incised channel fills containing conifers indicate that seasonally dry vegetation dominated pennsylvanian tropical lowlands the idea that the pennsylvanian tropical lowlands were temporally dominated by rainforest i e the coal forest is deeply ingrained in the literature here we challenge two centuries of research by suggesting that this concept is based on a taphonomic artifact and that seasonally dry vegetation dominated instead this controversial finding arises from the discovery of a new middle pennsylvanian moscovian fossil plant assemblage in southeast illinois united states the assemblage which contains xerophytic walchian conifers occurs in channels incised into a calcic vertisol below the baker coal these plants grew on seasonally dry tropical lowlands inferred to have developed during a glacial phase this xerophytic flora differs markedly from that of the typical clubmoss dominated coal forest developed during deglaciation events although preserved only very rarely we argue that such xerophytic floras were temporally as dominant and perhaps more dominant than the iconic coal forests which are overrepresented in the fossil record due to taphonomic megabias these findings require the iconography of pennsylvanian tropical lowlands to be redrawn

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

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

transitional changes in arborescent lignophytes at the devonian carboniferous boundary abstract it is usually considered that after the extinction of the devonian tree archaeopteri s no new arborescent lignophytes were established before the late tournaisian a reassessment of this pattern is presented here based on a three fold approach a re evaluation of the taxic diversity of tournaisian lignophyte trees based on descriptions of new plants from palaeotropical latitudes a study of the patterns of phenotypic changes occurring among early lignophytes using a principal coordinate analysis and a phylogenetic analysis of the affinities of the arborescent taxa the best supported results indicate that a substantial taxonomic and phenotypic diversity of arborescent lignophytes was already established in the first part of the tournaisian including some taxa that persisted until the serpukhovian two genera may have originated in the late devonian and crossed the devonian carboniferous boundary fewer originations and a decrease in phenotypic diversity occurred in the visean the phenotypic distinctiveness of tree stems compared with those of other growth forms in the lignophytes is assessed we propose a scenario in which the presence of lignophyte trees is continuous across the devonian carboniferous boundary with arborescent taxa distinct from archaeopteris already present in the latest devonian possibly in upland floras and diversifying significantly soon after the devonian carboniferous boundary supplementary material a list of taxa characters and matrices used in the principal coordinate analysis and phylogenetic analysis is available at http www geolsoc org uk sup18447

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

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

sex that moves mountains the influence of spawning fish on river profiles over geologic timescales abstract a key component of resilience is to understand feedbacks among components of biophysical systems such as physical drivers ecological responses and the subsequent feedbacks onto physical process while physically based explanations of biological speciation are common e g mountains separating a species can lead to speciation less common is the inverse process examined can a speciation event have significant influence on physical processes and patterns in a landscape when such processes are considered such as with ecosystem engineers many studies have focused on the short term physical and biological effects rather than the long term impacts here we formalized the physical influence of salmon spawning on stream beds into a model of channel profile evolution by altering the critical shear stress required to move stream bed particles we then asked if spawning and an adaptive radiation event similar to the one that occurred in pacific salmon species could have an effect on channel erosion processes and stream profiles over geological timescales we found that spawning can profoundly influence the longitudinal profiles of stream beds and thereby the evolution of entire watersheds the radiation of five pacific salmon from a common ancestor additionally could also cause significant geomorphic change by altering a wider section of the profile for a given distribution of grain sizes this modeling study suggests that biological evolution can impact landscape evolution by increasing the sediment transport and erosion efficiency of mountain streams moreover the physical effects of a species on its environment might be a complementary explanation for rapid radiation events in species through the creation of new habitat types this example provides an illustrative case for thinking about the long and short term coupling of biotic and abiotic systems

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

sedimentology and paleontology of a carboniferous log jam a localized sandstone split in the mary lee coal early pennsylvanian langsettian of the black warrior basin alabama has a channel form geometry and preserves a concentrated log and gravel pebbles cobbles and boulders assemblage at the top of the fill sequence gravel lithotypes within and amongst rooting structures of lycopsid cordaitean and calamitean trees are indicative of an appalachian orogenic provenance and support an allochthonous origin for some of the logs in addition a skolithos ichnological assemblage within the channel is indicative of opportunist colonization during channel fill a low sinuosity geometry characterizes the overall channel form belt exhibiting a general northwesterly trend paleocurrent measurements from the cross bedded sandstone at the margin of the channel belt indicate flow was to the northwest log orientations at these sites are subperpendicular to perpendicular to the overall sediment transport direction and are interpreted to represent an ancient log jam the genesis of the fluvial channel the introduction and emplacement of the concentrated log assemblage the effects of this floating log accumulation on sedimentation within the channel and the relationship between paleocurrent and log orientation are discussed the red river located in the southern united states is used as a modern analog for comparative purposes

