flow resistance in coarse gravel bed rivers flow resistance relations are deduced from data on coarse gravel bed reaches of new zealand rivers measurements of hydraulic variables were made during reasonably uniform subcritical flows at cross sections regular in confirmation channel bed and bank roughness are not distinguished and surface bedmaterial is characterized by the median size when the channel boundary is rigid the darcy weisbach friction factor is only a statistically significant function of the ratio of hydraulic radius to median size of surface bedmaterial a model of this form explained 60 percent of the friction factor variance inherent in the field data set with active bedload transport conditions and changing bed topography the froude number based on median surface bedmaterial size was statistically significant and 40 percent of friction factor variance was explained by this latter model

foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

fluid inclusions and hydrothermal alteration on the dixie valley fault nevada footwall rocks of the 1954 rupture segment of the dixie valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages an early biotite feldspar assemblage is followed by later fe chlorite and epidote both chlorite and epidote are replaced by hydrothermal sericite and cross cut by calcite hematite and quartz calcite veins biotite is partially replaced by prehnite the latest hydrothermal minerals are stilbite laumontite kaolinite alunite smectite illite and pervasive replacement of rock units with fine grained quartz chalcedony and opal secondary fluid inclusions trapped in healed microfractures in igneous quartz include type i inclusions that contain a moderate salinity aqueous liquid and vapor type ii inclusions that contain a moderate salinity aqueous liquid and co2 type iii inclusions that show eutectic melting temperatures below the nacl h2o eutectic and contain substantial cacl2 and type iv inclusions containing halite and other daughter minerals microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures salinities of type i inclusions vary from 0 1 to 12 9 wt nacl with the mode in the interval 0 to 1 salinities of type ii co2 bearing inclusions range from 0 62 to 6 81 wt nacl relative to h2o and salinities of type iii inclusions with low eutectic melting temperatures are 12 9 to 25 3 nacl equivalent wt salinities of halite bearing inclusions are 30 1 to 39 2 wt nacl homogenization temperatures span the range 120 to 400 c the processes of isochemical cooling with upward displacement of the footwall mixing of cool low salinity water with hotter components and mixing of cool evaporite brine with hotter components could be responsible for variable fluid inclusion compositions homogenization temperatures and densities the p t path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics the path includes a lithostatic fluid pressure at 305 c and 1570 bars along with cooling and escape of co2 from fluids the fluid p t path probably approaches hydrostatic pressure conditions at lower temperatures hydrothermal alteration product minerals fluid temperatures pressures and compositions in the footwall of the dixie valley fault constrain minimum fault age to 20 to 25 ma displacement to 6 km with about 3 km of pre 10 to 13 ma and 3 km of post 10 ma uplift fluid compositions and p t data suggest the following mechanism for rupture initiation and arrest ruptures may be initiated as a result of high fluid pressures then opening of dilatant fractures causes drastic decrease in fluid pressure separation of steam and co2 the drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced in areas where fluid pressure reduction is not accompanied by phase separation fractures are arrested by dilatant hardening

modeling of unsteady flows in alluvial streams a computer model is described to predict unsteady and nonuniform flows in alluvial streams the model uses a generalized expression for evaluating the energy slope in mobile boundary flows therefore it is possible to adopt different friction factor relationships into the model without affecting its structure it is also possible to upgrade the model easily as new expressions for alluvial bed roughness become available the model has been tested for laboratory and field conditions and shows good agreement with measured data it is capable of predicting long term changes in riverbed slope and thus is well suited for estimating chang in river regime caused by certain modifications to river flow such as river diversions meander cutoffs river training works dams and hydroelectric power plants

syndeformational fluid trapping in quartz determining the pressure temperature conditions of deformation from fluid inclusions and the formation of pure co2fluid inclusions during grain boundary migration observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids our results imply that pure co2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation recrystallization process rather than representing a primary metamorphic fluid where the temperature of deformation can be deduced by other means the densities of fluid inclusions trapped during recrystallization which we call recrystallization primary fluid inclusions can be used to constrain the ambient pressure during deformation using these constraints the data imply that the post metamorphic hercynian exhumation in sardinia brought rocks at 300 c to within 3km of the surface this conclusion is similar to that described for the rapidly uplifted southern alps in new zealand

conodonts as biostratigraphic tools for redefinition and correlation of the cambrian ordovician boundary the cambrian ordovician boundary is recognized at different horizons on various continents by utilizing several fossil groups conodonts are abundant diverse and less provincial and facies controlled than other fossils in this interval many species are widespread and some are cosmopolitan strata representing the cambrian ordovician boundary interval from asia australia and north america can be correlated easily when those strata are from cratonal or shelf environments strata from slope facies have fewer conodonts fewer taxa and taxa may have different ranges compared with cratonal and shelf facies it may be easier to correlate intercontinentally within cratonal shelf facies than to correlate intracontinentally from cratonal shelf facies to slope facies a new hierarchical arrangement of conodont interval zones and subzones is proposed for western north america these include the proconodontus tenuiserratus zone the p posterocostatus zone new the p muelleri zone new the eoconodontus zone new with eoconodontus notchpeakensis and cambrooistodus minutus subzones the cordylodus proavus zone emended with hirsutodontus hirsutus fryxellodontus inornatus and clavohamulus elongatus subzones the cordylodus intermedius zone new with hirsutodontus simplex and clavohamulus hintzei subzones the cordylodus lindstromi zone new and cordylodus angulatus zone new the boundary point for the base of the ordovician system will be chosen so as to coincide with a correlatable conodont zonal boundary other fossil groups will support correlation of this boundary point three alternative horizons are being considered the base of the cordylodus proavus zone is the most distinctive but is regarded by some as older than is appropriate for the base of the ordovician the base of the cordylodus intermedius zone is recognizable by faunal changes in several evolutionary lineages at a level that is slightly younger than the presently recognized boundary in australia north america and parts of asia but slightly older than the base of the tremadoc series of europe the base of the c lindstromi zone can be recognized in most areas by the lowest occurrence of the nominate species which is of questioned taxonomic validity and uncertain biostratigraphic utility this horizon is closest to the base of the tremadoc series of europe choice of a stratotype section has been narrowed to the cow head group in newfoundland eastern canada and to the fengshan and yehli formations in jilin province northeastern china the cow head group was deposited on and near the base of the continental slope erosion by debrisslide breccias resulted in a significant hiatus near the boundary interval in the broom point sections a condition contrary to guidelines for choice of boundary sections this may be less of a problem in other sections such as green point the dayangcha section in china was deposited on the outer part of a continental shelf and has acritarchs conodonts graptolites and trilobites additional study of the china section is needed to document fully the ranges of critical conodont taxa

