driftcretions the legacy impacts of driftwood on shoreline morphology this research demonstrates how vegetation interacts with physical processes to govern landscape development we quantify and describe interactions among driftwood sedimentation and vegetation for great slave lake which is used as proxy for shoreline dynamics and landforms before deforestation and wood removal along major waterways we introduce driftcretion to describe large persistent concentrations of driftwood that interact with vegetation and sedimentation to influence shoreline evolution we report the volume and distribution of driftwood along shorelines the morphological impacts of driftwood delivery throughout the holocene and rates of driftwood accretion driftcretions facilitate the formation of complex diverse morphologies that increase biological productivity and organic carbon capture and buffer against erosion driftcretions should be common on shorelines receiving a large wood supply and with processes which store wood permanently we encourage others to work in these depositional zones to understand the physical and biological impacts of large wood export from river basins

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

the impacts of land plant evolution on earth s climate and oxygenation state an interdisciplinary review abstract the paleozoic emergence of terrestrial plants has been linked to a stepwise increase in earth s o2 levels and a cooling of earth s climate by drawdown of atmospheric co2 vegetation affects the earth s o2 and co2 levels in multiple ways including preferential organic carbon preservation by decay resistant biopolymers e g lignin and changing the continental weathering regime that governs oceanic nutrient supply and marine biological production over shorter time scales 1 myr land plant evolution is hypothesized to have occasionally enhanced p weathering and fertilized the oceans expanding marine anoxia and causing marine extinctions oceanic anoxia would eventually become limited by oceanic o2 uptake as oxygen accumulates in the atmosphere and surface oceans when excess organic carbon is buried in marine sediments here we review hypotheses and evidence for how the evolving terrestrial ecosystems impacted atmospheric and oceanic o2 and co2 from the ordovician and into the carboniferous 485 298 9 ma five major ecological stages in the terrestrial realm occurred during the prolonged time interval when land was colonized by plants animals and fungi marked by the evolution of 1 non vascular plants 2 vascular plants with lignified tissue 3 plants with shallow roots 4 arborescent and perennial vegetation with deep and complex root systems and 5 seed plants the prediction that land vegetation profoundly impacted the earth system is justified although it is still debated how the individual transitions affected the earth s o2 and co2 levels the geological record preserves multiple lines of indirect evidence for environmental transitions that can help us to reconstruct and quantify global controls on earth s oxygenation and climate state

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

belowground rhizomes in paleosols the hidden half of an early devonian vascular plant abstract the colonization of terrestrial environments by rooted vascular plants had far reaching impacts on the earth system however the belowground structures of early vascular plants are rarely documented and thus the plant soil interactions in early terrestrial ecosystems are poorly understood here we report the earliest rooted paleosols fossil soils in asia from early devonian deposits of yunnan china plant traces are extensive within the soil and occur as complex network like structures which are interpreted as representing long lived belowground rhizomes of the basal lycopsid drepanophycus the rhizomes produced large clones and helped the plant survive frequent sediment burial in well drained soils within a seasonal wet dry climate zone rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants predating the appearance of trees with deep roots in the middle devonian plant rhizomes have long functioned in the belowground soil ecosystem this study presents strong direct evidence for plant soil interactions at an early stage of vascular plant radiation soil stabilization by complex rhizome systems was apparently widespread and contributed to landscape modification at an earlier time than had been appreciated

