terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

estimates of the amount and rate of sea level change across the rhaetian hettangian and pliensbachian toarcian boundaries latest triassic to early jurassic an attempt is made to determine the amount and rate of sea level change for two major events in the latest triassic to early jurassic both of which are associated with mass extinctions using the best available facies evidence and time scale the amount of marine deepening across the pliensbachian toarcian boundary based on analysis of the excellent yorkshire coast section is likely to have been a few tens of metres at a rate of between 1cm 1 2 ka 1 and 1cm 0 4 ka 1 the change across the rhaetian hettangian triassic jurassic boundary was different in that the sea level rise was immediately preceded by a sea level fall effectively a 9regression transgression9 couplet the earliest jurassic sea level rise is likely to have been much more rapid than that across the pliensbachian toarcian boundary at a rate of at least 1 cm 0 2 ka 1 whereas the speed of pliensbachian toarcian change is consistent with the growth of oceanic ridges the appreciably more rapid triassic jurassic change is suggestive of a different tectonoeustatic mechanism involving stress induced changes in plate density

early hettangian benthic planktonic coupling at doniford sw england palaeoenvironmental implications for the aftermath of the end triassic crisis abstract this paper presents a high resolution micropalaeontological study integrated with geochemical and sedimentological analyses of the triassic jurassic tr j transition at the doniford section sw england our analyses indicate the renewal of surface carbonate production in the blue lias formation early hettangian after the end triassic mass extinction based on the high abundance of surface carbonate producers schizosphaerellids which occurred in phase with development at sea floor of calcareous hyaline benthic foraminifers we deduce that a benthic pelagic coupling resulted in both the initial restoration of the biological carbonate pump and also a more efficient export production the presence of monospecific phytoplankton assemblages and benthic foraminiferal assemblages typical of poorly oxygenated environments suggest that the environmental stress continued after the end triassic maximal perturbation complete environmental recovery was prevented by a succession of alternating dysaerobic and anoxic phases that favoured the deposition of black shale sediments the hypothesis of a methane release mechanism as a trigger for the global carbon cycle perturbation and greenhouse conditions during the early jurassic is discounted based on evidence from the decoupled carbon isotope records of carbonate and organic matter apart from local control of a high amplitude sea level change across the tr j boundary the succession and nature of events at doniford are consistent with a scenario of global environmental and biotic changes triggered by the physical and chemical effects of the central atlantic magmatic province camp volcanism a super greenhouse climate in the aftermath of the end triassic mass extinction appears to be the results of the combination of the long term co2 accumulation in the atmosphere system due to the camp volcanic activity as well as the inefficiency of the biological pump due to reduced export production

uniquely extensive soft sediment deformation in the rhaetian of the uk evidence for earthquake or impact the lower part of the cotham member in the penarth group latest triassic rhaetian of the uk incorporates a uniquely extensive metre scale horizon of soft sediment deformation interpreted as a seismite it shows evidence for only a single seismic event even at its thickest development it is recorded from more than forty sites across at least eight discrete sedimentary basins covering n250 000 km 2 and originally must have covered a still larger area such a widespread horizon of soft sediment deformation unique for the uk phanerozoic and implying a seismic event of exceptional magnitude is difficult to account for by conventional terrestrial mechanisms contemporaneous volcanism in the central atlantic magmatic province camp was too far distant to cause the deformation and the tectonic setting of the region was not conducive to earthquakes on this scale slump fold long axes suggest an epicentre broadly in the southern irish sea or st george s channel impact of a km scale asteroid here potentially could produce the observed sedimentological effects across the uk but any late triassic impact structure would now be concealed by a km or more of younger strata at its thickest development in northern ireland the seismite is succeeded by a rip up breccia and hummocky and wave rippled cross stratification these facies and their position immediately above the seismite are consistent with the effects of a tsunami arising directly from the seismic event tentative evidence for a tsunamite of this age has also been reported from southern france the putative tsunamite in northern ireland is succeeded by a desiccation cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern england the hiatus in southern england correlates closely with a 13 c isotope excursion that has been traced from eastern europe across to western north america and is associated with significant biotic changes the ultimate cause of the seismite and associated tsunamite remains unclear no impact crater of appropriate age or location is currently known and other evidence for impact at this time is at best equivocal it is considered here that impact of a km scale asteroid may have caused the observed sedimentological effects in the lilstock formation across the uk area but was not necessarily a significant contributory factor in the generation of either the isotope excursion or of the biotic changes through the triassic jurassic boundary interval

the 210pb chronology of late holocene deposition in an eastern australian lake basin we report here the results of detailed 210pb analysis of a sequence of lake sediments from little llangothlin lagoon on the new england tablelands of new south wales australia 210pb dating has been rarely employed in australia and prior to this work no attempt had been made to evaluate the method using independent dating techniques the chronology of deposition in the lake has been modelled using the constant initial concentration cic and constant rate of supply crs methods changes in the palynology and geochemistry of the sediments can be closely matched with well documented historic events in the lake catchment the dates of these events have been used to assess the modelled chronologies within the limits of resolution of the sampling interval there is good agreement between the chronology modelled using the crs approach and the dates inferred for geochemical and palynological events in the sequence the cic method provides a less successful match with the historical record although the differences between the dates derived by the two models are small

