mangrove forest evolution in a sediment rich estuarine system opportunists or agents of geomorphic change the majority of the world s mangrove forests occur on mostly mineral sediments of fluvial origin two perspectives exist on the biogeomorphic development of these forests i e that mangroves are opportunistic with forest development primarily driven by physical processes or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology on the firth of thames coast new zealand we evaluate these two possible scenarios for sediment accumulation and forest development using high resolution sedimentary records and a detailed chronology of mangrove forest avicennia marina development since the 1950s cores were collected along a shore normal transect of known elevation relative to mean sea level msl activities for lead 210 pb 210 caesium 137 cs 137 and beryllium 7 be 7 and sediment properties were analysed with pb 210 sediment accumulation rates sars compensated for deep subsidence similar to 8 mm yr 1 used as a proxy for elevation gain at least four phases of forest development since the 1950s are recognized an old growth forest developed by the late 1970s with more recent seaward forest expansion thereafter excess 210pb profiles from the old growth forest exhibit relatively low sars near the top 7 12 mm yr 1 and bottom 10 22 mm yr 1 of cores separated by an interval of higher sars 33 100 mm yr 1 a general trend of increasing sar over time characterizes the recent forest biogeomorphic evolution of the system is more complex than simple mudflat accretion progradation and mangrove forest expansion surface elevation gain in the old growth forest displays an asymptotic trajectory with a secondary depocentre developing on the seaward mudflat from the mid 1970s two to ten fold increases in 210pb sars are unambiguously large and occurred years to decades before seedling recruitment demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales this suggests that mangrove forest development is largely dependent on physical processes with forests occupying mudflats once they reach a suitable elevation in the intertidal copyright c 2015 john wiley sons ltd

coastal upwelling by wind driven forcing in jervis bay new south wales a numerical study for 2011 abstract the princeton ocean model pom was used to investigate an upwelling event in jervis bay new south wales se australia with varying wind directions and strengths the pom was adopted with a downscaling approach for the regional ocean model one way nested to a global ocean model the upwelling event was detected from the observed wind data and satellite sea surface temperature images the validated model reproduced the upwelling event showing the input of bottom cold water driven by wind to the bay its subsequent deflection to the south and its outcropping to the surface along the west and south coasts nevertheless the behavior of the bottom water that intruded into the bay varied with different wind directions and strengths upwelling favorable wind directions for flushing efficiency within the bay were ranked in the following order n 0 northerly nne 30 northeasterly nw 315 northwesterly ne 45 northeasterly ene 60 northeasterly increasing wind strengths also enhance cold water penetration and water exchange it was determined that wind driven downwelling within the bay which occurred with nne ne and ene winds played a key role in blocking the intrusion of the cold water upwelled through the bay entrance a northerly wind stress higher than 0 3 n m 2 was required for the cold water to reach the northern innermost bay

synorogenic hydrothermal origin for giant hamersley iron oxide ore bodies geologic mapping basin analysis and calculated fluid compositions indicate that giant orebodies of microplaty hematite and possibly martite goethite in the hamersley province of western australia were formed by heated fluids driven by early paleoproterozoic orogenesis detrital grains of microplaty hematite in the mcgrath trough a foreland basin in front of the northward advancing ophthalmian fold belt constrain the age of the earliest microplaty hematite ore formation to 200 c and locally up to 400 c were involved regional circulation of hydrothermal fluids including heated surface water through reduced banded iron formations occurred during or soon after the ophthalmian orogeny we speculate that martite goethite orebodies previously considered mesozoic cenozoic could also be related to heated paleoproterozoic meteoric fluids migrating northward away from the ophthalmian fold belt

active fault motion in a coastal wetland matagorda texas abstract active growth faults contribute to the subsidence of deltaic basins around the world and can significantly augment local rates of relative sea level rise which can inundate and drown wetlands little information exists on the temporal frequency and spatial magnitude of motion along these faults our objective was to quantify fault activity and displacement at multiple time scales in a salt marsh wetland on the east matagorda peninsula texas we present evidence of this activity that includes remotely sensed aerial imagery lidar data ground penetrating radar data shallow seismic data lithostratigraphic and biostratigraphic evidence from core data and sub centimeter gps and survey monitoring the results support the interpretation that the matagorda fault is currently active and has been active in the past subsurface data to depths of 150 m displays evidence of disrupted strata at the fault plane as well as thicker strata on the downthrown side of the fault in the shallow subsurface down to 3 m of depth vertical displacement in stratigraphic markers and surface deformation exhibits a sinusoidal pattern that runs perpendicular to the fault plane which we interpret to represent fault propagation folding maximum throw on this fault is estimated at 0 75 m over the last 40 50 years we also recorded a vertical drop of 0 208 m in the span of a single year at a location close to the fault on its downthrown side records of yearly elevation change also show evidence of ongoing fault propagation folding we conclude that whereas the surface at the matagorda fault moves intermittently up and down at the yearly time scale fault displacement manifests as a sinusoidal pattern of displacement and deformation which has been integrated into the stratigraphic record at decadal to millennial time scales this study presents a rare look into active motion and details its effects on the modern evolution of unconsolidated sedimentary surfaces

surface elevation change and susceptibility of coastal wetlands to sea level rise in liaohe delta china abstract the liaohe delta in china is an ecologically and commercially important wetland system under threat from sea level rise and marsh subsidence sediments deposited in coastal marshes could offer wetlands a potentially important means for adjusting surface elevation with rising sea level yet coastal wetland stability in liaohe delta is not well understood due to limited data from long term experiments in this study wetland surface elevation and vertical accretion were measured from 2011 to 2015 using a surface elevation table set and feldspar marker horizons in two phragmites and two suaeda marshes receiving liaohe river water the analysis shows that the phragmites marshes exhibited higher rates of marsh accretion and elevation change than the suaeda marshes the two phragmites marsh sites had average surface elevation change rates at 8 8 and 9 3 mm yr 1 vertical accretion at 17 4 and 17 6 mm yr 1 and shallow subsidence at 8 6 and 8 3 mm yr 1 the average rates of elevation change vertical accretion and shallow subsidence at two suaeda marsh sites were 5 8 and 6 3 mm yr 1 13 6 and 14 8 mm yr 1 and 7 8 and 8 5 mm yr 1 respectively the trends suggest that coastal marshes in liaohe delta are experiencing changes in average soil elevation that range from a net increase of 0 3 mm y 1 to 6 9 mm y 1 relative to averaged sea level rise in bohai sea reported by the 2016 state oceanic administration people s republic of china projection 2 4 5 5 mm y 1 which indicated that the four wetland sites would adjust to the sea level rise and even continue to gain elevation especially for the phragmites sites nevertheless the vulnerability of coastal wetlands in liaohe delta need further assessment considering the accelerated sea level rise the high rate of subsidence and the declining sediment delivery owing to anthropogenic activities such as dam constructions in the river basin