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

the role of floodplain width and alluvial bar growth as a precursor for the formation of anabranching rivers abstract anabranching rivers are defined as a system of multiple channels separated by stable alluvial islands while substantial progress has been made in developing a physics based understanding of what drives the differences between meandering and braided river channels anabranching rivers have not been well integrated into these models here we propose that alluvial bar growth on the floodplain may be a precursor for the formation of anabranching rivers alluvial bar growth strongly depends on the aspect ratio of the flow width divided by depth and rivers with wide floodplains have flows with a large aspect ratio consistent with this idea remotely sensed measurements of floodplain width of four rivers from different climatic and tectonic settings show that anabranching river patterns are often associated with relatively wide floodplains to explore the physics behind that empirical relationship we carried out two sets of morphodynamic numerical simulations using boundary conditions from field scale modern anabranching rivers spanning different climatic and geologic settings as well as hypothetical floodplain widths results from the simulations show that for a given flood discharge widening the floodplain changes the river pattern from single channel to multi threaded with mobile bars to multi channeled with immobile islands multi channeled patterns arise because the emergence of bars causes flow bifurcation subsequent bifurcation instability leads to the emergence of multiple stable channels as the channels increase their cross sectional area shields stresses on intervening bars are reduced until the bars stabilize into islands we suggest that the presence of stable islands allows vegetation to grow or cohesive sediment to accumulate leading to enhanced channel bank strength and a stable anabranching pattern our results suggest that alluvial bar growth can be a precursor to formation of anabranching rivers compared with field measurements our simulations accurately predict the number of active channels to within 20 which seems to support the idea that some anabranching rivers may originate from alluvial bar growth

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

early plants and the rise of mud the geological record of our planet provides evidence for a handful of ways in which life has fundamentally altered processes and environments at earth s surface it was the evolution of photosynthesis nearly 2 5 billion years ago that oxygenated the atmosphere and oceans 1 greatly increasing the spectrum of minerals found in rocks 2 over the past 250 million years the production of mineral skeletons by algae in the oceans transformed the way in which sediments accumulate in marine basins 3 on page 1022 of this issue mcmahon and davies 4 illustrate how plants too have left an indelible mark in the geological record their signature written in mud

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

comparison of methods to estimate sediment flux in ancient sediment routing systems abstract the need to predict accurately the volume timing and location of sediments that are transported from an erosional source region into a basin depocentre sink is important for many aspects of pure and applied sedimentological research in this study the results of three widely used methods to estimate sediment flux in ancient sediment routing systems are compared using rich input datasets from two systems eocene south pyrenean foreland basin spain and late pleistocene to holocene gulf of corinth rift basin greece for which mapped dated sediment volumes provide an independent reference value of sediment accumulation rates the three methods are 1 the empirical bqart model which uses values of drainage basin area relief temperature lithology and water discharge 2 empirical scaling relationships between characteristic geomorphological parameters of sediment routing system segments and 3 the fulcrum model which uses the palaeohydrological parameters of trunk river channels to estimate downsystem sediment discharge the bqart model and empirical geomorphological scaling relationships were originally developed using modern sediment routing systems and have subsequently been applied to ancient systems in contrast the fulcrum model uses hydrological scaling relationships from modern systems but was developed principally for application in ancient systems our comparative analysis quantifies the sensitivity of the three methods to their input parameters and identifies the data required to make plausible estimates of sediment flux for ancient sediment routing systems all three methods can generate estimates of sediment flux that are comparable with each other and are accurate to at least one order of magnitude relative to independent reference values the bqart model uses palaeoclimatic and palaeocatchment input data which are accurate for sub modern systems but may be highly uncertain in deep time systems corresponding estimates of sediment flux are most sensitive to the accuracy with which the palaeocatchment area is constrained and to palaeoclimatic parameters that reflect temperature and precipitation the fulcrum model uses palaeohydrological input data its sediment flux estimates are sensitive to palaeochannel dimensions and in particular the duration of bankfull discharge which is invariably difficult to constrain accurately in deep time sediment routing systems this uncertainty can give rise to large potential ranges of sediment flux estimates geomorphological scaling relationships offer comparable order of magnitude accuracy for both sub modern and deep time sediment routing systems in which geomorphological segments can be identified but when used on relatively small sediment routing systems the ranges of sediment volumes deposited can vary greatly limiting the utility of the technique we suggest that methods to estimate sediment flux should be chosen for a particular sediment routing system based on the types and uncertainty of available data where input parameter values are highly uncertain such as in deep time systems monte carlo simulation is an effective tool to calculate probability distributions of estimated sediment flux

