sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

global sea level rise published values for the long term global mean sea level rise determined from tide gauge records exhibit considerable scatter from about 1 mm to 3 mm yr this disparity is not attributable to instrument error long term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year instead the differing estimates of global sea level rise appear to be in large part due to authors using data from gauges located at convergent tectonic plate boundaries where changes of land elevation give fictitious sea level trends in addition virtually all gauges undergo subsidence or uplift due to postglacial rebound pgr from the last deglaciation at a rate comparable to or greater than the secular rise of sea level modeling pgr by the ice 3g model of tushingham and peltier 1991 and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records the value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880 1980 is 1 8 mm yr 0 1 this result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality

relative sea level rise and climate change over the last 1500 years we constructed a detailed relative sea level rise curve for the last 1500 years using a novel approach i e charting the rate of relative sea level rise using microfaunal and geochemical data from a coastal salt marsh sequence clinton ct usa the composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively the resulting sea level rise curve with age control from 14c dating and the onset of anthropogenic metal pollution shows strong increases in the rate of relative sea level rise during modern global warming since the late nineteenth century but not during the little climate optimum ad 1000 1300 there was virtually no rise in sea level during the little ice age ad 1400 1700 most of the relative sea level rise over the last 1200 years in clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years changes from slow to fast rates of relative sea level rise apparently occurred over periods of only a few decades we suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea level rise along the northeastern usa seaboard relative sea level rise in that area is currently faster than the worldwide average which may result partially from an ocean surface effect caused by hydrodynamics our data show no unequivocal correlation between warm periods on a decaal to centennial time scale and accelerated sea level rise one period of acclerated sea level rise may have occurred between about ad 1200 and 1450 which was the transition for the little climate optimum to the little ice age i e a period of cooling at least in northwestern europe local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea level however the second period of accelerated sea level rise occurred during the period of modern global warming that started at the end of the last century

long term accretion rates on tidal salt marshes abstract long term variations in salt marsh accretion rates were estimated using data collected on the marshes of the north norfolk coast england fourteen discrete marsh areas were sampled all lying within a 20 km stretch of coast the age of each marsh had previously been determined using radiocarbon or archival evidence for the date of vegetation inception on each marsh surface marsh ages ranged from 10 years to 2000 years the elevation of each marsh surface was determined in the field using levelling techniques the relationship between age and surface elevation was assumed to be a function of the rate of marsh accretion within this area of coast statistical tests showed this to be a highly significant relationship while the accretion rates calculated from the age height curve agree closely with field measurements on these marshes accretion rates were found to vary from 1 7 cm yr on 10 year old marshes to less than 0 002 cm on marshes older than 500 years the age height relationship describes an asymptotic curve with the asymptote lying 0 8 m below the level of the highest spring tides and appears to be controlled by the frequency of tidal maxima which peaks at 0 8 m below the maximum value and declines sharply above that height

deep electromagnetic sounding in turkmenia summary this paper presents the results of interpretation of magnetotelluric and magnetovariational observations in a vast region including the southern part of the turanian plate and the south caspian megadepression both l d and 2 d interpretations fail to explain the main peculiarities of the natural magnetotelluric and magnetovariational fields observed in the region the 3 d interpretation used in the paper is based on thin sheet modelling and inversion algorithms developed by the authors the final model consists of an inhomogeneous surface layer and a conductive layer embedded in the otherwise laterally uniform medium in the crust under the kopet dagh mountains the surface layer conductance varies between 100 s and 13 ooo s and the crustal anomaly has a conductance of about 2500 s the layered regional structure includes a conductive layer at a depth of 80 100 km whose conductance is about 1800 s the model explains all of the main features of the observed magnetotelluric and magnetovariational fields in the region