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

functional ecomorphology feedbacks between form and function in fluvial landscape ecosystems abstract the relationship between form and function has been a central organizing principle in biology throughout its history as a formal science this concept has been relevant from molecules to organisms but loses meaning at population and community levels where study targets are abstract collectives and assemblages ecosystems include organisms and abiotic factors but ecosystem ecology too has developed until recently without a strong spatially explicit reference landscape ecology provides an opportunity to once again anneal form and function and to consider reciprocal causation between them this ecomorphologic view can be applied at a variety of ecologically relevant scales and consists of an investigation of how geomorphology provides a structural template that shapes and is shaped by ecological processes running water ecosystems illustrate several principles governing the interaction of landscape form and ecological function subsumed by the concept of functional ecomorphology particularly lucrative are ecosystem level interactions between geologic form and biogeochemical processes integrated by hydrologic flowpaths while the utility of a flowpath based approach is most apparent in streams spatially explicit biogeochemical processing pervades all landscapes and may be of general ecological application

severe selenium depletion in the phanerozoic oceans as a factor in three global mass extinction events abstract selenium se is one of the key trace elements required by all animal and most plant life and se deficiencies in the food chain cause pathologies or death here we show from new geochemical analyses of trace elements in phanerozoic marine pyrite that sustained periods of severe se depletion in the past oceans correlate closely with three major mass extinction events at the end of the ordovician devonian and triassic periods these represent periods of se depletion 1 5 2 orders of magnitude lower than current ocean abundances being within the range to cause severe pathological damage in extant se reliant organisms se depletion may have been one of several factors in these complex extinction scenarios recovery from the depletion extinction events is likely part of a natural marine cycle although rapid rises in global oxygen from sudden major increases in marine productivity and plant biomass after each extinction event may also have played a crucial role

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

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

first steps on land arthropod trackways in cambrian ordovician eolian sandstone southeastern ontario canada basal terrestrial deposits in the cambrian ordovician nepean formation potsdam group near kingston ontario contain arthropod produced trackways that extend the record of the first arthropod landfall back by as much as 40 m y the presence of large simple cross beds and of wind produced structures including adhesion ripples and wind ripple lamination indicates that the host strata were deposited in an eolian dune field probably in a marginal marine setting the trackways were preserved mainly as undertracks and record the activities of large amphibious arthropods possibly euthycarcinoids

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

evolution of fixed channel alluvial plains in response to carboniferous vegetation the establishment of terrestrial plants during the palaeozoic era was one of the most significant changes to the earth system during the phanerozoic eon the continuing evolution and expansion of land plants irrevocably altered the alluvial landscape the broad unconfined and unconsolidated blankets of coarse sediment found at the start of the cambrian period were replaced by a diverse array of braided and meandering channel styles and stable floodplains by the end of the devonian period here we show that the first appearance of a sedimentary facies suite attributed to low energy organic rich river systems with multiple channels and stable alluvial islands known as anabranching or anastomosing rivers occurred during the carboniferous period our field studies and literature review demonstrate that the appearance of these rivers coincides with the continuing evolution of tree like plants we suggest that increased floodplain stability and new triggers for channel avulsion were provided by the increase in complexity and diversity of root assemblages density of floodplain forests and production of woody debris associated with expansion of arborescence we conclude that the expansion of tree habitats led to the crossing of a threshold in vegetative control of floodplain and river morphology during the carboniferous

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

the effect of melt distribution on the rheology of plagioclase rocks abstract synthetic plagioclase aggregates were fabricated by hot isostatic pressing glass powder with an60ab40 composition at a confining pressure of 300 mpa and a temperature of 1223 k the residual glass content 15 vol was reduced to 1 3 vol by annealing the specimens at temperatures between 1423 and 1523 k at 0 1 mpa high resolution electron microscopy showed that the residual glass was confined to grain triple junctions when these samples were annealed at 0 1 mpa and above the solidus 1620 k they also contained silica rich amorphous phases at grain boundaries other samples were hot pressed at 1423 k they often have grain boundaries containing thin amorphous films 5 50 nm wide the chemical composition of the films differs from pure labradorite with up to 80 wt sio2 the volume fraction of si rich glass increases up to 2 vol for samples that contain 1 wt water uniaxial creep experiments were performed at temperatures of 1373 1638 k and stresses between 2 and 50 mpa the plagioclase aggregates deformed by grain size sensitive creep with a stress exponent n 1 the activation energy for grain boundary diffusion controlled creep of the partially molten aggregates was 400 20 kj mol 1 it remained unchanged with varying glass content and glass topology the strength of samples containing glass along grain boundaries is 4 10 times less than without amorphous grain boundary films the transition between diffusion and dislocation creep is shifted towards higher stresses for samples that contain glass films at grain boundaries

