deglacial chronology from county donegal ireland implications for deglaciation of the british irish ice sheet in the north of ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum we constrain the timing of three subsequent events by accelerator mass spectrometry 14 c dating of marine microfaunas from muds at corvish county donegal early and rapid deglaciation of the continental shelf off northwestern ireland occurred before 17 1 k 14 c years bp when marine muds formed in trawbreaga bay ice subsequently readvanced into the bay some time between 15 0 and 14 0 k 14 c years bp and compressed contemporary sea stacks and beach cobbles into a ridge at ballycrampsey early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 c ages between 16 0 and 15 2 k 14 c years bp the deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14 1 k 14 c years bp the early deglaciation in the north at c 17 k 14 c years bp is correlative with deglaciation recorded in the irish sea basin western ireland and northeastern scotland indicating a response of the entire british irish ice sheet to early warming of the north atlantic ocean that resulted in a loss of up to two thirds of its mass subsequent ice sheet readvance between 15 0 and 14 1 k 14 c years bp in the north is part of a widespread response of the british irish ice sheet to heinrich event 1 during the killard point stadial high relative sea levels that accompanied deglaciation at 17 k 14 c years bp and again at 14 1 k 14 c years bp indicate substantial loading and attendant isostatic depression by the british irish ice sheet

striated clast pavements products of deforming subglacial sediment studies of modern glaciers have recently drawn attention to the importance of subglacial sediment deformation to glacier dynamics and processes inferences regarding the probable shear strength of this sediment imply that large clasts may in some cases sink to underlying rigid sediment where abrasion by overlying deforming sediment could occur this scenario provides a formative mechanism for striated clast pavements commonly described from the base of fine grained massive diamictons associated with the late pleistocene laurentide ice sheet such a mechanism indicates that at the time of formation of clast pavements overlying diamictons associated with pavements had a low yield strength 0 5 kpa and were deforming mechanically like a debris flow clast pavements may therefore be an important criterion for recognition of sediments deposited by subglacial deformation transport

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

water salinization in arid regions observations from the negev desert israel abstract the processes affecting salinization of precipitation surface water vadose water and groundwater were studied in the negev desert israel observations spanning 18 years included the collection of rainfall at three rain sampling stations flood water at six flood stations vadose water from four coreholes penetrating chalk formations and groundwater from 16 monitoring wells tapping the chalk aquitard dissolved carbonate dust and evaporation of the falling raindrops result in ca hco 3 2 facies and increased ion concentration of the rainwater with respect to inland more humid regions the exposure of flood water to evaporation during flood events is minimal the observed ca hco 3 2 facies and salt enrichment by a factor of three to five in the flood water with respect to precipitation results primarily from interactions of the flood water with the chalk and limestone bedrock including ion exchange on na and k bearing minerals and the dissolution of calcite gypsum and halite the presence of these salts at and near land surface results from the complete evaporation of rainwater in land surface depression storage areas following most rain events except for a small portion moving through the low permeability chalk matrix most of the vadose water moves through preferential pathways and is typically not exposed to evaporation this dual movement of water accounts for the nacl facies of vadose water and the variable rates of isotopic depletion and salt dilution observed in the underlying heterogeneous groundwater in the saturated zone although the variable mixing with low salinity isotopically depleted water percolating from the fractures accounts for the depleted isotopic composition of the groundwater its relatively low solute content cannot modify the groundwater nacl facies consequently only groundwater salinity in the chalk is reduced by the preferentially flowing water but the ca hco 3 2 facies prevailing in the rainwater and flood water disappears and the nacl imprint from the vadose zone prevails

natural and anthropogenic influences on the geochemistry of quaternary lake sediments from holzmaar germany the accumulation of heavy metals and trace elements has been investigated in a well laminated sequence of holocene and late pleistocene lake sediments composed of diatomaceous gyttja tuff and silt and clay sediments varve chronology of the annually deposited gyttja yielded a continuous high resolution time sequence and allowed the absolute age dating of the sediment

amplitude preservation of radon based multiple removal filters this study examines the effect of filtering in the radon transform domain on reflection amplitudes radon filters are often used for removal of multiple reflections from normal moveout corrected seismic data the unweighted solution to the radon transform reduces reflection amplitudes at both near and far offsets due to a truncation effect however the weighted solutions to the transform produce localized events in the transform domain which minimizes this truncation effect synthetic examples suggest that filters designed in the radon domain based on a weighted solution to the linear parabolic or hyperbolic transforms preserve the near and far offset reflection amplitudes while removing the multiples whereas the unweighted solutions diminish reflection amplitudes which may distort subsequent amplitude versus offset avo analysis

toward true amplitude multiple removal the radon transform is a popular tool for regularization and preprocessing of seismic data prior to migration avo analysis and stratigraphic interpretation the most common uses of the radon transform are to suppress ground roll incoherent noise and multiples suppression of coherent noise greatly facilitates prestack migration velocity analysis

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

rain recharge in the kalahari a note on some approaches to the problem abstract previous workers maintained that rain recharge in the kalahari is inhibited by the covering sand according to this model which has been much cited in the literature the rain fills the pores in the upper part of the sand and is subsequently lost by evapotranspiration during the dry seasons direct observations on groundwaters indicate however that in parts of the kalahari recharge is active this is evidenced by elevated tritium and 14 c values rises of the water table following above average rainy years and a steady supply of water in shallow wells

classification of seafloor geology using multibeam sonar data from the scotian shelf abstract we describe a method for classifying multibeam sonar data and illustrate the method using data collected with a simrad em1000 sonar on the scotian shelf canada the method involves comparing various attributes of the bathymetry and backscatter with typical examples of specified seafloor types and computing their statistical degree of similarity sediment ponds are identified as areas of low echo amplitude and low topographic gradient and curvature ridges and troughs are identified by fitting a paraboloid to patches of the bathymetry once the sediments ridges and troughs are located we are able to use the database to extract orientations and other characteristics of these features for example the orientation of the topography can be computed from the paraboloid surface and rose diagrams of the ridge and trough orientations reflect the fabric of up turned cambro ordovician sedimentary beds outcropping in this area the unconsolidated sediments ponded within small basins have low topographic gradients with consistent tilts towards the southeast mean 133 which we interpret as due to offshore transport of holocene sediments possibly in response to storms

application of spatial cross correlation to detection of migration of submarine sand dunes knowledge of migration rates of bedforms provides an indirect indication of thebehavior of tidally averaged bottom currents enables optimization of hydrographic surveyfrequency and may enable calculation of bedload transport rate to measure bedformmigration rate we test the use of spatial correlation as a measurement method whichquantifies and locates a region of maximum similarity between two spatial variables forthe latter we use consecutive eight bit images of spatial gradient derived frombathymetric digital terrain models carrying out the correlation over this representation ofthe shape of the seabed rather than the bathymetric surface the digital terrain modelswere compiled from six repeat multibeam surveys of a headland associated bank nearsaint john new brunswick with a roughly 30 day interval vectors are drawn depictingthe movement of a sand dune at time t

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

process related classification of acoustic data from the hudson river estuary acoustic surveying provides valuable information on the distribution of sedimentary environments in subaqueous settings frequently differences in acoustic backscatter strength are used to distinguish sedimentary environments on the basis of their grain size composition here we are presenting acoustic backscatter data from the haverstraw bay section of the hudson river estuary that has been mapped using sidescan sub bottom profiling and multibeam bathymetry as part of the benthic mapping project of the hudson river estuary program funded by new york state in addition hundreds of gravity cores and grab samples provide ground truth for a classification of the river bottom into discrete substrate types analyses of sedimentary environments reveal patterns in backscatter strength beyond those that can be related to the sediment grain size distribution alone an integrated interpretation of sidescan sub bottom profiling and high resolution bathymetry data indicates that the backscatter pattern can be attributed to spatial variations in the modern depositional environments which cause differences in bottom roughness and sediment compaction based on an integrated interpretation of the acoustic and sample data sets we distinguished eight different sedimentary classes many of the classes can be linked to dynamic processes including contemporary deposition erosion and sediment migration in sand waves the results provide a better understanding of the dynamic processes of the hudson river estuary and improve the interpretation of the acoustic backscatter data from fine grained sedimentary environments

till tongue stratigraphy seismostratigraphic studies on the scotian and mid norwegian continental shelves have led to the development of a conceptual model for glacial deposition and erosion by ice sheets in a marine environment till tongue model some of the terminal deposits of the marine ending glaciers are composed in part of acoustically incoherent wedge shaped bodies the wedges are thought to be part of a grounding line system associated with a floating terminus according to the model the sedimentary wedges are formed through the accumulation of glacial debris by subglacial processes proximal to the grounding line together with a penecontemporaneous proglacial contribution from sediment gravity flows sedimentation rates appear to be highest near and proximal to the grounding line that is within a grounding line zone ice proximal stratified glaciomarine sediment accumulates from plumes within the water column and rain out of ice rafted debris the glaciomarine sediment interfingers with the till tongues resulting from oscillations of the grounding line till tongues represent discrete stratigraphic units formed in both vertical and lateral successions marginal to massive till deposits major till tongues can be correlated regionally for hundreds of kilometers and thus can provide a basis for stratigraphic correlation on the mid norwegian shelf lateral and vertical successions of till tongues delineate several large scale till units which represent major advances and retreats of the ice that probably were of both stadial and glacial rank we refer to this type of succession as a till tongue stratigraphy it appears that till tongue formation is limited to intermediate water depths which range from 75 to 1 000 m present water depth but those formed in water depths 600 700 in may not be strictly subglacial in origin we speculate that processes leading to the development of till tongues possibly give rise to the formation of subglacial undermelt till together with thin flow tills near the grounding line it is also possible that another type of subglacial till embracing concepts inherent in the expression deforming basal tills as described by alley and others 1989 may contribute to the formation of till tongues boundaries between the major till units of the mid norwegian shelf are mainly depositional in the zone of maximum glaciation near the shelf edge and upper slope proximal to this zone of major deposition intraformational erosional processes dominate and give rise to smooth widespread time transgressive erosional surfaces erosion progressively increases in a proximal direction beveling the earlier glacial deposits and ultimately reaches and modifies the bedrock surface these regional surfaces are analogous to the ross sea unconformity which was also formed by glacial erosion morainic deposits within a till tongue stratigraphy are termed grounding zone moraines and are subdivided into advance and retreat varieties with linear tabular and hummocky attributes fields of small morainic ridges lift off moraines form in basinal areas during recession

combining observations with acoustic swath bathymetry and backscatter to map seabed sediment texture classes the empirical best linear unbiased predictor seabed sediment texture can be mapped by geostatistical prediction from limited direct observations such as grab samples a geostatistical model can provide local estimates of the probability of each texture class so the most probable sediment class can be identified at any unsampled location and the uncertainty of this prediction can be quantified in this paper we show in a case study off the northeast coast of england how swath bathymetry and backscatter can be incorporated into a geostatistical linear mixed model lmm as fixed effects covariates parameters of the lmm were estimated by maximum likelihood which allowed us to show that both covariates provided useful information in a cross validation each observation was predicted from the rest using the lmms with i no covariates or ii bathymetry and backscatter as covariates the proportion of cases in which the most probable class according to the prediction corresponded to the observed class was increased from 58 to 65 of cases by including the covariates which also increased the information content of the predictions measured by the entropy of the class probabilities a qualitative assessment of the geostatistical results shows that the model correctly predicts for example the occurrence of coarser sediment over discrete glacial sediment landforms and muddier sediment in relatively quiescent localized deep water environments this demonstrates the potential for assimilating geophysical data with direct observations by the lmm and could offer a basis for a routine mapping procedure which incorporates these and other ancillary information such as manually interpreted geological and geomorphological maps

groundwater resources development in the eastern sahara abstract aspects of the regional hydrogeology of the nubian sandstone aquifer system in the sudan egypt and eastern libya and the associated tertiary aquifers of the sirte basin libya are described it is concluded that major groundwater resources are present that can be developed by abstraction adjacent to the river nile by groundwater mining or by abstraction from throughflow examples of aquifer control parameters and potential resources development are given the problems of in situ groundwater development in the harsh desert environment are discussed and it is indicated that such development is not constrained by groundwater resources potential but by socioeconomic factors the solution of groundwater conveyance adopted in libya is detailed

a review of aridity and groundwater surface hydrological studies are seen as inadequate in hyperarid and arid areas to provide reliable estimates of recharge in most such areas surface discharges are not present so that assessments of groundwater resources are dependent upon ground interpretation and denied the flow control found in assessments elsewhere groundwater models show that gradients are sustained by long term dewatering and very small amounts of modern indirect recharge recharge indications are well within the error of a hydrological balance discharges appear equally small the development of groundwater in arid areas frequently faces problems of salination due to recycling of irrigation water and rising groundwater heads abstraction is often inadequately managed so that uncontrolled mining of groundwater occurs the advantage that groundwater has however is that it offers staged development and staged appraisal

isotopic study of alluvial groundwaters south west lockyer valley queensland australia the isotopic chemistry of alluvial groundwaters from two adjacent valleys are described and hydrological processes within related aquifers are identified as evidenced by oxygen deuterium tritium and chloride data a plot of o against d values reveals isotopic enrichment of the groundwater by the recycling of spray irrigation water a plot of tritium versus chloride concentrations displays separate linear correlations for alluvial groundwaters within the two valleys the salinity has a common source therefore the separate correlations are interpreted as the past transfer of low salinity groundwater from the alluvial aquifers in one valley to the underlying sandstone aquifers

complexity of saharan paleoclimate reconstruction and implications for modern human migration abstract chronological and geochemical data from scarp and scarp foot depression sediments ssds have been used for deciphering saharan paleoclimates and patterns of migration of anatomically modern humans amh u th dating of thick accumulations of ssds indicates prevalent deposition during long lasting cool glacial periods marine isotope stage mis 6 8 10 and 12 and limited deposition during warm interglacial periods mis 5 7 and 13 in contrast quaternary sediments associated with short residence hydrologic systems in sinai yielded mis 2 osl ages of 27 7 to 10 2 ka the lack of ssds of mis 2 ages and the wide range of warm and cool stages in eastern sahara is attributed to 1 lengthy travel times of groundwater prior to discharge and deposition of ssds from deep groundwater originating from distant sources and 2 sampling and dating of ssds from depressions where natural discharge has been apparently continuous through wet and dry periods given that the previously dated depression ssds could have been deposited during dry periods and that the ages of ssds reflect the timing of groundwater discharge rather than the ages of the wet periods during which recharge occurred we suggest that earlier interpretations of saharan paleoclimate and amh migrations that heavily relied on dating of ssds should be revisited

ice flow stages and glacial bedforms in north central ireland a record of rapid environmental change during the last glacial termination satellite imagery is a useful tool to assess large scale 10 3 km 2 geological patterns satellite imagery of north central ireland shows cross cut and overprinted subglacial bedform patterns bedform lineations supported by sedimentary evidence are used to reconstruct four ice flow stages named a d during the termination of the last devensian glaciation 22 000 13 000 radiocarbon 14 c years bp flow stage a relates to southwesterly flow of scottish ice across eastern ireland flow stage b during the last glacial maximum c 25 000 22 000 14 c years bp records southeasterly ice flow from dispersal centres in northern parts of ireland transverse subglacial ridges rogen moraines formed during stage b are the largest area of this ridge type in western europe flow stage c records erosional headcutting in the rogen moraine field and sediment streamlining drumlinization by ice streams drawn into the irish sea basin this flow stage is constrained by ams radiocarbon dates from marine microfaunas to around 14 500 14 c years bp flow stage d records drumlinization from an inland centre in the lough neagh basin overall bedform patterns can be used to reconstruct ice mass history and evaluate controls on ice activity including millennial scale changes in amphi north atlantic climate field evidence of bedform relationships also casts doubt on current concepts of drumlinization and the role of pervasive sediment deformation in glacial systems

sedimentation in a subglacial lake enniskerry eastern ireland abstract field relationships between a subglacial lake fill from the enniskerry basin eastern ireland provide evidence for dynamic links between the sedimentary fill regional subglacial meltwater flow and regional ice dynamics the basin fill 6 7 km2 forms an integral part of an extensive 30 km subglacial meltwater system which developed parallel to north south ice flow along the western marginal sector of the late pleistocene irish sea glacier high magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two nye type channels and westwards by a rothlisberger type channel the resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross bedded sands and foreset gravels in places these are eroded and overlain by multistorey dish shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head a variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin facies variability within the ice proximal fans and spreads record deposition from a wide range of high and low density turbulent flows traction currents density underflows suspension and sediment gravity flows a surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down at one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof a series of sequential events is postulated for the evolution of the subglacial drainage system and subglacial lake development initially a rock ridge transverse to ice flow resulted in the development of a relatively low pressure lee zone along the northern margin of the basin ice sheet decoupling within the basin was enhanced by water migration into this low pressure lee zone which also melted an ice roof cavity closure and maintenance of the ice roof was prevented by a fast ice flux generated by intense marine downdraw in the main ice lobe centred in the irish sea basin regional ice directed meltwater pressure gradients and erosion enhanced subglacial lake development in the lowest topographic point of the system major inlet and outlet nye type channels incised transverse to the rims of the basin testify to the intensity of ice directed drainage along the marginal sector of the irish sea glacier in a wider context the concepts of high magnitude subglacial meltwater flow coupled with high rates of debris flux invoked for the subglacial basin fill are also necessary to explain the thick tidewater sequences present in adjacent sectors of the irish sea basin

hairpin erosional marks horseshoe vortices and subglacial erosion abstract crescentic erosional marks wrapped around obstacles and extending into straight grooves are termed hairpin erosional marks they are u shaped to semi circular in cross section are deepest around the upstream shoulders of the obstacles and range over seven orders of magnitude in scale some are asymmetrical with one groove better developed than the other the straight grooves may broaden and shallow rapidly in the downflow direction upstream grooves merge with rather than cross downstream crescentic marks grooves are distinct from glacial abrasion forms and many are not striated hairpin erosional marks are interpreted as being products of scour by horseshoe vortices in turbulent fluids this interpretation is supported by the close similarity of these marks to scours produced experimentally and in nature by horseshoe vortices estimated reynolds numbers show that such vortices are probable around obstacles in wind and flowing water but are extremely unlikely in ice aeolian hairpin erosional marks related to yardangs are illustrated to support this conclusion the surface texture cross sectional shapes and spatial patterns of hairpin erosional marks also discount formation by ice a model for the evolution of isolated erosional drumlins from an initial field of hairpin erosional marks extends earlier research on a meltwater hypothesis for drumlins

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

digital image processing techniques for enhancement and classification of seamarc ii side scan sonar imagery the recent growth in the production rate of digital side scan sonar images coupled with the rapid expansion of systematic seafloor exploration programs has created a need for fast and quantitative means of processing seafloor imagery computer aided analytical techniques fill this need a number of numerical techniques used to enhance and classify imagery produced by seamarc ii a long range combination side scan sonar and bathymetric seafloor mapping system are documented three categories of techniques are presented 1 preprocessing corrections radiometric and geometric 2 feature extraction and 3 image segmentation and classification an introduction to the concept of feature vectors is provided along with an explanation of the method of evaluation of a texture feature vector based upon gray level co occurrence matrices glcm an alternative to the a priori texel texture element subdivision of images is presented in the form of region growing and texture analysis regata this routine provides a texture map of spatial resolution superior to that obtainable with arbitrarily assigned texel boundaries and minimizes the possibility of mixed texture signals due to the combination of two or more textures in an arbitrarily assigned texel computer classification of these textural features extracted via the glcm technique results in transformation of images into maps of image texture these maps may either be interpreted in terms of the theoretical relationships shown between texture signatures and wavelength or converted to geologic maps by correlation of texture signatures with ground truth data these techniques are applied to seamarc ii side scan sonar imagery from a variety of geologic environments including lithified and nonlithified sedimentary formations volcanic and sedimentary debris flows and crystalline basaltic outcrops application of the above processing steps provided not only superior images for both subjective and quantitative analysis but also the critical ability to discriminate between outcrops with distinct lithologies but similar image intensity

groundwater development kharga oases western desert of egypt a long term environmental concern the groundwater reserves in kharga oases have been studied for the long term socioeconomic development in the area the nubian sandstone which consists of a thick sequence of coarse clastic sediments of sandstone sandy clay interbedded with shale and clay beds forms a complex aquifer system the nubian aquifer has been providing water to artesian wells and springs in the kharga oases for several thousand years

groundwater recharge characteristics in a semi arid environment of southwest idaho natural groundwater recharge characteristics were evaluated using precipitation data soil depth soil water and groundwater observations for a semi arid rangeland environment of southwest idaho recharge in these study was area occurs via three separate mechanisms by infiltration through low relief rubbly basalt outcrops infiltration through shallow soils and by transmission through bedrock channels during runoff and channel flow to initiate recharge rainfall in excess of 20 30 mm over 24 hr or higher intensity cloud burst storms are required time to peak the time from the end of a precipitation event to the peak of groundwater hydrograph was found to be independent of season depending only on soil depth regression analysis of time to peak vs soil depth produced a correlation coefficient of 0 941 the rate of groundwater recharge for the study area was computed at 4 6 10 4 cm min

inner shelf seismic stratigraphy off the north coast of northern ireland new data on the depth of the holocene lowstand new seismic stratigraphic data are presented from the inner shelf off the north coast of northern ireland the sequence preserved comprises an acoustic basement of till or solid bedrock overlain by a fine grained acoustically transparent unit interpreted as glacio marine sediment this is overlain by an upper reflective sandy unit which contains a discontinuous but widespread internal reflector interpreted as peat that developed during a late glacial holocene relative sea level fall and continued to accumulate until subsequent inundation the depth of the holocene lowstand is estimated at 30 in msl on the basis of the seaward extent of the sandy unit and its intercalated peaty horizons the presence of erosional notches and a widespread break in slope at this depth the lowstand is not definitively dated but on the basis of dated deposits in adjacent locations is inferred to have occurred between 10 000 and 11000 14c yr bp c 2002 elsevier science b v all rights reserved

drumlin formation related to inverted melt water erosional marks drumlin forms are described from maps and air photographs of a part of the athabasca plains northern saskatchewan three major forms spindle parabolic and transverse asymmetrical are recognized these forms which may show superimposed minor elements depart from classical descriptions of drumlins but are similar to moulds of erosional marks created by separated fluid flows assemblages of drumlins also show characteristics similar to those of erosional marks the form analogy between drumlins and moulds of erosional marks is carried to a conclusion that drumlins may be formed by the infilling of erosional marks created on the under side of glaciers by separated subglacial melt water flows estimates of specific discharge are obtained by means of an expected range of reynolds number geomorphological evidence is given for large scale erosion by subglacial melt water a discussion of the sedimentology stratigraphy and deformational structure of the interiors of drumlins shows that they may be explained by the erosional mark hypothesis this paper emphasizes the importance of melt water as a geomorphic agent and may have broad implications for ice sheet dynamics and profiles rates of deglaciation and the occurrence of bedrock thrusting by ice

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

glaciation and sea level change for ireland and the irish sea since late devensian midlandian time the sea level change around the coast of ireland and the irish sea for the past 20 000 years is primarily the combined result of the glacio isostatic adjustment of the crust to the removal of ice over the british isles and the total eustatic change from the global ice sheets however the isostatic effects due to the removal of ice from northern europe and north america and the addition of meltwater into the oceans also make a significant contribution predictions of sea level change based on glacio hydro isostatic models are compared with observations to constrain the ice volume over ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m the models predict well the spatial variability in sea level change observed across the region for holocene and lateglacial time with levels above present being predicted only for northeastern ireland and north of about morecambe bay the models do not support suggestions that lateglacial levels along the east coast of ireland or the coast of wales were 50 150 m above their present levels consistent models that would produce such large lateglacial highstands are incompatible with all other sea level and glacial evidence for the british isles palaeobathymetry and palaeoshoreline reconstructions for the irish sea indicates that a tenuous landbridge between britain and ireland developed only across the celtic sea between about 18000 and 14000 years bp

the july 1996 flood deposit in the saguenay fjord quebec canada implications for sources of spatial and temporal backscatter variations in july 1996 a major rainstorm and flood took place in the saguenay fjord backscatter strength measurements made with a simrad em1000 multibeam echosounder in 1993 1997 and 1999 have shown spatial and temporal variations which are interpreted in relation to the occurrence of the flood after empirical calibration of the different maps the data show an overall diminution of 5 db in backscatter strength in 1997 1 yr after the flood took place while the data sets obtained in 1993 and 1999 show comparable levels of backscatter strength the different data sets show a similar pattern of low and high backscatter patches which represent variations of the backscatter strength of a few decibels several grain size and water content measurements were also carried out on sediment box core and grab samples from the fjord bottom in 1997 and 1999 these have shown that the areas with higher acoustic backscatter correspond to the finer sediments while the low backscatter patches correspond to the coarser material the data show little relation between water content and backscatter strength thus indicating a poor dependence between the impedance terms bulk density and sound speed and the backscatter having taken this into account the major contribution to backscatter strength is assumed to result from differences in surface and volume roughness of the sediment since finer grain sizes offer higher backscatter the grain size of the sediment is not considered as being a major contributor to roughness and hence backscatter strength the major factor that seems to control roughness generation in the saguenay fjord is considered to be bioturbation the areas where geological processes most physically disturb the bottom which coincide with the areas where also most accumulation takes place and the coarser grain sizes are deposited are more sparsely colonized by organisms this results in a lower degree of bioturbation lower roughness and thus backscatter strength this hypothesis helps explain the variation in backscatter strength observed between the different measurement years the several million tons of sediment deposited in the fjord bottom after the 1996 flood buried the benthic fauna which was still recovering 1 yr later the less bioturbated sediment at this time would present lower roughness with respect to the 1993 and 1999 data resulting in a lower backscatter strength

till in the marine environment till is of common occurrence in the marine environment and can be both subglacial and proglacial in origin former glacial margins are often represented by till tongues that are interbedded with stratified glaciomarine sediment and the relationship is readily mappable using seismic reflection techniques it is inferred that within individual till tongues sediment gravity flow deposits form transitional contacts with till of subglacial origin but these contacts cannot be distinguished on seismic profiles these unstratified gravity induced deposits formed in close proximity to the glacial source at the grounding line are considered to be secondary tills flow till complex in terms of the inqua classification of tills till tongue successions and till deltas are large ice marginal depocentres associated with floating front ice margins and appear to be closely related in origin tabular and hummocky moraines of the mid norwegian shelf also are considered to be products of floating front margins and represent a large proportion of the retreat tills formed during ice recession seismostratigraphic evidence for channelisation in ice marginal deposits appears to provide a means of distinguishing between former tidewater and floating front margins

coincident swath acoustic backscatter and bathymetry for the interpretation of shallow water sediment composition and processes two surveys from the west of ireland demonstrate how the combination of high resolution geo referenced spatially coincident swath acoustic bathymetric and backscatter data is effective for understanding underwater geological processes and assisting the design of environmental monitoring programmes one case study corroborates terrestrial observations of quaternary glacial cycles around clew bay by identifying sea bed morphology that is consistent with a glacial advance from east to west followed by deglaciation and a subsequent readvance to the nw during the last glacial maximum the bathymetric data identify a palaeo coastline at water depths of c 30 m below present sea level and the underwater extension of an onshore end moraine the backscatter data corroborated by grab sampling identify mixed sediment outwash associated with the ice limit as well as sea bed depressions caused by subglacial erosion the other case study in lough corrib an inland lake identifies areas of mud from backscatter data swath bathymetry sub bottom profiling and grab samples suggest that the mud accumulates in bedrock depressions and is the preferred location of several elements related to eutrophication the combination of spatially coincident swath bathymetry and backscatter data is more effective for geological interpretations than backscatter data from conventional side scan sonar

stratified flow deposits in a late pleistocene drumlin in northwest ireland abstract extensive stratified flow deposits are present within a drumlin exposed on the eastern shore of donegal bay northwest ireland the stratified deposits are located towards the central lee portion of the drumlin infilling a major depression within a basal diamicton association and are overlain by a sand rich diamicton association the stratified sequence consists of laminated silts cohesive diamictic muds stratified diamictons well sorted massive sands and clast supported gravels a discernible upward vertical facies transition is apparent within the stratified deposits from fines and matrix dominant sediments to well sorted clastic sediments these facies variations appear to reflect increased hydrodynamic activity and a prograding sequence the sediments are interpreted as a subglacial conduit infill formed at the point of debouchure into a glaciomarine environment the envisaged increase in water availability and flow energy may have resulted from progressive enlargement of the conduit by basal melting and scouring associated with the water sediment flux within the conduit the depression in the basal diamicton association appears to have resulted from scour at the base of the conduit

glacimarine processes at grounding line fans and their growth to ice contact deltas abstract grounding line fans originate from subglacial and basal stream tunnels at grounding lines of glaciers terminating in a marine environment during melt seasons discharge forms a turbulent jet beyond the efflux over the initial zone of flow establishment in the jet it may remain in contact with the sea floor for up to 13 4 d d tunnel diameter along a runout distance if velocity is constant plug flow in this zone deposits marine outwash sediment commonly having chaotic texture and graded and welded contacts texture may vary rapidly because of discharge pulses and the jet may move laterally to produce sheet or cut and fill geometries imbricate gravel is deposited near the efflux then farther out are sheet or weakly channelized finer grained gravels and sands in some instances a migrating barchanoid bar forms at the detachment zone and forms large scale trough cross beds beyond the detachment zone the turbulent jet becomes vertical and sediment cascades from it in a veil this sediment is added to by flows from continuous failures of bed load sediment in the detachment zone resulting deposits are interstratified sediment gravity flows and thick coarse end members of cyclopsams the jet changes to a plume when inertial forces become less than buoyancy forces turbulent vorticies within the jet can re entrain particles into a buoyant plume the plume remains vertical although continuously spreading until reaching neutral buoyancy fan depocentres have been observed to accumulate at over 10 6 m 3 a 1 in temperate glacial areas eventually at quasi stable grounding lines fans may aggrade to sea level to form ice contact deltas at incipient deltas when the delta plain is intertidal coarse sediment is redistributed to the prodelta with each tidal cycle intense prodelta rhythmites mark the transition of a fan into a delta

the geological interpretation of side scan sonar recent developments in side scan sonar these parameters play a critical role in our ability to technology have increased the potential for fundamental calibrate and ultimately to interpret the new pictures of the changes in our understanding of ocean basins developed ocean floor acoustic image processing is a new applica in the late 1960s side looking sonars have been widely tion of an old and well established technique digital used for the last two decades to obtain qualitative estimates optical images have benefited from several decades of of the acoustic properties of the materials of the seafloor modern developments in the ability to obtain spatially correct digital data from side scan sonar systems have resulted in images that can be subsequently processed enhanced and quantified with appropriate processing these acoustic images can be made to resemble easily recognizable optical photographs any geological interpretation of these images requires an understanding of the inherent limitations of the data acquisition system when imagery is collected these limitations are largely centered on the concept of resolution in side scan sonar images there are several different types of resolution including along and across track resolution display the geology of the seafloor resolution and absolute instrumental resolution all of development in processing techniques these relatively sophisticated techniques have been applied to photographic images from satellites and spacecraft images which are noisy and difficult to obtain but extremely valuable side scan sonar systems on the other hand have only recently been able to produce spatially correct digital images of the seafloor the application of digital signal processing techniques to side scan sonar data willnow allow us to quantify what had been previously very subjective and qualitative interpretations of images of the seafloor the goal of all this processing of acoustic images remains clear the development of an interpretable map of featureless static environment has undergone dramatic modification in the last 50 years early depth sounding with mechanical devices and even early wide beam acoustic echo sounders gave us an extremely low resolu tion picture of the ocean basins this early image of the ocean bottom consisted largely of a flat lying seafloor with few hills and ridges of any consequence completely covered with a thick layer of sediment and only an occasional inexplicable outcrop of hard rock the few recovered rock samples were of little value in understand ing the scientific processes of the deep sea because they could not be placed within any sort of geological and morphological context acceptance of seafloor spreading and the vine matthews hypothesis in the 1960s altered forever our perception that the floor of the ocean basins was unchang ing at least on a geological time scale the initial drilling efforts of the deep sea drilling project also modified our view about the uniformity of the seafloor even on a scale of a few hundreds and perhaps tens of kilometers higher resolution maps using multiple narrow beam echo sounders strongly reinforced this newperception of a nonuniform and scientifically interest ing seafloor tyce 1986 the initial interest grew to excitement as our perspective was extended by visual observation in a very few places down to the scale of a few meters by early submersible expeditions to mid ocean ridge spreading centers ballard and van andel 1977 clearly a new tool beyond the wide beam echo sounder was needed to map features of the seafloor and to understand the processes at work there to be effective this would have to be a tool which had both a sufficiently wide view for tectonic context and adequate resolution for interpretation in terms of geological processes the efficiency of sound transmission in seawater and the development of both electronic and digital techniques capable of rapidly processing the high data rates necessary to generate images dictated that this tool would be some form of acoustic swath mapping the scientific need for

acoustic backscatter of the 1995 flood deposit on the eel shelf abstract acoustic swath mapping and sediment box coring conducted on the continental shelf near the mouth of the eel river revealed regional variations in acoustic backscatter that can be related to the shelf sedimentology the acoustic backscatter variations observed on the shelf were unusually narrow compared to the response of similar sediment types documented in other areas however the acoustic data revealed four principal bottom types on the shelf that can be related to sedimentologic differences observed in cores the four areas are 1 low acoustic backscatter associated with the nearshore sand facies and the prodelta terraces of the eel and mad rivers composed of fine sands and coarse silts with low porosity 2 high acoustic backscatter associated with fine silts characterized by high porosity and deposited by the 1995 flood of the eel river 3 intermediate acoustic backscatter in the outer shelf muds where clayey silts are accumulating and the 1995 flood apparently had limited direct effect and 4 intermediate acoustic backscatter near the fringes of the 1995 flood deposits and in areas where the flood sediments were more disrupted by post depositional processes the highest acoustic backscatter was identified in areas where the 1995 flood sediments remained relatively intact and near the shelf surface into the summer of 1995 cores collected from these areas contained wavy or lenticular bedding the rapid deposition of the high porosity muddy layers results in better preservation of incorporated ripple forms than in areas less directly impacted by the flood deposit the high porosity muddy layers allow acoustic penetration into the sediments and result in greater acoustic backscatter from incorporated roughness elements

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

chloride hydrochemical and isotope methods of groundwater recharge estimation in eastern mediterranean areas a case study in jordan jordan is classified as an arid to semi arid country with a population according to 1999 estimates of 4 8 millions inhabitants and a growth rate of 3 4 efficient use of jordan s scarce water is becoming increasingly important as the urban population grows this study was carried out within the framework of the joint european research project groundwater recharge in the eastern mediterranean and describes a combined methodology for groundwater recharge estimation in jordan the chloride method as well as isotopic and hydrochemical approaches recharge estimations using the chloride method range from 14 mm year 1 mean annual precipitation of 500 mm for a shallow and stony soil to values of 3 7 mm year 1 for a thick desert soil mean annual precipitation of 100 mm and values of well below 1 mm year 1 for thick alluvial deposits mean annual rainfall of 250 mm isotopically most of the groundwater in the hammad basin east jordan falls below the global meteoric water line and far away from the mediterranean meteoric water line suggesting that the waters are ancient and were recharged in a climate different than mediterranean tritium levels in the groundwater of the hammad basin are less than the detection limit 1 3 tu however three samples in east hammad where the aquifer is unconfined present tritium values between 1 and 4 tu copyright 2007 john wiley sons ltd

groundwater chemistry and palaeorecharge in the amadeus basin central australia abstract carbon isotope chemistry indicates episodic palaeorecharge of groundwater in the arid amadeus basin central australia in this hydrogeologically complex region groundwater has been recharged by three important mechanisms direct infiltration of rainwater through sand dune cover or fissures in calcrete through river bed sands following floods and through joints in bedrock outcrops modern and holocene groundwaters 0 5000 years b p are found in the unconfined calcrete and sand dune aquifers which have evolved hydrochemically to cl so4 na waters with ca and mg as a result of evaporative concentration holocene groundwaters 3 10 000 years b p have been dated in river bed recharge situations these groundwaters are mainly of the hco3 cl na type with ca and mg and preserve the hydrochemical signature of the flood recharge waters most groundwater sampled in the folded and jointed rocks of the basin has a low modern 14c content and was recharged in the holocene and late pleistocene 12 32 000 years b p these waters are intermediate in their ionic composition covering a spectrum between the hco3 cl na and cl so4 na types solution is the dominant process int heir hydrochemical evolution stable isotope signatures and derived parameters indicate that the intensity of rainfall is an important factor in the evolution of arid zone groundwaters modern reharged is limited implying that projected large scale groundwater development in this region will use an effectively nonrenewable resource and should be managed accordingly

detailed investigation of continental shelf morphology using a high resolution swath sonar survey the eel margin northern california abstract the eel shelf northern california lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the eel river a recent high resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region our analysis of the statistical character of bathymetry demonstrates a clear separation into large and small scale morphologies at a 3 10 km scale with smaller scale morphology heavily damped relative to large scale morphology the eel shelf bathymetry is subtle but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient some shelf structures are evidently related to depositional processes as evidenced by correlation with 100 yr sediment accumulation rates whereas others appear related to tectonic processes as evidenced by correlation with subsurface synclines and anticlines the sidescan structure of the shelf is dominated by the low backscatter over the eel and mad river subaqueous deltas evidently associated with the sand to mud transition however contrary to usual correlations between backscatter and grain size in this situation higher backscatter is associated with the muddy sediments in addition we observe a series of shore perpendicular striations or ribbons spaced 0 2 1 0 km apart which extend northward from the eel river subaqueous delta and lie at or near the sand to mud transition some aspects of ribbon morphology suggest that they may be associated with down slope flows

estimating aquifer recharge due to rainfall abstract an existing dynamic model of the annual water balance is modified to account for two phenomena peculiar to arid climates i e variable rainy season length and soil dessication during the dry season model parameter values are estimated for two locations in the central zone of saudi arabia and the cumulative distribution function of annual recharge from precipitation is found for two of the primary sedimentary aquifers outcripping in this zone results quantify the large uncertainty of annual recharge in such climates and confirm the accepted notion that these aquifers are being mined

sub ice shelf deposition during the late devensian glaciation in western ireland abstract glacigenic sediments preserved around the margins of clew bay western ireland record deposition in a tidally influenced sub ice shelf environment during the late devensian glaciation 21 13 14 c kyr thick massive to normally graded glacial diamictons tills are interbedded with laminated to massive silt and clay beds these sediments interbed with each other on scales ranging from millimetres to metres in a generally shallowing up sequence associated with a decrease in accommodation space isolated dropstones and a downward going clastic dike are also observed these structures and sediments reflect a waterlain environment with rhythmically varying levels of water energy and sediment supply tidally driven uplift and downdraw of a retreating ice shelf is a likely control on sedimentation patterns and glacial dynamics of this sensitive atlantic facing ice margin

teleseismic wavefield interpolation and signal extraction using high resolution linear radon transforms summary we present a new application of a method based on the radon transform for data interpolation and signal to noise separation of teleseismic wavefields recorded by regional seismic arrays the method exploits the plane wave nature of direct arrivals and receiver side scattered ar rivals from regional scale structure by decomposing the recorded wavefield into a plane wave basis linear radon transform casting the radon transform as an inversion problem allows the incorporation of time dependent weighting schemes and model variance tuning which are helpful in minimizing artefacts related to the transform process while enhancing lower ampli tude arrivals the procedure begins with an estimate radon transform of the input data panel a mute is applied in the radon domain to isolate portions of the radon panel that represent plane waves with different moveouts 025 s km 1 relative to the direct arrival the inverse transform of the estimated noise is subtracted from the input data to produce an estimate of the desired signal without plane waves following undesired moveouts white ambient noise and arrivals not represented well by plane waves diffractions inverse transformation of estimated signal in the radon domain produces a natural way to interpolate in the data domain due to the implicit assumption that a plane wave basis provides the most compact representation of the teleseismic wavefield this processing scheme presents an important addition to standard teleseismic imaging processing flows that attempt to exploit irregularly sampled data

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

microlevelling procedures applied to regional aeromagnetic data an example from the transantarctic mountains antarctica the extensive application of digital enhancement and filtering as a powerful tool for aeromagnetic interpretation not only of high resolution but also of regional data requires an improved levelling two microlevelling techniques were thus compared in order to find an effective but relatively simple procedure to remove or at least to reduce residual magnetic errors remaining after standard levelling processes this study was carried out on regional aeromagnetic data recently acquired at high magnetic latitudes along the transantarctic mountains in antarctica where it is particularly critical to remove time dependent magnetic variations two dimensional fft filters applied to the gridded data namely the butterworth and a directional cosine filter proved to be more effective than previously proposed one dimensional space domain filters in the reduction of the residual corrugation not removed by statistical levelling tectonic interpretation of trends detected in the total field magnetic anomaly map and in the 3d analytic signal improved after application of frequency domain microlevelling however we also show that when interpreting microlevelled data two factors must be considered i the possible presence of real geological trends aligned along the flight lines ii modifications in the results yielded by depth estimates of magnetic sources due to the fft filters applied during the microlevelling procedure such changes were seen both in the well established 2d fft method based on the slope of the energy spectrum and in the more recent 3d euler deconvolution technique overall our results indicate that microlevelling could profitably be applied to older gridded aeromagnetic data sets in antarctica thus improving the accuracy and geological significance of future regional magnetic compilations as already seen in other continents

characteristics and origins of lee side stratification sequences in late pleistocene drumlins northern ireland spindle and parabolic shaped drumlins examined at fifty five localities in northern ireland possess stratification sequences on their lee side flanks these forms lack the distinctive steep stoss and tapering lee ends of classical drumlins and tend to occur in linear zones transverse to late pleistocene ice flow in most cases 90 per cent the stratified deposits infill embayments excavated in the lee side of barkhanoid forms and in the remainder 10 per cent they are superimposed on the lee side of whaleback forms the stratification sequences developed as a result of sedimentation in interconnected subglacial water filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form stratigraphic evidence indicates that the lee side sequences developed during drumlin streamlining which supports the view that subglacial hydraulic processes played an important role in drumlin formation

seasonal variability of shallow biogenic gas in chesapeake bay abstract methane gas in chesapeake bay sediments occurs in buried paleodrainage channels incised during the last glacial sealevel lowstand repeat acoustic surveys of two chesapeake bay sites during the past year with a 2 15 khz chirp sonar profiler and 100 khz sidescan sonar show that the top of the zone of acoustically opaque gas bubbles in the sediments fluctuates vertically by up to 0 5 m apparently in response to seasonal temperature changes the vertical movement of the gas layer is most apparent in the main channel of the bay where the methane gas is very close to the seafloor in areas where the gas is seen to be very near the seafloor on the chirp profiler records the sidescan sonar data show corresponding high backscatter this does not appear to be the result of differing sediment types it is not likely that the sidescan signal is penetrating the seafloor at the shallow outer grazing angles of the sidescan swath therefore the gas must extend to the water sediment interface the areas of high backscatter caused by the gas are observed to change seasonally expanding during the summer high temperature period and shrinking during the winter low temperature period

identification and significance of ice flow transverse subglacial ridges rogen moraines in northern central ireland in the omagh basin north central ireland subglacial diamict ridges lie transverse to southwestward late devensian ca 23 13 ka ice flow these ridges 0 5 2 5 km long 100 450 m wide 15 35 m high are similar morphologically to rogen moraines which have not been described previously from the british isles the crests of some transverse ridges are streamlined cross cut or overprinted by drumlins whereas other ridges are unmodified and were not affected by later drumlinisation at kilskeery west east trending eskers overlying unmodified transverse ridges post date drumlinisation 17 14 14c ka esker formation shows that the subglacial thermal regime changed from cold based favouring bedform preservation to warm based with meltwater flowing through enclosed subglacial channels patterns of flow transverse ridges and spatial variations in the degree of bedform modification record dynamic changes in regional subglacial environments during the last deglacial cycle this ice mass variability cannot be reconciled with current irish glacial models which are based on immobile ice centres and ordered stages of ice retreat in a wider context these changes in bedform patterns and basal ice regimes have a similar signature to millennial scale ice mass oscillations recorded by dated proxy evidence elsewhere in the amphi north atlantic 1997 john wiley sons ltd

a comparison of recharge estimates to a fractured sedimentary aquifer in south africa from a chloride mass balance and an integrated surface subsurface model the paper describes the use of an integrated surface subsurface modelling approach to estimate recharge to a semi arid karoo aquifer and a comparison of the results with a chloride mass balance on a sub area scale parameters were not calibrated to test the success with which the model can be applied in regions of scarce data the chloride balance suggests a mean annual recharge of 4 5 mm year 1 based on a mean annual rainfall of 460 mm the model predicts 5 8 mm year 1 from a mean annual rainfall of 483 mm during the simulation period recharge was found to be highly variable in space with a positively skewed distribution in time spatial variability was attributed to differences in the distribution of soil moisture content resulting from variations in slope soil texture and depth both methods suggest that recharge is considerably less than the mean of 9 9 mm year 1 estimated from the currently prescribed rainfall recharge relationship for karoo aquifers

correlation of sidescan backscatter with grain size distribution of surficial seabed sediments the dependence of acoustic backscatter on sediment grain size distribution is examined using dual frequency 100 and 410 khz sidescan sonar and 22 sediment grab samples from the loch linnhe artificial reef site on the west coast of scotland the sidescan data were processed to remove an empirically estimated average grazing angle dependence on backscatter the processed data were analysed by forming histograms of pixels extracted from a 20 m 2 box around each ground truth site a positive correlation r 0 73 between mean backscatter intensity and mean grain size was obtained i e the coarsest samples had the brightest backscatter a positive correlation r 0 59 was also found between the standard deviations of the backscatter and grain size distributions i e poorly sorted sediments gave the most variable backscatter the performance of the sidescan data was compared to results from a co incident single beam echo sounder roxann survey the roxann roughness index e1 compared well with the sidescan whilst the roxann hardness index e2 did not this may be due to a physical link between the acoustic measures the comparison showed the sidescan to have delivered a significantly higher resolution image of the seabed for a similar amount of ship time imaging of the artificial reef modules themselves was found to be frequency dependent d 2004 elsevier b v all rights reserved

textural analyses of sidescan sonar imagery from two mound provinces in the porcupine seabight large mound structures have been discovered in the porcupine seabight northeast atlantic at a depth of 500 1200 m associated with the growth of cold water deep sea coral species such as lophelia pertusa l or madrepora oculata l during the training through research cruise in 1997 high resolution oretech sidescan sonar data were acquired over two provinces of these structures this article focuses on the presentation and quantitative interpretation of representative sections of these sidescan data from areas around the belgica and hovland mounds several image analysis tools were used but texture analysis based on grey level co occurrence matrices gave the best results entropy and homogeneity indices were calculated and the resulting images made it possible to discriminate between different seabed features on a quantitative basis mounds moats and background sediments could be delineated accurately and the image textures could be linked to the actual seafloor appearance through core descriptions and deep towed video data a major difference was found in the acoustic returns from the two provinces studied the belgica province shows much rougher textures this is due to an actual difference in seabed roughness caused by a difference in bottom currents and sediment dynamics in the two areas the combined effect of the northward directed north atlantic slope current and superimposed internal waves and tides appears to be much stronger in the belgica province the reported difference in current strength might well influence the growth of the deep water coral species in both areas

sources of the nitrate in phreatic groundwater in the western kalahari abstract elevated levels of nitrate occur in phreatic groundwater in the western kalahari namibia nitrate in water containing 0 4 3 1 meq no 3 l 1 of widespread occurrence has 15 n values in the range 4 9 to 8 0 suggesting natural derivation from the soil the sporadic occurrence of very high levels of nitrate 4 meq no 3 l 1 which has 15 n between 9 3 to 18 7 reflects pollution derived from animal waste the importance of considering the possible isotopic effects of denitrification and the significance of leaching in the nitrogen budget of the kalahari soil are also discussed

origin and history of nitrate in confined groundwater in the western kalahari abstract data are presented for nitrate dinitrogen and argon concentrations and 15 n 14 n ratios in groundwater with radiocarbon ages up to 40 000 yr for three confined sandstone aquifers in the western kalahari of south west africa namibia the nitrate is probably generated within the soil of the recharge areas and its production rate during the period 3000 40 000 b p has remained between 0 5 and 1 6 meq no 3 l 1 of recharge water with 15 n between 4 and 8 variations in the amount of nitrate and of excess air in groundwater recharge are found and can only reflect changes in the environmental conditions during recharge they must therefore be caused by the climatic changes that have taken place during the past 25 000 yr

hydrologic issues in arid unsaturated systems and implications for contaminant transport analysis of unsaturated flow and transport in arid regions is important not only in water resource evaluation but in contaminant transport as well partic ularly in siting waste disposal facilities and in remediat ing contaminated sites the water fluxes under consid eration have a magnitude close to the errors inherent in measuring or in calculating these water fluxes which makes it difficult to resolve basic issues such as direction and rate of water movement and controls on unsaturated flow the purpose of this paper is to review these issues on the basis of unsaturated zone studies in arid settings because individual techniques for estimating water fluxes in the unsaturated zone have limitations a variety of physical measurements and environmental tracers should be used to provide multiple independent lines of evidence to quantify flow and transport in arid regions the direction and rate of water flow are affected not only by hydraulic head gradients but also by temperature and air pressure gradients the similarity of water fluxes in a variety of settings in the southwestern united states indicates that vegetative cover may be one of the pri mary controls on the magnitude of water flow in the unsaturated zone however our understanding of the role of plants is limited most unsaturated flow in arid systems is focused beneath topographic depressions and diffuse flow is limited thick unsaturated sections and low water fluxes typical of many arid regions result in preservation of paleoclimatic variations in water flux and suggest that deep vadose zones may be out of equilib rium with current climate whereas water movement along preferred pathways is common in humid sites field studies that demonstrate preferential flow are restricted mostly to fractured rocks and root zones in arid regions results of field studies of preferential flow in humid sites generally restricted to the upper 1 2 m because of shallow water tables cannot be applied readily to thick vadose zones in arid regions

drumlins products of controlled or uncontrolled glaciodynamic response abstract two schools of thought on the process of drumlin formation have recently developed that have created a controversy within this ara of glacial geology one hypothesis contends that drumlins are in the main developed within a soft mobile subglacial debris zone the other school argues that for those drumlins that contain primary deposited stratified sediment formation during catastrophic subglacial flood events is necessary a classification of subglacial bed types is presented that allows for the accommodation of both schools it is proposed that a new paradigm for subglacial research may be needed in order that a closer relationship between glaciodynamics and sedimentological processes be established in future attempts at explaining glacial processes and froms

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd

evaporation rate from a salt pan estimates from chemical profiles in near surface groundwaters evaporation of water from saturated saline soils or sediments induces gradients of the solutes in the remaining interstitial solution these gradients lead to a systematic and predictable solute distribution in the soil solution which may be used in some cases to estimate the rate of evaporation simple one dimensional transport models for the distribution of cl and br indicate net evaporation rates from the salt covered surface of lake eyre south australia of between 0 9 and 2 8 cm yr 1 the former is a minimum estimate averaged over 20 yrs which includes the major 1974 filling event while the latter reflects the most recent summer evaporation period