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

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

palaeoenvironments of early devonian fish and other aquatic fauna of the campbellton formation new brunswick canada abstract the palaeoecology and palaeoenvironments of the classic fish bearing strata of the campbellton formation are here described a well documented fossil assemblage includes acanthodian placoderm chondrichthyan and cephalaspid fishes tracheophyte remains eurypterids ostracods and molluscs as part of the old red sandstone continent the emsian campbellton formation occupied a small basin within the mountainous terrain of the acadian orogen and may have connected through a narrow seaway to a closing foreland basin the highest diversity of vertebrate fossils was found above a basal unconformity with val d amour formation volcanics marked by fissure fills and unstratified breccia representing a craggy irregular palaeosurface that provided shelter for some fauna and sediment for rapid burial of skeletal remains overlying prodeltaic calcareous siltstones are also highly fossiliferous and represent a low energy habitat occurrences of pterygotid eurypterids cephalaspids and chondrichthyans in deltaic sandstones place these taxa in a habitat that may have been variably fresh or brackish the surrounding landscape was vegetated with primitive tracheophytes and abundant plant debris is preserved throughout the basin the diverse assemblage of fish arthropods gastropods plants and microbial growths suggests that a trophically complex ecosystem was in existence

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

influence of inclination and permeability of solitary woody riparian plants on local hydraulic and sedimentary processes the role of solitary woody riparian plants with respect to local erosion and deposition of sediments is investigated a focus is laid on the characteristics inclination and permeability of the plant s projected frontal area therefore two experimental studies using cylindrical obstacles were carried out in a laboratory flume one aiming at inclination the other at permeability the first series revealed that the total amount of mobilized sediment around the cylinder on average decreased by 8 10 per 5 increasing inclination in streamwise direction locations of maximum scour depth simultaneously shifted downstream a horseshoe vortex system causing the frontal and lateral scouring ceased to exist below inclinations of 25 30 the second series revealed that with increasing permeability frontal scour incision is delayed and the eroded sediment volume is significantly reduced with permeable obstacles two system states were observed first frontal scouring with leeside deposition at higher flow velocities and second moderate leeside scouring at lower flow velocities for up scaling and comparison a field study focussing on fluvial obstacle marks at poplars and willows in secondary channels of the river loire was additionally conducted a modified analytical model enabled us to quantify the amount of deposited sediments leeside of the plants leeside sediment ridges are significantly stabilized and have a higher preservation potential when covered by pioneer vegetation under such conditions they may indeed induce the development of stable islands eventually sediment ridge width turned out to be a suitable indicator for leeside deposited sediment volume irrespective of spatial scale copyright 2012 john wiley sons ltd

parametric transitions between bare and vegetated states in water driven patterns conditions for vegetation spreading and pattern formation are mathematically framed through an analysis encompassing three fundamental processes flow stochasticity vegetation dynamics and sediment transport flow unsteadiness is included through poisson stochastic processes whereby vegetation dynamics appears as a secondary instability which is addressed by floquet theory results show that the model captures the physical conditions heralding the transition between bare and vegetated fluvial states where the nonlinear formation and growth of finite alternate bars are accounted for by center manifold projection this paves the way to understand changes in biogeomorphological styles induced by man in the anthropocene and of natural origin since the paleozoic devonian plant hypothesis