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

correlation of the triassic jurassic boundary in england and austria an attempt is made to fix the triassic jurassic boundary at the classic locality of st audries bay somerset by reference to biostratigraphy in conjunction with lithostratigraphy utilizing comparison with the more fully marine sequence of the kendelbach gorge in austria the boundary is placed at the base of the blue lias formation

some considerations of the 210pb constant rate of supply crs dating model one of the most widely used radionuclides in the study of recent sedimentation processes is 210pb its depth profile in sediments is used as input for various dating models which provide chronologies mass fluxes and sedimentation rates in this work we revisited the crs constant rate of supply model widely used for dating sediments through 210pb a more general hypothesis periodic flux pf was proposed and although it confirmed the validity of crs chronology a detailed analysis of the mass sedimentation formula pointed out an inconsistency of the cited model a new mass sedimentation formula was proposed and validated with a lake sediment core and four marine sediment cores

bed sediment associated trace metals in an urban stream oahu hawaii of the 117 stream and lake systems sampled nationwide fish from manoa stream on oahu hawaii have consistently shown the highest pb concentrations therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5 8 km stretch of manoa stream a total of 123 samples 63 m were examined for 18 elements and 14 samples for 21 elements selected samples were also examined using different leach solutions to examine metal phase associations all trace metal data computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for cr and ni minor anthropogenic contamination for ba cd cu hg and zn and a very strong contamination signal for pb maximum pb contents up to 1080 mg kg 1 were associated with anthropogenic material dumping in minor tributaries storm sewer sediments and sediments in the lower section of the basin proportionally pb had the highest non residual component of elements examined dominantly in the reducible phase associated with mn and amorphous fe oxyhydroxides the contamination signal was typically lowest in the undisturbed headwater reach of the basin above 5 1 km with significant increases throughout the residential and commercial institutional zones of the mid basin the spatial pattern of bed sediment contamination and evidence from storm sewer outlet sediments strongly indicates that pb and to a lesser degree some other metals is still being transported to the stream and the primary agent is soil erosion and transport of metals sorbed to sediments the primary source of sediment associated metals is considered to be the automobile though other minor sources can not be ruled out

the impact of the central atlantic magmatic province on climate and on the sr and os isotope evolution of seawater abstract there is a wide range of geochemical sedimentological and palaeontological evidence suggesting that the interval at the end of the triassic and the beginning of the jurassic some 200 ma ago was a time of major environmental change the supercontinent pangaea began to rift eustatic sea level rose and there was a mass extinction in marine and terrestrial biota the eruption of at least 3 10 6 km 3 of basaltic lavas that comprise the central atlantic magmatic province camp also took place at that time and was intimately associated with the onset of rifting of pangaea emplacement of this large igneous province occurred within a relatively very short period of perhaps no more than 1 ma although relatively little of camp now remains the original province was extremely large extending from present day nova scotia to bolivia and from central southern usa to morocco of major relevance to the environmental impact of the camp was its relatively rapid emplacement and its original location across the equator recent advances in our understanding of the weathering of silicate rocks and in particular of fresh basaltic rocks have highlighted the importance of the weathering process in influencing environmental change in this contribution we examine the details of the seawater sr and os isotope records that span the triassic jurassic boundary in order to understand the nature and course of environmental change at that time correlation of sr isotope data from mainland europe and the uk shows that the rapid rate of decrease in the 87 sr 86 sr ratio of seawater which had started in the early rhaetian late triassic came to an end in the late rhaetian close to the triassic jurassic boundary at that time the 187 os 188 os ratio of seawater had also decreased to particularly low values in the late rhaetian the seawater 87 sr 86 sr ratio rapidly increased from 0 70765 to 0 70775 and then it and the seawater 187 os 188 os ratio both remained approximately constant for the duration of the hettangian the first 3 ma of the jurassic apart from a transient excursion to radiogenic os isotope values i e high 187 os 188 os ratios near the triassic jurassic boundary the unradiogenic 187 os 188 os ratio of seawater during the hettangian is interpreted as reflecting a major perturbation to global weathering patterns that was caused by the rapid weathering and erosion of the camp immediately after its emplacement we suggest that the rapid increase of seawater 87 sr 86 sr ratios in the late rhaetian and the approximately constant 87 sr 86 sr ratios throughout the hettangian were caused by the input of a large amount of additional radiogenic sr to the oceans which was likely to have been derived from a readily weathered lithology such as carbonate or evaporite at the start of the sinemurian the 87 sr 86 sr ratio of seawater began to decrease while at the same time the 187 os 188 os ratio of seawater increased to more radiogenic values we interpret the trends in the seawater sr and os isotope compositions at the start of the sinemurian as evidence that much of the camp had been removed by chemical weathering by which time the camp had ceased to have a major influence on earth s environment the patterns of change in the seawater sr and os isotope records that occurred in the latest triassic and earliest jurassic show many similarities with those that took place in the pliensbachian toarcian 183 ma ago overlapping the eruption of the karoo ferrar igneous province in both cases the seawater sr and os isotope records indicate that there was a relatively very brief interval during which rates of continental weathering increased greatly the similarities in the responses of the seawater sr and os isotope records at those times strongly suggest that the eruption and subsequent erosion of basaltic large igneous provinces have played a major role in defining the course of environmental change in the past