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

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

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

oxygen isotopic evolution of the solar nebula studies of the three oxygen isotopes in chondrite meteorites demonstrate that diverse o reservoirs characterized by their 17o values were present in the solar nebula the discovery that some chondritic materials have o isotopic compositions that cannot be explained by mass dependent fractionation of an initially well mixed reservoir has important implications for the history of the solar nebula on a plot of 17o versus 18o or 17o 16o versus 18o 16o terrestrial samples with the main exception of stratospheric ozone fall along a single line the terrestrial fractionation or tf line having a slope 0 52 an indication that the parental reservoir was homogenized a convenient measure of o isotopic heterogeneity is the deviation from the tf line 17o 17o 0 52 18o a popular model to explain the evolution of chondritic oxygen compositions during nebular and asteroidal aqueous alteration processes calls for the nebula to have formed from solids having 18o 40 and 17o 41 17o 20 and a gas having a composition roughly estimated to be 18o 30 and 17o 24 17o 9 this model encounters serious difficulties when examined in detail in particular it cannot readily account for the o isotopic compositions of both chondrules and refractory inclusions from individual chondrite groups or for the differences between groups particularly in the compositions of chondrules magnetite fe3o4 is a key phase for o isotope studies because during its formation by the oxidation of ferrous metal or fes all o comes from the oxidant probably h2o it appears that most and possibly nearly all magnetite formed during aqueous alteration processes that occurred in asteroids in all chondrite groups studied to date 17o of the magnetite is greater than or equal to that of the chondrule silicates if the h2o originated in the ambient local nebula then at the time of accretion the 17o of the nebular gas was generally higher than that of the solids an alternative view is that the heterogeneity in the o isotopic composition of chondrites indicates that the nebula formed from diverse batches of presolar materials the precise o isotopic composition of the mix varying during the accretion history of the nebula the large compositional gaps between groups suggest that agglomeration of nebular dust to form chondrites did not proceed at a constant rate but that periods with turbulence levels low enough to allow agglomeration were punctuated by periods of high turbulence during which the composition of the inner nebula sampled by chondrites changed appreciably

aeolian to marine transition in cambro ordovician cratonic sheet sandstones of the northern mississippi valley u s a cratonic quartz sandstones have presented several intractable problems besides their extreme textural and compositional maturity and paucity of shale their sheet like geometry is particularly notable if the sandstones were entirely marine as long supposed such geometry is difficult to explain in terms of modern shelf sediments which are generally held to be either relict or only slightly reworked by the holocene transgression palimpsest re study of two quartz sandstones in the northern mississippi valley region reveals evidence for significant non marine deposition followed by varying degrees of marine reworking during transgressions facies patterns are similar in the cambrian wonewoc and ordovician st peter sandstones both of which overlie unconformities in both a large scale cross stratified facies believed to represent aeolian ergs passes laterally into a planar and channelled facies inferred to represent sand plains composed of braided fluvial and aeolian sand sheet deposits criteria of aeolian deposition in both facies include adhesion structures large ripple index fine climbing translatent lamination grainfall and grainflow stratification criteria of braided fluvial deposition include shallow channels containing sequences of thinning upward sets of trough cross stratification reactivation surfaces low index ripples and polygonal cracks probable aeolian sand sheets contain flat bedding punctuated by small channels adhesion structures and coarse sand ripples with large index there is a conspicuous absence of trace and body fossils from these inferred non marine deposits in contrast is a burrowed and trough cross stratified facies characterized by medium scale cross bedding alternating with bioturbated intervals and rare brachiopod or trilobite mould coquinas which is interpreted as shallow marine in both formations this last facies replaces laterally and overlaps the other two reflecting transgression and variable reworking the main areas of non marine deposits in both formations are capped by a thin burrowed subfacies that represents the culmination of each transgression that is a stillstand during which sediment influx ceased and both physical winnowing and bioturbation were intense it is suggested that the sheet like geometry of many cratonic quartz sandstones is due primarily to initial sand dispersal by aeolian and fluvial processes that such processes must have been orders of magnitude more important on pre devonian vegetation free landscapes than they have been since not only helps to explain the sheet like character but also the exceptional maturity of the older cratonic sandstones

applications of algebraic reconstruction techniques to crosshole seismic data tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data the experiments were carried out at the retsoff salt mine in new york and at the underground radioactive waste study site at the stripa mine facility in sweden the traveltimes at restoff were high quality and were obtained over raypaths of up to 500 m in length the structure was quite complicated with velocity contrasts up to 50 percent the stripa site was in granitic rock with velocity contrasts of only a few percent the dimensions of the experiment were small with maximum ray lengths of just over 10 m the data at this site were collected with very high accuracy source and receiver locations were measured to better than 1 0 mm and traveltimes were read to 0 001 ms a number of algorithms similar to the algebraic reconstruction techniques art used in medical imaging have been applied to the data some modifications of the algorithms such as the application of weighting schemes damping parameters and curved raypaths were performed the resulting velocity fields were compared to the known fields and with each other to determine an optimal method the algorithms were found to be a rapid reliable means of reconstructing the slowness field of real data low velocity zones were recovered with accuracy in location and value it was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken otherwise poor reconstructions will result

oxygen diffusion in an fe rich basalt melt abstract the self diffusion of oxygen has been measured in an feti basalt melt at one atmosphere from 1320 1500 c under different oxygen fugacities diffusivities were determined by measuring isotopic exchange between spheres of melt and flowing oxygen in a vertical tube furnace the oxidation state of the melt was varied by performing experiments in either o2 or co2 gas the diffusion data for experiments in both gases can be fit to the equation d 1 4 10 exp 60 7 10 3 rt cm 2 s the observed self diffusivities for oxygen in the basalt melt are one to two orders of magnitude lower than published chemical diffusivities at one atmosphere diffusivities in basalt melt at each temperature in o2 and co2 gas are similar within experimental error 0 2 log d units at the 1 level and indicate that oxygen self diffusion is insensitive to the oxidation state of fe in natural basalt melts the redox independence of oxygen self diffusion observed in this study suggests that oxygen transport in natural magmas will not be significantly affected by changes in their redox state caused by degassing and or crystallization

