salt tectonics off northern israel the messinian evaporites in the eastern mediterranean represent a world class site to study thin skinned salt tectonic processes like gravity gliding or gravity spreading in contrast to the mesozoic evaporites in the atlantic the related structures are just slightly overprinted by additional tectonic events new high resolution reflection seismic data image for the first time the entire lateral succession of gravity gliding related features as they were suggested by analog models and demonstrate therewith the validity of those models for the messinian evaporites all three regimes of extension translation and compression are present within the range of the seismic profiles however additional observations lead to an adapted and improved model the generation of a critical slope angle caused by subsidence of the levantine basin is considered to be the main driving force for the thin skinned salt tectonics and the lateral basinward creep of the basinal messinian evaporites in the extensional section beneath or near to the continental slope where the basinal evaporites have been withdrawn listric and antithetic listric growth faults rollovers and keystone grabens form asymmetric turtleback structures above salt welds and salt rollers further basinwards an area with little or no deformation of the evaporites defines the translational segment in the compressional region the lower and thickest part of the evaporites show ductile deformation buckle folds and the upper evaporites reveal brittle deformation reverse faults and pop up structures here the basinal evaporites have a maximum thickness of about 1500 m the extensional zone shows continuous synsedimentary tectonic activity until recent times whereas the compressional structures have developed later in a rather sudden event there is clear evidence for neotectonics off the israeli coast which is not related to salt dynamics faults cut through the entire pile of evaporites and the post messinian overburden where the faults pierce the sea floor mud escape structures have been observed deep rooted faults have been interpreted at the base of the messinian paleo slope suggesting a shear zone off israel and parallel to the dead sea transform

aquifer recharge depletion and connectivity inferences from grace land surface models and geochemical and geophysical data data from the gravity recovery and climate experiment grace and outputs of the clm4 5 model were used to estimate recharge and depletion rates for large aquifers investigate the connectivity of an aquifer s subbasins and identify barriers and preferred pathways for groundwater flow within an aquifer system the nubian sandstone aquifer system and its subbasins dakhla northern sudan platform and kufra in northeast africa were used for demonstration purposes and findings were tested and verified against geological geophysical remote sensing geochronologic and geochemical data there are four major findings 1 the average annual precipitation data over recharge areas in the southern kufra section and the northern sudan platform subbasin were estimated at 54 8 km 3 and 32 8 km 3 respectively and knowing the annual extraction rates over these two areas 0 40 0 20 km 3 recharge rates were estimated at 0 78 0 49 km 3 yr and 1 44 0 42 km 3 yr respectively 2 grace derived groundwater depletion rates over the dakhla subbasin and the northern kufra section were estimated at 4 44 0 42 km 3 yr and 0 48 0 32 km 3 yr respectively 3 the observed depletion in the southern parts of the dakhla subbasin is apparently caused by the presence of the east west trending uweinat aswan basement uplift which impedes the south to north groundwater flow and hence reduces replenishment from recharge areas in the south 4 a major northeast southwest trending shear zone pelusium shear system is apparently providing a preferred groundwater flow pathway from the kufra to the dakhla subbasin our integrated approach provides a replicable and cost effective model for better understanding of the hydrogeologic setting of large aquifers worldwide and for optimum management of these groundwater resources

hydrologic and hydraulic effects of riparian root networks on streambank stability is mechanical root reinforcement the whole story abstract riparian vegetation has a number of effects on the mechanisms by which streambanks fail some positive and some negative previous research has shown that the effect of mechanical root reinforcement on soil stability can be considerable and can be successfully quantified and included in streambank stability models root networks contained within a soil matrix however also have effects on the hydrologic and hydraulic processes acting on a streambank and although these effects are often discussed they have generally been difficult to quantify this paper summarizes the results of field data collection laboratory testing and computer simulations carried out to better quantify the effects of riparian vegetation on hydrologic and hydraulic processes occurring along streambanks first the evapotranspiration potentials of different riparian species were isolated by setting up an experiment to grow young riparian trees and switch grass in separate soil columns each instrumented with tensiometers at 30 cm and 70 cm depths and compared against bare control columns the hydrological reinforcement provided to the soil from increased apparent cohesion as a result of enhanced matric suction was estimated to range from 1 0 to 3 1 kpa in spring when bank stability was most critical and up to a maximum of 5 0 kpa in the summer second a vertical jet test device was used to measure rates and volumes of scour in soils permeated by switch grass roots results showed that the volume of soil scoured during a test declined non linearly with increasing root volume per unit volume of soil and with increasing root length density rld and increasing root biomass calculation of relative soil detachment rates rsd showed that with the highest rooting densities measured in the field jet tests eroded soil volume was 10 of that in the tests with no roots third the effects of enhanced matric suction from evapotranspiration and decreased soil erodibility because of the presence of plant roots were modeled using bstem 5 1 to quantify the effects on streambank factor of safety fs and to compare with the effects of mechanical root reinforcement the sensitivity analysis showed that the change in soil matric suction from evapotranspiration provided the greatest potential benefit to fs but only during the summer months during the winter and spring months root reinforcement remained the most important contributor to fs the sensitivity analysis conducted here also showed that whilst roots are capable of reducing the volume of hydraulic scour the resulting effect on streambank geometry did not increase fs as much as changes in soil matric suction and or mechanical root reinforcement

wood recruitment and retention the fate of eroded trees on a braided river explored using a combination of field and remotely sensed data sources abstract this paper investigates wood recruitment and deposition dynamics in a large gravel bed braided river tagliamento river italy we used a combination of field measurements automatically repeated ground images and remotely sensed surveys to quantify wood input through bank erosion and associated downstream deposition two sites were investigated where floods caused the erosion of vegetated island edges a lidar survey preceding the erosion events provided data on the morphology and vegetation structure of the eroded areas allowing estimation of the number of trees that were uprooted sequences of ground based images acquired automatically and supported by field measurements showed the time number and location of deposited trees results show that the complex morphology of braided rivers induces specific deposition patterns we observed wide dispersal of wood on gravel bars with jams characterised by a small number of logs on average 2 3 and in many cases only a single log a large proportion of the eroded trees up to 40 were deposited on the nearest downstream bar this illustrates significant wood retention close to the recruitment site with the remaining wood dispersed widely downstream differences in the observed level of local wood retention were associated with the proximity of the erosion site to the main channel and differences were also observed in retention between the peak and the falling limb of flood events confirming that water depth and probably flow velocity are the crucial parameters controlling wood deposition

interpretation of aeromagnetic data across the central crystalline shield area of nigeria summary a residual map of the total magnetic field above 25 000 nt base is presented for a portion of the central crystalline shield area of nigeria and overlapping small portions of the chad basin and the benue rift 8 30 12 oo lat and 7 10 30 long the map based on a dataset digitized from recently released aeromagnetic sheets of nigeria leads to four results 1 a magnetic boundary evident on the map separates the younger granite complexes into two groups the groups are petrologically different and the boundary may be a fault line with uplift to the south 2 south of the boundary the map is dominated by a system of sub parallel anomalies striking ne sw possibly representing major tectonic trends and a set of fractures through which the younger granite complexes were intruded the trend of the system parallels the benue rift and lineaments in the oceanic crust off west africa 3 negative magnetic anomalies lie over most of the known ring complexes and over some suspected buried ring complexes and other intrusions 4 2 and 3 d modelling shows that the larger complexes extend to 12 km depth and the smaller ones to 6 km they have nearly vertical sides and magnetization contrasts range from 0 3 to 0 5 a m i

early cretaceous rifts of western and central africa an overview abstract the structure and evolution of early cretaceous rift basins in western and central africa are described two stages of rift development and fracturing have been identified 1 from neocomian to early aptian roughly e w and nw trending troughs upper benue n cameroon s chad sudan etc opened in response to a submeridian extensional regime in central africa while in western africa the n s trending transsaharian fault zone acted as a sinistral wrench 2 from middle aptian to late albian large northwest trending troughs e niger sudan sirte etc opened in response to a northeast extensional regime while the central african fault zone from benue to sudan exhibited strike slip movements generating pull apart basins these rift and fracture systems delimit three large blocks within the african plate a western block an arabian nubian block and an austral block the arabian nubian block tends to separate from the two other blocks migrating towards the north during the first stage of basin development and then towards the ne during the second stage the opening of the atlantic ocean was the dominant driving force for the western and austral blocks while the arabian nubian block probably moved in response to the opening of the indian ocean and to the evolution of the tethyan margin

a remanent and induced magnetization model of magsat vector anomalies over the west african craton scalar and vector magsat anomalies over the west african craton are analysed by forward and inverse models a forward model of the man shield is based on liberia induced magnetization contrasts due to sporadic iron formations and to regional metamorphic rocks and a contrast in remanent magnetization within the lower crust are included this combination reproduces the location magnitude and adopted local zero level of anomalies in the initial magsat maps an inverse model of the reguibat shield estimates the magnetization contrast of its lithosphere and when magnetism is restricted to shallower than 75 km both shields can be represented by a susceptibility contrast of 0 02 a residual anomaly between the shields involves a relative deficiency of induced magnetization along with other causes

anomalous opening of the equatorial atlantic due to an equatorial mantle thermal minimum abstract the geology of the equatorial atlantic is dominated by a broad east west megashear belt where a cluster of large fracture zones offsets anomalously deep segments of the mid atlantic ridge mar the origin and evolution of this megashear region may lie ultimately in an equatorial mantle thermal minimum the notion of a mantle thermal minimum in the equatorial atlantic is supported by an equatorial minimum of zero age topography a maximum in mantle shear waves seismic velocity and a minimum in the degree of melting indicated by the chemistry of mar basalts and peridotites this thermal minimum has probably been a stable feature since before the cretaceous separation of africa from south america it caused a pre opening equatorial continental lithosphere thicker and colder than normal the cretaceous benue trough in western africa and the amazon depression in south america are interpreted as morphostructural depressions created or rejuvenated by strike slip transpressional and transtensional tectonics ducing extension of the cold thick equatorial lithosphere the oceanic rift propagating northward from the south atlantic impinged against the equatorial thicker colder and therefore stronger than normal continental lithosphere that consequently acted as a locked zone this and a low magmatic budget due to the cold upper mantle caused a lower than normal rate of propagation of the oceanic rift into the equatorial belt with diffuse deformation during mostly amagmatic extension the thick cold lithosphere prevented major cretaceous igneous activity from the st helena plume eventually initial weak isolated nuclei oceanic lithosphere were emplaced separated by e w continent continent transforms opening occurred largely by strike slip motion along these initial transforms the consequences were that the equatorial atlantic opened prevalently along an e w direction in contrast to the n s opening of the north and south atlantic and that sheared continental margins are particularly well developed in the equatorial atlantic after further continental separation the cold equatorial mantle caused a low degree of melting with na rich morb and alkali basalt rather than normal morb and with undepleted mantle peridotities thin crust depressed ridge segments and a prevalence of amagmatic extension similar conditions still exist today long transforms offsetting short ridge segments kept sea floor spreading unstable and dominated by transform tectonics with transform migration transpression and transtension causing strong vertical motion emersion and subsidence of lithospheric blocks development of deep pull apart basins and preservation of relict slivers of old lithosphere occasionally even of continental lithosphere within younger crust the equatorial transforms are caused ultimately by a long lived thermal minimum in the upper mantle and not vice versa however they then create second order rebound thermal effects that help maintain the thermal minimum in the upper mantle it can be speculated that mantle thermal minima at the earth s equator might be related to true polar wander triggered by subduction of dense masses into the mantle

