new probable cnidarian fossils from the lower cambrian of the three gorges area south china and their ecological implications abstract lower cambrian assemblages of phosphatic and chitinous tubular fossils of probable cnidarian affinities were recovered from the yanjiahe shuijingtuo and shipai formations in the three gorges area south china terreneuvian cambrorhytium cf c major co occur with an unnamed taxon in the yanjiahe formation they can be compared with specimens from the ediacaran miaohe fauna in the three gorges area the most abundant and diversified cnidarian assemblages including cambrorhytium gracilis n sp cambrorhytium cf major cambrorhytium minor sphenothallus songlinensis sphenothallus taijiangensis sphenothallus kozaki sphenothallus sp byronia sp and mackenzia sp are reported from the overlying cambrian stage 3 4 shuijingtuo and shipai formations these new fossils show previously unknown evidence for cnidarian affinities such as an attachment disk clonal clusters and probable budding structures these diversified assemblages of probable cnidarian fossils further fill major gaps in the cambrian record of stem metazoans and document associated early evolutionary patterns in addition our discovery suggests that along with sponges these tubular fossils represent another important component of benthic ecosystems that colonized often dysoxic deep settings during the cambrian explosion the observed increases of average body size and biomineralization among these probable cnidarians are tentatively linked to oxygenation of deep oceanic settings and appearance of predatory pressure during the ediacaran cambrian transition respectively

the anomalous ca cycle in the ediacaran ocean evidence from ca isotopes preserved in carbonates in the three gorges area south china abstract the ediacaran cambrian was one of the most important periods for the evolution of life recent studies have provided detailed chemostratigraphies that decipher the linkages between ambient surface environmental changes and biological evolution the occurrence of skeletal fossils in ediacaran rocks suggests that the possible onset of ca biomineralization started in the latest neoproterozoic molecular clocks also predict the emergence of animals containing ca carbonate spicules in the neoproterozoic therefore it is important to estimate the transition of the ca cycle in seawater ancient ca cycles in the oceans are estimated from the calcium isotopic compositions of carbonate rocks however the lack of continuous ca isotopic data in the ediacaran leaves the ca cycle unresolved the almost continuously exposed ediacaran and cambrian strata in south china mainly comprise carbonate rocks with subordinate black shales and sandstones which contain many fossils suitable for the study of environmental and biological changes we conducted drilling from the liantuo via the nantuo doushantuo dengying and yanjiahe to the shuijingtuo formation at four sites in the three gorges area in order to obtain continuous fresh samples without surface alteration and oxidation we analyzed 44 ca 42 ca ratios in carbonate rocks with a multiple collector inductively coupled plasma mass spectrometer mc icp ms screened for diagenetic alteration the resultant 44 42 ca ratios exhibit a smooth curve the values of 44 42 ca are anomalously high relative to those in the phanerozoic and they gradually decrease towards the end of the ediacaran our new ca isotope chemostratigraphy suggests that a different ca cycle had existed during the ediacaran the long term high 44 42 ca is not simply explicable by changes in temperature differences in carbonate mineralogy or changes in the input output fluxes of ca to the ocean we propose three possible explanations for the observed high 44 42 ca ratios in the ediacaran high 44 42 ca ratios of ca inputs potential undiscovered sinks of ca with low 44 42 ca values and negligible isotope fractionation between carbonate and seawater we consider that one or all of these contributed to the high 44 42 ca ratios of these we prefer the small isotope fractionation which implies that the ca concentration in seawater was initially low in the early ediacaran and increased throughout that period

ediacaran remains from intertillite beds in northwestern canada a turbidite sequence within the twitya formation windermere supergroup in the ackenzie mountains northwestern canada has yielded an assemblage composed of simple centimetric annuli and discs which are interpreted as biogenic and referred to nimbia occlusa fedonkin vendetta sp and irridinitus sp they occur below a glaciomarine diamictite about 2 5 km below the base of the cambrian and they may represent the oldest ediacaran fossils now known the find has implications for models that relate the evolution of the ediacara fauna to the waning of the varanger glaciation

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

dam to delta sediment inputs and storage in the lower trinity river texas livingston dam on the trinity river in se texas usa disrupts the transport of sediment to the lower trinity river and the trinity bay galveston bay estuary however a sediment budget of the lower basin shows that the effects of this disruption are undetectable in the lower river sediment trapped in lake livingston is partly offset by channel erosion downstream of the dam and by inputs from the lower basin most importantly however the lower coastal plain reaches of the trinity are characterized by extensive alluvial storage and are a bottleneck that buffers the bay from effects of upstream changes in sediment flux storage is so extensive that the upper trinity basin and the lowermost river reaches were essentially decoupled in the sense that very little upper basin sediment reached the lower river long before the dam was constructed whereas sediment storage in lake livingston is extensive alluvial storage on the trinity flood plain is even more extensive dam related sediment starvation effects are noted for about 52 km downstream and the sediment budget suggests that a majority of the sediment in this reach is likely derived from channel scour and bank erosion the capacious alluvial storage in the lower trinity not only limits flux to the bay but the large amount of remobilizable alluvium also allows the system to adjust to localized sediment shortages as illustrated in the dam to romayor reach internal adjustments within the lower trinity river valley thus buffer the bay from changes in sediment supply upstream

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

determination of 88sr 86sr mass dependent isotopic fractionation and radiogenic isotope variation of 87sr 86sr in the neoproterozoic doushantuo formation abstract we measured both mass dependent isotope fractionation of 88sr 88sr 86sr and radiogenic isotopic variation of sr 87sr 86sr for the neoproterozoic doushantuo formation that deposited as a cap carbonate immediately above the marinoan related nantuo tillite the 88sr and 87sr 86sr compositions showed three remarkable characteristics 1 high radiogenic 87sr 86sr values and gradual decrease in the 87sr 86sr ratios 2 anomalously low 88sr values at the lower part cap carbonate and 3 a clear correlation between 87sr 86sr and 88sr values these isotopic signatures can be explained by assuming an extreme greenhouse condition after the marinoan glaciation surface seawater mixed with a large amount of freshwater from continental crusts with high 87sr 86sr and lighter 88sr ratios was formed during the extreme global warming after the glacial event high atmospheric co2 content caused sudden precipitation of cap carbonate from the surface seawater with high 87sr 86sr and lighter 88sr ratios subsequently the mixing of the underlying seawater with unradiogenic sr isotope compositions and normal 88sr ratios probably caused gradual decrease of the 87sr 86sr ratios of the seawater and deposition of carbonate with normal 88sr ratios the combination of 87sr 86sr and 88sr isotope systematics gives us new insights on the surface evolution after the snowball earth

