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

postseismic and interseismic displacements near a strike slip fault a two dimensional theory for general linear viscoelastic rheologies 1 we present an analytic solution for the deformation near an infinite strike slip fault in an elastic layer overlying a linear viscoelastic half space the theory is valid for any linear viscoelastic rheology and any earthquake sequence this is a generalization of the work of j c savage and colleagues which only holds for models with a uniform shear modulus maxwell viscoelastic lower half space and periodic rupture recurrence we demonstrate the theory for models of an elastic layer over a maxwell standard linear solid burgers and triviscous half space for each of these models we calculate example postseismic displacements interseismic displacements in a periodic earthquake sequence and interseismic displacements for a nonperiodic earthquake sequence our solution is for a simple geometry however the model presents an elegant tool to explore the evolution of displacements for relatively complex rheologies and rupture recurrence histories

controls on precambrian sea level change and sedimentary cyclicity abstract although uniformitarianism applies in a general sense to the controls on relative and global sea level change some influences thereon were more prominent in the precambrian short term base level change due to waves and tides may have been enhanced due to possibly more uniform circulation systems on wide low gradient precambrian shelves the lack of evidence for global glacial events in the precambrian record implies that intraplate stresses and cyclic changes to earth s geoid were more likely explanations for third order sea level change than glacio eustasy higher heat flow in the earlier precambrian may have led to more rapid tectonic plate formation transport and destruction along with an increased role for hot spots aseismic ridges and mantle plumes superplumes all of which may have influenced cyclic sedimentation within the ocean basins a weak cyclicity in the occurrence of plume events has an approximate duration comparable to that of first order supercontinental cycle sea level change second order cyclicity in the precambrian largely reflects the influences of thermal epeirogeny changes to mid ocean ridge volume as well as to ridge growth and decay rates and cratonic marginal downwarping concomitant with either sediment loading or extensional tectonism third order cycles of sea level change in the precambrian also reflected cyclic loading unloading within flexural foreland basin settings and filling deflation of magma chambers associated with island arc evolution the relatively limited number of studies of precambrian sequence stratigraphy allows some preliminary conclusions to be drawn on duration of the first three orders of cyclicity archaean greenstone basins appear to have had first and second order cycle durations analogous to phanerozoic equivalents supporting steady state tectonics throughout earth history in direct contrast however preserved basin fills from neoarchaean palaeoproterozoic cratonic terranes have first and second order cycles of considerably longer duration than phanerozoic examples supporting less evolved tectonism affecting cratonic plates it is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates the wide range of controls on precambrian sea level change allied to their apparent variability in rates and periodicity through precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study this underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of precambrian basins based on the relative importance of sequences rather than their temporal duration

estimation of relative recharge sequence to groundwater with minimum entropy deconvolution this study applies the minimum entropy deconvolution med for the estimation of the sequential groundwater recharge rate groundwater recharge rates have conventionally been estimated as an average value over some period of time e g annual or seasonal recharge rates such estimates however are not suitable for the analysis of the dynamic sequential behavior of the groundwater head fluctuation if the sequential groundwater recharge rate is obtained numerical groundwater models can be effectively applied to evaluate the effect of any change in the groundwater system following the change in natural or artificial components this study successfully applies med to estimate the sequential recharge rates as recharge rates are obtained by relative values a series of timed observations are necessary the validity of the estimated sequences of relative recharge rates can be checked by cross referencing cross correlations between the applied recharge sequence and the estimated results are above 0 985 in all study cases through the numerical test the suitability of med in the estimation of the recharge sequence to groundwater is investigated