mantle and crustal gases of the colorado plateau geochemistry sources and migration pathways abstract the colorado plateau hosts several large accumulations of naturally occurring non hydrocarbon gases including co2 n2 and the noble gases making it a good field location to study the fluxes of these gases within the crust and to the atmosphere in this study we present a compilation of 1252 published gas composition measurements the data reveal at least three natural gas associations in the field area which are dominated by hydrocarbons co2 and n2 he ar respectively most gas accumulations of the region exhibit compositions that are intermediate between the three end members the first non hydrocarbon gas association is characterized by very high purity co2 in excess of 75 mol hereafter many of these high purity co2 fields have recently been well described and interpreted as magmatic in origin the second non hydrocarbon gas association is less well described on the colorado plateau it exhibits he concentrations on the order of 1 10 and centered log ratio biplots show that he occurs proportionally to both n2 and ar overall ratios of n2 to he to ar are 100 10 1 and correlation in concentrations of these gases suggests that they have been sourced from the same reservoir and or by a common process to complement the analysis of the gas composition data stable isotope and noble gas isotope measurements are compiled or newly reported from 11 representative fields previously published data from 4 fields and new data from 7 fields gas sampled from the harley dome gas field in utah contains nearly pure n2 he ar the various compositional and stable and noble gas isotopic data for this gas indicate that noble gas molecule isotope ratios are near crustal radiogenic production values and also suggest a crustal n2 source across the field area most of the high purity n2 he ar gas accumulations are associated with the mapped surface trace of structures or sutures in the precambrian basement and are often accumulated in lower parts of the overlying phanerozoic sedimentary cover the high purity gas association mostly occurs in areas interior to the plateau that are characterized by a narrow range of elevated moderate heat flow values 53 74 mw m2 in the ancient 1 8 1 6 ga basement terranes of the region collectively the geochemical and geological data suggest that 1 the n2 he ar gas association is sourced from a crustal reservoir 2 the gas association migrates preferentially along structures in the precambrian basement and 3 the sourcing process relates to heating of the crust prospecting for noble gas accumulations may target areas with elevated cenozoic heat flow ancient crust and deep crustal structures that focus gas migration high purity co2 gas may also migrate through regional basement structures however there is not always a clear spatial association rather co2 accumulations are more clearly associated with zones of high heat flow 63 mw m2 that sit above hot upper mantle and are proximal to cenozoic volcanic rocks near the plateau margins these observations are consistent with previous interpretations of a magmatic gas source which were based on geochemical measurements

decadal changes in distribution and frequency of wood in a free meandering river the ain river france this study examined the temporal dynamics and longitudinal distribution of wood over a multi decadal timescale at the river reach scale 36 km and a meander bend scale 300 600 m in the ain river a large gravel bed river flowing through a forested corridor and adjusting to regulation and floodplain land use change at the 36 km scale more wood was recruited by bank erosion in 1991 2000 than since the 1950s the longitudinal distribution of accumulations was similar between 1989 and 1999 but in both years individual pieces occurred homogeneously throughout the reach while jam distribution was localized associated with large concave banks a relationship between the mean number of pieces and the volume recruited by bank erosion r 2 0 97 indicated a spatial relationship between areas of wood production and storage wood mass stored and produced and channel sinuosity increased from 1993 to 2004 at three meander bends sinuosity was related to wood mass recruited by bank erosion during the previous decade r 2 0 73 and both of these parameters were correlated to the mean mass of wood plot r 2 0 98 and 0 69 respectively appearing to control wood storage and delivery at the bend scale this suggests a local origin of wood stored in channel not input from upstream trapped by preferential sites the increase in wood since 1950 is a response to floodplain afforestation to a change from braided to meandering channel pattern in response to regulation and to recent large floods we observed temporal stability of supply and depositional sectors over a decade on a reach scale meander bends were major storage sites trapping wood with concave banks also delivering wood these results and the link between sinuosity and wood frequency establish geomorphology as a dominant wood storage and recruitment control in large gravel bed rivers

geochemical characteristics of he and co 2 from the ordos cratonic and bohaibay rift basins in china abstract according to the compositional and isotopic analyses of he co 2 and ch 4 of 95 gas samples from the ordos basin and 76 gas samples from the bohaibay basin in china this study carried out a detailed investigation on the geochemical characteristics of helium and co 2 from the cratonic and rift basins especially the cratonic ordos basin and rift bohaibai basin in china compared to the rift bohaibay basin the cratonic ordos basin has lower level of helium and co 2 lower r ra ratio and lower 13 c co2 maximum value when the content of co 2 is 2 associated with the hydrocarbon generation process and inorganic co 2 from the thermal decomposition of carbonates or dissolution of organic acid rift basin can also have co 2 20 and 13 c co2 of 6 2 or 4 9 which is of volcanic magmatic or mantle derived origin while cratonic basin has no such type of co 2 the cratonic basins ordos sichuan have co 2 13 c co2 i e 25 6 0 8 26 4 the rift basins have higher level of co 2 r ra ratios and 13 c co2 values the content of co 2 can reach 100 the r ra ratio can be up to 6 45 and the variation range of 13 c co2 is 34 7 27 bigger variation range of 13 c co2 implies stronger tectonic activities which is not favorable for the gas accumulation while smaller variation range means more stable structure which is favorable for the discovery of large gas fields sample in the cratonic basin in china generally has ch 4 3 he of 10 9 10 12 and r ra 4 3 he of 10 5 10 13 and r ra of 0 1 6 45 it is concluded that methane with ch 4 3 he 10 8 is of inorganic origin and methane with ch 4 3 he 10 11 is of organic origin the regression equation for the ch 4 3 he r ra in the cratonic basin is y 3e 11e 46 28x and it is y 4e 10e 1 791x in the rift basin both ordos and bohaibay basins found gas wells with he 0 05 which has significant commercial values and provides a clue for the exploration of helium rich gas fields traps with r ra 2 is a favorable clue for the discovery of co 2 gas fields seven co 2 gas fields have been found in the bohaibay basin but no systematic development has been carried out and only some liquid co 2 has been injected for tight oil from the huagou co 2 gas field

large wood recruitment and transport during large floods a review large wood lw elements transported during large floods are long known to have the capacity to induce dangerous obstructions along the channel network mostly at bridges and at hydraulic structures such as weirs however our current knowledge of wood transport dynamics during high magnitude flood events is still very scarce mostly because these are locally rare and thus unlikely to be directly monitored therefore post event surveys are invaluable ways to get insights although indirectly on lw recruitment processes transport distance and factors inducing lw deposition all aspects that are crucial for the proper management of river basins related to flood hazard mitigation this paper presents a review of the quite limited literature available on lw transport during large floods drawing extensively on the authors own experience in mountain and piedmont rivers published and unpublished the overall picture emerging from these studies points to a high catchment specific variability in all the different processes affecting lw dynamics during floods specifically in the lw recruitment phase the relative floodplain bank erosion vs hillslope landslide and debris flows contribution in mountain rivers varies substantially as it relates to the extent of channel widening which depends on many variables itself but also to the hillslope channel connectivity of lw mobilized on the slopes as to the lw transport phase within the channel network it appears to be widely characterized by supply limited conditions whereby lw transport rates and thus volumes are ultimately constrained by the amount of lw that is made available to the flow indeed lw deposition during floods was mostly in terms of volume observed at artificial structures bridges in all the documented events this implies that the estimation of lw recruitment and the assessment of clogging probabilities for each structure for a flood event of given magnitude are the most important aspects for the prediction of lw transport magnitude at any cross section along the river network finally the review discusses the optimal strategies to manage lw related hazard which should consider riparian vegetation and in channel dead wood as key components of river ecosystems and thus should interfere with lw as well as with sediment transport dynamics only for limited spatial and temporal scales

transport and deposition of large woody debris in streams a flume experiment abstract large woody debris lwd is an integral component of forested streams of the pacific northwest and elsewhere yet little is known about how far wood is transported and where it is deposited in streams in this paper we report the results of flume experiments that examine interactions among hydraulics channel geometry transport distance and deposition of floating wood these experiments were carried out in a 1 22 m wide 9 14 m long gravel bed flume using wooden dowels of various sizes as surrogate logs channel planforms were either self formed or created by hand and ranged from meanders to alternate bars floating pieces tended to orient with long axes parallel to flow in the center of the channel pieces were deposited where channel depth was less than buoyant depth typically at the head of mid channel bars in shallow zones where flow expanded and on the outside of bends we hypothesize that the distance logs travel may be a function of the channel s debris roughness a dimensionless index incorporating ratios of piece length and diameter to channel width depth and sinuosity travel distance decreased as the ratio of piece length to both channel width and radius of curvature increased but the relative importance of these variables changed with channel planform large pieces can move further than our debris roughness models predict if greater than 50 of the active channel area is deeper than the buoyant depth of the piece or if momentum is high enough to carry pieces across shallows our debris roughness model allows first order prediction of the amount of wood transport under various channel geometries

geochemistry origin and accumulation of co2 in natural gases of the yinggehai basin offshore south china sea geochemical and isotopic data indicate the presence of co2 of both organic and inorganic origin in the natural gas reservoirs of the yinggehai basin the natural gases with inorganic co2 commonly show a high content of co2 ranging from 15 to 85 a heavier carbon isotope value of co2 from 0 56 to 8 16 and a lower 3he 4he ratio ranging from 0 20 to 6 79 107 indicating a crustal origin these gases occur locally commonly related to diapir structures natural gases rich in hydrocarbons occur widely and are characterized by a low co2 content from 0 1 to 5 0 and a lighter c1 carbon isotope value from 10 59 to 20 7 indicating an organic origin geological background and geochemical data indicate that the sanya and meishan formations are the main source of hydrocarbon gases and the organic co2 pyrolysis experiments on tertiary calcareous shales and thermal history modeling both suggest that the calcareous shales occurring in the lower miocene strata are the main source of the inorganic co2 gas whereas thermal contact metamorphism of the paleozoic carbonates and or magmatic co2 may have made only a small contribution abnormally high paleogeothermal gradients 4 25 4 56c 100 m 12 09 12 26f 100 ft and a rapid heating rate caused the lower miocene calcareous shales to reach the threshold temperature about 300c 570f of their thermal decomposition at the burial depth of about 6500 m 21 300 ft and to generate great volumes of inorganic co2 gas diapir faults acted as the main pathways for the upward migration of deep inorganic co2 gases into reservoirs connected with shale diapirism along the central yinggehai basin the heavier carbon isotope values of associated methanes and a strong thermal anomaly in the co2 rich gas reservoirs provide evidence that the inorganic co2 gas migrated into the reservoirs later than their associated hydrocarbon rich gases this suggests that the earlier formed traps and sandstone reservoirs distant from shale diapir structures may have greater potential in the exploration for hydrocarbon rich gases

effects of deep co 2 on petroleum and thermal alteration the case of the huangqiao oil and gas field abstract the co2 rich natural gas from the huangqiao oil and gas field of the subei basin is produced along with crude oil the co2 content ranging from 80 56 to 99 30 and the 3he 4he ratio of 0 94 10 6 to 4 67 10 6 indicates that this includes a substantial fraction of mantle derived co2 in the huangqiao region although the positive carbon isotopic series of alkane gases i e 13c1 the crude oil of the huangqiao region is light or condensate oil with low densities of 0 7933 0 8255 g cm3 saturated hydrocarbons comprise 90 06 97 37 the crude oil while the aromatic non hydrocarbon and asphaltene fractions are very small the n alkanes range from c13 to c34 with highest abundances at c16 and c17 the gas chromatogram of the crude oil shows an unresolved hump or unresolved complex mixture ucm distribution of a complete n alkane series non odd even predominance and major n alkane peaks on the highest positions of the ucm distribution this may indicate that deep mantle derived co2 fluid extracted and accumulated the oil now found in the reservoirs or source rocks