nitrogen isotope chemostratigraphy of the ediacaran and early cambrian platform sequence at three gorges south china abstract the appearance of multicellular animals and subsequent radiation during the ediacaran cambrian transition may have significantly changed the oceanic ecosystem nitrogen cycling is essential for primary productivity and thus its connection to animal evolution is important for understanding the co evolution of the earth s environment and life here we first report on coupled organic carbon and nitrogen isotope chemostratigraphy from the entire ediacaran to early cambrian period by using drill core samples from the yangtze platform south china the results show that 15ntn values were high 6 until middle ediacaran gradually dropping down to 1 at the earliest cambrian then rising back to 4 in the end of the early cambrian organic carbon and nitrogen contents widely varied with a relatively constant c n ratio in each stratigraphic unit and do not apparently control the carbon and nitrogen isotopic trends these observations suggest that the 15ntn and c n trends mainly reflect secular changes in nitrogen cycling in the yangtze platform onset of the observed negative n isotope excursion coincided with a global carbon isotope excursion event shuram excursion before the shuram event the high 15n probably reflects denitrification in a nitrate limited oceanic condition also degradation of dissolved and particulate organic matter could be an additional mechanism for the 15n enrichment and may have been significant when the ocean was rich in organic matter at the time of the shuram event both 13ccarb and 15ntn values were dropped probably due to massive re mineralization of organic matter this scenario is supported by an anomalously low c n ratio implying that enhanced respiration resulted in selective loss of carbon as co2 with recycled organic nitrogen after the shuram event the 15n value continued to decrease despite that 13ccarb rose back to 4 the continued 15n drop appears to have coincided with a decreasing phosphorus content in carbonate this suggests that ocean oxygenation may have generated a more nitrate rich condition with respect to phosphorus as a limiting nutrient similar to the shuram event another negative 13ccarb event in the canglanpuan stage of the early cambrian is also characterized by carbon isotopic decoupling as well as the low c n ratio the results strongly support that the two stages of the decoupled negative 13ccarb excursions reflect a disappearance of a large organic carbon pool in the ocean the two events appear to relate with the appearance of new metazoan taxa with novel feeding strategies suggesting a link between ocean oxygenation nutrient cycling and the appearance and adaptation of metazoans the nitrogen isotope geochemistry is very useful to understand the link between the environmental ecological and biological evolutions

ediacarian sponge spicule clusters from southwestern mongolia and the origins of the cambrian fauna carbon and strontium isotopic data are used to show that the earliest sponge spicule clusters and associated phosphatic sediments with anabarites from southwestern mongolia are of ediacarian age spicule morphologies include bundles of oxeas arranged in three dimensional quadrules linked together at junctions by tetracts pentacts hexacts or polyactines all are referred to the phylum porifera class hexactinellida these sponge spicules provide the oldest remains that can be assigned without question to an extant phylum and also the first firm evidence for filter feeding and metazoan silica biomineralization in the fossil record it is suggested that siliceous and phosphatic members of the cambrian fauna may have had their origins in eutrophic and outer shelf facies of the late proterozoic

transitional ediacaran cambrian small skeletal fossil assemblages from south china and kazakhstan implications for chronostratigraphy and metazoan evolution abstract the ediacaran cambrian transition records distinct evolutionary changes of metazoans the ediacaran fossils i e ediacara type biota and tubular fossils are contrasting with the diverse small skeletal fossils ssfs from the early cambrian the apparent dissimilarities hindered studies deciphering their evolutionary relationships this also led to a popular assumption that there exists a mass extinction of the ediacara biota and cloudinids at the precambrian cambrian pc c boundary here we report for the first time a transitional fauna which consists of typical elements of ediacaran i e cloudinids and related tubicolous organisms together with cambrian ssfs including protoconodonts anabaritids and siphogonuchitids from south china and maly karatau kazakhstan the sediments yielding the transitional fauna are characterized by siliceous rocks in both regions and were previously considered to be unfossiliferous their chronostratigraphic assignment in south china has been debated for years based on the new fossil assemblage the siliceous strata of the daibu member northeast yunnan south china and the basal kuanchuanpu formation south shaanxi south china can be assigned to the earliest cambrian ssf biozone anabarites trisulcatus protohertzina anabarica assemblage zone and thus can be considered of early cambrian in age a new subzone of the earliest ssf zone in eastern yunnan south china is proposed herein defined as ganloudina symmetrica rugatotheca typica interval subzone the new fauna demonstrates that the cloudinids originally confined to the late ediacaran persisted into the cambrian fortunian and no major extinction event occurred at the pc c transition

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

carbon isotope excursions and the oxidant budget of the ediacaran atmosphere and ocean a possible global drop in marine carbon isotope values to as low as 12 peedee belemnite pdb recorded in the ediacaran shuram formation of oman has been attributed to the non steady state oxidation of oceanic dissolved organic carbon doc resulting from the rise in atmospheric oxygen to near modern values at the end of the precambrian geologic constraints indicate that the excursion lasted between 25 and 50 m y requiring a doc pool thousands of times to 10 000 times the modern inventory to conform with carbon isotope mass balance calculations for a 12 excursion at the consequent rates of doc oxidation oceanic sulfate and oxygen in the atmosphere and oceans are exhausted on a time scale of 800 k y oxidant depletion is incompatible with independent geochemical and biological indicators that show oceanic sulfate and oxygen levels were maintained or increased during the shuram excursion furthermore a doc driven excursion does not explain strong covariation between the carbon and oxygen isotope record these indicators show that negative isotope excursions recorded in the shuram and other ediacaran sections are unlikely to represent a global ocean signal

estimating the fluvial sediment input to the coastal sediment budget a case study of ghana knowledge of fluvial sediment supply to the coastal sediment budget is important for the assessment of the impacts on coastal stability such knowledge is valuable for designing coastal engineering schemes and the development of shoreline management planning policies it also facilitates understanding of the connection between rivers in the hinterland and adjoining coastal systems ghana s coast has many fluvial sediment sources and this paper provides the first quantitative assessments of their contributions to the coastal sediment budget the methods use largely existing data and attempt to cover all of ghana s significant coastal rivers initially work was hindered by insufficient direct measured data however the problem was overcome by the application of a regression approach which provides an estimated sediment yield for non gauged rivers based on data from gauged rivers with similar characteristics the regression approach was effective because a regional coherence in behaviour was determined between those rivers where direct measured data were available the results of the assessment revealed that ghana s coast is dissected by many south draining rivers stream and lagoons these rivers streams and lagoons supply significant amounts of sediment to coastal lowlands and therefore contribute importantly to beaches anthropogenic impoundment of fluvial sediment especially the akosombo dam on the volta river has reduced the total fluvial sediment input to the coast from about 71 106 m3 a before 1964 pre akosombo dam to about 7 106 m3 a at present post akosombo dam this sharp reduction threatened the stability of the east coast and prompted an expensive 83 million defence scheme to be implemented to protect 8 4 km long coastline at keta sections of ghana s coast are closely connected to the hinterland through the fluvial sediment input from local rivers therefore development in the hinterland that alters the fluvial sediment input from those local rivers could have significant effects on the coast there is the need therefore to ensure that catchment management plans and coastal management plans are integrated or interconnected