vegetation as a major conductor of geomorphic changes on the earth surface toward evolutionary geomorphology earth surface processes and landforms may have coadjusted with plant morphology biomechanics and life history we suggest that the colonization of land by plants at the early silurian and their propagation inside continents represent critical phases of the coupling between geomorphic and biological processes on the earth at a global scale the consideration of this coupling involving geomorphic biological feedback mechanisms at the scales of ecological succession and organisms evolution may promote the emergence of an evolutionary geomorphology copyright 2009 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

crossvalidation method for crosswall seismic tomography crosswell seismic tomography is used to determine the variation of elastic wave velocity or attenuation between two boreholes and if possible boreholes and the surface from which they are drilled in a transmission tomographic survey traveltimes or amplitudes are measured for many raypaths between the boreholes and the surface the data are inverted for velocity and attenuation respectively in this paper we only discuss traveltimes but the methods are equally applicable to amplitude inversions

crosswell traveltime tomography in three dimensions conventional crosswell direct arrival traveltime tomography solves for velocity in a 2 d slice of the subsurface joining two wells many 3 d aspects of real crosswell surveys including well deviations and out of well plane structure are ignored in 2 d models we present a 3 d approach to crosswell tomography that is capable of handling severe well deviations and multiple profile datasets three dimensional pixelized models would be even more seriously underdetermined than the pixelized models that have been used in 2 d tomography we therefore employ a thinly layered vertically discontinuous 3 d velocity model that greatly reduces the number of model parameters the layers are separated by 2 d interfaces represented as 2 d chebyshev polynomials that are determined using a priori structural information and remain fixed in the traveltime inversion the velocity in each layer is also represented as a 2 d chebyshev polynomial unlike pixelized models that provide limited vertical resolution and may be overparameterized horizontally this 3 d model provides vertical resolution comparable to the scale of wireline logs and reduces the degrees of freedom in the horizontal parameterization to the expected in line and out of well plane horizontal resolution available in crosswell traveltime data ray tracing for the nonlinear traveltime inversion is performed in three dimensions the 3 d tomography problem is regularized using penalty constraints with a continuation strategy that allows us to extrapolate the velocity field to a 3 d region containing the 2 d crosswell profile although this velocity field cannot be expected to be accurate throughout the 3 d region it is at least as accurate as 2 d tomograms near the well plane of each 2 d crosswell profile futhermore multiple profile crosswell data can be inverted simultaneously to resolve better the 3 d distribution of velocity near the profiles our velocity parameterization is quite different from pixelized models so resolution properties will be different using wave modeled synthetic data we find that near horizontal raypaths have the largest mismatch between ray traced traveltimes and traveltimes estimated from the data in conventional tomography horizontal raypaths are essential for high vertical resolution with our model however the highest resolution and most accurate inversions are achieved by excluding raypaths that travel nearly parallel to the geologic layering we perform this exclusion in both a static and model based manner we apply our 3 d method to a multiple profile crosswell survey at the cymric oil field in california an area of very steep structural dips and significant well trajectory deviations results of this multiple profile 3 d tomography correlate very well with the independently processed single profile results with the advantage of an improved tie at the common well

darwinian origin of landforms whilst earth surface landforms evolve largely as a result of the activity of certain living organisms the biologically driven geomorphic changes have evolutionary consequences on organisms and ecological communities recognition of complex biotic abiotic feedbacks may lead to deep changes in our understanding of geomorphology copyright 2007 john wiley sons ltd

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

pennsylvanian coniferopsid forests in sabkha facies reveal the nature of seasonal tropical biome pennsylvanian fossil forests are known from hundreds of sites across tropical pangea but nearly all comprise remains of humid coal forests here we report a unique occurrence of seasonally dry vegetation preserved in growth position along 5 km of strike in the pennsylvanian early kasimovian missourian of new mexico united states analyses of stump anatomy diameter and spatial density coupled with observations of vascular traces and associated megaflora show that this was a deciduous mixed age coniferopsid woodland 100 trees per hectare with an open canopy the coniferopsids colonized coastal sabkha facies and show tree rings confirming growth under seasonally dry conditions such woodlands probably served as the source of coniferopsids that replaced coal forests farther east in central pangea during drier climate phases thus the newly discovered woodland helps unravel biome scale vegetation dynamics and allows calibration of climate models

fluvial processes in a forested anastomosing river flood partitioning and changing flow patterns in an effort to further our understanding of multiple channel systems this paper presents data on the flood response of channels in one of the last wooded semi natural anastomosing systems in europe the gearagh ireland is characterized by hundreds of small islands separated by interconnected channels of low slope these include channels that cross islands at right angles to the main flow and blind anabranching channels islands are relatively stable and wooded with evidence of division by channel erosion and growth by in channel sedimentation four active zone cross profiles were surveyed each containing between seven and 13 channels velocities were measured in several channels before and during two separate floods from these observations channels have been categorised into three types fast shallow and trapezoidal slow deep and more irregular and flood channels during the floods interchannel flows were caused by variations in water surface elevations due to backing up behind debris dams and it is suggested that this is the origin of the anomalous cross island channels and one cause of island division another potential cause of island division blind anabranching channels is the result of concentrated bank scour between root masses biotic components such as debris dams tree root masses and tree throw pits play a key role in the partitioning of flow and cause variations in channel velocities and the overbank velocity distribution the implications of these observations for channel pattern maintenance are briefly discussed