palaeoenvironmental significance of carbon and oxygen isotope stratigraphy of marine triassic jurassic boundary sections in sw britain abstract carbon isotope stratigraphy is a useful tool for stratigraphic correlation especially for strata deposited during major perturbations of the carbon cycle that affected the marine terrestrial and atmospheric reservoirs for the triassic jurassic boundary effectively defined by a first order mass extinction major fluctuations in carbon isotope values have been well documented but these datasets have generally been derived from bulk rock samples hence the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained here carbon and oxygen isotope data are presented from well preserved oyster shells liostrea comprising low magnesium calcite a mineral species relatively resistant to diagenetic alteration samples were obtained from lavernock point glamorgan wales a coastal section close to a candidate stratotype for the base of the jurassic at st audrie9s bay somerset england the carbon isotope signature from st audrie9s bay previously defined on the basis of analysis of bulk organic matter is confirmed by our new data major features are 1 the upper part of an initial9 negative isotope excursion in the lowest part of the section followed by 2 a pronounced positive excursion and 3 an extended main9 negative isotope excursion in the highest part of the section the data confirm that the carbon isotope stratigraphy previously documented from bulk organic matter in sw england records the chemical composition of the contemporaneous seawater bulk carbonates sampled over the same interval near lyme regis england show similar trends to those from oyster calcite in the lower part of the study section but there are more 13 c depleted values up section these lower values probably result from an admixture of primary and diagenetic carbonate palaeotemperatures calculated from oxygen isotope values from lavernock point oyster shells are relatively cool at the beginning of the positive carbon isotope excursion and increased by up to 10 c during the main negative carbon isotope excursion the new results are compatible with the view that positive carbon isotope excursions correspond to times of low atmospheric carbon dioxide content whereas negative carbon isotope excursions correspond to times of high atmospheric carbon dioxide content as is also found to be the case during the early jurassic toarcian oceanic anoxic event the mg ca and sr ca ratios and 18 o of investigated liostrea hisingeri show no correlation supporting data from modern bivalves that indicate that incorporation of mg and sr is controlled mainly by factors other than temperature

identifying instrumental and historical earthquake records in the sw iberian margin using 210pb turbidite chronology 1 textural mineralogical and geochemical analyses of near surface sediments from six different stations offshore sw iberian peninsula revealed the presence of thin detrital intervals corresponding to very fine grained turbidites precise dating of the two most recent sedimentary layers based on 210pb and 137cs geochronology provides ages of 1971 3 ad and 1908 8 ad these ages correspond to high magnitude historical and instrumental earthquakes that occurred in the region the 1969 horseshoe earthquake mw 8 0 and the 1909 benavente earthquake mw 6 0 such a good correlation between turbidites and high magnitude mw 6 historical and instrumental seismic events suggests that the record of mass transport deposits can also be used as a paleoseismic indicator in low convergence margins

the occurrence and preservation of ammonites in the blue lias formation lower jurassic of devon and dorset england and their palaeoecological sedimentological and diagenetic significance abstract more than two thirds of beds in the lowest jurassic blue lias formation lack ammonites which are commonly preserved in irregular or planar bedded bioturbated limestones very rarely in laminated limestones and almost never in laminated black shales ammonites are preserved in 3d in nodular and planar bedded limestones and at any orientation to bedding co occurrence with macrobenthos and absence from beds without benthos suggest that blue lias ammonites were nektobenthonic scour structures and imbrication of ammonites in the best bed imply presence of traction currents lack of epifauna on large cephalopod shells and other fossils implies rapid deposition in event beds blue lias deposition was episodic not slow and continuous as the fine grain size implies undistorted trace fossils uncrushed ammonites and stable isotope values all suggest early cementation of limestone beds from pore waters of a similar composition to contemporary jurassic sea water a clear diagenetic trend exists with limestones having least and laminated black shales most modified stable isotope values contrast between trace fossil fills and host sediment demonstrates that blue lias rhythms are primary but limestone beds have been diagenetically cemented

observations of inner moraines near the terminus of mccall glacier in arctic alaska and laboratory experiments on the mechanism of picking up moraines into a glacier body abstract only

sea level change and facies development across potential triassic jurassic boundary horizons sw britain the late triassic to early jurassic aged succession of sw britain the penarth and lower lias groups comprises mudstone sandstone and limestone strata deposited in a variety of marine to non marine environments faunal and floral characteristics of these successions have led to the proposal that one location in sw england st audrie9s bay should serve as the global stratotype section and point gssp for the base of the hettangian stage and thus for the triassic jurassic tr j boundary the sections of sw britain have also been used previously to infer sea level change history and relate this to potential kill mechanisms associated with the tr j boundary mass extinction chemostratigraphic biofacies and lithofacies data are used here to suggest alternative models of sea level change in relation to possible tr j boundary horizons in the sections of sw britain a sea level lowstand surface of erosion is inferred to occur within the cotham member of the lilstock formation a unit deposited in an environment that was often subaerially exposed in contrast to previous interpretations the top surface of the overlying langport member here inferred to be deposited on a carbonate ramp of depositional or tectonic origin represents a drowning event of at least regional extent all horizons regarded as plausible levels at which to place the tr j boundary based on fossil distributions lie within strata deposited during relative sea level rise however it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and additionally there is no positive evidence that sea level fall had any relation to the genesis of proposed tr j marker horizons it is unlikely that sea level fall played a significant role in the tr j boundary extinctions in either a local or a global context

residence times of surface water and particle reactive 210pb and 210po in the east china and yellow seas 228ra 226ra 210pb and 210po were measured in the surface waters of the east china and yellow seas using mass balance equations for the ra isotopes we estimated the total flux of diffusion from sediments and desorption from suspended particles to be 0 1 dpm 226ra cm 2 a 1 and 1 dpm 228ra cm 2 a 1 and residence times to be 2 3 years for the waters on the east china sea shelf and 5 6 years for yellow sea waters box model calculations yielded generally congruent scavenging residence times for 210pb and 210po in the waters of 2 months on the shelf and 7 months in the kuroshio current these suggest that reactive heavy metals and pollutants discharged through rivers from the continent to the east asian continental shelf are largely deposited on the bottom sediments prior to transport to the pelagic ocean by lateral mixing