tectonics of the southern portion of the ribeira belt apiai domain abstract the name ribeira belt was originally used in a reference to a broad belt of deformed crust which strikes subparallel to the southeastern brazilian coastline it was originally believed to be neoproterozoic brasiliano panafrican but present investigations indicate that this age seems to be mainly related to the extensive arc related plutonism and tectono metamorphism that affected its most representative formations whereas the time of deposition of the supracrustals would be significantly older in this study the main tectono stratigraphic features of the apiai domain of the ribeira belt are described the lithostratigraphy is reviewed as well the paleogeographic structural geochemical and radiometric data and their implications for the tectonic evolution models for the region the marine sediments of the apiai domain were laid down on the borders of the parana and luis alves cratons and on an intervening mesoproterozoic 1 8 1 1 ga ocean crust they were intensively deformed by ocean closure and collision of the cratonic fragments and they constitute the majority of the local supracrustals designated as the acungui supergroup symmetrical continental passive margin deposits are represented to the northwest by a more proximal facies itaiacoca group probably related to the parana paleocontinent and by the capiru formation to the southeast between them lies the central domain formed by the votuverava group characterized by the remains of gradually deepening carbonatic platform sediments of the lajeado subgroup which grade eastward into distal turbiditic sequences of the ribeira subgroup where ocean floor and immature island arc magmatic rocks are present during the neoproterozoic the apiai domain behaved as a single continental mass into which basic rocks were intruded between 1 1 and 0 85 ga between 0 7 and 0 6 ga the apiai domain evolved into a cordilleran type magmatic arc related to the evolution of a subduction zone possibly situated to the southeast of the luis alves cratonic fragment this subduction caused metamorphism and migmatization of the supra and infra crustal rocks of the region and produced the extensive calc alkaline granitoid plutonism between 0 6 and 0 45 ga the majority of the southeastern continental blocks amalgamated during closure of the adamastor ocean followed by development of a system of regional dextral transcurrent shear zones related to oblique collision and or escape tectonics pull apart basins opened up and were filled with molasse sequences the region was intruded by post tectonic granitoids and then underwent regional cooling

validity of uniform flow hypothesis in one dimensional morphodynamic models local uniform flow luf hypothesis is a simplification of the governing equations describing river morphodynamics which is needed to determine the evolution of the bed profile and bed material composition in the case of large time and space scales this paper presents a rigorous analysis of the full one dimensional river hydrodynamic and morphodynamic mathematical model compared to its luf approximation the analysis establishes two criteria to assess the validity of the luf hypothesis 1 a criterion for rivers in equilibrium and 2 a criterion for evolving rivers i e in nonequilibrium the first criterion is based on the concept of the morphological box variations of the river bed longer than the box length are adequately reproduced by the luf hypothesis whereas only spatially averaged values are resolved within the box the second criterion is based on the concept of an evolution window temporal variations represented by wave periods larger than the evolution window can be adequately reproduced by the luf hypothesis whereas variations with shorter periods are averaged within this window the minimum size of morphological box and evolution window that limit the error introduced by the luf hypothesis increases when the froude number decreases further the minimum size of the evolution window increases for decreasing sediment concentration and increasing mixing layer thickness i e for larger bed forms the luf hypothesis is therefore best applied to small mountain rivers for which both the minimum size of the morphological box and the evolution window is relatively small so that spatial and temporal variations can be resolved in more detail applications using the luf hypothesis for large watersheds including the lowland portion of the fluvial network are possible but are limited to simulations over larger spatial and temporal intervals

fault valve action and vein development during strike slip faulting an example from the ribeira shear zone southeastern brazil abstract fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of neoproterozoic cambrian age in the ribeira river valley area southeastern brazil geometric and microstructural constraints indicate that foliation parallel and extensional veins were formed during dextral strike slip faulting both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates and were crystallized in the presence of co2 ch4 and h2o co2 ch4 nacl immiscible fluids following unmixing from a homogeneous parental fluid contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels foliation parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values 319 397 c and 47 215 mpa which is compatible with predicted fluid pressure cycle curves derived from fault valve action growth of extensional veins occurred in shallower structural levels under pressure fluctuating from near hydrostatic to moderately subhydrostatic values 207 218 c and 18 74 mpa which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone fluid immiscibility and precipitation of quartz in foliation parallel veins resulted from fluid pressure drop immediately after earthquake rupture fluid immiscibility following a local pressure drop during extensional veining occurred in pre seismic stages in response to the development of fracture porosity in the dilatant zone late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity 0 2 to 44 wt equivalent nacl h2o nacl cacl2 fluid inclusions trapped in healed fractures mainly in foliation parallel veins which also exhibit subordinate h2o nacl cacl2 co2 ch4 and h2o co2 ch4 nacl fluid inclusions trapped under subsolvus conditions in single healed microcracks recurrent circulation of aqueous carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes a fluid evolution trending toward ch4 depletion for co2 ch4 bearing fluids and salinity depletion and dilution approximation of the system h2o nacl for aqueous saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history

fault valve behaviour in optimally oriented shear zones an example at the revenge gold mine kambalda western australia abstract quartz vein systems developed in and adjacent to shear zones host major gold deposits in the kambalda region of the norseman wiluna greenstone belt at the revenge mine two groups of mineralised reverse shear zones formed as conjugate near optimally oriented sets during ese subhorizontal shortening adjacent to a major transpressional shear system the shear zones developed at temperatures of about 400 c in a transitional brittle ductile regime deformation was associated with high fluid fluxes and involved fault valve behaviour at transiently near lithostatic fluid pressures during progressive evolution of the shear system early brittle and ductile deformation was overprinted by predominantly brittle deformation brittle shear failure was associated with fault dilation and the formation of fault fill veins particularly at fault bends and jogs a transition from predominantly brittle shear failure to combined shear along faults and extension failure adjacent to faults occurred late during shear zone evolution and is interpreted as a response to a progressive decrease in maximum shear stress and a decrease in effective stresses the formation of subhorizontal stylolites locally subvertical extension veins and minor normal faults in association with thrust faulting indicates episodic or transient reorientation of the near field maximum principal stress from a subhorizontal to a near vertical attitude during some fault valve cycles local stress re orientation is interpreted as resulting from near total shear stress release and overshoot during some rupture events previously described fault valve systems have formed predominantly in severely misoriented faults the shear systems at revenge mine indicate that fault valve action and associated fluctuations in shear stress and fluid pressure can influence the mechanical behaviour of optimally oriented faults

tribes hill rochdale formations in east laurentia proxies for early ordovician tremadocian eustasy on a tropical passive margin new york and west vermont slow subsidence and tectonic quiescence along the new york promontory margin of laurentia mean that the carbonate dominated tribes hill and overlying rochdale formations serve as proxies for the magnitude and timing of tremadocian eustatic changes both formations are unconformity bound deepening shoaling depositional sequences that double in thickness from the craton into the parautochthonous western appalachian mountains a consistent layer cake succession of member level units of the formations persists through this region the tribes hill formation late early tremadocian late skullrockian late fauna b rossodus manitouensis chron unconformably overlies the terminal cambrian little falls formation as the lowest ordovician unit on the new york promontory it was deposited during the strong early tremadocian or stonehenge transgression that inundated laurentia brought dysoxic anoxic d a slope water onto the shelf and led to deposition of the schaghticoke d a interval black mudstone and ribbon limestone on the laurentian continental slope the uniform lithofacies succession of the tribes hill includes a lower sand rich member a middle dark grey to black mudstone that records d a in eastern exposures and an upper shoaling up carbonate highstand facies a widespread 12000 km 2 thrombolitic interval in the highstand carbonate suggests the new york promontory was rimmed by thrombolites during deposition of the tribes hill offlap and erosion of the tribes hill was followed by the relatively feeble sea level rise of the rochdale transgression new in laurentia and deposition of the rochdale formation the rochdale transgression correlated with the kierograptus drowning interval in baltica marks a eustatic rise the rochdale formation represents a short early ordovician interval early late tremadocian middle late stairsian macerodus dianae chron it correlates with a depositional sequence that forms the middle boat harbour formation in west newfoundland and with the rte 299 d a interval on the east laurentian slope the rochdale has a lower carbonate with abundant quartz silt comstock member new and an upper thrombolitic hawk member new high stand facies tribes hill and rochdale faunas are mollusc rich generally trilobite poor and have low diversity laurentian faunal province conodonts ulrichodina rutnika landing n sp is rare in rochdale conodont assemblages trilobites are also low in diversity but locally form coquinas in the middle tribes hill the poorly preserved rochdale trilobites include the bathyurid randaynia at least two hystricurid species and leiostegium