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

the campbellton formation new brunswick canada paleoenvironments in an important early devonian terrestrial locality strata of the campbellton formation nearly 1 km thick and known for its diverse fossil assemblage of early plants arthropods and fish can be divided into six facies associations 1 restricted lacustrine 2 marginal lacustrine 3 near shore lacustrine 4 coastal deltaic 5 sandy to gravelly alluvial plain and 6 gravelly proximal alluvial environments lacustrine deposits with restricted circulation due to depth or stagnation are fine grained with preserved organic material the marginal lacustrine association consists of massive siltstone and very fine sandstone interbedded with conglomerate the latter are interpreted to have shed from older volcanic units forming the basin walls the near shore lacustrine association is characterized by rippled sandstone with microbialites alluvial strata include interbedded imbricate to nonimbricate conglomerate trough cross stratified sandstone and barren to plant bearing siltstone rare exposures of thickly bedded imbricate to weakly imbricated

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

cubic b splines tomography at loma prieta abstract a high resolution tomographic study using cubic b splines parameterization and employing a systematic approach to the choosing of appropriate damping and smoothing parameters provided a three dimensional p wave velocity map of the loma prieta area used in the inversion were 11 977 high quality raypaths from 844 aftershocks of the 1989 loma prieta earthquake the velocity model exhibits a low velocity feature between the san andreas and zayante vergeles faults in the top 10 km of the crust this low velocity feature is interpreted as a sedimentary unit exposed to the northwest and separated from the salinian block by the zayante vergeles fault below 10 km no consistent change is observed between the salinian and the franciscan blocks there appears to be a high correlation of aftershock activity and localized high velocity anomalies southeast of the loma prieta mainshock whereas this anomaly may represent brittle rocks associated with a fault zone asperity that failed after the mainshock there is evidence to suggest it may be a body of serpentinite the serpentinite exhibits high velocities and is potentially less competent than surrounding country rock thus providing a sector along the fault more likely to be associated with many smaller earthquakes or creep behavior

cyclic changes in pennsylvanian paleoclimate and effects on floristic dynamics in tropical pangaea abstract wetland floras narrowly define perceptions of pennsylvanian tropical ecosystems the so called coal age such wetlands reflect humid to perhumid climate leading to characterizations of pennsylvanian tropics as everwet swampy these views are biased by the high preservation potential of wetlands sedimentation patterns paleosols and fossil floras indicate the presence of vegetation tolerant of subhumid to dry subhumid perhaps semi arid climate in basins between peat formation times understanding the significance of this seasonally dry vegetation has suffered from conceptual and terminological confusion a clearer view has emerged as models for framing the data have improved basinal floras typical of seasonally dry conditions relatively low soil moisture regimes are well documented but mainly from isolated deposits some of the earliest dominated by primitive pteridosperms flozfern floras occur in clastic rocks between european early pennsylvanian coal beds later early pennsylvanian fern cordaitalean vegetation different from coal floras is preserved in marine goniatite bullions conifers are first suggested by late mississippian potoniesporites pollen about the same time in north america broadleaf foliage lesleya and megalopteris occur in basin margin settings on drought prone limestone substrates the best known xeromorphic floras found between coal beds appear in the middle through late pennsylvanian containing conifers cordaitaleans and pteridosperms the middle pennsylvanian appearances of this flora are mainly allochthonous though parautochthonous occurrences have been reported parautochthonous assemblages are mostly late pennsylvanian the conifer flora became dominant in western and central pangaean equatorial lowlands in earliest permian location of the humid perhumid wetland flora during periods of relative dryness though rarely discussed is as or more perplexing than the spatial location of seasonally dry floras through time wetland plants had few migratory options and possibly survived in small refugia within and outside of basins coupled oscillations in climate sea level and vegetation were driven most likely by glacial interglacial fluctuations perhaps controlled by orbital cyclicity

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

mid carboniferous diversification of continental ecosystems inferred from trace fossil suites in the tynemouth creek formation of new brunswick canada we report skolithos scoyenia and mermia ichnofacies from sub humid tropical fluvial megafan deposits in the lower pennsylvanian tynemouth creek formation of new brunswick canada and discuss their evolutionary and palaeoecological implications especially regarding the colonization of continental freshwater terrestrial environments the skolithos ichnofacies comprises annelid arthropod spreite in the upper storey of a fluvial channel the scoyenia ichnofacies comprises tetrapod tracks arthropleurid trackways and shallow annelid arthropod burrows in active abandoned fluvial channels and rapidly aggrading levees splays in proximal interfluve areas the mermia ichnofacies comprises abundant xiphosuran trackways along with diverse traces of other arthropods annelids mollusks and fish in shallow freshwater lakes ponds and coastal bays in slowly aggrading distal interfluve areas transitional mermia scoyenia ichnofacies comprise tetrapod mollusk and annelid arthropod traces in coastal bay deposits on the distal edge of the megafan these trace fossil suites 1 provide the clearest documentation yet of the mid carboniferous diversification event when tropical continental environments became more densely populated 2 suggest that euryhaline visitors xiphosurans microconchids and other taxa from open marine settings played a key role in this episode of freshwater colonization and 3 provide empirical support for the deja vu effect the evolutionary concept that new or empty ecospace recurrent in spatially and temporally variable environments is colonized by simple ichnocoenoses