comparison of sediment plate methods to measure accretion rates in an estuarine mangrove forest new zealand abstract sedimentation is a fundamental process in aquatic receiving environments including vegetated habitats such as mangroves selection of appropriate methods to measure sedimentation depends on time scales of interest due to the variable nature of this process our study considers the appropriateness of methods to measure sediment accretion over time scales of months to years in estuarine mangroves sediment accretion has commonly been measured using marker horizons sediment erosion pins and buried plates bioturbation and erosion can make application of these methods problematic here sediment accretion rates for porous plastic mesh and impervious ceramic plates of two sizes 0 023 and 0 16 m2 were compared replicate plates of each type were installed on the substrate surface at nine rod surface elevation table rset sites distributed along a shore normal sedimentation gradient the plates were progressively buried by sedimentation 17 41 mm yr 1 measurements were made at seasonal to annual intervals over a seven year period 2012 2019 comparison of accretion rates on the plastic mesh with both types of ceramic plates showed strong positive correlations r2 0 96 with slopes close to unity mean 0 95 range 0 68 1 09 sediment accretion rates measured on the large and small ceramic plates were not measurably different from rates for the plastic mesh these results show that sediment accretion rates were spatially homogenous at sub metre to metre scales in the mangroves and sediment accretion rates did not measurably vary between different sediment plate methods the sediment plate method has a number of advantages over marker horizons for long term measurements of sediment accretion particularly where bioturbation alters the sediment profile mesh plates are easily maintained and provide a cost effective flexible precise and reproducible alternative to sediment marker horizons and solid plates for long term monitoring sediment accretion in mangroves and unvegetated intertidal habitats future studies including those employing rset should consider incorporating mesh plate measurements of sediment accretion

sea level and turbidity controls on mangrove soil surface elevation change increases in sea level are a threat to seaward fringing mangrove forests if levels of inundation exceed the physiological tolerance of the trees however tidal wetlands can keep pace with sea level rise if soil surface elevations can increase at the same pace as sea level rise sediment accretion on the soil surface and belowground production of roots are proposed to increase with increasing sea level enabling intertidal habitats to maintain their position relative to mean sea level but there are few tests of these predictions in mangrove forests here we used variation in sea level and the availability of sediments caused by seasonal and inter annual variation in the intensity of la nina el nino to assess the effects of increasing sea level on surface elevation gains and contributing processes accretion on the surface subsidence and root growth in mangrove forests we found that soil surface elevation increased with mean sea level which varied over 250 mm during the study and with turbidity at sites where fine sediment in the water column is abundant in contrast where sediments were sandy rates of surface elevation gain were high but not significantly related to variation in turbidity and were likely to be influenced by other factors that deliver sand to the mangrove forest root growth was not linked to soil surface elevation gains although it was associated with reduced shallow subsidence and therefore may contribute to the capacity of mangroves to keep pace with sea level rise our results indicate both surface sedimentation and subsurface root growth processes can influence mangrove capacity to keep pace with sea level rise within the same geographic location and that current models of tidal marsh responses to sea level rise capture the major feature of the response of mangroves where fine but not coarse sediments are abundant

review of methods to measure short time scale sediment accumulation this review paper aims at providing a list of methods available to measure sediment accumulation in underwater or intertidal environments over short term periods in the order of hours to months at the most both in situ and under laboratory conditions methods are classified based on two criteria a whether they measure sediment accumulation or sediment elevation change and b whether they allow continuous or discontinuous measurements the main characteristics of each method are outlined along with its vertical resolution its accuracy its temporal resolution its spatial coverage capacity and an indication of its relative cost typical examples of applications are also provided the purpose of this review is to be a starting point for readers who need an overview of existing techniques that measure short term sediment accumulation in order to guide and facilitate for instance the selection of an appropriate technique for a given application with set requirements

emplacement of a large igneous province as a possible cause of banded iron formation 2 45 billion years ago latest archaean and earliest palaeoproterozoic times from 2 6 to 2 2 billion years ago have generally been viewed as a largely quiescent period of earth history the geological record indicates the very slow deposition of pelagic and chemical sediments1 2 and bears only a limited record of magmatic and tectonic activity3 5 such quiescence is consistent with the contention that the earth s main banded iron formations bifs finely laminated chemical sedimentary rocks rich in iron oxide formed slowly as oxygen abundances in the oceans gradually increased thus reducing the capacity of sea water to retain dissolved iron6 10 here we show that a large igneous province comprising 30 000km3 of dolerite basalt and rhyolite accompanied deposition of a hamersley province bif 2 449 3 million years ago this observation indicates that hamersley bifs formed during a major tectono magmatic event and were deposited very much faster than previously thought at similar rates to or faster than modern pelagic sediments thus the largest palaeoproterozoic bifs rather than simply reflecting a gradual increase in the oxygen content of the oceans during a period of tectonic quiescence are more likely to have formed as a result of an increased supply of suboxic iron and silica rich sea water upwelling onto continental shelves during a pulse or pulses of increased submarine magmatic and hydrothermal activity