the flow of a polythermal glacier mccall glacier alaska u s a we have analyzed the flow of polythermal mccall glacier in arctic alaska using measurements of surface velocity from the 1970s and 1990s together with measurements of ice thickness and surface slope we have investigated both the present flow and seasonal and long term flow variations our analysis of the present flow reveals that i longitudinal stress coupling is important along the entire length of the glacier and ii there is significant basal sliding beneath a 2 km long section of the lower glacier this sliding exists year round and it accounts for more than 70 of the total motion there we have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up glacier from it both effects are reflected in the observed surface profile of mccall glacier the longitudinal stress coupling length of mccall glacier is three times the ice thickness almost twice that typical of temperate glaciers this is a direct effect of lower strain rates which themselves are associated with the smaller mass balance gradients of arctic and continental glaciers long term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution this means that long term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small seasonally velocities reach their annual minimum in spring and increase during the short summer melt season by up to 75 above mean winter values however the extra motion associated with the period of elevated velocities is only about 5 of the total annual motion the speed up is due to an increase in basal sliding this implies that most of the glacier bed is at the melting point the zone affected by the melt season speed up extends well up glacier of any moulins or other obvious sources for meltwater at the bed

early hettangian ammonites and radiolarians from the queen charlotte islands british columbia and their bearing on the definition of the triassic jurassic boundary abstract the triassic jurassic boundary t j boundary interval is one of the most important but poorly understood intervals in the phanerozoic here we fully document the ammonite and radiolarian successions at several sites in the queen charlotte islands qci british columbia eleven ammonite taxa are described and eighteen radiolarian taxa are discussed with the radiolarian genus tipperella described as new type species t kennecottensis n sp there are two continuous t j boundary sections in the qci one is located at kennecott point on graham island section i the other on the southeastern shore of kunga island section iii a second section at kennecott point contains fossils of early hettangian age only section ii radiolarian faunas include taxa from the upper rhaetian globolaxtorum tozeri zone in the two continuous sections and the lower hettangian canoptum merum zone in all three sections in each section the lowest hettangian fossils are radiolarians and a few collections contain rare rhaetian holdovers these mixed faunas may equate with the lowest hettangian ammonite zone the spelae zone of the north american succession the upper portion of section i contains a sparse ammonite fauna which indicates an early hettangian age this section has also provided carbon isotope data with a negative excursion spanning the t j boundary section ii contains a more diverse early hettangian ammonite assemblage that permits correlation of the upper portion of this section with the lower hettangian minutus zone section iii has been previously proposed as a potential basal hettangian global stratotype section and point gssp in addition to an outstanding radiolarian fauna the section contains moderately diverse early hettangian ammonites that permit correlation of the lower portion of the section with the minutus and pacificum zones and the upper portion with the lower hettangian polymorphum zone this section has previously provided a u pb date of 199 6 0 3 ma from 3 6 m below the t j boundary currently there are four candidates and no ideal gssp for the basal hettangian a section in new york canyon nevada has also been proposed as a potential gssp this section is easily accessible and provides a virtually complete ammonoid succession but lacks geochronology and microfossils the section on kunga island in the qci provides geochronologic data and excellent radiolarian constraints in essence the sections at kunga island in the qci and new york canyon in nevada are complementary close correlations between the two sections are possible using ammonite faunas we suggest the section from nevada be designated as holostratotype for the basal hettangian and the qci section be designated as a parastratotype to improve recognition of this interval

uniquely extensive seismite from the latest triassic of the united kingdom evidence for bolide impact a 2 4 m thick seismite in places overlain by a previously unreported tsunamite can be traced across 250 000 km 2 of the outcrop and subcrop of the latest triassic rhaetian cotham member of the penarth group united kingdom an extent unique for the british phanerozoic its consistent thickness intensity of deformation and preferred orientations of slump fold axes indicate a seismic event of m 10 with an epicenter 600 km w or nw of central britain the magnitude of the event is incompatible with known terrestrial mechanisms fault volcano but is consistent with a major bolide impact a short but unknown interval separates the top of the cotham member seismite from major geochemical and biotic perturbations associated with the end triassic extinction although a direct link between the seismite and these other events remains equivocal the exceptional extent of mega seismites such as this may prove a useful indicator of previously undocumented bolide impacts

the use of bomb spike calibration and high precision ams 14c analyses to date salt marsh sediments deposited during the past three centuries abstract a combination of bomb spike calibration and conventional calibration of ams 14c dating has been used to determine a detailed age depth model for a 1 m sediment section collected from a salt marsh in poole harbour southern england these data were compared with the chronology obtained from 210pb analysis and 137cs age markers we report post bomb values of over 1 46 f14c 146 modern 14c and both the rising and falling limbs of the atmospheric bomb spike are identified five pre bomb samples were analysed using multi target high precision 2 ams analysis and after the replicates were combined the one sigma uncertainty was as low as 9 14c yr on some ages these data and an additional three normal precision pre bomb 14c samples were calibrated using calib 5 0 and the chronology constrained using the prior knowledge of independent age markers obtained from the analysis of pollen and spheroidal carbonaceous particle scps no agreement was found between the 14c bomb spike dates and the crs 210pb chronology modelled for this sequence in addition poor agreement was found between the signal of the 1960s weapons test fallout indicated by the 14c bomb spike dates and the timing suggested by the 137cs data this disagreement is attributed to the influence of the local discharge of 137cs from the former ukaea site at winfrith we use our new chronology to confirm the existence of an acceleration in sedimentation rates in poole harbour during the last 100 yr previously reported for this site by long et al long a j scaife r g edwards r j 1999 pine pollen in intertidal sediments from poole harbour uk implications for late holocene sediment accretion rates and sea level rise quaternary international 55 3 16 and conclude that bomb spike 14c calibration dating may offer a more robust alternative to the use of 210pb chronologies for dating sediment deposition in salt marsh environments in addition we demonstrate how the use of high precision ams analysis has the potential for reducing some of the uncertainties involved in the high resolution dating of recent salt marsh sediments