extremely rapid cooling of a carbonaceous chondrite chondrule containing very 16o rich olivine and a 26mg excess we describe a phenocryst in a co chondrite type ii chondrule that we infer to have formed by melting an amoeboid olivine aggregate aoa this magnesian olivine phenocryst has an extremely 16o rich composition 17o 17o 0 52 18o 23 it is present in one of the most pristine carbonaceous chondrites the co3 0 chondrite yamato 81020 the bulk of the chondrule has a very different 17o of 1 thus the 17o range within this single chondrule is 22 the largest range encountered in a chondrule we interpret the o isotopic and fe mg distributions to indicate that a fine grained aoa assemblage was incompletely melted during the flash melting that formed the chondrule some fe mg exchange but negligible o isotopic exchange occurred between its core and the remainder of the chondrule a diffusional model to account for the observed fe mg and o isotopic exchange yields a cooling rate of 105 to 106 k hr 1 this estimate is much higher than the cooling rates of 101 to 103 k hr 1 inferred from furnace simulations of type ii chondrule textures e g lofgren 1996 however our cooling rate applies to higher temperatures near 1900 k than are modeled by the crystal growth based cooling rates we observed a low 26al 27al initial ratio 4 6 3 0 10 6 in the chondrule mesostasis a value similar to those in ordinary chondrites kita et al 2000 if the 26al 27al system is a good chronometer then chondrule i formed about 2 ma after the formation of refractory inclusions

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

the long term control of vegetation and woody debris on channel and flood plain evolution insights from a paired catchment study in southeastern australia abstract numerous case studies have demonstrated that alluvial and semi alluvial rivers in se australia have undergone dramatic metamorphosis in historical times however very few studies place these changes within a long term evolutionary context as a consequence the magnitude of and ultimate controls on the changes to river form and processes are not fully appreciated in this study a paired catchment analysis is undertaken between two moderate sized sand bed rivers in east gippsland australia from the thurra river direct insight is gained into the predisturbance control exerted by riparian vegetation and wood in a lowland alluvial river this river is effectively in the same condition today as it was at the time of the arrival of europeans in australia in contrast the adjacent cann river which has been settled by europeans for 150 years but was previously very similar to the thurra river exhibits stark differences today channel morphodynamics observed within the thurra river when coupled with historical and geomorphic evidence for the former condition of the cann river provide a detailed reference by which the recent changes to the cann river are measured chronostratigraphic evidence from both flood plains places recent channel behavior within an evolutionary context extending well into the pleistocene since european settlement the study reach of the cann river has experienced a 360 increase in channel depth a 240 increase in channel slope a 700 increase in channel capacity and up to a 150 fold increase in the rate of lateral channel migration the contemporary condition of the cann river channel differs profoundly to that which has prevailed over at least the previous 27 ka the first order control on the historical channel metamorphosis is the removal of riparian vegetation and woody debris wd numerous thresholds have been crossed as a result of historical channel changes particularly the relationship between average length of woody debris pieces and channel width consequently channel recovery will not simply be achieved by reintroducing the pre existing riparian vegetation and woody debris load devising sound management strategies and realistic management targets for the cann river or any similarly altered river requires an understanding of the long term channel and flood plain evolutionary history as well as the underlying controls on historical changes

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

vegetation induced sedimentary structures from fossil forests in the pennsylvanian joggins formation nova scotia vegetation induced sedimentary structures viss are primary structures formed by the interaction of detrital sediment with in situ plants viss provide physical evidence of vegetation s fundamental role in mediating sediment accumulation and erosion in clastic depositional systems despite the abundance of modern viss descriptions from the ancient record are surprisingly rare analysis of fossil forests in floodplain strata of the pennsylvanian joggins formation has identified seven types of viss five hydrodynamic types comprise simple forms developed around a single plant centroclinal cross strata scratch circles upturned beds and complex forms where structures have amalgamated between several plants coalesced scour fills scour and mound beds two types mudstone filled hollows downturned beds form by the decay of an entombed plant and represent infilling of an empty hollow and or soft sediment deformation hydrodynamic types are present in both dryland and wetland settings whereas decay related types occur only in dryland settings where the water table was perennially or periodically low viss represent significant accumulations of sediment and are present in a high proportion of joggins formation strata the paucity of descriptions from the ancient record suggests that these structures have been overlooked or misinterpreted as strictly hydrodynamic recognition of viss in early to middle palaeozoic strata may provide an important insight into the distribution of early land plants in oxidizing environments where organic material was not preserved