recharge estimation of a small karstic aquifer in a semiarid mediterranean region southeastern spain using a hydrological model mediterranean aquifers are frequently subject to the joint effect of intensive exploitation and low recharge values besides groundwater is the only available water resource in many mediterranean regions groundwater recharge studies are therefore necessary to underpin water management practices this manuscript presents a methodology to estimate groundwater recharge in a small limestone aquifer of southeastern spain the hydrobal model is used to calculate daily soil water balances on the basis of hydrological and soil data as well as on vegetation cover deep drainage model outputs are converted into water table variations using a lumped model add on the adjustment between observed and calculated water table levels is in the order of r2 0 87 this correlation coefficient suggests that hydrobal is a useful tool to estimate groundwater recharge in the region in addition differences in groundwater recharge rates are observed for dry average and wet years estimated recharge rates range between 0 and 18 of the mean annual rainfall which corresponds to a net recharge of 0 to 59 mm year 1 recharge rates increase proportionally with precipitation r2 0 90 copyright 2012 john wiley sons ltd

renewal rate estimation of groundwater based on radioactive tracers 3h 14c in an unconfined aquifer in a semi arid area iullemeden basin niger abstract estimation of groundwater recharge in arid and semi arid areas is difficult due to the low amount and variability of recharge a combination of radiotracers investigation based on simple mixing models allows direct investigation of relatively long term renewal rates of an aquifer the recharge process of the shallow continental terminal aquifer in the iullemeden basin niger was investigated using a geochemical and isotopic approach this study investigates the area in the one degree square of nianey 13 14 n 2 3 e in this area recharge is highly heterogeneous and mainly occurs through a drainage system of temporary streams and pools during the rainy season heterogeneity of the recharge is reflected through the wide variation in electrical conductivity and oxygen 18 content of the groundwater the carbon 14 activity range for most of the groundwater falls between 69 and 126 pmc showing pre and post aerial thermonuclear test recharge two renewal rate models have been investigated the first one models a well mixed reservoir and the second one is derived from a piston flow model in which mixing is in equal proportions major ions in tritium data analyses allow exclusion of non representative samples and confirm the carbon 14 renewal rate estimations both models give similar results for the relatively low renewal rate investigated in the area using carbon 14 the mean annual rates of groundwater renewal range from 3 to 0 03 of the aquifer volume with a median of 0 1 assuming the median is representative of the overall renewal rate of the area the recharge rate is in the order of 5 mm a 1 the shallow aquifer recharge extends from the last small humid period around 4000 a up to now high recharge rates are found in depressions whereas low recharge occurs below the plateaux

variations in neoarchean microbialite morphologies clues to controls on microbialite morphologies through time the neoarchean carawine formation hamersley group western australia is a carbonate ramp that preserves diverse microbial structures which are characteristic of specific depositional environments these distinctive structures are distributed in five shallow subtidal and two deeper water facies in the oakover area of the carawine formation the shallow subtidal facies are composed of biohermal and bedded stromatolites centimetre scale ridge shaped microbialites and wavy laminated microbialites the deeper water facies are composed of fenestrate microbialites planar laminated dolostone and dolostone with rolled up microbial laminae microbialites in the carawine formation lie within a continuum of archean to proterozoic microbial facies some shallow water microbial facies in the carawine formation are similar to proterozoic facies such as large bioherms internally composed of a variety of stromatolite morphologies in contrast fenestrate microbialites grew in quiet subtidal environments and are common in archean rocks but have not been documented in similar proterozoic environments the similarity of shallow water facies across the archean proterozoic transition before and after the oxidation of the atmosphere and surface oceans indicates that stromatolite growth in shallow subtidal environments was not strongly affected by the chemical changes associated with oxidation of the oceans or by biological responses to those chemical changes rather stromatolite morphology was controlled mostly by the physical environment and the corresponding biological responses to that environment in contrast the absence of fenestrate microbialites from proterozoic deep subtidal environments suggests that the morphology of deep subtidal microbial structures was influenced by chemical or biological changes that occurred in association with oxidation of the surface oceans

major ion chemistry of groundwaters in the continental terminal water table of southwestern niger africa numerous chemical analyses undertaken during the last 4 a in the niamey area of the continental terminal groundwaters sw niger africa reveal large seasonal variations and high no3 content up to 2 87 meq l the positive correlation between conductivity and depth to the water table indicates that the chemical change is associated with the recharge in the shallow wells this highly mineralised recharge reflects the rain composition variably concentrated by evaporation processes

studies on groundwater recharge characteristics at a reclaimed land site with an equatorial climate using time series and spectral analyses groundwater recharge studies are essential for investigating the feasibility of using the reclaimed lands in singapore for subsurface storage and recovery of water through time series and spectral analyses net recharge percentages and stress filtering characteristics at the reclaimed land were found to depend strongly on the stress transfer velocity which was a combined function of rainfall pattern and vadose zone thickness based on stress transfer velocity a theory was established to provide logical explanations for the rainfall recharge relationship the observed stress filtering characteristics and the recharge percentage characteristics at the unconfined sandy aquifer although the reclaimed land site has a lithollogically homogeneous soil profile a non uniform recharge pattern was observed to be influenced pronouncedly by the uneven density distribution of bush grasses under a bare soil condition significantly lower recharge percentages were observed for areas under the influence of offshore tides the unconfined sandy aquifer appears to dampen out the wave propagation of offshore tides rapidly within a short distance from the tidal source though it has a fairly straight shoreline and is created from highly compacted sand fills copyright 2006 john wiley sons ltd

hydrology of the hapex sahel central super site surface water drainage and aquifer recharge through the pool systems abstract the hydrology of the sahel is characterized by the degradation of the drainage network resulting in the lack of large watersheds over which the spatial integration of the hydrological processes could be studied the main hydrological units are small endoreic areas measuring a few hectares to a few square kilometres and the surface runoff is collected into pools a detailed investigation of the role of these pools in the hydrology of the hapex sahel central super site was carried out from 1991 to 1993 the first results of this investigation are presented a typology in three classes of the endoreic systems valley bottoms sinks plateaux is proposed the behaviour of one representative pool in each class is analysed showing that the partition between evaporation and deep infiltration depends on the level of filling of the pools the bottom of the pool is clogged by clay deposits which prevent infiltration above a threshold varying between 1 and 2 m most of the water stored in the pool after runoff infiltrates contributing to the recharge of the aquifers on a seasonal basis deep infiltration accounts for less than 50 of the water collected by the plateau pool and more than 80 for the valley bottom pools almost all the water running off to the sink pools infiltrates rapidly and deeply into the ground the valley pools both valley bottoms and sinks appear to be the major contributors to the recharge of the upper aquifer the proportion of the hapex sahel central super site water balance that is taken by the deep infiltration from the pools varies greatly depending on the temporal distribution of rainfall whereas similar seasonal rainfalls were recorded in 1991 and 1992 it is estimated that 5 of the water precipitated over the valley pool watershed infiltrated towards the aquifer in 1991 and 20 in 1992 this difference is explained by a very irregular time distribution of precipitation in 1992 most of the major rainfall events being observed over a short period during the intensive observation period in conclusion some preliminary figures are given regarding the importance of recharge from the pools as compared with in situ recharge

trace fossil preservation and the early evolution of animals abstract the trace fossil record is an important element in discussions of the timing of appearance of bilaterian animals a conservative approach does not extend this record beyond about 560 555 ma crucial to the utility of trace fossils in detecting early benthic activity is the preservational potential of traces made close to the sediment water interface our studies on the earliest cambrian sediments suggest that shallow tiers were preserved to a greater extent than typical for most of the phanerozoic this can be attributed both directly and indirectly to the low levels of sediment mixing the low levels of sediment mixing meant that thin event beds were preserved the shallow depth of sediment mixing also meant that muddy sediments were firm close to the sediment water interface increasing the likelihood of recording shallow tier trace fossils in muddy sediments preservation of surficial trace fossils in this type of setting remains problematic but the above factors suggest that also these can be expected to have left a reasonable record overall the trace fossil record can be expected to provide a sound record of the onset of bilaterian benthic activity the lack of convincing trace fossils significantly before the cambrian supports models of late appearance of macroscopic benthic bilaterians

the origin of decoupled carbonate and organic carbon isotope signatures in the early cambrian ca 542 520 ma yangtze platform abstract the early cambrian ca 542 520 ma strata in south china record two prominent negative carbonate carbon isotope 13ccarb excursions of early nemakit daldynian n d and early tommotian ages across each of these excursions carbonate and organic carbon isotopes 13ccarb and 13corg are strongly decoupled regional correlation across a shelf to basin transect shows lateral heterogeneity of 13corg during the early middle n d but more homogenized 13corg values across the basin during the late n d and tommotian the temporal and lateral variations in 13corg suggest that decoupled 13ccarb and 13corg across the n d 13ccarb excursion were possibly caused by diagenetic alteration of organic matter and or amplification of detrital organic carbon isotope signature in low toc carbonates in contrast decoupled 13ccarb and 13corg of the upper n d and tommotian were likely resulted from chemoautotrophic methanotrophic biomass contribution to toc in organic rich black shale and carbonates the decoupled 13ccarb 13corg pattern from the lower n d strata ca 542 ma shows striking similarities with those from the basal ca 635 ma and upper ca 551 ma doushantuo formation in all three cases decoupled 13ccarb 13corg are seen in organic poor carbonates toc 0 1 and coupled 13ccarb 13corg occur in organic rich black shale and carbonates at the end of the negative 13ccarb excursion these similarities suggest that the shift from decoupled to coupled 13ccarb 13corg has no causal link with the terminal oxidation of a large oceanic doc reservoir given the pervasive anoxia euxinia in ediacaran early cambrian oceans local doc rich environments may have been common but a large oceanic doc reservoir capable of buffering the 13c of marine organic matter requires independent evidence

deep infiltration through a sandy alluvial fan in semiarid niger inferred from electrical conductivity survey vadose zone chemistry and hydrological modelling abstract in semiarid southwestern niger most of the groundwater recharge is indirect and occurs through endoreic ponds elsewhere in the landscape there is no evidence of deep infiltration with a possible exception for gullies and alluvial fans on sandy slopes in order to verify this hypothesis a detailed geophysical and geochemical survey was conducted on a large representative mid slope fan 6 ha at this site distributed hydrological modelling conducted over the encompassing endoreic catchment 190 ha showed high losses of runoff water by infiltration electromagnetic mapping and 2 d electrical imaging survey were used to investigate the 35 m deep vadose zone in addition 8 boreholes were drilled following the geophysical survey to constrain the interpretation variations in apparent electrical conductivity measured in boreholes appear to be mainly linked with changes in the soil solution mineralization an extrapolation throughout the area shows that apparent electrical conductivity of the ground is systematically lower below channels this suggests localised leaching through the unsaturated zone a physically based 2 d distributed hydrologic model was used to estimate the amount of surface water loss by infiltration for the 1992 2002 period depending on year infiltrated volumes range from 1000 to 24 000 m3 this represents between 5 and 16 of the runoff that reaches the final outlet of the basin an endoreic valley bottom pond where recharge to the aquifer has been shown to occur because leaching of the vadose zone is observed down to a depth of 10 m below channels episodic groundwater recharge through sandy mid slope fans is highly probable during rainy years

comment on improving noble gas based paleoclimate reconstruction and groundwater dating using 20 ne 22 ne ratios by f peeters et al 2003 geochim cosmochim acta 67 587 600 1 1associate editor b marty

importance of stream infiltration data for modelling surface water groundwater interactions summary an infiltration experiment at the transect scale was performed in an ephemeral stream at the time it was dry resulting in direct estimates of stream infiltration groundwater heads measured in a transect of piezometers orthogonal to the stream highlighted the development of a groundwater mound displaced several meters into the streambank the experiment was modelled using the two dimensional integrated surface subsurface model hydrogeosphere and calibrated with pilot points using different combinations of groundwater heads and infiltration volume data modelling results showed that despite the fact that groundwater heads were all below the streambed and that an unsaturated zone was present beneath the streambed the stream and the aquifer become laterally connected within several hours of flow onset through a high permeability preferential path in the streambank although the model can be calibrated to produce a good match to measured groundwater heads accurate predictions of stream infiltration can be made only if the heads used for model calibration capture the groundwater mound the use of infiltration flux or volume during model calibration instead provides the best calibration results and thus estimates of stream infiltration during natural flow events given that heterogeneity of streambed and streambank sediments leads to the possibility that the groundwater mound developed during flow events will be poorly characterised or perhaps missed altogether incorporating infiltration flux or volume data into the model calibration increases the likelihood of obtaining accurate estimates of stream infiltration during natural flow events

interactions between ediacaran animals and microbial mats insights from lamonte trevallis a new trace fossil from the dengying formation of south china abstract a new ichnogenus and ichnospecies lamonte trevallis is formally described from the shibantan member limestone of the upper ediacaran dengying formation yangtze gorges area south china it is characterized by horizontal tunnels connected with short vertical burrows and surface trails the horizontal burrows are elliptical or bilobed in transverse cross section preserved in full relief and filled with carbonate intraclasts micrites as well as calcite and silica cements they occur exclusively in silty crinkled and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats no burrows have been found in intraclastic layers adjacent to the microlaminated layers the vertical traces are filled with the same material as the burrows but they typically project through the crinkled microlaminae and are exposed on the bedding surface the surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs the burrow infill has 18ocarb and 13ccarb values distinct from but intermediate between microlaminated and intraclastic layers consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements intraclasts and micrites bedding plane bioturbation intensity 20 40 measured as percentage of bedding plane area covered by l trevallis traces is comparable to similar measurements in pre trilobite cambrian carbonates the exclusive occurrence of l trevallis within microbial mats may have both taphonomic and ecological significance these mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows and they may have also facilitated early diagenetic cementation of burrow infill thus facilitating burrow preservation the close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources the trace makers of l trevallis were better able to utilize the resources around them than many other ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late ediacaran oceans at the dawn of the agronomic revolution

combined estimation of specific yield and natural recharge in a semi arid groundwater basin with irrigated agriculture a water budget approach is developed to jointly estimate specific yield and natural recharge in an unconfined aquifer with significant seasonal water table fluctuations water table fluctuations are due to distinct seasonality in groundwater recharge the separation of the hydrologic year into two or more extended seasons of recharge wet season and no recharge dry season with accompanying changes in water table allows for a split use of the water table fluctuation wtf method first to estimate specific yield from the water table drop during the dry season no recharge and second to estimate recharge from the water table rise during the wet season after considering all other water budget components explicitly the latter includes explicit computation of groundwater storage with the wtf method the application of the wtf method requires a large number of water level measurements throughout the unconfined aquifer before and after each season the advantage of the method is that specific yield and recharge are estimated at the scale of interest to basin hydrologic studies and that the method requires no extensive in situ instrumentation network here the method is demonstrated through a case study in a fractured hard rock aquifer subject to intensive groundwater pumping for irrigation purposes

mechanisms timing and rates of arid region mountain front recharge summary arid region mountain front recharge mfr for two catchments 17 5 and 25 6 km 2 in the silver island mountains utah usa was evaluated by an analysis of catchment precipitation mountain front and playa infiltration rates aquifer parameters and groundwater level responses in 59 shallow monitoring wells located at the distal end of the catchments the 3 7 km long mountain front surfaces transition from alluvial fan deposits to a thin alluvial covering on lacustrine pediment surfaces precipitation and groundwater level data were collected from october 2005 to october 2010 which represents five recharge cycles average annual precipitation for all rain gauges during the 2005 2010 water years was 14 9 cm monitoring well water levels increased 91 97 of the time in response to storm events during times of general monitoring well water level increases and 29 38 of the time during times of general monitoring well water level declines a surprising 81 7 of total catchment precipitation resulted in positive water level responses precipitation events as small as 2 mm resulted in positive water level responses and initial responses occurred within hours of some precipitation events water level responses that occur within hours of the larger precipitation events are attributed to focused groundwater recharge in near field braided stream channels the time lag between the end of precipitation events and the maximum water level responses which may be several days is attributed to far field recharge direct mfr was calculated using a modified version of the water table fluctuation method for the two catchments the average calculated direct mfr was 2 7 3 2 using prism precipitation data and 3 7 4 5 using rain gauge data

tension over equitable allocation of water estimating renewable groundwater resources beneath the west bank and israel competition for water resources between palestine and israel is an ongoing cause of tension the western aquifer basin forms a major part of the complex largely karst limestone system of the west bank mountain aquifer the aquifer crops out and is recharged solely in the semi arid uplands of the west bank and groundwater flows west beneath israel to discharge at the yarqon and nahal taninim springs near the mediterranean coast annual recharge to the aquifer is not easy to quantify but lies within the range 270 106 to 455 106 m3 a 1 and current uncertainties do not support definition of a single value of long term average recharge the resource is heavily exploited and abstraction is directly controlled and apportioned between israel and the west bank by israel the key to equitable apportionment is the determination of the long term average recharge to the basin which also requires definition of the eastern boundary of the basin to confirm the recharge area calculations include empirical formulae and process based models that are likely to constrain the best estimate provided that there is appropriate ongoing monitoring improved understanding can then be fed back into the model

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

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

taphonomy and depositional circumstances of exceptionally preserved fossils from the kinzers formation cambrian southeastern pennsylvania abstract the emigsville member of the kinzers formation cambrian southeastern pennsylvania is a deposit of exceptional preservation containing three main lithofacies that were part of a mixed siliciclastic carbonate debris fan developed seaward of a carbonate shelf along the appalachian margin of laurentia fossils were exceptionally preserved in a shelf environment subject to tempestite deposition most remains are fragmentary which emphasizes the importance of predation as a taphonomic process where emigsville sediments were deposited remains are preserved mostly as organic carbon films pyrite crusts and aluminosilicate films these preservation styles apparently depended upon the development of microbial consortia in isolated microenvironments and some of the microbes were autolithified sedimentary and biological evidence suggests that anoxia salinity fluctuations and sedimentary obrution played relatively minor roles in the emigsville member of the kinzers formation the abundance of exceptionally preserved remains suggests that exceptional sedimentary conditions were not necessary in the cambrian in order for exceptional preservation to occur the abundance of predation evidence in a deposit of exceptional preservation reinforces the concept that predation was the primary taphonomic filter during cambrian time

local and global hydrological contributions to time variable gravity in southwest niger p advances in methods of observation are essential to ensure a better understanding of changes in water resources considering climate variability and human activities the ghyraf gravity and hydrology in africa experiments aim to combine gravimetric measurements with dense hydrological surveys to better characterize the annual water storage variability in tropical west africa the first absolute gravimetric measurements were performed in southwest niger near a temporary pond where rapid infiltration to an unconfined aquifer occurs as gravity is sensitive both to local and global variations of water mass distribution the large scale hydrological contribution to time variable gravity has been removed using either grace satellite data or global hydrology models the effect of the local water storage changes was modelled using in situ measurements of the water table soil moisture and pond water level the adjustment of these simulations to residual ground gravity observations helped to constrain the specific yield to a value ranging between 1 8 and 6 2 per cent this range of value is consistent albeit on the low side with the aquifer water content 6 12 per cent estimated by magnetic resonance soundings which are known to slightly overestimate the specific yield in this geological context the comparison of these two independent geophysical methods shows their potential to constrain the local hydrogeological parameters besides this study evidences the worth of correcting the gravity signal for large scale hydrology before recovering local water storage parameters

water table fluctuation and recharge in semi arid climate some results of the hapex sahel hydrodynamic survey niger groundwater level measurements taken over a 4 year period from an extensive network of wells and boreholes within the hapex sahel hydrologic atmospheric pilot experiment in the sahel degree square south niger together with existing data have provided an insight into infiltration and recharge processes taking place in the porous phreatic aquifer of the continental terminal formation despite high spatial and temporal variability of aquifer response to rainfall rises of between 0 and 9 m are recorded a pattern of recharge can be recognised aquifer responses vary from site to site but the type of response at any single point tends to be consistent from year to year recharge is dominated by infiltration from temporary drainage networks pools and streams and aquifer response depends to a large extent on aquifer hydraulic characteristics and distance from the nearest infiltrating zone in many wells for which data extending back to 1987 is available water levels show a consistent year by year rise this is interpreted as a process of aquifer recovery following the severe drought of the 1970s and early 1980s though part may also be attributable to changing patterns of land management e g woodland clearance initial estimates of regional recharge are from 50 60 mm year 1 or in other words about 10 of annual rainfall the figure is supported by other methods of investigation hydrochemical analyses water budgets of pools

the spatial heterogeneity of riverbed saturated permeability coefficient in the lower reaches of the heihe river basin northwest china in arid region direct infiltration from rainfall contributes little to groundwater compared with localized recharge from streams how to quantify riverbed infiltration to groundwater systems is an important area of research in hydrology in this study saturated permeability coefficient of a riverbed in an arid inland river basin located in the northwest of china was obtained by guelph permeameter and laboratory analysis methods the characteristics of riverbed infiltration and its spatial patterns were analysed using geostatistical method and kriging method the results showed that the saturated permeability coefficient varied from 0 089 to 2 802 m d indicating moderate degree of variability the guelph permeameter and laboratory test methods provided consistent estimates of saturated permeability coefficient there was a strong spatial correlation for kfs of the riverbed in this study area when range a was less than 0 276 suggesting that the maximum sampling distance for saturated permeability coefficient of the riverbed was 0 276 under isotropic conditions the kfs near the centre of the riverbed was higher than the value near riverbank the kfs values decreased in the direction of upstream to downstream in the heihe river basin the riverbed mechanical composition initial soil water content and bulk density have significant influence up on the riverbed infiltration besides the topographical factors including the width altitude and distance factors of the riverbed together impacted the riverbed infiltration and the slope of the riverbed and also influenced the riverbed infiltration copyright 2015 john wiley sons ltd

carbon sinks in small sahelian lakes as an unexpected effect of land use changes since the 1960s saga gorou and dallol bosso sw niger for several decades global change has resulted in an increase in runoff in the sahelian belt provoking major changes in the quality and quantity of sediments transported by drainage networks one of the astonishing consequences is the establishment of numerous permanent lakes the origins of particulate organic matter om preserved within lacustrine sediments of three lakes were investigated by coupling optical observations palynofacies and bulk geochemistry rock eval 6 pyrolysis an initial estimate of particulate organic carbon oc stored in these lacustrine sediments was assessed soil organic matter som was sampled from the surface 0 10 cm of various land use and land cover areas and was characterized and compared with sedimentary organic matter our results reveal that lake tankalawal is subjected to high autochthonous organic sedimentation toc ranges between 3 0 and 10 0 wt while lakes bangou kirey and bi are characterized by weak sedimentation of non indigenous om originating from the soil erosion and shore vegetation toc 3 0 wt in sediments the effects of early diagenesis on the om induce not only a loss of labile and aquatic om but also a significant loss of terrestrial om which is supposed to be more resistant than its aquatic counterpart both the preservation of om in top sediments and the relative preservation of terrestrial om impact the oc storage in lakes indeed oc storage in lacustrine sediments lake bangou kirey was two to seven times higher than the oc storage in sahelian soils where greater contributions of terrestrial om to sedimentary om are associated with lower oc storage in lacustrine sediments for lakes bangou kirey and bi oc accumulation rates were also assessed due to the identification of a sedimentary limit corresponding to the establishment of permanent lakes dated earlier 1960s high oc fluxes were estimated and ranged between 104 and 213 g oc m 2 yr 1 compared with other oc accumulation rates for various african lakes these high values are similar to those calculated for reservoirs and are related to anthropogenic pressure soil textures favoring erosion and proper physical and chemical conditions for om preservation in sediments accordingly in these sahelian environments that are generally viewed as non efficient in storing oc we claim that global change could promote a new oc sink if other similar studies reinforce our assertion then regional c budgets should be revisited