response of the connecticut river estuary to late holocene sea level rise abstract the morphology of the modern connecticut river estuary has been inherited from an earlier tidal river the holocene evolution of the estuary has been dictated by the relative submergence of the coastline and the sediment trapping efficiency of the estuary and tidal river system the mid holocene tidal river system extended to the modern mouth of the estuary and subaerial floodplains stretched across the modern submerged shoals of the estuary submergence in excess of the long term sedimentation rate converted these floodplains into open backwater coves beginning about 4000 yr bp in the southern estuary and about 2700 yr bp in the upper estuary and it also initiated estuarine circulation in the tidal river approximately 1700 yr bp an abrupt decrease in the submergence rate caused freshwater marshes to prograde across the coves and across the remaining floodplain surfaces at 1000 yr bp salt marsh peat at the mouth of the estuary indicates estuarine circulation similar to that of t he modern estuary the marshes in the northern estuary have supported freshwater vegetation since their inception thus the continuum of modern environments present along the length of the estuary models the evolution of a single reach of the estuary through time continued submergence will increase the tidal prism and intensify estuarine circulation this effect will be regulated by the large excess sediment supply available to fill the volume of the estuary created by relative sea level rise

tidal wetland record of holocene sea level movements and climate history abstract paleontological geochemical and lithological indicators of former marine and nonmarine influence are correlated between 13 cores from a tidal wetland wolfe glade on the southeast coast of delaware bay twenty new radiocarbon dates are used to establish the chronostratigraphy of marsh facies sediment iron content weight loss on ignition and remains of plants diatoms and foraminifera known to tolerate specific tidal inundation cycles are used to describe cored facies originating from supratidal intertidal and subtidal salt marsh subenvironments pollen assemblages are used to infer local holocene climate fluctuations and to reconstruct paleoenvironments during marsh evolution the record of paleoclimatology suggests the atlantic chron was warm with variable humidity in the region whereas the subboreal was dominated by cool and humid conditions the subatlantic was warmer and initially dryer with a cool humid phase prior to about 1 ka returning to warmer humid conditions in the last several centuries local relative sea level movements are characterized by five rapid short term episodes when the rate of sea level rise accelerated relative to the rate of marsh aggradation these episodes are recorded by transgressive facies contacts at 5 3 0 2 ka 4 4 0 2 ka 3 25 0 2 ka and 1 8 0 2 ka sidereal years an earlier transgressive facies contact dated 6 9 0 2 ka is probably not the product of a true sea level movement sea level movements are recorded throughout the marsh as palustrine or high marsh peats or peaty overlain by lower intertidal or subtidal marine deposits several features suggest that these episodes are local relative transgressions produced by short term accelerations in the rate of sea level rise relative to marsh aggradation the contemporaneity and apparent suddenness of marine inundations the sequence of facies indicating marine drowning the presence of similar events in marshes elsewhere in delaware bay and the marsh wide extent of indicative facies transitions we propose that the rapid and frequent sea level movements observed in wolfe glade are the result of surges and relaxations in the gulf stream and associated spin up and partial collapse of the north atlantic gyre in response to winds generated by changes in the north atlantic atmospheric thermal gradient associated with holocene climate fluctuations

a backbarrier overwash record of intense storms from brigantine new jersey abstract analysis of aerial photographs and historic charts indicates that the barrier beach at brigantine nj has migrated landward 300 to 400 m since 1869 primarily as a result of overwash during hurricanes and winter storms a series of vibracores from the backbarrier salt marsh reveals a millennial scale stratigraphic record of overwash deposition carbon 14 c 14 and cesium 137 cs 137 radioisotopic methods were used to date overwash deposits washovers the ages of recent washovers are consistent with deposition during intense storms in 1938 1944 1950 and 1962 an additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788 two prehistoric overwash fans were likely deposited by intense storms striking the new jersey coast in the 7th to 14th centuries and 6th to 7th centuries a d the landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans the greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period the hurricane of 1821 the spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments

a sea level rise curve from guilford connecticut usa abstract high resolution stratigraphic studies based on sediment chemistry lithology macroflora and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at guilford connecticut show that coastal marshes are ephemeral environments marsh wide environmental variations were common and century long episodes of relative submergence alternated with emergence despite about 2 m of relative sea level rise rslr in connecticut over the last 1500 years the marshes have expanded both landwards and seawards and marsh accretion has been outpaced only marginally by rslr we used radiocarbon dating and the level of anthropogenic markers metal pollution as dated with 210 pb in the cores for age control for most of the last 1000 years the rate of rslr was between 1 3 and 1 8 mm yr but over the last 300 400 years it increased to 2 9 3 3 mm yr and has been faster than the accretion rate especially in the middle marsh the net submergence rate or submergence index ratio of the rate of rslr and marsh accretion rate averaged about 1 15 over the last 1000 years and increased to about 1 5 over the last 200 years the rate of rslr was very sluggish during the early part of the little ice age but we found a slightly higher rate during the little climate optimum this excursion is close to the noise level however the most significant observation is that rslr increased strongly around a d 1650 the onset of this acceleration falls in the middle to end of the little ice age and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases

influence of glacial isostatic adjustment on tide gauge measurements of secular sea level change modem tide gage records of secular sea level change are strongly contaminated by the ongoing influence of glacial isostatic adjustment in this paper we employ an accurate high resolution model of the glacial isostatic adjustment process to filter this signal from time series consisting of annual mean heights observed on over 500 tide gages from which records of duration longer than 10 years are available these records are all contained in the archive of the permanent service for mean sea level at bidston in the united kingdom prior to removal of the isostatic adjustment contamination from these records the secular sea level change signal is seen to exhibit both rising and falling levels depending upon geographic location with regions of falling level corresponding to those that were ice covered during the last glaciation event of the present ice age after filtering the geographic heterogeneity in rates is considerably reduced so much so that a globally coherent component consisting of a rise of sea level at a rate of 2 4 0 9 mm yr 1 is revealed this could conceivably be driven by the greenhouse effect although no particular mechanism has been unambiguously identified by our analyses we investigate the impact of a number of different variants of the analysis procedure upon the inferred global signal

nd isotopic evidence for the position of southernmost indian terranes within east gondwana abstract sm nd model ages of orthopyroxene bearing massif charnockites from the cardamom hills massif and adjoining supracrustal rocks from the kerala khondalite belt in southernmost india are used to infer some of the relationships within these rocks and between them and neighboring areas most of these rocks have model ages of 2 1 2 8 ga with most charnockites in the range 2 2 2 6 ga thus 3 0 3 4 ga archean rocks to their north did not contribute material to either suite and the two suites may have been juxtaposed after formation of the supracrustal rocks the similarity of sm nd isotope systems in the two units studied here supports an argument that the massif charnockites were the primary sole source of the detritus incorporated into the supracrustal rocks a cordierite gneiss representative of a relatively minor lithology in the supracrustal belt has a model age of 1 3 ga the protolith of this gneiss not only formed from much younger material than the rest of the belt but also formed significantly after the other metasedimentary rocks the source material of the gneiss protolith may have been located in the wanni and vijayan complexes of sri lanka the overlap of the model ages of rocks in this area and those in the highland complex of sri lanka supports the notion that these two sets of rocks were joined to each other in gondwana they belong to a belt that ran from antarctica through sri lanka and india into madagascar this belt was involved in pan african tectono metamorphism as reflected in the 550 ma age of the last granulite forming event throughout the belt

marine ice sheet decoupling as a mechanism for rapid episodic sea level change the record of such events and their influence on sedimentation abstract unlike terrestrial ice sheets marine ice sheets display more sensitivity to sea level than to climate and they are capable of rapid mass wasting this mass wasting involves ice shelf decoupling from the sea floor and rapid collapse followed by drawdown of the ice sheet glaciologists argue that the marine ice sheet decoupling mechanism could cause sea level rises of a few meters within several hundred years information regarding late wisconsinan holocene glacial history suggests that ice sheet deterioration did not occur at a steady rate studies of the antarctic continental shelf indicate ice sheets grounded over large portions of the shelf during the late wisconsinan glacial maximum and that their retreat from the continental shelf was rapid a study of the trinity sabine incised valley of the texas continental shelf yields a continuous record of holocene sedimentation and sea level change paired upper bay and tidal inlet estuarine systems reflect periods when relative sea level was either at a still stand or slowly rising the flooding surfaces of back stepping parasequences reflect periods of rapid sea level rise large sand bodies on the adjacent shelf used to derive previous sea level curves for the region may represent former shoreline deposits but they also show extensive reworking therefore the curves generated from studies of these sand bodies are inaccurate marine ice sheets have existed in antarctica since at least the late eocene so this mechanism for rapid sea level rise has been active throughout much of cenozoic time as well as during older glacial episodes

