 0 137 m3 m 2 a 1 that feed a large intertidal braided channel and delta system these local responses provide context for a conceptual model of the evolution of a wave dominated drift aligned beach foredune system that interacts with a backshore river this model may provide useful information to local park managers as erosion and sedimentation hazards threaten visitor safety and park infrastructure

structural styles and deformation fabrics of accretionary complexes intricately deformed stratally disrupted and mixed rocks produced at subduction zones have been considered structurally intractable however marine geophysical studies deep sea drilling analyses of subaerially exposed complexes and theoretical advances have recently produced breakthroughs in elucidating the structural enigmas of these accretionary complexes the penrose conference structural styles and deformational fabrics of accretionary complexes assembled specialists from the above and related research areas and addressed the research frontiers of this dynamic topic this conference in eureka california in may 1984 drew participants from great britain france canada japan and new zealand

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

a molybdenum isotope perspective on phanerozoic deoxygenation events the careful compilation and interpretation of molybdenum isotopes can track the expansion of sulfidic bottom waters a synthesis and analysis of data from two mesozoic ocean anoxic events and the palaeocene eocene thermal maximum applies these techniques to constrain past ocean deoxygenation

seasonal deposition of holocene banded sediments in the severn estuary levels southwest britain palynological and sedimentological evidence abstract banded sediments outcrop widely in the intertidal zone of the severn estuary and have been suggested on the basis of textural analysis to have formed in response to seasonal variations in sea temperature and windiness holocene 14 2004 536 here palynological and sedimentological analyses of banded sediments of mid holocene date from gold cliff on the welsh side of the severn estuary are combined to test and further develop the hypothesis of seasonal deposition pollen percentage and concentration data are presented from a short sequence of bands to establish whether textural variations in the bands coincide with variations in pollen content reflecting seasonal flowering patterns it is shown that fine grained band parts contain higher total pollen concentrations and a higher proportion of pollen from late spring to summer flowering plants than coarse grained band parts pollen in the coarser deposits appears primarily to reflect deposition from the buffering reservoir of suspended pollen in the estuarine water body and from rivers when there is little pollen in the air in winter while the finer sediments contain pollen deposited from the atmosphere during the flowering season superimposed on these background sources the potential of such deposits for refining chronologies and identifying seasonality of coastal processes is noted and the results of charcoal particle analysis of the bands presented as an example of how they have the potential to shed light on seasonal and annual patterns of human activity