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

development of fluid conduits in the auriferous shear zones of the hutti gold mine india evidence for spatially and temporally heterogeneous fluid flow abstract the gold mineralization of the hutti mine is hosted by nine parallel n s trending steeply dipping 2 10 m wide shear zones that transect archaean amphibolites the shear zones were formed after peak metamorphism during retrograde ductile d 2 shearing in the lower amphibolite facies they were reactivated in the lower to mid greenschist facies by brittle ductile d 3 shearing and intense quartz veining the development of a s 2 s 3 crenulation cleavage facilitates the discrimination between the two deformation events and contemporaneous alteration and gold mineralization ductile d 2 shearing is associated with a pervasively developed distal chlorite sericite alteration assemblage in the outer parts of the shear zones and the proximal biotite plagioclase alteration in the center of the shear zones d 3 is characterized by development of the inner chlorite k feldspar alteration which forms a centimeter scale alteration halo surrounding the laminated quartz veins and replaces earlier biotite along s 3 the average size of the laminated vein systems is 30 50 m along strike as well as down dip and 2 6 m in width mass balance calculations suggest strong metasomatic changes for the proximal biotite plagioclase alteration yielding mass and volume increase of ca 16 and 12 respectively the calculated mass and volume changes of the distal chlorite sericite alteration ca 11 ca 8 are lower the decrease in 18 o values of the whole rock from around 7 5 for the host rocks to 6 7 for the distal chlorite sericite and the proximal biotite plagioclase alteration and around 5 for the inner chlorite k feldspar alteration suggests hydrothermal alteration during two stage deformation and fluid flow the ductile d 2 deformation in the lower amphibolite facies has provided grain scale porosities by microfracturing the pervasive steady state fluid flow resulted in a disseminated style of gold sulfide mineralization and a penetrative alteration of the host rocks alternating ductile and brittle d 3 deformation during lower to mid greenschist facies conditions followed the fault valve process ductile creep in the shear zones resulted in a low permeability environment leading to fluid pressure build up strongly episodic fluid advection and mass transfer was controlled by repeated seismic fracturing during the formation of laminated quartz gold veins the limitation of quartz veins to the extent of earlier shear zones indicate the importance of pre existing anisotropies for fault valve action and economic gold mineralization

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

deformation related recrystallization processes abstract recrystallization is a common microstructural transformation that occurs during deformation metamorphism and diagenesis of rocks studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur the range of mechanisms is related to the various ways in which two basic processes grain boundary migration and new grain boundary formation combine to transform the microstructure two recent papers drury et al 1985 urai et al 1986 have proposed different schemes for the description of recrystallization mechanisms the purpose of this paper is to provide a unified framework for the description of mechanisms recrystallization mechanisms are divided into three main types rotation mechanisms which principally involve the formation of new grain boundaries migration mechanisms which principally involve grain boundary migration and general mechanisms which involve both basic processes a further distinction is made on the basis of the continuity of the microstructural transformation with respect to time each of the three main types of mechanism can be divided into a number of sub types depending on whether the processes of grain boundary migration new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time as the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation the terms discontinuai and continual are used to refer to the temporal continuity of the transformation it is recommended that the following aspects should be specified if possible in a general description of recrystallization mechanisms 1 1 how do the basic processes combine to transform the microstructure 2 2 if new grain development occurs what is the development mechanism and does new grain formation occur in a continual or discontinuai manner 3 3 if grain boundary migration is involved in the transformation what is the migration mechanism i e fast solute escape migration slow solute loaded migration fluid assisted migration etc and is migration a continual or discontinuai process the application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved the complicating effects of solid solution impurities dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material

modeling of riverbed evolution for bedload sediment mixtures a new computational methodology for fully coupled simulation of unsteady water and sediment movement in mobile bed alluvial rivers has been developed and tested the one dimensional approach treats bedload transport of nonuniform sediment mixtures with sorting and armoring effects considered spatial lag effects in nonequilibrium bedload transport are taken into account through innovative use of the recently developed notion of a loading law the new system of equations for water and sediment movement is solved in a fully coupled implicit manner using the preissmann finite difference scheme implemented to allow for either upstream or downstream induced mobile bed perturbations formal analysis of the coupled system sheds new light on boundary condition requirements for the multiple size class problem the fully coupled implicit solution has proven to be robust and stable and it respects the underlying volumetric conservation laws remarkably well as demonstrated in continuity analyses of computed bed e

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

modeling non uniform sediment fluvial process by characteristics method this paper presents a numerical model based on a multimode characteristics method for fully coupled simulation of water and sediment movement in mobile bed alluvial channels with nonuniform bed materials along with the characteristics the temporal evolutions of flow depth and velocity bed elevation and bed material composition of a well defined river reach with proper boundary conditions can be simultaneously determined from the results of the test runs the proposed model provides useful information about the interactions among disturbance waves of different orders of magnitude and their influence on the formation of flow field bed topography and bed material composition such information cannot be easily obtained from finite difference methods

fully coupled unsteady mobile boundary flow model a fully coupled one dimensional river model capable of predicting sediment transport and bed level changes under unsteady flow conditions is described the governing equations for mass and momentum balance of sediment water mixture under unsteady flow conditions in natural rivers with irregular geometries are solved simultaneously using the preissmann four point linear implicit scheme with weighting factors for space and time coordinates the resulting system of algebraic equations is solved using a solution procedure that bridges upstream and downstream boundary nodal values by successive substitutions the friction slope is expressed in a consistent form that allows the consideration of the changing alluvial roughness effect the system of governing equations is explicitly coupled by introducing the term representing the rate of change of bed level the fully coupled unsteady mobile boundary flow model fcm is applied to the classical problem of sediment deposition upstream of a dam with an arbitrar

paleogeographic significance of clavohamulus hintzei miller conodonta and other ibexian conodonts in an early paleozoic carbonate platform facies of the argentine precordillera pre tremadocian conodonts and trilobites and tremadocian conodonts are reported from the cambrian and ordovician la silla formation in the cerro la silla section in east southeast jachal san juan province argentina a shallow marine conodont fauna contains elements of clavohamulus hintzei miller a common species in north america but reported for the first time from the early paleozoic platform carbonates of the western argentine precordillera the presence of this species suggests a correlation with the clavohamulus hintzei conodont subbiozone of the cordylodus intermedius conodont biozone in north america considered early ordovician skullrockian stage ibexian series in north america but by south american and european standards this biozone would be of latest cambrian age c hintzei and associated conodonts of the la silla formation are typical of the tropical faunas of the north american midcontinent faunal province late cambrian trilobites from lower in the formation also are typical north american taxa the presence of these faunas in the platform carbonates is consistent with plate reconstructions suggesting that the precordillera was in a tropical or subtropical position close to laurentia during the late precambrian and early paleozoic these new paleontological data provide one more argument for recent models of the precordillera as a displaced terrane derived from the ouachita embayment at the southern margin of laurentia

the recommended cambrian ordovician global boundary stratotype of the xiaoyangqiao section dayangcha jilin province china this paper provides a brief outline of the current detailed inter disciplinary work on the xiaoyangquiao section trying to expose all the aspects for reference tied to the global single stratigraphic point gssp concept for defining the cambrian ordovician boundary the 45 m critical interval of this section outcrops very well along the steep bank of a stream and is free from folding faulting intrusions and has not been affected by weathering colour alternation of conodonts and acritarchs and crystallinity indices of illite all indicate a maximum thermal grade of 100 c the lithofacies being of great lateral persistence for a hundred kilometres consists mainly of a rhythmical sequence of lime mudstone and shales deposited in a moderately deep outer shelf environment of quiet water well below the normal storm wave base chemical investigation of the rocks demonstrates strong positive correlation between a12o3 content and those of k2o mgo fe2o3 tio2 be cr co ni zn and ba indicating these components are tied to the clay fractions a stable depositional environment is demonstrated by the uniform chemistries through the boundary interval close to the boundary itself p2o5 contents are low indicating continuous sedimentation at fairly substantial rates the major biological events the biostratigraphic framework and the stratigraphic range of conodont graptolite trilobite and acritarch taxa are illustrated briefly with diagrams following the majority views of the calgary plenary session the boundary level is to be chosen at a point marked by the first appearance datum fad of the selected conodont taxon or taxa in the vicinity of the level close to but below the first influx of nematophorous graptolites the following four points marked by the incoming of conodont taxon or taxa are recommended for consideration of the golden spike 1 fad of cordylodus intermedius at 5 28 m below the first influx of nematophorous graptolites 2 fad of hirsutodontus simpler cordylodus drucei albiconus postcostatus at 5 23 m 3 fad of semiacontiodus lavadamensis utahconus utahensis monocostodus sevierensis at 3 85 m 4 fad of cordylodus lindstromi at 2 23 m for the following reasons the fad of h simplex c drucei a postcostatus is favoured 1 the taxa are all distinct and widely dispersed 2 intensive evolutionary change took place in conodonts graptolites trilobites and acritarchs prior to or after this point all the fossil groups occur together providing correlation with many regions throughout the world 3 the point is in a position between the previously widely accepted boundary levels based on graptolites and trilobites 4 the proposed point lies within a thin laterally persistent rhythmical sequence the fad of cordylodus lindstromi is also a favourable point sharing many advantages mentioned above but this point is less satisfactory in being defined by the fad of a single taxon c lindstromi which also has an extremely small population size an isochron age of 500 7 7 4 ma is determined from clay fractions of mudstones 8 5 m below the proposed point by means of the rubidium strontium method the nd signature determined from conodonts trilobites hyolithids and acrotretid brachiopods has a mean value of 6 7 comparable with that of the coeval oceanic water mass occupying southeastern north america and europe and indicating that northeastern china bordered the same ocean the mean tdm model age determined was 1 26 ga at the time of sedimentation compatible with the mean tdm model age of approximately 1 1 ga for the pacific ocean today the relatively low value of the tdm model age indicates a substantial input from young orogenic volcanic island arcs and terranes

conodont palaeothermometry of contact metamorphism in middle ordovician rocks from the precordillera of western argentina the yerba loca formation middle upper ordovician exposed in the western precordillera san juan argentina is made up of clastic carbonate turbidites and basic ultrabasic rocks it is affected by regional siluro devonian very low grade metamorphism that locally reaches greenschist facies at ancaucha creek 45 conodont samples were taken from two sections that include 30 to 50 m thick sills in order to analyse the thermal alteration patterns produced by these intrusive bodies conodont colour alteration index cai is contrasted with optical petrography and x ray diffraction analyses of clay minerals the intrusions are dated as post darriwilian da2 as determined by conodont biostratigraphy of the host rock which indicates the paroistodus horridus subzone of the lenodus variabilis zone the distribution of cai values defines a thermal aureole of about 2 5 times intrusion thickness that prevailed over the later very low grade metamorphism metasomatism at ancaucha creek is recorded by cai values of 4 to 7 particularly restricted to a few layers close to the intrusions as indicated by conodont textures and rock fabric one dimensional thermal computer simulation conforms to empirical data indicating temperatures greater than 600 c for the contact zone although it points out slightly narrower thermal aureoles the clay mineral assemblage of most of the analysed samples chlorite illite smectite and i s mixed layers is complex and probably derives from several superimposed processes thus representing non equilibrium assemblages in turn ki values 0 27 0 32 indicate anchizone metamorphism in agreement with regional cai values of 4 consequently the occurrence of smectite and i s probably resulted from retrograde diagenesis processes

the role of fluids in syntectonic mass transport and the localization of metamorphic vein type ore deposists abstract in low to medium grade metamorphic environments the mobilization of species is closely associated with the operation of solution precipitation creep processes during foliation development such deformation processes involve dissolution of material from source sites which are usually discrete dissolution surfaces having orientations controlled by the applied stress and displacement fields mass transfer occurs via solute diffusion in an essentially static fluid network or by transport of dissolved species in a migrating fluid precipitation of material removed from dissolution sites occurs in a variety of sink sites including pore surfaces grain scale microcracks and veins sink sites may be close to or distantly removed from source sites the transport of material during deformation involving solution precipitation creep is largely controlled by the mobility of metamorphic fluids in regions of high fluid mobility significant mass transfer may occur over large distances fluid flow mass transfer paths and the development of sink sites in such cases are constrained by the structurally controlled development of high fluid pressure domains and the consequent mechanical enhancement of permeability by hydraulic fracture processes and the development of grain scale dilatancy these processes may result in focussed fluid flow and precipitation of mobilized species in restricted regions a proportion of syntectonically mobilized material is precipitated to form vein type deposits in hydraulic fracture arrays which develop in high fluid pressure environments the microstructures developed in minerals deposited in these sites reflect the interaction of a range of nucleation and growth processes which usually involve multiple generations of fracture growth and mineral crystallization the formation of syntectonic gold quartz vein deposits in central victoria australia illustrates the importance of structural controls on both the large scale migration of metamorphic fluids and the development of sites suitable for the precipitation of metamorphically mobilized species

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

comparative lower middle ordovician conodont oxygen isotope palaeothermometry of the argentine precordillera and laurentian margins abstract stratigraphic palaeontologic and palaeomagnetic data support a hypothesis that argues for the argentine precordillera rifting from the southwestern margin of laurentia in low latitudes during the cambrian migrating across the iapetus ocean colliding with the gondwanan margin in the late middle ordovician and receiving glaciogenic sediments in the late ordovician an alternative model proposes that the precordillera originated as a low latitude segment of gondwana migrated southward through major transform faulting toward high latitudes in the late middle ordovician to reach its present position in the devonian new conodont oxygen isotope compositions 18ophos have been determined by ion microprobe shrimp ii using samples from both the precordillera and laurentia marathon area of texas wilcox pass in alberta and western newfoundland significantly the 18o values of conodonts from all four widely separated areas show a consistent pattern of a cyclic but overall increasing trend in 18o ca 16 to 18 hence ocean cooling through the early and middle ordovician an apparent change occurs at the basal late ordovician where 18o values obtained from conodonts in the uppermost sample from the precordillera are significantly higher 1 5 than those from laurentia albeit from a single sample this higher value implies significantly cooler conditions as would be anticipated with a southerly poleward migration of the precordillera irrespective of either hypothesis the virtual absence of conodont bearing carbonates in most of the precordilleran upper ordovician precluded analysis of younger samples when combined with existing macrofaunal and palaeomagnetic data the oxygen isotope data would tend to favour the model of a drift of the precordillera from tropical to higher latitudes during the ordovician however further studies are needed to determine unequivocally whether the precordillera originated from southern laurentia ouachita embayment these new oxygen isotope values provide the best and regionally most consistent data through the early middle ordovician

extensional tectonics and gravitational collapse in an ordovician passive margin the western argentine precordillera abstract the paper describes ubiquitous extensional structures developed in a passive margin of ordovician age in the argentine precordillera these extensional structures include normal faults and boudinaged sequences in some places the boudinage reaches very high extension values giving rise to block in matrix formations most of these extensional structures developed when sediments were not well lithified as recorded by hydroplastic fractures slump folds and pinch and swell structures the presence of slump folds coeval with the extensional deformation the variable extension directions obtained from the kinematic analysis and a weak cleavage recording layer perpendicular shortening support the interpretation that gravitational collapse related to submarine sliding was the cause for extensional deformation well consolidated rocks located at the lower part of the stratigraphic sequence also display scarce extensional faults these extensional faults predate folding because they were breached by flexural slip faults and as a result of their passive rotation in fold limbs these initial normal faults may now appear as reverse faults particularly in steep and overturned limbs the truncation of extensional faults by flexural slip faults produces typical bed thickness changes across the extensional faults giving rise to apparent synsedimentary faults these normal faults can be attributed to the crustal extension that generated the passive continental margin or may represent deep parts of faults related to gravitational collapse

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

terminal cambrian and lowest ordovician succession of mexican west gondwana biotas and sequence stratigraphy of the tinu formation the tinu formation of oaxaca state is the only fossiliferous lower palaeozoic unit between the laurentian platform in northwest mexico and gondwanan successions in andean south america the tinu traditionally has been referred to the lower ordovician tremadoc and regarded as having a provincially mixed fauna with laurentian avalonian and gondwanan elements bio and lithostratigraphic re evaluation demonstrates that the tinu is a gondwanan passive margin succession it includes a lower thin to 16 m condensed uppermost cambrian yudachica member new the yudachica nonconformably overlies middle proterozoic basement as a result of very high late late cambrian eustatic levels the yudachica changes from storm dominated but slightly dysoxic shelf facies fossil hash limestone and shale in the south to an upper slope facies with debris flows 50 km to the north three biostratigraphically distinct depositional sequences comprise the yudachica the yudachica has gondwanan aspect trilobites with low diversity conodonts characteristic of unrestricted marine temperate facies the upper tinu or rio salinas member new is a lower ordovician tremadoc depositional sequence that records strong early but not earliest tremadoc eustatic rise marked by graptolite and olenid bearing dysoxic mudstones higher strata shoal upward into shell hash limestones and proximal tempestite sandstones with upper lower tremadocian unrestricted marine temperate conodonts new taxa include orminskia rexroadae landing gen et sp nov from the cordylodus andresi zone this euconodont is related to hyaline coniform genera best known from ordovician tropical platform successions cornuodus clarkei landing sp nov resembles the coeval upper lower tremadoc tropical species scalpellodus longipinnatus ji barnes

salterella in the argentine precordillera an early cambrian palaeobiogeographic indicator of laurentian affinity abstract this paper documents salterella maccullochi murchison in the precordillera of western argentina in the present day southern hemisphere the record of these early cambrian small conical shaped fossils assigned to the extinct phylum agmata provides further palaeobiogeographic evidence to consider the argentine precordillera an exotic terrane to gondwana that originally rifted from laurentia for palaeogeographic reconstructions salterella can be considered as an organism equally important and biogeographically as meaningful as the olenellid trilobites due to their limited dispersal and demonstrated link to laurentian shallow water inner shelf facies it has not been found anywhere in gondwana salterella existed for only a very short interval of time but spread almost instantaneously around laurentia on this basis the early cambrian of the precordillera terrane remains the more conclusive palaeobiogeographical link to laurentia salterella provides another line of evidence supporting palaeontological sedimentologic stratigraphic palaeomagnetic and isotopic evidence for a laurentia origin of the precordillera terrane

cohesion influences on erosion and bed load transport 1 studies on erosion and transport rates of cohesive sediment mixtures containing gravel are not reported so far in the literature to the best of our knowledge results from laboratory experiments on the process of erosion of cohesive sediment mixtures by open channel flow are presented the sediment used for experimentation consisted of fine gravel mixed with clay in proportions varying from 10 to 50 and fine gravel fine sand in equal proportion by weight mixed with clay proportions again varying from 10 to 50 by weight experimental observations have revealed that the process of detachment of cohesive sediment mixtures containing gravel is significantly different from that of cohesionless sediments also it is different from the detachment process of cohesive sediment mixtures not containing coarser size material experimental data on transport rates of the bed load of the cohesive sediment mixtures are presented on the basis of dimensional considerations a computational procedure is proposed to determine the bed load transport rates generated from erosion of the different size fractions of sediment mixtures clay percentage and unconfined compressive strength of the sediment bed were the main parameters controlling bed load transport rate of such sediments in the absence of cohesion the proposed method reduces to the patel and ranga raju 1996 method for bed load transport rate computation of nonuniform cohesionless sediments

structural evolution of the argentine precordillera the rio san juan section abstract the argentine precordillera ap represents a high level fold and thrust belt which was formed during the andean tertiary crustal shortening in a w e transect studied mostly e directed imbrications are combined with folding and involve a pile of cambrian to tertiary sediments the thrust belt is detached above a main decollement within the ordovician to lower devonian strata to the east it is bounded by a back thrust zone directed westwards restored sections allow an estimate of crustal shortening and also provide insight into the structural development during pre tertiary times carbonate platform sequences of cambrian to ordovician age grade into a volcani clastic succession with transitional melanges representing deposits along a western continental slope in the western and easternmost parts of the ap cambrian to silurian deposits are affected by a first folding which to the west is combined with a slight metamorphic overprint during carboniferous to permian times intensified mobility along the eastern rim and in the western parts of the ap leads to crustal extension which partly was triggered by the formation of synsedimentary normal faults in the central ap no angular unconformities at the base of carboniferous permian deposits were found there was no field evidence found to postulate a terrane boundary within the ap area and an onset of thrust tectonics during cretaceous to early tertiary times

one dimensional model for transient flows involving bed load sediment transport and changes in flow regimes this study presents a novel simple but rather accurate approximation of the eigenvalues of the system formed by the saint venant exner equations based on the comparison between eigenvalues for the complete system and eigenvalues for the water phase only moreover a strategy is proposed to compute efficiently the intercell fluxes by properly adapting a harten lax and van leer scheme for each equation two examples of transient transcritical flows are developed the erosive migration of a knickpoint induced by an increase in the bed slope and the evolution of a hydraulic jump over a mobile bed

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

linking high grade gold mineralization to earthquake induced fault valve processes in the porgera gold deposit papua new guinea processes responsible for high grade gold enrichment are of significant economic interest and have long been elusive structural and geophysical models postulate that earthquake induced fault valve processes are frequently responsible for gold mineralization in structurally controlled hydrothermal systems although a comprehensive geochemical record of these processes has been lacking the porgera gold deposit papua new guinea provides an opportunity to examine the complex processes surrounding high grade au mineralization in structurally controlled hydrothermal systems new high resolution trace element and sulfur isotope data obtained in situ by laser ablation inductively coupled plasma mass spectrometry and sensitive high resolution ion microprobe stable isotope analysis of pyrite across a well constrained paragenetic sequence reveal a temporal evolution in fluid chemistry the data uncover a stratigraphy of repeated high au negative 34 s and low au positive 34 s zones within individual pyrite crystals present in the highest grade gold event stage ii results provide the first clear geochemical documentation of rapid complete switching in ore forming processes preserved in individual pyrite crystals throughout an evolving hydrothermal system it is postulated that geochemical variations are attributable to rapid au deposition during pressure release due to fault failure followed by switching to more reduced rock buffered metal poor fluids from adjacent sediments as the rupture seals the cyclicity of this process is reflected in the pyrite zonation seen at the porgera deposit this study demonstrates the usefulness of applying contemporary analytical techniques to pyrite in hydrothermal systems to gain new insights into ore genesis and fluid pathways revealing that deposition of exceptionally high grade ore at the porgera deposit was the result of multiple events in a fluctuating ore forming environment

new conodont records of the los sombreros formation cambrian ordovician from the western precordillera argentina biostratigraphic and palaeoenvironmental implications

fluid evolution in the el sid gold deposit eastern desert egypt auriferous quartz carbonate veins in the el sid mine cut through the western margin of the fawakhir granitic intrusion and the immediate country ophiolites gold mineraliz ation is spatially and temporally associated with ene wsw fault shear zones developed late in the deformational history of the area field and microscopic studies suggest two distinct ore stages namely an early gold fe as sulphide and a late gold base metal mineralization new microthermometric and raman data suggest gold deposition as a result of a complex history of fluid immiscibly dilution of low salinity aqueous carbonic fluids in the early mineralization stage while wall rock alteration and pressure loss precipitated au from intermediate salinity aqueous ore fluids during the late stage fluid inclusion isochoric reconstructions combined with oxygen and sulphur isotope data indicate conditions of 320 20 8c and 1 3 0 2 kbar for the early gold fe as sulphide mineralization and c 200 15 and 0 6 0 9 kbar for the late gold zn pb cu sulphide stage the clockwise evolution path in pressure temperature space likely documents gold mineralization under post peak metamorphic conditions the calcu lated sulphide d 34 sh2s equilibrium values 29 04 to 4 75 may refer to a variable redox state of sulphur in the ore fluids from the early to late mineralization stages the stable isotope signature of the vein quartz and calcite suggest mixed magmatic and metamorphic fluid sources d 18 o h2o 4 9 to 7 4 unusually low d 13 c values of calcite in the late mineralization 213 9 to 214 7 may reflect input of magmatic co2 and or oxidized carbonaceous mate rial in the infiltrating fluid gold bearing quartz veins associated with variably tectonized ophiolitic and island arc rocks or adja cent to their interferences are common in the southern and central sectors of the eastern desert of egypt whereas gold occurrences confined to granitic intrusions that are in some cases associ ated with felsic subvolcanic porphyries is a com mon feature in the northern eastern desert e g moharram et al 1970 sabet bordonosov 1984 klemm et al 2001 botros 2004 based on sev eral geological and mineralogical studies a gold granitoid association in the eastern desert has been suggested by many authors e g garson

one dimensional numerical model for nonuniform sediment transport under unsteady flows in channel networks in this study the proposed one dimensional model simulates the nonequilibrium transport of nonuniform total load under unsteady flow conditions in dendritic channel networks with hydraulic structures the equations of sediment transport bed changes and bed material sorting are solved in a coupling procedure with a direct solution technique while still decoupled from the flow model this coupled model for sediment calculation is more stable and less likely to produce negative values for bed material gradation than the traditional fully decoupled model the sediment transport capacity is calculated by one of four formulas which have taken into consideration the hiding and exposure mechanism of nonuniform sediment transport the fluvial erosion at bank toes and the mass failure of banks are simulated to complement the modeling of bed morphological changes in channels the tests in several cases show that the present model is capable of predicting sediment transport bed changes and bed material sorting in various situations with reasonable accuracy and reliability

constraining the age of the iporanga formation with shrimp u pb zircon implications for possible ediacaran glaciation in the ribeira belt se brazil abstract the ribeira belt in se brazil is a neoproterozoic to early palaeozoic orogen whose architecture and history is not yet fully understood the depositional age of many of the sedimentary sequences in the ribeira belt remains unconstrained and with debate concerning their depositional environment and tectonic setting in this paper we present shrimp zircon u pb age constraints for one such problematic unit in the ribeira belt the iporanga formation and discuss the significance of this age with regards to the timing of neoproterozoic glacial events in southeast brazil using a felsic volcanic unit immediately under the iporanga formation and granite cobbles from breccias in its basal parts a reconnaissance shrimp u pb zircon maximum depositional age of 580 ma is assigned for the base of this unit this age is marginally younger than the 625 605 ma ages for intrusions into the lajeado and ribeira subgroups with which the iporanga formation is in tectonic contact this indicates that the lajeado and ribeira subgroups are not stratigraphically equivalent to the iporanga formation as thought previously by some workers the maximum depositional age of 580 ma also places a maximum time constraint on the tectonic juxtaposition of the iporanga formation with other supracrustal units and on the greenschist facies metamorphism and isoclinal folding that affected it the potential glacial origin for the iporanga formation if correct would place it in the late ediacaran provisionally equivalent to the gaskiers glaciation

comparison of coupled and semicoupled numerical models for alluvial channels contrary to general statements in the literature the investigations reported in this paper show that semicoupled models are not necessarily unstable and give results comparable to those of coupled models for this purpose a two dimensional model is developed to calculate bed variations in alluvial channels vertically averaged navier stokes equations in transformed coordinates are numerically solved in conjunction with the sediment transport equation for the bed load these equations are solved simultaneously in a fully coupled model and separately in a semicoupled model using the beam and warming alternating direction implicit scheme both models are applied to predict bed level changes due to sediment overloading and sediment shut off the computed results compare satisfactorily with the experimental results obtained in a laboratory flume the results obtained by the semicoupled model are relatively close to that of the fully coupled model because the former algorithm permits any sediment formula and armoring effect to be easily incorporated the semicoupled model appears to be more attractive for general applications to real life systems than the coupled model

ordovician metamorphic event in the carbonate platform of the argentine precordillera implications for the geotectonic evolution of the proto andean margin of gondwana an ordovician metamorphic event is recorded by means of conodont paleothermometry in the slope sedimentary sequences of the western precordillera allochthonous conodonts from reworked deposits of the eastern carbonate platform with cai 4 5 5 and autochthonous conodonts from the olistostrome matrix with cai 3 allow for constraining the metamorphic age within the paltodus deltifer and lenodus variabilis zones i e ca 480 465 ma the conodont data support an ordovician instead of an alternative devonian collision for the cuyania terrane with the proto andean margin of gondwana which is consistent with the earlier proposed but still contentious microcontinent model in the latter scenario the collision of the cuyania terrane caused unroofing and cannibalism of the leading edge of the carbonate succession and basement rocks the erosion of these rocks supplied detritus and metamorphosed conodonts to the deeper basinal settings of the western precordillera as the deformation front migrated into the peripheral foreland of the eastern and central precordillera nonmetamorphosed conodonts were eventually incorporated into the west prograding synorogenic clastic wedge the occurrence of allochthonous and autochthonous conodonts in the slope facies of the western precordillera provides a time constraint for the early accretion of the cuyania terrane and its transition to an evolving foreland mountain system in the ordovician period

variscan sb au mineralization in central brittany france a new metallogenic model derived from the le semnon district numerous sb au deposits are known in the european variscan belt and are often associated with the latevariscan hydrothermal events linked to postorogenic extension and strike slip faults through the whole belt thecentral part of the armorican massif central brittany hosts several sb au deposits such as the le semnondeposit however little is known about its formation its structural control or hydrothermal history in order toprovide new constraints on the sb au mineralization framework of the variscan armorican massif structural geochronological and chemical analyses have been performed on the le semnon sb au deposit first wehighlight that sb au mineralization consists of fault fill and flat extensional vein systems resulting from smallscalefault valve mechanism controlled by fluid overpressure at shallow depth indeed this deposit is characterizedby the presence of dolerite dykes which acted as the plumbing system for fluids within impermeableslates the low permeability of the slates permitted the establishment of local supralithostatic fluid pressure in apredominantly hydrostatic regime coupled with new micro textural evidences a reappraisal of the parageneticevolution and new physico chemical data 40ar 39ar and u pb analyses show that the le semnon sb aumineralization was emplaced around 360 ma and therefore indicates an early hydrothermal event in thevariscan history of the armorican massif moreover absolute dating of mafic magmatism coupled with hydrothermalalteration associated with the deposition of sb au mineralization strongly suggest that the emplacementof the sb au mineralization was coeval with the emplacement of the host rock doleritic dyke furthermore the high temperature recorded in fluid inclusions and the paragenetic evolution suggests an elevatedthermal anomaly in central brittany thus we propose that the emplacement of the widespread maficmagmatism at ca 360 ma played a major role in the mobilization of fluid flows and the redistribution of metalsin the armorican crust

the proposed cambrian ordovician global boundary stratotype and point gssp in western newfoundland canada sections exposing the cambrian ordovician boundary interval at broom point in western newfoundland have been proposed earlier for a global systemic boundary stratotype these lie within the cow head group a late middle cambrian to early middle ordovician allochthonous unit of limestone shale and conglomerate deposited at the toe of the ancient continental slope and on the adjacent continental rise several recent studies have further investigated the stratigraphy sedimentology and palaeontology of the cow head group and others are under way on magnetostratigraphy and chemostratigraphy these aspects are reviewed for six key boundary sections representing proximal to distal facies cow head ledge broom point south broom point north st pauls inlet quarry martin point and green point in particular new data are presented from 260 conodont samples that yielded 15500 conodonts this intense sampling has allowed the discrimination of minor hiatuses in the proximal to intermediate facies where conglomerates have eroded and cannibalized underlying strata new conodont data from broom point north have lowered the base of the c lindstromi zone into unit 74 conglomerates thereby making this section unsuitable as a boundary stratotype new collections from green point have yielded abundant conodonts and over 9400 conodonts have been recovered from 77 samples the conodont graptolite and trilobite biostratigraphy through the boundary interval is documented allowing accurate correlation between sections and more precisely revealing small hiatuses in the proximal and intermediate facies the sequence of conodont zones is eoconodontus notchpeakensis cordylodus proavus c caboti c intermedius c lindstromi and c angulatus these can be correlated with trilobite zones established from both in situ and clast faunas from the proximal to intermediate facies and with graptolite assemblages of cooper 1979 especially in the intermediate to distal facies three new species of cordylodus are described c andresi c hastatus and c tortus and the full apparatus of iapetognathus preaengensis is illustrated the criteria for selecting a global boundary stratotype and point gssp are reviewed in terms of the cow head sections the green point section is shown to meet and largely surpass the prerequisites required of a stratotype the green point section is proposed to be the global boundary stratotype with the base of the ordovician system defined at the base of unit 23 which is the base of the broom point member green point formation at a level coincident with the base of the cordylodus lindstromi zone in addition to an abundant and superbly preserved conodont fauna this section preserves the best sequence of earliest planktic graptolites through a 40 m interval the first nematophorous graptolites of assemblage 1 occur in unit 25 6 9 m above the base of the c lindstromi zone this level can be readily correlated into the proximal facies where both deep and shallow water trilobites in situ and in clasts respectively show the base of the c lindstromi zone to lie within the symphysurina brevispicata trilobite subzone

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

auriferous mineralization in some shear zones a three stage model of metallogenesis studies of numerous shear zones hosting auriferous quartz veins suggest a three stage model of formation for such veins these stages are indicative of the progressive increase of the gold concentration with the evolution of the shear zone and comprise an early stage with invisible gold an intermediate stage with finegrained gold and a late stage with gold nuggets the early stage consisting of two consecutive episodes comprises the development of the shear zone sensu stricto which results in the formation of a structure characterized by mylonite this structure subsequently acts as a drain for hydrothermal fluids under the combined action of deformation and hydrothermal circulation the rocks in this structure undergo mineralogical transformations that depend on the initial composition of the rock these phenomena occur with increasing intensity towards the cores of the structures the sites of substantial silicification and sulfidation gold is first fixed in the crystal lattice of pyrrhotite up to 30 ppm of gold disseminated throughout the structure as a whole in the core it is destabilized to pyrite marcasite during the second episode of this early stage and the gold thus freed is trapped in the lattice of locally abundant ferriferous sulfides pyrite arsenopyrite up to 1 6 wt gold and berthierite at the intermediate stage again consisting of two consecutive episodes the shear zone can generate openings allowing the emplacement of lenses and veins of milky white quartz when these various veins are in turn crushed by continuing tectonic activity microsaccharoidal quartz forms by cataclasis and acts as a receptacle for the gold mineralization therefore textbook auriferous quartz veins are only one particular aspect of this stage characterized by the appearance of visible native gold caused by destabilization of the auriferous sulfides of the early stage this gold is generally very fine grained several micrometres and relatively silverfree the late stage i e the fifth episode in a brittle domain can occur within a structure of the early or intermediate stage it corresponds to a stage of opening during which stockworks of quartz or of quartz and carbonate form causing in situ remobilization of the auriferous mineralization from the earlier stages this phenomenon is accompanied by the appearance of gold nuggets several millimetres in size very often rich in silver electrum

fluid pressure transients on seismogenic normal faults abstract fluid inclusions in hydrothermally altered footwall rocks of the dixie valley fault nevada and the wasatch fault utah indicate that pore fluid pressure fluctuated minimum entrapment pressures for fluid inclusions consisting of h2o co2 nacl ranged from 295 mpa to 60 mpa in the temperature range 350 to 170 c on the wasatch fault and from 158 to 35 mpa in the temperature range 350 to 200 c on the dixie valley fault scatter in the pressure estimates at constant temperature is interpreted as paleo fluid pressure transients at depths of up to 11 km on the wasatch fault and 3 to 5 km on the dixie valley fault observed pressure transients range from 5 mpa within the limits of error in pressure determination to 120 mpa on the wasatch fault and 7 to 126 mpa on the dixie valley fault the pressure transients are greatest on both faults in the temperature range 270 to 310 c the fluids represented by fluid inclusions play a key role in nucleation and propagation of earthquake ruptures high fluid pressures may initiate rupture then dilatancy pore pressure reduction and dilatant hardening may arrest the rupture however decompression of the fluids and phase separation produces a decrease in fluid bulk modulus of 41 to 90 which reduces the dilatant hardening effect and may permit ruptures to propagate

late cambrian biogeography conodont bioprovinces from korea abstract although the collisional belt between the north and south china blocks has been well defined in china the location of its eastward extension in the korean peninsula is highly controversial the cambro ordovician sedimentary rocks in south korea the joseon supergroup accumulated in the ogcheon belt which has been proposed as the suture zone between the north and south china blocks or the block boundary the joseon supergroup comprises five different lithostratigraphic units and may be divided into two tectonic blocks by the honam shear zone hsz in the ogcheon belt based on the affinities of the cambrian trilobite faunas previous studies correlated the yeongweol unit in the western part of the hsz with south china and the duwibong unit in the eastern part of the hsz with north china to test the above geodynamic interpretation this study analyzed and compared the degree of the provinciality of upper cambrian conodonts from the yeongweol and duwibong units and north and south china the quantitative test for the upper cambrian provincialism shows high bioprovincial affinities between the yeongweol and duwibong units and both conodont faunas from the two units display higher bioprovincial affinities with that of north china rather than with that of south china their high conodont faunal similarity suggests that the korean peninsula might have been included in a larger continental block including the north china and the korean peninsula the sino korean block in early paleozoic time this result is supported by recent studies on lower paleozoic biogeography stratigraphy and sedimentology that suggest that the yeongweol unit of the joseon supergroup is more closely correlated with north china than with south china

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

cambrian ordovician conodonts from slump deposits of the argentine precordillera new insights into its passive margin development fil voldman gustavo gabriel consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet cordoba centro de investigaciones en ciencias de la tierra universidad nacional de cordoba facultad de ciencias exactas fisicas y naturales centro de investigaciones en ciencias de la tierra argentina

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

fluid pressure and salinity variations in shear zone related veins central pyrenees france implications for the fault valve model abstract fluid inclusion microthermometry data is presented from quartz veins associated with high angle reverse shear zones cutting the neouvielle massif in the central french pyrenees a complex series of veins were formed during both normal and reverse movement on brittle faults within the shear zone brittle structures developed contemporaneously with quasi plastic deformation in the shear zones fluid inclusion data are presented from a variety of vein types and shows that a wide variation in fluid density and salinity is present in the fault system these variations occur both within individual veins and between different vein types temperatures at the time of vein filling are constrained to be in the range 310 360 c by chlorite microthermometry the variation in homogenisation temperature is too large to be accounted for by variations in the fluid temperature and is interpreted to reflect variations in fluid pressure between lithostatic 500 mpa and hydrostatic 200 mpa values at the time of quartz growth in the veins the shear zones carry modest displacements and may not themselves have been seismogenic a model is presented in which fluid pressure variations and stress cycling within the steeply dipping shear zones is controlled by the seismogenic cycle on large underlying thrust structures the model predicts that the highest maximum trapping pressures should occur in fluid inclusions from low angle veins formed in a high pfluid compressional regime immediately before earthquake rupture lower maximum pressures are expected in steep veins related to extension and normal fault movement across the shear zones immediately after rupture the fluid inclusion data support this model when maximum trapping pressures are considered but the majority of inclusions in all vein types formed at pressures well below lithostatic values this suggests that the dominant factor causing quartz precipitation was the sudden pressure drop immediately after earthquake rupture regardless of vein type

experimental and numerical investigations on degradation of channel bed of cohesive sediment mixtures 1 experimental observations on a degradation profile of channel beds consisting of cohesive sediment mixtures are presented the sediment used for the experimentation consisted of fine gravel mixed with clay in varying proportions 10 50 by weight and fine gravel and fine sand in equal proportions mixed with varying proportions of clay 10 50 by weight the clay percentage in bed material and unconfined compressive strength of channel bed were found to be the main factors controlling the depth of degradation of channel bed of cohesive sediment mixtures as degradation depth reduces considerably with an increase in clay percentage and unconfined compressive strength of sediment bed an algorithm is also proposed to compute transient bed and water surface profiles in a channel bed made up of such cohesive sediment mixtures for this purpose the predictor corrector based essentially nonoscillatory finite difference numerical scheme is utilized for the solution of governing equations through the use of appropriate initial and boundary conditions the recently proposed relationships by the authors for bed and suspended load transport of cohesive sediment mixtures were used as the auxiliary equations in the proposed algorithm the observations on degradation of channel beds consisting of such cohesive sediment mixtures have not been reported so far in the literature to the best of our knowledge

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

coupled modeling of alluvial flows full recognition of the physical coupling of water and sediment phases of alluvial flows leads to the need for a concurrent solution of the water routing and sediment routing components in mobile bed river modeling in this paper the coupled and uncoupled methods of alluvial stream modeling are compared a newly developed coupled model of one dimensional riverine water and sediment flow called coupflex is briefly introduced several schemes in discretization of the sediment continuity equation often used in uncoupled approaches are mentioned two elaborate flume tests on river degradation are briefly described experimental data is used to compare the performance of coupflex with that of the uncoupled approaches this comparison highlights the advantages of the coupled method over the traditional uncoupled method performing several numerical tests some aspects of numerical modeling of alluvial flows are briefly dealt with these include problems resulting from the use of equilibrium relations in nonequilibrium situations the dominant role of empirical sediment transport and hydraulic resistance formulas in the accuracy of the answers from any alluvial flow model significance of the computational time step violation of the sediment mass conservation law and the use of approximate water routing models

fluid inclusion evidence for p v t x evolution of hydrothermal solutions in late alpine gold quartz veins at brusson val d ayas northwest italian alps

reply to comment by cao and hu on long waves in erodible channels and morphodynamic influence 1 we thank cao and hu 2008 very much for their comment we must honestly say that at first sight we felt that their point reproducing that raised by cao and carling 2003 to challenge the formulation of the 1 d governing equations proposed by lisle et al 2001 had already been proven to be erroneous by cui et al 2005 however after more careful examination of the matter we have concluded that both the final forms of the continuity equation derived by cao and hu 2008 hereinafter referred to as ch and lanzoni et al 2006 hereinafter denoted as lsfs are not wholly correct indeed while the main point raised by ch is definitely correct they reach slightly incorrect conclusions employing a framework which ignores the distinction between bed load and suspended load on the other hand the lsfs derivation is also incorrect in that it will be seen to ignore the defect of water flux due to the presence of particles transported as bed load an effect which turns out to be of the same order of magnitude as that of the retained contributions this effect modifies the final form of the continuity equation for the fluid phase which does indeed include a sediment transport correction whose structure will be seen to be intermediate between the one derived by lsfs and that suggested by ch while as shown in section 4 this modification does not affect the treatment of one dimensional long sediment waves presented by lsfs the issue is of conceptual importance we are therefore grateful to ch for motivating us to provide a hopefully more conclusive clarification of the matter we are confident that the analysis presented below will be instructive for the reader as it was for us