elevation and accretion dynamics at historical plots in the biloxi marshes mississippi delta abstract the objectives of this study were to examine changes in accretion and elevation change over periods of up to 15 years for the biloxi marsh complex bmc in southeastern louisiana part of the mississippi deltaic plain identify factors affecting accretionary dynamics and put these findings in the context of ongoing restoration we present elevation and accretion data from surface elevation table set and feldspar marker horizon sites first established in 2003 the sites were clustered in two areas east and west in the central bmc on the eastern edge of the mississippi delta accretion markers were used in conjunction with elevation measurements to calculate shallow subsidence these data were analyzed along with similar data from nearby coastwide reference monitoring system crms sites located around the periphery of the bmc elevation decreased at the western sites by 0 35 0 13 cm yr and increased at the eastern and crms sites by 0 40 0 03 cm yr and 0 72 0 09 cm yr respectively the rate of accretion was similar at the western 0 49 0 14 cm yr and eastern 0 64 0 07 cm yr sites and over twice as much 1 30 0 11 cm yr at the crms sites shallow subsidence calculated as the difference between vertical accretion and surface elevation change was 0 76 0 49 cm yr at the western sites 0 23 0 06 cm yr at the eastern sites and 0 58 0 11 cm yr at the crms sites these trends are consistent with the observation that sediment is brought in from chandeleur sound to the east and is attenuated as deposition occurs across the landscape from east to west and that levee flank depressions associated with bayou la loutre an abandoned mississippi river distributary ridge are causing locally high subsidence in the western region without intervention these localized areas of the western region will be submerged within the next several decades at current rates of elevation loss and eustatic sea level rise while the eastern sites and the wetlands on the periphery of the bmc are likely to keep pace with sea level rise well into the second half of this century these results demonstrate the importance of accurate knowledge of both subsidence and accretionary dynamics in determining coastal wetland sustainability and restoration approaches

winter processes on northern salt marshes evaluating the impact of in situ peat compaction due to ice loading wells me abstract new england salt marshes are dominated by the supratidal high marsh grass spartina patens this grass forms a nearly planar surface which makes it highly vulnerable to the predicted regime of accelerated sea level rise slr if the high marsh cannot keep pace with rising sea level it will be transformed to intertidal environments leading to unusually rapid coastal evolution winter processes such as ice loading of surface peat may degrade the marsh surface large volumes of snow and ice compress peat resulting in shallow compaction and a net loss of elevation in some areas on the webhannet marsh in maine a simulated ice compaction experiment indicates that thick ice can compress marsh peat 46 cm simulated ice produced 6 9 0 3 mm of compaction 24 cm ice produced 3 0 0 8 mm experimental data suggest that ice thicknesses greater than 10 cm depress the marsh surface by 2 mm for each cm of total ice thickness however surface elevations rebounded to near control levels within 2 weeks of the removal of simulated ice from the surface of the marsh normal winter ice accumulations on new england marshes therefore do not appear to be sufficient to permanently compact marsh surface peat and lead to loss in marsh surface elevation

saltmarsh sustainability throughout the holocene in boston harbor a new sea level curve for the lower gulf of maine and implications of recent anthropogenic alteration abstract saltmarsh evolution is closely linked to sea level rise slr and sediment supply in a regime of accelerating slr saltmarsh survival depends on the ability of the marsh platform to grow vertically through organic and inorganic accumulation and laterally via transgression over adjacent uplands in formerly glaciated settings the formation and maintenance of a saltmarsh are complicated by steep uplands low sediment availability isostatic rebound changes to tidal amplitudes and anthropogenic alteration while much work has examined the development of large saltmarshes in new england since the mid holocene and anthropocene little is known about the smaller isolated saltmarshes that form in pockets along the glaciated coastline we use radiocarbon dates from newly uncovered index points basal peat within boston harbor to date one of the oldest saltmarshes in the region 4 2 ka and calculate the polynomial relative sea level curve rslr for the lower gulf of maine taking into account tidal amplification throughout the holocene this study informs the historical persistence of isolated saltmarshes under varying rates of sea level rise magnitude as much as 2 mm yr 1 additionally we refine the timing and rates of the mid holocene sea level deceleration in this region between 2 8 and 3 3 ka slowing from 2 1 mm yr 1 to 0 5 mm yr 1 rslr determined from the past century of tide gauge data is 2 86 mm yr 1 five times greater than historic rates over the past 2000 years recent vertical accretion rates determined from marker horizons and 210pb data indicate that portions of boston harbor s saltmarshes are able to keep pace with current rslr however historical diking and ditching practices appear to have resulted in elevation loss and conversion from high saltmarsh platforms to low saltmarsh platforms largely influencing the amount of inorganic sediment needed to help maintain marsh surfaces these results highlight that knowledge of historical anthropogenic modifications and changes in hydroperiod are critical when interpreting vertical accretion results more importantly anthropogenic modification within sediment starved saltmarshes may be the cause for cannibalization of marsh shorelines whereby inorganic sediment eroded from marsh edges is recycled and delivered to the surface facilitating vertical accretion that offsets rslr under modern accelerated sea level rise and decreased sediment supply this cannibalization process may now be the only pathway for saltmarsh survival

the effect of heterogeneous stress and strain on metamorphic fluid flow mary kathleen australia and a model for large scale fluid circulation in the proterozoic mary kathleen fold belt northern australia infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite facies metamorphism and deformation this paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation intense fluid flow was localized within strong relatively brittle meta intrusive bodies and in discrete veined brecciated and altered zones around their margins in metasediments folded in a ductile manner outside these areas fluid infiltration was negligible the direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement and hence fluid flow by deformation finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the strain shadow zones adjacent to the strong bodies other dilatant zones around the bodies and the bodies themselves this geometry is favourable not only for localized brittle deformation under amphilobite facies conditions but also for focused fluid flow in the low mean stress regions as evidenced by the abundance of veins fluid access through these metamorphic aquifers occurred during tensile failure episodes with particularly large dilations and decimetre scale veining in areas of strain incompatibility it appears likely that fluid circulated many times through the fold belt with flow concentrated in the metamorphic aquifers a model is developed that explains both the structurally focused fluid flow and the postulated multi pass recirculation by dilatancy pumping the pump engines comprising the low mean stress zones

