calibrating the end permian mass extinction the end permian mass extinction was the most severe biodiversity crisis in earth history to better constrain the timing and ultimately the causes of this event we collected a suite of geochronologic isotopic and biostratigraphic data on several well preserved sedimentary sections in south china high precision u pb dating reveals that the extinction peak occurred just before 252 28 0 08 million years ago after a decline of 2 per mil in 13c over 90 000 years and coincided with a 13c excursion of 5 that is estimated to have lasted 20 000 years the extinction interval was less than 200 000 years and synchronous in marine and terrestrial realms associated charcoal rich and soot bearing layers indicate widespread wildfires on land a massive release of thermogenic carbon dioxide and or methane may have caused the catastrophic extinction

prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

bubble induced porewater mixing a 3 d model for deep porewater irrigation porewater data from vent sites of the northeastern shelf off sakhalin island sea of okhotsk exhibit bottom water concentrations down to a sediment depth of up to 300 cm below this depth solute concentrations rapidly change due to methanogenesis and anaerobic methane oxidation amo the profile shapes suggest an irrigation like process that mixes on a meter scale at these sites active gas emanation into the overlying water column and near surface gas hydrates are commonly observed we propose that methane gas bubbles rise through the soft surface sediments and cause mixing of the porewater mathematically the bubble induced irrigation can be described by eddy diffusion enhancing the diffusive transport of solutes by several orders of magnitude a 3 d numerical transport reaction model was developed to investigate the parameters defining the mixing process such as bubble rise velocity tube size tube distribution in the sediment and ebullition frequency model consistency with the field data requires eddy diffusivities 1 105 cm2 a tube densities of 4 tubes m2 equivalent to a tube spacing of 40 cm active gas seepage for more than a few weeks or months and moderate to low diagenetic reaction rates of solutes the corresponding methane gas fluxes that are predicted from the results of the model realizations range from 1 103 5 105 l m2 a due to bubble mixing solute fluxes in these sediments are increased by a factor of 3 and the maximum amo rate by a factor of 7

the terrestrial end permian mass extinction in south china abstract the end permian mass extinction reflects the most severe life crisis during the phanerozoic and was associated with major global environmental changes however the consistency of the time and pattern of the terrestrial and marine extinctions remains controversial in this paper we presented detailed analyses of the high resolution biostratigraphical and geochemical data from terrestrial sections in south china our analyses show that the transitional kayitou formation actually recorded the process of terrestrial mass extinction as evidenced by the mass disappearance of the gigantopteris megaflora in the lower part the dramatic reduction in abundance of palynomorphs in the middle and the last occurrences of plant remains and abundant charcoal fossils in the uppermost part it is associated with a distinct negative shift of 13corg beginning in the middle part of the formation which is correlative with that in the top of bed 26 at the marine meishan section in addition the kayitou formation is characterized by a distinct shift of lithofacies of fresh lake swamp or river flat environment from olive grey black mudstone siltstone fine to coarse sandstone in the lower part to gradually increasing maroon rocks to purely maroon mudrocks with poorly sorted breccia calcic palaeosols and calcareous nodules in the lowest part of the dongchuan formation which indicates a dramatic collapse of soil system associated with rapid deforestation and climatic warming and drying in the coastal area the kayitou formation contains marine beds with the typical permian triassic mixed faunas and floras which are correlative with the latest changhsingian marine mixed fauna 1 at meishan the kayitou formation also recorded a distinct transgression that began in the latest changhsingian all above phenomena suggest that the kayitou formation is actually the witness of the terrestrial end permian mass extinction and it is mostly or entirely of latest changhsingian permian rather than triassic age

distribution and characteristics of natural gas hydrates in the shenhu sea area south china sea abstract structure type gas composition and cage occupancy are important gas hydrate characteristics which play an important role in calculating gas hydrate stability and estimating the amount of global hydrate bound methane china conducted the fourth gas hydrate drilling campaign gmgs4 in the shenhu sea area ssa of the south china sea in 2016 during which comprehensive logging while drilling lwd data and natural gas hydrate samples were obtained the lwd data shows high electrical resistivity and high sound velocity at various depth indicating the occurrence of gas hydrate in this area coexistence of structure i si and structure ii sii gas hydrates in the south china sea was confirmed for the first time by using raman spectra analysis the methane cage occupancies of large cages and small cages in si hydrate are 0 95 and 0 96 respectively the hydration number of si hydrate is 6 03 gas composition analysis shows that methane 98 7 is the dominate gas with small amount of heavier hydrocarbon gases ethane 0 006 0 976 propane 0 033 0 216 isobutane 0 004 0 047 and other non hydrocarbon gases carbon dioxide

global methane emission through mud volcanoes and its past and present impact on the earth s climate mud volcanism is an abundant global phenomenon whereby fluid rich low density sediments extrude both on land and offshore methane which generally exceeds 90 vol of the gas phase is emitted at high rates during and after emplacement of the mud domes and is known for its high global warming potential gwp this comprehensive estimate of the annual contribution of mud volcano degassing assesses the significance of mud volcanism for the accumulation of greenhouse gases in the atmosphere a first order estimate for the earlier pre anthropogenic volume of methane released through mud volcanoes further supports their profound effect on the earth s climate since at least the paleozoic 570 ma

analytical approach to river regime rational regime relationships for the width depth and slope of a channel in equilibrium are developed using the ackers and white sediment transport formulae and the white paris and bettess friction relationships together with the principle of maximum sediment transporting capacity favorable comparisons are made with data from sand and gravel channels and with existing empirical regime relationships

catastrophic fluid escape venting tunnels and related features associated with large submarine slides on the continental rise off vesteralen troms north norway abstract video inspection of the seabed on the continental rise ca 2200 m water depth off vesteralen troms north norway has revealed several remarkable features including large tunnels small tunnels chimney tunnels carbonate crusts and bacterial mats the structures occur in landslide areas with slide blocks up to 2 km long 1 km wide and 100 m high we hypothesize that the large seabed tunnels in and between slide blocks and with opening diameters up to 1 m and apparent inner diameters of 10 20 cm are formed by dewatering of fine grained sediments buried by the slide masses and possibly venting of underground gas reservoirs related to sliding and loading this process probably occurred instantaneously after sliding numerous small tunnels with diameters up to a few centimetres in slide blocks of compacted sediments may have formed by dewatering following sudden pressure release or by decomposition of gas hydrates following off loading of sediments due to sliding bacterial mats and carbonate crusts indicate active leakage of subsurface fluids and methane through the seabed and the gas hydrate stability zone either from thermogenic sources or from shallow reservoirs cemented chimney tunnels up to 15 cm tall and with inner diameters up to a few centimetres occur both on slide blocks and on flat and even seabed the presence of apparently both inactive and active chimney tunnels indicates that gas and fluid release is a process that has been periodically active possibly from before sliding up to the present