spatial patterns and variation of suspended sediment yield in the upper indus river basin northern pakistan summary much of the flow of the indus originates in the mountainous regions of the karakoram and himalayas resulting in a high sediment yield that creates a number of operational and maintenance problems for downstream water use in pakistan analysis of the available hydro climatological data indicates that the upper indus basin can be subdivided into three characteristic regions based on whether runoff production is controlled by temperature region 1 upper glacierized sub basins precipitation caused by the monsoon and western disturbances region 3 lower sub basins or a combination of the two region 2 middle reach sub basins the runoff and sediment transport regimes for the shyok gilgit hunza and indus rivers in region 1 show the role of snow and ice melt in generating high runoff and 80 85 of the annual sediment load is transported in july and august the astore river at doyian in region 2 shows an early rise of the sediment yield starting in may due to the interaction of rainfall and snowmelt at lower elevations and a comparatively lower sediment yield in august indicating a lesser influence of glacier melt region 3 experiences two types of rainfall summer monsoons and the western disturbances in late winter and early spring consequently the gorband river at karora in region 3 exhibits two separate sediment yield peaks of equal height in april and july the runoff and sediment transport regime along the main stem of the indus river is dominated by the melt of snow and ice in its headwaters and consequently is similar to the regimes of the region 1 sub basins contrary to the conventional model the specific sediment yield increases markedly with drainage area along the indus river from 355 t km 2 yr 1 at kharmong to 1197 t km 2 yr 1 at besham qila likely because of the large number of small and relatively steep catchments discharging straight into the indus river analysis of the magnitude frequency characteristics of sediment transport for the tributaries shows that the effective discharge in the basin ranges from 1 5 2 0 to 5 5 6 0 times the average discharge and decreases downstream the main indus river however shows a consistent effective discharge of 2 5 3 0 times the average discharge

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

the significance of fixed ammonium in palaeozoic sediments for the generation of nitrogen rich natural gases in the north german basin in contrast to predominantly hydrocarbon rich natural gases in the western part of the central european basin ceb accumulations of natural gases from the eastern part of the north german basin ngb are nitrogen rich with up to 90 n2 this study is focused on the behaviour of fixed ammonium in clay minerals of organic rich palaeozoic sediments in the eastern part of the ngb as a major source of nitrogen rich natural gases carboniferous shales have been investigated for a better understanding of nitrogen fixing during diagenesis storage during burial and release during devolatilization processes or fluid rock interactions the total nitrogen contents in the studied carboniferous shales of the ngb reach up to 2700 ppm with an inorganic fixed portion in the form of nh4 n of more than 60 the results of this study indicate an increasing proportion of the mineralogically fixed ammonium with increasing thermal maturity and storage up to catagenetic conditions the isotopic composition of fixed nh4 is relatively homogeneous in the majority of the shales and ranges from 1 to 3 5 in contrast samples from the basin centre show a significant decrease in ammonium contents down to 460 ppm coupled with a shift in 15n up to 5 6 suggesting a release of nitrogen on a large scale calculation of nitrogen loss and isotopic fractionation indicate that more than 30 of nitrogen was released as ammonium probably as a consequence of fluid rock interaction with highly saline brines

observations of banding in first year arctic sea ice 1 horizontal banding features alternating dark and bright horizontal bands apparent in ice cores and stratigraphic cross sections have long been observed in first year sea ice and are frequently associated with bands of high and low brine or gas porosity observations on the land fast ice near barrow alaska in recent years have revealed particularly striking banding patterns and prompted a study of their macroscopic and microscopic characteristics the banding patterns are quantified from photographs of full depth sections of the ice and examples are presented from the chukchi sea and elson lagoon statistics on band spacing are presented and the growth records for three seasons are employed to estimate their time of formation these data provide insight into the periodicity of the underlying phenomena micrographs are used to examine the microstructural variations associated with various banding features and to quantify the geometry of the constituent brine inclusions associated with high and low porosity bands the micrography revealed that the area fraction of brine inclusions varied by a factor of nearly 3 through the more pronounced high and low porosity bands vertical micrographs obtained shortly after the materials removal from the ice sheet showed that significantly larger inclusions form abruptly at the start of the high porosity bands and frequently terminate abruptly at the end of the band crystallographic observations indicated that the high porosity bands supported the nucleation and growth of crystals having substantially different orientations from the very well aligned columnar structure that characterized the bulk of the sheet

observations of brine drainage networks and microstructure of first year sea ice brine drainage networks and the microstructure of first year sea ice have been examined at two locations near barrow northern alaska a method for obtaining full depth sections of ice sheets up to 1 8 m thick is presented and shown to provide information on the spatial distribution and geometry of brine drainage networks on a scale of meters a number of such sections from the two test sites are presented which reveal a greater variety of main channel and side branch configurations than is typically observed in ice grown in the laboratory vertical and horizontal micrographs and thin section photographs were obtained in november 1993 and march and may 1994 at a test site in the relatively protected elson lagoon the resulting time series of photographic records provide detailed information on the size shape and spatial distribution of the brine and gas filled inclusions and a means to quantify their size and shape changes with time an example of the changes with time in inclusion sizes and aspect ratios in the vertical and horizontal directions for a depth of 0 2 m with a given thermal history is also presented

rare helical spheroidal fossils from the doushantuo lagerstatte ediacaran animal embryos come of age a small quantity of helically coiled spheroidal fossils has been recovered from acid digestion of phosphorite samples from the ediacaran doushantuo formation south china these fossils consist of an internal body enclosed in a sculptured envelope that is very similar to that of doushantuo animal eggs and blastula embryos such as megasphaera ornata a hallmark of these fossils is a three dimensional spiral structure which always consists of three clockwise coils and occurs on both the envelope and the internal body the spiral structure consists of a spiral tunnel or canal flanked by two raised levees and it is punctured by a series of holes some specimens show evidence of uncoiling invagination along the spiral structure or bipectinate furrowing on the band between canals a possible ontogenetic link between these helical spheroidal fossils and megasphaera ornata is suggested by similar size similar envelope sculptures and co occurrence we tentatively interpret these fossils as postblastula embryos related to megasphaera ornata thus they may represent the most advanced embryonic fossils so far known from the ediacaran although their adult morphologies and phylogenetic affinity remain unknown