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

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

composition and architecture of braided and sheetflood dominated ephemeral fluvial strata in the cambrian ordovician potsdam group a case example of the morphodynamics of early phanerozoic fluvial systems and climate change abstract two fluvial facies associations braided and ephemeral fluvial are recognized in strata of the cambrian ordovician potsdam group in the ottawa embayment and quebec basin in northeastern north america braided fluvial sedimentation was dominated by the migration of coarse grained sandy dunes and rare unit bars and local gravels that built up low relief 0 4 5 m thick downstream accreting compound bars in very wide and shallow braided channels rare meter scale confluence scours incision and filling of decimeter thick bypass channels and thin 7 cm overbank deposition also occurred ephemeral fluvial sedimentation was dominated by the progradation of lobate terminal splays most of which were deflated and or reworked into thin 10 95 cm sheets by eolian processes during the long recurrence intervals between floods these strata were locally incised by rare 0 3 1 9 m thick scour filling high energy supercritical bedform strata and decimeter thick bypass channels both braided and ephemeral fluvial deposits consist of meter scale stacked high order stratal units separated by horizontal laterally extensive surfaces recording the recurring buildup avulsion and finally abandonment of channel belts in braided fluvial strata of the potsdam the dominance of thin 2 m elongated compound bars with low relief 5 bar margins and internal accretion surfaces 15 suggest that braided channels and in channel compound bars expanded laterally with negligible increase in flow depth during periods of increased discharge in the absence of bank stabilizing vegetation similar to other examples of the pre vegetated sheet braided style however in areas where bedrock topography inhibited the lateral expansion of channels thicker compound braid bars 1 2 3 5 m with higher relief accretion surfaces up to 35 like those observed in post silurian and modern systems preferentially formed in relatively deep channels ephemeral fluvial deposits here are similar to ephemeral examples throughout geologic history in that they mostly comprise poorly confined sheet like terminal splays that accumulated in topographic lows however compared to several post silurian examples strata in the potsdam exhibit considerably more eolian reworking of splays and preservation of supercritical bedform strata a manifestation of greater rates of surface water infiltration due to a lack of sheltering by rooted plants and propensity for unconfined flooding finally in the upper part of the potsdam two regional ephemeral fluvial units are interstratified with two braided fluvial units providing evidence for shifts in regional climate the sharp areally extensive surfaces that separate these fluvial systems are interpreted to approximate time lines and therein provide a means for relative and absolute chronostratigraphic correlation these changes are correlated with documented late cambrian to earliest ordovician global climate fluctuations with semiarid conditions and related ephemeral fluvial systems corresponding to global cooling events at ca 491 and 487 ma

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

considering river structure and stability in the light of evolution feedbacks between riparian vegetation and hydrogeomorphology river ecological functioning can be conceptualized according to a four dimensional framework based on the responses of aquatic and riparian communities to hydrogeomorphic constraints along the longitudinal transverse vertical and temporal dimensions of rivers contemporary riparian vegetation responds to river dynamics at ecological timescales but riparian vegetation in one form or another has existed on earth since at least the middle ordovician c 450 ma and has been a significant controlling factor on river geomorphology since the late silurian c 420 ma on such evolutionary timescales plant adaptations to the fluvial environment and the subsequent effects of these adaptations on fluvial sediment and landform dynamics resulted in the emergence from the silurian to the carboniferous of a variety of contrasted fluvial biogeomorphic types where water flow morphodynamics and vegetation interacted to different degrees here we identify several of these types and describe the consequences for biogeomorphic structure and stability i e resistance and resilience along the four river dimensions of feedbacks between riparian plants and hydrogeomorphic processes on contrasting ecological and evolutionary timescales

evolution of soil wetting patterns preceding a hydrologically induced landslide inferred from electrical resistivity survey and point measurements of volumetric water content and pore water pressure 1 the hydrological state of a hillslope prior to a sprinkling induced shallow landslide was monitored using electrical resistivity tomography ert along a 47 m long transect supplemented by local time domain reflectometry tdr and tensiometer measurements the spatial and temporal evolution of wetting patterns in the soil material indicated attainment of a stationary fully saturated profile in a slope region underlain by shallow sandstone bedrock the significant decrease in spatially averaged standard deviation of water saturation has not been observed during an earlier failed attempt to trigger a landslide by intense sprinkling while for the stable experiment no landslide was triggered water saturation and soil moisture variability were still increasing with time the unstable experiment reached a time invariant state of high pore water pressures and saturations until it finally failed the results indicate that when large and interconnected regions of hillslope are saturated as confirmed by high volumetric water content and low standard deviation of water saturation additional water cannot be redistributed to empty drier regions and may eventually enhance local pore water pressure and seepage force initiating large shear deformation and failure accordingly a transition to such a critical steady state of high average water saturation associated with low and constant spatial standard deviation may serve as additional hydro geophysical indicator for the imminence of a landslide release