determination of recent deposition rates in lake constance with radioisotopic methods sedimentation rates were determined with the 210pb method in eight sediment cores from lake constance the rate of deposition in the main basin obersee varies from about 0 06 g cm 2 y 1 in the central part to 0 13 g cm 2 y 1 in the eastern part of the lake and then increases rapidly towards the rhine delta in the central lake area the rate of deposition has been approximately constant since 1900 and dating with the 210pb method is in good agreement with sedimentological observations in the konstanzer trichter area the deposition rate has been increasing since about 1955 as a result of eutrophication and subsequent high carbonate production dating with 137cs is fairly accurate for sediments deposited at a high rate but is questionable for slowly accumulating ones a positive correlation of 210pb fluxes and sedimentation rates indicates that 210pb flux into sediments follows the distribution pattern of solids 210pb profiles in four sediment cores interpreted in terms of a constant flux model display synchronous fluctuations of the sedimentation rate however their relation to long range particulate input variations remains to be proved sedimentation rates determined with the 210pb method were used to calculate recent nutrient and heavy metal fluxes anthropogenic fluxes of zn and pb are in the same range of magnitude as in other polluted areas in europe and america

palaeoenvironmental interpretation of a triassic jurassic boundary section from western austria based on palaeoecological and geochemical data a section spanning the triassic jurassic boundary is described from near the village of loruns in the vorarlberg region of western austria at loruns the uppermost triassic is characterised by bedded carbonates of the kossen formation supporting a stenotopic fauna indicative of a shallow sub tidal environment of normal marine salinity the triassic jurassic boundary may be represented as a sequence boundary developed on top of a 1 1 m thick red mudstone of the lower schattwald shale which is interpreted to have been deposited in a marginal marine environment possibly a mud flat above the boundary beds the upper schattwald shale is characterised by thin bedded marl and dark limestone beds with an earliest hettangian macrofauna dominated by epifaunal filter feeding bivalves including ostreids mytilids and oxytomids which suggest a shallow subtidal salinity controlled environment typical of an interplatform lagoon carbonate production rejuvenated in the later early hettangian with development of the loruns oolite a shallow subtidal oolitic and oncolitic unit bearing echinoderms indicative of normal marine conditions low thu ratios from the remainder of the section are a result of reduced thorium in carbonate rich sediments and not from authigenic uranium in anoxic sediments in the boundary beds evidence for marine anoxia or dysoxia is absent where thu values determined by gamma ray spectrometry are above 5 the negative excursion in 13c and positive excursion in 18o in the boundary beds may be due to secondary geochemical effects due to organic diagenesis or the precipitation of caliche during paleosol development alternatively the excursions may reflect a primary geochemical signal recording short term decline in primary productivity comparison in 18o and 13c values between the kossen formation and lorfus oolite indicate no significant long term geochemical changes are evident in the section and suggest that any environmental perturbations were restricted to the boundary beds and possible sequence boundary

vertical accumulation of potential toxic elements in a semiarid system that is influenced by an abandoned gold mine abstract the mining zone at el triunfo baja california sur mexico was exploited for gold extraction for 200 years this area includes more than 100 abandoned mining sites these sites contain mine tailings that are highly contaminated with potential toxic elements pte such as as cd pb sb zn and other associated elements over time these wastes have contaminated the sediments in the adjacent fluvial systems our aim was to assess the vertical pte variations in the abandoned mining zone and in the discharge of the main arroyo into a small lagoon at the pacific ocean sediments were collected from the two following locations in the mining zone near the arroyo basin tailings 1 an old alluvial terrace overbank and a test pit tp and 2 two sediment cores locations at the arroyo discharge into a hypersaline small lagoon samples were analyzed by icp ms icp oes and inaa and the methods were validated the overbank was the most contaminated and had as cd pb sb and zn concentrations of 8690 226 84 700 17 400 and 42 600 mg kg 1 respectively which decreased with depth in addition the tp contained elevated as cd pb sb and zn concentrations of 694 18 8 5001 39 2 and 4170 mg kg 1 respectively the sediment cores were less contaminated however the as cd pb sb and zn concentrations were greater than the concentrations that are generally found in the earth s crust the normalized enrichment factors nefs which were calculated from the background concentrations of these elements in the system showed that extremely severe as cd pb sb and zn nef 50 enrichment occurred at the overbank the tp was severe to very severely enriched with as cd pb sb and zn nef 10 50 the sediment cores had a severe enrichment of as pb and zn nef 10 25 their vertical profiles showed that anthropogenic influences occurred in the historic sediment deposition at the overbank and tp and in the sediment cores in addition the as pb and zn concentrations in the sediment cores were related to the deposition of fine sediments and organic carbon

major environmental change and bonebed genesis prior to the triassic jurassic mass extinction we present new geochemical and sedimentological data from marginal marine strata of penarth bay south wales uk to elucidate the origin of widespread but enigmatic concentrations of vertebrate hard parts bonebeds in marine successions of rhaetian age late triassic sedimentological evidence shows that the phosphatic constituents of the bonebeds were subjected to intense phosphatization in shallow current dominated settings and subsequently reworked and transported basinward by storms interbedded organic rich strata deposited under quiescent and poorly oxygenated conditions record enhanced phosphorus regeneration from sedimentary organic matter into the water column and probably provided the main source of phosphate required for heavy bonebed clast phosphatization the stratigraphically limited interval showing evidence for oxygen depletion and accelerated p cycling coincides with a negative 4 organic carbon isotope excursion which possibly reflects supra regional changes in carbon cycling and clearly predates the initial isotope excursion characterizing many triassic jurassic boundary strata our data indicate that rhaetian bonebeds are the lithological signature of profound climatically driven changes in carbon cycling and redox conditions and support the idea of a multi pulsed environmental crisis at the end of the triassic possibly linked to successive episodes of igneous activity in the central atlantic magmatic province supplementary material sample positions data table and a detailed stratigraphic log from the upper triassic of penarth bay south wales uk are available at http www geolsoc org uk sup18510