the formation and morphology of ice stalactites observed under deforming lead ice during the leadex main field experiment held in april 1992 in the alaskan beaufort sea a number of large ice stalactites were observed growing under young lead ice formation of the stalactites was associated with rafting of the thin highly saline ice the rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water which in turn caused ice to form in a hollow cylinder around the brine plume within a 15 h period after the rafting event the stalactites which were located approximately 10 m apart in a line along the up wind edge of a 150 m wide lead had grown to a length of 2 m a detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel down which the brine flowed was bounded by a zone of frazil ice that developed into a shell of columnar ice the growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in ther immediate vicinity of the lead

fluvial sediment delivery to a coastal plain estuary in the atlantic drainage of the united states abstract drastic changes in sediment production in drainage basins can have significant impacts on sediment yield to estuaries however significant but less spectacular changes in fluvial sediment regimes have not greatly influenced sediment output of some rivers in the united states atlantic drainage the limited influence of moderate or incremental changes in fluvial sediment systems on estuarine sediment delivery may be attributable to the large proportion of eroded sediment which is stored within the basins and the transport limited nature of long term sediment yields a sediment budget for the pee dee river basin and waccamaw river winyah bay estuary of the carolinas shows that only a small proportion of gross eroded sediment within the basin about 4 reaches the estuary on an average annual basis because the system appears to be transport limited it is estimated that an 88 reduction in the quantity of eroded sediment reaching streams would be necessary to produce significant change in sediment yield to the estuary any increase in sediment production would not be reflected at all in the estuary unless it was accompanied by a corresponding increase in fluvial sediment conveyance capacity estuarine sedimentary records thus may not reflect some significant changes in fluvial sediment systems

percolation blockage a process that enables melt pond formation on first year arctic sea ice melt pond formation atop arctic sea ice is a primary control of shortwave energy balance in the arctic ocean during late spring and summer the ponds determine sea ice albedo and how much solar radiation is transmitted into the upper ocean through the sea ice the initial formation of ponds requires that melt water be retained above sea level on the ice surface both theory and observations however show that first year sea ice is so highly porous prior to the formation of melt ponds that multi day retention of water above hydraulic equilibrium should not be possible here we present results of percolation experiments that identify and directly demonstrate a mechanism allowing melt pond formation the infiltration of fresh water into the pore structure of sea ice is responsible for blocking percolation pathways with ice sealing the ice against water percolation and allowing water to pool above sea level we demonstrate that this mechanism is dependent on fresh water availability known to be predominantly from snowmelt and ice temperature at melt onset we argue that the blockage process has the potential to exert significant control over inter annual variability in ice albedo finally we suggest that incorporating the mechanism into models would enhance their physical realism full treatment would be complex we provide a simple temperature threshold based scheme that maybe used to incorporate percolation blockage behavior into existing model frameworks this article is protected by copyright all rights reserved

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

a review of nitrogen isotopic alteration in marine sediments key points use of sedimentary nitrogen isotopes is examined on average sediment 15n 14n increases approx 2 per mil during early burial isotopic alteration scales with water depth abstract nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record however bulk sedimentary nitrogen isotope ratios which can be determined routinely and at minimal cost may be altered during burial and early sedimentary diagenesis particularly outside of continental margin settings the causes and detailed mechanisms of isotopic alteration are still under investigation case studies of the mediterranean and south china seas underscore the complexities of investigating isotopic alteration in an effort to evaluate the evidence for alteration of the sedimentary n isotopic signal and try to quantify the net effect we have compiled and compared data demonstrating alteration from the published literature a 100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that at sites located off of the continental margins an increase in sediment 15n 14n occurs during early burial likely at the seafloor the extent of isotopic alteration appears to be a function of water depth depth related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of n isotopic alteration moreover the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global n cycle

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

establishing fine grained sediment budgets for the pang and lambourn locar catchments uk summary an integrated approach to data collection combining the use of 137cs measurements sediment source fingerprinting bed sediment surveys and conventional river monitoring has been successfully employed to establish the fine grained sediment budgets of two lowland groundwater fed catchments in the uk gross surface erosion is higher on cultivated land pang 55 263 t yr 1 or 507 t km 2 yr 1 lambourn 79 997 t yr 1 or 437 t km 2 yr 1 than on pasture pang 1960 t yr 1 or 140 t km 2 yr 1 lambourn 1425 t yr 1 or 95 t km 2 yr 1 in both study areas and a substantial proportion of the mobilized sediment is sequestered within the fields pang 28 058 t yr 1 or 228 t km 2 yr 1 lambourn 55 575 t yr 1 or 281 t km 2 yr 1 and between the individual fields and the river channel network pang 28 672 t yr 1 or 233 t km 2 yr 1 lambourn 24 782 t yr 1 or 125 t km 2 yr 1 the sediment contribution from banks and subsurface sources is relatively low and typically ca 5 t yr 1 in the pang and ca 11 t yr 1 in the lambourn representing only about 1 of the suspended sediment output from each study catchment the mean level of fine grained sediment storage in the main channel system is equivalent to 38 pang and 21 lambourn of the respective mean annual suspended sediment yields of the two catchments the estimated sediment delivery ratio for both study catchments is ca 1

possible ree constraints on the depositional and diagenetic environment of doushantuo formation phosphorites containing the earliest metazoan fauna abstract the neoproterozoic doushantuo formation south china preserves a unique assemblage of what are probably the earliest metazoan fossils sponges cnidarians and bilaterians in the world that could contribute to a better understanding of early faunal evolution on earth the formation spans an interval of dramatic biological chemical and climatic change in weng an mine in southwest china extensive paleontological investigations show embryonic larval and adult animal fossils occur in the upper ore bed of the doushantuo phosphorite but no animal forms have been found in the lower ore bed taphonomy and experiments on fossilization suggest that no fauna lived on or in the lower ore bed as it was deposited rare earth element ree data for the doushantuo phosphorites in weng an document the paleoenvironmental condition under which the phosphorites were deposited the shale normalized ree patterns of the upper phosphorite bed upb are characterized by old vendian early cambrian phosphorite patterns the ree patterns of the lower phosphorite bed lpb are significantly different with less negative ce anomalies and less lree and hree depletion the ree characteristics suggest that the doushantuo phosphorites record seawater condition at the time of sediment deposition and are not affected by subsequent diagenesis the ree compositions of the doushantuo phosphorites show that the marine depositional environment changed from anoxic in the lower ore bed to oxic in the upper ore bed the uniquely diverse and abundant doushantuo eukaryote fossil accumulations at weng an thus may be related to a change from anoxic to oxic bottom water conditions