high precision measurements of wetland sediment elevation i recent improvements to the sedimentation erosion table abstract the sedimentation erosion table set developed by boumans and day 1993 is herein renamed the surface elevation table set to better reflect the conceptual view of the processes being measured the set was designed for making high resolution measurements of small scale changes in elevation of loose unconsolidated sediments in shallow water and mudflat habitats the set has undergone three major improvements to increase precision and so that it can be used to measure sediment elevation in vegetated wetlands as well as shallow water habitats the remote release sliding plate mechanism has been replaced with a single plate collars first 2 5 cm then 7 5 cm in length have been attached to the plate to reduce play in the placement of the measuring pins and the brass measuring pins have been replaced with fiberglass pins to reduce bending and consequent loss of precision under ideal laboratory conditions the 95 confidence limit for individual pin measurements averaged about 1 4 mm range 0 7 to 1 9 mm these modifications have resulted in a reduction of error by about 50

measuring sediment deposition and accretion on anthropogenic marshland part i methodical evaluation and development abstract the north frisian halligen northern germany are inhabited and highly anthropogenic modified coastal marshlands today a lack of knowledge about sedimentological parameters prevent for a predicated discussion on their adaptation capacity to recent and future sea level changes a combined field and laboratory method to calculate marshland accretion rates based on short term 2010 2013 measurements of sediment depositions was developed all studies were carried out at the marshlands of the halligen hooge langeness and nordstrandischmoor one litre ldpe bottles and small synthetic turf mats were used as simple but coast time and quantity efficient sediment trap devices up to a deposition rate of 2 0 kg m2 both devices gained comparable results above this threshold the retention efficiency of the turf mats is decreasing compared to the ldpd bottles the combined use of bottles and mats especially when deposition rates are not exceeding the threshold allows to 1 checking internal consistency of the data 2 detecting outliers with respect to cattle or man made damage and 3 estimating possible effects of post storm sediment remobilization to transfer sediment depositions into rates of vertical accretion the bulk dry density as well as the organic matter concentration of the correspondent marsh soil was considered using data from shallow percussion cores these parameters are different among all halligen higher inundation frequencies cause lower soil organic matter concentrations resulting in higher bulk dry densities bdd of the soil hooge 0 64 g cm3 langeness 0 67 g cm3 nordstrandischmoor 0 83 g cm3 autochthonous organic material by source of the marshland vegetation contributes by 9 0 1 4 hooge to 21 4 6 6 nordstrandischmoor to marshland accretion for a correspondent time scale of 1915 2011 average accretion rates 2010 2013 were calculated with 1 2 0 8 mm a for langeness 1 5 0 9 mm a for hooge and 2 6 0 9 mm a for nordstrandischmoor

evaluating deep subsidence in a rapidly accreting mangrove forest using gps monitoring of surface elevation benchmarks and sedimentary records abstract ultimately the fate of mangrove forests depends on substrate elevation gains keeping pace with relative sea level rise rslr some of the world s largest mangrove forests occur on tectonically active margins river deltas and sedimentary basins where sea level trends are largely controlled by vertical land motion i e subsidence so that rslr can be markedly higher than sea level rise induced by climate warming the rod surface elevation table marker horizon rset mh method has been applied globally to evaluate coastal wetland resilience to slr by quantifying net rates of elevation change relative to a benchmark a limitation of the rset method is that the stability of the benchmark i e vertical trend is unknown and rslr in wetlands is typically inferred from regional tide gauge records in the present study we evaluate rslr in a rapidly subsiding avicenna marina mangrove forest with a large terrigenous sediment supply firth of thames new zealand using independent and complimentary methods 1 campaign gps surveys of the stability of three rset benchmarks driven 18 m into unconsolidated sediment a tide gauge some 10 km distant and a reference station located on basement rock 2007 2016 that are tied to a network of satellite based geodetic sites and 2 137cs validated 210pb sediment accumulation rates sar measured in cores as a proxy for rslr the similarity of deep subsidence rates at the rset benchmarks located several hundred metres apart 7 7 0 5 to 9 4 0 5 mm yr 1 provides confidence in these results these subsidence rates are two to five fold higher than recorded at the nearby tide gauge 3 6 0 7 mm yr 1 and reference station 1 6 0 5 mm yr 1 weighted average 210pb sar of 9 9 mm and 9 3 mm yr 1 yield similar estimates of deep subsidence i e 8 4 and 6 9 mm yr 1 slr adjusted for vertical land motion indicating that this geological process is the major driver of the long term sea level trend in the mangrove forest our findings suggest that regional tide gauge records may not provide reliable estimates of rslr for all coastal wetlands due to local subsidence associated with natural processes and human activities subsidence rates and rslr within coastal wetlands can be evaluated using campaign gps surveys of rset benchmarks and independently from longer term sedimentary records finally evaluations of the resilience of coastal wetlands to rising sea levels over the coming decades must be based on measurements of rslr from these systems themselves

a method for measuring vertical accretion elevation and compaction of soft shallow water sediments high resolution measures of vertical accretion elevation and compaction of shallow water sediments are fundamental to understanding the processes that control elevation change and the mechanisms of progradation e g development of mudflats and intertidal wetlands in coastal systems yet measurements of elevation by traditional survey methods often are of low accuracy because of the compressible nature of the substrates nor do they provide measures of vertical accretion or sediment compaction this paper evaluates the use in shallow water systems of an approach designed to measure these variables in vegetated wetlands the approach employs simultaneous measures of elevation from temporary benchmarks using a sedimentation erosion table set and vertical accretion from marker horizons with sediment cores collected with a cryogenic coring apparatus the measures are made with a level of resolution sufficient to distinguish between the influence of surface and subsurface processes on elevation thus providing quantitative estimates of shallow subsidence the set marker horizon approach was evaluated on a developing splay created by an artificial crevasse of a distributary in the mississippi river delta the approach provided high resolution measures of vertical accretion 48 3 2 0 cm and elevation 36 7 1 6 cm over a 4 year period with the difference between the two indicating the amount of shallow subsidence in addition by laying new marker horizons in later years the approach provided rates not only of shallow subsidence 3 9 0 5 cm y 1 but also compaction of newly deposited sediments 2 1 0 6 cm y 1 and compaction of underlying sediments 1 8 0 20 cm y 1 over a two year period hence the set marker horizon approach has widespread applicability in both emergent wetland and shallow water environments for providing high resolution measures of the processes controlling elevation change