theoretical regime equations for mobile gravel bed rivers with stable banks a system of rational regime equations is developed for gravel bed rivers with stable banks using the optimality theory ot the optimality theory is based on the premise that equilibrium river geometry is characterised by an optimum configuration defined here as maximum sediment transport efficiency theoretical dimensionless equations are derived for width depth slope width depth ratio and meandering braiding transition independent dimensionless variables comprise discharge sediment concentration and relative bank strength which is defined as the ratio of the critical shear stresses for the bank and bed sediments discharge exponents and general form of the equations agree well with previously developed empirical relations relative bank strength is used to parameterise the influence of riparian vegetation on bank strength and is evaluated by calibrating against observed width depth ratio once calibrated the hydraulic geometry of natural gravel rivers is well described by the theoretical equations including discrimination between meandering and braiding channels the results provide strong support for the assumption that equilibrium or regime river behavior is equivalent to an optimal state and underline the importance of bank strength and sediment load as controls on hydraulic geometry

grain size sediment transport regime and channel slope in alluvial rivers the general relationship between channel morphology and the grain size of sediment in the channel bed is an important but poorly known aspect of alluvial rivers an analysis of an equation for total sediment flux in the limits of suspension bedload and mixed modes of transport indicates distinct steady state regimes of channel morphology such regimes are readily seen in published data for modern alluvial rivers by way of a conventional shields plot or a plot of channel slope as a function of relative grain size d h and the ratio ws u where d and ws are respectively mean diameter and fall speed of bed sediments and h and u are respectively mean depth and friction velocity of the flow with slope and mode of transport in an alluvial river constrained by grain size and channel depth alone estimates of discharge and sediment flux follow directly introduction of the sediment flux relationship into conventional diffusion models for the evolution of an alluvial system provides nominal estimates of

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

a new estimate of global methane flux from onshore and shallow submarine mud volcanoes to the atmosphere a new estimate of global methane emission into the atmosphere from mud volcanoes mvs on land and shallow seafloor is presented the estimate considered a lower limit is based on 1 new direct measurements of flux including both venting of methane and diffuse microseepage around craters and vents and 2 a classification of mv sizes in terms of area km2 based on a compilation of data from 120 mvs the methane flux to the atmosphere is conservatively estimated between 6 and 9 mt y 1 this emission from mvs is 3 6 of the natural methane sources and is comparable with ocean and hydrate sources officially considered in the atmospheric methane budget the total geologic source including mvs seepage from seafloor microseepage in hydrocarbon prone areas and geothermal sources would amount to 35 45 mt y 1 the authors believe it is time to add this parameter in the intergovernmental panel on climate change official tables of atmospheric methane sources

an environmental gradient of vegetative controls upon channel planform in the source region of the yangtze and yellow rivers abstract alluvial reaches in the source region of the yangtze and yellow rivers located atop the qinghai tibetan plateau and mostly at elevations that are typically higher than 3500 m have similar slope and valley setting conditions however alluvial reaches in the source region of the yangtze river exhibit predominantly braided channel planforms while equivalent reaches in the source region of the yellow river have more diverse planform morphologies including anastomosing braided anabranching braided and anabranching anastomosing reaches the regional gradient of variation in riparian vegetation and interactions between vegetation development and hydrologic process are shown to be major factors influencing this difference in channel planforms a short period above freezing coincident with recurrent yet pulsed flows in the source region of the yangtze river suppress riparian vegetation growth promoting the development of braided channel morphologies in contrast a milder climate coincident with less variable flows in the source region of the yellow river permit the establishment of different forms of riparian vegetation thereby supporting the development of a wider range of channel planform morphologies

the development mechanism of gravel bars in rivers the development stability and growth direction of gravel mid channel bars in rivers were studied by analyzing sediment distribution and vegetation development along the bars field studies and sediment sampling were conducted in the source region of the yellow and lancang rivers on the qinghai plateau the results showed that the gravel bars in rivers always grow in the upstream direction because gravel and sand are deposited at the upstream end of the bars gravel bedload stopped at the bar head sand and silt moved as suspended load during the flood season and were deposited at the bar tail due to vegetation resistance consequently sediment size varied from gravel to sand and silt along the bars from the head to the tail on the bar surface dense vegetation coverage normally grew at the bar tail while only pioneer species occurred at the bar head the prevalent phenomena demonstrated the upstreamward growth of mid channel bars

assessing channel changes of the ganges padma river system in bangladesh using landsat and hydrological data abstract the ganga ganges 1 is an important river system in south asia which supports the life and livelihoods of millions of people both in india and bangladesh the system has a number of names throughout its length below its confluence with the brahmaputra at aricha it is known as the padma which in turn merges with the upper meghna at chandpur below which the channel is known as the lower meghna there is a growing concern about this large river system because its channels are subject to frequent migration threatening engineering structures and resulting in various environmental and social consequences which may be compounded by climatic variability land use change and agricultural intensification as the basin experiences rapid population growth concerns have been expressed that the construction of a barrage just upstream of the indo bangladesh border has adversely affected the ganges reach in bangladesh partly in order to investigate this the planform changes of the ganges and the padma within bangladesh was analysed over the period 1973 to 2011 using multitemporal landsat images and long term flow data in eight epochs with an average duration of 4 5 years the padma reach is less affected by the barrage and provides a useful control study areas of erosion and deposition were determined from sequential changes in the bankline positions mean channel width sinuosity and braiding index were analysed using a geographic information system gis flood frequency duration and magnitudes were studied using long term discharge records generally channel planform evaluation indicated that both the ganges and the padma experienced contraction expansion and readjustment in configuration over the last 38 years erosion and deposition statistics of the ganges indicate that 57 km2 of land was lost along the right bank whereas around 59 km2 has been gained along the left bank during the assessment period suggesting that the erosion and accretion of both banks is roughly balanced with a general movement towards the right bank the width of the ganges varied from a maximum of 5 36 to a minimum of 3 23 km during the observation period changes to sandbar area are in general much more radical than changes to the overall width and area of the channel measurement of areas of erosion and accretion showed that both banks of the padma experienced considerable loss of land the total net loss for left bank and right bank was 155 and 28 km2 respectively the padma is approximately twice the width of the ganges and the changes to its channel area are not as temporally dynamic as the ganges the relationship between bank curvature and erosion accretion of the river banks for both rivers was analysed and the results contradict established meander theory regression analysis between bank erosion rates annual average discharge and mean flood flow data showed that bank erosion was significantly correlated with annual average discharge for the padma r2 0 6283 and that the ganges bank erosion rate is influenced by mean flood flow r2 0 6738 the flood frequency shows generally good stability across the first eight of the nine epochs for the ganges but for the padma the frequency showed even greater stability we were unable to support the widely held belief that the upstream barrage has a deleterious effect on the ganges but note that there is a slight effect due to the periodic release of sediment through scour sluices

