arid zone groundwater recharge and salinisation processes an example from the lake eyre basin australia in arid central australia the 1 14 m km2 endorheic lake eyre basin leb experiences sporadic floods and contains saline shallow groundwater in this basin where on ground physical and chemical data are very sparse new observations of major ion chemistry stable isotopes 2h 18o 13c radiogenic isotopes 3h 14c and remote sensing modis data were used to investigate groundwater recharge and salinisation processes in 2006 2007 in january 2007 there was a large and intense local rainfall event followed by flooding to the normally dry lake eyre resulting from heavy rainfall in the northern leb that took 2 months to arrive at lake eyre groundwater chemistry from this study show no evidence of recharge from the floodwaters or the local rainfall however this does not preclude the process low transit times and low infiltrating volumes may mean that the recharge event has not yet been detected over the longer term the stable isotope chemistry indicates that groundwater is predominantly diffusely recharged during heavy local rainfall events 100 150 mm month and radiogenic isotopes reflect an older shallow groundwater efficiently mixing with recent decadal recharge the high total dissolved solids tds of regional shallow groundwater up to 52 5 g l is intrinsically linked with these recharge processes where infiltrating diffuse rainfall is evaporated and heavy rainfall events transport saline pore water saline due to evaporation in the unsaturated zone to the groundwater system the high tds of shallow groundwater beneath the dry lake eyre bed up to 322 g l is also controlled by evaporation however although evaporite minerals are prolific in the lake area the non conservative behaviour of br in pore water limits analysis of the role of halite mineral dissolution and precipitation reactions controlling groundwater salinity evaporation driven salinisation of shallow groundwater in arid central australia is distinct from the transpiration driven salinisation of groundwater in the australian murray basin located in a semi arid climate and results in relatively high groundwater salinity values compared with many other large arid zone endorheic basins across the world

flow transmission along an arid zone anastomosing river cooper creek australia cooper creek is characterized by an exceptionally wide floodplain and a complex system of anastomosing channels which together can accommodate a large range of highly variable flows in consequence flood frequency curves are unusually steep with minimal tributary contribution over the two study lengths currareva nappa merrie 400 km and nappa merrie innamincka 32 km downstream output is largely controlled by upstream input so that similar flow regimes and hydrograph forms can be maintained despite transmission losses and the variable activation of channels input output relationships defined in terms of total flow volume and peak discharge suggest that above a threshold flow of about 25 duration transmission losses exceed 75 on average over the currareva nappa merrie length the large difference in absorption between primary channels on the one hand and subsidiary channels and the floodplain surface on the other means that transmission losses vary non linearly with stage they are relatively low when flow is confined to the primary channels but increase at higher stages as lesser channels and the floodplain are activated early levels do not recur until flows of 0 5 duration are attained when output input ratios increase rapidly with discharge the influences of seasonality and background flow on output discharge are small relative to that of input discharge despite the long river distance peak flows at currareva and nappa merrie are well correlated however over the shorter nappa merrie innamincka length with its more confined system of channels correlations are better and transmission losses less they vary from 60 just above the threshold discharge to lo at flows below 20 duration over this length outflow hydrographs can be effectively estimated by the three parameter muskingum procedure at least on an event by event basis but further application must await additional records to understand fully how the parameters vary in an environment where streamflow is transmitted through a highly variable system of channels

evolution of salt structures during burial of salt sheets on the slope northern gulf of mexico abstract shallow buried allochthonous salt sheets are the dominant type of salt structure along the lower slope of the northern gulf of mexico trailing landward margins of the sheets are buried during continental margin progradation while their leading edges advance basinward under thin cover during burial a series of daughter structures including stocks massifs and remnant structures evolved as the sheet was segmented by extension and differential loading during extension fault bound basins on the upper surface of the sheet initiated the growth of salt rollers some rollers matured into stocks and massifs as sediment accumulated rapidly in circular salt withdrawal basins that were localized over the initial fault bound basins lateral extension is a key mechanism in initiating salt structural evolution however simple vertical subsidence of sediments is the primary displacement mechanism where the salt is completely displaced a salt weld discontinuity identifies its former stratigraphic position a variety of structures in the eastern green canyon area have been identified overlying a neogene salt weld including remnant salt structures mature stocks massifs and sedimentary structures such as turtle structure anticlines

a deep seismic reflection profile across the nova scotia continental margin offshore eastern canada results from two deep seismic reflection lines are presented when combined these lines span the rifted continental margin off nova scotia from crust unaltered by rifting to the ocean basin these data provide crustal and upper mantle reflection geometry to depths of over 50 km and elucidate the rifting process on this margin which occurred during the mesozoic breakup of pangaea the continental crust below the continental shelf and slope becomes progressively thinner toward the ocean continent boundary in the upper crust normal faults accommodated mesozoic extension and these flatten and terminate at 5 6 s two way time in the lower crust and upper mantle mesozoic rifting may be reflected in dipping events which are interpreted to be normal faults all mesozoic extensional faulting could be controlled by the preexisting fabric of the crust which in this region would be related to appalachian compression within the meguma terrane below the continental rise there is some evidence for magmatic un

inbank and overbank velocity conditions in an arid zone anastomosing river relative to those at sub bankfull flow hydraulic conditions at overbank flow whether in the channel or on the floodplain are poorly understood here velocity conditions are analysed over an unusually wide range of flows in the arid zone river of cooper creek with its complex system of anastomosing channels and large fluctuations in floodplain width at a station hydraulic geometry relationships reveal sharp discontinuities in velocity at the inbank overbank transition the nature of the discontinuity varying with the degree of flow confinement and the level of channel floodplain interaction however despite inter sectional differences velocities remain modest throughout the flow range in this low gradient river and the large increases in at a station discharge are principally accommodated by changes in cross sectional area velocity distribution plots suggest that within channel conditions during overbank flow are characterized by a central band of high velocity which penetrates far toward the bed helping to maintain already deep cross sections floodplain resistance along cooper creek is concentrated at channel bank tops where vegetation density is highest and the subsequent flow retardation is transmitted across the surface of the channels over distances as large as 50 70 m the rough floodplain surface affects flood wave transmission producing significant decreases in wave speeds downstream the character of the wave speed discharge relationship also changes longitudinally from log linear in the upper reaches to nonlinear where the floodplain broadens appreciably the nonlinear form is similar in several respects to relationships proposed for more humid rivers with flood wave speed reaching an intermediate maximum at about four fifths bankfull discharge before decreasing to a minimum at approximately q2 33 it does not regain the value at the intermediate maximum until the 10 year flood by which time floodplain depths have become relatively large and broad floodways more active copyright 2002 john wiley sons ltd

acid sulfate soil evolution models and pedogenic pathways during drought and reflooding cycles in irrigated areas and adjacent natural wetlands abstract the severe millennium drought 2007 2010 left an area of over 5000 ha in the lower murray river south australia dried cracked and acidified as river and groundwater levels fell nearly 2 m in this study we examined irrigated agricultural areas and an adjacent natural wetland for comparison which were both affected by the drought approximately 3 m deep soil cores were collected along transects in three sections of the lower murray reclaimed irrigation area lmria on multiple occasions between 2011 and 2015 and an adjacent natural wetland in 2007 soil properties measured included ph reduced inorganic sulfur ris pyrite titratable actual acidity taa retained acidity acid neutralising capacity anc x ray diffraction analyses and scanning electron microscopy a series of explanatory soil regolith hydro toposequence models were developed during the pre drought period drying period and subsequent wetting reflooding post drought period these models indicate that prior to draining of the natural wetlands for irrigated agriculture the region cycled between wetting and flushing and partial drying conditions in response to seasonal and climatic cycles causing the build up of hypersulfidic material to be kept in check by oxidation of pyrite during dry periods droughts and removal during scouring floods as the region became managed for navigation and irrigation by installing barrages and locks pyrite began to build up the extreme lowering of the water table during the millennium drought resulted in deep oxidation of sulfides in anaerobic hypersulfidic material to depths 3 5 m in the previously saturated irrigated pastures and within 50 cm of the soil surface in the natural wetlands oxidation and acidification between 0 5 and 3 5 m of hypersulfidic clayey soils was enhanced by the formation of large cracks up to 3 5 m deep rewetting and flooding after the drought caused mobilization of sulfuric acid soluble sulfates ferrous iron nutrients and metals with transport into the river murray our findings highlight that irrigated areas formed deeper sulfuric materials 3 5 m than in adjacent natural wetlands 3 5 m acid sulfate soils with sulfuric material containing extensive retained acidity jarosite which can persist for decades or longer

influence of rice cultivation on the abundance and fractionation of fe mn zn cu and al in acid sulfate paddy soils in the pearl river delta abstract many of the areas dominated by acid sulfate as soils in southern china have been reclaimed for rice cultivation and represent an important source of agricultural production and food security for the local population in this study we examined the abundance and partitioning of fe mn zn cu and al in both rice paddy fields and uncultivated fields by using a six step sequential extraction procedure rice cultivation significantly reduced acidity levels at soil depths of 0 100 cm but acidity at depths of 100 140 cm increased significantly a substantial loss of mn in the oxide and acidified soil layer 0 100 cm compared to the underlying parent material was observed but there were few changes in the concentrations of fe and zn throughout the soil profile however both cu and al were substantially enriched in the superficial soil 0 40 cm compared to the underlying subsoil 40 140 cm in general leaching of fe mn and al was higher in the paddy fields because of intensified irrigation and flood conditions whereas accumulation of cu mainly in the form of acid soluble and crystalline iron oxide cu was higher in the paddy fields than in the uncultivated fields the most marked declines in metal concentrations occurred in the labile and acid soluble fractions as a result of rice cultivation which increased leaching of the readily mobilized labile and acid soluble fractions of heavy metals in these soils

sulfur iron and carbon cycling following hydrological restoration of acidic freshwater wetlands abstract freshwater re flooding is a relatively novel approach to remediate drained acid sulfate soil ass wetlands this study documents the geochemical consequences of restoring freshwater re flooding for contemporary reduced inorganic sulfur ris and iron species in two coastal floodplain ass wetlands re flooding has established predominantly reducing suboxic conditions and encouraged organic carbon accumulation in surface sediments 20 30 the ph of former sulfuric horizons has increased by 2 3 units partly in response to alkalinity generation from anaerobic metabolism of organic carbon coupled with fe iii and so 4 2 reduction despite considerable sulfidisation reactive fe fe r sum of 1 m hcl and citrate dithionite extracts and non sulfidic fe ii remain abundant in both wetlands high concentrations of fe 2 up to 5 mm in wetland porewaters represent a considerable pool of labile net acidity and is partly a result of insufficient s ii to sequester excess fe 2 accumulation of iron sulfides appears to be constrained more by so 4 2 and carbon availability rather than fe r reformation and accumulation of ris species is greatest in organic rich surface horizons 40 500 mol g 1 where time integrated ris accumulation rates approximate 10 100 nmol g 1 d 1 while pyrite is the dominant ris species to have formed since re flooding there is anomalous accumulation of s 0 up to 80 mol g 1 accounting for 50 of the ris pool in some samples greigite fe 3 s 4 has formed in near surface sediments and while avs s is a minor component of the ris pool overall at some locations maximum concentrations exceed 300 mol g 1 contemporary near surface pyrite is characterised by abundant small 200 300 nm crystals in contrast to relic sedimentary pyrite of estuarine origin that is dominated by larger crystals with diverse habit although fe and so 4 2 reduction are partly responsible for wetland scale recovery from acute acidification the resultant accumulation of diverse ris species in surficial sediments indicates an oxidative component to the s cycle and represents a hysteresis in s cycling that contrasts markedly with the drained conditions existing before remediation analysis of seasonal climate fluctuations suggests that near surface sediments containing contemporary ris are vulnerable to oxidation and possible temporary re acidification during future drought episodes this study underscores the long term legacy of ass wetland drainage and highlights the need for both considered hydrological management of re flooded wetlands and further study to quantify possible re acidification risks associated with seasonal drought

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

the impact of analogue material properties on the geometry kinematics and dynamics of convergent sand wedges abstract simulation of geodynamic processes in sandbox experiments requires analogue materials with a deformation behaviour that reproduces the deformation mechanisms of typical crustal rocks we present data on the frictional strength of different sand types employing static and dynamic shear tests the sand types analysed are characterised by an elastic frictional plastic mechanical behaviour with a transient strain hardening and strain softening phase prior to transition to stable sliding this is in conflict with the standard assumption of an ideal cohesionless coulomb material with constant frictional properties the influence of the identified transient material properties on the kinematics growth mechanisms and internal deformation patterns of convergent sand wedges results in characteristic wedge segments which vary depending on material compaction between wedges with well defined segments i e frontal deformation zone frontal imbrication zone and internal accumulation zone with straight slopes and wedges with a continuous convex topographic profile for most materials only the frontal part of the wedge is critical during experimental runs taper and strength of the wedge segments can be shown to be controlled by the frictional properties of active faults wedge segmentation is controlled by a bulk strength increase toward the rear of the wedge due to fault rotation in mechanically less favourable orientations and plastic material hardening the limit between the frontal critical parts of a wedge and internal stable parts is largely controlled by a critical state of stress upon which either renewed failure or fault inactivation occurs on this basis we suggest that critical taper analysis of wedges must be restricted to specific kinematic segments comparison of the experimental results with the nankai accretionary wedge suggests that our interpretation also applies to natural convergent wedges moreover we provide constraints for the selection of adequate granular analogue materials to simulate typical crustal rocks in natural convergent wedges

raft tectonics the effects of basal slope angle and sedimentation rate on progressive extension abstract in the gulf of guinea the upper cretaceous tertiary sedimentary cover has undergone gravity gliding above an aptian salt layer for various basal slope angles from 0 to 4 gliding started during albian time and evolved up to the present with variable sedimentation rates faulting patterns are seen to vary in particular as a function of the basal slope angle and the syn kinematic sedimentation rates a series of laboratory experiments on small scale models is used to study the effects of the two parameters mentioned above models are composed of two layer slabs with newtonian silicone putty at the base to represent a basal salt decollement and dry sand on top to represent the sedimentary overburden models are allowed to deform under their own weight for various basal slope angles ranging from 0 to 5 with two different syn kinematic sedimentation rates it is shown that the basal slope angle controls the location of faulting in the overburden within a single downslope deformation domain for values smaller than 2 and within two domains lying downslope and upslope for higher values of the width of the deformation domains also varies as a function of overburden faulting always starts with syn kinematic grabens which evolve into symmetric or asymmetric grabens or into tilted blocks bounded by listric normal faults while synthetic listric normal faults characterize the downslope deformation domains both synthetic and antithetic listric normal faults can occur in the upslope deformation domain ductile deformation within the basal decollement layers results from variable combinations of pure shear and simple shear interaction of ductile deformation in the ductile decollement layer with faulting in the overburden locally produces complex and heterogeneous strain patterns notably within salt rollers finally increasing rates of syn kinematic sedimentation are seen to increase the rate of downslope displacement and to enhance and favour the development of listric normal faults

construction of a hydrologic model for estimating wadi runoff and groundwater recharge in the eastern desert egypt we constructed a hydrologic model to estimate the groundwater recharge rate for alluvial aquifers of the eastern desert from sporadic precipitation over the red sea hills to estimate initial losses over sub basins transmission losses through channel routing and downstream runoff we developed an integrated model combining spatial rainfall distribution an appropriate basin unit hydrograph and appropriate infiltration parameters watersheds and stream networks identified from digital terrain elevation data were verified by comparison with co registered landsat thematic mapper scenes and geologic maps records of a november 1994 storm event acquired from rain gauges along the nile river and the red sea shore were used to generate a spatial precipitation distribution for the study area a 2 hour design hyetograph was adopted from rain gauge data for the 1994 flood event the model was tested against records from the november 1994 flood event at the outlets of the tarfa and hammamat watersheds groundwater recharge rates were estimated for the alluvial aquifers within the major watersheds of the north eastern desert we estimated that during the 1994 flood event the ground water recharge through transmission losses ranged from 21 to 31 tarfa 15 8 x 10 sup 6 m sup 3 asyuti 20 x 10 sup 6 more m sup 3 qena 49 x 10 sup 6 m sup 3 hammamat 59 x10 sup 6 m sup 3 of the precipitated volume the initial losses ranged from 65 to 77 only 3 7 of the precipitation reached the watershed outlets archival data show that rainfall events of the size of the november 1994 storm or larger occur every 40 months thus the annual recharge rates for the tarfa asyuti qena and hammamat alluvial aquifers are estimated at 4 7 x 10 sup 6 m sup 3 6 x 10 sup 6 m sup 3 14 7 x 10 sup 6 m sup 3 and 17 7 x10 sup 6 m sup 3 respectively implications for the use of these renewable ground waters and similar water resources in other arid areas of egypt and in neighboring countries are clear less

a new conceptual model for the structural evolution of a regional salt detachment on the northeast scotian margin offshore eastern canada in this study we examine using seismic data in conjunction with numerical modeling a regional scale salt detachment and associated synkinematic sediments from the scotian margin offshore eastern canada this part of the scotian margin is characterized by an up to 4 5 km 2 8 mi thick and approximately 175 km 108 mi long synkinematic wedge of jurassic sediments with internal sigmoidal landward dipping reflectors the synkinematic wedge is laterally extensive encompassing an area of approximately 30 000 km2 11 600 mi2 and soles into an interpreted salt detachment the jurassic synkinematic wedge which is interpreted to have formed as an open ended allochthonous salt nappe was loaded by prograding sediments during the jurassic this loading squeezed the salt seaward and caused the overlying sediments to undergo extension and gravity spreading and gliding detaching on the salt sheet the open ended nappe model provides a mechanism for producing a large amount of extension with very little compensating contraction numerical model results indicate that high rates of extension detaching on even a thin salt layer can result in similar sigmoidal landward dipping strata based on the numerical modeling and seismic interpretation results we propose a new conceptual model for the jurassic paleogene structural evolution of the study area this model may also have implications for other passive margin salt basins with regional salt detachments

a systematic technique for the sequential restoration of salt structures abstract a method is described for the sequential restoration of cross sections in areas of salt tectonics where deformation is confined to the salt and higher layers the subsurface geometry evolves with time through the interaction of various processes sedimentation compaction isostatic adjustment thermal subsidence if present faulting and salt withdrawal diapirism the technique systematically calculates and removes the effects of each of these processes during specified time intervals defined by the interpreted horizons it makes no assumptions about salt kinematics and generally results in the area of the salt layer changing through time the method is described for restoration of extensional terranes but it is also suitable for areas of contractional salt tectonics with only minor modifications after converting an interpreted seismic profile to depth the top layer is stripped off and the underlying section is decompacted according to standard porosity depth functions a deep baseline unaffected by compaction or deformation is used to restore any isostatic compensation or thermal subsidence isostasy is calculated according to the airy model and differential sedimentary loading across a section is shown to be approximately balanced by changes in salt thickness so that the load is evenly distributed after these processes have been reversed the resulting geometry and the seismic data are used to create the sea floor template for structural restoration fault offsets are removed and the layers down to the top salt are restored to this template while the base salt remains fixed the resulting space between the restored top salt and the fixed base salt defines the restored salt geometry in addition the difference between the sea floor template and a fixed sea level provides a measure of the change in water depth ignoring eustatic changes in sea level the technique is applied to an interpreted seismic profile from the eastern green canyon ewing bank area of offshore louisiana the section is characterized by a variety of salt structures including salt rollers a diapiric massif a remnant salt sheet and a salt weld which are shown to have derived from an originally continuous salt sheet which has been modified by sedimentary loading early loading created vertical basin growth that was accommodated primarily by salt withdrawal and associated diapiric rise through the process of downbuilding once the salt weld formed continued sedimentation was accommodated by a lateral increase in basin size caused by down dip extension on listric growth faults

historical developments in the understanding of acid sulfate soils abstract literature about the historical and current recognition of kinds names and classification for overall processes sulfidization and sulfuricization that form and conditions that induce the formation of potential active and post active acid sulfate soils are reviewed to set the stage for papers presented elsewhere in this special issue of geoderma that contains some of the papers presented at the eighth international acid sulfate soils conference held at the university of maryland college park md usa july 17 23 2016 mention is made and examples cited of environmental problems such as amd acid mine drainage and ard acid rock drainage fish kills in waters receiving drainage from acid sulfate soils even from ones considered post active and special land reclamation and management practices to produce crops on land disturbed often deeply by humans including engineers poorly educated about acid sulfate soils or by natural causes sea level rise or fall or extreme drought such as the recent millennium drought in the murray darling basin of australia the global distribution of acid sulfate soils is considered recognizing that post active ones are extensive with many likely currently unrecognized although features in some of them such as silcrete and ferricrete likely owe their origin to acid sulfate weathering phenomena most coastal subaqueous soils are influenced by sulfidization and constitute sulfidic materials that if dredged and deposited in upland disposal areas become exposed to aerobic conditions and are likely to give rise to active acid sulfate soils with sulfuric horizons

mineralogical control of rare earth elements in acid sulfate soils abstract major trace and rare earth element concentrations were measured in porewater surface water and sediments at an acid sulfate soil site the concentrations of la and ce in porewater are up to 1 3 ppm there is a strong correlation between ree concentration and acidity except that the maximum concentrations were consistently found below the horizon of maximum acidity associated with an increase in ph to ca 4 and change in mineralogy from jarosite dominated to goethite dominated mottles jarosite replacement by goethite is as expected with the rise in ph which in turn is due to the occurrence of a fossil shell bed just below the rare earth element patterns in the porewaters are enriched in the mree with respect to post archaean australian shale paas measurements and calculations show that this is in accord with experiments on low degree partial dissolution of jarosite even when the jarosite itself is highly enriched in lree there is a clear fractionation in the patterns between the clay rich soil matrix which is slightly depleted in the lree when normalized to paas la ybpaas 0 5 and the secondary mineral phase jarosite which is enriched in the lree la ybpaas 15 50 the ree pattern in the porewater changes with the transition from jarosite to goethite rich mottles becoming relatively more enriched in the lree compared to the hree which is consistent with the incongruent dissolution of jarosite to form goethite and the release of greater amounts of jarosite ree to solution including proportionately more of the jarosite compatible lree maximum surface water ree concentrations in acidic water were 100 200 ppb la and ce ree patterns in surface water were very similar to the porewater transition zone enriched in the mree but asymmetric relatively enriched in the lree compared to the hree

radial gravitational gliding on passive margins abstract gravitational gliding of uppermost sediments down a passive margin is possible if there is a basal layer of evaporite or other soft material to allow detachment in examples from the gulf of mexico and the brazilian margin gliding has produced three main structural domains an uppermost domain of downdip extension an intermediate domain of rigid gliding and a lowermost domain of downdip contraction domain boundaries are established by changes in slope in this paper we examine three kinds of gravitational gliding depending on the paths followed by material particles in ideal parallel gliding particle paths are parallel straight lines trending downslope this should occur where the margin is perfectly straight in ideal radial gliding particle paths are radii of a circle and the margin is shaped like a circular cone natural margins will not have ideal shapes but divergent gliding will tend to occur off coastal salients convergent gliding off coastal re entrants a simple kinematic model based on ductile behaviour illustrates some essential features of radial gliding changes in radius during divergent gliding produce strike parallel extension during convergent gliding they produce strike parallel contraction vertical strains also differ divergent gliding produces an uppermost domain of strong vertical thinning balanced by extensions in all horizontal directions similarly convergent gliding produces a lowermost domain of strong vertical thickening balanced by contractions in all horizontal directions these deformed states cannot be restored by simple techniques based on section balancing we have done three experiments using analogue materials sand to model the brittle behaviour of sediments silicone putty to model the ductile behaviour of basal layers of evaporite the experiments were properly scaled to account for gravitational forces experiment i reproduced convergent gliding above a basement with a conical upper surface strike parallel contraction was responsible for radial folds on the lower slopes the lowermost domain had a complex fold pattern indicating contraction in all horizontal directions experiment 2 reproduced divergent gliding above a basement with a pyramidal upper surface strike parallel extension produced radial rifts on the upper slopes the uppermost domain had a complex polygonal pattern of normal faults indicating extension in all horizontal directions experiment 3 also reproduced divergent gliding but due to non uniform sediment thickness we have examined the many seismic profiles both downdip and alongstrike available for the brazilian margin alongstrike profiles show structures which we attribute to strike parallel strains around the santos re entrant syn sedimentary growthfolds indicate strike parallel contraction increasing downslope this argues for a mechanism of convergent gliding in contrast around the campos salient normal growth faults and associated salt rollers indicate strike parallel extension decreasing downslope this argues for a mechanism of divergent gliding the pattern of oil fields in the campos area including the giant marlim field seems to be closely controlled by divergent gravitational gliding and associated processes radial gliding should occur on other passive margins as well especially where the coastline is sinuous structures around the western gulf of of mexico seem to indicate convergent gliding at the scale of the entire gulf structures at a smaller scale around the mississippi delta seem to indicate divergent gliding

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement abstract this paper discusses the differences in mechanical properties and kinematics between fold and thrust belts detaching on evaporitic decollements and those detaching on stronger detachments physical experiments are described that model shortening of a thick brittle cover overlying a weak viscous decollement to gain a better understanding of these differences we tested the influence of 1 the decollement layer thickness and 2 the presence of a deformable backstop on the hinterland side and of a decollement pinch out on the foreland side because of the very low shear strength of the viscous decollement folds and thrusts did not propagate according to a piggy back sequence but by centripetal back and forth propagation additional shortening was accommodated by growth of all existing structures fold symmetry and thrust vergence varied between experiments models confined between two rigid vertical endwalls always deformed by symmetric folding and thrusting in models having a deformable backstop and a foreland decollement pinch out forethrusting initially dominated folds were asymmetric and fault blocks rotated in models having a thick decollement layer folds kept growing asymmetrically diapirism also depended on the initial decollement geometry diapirs formed only in models having a deformable backstop and were restricted to the hanging wall of a fault related fold finally the implications of such kinematics on the thermal history are discussed as well as the likelihood of hydrocarbon maturation and preservation

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

an integrated physically based model for arid region flash flood prediction capable of simulating dynamic transmission loss this paper outlines a physically based model developed for prediction of both arid region flash floods and associated transmission loss it is based on coupling numerical solutions of the st venant equations and the kinematic wave equation for channel and overland flow routing respectively with the richards equation for the determination of infiltration these hydrological components are integrated in one comprehensive model for the above mentioned purposes the robustness of the model and its components have been tested and it has then been applied to a medium size catchment in an arid region the results indicate that reasonable simulations can be achieved with a minimum of calibration but point to problems of representing input rainfall conditions with the necessary time and space resolutions 1998 john wiley sons ltd

waterhole form and process in the anastomosing channel system of cooper creek australia one of the most distinctive features of cooper creek s anastomosing channel system is the preponderance of waterholes enlarged segments of channel ranging in length from 100 m to over 20 km enlargement occurs in both the width and depth dimensions to give bankfull cross sectional areas four to eight times the average size of individual anastomosing channels the anastomosing system is cut into a floodplain of subtle relief but depths of incision can be highly variable giving rise to changes in the degree of anastomosis as different sets of channels are activated during the filling stage of a flood also cross sectional form and bed topography can vary markedly over short channel distances which has implications for local flow conditions and erosive potential hydraulic geometry analyses suggest that cross sectional area adjusts much more readily than velocity to increasing discharge in waterholes particularly if there is limited lateral confinement consequently velocities tend to be rather modest across a wide spectrum of flows with average values rarely reaching 1 m s 1 nevertheless observations made during a 1 20 year flood reveal a deeply penetrative band of relatively high velocity in one waterhole suggesting that localized values of bed shear could be quite large even when sectional averages are moderate waterholes appear to be a product of the present regime since they concentrate flow from both feeder channels and the floodplain during flood discharges in several respects they resemble chains of ponds morphology eyles r j 1977 birchams creek the transition from a chain of ponds to a gully aust geogr stud 15 146 157 and could represent the discontinuous sections of a present day channel which cannot be maintained in that form over its entire length that the one waterhole to accommodate the entire cross valley flow at bankfull stage meringhina waterhole has cross sectional dimensions similar to those predicted by appropriate regime equations lends support to this argument essentially waterholes are self maintaining scour features which play a significant hydrological and geomorphological role in the cooper creek anastomosing system they provide long term water storage in an arid environment and their fixed position helps to maintain the stability of the multi channel pattern

growth fault rollover systems birth growth and decay growth fault rollover systems are extremely common structures of thin skinned extensional systems resulting from gravity gliding above salt their development is studied using laboratory experiments based on brittle ductile models where the sedimentary cover and synkinematic sediments are simulated using brittle sand and the underlying decollement layer by viscous silicone putty the experiments are compared to natural examples from seismic lines the experimental results are used to present the evolution of growth fault rollover systems these being the result of a finite amplitude instability with three distinct stages birth growth and decay each of these stages is identified with typical structures which can be recognized on seismic sections a discussion is presented on the interactions in time and space between synthetic and antithetic listric faults parallel and transverse to the direction of displacement

the geochemistry during management of lake acidification caused by the rewetting of sulfuric ph 4 acid sulfate soils abstract understanding the geochemistry and kinetics of acidification events arising from acid sulfate soils is important to enable effective management and risk assessment large scale exposure and oxidation of acid sulfate soils occurred during a drought in the lower lakes murray darling basin of south australia we examined the geochemical changes that occurred in one region boggy lake that experienced surface water acidification and was subsequently neutralised via aerial limestone caco3 dosing and dilution via natural lake refill very low ph

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico part ii structure abstract the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope autochthonous salt allochthonous salt and detached allochthonous salt are typical stages of evolution major down to the basin growth faults separate allochthonous salt sheets from their original feeder stocks extension along down to the basin master growth faults is compensated mainly by salt withdrawal and partly by basinward shortening

oxygenation of acid sulfate soils stimulates co2 emission roles of acidic dissolution and hydroxyl radical oxidation abstract emission of co2 from acid sulfate soil regions has received great attention in recent years production of co2 due to microbial respiration has been documented by previous studies but the abiotic mechanisms are poorly understood in this study co2 production was measured from oxygenation of 60 acid sulfate soil samples that were collected from a typical acid sulfate soil region the soil samples were characterized by low ph 3 3 5 8 and high sulfate content 0 51 5 03 mg g the cumulative concentrations of co2 were 0 76 54 54 mol per g dry soil upon oxygenation for 24 h when 0 1 hgcl2 was added into soil suspension to kill microbes the yield of co2 decreased by 8 7 41 1 which suggests that both microbial respiration and abiotic pathways contributed to co2 production and abiotic pathway played a major role both acidic dissolution and hydroxyl radical oh oxidation were identified to be the abiotic mechanisms for co2 production for acidic dissolution co2 was produced from the decomposition of carbonate by h generated production of co2 from acidic dissolution was dependent on the content of carbonate and the generation of h a combination of fe speciation sequential extraction and kinetic model shows that h was mainly generated from the oxidation of both fe2 and pyrite by o2 for oh oxidation co2 was produced from the oxidation of organic carbon by oh produced and its relative importance for co2 production was estimated to be 14 6 27 6 oh was mainly produced from exchangeable fe ii oxidation in sulfuric horizon but from pyrite oxidation in potential acid sulfate soils this study presents the overlooked abiotic mechanisms acidic dissolution and oh oxidation for co2 emission in acid sulfate soils when perturbed by o2 our findings implicate that contribution of microbial respiration for co2 production is not as large as previously thought to be in acid sulfate soils and instead abiotic mechanisms contribute largely particularly for oxygenation of potential acid sulfate soils

modelling streamflow in a large anastomosing river of the arid zone diamantina river australia anastomosing rivers form a subset of the anabranching family of river types and provide considerable challenges to modelling of their streamflow because of complex flow patterns across greatly varying floodplain widths estimates of distributed flow data are required for catchment management purposes and ecological studies of these rivers but are hindered by a paucity of measured discharge data a grid based semi distributed conceptual model structure is applied to a 330 km reach of the arid zone diamantina river of central australia model complexity is constrained by data availability with only a single gauging station located at the downstream end of the reach to provide discharge data for model calibration the model uses a simple conceptual bucket structure and accounts for exceptionally high transmission losses as well as flow patterns and wave speeds that vary with discharge within the reach the intricate flow patterns across the floodplains widths of up to 50 km are simulated using a grid based structure that required the following features i cell connections that are explicitly defined using a code that allows for multi directional flow from a cell and ii each cell having a binary flow pattern with the second connection pattern being triggered when the surface storage of the cell exceeds a calibrated level for a given land type satellite images were used to define the flow paths and hence cell connection patterns utilised by various sized floods the model was able to provide acceptable simulation of large floods but with decreasing model performance in the simulation of small to medium sized floods simulation suggested that incorrectly defined flow paths for the smaller floods were a major factor in this decreased performance the capability of the model would be improved by further detailed mapping using satellite imagery of spatial patterns of inundation as discharge varies

model for salt deformation on deep margin of central gulf of mexico basin based on available nonexclusive seismic data a preliminary model has been developed for salt deformation on the deep margin of the central gulf of mexico basin in this model the tertiary clastic wedge prograded to the basinward limit of original jurassic salt by the middle miocene as the salt and overburden thinned basinward lateral flow combined with a strong component of downward force exerted by subsiding voluminous middle miocene loading caused the basinward limit of the louann salt to effectively shear off deposition of the upper miocene and pliocene sediments was confined primarily shoreward of an incipient salt swell but pleistocene sediments were eventually able to breach the barrier deformation of the detached salt produced the features present on the slope today preliminary work indicates that most of the detached salt was propelled basinward and upsection toward the present sigsbee escarpment leaving pinch and swell salt structures behind the various types of residual salt structures have been formed as a result of differences in the history of sedimentary loading different stages of development of pinch and swell structures shown on seismic sections illustrate this model

the shaping of salt diapirs abstract six parameters shape the geometry of passive diapirs associated with stiff overburden rates of salt supply s dissolution d sediment accumulation a erosion er extension e and shortening sh these parameters change in space and time and hence influence the geometry of the structure as it forms a complex six parameter plot representing the evolution history of a salt diapir can be simplified into three separate graphs this study recommends adding to plots of s against a a second of rate of salt supply s this time with extension rate e and a third of rate of sediment accumulation a plotted against extension rate e integrating these three plots on a single diagram results in a complete description of the evolution history of a diapir when it is applied to three dimensional data however if applied to a profile the plot shows only the two dimensional evolution history of the diapir lateral forces extension or compression have a significant role in moulding the geometry of a salt diapir by influencing the space which it occupies by incorporating extension in the moulding plots of salt diapirs this study introduces the rate of sediment accumulation multiplied by extension e a as a significant factor in moulding salt diapirs by using this rate against the rate of salt supply this study redefines the conventionally accepted interpretation of upward narrowing upward widening and columnar diapirs upward narrowing diapirs form when the rate of salt supply is less than the rate of sediment accumulation multiplied by extension upward widening diapirs form when the salt supply is greater than the rate of sediment accumulation multiplied by extension columnar diapirs form when the rate of salt supply is equal to the rate of sediment accumulation multiplied by extension this new relationship explains the absence of columnar and upward widening diapirs in passive margins where thin skinned extension dominates and emphasizes the significance of lateral movement extension and shortening in moulding the geometry of salt diapirs

satellite derived digital elevation model dem selection preparation and correction for hydrodynamic modelling in large low gradient and data sparse catchments digital elevation models dems that accurately replicate both landscape form and processes are critical to support modelling of environmental processes topographic accuracy methods of preparation and grid size are all important for hydrodynamic models to efficiently replicate flow processes in remote and data scarce regions high resolution dems are often not available and therefore it is necessary to evaluate lower resolution data such as the shuttle radar topography mission srtm and advanced spaceborne thermal emission and reflection radiometer aster for use within hydrodynamic models this paper does this in three ways i assessing point accuracy and geometric co registration error of the original dems ii quantifying the effects of dem preparation methods vegetation smoothed and hydrologically corrected on hydrodynamic modelling relative accuracy and iii quantifying the effect of the hydrodynamic model grid size 30 2000 m and the associated relative computational costs run time on relative accuracy in model outputs we initially evaluated the accuracy of the original srtm 30 m seamless c band dem srtm dem and second generation products from the aster aster gdem against registered survey marks and altimetry data points from the ice cloud and land elevation satellite icesat srtm dem rmse 3 25 m had higher accuracy than aster gdem rmse 7 43 m based on these results the original version of srtm dem the aster gdem along with vegetation smoothed and hydrologically corrected versions were prepared and used to simulate three flood events along a 200 km stretch of the low gradient thompson river in arid australia using five metrics peak discharge peak height travel time terminal water storage and flood extent the hydrologically corrected dems performed best across these metrics in simulating floods compared with vegetation smoothed dems and original dems the response of model performance to grid size was non linear and while the smaller grid sizes 120 m improved the hydrodynamic model results these offered only slight improvements at very significant computational costs compared to grid size of 120 m with grid sizes 250 m and greater decreasing in model accuracy this study highlights the important impact that the quality of the underlying dem has and in particular how sensitive hydrodynamic models are to preparation methods and how important vegetation smoothing and hydrological correction of the base topographic data for modelling floods in low gradient and multi channel environments

acid sulphate soil landscape relationships in the pearl river delta southern china abstract relationships between the development of acid sulphate soil and landscape characteristics were examined in a fluvial dominated estuarine deltaic plain of the south china coast it was found that the accumulation of pyrite potential acid sulphate material has been limited generally by rapid sedimentation rates and insufficient supply of sulphate ion the occurrence of the pyritic sediments is however closely associated with a particular depositional pattern i e surrounding island deposition the acid sulphate soils in the area frequently occur within narrow zones surrounding present day s rocky hills previously bedrock islands this provides a guide for predicting the occurrence of potential acid sulphate soils in the area apart from the naturally large input of fluvial sediment human activities have also accelerated the delta progradation and limited the vertical accretion of the deltaic surface these effects have had significant impacts on the thickness and occurrence depth of the pyritic layer with a history of more than 1000 years of land reclamation the intensive cultivation in the area has turned most of the potential acid sulphate soils into actual acid sulphate soils however the soil properties vary markedly with landuse types the case of the pearl river delta is generally in agreement with pons and van breemen s 1982 conclusion in that the accumulation of pyrite is inversely related to the rate of sedimentation our results show that the existence of bedrock islands in the estuary basin provided zones of slow sedimentation and therefore enhanced pyrite accumulation on the other hand human intervention over the past 2000 years has acted to reduce pyrite accumulation both through landward catchment clearing that increased sediment discharge to the estuary and through empolderment and associated land management practices

implications of salt sediment interactions on the architecture of the gulf of lions deep water sedimentary systems western mediterranean sea we integrated structural analysis of multichannel seismic data and isopach maps of the quaternary sedimentary cover to evaluate how salt tectonics has influenced the stratigraphic evolution offshore the gulf of lions the interplay between salt tectonics and sedimentation occurs at two scales at local scale listric normal faults create bathymetric relief able to deviate sediment transport axes with implications on depocenters configuration at depocenter scale overburden vertical movements due to salt evacuation or salt diapiric rise create sub basins providing accommodation space for clastic deposition these mechanisms have significant implications on the architecture and the internal organization of turbidite systems offshore the gulf of lions

environmental character and history of the lake eyre basin one seventh of the australian continent abstract one of the world s largest internally drained endorheic basins the 1 14 million km 2 lake eyre hydrological basin leb covers nearly 15 of the australian continent palaeoclimatic and associated flow regime variations are recorded in an archive of fluvial aeolian and lacustrine sediments that are particularly accessible for deposits from the past 300 ka and are especially relevant for the past 50 ka during which humans have inhabited australia due to its great size economic resources and diverse latitudinal extent it has for over six decades been the focus of environmental scientific and resource based studies across numerous disciplines with an emphasis on assessing the scientific and environmental research over this period this paper is divided into four parts part a provides an introduction and background part b provides the geological history including evidence of substantial tertiary and quaternary climate change part c covers the contemporary environmental conditions and part d presents a conclusion and summary this not only represents the first comprehensive review of current knowledge of any of the world s truly large dryland drainage basins but also highlights how more multi disciplinary research is required key remaining questions revolve around the impact of global weather systems on the leb the lake level story in relation to a more precise picture of late quaternary climate change the role of humans and climate in the demise of the megafauna modern hydrological changes the role of vegetation in altering channel morphology and flow efficiencies and nature of flood transmissions

listric normal faults an illustrated summary movement along listric normal faults is instrumental in formation of several types of structural traps e g rollover anticlines and upthrown fault block closures this type of fault may occur where brittle rocks overlie ductile rocks in an extensional regime the extensional regime may be locally derived within a broader stress regime of another type as evidenced by transtension associated with strike slip movement and arched strata in a compressive setting the flattening of the fault reflects an increase in ductility of the rocks with depth and in some cases deformation of the fault due to compaction or tilting of the upthrown block the dip angle may vary along the strike of the fault in response to changes in throw in cross section a listric fault may consist of relatively short en echelon fault segments this geometry may be particularly characteristic of growth faults sedimentary faults may sole in ductile strata or they may represent the brittle part of a fault flow system fault patterns commonly are characterized by bifurcation some of which may occur near the ends of individual faults comprising a zone although unequivocal recognition of listric normal faults requires unusually extensive outcrop data close subsurface control or high quality seismic data their presence is suggested indirectly by such features as increasing dip either depth toward the controlling fault reverse drag thick progradational sandstone overlying ductile strata and in some cases arcuate fault patterns basins or uplifts listric normal faults form during rifting drifting and evolution of passive continental margins with concomitant basinal development the basement is offset by listric faults as a fundamental element in the development of other types of basins including those which formed during postorogenic extension they also occur as secondary extensional features in an overall compressive stress regime due to plate convergence and during transform or strike slip faulting modified journal abstract

salt flow by aggrading and prograding overburdens the mechanisms responsible for segmentation of salt sheets and their emplacement into higher stratigraphic levels are not separable and act simultaneously three sets of centrifuge models with strongly planar anisotropic anisotropy the ratio between the effective viscosities in pure and simple shear ranging between 4 8 and 16 4 microlaminate overburdens are used to study the effect of aggradation and progradation on segmentation and emplacement of allochthonous salt sheets in the first set of models a tabular buoyant source layer was overlain by tabular anisotropic overburden simulating aggradation during centrifuging the underlying ductile source layer was segmented into individual wall like diapirs by the subsiding blocks formed due to extension and faulting of the overburden the extensional zone in these models started at the spreading edge free face of the model and migrated backwards in the second set of models a tabular buoyant source layer was overlain successively by wedges of anisotropic overburdens simulating progradation during centrifuging the buoyant layer was displaced from the back of the model where loading was higher towards the free face in the front of the model where overburden units were thinner overburden units extended at the back and the middle of the model while contractional structures dominated at the front where asymmetric diapirs formed overhangs that spread basinward to form salt sheets in the third set of models a wedge shaped buoyant source layer was overlain successively by wedges of anisotropic overburden simulating progradation the overburden wedge created a lateral pressure gradient ranging from 144 pa at the back of the model to 80 pa at the front when deformed in the centrifuge in these models as in the second set of models the underlying buoyant mass was displaced basinward by the subsiding thicker overburden units at the back of the model contractional structures dominated the deformation at the leading edge of the wedge comparison of model results suggests that progradation as in the second and third sets of models loads underlying salt differentially displaces it downdip and segments it as it segments at the back the salt flows laterally to areas of lower loading by intruding through the thinner overburden units and forming secondary salt sheets at the front on the other hand aggradation of uniform overburden segments a buoyant sheet into two dimensional salt walls or stocks as in the first set of models