sedimentology geochemistry and osl dating of the alluvial succession in the northern gujarat alluvial plain western india a record to evaluate the sensitivity of a semiarid fluvial system to the climatic and tectonic forcing since the late marine isotopic stage 3 abstract the alluvial successions in the northern gujarat alluvial plain western india have been investigated for reconstructing the climatic fluctuations during the last 40 ka alluvial architecture and geochemical proxies indicate prevalence of a strengthened indian summer monsoon ism with fluctuations between the late marine isotopic stage 3 mis 3 37 ka to the early mis 2 27 ka a gradual onset of aridity declining ism after 27 ka with peak aridity at 22 ka is observed a gradual strengthening of ism at around 18 and 12 ka followed by a short reversal in ism intensity between 12 and 11 ka is attributed to the younger dryas yd cooling event the aeolian sand sheet dated to 6 and 3 5 ka represents the onset of regional aridity following this a short lived humid phase was observed after 2 ka which includes the medieval warm period mwp the study suggests that the variability in the ism to the latitudinal migration of the inter tropical convergence zone was caused by insolation driven cooling and warming events in the north atlantic the incision of the valley fill alluvium occurred in two distinct phases the older incision phase occurred after 11 ka and before 6 ka whereas the younger incision phase that led to the development of present day topography is bracketed between 3 5 ka and before 1 ka the older incision phase is ascribed to the early to mid holocene enhanced ism climatically driven whereas the younger incision seems to be modulated by the activation of basement faults tectonically driven

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

ecohydrologic feedbacks controlling sizes of cypress wetlands in a patterned karst landscape author s dong x murray ab heffernan jb abstract 2018 john wiley a sons ltd many landforms on earth are profoundly influenced by biota in particular biota play a significant role in creating karst biogeomorphology through biogenic co 2 accelerating calcite weathering in this study we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in south florida big cypress national preserve as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes specifically we are interested in 1 whether cypress depressions on the landscape have reached or will reach equilibrium size 2 if so what feedback mechanisms stabilize the size of depressions and 3 what distal interactions among depressions give rise to the even distribution of depressions in the landscape we hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism we show that a soil cover feedback i e a smaller fraction of co 2 reaches the bedrock surface for weathering as soil cover thickens is the major feedback stabilizing depressions followed by a biomass feedback i e inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale the individual depressions however are not yet in steady state but would be in 0 2 0 4 million years this represents the first study to demonstrate the decoupling of landscape scale self organization and the self organization of its constituent agents 2018 john wiley a sons ltd

middle moscovian climate of eastern equatorial pangea recorded in paleosols and fluvial architecture abstract fluvial architecture in conjunction with the morphology petrographical mineralogical and geochemical composition of intercalated paleosols of the middle moscovian upper radnice member of the continental kladno rakovnik basin czech republic were studied in order to decipher climatic signals in the eastern pangea region during the late paleozoic ice age analysis of architectural elements reveals vertical changes from strongly amalgamated channel fills of bedload dominated braided streams to isolated ribbon like meandering channel fills in mud dominated floodplain strata the resulting large scale fining upward cycles separated by laterally widespread bounding surfaces are interpreted as having been formed in response to allocyclic processes driven by variable intensities of precipitation which affected the density of vegetation cover across the landscape and in turn the amount and character of sediment supply bedload dominated parts of the cycles were deposited during periods of low water tables and sparse vegetation whereas periods of maximum precipitation resulted in higher water tables and a greater density of vegetation cover which in turn stabilized the floodplains and fixed streams to narrow meandering anastomosing channels in mud dominated floodplain strata associated paleosols resemble modern vertisols which form under seasonal precipitation in modern settings however coeval formation of inertinite rich peat represented by histosols and gleyed low chroma vertisols in the stratigraphically lowest paleosol succession occurred under overlapping marginal conditions for the climatically different types of soils i e under a seasonal climate where precipitation exceeds evapotranspiration for 6 to 8 months out of the year mean annual precipitation calculated from the geochemistry of b horizons of vertisols calmag proxy varies between 1815 and 1730 mm yr