a shoreline evolution model considering the temporal variability of the beach profile sediment volume sediment gain loss abstract the prediction of shoreline variability along sandy coastlines is a valuable skill for a broad range of coastal engineering applications currently there are multiple proposals in the literature for equilibrium cross shore shoreline evolution models based on a constant equilibrium condition correlated with the shoreline position the aim of this paper is to present an extension of an existing equilibrium shoreline evolution model adding a rate of change component which in turn modifies the relationship between the equilibrium shoreline position and the incident wave energy as a function that advances or retreats over time the proposed model is applied to two study sites on the spanish coast on the one hand one and a half years of shoreline position data obtained from a video camera system at nova icaria beach catalonia are used to evaluate the shoreline evolution during a period of sediment contribution which is attributed to a sand bypass coming from bogatell beach on the other hand 16 years of shoreline position data acquired from beach profile surveys in campo poseidon huelva are used to reproduce the shoreline evolution taking into account the trend of sediment loss due to sediment drift alongshore the results obtained from both study sites using the proposed model show overall good performance the model successfully represents the general shoreline erosion accretion oscillations and the progressive trend of sediment gains or losses through the evolutionary relationship between the equilibrium shoreline position and the incident wave energy

effects of stronach dam removal on fluvial geomorphology in the pine river michigan united states abstract although dam removal has been increasingly used as an option in dam management and as a river restoration tool few studies provide detailed quantitative assessment of the geomorphological response of rivers to dam removal in this study we document the response of the pine river michigan to the gradual removal of stronach dam in 1996 prior to the initiation of removal 31 permanent cross sectional transects were established in the 10 km study area these transects were surveyed annually during the course of the removal 1996 2003 and for the three years following removal 2004 2006 dam removal resulted in progressive headcutting of sediments in the former impoundment extending upstream 3 89 km of the dam over the course of the 10 years since dam removal was initiated a net total of 92 000 m 3 of sediment erosion occurred the majority of sediments stored in the former reservoir remained in place with only 12 of the estimated reservoir sediment fill being eroded approximately 14 of the net erosion was deposited within the stream channel 1 km downstream of the dam location with the remainder being transported further downstream or deposited in the floodplain sediment fill incision resulted in a narrower and deeper channel upstream with higher mean water velocity and somewhat coarser substrates downstream deposition resulted in a wider and shallower channel with little change in substrate size composition counter intuitively water velocity also increased downstream because of the increased slope that developed prior to removal bedforms in the former impoundment were dominated by runs but are showing signs of restoration toward reference conditions continuing changes in river geomorphology are evident even three years following removal and are likely to occur for years to come

petrographic analysis of new specimens of the putative microfossil vernanimalcula guizhouena doushantuo formation south china the neoproterozoic doushantuo formation contains some of the earliest evidence for animals and animal embryos including the putative bilaterian vernanimalcula guizhouena samples of the black facies of the weng an phosphate member of the doushantuo formation were disaggregated in a weak buffered formic acid solution in order to concentrate microfossils and mounted in epoxy the resulting grain mounts were made into thin sections and examined petrographically five specimens with morphology matching what was described as vernanimalcula were found in a single sample from the black facies up to five individual repeated structures are found in each specimen measurements of lengths and widths of morphological features were made on the new specimens these measurements are found to be consistently similar across the new specimens and within the range reported for the original specimens a diagenetic sequence is constructed using the available evidence this sequence consists of the early phosphatization of a biological structure a second phase of internal sedimentation compaction and dewatering and a later phase of phosphatic cementation while this study does not constitute the final word on the biogenicity of these morphologies it seems unlikely that phosphatization alone could be responsible for a large number of specimens with the same repeated form with the same dimensions the strikingly similar sizes and morphologies as well as the observed diagenetic sequence lead us to conclude that these specimens are likely biogenic in nature

the phase evolution of young sea ice sea ice forms as a porous matrix consisting of pure ice crystals in equilibrium with brine we present an experimental and theoretical study that reveals that the brine expelled by growing sea ice initially remains trapped within the crystalline interstices but that drainage into the underlying water is ultimately triggered abruptly due to the onset of buoyancy driven convection the onset is quantified by a critical porous medium rayleigh number and we present an empirical marginal stability diagram that defines the transition

interpreting late precambrian microfossils chia wei li et al describe microfossils found in doushantuo phosphate rocks from guizhou province south china that are about 580 million years old 1 1 well preserved macroscopic multicellular fossils associated with prokaryotic and eukaryotic microfossils from the same source rocks have been

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

eumetazoan fossils in terminal proterozoic phosphorites phosphatic sedimentary rocks preserve a record of early animal life different from and complementary to that provided by ediacaran fossils in terminal proterozoic sandstones and shales phosphorites of the doushantuo formation south china contain eggs egg cases and stereoblastulae that document animals of unspecified phylogenetic position small fossils containing putative spicules may specifically record the presence of sponges microfossils recently interpreted as the preserved gastrulae of cnidarian and bilaterian metazoans can alternatively be interpreted as conventional algal cysts and or egg cases modified by diagenetic processes known to have had a pervasive influence on doushantuo phosphorites regardless of this interpretation evidence for doushantuo eumetazoans is provided by millimeter scale tubes that display tabulation and apical budding characteristic of some cnidaria especially the extinct tabulates like some ediacaran remains these small benthic colonial fossils may represent stem group eumetazoans or stem group cnidarians that lived in the late proterozoic ocean

geology geography and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean abstract sediment flux to the coastal zone is conditioned by geomorphic and tectonic influences basin area and relief geography temperature runoff geology lithology ice cover and human activities reservoir trapping soil erosion a new model termed bqart in recognition of those factors accounts for these varied influences when applied to a database of 488 rivers the bqart model showed no ensemble over or underprediction had a bias of just 3 across six orders of magnitude in observational values and accounted for 96 of the between river variation in the long term 30 years sediment load or yield of these rivers the geographical range of the 488 rivers covers 63 of the global land surface and is highly representative of global geology climate and socioeconomic conditions based strictly on geological parameters basin area relief lithology ice erosion 65 of the between river sediment load is explained climatic factors precipitation and temperature account for an additi

proterozoic modular biomineralized metazoan from the nama group namibia we describe a proterozoic fully biomineralized metazoan from the omkyk member 549 million years before the present of the northern nama group namibia namapoikia rietoogensis gen et sp nov is up to 1 meter in diameter and bears a complex and robust biomineralized skeleton it probably represents a cnidarian or poriferan namapoikia encrusts perpendicular to the walls of vertical synsedimentary fissures in microbial reefs this finding implies that large modular metazoans with biologically controlled mineralization appeared some 15 million years earlier than previously documented

