environmental isotopes meet 3d geological modelling conceptualising recharge and structurally controlled aquifer connectivity in the basalt plains of south western victoria australia summary to develop a conceptual model of recharge and inter aquifer connectivity for a complex aquifer system in southwestern victoria australia a three dimensional 3d geological model was constructed and used to examine the influence of the regional geology on groundwater composition and age as well as recharge mechanisms the major aquifers are three basalts differentiated on age and geomorphological features and an underlying palaeovalley deep lead system the upper fine grained sediments of the deep lead form an aquitard that separates the basalt from the permeable sands and gravels beneath recharge calculations chloride mass balance and water table fluctuation methods salinity stable isotope tritium and radiocarbon data show that volcanoes and the youngest basalts although volumetrically minor form preferential recharge areas for all the basalts up to 30 mm year and also recharge the deep lead sediments through volcanic necks that penetrate the aquitard infiltration through the thick clay rich soils on the older basalts is small typically 1 2 mm year and saline resulting in a progressive increase of groundwater salinity along the flow path in these basalts the comparison of fault location with groundwater age in the deep lead aquifer suggests that in some areas faults exert significant structural control on groundwater flow this study demonstrates the value of integrating geological hydrogeological and hydrochemical data to identify preferential recharge areas inter aquifer connectivity and the influence of faults on groundwater flow in a complex aquifer system

contribution of deep seismic profiling to the knowledge of the lower crust in france and neighbouring areas abstract in france and neighbouring areas the crust is essentially formed of segments of the variscan orogen 380 300 ma and older formations cratonic basins began to form in the permian but extensive subsidence only occurred from the lias in basins such as the paris and aquitaine basins and also along the margin of the alpine tethys ocean the pyrenees and alps range eventually formed during the tertiary as a result of the collision between the european and african continental plates large grabens were also rifted in the rhine and rhone valleys deep seismic profiles show remarkable features common to the crust of the whole area although it underwent such a complicated geological history the most striking feature is the occurrence of conspicuous flat reflections densely distributed in the lower part of the crust below a comparatively transparent upper crust these reflections hereafter called laminations have been found to occur on most profiles within a large area covering western europe although they vary in depth thickness and energy dipping reflections have frequently been observed in the upper crust some of them extend across the lower crust and even penetrate into the upper mantle they may be reasonably interpreted as variscan compressional features by correlation with surface geology and comparison with similar features found in deep seismic profiles from other regions the origin of the flat laminations which generally lie in the lower part of the crust is more controversial this paper attempts to use the well known geological history of the region to place some constraints on the hypotheses which may be advanced to explain the formation of these laminations these features may be explained by the following tectonothermal events 1 1 compression which prevailed during the variscan orogeny may have formed the laminations as a result of delamination and shearing near the bottom of the crust associated with melting intrusion and metamorphism during the different stages of the crustal evolution 2 2 the thermal equilibration of the upper mantle which occurred in the permian at the end of the variscan orogeny may have caused metamorphism and magmatism in the overlying crust 3 3 a regional thermal event which might be associated with subordinate extension occurred during the rifting of the alpine tethys and the initiation of mesozoic cratonic basins in late triassic middle jurassic times it may also have caused metamorphism and magmatism in the lower crust while the first model implies conservation of the crust material the other two suggest that the crust mantle transition has been somewhat uplifted since the end of the variscan orogeny the latter hypothesis is one way to explain the undeniable occurrence of seismic events below the present moho reflection the above three models are not mutually exclusive and all these phenomena may well have affected the crust to some extent however the data at hand are still insufficient to determine what parts tectonic and nontectonic processes have played in the creation of the laminations in the lower crust and the moho further experiments are needed to check these hypotheses

lithospheric structures and possible processes in phanerozoic eastern australia from deep seismic investigations abstract the eromanga basin in eastern australia developed during four major episodes on the rifted eastern margin of the australian precambrian craton seismic reflection profiling together with coincident wide angle reflection refraction profiling indicates structures and compositions in the crust which are dominant in various depth ranges some structural features seem to be limited to the upper crust other deep reflection events and high crustal velocities predominate in the lower crust with mafic intrusion from upper mantle sources being one preferred interpretation these features emphasize the difference in structures and composition between the upper and lower parts of the crust yet other structural and deep reflection features are interpreted as being truly lithospheric in scale because they seem to have seismic expression right from the surface to the upper mantle similar interpretations are made for other continental regions indicating that lithospheric processes affect different depth ranges of the crust and upper mantle in a variety of ways any modelling of such processes in the lithosphere must lead to these quite different end results at appropriate depth ranges

composition diagenesis and weathering of the sediments and basement of the callabonna sub basin central australia implications for landscape evolution abstract the evolution of the callabonna sub basin central australia is described in terms of sediment provenance stratigraphy sedimentology and postdepositional mineral and chemical alteration six mineral exploration drillholes in the mundi mundi plain were studied using a combination of qualitative and quantitative xrd pimatm portable infrared mineral analyzer xrf normative analysis and sem the sedimentary cover consists of 160 210 m of diagenetically modified fluvio lacustrine tertiary clay silt and sand comprising sandy mottled and gray clay units overlain by quaternary soil the basement consists of weathered proterozoic schist gneiss siltstone and shale quartz kaolinite smectite and muscovite are the dominant minerals within the sediments whereas the weathered bedrock contains quartz feldspar kaolinite illite and muscovite characteristic wavelength absorption features from pimatm show that the youngest sandy clay unit exhibits the lowest reflectance intensities because of its lower diagenetic maturity weathering of primary minerals within the basement produced an illite kaolinite rich saprolite whose clays exhibit strong reflectance intensities and well developed crystallinity the micromorphology of all secondary products reflects their environment of crystallization low porosity and anoxic conditions within the sediments resulted in poorly developed clays of variable textures colors and compositions conversely the weathered bedrock developed over protracted periods of in situ weathering resulting in better developed secondary products this study distinguishes between preburial weathering of the basement detrital mineralogy postdepositional alteration of the sedimentary cover and subsequent weathering of previously formed mineral assemblages this has widespread implications for paleotopographic weathering reconstitution and landscape evolution thus 1 the extent of weathering of basement relative to diagenesis and maturity of sediments and gradational nature of their unconformity suggests that most of the alteration of basement occurred prior to and was sustained after deposition of sediments and 2 morphotectonic evolution of the region controlled the composition of transported materials by changing the style and patterns of fluvial systems further influencing the distribution and preservation of sediments and weathered bedrock and hence regional landscape morphology

evaporation induced 18o and 13c enrichment in lake systems a global perspective on hydrologic balance effects growing pressure on sustainable water resource allocation in the context of global development and rapid environmental change demands rigorous knowledge of how regional water cycles change through time one of the most attractive and widely utilized approaches for gaining this knowledge is the analysis of lake carbonate stable isotopic compositions however endogenic carbonate archives are sensitive to a variety of natural processes and conditions leaving isotopic datasets largely underdetermined as a consequence isotopic researchers are often required to assume values for multiple parameters including temperature of carbonate formation or lake water delta o 18 in order to interpret changes in hydrologic conditions here we review and analyze a global compilation of 57 lacustrine dual carbon and oxygen stable isotope records with a topical focus on the effects of shifting hydrologic balance on endogenic carbonate isotopic compositions through integration of multiple large datasets we show that lake carbonate delta o 18 values and the lake waters from which they are derived are often shifted by 10 parts per thousand relative to source waters discharging into the lake the global pattern of delta o 18 and delta c 13 covariation observed in 70 of the records studied and in several evaporation experiments demonstrates that isotopic fractionations associated with lake water evaporation cause the heavy carbon and oxygen isotope enrichments observed in most lakes and lake carbonate records modeled endogenic calcite compositions in isotopic equilibrium with lake source waters further demonstrate that evaporation effects can be extreme even in lake records where delta o 18 and delta c 13 covariation is absent aridisol pedogenic carbonates show similar isotopic responses to evaporation and the relevance of evaporative modification to paleoclimatic and paleotopographic research using endogenic carbonate proxies are discussed recent advances in stable isotope research techniques present unprecedented opportunities to overcome the underdetermined nature of stable isotopic data through integration of multiple isotopic proxies including dual element c 13 excess values and clumped isotope temperature estimates we demonstrate the utility of applying these multi proxy approaches to the interpretation of paleohy droclimatic conditions in ancient lake systems understanding past present and future hydroclimatic systems is a global imperative significant progress should be expected as these modern research techniques become more widely applied and integrated with traditional stable isotopic proxies c 2015 elsevier ltd all rights reserved

chloride imbalance in a catchment undergoing hydrological change upper barwon river southeast australia documenting whether surface water catchments are in net chemical mass balance is important to understanding hydrological systems catchments that export significantly greater volumes of solutes than are delivered via rainfall are not in hydrologic equilibrium and indicate a changing hydrological system here an assessment is made of whether a saline catchment in southeast australia is in chemical mass balance based on cl the upper reaches of the barwon river southeast australia has total dissolved solids tds concentrations of up to 5860mg l and cl concentrations of up to 3370mg l the high river tds concentrations are due to the influxes of groundwater with tds concentrations of up to 68 000mg l between 1989 and 2011 the median annual cl flux from the upper barwon catchment was 17 8 106kg 140kg a ha this represents 340 2230 of the annual cl input by rainfall to the catchment major ion and stable isotope geochemistry indicate that the dominant source of solutes in the catchment is evapotranspiration of rainfall precluding mineral dissolution as a source of excess cl the upper barwon catchment is not in chemical mass balance and is a net exporter of solutes the chemical imbalance may reflect the transition within the last 100ka from an endorheic lake system where solutes were recycled producing shallow groundwater with high tds concentrations to a better drained catchment alternatively a rise in the regional water table following land clearing may have increased the input of groundwater with high tds concentrations to the river system

micromorphology of iceberg scour in clays glacial lake agassiz manitoba canada abstract icebergs plough through unconsolidated lake sea sediments gouging out kilometre long grooves 100s of metres wide and tens of metres deep although the surface morphology of iceberg scours is well documented little is known about what scours look like in stratigraphic section particularly where surface characteristics are absent e g through decay or burial this investigation establishes a definitive suite of diagnostic criteria for identifying iceberg scours in clays by macroscopically and microscopically 2d thin sections examining sediment deformation below iceberg scours in former glacial lake agassiz manitoba canada structures unequivocally attributed to iceberg scour in this investigation include sub horizontal microfabrics folds sheath folds augen shapes normal faults reverse thrust faults discrete shears partially destroyed clasts intraclasts type iii multiple domains water escape structures flow structures unistrial plasmic fabric dropstones realigned bedding and specific structural sequences this research will be particularly valuable in palaeoenvironmental reconstruction and in predicting glacial dynamics in addition it may eventually aid structural engineering on polar shelves which could be of great value to oil and gas companies

strontium and carbon isotope tracers and the origins of soil carbonate in south australia and victoria abstract calcium carbonate occurs in soils in association with a variety of rock types in coastal and inland south australia and victoria the 87 sr 86 sr ratios of the coastal soil carbonates fall between 0 7094 and 0 7098 showing that the ocean is the principal source of calcium to nearly all soils near the coast and that contributions from bedrock are generally small an exception is the soil formed on the young volcano at mt gambier in which the average ratio for carbonate is about 0 7070 compared to 0 7041 for the volcanic ash the basaltic ash of the volcano is readily weathered and rich in calcium roughly 40 of strontium and 10 to 20 of the calcium in the soil carbonate derives from the ash and the balance from marine sources the 87 sr 86 sr ratios from soil carbonate gradually increase inland reaching values of 0 7152 these higher ratios reflect at least in part the increasing 87 sr 86 sr ratio of inland dust in contrast the ocean does not contribute significantly to the carbon pool of the soils we studied the 13 c pdb values of soil carbonates on kangaroo island and the higher rainfall areas of eastern victoria fall between 11 0 and 8 7 indicating that the carbonate formed in equilibrium with the c3 dominated vegetation typical of the region in the warmer inland areas to the north such as the eyre peninsula the 13 c value of soil carbonate averages 5 3 reflecting the higher proportion of c4 plants in the local biomass mixing with marine sources of carbonate cannot account for the observed carbon isotopic patterns the flux of carbon into soils from the ocean therefore must be small compared to that derived from plant respiration and decay

tensile strength of dry remoulded soils as affected by properties of the clay fraction abstract changes in tensile strength with clay type clay particle size and amounts of spontaneously and mechanically dispersible clays were assessed for dry remoulded samples of eight australian vertisols and alfisols varying in clay mineralogy the effects of different clay content and particle size on tensile strength were also measured the average particle sizes of whole clay and of spontaneously and mechanically dispersible clays were also determined tensile strength of soils was influenced by the type and amount of clay present clay particle size and amount of dispersible clay soil strength increased with increasing clay content when the clay content increased beyond 20 there was a dramatic increase in soil strength indicating the possible role of particle arrangement correlations between different clay types clay particle sizes cation exchange capacity and tensile strength clearly illustrated that the sensitivity of tensile strength to these factors was greatest in soils dominated by smectite followed by illitic and then kaolinitic soils tensile strength of soils was positively and significantly correlated with both spontaneously and mechanically dispersible clays a significant negative correlation was obtained between clay particle size and tensile strength for illitic soils whereas the same linear relationship was not significant for smectitic soils however a significant negative exponential regression was obtained between the cube of clay particle size and tensile strength when the results of all soil samples were pooled together transmission electron micrographs tem showed a wider clay particle size distribution in smectites than in illites soils with the highest amounts of fine clay and the widest clay particle size distribution had higher tensile strengths the size of spontaneously dispersed clay particles was smaller than that of mechanically dispersed clay no difference in clay particle size was found between spontaneously and mechanically dispersible clays from mixtures of a fine clay with a basic sand and silt matrix regression collinearity diagnostics and principal component analyses were used to analyse the data a high correlation was found between the cation exchange capacity cec of clays and soil strength the principal component analysis indicated that spontaneously dispersible clay percentage of randomly interstratified minerals rim and cec were important factors in predicting the strength of remoulded soils

physical hydrogeology and environmental isotopes to constrain the age origins and stability of a low salinity groundwater lens formed by periodic river recharge murray basin australia summary a low salinity total dissolved solids tds 25 000 mg l is marked by a hectometer to kilometer scale transition in tds concentrations that is not stratigraphically controlled rather this boundary represents a mixing zone with the regional groundwater the position of which is controlled by the rate of recharge from the river the lens is part of an active and dynamic hydrogeological system that responds over years to decades to changes in river levels the lens has shrunk during the drought of the late 1990s to the mid 2000s and it will continue to shrink unless regular high flows in the murray river are re established over longer timescales the rise of the regional water table due to land clearing will increase the hydraulic gradient between the regional groundwater and the groundwater in the lens which will also cause it to degrade replacement of low salinity groundwater in the lens with saline groundwater will ultimately increase the salinity of the murray river reducing its utility for water supply and impacting riverine ecosystems

measured and calculated elastic wave speeds in partially equilibrated mafic granulite xenoliths implications for the properties of an underplated lower continental crust ultrasonic compressional wave velocities measured at 1 0 gpa and room temperature are compared with calculated velocities based on single crystal data and modal mineralogy for a suite of mafic granulite xenoliths from the chudleigh volcanic province north queensland australia the xenoliths have nearly constant major element compositions but widely variable modal mineralogy reflecting recrystallization under variable pressure temperature conditions at depth in the continental crust 20 45 km they thus provide an excellent opportunity to investigate velocity variation with depth in a mafic lower crust measured p wave velocities corrected for the decompression induced breakdown of garnet range from 6 9 to 7 6 km sec and correlate with derivation depth these velocities are 5 12 lower than the calculated velocities 7 5 8 0 km sec apparently as a result of grain boundary alteration as well as irreversible changes that occurred in the xenoliths during rapid decompression calculated p wave velocities are similar to those estimated by furlong and fountain 1986 and sobolev and babeyko 1989 for mafic granulites formed through basaltic underplating of the continental crust depending upon in situ temperature p wave velocities in the deepest samples may be interpreted as crustal e g 7 3 7 6 km sec if heat flow is high or mantle 7 7 7 8 km sec in areas of low heat flow the range of velocities in the xenolith suite is larger than predicted for a fully equilibrated underplated basaltic layer highlighting the importance of kinetic effects in determining the ultimate velocity profile of magmatically underplated crust comparison of our results with seismic profiles illustrates that the lower crust rarely reaches such high velocities suggesting quartz bearing rocks country rocks are present within magmatically underplated layers of the deep crust

a seismic refraction study of the quilpie trough and adjacent basement highs eromanga basin eastern australia abstract the jurassic cretaceous eromanga basin in eastern australia is a relatively undisturbed sedimentary sequence covering the devonian quilpie trough and the early palaeozoic canaway ridge and cheepie shelf seismic refraction recording across these three features with additional reflection gravity and well information has been used to determine the velocity structure to a depth of 10 km the thickness of the eromanga basin sequence along the traverse varies between 1 1 and 1 4 km with p wave velocities ranging from 2 0 to 3 8 km s the maximum thickness of the underlying quilpie trough is about 3 8 km but the base of the trough is hard to define the velocities in this devonian sequence range from 4 0 to 5 0 5 5 km s two small bodies with a velocity of 4 0 4 5 km s occur immediately below the eromanga basin sediments on the canaway ridge and the cheepie shelf they may be remnants of devonian sediments on an erosion surface the velocities within the ordovician basement are less below the canaway ridge than under the cheepie shelf and quilpie trough they reach 6 0 km s at 7 km depth below the ridge at 4 km depth under the shelf and at an intermediate depth under the trough from gravity modelling the density of the basement to the quilpie trough increases at a depth of about 7 km this may be related to volcanics found in the basement further north the canaway ridge has a lower density than the cheepie shelf or the basement of the quilpie trough relative vertical movement between these three features may in part be related to these density differences

p wave velocity features of the lithosphere under the eromanga basin eastern australia including a prominent mid crustal conrad discontinuity abstract the crustal structure of the central eromanga basin in the northern part of the australian tasman geosyncline revealed by coincident seismic reflection and refraction shooting contrasts with some neighbouring regions of the continent the depth to the crust mantle boundary moho of 36 41 km is much less than that under the north australian craton to the northwest 50 55 km and the lachlan fold belt to the southeast 43 51 km but is similar to that under the drummond and bowen basins to the east the seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the north australian and lachlan provinces in particular there is a sharp velocity increase at mid crustal depths 21 24 km which has not been observed with such clarity elsewhere in australia the conrad discontinuity in the lower crust the many discontinuous sub horizontal reflections are in marked contrast to lack of reflecting horizons in the upper crust further emphasising the differences between the upper and lower crust the crust mantle boundary moho is characterised by an increase in velocity from 7 1 7 7 km s to a value of 8 15 0 04 km s the depth to the moho under the canaway ridge a prominent basement high is shallower by about 5 km than the regional moho depth there is also no mid crustal horizon under the canaway ridge but there is a very sharp velocity increase at the moho depth of 34 km the ridge could be interpreted as a horst structure extending to at least moho depths but it could also have a different intra crustal structure from the surrounding area the sub crustal lithosphere has features which have been interpreted from limited data as being caused by a velocity gradient at 56 57 km depth with a low velocity zone above it because of the contrasting crustal thicknesses and velocity gradients the lithosphere of the central eromanga basin cannot be considered as an extension of the exposed lachlan fold belt or the north australian craton the lack of seismic reflections from the upper crust indicates no coherent accoustic impedance pattern at wavelengths greater than 100 m consistent with an upper crustal basement of tightly folded meta sedimentary and meta volcanic rocks the crustal structure is consistent with a pericratonic or arc back arc basin being cratonised in an episode of convergent tectonics in the early palaeozoic the seismic reflections from the lower crust indicate that it could have developed in a different tectonic environment

experimental study of soil microfabrics induced by isotropic stresses of wetting and drying this experimental study examines the relationship between texture and microfabric under isotropic stresses generated by wetting and drying this can be achieved by observing and measuring the reorganization of microfabrics plasmic fabrics and related distribution pattern rdp microfabrics are produced in the laboratory by mixing montmorillonite with various proportions of sand and silt and subjecting them to wetting and drying without confinement thin sections are cut to study their microfabrics results show broad and systematic variations in fabric with changes in texture fine matrix silt plus clay in physical continuity is developed in samples with low sand silt ratio and regardless of this ratio at high clay levels coarse porphyric and fine porphyric rdp are formed at low and high clay contents respectively plasmic fabrics are represented mainly by insepic and weakly developed mosepic and masepic fabrics in the matrix in the form of small plasma separations with random orientation and weak skelsepic plasma as embedded grain argillans on the other hand coarse matrix sand grains in physical continuity dominates the sandy samples which are associated with relatively thick and strongly birefringent free grain argillans giving well developed skelsepic fabric the rdp follows two major paths beginning with orthogranic very low clay content along the iunctic sequence at low clay silt ratio and along the chlamydic sequence at high ratio the regularities in fabric development are interpreted in the light of the dynamic properties and behaviour of the active clay fraction in a clay water system the pedogenetic implications of the results are explored and the term erdic fabric defined

understanding the salinisation process for groundwater in an area of south eastern australia using hydrochemical and isotopic evidence abstract increases in groundwater salinity down gradient are a common occurrence in catchments throughout australia exacerbating the effects of dryland salinisation in discharge areas groundwater hydrochemical and isotopic data from the willaura catchment in south eastern australia which is affected by both primary natural and secondary human induced salinity allowed the factors that cause the down gradient trend in salinisation within this catchment to be determined the overall salinity of the groundwater 0 8 70 ms cm is controlled by evapotranspiration which concentrates cyclic salts in the unsaturated zone greatly increasing the salinity of the soil water to 3700 6400 mg l cl the progressive addition of this saline soil water to fresher groundwaters recharged on the catchment margins causes a gradual increase in salinity down gradient the groundwater stable isotope compositions show that most recharge occurs in winter and spring groundwater salinities increase around the saline lakes of the discharge zone due to direct evaporation from shallow watertables and minor dissolution of halite as indicated by cl br ratios mineral water interactions within the aquifers cause a slight overall reduction in salinity conversion of kaolinite to smectite and illite and cation exchange of na for ca2 on smectites cause na cl mg2 cl k cl si cl and hco3 cl ratios to progressively decline and ph to gradually increase down gradient oxidation of organic matter causes a strong decrease in the redox potential of the groundwaters down gradient the groundwater ages increase from modern containing tritium on the catchment margins to 8000 years based on 14c dating at the end of the 25 km flow path the older groundwaters are isotopically heavier than the younger waters probably due to recharge during a wetter climate in the early holocene the groundwater ages show clearly that the progressive addition of saline soil water causing groundwaters to become more saline down gradient has occurred throughout the holocene and may explain the occurrence of primary salinisation within many australian catchments

seismic crustal structure of the proterozoic north australian craton between tennant creek and mount isa seismic recording along a 600 km traverse across the southern part of the north australian craton indicates that lateral velocity variations exist in the middle lower crust taken together with other data from the craton there is evidence for midcrustal velocities increasing from east to west and from south to north these trends could result from a greater proportion of high velocity granulites being emplaced at higher levels in the crust between tennant creek and mount isa the velocity structures near the surface are compatible with an assemblage of younger and older metamorphic rocks intruded by granites near surface 0 5 km p wave velocities on the tennant creek inlier increase from 5 47 km s at the surface to about 6 2 km s at 6 km depth and correspond with low grade metamorphics of the warramunga group interspersed with weathered granites overlying amphibolite facies rocks of older metamorphic domains in the mount isa geosyncline velocities of 6 03 6 15 km s correspond to the leichhart metamorphics interspersed with granites in the middle crust p wave velocities of 6 85 km s occur at a depth of 26 km near tennant creek whereas such velocities are not evident until depths of about 37 km near mount isa there is therefore a trend for midcrust velocities to increase from east to west the lower crust is characterized by velocities of 7 3 7 5 km s and the upper mantle velocities of 8 16 8 20 km s are reached at depths of 51 54 km exposed granulite facies rocks in central australia are low in heat producing elements and are compatible with the low surface heat flow generally measured in precambrian australia these data taken together with laboratory velocity measurements on worldwide samples reported elsewhere indicate that middle to lower crustal rocks could be an assemblage of granulite facies rocks varying from pyroxene granulite in the middle crust through hornblende granulite to garnet granulite in the lower crust

in situ neutron flux 36cl production and groundwater evolution in crystalline rocks at stripa sweden the meteoric input of36cl due to cosmogenic or nuclear weapon produced36cl cannot contribute significantly to the36cl present in the saline groundwaters up to 700 mg l 1 cl from the stripa granite the extent of in situ production of36cl has been estimated on the basis of the neutron fluxes within the granite and its surrounding leptite the36cl present in the groundwaters is attributed to either admixture of labelled cl from the leptite with cl from the granite or to the total derivation of groundwater chlorinity within the leptite followed by radiochemical ingrowth of36cl during subsequent groundwater residence within the granite the chloride derived from the leptite may be either matrix chloride or chloride from an external source which has had a long residence time within the leptite the implications of36cl in situ production for the estimation of groundwater residence times and for the geochemical evolution of groundwater chlorinity are discussed

velocity depth modelling using reflection and refraction data recorded in the central eromanga basin queensland australia abstract seismic refraction recordings along a line extending from mt howitt no 1 well to eromanga in southwest queensland over the eromanga and cooper basin sediments revealed two intra basement refractors not recorded by coincident reflection profiling these refractors were recorded at 3 5 km and 5 0 km depth between the basin basement unconformity at 2 4 km depth and a low velocity zone at about 8 0 km depth precise modelling of the refracted first arrival times showed that the basin structure and faults seen on the reflection profile extended into basement to at least 5 5 km depth with increasing displacement on the faults with depth causing lateral variation of structure and velocity a feature of the seismic refraction data in this region is a series of up to five multiples which can be observed from 10 km to at least 40 km distance travel time characteristics indicate that these multiples are waves refracted within basement and multiply reflected at the surface travel time modelling of the refracted first arrivals multiples and two way reflection times provides a tight constraint on velocity and structure to a depth of about 5 5 km

sources of chloride and implications for 36cl dating of old groundwater southwestern great artesian basin australia we investigate the relative importance of a number of processes that affect cl and 36cl distribution in the southwestern flow systems of the great artesian basin australia to provide more precise estimates of age and flow and recharge rates in situ production of 36cl secular variations in the rate of production of 36cl and its subsequent fallout as well as rates of diffusion of stable cl from adjacent aquitards mask the interpretation of rates of decay of 36cl cl along hydraulic gradients and can preclude estimating absolute groundwater ages however mean flow velocities calculated from absolute cl concentrations are 0 24 0 03 m yr and are a more reliable parameter than calculated ages because fewer assumptions and approximations are required recharge rates to the main cadna owie formation and algebuckina sandstone aquifer of the great artesian basin estimated from cl mass balance in the unconfined aquifers are 0 16 0 08 mm yr and were probably up to a factor of 3 higher 30 kyr ago as indicated by decreasing cl and 18o concentrations along the head gradient

differences in groundwater and chloride residence times in saline groundwater the barwon river catchment of southeast australia abstract the residence times of groundwater and chloride and the processes contributing to the development of saline total dissolved solids tds up to 45 379 mg l groundwater within the barwon river catchment of southeast australia were investigated using major ion stable isotope 18 o 2 h and 13 c and radioactive isotope 3 h 14 c 36 cl geochemistry the elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite silicate and calcite minerals groundwater residence times estimated from 14 c vary from modern to 20 ka for groundwater with lower 14 c activities the estimated residence times vary significantly depending on the assumed flow model and the 14 c activity of recharge chloride residence times downgradient of lake murdeduke a saline through flow lake in the centre of the catchment are greater than the corresponding groundwater residence times due to the recycling of cl within the lake precise estimates of chloride residence time could not be determined using 36 cl due to r 36 cl in precipitation being lower than that of groundwater this is most likely due to r 36 cl values in rainfall having been higher in the past than they are at present due to climate variability 18 o 2 h and 13 c values also suggest that the region has experienced increasingly more evaporative conditions with time the results of this study demonstrate that while cl is a useful tracer of hydrological processes it must be applied carefully in arid and semi arid regions of the world in particular recharge rates calculated using chloride mass balance may be underestimated where recycling of cl has occurred

the australian central eromanga basin project an introduction abstract the australian bureau of mineral resources is carrying out a major multidisciplinary program of geological and geophysical studies in southwestern queensland in cooperation with the geological survey of queensland the project is aimed at providing information on the regional structure and depositional history of the central eromanga basin and the underlying adavale cooper and galilee basins the information being obtained is particularly relevant to a better understanding of the petroleum prospectivity of the area the program includes geophysical surveys involving 1400 km of new six fold cdp seismic reflection coverage on regional traverses up to 400 km long crossing the main structural elements of the area gravity measurements along all new seismic reflection traverses refraction surveys along two major east west and north south traverses and magnetotelluric soundings along the same major east west traverse landsat imagery studies are providing new perspective on many regional structures when used in conjunction with seismic and gravity information wireline logs and synthetic seismograms are being used with the new seismic data to re examine stratigraphic correlations palynologic and lithologic studies are underway to assist in determining depositional environments source rock maturation hydrological and geochemical studies are providing information on the generation and migration of hydrocarbons a significant feature of the program is the extension of the recording time of all new reflection data to 20 s to obtain good quality deep crustal reflection information comparable to that obtained on cocorp programs in the united states the reflection data is being interpreted with the refraction gravity and magnetotelluric data to investigate the relationship of deep crustal and upper mantle features to the sedimentary basins in the central eromanga basin area

a new precipitation weighted method for determining the meteoric water line for hydrological applications demonstrated using australian and global gnip data summary the relationship between 2h and 18o in precipitation at a site known as the local meteoric water line lmwl is normally defined using an ordinary least squares regression olsr which gives equal weighting to all data points regardless of the precipitation amount they represent however smaller precipitation amounts are more likely to have a lower d excess due to re evaporation of raindrops below the cloud base or biases in the sampling method in this paper we present an equation for a precipitation amount weighted least squares regression pwlsr that will correct these biases for use in groundwater and surface hydrology applications new lmwl equations are presented for australian sites in the global network of isotopes in precipitation gnip where the pwlsr consistently produces a lmwl with a larger gradient than the olsr perth and alice springs exhibit the largest change in slope this is consistent with the higher frequency of small monthly precipitation amounts with low d excess values occurring at these sites in summer for perth and throughout the year for alice springs the pwlsr method was also applied to 288 stations in the gnip data base n 36 and the difference between the slopes of the lmwls a slopepwlsr slopeolsr calculated for these stations the mean change in slope a was 0 12 with 56 of sites showing an increase in slope or positive a value and 44 having a decrease in slope or negative a sites with mediterranean climates showed the greatest increase in slope the magnitude of the change in slope followed some general trends showing a positive correlation with average 2h and 18o composition and rainfall variability and negative correlation with period of record n

stress shear deformation and micromorphological clay orientation a synthesis of various concepts summary microscopic oriented clay bodies known as plasma separations to soil micromorphologists show various degrees of symmetry and regularity in their patterns they could be regarded as sensitive and reliable indicators of stress strain regime of a soil empirical and experimental evidence signifies the importance of stress specifically that generated by in situ swelling in the genesis of plasmic fabrics hitherto most work in this field is confined to geometric characterization with limited attempts to dynamic interpretations of their origin this paper enlists appropriate concepts in soil mechanics structural geology and agricultural engineering to interpret the possible stress strain components that rearrange fabric units into plasma separations some pertinent concepts including physico chemical behaviour of the clay water system shrink swell phenomenon stress strain deformation and failure of soil are employed to explain the origin of plasmic fabrics by mechanical principles a conceptual model is suggested to synthesize the conditions changes and consequences related to the formation of plasmic fabrics strongly developed plasma separations in natural soils are attributed to the establishment of an anisotropic state of stress generated by in situ swelling in conjunction with the passive pressure of lateral confinement and vertical overburden the difference between the maximum and minimum principal stresses produces a deviatoric stress that can at certain stages of a shrink swell cycle exceed the shear strength of the soil the extra stress is relieved plastically by shear deformation which is manifested as the alignment of platy particles in domain configuration by rotation and translation along the shear planes soil mainly fails in compressive plastic mode along a large number of small shear planes which form the plasma separations the formation of different types of sepic plasmic fabrics is discussed in relation to the stress strain regimes of soils

low velocity zone reflections observed in geometrical shadows of refraction profiles summary a low velocity zone lvz shadow on a refraction profile may contain coherent energy if the lvz contains reflectors the corresponding pre critical reflection branches will lie within the geometrical shadow such energy is observed in data and can via inversion or synthetic seismogram modelling potentially provide information on the location and character of the main structural features those with significant reflectivity within the lvz

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

eocene paleosols on king george island maritime antarctica macromorphology micromorphology and mineralogy abstract we investigated the origin of reddish layers between basalt flows in an early eocene volcanic succession in king george island maritime antarctica previous studies in the area classified these layers as regolith surfaces baked zones and paleosols but the properties of these layers and the reasons for their classification are not clarified since the early eocene epoch was one of the warmest phases on earth during the cenozoic a proper investigation of these layers is crucial to obtain additional regional information about the paleoenvironment the focus of this study is on three profiles located in the admiralty bay on king george island they were classified as paleosols based on field micromorphological and mineralogical properties main soil forming processes identified by micromorphological analyses were clay neoformation pedo bioturbation and a weak redoximorphosis the occurrence of plant residues in all profiles was a reliable indicator that these soils formed a land surface during the early eocene abundant weathered volcanic glass and pyroclasts may indicate andosolization although the main diagnostic features for andosols which are the presence of nanocrystalline minerals and organic matter accumulation were not detected or only in small amounts respectively the long term burial of the paleosol could be a reason for lacking of these diagnostic features clay minerals associated with moderately weathered volcanic soils smectite were detected in the x ray diffraction analysis a predominantly reddish colour of most of the soil horizons is given by hematite confirmed by the determination of pedogenic oxides nevertheless rubification was not solely a result of pedogenesis but also of reddening of oxyhydroxides by dehydration during diagenesis other diagenetic processes were burial compaction loss of organic matter and induration in the horizons directly buried by a basalt flow voids were filled by zeolite crystals an effect related to lava cooling another possible diagenetic effect was the geochemical rejuvenation and homogenization of the profiles despite the occurrence of these features the results are in agreement with previous studies indicating a humid temperate paleoclimate for king george island during the early eocene

early tectonic evolution of the thomson orogen in queensland inferred from constrained magnetic and gravity data abstract the crustal architecture as well as the kinematic evolution of the thomson orogen in queensland is poorly resolved because the region is concealed under thick phanerozoic sedimentary basins and the basement geology is known from limited drill holes combined potential field and seismic interpretation indicates that the thomson orogen is characterized by prominent regional ne and nw trending structural grain defined by long wavelength and low amplitude geophysical anomalies the smooth magnetic signature is interpreted to reflect deeply buried source bodies in the mid to lower crust short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions they appear to be focused along major fault zones that might have controlled the locus for magmatism the eastern thomson orogen is characterized by a prominent ne structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs the western thomson orogen consists of a series of nw trending structures interpreted to reflect reverse faults sedimentation and basin development are interpreted to have initiated in the neoproterozoic to early cambrian during e w to ene wsw extension possibly related to the rodinia break up this extensional event was followed by late cambrian shortening recorded in the maneroo platform and the diamantina river domain which possibly correlates with the delamerian orogeny renewed deposition and volcanism occurred during the ordovician and may have continued until late silurian resulting in thinned proterozoic basement crust and extensive basin systems that formed in a distal continental back arc environment our interpretation places the thomson orogen to the west of the neoproterozoic passive margin preserved in the anakie inlier the region is likely to represent the internal extensional architecture during the rodinia break up that has been subsequently extensively modified by multiple extensional basin forming events and transient episodes of crustal shortening and basin inversion

chlorine 36 dating of very old groundwater 1 the great artesian basin australia chlorine 36 has many advantages as a dating tool for very old groundwater these advantages include a suitable half life 3 01 x 10 sup 5 years simple geochemistry conservative behavior in groundwater and a general absence of subsurface sources at levels comparable to the atmospheric input recent advances in tandem accelerator mass spectrometry have permitted the analysis of sup 36 cl at low abundance expected following residence in the subsurface for 10 sup 6 years or more in order to test the suitability of sup 36 cl for dating very old groundwater the sup 36 cl cl ratios of 26 groundwater samples from the great artesian basin of australia have been measured groundwater ages calculated from the sup 36 cl data compare favorably with ages computed independently from hydrodynamic simulations

polygenetic vertisols of the purna valley of central india the purna valley a part of the payanghat plain is an oval basin covering an area of about 1 9 mha in central india the soils are deep calcareous clayey and very dark greyish brown to dark brown in colour and meet criteria for the vertisols order of soil taxonomy cracks extend down to the slickenside zones in soils of the northeastern part of the valley but cut through the slickenside zones in the soils of the southwestern part soils of the southwestern part are strongly alkaline with exchangeable sodium percentages esps of 5 26 whereas those of the northeastern part are moderately alkaline and have esp values 5 despite their similar coefficients of linear extensibility volumetric shrinkage potentials clay contents and amounts of fine clay smectite the plasmic fabric of the slickenside horizons in soils of the northeastern part is porostriated whereas in soils of the southwestern part it is stipple speckled to mosaic speckled indicating weak plasma separation the soils have both pedogenic and nonpedogenic calcium carbonate but those of the southwestern part have more pedogenic carbonate than those in the northeastern part the semiarid climate removes ca2 ions from the soil solution by precipitating carbonate and also causes the esp and sodium absorption ratio to increase with depth the lack of soil water in soils of the southwestern area is thought to be the reason for weak swelling of smectite for larger amounts of pedogenic carbonate and for cracks cutting through the slickenside zones the vertisols of the southwestern part of the of the purna valley are therefore polygenetic because they exhibit distinctly different soil properties resulting from increasing aridity in the valley during the late holocene

geothermal profile and crust mantle transition beneath east central queensland volcanology xenolith petrology and seismic data geothermobarometry of garnet granulite and garnet websterite xenoliths in basalts from numerous localities in east central queensland gives p t points that fall along the geotherm previously defined for southeastern australia this elevated geotherm is ascribed to the advective transport of heat by tertiary recent magmas ponded at the crust mantle boundary the lower crust in this region consists dominantly of mafic granulites representing frozen basaltic melts and cumulates spinel lherzolite becomes a dominant rock type at depths of ca 30 km and persists interlayered with pyroxenites to depths of ca 55 km seismic reflection profiles show a layered lower crust between depths of 20 and 36 km depth the lithologically defined crust mantle boundary lies within this zone at least 6 km above the seismically defined moho this interpretation is consistent with the observed velocity vp gradient downward through the layered zone the constructed geotherm implies that the bottom of the lithosphere beneath eastern australia is shallower than ca 100 km this makes it unlikely that the diamonds of eastern australia are derived from local intrusions unless these are 200 ma old

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

can mima like mounds be vertisol relics far north region of cameroon chad basin abstract non anthropogenic earth mounds defined as mima like mounds in this study have recently been observed in non carbonate watersheds along the sudano sahelian belt in the chad basin in the diamare piedmont northern cameroon they are particularly well developed within stream networks in less eroded areas they occur as whaleback flattened morphologies or even as buried features all these shapes are composed of clay rich sediment associated with high proportions of secondary carbonate nodules and fe mn micro nodules their soil structure is prismatic to massive and vertical cracks are observed locally grain size distributions emphasize the clay rich nature of the sediment with average clay contents of 32 12 8 n 186 which is significantly higher than the clay content in the adjacent sediments in the landscape mean 10 4 n 21 moreover high proportions of smectite characterize the soil with average contents of 34 7 n 25 at the micro scale the groundmass has a cross striated b fabric with embedded smooth subangular quartz and feldspar grains of the silt size fraction all the characteristics point to altered vertic properties in the clay rich sediment composing the mima like mounds mima like mounds are thus interpreted as degraded vertisols compared to present day vertisols occurring in the piedmont mima like mounds are located upstream it is thus proposed that the vertisol areas were more extensive during a former and wetter period than the present day subsequent changing climatic conditions increased erosion revealing the gilgai micro relief by preferential erosion in micro lows rather than in micro highs mima like mounds of the chad basin might thus result from pedogenesis combined with later erosion these local processes can be inherited from regional climatic variations during the late pleistocene holocene and likely be related to the african humid period

deep crustal reflection results from the central eromanga basin australia abstract from 1980 to 1982 deep seismic reflection profiles were recorded across the central eromanga basin in eastern australia to study the regional structure stratigraphy and geological history of the eromanga basin and infra basins the reflection data were recorded to 20 s to obtain additional information on the nature and structure of the crust below the sediments and their relationship to the development of the basins the seismic sections show good quality reflections from the deep crust as well as from the sedimentary layers based on the character strength coherence continuity and spatial distribution of the reflections the sections can be divided into four zones the tope zone between 0 and 2 5 s shows fairly uniform coherent and continuous events which correlate with the mesozoic and late palaeozoic sediments the zone from 2 5 to 8 s 4 to 22 km does not show any primary reflections and is interpreted as the highly deformed metasedimentary and metavolcanic rocks of the early palaeozoic thomson orogen underlying the sediments without any recognisable reflection or diffraction patterns in this zone it is difficult to say whether the faulting and folding observed in the sediments extend into the upper crustal basement the deeper zone of numerous reflection segments between 8 and 12 5 s 22 to 36 km is interpreted as thin laminae of alternating low and high velocity intermediate and basic rocks and correlates with the lower crust bounded by refraction velocity discontinuities the lowest zone of no reflections below 12 5 s corresponds with the upper mantle the reflection character and thickness as well as the refraction velocity structure of the crust under the central eromanga basin area are significantly different from those of the precambrian crust under the georgina basin to the northwest it is proposed that the crust under the eromanga basin is extensionally attenuated crust which had been intruded by sills of basaltic melt from the underlying asthenosphere

hydrogeochemical and isotopic constraints on the origins of dryland salinity murray basin victoria australia abstract combined hydrogeological and hydrogeochemical data allow flow systems and the origins of solutes in the honeysuckle creek area of the southeastern murray basin which is an area affected by dryland salinity to be constrained recharge occurs both on the uplands that are composed of fractured violet town volcanic rocks and the riverine plain that comprises sediments of the shepparton and coonambidgal formations groundwater from the violet town volcanics has low salinity 20 mmol l groundwater has intermediate cl br ratios 600 1000 which indicate that the high salinities do not simply result from halite dissolution rather mixing of groundwater homogenises cl br ratios and evaporation as a consequence of a shallow water table is the dominant process that increases salinity oxygen and h isotopes also indicate that mixing and evaporation have occurred these results indicate that land use over the whole region not just the uplands needs to be considered in any salinity management plans additionally future development of salinity is controlled by depth to the water table on the plains and the efficiency of recharge rather than by salt stores halite or brines in the unsaturated zone

decoupling of solutes and water in regional groundwater systems the murray basin australia documenting the origins residence times and movement of groundwater and the solutes that it contains is critical to understanding hydrogeological systems this study uses cl mass balance to determine the cl accession time i e the time required for cl to accumulate and cl to estimate the residence times of cl in the victorian portion of the murray basin southeast australia much of the murray basin contains saline groundwater with total dissolved solids tds concentrations commonly 14 000 mg l and locally up to 300 000 mg l the total mass of cl stored in the victorian portion of the basin is estimated as between 12 400 and 47 100 mt using present day rainfall totals and cl concentrations in rainfall the cl accession time is 170 to 650 ka aquifer thicknesses and groundwater salinity both increase westwards in this part of the murray basin consequently the cl accession times increase westward from 0 1 0 6 ka to 286 1080 ka by contrast c activities of the majority of the groundwater are 2 pmc and commonly much higher notwithstanding the difficulty in correcting c residence times the widespread occurrence of groundwater with above background c activities implies that groundwater residence times are generally 30 ka which is substantially shorter than the cl accession times rcl the ratio of cl to total cl 10 values of the groundwater are between 20 and 230 and are uncorrelated with cl concentrations while it is difficult to determine precise cl residence times the observation that the rcl values are significantly higher than those that represent secular equilibrium with the aquifer matrix rcl of 5 to 10 indicates that they are up to a few hundred thousand years and similar to the cl accession times the rcl values together with the geology of the aquifers stable isotope ratios and major ion geochemistry precludes halite dissolution incorporation of connate water or the long term diffusion of cl from clays as mechanisms of producing the elevated cl concentrations rather it is most likely that the high cl concentrations result from recycling of solutes in saline lakes and playas or repeated cycles of evapotranspiration in the unsaturated zone

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

constraining groundwater flow residence times inter aquifer mixing and aquifer properties using environmental isotopes in the southeast murray basin australia environmental isotopes particularly d 18 o d 2 h and d 13 c values 87 sr 86 sr ratios and a 14 c constrain geochemical processes recharge distribution and rates and inter aquifer mixing in the riverine province of the southern murray basin due to methanogenesis and the variable d 13 c values of matrix calcite d 13 c

clay mineralogy as a crucial factor in badland hillslope processes abstract comprehensive and important work has been done in understanding badland processes on both the big scale and more recently on smaller scale in order to understand the subtle differences between sites however most studies lack important information regarding clay mineralogy and their importance for weathering processes type and rate of weathering depend on material physico chemical properties climatic regimes and slope characteristics as weathering progresses the surface conditions change influencing erosion processes usually badland lithologies are reported as sodium rich highly dispersive materials but that is not invariably true the primary objective of this study is to show that clay minerals have an important role in defining surface and subsurface processes on badland hillslopes field studies conducted in dinosaur park badlands alberta canada chinguacousy badlands ontario canada and sestino badlands tuscany italy have shown that there are two dominant clay rich lithologies smectite rich and smectite poor mudrocks different surface crust and weathering profiles were observed on smectite rich mudrocks during two field years with distinct precipitation inputs after a dry fall winter season the popcorn surface was very well developed 2 3 cm the subsurface layer 10 15 cm thick overlaid the layer of smaller shards followed by the unweathered material after a very wet fall winter season the surface layer was denser and thinner 0 5 cm with wider cracks and a thin subsurface layer attached to the crust weathering profiles on smectite poor lithologies did not show any differences with variable climatic conditions a thin surface layer was composed of soft thin and small 0 5 0 3 0 1 cm shards a layer of larger shards overlying unweathered material was beneath it in order to better understand the described occurrences badland materials were monitored in controlled laboratory conditions during an incremental weathering experiment six samples of each material were subjected to 10 cycles of simulated rainfall which duration ranged 10 60 min very short rainfalls 10 20 min can cause swelling of clay minerals in smectite rich materials and formation of popcorn surface during drying periods during subsequent wetting drying periods the crust becomes flatter and denser and desiccation cracks become wider and deeper samples subjected to 50 and 60 min of rainfall showed maximum swelling after only one cycle of rainfall after this swift swelling samples became unstable and dispersive during subsequent wetting dispersion became dominant resulting in flatter surfaces thinner crust and narrower desiccation cracks smectite poor mudrocks appeared to be resistant to variable wetting and drying large shards broke down into smaller due to differential swelling of illite and chlorite once they were reduced to tiny flaky shards the surface became compacted the surface cracks served as the initial pathways for sediment and water movement knowing if the material is smectite rich or smectite poor can help in prediction of processes and the erosion rates the amount intensity and duration of precipitation will determine not only the rate of weathering but also the type of the weathered surface on smectite rich surfaces smectite poor materials appear to be more resistant to change in precipitation

micromorphology of diamicton affected by iceberg keel scouring scoresby sund east greenland this research was primarily funded by the university of brighton s rising stars initiative and the school of environment and technology research investment fund with supplementary funds awarded by the quaternary research association the funding sources had no involvement in study design in collection analysis and interpretation of data in the writing of the article and in the decision to submit the article for publication

mid crustal detachments controlling basin deformation ramp synforms in southwestern queensland abstract deep seismic data from the adavale basin region of southwestern queensland suggest that westward carboniferous movement of the upper crust over mid crustal ramps was responsible for the present day geometry of two synforms containing devonian sediments we interpret the troughs as hanging wall synforms formed by sub vertical simple shear within the upper crust during down dip movement over the ramp one of these structures the quilpie trough in the southern adavale basin is an asymmetric trough interpreted to be an extensional ramp syncline it overlies a west dipping ramp in the boundary between the seismically non reflective upper crust and the seismically reflective lower crust formation of this basin by the relative movement of the upper crustal thomson fold belt over the mid crustal ramp is postulated the significant asymmetry of the trough suggests that lower crustal extension by pure shear may have occurred during upper crustal translation the other structure the westgate trough contains two palaeozoic sequences we propose that the devonian lower sequence is in a ramp syncline formed by folding of the sediments in a conveyor belt style mechanism during a translation of the upper crust the upper sequence is interpreted as a ramp basin in which sediments were deposited in the synform as it developed deep seismic reflection data from the central eromanga basin region indicate that relative horizontal translation can occur between the upper and lower crust on mid crustal detachments the geometry of the synforms suggests that above these detachments crustal deformation has a sub vertical simple shear style whereas the lower crust below the detachments seems to deform in a pure shear style recognition of relative movement of tens of kilometres on mid crustal detachments is important for our understanding of basin geometry and development in the central eromanga basin

determination of earthquake focal mechanisms and crustal structure in eastern australia using surface waves abstract the surface waves from two medium sized m 5 5 earthquakes in southeast australia 1966 mt hotham and 1982 wonnangatta were examined to determine average s wave crustal structure for the region and the focal mechanisms of the two earthquakes the s wave models were determined from an analysis of the group velocities of the rayleigh waves for all paths a two layer crust overlying a moho at about 40 km is required to fit the observations in the upper layer down to about 25 km the velocity gradients are very small and the s wave velocities are in the range 3 4 3 6 km s in the lower crust the s wave velocities increase gradually to about 4 6 km s at the moho where the velocity gradients are again very small the region where the s wave velocities increase significantly with depth corresponds to the region of the lower crust which generates strong seismic reflections mathur 1983 the thin crust postulated beneath bass strait and tasmania johnson 1973 is not substantiated by these data and a crustal thickness of about 40 km is also required for this region for the longer profiles 1800 km to the north and northwest of the earthquakes the velocity step at the moho is smaller than for the shorter profiles 700 km however because the surface waves are less dispersed for the shorter profiles the resolution is poorer and the models less reliable for the 1982 wonnangatta earthquake the surface wave synthetics from a focal mechanism similar to that obtained by denham et al 1985 fit the observations at five regional stations very well and confirm the nw se compressive stress regime found by other workers however for the 1966 mt hotham earthquake the surface wave synthetics generated from the normal faulting solution which was obtained from an analysis of p wave first motions denham et al 1985 do not agree with the rayleigh wave trains observed at australian stations rather the surface wave observations support a thrust fault type mechanism with the pressure axis having a similar direction to that obtained from the 1982 wonnangatta earthquake and other earthquakes in the region

the mid crustal horizon under the eromanga basin eastern australia abstract long line explosion seismic recordings indicate that a major mid crustal p wave velocity increase exists under the eromanga basin which contrasts the crust of this region from its neighbouring tectonic provinces the velocity increase is shown to be a regional feature and to correspond to the upper boundary of a zone of discontinuous seismic reflections characteristic of the lower crust the velocity increase of 0 35 0 6 km s occurs over a small depth range at an average depth of 24 km this velocity gradient produces conspicuous wide angle reflections at distances greater than 60 km from the shot point the seismic data present the clearest evidence to date of the existence of a major mid crustal horizon in continental australia a feature not prominent in other cratonic provinces which have been investigated in detail the velocity in the lower crust below the horizon is 6 7 7 0 km s the horizon represents a boundary between the upper and lower crust which could imply a different tectonic history for these two zones

helium 4 characteristics of groundwaters from central australia comparative chronology with chlorine 36 and carbon 14 dating techniques summary helium isotope and concentration characteristics were determined for a suite of groundwater samples from the amadeus basin in central australia two study areas include a wellfield south of alice springs and the dune plains and mututjulu aquifers near uluru measurements of 36cl cl and 14c on the same sample suite enable us to assess the relative applicability of the three groundwater chronometers over a range of anticipated groundwater residence times ages and to investigate possible causes of discordant ages derived from the different groundwater dating techniques results from the analyses of 39 groundwater samples reveal helium 4 4he concentrations that range from 0 80 to 98 8 10 7 cm3 stp g 1 h2o in the alice springs samples and from 0 47 to 65 6 10 7 cm3 stp g 1 h2o in the uluru samples 4he concentrations yield uncorrected groundwater residence times i e time since recharge of between modern to 2500 ka near alice springs and modern to 1600 ka near uluru assuming an effective porosity of 20 and uranium and thorium contents of 1 7 and 6 1 ppm respectively 36cl cl ratios on the same samples range from 93 to 158 10 15 near alice springs and from 80 to 335 10 15 near uluru representing groundwater residence times near alice springs from modern to 200 ka and from modern to 300 ka near uluru percent modern carbon pmc on the same samples ranged from 64 9 to 12 5 pmc near alice springs and from 93 5 to 30 ka for the amadeus basin groundwater samples the 4he method uncorrected over estimates groundwater residence time compared to 36cl and 14c techniques this implies the presence of an extraneous he component or basal flux of he j0 to reconcile groundwater 4he and 14c residence times it is necessary to adopt j0 values between 0 and 30 10 8 cm3 stp he cm 2 a 1 which supplements in situ produced he within the aquifer adoption of j0 values over this range lowers 4he residence times relative to 36cl and produces closer agreement between the 4he and 14c chronometers the extraneous he component basal flux in amadeus basin samples is dominated by radiogenic crustal 4he without a detectable amount of mantle derived 3he we conclude that the stable tectonic regime albeit with the presence of major faults within the basin inhibits the input of mantle volatiles to the groundwater system so that in this region diffusion is the dominant transport mechanism for he in the crust

source mechanisms of moderate size earthquakes and stress orientation in mid plate south america summary fault plane solutions of six mid plate earthquakes with magnitudes ranging from 4 8 to 5 5 mb were determined using p wave first motion data and the relative amplitudes of short period teleseismic depth phases pp and sp these results together with previous studies show a predominance of reverse and strike slip faulting indicating horizontal compressional stresses in mid plate south america the orientation of the p axes however is not uniform in western and southwestern brazil the p axes are oriented approximately e w probably due to the nazca south america plate convergence in eastern brazil the direction of the p axes show more scatter but an average e w direction is consistent with the available data on the contrary in northern brazil the p axes of two events in the amazon basin trend approximately n s a direction perpendicular to the direction of absolute plate motion as well as to the relative plate motions nazca south america and south america africa

a classification of soil microfabrics abstract the definitions of some terms to describe the distribution pattern of micromorphological components are given and discussed five existing schemes for the characterization of related distribution patterns in soil micromorphology are summarized in a table compared and evaluated the replacement of the terms related distribution pattern by microfabric and fabric sequence by fabric groups are suggested a scheme based on existing terminology and augmented with new terms to describe the hitherto neglected poorly structured soils is proposed four fabric groups are drawn from existing terminology namely iunctic and chlamydic for coarse matrix and fragmic and matrigranic for fine matrix fabrics two new fabric groups namely planvic and equanvic are proposed to describe poorly structured soils according to the shapes and volumes of voids the six fabric groups are arranged in a synoptic diagram to illustrate a comprehensive classification of soil microfabrics a dichotomous key to aid fabric identification is provided use of standardized short forms for fabric names is suggested

groundwater residence time and palaeohydrology in the otway basin south australia 2h 18o and 14c data stable isotopes 2h 18o and 13c and radiocarbon 14c have been used in conjunction with chemical data to evaluate recharge mechanisms groundwater residence time and palaeohydrology within the confined dilwyn sand aquifer in the gambier embayment of the otway basin this aquifer does not receive recharge down gradient of the hydraulic hinge line and data have been interpreted along two discrete flow lines the mean residence time of groundwater determined by 14c in the confined aquifer from the hydraulic hinge position to the sea a distance of about 50 km along an inferred flow path is approximately 12 800 years the corresponding hydraulic travel time calculated from darcy s law is approximately 49 000 years the apparent discrepancy may be a result of eustatic sea level lowering during the last glacial because the groundwater system is hydraulically connected to the sea lower sea level would result in increased gradients and a decrease in groundwater residence time variations in stable isotopic composition along flow lines suggest a number of recharge mechanisms stable isotope data indicate progressive depletion of 2h and 18o in the groundwaters over the past 30 000 years groundwaters older than about 10 000 years b p were recharged either during a cooler climate climatic regime lower precipitation evapotranspiration and temperature and or the vapour source s had travelled over greater continental mass than those recharged over the past 10 000 years lower chloride concentrations in some of the older groundwaters indicate lower evapotranspiration rates in the recharge areas before 10 000 years ago

deep seismic reflection data suggest major compressional deformation of the crust in the central eromanga basin area during the mid carboniferous abstract scismic reflection data recorded to 20 s in the central eromanga basin area show good quality reflections from the deep crust as well as the shallow sedimentary layers the data along a 270 km long east west traverse indicate warping and low angle faulting in the lower crust which is compatible with asymmetric folding in the devonian sediments this interpretation is consistent with a major compressional deformation of the crust in this area during the mid carboniferous kanimblan orogeny

structural styles and basin evolution in eromanga region eastern australia the eromanga region of eastern australia has undergone at least four major tectonic cycles the results of which are recognized in the structures seen on seismic sections the late proterozoic early phanerozoic cycle ended with the formation of the thomson foldbelt which forms basement in the region the subsequent reactivations of the fault systems within this basement and deeper lithosphere have produced the structural styles now important as exploration targets most reactivations are interpreted as resulting from crustal shortening events affecting sedimentary strata deposited in an epicontinental shallow water environment with small strike slip adjustments affecting some structures the dominant style of deformation evident from the seismic sections is that seen across high angle thrust faults in other parts of the world with the amount of overthrusting being comparatively small generally the maximum throw on faults in the devonian strata can be measured in thousands of meters whereas those in the permian triassic and jurassic cretaceous strata are a few hundred meters at most the devonian sequences of the adavale basin and associated troughs were deformed during two carboniferous events the first with crustal shortening in a north south direction and the second in an east west direction associated small strike slip movements were accommodated along a number of faults including the warrego grenfield warbreccan and canaway faults southwest of our study area in the permian triassic cooper basin other workers have interpreted a northwest southeast crustal shortening event during the late permian and another wrench induced northeast southwest crustal shortening during the triassic during the middle tertiary a crustal shortening event regionally affected the jurassic cretaceous eromanga basin sequence and older sedimentary rocks this event is seen pro inently in a deformation zone between the canaway and cunnavalla faults with the direction of crustal shortening being northeast southwest small strike slip movements are interpreted as partially decoupling events from neighboring provinces the adavale basin and cheepie shelf to the east and southeast and the cooper basin and warbreccan dome to the southwest and northwest respectively in this partial decoupling the canaway cunnavalla warrego and warbreccan faults are interpreted as playing an important role the basin modifying tectonic episodes within the lithosphere control structural style these relatively small scale events have resulted in structures that provide attractive petroleum prospects

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

equilibration temperatures and elastic wave velocities for upper mantle rocks from eastern australia implications for the interpretation of seismological models abstract this study integrates available geological geophysical and petrophysical data for deep seated lithologies which occur beneath eastern australia and which are accessible at the surface as xenoliths in basaltic host rocks it is shown that spinel lherzolite mantle wall rock occurs over a depth range commencing at about 30 km and extending to about 55 km this represents a temperature range of 850 1000 c acoustic wave velocity measurements were carried out on three types of spinel lherzolites and one mantle derived garnet pyroxenite the acoustic velocities range from 7 7 to 7 9 km s 1 for the pressure and temperature conditions beneath eastern australia derived from xenolith geothermobarometry these values demonstrate that the use of dunite as a generalised mantle rock results in overestimation of model mantle vp especially when used with a standard continental model geotherm the measured spinel lherzolites also show variable anisotropy in acoustic wave velocity 5 8 for these moderately foliated samples it is demonstrated that by using a combination of the measured acoustic velocities and single crystal elasticity data for constituent minerals it is possible to interpolate vp for a wide modal range of rock types relevant to the lower crust and upper mantle triangular grids which allow graphical estimation of vp for spinel lherzolites garnet lherzolites and garnet pyroxenites have been constructed the petrologic and petrophysical results are used to constrain models of the lower crust and upper mantle profiles based on available seismic data for eastern australia

recent and old groundwater in the niebla posadas regional aquifer southern spain implications for its management summary the niebla posadas np aquifer in southern spain is one of the main groundwater sources for the lower guadalquivir valley a semiarid region supporting an important population agriculture and industry to contribute to the understanding of this aquifer the assessment of sustainable use of groundwater the residence time of groundwater in the np aquifer has been estimated using 3 h 14 c and 36 cl along the flow paths recharged groundwater mixes with nacl type waters and undergoes calcite dissolution and is further modified by cation exchange ca na consequently the water loses most of its calcium and the residual 13 c dic in the groundwater is isotopically enriched further modifications take place along the flow path in deeper zones where depleted 13 c dic values are overprinted due to so 4 2 and iron oxide reduction triggered by the presence of organic matter dating with 3 h 14 c and 36 cl has allowed the differentiation of several zones recharge zone 30 ky an apparent link between the tectonic structure and the groundwater residence time zonation can be established regional faults clearly separates deep zone 1 from the distinctly older age 30 ky deep zone 2 from the estimated residence times two groundwater areas of different behavior can be differentiated within the aquifer

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

new seismic reflection results in the central eromanga basin queensland australia the key to understanding its tectonic evolution abstract regional seismic traverses were recorded from 1980 to 1982 by the bureau of mineral resources geology and geophysics as part of a major multidisciplinary program aimed at studying the geological evolution of the central eromanga basin area and its petroleum potential six fold cdp reflection data were obtained to 20 s reflection time on 1400 km of traverses up to 400 km long crossing the main structural features of the area additional seismic reflection information to complement the study was obtained from 2300 km of older mainly single coverage analogue data which was transcribed to digital format and reprocessed the central eromanga basin area has a complex history and contains four phanerozoic potentially hydrocarbon bearing basins each separated by unconformities i e the devonian adavale basin the late carboniferous to triassic cooper and galilee basins and the jurassic cretaceous eromanga basin the seismic results are being interpreted with the aid of synthetic seismograms from key wells to provide information on the extent nature and relationship of these basins the quality of the reflection data from the devonian sequence is generally very good and these data are proving to be most useful in the study thick devonian sediments were deposited over a wide area well beyond the present confines of the adavale basin and its associated troughs intensive folding and faulting accompanied by major basement uplift including the canaway ridge in the centre of the area took place during the mid carboniferous kanimblan orogeny this was followed by a period of erosion which truncated the devonian sequence and resulted in separation of the adavale basin from the other devonian troughs in the area the preliminary seismic results give some indication also of the extent and nature of the cooper and galilee basins sediments these are generally thin in the central area and thicken to the west and east respectively where coal measures produce good lithologic and seismic markers gentle folding and minor faulting apparent in the seismic reflection sections from the overlying eromanga basin sequence have resulted mainly from basement uplift and minor movements along pre existing faults continuing into the late mid tertiary and possibly from some compaction of the thick sedimentary section the seismic information is also assisting in studies of the petroleum potential of the area providing information particularly on structuring timing and depth of burial of the prospective sediments

crustal heterogeneity in south australia earthquake evidence summary lateral velocity variations in the south australian crust have been mapped using the relatively new technique of seismic tomography the input data comprised p1 travel times from 1340 local earthquakes recorded on the south australian seismic network during the period 1978 1983 to reduce errors in the earthquake locations focal depths and origin times we used an averaging technique of dividing the area under consideration into a series of overlapping cylindrical cells all earthquakes and seismic stations were assigned to the centre of the nearest cell travel times between all centres were computed by averaging over all relevant cell pairs after first scaling all travel times by a factor equal to the distance between cell centres divided by the actual ray path length only ray paths appropriate to the p1 phase were considered starting with a first guess model based on the number of ray intersections with each cell the travel times were computed along all ray paths and compared with the observed averaged values the errors and residuals were back projected for each ray over all the chords along the ray and the average cell slowness adjusted in an iterative sense until the computed and observed travel times agreed within a specified error tolerance the areas with poor raypath coverage lack of earthquakes and or stations could not be imaged the area covered lies mostly within the adelaide geosyncline where there is believed to be a thick cover of proterozoic sediments the velocity image is of the upper 20 km of the crust so no direct correlation between the surface geology and the crustal velocity is to be expected results indicate a significant variation in crustal velocity from 5 9 to 6 5 km s 1 the velocities correlate remarkably with time terms computed in a separate study of moho refracted arrivals pn low time terms correspond to high crustal velocity and high time terms reflect anomalously low crustal velocity the residual component of the time terms can be explained in terms of variations in depth to the moho throughout the geosyncline of the order of 10 km the prominent features of the tomographic velocity map are a n s trending velocity low over the spencer gulf graben and a ridge of high velocity beneath the flinders ranges the velocity low can be associated with a region of low gravity aligned parallel to the torrens hinge zone which marks the western boundary of the geosyncline the northern end of the high velocity ridge coincides with a region of positive bouguer gravity teleseismic residuals from both earthquakes and nuclear explosions show a similar trend to the pn time terms and indicate lateral variability in crustal thickness and velocity a component of the residual must be attributed to mantle velocity inhomogeneity which extends to depths of 300 km

using 3h and 14c to constrain the degree of closed system dissolution of calcite in groundwater abstract this study uses 3h concentrations 14c activities a14c 87sr 86sr ratios and 13c values to constrain calcite dissolution in groundwater from the ovens catchment se australia taken in isolation the 13c values of dissolved organic c dic and 87sr 86sr ratios in the ovens groundwater imply that there has been significant calcite dissolution however the covariance of 3h and 14c and the calculated initial 14c activities a014c imply that most groundwater cannot have dissolved more than 20 of 14c free calcite under closed system conditions rather calcite dissolution must have been partially an open system process allowing 13c and 14c to re equilibrate with co2 in the unsaturated zone recognising that open system calcite dissolution has occurred is important for dating deeper groundwater that is removed from its recharge area in this and other basins the study is one of the first to use 14c and 3h to constrain the degree of calcite dissolution and illustrates that it is a valuable tool for assessing geochemical processes in recharge areas

explosion seismic determination of crustal structure beneath the adelaide geosyncline south australia abstract the structure of the earth s crust beneath the adelaide geosyncline south australia has been investigated over the last few decades using both earthquake and explosion seismic techniques these studies have led to the simple average model of a single homogeneous layer having a p wave velocity of 6 32 km s 1 and thickness of 38 km overlying a homogeneous mantle with a velocity of 8 05 km s 1 the only compelling evidence for crustal layering comes from two recent long range refraction profiles recorded along n s and perpendicular e w to the axis of the geosyncline using quarry blast sources head waves and wide angle reflections have been identified as originating from a mid crustal boundary separating an upper crust of velocity 5 94 km s 1 from a lower crust of velocity 6 42 km s 1 at a depth of 10 to 18 km the depth variation to this boundary and the corresponding moho topography were interpreted using an iterative ray tracing technique both discontinuities shallow towards the murray basin which flanks the geosyncline to the south east the crustal model obtained was further investigated by means of a synthetic aperture seismic array experiment carried out on the n s refraction profile at a source offset of 120 km recordings were made on a 21 element unreversed linear profile using digital seismographs spaced at 0 5 km intervals an accurate p 1 velocity of 5 88 km s 1 was obtained secondary p arrivals were studied with the aid of beam formers and tau p processors tentative reflections from within the crust and upper mantle were obtained however the variation in seismic waveform generated by different blasts was a definite drawback of the experiment prominent dipping reflectors and faults at depths of several kilometres have been observed in near normal incidence reflection surveys shot in porterozoic rocks just west of the adelaide geosyncline the reflectors may represent layering within the crystalline basement or they may relate to the rifting stage of basin development