facies model for fluvial systems in the seasonal tropics and subtropics facies models that summarize the deposits of fluvial systems are well established for humid climate settings and for desert environments but the deposits of rivers in the sub humid and semiarid seasonal tropics have been largely ignored our observations and data from modern streams and recent deposits in northeastern australia show how such rivers with extremely variable discharge have distinctive deposit characteristics that are substantially different from conventional fluvial facies models these properties include 1 erosionally based channel fill lithosomes that exhibit complex lateral facies changes with 2 abundant pedogenically modified mud partings 3 complex internal architecture that may lack the macroform elements typical of other fluvial sediment bodies 4 an abundance of sedimentary structures formed under high flow stage and 5 an abundance of in situ trees that colonize channel floors and are adapted to inundation by fast flowing water we illustrate examples of this fluvial style from the rock record and set out a new facies model the recognition of such a distinctive fluvial character and of changes in character through vertical successions will aid paleoclimate and reservoir analysis

global change in the late devonian modelling the frasnian famennian short term carbon isotope excursions a model of the global biogeochemical cycles coupled to a energy balance climate model the combine model is used to identify the causes of two large n 13 c value excursions across the frasnian famennian f f boundary we test a scenario that links the sea level rise to stratification of the proto tethys ocean through the formation of warm saline deep waters in extended epicontinental seas even though this scenario can produce dysoxia below 100 m depth it fails to increase the global burial flux of organic carbon and thus seawater n 13 c values since stratification of the ocean leads to decreased productivity in surface waters several scenarios postulating a continental origin of the perturbations in the late devonian biogeochemical cycles are then tested we found that weathering of platform carbonates exposed during the early famennian sea level fall can account for a maximum positive shift in n 13 c value of 0 7x at the end of the sea level fall episode another 1 0x increase in n 13 c might originate from rapid spreading of vascular land plants near the f f boundary postulating that higher plants globally increased the weatherability of continental surface and that colonized continental area increased by 30 across the f f boundary finally the n 13 c excursion observed at the base of upper rhenana zone and the rapid increase of the carbon isotope ratios at the f f boundary require an increase of phosphorus delivery to the ocean by 40 coeval with the sea level rises once the calculated n 13 c values are in agreement with the measured data the combine model calculates a decrease in atmospheric pco2 from pre perturbation 2925 ppmv in the lower rhenana conodont zone to 1560 ppmv in the upper triangularis zone this decrease in pco2 is due to the increase in burial of organic matter during the kellwasser events and increased continental weatherability triggered by the spreading of continental vascular plants these changes occur within 4 million years the corresponding global climatic cooling reaches 4 4 c at the pole and 2 1 c at the equator f 2003 elsevier b v all rights reserved

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

fluvial islands first stage of development from nonmigrating forced bars and woody vegetation interactions abstract fluvial islands can develop from the channel bed by interactions between pioneer trees and bars although vegetation recruitment and survival is possible on all bar types it is easier for trees to survive on nonmigrating bars developed from a change in channel geometry or to the presence of a steady perturbation this field study details the first stages of development of a vegetated mid channel nonmigrating or forced bar and its evolution toward an island form over six years analysis of bed topographical changes vegetation density and roughness scour and fill depths sediment grain size and architecture and excess bed shear stress highlighted a specific signature of trees on topography and grain size segregation two depositional processes combining the formation of obstacle marks and upstream shifting deposition of sediments led to the vertical accretion of the vegetated bar during the first stage of the bar accretion bedload sediment supply coming from surrounding channels during floods was identified as a key process modulated by the presence of woody vegetation and a deflection effect induced by the preexisting topography grain size segregation between vegetated and bare areas was also highlighted and interpreted as an important process affecting the development of surrounding channels and the degree of disconnection and hence the speed of development of a growing island the heterogeneity of bedload supply can explain why sediment deposition and density of trees are not strictly related a general conceptual model detailing the first stages of evolution from a bar to an established island is proposed for relatively large lowland rivers

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

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

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

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

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

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

riparian vegetation and the late holocene development of an anabranching river magela creek northern australia many anabranching rivers are characterized by dynamic interactions between fluvial processes and riparian vegetation but uncertainties surround the processes and time scales of anabranch development we use geomorphological investigations and optically stimulated luminescence osl dating to determine spatial and temporal trends in the development of anabranching along a 6 5 km long reach of magela creek in the seasonal tropics of northern australia many trees and shrubs that survive the wet season floods establish on the sandy beds and lower banks such that anabranches divide and rejoin around numerous ridges and islands that are formed mainly by accretion in the lee of in channel vegetation and less commonly by excision from formerly continuous island or flood plain surfaces once ridges and islands form colonizing vegetation maintains their stability by increasing sediment cohesion and decreasing flow erosivity over the holocene magela creek has vertically aggraded and extended in length by delta progradation into madjinbardi billabong resulting in a time sequence of anabranches and associated ridges and islands from older upstream to younger downstream osl ages for islands in the upstream and middle reaches are ca 1 6 ka and older and the narrow deep anabranches width depth w d typically 10 30 have few in channel obstructions farther downstream island osl ages are ca 0 7 ka and younger anabranches tend to be wider and shallower w d 30 with more obstructions and splays and locally scoured island and floodplain surfaces are more common based on these findings previous flow and sediment transport measurements and theoretical analyses we posit that there is a decline in anabranch efficiency from an upstream equilibrium system in mass flux balance to a downstream disequilibrium system characterized by bed aggradation and localized island and floodplain erosion in the downstream reaches inefficient high w d and obstructed anabranches do not persist because they either aggrade and are abandoned or they are subdivided into more efficient lower w d and less obstructed anabranches as a result of the interactions between in channel vegetation growth and ridge and island accretion or local excision consequently a more efficient anabranching system gradually develops with characteristics similar to those in the upstream reaches this enhances downstream sediment transfer which enables ongoing delta progradation and provides fresh sediment surfaces for vegetation to colonize and initiate new anabranches the osl ages from magela creek demonstrate that a recognizable but relatively inefficient anabranching system can develop within a few centuries while adjustment to a more efficient system occurs over a few millennia