integrated chemostratigraphy of the doushantuo formation at the northern xiaofenghe section yangtze gorges south china and its implication for ediacaran stratigraphic correlation and ocean redox models abstract the ediacaran doushantuo formation in the yangtze gorges of south china plays an important role in our understanding of biological evolution global correlation and ocean redox conditions because of the availability of high resolution paleontological and geochemical data and numerous radiometric dates however integrated study has been focused on the jiulongwan section that was largely deposited below wave base in a restricted shelf lagoon jiang et al 2011 zhu et al 2011 studies of shallower water successions are lacking and this presents a challenge to test ediacaran stratigraphic correlation and ocean redox models to fill this knowledge gap we conducted a high resolution integrated study of the doushantuo formation at the northern xiaofenghe nxf section approximately 35 km to the northeast and paleogeographically updip of the jiulongwan section with the exception of the basal 20 m nxf sediments were deposited above normal wave base integrated biostratigraphic and chemostratigraphic data indicate that the 140 m thick nxf section correlates with the lower doushantuo formation member i and much of member ii i e the lower ca 70 m of the formation at jiulongwan geochemical data from nxf and other doushantuo sections indicate that euxinic conditions may have been limited to a shelf lagoon represented by the jiulongwan section that was restricted between the proximal inner shelf and a distal shelf margin shoal complex at least during early doushantuo time following the deposition of the doushantuo cap dolostone further integrated studies are necessary to test whether euxinic conditions existed in open marine shelves in south china and elsewhere during the ediacaran period

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

marine biogeochemical cycling during the early cambrian constrained by a nitrogen and organic carbon isotope study of the xiaotan section south china the precambrian cambrian boundary is claimed as one of the most crucial biological breakthroughs on our planet when changes in chemical and physical conditions together with key biological innovations helped to trigger a biodiversity explosion the yangtze platform south china mainly characterized by continuous and unaltered successions of this age is ideally suited to high resolution palaeomarine investigations of this event in this study 15n and 13corg records from xiaotan section yunnan sw china were investigated in order to provide insight into variations in primary productivity ecological developments and marine environment the ediacaran early cambrian xiaotan section is characterized by relatively high sedimentation rates and variable lithologies carbonates cherts phosphorites sandstones and siltstones that alternate through nearly 600 meters thickness organic carbon isotope values vary between 36 and 21 tightly following and helping to complete published 13ccarb trends the base of the cambrian is characterized in this section by a significant drop from 25 to 35 mirroring the 13ccarb fall observed at this and other sections worldwide higher in the section in the dahai member values increase to 20 again demonstrating communication between doc and dic pools during the early cambrian on 105 106 year time scales from the base of the overlying shiyantou formation 13corg values remain around 30 until the end of the section testifying to an interval of more modest change in dic 13c that would be consistent with biostratigraphic correlations nitrogen isotope values vary independently from carbon isotope trends exhibiting several major 15n cycles with values fluctuating between 9 and 1 robust trends in 15n within the dahai member testify to changes in the ratio between nitrogen fixation and denitrification possibly reflecting fluctuations in the water column chemocline as 13c values reached their global acme up section nitrogen isotope values show dampened cyclicity with values remaining between 0 and 5 indicating establishment of an equilibrium state in marine biogeochemistry and nutrient cycles the overall variability in 15n closely resembles that of recent marine sediments while the observed cyclicity is defined by several samples in all cases these observations argue for good preservation of original isotopic signatures which bodes well for future n isotope studies of the precambrian cambrian boundary

prokaryotic and eukaryotic microfossils from a proterozoic phanerozoic transition in china cherts of the doushantuo formation in the yangtze gorges south china contain a superbly preserved heterogeneous assemblage of bacteria cyanobacteria planktonic algae submillimetre sized burrows and problematica the microbiota has a bearing on defining the precambrian cambrian boundary baltisphaeridium and associated spinose microfossils in the chert suggest an early cambrian age whereas other acritarchs vendotaenids and pretrilobite small shelly fossils from the conformably overlying the dengying formation indicate a late proterozoic age for the doushantuo this mixed benthic planktonic assemblage preserved in silicified laminated microbial mat like fabrics provides a unique sample of diverse microbiotic elements existing at the dawn of the phanerozoic and records the earliest evidence of meiofauna

towards a sediment budget for the santa cruz shelf a conceptual model is presented for the northern monterey bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine grained sediment introduced into monterey bay the principal sources of the fine sediment are the three rivers that enter monterey bay the san lorenzo pajaro and salinas rivers accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion and also are high relative to other documented mud accumulations of the west coast continental shelves

formation and structure of refrozen cracks in land fast first year sea ice 1 this study characterizes the healing process and structure of undeformed linear parallel sided flooded cracks in land fast sea ice field investigations and refreezing experiments were performed in mcmurdo sound ross sea antarctica between 1998 and 2002 data from a two dimensional thermistor array are used to show that the ice water interface of freezing cracks is arch shaped due to bidirectional heat flow to the surrounding ice cover and to the atmosphere ice growing laterally into the crack is found to desalinate over a prolonged period of time until the isotherms are approximately horizontal superposition of heat flow to the atmosphere and to the host sea ice sheet allows the refreezing progress to be modeled analytically close to the ice air interface the salinity is higher at the sides of wide refrozen cracks than it is at the center however deeper down and in narrower cracks in general the salinity is higher at the center than at the sides a finite volume computational fluid dynamics cfd model reproduces the generally arch shaped alignment of brine pockets this pattern is attributed to convection in the mushy layer crystals are found to grow upstream into the crack due to a salinity gradient in the buoyant convective flow

precambrian cambrian trace fossils from the yangtze platform south china and the early evolution of bilaterian lifestyles abstract siliciclastic carbonaceous and phosphoritic shallow marine sediments from several neoproterozoic ediacaran and precambrian cambrian pc c boundary sections on the yangtze platform south china contain remarkable trace fossil assemblages the present paper provides a general overview on the distribution and the possible palaeobiological and palaeoenvironmental significance of these trace fossil assemblages from selected pc c boundary sections on the passive yangtze platform margins comparative investigations of the typology of neoproterozoic ediacaran ichnofaunas as well as of the related sedimentary environments accompanying the ichnoassemblages demonstrate in general correspondence with other studies worldwide that the neoproterozoic ichnofaunas are mainly composed of slightly curved to straight and unbranched horizontal traces which are usually related to the occurrence of shallow marine softgrounds sealed by microbial mats rare traces show ichnomorphological patterns that indicate developments toward a more effective horizontal exploitation of the feeding ground during the late neoproterozoic and earliest cambrian the majority of these traces appear to represent undermat miners with simple feeding strategies during the earliest phanerozoic early meishucunian stage equivalent to the nemakit daldynian stage of siberia the oxic shallow water environments along the ancient continental passive margins of the yangtze platform were populated by large as yet unknown arthropods which produced rusophycus type trace fossils the late precambrian to early phanerozoic sediments of the yangtze platform generally provide excellently preserved trace fossil records which together with the presence of index fossils ssf from the nemakit daldynian stage provide a more detailed insight into the development of pc c palaeoenvironments and the evolution of lifestyles among early bilaterian metazoans a preliminary comparison of the neoproterozic biotas occurring on the yangtze platform and in other time equivalent ediacaran habitats demonstrates general similarities but also some striking differences probably due to palaeoenvironmental variations the data presented here from south china are critically discussed in the light of current palichnological approaches and theories

on the coevolution of ediacaran oceans and animals fe speciation and s isotope of pyrite data from the terminal proterozoic sheepbed formation in canada and doushantuo formation in china reveal that ocean deep waters were anoxic after the global glaciations snowball earth ending 635 million years ago but that marine sulfate concentrations and inferentially atmospheric oxygen levels were higher than before the glaciations this supports a long postulated link between oxygen levels and the emergence of eumetazoa subsequent ventilation of the deep ocean inferred from shifts in fe speciation in newfoundland previously published data and western canada this report paved the way for ediacaran macrobiota to colonize the deep seafloors