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

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

cascades of sub decadal channel floodplain changes in low gradient non vegetated reaches near a dryland river terminus salar de uyuni bolivia

low gradient single threaded rivers prior to greening of the continents the silurian age rise of land plants is hypothesized to have caused a global revolution in the mechanics of rivers in the absence of vegetation controlled bank stabilization effects pre silurian rivers are thought to be characterized by shallow multithreaded flows and steep river gradients this hypothesis however is at odds with the pancontinental scale of early neoproterozoic river systems that would have necessitated extraordinarily high mountains if such river gradients were commonplace at continental scale which is inconsistent with constraints on lithospheric thickness to reconcile these observations we generated estimates of paleogradients and morphologies of pre silurian rivers using a well developed quantitative framework based on the formation of river bars and dunes we combined data from previous work with original field measurements of the scale texture and structure of fluvial deposits in proterozoic age torridonian group scotland a type example of pancontinental prevegetation fluvial systems results showed that these rivers were low sloping gradients 10 5 to 10 4 relatively deep 4 to 15 m and had morphology similar to modern lowland rivers our results provide mechanistic evidence for the abundance of low gradient single threaded rivers in the proterozoic eon at a time well before the evolution and radiation of land plants despite the absence of muddy and vegetated floodplains single threaded rivers with stable floodplains appear to have been a persistent feature of our planet despite singular changes in its terrestrial biota

acoustic emissions monitoring during inelastic deformation of porous sandstone comparison of three modes of deformation in some reservoirs large deformations can occur during oil or gas production because of the effective stress change for very porous rocks these production operations can be sufficient to cause inelastic deformation and irreversible damage rock formations can undergo deformation by different mechanisms including dilatancy or pore collapse in the laboratory it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive indeed when subjected to an overall compressive loading a porous rock may fail by shear localization compaction localization or by cataclastic compaction acoustic emission ae records provide important information to understand the failure mode of rocks the spatial evolution of damage as well as the source mechanisms can be followed using this technique in this paper we present three different laboratory axisymmetric compression experiments performed on bleurswiller sandstone which enable us to compare the acoustic emission signature of these three modes of deformation our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures in terms of ae sources characteristics and evolution of ae number in comparison to the acoustic signature from shear localization this implies similar micromechanisms involved during compaction bands formation and cataclastic compaction

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

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

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

cross bedded woody debris from a pliocene forested river system in the high arctic beaufort formation meighen island canada abstract cross bedding the inclined internal stratification that records the migration of certain transverse sedimentary bedforms is nearly ubiquitous in current transported bedload sediments although examples of the structure are known from inorganic clastic sediments and sedimentary rocks from practically all depositional environments and intervals of geologic history here we report cross bedded lenses that are composed wholly or significantly of woody debris in pliocene alluvium of the beaufort formation in the canadian high arctic the uniqueness of cross bedded woody debris has hitherto been overlooked but we demonstrate that in the entire phanerozoic record it is apparently restricted to alluvium deposited during a warm climatic interval that permitted the growth of boreal type forests within 10 latitude of the north pole the marked spatiotemporal restriction of cross bedded woody debris implies that there may be environmental factors unique to polar forests which promote the subaqueous transport of large amounts of fine woody debris as fluvial bedload we propose a non uniformitarian conceptual model for the formation of cross bedded woody debris in forested polar rivers whereby an exceptional abundance of woody debris could accumulate and become saturated and denser than water due to reduced decomposition on forest floors that were subject to prolonged periods of darkness and subzero temperatures