quaternary uplift and sea level change at an active plate boundary cyprus a combination of northward underthrusting of the african plate and serpentinite diapirism resulted in progressive uplift of cyprus during the quaternary the uplift was associated with the development of succession of alluvial fans and marine terraces marine terraces in coastal southern cyprus are developed at 350 360 m 110 100 m 60 50 m 11 8 m and 2 3 m above present sea level the terraces display sequences of regressive deltaic carbonate and siliciclastic sub littoral to littoral and sub aerial type alluvial fans of the fanglomerate group crop out on the northern flanks of the troodos massif forming extensive dissected peneplaned terraces later uplift resulted in the formation of channel fans and river terraces proximal sheetflood conglomerates pass distally into channelized braid plain environments on the southern margin of the troodos massif the fanglomerate group comprises braided channelized and floodplain sequences which pass laterally into littoral facies provenence studies indicate that uplift and resulting erosion of cyprus was centred on the troodos massif mount olympus radiometric dates indicate that uplift was rapid in the early and mid pleistocene in the late pleistocene holocene eustatic sea level changes and anthropogenic effects dominated while the rate of uplift was reduced with local submergence of southern coastal areas

combined sea level and climate controls on limestone formation hiatuses and ammonite preservation in the blue lias formation south britain uppermost triassic lower jurassic

disequilibrium between 226ra and supported 210pb in a sediment core from a shallow florida lake sup 210 pb dating can be used to assign ages in lake sediment cores calculate rates of sediment accumulation and determine the timing of recent changes in lake watershed ecosystems we used low background gamma counting to measure sup 226 ra and total sup 210 pb activity in a core from lake rowell florida sup 226 ra activity was high and strongly variable throughout the core even exceeding total sup 210 pb activity in recently deposited sediments we traced one source of ra rich sediments to the only inflow alligator creek where stream bottom deposits display disequilibrium between sup 226 ra and supported sup 210 pb high and variable sup 226 ra activity in the lake rowell profile argues for direct estimates of in situ ra in lake sediment cores from disturbed watersheds that have ra bearing bedrock isotopic disequilibrium between sup 226 ra and supported sup 210 pb makes it difficult to distinguish between supported and unsupported sup 210 pb activity throughout the lake rowell core and would require special assumptions and nonconventional dating models to establish age depth relationships 78 refs 3 figs 1 tab

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

the basal ice layer of glaciers and ice sheets abstract in many glaciers and ice sheets there is a basal ice layer bil in which the ice is conditioned primarily by processes operating at the bed the bil is chemically and physically distinctive and is characterised by a component of basally derived sediment the bil is a rheological control on ice sheet dynamics an indicator of subglacial conditions and processes an agent of subglacial geologic processes the source of a substantial proportion of glacial sediments a limit to the downward extension of the climate record from deep ice cores if debris characteristics of the bil are preserved in glacial sediments former glacier conditions can be inferred analysis of stable isotopes gas and cation composition ice crystallography debris composition and structural glaciology has elucidated many mechanisms for bil formation common elements can be identified from a range of locations key issues are entrainment of ice and debris from the bed formation of new ice metamorphism of existing ice in the bil and thickening of the bil by deformation a distinction can be made between basal ice formed by accretion of material from the bed stratified facies and basal ice formed by metamorphic processes within the ice close to the bed dispersed facies

three decades of dating recent sediments by fallout radionuclides a review this paper reviews the 210pb dating programme carried out at the university of liverpool over a period of three decades since its inception by frank oldfield in the mid 1970s the work at liverpool

testing the precision of bioevents deciding which of two bioevents is the less diachronous is a common problem in biostratigraphy the most accurate correlation uses the finest timescale available chemostratigraphy or cyclostratigraphy offer a potential precision of about 10 ka graphic correlation can then be used to test the precision of bioevents and to quantify any mismatch it can also be used to determine in which section any event occurs earlier application of these ideas to correlation of the cenomanian turonian and coniacian santonian boundaries demonstrates that some bioevents are as precise as chemo and cyclostratigraphy but that most are not two problems occur with bioevents first they may not be recognizable in all sections second where they are recognizable they may be diachronous in the former case calculating confidence intervals on known ranges in sections where the relevant fossil has been recorded is an alternative test large confidence intervals suggest that both first and last occurrences of a fossil may be diachronous bioevents at the cenomanian turonian boundary the following bioevents in stratigraphic order appear to be reliable time planes for international correlation the last occurrences of 1 corolithion kennedyi 2 rotalipora greenhornensis 3 axopodorhabdus albianus 4 rotalipora cushmani 5 lithraphidites acutus 6 microstaurus chiastius and 7 the first occurrence of quadrum gartneri at the coniacian santonian boundary only the first and last occurrences of platyceramus undulatoplicatus and the first occurrences of platyceramus cycloides and lucianorhabdus cayeuxii have been identified as potentially reliable bioevents

