geochemical isotopic and remote sensing constraints on the origin and evolution of the rub al khali aquifer system arabian peninsula summary chemical and stable isotopic compositions of groundwater samples from the rub al khali rak in southern saudi arabia were analyzed samples were collected from wells of variable depth 1 5 800 m along the perimeter of the eastern half of the rak including flowing artesian wells pumped wells formerly artesian and shallow hand dug wells encompassing those in sabkha areas data indicate that the water from the artesian and formerly artesian wells represents the contents of confined aquifers such water group 1 is isotopically depleted 2h values ranging from 60 to 35 and has total dissolved solids tds concentrations ranging from 1300 to 76 000 mg l indicating that much of the salinity is acquired in the subsurface water from shallow hand dug wells including those in sabkha areas group 2 has experienced significant evaporation 2h values ranging from 34 to 19 as well as salinization tds as high as 92 000 mg l by dissolution of sabkha salts including halite and gypsum stable isotope data for the group 2 water samples define an evaporation trend line originating from the group 1 water samples this relationship indicates that the group 2 type water evolved from group 1 type water by ascending through structural discontinuities dissolving evaporative salts and undergoing substantial near surface evaporation in groundwater discharge zones sabkhas characterized by shallow groundwater levels

the magnetostratigraphy of leg 73 sediments abstract the main objectiveof dsdp leg 73 was to obtain high quality records of major paleooceanographic events in the south atlantic this was achieved by coringsix sites on the african plate the sediments thus recovered span the cenozoic and five of the six sites proved ideally suited for magnetostratigraphic analysis the results presented in this paper and elsewhere in this volume constitute the first opportunity to extend the direct correlation of the magnetostratigraphic and biostratigraphic time scales into the paleogene in deep sea cores the magnetostratigraphic analyses from dsdp leg 73 sediments are presented in this paper the correlation of the magnetostratigraphy to the magnetic polarity time scale provides tight age depth control for the five sites analyzed allowing the accurate calculation of sediment accumulation rates the data presented here represent a remarkable record of the fine scale polarity history of the earth s magnetic field these data place constraints on the interpretation of small scale marine magnetic anomalies which are modelled equally effectively by field intensity fluctuations as polarity reversals at least some of the tiny wiggles correspond to very short polarity units in the magnetostratigraphic record by assuming an axial geocentric dipole the inclination of the time averaged magnetic field recorded in the sediments can be used to calculate the paleolatitude at which the sediments were deposited combining the age and average inclination information available from the magnetostratigraphy we present paleolatitudes versus time for the leg 73 drill sites

groundwater dynamics in fossil fractured carbonate aquifers in eastern arabian peninsula a preliminary investigation abstract eastern arabian peninsula represents the main natural groundwater discharge area of the arabian platform fossil aquifer system in such settings connections between aquifers could strongly affect the flow dynamics water quality and availability as well as karst formation and landscape evolution geological structures such as folds and faults are central to aquifer connectivity yet their role on groundwater flow is poorly understood herein we perform mapping of exposed and buried structural features in the qatar peninsula using landsat sentinel 2 and alos palsar scenes correlated with field gpr and isotopic data to assess their role in aquifer connections and groundwater dynamics our results suggest that ene wsw oriented fold related faults act as vertical conduits along which artesian upward leakages from the deep aruma aquifer take place into the shallower main aquifer unit i e umm er radhuma and rus in southern qatar peninsula on the other hand downward leakage from the freshwater lens in the dammam aquifer take place in northern qatar peninsula the deep brackish and gaseous rich waters ascending along faults in south qatar peninsula in addition to degrading the water quality in the main aquifer unit enhance dissolution of carbonates and evaporites leading to strong karstification that produces abundant collapse features our findings suggest that structure controls can add significant complexity to recharge mechanisms and groundwater dynamics in fossil aquifers future large scale radar subsurface mapping will be essential to resolve the variability of the water heads in such areas and its correlation to structural discontinuities