estimating shallow subsidence in microtidal salt marshes of the southeastern united states kaye and barghoorn revisited abstract simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow 3 5 m subsurface datum were made in selected coastal salt marshes of louisiana florida and north carolina to quantitatively test kaye and barghoorn s contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate rates of subsidence of the upper 3 5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation erosion table surface elevation change was significantly lower than vertical accretion at each site after 2 years indicating a significant amount of shallow subsidence had occurred ranging from 0 45 to 4 90 cm the highest rate of shallow subsidence occurred in the mississippi delta results confirm kaye and barghoorn s contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate including not only compaction but also apparently shrink swell from water storage and or plant production decomposition at some sites indeed surface elevation change was completely decoupled from vertical accretion at the florida site the assumption of a 1 1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes consequently the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits these findings also indicate the need for greater understanding of the influence of subsurface and small scale hydrologic processes on marsh surface elevation

sedimentation and response to sea level rise of a restored marsh with reduced tidal exchange comparison with a natural tidal marsh along coasts and estuaries formerly embanked land is increasingly restored into tidal marshes in order to re establish valuable ecosystem services such as buffering against flooding along the scheldt estuary belgium tidal marshes are restored on embanked land by allowing a controlled reduced tide crt into a constructed basin through a culvert in the embankment in this way tidal water levels are significantly lowered ca 3 m so that a crt marsh can develop on formerly embanked land with a ca 3 m lower elevation than the natural tidal marshes in this study we compared the long term change in elevation e within a crt marsh and adjacent natural tidal marsh over a period of 4 years the observed spatio temporal variations in e rate were related to variations in inundation depth and this relationship was not significantly different for the crt marsh and natural tidal marsh a model was developed to simulate the e over the next century 1 under a scenario without mean high water level mhwl rise in the estuary the model shows that the marsh elevation e feedback that is typical for a natural tidal marsh i e rising marsh elevation results in decreasing inundation depth and therefore a decreasing increase in elevation is absent in the basin of the crt marsh this is because tidal exchange of water volumes between the estuary and crt marsh are independent from the crt marsh elevation but dependent on the culvert dimensions thus the volume of water entering the crt remains constant regardless of the marsh elevation consequently the crt mhwl follows the increase in crt surface elevation resulting after 75 years in a 2 2 5 times larger elevation gain in the crt marsh and a faster reduction of spatial elevation differences 2 under a scenario of constant mhwl rise historical rate of 1 5 cm a 1 the equilibrium elevation relative to mhwl is 0 13 m lower in the crt marsh and is reached almost 2 times faster 3 under a scenario of accelerated mhwl rise acceleration of 0 02 cm a 1 the crt marsh is much less able to keep up with the mhwl rise after 75 years the crt elevation is already 0 21 m lower than for the natural marsh in conclusion this study demonstrates that although short term 4 years e rates are similar in a restored crt marsh and natural tidal marsh these ecosystems may evolve differently in response to sea level rise in the longer term 10 100 years

high surface elevation gains and prediction of mangrove responses to sea level rise based on dynamic surface elevation changes at dongzhaigang bay china abstract mangrove forest responses to sea level rise slr are likely misestimated in many studies because current assessment methods often assume a constant rate of surface elevation change along the intertidal profile most studies also neglect the ecogeomorphic feedback process known to accelerate soil building with slr here an empirical dynamic model that accounts for the above processes is constructed for the intertidal zone of a mangrove bay in hainan china the model allows us to explore the response of a tide dominated mangrove forest to different rates of slr rod surface elevation table marker horizon rset mh data 2015 2018 indicate rather high rates of surface accretion 13 3 57 9 mm yr 1 and surface elevation changes 7 9 35 5 mm yr 1 surface accretion and surface elevation change decreased exponentially with increasing ground elevation our model showed that slr at rates of 4 and 16 mm yr 1 would not lead to the loss of mangrove cover but that it could alter mangrove species zonation along the intertidal profile by 2100 due to a rich sediment supply and ecogeomorphic feedback importantly rapid slr and landward barriers can pose a considerable threat to the high intertidal community by causing increased inundation of the high intertidal zone subsequent shifts in species zones and the loss of mangrove biological and structural diversity along the intertidal profile overall this study predicts probabilities of habitat suitability for mangrove species under slr and expands our current understanding of the impacts of slr on tide dominated mangrove forests in sediment rich systems incorporation of extensive long term rset data into this kind of dynamic model could contribute to the better prediction of mangrove responses to slr at large scales in the future

seasonal and annual variations in the volumetric sediment balance of a macro tidal salt marsh abstract this paper examines the spatial and temporal variability in the volumetric sediment balance of allen creek marsh a macro tidal salt marsh in the bay of fundy the volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996 2002 and detailed margin surveys were conducted in 1997 1999 and 2001 using a differential global positioning system changes in surface area were calculated using gis overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system currently the volumetric sediment balance at allen creek marsh is positive however the processes of erosion and accretion demonstrate seasonal annual and spatial variability inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments sediment is deposited onto the marsh surface year round even during the winter when vegetation cover is sparse and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations based on the data from 1996 to 2002 the mid and high marsh zones experience mean accretion rates of approximately 1 4 cm year 1 whereas accretion rates in the low marsh region are statistically significantly lower 0 8 cm year 1 the absolute amount of accretion varies between seasons and from year to year the main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters the volume of material removed from the marsh margin almost tripled between 1997 169 m3 and 2001 502 m3 following breaching of the side of a tidal creek channel altering the patterns of margin erosion and deposition in the marsh system during this time however other sheltered areas of the marsh system such as along the tidal creek banks showed evidence of new vegetation growth increasing the amount of vegetated surface area available for deposition the processes of erosion and deposition on the marsh surface exhibit considerable spatial variability with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system namely wave activity vegetation ice and water depths a key factor in predicting how a marsh will evolve and respond to a number of different controls e g sea level rise or reduced sediment supply is to quantify both accretion of the marsh surface and erosion of the marsh margin evaluating the marsh system as a volumetric whole this study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation this is particularly important for open coastal marshes exposed to the erosive action of waves