shallow marine tsunami deposits in teluk banten nw java indonesia generated by the 1883 krakatau eruption teluk banten tb is a tropical shallow marine embayment with coral reef islands close to the krakatau volcanic complex the 1883 krakatau eruption generated a tsunami which had a devastating effect on the neighboring coastal areas the effects of the 1883 krakatau eruption and the associated tsunami on the bottom sediments in tb are assessed using textural compositional and 210 pb geochronological data an important diagnostic criterion consists of the occurrence of tephra conform descriptions of the 1883 eruption tephra the tsunamite consists of a sandy layer with abundant reworked shell and other carbonate fragments coarse components in the tsunamite consist of locally derived material eroded from the seabed land derived components are incorporated in the tsunamite only in close proximity to the coast the tsunamite is thickest in localized areas of the central part of the bay along the northern open sea facing slope of tb the tsunamite is relatively thin 6 7 cm thick but well preserved as little postdepositional modifications have occurred in the eastern bay area recent erosion since the redirection of the ciujung river in the 1920s has removed the krakatau tsunamite along the west coast of tb the only signature of the 1883 krakatau eruption consists of tephra and evidence for a high energy event is lacking presumably the western area was sheltered from the tsunami wave coming from the northwest at the shallower stations with low accumulation rates the tephra has been thoroughly mixed by bioturbation 2003 elsevier science b v all rights reserved

trace element fluxes during the last 100 years in sediment near a nuclear power plant abstract the salada coastal lagoon is located in veracruz mexico near the laguna verde nuclear power plant lvnpp currently the lagoon receives the cooling waters used in the lvnpp to evaluate the fluxes and mobilization of trace elements due to human activities in the area two sediment cores from the coastal flood plains of salada lagoon were analysed cores were collected using pvc tubes sediments cores were analysed every centimetre for dating 210 pb by alpha detector and trace metal analysis using icp mass spectrometry the dating of both sediment cores covers the period from 1900 to 2013 which includes the construction of the lvnpp 1970 s the normalized enrichment factor shows enrichment of ag as and cr in both sediment cores these enrichments correspond to the extent of mining activity which reached a maximum in the 1900 s and to the geological setting of the coastal zone the profiles of the element fluxes in both sediment cores reflected the construction and operation of the lvnpp however the elements content did not show evidence of pollution coming from the lvnpp

rates of particle scavenging sediment reworking and longitudinal ripple formation at the hebble site based on measurements of 234th and 210pb between 1982 and 1986 seabed and water column samples were collected on five cruises to the hebble site two particle reactive radionuclides 234th and 210pb have been used to examine rates of particle scavenging in bottom waters sediment reworking in the surface seabed and formation of longitudinal ripples settling particles at the hebble site which have been resuspended by strong bottom currents and benthic storm activity scavenge approximately 60 of the 234th half life of 24 days produced in the bottom 100 m of the water column corresponding to removal of 15 dpm cm2 234th inventories from cores collected during a single cruise show substantial variability e g 1 18 dpm cm2 over the 8 km2 study area indicating that resuspended particles are not deposited uniformly across the seabed after storm events the activity of benthic fauna and non uniform deposition over a topographically variable seabed are important processes affecting boundary layer sedimentation and the development of radionuclide inventories in surface sediments the mean 234th seabed inventory from individual cruises to the hebble area varies to a greater extent 2 to 38 dpm cm2 than the mean 210pb inventory 47 to 82 dpm cm2 because 234th inventories are dominated by sedimentary processes associated with an individual storm event whereas 210pb inventories integrate these processes over several cycles of deposition and erosion sediments at the hebble site are biologically reworked very rapidly on a 100 day time scale with 234th mixing coefficients db 1 to 33 cm2 yr comparable to values observed in nearshore environments on time scales of months to years 210pb data indicate that strong currents and benthic storm activity have eroded and redeposited the upper 5 10 cm in 17 of the 20 cores examined reoccupying field sites during the 4 year field program provided the unique opportunity to evaluate steady state models commonly used to determine rates of sediment reworking 210pb profiles and inventories showed significant temporal variations at hebble sites occupied between 1982 and 1986 steady state models should not be used to evaluate profiles of 210pb or other tracers with comparable half life in a dynamic environment like the hebble area because steady state assumptions are not justified and rates of sediment reworking can be underestimated by nearly an order of magnitude 234th and 210pb analyses of core samples from two longitudinal ripples suggest that these sedimentary features form on a time scale of months and consist of a mixture of recently deposited material from the water column and older sediment from depth the absence of 234th activity in one of the ripples indicates that these bedforms may be stable for periods of months without significant growth

reply to the comment by j m mcarthur on the impact of the central atlantic magmatic province on climate and on the sr and os isotope evolution of seawater by cohen a s and coe a l

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

the base of the jurassic system new data on the first appearance of psiloceras planorbis in southwest britain recent collecting in the lower lias of localities at st audrie s bay north somerset sedbury cliff gloucester and lavernock point south glamorgan has yielded psiloceras planorbis j de c sowerby in beds considered by some to be of rhaetian triassic age these are the earliest records of this ammonite to date in southwest britain evidence is provided of a major facies change at the top of the pre planorbis beds followed by the diachronous first occurrence of psiloceras planorbis these new data have implications for the use of earliest occurrence of psiloceras planorbis as a chronostratigraphic marker in defining the base of the jurassic system and for the definition of the base of the hettangian stage in the recently proposed candidate global stratotype section at st audrie s bay

distribution of grain sizes across a transgressive shoreface abstract distributions of seventeen grain sizes in the sand fraction of the shoreface sediments south of long island new york can be categorized into middle and lower shoreface species very fine sand upper shoreface species fine sand shoreface depleted species medium sand and swash zone species coarse sand the long term fair weather wave base of the study area at a depth of about 16 m is determined on the basis of the characteristic response of grain sizes to the average shoreface hydrodynamics the crosshore deviations from the mean distribution for each grain size were examined by using empirical orthogonal function eof analysis these results show differential associations of grain size deviations with various dynamic zones on the shoreface the hydrodynamic processes of the modern shoreface are speculated to winnow out fine and very fine sands and transport them onshore leaving behind on the lower shoreface and inner continental shelf a lag deposit of transgressive sand sheet composed mainly of medium sand