natural discharge a key to sustainable utilization of fossil groundwater summary rising demands for fresh water supplies in arid lands are leading to excessive exploitation and unsustainable mining of non renewable fossil groundwater using the nubian aquifer of saharan africa as a test site we demonstrate an integrated approach to identify areas of discharge that could have gone undetected and to model extraction that is sustained by natural discharge using isotopic and geochemical analyses along with field and remote sensing data we show that discharge of the nubian aquifer is occurring on a larger scale primarily through deep seated fault systems and that ascending groundwater discharges into relatively thick alluvial aquifers proximal to the fault complex that defines the river nile and the gulf of suez we develop a hydrologic model to assess the discharge and to constrain sustainable extraction in the asyuti area along the river nile and to demonstrate a replicable model for similar reservoirs a two dimensional groundwater flow model was constructed and calibrated against head data from 19 wells results point to a significant contribution to the asyuti groundwater system from rising nubian groundwater 3 19 10 7 m 3 yr 75 of incoming flow and a modest contribution 1 08 10 7 m 3 yr 25 of incoming flow from surface runoff approximately 2 5 10 7 m 3 yr of groundwater could be used in a sustainable manner in asyuti assuming geologic settings and discharge rates similar to those at asyuti we estimate that 70 10 7 m 3 yr of groundwater may be available for sustainable development in similar settings around the river nile and the gulf of suez

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

identifying fluvial recharge and artesian upwards leakage contributions to arid zone shallow unconfined groundwater evaporation losses from unconfined groundwater can form an important part of the water balance of arid zone groundwater systems however in artesian groundwater systems the discrimination between artesian leakage and surface recharge contributions to the unconfined water table is required we use hydrochemical analysis techniques and isotopic data to investigate the provenance of unconfined groundwater in zones of artesian discharge along the margin of the great artesian basin gab of australia forward modelling of evapoconcentration and use of trilinear plots identified unconfined groundwater that was largely derived from fluvial recharge compared to upwards artesian leakage particularly in areas where the artesian groundwater had a na hco3 cl composition in contrast to the na cl so4 composition more typical of arid zone meteoric recharge mixing models combined with forward evapoconcentration models confirmed that the contribution of artesian groundwater was minimal in areas of na cl so4 unconfined groundwater underlain by na hco3 cl artesian groundwater however the evaporation modelling was still useful in identifying probable artesian versus meteoric contributions from na cl so4 composition artesian groundwater stable isotope data were consistent with the unconfined groundwater being evapoconcentrated from the artesian groundwater end member and were unable to discriminate between contributions from fluvial recharge and artesian discharge the hydrochemical analysis techniques can assist in water balance studies of aquifers with na hco3 cl composition groundwater discharging into semi arid and arid environments in addition to identifying areas of local fluvial recharge

geologic and hydrologic settings for development of freshwater lenses in arid lands satellite observations were used to test the validity of previously identified favourable conditions for the formation of freshwater lenses identify additional potential occurrences and model modern potential recharge in the raudhatain watershed 3696 in northern kuwait favourable conditions include infrequent yet intensive precipitation events drainage depressions to collect the limited runoff and presence of conditions e g high infiltration capacity that promote groundwater recharge and preservation e g underlying saline aquifer of infiltrating groundwater as freshwater lenses floating over saline aquifer water due to differences in density specifically the following field and satellite based observations were noted for the raudhatain watershed 1 over 30 precipitation events were identified from the tropical rainfall measuring mission precipitation data 1998 2009 2 slope is gentle 2 m km and the surface is largely 80 covered by alluvial deposits with high infiltration capacities up to 9 m day 3 no flows and long term ponding were reported at the watershed outlet or detected from landsat thematic mapper images 4 infiltration is high based on increases in soil moisture content from an advanced microwave scanning radiometer and vegetation index following large precipitation events and 5 freshwater lenses that overlie highly saline total dissolved solids tds 35 000 unconfined aquifers underlying the watershed are absent in the southern regions where infiltrating fresh water mixes with the less saline groundwater tds 10 000 twenty potential locations size 1 to 75 km2 for freshwater lens development were identified in northern kuwait and continuous rainfall runoff models soil water and assessment tool were applied to provide a first order estimation of the average annual recharge in the watershed 127 106 m3 and freshwater lenses 8 17 106 m3 results demonstrate the settings for enhanced opportunities for groundwater recharge outline the amounts of and preservation conditions for the groundwater feeding the freshwater lenses and highlight potential applications and locations of freshwater lenses in similar settings elsewhere in the arabian peninsula and beyond copyright 2013 john wiley sons ltd