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

high precision measurements of wetland sediment elevation ii the rod surface elevation table abstract a new high precision device for measuring sediment elevation in emergent and shallow water wetland systems is described the rod surface elevation table rset is a balanced lightweight mechanical leveling device that attaches to both shallow 1 m in order to be stable the pipe is driven to refusal but typically to a depth shallower than the rod bench mark because of greater surface resistance of the pipe thus the rset makes it possible to partition change in sediment elevation over shallower e g the root zone and deeper depths of the sediment profile than is possible with the set the confidence intervals for the height of an individual pin measured by two different operators with the rset under laboratory conditions were 1 0 and 1 5 mm under field conditions confidence intervals for the measured height of an individual pin ranged from 1 3 mm in a mangrove forest up to 4 3 mm in a salt marsh

experimental stretching of fluid inclusions in calcite implications for diagenetic studies homogenization temperatures of fluid inclusions trapped in calcite crystals may change with increased heating beyond the homogenization temperature fluid inclusions trapped in calcite during basin subsidence will tend to yield homogenization temperatures approaching maximum burial temperatures diagenetic studies that depend on these data will be biased coarse crystalline calcite containing saline fluid inclusions was used to examine the influence of increased temperatures and pressures on measured homogenization temperatures stepped heating experiments were conducted at 1 atm over a temperature range of 90 to 245 c along with hydrothermal experiments at confining pressures of 173 and 691 bar and temperatures of 160 250 and 350 c in all cases significant increases in the homogenization temperatures of the inclusion population were recorded presumably stresses generated during heating of the fluid inclusions exceeded the combined strength of the calcite crystal and the external pore pressure and thus caused fluid inclusion stretching size is a secondary factor that controls fluid inclusion reequilibration

integrating geochronologic and instrumental approaches across the bengal basin constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins the geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem because the viability of methods can be highly influenced by geomorphic attributes for example sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating similarly the rate of sediment transport from source to sink may determine the maturity and or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating here we explore the viability and quirks of dating and instrumental methods that have been applied in the bengal basin and review the records that they have yielded this immense dynamic and spatially variable system hosts the world s most inhabited delta outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans here and in other populated deltas worldwide our review covers radiocarbon dating luminescence dating archaeological records and historical maps short lived radioisotopes horizon markers and rod surface elevation tables geodetic observations and surface instrumentation combined these tools can be used to reconstruct the history of the bengal basin from late pleistocene to present day the growing variety and scope of bengal basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales

the mount bruce megasequence set and eastern yilgarn craton examples of late archaean to early proterozoic divergent and convergent craton margins and controls on mineralization abstract the late archaean to early proterozoic mount bruce megasequence set formerly the mount bruce supergroup overlies and is restricted to the pilbara craton and comprises two megasequences which comprise a total of six supersequences or supersequence packages that formed in different but related tectonic settings the chichester range megasequence which is the older of the two megasequences comprises two supersequences overlain by a supersequence package the lower two supersequences are dominated by tholeiitic flood basalt and terrigenous clastic sedimentary rock with only minor placer gold and uranium mineralization these formed during the breakup of a late archaean craton between about 2 77 and 2 70 ga the overlying supersequence package is dominated by mudrock carbonate sedimentary rock iron formation and was deposited in a divergent marginal setting bordering an open ocean between about 2 69 and 2 60 ga the hamersley range megasequence comprises clastic sedimentary rock iron formation carbonate sedimentary rock and felsic volcanic rock was deposited between 2 47 ga and 2 9 ga volcano sedimentary assemblages gold mineralization occurred during the late stages of this orogeny which involved transfer of strain from the eastern yilgarn limited crustal thickening metamorphism and granitoid emplacement accretion into orogenic belts provides the best chance of preserving mineralization formed in deep marine environments such as komatiite associated ni and volcanogenic massive sulphide mineralization and explains the common close spatial association of these deposits with gold mineralization in greenstone belts

hydrothermal origin for the 2 billion year old mount tom price giant iron ore deposit hamersley province western australia giant iron ore deposits such as those in the hamersley province of northwestern australia may contain more than a billion tonnes of almost pure iron oxides and are the world s major source of iron it is generally accepted that these deposits result from supergene oxidation of host banded iron formation bif accompanied by leaching of silicate and carbonate minerals new textural evidence however shows that formation of iron ore at one of those deposits mount tom price involved initial high temperature crystallisation of magnetite siderite iron silicate assemblages this was followed by development of hematite and ferroan dolomite bearing assemblages with subsequent oxidation of magnetite leaching of carbonates and silicates and crystallisation of further hematite preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids initial hematite crystallisation occurred at about 250 c and high fluid pressures and continued as temperatures decreased although the largely hydrothermal origin for mineralisation at mount tom price is in conflict with previously proposed supergene models it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation

a pre 2 2 ga age for giant hematite ores of the hamersley province australia one current model for the origin of giant hematite ores of the hamersley province requires a two step process formation of martite and goethite by supergene enrichment followed by burial metamorphism to convert goethite to microplaty hematite our new structural stratigraphic and geoehronological data suggest that at least some microplaty hematite ores were present before metamorphism owing to burial under the lower wyloo group a shrimp u pb zircon age from volcaniclastic breccia within the lower wyloo group suggests that hematite detritus in that group was derived from hematite ores older than 2209 or 15 ma the action of pre 2 2 ga oxidizing fluids is implied although their origin supergene versus hypogene remains controversial