holocene sea levels paleoceanography and late glacial ice configuration near the northumberland strait maritime provinces work on new cores from old core sites in baie verte new brunswick led to the identification of submerged salt marsh peats reported earlier as freshwater ones a comprehensive sea level curve between 9 and 15 m below present is based on marsh foraminiferal assemblages these data indicate that between 4500 and 5400 bp relative sea level rsl rise was comparatively slow about 10 cm 100 years the rate increased dramatically between 4500 and 4000 bp 1 m 100 years and decreased between 2000 and 4000 bp to its present rate of 15 cm 100 years we suggest rsl was falling before 5400 bp and that the sequence in our deepest core is similar to some observed in the bay of fundy and nova scotian atlantic coast where early rsl fall is documented to account for this sea level record and others nearby we suggest that the ice history here is complex with three separate ice caps thinning towards this area in late glacial times earlier work also indicated a number of sediment sequences barren of benthonic foram

towards a quantitative chemostratigraphic model for sediments of late flandrian age in the severn estuary u k abstract because the severn estuary is physically well mixed the complex sequence of late flandrian lithostratigraphic units accumulated along its extensive muddy shores can in part be correlated and dated relatively on the basis of the levels of the contained pollutants an improved pollutant based stratigraphic model is advanced on the supposition that the estuary is perfectly mixed and that any sample of muddy sediment from the area consists of a mixture of two pure lithologies of contrasted grain size either or both of which may contain a particular pollutant there is little spatial variation in the abundance levels of the clay minerals kaolinite illite mixed layer chlorite and pollutants fly ash coal dust zn cu pb cr present in a set of samples of contemporary mud drawn from all parts of the estuary the use of pollutant levels as a semi quantitative stratigraphic tool in the severn estuary is therefore fully justified however although the trends are very weak the spatial variation in the amounts of coal zinc and lead in the muddy sediments of the estuary is statistically significantly different 5 level from what is expected of a perfectly mixed system until these trends are better defined the pollutants cannot be used as a fully quantitative stratigraphic tool

constraints on measurement of sea level movements from salt marsh accretion rates the use of sediment accretion rates measured on coastal and estuarine salt marshes as a surrogate for rates of sea level change rests on the usually implicit assumption that marsh maturity is unchanged over the measurement period this assumption is inherently difficult to test empirically but a simple mathematical analysis shows that it is true only in a severely restricted case under most practical conditions measured accretion rates either over estimate or under estimate the rate of sea level change under certain circumstances they may indicate an upward trend when the tendency is actually downward a knowledge of marsh history is critical to the evaluation of such measurements sea level movements estimated from accretion rates are theoretically most reliable in the case of relatively old marshes and comparatively short measurement periods

sea level rise acceleration and the drowning of the delaware bay coast at 1 8 ka cores from delaware bay tidal marshes separated by over 100 km reveal correlative transgressive overlap boundaries dated at 1 8 to 2 0 ka sedimentary facies at these boundaries that show strong marine influence abruptly but conformably overlie facies showing strong terrestrial influence the transgressive overlap boundaries correlate with a transgression in wetland deposits of the new jersey shore of delaware bay further suggesting the occurrence of a significant regional sea level movement because other mechanisms rapid subsidence autocompaction rapid lateral erosion by tidal streams and reduced sediment supply are less likely we propose that these transgressive facies transitions were produced by an acceleration in the rate of sea level rise at 1 8 ka in the delaware bay