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

predicting downstream hydraulic geometry a test of rational regime theory 1 the classical equations of hydraulic geometry are purely empirical but the widespread similarity of the scaling downstream form of them suggests that they express some important underlying regularities in the morphology of stream channels through the drainage network a successful physical theory of river regime must be able to reproduce and explain this regularity in this paper we test the regime theory of eaton et al 2004 using selected data of hydraulic geometry we first use data from environments in which bank strength presumably does not vary greatly such as in anabranched channel systems and deltas regime models parameterized by assuming uniform relative bank strength plausibly describe the observed bankfull channel geometries in these systems we then test a modified bank strength formulation for vegetated gravel bed rivers against downstream hydraulic geometry data sets in which relative bank strength is supposed to vary with channel scale assuming a uniform effective cohesion due to riparian vegetation the regime model is again able to reproduce details of the channel geometry both analyses show that the classical hydraulic geometry represents only an approximation of the variation of channel form if we have confidence in the theory we may infer information about bank strength and bed material transport the pattern of variation in these quantities as well as discharge through the drainage system lends approximate regularity to stream channel scaling that is summarized in the empirical relations

stability morphology and surface grain size patterns of channel bifurcation in gravel cobble bedded anabranching rivers this study presents the first detailed field based analysis of the morphology of bifurcations within anabranching cobble gravel rivers bifurcations divide the flow of water and sediment into downstream anabranches thereby influencing the characteristics of the anabranches and the longevity of river islands the history morphology bed grain size and flow vectors at five bifurcations on the renous river new brunswick canada were studied in detail the angles of bifurcations within five anabranching rivers in the miramichi basin were investigated the average bifurcation angle was 47 within the range of values cited for braided river bifurcations bifurcation angle decreased when anabranches were of similar length shields stresses in channels upstream of bifurcations were lower than reported values for braided rivers stable bifurcations displayed lower shields stresses than unstable bifurcations contrary to experimental results from braided river bifurcations bifurcations in anabranching rivers are stabilized by vegetation that slows channel migration and helps to maintain a uniform upstream flow field the morphology of stable bifurcations enhances their stability a large bar shaped like a shallow ramp that increases in elevation to floodplain level forms at stable bifurcations floodplains at stable bifurcations accrete upstream at rates between 0 9 and 2 5 m a 1 bars may also form within the entrance of an anabranch downstream of the bifurcation node these bars are associated with bifurcation instability forming after a period of stability or an avulsion channel abandonment occurs when a bar completely blocks the entrance to one anabranch the stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term copyright 2006 john wiley sons ltd

channel patterns braided anabranching and single thread a new channel pattern classification is presented based on theoretically derived channel pattern discriminant functions the thresholds are formulated as power laws that relate the critical slope associated with a change in channel pattern to dimensionless discharge and relative bank strength one threshold demarcates the boundary between stable single thread channels both straight and meandering and stable multiple thread channels anabranching another threshold separates anabranching from braided channels where braided channels are considered to be fundamentally unstable the exponents of the thresholds are nearly identical to that in the threshold equation originally proposed by leopold and wolman 1957 and the coefficients are quite similar as well an analysis of their data set using our dimensionless approach reveals that no fundamental difference exists between meandering and straight patterns and thus data from both types are grouped together under the more general heading of single thread channels furthermore we demonstrate that over a limited range of conditions an unstable single thread channel can form stable multiple threads but that for systems far from the threshold bounding the single thread channels the number of divisions required to produce stable anabranches grows geometrically this motivates a separation of multiple thread channels into anabranching and braided types our theoretical thresholds are then compared against several large data sets of field data and the results broadly confirm our proposed thresholds

understanding the temporal dynamics of the wandering renous river new brunswick canada wandering rivers are composed of individual anabranches surrounding semi permanent islands linked by single channel reaches wandering rivers are important because they provide habitat complexity for aquatic organisms including salmonids an anabranch cycle model was developed from previous literature and field observations to illustrate how anabranches within the wandering pattern change from single to multiple channels and vice versa over a number of decades the model was used to investigate the temporal dynamics of a wandering river through historical case studies and channel characteristics from field data the wandering renous river new brunswick was mapped from aerial photographs 1945 1965 1983 and 1999 to determine river pattern statistics and for historical analysis of case studies five case studies consisting of a stable single channel newly formed anabranches anabranches gaining stability following creation stable anabranches and an abandoning anabranch were investigated in detail long profiles hydraulic geometry channel energy grain size and sediment mobility variables were calculated for each channel within the renous study area the frequency of channel formation and abandonment were similar over the 54 years of analysis indicating that the wandering pattern is being maintained eight anabranches were formed through avulsions five were formed through the emergence of islands from channel bars and 11 anabranches were abandoned the stable anabranch pair displayed similar hydraulic geometry and channel energy characteristics while unstable anabranch pairs did not the anabranch pair that gained stability displayed more similar channel energy characteristics than the anabranch pair that was losing stability abandoning it appears that anabranch pairs with similar energy characteristics are more stable than anabranches where these characteristics are out of balance this is consistent with the hypothesis that anabranch pairs of similar length will be more stable than those with dissimilar lengths copyright 2005 john wiley sons ltd

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

relations between mud volcanoes thrust deformation slope sedimentation and gas hydrate offshore north panama abstract seamarc ii swath mapping and migrated seismic reflection data show a high concentration of mud volcanoes in the primary sediment depocentre along the lower slope of a thrust belt offshore north panama the mud volcanoes are 0 4 2 0 km wide sonar reflectivity backscattering sediment cores and seismic stratigraphic relations indicate that the depocentre contains thick sequences of basinal turbidites which are ponded between the anticlinal ridges the ridges are composed of the deformed turbidites of the colombian basin and exhibit a strong bottom simulating reflector bsr apparently associated with a gas hydrate layer based on the concentration of mud volcanoes along the crests of the anticlinal ridges in the depocentre and the structural position of the bsr we suggest that folding along the deformation front sediment ponding leading to differential loading methane migration and accumulation in the anticlines and gas hydrate formation are important factors in the development of mud volcanoes in this region

bank stability analysis for regime models of vegetated gravel bed rivers a new bank stability analysis procedure is developed for use in rational regime models predicting reach average channel dimensions the performance of a regime model using this new bank stability formulation is compared against that for a model using the modified friction angle approach proposed by millar and quick 1993 the bank stability assessment is based on a conceptual model that more closely represents conditions found in gravel bed rivers with vegetated floodplains the primary effect of vegetation is its contribution to a stable upper bank the position of which is determined by erosion of unvegetated bed material at the toe of the bank the vertical height of the upper bank is estimated using a simple slab failure model and assigning an effective cohesion to the vegetation reinforced soil the geometry of the lower slope and the width of the channel are determined iteratively using the regime approach described by eaton et al 2004 a comparison of the predicted stream channel widths for stable gravel bed channels classified according to riparian vegetation type hey and thorne 1986 showed that this new formulation increases model accuracy especially for the more densely vegetated channel types since the strength parameters used in the model can be estimated from the observed bank geometry the potential for applying and testing rational regime models in the field has been significantly improved copyright 2006 john wiley sons ltd