short term 2 yrs estuarine mudflat and saltmarsh sedimentation high resolution data from ultrasonic altimetery rod surface elevation table and filter traps rates of short term up to 2 years bed elevation change and sedimentation from mudflats to salt marshes were measured in a rapidly infilling macrotidal estuary using an original combination of three high resolution techniques an ultrasonic altimeter the rod surface elevation table rset method and filter traps the authie estuary is located on a straight sand rich coast and is undergoing rapid infill under the influence of flood dominant tides reinforced by wave action the estuarine sediment suite consists of both mud and sand derived from the sea of sand derived from storm wave erosion of dunes lining the north bank of the estuary and to a much smaller extent of mud from the river catchment bed elevation change and sedimentation rates show an expected increase with the duration of tidal flooding hydroperiod in both space and time the estuarine bed sediment suite changes from sandy at the mouth to muddy within the low energy inner estuary where mudflats are rapidly accreting paving the way for the formation of increasingly denser and mature salt marshes from the high sedimentation pioneer zone to the upper marsh where annual sedimentation is very low recorded variability in rates of bed elevation change and sedimentation reflect the influence of estuarine macro scale and local sediment transport and depositional processes in a macrotidal context dominated by high inputs of allochthonous sediments

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

veins and hydrothermal fluid flow in the mt whaleback iron ore district eastern hamersley province western australia abstract with the advent of recent hydrothermal models for genesis of giant microplaty hematite ore deposits of the hamersley province we have undertaken regional scale analysis of veins and rocks surrounding the mt whaleback deposit with an aim to characterize the nature of fluid flow before during and after ore formation at least five groups of veins formed in the brockman iron formation in deformational events associated with the paleoproterozoic interaction between the yilgarn and pilbara cratons in a 600 km 2 area around the mt whaleback microplaty hematite orebody the five main veining events most likely correspond to the collisional d 2 and extensional collapse d 3 phases of the ca 2300 2200 ma ophthalmian orogeny with one or two later phases probably associated with the waning stages of the ca 1700 1650 ma capricorn orogeny d 4 and or later proterozoic events the abundance of veins associated with d 2 contraction and d 3 extensional fabrics and the composition up to 15 wt nacl equivalent and pressure corrected homogenisation temperatures of primary fluid inclusions 200 400 c indicate that the temperature salinity and likely volume of fluid reached a peak during the last stages of the ophthalmian orogeny and the first stages of post ophthalmian extension paragenesis of veins relative to the deformation history and localization of highest vein densities in the dales gorge member provides circumstantial evidence that the peak of hydrothermal activity in the district was synchronous with the main phase of microplaty hematite ore formation at mt whaleback we propose that the veins record part of the fluid flow system related to the genesis of this giant ore deposit

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

sediment dynamics and morphological stability of estuarine mangrove swamps in sherbro bay west africa abstract the relationship between the circulation of fine suspensions in a mangrove colonised estuarine complex short term mangrove substrate accretion and medium term mangrove swamp geomorphic evolution was studied in sherbro bay an infilling microtidal to mesotidal embayment in southern sierra leone formed behind holocene sandy beach ridge barriers the estuarine reaches of streams debouching into the bay have relatively high suspension concentrations sc of silts and clays that ranged during the survey period in 1991 from 0 8 to 40 g l 1 in association with the constitution of turbidity maxima 5 50 g l 1 at the interface between freshwater drainage and the saltwater intrusion however the surveyed mangrove swamp plots showed much lower suspension concentrations 0 09 0 6 g l 1 and low albeit minimum rates of accretion 1 1 3 mm a 1 monitored between 1980 and 1989 these low rates are attributed mainly to the short duration of tidal flooding due to a high substrate elevation within the tidal range and to the low settling potential of the very fine grained suspensions circulating over the swamps a comparison of two sets of aerial photographs 1954 1960 and 1976 showed that these swamps and their channel networks are also characterised by a remarkable medium term morphodynamic stability this stability and the low accretion suggest that the swamps and their channel networks are largely in equilibrium with the hydrology notably flooding duration and sediment loads settling out of mud from the turbidity zones contributes to higher accretion rates up to 12 mm a 1 not taking into account the effects of shallow subsidence on parts of the mudflats fronting the mangroves which are flooded for longer periods some of the mud is deposited over sandy channel bars in the main bay channel and the rest exported seaward it is tentatively suggested that an increase in the duration of tidal flooding generated by global sea level rise at the presently predicted rates could lead to higher sedimentation in the mangrove swamps thus enhancing accretion and the chances of mangrove survival

impact of land use change and hard structures on the evolution of fringing marsh shorelines estuarine fringe marshes provide essential ecosystem services to coastal regions including carbon sequestration and provision of shelter and nursery grounds for aquatic and terrestrial animals the ability of a marsh to sustain itself by vertical accretion in response to sea level rise is in part limited by inorganic sediment supply models attempting to forecast salt marsh response to future sea level rise commonly ignore land use changes despite the recent coastal population boom and the potential of land use changes to alter sediment sources and modify established sediment transport pathways this study investigates the impacts of landscape modifications which are typical of coastal areas on the nearshore sedimentation and edge evolution of two fringing marshes the sites examined include a marsh fringing the upper bay and a marsh fringing a beach ridge on the estuarine shoreline of a barrier island both sites are located in the same estuarine system have similar hydrologic settings and comparable vegetation densities previous work marsh cores and a historical record from aerial photos indicate that although the fringe marshes are in different geomorphic locations prior to anthropogenic modifications they were similar in terms of nearshore sediment composition scarp shoreline morphology and shoreline trajectory the upper bay marsh was impacted by the introduction of tree farming in the watershed of a tributary creek to the upper bay which increased upland erosion and caused higher sedimentation rates in the estuary the back barrier marsh which received no contribution from the tree farm because it is distal with respect to river input was modified by the installation of a pier and rock sill terrestrial lidar surface elevation tables and accretion rates obtained from radioisotope analyses show that the deforestation induced high rates of nearshore and marsh accretion at the upper bay site which is promoting marsh colonization and expansion these same types of data in addition to aerial photos were obtained at the back barrier site and show increased rates of marsh shoreline erosion adjacent to the structures the fringing marshes were once similar but started to evolve differently over a short time period as a result of human induced changes to the landscape coastal development can significantly influence marsh shoreline behavior which must be taken into account when developing models of coastal response to sea level rise