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

conodont biostratigraphy of the mid carboniferous boundary in western ireland two stratigraphic sections spanning the mid carboniferous boundary were examined in the clare shale formation of the shannon basin in western ireland calcareous nodules intermittently occur within these generally non calcareous organic rich shales and these have yielded serpukhovian and bashkirian conodont elements the biostratigraphic range of the irish material is illustrated here for the first time results show that the mid carboniferous and arnsbergian chokierian boundaries are coincident at ballybunion gnathodus girtyi is restricted to the lower part of the serpukhovian stage late mississippian while g bilineatus bollandensis persists into much younger strata close to the first occurrence of declinognathodus noduliferus s l one element belonging to g postbilineatus is also present these findings support the argument that d noduliferus s l developed from g b bollandensis rather than from g girtyi the biostratigraphical tool for the identification of the mid carboniferous boundary globally and the suitability of the section at arrow canyon usa as a gssp may therefore need to be reassessed

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

the middle rhuddanian lower silurian hot shale of north africa and arabia an atypical hydrocarbon source rock an important hydrocarbon source rock a hot shale has been identified from the middle rhuddanian llandovery lower silurian of a number of localities in north africa and arabia it is unusual in having been deposited during a eustatic fall in sea level evidence for this sea level fall in libya and jordan is manifested in a wide variety of palynological proxy data including reduced acritarch and chitinozoan total abundance reduced acritarch diversity and changes in the relative abundances of various environmentally sensitive acritarch morphogroups and from the presence of a minor positive 13corg excursion at the same stratigraphical level as the hot shale the environment of deposition was anoxic before during and after deposition of the hot shale except for some very brief incursions of more oxygenated water that enabled the development of a very limited burrowing benthos and graptolite preservation as three dimensional pyrite internal moulds these incursions occurred just before and during deposition of the hot shale and are interpreted as resulting from the influx of sediment laden oxygenated currents from shallower water environments enhanced organic matter preservation within the hot shale is attributed to greater productivity resulting from increased nutrient input particularly from wind blown dust more rapid descent through the water column of organic matter in post bloom marine snow macroaggregates development of geochemically sealing microbial mats at the sea floor and more rapid burial of organic material than had occurred earlier in the rhuddanian

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

formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors we describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized isere river in france the channel was laterally confined with embankments and mostly straightened from the beginning of the 1970s to the end of the 1990s alternate bars were progressively but heavily colonized by vegetation this context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions based on a gis analysis of aerial photographs between 1948 and 1996 we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age size and mobility field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars a highly significant statistical association of geomorphological and vegetation variables rv of co inertia analysis 0 41 p 0 001 explained 95 of the variability in just one axis supporting the existence of very strong feedback between geomorphological changes i e the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest and vegetation succession such dynamics reflect the fluvial biogeomorphological successions model as described by the authors earlier 2020 john wiley sons ltd

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

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

quantifying sediment supply to continental margins application to the paleogene wilcox group gulf of mexico sediment supply to the ocean influences basin margin growth and reflects upstream landscape evolution including patterns of sediment routing denudation and tectono climatic perturbations in source areas constraining sediment supply is useful for inputs to stratigraphic forward models and for predictions of reservoir presence and quality because of the importance of sediment supply geoscientists have developed various methods to estimate it here we apply monte carlo simulation mcs to the bqart model that is used to describe an empirical relationship between river catchment paleogeography climate and sediment load we calculate a range of sediment supply from north american source areas to the gulf of mexico that suggests an overall decrease in median sediment supply from the late paleocene to the early eocene from 404 514 to 144 204 million tons per year depending on the published paleogeographic model that we used to guide our selection of input variables comparison of these estimates with downstream sediment records shows that the subsurface depositional rates are within the 10th 90th percentile range of this bqart mcs uncertainty model the 50th percentile values of bqart mcs results are overall larger than the published wilcox sediment volume which indicates that the size of wilcox deep water fans might be underestimated we use source of change analysis to show the influence of each river catchment input of the bqart model on change in sediment supply from the late paleocene to the early eocene integration of empirical based methods such as bqart with physics based experimental and modeling approaches might provide better constrains on sediment supply and deposition in frontier areas of oil and gas exploration