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

lateral geomorphic connectivity in a fluvial landscape system unraveling the role of confinement biogeomorphic interactions and glacial legacies abstract the rates at which sediment from the landscape is recruited to channel networks reflect lateral geomorphic connectivity and have significant implications for biophysical river systems by strongly influencing sediment supply regime such inputs control the dynamics and characteristics of the channel as well as the associated habitat and biota the main objective of this research was to disentangle the relative importance of geomorphic and biological factors which define spatial patterns in lateral connectivity by promoting or restricting bank erosion avulsions and slope failures focusing on a forested formerly glaciated mountain basin in the interior pacific northwest we combined extensive field surveys with remote sensing data lidar aerial imagery to obtain metrics representing this complex suite of landscape characteristics the interpretation of evidence yielded by correlations between these variables a regime model and qualitative observations suggest that at a multi decadal timescale between major landscape disturbances lateral connectivity patterns in sullivan creek may be to a large extent governed by a combination of biotic factors and glacial legacies in particular forest canopy metrics were key predictors of hillslope stability as well as bank and valley floor resistance suggesting a pivotal influence of root reinforcement on the other hand instream large wood abundance was closely related to channel splitting which reflects its role in promoting channel avulsions more extensive bank erosion in reaches dominated by drift deposits appeared to indicate glacial legacies furthermore a strong association between bank erosion and colluvial inputs suggested a close coupling within the channel hillslope system lateral confinement defined as the proportion of the channel length abutting against bedrock terraces fans and roads was negatively associated with channel braiding the relationships linking confinement with bank erosion and the magnitude of colluvial inputs negative and positive association respectively were relatively weak taken together findings emerging from this research suggest that better understanding of lateral geomorphic connectivity patterns in mountain river basins similar to our study site requires that both channel processes and broader biophysical landscape system be considered

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

terrestrial permian triassic boundary in southern china new stratigraphic structural and palaeoenvironment considerations the permian triassic boundary is located above the main phanerozoic terrestrial and marine biotic crisis southwest china eastern yunnan and western guizhou is considered as an ideal place in asia to study the terrestrial permian triassic boundary its correlation with the stratigraphically equivalent marine deposits and to discuss the contemporaneity between the marine and terrestrial extinctions the chahe and zhejue sections which have already been studied in detail especially using 13c isotopic analyses for both sections and geochronology for the chahe section are considered to be the reference terrestrial sections to discuss changes both through time and space in macroflora pollen diversity and paleoenvironment based on new structural analyses of these sections we demonstrate that they have been strongly affected by polyphase deformations and are therefore not suitable to discuss the vertical and or lateral evolutions of the depositional environments within the permian triassic succession the use of the chahe and zhejue sections to study the contemporaneity between marine and terrestrial extinction events at the end of the permian in southern china as well as the stratigraphic correlations and the palaeoenvironment reconstitution of western guizhou and eastern yunnan therefore must be reconsidered

the response of braided planform configuration to flow variations bed reworking and vegetation the case of the tagliamento river italy morphological features of braided rivers bars channels and pools experience major changes in area shape and spatial distribution as a response to i the pulsation of discharge during a flood and ii the bed evolution induced by floods in this work at a station relationships between water level and planform configuration were investigated on the tagliamento river a large gravel bed braided river in northeast italy over a 2 year study period comprising three bankfull events and several small to medium floods the analysis was performed on two 1 km long reaches characterized by different riparian vegetation cover ground based images with an hourly temporal resolution were acquired using software controlled digital cameras bars channels pools and vegetated patches were manually digitized on more than 100 rectified images sequences of constant level images spanning the study period were used to quantify the impact of floods on the stability of at a station relationships and on the turnover rate of water bodies the analysis shows that wetted area increased almost linearly with water level in both reaches the average number of branches per cross section peaked at intermediate flow levels increasing from 2 at low flow up to 6 7 the number of branches displayed the largest fluctuations over time with significant changes produced also by moderate floods turnover rates were high in both reaches with more than 30 of wetted areas at low flow converting into bare gravel in less than 2 months vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer deeper anabranches the number of channels per cross section was 30 40 less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3 to 14 copyright 2012 john wiley sons ltd

methane emission from the mud volcanoes of sicily italy 1 mud volcanoes represent the largest expression of natural methane release into the atmosphere however the gas flux has never been investigated in detail methane output from vents and diffuse soil degassing is herewith reported for the first time measurements were carried out at 5 mud volcano fields around sicily italy each mud volcano is characterized by tens of vents and bubbling pools in the quiescent phase methane emission from single vents ranges between 0 01 and 6 8 kg day diffuse soil leakage around the vents is in the order of 102 104 mg m 2 d 1 an exceptional flux of 106 mg m 2 d 1 was recorded close to an everlasting fire soil ch4 flux is positive even at large distances from the mud volcano fields suggesting a diffuse microseepage over wider areas a total of at least 400 tons ch4 per year can be estimated over the area investigated alone 1 5 km2

global methane emission through mud volcanoes and its past and present impact on the earth s climate a comment the role of mud volcanoes mvs as a source of methane ch4 flux to the atmosphere and the ocean has been increasingly recognised in the last several years milkov 2000 dimitrov 2002 2003 etiope and klusman 2002 kopf 2002 2003 milkov et al 2003 etiope and milkov 2004 in one of the most recent papers kopf 2003 claims to report a reliable estimate of the global ch4 emission from mvs however the significance and usefulness of the estimate presented by kopf 2003 are rather poor the used dataset is smaller than in previous studies although the author makes a reverse claim and some previously published works are misquoted and misinterpreted numerous arithmetic mistakes made during simple calculations and data manipulations lead to confusing results and conclusions in this comment we highlight some of the most significant problems with the estimates published by kopf 2003