measured rates of sedimentation what exactly are we estimating and why abstract data on rates of sedimentation are essential in studies of sedimentation systems these data are obtained in three main study contexts 1 the study of sedimentation systems that are active today 2 the source to sink study of sedimentation systems that no longer are active and 3 the study of the relationship between accumulation rate and measurement timespan the aim of this paper is to question the meaning of measured rates of sedimentation and their interpretability particularly in these three contexts individual measurements of rate of sedimentation must always be interpreted with care firstly there are different definitions for instance with different statistical support or measurement dimension values that are defined differently cannot be compared directly secondly appropriate sampling schemes must have been used for the measurement this minimises sampling bias thirdly the inherent limitations of the data sources must be taken into account rates of sedimentation can usually be measured successfully in active sedimentation systems the same is not true for systems that are no longer active these can only be studied using the stratigraphic successions left behind rates of erosion can never be measured successfully in stratigraphic successions rate of sedimentation is essentially a ratio an amount of sedimentation per length of time therefore the obvious strategy to use in determining it is first to measure the amount and the time independently then to combine the values the amount can be measured in terms of thickness or volume or mass per unit area the duration of the time interval can be preset using quasi continuous measurement techniques or site reoccupation or it can be identified from interval specific sedimentary structures or it can be measured using dated horizons an alternative strategy is to use a surrogate measurement variable rates of erosion in ancient systems are usually measured in this way using cosmogenic radionuclide concentrations these two strategies are reviewed in this paper sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole this estimation is best carried out using geostatistical estimation techniques the alternative is simply to average the measured rate values this latter approach should not be used however because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries it says nothing at all about how the system is operating or about its spatial and temporal variability measurements of rates of sedimentation made for source to sink studies are necessarily made in stratigraphic successions the measurements are used to estimate quantities in the sediment mass budget equation the amount of decumulation is inherently incapable of being measured in stratigraphic successions therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere this means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non erosional for that entire time interval a highly unrealistic situation the consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale invariant this in turn is often taken as indicating that the stratigraphic record is fractal in nature there are nevertheless grounds for doubt all of which relate to the ways that the data are collected and used for estimation the relationship is in fact the natural mathematical result of last in first out lifo operation and is produced in any type of system in which addition and removal processes both operate it says nothing particular about sedimentation processes the future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a lifo model

conditions of vein formation in the southern appalachian foreland constraints from vein geometries and fluid inclusions abstract the nolichucky shale in the whiteoak mountain thrust sheet of the southern appalachian foreland contains four coeval bed normal calcite vein sets that trended 015 055 090 and 320 before thrusting the pretectonic veins were displaced by syn tectonic bed parallel slickensided calcite veins during local alleghanian thrusting fluid inclusion thermometry indicates precipitation of both bed normal and bed parallel veins from nacl cacl2 brines 27 wt nacl equiv salinity at 80 110 c for bed normal veins and 110 c for bed parallel veins these temperatures correspond to burial depths of 2 4 3 6 km which were attained after the middle mississippian these pressure corrected homogenization temperatures are comparable to time temperature indicators such as cai and illite crystallinity and indicate that inclusions were trapped near maximum burial conditions and were not deformed after trapping this conclusion is supported by the absence of petrographic evidence for inclusion failure and a worst case mechanical analysis that indicates a lack of brittle deformation to inclusions after trapping the four coeval bed normal vein sets could not be formed by one simple stress field nor by the development of a single structure but required the interaction of at least two stress components or structures it is proposed that the interaction of the alleghanian and ouachita orogenic stress components beyond the limits of thrusting produced the sets as coeval alleghanian orthogonal 055 320 and ouchita sub orthogonal 015 090 mode i fractures

experimental decrepitation and re equilibration of fluid inclusions in synthetic quartz abstract strong discrepancies between densities of the fluids trapped in fluid inclusions f i and p tp couples deduced from other geological considerations are common so it was decided to test experimentally the possible f i re equilibrations when bringing the host crystal in p tp conditions different from trapping conditions runs were conducted on synthetic quartz in a gas apparatus and in a griggs solid medium apparatus the following modifications of the f i were observed 1 1 drastic shape changes of the primary f i and appearance of clusters or trails of small secondary inclusions sometimes related to a crack 2 2 lowering of the fluid densities such a re equilibration is a decrepitation phenomenon first hydraulic fracturing then sealing of the cracks with appearance of secondary inclusions when using the gas apparatus the new measured densities are in very good accordance with the nominal p tp conditions when using the solid medium apparatus the new densities are surprisingly low relative to the nominal p t conditions probably due to a strongly anisotropic stress state in the apparatus

holocene eolian sediments on the southern border of the duero basin spain origin and development of an eolian system in a temperate zone abstract holocene eolian sediments accumulated in the interior of the iberian peninsula far from typical eolian environments deserts coasts and periglacial arid belts these eolian deposits are interpreted as a wet eolian system with dunes interdune areas and sand sheet areas parabolic dunes predominate indicating a dominant wind direction to the ne interdune areas may be either dry or wet the eolian system is partly relict but also contains sporadically active dunes with visible slipfaces and partial vegetative cover several dunefields exist having larger and more complex dunes at the center and downwind areas dunes originated from dome shaped accumulations in the sand sheet which became simple parabolic dunes and ramps larger compound and complex parabolic dunes and ramps originated by merging and stacking of simple dunes finally transverse dunes originated when the noses of parabolic dunes were stopped by water and the arms continued to move forward the origin and development of the eolian system was related to abundant sand from underlying fluvial terraces deposition in a depression with considerable relief and open to the wind and changes in the water table which controlled eolian accumulation the presence of those eolian deposits in a temperate region suggests that with the appropriate factors eolian sedimentation is relatively independent of climate the potential preservation of these sediments in temperate climates is problematic because they are vulnerable to erosion mainly by water