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

leaky rivers implications of the loss of longitudinal fluvial disconnectivity in headwater streams article i nfo naturally induced longitudinal disconnectivity in the form of channel spanning logjams creates backwaters along headwater streams that reduce velocity and transport capacity create at least temporary storage sites for finer sediment and organic matter and enhance biological processing and uptake of nutrients land uses that reduce wood recruitment and instream storage result in reduced stream complexity and in creased longitudinal connectivity in headwater rivers we examine three scales of naturally occurring longi tudinal disconnectivity in headwater streams of the colorado front range and the implications for channel process and form of historical alterations in disconnectivity basin scale disconnectivity at channel lengths of 10 2 10 3 m results from downstream alternations between steep narrowly confined valley segments with single thread channels and lower gradient wider valley segments with multi thread channels this variation in valley geometry likely reflects differences in average spacing between joints in bedrock outcrops which influences bedrock weathering and erosion greater volumes of wood stored in the wide valley seg ments correlate with more closely spaced channel spanning logjams and greater storage of fine sediments and organic matter reach scale disconnectivity at channel lengths of 10 1 10 2 m results from the presence of numerous closely spaced channel spanning logjams which cumulatively store substantial amounts of fine sediment and organic matter the backwater effects associated with an individual jam can result in the accumulation of up to 11 m 3 of fine sediment upstream from the jam of which as much as 21 is organic

riparian vegetation and island formation along the gravel bed fiume tagliamento italy after more than 300 years of river management scientific knowledge of european river systems has evolved with limited empirical knowledge of truly natural systems in particular little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels the dynamic gravel bed fiume tagliamento italy provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small against a background of a strong alpine to mediterranean climatic and hydrological gradient this paper explores relationships between topography sediment and vegetation at eight sites along the active zone of the tagliamento a conceptual model of island development is proposed which integrates the interactions between large woody debris and vegetation geomorphic features sediment calibre and hydrological regime islands may develop on bare gravel sites or be dissected from the floodplain by channel avulsion depositional and erosional processes result in different island types and developmental stages differences in the apparent trajectories of island development are identified for each of the eight study sites along the river the management implications of the model and associated observations of the role of riparian vegetation in island development are considered in particular the potential impacts of woody debris removal riparian tree management regulation of river flow and sediment regimes and changes in riparian tree species distribution are discussed

geochemistry and occurrence of inorganic gas accumulations in chinese sedimentary basins abstract inorganic gases are commonly seen in eastern china and occasionally in southern china from the shallow water columns above hot and cold springs the gases contain 68 to nearly 100 co2 with 13 c co 2 and 13c1 values in the range of 1 18 to 6 00 and 19 48 to 24 94 respectively all of the 34 large inorganic co2 and one inorganic methane accumulations discovered in china are distributed in eastern parts of the country from both onshore and continental shelf basins no commercial inorganic gas accumulation has been found in central and western china this is a review of the occurrence and geochemical characteristics of inorganic gas accumulations in chinese sedimentary basins a detailed study of gas samples collected from four representative inorganic co2 pools and one possible inorganic methane pool indicates that inorganic alkane gases typically show 13c1 values greater than 10 versus pdb mostly 30 with a positive stable carbon isotope sequence of 13c1 13c2 13c3 13c4 inorganic gases also tend to show less negative 13 c co 2 values 10 than biogenic gases

the pelusium megashear system across africa and associated lineament swarms the pelusium megashear system neev 1977 extends from the border zone of anatolia along the eastern mediterranean and across africa from the nile delta to the delta of the niger in the gulf of guinea it appears to continue beyond africa via the atlantic equatorial fracture zones into the amazon basin it has functioned as a system of en echelon left lateral megashears since precambrian times at least four other geosutures also cross africa paralleling the pelusium system and similarly continuing into the atlantic as fracture zones swarms of lineaments observed in landsat image mosaics of central and northeast africa are associated with the pelusium megashear system they are interpreted to be of tectonic origin linear dunes and yardangs oriented parallel to the lineaments appear to have been formed by winds deviated and channeled by the tectonic lineaments these eolian features should not be considered therefore as reliable indicators for higher altitude atmospheric circulation whereas the patterns of the swarms are affiliated to that of the pelusium megashear system they are not related to most of the other nearby geologic features both the pelusium megashear system and its associated lineament swarms exhibit northeastward convergence patterns which suggest counterclockwise rotation of the crust these probably result from left lateral shear movements within the asthenosphere which have continued since the precambrian

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

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

seismic reflection imaging of a major strike slip fault zone in a rift system paleogene structure and evolution of the tan lu fault system liaodong bay bohai offshore china the tan lu fault system in the liaodong bay bohai offshore china affords an exceptional opportunity to document the structural features of a major strike slip fault using two and three dimensional seismic reflection data as well as evolution of a strike slip fault developed coeval with a rift system the fault zone displays a relatively straight throughgoing trace longitudinally bisecting the rift valley it consists of positive and negative flower structures and en echelon folds in the south bay and three parallel flower structure systems northward the middle fault bifurcates northward into two semiparallel vertical fault strands to the north the west strand bends clockwise and merges with the east strand the stepping pattern and orientation of en echelon structures indicate right lateral sense and about n10 35e azimuth of slip the fault apparently accrued about 30 40 km 20 25 mi of post early eocene slip based on the current distribution of deformation zones and depocenters tan lu fault segments with clockwise and counterclockwise orientation relative to the regional slip direction are characterized by divergent and convergent structures i e restraining and releasing bends respectively waning of rifting eliminated the cause of a major restraining bend putting an end to development of associated convergent structures in the south bay area near the central north bay deformation occurred along major normal faults related to the basin rifting although a prominent feature reflecting regional strain partitioning the tan lu fault apparently was not a major factor in the paleogene opening of the liaodong bay basin and the larger north china rift basin

origin and accumulation of carbon dioxide in the huanghua depression bohai bay basin china the co2 content in natural gas in the huanghua depression bohai bay basin china is highly variable ranging from 0 003 to 99 6 understanding the origin and distribution of the co2 is important to assess risk prior to drilling this study uses gas geochemistry to identify the origins of co2 in the sedimentary basin and places these findings within a geologic context chemical compositions 3he 4he and 40ar 36ar were measured for 50 gas samples collected from gas and oil producing wells located in different tectonic regions in the depression from these analyses we determined that the co2 in the huanghua depression originated from three sources thermal decomposition of organic matter thermal decomposition of carbonate minerals and mantle degassing gases with low amounts 3 of co2 tend to be organogenic this organogenic co2 occurs in hydrocarbon accumulations and is characterized by values ranging from 20 to 10 and low 3he 4he r ra 1 herein r and ra represent the 3he 4he ratio of sample and air respectively carbon dioxide originating from thermal carbonate decomposition occurs as a minor component 10 in hydrocarbon gas accumulations and is characterized by a narrow range of 2 to 2 and r ra 1 huanghua depression natural gases with co2 content in excess of 15 resulted from mantle degassing and mainly occur at the intersection of faults these gases have 3he 4he ratios in excess of atmospheric value r ra 1 and ranging from 5 to 3 volatiles from mantle degassing during the postmagmatic stage are the most likely major source for co2 in these high co2 content reservoirs basement faults likely provide pathways for the upward migration of co2 rich mantle fluids consequently co2 rich gas pools are locally concentrated in the gangxi and dazhongwang fault zones within the depression

late tertiary faulting along the coastal plain of israel 1 this study documents a 70 km long and 200 400 m high step at the base of the pliocene section in the israeli coastal plain depositional explanations for this lineament such as a buried shelf edge or reef front are very unlikely whereas a fault scarp explanation is supported by seismic profiles and geological cross sections the eastern elevated side of the fault was eroded before its burial though a quantitive distinction between this erosion earlier truncations and original hiatuses is not possible at this stage sediments covering the fault scarp constrain its age to late miocene and or early pliocene the presence of such a fault along the israeli coastal plain may also shed light on numerous post mid cretaceous faults previously documented along the coastal plain but never explained in a wider perspective the fault described here along with other documented processes indicate that in the late tertiary tectonism along the levant continental margin resumed after a long passive history this renewed activity is coeval with the africa arabian breakup and the red sea suez rifting in particular the fault described here is coeval with plate reorganization and vertical motions along the dead sea transform and possibly along the cypriot arc during the late miocene early pliocene

spatial distribution of coarse woody debris dams in the lymington basin hampshire uk abstract debris dams of coarse woody debris have a significant influence on channel processes in forested areas but few detailed studies have been made of variations within a single basin results from previous research are standardised and show that average variations throughout basins include densities of debris dams up to 40 per 100 metres of channel and can involve a loading value of up to 225 kg per m2 of channel variations have been ascribed to distance downstream to channel width to land use effects to felling and to the management of coarse woody debris in streams this study of the lymington basin 110 4 km2 in drainage area shows that the input of storm debris resulting from blowdown accounts for 45 of the gross load the remaining 55 net load varies to distance downstream to land use with the greatest loads in deciduous woodland areas and according to management removal of debris from streams and multiple regression equations are provided it is deduced that as a consequence of long term management the present channel debris may be as little as 7 of the total net load that could have been present if no management had occurred

understanding processes of island development on an island braided river over timescales from days to decades this is the peer reviewed version of the following article gurnell a m bertoldi w francis r a gurnell j and mardhiah u 2019 understanding processes of island development on an island braided river over timescales from days to decades earth surf process landforms 44 624 640 https doi org 10 1002 esp 4494 which has been published in final form at https doi org 10 1002 esp 4494 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

aeromagnetic anomalies and tectonic trends in and around the benue trough nigeria four major fracture zones cutting the atlantic sea floor off the west coast of africa st paul s romanche chain and charcot have been delineated offshore using bathymetrie seismic gravity and magnetic data respectively1 but the extrapolation of these fractures onto the african continent is uncertain here we analyse recently compiled aeromagnetic data2 for the benue trough and adjacent areas of nigeria and demonstrate the existence of narrow magnetic lineaments parallel to the margins of the benue trough which can be matched with the oceanic fractures alkaline ring complexes which predate the opening of the atlantic ocean are concentrated along these lineaments suggesting that they represent pre existing zones of weakness in the african crust which may have influenced the rifting of the continental margins and the early development of atlantic fracture zones

cenozoic structural deformation and dynamic processes of the bohai bay basin province china abstract cenozoic structures in the bohai bay basin province can be subdivided into eleven extensional systems and three strike slip systems the extensional systems consist of normal faults and transfer faults the normal faults predominantly trend nne and ne and their attitudes vary in different tectonic settings paleogene rifting sub basins were developed in the hanging walls of the normal faults that were most likely growth faults neogene quaternary sequences were deposited in both the rifting sub basins and horsts to form a unified basin province the extensional systems were overprinted by three nne trending right lateral strike slip systems fault zones although the principal displacement zones pdz of the strike slip fault zones are developed only in the basement and lower basin sequences in some cross sections the structural deformation characteristics of the upper basin sequences also indicate that they are basement involved right lateral strike slip fault zones according to the relationships between faults and sedimentary sequences the extensional systems were mainly developed from the middle paleocene to the late oligocene whereas the strike slip systems were mainly developed from the oligocene to the miocene strike slip deformation was intensified as extensional deformation was weakened extensional deformation was derived from horizontal tension induced by upwelling of hot mantle material whereas strike slip deformation was probably related to a regional stress field induced by plate movement