effect of bank stability on geometry of gravel rivers a bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel bed channel the new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability the bank stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment cementing by fines and binding of the sediment by root masses the two key parameters in the bank stability analysis are the median grain diameter of the bank sediment d50bank and the modified friction angle of the bank sediment a sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry this is supported by testing the theory on published field data the bank sediment size was assumed to equal the bed sediment size and the variation of the friction angle was investigated the estimated values are seen to increase systematically

palynology and vegetation dynamics across the permian triassic boundary in southern tibet abstract the end permian mass extinction epme is regarded as the most severe biotic crisis in earth history which is particularly well documented in the marine fossil record despite compelling evidence that dramatic global environmental changes probably drove this extinction event its effects on terrestrial plants are still highly controversial here we present changhsingian latest permian to late smithian latest early triassic composite palynological successions from the lagoonal to open marine qubu and tulong sections in southern tibet quantitative analyses of palynomorph distributions range charts and relative abundance data allow us to differentiate five distinct informal palynofloral assemblages in ascending order the scheuringipollenites ovatus vitreisporites pallidus op assemblages the reduviasporonites catenulatus assemblage the endosporites papillatus pinuspollenites thoracatus pt assemblages the lundbladispora brevicula densoisporites nejburgii bn assemblages and the falcisporites nuthallensis alisporites landianus nl assemblages these palynological assemblage intervals and the associated ammonoid and conodont biostratigraphy resolve vegetation changes across the permian triassic boundary ptb on the northern tethyan margin of gondwanaland in great detail and high resolution principal component analysis pca of palynological data indicates that the op assemblages which are dominated by non taeniate bisaccate pollen represent a vegetation in a cool and dry climate during the changhsingian in the qubu section the palynological turnover from the op assemblages to the c assemblage 0 81 m below the ptb coincides with abrupt sea level fluctuations in the latest permian as this turnover further coincides with an extreme negative 13corg shift a great abundance of amorphous organic matter aom and marine acritarchs as well as the frequent occurrence of reduviasporonites catenulatus the c assemblage is tentatively interpreted to represent the fungal spike reported worldwide at the onset of the epme in southern tibet the epme appears to result only in a short term disturbance and range contraction of land plant communities surprisingly the early dienerian pt assemblages postdating the epme by about 500kyrs closely resemble the late changhsingian op assemblages suggesting a resurgence of those land plant groups that were dominant during the late changhsingian this recovery was disrupted with the onset of the late dienerian bn assemblages in the qubu section which is represented by a peak abundance of cavate trilete spores reflecting large scale deforestation for nearly one million years the regional vegetation appears to have been dominated by pioneer communities of quillworts and spike mosses only towards the end of the smithian bisaccate gymnosperm pollen regained dominance with the onset of the nl assemblages in the tulong section integrating the results of the principal component analysis on our new palynological data and conodont apatite oxygen isotope data from neighbouring sections in pakistan the contraction of gymnosperm forests during the early dienerian smithian in southern tibet is interpreted to be accompanied by an abrupt change to an episode with a warmer and more humid climate this observation supports the hypothesis that the secondary eruptions of the siberian large igneous province during the induan led to long term global warming and as a side effect to more humid conditions in the southern temperate zone as a result of altered precipitation and evaporation patterns

least action principle equilibrium states iterative adjustment and the stability of alluvial channels the energy based least action principle lap has proven to be very successful for explaining natural phenomena in both classical and modern physics this paper briefly reviews its historical development and details how in three ways it governs the behaviour and stability of alluvial rivers first the lap embodies the special stationary equilibrium state of motion and so its incorporation with the principle of energy conservation explains why so many optimizing hypotheses have been proposed in fluvial geomorphology second the variational approach underlying the lap provides a more straightforward and simpler fuzzy object orientated method for solving river regime problems than do the various complex newtonian formulations third it is shown that in fluvial systems with surplus energy the surplus can be expended with slope and or channel geometry adjustments with the degree of channel geometry adjustment quantified by the dimensionless numbers f for depth dominated adjustment and h for width depth dominated adjustment different planforms are preferred at different energy levels with h providing a quantitative measure of the flow s efficiency for moving sediment in rivers with insufficient energy the interactions of endogenous and exogenous factors are shown to be capable in certain circumstances of achieving a stationary equilibrium condition which acts as the attractor state importantly this study describes how iterative changes enable systems to achieve such a stable equilibrium copyright 2007 john wiley sons ltd

stable width and depth of gravel bed rivers with cohesive banks an analytical model is developed to determine the influence of the bank stability on the stable width and depth of alluvial gravel bed rivers with cohesive banks the formulation of the model is based on the assumption that the stable width corresponds with an optimum condition that is equivalent to the maximum bed load transporting capacity the optimum condition develops when the channel banks are at their limiting stability with respect to either mass failure or fluvial erosion two basic channel types are identified bank height and bank shear constrained mass failure stability is estimated using a simple total stress approach a method for estimating the critical bank shear stress based on model calibration is proposed analysis of field data indicates that the effect of the bank vegetation on bank stability can be expressed in terms of the critical bank shear stress the average critical bank shear stress value calculated for riverbanks covered by vegetation with well developed root networks was fo

a graded stream response relation for bed load dominated streams 1 the relation between equilibrium stream channel morphology and three independent governing variables discharge sediment supply and valley slope is investigated using a stream table the experiments are based on a generic physical model of a laterally active gravel bed stream and directed by a recently published rational regime model while a variety of channel adjustments are possible the primary adjustment observed was in the channel slope other adjustments such as surface armor composition and cross sectional shape were minor in comparison the equilibrium slope is well predicted by a linear function of sediment concentration which is bounded by two thresholds one associated with the minimum stream power necessary to deform the bed and the other associated with the maximum sediment feed that can be transported by the available flow the results suggest that the system tends to move toward the minimum slope capable of transporting the sediment supply in the process increasing the flow resistance for the system whether or not a minimum slope or a maximum system scale flow resistance is reached cannot be determined given the available data but there appears to be a unique slope or at least a limited range of slopes for which a stable alluvial channel morphology can be established for a given sediment concentration the implications of this behavior are evaluated for the theoretical basis of the extremal hypothesis used to close the formulation of a rational regime model