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

ammonium concentration and nitrogen isotope composition in metasedimentary rocks from different tectonometamorphic units of the european variscan belt the content and isotopic composition of ammonium nh4 were measured by using kjeldahl distillation for 63 samples of predominantly metasedimentary rocks from two different geological settings of the european variscides i e the erzgebirge and the zone of erbendorf vohenstrauss in germany the studied erzgebirge schists represent an early paleozoic passive margin sequence that reappears in different deep subducted metamorphic units this allows an efficient examination of nitrogen loss and isotope fractionation during prograde metamorphism ammonium is found to be progressively depleted accompanied by a shift in 15n from the low grade units 2 kbar 300 c with 638 124 ppm and 15n 2 2 0 6 to the garnet phyllite unit 9 kbar 470 c with 621 190 ppm and 15n 3 5 0 9 the mica schist eclogite unit 12 kbar 550 c with 394 113 ppm and 15n 3 9 0 8 and to the gneiss eclogite unit 12 kbar 730 c with 99 32 ppm and 15n 7 7 2 0 using equilibrium models for rayleigh distillation and batch volatilization suggest that the nitrogen depletion took place by ammonia release only for the mica schists this isotope fractionation can be explained by the loss of molecular nitrogen in comparison with the early paleozoic schists the proterozoic ortho and paragneisses of the erzgebirge gneiss unit 6 8 kbar 650 c contain significantly lower amounts of ammonium 70 ppm and reach relatively low 15n values 2 5 to 3 6 the paragneisses from the zone of erbendorf vohenstrauss zev sampled from the ktb pilot hole represents a separate tectonometamorphic unit that has undergone polyphase metamorphic conditions with the major imprint being amphibolite facies 7 kbar 650 700 c the metagraywackes have nh4 contents of 80 ppm and 15n of approximately 6 gneisses in the vicinity of a late cataclastic shear zone at 2000 m depth are characterized by a shift in nh4 250 ppm and 15n up to 12 which suggest late fluid rock interactions with a nitrogen and 15n enriched fluid

reductions in fluvial sediment discharge by coastal dams in california and implications for beach sustainability abstract the long term sustainability of california s beaches depends on periodic deliveries of sand and gravel from coastal rivers and streams to assess the long term health of california s beaches this study characterized the current state of fluvial sediment delivery and quantified on a littoral cell basis the cumulative impacts of dams in decreasing annual discharge presently more than 500 dams impound more than 42 000 km2 or 38 of california s coastal watershed area flow modeling suggests that by diminishing flood hydrographs these dams have reduced the average annual sand and gravel flux to 20 major littoral cells by 2 8 million m3 yr or 25 in 70 of the streams considered in this study suspended sediment loads during equivalent discharge events have declined over the past three decades which indicates that dams have also significantly reduced downstream sediment supplies approximately 23 or 274 km of the 1193 km of beaches in california are downcoast from rivers that have had s

a statistical description of the microstructure of young sea ice in order to fully exploit microwave models of sea ice the standard ice characterization must be supplemented by a statistical description of the ice microstructure for the strong fluctuation theory this statistical description takes the form of the mean and variance of the permittivity plus correlation lengths we have computed these statistics for over 50 samples of young ice including both columnar congelation ice and desalinated bubbly ice samples were taken from different vertical depths and horizontal positions within the ice sheet and encompassed a comprehensive range of ice temperatures and brine volumes for each of these samples horizontal thin sections were photographed then digitized and analyzed on a personal computer based image processing system results indicate that correlation lengths correspond to the physical dimensions of the inclusions the brine pocket size typically tenths of a millimeter for saline ice and the air bubble size typically millimeters for desalinated ice for saline ice the shape of the correlation function was elliptical similar to the shape of the brine pockets in one case as the ice warmed from 20 to 1 c and the brine volume increased from 2 to 37 the correlation length increased from 0 14 to 0 22 mm

compartmentalisation of beachface sediments along the southwestern coast of australia abstract identification of littoral cells is a prerequisite for the determination of sediment budgets on sandy coasts in this context the aims of the project were first to investigate the applicability of statistical techniques particularly auto correlation and cluster analysis to the definition of littoral cell boundaries second add detail to sedimentological and environmental observations previously reported for the southwestern australian coast and third provide a basis for future examination of sediment transport in a nearshore environment that is generally subject to low wave energy the alongshore component of sediment compartmentalisation has been determined for the sandy beaches of the study area and relationships between environmental parameters and beachface sediment characteristics have been established using data describing textural and compositional attributes the systematic alongshore variation in sediments was determined from the cluster analysis and auto correlation results from the grouping of sediments were then used in conjunction with geomorphic variables to determine boundaries of six sediment compartments littoral cells are better developed on the southern sector of the coast where shoreline salients and headlands are larger and act as boundaries these barriers limit but do not prevent inter compartment sediment transport the findings of this study provide a context for further investigation of littoral cell dynamics and coastal sediment transport the statistical techniques applied to data describing the alongshore distribution of sediments are readily repeatable in other contexts and have general applicability and offer a rigorous procedure for definition of coastal regions