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

temporal variations of large wood abundance and mobility in the blanco river affected by the chaiten volcanic eruption southern chile abstract the aim of this study is to analyze the temporal variation in abundance and transport of in channel wood along a river affected by a volcanic eruption considering the mobility and retention rates in detail the 2008 eruption of chaiten volcano southern chile severely affected the blanco river basin causing changes in channel morphology and large wood lw dynamics along the fluvial corridor of the river a fourth order stream on the southern slope of the volcano temporal dynamics of lw were investigated from january 2015 until march 2016 in three 80 m long study reaches of the active channel in the lower course of the river every wood element 1 m in length and 0 1 m in diameter within the active channel of each reach was georeferenced measured tagged and characterized wood mobility rate defined as the number of tagged wood pieces repositioned or not found within each study reach to total tagged lw in the same reach and retention rate defined as the number of tagged lw pieces found within each study reach to total tagged wood pieces in the same reach were calculated considering two periods one in summer and one in autumn winter a regional flood frequency analysis estimated flood magnitude defining a recurrence interval of 1 year for summer floods and 10 25 years for autumn winter floods results highlighted how eight years after the eruption the types of lw are still influenced by the impacts of pyroclastic density currents on riparian vegetation the characteristics and abundance of monitored lw are typical of a river system with frequent wood transport the mobility rate ranges between 42 and 94 during the summer and autumn winter period respectively while the wood volume decreases during the summer and increases in autumn winter large wood mobility was also found to vary according to the predominant morphological settings with lower values in narrower channels compared to wider wetted areas in this context the greatest abundance of lw was detected after the higher floods corresponding to an input of lw up to 285 35 m3 ha 1 along the blanco river ordinary floods deliver lw mainly through fluvial transport and bank erosion during higher floods appears as an additional and important wood recruitment process the bank erosion processes with up to 5200 m2 of eroded area confirmed the widening tendency occurring in river systems following volcanic disturbances as there are dead riparian trees along the easily erodible banks it is reasonable to suppose that the blanco river will continue to widen for a long period recruiting and transporting downstream huge volumes of lw in this context these analyses appear of fundamental importance to better manage the river system also for decreasing hazards to the downstream village of chaiten

the distribution of large woody debris accumulations and pools in relation to woodland stream management in a small low gradient stream this paper focuses upon the natural dynamics of large woody debris lwd the impact of management on lwd dynamics and the impact of lwd removal and channelization on the distribution and size of pools in a british second to third order headwater catchment the study stream is rather different from those subject to lwd accumulations which have been studied in north america the most important contrast is that it is surrounded by predominantly deciduous rather than coniferous woodland in terms of its width 1 8 4 5 m and gradient 0 013 m m 1 it falls within the lower range of channels studied in north america nevertheless there are similarities in lwd dam and pool spacing with some north american studies the information on lwd dynamics during a period without management and on recovery of lwd dams after clearance covers a 16 year period 1982 1997 the paper illustrates that seven to eight years after clearance the total number of lwd dams has recovered but the most hydraulically active dam type has not recovered to pre clearance levels an analysis of geomorphological maps of the channel surveyed in 1982 and 1996 97 shows an overall decrease in the number and size of pools along the section that was cleared of lwd dams the magnitude of the decrease and the associated adjustments in pools through changes in their size and location differ according to location with respect to a section of the study stream which was channelized in c 1966 and which has subsequently incised its bed copyright 1998 john wiley sons ltd

tectonic implications of recent microearthquake data from israel and adjacent areas a recently installed seismograph network in israel enables for the first time a systematic examination of the microearthquake activity and its relation to the regional tectonics the observed microearthquake activity is widespread and not limited to the dead sea rift plate boundary in the rift itself the more seismically active parts are north of the sea of galilee and in the dead sea basin a possible seismic quiescence appears in the jordan valley to the north of the dead sea basin and may be associated with that segment of the plate boundary which broke recently 1927 thus indicating a low strain level inside israel the active nature of the carmel farah fault systems was determined its present level of seismicity appears to be comparable to that of the rift itself indicating the significance of this fault system in the active tectonics of the area the high microseismic activity on these faults and their location in densely populated areas mark them as possibly important sources of seismic hazards diffused seismicity is observed throughout much of israel although the nature of these earthquakes is not yet understood the small magnitude earthquakes near the rift are most probably part of a seismic halo around the plate boundary pronounced seismicity is also observed in the mediterranean sea off the coast of southern lebanon and northern israel this microearthquake activity decreases from north to south and to some extent from east to west whereas near the coast of northern israel and southern lebanon the microearthquake activity is relatively high in the south near the coast of the sinai peninsula it is very low this difference is attributed to a possible combination of a higher strain level in the african plate as it approaches the africa eurasia plate boundary and hinge faulting near the coast

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

cenozoic tectonic evolution of liaodong dome northeast liaodong bay bohai offshore china constraints from seismic stratigraphy vitrinite reflectance and apatite fission track data abstract the liaodong dome is a region of localized uplift and deformation within the liaodong bay bohai offshore china 3 d seismic dataset vitrinite reflectance and apatite fission track data provide an exceptional opportunity to document the evolution of the liaodong dome which developed coeval with the tan lu strike slip fault zone with a rift system the 3 d seismic data demonstrates that the dome formed before the deposition stage of esm sequence 40 ma and it uplifted again during or after the depositional stage of ed sequence 32 24 ma apatite fission track and vitrinite reflectance data indicate that the dome experienced two stages of cooling episodes paleocene to early middle eocene 65 40 ma and late oligocene to late miocene 30 11 5 ma usually indicating uplifting both the seismic stratigraphy and thermal history analysis show that 1 the liaodong dome is part of the jiaoliao terrane 2 regional continental rifting climaxed during 65 40 ma as it did the rift shoulder uplift of the dome 3 the reactivation of the tan lu fault caused a second uplift processes of the liaodong dome during 30 11 5 ma 4 the liaodong dome uplifted independently and separated from the jiaoliao terrane our results also suggest that it is important to take uplifting evolution into consideration to target a potential petroleum reservoir

large woody debris physical process and riparian forest development in montane river networks of the pacific northwest abstract we present a conceptual biogeomorphic model of riparian forest development in montane river networks the role of physical process in driving the structure composition and spatial distribution of riparian forests is examined we classify the drainage network into disturbance process based segments including 1 debris flow and avalanche channels 2 fluvial and debris flow channels and 3 fluvial channels riparian forests are shown to be significant in the development of channel morphology through the stabilization of active floodplains and as sources of large woody debris olwd lwd is operationally defined as wood 0 1 m diameter and 1 m length lwd plays a key role in the development of montane riparian forests lwd deposited in the active channel and floodplain provides sites for vegetation colonization forest island growth and coalescence and forest floodplain development riparian forest patterns parallel the distribution of hillslope and fluvial processes through the network riparian forest structure composition and spatial distribution through the network are driven by the major disturbance processes including 1 avalanches 2 debris flows and 3 flooding riparian forest patterns also reflect the action of lwd in the organization and development of forested floodplains in gravel bedded montane river networks the focus of our examples are montane river networks of the pacific northwest usa

channel adjustments and vegetation cover dynamics in a large gravel bed river over the last 200 years article i nfo the timing and extent of the morphological changes that occurred in the last 200 years in a large gravel bed river the piave river eastern italian alps that was heavily impacted by human activities training structures hydropower schemes and gravel mining have been analyzed by historical maps aerial photos repeated topographic measurements and geomorphological surveys results show that the channel underwent a strong narrowing during the twentieth century but with a faster pace during the 1970s 1990s and with an associated shift from a dominant braided pattern to a wandering morphology bed incision up to 2 m mostly from gravel mining has been documented for this period large areas of the former active channel were colonized by riparian forests both as islands and as marginal woodlands the ceasing of gravel extraction in the late 1990s seems to have determined a reversal in the evolutionary trend with evidence of vegetation erosion channel widening even though a significant aggradation phase is not present we conclude that alteration of sediment regime has played a major role on the long term channel evolution however only relevant flood events rin10 15 years appear to determine substantial island erosion and therefore the proportion of island vs channel area fluctuates depending on flood history

physical modelling of the combined effect of vegetation and wood on river morphology abstract the research reported in this paper employs flume experiments to investigate the potential effects of living vegetation and large wood on river morphology specifically aiming to explore how different wood input and vegetation scenarios impact channel patterns and dynamics we used a mobile bed laboratory flume divided into three parallel channels 1 7 m wide 10 m long and filled with uniform sand to reproduce braided networks subject to a series of cycles of flooding wood input and vegetation growth temporal evolution of river configuration in terms of the braiding index vegetation establishment and erosion and wood deposition amount and pattern was recorded in a series of vertical images the experiments reproduced many forms and processes that have been observed in the field from scattered logs in unvegetated dynamic braided channels to large wood jams associated with river bars and bends in vegetated stable single thread rivers results showed that the inclusion of vegetation in the experiments changes wood dynamics in terms of the quantity that is stored and the depositional patterns that develop vegetated banks increased channel stability reducing lateral erosion and the number of active channels this promoted the formation of stable wood jams where logs accumulated continuously at the same locations during subsequent floods reinforcing their effect on river morphology the feasibility of studying these processes in a controlled environment opens new possibilities for disentangling the complex linkages in the biogeomorphological evolution of the fluvial system and thus for promoting improved scientific understanding

geothermal regime and hydrocarbon kitchen evolution of the offshore bohai bay basin north china the offshore bohai bay basin located in the central bohai bay basin north china one of the most petroliferous basins in china in this article based on formation testing temperature drill stem tests and bottom hole temperature data 80 thermal gradient values at the depth interval of 0 to approximately 3000 m 9843 ft in the offshore bohai bay basin were obtained the basinwide average thermal gradient is 31 8 4 6c km based on the above thermal gradient data and the corresponding average weighted thermal conductivity data 80 measured terrestrial heat flow values were obtained these values range from 33 5 to 84 0 mw m2 with an average value of 60 8 8 7 mw m2 the heat flow and thermal gradient distribution in this region generally show higher values in the uplifts and lower ones in the sags a thermal history derived from vitrinite reflectance and apatite fission track data indicates that paleogene cooling occurred after a period of much higher paleogeothermal gradient 3854c km tectonic subsidence analysis reveals that the area experienced initial synrift subsidence during the paleogene followed by subsequent thermal subsidence since the neogene thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of petroleum source rock maturation the maturation and hydrocarbon expulsion histories of the paleogene shahejie 3 formation e2s3 which is the most important source rock in the offshore bohai bay basin are modeled results show that the shahejie 3 formation is in a high mature stage at the present day and the bozhong and qikou sags are the most important kitchens the huanghekou sag became the third most important hydrocarbon kitchen in the early neogene based on this hydrocarbon kitchen evolution oil and gas mainly accumulated after 12 ma the evolution of kitchen areas may provide new insights for the understanding of the oil and gas exploration potential of the offshore bohai bay basin

uranium isotopic evidence for the origin of the bahariya iron deposits egypt abstract the economic iron ore deposits of egypt are located at bahariya oasis in the lower middle eocene limestone the main iron minerals are goethite hematite siderite pyrite and jarosite manganese minerals are pyrolusite and manganite gangue minerals are barite glauconite gibbsite alunite quartz halite kaolinite illite smectite palygorskite and halloysite geochemical comparison between the ore and the nubia sandstone showed that the ore is depleted in the residual elements al ti v and ni and enriched in the mobile elements fe mn zn ba and u which indicates that the bahariya iron ore is not a lateritic deposit despite the deep weathering in this area on the other hand the nubia sandstone showed depletion in the mobile elements which demonstrates the leaching process in the nubia aquifer the presence of such indicator minerals as jarosite alunite glauconite gibbsite palygorskite and halloysite indicate that the ore was deposited under strong acidic conditions in fresh water isotopic analyses of the uranium in the amorphous and crystalline phases of the ore in the country rocks and dissolved in the nubia aquifer water all support the conclusion that u and fe were precipitated together from warm ascending groundwater u and fe display strong co variation in the ore and the 234u 238u activity ratio of the newly precipitated u in the country rock and the leached component of u in the groundwater are identical there is only slightly more uranium in the amorphous phase than in the crystalline and only a slightly lower 234u 238u activity ratio suggesting that the iron in the two phases have a similar origin comparison of the excess 234u in the water and in the total ore leads to the conclusion that the precipitation of the u and by inference the iron occurred within the last million years however that both precipitation and leaching of u have occurred over the last 300 000 years is evidenced by the extreme 230th 234u disequilibria observed in some of the samples some of the amorphous depositional events have been very recent perhaps within the last 10 000 years