high resolution terrestrial permian triassic eventostratigraphic boundary in western guizhou and eastern yunnan southwestern china the adjoining area of western guizhou and eastern yunnan provinces in southwest china is an ideal place to investigate the feasibility of correlating marine and nonmarine permian triassic boundary ptb sequences as it contains outcrop sections of shallow marine marginal marine or paralic and terrestrial ptb sections all in close geographic proximity this paper documents for the first time multiple stratigraphic data from several well preserved terrestrial ptb sections in the area and attempts to use these data to define locate and correlate the ptb in the area a study of the spores and pollen and vegetation types across the terrestrial ptb sections in the study area suggests three distinct evolutionary stages across the boundary stage 1 xuanwei formation is characterised by late permian or paleozoic type ferns and pteridosperms 85 0 with a few gymnosperms 15 0 stage 2 is marked by an abrupt drop of sporopollen elements of late permian aspects coupled with the appearance of fungal spores and limited early triassic palynomorphs stage 3 top xuanwei formation and kayitou formation is dominated by gymnosperm pollen 58 8 of clearly early triassic aspect although still retaining limited ferns and pteridosperms the three biotic stages seem to well correspond with the changing trend of the 13corg curves from the same sections which is characterized by a sharp drop just before the ptb followed by a short term partial recovery across the boundary and then succeeded by a gradual decline after the ptb in the early triassic combining evidence from eventostratigraphic i e the succession of boundary clay beds biostratigraphic using both macroplants and palynomorphs and chemostratigraphic i e organic carbon isotope excursion signals we propose that a high resolution ptb succession closely correlatable to its marine counterpart at the meishan section in eastern china is recognisable at the terrestrial ptb sections in the western guizhou eastern yunnan area in southwest china

channel stability in bed load dominated streams with nonerodible banks inferences from experiments in a sinuous flume 1 experimental and computational evidence shows that bed state adjustments can accommodate a twofold to fourfold change in sediment supply without otherwise affecting the morphology of a sinuous gravel bed stream channel with nonerodible banks in contrast previously published experiments of the same kind but with erodible channel banks suggest that changes in sediment supply are taken up almost exclusively by changes in channel sinuosity and hence the reach average water surface gradient it appears that stream channel response to changes in sediment supply is strongly conditioned by the nature of the stream boundary and that determines which of several potential adjustments are possible

effects of sediment supply on surface textures of gravel bed rivers using previously published data from flume studies we test a new approach for quantifying the effects of sediment supply i e bed material supply on surface grain size of equilibrium gravel channels textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size d9 50 we find that surface median grain size d50 varies inversely with sediment supply rate and systematically approaches the competent value d9 at low equilibrium transport rates furthermore equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes d9 and d50 consequently we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size while the approach appears promising we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions

terrestrial paleoenvironment characterization across the permian triassic boundary in south china well preserved marine fossils in carbonate rocks permit detailed studies of the end permian extinction event in the marine realm however the rarity of fossils in terrestrial depositional environments makes it more challenging to attain a satisfactory degree of resolution to describe the biotic turnover on land here we present new sedimentological paleontological and geochemical x ray fluorescence analysis from the study of four terrestrial sections chahe zhejue mide and jiucaichong in western guizhou and eastern yunnan yangtze platform south china to evaluate paleoenvironmental changes through the permian triassic transition our results show major differences in the depositional environments between the permian xuanwei and the triassic kayitou formations with a change from fluvial lacustrine to coastal marine settings this change is associated with a drastic modification of the preservation mode of the fossil plants from large compressions to small comminuted debris plant fossils spanning the permian triassic boundary show the existence of two distinct assemblages in the xuanwei formation a late permian changhsingian assemblage with characteristic cathaysian wetland plants mainly gigantopteris dictyophylloides gigantonoclea guizhouensis g nicotianaefolia g plumosa g hallei lobatannularia heinanensis l cathaysiana l multifolia annularia pingloensis a shirakii paracalamites stenocostatus cordaites sp is identified in the lowermost kayitou formation an early triassic induan annalepis peltaspermum assemblage is shown associated with very rare relictual gigantopterids palynological samples are poor and low yield samples show assemblages almost exclusively represented by spores a similar to 1 m thick zone enriched in putative fungal spores was identified near the top of the xuanwei formation including diverse multicellular forms such as reduviasporonites sp this interval likely corresponds to the ptb fungal spike conventionally associated with land denudation and ecosystem collapse while the floral turnover is evident further studies based on plant diversity would be required in order to assess contribution linked to the end permian mass extinction versus local paleoenvironmental changes associated with the transition between the xuanwei and kayitou formations c 2014 elsevier ltd all rights reserved less

the relationship between flow shear stress and stream pattern based on simple hydraulic reasoning a discharge q slope s diagram for streams is given a physical interpretation permitting the assignment of a relative shear stress value to each stream a sample of 359 streams is used ranging in mean annual discharge from 900 000 to 0 05 ft 3s 1 varying in pattern from highly sinuous p 3 1 to straight and braided sorted according to their relative shear stress values 0 avg streams of high sinuosity p 1 5 are characterized by low relative shear stress median 0 56 which is significantly lower than that characterizing braided streams median 1 70 it is concluded that for natural stream populations the passage from one pattern to another is gradual and the geomorphic thresholds defined by relative shear stress are fuzzy ones

fluvial connectivity and climate a comparison of channel pattern and process in two climatically contrasting fluvial sedimentary systems in south africa abstract the aim of this research was to investigate the dynamics of valley formation sediment delivery and channel pattern in two climatically contrasting fluvial sedimentary systems in south africa each system comprised a network of headwater valley fills and floodplains underlain by sedimentary karoo supergroup rocks that are intersected by resistant dolerite dykes and sills the seekoei river floodplain and gordonville valley fill site in the great karoo however experience less than half the annual precipitation of the nsonge river floodplain and hlatikhulu valley fill in the kwazulu natal drakensberg foothills furthermore rainfall is more variable in the karoo despite climatic differences headwater valley fills were geomorphically similar in contrast floodplains in the two regions were vastly different even when the same downstream control a resistant dolerite intrusion crossing the drainage line was considered upstream of a dolerite dyke the nsonge river is highly sinuous and located in a wide floodplain that has been carved by lateral planation of the underlying bedrock in comparison the seekoei river located upstream of a dolerite sill is discontinuous and characterized by floodouts and avulsing distributaries that undergo periods of bedrock incision followed by infilling it is likely that this disparity is caused by the inability of infrequent unsustained flows to develop meanders and thus adjust the channel planform to changes in discharge sediment load and valley slope flow variability thus exercises a strong control on channel pattern and causes floodouts in headwater settings and the semi arid karoo floodplain as a result sediment transport in the seekoei river is likely to be episodic and net retention of sediment in the semi arid floodplain is greater than in the sub humid nsonge river floodplain where sediment depth is limited

an approach for measuring confinement and assessing the influence of valley setting on river forms and processes valley setting and confinement or lack thereof are primary controls on river character and behaviour although there are various proxies for valley confinement direct measures that quantify the nature and extent of confinement are generally lacking and or inconsistently described as such they do not lend themselves to consistent analysis over large spatial scales here we clearly define forms of confinement to aid in quantification of degrees of confinement types of margin that can induce confinement are differentiated as a valley margin valley bottom margin and or anthropogenic margin such margins sometimes overlap and share the same location and in other situations are separated giving immediate clues as to the valley setting we apply this framework to examples from australia united states and new zealand showing how this framework can be applied across the spectrum of river diversity this method can help to inform interpretations of reach scale river behaviour highlighting the role of antecedent controls on contemporary forms and processes clear definitions of confinement are shown to support catchment scale analysis of river patterns along longitudinal profiles and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments e g process zone distribution lateral sediment inputs and dis connectivity copyright 2015 john wiley sons ltd