heavy metals in sediment cores from a tropical estuary affected by anthropogenic discharges coatzacoalcos estuary mexico large scale industrial development has taken place in the coatzacoalcos river estuary se mexico over the last 32 years and the area is now regarded as the most polluted coastal area of mexico a series of sediment cores were taken from the lower coatzacoalcos river and the estuary and the concentrations of trace elements zn co cu cr ni pb v major elements al si mn fe ti ca mg na k p and organic matter determined heavy metal concentration seems to be largely dependant on proximity to industrial areas with highest metal concentrations particularly for zn ni and cu found at teapa the most heavily industrialized site and lowest values found at jicaro upstream of the main industrial areas at all of the sites examined heavy metals either show a relatively uniform distribution with depth or subsurface maxima which reflect changes in sediment composition there is little evidence for significant early diagenetic remobilization at any of the sites studied 210pb and 137cs data at teapa indicate that the sediments have accreted rapidly and may be vigorously mixed and so these sediment cores cannot be used to reliably reconstruct temporal changes in pollutant input

sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research

the 129iodine bomb pulse recorded in mississippi river delta sediments results from isotopes of i pu cs pb and c 129i t1 2 1 56 107 yr has both natural as well as anthropogenic sources anthropogenic sources from nuclear reprocessing discharges and bomb test fallout have completely overwhelmed the natural signal on the surface of the earth in the last 50 years however the transfer functions in and out of environmental compartments are not well known due to temporal variations in the sources of 129i and to a lack of knowledge regarding the forms of iodine from a vertical profile of 129i 127i ratios in sediments located in the mississippi delta region in approximately 60 meters water depth the 129i input function to this region was reconstructed dates in the core were assigned based on the plutonium peak at 20 cm depth assumed to have been deposited in 1963 and the excess 210pb profile in the same depth interval and below that based on the steadily decreasing 240pu 239pu ratios from a ratio of 0 18 at 22 cm to 0 05 at 57 cm depth the 1953 horizon these low 240pu 239pu values are attributed to low yield close in tropospherically transported bomb fallout produced from the nevada test site in the early 1950s which had a value of about 0 035 and strongly suggest a terrestrial source for pu isotopes 129i 127i ratios increased from 2 10 10 at 3 cm to 4 10 10 at 20 cm and from there decreased monotonously to pre anthropogenic values at 53 cm and below 129i concentrations ranged from 8 13 106 atoms g in the top 20 cm and decreased to values of less than 1 106 atoms g below 50 cm atom ratios of 129i 137cs decay corrected to 1962 the year of maximum radionuclide production are about 0 3 very close to the production ratios of about 0 2 during atomic bomb tests this evidence combined with other observations strongly suggests that 129i in mississippi river delta sediments originates from atomic bomb fallout eroded from soils of the mississippi river drainage basin with little alteration of the isotopic ratios during transport from watershed to coastal deposits this is further corroborated by a close correspondence between 129i 127i ratios and other bomb fallout nuclides in this core based on these observations and on laboratory evidence we propose a conceptual model which explains this correspondence and the low 129i 127i ratios found in our sediment core as caused by geochemical i isotope fractionation processes during organic carbon leaching from erodible soils in the mississippi river watershed differences in mobilities of the different chemical forms of 129i and 127i as well as the variances in chemical forms of 129i from nuclear bomb fallout versus nuclear fuel reprocessing are proposed to have created such a correspondence between i isotope ratios and bomb fallout nuclides without revealing recent inputs from nuclear fuel reprocessing releases to the northern hemisphere observed in watersheds of the usa and europe

new geochemical evidence for the onset of volcanism in the central atlantic magmatic province and environmental change at the triassic jurassic boundary the late triassic early jurassic was a time of major global change however the fundamental processes driving these changes are less than clear we have determined the re and os abundances and os isotope compositions of marine mudrock samples that span the triassic jurassic boundary in the uk and have established that major isotopic and geochemical shifts in the composition of seawater took place in the latest triassic we argue that these shifts were caused by the sudden initiation of widespread igneous activity within the central atlantic magmatic province associated with rifting of the supercontinent pangea the os isotope composition of seawater responded rapidly to these events demonstrating that the seawater os isotope system has great potential in identifying the nature and precise timing of major environmental change

sedimentary geochemical record of historical anthropogenic activities affecting guanabara bay brazil environmental quality a sediment core from guanabara bay brazil was analyzed for 210pb dating grain size total organic carbon toc and total nitrogen carbon stable isotope ratio 13c nitrogen stable isotope ratio 15n and the metals fe mn ni co cu pb v and zn to assess the influence of land use changes on the aquatic system in a region for which large industrial and urban development is expected in the next few decades to obtain baseline data for improving the monitoring of the expected increase in anthropogenic impacts from surrounding drainage basins a multivariate analysis of data from different sediment layers was carried out to evaluate the dated sediment record the geochemical data suggested three different sedimentary phases along the last 200 years before the 1880s the highest clay and toc contents were observed where the c n ratios and the 13c values suggested a mixture of algal and terrestrial organic matter and the lowest concentrations of co cu pb v and zn for which background levels were estimated 4 6 2 7 14 9 24 3 and 70 2 mg kg 1 respectively from the 1880s to the 1950s the metal concentrations and sand particles increased but no change in organic matter quality was observed reflecting a period of land use change still without significant sewage input after the 1950s the sedimentation rate increased from 0 42 to 0 77 cm year 1 and increasing urban sewage input was evidenced by lower c n ratios higher 15n decrease of fe and mn concentrations and increased fluxes of metals and toc which showed a good relationship with population growth data