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

rules of the road a qualitative and quantitative synthesis of large wood transport through drainage networks abstract to effectively manage wood in rivers we need a better understanding of wood mobility within river networks here we review primarily field based and some numerical studies of wood transport we distinguish small medium large and great rivers based on wood piece dimensions relative to channel and flow dimensions and dominant controls on wood transport we suggest further identification and designation of wood transport regimes as a useful way to characterize spatial temporal network heterogeneity and to conceptualize the primary controls on wood mobility in diverse river segments we draw analogies between wood and bedload transport including distinguishing eulerian and lagrangian approaches exploring transport capacity and quantifying thresholds of wood mobility we identify mobility envelopes for remobilization of wood with relation to increasing peak discharges stream size and dimensionless log lengths wood transport in natural channels exhibits high spatial and temporal variability with discontinuities along the channel network at bankfull flow and when log lengths equal channel widths although median mobilization rates increase with increasing channel size maximum mobilization rates are greatest in medium sized channels most wood is transported during relatively infrequent high flows but flows under bankfull can transport up to 30 of stored wood we use conceptual models of dynamic equilibrium of wood in storage and of spiralling wood transport paths through drainage networks as well as a metaphor of traffic on a road to explore discontinuous wood movement through a river network the primary limitations to describing wood transport are inappropriate time scales of observation and lack of sufficient data on mobility from diverse rivers improving models of wood flux requires better characterization of average step lengths within the lifetime travel path of a piece of wood we suggest that future studies focus on i continuous or high frequency monitoring of wood mobility ii monitoring changes in wood storage iii using wood characteristics to fingerprint wood sources iv quantifying volumes of wood buried within river corridors v obtaining existing or new data from unconventional sources such as citizen science initiatives and vi creating online interactive data platforms to facilitate data synthesis

a global biogeochemical perturbation across the silurian devonian boundary ocean continent biosphere feedbacks abstract the large scale global biogeochemical perturbation across the silurian devonian s d boundary recorded in the major positive excursion of the 13c time curve klonk event of an amplitude of 2 5 to 3 0 max 4 0 in europe and up to 5 0 in north america reflects a unique combination of palaeogeographic biogeochemical and evolutionary processes in the late caledonian geodynamic setting the steady sulfur isotopic ratios show an overall stability of the s d oceanic geochemical system as a whole and do not indicate any synchronous changes in anoxic deep oceanic and sediment processes therefore this led us to a hypothesis that the crucial changes that contributed to the recorded carbon cycling turnover are related to rapidly evolving ocean continent biosphere feedback coastal zones of the latest silurian epicontinental seas accumulated considerable quantities of organic carbon from early vascular vegetation which explosively expanded to inhabit vast near coastal shallows and deltas large primary production of these early terrestrial plants and rapidly enhanced sedimentary burial of organic carbon were also responsible for co2 drawdown which have resulted in reversed greenhouse effect and a global climatic cooling tendency this feedback was blocked when the sea level gradually dropped and led to shrinking of the silurian epicontinental seas and the growing climatic deterioration during the s d transition limited primary production furthermore continued processes of regressive abrasion and erosion limited the storage of organic carbon as well as the efficiency of the carbonate factory during the following early devonian greenhouse interval marine regression and active latest caledonian tectonism promoted progressive weathering of the sedimentary organic matter the oxidation of c rich deposits caused the subsequent growth of co2 levels in the early devonian culminating in the warming of global climate

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

pre vegetation alluvial fan facies and processes an example from the cambro ordovician rozel conglomerate formation jersey channel islands prior to the silurian a lack of land vegetation is expected to have influenced the processes of sedimentation on alluvial fans principally by causing increased rates of run off and erosion in the fan catchments in the cambro ordovician rozel conglomerate formation this effect was central to the generation of alluvial fan deposits that are unusually deficient in sand and clay despite being sourced from a catchment dominated by sandstone and mudstone seven facies are identified interpreted as representing the deposits of i shallow stream and sheetfloods ii channelized non cohesive debrisflows iii sub aerial mud rich debrisflows iv sub aqueous mud rich debrisflows v low energy streams that reworked abandoned fan sectors vi a sandflat playa lake system and vii talus slopes the first two facies are both clast supported conglomerate comprise 98 of the deposit and represent deposition on active depositional lobes and in the fan head trench the remaining facies are the products of infrequent sedimentary processes fan abandonment processes and marginal sub environments the facies assemblage in many ways mimics that of a modern day water lain arid region fan however the palaeolatitude of these fans was high and the climate is inferred to have been cool and wet the near absence of sandstone and mudstone beds with few mudflows is ascribed to rapid hinterland uplift and high rates of erosion resulting in minimal chemical breakdown of source rocks in the catchments such high rates of erosion are in turn ascribed to a combination of frequent rainstorms and an absence of vegetation cover