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

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

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

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

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

the role of vegetation and large wood on the topographic characteristics of braided river systems riparian vegetation and large wood play a crucial role in shaping rivers on the one hand vegetation tends to increase bank stability reduce channel width and reduce the braiding index in gravel bed rivers conversely large wood tends to increase channel dynamics and promote avulsions the effects of vegetation and large wood have been rarely simulated together in flume experiments in this paper we present a series of experimental runs conducted in a large flume facility using cylindrical wooden dowels and alfalfa seedlings to represent logs and vegetation respectively in order to investigate their role on determining the topographical nature of braided river systems a terrestrial laser scanner was used to measure in detail the topography of the channels and bars and distribution of the elevations and second order structure functions were used to explore the topography that large wood and vegetation imposed on the braided pattern in the flumes results show that vegetation reduced the braiding index and produced wider and deeper channels the standard deviation of the bed elevations was higher than in flumes without vegetation large wood alone was not effective in changing the braiding index or the standard deviation of the elevations when vegetation and large wood acted together in the flume the braiding index reached a minimum value and the skewness of the distribution of elevation increased revealing shallower pools if compared with runs conducted with only vegetation

formation of a cohesive floodplain in a dynamic experimental meandering river field studies suggest that a cohesive floodplain is a necessary condition for meandering in contrast to braided rivers however it is only partly understood how the balance between floodplain construction by overbank deposition and removal by bank erosion and chutes leads to meandering this is needed because only then does a dynamic equilibrium exist and channels maintain meandering with low width depth ratios our objective is to understand how different styles of floodplain formation such as overbank deposition and lateral accretion cause narrower channels and prevent chute cutoffs that lead to meandering in this study we present two experiments with a self forming channel in identical conditions but to one we added cohesive silt at the upstream boundary the effect of cohesive silt on bank stability was tested in auxiliary bank erosion experiments and showed that an increase in silt reduced erosion rates by a factor of 2 the experiment without silt developed to a braided river by continuous and extensive shifting of multiple channels in contrast in the meandering river silt deposits increased bank stability of the cohesive floodplain and resulted in a reduction of chute cutoffs and increased sinuosity by continuous lateral migration of a single channel overbank flow led to deposition of the silt and two styles of cohesive floodplain were observed first overbank vertical accretion of silt e g levee overbank sedimentation or splays and second lateral point bar accretion with silt on the scrolls and in the swales the first style led to a reduction in bank erosion while the second style reduced excavation of chutes we conclude that sedimentation of fine cohesive material on the floodplain by discharge exceeding bankfull is a necessary condition for meandering

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

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

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

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

reconstruction of ice sheet changes in the antarctic peninsula since the last glacial maximum this paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the antarctic peninsula ice sheet apis from the last glacial maximum lgm through deglaciation to the present day these data are used to reconstruct grounding line retreat in 5 ka time steps from 25 ka bp to present glacial landforms and subglacial tills on the eastern and western antarctic peninsula ap shelf indicate that the apis was grounded to the outer shelf shelf edge at the lgm and contained a series of fast flowing ice streams that drained along cross shelf bathymetric troughs the ice sheet was grounded at the shelf edge until 20 cal ka bp chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains as well as cosmogenic nuclide dates on erratics and ice moulded bedrock retreat in the east was underway by about 18 cal ka bp the earliest dates on recession in the west are from bransfield basin where recession was underway by 17 5 cal ka bp ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid shelf the timing of initial retreat decreased progressively southwards along the western ap shelf the large ice stream in marguerite trough may have remained grounded at the shelf edge until about 14 cal ka bp although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka bp between 15 and 10 cal ka bp the apis underwent significant recession along the western ap margin although retreat between individual troughs was asynchronous ice in marguerite trough may have still been grounded on the mid shelf at 10 cal ka bp in the larsen a region the transition from grounded to floating ice was established by 10 7 10 6 cal ka bp the apis had retreated towards its present configuration in the western ap by the mid holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier by the start of the holocene mid to late holocene retreat was diachronous with stillstands re advances and changes in ice shelf configuration being recorded in most places subglacial topography exerted a major control on grounding line retreat with grounding zone wedges and thus by inference slow downs or stillstands in the retreat of the grounding line occurring in some cases on reverse bed slopes

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