two cryogenian glacial successions compared aspects of the sturt and elatina sediment records of south australia abstract two cryogenian glacial sequences the sturt and elatina occur within the adelaide rift complex s australia and are part of an 8 km thick succession recording rodinia fragmentation and subsequent passive margin development we compare and contrast these glacial successions presenting new data including detailed logged sections for both glacial sequences facies analysis reveals a total of six facies associations recording a range of glacial and glacially related processes these are a diamictite facies association ice proximal debris flows a sheet sandstone facies association fluvial deposits a flaser and rhythmically bedded facies association tidal flat a hummocky cross stratified sandstone facies association shoreface to offshore transition zone deposits and an underflow facies association recording offshore deposition a sixth facies association a ferruginous lonestone bearing siltstone is restricted to the top of the elatina formation and records rapid environmental amelioration and emergence from glaciation in the central flinders ranges the sturt succession commences with a glacial erosion surface ges which in agreement with previous workers was probably enhanced by rifting this ges is overlain in ascending order by the pualco tillite holowilena ironstone and wilyerpa formation with the warcowie dolomite member at the base of this latter formation a second ges is preserved within this latter unit and is overlain by a stratigraphic motif that records an alternation of offshore transition zone and offshore deposits significant base level falls within the wilyerpa formation are identified by fluvial deposits sitting disconformably upon offshore deposits in contrast within the elatina formation a single ges is proposed which defines the base of the formation the elatina formation is split into two informal members on the basis of analysis of sediment stacking patterns and the recognition of a sharp stratigraphic surface that divides the formation apart from a locally preserved basal diamictite the lower member consists of fluvial deposits whereas the upper member is dominated by a mixture of tidal flat sediments and debris flow deposits the boundary between these units is therefore interpreted as a hybrid surface recording tidal ravinement in some areas and a glacial advance in others deglaciation left contrasting deposits the sturt deglaciation culminated in deposition of black shale of the tindelpina shale member of the tapley hill formation seemingly as a sheet like deposit over the adelaide rift complex and beyond into the amadeus basin of central australia the elatina deglaciation meanwhile began first with deposition of the sixth facies association ferruginous dropstone bearing siltstone then proceeded with deposition of cap dolostone of the nuccaleena formation

sedimentary challenge to snowball earth evidence from the magnetic field fossilized in sedimentary rocks suggests that more than 600 million years ago ice occupied tropical latitudes a popular explanation for these findings the snowball earth concept envisages a fully frozen earth for millions of years caused by a runaway ice albedo feedback a rapid catastrophic meltback at very high levels of atmospheric carbon dioxide is thought to have ended this extreme climatic state however sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans throughout the glacial cycle the sedimentary evidence therefore indicates that despite the severity of glaciation some oceans must have remained ice free significant areas of open ocean have important implications for the survival and diversification of life and for the workings of the global carbon cycle the snowball earth concept envisages a fully frozen earth for millions of years several times during the neoproterzoic era between 1 000 and 542 million years ago however the sedimentary evidence suggests that despite the severity of glaciation some oceans must have remained ice free

a spatially explicit model of runoff evaporation and lake extent application to modern and late pleistocene lakes in the great basin region western united states 1 a spatially explicit hydrological model was applied to the great basin in the western united states to predict runoff magnitude and lake distributions under modern and late pleistocene conditions the model iteratively routes runoff through depression to find a steady state solution and was calibrated with mean annual precipitation pan evaporation temperature and stream runoff data the predicted lake distribution provides a close match to present day lakes for the late pleistocene the sizes of lakes bonneville and lahontan are well predicted by linear combinations of 0 2 5 8 c decreases in temperature and corresponding increases in precipitation from 2 0 to 1 0 times modern values this corresponds to runoff depths ranging from 1 7 to 4 1 times the present values and yearly evaporation from 0 4 to 1 times modern values to reproduce lake manly however combinations of temperature decreases up to 9 c or precipitation up to 2 8 times the present values were required

leachate detection via statistical analysis of electrical resistivity and induced polarization data at a waste disposal site northern israel landfill site is an intensely heterogeneous medium in which application of 2 d geophysical techniques frequently does not enable its accurate examination due to the lack of correlation between different geophysical profiles the study was aimed to eliminate such difficulty hereafter the leachate detection methodology is presented including 2 d smoothness constrained inversion of geoelectrical raw data collected in situ the inverted data normalization and statistical examination to eradicate influence of high heterogeneity of the landfill body the generalized statistical model of the entire site was created including the likelihood analysis of the entire normalized data set three geoelectrical parameters were involved in the analysis inversed electrical resistivity inversed chargeability ip and the ratio of inversed chargeability to inversed electrical resistivity ip res the study was combined with the synthetic modeling the analysis of bulk versus fluid electrical resistivity relationship and test borehole drillings such generalized analysis ensures independency of the results from the locality of sampling measurements it was shown that leachate detection can be correctly performed utilizing the ip res ratio while the anomaly s likelihood is higher than 90

is there a conflict between the neoproterozoic glacial deposits and the snowball earth interpretation an improved understanding with numerical modeling the behavior of the terrestrial glacial regime during the neoproterozoic glaciations is still a matter of debate some papers claim that the glacial sequences cannot be explained with the snowball earth scenario indeed the near shutdown of the hydrological cycle simulated by climatic models once the earth is entirely glaciated has been put in contrast with the need for active wet based continental ice sheets to produce the observed thick glacial deposits a climate ice sheet model is applied to the older extreme neoproterozoic glaciation around 750 ma with a realistic paleogeographic reconstruction of rodinia our climate model shows that a small quantity of precipitation remains once the ocean is completely ice covered thanks to sublimation processes over the sea ice at low latitudes acting as a water vapor source after 10 ka of the ice sheet model the ice volume in the tropics is small and confined as separate ice caps on coastal areas where water vapor condenses however after 180 ka large ice sheets can extend over most of the supercontinent rodinia several areas of basal melting appear while ice sheets reach their ice volume equilibrium state at 400 ka they are located either under the two single domed ice sheets covering the antarctica and the laurentia cratons or near the ice sheet margins where fast flow occurs only the isolated and high latitude cratons stay cold based finally among the simulated ice sheets most have a dynamic behavior in good agreement with the needs inferred by the preserved thick formations of diamictite and share the features of the antarctica present day ice sheet therefore our conclusion is that a global glaciation would not have hindered the formation of the typical glacial structures seen everywhere in the rock record of neoproterozoic times

bolla bollana boulder beds a neoproterozoic trough mouth fan in south australia the bolla bollana formation is an exceptionally thick ca 1500 m rift related sedimentary succession cropping out in the northern flinders ranges south australia which was deposited during the sturtian mid cryogenian glaciation lithofacies analysis reveals three distinct facies associations which chart changing depositional styles on an ice sourced subaqueous fan system the diamictite facies association is dominant and comprises both massive and stratified varieties with a range of clast compositions and textures arranged into thick beds 1 to 20 m representing stacked ice proximal glaciogenic debris flow deposits a channel belt facies association most commonly consisting of normally graded conglomerates and sandstones displays scour and fill structure of ca 10 m width and 1 to 3 m depth these strata are interpreted as channelized turbidites rare mud filled channels in this facies association bear glacially striated lonestones finally a sheet heterolithics facies association contains a range of conglomerates through sandstones to silty shales arranged into clear normally graded cycles from the lamina to bed scale these record a variety of non channelized turbidites probably occupying distal and or inter channel locations on the subaqueous fan coarsening and thickening up cycles capped by dolomicrites or mudstones are indicative of lobe build out and abandonment potentially as a result of ice lobe advance and stagnation dropstones recognized by downwarped and punctured laminae beneath pebbles to boulders in shale or in delicate climbing ripple cross laminated siltstones are clearly indicative of ice rafting the co occurrence of ice rafted debris and striated lonestones strongly supports a glaciogenic sediment source for the diamictites comparison to pleistocene analogues enables an interpretation as a trough mouth fan most probably deposited leeward of a palaeo ice stream beyond emphasizing the highly dynamic nature of sturtian ice sheets these interpretations testify to the oldest trough mouth fan recorded to date

comparison of warm and wet and cold and icy scenarios for early mars in a 3 d climate model we use a 3 d general circulation model to compare the primitive martian hydrological cycle in warm and wet and cold and icy scenarios in the warm and wet scenario an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice free northern ocean precipitation shows strong surface variations with high rates around hellas basin and west of tharsis but low rates around margaritifer sinus where the observed valley network drainage density is nonetheless high in the cold and icy scenario snow migration is a function of both obliquity and surface pressure and limited episodic melting is possible through combinations of seasonal volcanic and impact forcing at surface pressures above those required to avoid atmospheric collapse 0 5 bar and moderate to high obliquity snow is transported to the equatorial highland regions where the concentration of valley networks is highest snow accumulation in the aeolis quadrangle is high indicating an ice free northern ocean is not required to supply water to gale crater at lower surface pressures and obliquities both h2o and co2 are trapped as ice at the poles and the equatorial regions become extremely dry the valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41 8 obliquity but uncorrelated with precipitation produced by the warm and wet simulation because our simulations make specific predictions for precipitation patterns under different climate scenarios they motivate future targeted geological studies

late pleistocene and early holocene rivers and wetlands in the bonneville basin of western north america abstract field investigations at dugway proving ground in western utah have produced new data on the chronology and human occupation of late pleistocene and early holocene lakes rivers and wetlands in the lake bonneville basin we have classified paleo river channels of these ages as gravel channels and sand channels gravel channels are straight to curved digitate and have abrupt bulbous ends they are composed of fine gravel and coarse sand and are topographically inverted i e they stand higher than the surrounding mudflats sand channels are younger and sand filled with well developed meander scroll morphology that is truncated by deflated mudflat surfaces gravel channels were formed by a river that originated as overflow from the sevier basin along the old river bed during the late regressive phases of lake bonneville after 12 500 and prior to 11 000 14c yr b p dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11 000 to 8800 14c yr b p and are probably related to continued sevier basin overflow and to groundwater discharge paleoarchaic foragers occupied numerous sites on gravel channel landforms and adjacent to sand channels in the extensive early holocene wetland habitats reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting paleoarchaic foragers in the old river bed delta were less mobile than elsewhere in the great basin

simulated degradation of lunar impact craters and a new method for age dating farside mare deposits with the advent of clementine data it is now possible to determine the lithology and extent of geologic materials on the moon particularly the farside mare deposits however traditional crater counting techniques do not provide reliable age estimates of these materials owing to their small surface areas to support such studies we present a model for estimating their age by analyzing the morphometry of degraded craters 1 3 km in diameter a photoclinometric model was adapted for use with monoscopic 0 750 m ultraviolet visible and high resolution images where we extracted the topography of fresh craters a two dimensional computer model simulating linear diffusional creep was applied to fresh craters at a variety of diameters the resulting profiles were then compared to photoclinometric profiles of degraded craters of known ages for calibration application of the resulting model to degraded craters in the mare deposit of the central apollo basin 36 5 latitude 208 0 longitude indicates that this material was emplaced during the early imbrian period 3 85 ga by calculating the amount of material eroded from each of the degraded craters observed in this unit the average erosion rate is estimated to be 2 0 0 1 10 7 mm yr on the moon since the imbrian the estimated amount of material eroded during any given period suggests that the erosion rate has decreased with time implying that the flux of larger impactors has as well

depositional environment and regional stratigraphic significance of the serle conglomerate a late proterozoic submarine fan complex south australia abstract the serle conglomerate is a lenticular unit 8 km 160 m at the top of the late proterozoic sturtian glacigenic yudnamutana subgroup in the northeastern part of the adelaide geosyncline in its type area at the west end of the fitton trough it can be subdivided into five stratigraphic units interpreted as the products of deposition in the mid to upper portions of a submarine fan complex progradation of submarine fans under conditions of eustatic sea level rise was probably due to concomitant fault activity and isostatic readjustments along the basin margins in an area about 10 km west of the type area similar conglomerates overlie glacigenic rocks of the yudnamutana subgroup with an erosional contact and therefore are younger than them there is no definitive evidence of glacial influence during deposition of the serle conglomerate so that previous correlations with glacigenic diamictites elsewhere in the adelaide geosyncline are unlikely there is no justification in this area for inferring two separate early sturtian glaciations

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

topographic influences on development of martian valley networks 1 some morphometric differences between terrestrial and martian valley networks may reflect the precursor topography on mars particularly impact basins or tectonic slopes to evaluate these possible influences we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings we collected data including latitude longitude watershed length divide and terminal elevations watershed relief and slope slope orientation and qualitative descriptors including whether a drainage basin was open or closed the longest valley networks and most overflowed basins occur on preexisting intercrater slopes of 0 1 1 particularly on north facing slopes associated with the crustal dichotomy the control of watershed length by earlier noachian topographic features which the relict networks did not significantly modify suggests that the early to middle noachian geomorphic environment was nominally much drier than the later noachian to hesperian transition the distribution of fluvial valleys and likely orographic effects created by the crustal dichotomy suggest that evaporation from the northern lowlands was an important source of atmospheric humidity over short time scales much of the highland plateau consists of smaller enclosed watersheds which along with cooler temperatures detained surface water at high elevations lengthening or impeding the global water cycle ponding and evaporation may have partly offset a continentality effect of the highland landmass prolonged modification of the intercrater geomorphic surface prior to incision of valley networks included substantial weathering reduction of relief and gravity driven sediment transport indicating a long term role for surface water in a transport limited arid to hyperarid noachian paleoclimate

variation in groundwater salinity in a tidal salt marsh basin north inlet estuary south carolina abstract groundwater flow of freshwater from upland forests into salt marshes is influenced by hydrologic forces that operate over a wide range of temporal scales including storm events tidal fluctuations seasonal variations in rainfall and evapotranspiration et groundwater salinity can be a useful first order indicator of the balance between these flow processes a dipole dipole electrical resistivity survey was conducted approximately monthly during 2005 to measure groundwater salinity across a portion of crabhaul creek a tidal salt marsh basin at the boundary of the upland forest and the north inlet marsh in south carolina the monthly electrical resistivity surveys were designed to provide a detailed spatially continuous measurement of subsurface conductivity to a depth of 4 m in order to further investigate the seasonal variation in groundwater salinity resistivity models were corroborated by simultaneous measurements of salinity in nearby piezometers the freshwater brackish water interface was clearly imaged by the resistivity movement of this interface occurs on a timescale of months rather than a regular seasonal variation the average salinity in the marsh basin is highest in late summer july august when et is highest and lowest during the winter november december the position of the brackish freshwater interface changes but is not well correlated to local rainfall or tidal cycles except under specific circumstances a steady state hydrological model correctly predicts the average position of the freshwater brackish interface and suggests a linear relationship between the height of the water table and the location of the interface these results suggest a complex relationship between precipitation events and groundwater flow from the forest into the marsh

sea ice free conditions during the sturtian glaciation early cryogenian south australia in the neoproterozoic snowball earth hypothesis shutdown of the planet9s hydrological system has been attributed to a global ice cover during one or more extreme glaciations in the central flinders ranges south australia the yudnamutana subgroup of sturtian age includes diamictite sandstone and siltstone units of glaciomarine origin as much as 5000 m thick and is overlain by postglacial transgressive siltstone and shale of the tindelpina shale member tapley hill formation in the central flinders ranges the yudnamutana subgroup consists of 1 the pualco tillite gravity resedimented glacial deposits 2 the holowilena ironstone glacioturbidites 3 poorly stratified pebbly diamictite of the warcowie dolomite member lowermost wilyerpa formation gravity resedimented glacial deposits succeeded by 4 siltstones and sandstones with abundant hummocky cross stratification hcs storm deposits and 5 a lonestone bearing succession with cobble sized clasts in the upper wilyerpa formation ice rafted debris interpreted to record a glacial re advance in which hcs is absent because the action of oscillating waves is required to produce hcs on the seafloor its presence indicates an interval of significant meltback prior to glacial re advance given that the hcs occurs 2 km beneath the tindelpina shale member it signifies a major ice free interval during the sturtian glaciation

monitoring and simulation of salinity changes in response to tide and storm surges in a sandy coastal aquifer system tidal dynamics and especially storm surges can have an extensive impact on coastal fresh groundwater resources combined with the prospect of sea level rise and the reliance of many people on these resources this demonstrates the need to assess the vulnerability of coastal areas to these threats in this study we investigated the impact of tides and storm surges on coastal groundwater at a pilot location on the dutch coast viz the sand engine to monitor changes in groundwater salinity under a variety of conditions we performed automated measurements with electrical resistivity tomography for a period of 2 months between november 2014 and january 2015 the obtained resistivity images were converted to salinity images and these images served effectively as observations of the impact of tidal fluctuations salt water overwash during storm surges and the recovery of the freshwater lens after land surface inundations most of the observed changes in groundwater head and salinity could be reproduced with a two dimensional variable density groundwater flow and salt transport model this shows that groundwater models can be used to make accurate predictions of the impact of tides and storm surges on fresh ground water resources given a thorough understanding of the local system comparisons of measurements and model simulations also showed that morphological changes and wave run up can have a strong impact on the extent of land surface inundations in low elevation dynamic coastal environments and can therefore substantially affect coastal fresh groundwater resources

the equilibrium size frequency distribution of small craters reveals the effects of distal ejecta on lunar landscape morphology abstract small craters of the lunar maria are observed to be in a state of equilibrium in which the rate of production of new craters is on average equal to the rate of destruction of old craters crater counts of multiple lunar terrains over decades consistently show that the equilibrium cumulative size frequency distribution sfd per unit area of small craters of radius r is proportional r 2 and that the total crater density is a few percent of so called geometric saturation which is the maximum theoretical packing density of circular features while it has long been known that the primary crater destruction mechanism for these small craters is steady diffusive degradation there are few quantitative constraints on the processes that determine the degradation rate of meter to kilometer scale lunar surface features here we combine analytical modeling with a monte carlo landscape evolution code known as the cratered terrain evolution model to place constraints on which processes control the observed equilibrium size frequency distribution for small craters we find that the impacts by small distal ejecta fragments distributed in spatially heterogeneous rays is the largest contributor to the diffusive degradation which controls the equilibrium sfd of small craters other degradation or crater removal mechanisms such cookie cutting ejecta burial seismic shaking and micrometeoroid bombardment likely contribute very little to the diffusive topographic degradation of the lunar maria at the meter scale and larger

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

electrical imaging and fluid modeling of convective fingering in a shallow water table aquifer free to read unstable density driven flow can lead to enhanced solute transport in groundwater only recently has the complex fingering pattern associated with free convection been documented in field settings electrical resistivity er tomography has been used to capture a snapshot of convective instabilities at a single point in time but a thorough transient analysis is still lacking in the literature we present the results of a 2 year experimental study at a shallow aquifer in the united arab emirates that was designed to specifically explore the transient nature of free convection er tomography data documented the presence of convective fingers following a significant rainfall event we demonstrate that the complex fingering pattern had completely disappeared a year after the rainfall event the observation is supported by an analysis of the aquifer halite budget and hydrodynamic modeling of the transient character of the fingering instabilities modeling results show that the transient dynamics of the gravitational instabilities their initial development infiltration into the underlying lower density groundwater and subsequent decay are in agreement with the timing observed in the time lapse er measurements all experimental observations and modeling results are consistent with the hypothesis that a dense brine that infiltrated into the aquifer from a surficial source was the cause of free convection at this site and that the finite nature of the dense brine source and dispersive mixing led to the decay of instabilities with time this study highlights the importance of the transience of free convection phenomena and suggests that these processes are more rapid than was previously understood

constraining electric resistivity tomography by direct push electric conductivity logs and vibracores an exemplary study of the fiume morto silted riverbed ostia antica western italy the inversion of geoelectric data is non unique therefore electric resistivity tomography ert usually results in different subsurface models that fit observed apparent resistivity values equally well to reduce the uncertainty constraints on both geometry and resistivity of subsurface structure can be incorporated into the ert inversion in our study we test different ways of constraining ert by a applying improved starting models b applying structural constraints and c applying both structural and resistivity constraints a priori information is needed for these approaches which is acquired from direct push electrical conductivity dp ec logs and vibracores in our study we found that adapting high vertical resolution of dp ec logs to coarser ert resolution requires blocking of the logs these blocked logs can be used for constraining the ert inversion with resistivity and structural constraints along so called regions around the log locations which was found to be the best approach in this

composition of the drainage network on early mars abstract among the 2208 martian fluvial features plotted in a previous study z geomorphol 37 1 1993 57 the hydrological characteristics of 71 pristine fluvial valley networks located between 18 0 n and 55 0 s were surveyed using viking orbiter photomosaic bases at 1 2 million scale the surveyed networks display 1 systems organized mainly as first order streams 85 of which have lengths not exceeding 1000 km with a large amount of the statistical sample having lengths between 200 and 500 km generally shorter than the degraded valleys studied by baker and partridge j geophys res 91 1986 3561 2 drainage basins with average areas of about 5000 km2 3 a random distribution and 4 headwater tributary drainage densities kd ranging systematically between 0 03 and 0 2 km 1 which are comparable to terrestrial drainage densities in arid climates the compositions of the surveyed pristine valley networks are comparable to the degraded fluvial systems that dissect older martian surface materials thus it appears that no dramatic changes occurred in martian hydrology since the earlier period of formation of the degraded valleys such as described by baker and partridge j geophys res 91 1986 3561 subsurface aquifer drainage may have been a large contributor to drainage basin formation since early in mars history

integrating non colocated well and geophysical data to capture subsurface heterogeneity at an aquifer recharge and recovery site abstract geophysical data have proven to be very useful for lithological characterization however quantitatively integrating the information gained from acquiring geophysical data generally requires colocated lithological and geophysical data for constructing a rock physics relationship in this contribution the issue of integrating noncolocated geophysical and lithological data is addressed and the results are applied to simulate groundwater flow in a heterogeneous aquifer in the prairie waters project north campus aquifer recharge site colorado two methods of constructing a rock physics transform between electrical resistivity tomography ert data and lithology measurements are assessed in the first approach a maximum likelihood estimation mle is used to fit a bimodal lognormal distribution to horizontal crosssections of the ert resistivity histogram in the second approach a spatial bootstrap is applied to approximate the rock physics relationship the rock physics transforms provide soft data for multiple point statistics mps simulations subsurface models are used to run groundwater flow and tracer test simulations each model s uncalibrated predicted breakthrough time is evaluated based on its agreement with measured subsurface travel time values from infiltration basins to selected groundwater recovery wells we find that incorporating geophysical information into uncalibrated flow models reduces the difference with observed values as compared to flow models without geophysical information incorporated the integration of geophysical data also narrows the variance of predicted tracer breakthrough times substantially accuracy is highest and variance is lowest in breakthrough predictions generated by the mle based rock physics transform calibrating the ensemble of geophysically constrained models would help produce a suite of realistic flow models for predictive purposes at the site we find that the success of breakthrough predictions is highly sensitive to the definition of the rock physics transform it is therefore important to model this transfer function accurately

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

crossover analysis of mars orbiter laser altimeter data in its first 15 months of continuous operation the mars orbiter laser altimeter mola instrument aboard mars global surveyor ranged to mars over 330 million times generating more than 5000 orbital profiles with a ranging precision of 0 4 m over smooth terrain the accuracy of the profiles depends on knowledge of the spacecraft position orientation and observation time which are subject to errors we model these errors via the analysis of over 24 million altimetric crossovers a quasiperiodic once per revolution adjustment of the ground tracks as a function of time in three locally orthogonal directions minimizes the altimetric residuals via least squares using a sparse matrix technique computational effort scales linearly with the number of crossovers and only marginally with the number of parameters orbital errors mainly result from poor modeling of spacecraft thrusting events in the absence of tracking seasonal effects likely due to changing thermal environment as well as residual miscalibrations are evident in the pointing solutions incorporating multiple parameters per revolution significantly improves crossover residuals and resolves pointing aberrations during orbital transitions from night to day altimetry from the adjusted tracks generates a topographic model whose accuracy is typically better than 1 m vertically with respect to the center of mass of mars the centroid position of each mola shot is typically accurate to 100 m horizontally terrain models from accurately located lidar data can be gradient shaded to illuminate geological structures with 1 in 1000 slopes that are invisible to cameras temporal changes in elevation e g frost deposition ablation at decimeter levels may also be assessed using crossovers but results must be interpreted with caution due to uncertainties in range walk correction

an evaluation of the electrical resistivity method for water reservoir salinity studies an important potential application of the electrical resistivity method occurs in salinity studies of lakes and water reservoirs however uncertainty exists because there is a problem of equivalence in resistivity data interpretation and because the resistivity variation in the water layer in reservoirs is subtle contrasts of a factor of two and changes over short intervals of time typically in hours or days we carry out numerical modeling and inversion of synthetic data and field resistivity data from lake whitney texas u s a to examine how accurately resistivity in the water column in reservoirs can be determined using the electrical resistivity method our objective is to advance the method as a tool in limnologic research for mapping freshwater zones in impacted lakes and water reservoirs the simulated freshwater target in the synthetic data effectively is realized from the inversion with root mean square rms error less than 10 however the resolutionof the inverted sections decreases w

sequencing the sturtian icehouse dynamic ice behaviour in south australia the cryogenian record of south australia includes the type region of the sturtian glaciation the oldest of three pan global icehouse intervals during the neoproterozoic data are presented from previously little described sections at holowilena creek oladdie creek and hillpara creek in the central and southern flinders ranges where five facies associations are recognized these are 1 diamictite and conglomerate 2 interbedded heterolithic deposits 3 hummocky cross stratified sandstone 4 lonestone bearing siltstone and 5 ferruginous siltstone and sandstone the succession reveals significant lateral and vertical facies variation which is linked to a complex inherited palaeotopography and distance from the sediment source repeated stratigraphic occurrences of striated clasts and abundant ice rafted debris strongly support recurrent glacial influence on sedimentation the intercalation of gravitationally reworked diamictites dropstone bearing siltstone and dropstone free siltstone testifies to dynamic sedimentation within a periodically glacially influenced subaqueous environment sequence stratigraphic analysis identifies four glacial advance systems tracts separated by three glacial retreat systems tracts wherein hummocky cross stratified sandstones attest to open water conditions these findings support dynamic ice sheet behaviour in south australia and provide clear evidence for repeated intra sturtian ice sheet recession

the timing of alluvial activity in gale crater mars the curiosity rover s discovery of rocks preserving evidence of past habitable conditions in gale crater highlights the importance of constraining the timing of responsible depositional settings to understand the astrobiological implications for mars crater statistics and mapping reveal the bulk of the alluvial deposits in gale including those interrogated by curiosity were likely emplaced during the hesperian thereby implying that habitable conditions persisted after the noachian crater counting data sets and upper peace vallis fan morphology also suggest a possible younger period of fluvial activation that deposited 10 20 m of sediments on the upper fan after emplacement of the main body of the fan if validated water associated with later alluvial activity may have contributed to secondary diagenetic features in yellowknife bay

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

contribution of electrical resistivity tomography to the study of detrital aquifers affected by seawater intrusion extrusion effects the river velez delta velez malaga southern spain abstract the coastal aquifer of the plio quaternary delta sediment deposits of the velez river province of malaga spain presents a highly irregular basement morphology and widely varying fill thickness 10 80 m between neighbouring sectors the basin which is tectonically controlled is filled with lutite facies alternating with channel filling rudites this detrital aquifer is affected by seasonal seawater intrusion extrusion processes due to increasing withdrawal of groundwater for human consumption and irrigation during dry periods a study was performed to improve the hydrogeological knowledge of this coastal aquifer system the study examined the morphology of the impervious substratum the facies distribution and the position of the seawater wedge for this purpose an electrical resistivity tomography ert geophysical technique was used and the tomographic data were calibrated using geological observations and borehole studies an analysis was carried out to compare the direct information obtained from the 35 boreholes with the indirect data corresponding to the four electrical tomography profiles in the study over 9660 resistivity data points were processed the ert profiles perfectly corroborated the information derived from the boreholes the profiles made it possible to detect thickness changes lithological changes and the presence of faults moreover from a hydrogeologic standpoint this research technique is capable of detecting the position of the phreatic level and in coastal aquifers such as the one examined in this study the possible horizontal or vertical penetration of seawater intrusion therefore the electrical geophysical prospecting based on ert can be highly useful in areas lacking sufficient geological information and or mechanical borehole data

mapping soil layers using electrical resistivity tomography and validation sandbox experiments abstract knowledge of the geologic structure at a field site is a useful piece of information for hydrologic modeling since it can serve as more site specific prior information about the hydraulic parameter patterns at the site than generic spatial statistics widely accepted electrical resistivity tomography ert survey for mapping subsurface anomalies could be a viable tool for acquiring this information however their ability to delineate geologic structures has not been thoroughly investigated in this study two dimensional ert numerical experiments were first conducted to study the effects of boundary conditions on the dipole dipole and pole pole array configurations an ert setup subsequently was implemented in a sandbox consisting of complex layers of different sands a continuous copper wire was installed along the sides of the sandbox to impose potential boundaries using data collected with the pole pole array in the sandbox under different degrees of drainage and the successive linear estimator sle algorithm we show that ert yields electrical conductivity estimates of complex layer structures with small uncertainties in addition using sle with physically meaningful correlation scales as prior information can lead to an electrical conductivity field that is consistent with visually observed layer structures the correlation scale concept also was demonstrated to provide guidance to the design of the electrode spacing in the surveys moreover the estimated field was validated by predicting electrical potential fields from two independent ert surveys using electrodes at different locations results of this study suggest that the combination of ert and sle is a viable geophysical survey tool for mapping geologic layer structures research significance this study develops a method to implement prescribed potential boundaries for enhancing the pole pole ert survey illustrates the importance of correlation scales and develops an approach for validating ert results

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

palaeoclimate implications from deep drilling of neoproterozoic strata in the officer basin and adelaide rift complex of australia a marine record of wet based glaciers abstract two prominent episodes of neoproterozoic glaciation in australia are recorded in the cryogenian sturtian

out of plane effects in 2d borehole to surface resistivity tomography and applications in mineral exploration in this paper we discuss the effects of anomalous out of plane bodies in two dimensional 2d borehole to surface electrical resistivity tomography with numerical resistivity modelling and synthetic inversion tests the results of the two groups of synthetic resistivity model tests illustrate that anomalous bodies out of the plane of interest have an effect on two dimensional inversion and that the degree of influence of out of plane body on inverted images varies the different influences are derived from two cases one case is different resistivity models with the same electrode array and the other case is the same resistivity model with different electrode arrays qualitative interpretation based on the inversion tests shows that we cannot find a reasonable electrode array to determine the best inverse solution and reveal the subsurface resistivity distribution for all types of geoelectrical models because of the three dimensional effect arising from neighbouring anomalous bodies the qualitative interpretation of inverted images from the two dimensional inversion of electrical resistivity tomography data without prior information can be misleading two dimensional inversion with drilling data can decrease the three dimensional effect we employed two and three dimensional borehole to surface electrical resistivity tomography methods with a pole pole array and a bipole bipole array for mineral exploration at abag banner and hexigten banner in inner mongolia china different inverse schemes were carried out for different cases the subsurface resistivity distribution obtained from the two dimensional inversion of the field electrical resistivity tomography data with sufficient prior information such as drilling data and other non electrical data can better describe the actual geological situation when there is not enough prior information to carry out constrained two dimensional inversion the three dimensional electrical resistivity tomography survey is the better choice

salt water infiltration in two artificial sea inlets in the belgian dune area in the dune area of the westhoek nature reserve situated in the western belgian coastal plain two artificial tidal inlets were made aiming to enhance biodiversity the infiltration of salt water in these tidal inlets was carefully monitored because a fresh water lens is present in the phreatic dune aquifer this forms an important source of fresh water which is for instance exploited by a water company the infiltration was monitored over a period of two years by means of electromagnetic borehole measurements em39 and by measurements of fresh water heads and temperature using a large number of observation wells em39 observations point to aquifer heterogeneity as a determining factor in the movement of the salt infiltration water it is shown that part of the infiltration water moves further in the dunes instead of towards the sea on the long term run possibility exists that salt water enters the extraction s capture zone this issue needs further monitoring and study fresh water head and temperature data illustrate that the main period of infiltration is confined to spring tide when large amounts of salt water enter the tidal inlets

imaging rainfall infiltration processes with the time lapse electrical resistivity imaging method electrical resistivity imaging eri was carried out continuously for 10 days to map the subsurface resistivity distribution along a potentially hazardous hillslope at the jieshou junior high school in taoyuan taiwan the reliability of the inverted resistivity structures down to about 25 m depth was examined with synthetic modeling using the same electrode arrangements installed on land surface as in field surveys together with a doi depth of investigation index calculated from the eri data the subsurface resistivity distribution is consistent with results from well logging these eri recordings were taken daily and provided highly resolved imagery of the resistivity distribution underground and illustrated the dynamical fluid flow behavior due to heavy rainfall infiltration using archie s law the resistivity distribution was transformed into a map of relative water saturation rws which is strongly correlated with the rainfall infiltration process we then found that the averaged rws is significantly correlated with daily precipitation our observations indicate that time lapse eri is effective in monitoring subterraneous rainfall infiltration moreover the preferential flow paths can be delineated according to the changes in averaged rws derived from the eri data

calibration of seawater intrusion models inverse parameter estimation using surface electrical resistivity tomography and borehole data electrical resistivity tomography ert can be used to constrain seawater intrusion models because of its high sensitivity to total dissolved solid contents tds in groundwater and its relatively high lateral coverage however the spatial variability of resolution in electrical imaging may prevent the correct recovery of the desired hydrochemical properties such as salt mass fraction this paper presents a sequential approach to evaluate the feasibility of identifying hydraulic conductivity and dispersivity in density dependent flow and transport models from surface ert derived mass fraction in the course of this study geophysical inversion was performed by using a smoothness constraint tikhonov approach whereas the hydrological inversion was performed using a gradient based levenberg marquardt algorithm two synthetic benchmarks were tested they represent a pumping experiment in a homogeneous and heterogeneous coastal aquifer respectively these simulations demonstrated that only the lower salt mass fraction of the seawater freshwater transition zone can be recovered for different times this ability has here been quantified in terms of cumulative sensitivity and our study has further demonstrated that the mismatch between the targeted and the recovered salt mass fraction occurs from a certain threshold we were additionally able to explore the capability of sensitivity filtered ert images using ground surface data only to recover in both synthetic cases the hydraulic conductivity while the dispersivity is more difficult to estimate we attribute the latter mainly to the lack of ert derived data at depth where resolution is poorer as well as to the smoothing effect of the ert inversion

electrical resistivity imaging for aquifer mapping over chikotra basin kolhapur district maharashtra electrical resistivity study assumes a special significance for mapping aquifers in hard rock areas a two dimensional 2d resistivity survey of chikotra basin southern part of kolhapur district in the deccan volcanic province of maharashtra was conducted the aim of this work was to determine the aquifer zones of the study area using electrical resistivity imaging technique the hydro geological section derived from the available dug well borehole lithology suggests that the top layer comprises red bole laterite or black soil followed by weathered fractured rock grading into compact basalts the sources of groundwater appear to be available in weathered and fractured basalt trapped between weathered overburden and hard rock results from the 2d inverted models of resistivity variation with depth suggest the occurrence of aquifers mostly in weathered fractured zones within the traps or beneath it the resistivity models suggest that the northern part of the study area represents a promising aquifer zone with reasonable thickness of weathered basement the models further indicate that there are several locations throughout the basin for possible groundwater exploration as it exhibited strong water bearing potential in the subsurface rocks

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

combined inversion of land and marine electrical resistivity tomography for submarine groundwater discharge and saltwater intrusion characterization electrical resistivity tomography ert is particularly suited for the characterization of saltwater intrusion and submarine freshwater discharge given its sensitivity to the electrical conductivity of pore water a comprehensive survey might combine land ert collected during low tide and marine ert acquired with lower sensitivity due to the presence of a seawater layer most often inverted separately in this contribution we propose a new methodology to jointly invert land and marine ert acquired along a same profile bringing them to a common situation at high tide we first estimate the electrical resistivity distribution under the land profile then we compute a corrected data set for land ert simulating a data set collected with the same level of water as the marine ert finally both land and marine ert data sets are inverted jointly we show that the approach allows to better image the freshwater saltwater distribution across the shoreline

the cryogenian record of glaciation and deglaciation in south australia abstract this paper reviews the state of our current knowledge of the cryogenian glacial and deglacial sedimentary records of south australia two distinct glacial intervals are recognised within rocks of cryogenian 850 630 ma age separated by an interglacial succession that by definition lacks glacial facies the glacial successions were laid down during the sturt and elatina glaciations each of these glaciations is arguably of global extent under the snowball earth hypothesis hoffman and schrag 2002 evidence for glaciation has been known for over one hundred years from the sturt tillite howchin 1900 when compared like for like in a systematic facies analysis both glacial successions show some similarities notably the occurrence of diamictites representing glacial deposition and slope reflux and dropstone bearing intervals but also show some dramatic differences notably deposition of the sturt succession was strongly influenced by extensional tectonics for which evidence is provided by dramatic thickness variations either side of major faults and palaeocurrent data sub basins formed during regional extension contain diamictites 4 6000 m thick e g the yudnamutana and baratta troughs in the northern and central flinders ranges respectively deposition of the younger elatina glacial deposits was locally influenced by diapirism in the central flinders ranges but otherwise these younger deposits seem to maintain a relatively constant thickness of

imaging artificial salt water infiltration using electrical resistivity tomography constrained by geostatistical data summary electrical resistivity tomography is a well known technique to monitor fresh salt water transitions in such environments boreholes are often used to validate geophysical results but rarely used to constrain the geoelectrical inversion to estimate the extent of salt water infiltration in the dune area of a natural reserve westhoek belgium electrical resistivity tomography profiles were carried out together with borehole electromagnetic measurements the latter were used to calculate a vertical variogram representative of the study site then a geostatistical constraint in the form of an a priori model covariance matrix based on the variogram was imposed as regularization to solve the electrical inverse problem inversion results enabled to determine the extension of the salt water plume laterally and at depth but also to estimate the total dissolved solid content within the plume these results are in agreement with the hydrogeological data of the site a comparison with borehole data showed that the inversion results with geostatistical constraints are much more representative of the seawater body in terms of total dissolved solids extension and height than results using standard smoothness constrained inversion the field results obtained for the westhoek site emphasize the need to go beyond standard smoothness constrained images and to use available borehole data as prior information to constrain the inversion

an exceptionally thick upper proterozoic sturtian glacial succession in the mount painter area south australia the yudnamutana subgroup is a thick succession of upper proterozoic sturtian glacigenic rocks preserved in the yudnamutana trough in the northeastern part of the adelaide geosyncline in ascending order the subgroup comprises the fitton bolla bollana and lyndhurst formations the name hamilton creek member is proposed for a locally developed conglomeratic facies at the base of the fitton formation these rocks are interpreted as the products of two glacial advances the first is evidenced by the hamilton creek member which includes sediment gravity flows derived from subaqueous glacial outwash the fitton formation is composed mainly of basinal siltstones and mudstones with associated coarser grained rocks that are largely sediment gravity flows diamictites in the upper part of the formation signify the onset of a second glacial advance thick diamictites of the bolla bollana formation are interpreted as rainout deposits from floating ice derived from ice streams debouching from a steep and high hinterland into a fault controlled basin the lyndhurst formation is mainly fine grained rocks dropstones and sparse diamictites attest to the presence of some floating ice but some of the diamictites are probably mass flow deposits paleocurrent data from the yudnamutana subgroup indicate transport to the west northwest the sturtian glacigenic rocks are overlain by a transgressive shale stratigraphic similarities exist between the yudnamutana subgroup and thinner successions to the west these stratigraphic similarities probably reflect paleoclimatic changes the twice repeated sequence of diamictite followed by mudstone is attributed to two glacial advance retreat cycles local variations in thickness and stratigraphic succession are probably related to contemporaneous faulting

hydrology of early mars valley network incision 1 widespread occurrences of valley networks on mars provide geomorphic evidence for an active hydrologic cycle to constrain the climatic conditions capable of forming the valley networks a hydrological model was used to analyze the valley incision depth and volume of eroded valleys because the absolute magnitudes of precipitation runoff and evaporation are uncertain we have used the ratio of these quantities the x ratio to express climatic conditions the spatial distribution and strength of the correlations between 1 the estimated depth and volume of eroded material and 2 estimated flood magnitude and valley gradients were investigated as a function of the assumed x ratio we also conducted an analysis of conditions required to have appreciable discharge in selected valley networks which provided the most definitive constraint on martian paleoclimate the other methods show a relatively weak dependency of incision depths and volumes upon the assumed x ratio the multiple regression analyses indicate that incision depth is strongly influenced by gradient and weakly related to modeled flood discharge the factors determining relative depth of incision depend partly on the type of channel bed however postflow modification of the valley networks by mass wasting cratering aeolian infilling and ice related processes precludes direct determination of bed morphology our hydrological analyses suggest that climatic conditions on early mars were at least as moist as those that occurred in the great basin region of the u s when large lakes were present during the pleistocene in terms of the balance of runoff and lake evaporation

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

statistical analysis of resistivity anomalies caused by underground caves geophysical prospecting of underground caves being performed on a construction site is often still a challenging procedure estimation of a likelihood level of an anomaly found is frequently a mandatory requirement of a project principal due to necessity of risk safety assessment however the methodology of such estimation is not hitherto developed aiming to put forward such a methodology the present study being performed as a part of an underground caves mapping prior to the land development on the site area consisted of application of electrical resistivity tomography ert together with statistical analysis utilized for the likelihood assessment of underground anomalies located the methodology was first verified via a synthetic modeling technique and applied to the in situ collected ert data and then crossed referenced with intrusive investigations excavation and drilling for the data verification the drilling excavation results showed that the proper discovering of underground caves can be done if anomaly probability level is not lower than 90 such a probability value was shown to be consistent with the modeling results more than 30 underground cavities were discovered on the site utilizing the methodology

geoelectrical resistivity variations and lithological composition in coastal gypsum rocks a case study from the lesina marina area apulia southern italy abstract the lesina marina village apulia southern italy lies on an exotic rocky body basically composed of triassic gypsum surrounded and covered by thin quaternary sandy deposits during the last two decades instability phenomena connected to gypsum dissolution and cover suffusion sinkholes occurred mainly along the acquarotta canal and in the urbanized area in this study electrical resistivity tomographies field and petrographic observations have been carried out just ca 300 m to the south of the residential area the east west striking geoelectrical profile has a length of 1900 m intercepts two boreholes and crosscuts the acquarotta canal close to the boreholes higher resolution geoelectrical profiles both perpendicular and parallel to the former were performed the two boreholes highlight the presence from the top to the bottom of quaternary sandy deposits coarse grained gypsum and layered finer grained gypsum in correspondence electrical resistivities are very low for the wet sandy deposits up to 5 m increase for coarse grained gypsum 20 120 m and reach the maximum values for the layered finer grained gypsum greater than 300 m the relationship between the electrical resistivity and the lithological composition of the studied rocks is strongly controlled by their fracturing and water saturation degree thus considering the main geological features here recovered are the impermeable bedrock and the above rocky body involved by mineral transformations and karstification phenomena additionally the anhydrite gypsum transformation and the gypsum dissolution are related to the groundwater circulation and localized within massive coarse grained gypsum rocks therefore the hazard related to karst processes involves both an area and a depth greater than those considered up to now

a geostatistical framework for incorporating seismic tomography auxiliary data into hydraulic conductivity estimation abstract a geostatistical approach is presented for the inclusion of seismic tomography data and sonic log data into the estimation of hydraulic conductivity the procedure accounts for the errors in seismic tomography inversion and for the correlation of such errors the proposed methodology consists of two steps 1 the cross variogram inference is carried out using only the data at the wellbore both hydraulic and seismic 2 a co kriging procedure takes the cross well data into account to interpolate between boreholes no postulated a priori relationship is needed in order to illustrate the methodology a synthetic data set is generated on the basis of evidence from published case studies and simplified physical considerations the numerical experiments show that the choice of the excitation frequency is critical a trade off exists between the need for a high resolution survey asking for higher frequencies and the need for a good correlation between hydraulic conductivity and seismic properties asking for frequencies below the squirt frequency of the medium in the simulation using seismic data with the best excitation frequency 1 khz in this case the mean squared error of the hydraulic conductivity estimate is two thirds lower than using hydraulic data alone it is important to note also that only a part of the interwell region is adequately sampled by the tomographic experiment such a region can be readily identified by calculating the energy of the quasi null space through singular value decomposition of the tomographic matrix in planning this type of experiments it is necessary to carefully verify case by case whether the adopted range of high frequencies does not prevent the seismic energy from propagating effectively from sources to receivers

paleotemperatures from fluid inclusions in halite method verification and a 100 000 year paleotemperature record death valley ca abstract maximum homogenization temperatures of fluid inclusions thmax in halite laboratory grown crystals and modern samples death valley ca match maximum brine temperatures during halite precipitation maximum brine temperatures during halite precipitation in death valley late april 1993 34 4 c agree with thmax 34 c and correlate well with average maximum air temperatures in april 31 3 c and may 37 6 c thmax may be used for paleoclimate interpretations based on the close relationship between saline lake temperatures and average air temperatures from modern settings lower homogenization temperatures demonstrably below the temperatures at which halite grew are interpreted to reflect collapse of some fluid inclusion walls due to the pressure difference between the inside and outside of inclusions by only using thmax the problems of anomalously low homogenization temperatures due to possible collapse of fluid inclusions are avoided halite samples from 30 stratigraphic intervals 90 to 0 m 100 to 0 ka core dv93 1 death valley ca were used to measure homogenization temperatures of fluid inclusions virtually all homogenization temperatures from core dv93 1 are below the modern thmax of 34 c halite precipitation late april 1993 lacustrine halites deposited in a perennial saline lake 35 to 10 ka have thmax between 19 c and 30 c which suggests brine temperatures approximately 4 c to 15 c below modern late april values ephemeral saline lake halites precipitated 60 to 35 ka have thmax between 23 c and 28 c 6 to 11 c below modern values the highest thmax value in the 100 ka record up to 35 c is from a halite sample formed approximately 100 ka in a climate regime somewhat colder than the modern

resurfacing of the martian highlands in the amenthes and tyrrhena region the southern cratered highlands of mars contain a large population of flat floored rimless craters which have previously been interpreted to have formed by aeolian mantling or flood volcanism neither of these geologic processes accurately explains the observed morphology or the crater statistics geologic mapping in the amenthes and tyrrhena region indicates that craters with this morphology occur on undulating intercrater materials near the dichotomy boundary and on more rugged materials farther into the highlands containing numerous ancient valley networks cumulative size frequency distribution curves indicate ages of n 5 790 early to middle noachian and n 5 540 middle noachian for the cratered plateau and cratered highland materials respectively opposite the observed stratigraphic relations for crater diameters 16 km the population of impact craters is consistent with stratigraphy but the population of smaller craters in the region indicates the importance of resultacing superposed fresh craters indicate a resultacing event that ceased at n 5 200 250 late noachian to early hesperian crater counts divided into 5 o latitudinal bins show an increase in the number of craters between the 8 and 50 km diameter range with increasing northerly latitudes suggesting that the resurfacing was not a single event statistical modelling of an erosive event capable of removing the continuous ejecta deposits from the craters eroding them to reduce the apparent diameter and simultaneously burying smaller eroded craters explains both the morphology of the flat floored rimless craters and their population distribution matching the slope of the modelled curves with that of the cratered highland materials suggests that up to 1400 m of erosion may have taken place in the highlands some of this eroded material probably remained locally burying the smaller craters later stripping of this material indicated by exposed layering and inverted topography has exhumed the smaller craters in the cratered plateau material resulting in the apparent age discrepancy determined from crater counts up to 1 0 km of material may have been removed by this later erosive event to explain the low density of ancient valley networks in the cratered plateau materials

quantifying geophysical inversion uncertainty using airborne frequency domain electromagnetic data applied at the province of zeeland the netherlands an accurate understanding of the fresh saline distribution of groundwater is necessary for effective groundwater management airborne electromagnetic aem surveys offer a rapid and cost effective method with which to map this offering valuable additional information about the subsurface to convert aem data into electric conductivity and ultimately groundwater salinity an inversion is undertaken a number of algorithms are available for this purpose however these are affected by significant uncertainty owing to inherent nonunique characteristics of this process the most commonly used inversion codes in hydrogeophysical studies were quantitatively tested using frequency domain aem and ground data from the province of zeeland the netherlands these include ubc1dfm code and quasi 2d laterally constrained inversions following an investigation of inversion parameter settings data were inverted for four inversion methods and interpolated into 3 d volumes using geological data and empirical electrical conductivity and water salinity relationships each inversion was converted into groundwater electrical conductivity and split into fresh brackish saline regions for groundwater volume estimates out of a total volume of 2 8 billion m3 a fresh groundwater estimate could differ by as much as 178 million m3 depending on the inversion used the primary factor here was the choice of model smoothness which was shown to affect the thickness of the brackish interval fresh brackish saline interfaces were consistently mapped with an accuracy of 3 m the brackish being the most accurately resolved the few layer method was less successful at resolving smoothly varying salinity distributions but more successful at mapping the brackish interface at greater depth

aeolian processes as drivers of landform evolution at the south pole of mars abstract we combine observations of surface morphology topography subsurface stratigraphy and near surface clouds with mesoscale simulations of south polar winds and temperature to investigate processes governing the evolution of spiral troughs on the south pole of mars in general we find that the south polar troughs are cyclic steps that all formed during an erosional period contrary to the troughs at the north pole which are constructional features the shallow radar instrument sharad onboard mars reconnaissance orbiter detects subsurface stratigraphy indicating relatively recent accumulation that occurred post trough formation in many locations using optical instruments especially the thermal emission imaging system themis we find low altitude trough clouds in over 500 images spanning 6 mars years the locations of detected clouds correspond to where recent accumulation is detected by sharad and offers clues about surface evolution the clouds migrate by season moving poleward from 71 s at l s 200 until l s 318 when the last cloud is detected our atmospheric simulations find that the fastest winds on the pole are found roughly near the external boundary of the seasonal co 2 ice cap thus we find that the migration of clouds and katabatic jumps corresponds spatially to the retreat of the co 2 seasonal ice as detected by titus 2005 and that trough morphology through recent accumulation is integrally related to this seasonal retreat