channel pattern and river floodplain dynamics in forested mountain river systems channel pattern effectively stratifies the dynamics of rivers and floodplains in forested mountain river systems of the pacific northwest usa straight channels are least dynamic with relatively slow floodplain turnover and floodplains dominated by old surfaces braided channels are most dynamic with floodplain turnover as low as 25 years and predominantly young floodplain surfaces island braided and meandering channels have intermediate dynamics with moderately frequent disturbances erosion of floodplain patches maintaining a mix of old and young surfaces return intervals for the erosion of floodplains increase in the order of braided island braided meandering and straight 8 33 60 and 89 years respectively a threshold for the lateral migration of a channel occurs at a bankfull width of 15 20 m the most likely mechanism underlying this threshold is that larger channels are deep enough to erode below the rooting zone of bank vegetation above this threshold channels not confined between valley walls exhibit channel patterns distinguishable by slope and discharge and slope discharge domains can be used to predict channel patterns meandering and braided patterns are most consistently identified by the model and prediction errors are largely associated with indistinct transitions among channel patterns that are adjacent in plots of slope against discharge locations of straight channels are difficult to identify accurately with the current model the predicted spatial distribution of channel patterns reflects a downstream decline in channel slope which is likely correlated with a declining ratio of bed load to suspended load ecological theory suggests that biological diversity should be highest where the intermediate disturbance regime of island braided channels sustains high diversity of habitat and successional states through time

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

methane emission from mud volcanoes in eastern azerbaijan methane ch4 flux to the atmosphere was measured from gas vents and for the first time from soil microseepage at four quiescent mud volcanoes and one everlasting fire in eastern azerbaijan mud volcanoes show different activity of venting craters gryphons and bubbling pools with ch4 fluxes ranging from less than one to hundreds of tons per year microseepage ch4 flux is generally on the order of hundreds of milligrams per square meter per day even far away from the active centers the ch4 flux near the everlasting fires on the order of 105 mg m 2 d 1 represents the highest natural ch4 emission from soil ever measured the specific ch4 flux to the atmosphere between 102 and 103 t km 2 yr 1 was similar to specific flux from other mud volcanoes in europe at least 1400 tons of ch4 per year are released from the investigated areas it is conservatively estimated that all onshore mud volcanoes of azerbaijan during quiescent activity may still emit 0 3 0 9 106 t of ch4 per year into the atmosphere the new data fill a significant gap in the worldwide data set and confirm the importance of geologic sources of greenhouse ch4 although they are not yet considered in the climate study budgets of atmospheric ch4 sources and sinks

comments on terrestrial permian triassic boundary in southern china new stratigraphic structural and palaeoenvironment considerations by bourquin et al 2018 abstract the terrestrial permian triassic transitional section at chahe in western guizhou province south china has served as a key reference section for the study of terrestrial ptb as well as the end permian mass extinction on land in south china however bourquin et al 2018 recently reported that the ptb interval at chahe has undergone serious tectonic deformation and thus is not suitable for studying the ptb transition or the terrestrial end permian extinction due to an unknown amount of stratigraphy removed displaced by faulting in order to clarify the observations of bourquin et al 2018 we re surveyed the chahe section in further detail recently and our observations suggest that the interpreted deformation by bourquin et al 2018 cannot be verified and it also contradicts the regional litho and bio stratigraphic and chemostratigraphic results we provide detailed outcrop imagery and data for all colleagues who are interested in this section to check our observations

assessing the effect of vegetation related bank strength on channel morphology and stability in gravel bed streams using numerical models bank strength due to vegetation dominates the geometry of small stream channels but has virtually no effect on the geometry of larger ones the dependence of bank strength on channel scale affects the form of downstream hydraulic geometry relations and the meandering braiding threshold it is also associated with a lateral migration threshold discharge below which channels do not migrate appreciably across their floodplains a rational regime model is used to explore these scale effects it parameterizes vegetation related bank strength using a dimensionless effective cohesion cr the scale effects are explored primarily using an alluvial state space defined by the dimensionless formative discharge q and channel slope s which is analogous to the q s diagrams originally used to explore meandering braiding thresholds the analyses show that the effect of vegetation on both downstream hydraulic geometry and the meandering braiding threshold is strongest for the smallest streams in a watershed but that the effect disappears for q 106 the analysis of the migration threshold suggests that the critical discharge ranges from about 5 m3 s to 50 m3 s depending on the characteristic rooting depth for the vegetation the analysis also suggests that where fires frequently affect riparian forests channels may alternate between laterally stable gravel plane bed channels and laterally active riffle pool channels these channels likely do not exhibit the classic dynamic equilibrium associated with alluvial streams but instead exhibit a cyclical morphologic evolution oscillating between laterally stable and laterally unstable end members with a frequency determined by the forest fire recurrence interval copyright 2008 john wiley sons ltd

vegetation changeover across the permian triassic boundary in southwest china extinction survival recovery and palaeoclimate a critical review abstract this paper reviews critically the permian triassic p tr fossil plants and microflora recorded in three well studied terrestrial permian triassic boundary ptb sections namely chahe zhejue and jiucaichong and two marine terrestrial transitional ptb sections namely mide and tucheng in western guizhou province and eastern yunnan province wgey southwest china distinct floral composition abundance and diversity across the ptb allow the establishment of two terrestrial macrofloral assemblages the lobatannularia multifolia gigantoclea guiyangensis l g assemblage was recognized from the upper xuanwei formation while the annalepis peltaspermum a p assemblage from the lower kayitou formation the former flora comprises 105 species in 39 genera and is late changhsingian in age the latter assemblage includes 18 species in 14 genera and is induan in age the changhsingian assemblage is characterized by the loss of many wuchiapingian elements of the gigantopteris flora and an increase of the gymnosperms most of the permian type plant taxa were wiped out in the ptb crisis on land with only few relicts persisting into the early triassic which saw the flourishing of annalepis and common presence of peltaspermum and permian relicts of the gigantopterids during the permian triassic transition some rare gigantopterids elements as well as some peltaspermum representatives survived the biocrisis annalepis a pioneering lycopsid genus in the recovery of the triassic land plants and its proliferation marks the recovery of land plants after the ptb crisis on land in wgey accordingly vegetation changeover across the ptb is marked by a dramatic turnover of plants on land from the permian gigantopteris flora to the triassic annalepis dominated assemblage palynofloras are characterized by a dramatic drop of palynomorphs in both abundance and diversity and show a stepwise extinction pattern moreover macro and microfloras of the wgey region indicate that humid and warm climate regime prevailed through the p tr transition in southwest china the coal forming swamps gradually migrated westward due to marine transgressions throughout the late permian the gigantopteris flora also migrated from east to west and a few species can survive into the earliest triassic in the wgey region but disappeared soon after

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

gas flux to the atmosphere from mud volcanoes in eastern romania gas flux measurements have for the first time been taken from vents and soil of eastern romania mud volcanoes the largest geological structures in europe releasing methane into the atmosphere in the quiescent phase the methane emission from single vents is up to 28 t yr 1 diffuse soil microseepage is of the order of 10 2 10 5 mg m 2 day 1 a total output of at least 1200 tonnes of ch4 per year can be conservatively estimated over the area investigated alone 2 3 km 2 helium fluxes are up to five orders of magnitude higher than the average flux in a stable continental area pointing to a close link between mud volcanoes and crustal degassing through faults crossing the deep hydrocarbon reservoirs these data represent a key contribution towards refining global ch4 emission estimates which indicate mud volcanoes as a significant and unavoidable source of greenhouse gases for the atmosphere

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

sublacustrine mud volcanoes and methane seeps caused by dissociation of gas hydrates in lake baikal four lake floor seeps have been studied in the gas hydrate area in lake baikal s south basin by using side scan sonar detailed bathymetry measurements of near bottom water properties heat flow measurements and selected seismic profiles in relation to results from geochemical pore water analysis the seeps at the lake floor are identified as methane seeps and occur in an area of high heat flow where the base of the gas hydrate layer shallows rapidly toward the vent sites from 400 m to 150 m below the lake floor at the site of the seep a vertical fluid conduit disrupts the sedimentary stratification from the base of the hydrate layer to the lake floor the seeps are interpreted to result from local destabilization of gas hydrate caused by a pulse of hydrothermal fluid flow along an active fault segment this is the first time that methane seeps and or mud volcanoes as sociated with gas hydrate destabilization have been observed in a sublacustrine setting the finding demonstrates the potential of tectonically controlled gas hydrate destabiliza tion to cause extreme pore fluid overpressure and short lived mud volcanism

wandering miramichi rivers new brunswick canada abstract six rivers within the miramichi basin of new brunswick display long sections with multiple channels that surround semi permanent islands linked by single channels this type of anabranching river may be termed wandering displaying a similar planimetric pattern to wandering rivers in western canada this research addresses three objectives 1 to provide a detailed description of the location pattern characteristics and boundary conditions of wandering miramichi rivers 2 to compare the pattern characteristics among wandering rivers within the miramichi basin and to other wandering meandering and braided rivers and 3 to investigate formative processes for wandering miramichi rivers wandering rivers within the miramichi region occur in larger valleys located downstream of an abrupt change in bedrock from resistive to more erosive bedrock lithology larger rivers display greater braid indices than smaller rivers wandering miramichi rivers display more similarities to meandering rivers than braided rivers exhibit an anabranching pattern yet have characteristics markedly different from anastomosed rivers energy levels mid channel bar formation migration rates and width depth ratios are all within the meandering range lower than braided and higher than anastomosed once anabranches are created larger rivers apparently maintain a greater number of anabranches because of greater discharge wandering miramichi rivers may represent another anabranching river pattern type different from anastomosed and previously described wandering rivers

palynological assemblages of non marine rocks at the permian triassic boundary western guizhou and eastern yunnan south china abstract marine and non marine facies of the permian triassic boundary stratigraphic set ptbst are well developed in south china palynological assemblages enable subdivision and correlation of the permian triassic boundary ptb rocks three palynological assemblages are recognized across the ptbst in two terrestrial ptb sections in western guizhou and eastern yunnan south china assemblage 1 xuanwei formation is a late permian palynological assemblage dominated by ferns and pteridosperms with minor gymnosperms most taxa are typical long ranging paleozoic forms but the appearance of lueckisporites confirms a late permian age for this assemblage assemblage 2 ptbst is marked by an abrupt decrease in palynomorph abundance and diversity and thriving fungal algal spores assemblage 2 is still dominated by ferns and pteridosperms with a few gymnosperms but is characterized by a mixed palynoflora containing both late permian and early triassic elements most taxa are typical late permian ones also found in assemblage 1 however some taxa of early triassic aspect e g lundbladispora and taeniaesporites appeared for the first time in assemblage 3 top xuanwei formation and kayitou formation the proportion of gymnosperm pollen increases rapidly exceeding that of ferns and pteridosperms but the abundance of palynomorphs is still low typical early triassic taxa such as lundbladispora aratrisporites and taeniaesporites are present in greater abundance and confirms an early triassic age for this assemblage

predicting natural channel patterns based on landscape and geomorphic controls in the columbia river basin usa 1 based on known relationships of slope discharge valley confinement sediment supply and sediment caliber in controlling channel patterns we developed multivariate models to predict natural channel patterns across the 674 500 km2 columbia river basin usa we used readily available geospatial data sets to calculate reach slopes 2 year flood discharge and valley confinement as well as to develop hypothesized landscape level surrogates for sediment load and caliber relative slope percent of drainage area in alpine terrain and percent of drainage area in erosive fine grained lithologies using a support vector machine svm classifier we found that the four channel patterns were best distinguished by a model including all variables except valley confinement 82 overall accuracy we then used that model to predict channel pattern for the entire basin and found that the spatial distribution of straight meandering anabranching and braided patterns were consistent with regional topography and geology a simple slope discharge model distinguished meandering channels from all other channel patterns but did not clearly distinguish braided from straight channels 68 overall accuracy addition of one or more of the hypothesized sediment supply surrogates improved prediction accuracy by 4 14 over slope and discharge alone braided and straight channels were most clearly distinguished on an axis of relative slope whereas braided and anabranching channels were most clearly distinguished by adding percent alpine area to the model

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

types of river channel patterns and their natural controls river channel patterns are thought to form a morphological continuum this continuum is two dimensional defined by plan features of which there are three straight meandering branching and structural levels of fluvial relief of which there are also three floodplain flood channel low water channel combinations of these three categories define the diversity of patterns one of the most important factors in channel development is stream power defined by water discharge and river slope the greater the stream power the stronger the branching tendency but threshold values of stream power are different for the three different hierarchical levels of channel relief the critical stream power values and hydrological regime together define the channel pattern and analysis of the pattern type can be undertaken using effective discharge curves 1998 john wiley sons ltd