what can the grace seasonal cycle tell us about lake aquifer interactions abstract lake aquifer interactions have been the subject of investigation and debate for decades traditional investigation methods include measurement of water flux across the groundwater surface water interface application of heat and environmental tracer methods conducting numerical simulations of the water flow and mass balance based approaches we first review evaluate and describe the different approaches that have been applied for examining lake aquifer interactions and propose an additional complementary approach while the leakage from lakes and its slow movement through porous media laminar flow is well characterized by existing methods modeling the rapid and turbulent flow through preferred pathways faults karst remains a challenging task to better understand the nature and the full scale of the lake aquifer interactions and using lake nasser and the underlying dakhla subbasin of the nubian sandstone aquifer system nsas in the western desert of egypt area 0 66 106 km2 as a test site we examine model and correlate temporally and spatially the variations in gravity recovery and climate experiment terrestrial water storage gracetws solutions with precipitation lake levels area and water volume we review current grace applications in hydrology and present our novel approach findings include firstly large seasonal fluctuations peak nov dec trough july aug in lake nasser s surface water levels average annual fluctuations from 3 7 m to 7 5 m area average area 3622 km2 but up to 4530 km2 and volume annual average 13 4 km3 and up to 34 km3 are observed throughout years 2006 to 2015 these fluctuations are accompanied by an increase in gracetws average 50 13 mm yr up to 77 18 mm yr over lake nasser and by a progression of a front of increasing gracetws values 50 13 mm away from the lake reaching distances of up to 700 km some 3 to 5 months following peak lake level periods the areas witnessing the seasonal increase in gracetws display a progressive increase in phase and decrease in amplitude with distance from the lake secondly the negligible precipitation over the dakhla subbasin cannot account for the observed seasonal gracetws patterns and neither can the leakage signal from lake nasser thirdly overall similarities in the distribution of gracetws seasonal spatial patterns are observed during high lake level periods e g dec 2007 feb 2015 additional and more distant areas from lake nasser saw increases in gracetws and vice versa during low lake level periods e g july 2006 aug 2010 these observations are consistent with lake nasser being the main source of modern recharge for the dakhla subbasin and suggest a new conceptual model for the subbasin a slow groundwater flow through a porous matrix and a rapid groundwater flow along a network of faults fractures and karst topography across the matrix we suggest that the proposed conceptual model for the interaction between lake nasser and the dakhla subbasin could be applicable to aquifers of similar geologic climatic and hydrologic settings worldwide and that approaches similar to those advocated here could be used to investigate the validity of this suggestion

the chemical and isotopic compositions of volatiles in magmatic hydrothermal fluids beneath the songliao basin northeastern china abstract it is controversial whether deep fluids can make contributions to natural gas accumulations in the songliao basin ne china the occurrence of magmatic hydrothermal quartz veins in crystalline basement of the basin provides a way to understand the characteristics of deep fluids and their significance for natural gas accumulation three types of fluid inclusions were identified in hydrothermal quartz aqueous inclusions h2o co2 rich inclusions and h2o co2 ch4 rich inclusions the primary inclusions show high homogenization temperatures 280 433 c which are typical of magmatic hydrothermal fluids the oxygen and hydrogen isotopic compositions 18o and d of water are 2 0 to 4 6 and 91 6 to 75 7 respectively the o h isotopic compositions suggest that hydrothermal fluids associated with the quartz veins were derived from the primary magmatic system and mixed by small amounts of meteoric water two types of magmatic hydrothermal volatiles were identified in the study both types of volatiles are dominated by co2 co2 in type i volatiles shows more negative 13c values 13 8 to 9 7 than typical magmatic co2 which likely resulted from carbon isotopic fractionation during magma degassing type ii volatiles have higher 13c values 5 5 to 3 3 and are similar to typical magmatic co2 small amounts of hydrocarbons were observed in both types of magmatic hydrothermal fluids hydrocarbons in type i volatiles have relatively high 13cch4 values 30 6 to 24 1 and reversed carbon isotopic trends while hydrocarbons in type ii volatiles have more negative 13cch4 values 49 7 to 37 6 and orderly carbon isotopic trends co2 in hydrothermal fluids is a potential source for co2 gas accumulations hydrocarbons in hydrothermal fluids however can hardly make significant contributions to the commercial gas reservoirs due to their low concentration

size frequency distribution of longitudinal dune rippled flank sands compared to that of slipface sands of various dune types rippled flanks of longitudinal dunes and the slip faces of various dune types can be distinguished granulometrically by comparing the top to bottom trend of changes of sorting in the sand population of each individual slope flank sands which are prone to sorting processes through migration of ripples alongslope are always better sorted upslope whereas slipface sands which are controlled by avalanche and grainfall of sands become better sorted downslope considering the absolute values of the bottom samples the sands of the slip faces are both better sorted and the size distribution more symmetrical than those of the rippled flanks applying this approach in investigating ancient sediments could improve palaeogeographical interpretations

the floodplain large wood cycle hypothesis a mechanism for the physical and biotic structuring of temperate forested alluvial valleys in the north pacific coastal ecoregion abstract a floodplain large wood cycle is hypothesized as a mechanism for generating landforms and influencing river dynamics in ways that structure and maintain riparian and aquatic ecosystems of forested alluvial river valleys of the pacific coastal temperate rainforest of north america in the cycle pieces of wood large enough to resist fluvial transport and remain in river channels initiate and stabilize wood jams which in turn create alluvial patches and protect them from erosion these stable patches provide sites for trees to mature over hundreds of years in river valleys where the average cycle of floodplain turnover is much briefer thus providing a future source of large wood and reinforcing the cycle different tree species can function in the floodplain large wood cycle in different ecological regions in different river valleys within regions and within individual river valleys in which forest composition changes through time the cycle promotes a physically complex biodiverse and self reinforcing state conversely loss of large trees from the system drives landforms and ecosystems toward an alternate stable state of diminished biogeomorphic complexity reestablishing large trees is thus necessary to restore such rivers although interactions and mechanisms may differ between biomes and in larger or smaller rivers available evidence suggests that large riparian trees may have similarly fundamental roles in the physical and biotic structuring of river valleys elsewhere in the temperate zone

cenozoic tectonic evolution of the bohai bay basin and its coupling relationship with pacific plate subduction abstract the bohai bay basin is a mesozoic cenozoic rift basin in eastern china based mainly on a balanced section analysis this study compares the spatio temporal differences of tectonic evolution in relation to strike slip faults among different depressions within the basin in combination with the analysis of subsidence characteristics the study also attempts to clarify the cenozoic tectonic evolution of the basin and its coupling relationship with the subduction of the pacific plate it was found that 1 the strike slip faults were activated generally from south to north and from west to east during the cenozoic 2 there is a negative correlation between the intensity of tectonic activity in the bohai bay basin and subduction rate of the pacific plate and 3 the migration direction of the basin depocenters is consistent with the direction of pacific plate subduction

aftershocks and surface faulting associated with the intraplate guinea west africa earthquake of 22 december 1983 abstract this study reports on the results of geological and seismological field studies conducted following the rare occurrence of a moderate sized west african earthquake m b 6 4 with associated ground breakage the epicentral area of the northwestern guinea earthquake of 22 december 1983 is a coastal margin intraplate locale with a very low level of historical seismicity the principal results include the observation that seismic faulting occurred on a preexisting fault system and that there is good agreement among the surface faulting the spatial distribution of the aftershock hypocenters and the composite focal mechanism solutions we are not able however to shed any light on the reason s for the unexpected occurrence of this intraplate earthquake thus the significance of this study is its contribution to the observational datum for such earthquakes and for the seismicity of west africa the main shock was associated with at least 9 km of surface fault rupture trending east southeast to east west measured fault displacements up to 13 cm were predominantly right lateral strike slip and were accompanied by an additional component 5 to 7 cm of vertical movement southwest side down the surface faulting occurred on a preexisting fault whose field characteristics suggest a low slip rate with very infrequent earthquakes there were extensive rockfalls and minor liquefaction effects at distances less than 10 km from the surface faulting and main shock epicenter main shock focal mechanism solutions derived from teleseismic data by other workers show a strong component of normal faulting motion that was not observed in the ground ruptures a 15 day period of aftershock monitoring commencing 22 days after the main shock was conducted eleven portable analog short period vertical seismographs were deployed in a network with an aperture of 25 km and an average station spacing of 7 km ninety five aftershocks were located from the more than 200 recorded events with duration magnitudes of about 1 5 or greater analysis of a selected subset 91 of those events define a tabular aftershock volume 26 km long by 14 km wide by 4 km thick trending east southeast and dipping steeply 60 to the south southwest composite focal mechanisms for groups of events distributed throughout the aftershock volume exhibit right lateral strike slip motion on subvertical planes that strike almost due east although the general agreement between the field geologic and seismologic results is good our preferred interpretation is for three en echelon faults striking almost due east west

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

stretching factor estimation for the long duration and multi stage continental extensional tectonics application to the baiyun sag in the northern margin of the south china sea abstract conventional subsidence analysis methods are generally based on the assumption of instantaneous stretching which totally ignores the heat loss during continental rifting for long duration or multi episodic extensional tectonics such assumption is no longer valid and could cause significant deviation from real subsidence here i extend original finite stretching model to a multi stage scenario in terms of geothermal and structural successions between two adjacent rifting events a procedure is designed to estimate stretching factor by fitting the whole tectonic subsidence history in a self consistent manner on the basis of the extended model i apply this procedure to the baiyun sag in the continent slope of the south china sea subsidence analysis shows that the sag is characterized by two episodes of rifting the first stage 49 to 23 8 ma resulted in stretching factors in the range of 1 3 to 4 0 with the greatest stretching at the sag center while the second one 17 5 to 10 5 ma yielded minor stretching factors of 1 1 to 1 2 these estimates agree well with that determined from crustal thinning for the northern and central potions of the sag but significant discrepancy occurs between the southern edge of the sag and the present continent ocean boundary where the crustal thickness is less than 20 km and potentially extensive magmatic intrusion was well imaged in the seismic profiles i suggest that the magma assisted rheologically weakening and possible lower crust ductile flow contributed to the extension discrepancy the margin north of the baiyun sag having a relatively thick crust and vacant of magmatic activity was basically stretched in a depth uniform style it is inferred that preexisting weakness in the lithosphere and abundant sediment supply were responsible for the extremely thick cenozoic sediment developed in the baiyun sag

origin of the sinai negev erg egypt and israel mineralogical and geochemical evidence for the importance of the nile and sea level history abstract the sinai negev erg occupies an area of 13 000 km 2 in the deserts of egypt and israel aeolian sand of this erg has been proposed to be derived from the nile delta but empirical data supporting this view are lacking an alternative source sediment is sand from the large wadi el arish drainage system in central and northern sinai mineralogy of the negev and sinai dunes shows that they are high in quartz with much smaller amounts of k feldspar and plagioclase both nile delta sands and sinai wadi sands upstream of the dunes also have high amounts of quartz relative to k feldspar and plagioclase however sinai wadi sands have abundant calcite whereas nile delta sands have little or no calcite overall the mineralogical data suggest that the dunes are derived dominantly from the nile delta with sinai wadi sands being a minor contributor geochemical data that proxy for both the light mineral fraction sio 2 10 al 2 o 3 na 2 o k 2 o cao and heavy mineral fraction fe 2 o 3 mgo tio 2 also indicate a dominant nile delta source for the dunes thus we report here the first empirical evidence that the sinai negev dunes are derived dominantly from the nile delta linkage of the sinai negev erg to the nile delta as a source is consistent with the distribution of osl ages of negev dunes in recent studies stratigraphic studies show that during the last glacial period when dune incursions in the sinai negev erg began what is now the nile delta area was characterized by a broad sandy minimally vegetated plain with seasonally dry anastomosing channels such conditions were ideal for providing a ready source of sand for aeolian transport under what were probably much stronger glacial age winds with the post glacial rise in sea level the nile river began to aggrade post glacial sedimentation has been dominated by fine grained silts and clays thus sea level along with favorable climatic conditions emerges as a major influence on the timing of dune activity in the sinai negev erg through its control on the supply of sand from the nile delta the mineralogy of the sinai negev dunes is also consistent with a proposed hypothesis that these sediments are an important source of loess in israel

a tectonostratigraphic synthesis of the sub andean basins inferences on the position of south american intraplate accommodation zones and their control on south atlantic opening it has been shown in the accompanying paper that the sub andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains to test the hypothesis that changes in palaeo depositional setting rely on the presence of a series of transverse zones of structural accommodation data have been digitally compiled from across the south american continent spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries structural accommodation zones and patterns of subsidence and intraplate deformation the results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which on a regional scale interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization their strong spatial relationship with mesozoic intraplate alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during gondwana breakup these localized zones of high heat flow have important implications for source rock maturity in the interior phanerozoic intracratonic basins of south america on the south atlantic margin the majority of these crustal lineaments correlate with failed arms of triple junction rifts and define the boundaries to tectonostratigraphic domains recognized along the south atlantic rift system

petrology of the bimodal cenozoic volcanism of the kapsiki plateau northernmost cameroon central africa the kapsiki plateau is the northernmost volcanic zone of the cameroon line the volcanism 27 35 ma is of alkaline type and has a typical bimodal lava series diversity with basalts and hawaiite as mafic lavas and phonolites trachytes and rhyolites as felsic lavas mg rich olivine phenocrysts occur only in basalts the hawaiite contains andesine olivine and ca rich pyroxene phenocrysts and sanidine and quartz xenocrysts the phonolites contain alkali feldspar and na rich clinopyroxene phenocrysts two types of trachytes occur peralkaline trachytes with ti na and f rich aegirine augite richterite arfvedsonite phenocrysts and non peralkaline trachytes with an aenigmatite type undetermined mineral ti rich biotite and zircon phenocrysts similarly two types of rhyolites occur peralkaline with quartz and arfvedsonite phenocrysts and non peralkaline with quartz and biotite phenocrysts differentiation indices thornton and tuttle 1960 of the lavas range from 22 to 97 with a large gap in the range 34 82 some basalts are primitive 530 ppm ni 1100 ppm cr in basaltic lavas phonolites and non peralkaline trachytes and rhyolites zr and nb covary with approximately constant ratios o3 1 zr nb 5 3u however peralkaline trachytes and rhyolites have high concentrations in zr up to 2180 ppm and nb up to 780 ppm with correlative higher zr nb ratios 6 3 8 3 some rhyolites have abnormal ree patterns with kinks depleted in light ree probably resulting from stability of na ree f complexes under hydrothermal conditions despite a large gap between basaltic and felsic lavas major and trace element distributions indicate co magmatism for both the basaltic and felsic lavas the differentiation of the lava series is dominated by crystal fractionation the role of fluids in rhyolite genesis being of minor effect as evidenced by constant values of y ho and zr hf throughout the series the kapsiki plateau basalts are similar in their chemical and isotopic data character to other basalts from both the continental and oceanic sectors of the cameroon line the continental crust appears to have no significant role in their genesis the hawaiite mineralogical and geochemical characteristics are consistent with an origin by mixing of basaltic and felsic phonolitic magmas the kapsiki plateau basaltic magmas may have originated from an infra asthenospheric reservoir similarly to other basaltic magmas generated throughout the cameroon line the sr isotope variations observed in trachytes and rhyolites point to some contamination of the magmas by crustal materials while the nd isotopic composition is only slightly affected q 2000 elsevier science b v all rights reserved

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

propagating rifts crustal extension during continental rifting propagating rifts may not be incompatible with plate tectonic tenets which are considered at the appropriate scale propagation of a rift is a natural consequence of relative motion about a pole of rotation it is not necessarily valid that 1 rifts propagate in one direction or 2 crustal stretching increases with progressive propagation of a rift

petroleum charge and entrapment along active faults study of the accumulation mechanism of the qinhuangdao 29 oil field on the slope of the shijiutuo uplift bohai sea in the qinhuangdao 29 qhd29 oil field oil generated from the first member of the shahejie source rocks is mainly contained in paleogene reservoirs whereas deeper oil sourced from the third member of the shahejie es3 source rocks is generally accumulated in neogene reservoirs the present study was undertaken to better understand the differences in petroleum accumulation in the qhd29 oil field and to provide suggestions for future petroleum exploration on the shijiutuo uplift laser raman spectroscopy reveals that carbon dioxide co2 exists with hydrocarbon gas in the same fluid inclusions measured homogenization temperatures of aqueous inclusions range from 80 c to 160 c 176 f to 320 f indicating late stage rapid petroleum accumulation with a charging time of no earlier than 5 1 ma the results of grains containing oil inclusions measurements reveal the presence of paleo oil accumulation in the current natural gas column in terms of the boundary fault activity rate far co2 distribution is quite relevant to the late stage activity of boundary faults with high content of co2 corresponding to the section of the f1 fault with high intensity activity higher far values both neogene and paleogene reservoirs in well a1 contained predominantly es3 derived oil and were accompanied by abundant mantle co2 this reveals the segmented vertical transport of petroleum in the fault both the mantle derived co2 and hydrocarbons vertically migrated and accumulated in shallower reservoirs in the high activity intensity section of the boundary fault this may account for the occurrence of predominantly es3 derived oil in the reservoirs near the section of the fault with high activity intensity in the eastern part of the qhd29 oil field vertical migration may have been limited because of the relatively low intensity of fault activity and the distribution of sandstones seems to dominate the petroleum accumulation our research reveals that lithologic traps in the es3 stratum may still have great potential for exploration along the slope of the shijiutuo uplift

flood plain and channel dynamics of the quinault and queets rivers washington usa abstract comparison of historic channel migration rates modern planform conditions and overall sediment wood and flow conditions and interactions for the quinault river and queets river in the western olympic peninsula washington reveals decadal to century scale interactions between gravel bed channels and forested flood plains in temperate maritime environments the downstream alluvial portions of these two rivers can be divided into three reaches of different slope flow sediment and wood regimes i the upper quinault river is aggrading behind lake quinault a natural lake that traps most sediment and wood transported from the olympic mountain headwaters ii the lower quinault river downstream of lake quinault transports only sediment and wood derived from reworking of flood plain deposits and contributed from valley margins iii the queets river has unimpeded movement of sediment and water from the mountainous headwaters to the pacific ocean measurements of channel planform characteristics and historic migration rates and patterns show that these three reaches have correspondingly distinct channel and flood plain morphologies and dynamics the aggrading and sediment rich upper quinault river has the widest flood plain widest active channel greatest number of low flow channels and flanking gravel bars and an average channel migration rate of 12 7 3 3 m year between 1900 and 1994 the comparatively sediment poor lower quinault river has the narrowest flood plain narrowest active channel and lowest channel migration rate 4 0 1 2 m year and most flow is through a single channel with few adjacent gravel bars the queets river has attributes intermediate between the lower and upper quinault rivers including an average channel migration rate of 7 5 2 9 m year flood plain turnover rates are similar for all three reaches with channels eroding the flood plain at the rate of about 0 2 of the flood plain area per year and with corresponding flood plain half lives of 300 to 500 years observations from this study and previous studies on the queets river show that channel and flood plain dynamics and morphology are affected by interactions between flow sediment and standing and entrained wood some of which likely involve time frames similar to 200 500 year flood plain half lives on the upper quinault river and queets river log jams promote bar growth and consequent channel shifting short distance avulsions and meander cutoffs resulting in mobile and wide active channels on the lower quinault river large portions of the channel are stable and flow within vegetated flood plains however locally channel spanning log jams have caused channel avulsions within reaches that have been subsequently mobile for several decades in all three reaches log jams appear to be areas of conifer germination and growth that may later further influence channel and flood plain conditions on long time scales by forming flood plain areas resistant to channel migration and by providing key members of future log jams appreciation of these processes and dynamics and associated temporal and spatial scales is necessary to formulate effective long term approaches to managing fluvial ecosystems in forested environments

wood storage in three mountain streams of the southern andes and its hydro morphological effects this study analyses large wood lw storage and the associated effects on channel morphology and flow hydraulics in three third order mountain basins drainage area 9 12 km2 covered in old growth nothofagus forests ranging from the temperate warm chilean andean cordillera to the sub antarctic tierra del fuego argentina amount characteristics and dimensions of large wood 10 cm diameter 1 m long were recorded as well as their effects on stream morphology hydraulics and sediment storage results show that major differences in lw abundance exist even between adjacent basins as a result of different disturbance histories and basin dissection massive lw volumes i e 1000 m3 ha 1 can be reached in basins disturbed by fires followed by mass movements and debris flows potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams with a gross sediment volume stored behind wood dams of around 1000 m3 km 1 which appears to be of the same order as the annual sediment yield finally the presence of wood dams may increase flow resistance by up to one order of magnitude copyright 2007 john wiley sons ltd

roles of fault structures on the distribution of mantle derived co2 in the bohai bay basin ne china abstract based on studies on the contents origin and filling history of co2 and the seismic interpretation of the bohai sea the sea area of the bohai bay basin the distribution of mantle derived co2 and roles of fault structures have been examined in this study mantle derived co2 is mainly distributed in the structures within the bozhong area the center of the bohai sea laser raman spectrum shows that co2 inclusions are symbiotic with hydrocarbon inclusions with a charging time no earlier than 5 1 ma late stage 5 1 0 ma active basement faults are the major pathways for the migration of mantle derived co2 the intensity of the activity influences the co2 content abundant co2 occurs in the structures with basement faults that have relatively high fault activity rate far values along the basement fault high co2 content appears near the segments with high far values fault combination patterns affect the accumulation layers of mantle derived co2 structures with fault combination patterns that resemble a flower or y commonly accumulate co2 in cenozoic shallow layers as well the branch faults that intersect with basement faults facilitate the adjustment of co2 from deep to shallow layers the uplifted mantle is the deep tectonic context and the upwelling mantle magma is the source of the development of mantle derived co2 below the middle crust mantle derived co2 may be vertically transported along the lithosphere scale strike slip faults within the middle and upper crust the late stage active basement faults are the major conduits for mantle derived co2

kimberlites in western liberia an overview of the geological setting in a plate tectonic framework the liberian kimberlite field lies in the southern part of the west african craton closely associated kimberlites are present in sierra leone ivory coast guinea and mali and as a group are structurally controlled within the archean basement complex of the leo uplift three major kimberlite dike lineaments are recognized in the northwest sector of liberia all with prominently developed n ne trends these lineaments are termed the kumgbo wuese trend the border trend and the lofa trend the areas of dike intrusion are covered by the bopolu geological quadrangle map of liberia the border trend is close to sierra leone the kumgbo wuese trend is to the east and the lofa trend is coincident with the lofa river only one kimberlite pipe has been recognized in liberia mano godua but a second may be present and both lie along the kumgbo wuese trend the kimberlite bodies intrude the 2700 m y old liberian age province which is comprised of granitic and granodioritic gneiss complexes two prominently developed features dominate the province a general ne sw basement fabric and an en echelon dolerite dike system that parallels the coast dated at 180 m y and considered to represent intrusion at the onset of continental fragmentation transecting dikes and related faults suggest a relative age for the kimberlites of 180 m y an estimate that corresponds to the 92 to 140 m y age for the sierra leone field there is indirect evidence that kimberlites in guinea and mali are of a similar age based on the fact these are on strike with kimberlites in liberia and sierra leone respectively trans atlantic correlations between west africa and northeast south america reveal a cyclic eruption of magma types that were generated in response to plate and continental movements it is postulated that liberian kimberlite emplacement was related to postplate motion crustal flexuring that reactivated precambrian basement sutures these sutures are parallel to and correlate with recognizable paleorift and paleocompressional zones within and adjacent to the west african craton long sustained periods of tectonic activity can be demonstrated and it is proposed that if brittle fractures are continuously reactivated these will serve as conduits to the upper mantle tapping kimberlite source regions at depths in excess of 100 km

cenozoic lithospheric evolution of the bohai bay basin eastern north china craton constraint from tectono thermal modeling abstract it is well established that the lithosphere beneath the eastern north china craton ncc had been thinned before the cenozoic a 2d multi phase extension model in which the initial crustal and lithospheric thicknesses are variable is presented to reconstruct the initial thicknesses of the crust and lithosphere in the early cenozoic and to further investigate the lithospheric evolution beneath the eastern ncc through the cenozoic we conduct thermal modeling along three profiles from east to west in the bohai bay basin which is the center of the lithospheric destruction and thinning of the ncc using multiple constraints such as tectonic subsidence the present day heat flow and the moho depth we determine the initial crustal and lithospheric thicknesses of the bohai bay basin before the cenozoic rift to be 33 36 km and 80 105 km respectively the model results show that the most rapid lithospheric thinning during the cenozoic occurred in the middle eocene for most depressions and the thinning activity ceased at the end of the oligocene reaching a minimum lithospheric thickness of 53 74 km followed by a thermal relaxation phase combined with previous studies we infer that the lithosphere beneath the eastern ncc experienced two stages of alternating thinning and thickening notable thinning in the early cretaceous and paleogene and thickening in the late cretaceous and late cenozoic we believe that thermo chemical erosion together with extension was probably the major mechanism of the significant lithospheric removal during the mesozoic whereas the cenozoic lithospheric thinning was mainly dominated by tectonic extension in the eastern ncc lithospheric thickening was generally a result of thermal cooling

groundwater controls on biogeomorphic succession and river channel morphodynamics biogeomorphic succession describes feedbacks between vegetation succession and fluvial processes that at the decadal timescale lead to a transition from bare river deposited sediment to fully developed riparian forest where the rate of stabilization by biogeomorphic succession is greater than the rate of ecological disturbance by fluvial processes a river is likely to evolve into less dynamic states while river research has frequently considered the physical dimensions of morphodynamics less is known about physical controls on succession rates and how these impact stream morphodynamics here we test the hypothesis that groundwater dynamics influence morphodynamics via the rate of biogeomorphic succession we applied historic imagery analysis in combination with dendroecological methods for willows growing on young gravelly fluvial landforms along a steep groundwater depth gradient we determined the following floodplain morphodynamics and plant encroachment at the decadal scale pioneer willow growth rates and their relationships to hydrological variables willow growth rates were correlated with moisture availability groundwater discharge and precipitation variability in the downwelling reach while little correlation was found in the upwelling reach after a reduction in ecological disturbance frequency data suggest that where groundwater is upwelling biogeomorphic succession is fast the engineering effect of vegetation is quickly established and hence channel stability increased and active channel width reduces where groundwater is downwelling deeper and more variable biogeomorphic succession is slower the engineering effect is reduced and a wider active width is maintained thus groundwater is an important control on biogeomorphic feedbacks intensity and through the stabilizing effect of vegetation may drive long term river channel morphodynamics

morphological adaptation of river channels to vegetation establishment a laboratory study while the scientific community has long recognized that alluvial rivers are the product of interactions between flowing water and bed material transport it is increasingly evident that vegetation mediates these interactions and influences the stream channel characteristics in a novel set of mobile bed laboratory experiments with variable discharge we demonstrate that vegetation colonization affects bank erosion rates channel shape channel sinuosity and bar pattern our analyses compared the morphological evolution of channels with initially steady bars considering the following three scenarios 1 channel without vegetation 2 channel with vegetation added to the floodplains and 3 channel with vegetation added to both the floodplains and the bar surfaces that emerge at low flows absence of vegetation produced the widest and shallowest channel with the lowest sinuosity floodplain vegetation in the second scenario reduced bank erosion and resulted in a deeper and more sinuous channel with shorter bars in the third scenario vegetation establishment on emerging bar surfaces intensified erosion on the opposing bank enlarging the amplitude of bends enhanced sedimentation on vegetated bar areas increased both bar elevation and bar length compared to the second scenario the results show that the colonization of bar surfaces by plants creates the conditions for new floodplain and island formation fostering channel meandering and anabranching finally our experiments emphasize the role of alternating high and low flows on the morphological development of streams mediated by vegetation

wood storage in a wide mountain river case study of the czarny dunajec polish carpathians storage of large woody debris in the wide mountain czarny dunajec river southern poland was investigated following two floods of june and july 2001 with a seven year frequency within a reach to which wood was delivered only by bank erosion and transport from upstream wood quantities were estimated for eighty nine 100 m long channel segments grouped into nine sections of similar morphology results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded wooded banks and river width and inversely related to unit stream power at the flood peak the largest quantities of wood up to 33 t ha 1 were stored in wide multi thread river sections here the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest in these sections a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area very low amounts of wood were stored in narrow single thread sections of regulated or bedrock channel high stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel considerable differences in the character of deposited wood existed between wide multi thread channel sections located at different distances below a narrow 7 km long channellized reach of the river wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams whereas further downstream well preserved shrubs and trees prevailed this apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks wood can be transported long distances along relatively narrow single thread reaches but is preferentially deposited in wide multi thread reaches copyright 2005 john wiley sons ltd

experimental study and active tectonics on the zhangjiakou penglai fault zone across north china abstract the zhangjiakou penglai fault zone zpfz as a large scale wnw trending active fault zone with frequent seismic activity is an area prone to moderate to intense earthquakes across north china a detailed analysis of the zpfz has been carried out based on earthquake activity deep structural response dynamic mechanism and physical simulation by conducting an en echelon fault model experiment the results show that the zpfz is a lithospheric active fault zone that has controlled some small en echelon quaternary pull apart basins and has triggered many earthquakes as seismogenic structures the earthquake location and intensity distribution by the experimental simulation fit well with those of actual earthquakes the earthquake distribution is controlled obviously by the en echelon structural properties the intensity of seismic activity is strong in the middle and weak at the western and eastern ends of the fault zone migrating from the southeast to the northwest along the entire fault zone this wnw trending fault zone in north china is closely related to the surrounding plate activities the zpfz is not only dominated by the collision of the indian plate to the eurasian plate but is also influenced by the subduction of the pacific plate it depends on the comprehensive reflection of two geodynamic settings from the western collision of the indian to the eurasian plates and the eastern subduction of the pacific ocean plate to the eurasian plate

input storage and distribution of large woody debris along a mountain river continuum the drome river france abstract large woody debris lwd input storage and distribution were studied along the drome river a french alpine river with an active shifting channel and a well developed riparian forest lwd input from the floodplain is low 669 6 mg year 1 between 1948 and 1971 and 569 3 mg year 1 between 1971 and 1991 based on estimates of average lwd mass per study plot a range of 766 2122 mg year 1 of lwd were stored within the active channel e g unvegetated bars and low flow channel 60 km course covering 492 ha lwd accumulations are mainly observed on gravel bars at a limited number of preferential sites they are relatively rare and are randomly distributed in the low flow channel consequently lwd location is mainly associated with the decrease of flow level in shallow sectors in the low flow channel lwd stop en route is primarily caused by in channel structures such as boulders or vegetated islets general geomorphological factors e g pattern slope etc provide less explanation of lwd distribution moreover the residence time of lwd accumulations on the drome river is short lwd storage 1 3 3 7 times the annual lwd input from the floodplain and their morphogenic role is negligible few of the accumulations are buried or characterized by vegetation shoots and associated pools

controls on hydrocarbon properties in a paleozoic petroleum system in saudi arabia exploration and development implications the unpredicted discovery of downdip oil in permian carboniferous unayzah sandstone reservoirs along the southern flank of the predominantly gas condensate ghazal field in saudi arabia highlighted the need for a thorough assessment of controls on hydrocarbon properties with the aim to improve prediction and reduce uncertainty primary controls on hydrocarbon property variations condensate to gas ratio here appear to be compartmentalization multiple charging presumably from a lower silurian qusaiba kitchen to the south and east within the late oil to wet gas generation window and dysmigration to the north and west gas on production represents mostly unmixed thermogenic accumulations of variable maturities with no sign of biodegradation or thermal cracking light oil 1 06 1 21 calculated vitrinite reflectance rc in the southern part of the field represent late mature accumulations that apparently escaped flushing by subsequent gas condensate charges generated near the wet gas generation window 1 41 1 55 rc and currently occupying the field to the north constant maturity variations for both gasoline range and heavier components in each sample testify to a lack of mixing between the hydrocarbon phases petroleum inclusions similarly comprise either light oil or gas condensate that coexist with significantly overlapping homogenization temperatures suggesting considerable overlap in their trapping history 135 35 ma less mature petroleum has not been identified in the field possibly because of a lack of trap closure or migration focus prior to the inferred late jurassic filling or because of displacement to updip structures thereby high grading the probability of undiscovered oil west and northwest of ghazal if thermal generation instead of retrograde condensation or phase separation controls this petroleum system then the potential for deeper oil accumulations is limited

effect of sampling time in the laboratory investigation of braided rivers we focus on the measurement of the bed elevation of braided networks in flume experiments in particular the effect of the survey frequency on the measurement accuracy is studied to this aim an innovative measurement system is adopted it consists of a laser ultrasonic sensor and can survey the bed elevation under owing water this measurement system was used to profile a flume transect with a frequency of 4 minutes without stopping the water discharge by this technique the topography of a single transect was continuously acquired during the evolution of a braided river model twelve braided rivers generated with different experimental conditions were studied the main results are i there exists a threshold survey frequency 4 8 minutes in our analysis which guarantees that the morphological evolution of the braiding channels is fully measured ii if this threshold frequency of survey is exceeded significant errors occur in the balance of the eroded deposited sediments and in the evaluation of the bed elevation dynamics and iii these errors depend on the river stream power

magnetic anomalies in the nigerian continental mass based on aeromagnetic surveys abstract analysis of aeromagnetic data from the nigerian continental mass reveals magnetic lineations and regions of distinct magnetic character and field level which are interpreted as expressions of tectonic features related to igneous intrusives of various ages the total field magnetic intensity data derives from the crystalline shield area with its characteristic jurassic granitic ring complexes and neogene volcanics and the benue trough which is considered to be a failed rift arm classical analytical techniques were adopted for upward and downward continuation frequency domain filtering of the data and for the interpretation of surface and subsurface structures in the area major intrusives and fault zones were clearly delineated the results of the analyses also revealed aspects of the regional tectonic framework of west africa and its relationship with major structures in the adjacent atlantic basins

on the long term seismic hazard analysis in the zhangjiakou penglai seismotectonic zone china abstract the zhangjiakou penglai seismotectonic zone zpsz lies in the northern part of north china and extends along the zhangjiakou beijing tianjin bohai bay penglai yellow sea it is about 900 km long and some 250 km wide in a northwest direction the great sanhe pinggu ms 8 0 earthquake occurred on september 1679 and the tangshan ms 7 8 earthquake on july 1976 caused serious economic and life losses according to some differences in crust structure and regional tectonic stress field the zpsz is divided into western and eastern segment by the 117 e line for study on long term seismic hazard analysis an analysis of gutenberg richter s empirical relation of earthquake frequency and time process of historic and recent earthquakes along the eastern and western segments shows that the earthquake activity obeys a poisson process and these calculations indicate that the earthquake occurrence probability of ms 6 0 6 9 is 0 77 0 83 in the eastern segment and the earthquake occurrence probability of ms 7 0 7 9 is 0 78 0 80 in the western segment of the zpsz during a period from 2005 to 2015

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

geochemistry and accumulation of carbon dioxide gases in china we propose the following identification indicators for co2 of different origins based on data obtained from analyzing the molecular composition of 1198 gas samples the co2 carbon isotope values of 390 samples and the helium isotope composition of 256 samples collected from wells of 16 oil and gas bearing basins and gas seepages in china and reviewing literature on organic and inorganic co2 throughout the world co2 is of organic origin if co2 content 13cco22 is of inorganic origin if dgr13cco2 8 pmil or co2 60 and co2 is of either organic or inorganic origin or a mixtur of organic and inorganic origins if 10 pmil 13cco213cco2 values of organic co2 mainly range from 10 to 22 pmil in tectonically stable oil and gas bearing basins where deep faults and magmatism are undeveloped organic co2 occurs almost exclusively in tectonically active oil and gas bearing basins where active faults and magmatism are present or in areas of modern volcanic activity the dgr13cco2 values of inorganic co2 range from 2 to 8 pmil and are distributed along faults the inorganic co2 with a dgr13cco2 value of 0 3 pmil is of metamorphic origin and that with dgr13cco2 values of 6 2 pmil is mantle derived and of magmatic origin in china the dgr13cco2 values of inorganic co2 gas pools range from 3 41 to 8 44 pmil and the helium ratio r ra is 1 which indicates that these gases are typically derived from the mantle

mantle derived co2 migration along active faults within an extensional basin margin fiumicino rome italy abstract fluid migration along faults can be highly complex and spatially variable with the potential for channeled flow accumulation in capped porous units fault cross flow lateral migration along strike or complete sealing extensional basin margins can be important for such migration given the associated crustal thinning and decompression that takes place combined with potential geothermal or mantle gas sources one such example is near the urban area of rome situated along the active extensional continental margin of the tyrrhenian back arc basin and surrounded by middle upper pleistocene k rich and arc related volcanoes recent research activities in the area around fiumicino a town 25 km to the west of rome has highlighted the close spatial link between degassing co 2 and the faults that provide the necessary vertical migration pathways in particular detailed soil gas and gas flux surveys have highlighted the release at surface of large volumes of asthenospheric mantle co 2 in correspondence with normal faults observed in a new seismic reflection profile acquired along the tiber river detailed reconstruction of the pleistocene holocene stratigraphy of the area dates fault activity from 20 000 to 9000 years bp it is proposed that the gas migrates preferentially along the cataclastic tectonic breccias of the faults until it encounters recent unconsolidated sediments porous units within this shallow stratigraphy act as temporary secondary traps for the leaking gas with local gas release at the ground surface occurring where the sealing of the overlying aquitards has been compromised degassing and active faults confirm the extensional tectonics affecting the area and the geodynamic scenario of a mantle wedge beneath the western apennines associated with ongoing w directed subduction moreover degassing highlights the potential geochemical and seismic risks for the highly populated urban areas near rome

porosity and volume assessments of large wood lw accumulations abstract the formation of large wood lw accumulations during floods represents a major hazard for constricted river cross sections e g bridges and weirs as it affects flow hydraulics and sediment transport to better assess lw accumulations reliable strategies and techniques are required there are currently practical limits on monitoring accumulation configurations both laser scans and photogrammetric techniques can be used to scan the outer contours of lw accumulations but cannot practically assess the wood content and porosity details of the outer deposit are captured in high resolution but the core of the deposit remains occluded and estimation is necessary this becomes more challenging for deposits of increasing size relative to wood elements to develop a more efficient workflow for lw accumulation assessment in the field we performed a laboratory study to develop a relationship between the envelope volume of water worked lw jams during a single flood hydrograph and the volume of woody elements within explicitly accounting for porosity we used photogrammetric techniques now in common use for reconnaissance surveys of debris accumulations on wood accumulations scaled for the laboratory the study s aim is to develop a semi automated assessment method enabling efficient image acquisition processing and computation of lw accumulation volume using a multi camera array above the laboratory channel and applying structure from motion photogrammetry we developed 3d models for 16 experimental flow formed wood accumulations each with 50 individual wooden dowels no correlations were found between porosity and flow magnitude porosity was found to be similar for most deposits 66 as a result of this accumulation structure the envelope volume used in 3d and 2 5d photogrammetric methods tended to overestimate wood content by 3 and 2 6 respectively the results obtained here will contribute to a more reliable volumetric assessment for inventories of wood mass in river systems

natural gas constituent and carbon isotopic composition in petroliferous basins china abstract there are abundant gas resources in petroliferous basins of china large to midsize gas fields are found in eastern central and western of china however origin constituents and isotopic composition of natural gas in different gas fields are varied distinctly and some present strong chemical secondary alteration and show variation both in age and space based on the systematic analysis of constituents and carbon isotope of a large number of gas samples combined with the geological characteristics this paper classifies the origins of the gases explores the gas isotope characteristics and evolutionary regulation with the variation time and space and further discusses the distinctive geochemistry of the gases in china these gases are dominated by dry gas its methane carbon isotope values range from 10 to 70 ethane from 16 to 52 propane from 13 to 43 and butane from 18 to 34 the carbon isotopes of most gases show the characteristics of humic derived gas and crude oil cracked gas in addition large primary biogenic gas fields have been discovered in the qaidam basin inorganic derived alkane gases have been discovered in deep of the songliao basin half of these gas fields are characterized by the alkane carbon isotope reversal in different degrees research indicates there are several reasons can result in carbon isotope reversal firstly gas charge of different genetic types or different source in one gas reservoir may cause carbon isotope reversal besides high over mature evolution of gas can also lead to the carbon isotopic reversal of alkanes thirdly secondary alteration of hydrocarbons may also result in abnormal distribution of carbon isotope isotope transforms to unusual light and heavy

linked fault families in basin formation abstract recent models of faulting tectonics in basins and passive margins have emphasized the linked nature of faults in a way that is analogous to that developed for thrust regimes a linked fault system requires three components ramps flats and sidewalls or transfers basins that are the result of other processes are not considered in this contribution and the examples used are drawn from the midland valley and northumberland basins of the u k where existing mapping by the british geological survey as well as field work undertaken by the author indicate that such models are appropriate this paper summarizes the geometric features and constraints of such models and emphasizes the role of each of the three critical components of a linked system for large deformations that result in the formation of major extensional and strike slip basins the principal geometries can be understood by reference to regionally and locally balanced fault models that involve detachment ramp and sidewall or transfer elements tip strains and both lateral and vertical accommodation zones are included in the general model but these probably account for less than 10 of the total upper crustal strain the basic analysis of a linked basin system requires the transfer of displacement on and between the fault and shear zone components the geometry of the stratigraphic units is used to deduce the active linkage on the fault system in oblique slip systems and where the dominant extensional ramp is connected to oblique transfer and detachment systems lateral and sidewall sub basins and intra basin uplifts occur as part of continuing slip on the fault system these control facies distribution and depocentre evolution the existence of a basin forming linked system frequently controls later deformation of basins and margins and an appreciation of basin growth faults and stratigraphic geometry is essential in the interpretation of inverted basins and orogenic belts involving supracrustal formations

wood distribution along streams draining old growth floodplain forests in congaree national park south carolina usa abstract we measured wood volume and other characteristics along a series of instream and floodplain transects in and around congaree national park south carolina seven transects were surveyed at most sites one within the bankfull channel and three on each bank at 10 50 and 100 m lateral distances respectively from the channel along each transect we measured piece dimensions location along transect orientation and decay category we also characterized channel width drainage area vegetation type average forest basal area and inundation category for each transect forest transects 100 m from a channel were also surveyed instream wood loads for unmanaged channels draining old growth forests were 102 178 m 3 ha which is lower than most instream wood loads documented for old growth temperate forests we attribute the lower wood loads to the combined effects of high transport capacity and rapid decay floodplain wood loads are lowest close to the channel but increase with distance reaching comparable values up to 172 m 3 ha at distances 100 m from a channel channel geometry does not appear to exert the significant influence on instream wood loads that has been documented for more laterally constrained channels channel spanning jams are uncommon and appear to be transient features

influence of large woody debris on morphological evolution of incised sand bed channels this paper documents the influence of large woody debris lwd on the morphological evolution of unstable degrading sand bed rivers in the yazoo basin north mississippi usa the study was performed as part of the demonstration erosion control dec project twenty three river reaches were studied with the aim of determining whether the presence of lwd was beneficial or detrimental to the recovery of stability in degrading sand bed river systems and to provide the geomorphic understanding necessary to underpin enhanced lwd management strategies the results demonstrate that locations of lwd inputs volumes of lwd stored in different reaches and number of jams per unit channel length are causally related to the morphological processes occurring during different stages of adjustment in these unstable incised fluvial systems and may be explained using a channel evolution model cem the net impact of lwd jams on reach scale sediment budgets was found in general to be positive that is jams trap more sediment than they mobilise this suggests that lwd probably accelerates rather than retards recovery of a stable longitudinal profile and channel configuration following incision field typing of lwd jams based on their impacts on the flow pattern reveals that jam type is a function of the size of large key elements in the jam in relation to the channel width a debris jam classification scheme is proposed on this basis with the spatial relationship between jam type and drainage basin area expressed using a dimensionless function of the ratio between channel width and average riparian tree height the scheme features four jam types underflow dam deflector and flow parallel bar head each of which has a different morphological impact on local channel geometry these jam types may be used to classify lwd jams as an aid in determining appropriate management strategies according to their location within the drainage basin

the noble gas geochemistry of natural co2 gas reservoirs from the colorado plateau and rocky mountain provinces usa identification of the source of co2 in natural reservoirs and development of physical models to account for the migration and interaction of this co2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of co2 in the subsurface we present the results of 57 noble gas determinations in co2 rich fields 82 from three natural reservoirs to the east of the colorado plateau uplift province usa bravo dome nm sheep mountain co and mccallum dome co and from two reservoirs from within the uplift area st john s dome az and mcelmo dome co we demonstrate that all fields have co2 3he ratios consistent with a dominantly magmatic source the most recent volcanics in the province date from 8 to 10 ka and are associated with the bravo dome field the oldest magmatic activity dates from 42 to 70 ma and is associated with the mcelmo dome field located in the tectonically stable centre of the colorado plateau co2 can be stored within the subsurface on a millennia timescale the manner and extent of contact of the co2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic co2 we show that coherent fractionation of groundwater 20ne 36ar with crustal radiogenic noble gases 4he 21ne 40ar is explained by a two stage re dissolution model stage 1 magmatic co2 injection into the groundwater system strips dissolved air derived noble gases asw and accumulated crustal radiogenic noble gas by co2 water phase partitioning the co2 containing the groundwater stripped gases provides the first reservoir fluid charge subsequent charges of co2 provide no more asw or crustal noble gases and serve only to dilute the original asw and crustal noble gas rich co2 reservoir scale preservation of concentration gradients in asw derived noble gases thus provide co2 filling direction this is seen in the bravo dome and st john s dome fields stage 2 the noble gases re dissolve into any available gas stripped groundwater this is modeled as a rayleigh distillation process and enables us to quantify for each sample 1 the volume of groundwater originally stripped on reservoir filling and 2 the volume of groundwater involved in subsequent interaction the original water volume that is gas stripped varies from as low as 0 0005 cm3 groundwater cm3 gas stp in one bravo dome sample to 2 56 cm3 groundwater cm3 gas stp in a st john s dome sample subsequent gas groundwater equilibration varies within all fields each showing a similar range from zero to 100 cm3 water cm3 gas at reservoir pressure and temperature

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