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

nitrogen isotope compositions of metasedimentary rocks in the catalina schist california implications for metamorphic devolatilization history abstract in the catalina schist subduction zone metamorphic complex california metasedimentary rocks show a decrease in n concentration and an increase in 15nair with increasing metamorphic grade lowest grade lawsonite albite rocks contain 632 185 ppm n with 15 n 1 9 0 6 whereas highgrade amphibolite equivalents contain 138 76 ppm n with 15 n 4 3 0 8 loss of n accompanied devolatilization reactions that evolved h2o rich c o h s n fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite biotite garnet and kyanite whole rock n concentrations of up to 200 ppm in veins and pegmatites produced during high p t metamorphism reflect the redistribution of n during devolatilization and partial melting of the metasedimentary rocks bulk fluid rock n isotope fractionations 15n 15nfluid 15nrock of 1 5 1 were calculated with the rayleigh distillation equation taking into account variability in rock composition by comparison of samples with similar k2o concentrations these fractionations are similar to but slightly lower than published calculated fractionations for n2 nh4 exchange at the temperature range of 350 600 c over which most of the devolatilization occurred in the catalina schist approximately 3 4 to 2 25 the n systematics appear to be explained by n2 nh4 exchange and a devolatilization process intermediate in behavior to batch volatilization and rayleigh distillation the observed shifts in n concentration and 15n cannot be explained by nh3 nh4 exchange at these temperatures using the equilibrium models the distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization e g b cs u similarity of the calculated fluid 15n 1 5 to 5 5 with compositions of natural gases inferred to be derived from metasedimentary sources indicates the possibility of using n as a tracer of large scale volatile transport

a quantitative description of sea ice inclusions structurally sea ice consists of an ice matrix with inclusions of brine and air a quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice photomicrographs of ice thin sections were analyzed using a personal computer based image processing system to determine the number of inclusions the inclusion size distributions and statistics for brine pockets in young ice and first year ice and for air bubbles in a multiyear hummock inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured in all cases a two parameter lognormal distribution fits the cumulative inclusion size distributions well correlation coefficient greater than 0 99 this includes brine pockets in both granular and columnar ice and a range of brine volumes from 2 to 40 as ice warms and its brine volume increases the size distribution shifts toward larger brine pockets this increase in brine pocket size is particularly pronounced for brine volumes greater than 10 as individual brine pockets coalesce air bubbles are much larger than brine pockets with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets observations of inclusion shape factors indicate that in general brine pockets are more elongated than air bubbles

comment on small bilaterian fossils from 40 to 55 million years before the cambrian chen et al 1 1 reported coelomate bilaterians from the 600 million year old doushantuo phosphorites in southern china such a find might meet some common expectations of small simple bilaterians emerging after the worldwide glaciations of the neoproterozoic the interpretation is not

in situ analyses of phosphorus contents of carbonate minerals reconstruction of phosphorus contents of seawater from the ediacaran to early cambrian abstract the ediacaran and cambrian periods were one of the most important periods for the evolution of life the biodiversity drastically expanded in the period however the origins are still ambiguous because surface environmental changes through the time have not been well understood yet we conducted in situ analyses of the phosphorus contents of carbonate minerals with a laser ablation inductively coupled plasma mass spectrometer la icp ms to estimate the phosphorus contents of seawater from the ediacaran to the early cambrian carbonate rocks contain not only the carbonate minerals but also detrital and authigenic materials such as silicate and phosphate minerals therefore the whole rock compositions of carbonate rocks are not directly related with seawater composition to avoid the influence of the involvement of the phosphate minerals we performed the microscopic observation elemental mapping of si ca mg fe and p contents with an electron probe microanalyzer epma and investigation of time profiles of signal intensities of ca sr mn p la and ba with the la icp ms especially samples with low mn sr ratios and primary textures such as oolites are suitable to estimate the primary phosphorus contents of the carbonates the chemostratigraphy of the phosphorus contents of carbonates from the drill core and outcrop samples displays that the phosphorus contents decrease from ca 400 ppm in the ediacaran through ca 200 ppm around the terminal ediacaran and the beginning of the cambrian to ca 50 ppm in the early cambrian previous works on 87sr 86sr chemostratigraphy from the ediacaran to the cambrian sections suggested relatively high continental influx in the middle ediacaran and around the precambrian cambrian pc c boundary the high phosphorus content in the ediacaran was possibly due to the high continental flux on the other hand previous works on chemostratigraphy of carbon isotope values of carbonate carbon from the ediacaran to the cambrian sections showed some large negative anomalies in the ediacaran and around the precambrian cambrian pc c boundary and suggested that the negative anomalies were caused by remineralization and respiration of dissolved organic matter the degradation of the organic matter also accounts for the high phosphorus contents in the ediacaran the high phosphorus content of seawater favors enhancement of primary productivity and formation of phosphorites the high phosphorus contents in the seawater possibly led to the emergence of the large and motile organism through the enhancement of primary productivity and the consequent increase of oxygen content of the seawater

carbon isotope chemostratigraphy and sedimentary facies evolution of the ediacaran doushantuo formation in western hubei south china abstract the doushantuo formation of south china consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies is one of the key sedimentary units in the world for understanding ediacaran geobiological processes however stratigraphic correlation and sedimentary facies evolution of the doushantuo formation remain controversial sedimentary facies analysis of the well known sections of the yangtze gorges area and new sections in northern yichang western hubei indicate that the doushantuo succession in the yangtze gorges area was deposited in an offshore intra shelf basin within the yangtze platform in contrast the doushantuo formation in the northern yichang area which is characterized by one or a few phosphate rich horizons represents deposition on the subtidal or intertidal shelf and so is similar to the succession in the weng an area central guizhou province the carbon isotope profiles of the different sections exhibit significant variation which is interpreted to result from facies differences sequence and high resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the doushantuo formation on the yangtze platform the results confirm that a prominent negative 13ccarb excursion baince nadir down to 5 in the middle portion of the second sequence of the doushantuo formation is a widely traceable event baince together with three other 13ccarb excursions namely cance at the base wance near the first sequence boundary near the middle and dounce at the top of the doushantuo formation constitute a complete carbon isotope profile for the doushantuo formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the ediacaran period

speciation and isotope ratios of nitrogen in fluid inclusions from seafloor hydrothermal deposits at 3 5 ga abstract we report here the results of our study on speciation and isotope ratios of n in fluid inclusions preserved in 3 5 ga hydrothermal deposits silica dikes and quartz veins from the north pole area of the pilbara craton western australia crush leach analysis and raman microspectrometry revealed that n within the fluid inclusions exists as n2 and nh4 a negative correlation between the so42 na and 40ar 36ar ratios of the fluid inclusions suggests mixing of two end members hydrothermal fluid with low so42 na and high 40ar 36ar ratios and 3 5 ga seawater with high so42 na and low 40ar 36ar ratios values of 15nn2 from the hydrothermal component vary over a considerable range 3 0 to 3 7 and those of the seawater component are well within this range i e 0 7 to 0 2 this suggests that the isotope ratio of n2 dissolved in the 3 5 ga seawater would have been 0 7 to 0 2 since isotope fractionation between n2 in the atmosphere and n2 dissolved in seawater is minimal the 15nn2 value of the 3 5 ga atmosphere would have been within the range 2 0 which is similar to the 15nn2 value of the present day atmosphere 15nn2 0 this study also suggests that the fluid inclusions contain nh4 that would have been derived from the seawater and or mantle at 3 5 ga therefore kerogens in archean cherts might have been partly derived from biological assimilation of nh4 in hydrothermal fluids

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

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge