the non geometric p s wave in high resolution seismic data observations and modelling summary in data from a high resolution seismic survey conducted over a near surface environment consisting of homogeneous soft clay we consistently observe a distinct seismic phase arriving between the direct compressional wave and the rayleigh wave this phase is characterized by high amplitudes at near offsets and a phase velocity corresponding to about twice the shear wave velocity based on analytical and numerical analyses this signal could be unambiguously identified as a non geometric wave which is excited if the source is located near the earth s surface and the poisson s ratio in the vicinity of the source is unusually high to date there are only a few speculative observations of this particular non geometric seismic wave phenomenon however given the commonly very high poisson s ratio of surficial materials we expect this phase to be present albeit unidentified in many near surface seismic surveys the presence of this non geometric wave increases the complexity of the seismic record and failure to identify it may result in misinterpretations particularly of high resolution seismic reflection data as well as of shear wave and surface wave data potential applications of this seismic phase may arise from its high sensitivity to the shear wave velocity in the immediate source region

river stabilisation due to changing climate and vegetation during the late quaternary in western tasmania australia abstract the stanley river in western tasmania australia contains sub fossil rainforest logs within the channel and floodplain of the more than 85 radiocarbon dates obtained all but 3 date from 17 ka to the present and permit an interpretation of fluvial and related environmental changes over this period particular attention is focused on the interactive relationship between the river and its riparian rainforest following the last glacial maximum the stanley river was a laterally active gravel load system reworking most of its valley floor in the upstream reaches with ameliorating conditions at the end of the pleistocene climate became less seasonal and flow regimes less energetic huon pines already present in the catchment re asserted themselves in the form of dense tree cover along the river banks and floodplains with basal floodplain deposition shifting from gravels to coarse sands and granules by about 3 5 ka a further change in climate reduced stream discharges substantially as a result the channel reduced in size transported finer sediment became laterally stable and the floodplain accreted with overbank deposits of sand and silt huon pines falling into the channel formed obstructions of woody debris some surviving for 2 ka these have reduced stream power and boundary shear stress further contributing to channel stability generational sequences of huon pines on the river banks some extending back 1 2 ka are additional evidence of this stability since the pleistocene changing climate and the re establishment of dense riparian rainforest appear to have stabilised the river channels and floodplains of western tasmania

mineral weathering and soil development in the earliest land plant ecosystems land colonization by plants and their fungal and bacterial symbionts during the paleozoic was fundamental to the evolution of terrestrial ecosystems but how these early communities influenced mineral weathering and soil development remains largely unknown we investigated cryptogamic ground covers cgcs in iceland to identify modern analogous communities and to characterize soil structure and biologically mediated weathering features using a novel application of x ray microcomputed tomography we show that moss dominated cgcs and their soils are not adequate analogues of early communities comparisons with the 407 ma rhynie chert scotland biota indicate that modern cgcs dominated by lichens liverworts and their associated symbionts fungi cyanobacteria are more representative of early soil forming communities liverwort and lichen soils are thin and their depth and complexity are constrained by the size and growth form of the dominant plants or lichens they are aggregated and stabilized by cyanobacteria mycorrhizal and lichenized fungi rhizoids and associated exudates smectite was associated with liverwort but not with moss cgc soils soil grain dissolution features are diverse and attributable to different organisms e g bacteria fungi and types of interaction e g symbiosis we postulate that such features provide a novel indirect means of inferring biotic interactions in paleosols

carbon isotopic evidence for organic matter oxidation in soils of the old red sandstone silurian to devonian south wales uk petrographic and calcrete carbon isotope data from seasonally waterlogged upper silurian p idoli to lower devonian pragian palaeo vertisols of the old red sandstone south wales uk are presented the 13 c values mostly range from 9 to 12 vpdb suggesting that the soils were inhabited by abundant vegetation that when oxidized perhaps with microbial assistance resulted in co 2 rich soils such soils would favour calcrete precipitation through equilibration of soil zone co 2 with the relatively lower atmospheric p co 2 however reliably estimating palaeoatmospheric p co 2 using these carbon isotope data is a challenge supplementary material detailed information on stable isotope measurement methods descriptions of the samples and carbon and oxygen isotope data are available at www geolsoc org uk sup18754

amplification of seismic ground motion in the tunis basin numerical bem simulations vs experimental evidences this paper aims at the analysis of seismic wave amplification in a deep alluvial basin in the city of tunis in tunisia this sedimentary basin is 3000m wide and 350m deep since the seismic hazard is significant in this area the depth of the basin and the strong impedance ratio raise the need for an accurate estimation of seismic motion amplification various experimental investigations were performed in previous studies to characterize site effects the boundary element method is considered herein to assess the parameter sensitivity of the amplification process and analyse the prevailing phenomena the various frequencies of maximum amplification are correctly estimated by the bem simulations the maximum amplification level observed in the field is also well retrieved by the numerical simulations but due to the sensitivity of the location of maximum amplification in space the overall maximum amplification has to be considered the influence of the wave field incidence and material damping is also discussed

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

modelling strong seismic ground motion three dimensional loading path versus wavefield polarization seismic waves due to strong earthquakes propagating in surficial soil layers may both reduce soil stiffness and increase the energy dissipation into the soil to investigate seismic wave amplification in such cases past studies have been devoted to one directional shear wave propagation in a soil column 1d propagation considering one motion component only 1c polarization three independent purely 1c computations may be performed 1d 1c approach and directly superimposed in the case of weak motions linear behaviour this research aims at studying local site effects by considering seismic wave propagation in a 1 d soil profile accounting for the influence of the 3 d loading path and non linear hysteretic behaviour of the soil in the proposed 1d 3c approach the three components 3c polarization of the incident wave are simultaneously propagated into a horizontal multilayered soil a 3 d non linear constitutive relation for the soil is implemented in the framework of the finite element method in the time domain the complex rheology of soils is modelled by mean of a multisurface cyclic plasticity model of the masing prandtl ishlinskii iwan type the great advantage of this choice is that the only data needed to describe the model is the modulus reduction curve a parametric study is carried out to characterize the changes in the seismic motion of the surficial layers due to both incident wavefield properties and soil non linearities the numerical simulations show a seismic response depending on several parameters such as polarization of seismic waves material elastic and dynamic properties as well as on the impedance contrast between layers and frequency content and oscillatory character of the input motion the 3 d loading path due to the 3c polarization leads to multi axial stress interaction that reduces soil strength and increases non linear effects the non linear behaviour of the soil may have beneficial or detrimental effects on the seismic response at the free surface depending on the energy dissipation rate free surface time histories stress strain hysteresis loops and in depth profiles of octahedral stress and strain are estimated for each soil column the combination of three separate 1d 1c non linear analyses is compared to the proposed 1d 3c approach evidencing the influence of the 3c polarization and the 3 d loading path on strong seismic motions

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

a quantitative approach to soil occurrence in alluvial deposits and its application to the old red sandstone of britain palaeosols fossil soils are a major component of alluvial deposits in the geological record not only do these typically show considerable variations in their degrees of development within single formations but they also exhibit highly complex stratigraphic relationships with one another a simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil palaeosol development within a sequence with calcic or petrocalcic horizons to illustrate the approach a range of palaeosols from the siluro devonian old red sandstone of britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation in particular two alluvial suites from the manorbier area of south wales are analysed using this approach the technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates

sediment recycling on siluro devonian floodplains some of the red mudstones in the red mark old red sandstone of llansteffan dyfed are interpreted as originating as sand sized mud aggregates pellets produced in soils and deposited from bed load in small sinuous channels by analogy with the channel country of australia such channels may represent periods of low discharge and reduced hydraulic efficiency when the floodplains were locally reworked in contrast larger channel fills with extraneous sediments may represent pluvial periods with increased discharge

palaeozoic landscapes shaped by plant evolution fluvial landscapes diversified markedly over the 250 million years between the cambrian and pennsylvanian periods the diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover in the absence of widespread vegetation landscapes during the cambrian and ordovican periods were dominated by rivers with wide sand beds and aeolian tracts during the late silurian and devonian periods the appearance of vascular plants with root systems was associated with the development of channelled sand bed rivers meandering rivers and muddy floodplains the widespread expansion of trees by the early pennsylvanian marks the appearance of narrow fixed channels some representing anabranching systems and braided rivers with vegetated islands we conclude that the development of roots stabilized the banks of rivers and streams the subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels our contention is supported by studies of modern fluvial systems and laboratory experiments in turn fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems we suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms

distribution recruitment and geomorphic significance of large woody debris in an alluvial forest stream tonghi creek southeastern australia the complex yet poorly understood interactions between riparian vegetation large woody debris and fluvial geomorphology in an anthropogenically undisturbed reach of an alluvial sand bed forest stream in se australia have been determined riparian vegetation exhibits lateral and vertical zonation of understorey and overstorey species the dominant riparian tree species tristaniopsis laurina water gum grows within the channel and on the floodplain within one channel width of the stream larger eucalyptus species only grow on the highest parts of the floodplain and on a low pleistocene river terrace a complete large woody debris lwd census conducted in the 715 m long study reach revealed that water gum comprises 17 6 of the total lwd loading which at 576 m 3 ha 1 is high for a stream with a catchment area of 187 km 2 although most lwd has a small diameter 0 1 0 3 m the greatest contribution to the total volume of lwd is by pieces with a diameter between 0 3 and 0 7 m a high proportion of lwd 10 4 has a blockage ratio greater than 10 the spatial distribution of lwd is random both longitudinally and within individual meander bends dominant recruitment processes of lwd vary by species t laurina trees are recruited to the channel by minor bank erosion and senescence while the eucalyptus species are predominantly recruited from the highest parts of the floodplain low river terrace by episodic windthrow during large storms multiple radiocarbon dates of outer wood of immobile lwd indicate a maximum residence time of 240f40 years bp for t laurina timber the high loading of lwd combined with the extensive root systems of riparian vegetation stabilize tonghi creek log steps form natural wooden drop structures with a mean height of 29 mm that were responsible for 20 5 of the total head loss under base flow conditions q 0 08 m 3 s 1 large woody debris is buried in the bed at depths of up to 2 3 m and is responsible for an estimated 49 of the 11 600 m 3 of sand stored in the study reach pools are spaced at 0 8 channel widths and 82 of pools are formed by scour over under around or beside lwd or by the impoundment of water upstream of debris dams due to the high density of hardwood timber species debris dams however do not readily form in tonghi creek as the timber is difficult to transport and lwd usually sinks to the bed of the stream despite the high degree of

plant driven fungal weathering early stages of mineral alteration at the nanometer scale plant driven fungal weathering is a major pathway of soil formation yet the precise mechanism by which mycorrhiza alter minerals is poorly understood here we report the first direct in situ observations of the effects of a soil fungus on the surface of a mineral over which it grew in a controlled experiment an ectomycorrhizal fungus was grown in symbiosis with a tree seedling so that individual hyphae expanded across the surface of a biotite flake over a period of three months ultramicroscopic and spectroscopic analysis of the fungus biotite interfaces revealed intimate fungal mineral attachment biomechanical forcing altered interlayer spacings substantial depletion of potassium 50 nm depth oxidation of the biotite fe ii and the formation of vermiculite and clusters of fe iii oxides our study demonstrates the biomechanical chemical alteration interplay at the fungus biotite interface at the nanometer scale specifically the weathering process is initiated by physical distortion of the lattice structure of biotite within 1 m of the attached fungal hypha only subsequently does the distorted volume become chemically altered through dissolution and oxidation reactions that lead to mineral neoformation

late silurian and early devonian terrestrialisation ichnological insights from the lower old red sandstone of the anglo welsh basin u k abstract late silurian to early devonian deposits from the lower old red sandstone anglo welsh basin preserve a diverse assemblage of trace fossils that collectively comprise an important record of early terrestrialisation five main palaeoenvironmental categories are represented 1 perennial rivers 2 ephemeral rivers 3 floodplain lakes 4 alluvial fan and 5 marginal marine ichnocoenoses mainly reflect the activity of aquatic and or semi aquatic animals fluvial deposits preserve evidence for colonisation by eurypterids fish and myriapods ephemeral river channel margins splays preserve the most diverse ichnofauna composed of deposit feeders burrows and trackways produced by arthropods feeding and foraging in channel margin soft grounds that were colonised after fluvial flood events high densities of deposit feeding structures may indicate of explosive population growth in response to periodic acyclical replenishment of nutrients in these aquatic settings ichnotaxa common to both perennial and ephemeral fluvial environments suggest that there might have been only one aquatic ecosystem the degree to which the channel margin ichnofaunas record a truly subaerial terrestrial arthropod signature is difficult to ascertain and most trace makers were probably semi aquatic some terrestrial animals invaded channel margin areas to feed and were also capable of inhabiting high energy alluvial fan environments however the fans contain low diversity ichnological assemblages and were likely to have been inhabited by an opportunistic fauna possibly the only truly subaerial terrestrial ichnocoenosis is that of pedogenically modified mudrock with scoyenia which represents an early soil ichnofauna the majority of ichnocoenoses described from continental palaeoenvironments could be classified under the scoyenia ichnofacies marginal marine deposits contain an impoverished skolithos cruziana ichnofacies typical of silurian devonian brackish water assemblages

plant induced weathering of hawaiian basalts abstract the rise of rooted upland vascular plants during the devonian probably had a major effect on the rate of weathering of silicate rocks and consequently on levels of atmospheric co2 at that time in order to better understand the role of plants in rock weathering an electron microscope microprobe study of the root rock interface has been done on several young 100 3000 year old hawaiian basalts we observe the development of porosity due to dissolution of minerals by solutions secreted by symbiotic microbiota associated with plant roots in nearby plant free parts of the same basalt flows similar porosity development is essentially absent also in nearby areas covered by lichens the extent of rock dissolution is much less in these early stages of weathering dissolution is complete and voids are not infilled by fine grained weathering products quantitative measurement of porosity around roots developed on flows of known age enables the calculation of a rate of basalt weathering that is in order of magnitude agreement with results based on the study of global volcanic weathering based on the chemistry of river water

tetrapod trackways from the early middle devonian period of poland the fossil record of the earliest tetrapods vertebrates with limbs rather than paired fins consists of body fossils and trackways the earliest body fossils of tetrapods date to the late devonian period late frasnian stage and are preceded by transitional elpistostegids such as panderichthys and tiktaalik that still have paired fins claims of tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers here we present well preserved and securely dated tetrapod tracks from polish marine tidal flat sediments of early middle devonian eifelian stage age that are approximately 18 million years older than the earliest tetrapod body fossils and 10 million years earlier than the oldest elpistostegids they force a radical reassessment of the timing ecology and environmental setting of the fish tetrapod transition as well as the completeness of the body fossil record

mineral accumulations induced by biological activity on granitic rocks in qinghai plateau china fragments of weathered granitic rocks from the kunlun shan qinghai plateau china were investigated to elucidate the influence of biotic crusts on the breakdown of granitic rocks in an alpine environment scanning electron microscopy with energy dispersive system and x ray diffractometry were used to describe the nature and properties of mineral accumulations on the rock surface results showed that organic salts such as calcium oxalate and calcium formate are associated with aspicilia caesiocinera nyl ex malbr arnold caloplaca sp xanthoria elegans link th fr and lecidea plana lahm nyl secondary accumulations of 2 i clays minerals are found in a caesiocinera while oxides of manganese are associated with x elegans coatings of goethite iron oxides are believed to form from biological activity associated with the presence of hyphae and rodlet structures on the flakes calcium oxalate crystallizes into several morphologies such as druse hexagonal plates and lenticular containing between 20 and 48 per cent calcium by weight calcium formate and iron oxide goethite occur together in the form of red desert varnish observed black coatings contain as much as 37 per cent manganese and 22 per cent iron clay accumulations have plate like morphology and contain c 2 1 silicon to aluminium contents we argue that organic acids from the activities of biotic crusts contribute to the breakdown of granitic rocks fungi accelerate the breakdown of granitic rocks through the growth of fungal hyphae along the 001 cleavage planes in primary chloritic minerals copyright c 2003 john wiley sons ltd

alluvial facies evolution during the palaeozoic greening of the continents case studies conceptual models and modern analogues the palaeozoic greening of the continents the appearance and expansion of embryophytes land plants in terrestrial environments was arguably the most fundamental phanerozoic change to the earth system thirteen case studies of cambrian to devonian fluvial deposits from north america and europe are documented here to illustrate the evolution of fluvial style during this period during the cambro ordovician prior to the advent of terrestrial vegetation fluvial systems laid down relatively coarse sands with little mud resulting in self formed channels and an architecture dominated by broad sheets of trough cross beds sheet braided style similar deposits formed across a wide range of latitudes and passed basinward into sandy coastal deposits from the mid ordovician onwards an increase in floodplain mudstone corresponds broadly with the appearance of embryophytes which would have progressively enhanced upland weathering mud production and floodplain storage of fines during the late silurian small heterolithic channel bodies with lateral accretion sets provide the first evidence of meandering channels and floodplain mudstones contain more varied palaeosols especially calcretes which appear abundantly for the first time by the early devonian channel deposits comprise sandstone lenses channelled braided style probably due to the increased bank strength and cohesion and reduced potential for sediment sorting imparted by sand mud mixtures muddy coastal deposits are prominent by the upper devonian fluvial deposits commonly contain fossil trees and large mainstem meandering channels with lateral accretion sets indicating that rooted vegetation stabilized channels the advent of stable floodplains with levees crevasse splays and organic litter would have encouraged the diversification of terrestrial invertebrates which left alluvial ichnological signatures from the late silurian onwards

patterns and processes of wood debris accumulation in the queets river basin washington field surveys in the 724 km 2 queets river basin on the west slope of the olympic mountains in nw washington reveal basin wide patterns of distinctive wood debris wd accumulations that arise from different mechanisms of wd recruitment hydraulic geometry and physical characteristics of wd individual pieces of wd in an accumulation or jam can be separated into key racked and loose members ten types of wd accumulations are identified based on the mode of recruitment and the orientation of key racked and loose debris relative to the channel axis although some types of wd accumulation have few geomorphic effects others form stable in stream structures that influence alluvial morphology at both subreach and reach length scales ranging from less than 1 to greater than 10 channel widths in the queets river stable accumulations of wd directly influence channel anabranching planform geometry flood plain topography and establishment of long term riparian refugia for old growth forest development the classification of wood debris accumulations in the queets river basin is based on physical observations that offer a template potentially applicable to other forested mountain regions d 2002 elsevier science b v all rights reserved

seismic effects of a small sedimentary basin in the eastern tibetan plateau based on numerical simulation and ground motion records from aftershocks of the 2008 mw7 9 wenchuan china earthquake abstract in this study the ground motions that can be attributed to the aftershocks of the 2008 mw7 9 wenchuan china earthquake recorded in the wudu basin which is a small basin in the eastern tibetan plateau are analyzed to investigate the seismic effect of a small sedimentary basin in case of the wudu basin the site responses from the basin edge are stronger than those from the basin center the monitoring sites located near the wudu basin edge and the wudu basin center are sensitive to the low frequency 5 hz components of ground motion respectively it indicates that some different seismic phenomena occurred in a small sedimentary basin compared with a large sedimentary basin to further study the ground motion in a small sedimentary basin a simulation of the wudu basin was conducted using the finite element method with a viscous elastic artificial boundary the grid size of the surface layer of the basin is 2 5 2 5 m2 and high frequency up to 10 hz components of a synthetic waveform were obtained the simulation denoted that the surface wave initially appeared in the wudu basin edge and subsequently propagated into its interior the near surface soil layers exhibiting a relatively low wave velocity magnified the amplitude of the seismic wave in the wudu basin furthermore the numerical simulation results are basically consistent with the actual ground motion records especially with the same predominant frequencies of ground motions at the sites located near the wudu basin edge

assessment of site effects in the kathmandu valley nepal during the 2015 mw 7 8 gorkha earthquake sequence using 1d and 2d numerical modelling abstract the paper reports on the results of 1d and 2d site response analyses carried out in the kathmandu valley nepal in order to investigate how site effects influenced the seismic response during the 2015 mw 7 8 gorkha earthquake sequence the mainshock and a mw 6 6 aftershock for which recordings at both rock and soil sites are available were considered first 1d analyses were carried out for the pulchowk soft soil site where a borehole was drilled the shear wave velocity profile was defined using several 2d seismic array surveys carried out in the valley and constrained by noise measurements at pulchowk site the nonlinear soil behavior was characterized by means of cyclic simple shear tests carried out on undisturbed soil samples both equivalent and nonlinear approaches were adopted in the 1d analyses overall the 1d model was capable to capture some relevant features shown by mainshock recordings such as the de amplification of medium to high frequencies on the contrary the unusual high spectral amplification at long periods 3 6 s recorded during the mainshock was better captured by the 2d finite element analyses carried out on a 20 km large cross section of the entire valley thus supporting the hypothesis of the occurrence of basin effects the paper contributes to the understanding of site effects in kathmandu valley for the implementation of seismic risk mitigation strategies in the area

subaqueous silicification of the contents of small ponds in an early devonian hot spring complex rhynie scotland the early devonian rhynie and windyfield cherts of northeast scotland originated as siliceous sinters deposited by hot springs silicification affected both subaerial and subaqueous environments preserving a diverse terrestrial and freshwater biota cherts originally deposited in small shallow pools can be recognised on the basis of both texture and fossil content textures comprise clotted and microcoprolitic textures bacterial coatings on plant axes that can be stromatolitic and a variety of bacterial and fungal meshworks the crustacean lepidocaris the euthycarcinoid heterocrania the charophyte alga palaeonitella and chytrid fungi are typical elements of the aquatic biota observations of modern hot springs in yellowstone national park wyoming u s a demonstrate that shallow ponds and streams on low angle outwash areas and dormant vent orifices provide suitable environmental analogues textures comparable to those described from rhynie are recorded from yellowstone sinters but examples of the

topographic and ecologic controls on root reinforcement shallow landslides are a significant hazard in steep soil mantled landscapes during intense rainfall events the distribution of shallow landslides is controlled by variations in landscape gradient the frictional and cohesive properties of soil and roots and the subsurface hydrologic response while gradients can be estimated from digital elevation models information on soil and root properties remains sparse we investigated whether geomorphically controlled variations in ecology affect the spatial distribution of root cohesion by measuring the distribution and tensile strength of roots from soil pits dug downslope of 15 native trees in the southern appalachian mountains north carolina united states root tensile strengths from different hardwood tree species were similar and consistently higher than the only native shrub species measured rhododendron maximum roots were stronger in trees found on noses areas of divergent topography relative to those in hollows unchanneled convergent topography coincident with the variability in cellulose content this cellulose variability is likely related to topographic differences in soil water potential for all species roots were concentrated close to the soil surface with roots in hollows being more evenly distributed in the soil column than those on noses trees located on noses had higher mean root cohesion than those in hollows because of a higher root tensile force r maximum had the shallowest weakest roots suggesting that recent expansion of this species due to fire suppression has likely lowered the root cohesion of some hollows quantification of this feedback between physiologic controls on root growth and slope hydrology has allowed us to create a curvature based model of root cohesion that is a significant improvement on current models that assume a spatially averaged value

seismic wave propagation in alluvial basins and influence of site city interaction the geometrical and mechanical features of alluvial deposits have a major influence on seismic wave propagation and amplification however for alluvial basins located in densely urbanized areas the surface structures such as buildings could influence seismic wave propagation near the free surface in this article the influence of surface structures on seismic wave propagation is analyzed numerically in the case of an actual two dimensional 2d shallow basin at a local scale the vibration of a surface structure can induce a seismic wave field in the surficial soil layers at the scale of an alluvial basin the site city models considered herein show that the city effect can lead to a significant seismic wave field modification when compared to the free field case the coincidence between the fundamental frequencies of the soil layers and eigenfrequencies of the surface structures is a key parameter to investigate site city interaction when comparing simplified sitecity models kham et al 2006 to the basin city model the influence of the lateral heterogeneities on the site city interaction is found to be significant indeed the seismic wave field radiated by the city appears to be trapped within the alluvial basin and specific directivity features are found for this wave field the influence of site city interaction on the free field seismic hazard may then be significant the effects of the site city interaction are beneficial in some parts of the city or detrimental in other parts especially city boundaries these effects strongly depend on the urban configuration city heterogeneity building density etc finally the full characterization of the seismic wave field in densely urbanized areas could often raise the need for investigating site city interaction and consider such parameters as basin and city fundamental frequencies building density and city arrangement as well as basin effects combined with the seismic wave field radiated by the city

numerical modeling of seismic site effects in a shallow estuarine bay suai bay shantou china abstract this paper presents the results of numerical modeling of seismic site effects in a shallow estuarine bay suai bay shantou china which is meaning for seismic hazard assessment and mitigation of estuarine and coastal structures such as immersed tunnels pipelines caissons and breakwaters the subsurface stratum and soil properties in the study area are obtained from geological and geotechnical surveys large scale 2d finite element refined nonlinear modeling is used to simulate ground motion for near field and far filed input motions with different design earthquake levels the results show that for the study area 1 the spatial distribution of pga amplification factor presents obvious vertical and horizontal variations and is strongly affected by the overall geometry of interfaces of different materials 2 the attenuation in soft sediments have significant influences on surface ground motion which leads to a deamplification of the acceleration amplitude a prolongation of the significant duration and a filtration of the high frequency spectral content 3 the pga alone cannot be regarded as an adequate parameter to quantify nonlinear site effects while the energy content expressed by arias intensity is more closely related to transfer functions patterns 4 the seismic intensity at surface is greater than the intensity of input motion during weak motions while the seismic intensity at surface is smaller than the intensity of input motion during strong motions suggesting that isolation effects may be expected in the areas having thick soft soils with a low plasticity index during strong motions

seismic site city interaction main governing phenomena through simplified numerical models this work focuses on the analysis of the multiple interactions between soil layers and civil engineering structures in dense urban areas submitted to a seismic wave to investigate such phenomena called site city interaction sci herein two simplified site city configurations are considered a homogeneous periodically spaced city and a heterogeneous nonperiodically spaced city both on a constant depth basin model these 2d boundary element method models are subjected to a vertically incident plane sh ricker wavelet a parametric study of the city parameters density of buildings and their natural frequencies and the thickness of the basin is carried out to characterize the sci and to investigate its sensitivity to some governing parameters the following parameters are analyzed building vibrations induced ground motion ground motion perturbations inside and outside the city spatial coherency and kinetic energy of the urban wave field a so called site city resonance is reached when the soil fundamental frequency and structure eigenfrequencies coincide building vibrations and ground motion are then significantly decreased and the spatial coherency of the urban field is also strongly modified building density and city configuration play a crucial role in the energy distribution inside the city

wood storage within the active zone of a large european gravel bed river wood storage within the active zone of the dynamic gravel bed fiume tagliamento italy was investigated at eight sites along the river s main stem the quantity nature and mode of wood storage revealed a number of trends related to active zone morphology cover type and distance from the river s source relatively small quantities of wood were stored on open gravel surfaces estimates ranged from 1 to 21 t ha 1 intermediate quantities were associated with established islands 24 186 t ha 1 and large quantities were associated with pioneer islands 293 1664 t ha 1 thus variations in the geomorphological style of the river which are associated with changes in these three cover types are reflected in variations in the amount of wood that is stored in different reaches in addition although wood was found in many locations within the active zone it was preferentially stored in three specific locations i bar crests the main open gravel location for wood accumulations and pioneer islands ii the margins and iii surfaces of established islands the proportion of the stored wood that was living sprouting increased downstream and was higher on the open gravel than in association with established islands there was a downstream gradient in the dominant type of wood accumulation individual logs predominated at the most upstream site thereafter on the open gravel whole shrubs and trees dominated the more confined sites in the headwaters and middle reaches whereas jams were the most frequent form of accumulation in the downstream reaches jams were the most frequent type of accumulation associated with established islands throughout the river in contrast to small streams where debris dams constitute the major type of wood accumulation complex patterns and trends of wood storage were revealed along the tagliamento although further studies are needed it is clear that erosion of woody vegetation its subsequent transport and deposition play a major role in structuring the geomorphological and ecological character of this relatively natural large european river system insight into the mechanisms underlying the observed spatial patterns will contribute to a better understanding of the dynamic processes involved and is essential for more effective management of river ecosystems

converted waves in a shallow marine environment experimental and modeling studies seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear wave velocity information but also for improved processing of deeper reflection data these waves generated at deep seas have been used successfully in hydrocarbon exploration however acquisition of good quality converted wave data in shallow marine environments remains challenging we have looked into this problem through field experiments and synthetic modeling a high resolution seismic survey was conducted in a shallow water canal using different types of seismic sources data were recorded with a four component water bottom cable observed events in the field data were validated through modeling studies compressional waves converted to shear waves at the water bot tom and at shallow reflectors were identified the shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments modeling results indicated the presence of a nongeometric shear wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water sediment interface as observed in air gun data this type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source thus these shear waves excited by the source water bottom coupled system kinematically behave as if they were generated by an s wave source placed at the water bottom in a shallow water environment the condition appears to be favorable for exciting such shear waves with nongeometric arrivals these waves can provide useful information of shear wave velocity in the sediments

simulation of the seismic response of sedimentary basins with vertical constant gradient velocity for incident sh waves the simulation of the seismic response of heterogeneous sedimentary basins under incident plane waves is computed using the indirect boundary element method ibem to deal with these kinds of basins we used approximate analytical expressions for the two dimensional green s functions of a medium with constant gradient wave propagation velocity on the other hand for the homogeneous half space underlying the sedimentary basin the full space green s functions were used the response of semi circular heterogeneous basins under incident sh waves is explored by means of the displacements in the frequency space diagrams and synthetic seismograms moreover we compared these results with those obtained for other homogeneous semi circular models the principal differences among them are pointed out this simulation provided interesting results that displayed a complex amplification pattern in a rich spectrum of frequencies and locations the maximum amplitudes levels were found around the edges of the heterogeneous sedimentary basins in time domain some features characterize the seismic response of the basin which include enhanced generation and trapping of surface waves inside the sediments and the reduced emission of seismic energy to the hard rock in the heterogeneous models the lateral reflections of surface waves greatly influence the total displacements at the free surface in comparison with the homogeneous models where the displacements have a shared influence among both vertical and lateral reflections

environment of the early paleozoic vertebrates abstract a comprehensive review of the known pre devonian vertebrate localities suggests that the non marine environment was not invaded until about wenlock early mid silurian time known well dated late cambrian ordovician and early silurian vertebrate localities are all in the marine environment considerations of paleogeography for the pre wenlock indicate that most of the vertebrate localities are too distant from shorelines to provide any basis for transport from the non marine environment to a marine depositional site as a favored explanation the articulated nature of the vertebrates from some of these pre wenlock occurrences also supports this interpretation reconsideration of both the physiological and embryological evidence relative to living vertebrates and some related chordates is also consistent with the view that the vertebrates originated in the marine environment

first plants cooled the ordovician the late ordovician period ending 444 million years ago was marked by the onset of glaciations the expansion of non vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets

nonlinear seismic response in the western l aquila basin italy numerical fem simulations vs ground motion records abstract in the western l aquila basin italy six seismic stations of the italian strong motion network which were used on both soil and rock outcrops recorded a huge amount of weak and strong motion data near an active fault during the 2009 l aquila seismic sequence this paper analyzes the ground motion records of events with magnitudes ranging between 1 6 and 6 3 and compares the observed peak accelerations and the h v and v h spectral ratios with those revealed from numerical simulations the finite element method is considered herein to perform 2d dynamic modeling on a geologic cross section of the upper aterno river valley which is 1000 m wide and 50 m deep based on the reviewed geologic geotechnical and geophysical investigations that were performed in previous studies the martin finn seed s pore water pressure model is used in the simulations the observed peak accelerations the frequencies and the levels of maximum amplification are correctly estimated using the fem simulations the consistency between the computed and the experimental results shows a seismic response that is sensitive to the level of earthquake magnitude and mainly depends on the rock and soil elastic and dynamic properties the intensity and the depth of the seismic impedance contrast the water table depth the two dimensional irregular configuration the dip angle of strata the shape and the frequency content of the input motion record the seismic motion amplification is usually higher at station aqv which is located near the valley center where a peak acceleration value of 0 66 g was recorded both the pga amplification factor and the maximum amplification frequency of the horizontal component decrease when the earthquake magnitude level increases which shows a nonlinear seismic response at the stations aqg on fractured and weathered rock aqa and aqv on alluvium the simulation of the 2009 mw 6 3 l aquila earthquake confirms the observed nonlinear effective stress behavior and allows us to relate it to the generation of excess pore water pressure which ranges between 50 and 300 kpa

eolian action and the distribution of cambrian shales in north america prolonged eolian action on the barren prevegetation craton provides a better explanation for the absence of shale in the cambrian and lower ordovician orthoquartzite carbonate suite of east central and arctic north america than does marine bypassing it is hypothesized that paleo trade winds transported much of the missing silt and clay to the southern and western united states and southwestern canada while the remainder diffused radially off the craton under the influence of variably directed storm winds the distribution of shale in the sauk sequence supports this and indicates that the orthoquartzite carbonate suite of upwind regions is replaced by a shale carbonate suite in downwind areas

biologically mediated weathering in modern cryptogamic ground covers and the early paleozoic fossil record specific micro weathering features and biochemically derived residues formed by living organisms can be used as biomarkers to infer the presence of biological communities within sedimentary units of ancient ecosystems we examined basaltic soil minerals from modern cryptogamic ground covers cgcs in iceland and compared these with two early paleozoic fossil systems nine biologically mediated weathering features bwfs were identified in modern soils including micron scale surface trenching and penetrative tunnels which are attributed to the actions of bacteria fungi and exudates specific bwfs are associated with fe residues and with fe rich bio precipitated nodules further putative comparable features and fe enrichment are identified in palaeosols from the late silurian llansteffan south wales and the early devonian rhynie chert scotland although we are cautious about attributing biological affinity to individual isolated features our results demonstrate the potential of using multiple bwf types as a collective together with their chemical signatures as new proxies to understand community structure and interactions in early terrestrial ecosystems this new information is the first evidence of interactions between ancient cgc like organisms and substrate or soil inorganic components in the fossil record and demonstrates the ability of cgc like biospheres to contribute to mineral weathering soil development and biogeochemical cycling during the early paleozoic supplementary material fieldwork geomorphological information and triplot sem eds data are available at https doi org 10 6084 m9 figshare c 4373717

effects of vegetation on braided stream pattern and dynamics 1 investigations using a 16 m by 2 m recirculating experimental flume model of an ephemeral braided river indicate that the presence of large and erosion resistant plants within the channel e g trees or shrubs can have a significant impact on channel pattern and planform dynamics simulations show that these plants have two effects first they act as obstructions in some cases forcing the flow to divide this flow separation can allow the deposition of a small island immediately in the lee of the plant splitting the channel the net result is a substantial increase in the number of channels and correspondingly the braid index this is in direct contrast to previous studies where increased levels of vegetation in perennial streams have decreased the braid index second the plants stabilize braid bars and can form relatively stable islands in their lee significantly reducing the longitudinal migration of islands typically associated with braided rivers

theoretical analysis of non geometric ps waves recorded at the water bottom interface when a seismic source is placed in the water at a height less than a wavelength from the water solid interface a prominent s wave arrival can be observed it travels kinematically as if it was excited at the projection point of the source on the interface this non geometric s wave has been investigated before mainly for a free surface configuration however as was shown in a field experiment the non geometric swave can also be excited at a fluid solid configuration if the s wave speed in the solid is less than the sound speed in the water the amplitude of this wave exponentially decreases when the source is moved away from the interface revealing its evanescent character in the fluid in the solid this particular converted mode is propagating as an ordinary s wave and can be transmitted and reflected as such there is a specific region of horizontal slownesses where this non geometric wave exists depending on the ratio of the s wave velocity and the sound speed of water only for ratios smaller than 1 this wave appears lower ratios result in a wider region of appearance due to this property this particular p s converted mode can be identified and filtered from other events in the radon domain

comparing petrographic signatures of bioalteration in recent to mesoarchean pillow lavas tracing subsurface life in oceanic igneous rocks abstract bioalteration of basaltic glass in pillow lava rims and glassy volcanic breccias hyaloclastites produces several distinctive traces including conspicuous petrographic textures these biologically generated textures include granular and tubular morphologies that form during glass dissolution by microbes and subsequent precipitation of amorphous material such bioalteration textures have been described from upper in situ oceanic crust spanning the youngest to the oldest oceanic basins 0 170 ma the granular type consists of individual and or coalescing spherical bodies with diameters typically around 0 4 m these are by far the most abundant having been traced up to 550 m depths in the oceanic crust the tubular type is defined by distinct straight to irregular tubes with diameters most commonly around 1 2 m and lengths exceeding 100 m the tubes are most abundant between 50 m and 250 m into the volcanic basement we advance a model for the production of these bioalteration textures and propose criteria for testing the biogenicity and antiquity of ancient examples similar bioalteration textures have also been found in hyaloclastites and well preserved pillow lava margins of phanerozoic to proterozoic ophiolites and archean greenstone belts the latter include pillow lavas and hyaloclastites from the mesoarchean barberton greenstone belt of south africa and the east pilbara terrane of the pilbara craton western australia where conspicuous titanite mineralized tubes have been found petrographic relationships and age data confirm that these structures developed in the archean thus these biologically generated textures may provide an important tool for mapping the deep oceanic biosphere and for tracing some of the earliest biological processes on earth and perhaps other planetary surfaces

ichnotaxonomy of microbial trace fossils in volcanic glass abstract ancient microbial activity in volcanic glass creates micron sized cavities that can be regarded as trace fossils these are common in glassy rims of oceanic pillow lavas and volcanic breccias morphologically comparable mineralized traces are also found in meta volcanic glasses from ophiolites and precambrian greenstone belts multiple lines of evidence indicate microbial formation of these borings although the affinity of the trace maker s is poorly constrained two broad morphological types have been previously recognized and termed granular9 and tubular9 bioalteration textures here optical microscopy and sem observations are used to erect two new ichnogenera granulohyalichnus igen nov and tubulohyalichnus igen nov five ichnospecies are also defined granulohyalichnus vulgaris isp nov a granular species tubulohyalichnus simplus isp nov an unornamented tubular species tubulohyalichnus annularis isp nov an annulated tubular species tubulohyalichnus spiralis isp nov a helicoidal tubular species tubulohyalichnus stipes isp nov a branched tubular species this systematic taxonomy is advanced to allow reliable comparisons to be made between new and existing reports of these microbial borings moreover the adoption of a taxonomic framework will aid the development of these ichnofossils as palaeoenvironmental indicators and tracers of microbial evolution

cellular dissolution at hypha and spore mineral interfaces revealing unrecognized mechanisms and scales of fungal weathering fungus mineral interactions play unparalleled roles in shaping the planet earth but are underappreciated relative to bacterial influences unique to fungus but largely unknown are the interfacial processes and extensiveness of hypha versus spore mineral interactions given the associated turgor pressure differences and the vast contact areas between mycelia and minerals in the critical zone here we examine lizardite mg3si2o5 oh 4 dissolution by single cells of a native fungal strain using confocal laser scanning microscopy atomic force microscopy and transmission electron microscopy energy dispersive x ray spectroscopy to explore the mechanism driving force and magnitude of the interfacial reactions results from our inspection showed 1 significant ph reduction in the vicinity of cells upon mineral surface attachment 2 exclusive fe loss from the mineral at the cell mineral interfaces and 3 destruction of the mineral crystal structure below the area colonized by hyphae but not that by spores compared to the results from bulk experiments and at the mineral water interface these observations indicate that 1 only attached cells release siderophores and 2 biomechanical forces of hyphal growth are indispensable for fungal weathering and strong enough to breach the mineral lattice estimated mineral mass loss at the interface suggests that cellular dissolution can ultimately account for 40 50 of the overall bio weathering significantly larger than the previous estimate of 1 contribution

in channel woody vegetation controls on sedimentary processes and the sedimentary record within alluvial environments a modern example of an anabranch of the river loire france a multidisciplinary approach was used to analyse the role of pioneer trees populus nigra on bar formation in the modern fluvial system of the river loire france data were collected on seven plots located on a secondary channel chosen for their vegetation cover and their sedimentary context physical features of vegetation topographical evolution sediment grain size and flow velocity were investigated during and after floods between 2001 and 2003 woody vegetation responds morphologically to fast flowing waters and sediment deposition these adaptations influence the role played by trees on local sedimentary processes some morphological types of trees exert a strong influence during flood events by deflecting reducing or increasing the flow energy as a consequence the evolution of bedforms distribution of sediment grain size and slopes are controlled by the flood type the morphological context i e high or low energy zones the morphology of the vegetated bar and the characteristics of vegetation conceptual models are proposed to account for local processes and evolution of tree groves the first model which describes the behaviour of groves during a single flood underlines the sediment deposition downstream of the trees and the trapping of bedload sediments during the falling stage of the flood the reorientation of current streams constrained by both local bed topography and woody vegetation induces transverse sediment fluxes for these water levels the control exerted by trees on small scale sedimentary processes becomes significant the second model shows the evolution of vegetation bands over several flood events in particular it describes the influence of vegetation on the fixing and reworking of bedload sediments during the falling limb of the hydrograph the coalescence of vegetation induced bedforms and the resulting morphological changes increase the deflection power of the vegetated bar inducing the deposition of finer sediments

possible climate variability in the lower old red sandstone conigar pit sandstone member early devonian south wales uk abstract the early devonian conigar pit sandstone member cpsm of the freshwater west formation lower old red sandstone lochkovian age at freshwater west in south wales comprises a heterolithic predominantly alluvial suite mudstones fine to coarse grained sandstones conglomerates with varying depositional architecture a number of discrete facies associations are observed the fine grained inclined and non inclined heterolithic association is dominant within the cpsm it represents dryland sinuous channelized flow ihs bedsets and unconfined flow non inclined bedsets at terminal and intermediate floodouts deposited under semi arid conditions mudstones were deposited in two distinct environments associated with this semi arid river system laminated and burrowed reddish brown mudstones were deposited in shallow semi permanent lakes or pools on the floodplain massive mudstones were deposited as within channel muddy braid bars with sedimentary structures being lost during subsequent compaction the mudstones exhibit vertisol pedogenesis reflecting the seasonal wetting and drying associated with the semi arid climate periods of intense desiccation are indicated by deep desiccation cracks and associated rubbly surfaces possible though unproven tidal conditions influenced a small percentage of the heterolithic channels at freshwater west the extent of these channels is uncertain the coarser grained multi storey sandstone association was deposited by low sinuosity rivers with a fluctuating but perennial discharge associated with these laterally extensive sandbodies was a high water table with surface ponding wetlands that enabled the preservation of plant detritus during high discharge events flow expanded over the contemporaneous floodplain depositing the sheet sandstone association within splay complexes the interpretation that perennial discharge may have been triggered by basin wide climate change challenges the long held view that the lower ors climate was continuously semi arid in nature the spatial temporal extent of this climate change is uncertain as it is possible that the multi storey sandbodies were deposited by allogenic rivers draining a distant possibly uplifted source area a decrease in the observed frequency and maturity of vertisol profiles and a corresponding increase in multi storey sandbodies upward through the succession may reflect a long term episodic pattern of climate change

computation of ground motion amplification scenario in nct delhi for earthquake engineering purposes and seismic microzonation this paper presents a scenario for the spatial variation of the fundamental frequency of the sediment deposits above the basement and the corresponding amplification as well as the average spectral amplification in different frequency bandwidths for the national capital territory delhi the capital of india the exposed central quartzite ridge and the yamuna river channel are responsible for very large spatial variations of the fundamental frequency in the eastern part of the national capital territory delhi at 20 of the considered sites a good match is obtained between the fundamental frequency computed numerically using available s wave velocities to a certain depth and their extrapolation and that obtained experimentally the computed fundamental and dominant frequencies reveal that both medium rise 5 10 storey and high rise 10 storey buildings in the western part and medium rise buildings lying in the localities east of or very near to the yamuna river may suffer heavy to very heavy damage due to the occurrence of the double resonance phenomenon furthermore 1 2 storey buildings lying on the weathered exposed quartzite rock may also suffer heavy damage during local earthquakes because of the occurrence of double resonance the possible reasons behind the lack of earthquake damage to the qutab minar the tallest brick masonry minaret in the world over the last 800 years may be the nonoccurrence of double resonance and almost no amplification in the low frequency range there are two localities in the western part of the national capital territory delhi namely kanganheri chhawla and buradi wherein all sorts of buildings are highly vulnerable to earthquake damage for the closed chhatarpur basin and a semiclosed basin to its northeast formed due to exposed quartzite rock three dimensional 3d simulations are required to predict the characteristics of basin generated surface waves and their focusing effects in the chhatarpur basin the average spectral amplification map developed for the 0 10 hz bandwidth depicts a range of 2 25 4 82 in the national capital territory delhi and may be directly used to transfer the estimated seismic hazard at basement to the free surface

carbon isotopes support the presence of extensive land floras pre dating the origin of vascular plants abstract multiple lines of evidence indicate that earth s land masses became green some 2 7 ga ago about 1 billion years after the advent of life about 2 2 billion years later land plants abruptly appear in the fossil record and diversify marking the onset of ecologically complex terrestrial communities that persist to the present day given this long history of land colonization surprisingly few studies report direct fossil evidence of emergent vegetation prior to the continuous record of life on land that starts in the mid silurian ca 420 425 ma ago here we compare stable carbon isotope signatures of fossils from seven ordovician silurian 450 420 ma old appalachian biotas with signatures of coeval marine organic matter and with stable carbon isotope values predicted for ordovician and silurian liverworts bryocarb model the comparisons support a terrestrial origin for fossils in six of the biotas analyzed and indicate that some of the fossils represent bryophyte grade plants our results demonstrate that extensive land floras pre dated the advent of vascular plants by at least 25 ma the appalachian fossils represent the oldest direct evidence of widespread colonization of continents these findings provide a new search image for macrofossil assemblages that contain the earliest stages of land plant evolution we anticipate they will fuel renewed efforts to search for direct fossil evidence to track the origin of land plants and eukaryotic life on continents further back in geologic time

evolution of alluvial mudrock forced by early land plants mudrocks are a primary archive of earth s history from the archean eon to recent times and their source to sink production and deposition play a central role in long term ocean chemistry and climate regulation using original and published stratigraphic data from all 704 of earth s known alluvial formations from the archean eon 3 5 billion years ago to the carboniferous period 0 3 billion years ago we prove contentions of an upsurge in the proportion of mud retained on land coeval with vegetation evolution we constrain the onset of the upsurge to the ordovician silurian and show that alluvium deposited after land plant evolution contains a proportion of mudrock that is on average 1 4 orders of magnitude greater than the proportion contained in alluvium from the preceding 90 of earth s history we attribute this shift to the ways in which vegetation revolutionized mud production and sediment flux from continental interiors

paleozoic vegetation and the siluro devonian rise of fluvial lateral accretion sets a long standing hypothesis links the increased prominence of meandering rivers in the middle paleozoic to the colonization of terrestrial environments by vegetation this hypothesis is tested using a data set of cambrian to devonian fluvial literature and field examination of key stratigraphic units according to some researchers cambrian to mid silurian river systems were braided in planform with a sharp increase in the abundance of meandering rivers during the silurian devonian although meandering systems were largely identified on the basis of thick mudstones and organized channel deposits the data set record of lateral accretion sets appears to be a robust proxy for the abundance of meandering river point bars lateral accretion is first recorded from pridolian lochkovian strata but is noted in nearly 40 of fluvial case studies by the famennian this trend matches the known record of rooted vegetation suggesting that vegetation progressively stabilized river banks and promoted single thread channels however the presence of precambrian and extraterrestrial meandering systems indicates that vegetation is not essential for meandering and the lack of evidence for cambrian to silurian ludlow point bars is surprising if originally present they may largely have been destroyed by extreme floods chute cut offs in coarse grained meandering systems and eolian activity

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes