strontium and carbon isotope constraints on carbonate solution interactions and inter aquifer mixing in groundwaters of the semi arid murray basin australia abstract strontium and carbon isotopes are used to study the effect of carbonate mineral dissolution and inter aquifer mixing on the chemical evolution of groundwater from the murray group limestone aquifer in semi arid se australia the 87 sr 86 sr ratio of groundwater evolves from 0 7097 at the basin margin to a less radiogenic value of 0 7084 about 250 km down gradient which is similar to the 87 sr 86 sr ratio of the aquifer carbonate matrix the concomitant increase in 13 c dic sr ca and mg ca ratios in the groundwater along a 250 km transect suggests that incongruent dissolution of high mg calcite controls the carbonate geochemistry in this aquifer further down gradient the groundwater is characterized by a relatively more radiogenic 87 sr 86 sr ratio caused by upward leakage and mixing with more radiogenic groundwater from the renmark group sand aquifer a mixing model using 87 sr 86 sr ratio suggests that the fraction of water that contribute to the murray group aquifer through upward leakage from underlying renmark group aquifer ranges from 15 to 85

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

estimating groundwater recharge in fractured rock from environmental 3h and 36cl clare valley south australia 1 vertical profiles of 3h and 36cl concentrations are obtained from piezometer nests installed in fractured metasedimentary aquifers in the clare valley south australia because 3h is lost during evapotranspiration with negligible fractionation while 36cl is retained within the soil comparison of 3h and 36cl concentrations allows estimation of the aquifer recharge rate an analytical solution for the transport of 3h and 36cl through planar parallel fractures is used to investigate the effect of variations in matrix porosity tortuosity fracture aperture fracture spacing and aquifer recharge rate on tracer profiles and then to reproduce observed profiles within piezometer nests while the measured distributions of these tracers are not able to constrain most model parameters they are able to tightly constrain the aquifer recharge rate the broad nature of the 36cl and 3h peaks measured at our sites is simulated using a constant fracture spacing lognormal distributions of fracture apertures and mean recharge rates of 60 75 mm yr 1

banktop responses to quaternary fluctuations in sea level recorded in periplatform sediments periplatform sediment from a 12 m core recovered from northwest providence channel bahamas contains a geochemical and paleontological record of sea surface temperatures ice volumes and the response of banktops to highstands of sea level a comparison of these data suggests that fluctuations of carbonate mineralogy in periplatform sediments result from fluctuations of sea level and from patterns of banktop sedimentation highstands of sea level that flood carbonate platforms are recorded in periplatfonn sediments as abrupt increases of exported sr rich aragonite derived from banktop orgiuiisms superposed on a background of sr poor aragonite pteropods and calcite foraminifera and coccoliths derived from planktonic sources the pulses of banktop sediment coincide with increases of water temperature determined from foraminiferal assemblages and with decreases in ratios of oxygen isotopes indicating decreased ice volume and rising sea level following these abrupt changes is a more gradual decline in bank derived sediment although paleotemperatures from foraminiferal assemblages and oxygen isotopic data clearly show that warm conditions and a highstand of sea level persist we suggest that this decrease of offbank transport is part of autocyclic sedimentation patterns of shallow water carbonate environments offbank transport is restricted as reefs sand shoals and islands reach sea level also green algal production may decline because progradation of tidal flats decreases lagoon area and the hydrologic and ecologic conditions change as lagoons are filled

anatomy of the buried burdekin river channel across the great barrier reef shelf how does a major river operate on a tropical mixed siliciclastic carbonate margin during sea level lowstand abstract a large palaeochannel on the northeastern australian continental shelf has been imaged by a series of shallow seismic reflection profiles the buried channel forms an important pleistocene route of the burdekin river and extends almost continuously for 160 km from the present coast to the outermost reef the channel floor profile steps across the shelf with alternating segments of gentle gradient flats and steeper gradient ramps channel sinuosity as interpreted from seismic records varies among segments between 1 and 1 72 with no consistent relationship between sinuosity and gradient the lower and upper parts of the channel fill have different geometry and reflection character suggesting channel excavation and initial filling occurred during a different regime than final filling in one section of the shelf about the 50 m isobath the channel is difficult to define and appears to have wandered significantly either because it has been modified by shoreface erosion ca 10 5 ka or because the river encountered a change in topography in front of karstified reefs as the channel passes between the numerous outer shelf reefs in water depths of 70 80 m it becomes progressively smaller conspicuously underfilled and absent entirely over the outermost 10 km of the shelf no discrete lowstand river mouth could be recognised on the present shelf edge the elevations of flat segments on the channel floor profile show considerable similarity to published elevations of stillstands or brief rises in sea level attained during the long term drawdown associated with the last glacial cycle 125 20 ka and are interpreted to have formed during this stepwise drop in sea level channels were cut and partially filled during the fall and lowstand and then backfilled during the holocene transgression the ancestral channel of the burdekin river therefore preserves a rare insight into the stratigraphic record of falling sea level during the last glacial

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

groundwater recharge and discharge dynamics in an arid zone ephemeral lake system australia the coongie lakes are a series of ephemeral freshwater lakes on the lower reaches of cooper creek a large intermittent river of the arid lake eyre basin australia hydrogeological chemical and isotopic observations in conjunction with numerical modeling of groundwater responses to lake inundation events have been used to identify the dominant processes linking shallow unconfined groundwater with the hydrology of the lakes during wet and dry periods the lakes are predominantly zones of net groundwater recharge during inundation events however soil profile data suggests that drying of some of these lakes allows evaporative groundwater discharge to occur through the soil profile of the dry lake beds resulting in salinization of the soil profile of the more ephemeral lakes the occurrence of young high salinity groundwater is best explained by variations in soil profile flushing in response to wet and dry interannual periods of river discharge during interannual drier phases when filling of previously dry lakes is more common recharge is mostly via macropore flow during the rising stage of the inundation increased salinization of the lake bed sediments occurs during longer dry periods due to transport of solutes to the near surface from lake bed evaporation and limited flushing of the soil profile because of the macropore dominated flow during recharge during wet periods recharge is more likely dominated by matrix flow that results in leaching of the soil profile and increased export of solutes into the alluvial aquifer

mechanisms of recharge in a fractured porous rock aquifer in a semi arid region abstract eleven porewater profiles in rock core from an upland exposed sandstone vadose zone in southern california with thickness varying between 10 and 62 m were analyzed for chloride cl concentration to examine recharge mechanisms estimate travel times in the vadose zone assess spatial and temporal variability of recharge and determine effects of land use changes on recharge as a function of their location and the local terrain the profiles were classified into four groups reflecting the range of site characteristics century to millennium average recharge varied from 4 to 23 mm y 1 corresponding to 1 moreover the temporal variability of recharge was estimated and along each profile past recharge rates calculated based on the sequence of cl concentrations in the vadose zone recharge rates increased at specific times coincident with historical changes in land use the consistency between the timing of land use modifications and changes in cl concentration and the match between observed and simulated cl concentration values in the vadose zone provide confidence in porewater age estimates travel times recharge estimates and reconstruction of recharge histories this study represents an advancement of the application of the chloride mass balance method to simultaneously determine recharge mechanisms and reconstruct location specific recharge histories in fractured porous rock aquifers the proposed approach can be applied worldwide at sites with similar climatic and geologic characteristics

holocene depositional history of the burdekin river delta of northeastern australia a model for a low accommodation highstand delta abstract the burdekin river of northeastern australia has constructed a substantial delta during the holocene delta plain area 1260 km2 the vertical succession through this delta comprises 1 a basal coarse grained transgressive lag overlying a continental omission surface overlain by 2 a mud interval deposited as the coastal region was inundated by the postglacially rising sea in turn overlain by 3 a generally sharp based sand unit deposited principally in channel and mouth bar environments with lesser volumes of floodplain and coastal facies the holocene burdekin delta was constructed as a series of at least thirteen discrete delta lobes formed as the river avulsed each lobe consists of a composite sand body typically 5 8 m thick the oldest lobes formed during the latter stages of the postglacial sea level rise 10 5 5 kyr bp are larger than those formed during the highstand 5 5 3 kyr bp which are in turn larger than those formed during the most recent slight sea level lowering and stillstand 3 0 kyr bp radiocarbon ages and other stratigraphic data indicate that inter avulsion period has decreased through time coincident with the decrease in delta lobe area the primary control on holocene delta architecture appears to have been a change from a pluvial climate known to characterize the region 12 4 kyr bp to the present drier enso dominated climate in addition to decreasing the sediment supply via lower rates of chemical weathering this change may have contributed to the shorter avulsion period by facilitating extreme variability of discharge more frequent avulsion may also have been facilitated by the lengthening of the delta plain channels as the system prograded seaward

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

mixed carbonates and siliciclastics in the quaternary of southern belize pleistocene turning points in reef development controlled by sea level change the belize barrier and atoll reefs represent one of the largest reef structures in the atlantic ocean the southern shelf of belize is a classic location of a modern mixed carbonate siliciclastic system whereas knowledge of the holocene deposits in the area is extensive data on the pleistocene system are fragmentary open questions include i the nature of the reef foundations carbonate versus siliciclastics ii the ages of the deposits including the initiation of the barrier reef and iii the response of the mixed system to sealevel fluctuations the results of a study of borings on the southern belize shelf are presented here six up to 105 m long borings were made to better understand the history of this important mixed system uranium series dating in the pleistocene was not possible because of diagenetic alteration however lithostratigraphy strontium isotopes and calcareous nannofossil biostratigraphy were used to constrain stratigraphic ages results support the contention that the quaternary development in belize was quite similar to that of other major barrier reefs such as the florida reef tract and further afield the great barrier and the new caledonian barrier reefs all of these barrier reefs are mixed carbonate siliciclastic systems and significant reef growth only began after the onset of high amplitude eccentricity controlled sea level changes and as late as during the exceptionally long and warm marine isotope stage 11 some 400 ka in belize early pleistocene sections at bases of borings include mollusc rich wackestones rare coral packstones and marls which were deposited under low to moderate energy conditions in a ramp setting before ca 900 ka during the high sea levels of marine isotope stage 25 and possibly earlier marine isotope stage 31 or 37 the belize shelf was subaerially exposed for most of the mid pleistocene and was dominated by siliciclastic sedimentation possibly during marine isotope stages 24 to 12 when highstands were comparatively low continuous reefs at the shelf margin were developing during highstands in the late pleistocene beginning with the long and high highstand of marine isotope stage 11 some 400 ka the southern shelf was flooded entirely and carbonates started to dominate once more reefs developed on top of siliciclastic deposits on the shelf a continuous barrier reef came into existence and largely developed on top of carbonates at the shelf margin during late pleistocene lowstands siliciclastics presumably no longer reached the shelf margin because of the topographic high of the barrier reef platform the quaternary belize example may serve as a model for reconstructing ancient mixed systems in icehouse worlds however any extrapolations are limited by the fact that fast growing scleractinian reef builders had not yet evolved in the palaeozoic

groundwater flow regime within the gambier embayment of the otway basin australia evidence from hydraulics and hydrochemistry a conceptual groundwater flow model for the cainozoic sequence of the gambier embayment of the otway basin south australia is developed using hydraulic head distribution environmental isotopes and hydrochemical data local flow cells occur within the upper sequence of the gambier unconfined aquifer and are recognised by local relief of the water table and as rapid lateral variations in chloride 14c 2h and 18o concentrations indicating that regional flow is not dominant in the upper portion of the unconfined aquifer these localised systems are topographically controlled and have developed in response to undulating stranded coastal dune ridges of the bridgewater formation recharge areas correspond to dune highs while discharge is focused towards the lower lying interdunal regions total dissolved solids concentrations are controlled by evapotranspiration processes during recharge and ion ratios are modified by water rock interactions within the groundwater system groundwaters are more dilute in the southern section of the basin where the surplus of precipitation over evapotranspiration in the winter months is greater than that in the northern section of the basin a regional flow system with interaquifer mixing has developed within the confined dilwyn aquifer system recharge to the dilwyn aquifer has been identified downgradient from the basin margin via downward leakage from an intermediate flow system within the gambier unconfined aquifer to the deeper regional flow system of the confined dilwyn aquifer interaquifer mixing appears to be geologically controlled in the south by the elevated gambier axis and in the north by the kanawinka fault downgradient of the zero head difference line lateral flow appears to be the dominant transport mechanism within the dilwyn aquifer as indicated by constant chloride concentrations monotonic decrease in radiocarbon concentration and more negative 2 and 18 o composition

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

siliciclastic foundations of quaternary reefs in the southernmost belize lagoon british honduras analyses of a closely spaced lattice of seismic profiles from the southernmost belize lagoon combined with logs of nearby drill holes reveal that the quaternary late pleistocene plus holocene reefs and carbonate sediments are growing on siliciclastic sediments which have an alluvial and delta like morphology the residual relief of these coastal plain deposits localized initial coral growth or an accumulation of calcareous skeletal material favored sites for these were elevations such as levees and bars of remnant channels and deltaic lobes

new evidence for drowned shelf edge reefs in the great barrier reef australia we present four new high resolution multibeam bathymetry datasets from the shelf edge of the northern great barrier reef gbr analysis of these data combined with chirp sub bottom profiles and existing submersible observation data provides a fresh insight into the detailed morphology and spatial distribution of submerged reefs and terraces at the shelf edge an extensive and persistent line of drowned shelf edge reefs exist on the gbr margin in about 40 to 70 m they appear as barrier reefs up to 200 m wide and comprising twin parallel ridges of rounded pinnacles subtle yet consistent terrace and step features lie between 78 and 114 m seaward of the shelf edge reefs in the southern study area submersible observations confirm that the drowned reefs now provide a favorable hard substrate for live soft corals and algae they form a consistent and extensive seabed habitat that extends for possibly 900 km along the gbr shelf edge the submerged reef and terraces features may reflect a complex history of growth and erosion during lower sea levels and are now capped by last deglaciation reef material

renewal rate estimation of groundwater based on radioactive tracers 3h 14c in an unconfined aquifer in a semi arid area iullemeden basin niger abstract estimation of groundwater recharge in arid and semi arid areas is difficult due to the low amount and variability of recharge a combination of radiotracers investigation based on simple mixing models allows direct investigation of relatively long term renewal rates of an aquifer the recharge process of the shallow continental terminal aquifer in the iullemeden basin niger was investigated using a geochemical and isotopic approach this study investigates the area in the one degree square of nianey 13 14 n 2 3 e in this area recharge is highly heterogeneous and mainly occurs through a drainage system of temporary streams and pools during the rainy season heterogeneity of the recharge is reflected through the wide variation in electrical conductivity and oxygen 18 content of the groundwater the carbon 14 activity range for most of the groundwater falls between 69 and 126 pmc showing pre and post aerial thermonuclear test recharge two renewal rate models have been investigated the first one models a well mixed reservoir and the second one is derived from a piston flow model in which mixing is in equal proportions major ions in tritium data analyses allow exclusion of non representative samples and confirm the carbon 14 renewal rate estimations both models give similar results for the relatively low renewal rate investigated in the area using carbon 14 the mean annual rates of groundwater renewal range from 3 to 0 03 of the aquifer volume with a median of 0 1 assuming the median is representative of the overall renewal rate of the area the recharge rate is in the order of 5 mm a 1 the shallow aquifer recharge extends from the last small humid period around 4000 a up to now high recharge rates are found in depressions whereas low recharge occurs below the plateaux

neogene evolution of the mixed carbonate siliciclastic system in the gulf of papua papua new guinea this paper outlines the evolution of the late cenozoic mixed carbonate siliciclastic depositional system in the gulf of papua gop using seismic gravity multibeam bathymetry well data sets and landsat imagery the deposition of the mixed sedimentary sequences was influenced by dynamic interplay of tectonics eustasy in situ carbonate production and siliciclastic sediment supply the roles of these major factors are estimated during different periods of the gop margin evolution the cenozoic mixed system in the gop formed in distinct phases the first phase late cretaceous paleocene was mostly driven by tectonics rifting created grabens and uplifted structural blocks which served later as pedestals for carbonate edifices active neritic carbonate accumulation characterized the second phase eocene middle miocene during this phase mostly eustatic fluctuations controlled the large scale sedimentary geometries of the carbonate system the third phase late miocene early pliocene was characterized by extensive demise of the carbonate platforms in the central part of the study area which can be triggered by one or combination of several factors such as eustatic sea level fluctuations increased tectonic subsidence uplift sudden influx of siliciclastics or dramatic changes in environmental conditions and climate the fourth phase late pliocene holocene was dominated by siliciclastics which resulted in the burial of drowned and or active carbonate platforms although some platforms still remain alive until present day

reconstruction of tertiary progradation and clinoform development on the new jersey passive margin by 2 d backstripping we have reconstructed the oligocene to middle miocene paleobathymetry and stratigraphy of the new jersey margin using a modified backstripping technique by analyzing the geometry of the margin through time we investigate its response to fluctuating sea level changing climate and variable sediment supply during the tertiary the reconstructions reveal a change in the margin morphology from a more steeply dipping 1 300 to 1 500 carbonate ramp in the eocene to a flatter shelf with a sharp shelf edge at present this was accomplished by an increase in the terrigenous sediment supply that filled available accommodation and caused progradation across the margin we link the increase in sediment flux with climatic cooling rather than tectonic processes the progradation is evidenced by a series of clinoforms whose formation was modulated by sea level and which extend over 100 km across the shelf the height and dip of the clinoforms increased as they extended onto the deeper parts of the earlier ramp the miocene clinoform rollovers at the new jersey margin had water depths of60 130 m and are interpreted as the edge of a new continental shelf built over the older ramp sea level fall was probably insufficient to drive the miocene shorelines past the shelf breaks thus measurements of sea level amplitude based upon coastal onlap over the clinoforms are not reliable 1999 elsevier science b v all rights reserved

carbon 14 and stable isotope data for an area in the murray basin its use in estimating recharge measurements of the carbon 14 concentration of water in 33 boreholes in a saline unconfined aquifer in southern australia have been interpreted to show that local recharge under natural conditions has a mean annual value which falls between 0 1 and 0 2 mm yr 1 the chloride concentration of groundwater is log normally distributed suggesting that its source is rainfall the estimate of mean annual recharge to the aquifer made using chloride is 0 25 mm yr 1

geochemistry of ground waters from the great artesian basin australia herczeg a l torgersen t chivas a r and habermehl m a 1991 geochemistry of ground waters from the great artesian basin australia j hydrol 126 225 245 ground waters from the confined lower cretaceous jurassic aquifer of the great artesian basin australia gab are characterised by na hco 3 type waters throughout the eastern and central parts of the basin and na sq c1 type waters in the western part sodium and bicarbonate increase in concentration from the northeastern margins to the southwestern discharge areas along the regional groundwater flowlines a mass balance and equilibrium model for major dissolved species and stable carbon isotopes of dissolved inorganic carbon show that the chemical trends observed are caused by mass transfer reactions involving cation exchange of na for ca mg carbonate dissolution and reactions between na and kaolinite to form na smectite the stable carbon isotopic composition of dissolved inorganic carbon dic increases from values of about 15 o near the basin margins to 6 o in the interior of the basin an inverse relationship exists between 6 3c and dic indicating addition of enriched carbon as the ground waters move basinwards a t2c 3c mass balance indicates that the trend toward heavier 6 3c values in the interior of the basin results from bacterial reduction of carbon dioxide to produce methane rather than dissolution of and equilibration with carbonate minerals the gab aquifer system is apparently open to co which is the product of in situ anaerobic fermentation producing co 2 enriched in t3c the chemical evolution of the major dissolved species and carbon isotope distribution in the eastern and central parts of the gab can then be envisaged as an initial pco 2 up to several orders of magnitude above atmospheric level is acquired within the recharge area by plant respiration and oxidation of organic matter in the soil zone initially silicate and carbonate minerals may dissolve at least in some parts of the basin resulting in increased alkalinity higher ca and mg concentrations and a 6 3c concentration of the dic of around 12 0 processes such as cation exchange of na for ca and mg in addition to the removal of some na by reverse weathering which produces a na smectite dominate in the interior of the gab the chemistry of ground waters derived from the western recharge areas is controlled by evaporite dissolution as indicated by very high ci br ratios

a survey of groundwater levels and hydrogeochemistry in irrigated fields in the karamay agricultural development area northwest china implications for soil and groundwater salinity resulting from surface water transfer for irrigation analysis of the water budget along with hydrochemistry and stable isotopes in shallow groundwater were carried out in the karamay agricultural development area kada in order to assess the impact of transfer of irrigation water from the irtysh river in particular in relation to the mechanisms of salinization and the nature of the water table regime in terms of aquifer dynamics the addition of the irrigation water without any groundwater abstraction has caused a sharp rise in the water table is and the development of serious soil salinity together with an almost complete attenuation of inter seasonal water table oscillations the mean rise in the groundwater table from september 1997 to october 2009 was 6 9 m representing an accumulated total water storage change of close to 150 million cubic meters the analysis of aquifer water budget shows that infiltration of irrigation water occupied over 90 of the total recharge of the groundwater in the kada sources of groundwater recharge and mechanisms of salinization in the kada were also investigated using geochemical and isotopic techniques the groundwater is characterized by cl so 4 na type generally becoming more na and cl dominated with increasing salinity the total dissolved solids tds content of the groundwater ranges from 0 5 g l to over 65 g l with greater tds values in areas of low topographic relief and shallow water tables where the sediments are more permeable e g due to the presence of palaeochannels tds values are generally lower and the seasonal water table fluctuations greater the ratios of k cl ca cl na cl and mg cl decrease with increasing cl concentrations especially in the shallow groundwater from 10 to 15 m depth indicating hydrogeochemical evolution via minor water rock interaction feldspar weathering and significant evaporation the stable isotopic compositions show a characteristic evaporation effect in the shallow groundwater and confirm that direct infiltration of precipitation is generally not a volumetrically important source of recharge to the shallow aquifer preferential recharge of river water after irrigation events and or precipitation from rare heavy rain events is likely responsible for the depleted 2 h and 18 o values in some of the groundwater samples the negative relationship between deuterium excess and 18 o values indicates that even in groundwater with relatively depleted 2 h and 18 o values evaporation has occurred to a significant degree careful management of water quantity and quality and implementation of salinity management strategies are considered necessary in order to reduce the risk of further salt accumulation and damage to farming and local ecosystems

using hydrogeochemistry to understand inter aquifer mixing in the on shore part of the gippsland basin southeast australia groundwater in the latrobe valley in the gippsland basin of southeast australia is important for domestic agricultural and industrial uses this sedimentary basin contains a number of aquifers that are used for water supply dewatered for open pit coal mining and which are potentially influenced by off shore oil and gas production major ion chemistry together with stable and sr isotope data imply that the main hydrogeochemical processes are evapotranspiration with minor silicate and carbonate weathering methanogenesis and so4 reduction in reduced groundwater associated with coal deposits have also occurred groundwater has estimated 14c ages of up to 36ka and is largely 3h free carbon 14 ages are irregularly distributed and poorly correlated with depth and distance from the basin margins the observations that the geochemistry of groundwater in aquifers with different mineralogies are similar and the distribution of 14c ages is irregular implies that the aquifers are hydraulically connected and horizontal as well as vertical inter aquifer mixing occurs the connection of shallow and deeper aquifers poses a risk for the groundwater resources in gippsland as contaminants can migrate across aquifers and dewatering of shallow units may impact deeper parts of the groundwater system

cenozoic evolution of sediment accumulation in deltaic and shore zone depositional systems northern gulf of mexico basin abstract paleogeographic and volumetric lithofacies mapping of 18 cenozoic genetic sequences within the northern gulf of mexico basin quantifies the proportional sequestering of sediment within wave dominated shore zone vs deltaic systems through time three long term depositional phases are revealed by plots based on paleogeographic and sediment isochore maps of total shore zone system area and volume to total delta system area and volume sz d 1 sz d area and volume ratios are highly variable in paleocene through eocene sequences however typical volume ratios for major genetic sequences upper middle and lower wilcox queen city qc and yegua range between 0 2 and 0 6 minor sequences sparta sp jackson js which record very low rates and volumes of sediment accumulation have the greatest variability in their ratios 2 oligocene and miocene sequences display consistently high proportions of shore zone sediment sz d area ratios range from 0 6 to 1 0 and volume ratios cluster between 0 4 and 0 8 3 a substantial late neogene decrease in sz d ratios is presaged in the late miocene sequence pliocene and pleistocene sequences are uniformly characterized by very low ratios of

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

recharge history and controls on groundwater quality in the yuncheng basin north china environmental isotopes and water quality indicators e g tds and no 3 contents were used to characterize the age recharge history and controls on the quality of groundwater resources in the yuncheng basin north china where extensive extraction occurs for agriculture and domestic supply delta 18 o and delta 2 h values as low as 10 6 and 73 parts per thousand respectively together with low radiocarbon activities 70 pmc indicating a significant component of modern post 1950s recharge the shallow groundwater has higher delta 18 o and delta 2 h values up to 8 1 and 54 parts per thousand that are similar to those in modern summer monsoon rainfall indicating that current recharge is via direct infiltration and or leakage of ephemeral streams during heavy rain events historic recharge rates estimated using radiocarbon ages are between 1 and 10 mm year corresponding to 20 mg l in some deep wells 180 m preferential leakage has occurred near the linyi fault in the northern sushui river basin salinisation nitrate contamination and excessive drawdown of deep groundwater are major concerns for the future of the groundwater resources in this region c 2010 elsevier b v all rights reserved

post glacial seismic stratigraphy central great barrier reef australia a regional programme of continuous seismic boomer profiling in the central great barrier reef province has identified a widespread shallow seismic discontinuity reflector a which is interpreted as the pre holocene surface nine seismic facies units are distinguished primarily on the basis of the seismic records but also with the aid of additional criteria such as location and surface sediment types two units underlie reflector a and are pre holocene these units are interpreted as a permo carboniferous bedrock and b pleistocene tertiary sediments consisting of both shelf wide terrigenous units and carbonate mounds and platforms under present reefs seven units are post glacial and overlie reflector a these units are interpreted as c fluvial estuarine channel fill d relict delta front deposits e relict transgressive veneer f coastal coarse and g fine deposits h modern reef and i reef talus in general post glacial sediment cover is very thin and in many places on the mid shelf the pre holocene units crop out substantial post glacial accumulations are limited to protected coastal embayments and to offshore reef masses

geomorphology of submerged reefs on the shelf edge of the great barrier reef the influence of oscillating pleistocene sea levels the submerged reefs on continental margins and surrounding oceanic islands are important archives of past climates eustatic sea level oscillations and oceanographic processes australia s north eastern submerged shelf edge reefs have previously been explored but all studies have been limited by either low resolution single beam profiles or by their limited spatial extent the aim of this study is to improve the understanding of the origin and development of submerged shelf edge reefs terraces and related features on the great barrier reef gbr and the influence of pleistocene sea level oscillations on their distribution and geomorphology we investigated the first large scale 1400 km2 3d bathymetry and acoustic backscatter dataset of four widely spaced sites located across ca 650 km along the shelf edge at ribbon reefs 1 5 noggin pass viper reef and hydrographers passage we provide a comprehensive description and systematic classification of the shelf edge features and constrain their spatial distribution and geomorphologic variability using a wide range of quantitative morphometrics fifteen features are defined four of which are the focus of this study including terraces pinnacles ridges and channels using modern reefs within the gbr for comparison we interpret these as fringing reefs patch and barrier reefs and tidal channels respectively the influence of gross shelf geomorphology and oceanographic factors driving the observed variability within and between sites is discussed in conjunction with mid late pleistocene sea level oscillations we observed two distinct types of reef growth characterised by the degree of development which we interpret as analogous to juvenile and mature modern reefs of the gbr juvenile reefs are very common and occur within each site at depths of less than 50 m to greater than 100 m they are defined as discontinuous peaked barrier reefs peaked patch reefs and fringing reefs mature reefs are less common and develop exclusively at a depth range of ca 50 70 m these reefs are defined as flat topped continuous barrier and double barrier reefs through a comparison with published mid late pleistocene sea level oscillations we note that the depth range of mature reefs is consistent with the depth of repeated low amplitude 20 m eustatic sea level oscillations and independent of the relative time spent at sea level we conclude that repeated low amplitude sea level rises provide the much needed accommodation space for vertical accretion that is not provided during stillstands without inducing reef drowning which can be caused by high amplitude sea level rise low amplitude sea level falls are also less detrimental than high amplitude falls in terms of habitat compression together the effects of enhanced reef accretion and limited habitat compression at depths of 50 70 m have lead to a concentrated net gain in vertical relief that is not observed elsewhere on the shelf edge

late quaternary siliciclastic carbonate sedimentation model for the capricorn channel southern great barrier reef province australia abstract a model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial interglacial cycle in the capricorn channel southern great barrier reef gbr stable isotope ratios grainsize carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level mbsl results show variations in the flux of terrigenous neritic and pelagic sediments to the continental slope over the last sea level cycle during the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl the percentages of quartz and feldspar in the cores decreased with water depth while the percentage of clay increased x ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the fitzroy river which debouched directly into the northwest sector of the capricorn channel at this time the cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite hmc during the glacial the influx of hmc and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial and also from hmc ooids precipitated at the head of the capricorn channel at this time mass accumulation rates mars are high 13 5 g cm 3 kyr 1 during the glacial and peak at 20 g cm 3 kyr 1 in the early transgression 16 14 ka bp mars then decline with further sea level rise as the fitzroy river mouth retreats from the edge of the continental shelf after 13 5 ka bp mars remain low 4 cm 3 kyr 1 throughout the holocene highstand data for the holocene highstand indicate there is a reduction in siliciclastic influx to the capricorn channel with little quartz and feldspar below 350 mbsl however fine grained fluvial sediments presumably from the fitzroy river were still accumulating on the mid slope down to 2000 mbsl the proportion of pelagic calcite in the core tops increases with water depth while hmc decreases and is present only in trace amounts in cores below 1500 mbsl the difference in the percentage of hmc in the deeper cores between the glacial and holocene may reflect differences in supply or deepening of the hmc lysocline during the glacial sediment accumulation rates also vary between cores in the capricorn channel and do not show the expected exponential decrease with depth this may be due to intermediate or deep water currents reworking the sediments it is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments comparison of the capricorn channel mars with those for other mixed carbonate siliciclastic provinces from the northeast margin of australia indicates that peak mars in the early transgression in the capricorn channel precede those from the central gbr and south of fraser island the difference in the timing of the carbonate and siliciclastic mar peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces the only common trend in the mars from the northeast margin of australia is the near synchronicity of the carbonate and siliciclastic mar peaks in individual sediment cores which supports a coeval sedimentation model

constraining groundwater recharge and the rate of geochemical processes using tritium and major ion geochemistry ovens catchment southeast australia summary constraining recharge is essential for understanding and managing groundwater systems this study uses high precision tritium 3 h concentrations together with major ion and environmental isotope sr c o h geochemistry to constrain rates of recharge and geochemical processes in the ovens catchment of the southeast murray basin australia 3 h concentrations of groundwater in the ovens catchment decline with depth but not with position in the catchment implying that recharge occurs over broad areas recharge rates calculated using an exponential piston flow model are 120 180 mm yr in the coarse grained alluvial gravels of the upper and middle ovens and 30 45 mm yr in the finer grained sediments of lower ovens these recharge rates are similar to those calculated from the response of shallow bore hydrographs to rainfall the geochemistry of groundwater with low 60 160 mg l total dissolved solids tds from the upper and middle ovens indicates that dissolution of both silicate minerals and calcite has occurred major ion geochemistry 87 sr 86 sr ratios and 13 c values in the upper and middle ovens groundwater are correlated with groundwater residence times and constrain the progress of mineral reactions dissolution of silicates with high 87 sr 86 sr ratios biotite and k feldspar occurs prior to dissolution of silicates with low 87 sr 86 sr ratios plagioclase and calcite mineral dissolution mainly occurs in the upper 20 m of the aquifer system with relatively little change in geochemistry deeper in the flow system groundwater from the lower ovens has higher tds contents 600 9600 mg l due to higher degrees of evapotranspiration although a correlation between tds and groundwater residence times exists it is more likely to reflect differential recharge rates and not the rate of evapotranspiration the conclusion that recharge occurs across the ovens catchment indicates that protection of groundwater from surface contamination is dependent on the protection and management of large areas

the hydrogeology hydrochemistry and environmental isotopes of the campaspe river aquifer system north central victoria australia the campaspe river hydrogeological system of north central victoria consists of two major units 1 the tertiary deep lead aquifer a combination of the renmark group and calivil formation which forms the major aquifer of the region and 2 the plio pleistocene shepparton formation which forms a complex aquitard aquifer system on top of the deep lead recharge to the deep lead aquifer is twofold 1 a major component of recharge occurs along the southern reaches of the campaspe river where the overlying shepparton formation is thin and becomes more permeable and 2 recharge occurs by vertical downward movement of water from the shepparton formation whose heads are everywhere higher than those of the deep lead natural discharge from the system occurs further to the northwest beyond the murray river salinity gradually increases down gradient in the deep lead with an abrupt increase to greater than 6000 mg l 1 total dissolved solids close to the murray river except in the goornong area in the south which appears to be separated from the main deep lead system this increase is characterised by a certain hydrochemical evolution of the water wherein very fresh recharge with a mnacl 1 0 changes to an oceanic type composition while still in the low salinity range this is due largely to concentration of the original solutes in the system and is the consequence of salt remobilisation within the catchment the shepparton formation waters on the other hand are characterised by disorder namely fresh to saline water juxtaposed both horizontally and vertically heads in both the shepparton formation and the deep lead had been increasing at the rate of about 15 20 cm yr 1 for at least several decades the advent of large scale withdrawal from the deep lead in the early 1980s has arrested this trend in the northern and central portions of the area a decline in aquifer pressures is evident this decline will induce increased leakage from the shepparton formation down into the deeper aquifer and such leakage could possibly result in a degradation of its water quality stable isotope data indicate that under the existing hydrologic regime little irrigation drainage water has penetrated to the deep system

facies in a shelf edge delta an example from the subsurface of the gulf of mexico middle pliocene mississippi canyon block 109 two vertically stacked shelf edge delta systems in the middle pliocene of mississippi canyon block 109 have been described using a three dimensional seismic survey 400 ft 122 m of conventional core and electric logs possible characteristic facies associations and features of these shelf edge deltas include extensive upper delta slope deformation locally ponded slump induced turbidites in the upper slope a complex association of gravity and tractional deposits relatively thin preserved mouth bar deposits and the absence of delta plain facies six facies have been identified in cores 1 structureless sands interpreted as high density turbidites 2 laminated sands 2 1 sharp based planar horizontal laminations interpreted as bouma b and bc division turbid tes 2 2 low angle discordant laminations interpreted as strong wave activity deposits 2 3 a complex mixture of lamination styles that may be a product of turbidity currents waves or possibly river fed underflows 3 thinly interbedded ripple laminated sands including 3 1 asymmetrical cross laminations interpreted as unidirectional traction current lamination and 3 2 c division turbidites or ripple lamination with mud drapes on foresets or with a symmetrical form interpreted as wave or possibly tidal current lamination 4 contorted muddy fine sands and silts interpreted as mud flows and slumps 5 laminated silts and muds interpreted as low energy wave deposits or possibly d division turbidites and 6 muds interpreted as quiet water deposits in the cored intervals o the deltas turbidite sands immediately overlie muddy slumps in the upper delta slope suggesting that retrogressive slope failure of developing slump structures tapped back into the mouth bar causing sandy turbidity currents to develop the upper delta is represented on seismic data as a series of prograding clinoforms approximately 400 ft 122 m thick electric logs indicate these clinoforms are composed of a lower mud dominated interval an upper delta slope dominated by slumps with areally restricted turbidite sands and coarsening and cleaning upward mouth bar deposits composed of ripple laminated and parallel laminated sands interbedded with muds and silts the lower delta contains similar vertical sequences but also contains a distinct log and seismic facies that may be either a major shelf edge failure or a later channel feature incised across the entire delta apart from this possible channel neither delta shows evidence of emergent delta plain facies

groundwater recharge assessment in an upland sandstone aquifer of southern california abstract the chloride mass balance cmb method was used to obtain long term recharge values for the santa susana field laboratory ssfl site which features a groundwater flow system beneath an upland ridge formed of sandstone and shale beds in the simi hills ventura county southern california this application relied on the availability of on site measurements of bulk atmospheric chloride deposition comprised of dry fallout and wet concentration a large number of groundwater samples 1490 collected over three decades from 206 wells spanning a depth range from 10 to 360 m and measurements of chloride in surface runoff during rain events the use of the cmb method is suited to the assessment of recharge for the study area because the mean chloride values in groundwater show minimal spatial trends indicating no sources other than atmospheric in addition the cl br ratio was used to exclude wells with possible anthropogenic chloride the site wide average recharge ranges between 1 8 and 9 5 of the mean annual precipitation 455 mm with a mean value of 4 2 the measured surface runoff varies from 2 3 to 10 2 with mean value of 6 1 28 mm and therefore the volume of water lost to evapotranspiration is between 95 9 and 80 3 with a mean value of 89 6 408 mm the long term recharge calculated using the cmb method is consistent with tritium distribution based on a subset of groundwater monitoring wells and with an analysis of steady flow in the groundwater mound beneath the ssfl furthermore the recharge value matches those in the literature for sandstone aquifers in arid and semi arid climates this recharge estimate has important relevance for site characterization in terms of constraining the volumetric groundwater flow rates and water balance and understanding the mechanisms of transport towards the water table moreover this is the first application of the cmb in an upland area of california hence the method is demonstrated to be robust and applicable to many upland bedrock areas in southern california and similar regions around the world and can be used to quantify groundwater flow rates and supplies relevant to water resource management

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

island groundwater resources impacts of abstraction and a drying climate rottnest island western australia abstract coastal aquifers provide a source of water for more than one billion people with island freshwater lenses being some of the most vulnerable coastal groundwater systems due to their susceptibility to saltwater intrusion basic hydrogeological and hydrochemical knowledge regarding the recharge and salinisation processes of freshwater lenses is important to ensure sustainable utilisation especially considering possible climate change effects this paper makes an assessment of the fate of a freshwater lens in a drying climate through a comparison of current and historic hydrochemical data which to the author s knowledge is unique to this study fresh groundwater stable isotope signatures 18 o 2 h reflect local amount weighted rainfall signatures 18 o 3 8 2 h 15 1 and confirm rainfall as the origin of fresh groundwater 18 o 4 47 to 3 82 2 h 20 0 to 16 6 mixing with seawater was identified through enriched groundwater 18 o and 2 h signatures maximum values of 0 36 and 1 4 respectively compared to local rainfall and higher salinity maximum 29 267 mg l total dissolved solids tds in a number of monitoring wells around the freshwater lens enhanced seawater intrusion detected in the northern section of the lens area was identified through significantly increased tds values over the last 20 40 years with increases of up to 3000 observed between 1990 and 2014 a reduction in the extent of freshwater by approximately 1 km 2 was identified since 1977 which was found to be primarily caused by a reduction in recharge to the freshwater lens due to a 20 decline in winter rainfall in the south west western australian region since the mid 1960s groundwater abstraction was found to equate to between 5 and 9 of the estimated recharge for the island and is not a significant factor in the reduction of the lens extent compared to the observed decline in rainfall recharge interestingly seawater intrusion into the fresh water lens was found to occur by older seawater 0 03 0 09 tu in regions of the lens that were previously fresh or slightly brackish while one sample 0 67 tu suggests either modern seawater intrusion or mixing of older saline groundwaters 60 years with rainfall recharge the use of tritium dating in this island aquifer was essential in identifying older seawater that was previously unidentified until now the isotopic and hydrochemical tools used in this paper quantify the effects of groundwater abstraction and climate variability on the freshwater lens and have implications for the sustainable management of the groundwater resource on rottnest island and elsewhere

late quaternary sedimentation on the great barrier reef continental shelf and slope east of townsville australia cores collected in a shelf to basin transect from northeastern australia document the stratigraphic development of late quaternary deposits low sea level to 120 m slope sedimentation is dominated by prograding fluvial deposits with wave dominated deltas forming on the shelf edge and upper slope the onset of sea level transgression into the excavated shelf river channels on the outer shelf resulted in estuarine sedimentation along an indented coastline 15 000 11 000 yrs b p reducing terrigenous sediment supplies to the slope on the outer shelf halimeda muddy sandy gravels were deposited over a pleistocene limestone erosional surface from about 10 500 yrs b p transgression submerged the limestone outcrops and estuaries of the middle shelf where coral reef complexes formed the outer and middle parts of the shelf thus became dominated by carbonate sedimentation while the inner shelf received fluvial input mixed with locally derived carbonates the sequence is bounded by an unconformity clearly marked by erosional down cutting the results of the study are combined with those of previous workers to develop transgressive and continued high sea level system tract models the latter continued high sea level model is used to extrapolate present high sea level sedimentation patterns into the future providing a model for comparison with ancient sequences which may also have formed in such a depositional environment

factors affecting groundwater recharge following clearing in the south western murray basin abstract data from 18 field studies in the south western murray basin australia and a simple water balance model were used to study the importance of factors which affect diffuse recharge in that area generally as the texture of the soil became heavier the recharge decreased under cropped land as the clay content in the top 2 m of the soil profile increased from 0 to 20 recharge decreased by one order of magnitude from about 30 to about 3 mm year 1 for a mean annual rainfall of 310 380 mm as mean annual rainfall increased the mean annual recharge also increased sites with an average clay content of about 10 in the top 2 m and a mean annual rainfall of 270 mm had an estimated recharge of about half that of sites with a mean annual rainfall of 310 380 mm data from land which was grazed but not cropped showed similar relationships however the data set did not allow a detailed analysis of the effect of land use on recharge

estimating recharge in fractured aquifers of a temperate humid to semiarid volcanic island jeju korea from water table fluctuations and cl cfc 12 and 3h chemistry summary groundwater table fluctuations wtf chloride mass balance cmb apparent groundwater chlorofluorocarbon cfc 12 ages and tritium 3 h mean residence times were used to assess recharge rates on jeju island korea where groundwater is the main source of potable water given the limitations of various techniques and the respective data the methods yield median values of 687 mm yr wtf 429 mm yr cmb 423 mm yr cfc 12 and 394 mm yr 3 h which are lower than the multi annual 1993 2002 average value calculated using the soil water budget swb method 911 mm yr these underestimates are mainly due to most groundwater samples used for the analyses being located in the more arid lowland areas of the island all methods yield highest recharge rates in the southern and eastern districts of jeju implying a strong control of rainfall on the spatial recharge distribution the spatial variability of recharge at the catchment scale is caused by spatially and temporally variable rainfall and evapotranspiration as well as the wide range in effective porosity and specific yield values of the aquifer lithologies the wtf method yields reliable results in the coastal regions where low hydraulic gradients prevail the cmb technique underestimates the recharge values of the swb in all geographic districts probably as a result of anthropogenic cl additions to groundwater and unaccounted for atmospheric cl dry deposition median recharge estimates from the cfc 12 and 3 h data show the lowest spatial correlation with those from the swb mainly as a result of vertical anisotropies and uncertainties in the determination of effective aquifer thicknesses particularly in the perched high level areas the here applied methods are useful for local calibration and validation of swb estimates in lower parabasal regions where thin unsaturated zones prevail however due to their inability to predict recharge in the more remote upslope areas from which as of yet no groundwater data could be obtained they cannot be applied to predict average recharge values representative for the whole island

the brigalow catchment study revisited effects of land development on deep drainage determined from non steady chloride profiles summary a large area of woodland in the brigalow bioregion in semi arid central queensland was cleared for agriculture from the 1960s to the 1980s to assess the risk of salinity associated with land clearing soil chloride cl was monitored at the brigalow catchment study bcs in brigalow acacia harpophylla scrub a cropped catchment and a pasture catchment before and after clearing in 1982 the monitoring sites include three landscape positions two on clay soils and one on a sodic duplex sodosol within each catchment an earlier report of deep drainage using the early soil cl profiles and steady state and transient chloride sodics mass balance was revisited after a further 13 yr and four more sampling times profile cl mass changed little in 18 4 yr at scrub sites justifying the use of native vegetation sites to represent pre clearing cl for paired cleared sites steady state cl mass balance cmb gave deep drainage of 0 13 0 34 mm yr for nine pre clearing scrub sites large losses of soil cl occurred under cropping and smaller losses occurred under pasture transient cmb gave average deep drainage of 59 and 32 mm yr for crop and pasture catchments respectively during the development phase 1981 1983 when the land was bare following clearing of native vegetation and prior to establishment of crops or pastures in the 16 7 yr following establishment of agricultural land uses 1983 2000 transient cmb gave average deep drainage of 19 8 range 3 3 50 and 0 16 2 2 to 1 4 mm yr respectively in crop and pasture catchments the drainage rate under pasture was similar to that under brigalow scrub in the cropped catchment drainage for modern farming systems less tillage more summer opportunity crops was about half that of older farming systems wheat summer fallow more tillage less stubble retention drainage was greater for the sodosol than for the clay soils under cropping deep drainage occurred under cropping even though the soils are considered to have low permeability and the climate is semi arid with potential evaporation exceeding rainfall on average in all months increased drainage at cropped sites has driven a clear exponential loss of soil cl as predicted by the transient cmb theory one cropped site is at or near a new steady state and the others will reach a new steady state 50 200 yr after clearing the leachate is saline with an average cl concentration of 7000 mg l and would salinised any groundwater it entered the salinity risk associated with the drainage is not well understood as yet and will depend on local hydrogeological conditions which are poorly mapped in the fitzroy effects of these losses of salts on sodicity soil structure and permeability should also be investigated

late pleistocene history of turbidite sedimentation in a submarine canyon off the northern great barrier reef australia cores from slopes east of the great barrier reef gbr challenge traditional models for sedimentation on tropical mixed siliciclastic carbonate margins however satisfactory explanations of sediment accumulation on this archetypal margin that include both hemipelagic and turbidite sedimentation remain elusive as submarine canyons and their role in delivering coarse grained turbidite deposits are poorly understood towards addressing this problem we investigated the shelf and canyon system bordering the northern ribbon reefs and reconstructed the history of turbidite deposition since the late pleistocene high resolution bathymetric and seismic data show a large paleo channel system that crosses the shelf before connecting with the canyons via the inter reef passages between the ribbon reefs high resolution bathymetry of the canyon axis reveals a complex and active system of channels sand waves and local submarine landslides multi proxy examination of three cores from down the axis of the canyon system reveals 18 turbidites and debrites interlayered with hemipelagic muds that are derived from a mix of shallow and deep sources twenty radiocarbon ages indicate that siliciclastic dominated and mixed turbidites only occur prior to 31 ka during marine isotope stage mis 3 while carbonate dominated turbidites are well established by 11 ka in mis1 until as recently as 1 2 ka the apparent lack of siliciclastic dominated turbidites and presence of only a few carbonate dominated turbidites during the mis2 lowstand are not consistent with generic models of margin sedimentation but might also reflect a gap in the turbidite record these data suggest that turbidite sedimentation in the ribbon reef canyons probably reflects the complex relationship between the prolonged period 25 ka of mis3 millennial sea level changes and local factors such as the shelf inter reef passage depth canyon morphology and different sediment sources on this basis we predict that the spatial and temporal patterns of turbidite sedimentation could vary considerably along the length of the gbr margin

filling the gap a 60 ky record of mixed carbonate siliciclastic turbidite deposition from the great barrier reef abstract late pleistocene to holocene margin sedimentation on the great barrier reef a mixed carbonate siliciclastic margin has been explained by a transgressive shedding model this model has challenged widely accepted sequence stratigraphic models in terms of the timing and type of sediment i e carbonate vs siliciclastic deposited during sea level oscillations however this model documents only hemipelagic sedimentation and the contribution of coarse grained turbidite deposition and the role of submarine canyons in this process remain elusive on this archetypal margin here we present a new model of turbidite deposition for the last 60 ky in the north eastern australia margin using high resolution bathymetry 58 new and existing radiometric ages and the composition of 81 turbidites from 15 piston cores we found that the spatial and temporal variation of turbidites is controlled by the relationship between sea level change and the variable physiography along the margin siliciclastic and mixed carbonate siliciclastic turbidites were linked to canyons indenting the shelf break and the well developed shelf edge reef barriers that stored sediment behind them turbidite deposition was sustained while the sea level position allowed the connection and sediment bypassing through the inter reef passages and canyons carbonate turbidites dominated in regions with more open conditions at the outer shelf and where slope confined canyons dominated or where canyons are generally less abundant the turn on and maintenance of carbonate production during sea level fluctuations also influenced the timing of carbonate turbidite deposition we show that a fundamental understanding of the variable physiography inherent to mixed carbonate siliciclastic margins is essential to accurately interpret deep water coarse grained deposition within a sequence stratigraphic context

the structural and sedimentological controls on the reoccupation of quaternary incised valleys belize southern lagoon a grid of high resolution single channel seismic data from the belize southern lagoon has documented the development of several generations of stacked late pleistocene 400 ka holocene incised valley fills a feedback mechanism between tectonics reefal buildups and incised valley location is apparent in the data incised valleys are recognized as medium to high amplitude reflections that truncate reflections produced by older strata on the seismic data the holocene valley fills in the belize southern lagoon contain three seismic facies units from bottom to top 1 a basal unit characterized by moderately high amplitude chaotic reflections or progradational patterns that downlap onto the valley floor 2 a middle unit characterized by continuous horizontal near transparent reflections that drape the basal unit and onlap the valley walls and 3 an upper unit that consists predominantly of transparent to low amplitude low angle downlapping reflections the middle and upper units are separated by an erosional surface based on core evidence and seismic facies analysis the basal middle and upper seismic and sedimentary facies units are interpreted as fluvial and carbonate sands estuarine muds and marine sands and muds respectively the erosional surface separating the upper and middle units is interpreted to be a ravinement surface that marks the transition from brackish estuarine conditions to open marine conditions faulting decreases and reefal buildups increase upsection the oldest valleys mimic structural trends and flow through areas currently occupied by extensive carbonate reefs rapid high amplitude late pleistocene sea level rises may have led to wides pread reef development creating a template that subsequent incisions reoccupation valleys followed regardless of structural trends the intimate relationship among tectonics sea level change carbonate reef buildups and incised valley reoccupation serves as a model for understanding ancient tropical mixed carbonate siliciclastic systems accelerator mass spectrometer 14c dates of sediment core samples marine gastropods marine mollusks barnacles worm tubes peat and oysters indicate all the sediment cored 1 4 m in this study is holocene in age between 4740 60 and 11 230 90 14c age this radiocarbon dating consistently links the erosional surface between the upper and middle units with the intersection of the regional sea level curve nonmarine marine boundary

constraining modern and historical recharge from bore hydrographs 3h 14c and chloride concentrations applications to dual porosity aquifers in dryland salinity areas murray basin australia summary water table fluctuations and renewal rates based on 3h and 14c concentrations in bores screened within 5 m of the water table were used to estimate recharge rates in five dryland salinity areas in northern victoria australia given the resolution of each technique both methods yield broadly similar results of 4 90 mm yr up to 14 of modern rainfall that reflect the recharge rates following land clearing over the last 200 years deeper bores show mixing of modern recharge with older water flowing laterally through the aquifers recharge estimates based on cl concentrations are up to two orders of magnitude lower

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

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

quaternary aragonite cycles and oxygen isotope record in bahamian carbonate ooze carbonate ooze in bahamian troughs displays cyclic variation in the content of aragonite a 10 m core devoid of turbidites shows 3 5 cycles each defined by a sharp increase followed by a gradual decrease of aragonite the aragonite curve matches closely the oxygen isotope curve of planktic foraminifera from the same core aragonite highs correspond to light oxygen isotope values and thus to interglacial stages content of terrigenous material is low during interglacials and higher during glacial periods intermittent flooding and exposure of the bahama banks is most probably not the cause of the cycles because the latest increase in aragonite precedes bank flooding by 8 000 yr and because the cycles are distinctly asymmetric with rapid increase and gradual decrease of aragonitic content carbonate dissolution cycles tied to the glacial rhythm of earth9s climate are a more likely explanation of the variations in aragonite content

upper wilcox rosita delta system of south texas growth faulted shelf edge deltas the rosita delta system a heretofore unrecognized major depositional system preserved in the deep upper wilcox of south texas was delineated by detailed correlation of approximately 500 well logs the rosita delta system comprises at least three delta complexes each of which can be traced up to tens of miles along strike and up to approximately 15 mi 24 km downdip basinward across the growth fault zone each delta complex thickens from about 600 ft 180 m to more than 3 000 ft 900 m the growth faults were activated by progradation of deltas over unstable prodelta slope muds at the contemporary shelf margin the three upper wilcox delta complexes studied in detail are from oldest to youngest the duval zapata and live oak deltas named for the counties in which they are centered each complex consists of several lobes some of which can be traced across the deep zones where the thickness increases by as much as tenfold owing to progradation over active growth faults characteristic coarsening upward progradational units are interpreted from electric log patterns to include prodelta shales delta front sandstones distributary channel and channel mouth bar sandstones and interdistributary shales and sandstones appreciable variability in sandstone distribution in the deltas may reflect changing importance of fluvial versus marine currents in distributing sediment along the delta front however all of the deltas prograded abruptly toward the shelf margin the gulfward extent of these delta complexes is unknown and it is concluded that appreciable quantities of sandstone remain to be explored in the deep subsurface of the trend

clinoform development by advection diffusion of suspended sediment modeling and comparison to natural systems clinoforms are the building blocks of prograding stratigraphic sequences these sig moid shaped surfaces can be found forming today on modem deltas sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions with a maximum accumulation rate on the upper foreset region we pres ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river model clino form surfaces are generated using an equation for the conservation of suspended sediment concentration together with a conservation of fluid equation for simple time averaged flow velocity fields in the model suspended sediment is advected horizontally into a basin and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion in shallow water shear stresses are too large to allow deposition and sediment bypasses the topset region with increasing water depth near bed shear stresses decrease and sediment is allowed to deposit at the foreset region with gradually decreasing rates toward deeper water this sedimentation pattern leads to progradation of the clinoform surfaces through time the clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms these include the gradual slope rollover at the topset and bottomset steeper foreset slopes with increased grain size and an increase in foreset slope through time as clinoforms prograde into deeper water because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems the model is an important step toward unraveling the physical processes associated with these deposits

the importance of silicate weathering of a sedimentary aquifer in arid central australia indicated by very high 87sr 86sr ratios with the exception of brine systems and crystalline rock aquifers groundwater 87sr 86sr ratios rarely differ by more than 0 01 from the phanerozoic seawater value of 0 70923 groundwater 87sr 86sr ratios from central australia 0 72562 0 76248 are the highest ever recorded for a low salinity sedimentary aquifer we propose a model for the evolution of these 87sr 86sr ratios and demonstrate how the lowest 87sr 86sr ratios reflect water rock interactions with predominantly carbonate minerals while the highest 87sr 86sr ratios are ultimately controlled by weathering of old primary silicate minerals detailed analysis of aquifer core material identified albite and microcline as the most prevalent primary silicates and where these minerals were abundant relatively high rb concentrations were measured high rb combined with long time scales since deposition has produced very high 87sr 86sr ratios in the rocks and subsequently the groundwater therefore strontium isotopes can provide further constraints for chemical models of arid zone groundwater systems particularly when silicate hydrolysis is believed to significantly contribute to dissolved solute compositions

uncertainties around modelling of steady state phreatic evaporation with field soil profiles of δ18o and chloride summary the application of the general advection diffusion equation to model phreatic evaporation flux rates from solute concentration soil profiles has been applied to a variety of arid zone locations but the effects of heterogeneous and uncertain field data on modelling performance are rarely described we revisit and extend the model by accounting for the effects of variable water content and sediment type on the impedance factor and in turn effective diffusion coefficient we explore the local sensitivity of the extended model to its major assumptions and parameter values the mean diffusion coefficient of the soil profile data is most sensitive to the volumetric water content close to the evaporation front and so modelled evaporation results can be very sensitive to uncertainty around the position of the evaporation front the uncertainty in the position of the groundwater reservoir and its concentration has little effect where the lower part of the profile shows an asymptotic trend towards a representative value of groundwater concentration but can vary substantially with different values of groundwater depth and concentration if this is not the case field data from the southern margin of the great artesian basin are shown to exhibit considerable uncertainty around the boundary conditions of the advection diffusion model e g position of evaporation front depth and concentration of lower groundwater boundary condition resulting phreatic evaporation flux estimates show a wide range that needs to be considered when using these data in water balance studies of groundwater systems

hyperpycnites deposited 700 km away from river mouths in the central japan sea abstract relatively little is known about the characteristics of deposits and potential runout distances of hyperpycnal currents this study describes and discusses evidence of sediment deposition from sustained long duration quasi steady turbidity currents in the distal part of the toyama deep sea channel which extends ca 700 km from river mouths in the central japan sea the study is based on gravity cores and airgun seismic reflection profiles obtained from the channel distal reaches the silty turbidite beds of the channel s terminal fan show rhythmic layering that indicates sustained turbidity currents with distinct flow strength fluctuations some of the rhythmite beds show a fining upward internal trend net flow strength waning whereas others show an upward coarsening net flow strength waxing followed by fining seismic reflection profiles from the channel levees show large bedforms of climbing dune type attributed to the spillover of thick sustained turbidity currents the deposition of the terminal fan rhythmites and accretionary levee bedforms is attributed to turbidity currents generated by hyperpycnal river effluent a quantitative assessment of sediment concentrations in the coastal rivers indicates that their effluents could become hyperpycnal nearly every year or during every major seasonal flood the density of a river generated underflow would increase by the entrainment of saline water and seafloor sediment on the steep slope of the toyama bay resulting in robust long runout turbidity currents the estimated flow velocities of these currents were around 0 3 m s and their recurrence period for the last 1000 years was of the order of 70 years the estimated duration of hyperpycnal flows required for the deposition of rhythmite beds 700 km away from the river mouth is of the order of several days to 3 4 weeks the study provides new insights into the recognition and classification of hyperpycnites in distal zones of deep marine turbiditic systems

a new chloride leaching approach to the estimation of diffuse recharge following a change in land use abstract a new approach has been developed to estimate the increase in groundwater recharge following land use modification the approach uses the degree of leaching of chloride to quantify soilwater drainage below the root zone which ultimately leads to groundwater recharge it is more general than similar previously reported techniques for analysing transient chloride profiles to infer recharge rates and hence has wider application we have applied the technique to a field situation in southern australia where clearing of native vegetation for agricultural production leads to large increases in groundwater recharge the examples serve to demonstrate the technique and some of the practical difficulties in the application of solutes techniques to recharge estimation

sediment fluxes to marion plateau southern great barrier reef province over the last 130 ky new constraints on transgressive shedding off northeastern australia generic models for sediment accumulation predict that fluxes of siliciclastic and neritic carbonate material to continental slopes of tropical mixed systems will be out of phase over cycles of sea level change siliciclastic and carbonate fluxes should be highest during lowstands and highstands respectively and condensed sections should form during transgressions recent studies have documented the opposite response for slopes along portions of the largest modern tropical mixed system the northeast australian margin siliciclastic and carbonate fluxes are in phase and highest during transgression an outstanding issue however is the extent of this response because studies to date have mostly focused on sedimentation over the last 40 ky off the central gbr province an area flanked by a narrow shelf and a wet tropical hinterland here we investigate mixed sediment deposition in a core from marion plateau offshore a wide shelf and a dry tropical hinterland in the southern gbr province bulk carbonate content and carbonate mineralogy were determined downcore while foraminiferal oxygen isotopes and radiocarbon ages were used to constrain ages and accumulation carbonate content and mineralogy vary predictably with changes in sea level over the last 130 ky carbonate and aragonite are more abundant during highstands and less abundant during lowstands however component mass accumulation rates reveal that highest fluxes of all material siliciclastic low mg calcite aragonite and high mg calcite occurred during transgressions sedimentation consistently diverges from conventional models in all cores examined to date from slopes of the northeast australian margin regardless of core location and modern differences in climate and physiography the unexpected sediment response could result from changes in climate particularly increased precipitation during deglaciations although this does not explain elevated fluxes of low mg calcite alternatively fluvial sediments and diagenetically altered carbonate aggraded on the shelf during lowstands and were eroded and transported to the slope during transgressions

dynamic changes and processes in the mississippi river delta research in the modern delta of the mississippi river has revealed short term changes and processes that are of significant magnitude deltaic lobes each lobe covering an area of 30 000 sq km and having an average thickness of 35 km switch sites of deposition on an average of every 1 500 yr through short periods of geologic time this process results in a relatively thick accumulation of stacked deltaic cycles covering extremely large areas within a single delta lobe and operating on an even higher frequency are bay fills and overbank splays bay fills having areas of 250 sq km and thickness of 15 m require only 150 yr to accumulate four major events have taken place in the modern balize delta since 1838 overbank splays are much smaller covering areas of less than 2 sq km and having thicknesses of 3 m but are associated with high floods on the river at the river mouth continued progradation of the distributary channel can form distributary mouth sand bodies that have dimensions of 17 km long 8 km wide and a thickness of 80 m in a period of only 200 yr differential sedimentary loading at the river mouth results in formation of diapirs that display vertical movements in excess of 100 m in a period of 20 yr on the subaqueous delta platform sediment instabilities operate nearly continuously mass moving large quantities of shallow water deposits to deeper water environments via arcuate rotational slides and mudflow gullies and depositional lobes all of these changes and processes operate at differing spatial and temporal scales but all result in deposition of large volumes of sediment over extremely short periods of time

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

cl br ratios and environmental isotopes as indicators of recharge variability and groundwater flow an example from the southeast murray basin australia abstract systematic variations in cl br ratios together with r 36 cl values 14 c activities and 18 o values reflect differences in groundwater recharge and define groundwater flow paths in the riverine province of the southeast murray basin in groundwater from the shallowest shepparton formation homogenisation of cl br and 18 o values and a decline in 14 c activities with depth imply that vertical flow dominates the 14 c activities define variations in pre land clearing recharge in the palaeovalleys of present day rivers deep leads which contain sandier sediments higher recharge 0 5 to 1 4 mm year produced relatively fresh groundwater tds 36 cl values in groundwater from the goulburn subcatchment zones of groundwater with variable cl br ratios in the deeper calivil renmark aquifer also allow the detection of rapid leakage from the surface that has the potential to compromise groundwater resources

shelf edge deltas and drowned barrier island complexes on the northwest florida outer continental shelf abstract a high resolution multibeam survey of the northwest florida shelf mapped six relict shelf edge deltas each with a drowned barrier island system developed on its south and southwestern rims the deltas appear to have formed during periods of sea level stasis that occurred between 58 000 and 28 000 years ago the barrier islands formed on the deltas during periods of slow regression during this same time interval large fields of asymmetric dunes are found on the delta surfaces as well as on the south and southwestern flanks of the deltas the asymmetry and orientation of the dunes suggest that a northward flowing current was sheared by the presence of the delta topography and as a result the upper layer of the flow continued to the north whereas the lower layer was steered by the topography the topographic steering accelerated the northward flow around the south and southwestern flanks with speeds adequate to form large dunes the flow slowed after rounding southwestern flank but accelerated again as it encountered the next delta flank to the north the age of the dune formation is unknown and no northward flowing geostrophic flow has been reported in the literature from this area

shelf edge delta and reef development on a mixed siliciclastic carbonate margin central great barrier reef the great barrier reef gbr is the world s largest extant mixed silicilastic carbonate margin previous research on the great barrier reef has suggested that the extensive barrier reef system may act as an impermeable barrier and limit the development of delta systems during lowstands but sufficient geophysical data to support this hypothesis are lacking we use dense sparker seismic and sub bottom profiler data to better understand the structure of a large lobe shaped feature 10 km 10 km on the shelf edge of the central gbr and the interactions between siliciclastic and carbonate sedimentary systems interpreted sparker seismic contains prograding clinoforms and suggest that the lobe shaped feature was a river dominated shelf edge delta a delta on the shelf edge implies that the presence of an exposed barrier reef was not a major impediment to deposition and that other adjacent lobe shaped features are also deltaic deposits the shelf edge deltas were deposited onto a broad upper slope terrace that allowed continued progradation and limited incision when sea level fell below the shelf edge delta foresets are commonly colonized by coral reefs but the spatial and temporal relationship between reefs and some deltaic units remains unclear the presence of multiple shelf edge deltas that link to previously mapped burdekin river paleo channels indicates a complex history of sedimentation with the burdekin river delta migrating up to 100 km along the gbr margin during the late quaternary regional bathymetric data suggest that large modern or recent shelf edge deltas are rare on the gbr and that there was a broad range of sedimentary processes operating along the margin of the gbr during periods of low sea level

late quaternary shedding of shallow marine carbonate along a tropical mixed siliciclastic carbonate shelf great barrier reef australia the north east australian margin is the largest modern example of a tropical mixed siliciclastic carbonate depositional system with an outer shelf hosting the great barrier reef gbr and an inner shelf dominated by fluvially sourced siliciclastic sediment wedges the long term interplay between these sediment components and sea level is recorded in the queensland trough a 1 2 km deep n s elongate basin situated between the gbr platform and the queensland plateau in this paper 154 samples from 45 surface grabs and six well dated piston cores were analysed for total carbonate content carbonate mineralogy and sr concentration to establish spatial and temporal patterns of carbonate accumulation in the queensland trough over the last 300 kyr surface carbonate contents are lowest on the inner shelf 5 and in the trough axis 60 because of siliciclastic dilution carbonate on the shelf is mostly sr rich aragonite and high mg calcite hmc whereas that in the basin is mostly low mg calcite once normalized to remove the effects of siliciclastic dilution surface sr rich aragonite and hmc abundances decrease linearly to background levels 100 km seaward of the shelf edge core samples show that over time normalized aragonite and sr abundances are greatest during periods of shelf flooding and lowest when sea level drops below the shelf edge this is consistent with changes in the production of coral and calcareous algae and the shedding of their debris from the shelf interestingly normalized hmc concentrations on the slope peak during periods of major transgression perhaps because of maximum off shelf transport from inter reef areas or intermediate water dissolution after accounting for siliciclastic dilution there are strong similarities in both spatial and temporal patterns of carbonate minerals between slopes and basins of the north east australian margin and those of pure carbonate margins such as the bahamas a limited set of basic processes including the formation and breakdown of carbonate on the shelf the transport of carbonate off the shelf and eustatic sea level probably controls carbonate accumulation in slope and basin settings of tropical environments irrespective of proximal siliciclastic sediment sources

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

shelf edge delta regime as a predictor of deep water deposition abstract shelf edge delta depositional style and particularly the presence of river dominated shelf edge deltas is a reliable indicator of deep water sand delivery as documented by a dataset of some 29 shelf margin clinoforms shelf edge delta regime defined as the sum of the effects of fluvial tidal wave and other oceanographic currents impacting deltas as they arrive at the shelf edge is a key predictor for likelihood of sand transport off the shelf edge to deep water conventional sequence stratigraphic concepts assume that delivery of sand to the deep water occurs primarily during falling and lowstand of relative sea level and that basinward transport is associated with shelf edge incision and sediment bypass recent analysis of outcrop and subsurface datasets has shown that sediment can also be transported to the deep water during rising and highstand of sea level provided sediment flux is high in addition some examples with documented shelf edge entrenchment associated with sea level fall did not deliver significant sand volumes to the deep water in contrast to the emphasis given to sea level and supply the role of the shelf edge delta itself and especially its process regime has received relatively little attention the data suggest that the behavior and process regime of the delta at the shelf edge is critical except where shelf width is minimal

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

paleohydrologic implications of some deep soilwater chloride profiles murray basin south australia abstract a chloride mass balance approach to estimating soilwater ages and paleorecharge rates was tested in an area where considerable paleoclimatic data were available for comparison application of the method to data from four cores of the unsaturated zone taken in the western murray basin showed that the soil water at the base of the chloride build up or bulge associated with the root zone of the native mallee vegetation was emplaced during the last glacial interval at least 20 000 years bp furthermore recharge rates at this time were very low these observations agree with independent paleoclimate evidence that suggest that this time was colder windier and drier results are consistent with the notion that the root zone chloride bulge so typical of the murray mallee region developed in response to aridity that peaked during the last full glacial interval in australia the chloride method is a useful tool in paleohydrology especially when used in concert with other evidence