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

variability of intertidal foraminiferal assemblages in a salt marsh oregon usa we studied 18 sampling stations along a transect to investigate the similarity between live rose bengal stained foraminiferal populations and dead assemblages their small scale spatial variations and the distribution of infaunal foraminifera in a salt marsh toms creek marsh at the upper end of the south slough arm of the coos bay estuary oregon usa we aimed to test to what extent taphonomic processes small scale variability and infaunal distribution influence the accuracy of sea level reconstructions based on intertidal foraminifera cluster analyses have shown that dead assemblages occur in distinct zones with respect to elevation a prerequisite for using foraminifera as sea level indicators our nonparametric multivariate analysis of variance showed that small scale spatial variability has only a small influence on live rose bengal stained populations and dead assemblages the dissimilarity was higher however between live rose bengal stained populations in the middle marsh we observed early diagenetic dissolution of calcareous tests in the dead assemblages if comparable post depositional processes and similar minor spatial variability also characterize fossil assemblages then dead assemblage are the best modern analogs for paleoenvironmental reconstructions the toms creek tidal flat and low marsh vascular plant zones are dominated by miliammina fusca the middle marsh is dominated by balticammina pseudomacrescens and trochammina inflata and the high marsh and upland marsh transition zone are dominated by trochamminita irregularis analysis of infaunal foraminifera showed that most living specimens are found in the surface sediments and the majority of live rose bengal stained infaunal specimens are restricted to the upper 10 cm but living individuals are found to depths of 50 cm the dominant infaunal specimens are similar to those in the corresponding surface samples and no species have been found living solely infaunally the total numbers of infaunal foraminifera are small compared to the total numbers of dead specimens in the surface samples this suggests that surface samples adequately represent the modern intertidal environment in toms creek

the formation of coastal peat marshes under an upward tendency of relative sea level the upward growth of a tidal mudflat marsh within the tidal frame is determined theoretically by the rates of minerogenic sediment supply organogenic sediment supply long range sediment compaction and movement of relative sea level where the movement of relative sea level is upward a marsh can achieve a state of dynamic equilibrium in which the composition of the sediment accumulating on its surface is governed by the balance between the rates of organogenic supply and sea level change a peat organogenic marsh should arise where the former rate roughly equals or exceeds the latter a minerogenic marsh should form where the rate of sea level rise is dominant even though the absolute availability of mineral fine sediment may be so high as to appear to suggest that build up to extreme tidal levels where vegetation would dominate should have occurred

vertical salt marsh accretion since the roman period in the severn estuary southwest britain abstract using three methods of measurement and averaging over the whole estuary the vertical sediment accretion on mature clastic salt marshes amounts to 1 22 m since the roman period ca a d 150 1 05 m since the medieval period ca a d 1250 0 54 m since ca a d 1845 and 0 21 m since ca a d 1945 these data are cautiously interpreted to mean that the trend of relative sea level in the severn estuary is continuing upward shorter term negative tendencies are not excluded and that the current rate of rise could be a few millimetres per year the measured sediment thicknesses cannot be equated directly with relative movements of sea level however because of effects related mainly to 1 changes in the tidal range with general deepening 2 the possible transgression up the severn vale of the estuary as a whole and 3 the possible raising of tidal levels due to wetland reclamation after estimating for all these factors the true relative rise since the roman period could have amounted to 1 6 1 7 m

flandrian sea level changes in the fenland ii tendencies of sea level movement altitudinal changes and local and regional factors stratigraphic micropalaeontologic and radiocarbon data show that since c 6500 bp the fenland has been influenced by 7 periods of positive sea level tendencies and by 6 periods of negative sea level tendencies despite the numerous problems associated with the reconstruction of past altitudes of sea level the periods of positive sea level tendencies were clearly characterised by a rise in sea level the development of transgressive overlaps and a landward movement of the coastline the periods of negative sea level tendencies were characterised by the development of regressive overlaps a seaward movement of the coastline and a reduced or negative rate of sea level rise the various altitudinal errors do not permit the incontrovertible distinction of periods of falling sea levels all changes within the fenland were not synchronous and local factors influenced the exact nature of each sea level indicator dominant regional and local factors have been identified for different areas and different time periods the chronological and spatial characteristics of the sequences within the fenland are best explained by a palaeocoastline without supratidal barriers controlling sedimentation the data indicate an average crustal subsidence in the fenland of 0 9m 1000 years since c 6500 bp and the pattern of positive and negative tendencies of sea level movement is also seen in the chronologies for north west england and north east scotland