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

land subsidence triggered by groundwater withdrawal under hyper arid conditions case study from central saudi arabia natural and human induced groundwater dynamics in hyper arid aquifers play a crucial role in the evolution of the landscape the area overlying the saq aquifer in particular the al qassim area within the central part of the kingdom of saudi arabia has witnessed numerous land deformation land subsidence and fissures events throughout the last two decades an integrated remote sensing and hydrogeologic approach is adapted to identify areas affected by the land deformation and also to better understand the role of human induced groundwater dynamics in the formation of these deformation features a fourfold approach was implemented including 1 conducting field surveys to collect observations and validate the reported deformation features 2 applying a spatial correlation in a gis environment for the reported damaged locations together with surface and subsurface geological features and groundwater extraction 3 extracting the subsidence rates using sbas radar interferometric technique using envisat data sets and 4 correlating these subsidence rates spatially and temporally with grace mass variations data the results show that high subsidence rates of 5 to 12 mm year along a northwest southeast direction coincident with areas witnessing a significant drawdown in the fossil groundwater levels up to 150 m and a depletion 10 1 1 2 mm year in grace derived terrestrial water storage findings from the present study draw attention to the quick responses of landscapes to human induced groundwater dynamics under hyper arid conditions

palaeo environmental implications derived from lake and sabkha deposits of the southern rub al khali saudi arabia and oman abstract shallow lakes and sabkha deposits are evidence of past periods of higher groundwater table than today and hence reflect increased humidity in the rub al khali the large desert in the southern part of the arabian peninsula reported here are the observations made during four expeditions into this remote area in combination with luminescence dating constraining the age of the deposits the results presented extend the spatial coverage of evidence and show that most of the deposits correlate to mis 5 ca 130 70 ka and the early mid holocene ca 11 5 5 ka a single sample points towards potentially more humid conditions during the transition mis 4 3 ca 65 55 ka the presence of the mussel unio in some of the deposits attributed to mis 5 is indirect evidence for the presence of fish in the lakes which must have supported a rich and diverse fauna and probably also flora together with other evidence this demonstrates that a number of small persistent lakes were spread across the rub al khali for at least some of the time these lakes would not only have been a potential source of freshwater but could also have provided an additional and easy accessible food source via the fish for humans migrating through the area the presented palaeoenvironmental data underlines that parts of mis 5 represent a time window of opportunity for a potential expansion of modern humans across arabia

the karakorum block in central asia from ordovician to cretaceous abstract the karakorum block records a predominantly marine ordovician to cretaceous sedimentary history six major sedimentary cycles are recognised the oldest sediments early ordovician transgress over a crystalline basement the 1 km thick ordovician silurian mostly shaly succession contains rare carbonate intercalations in the early devonian a wide peritidal platform spread over the craton sedimentation rates were low 10 20 m ma and upper devonian probable lower carboniferous carbonates and clastics rest unconformably on the early devonian carbonates no evidence has been found for either late carboniferous or glaciogenic deposits sedimentation rates increased during the permian up to 50 m ma with thicknesses between 1 and 2 5 km three steps are identified 1 a huge alluvial to marginal marine terrigenous prism aggraded during the asselian sakmarian 2 the artinskian murgabian is characterised by local emergence and erosion linked to extension with block rotations 3 greater differentiation occurred from late permian to middle triassic when a peritidal carbonate flat developed in the southwest facing a deeper basin to the northeast carbonate sediments prevailed throughout the carnian norian the permo triassic evolution is interpreted as the passive margin stage of the karakorum block which previously belonged to the perigondwanian fringe when like mega lhasa it drifted northward on the tethyan transit plate mega lhasa is considered as a collage of blocks possibly separated by thinned crust or short lived seas with ocean crust quartzo lithic sandstones with grains of mafic volcanics and serpentinite overlain with gentle unconformity by pliensbachian toarcian red sandstones with sedimentary and metasedimentary clasts record the eo cimmerian deformation in the karakorum this orogenic episode was over by the aalenian when a shallow water carbonate ramp aggraded onto the previously emergent area the pre barremian upper jurassic and lower cretaceous are poorly documented in post barremian times the sedimentary succession of n karakorum was severely deformed in huge thrust sheets including slabs of crystalline basement a coarse conglomerate of mid cretaceous age sealed the thrust sheet edifice finally isolated campanian pelagic mudstones are recorded anticlockwise rotation of mega lhasa followed the late triassic docking of the iranian spur using the latter as pivot the rotation was completed during the middle jurassic when se pamir shaksgam and karakorum joined the qiangtang more closely assembling mega lhasa as it approached the asian margin

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

assessment of age origin and sustainability of fossil aquifers a geochemical and remote sensing based approach abstract an integrated approach was developed to assess the sustainability origin age evolution and groundwater potential of large fossil aquifers using the mega aquifer system mas area 2 106 km2 in the arabian peninsula as a test site a two step exercise was adopted the sustainability of the mas was first investigated through the analysis of grace data and land surface model lsm outputs then integrated geochemical remote sensing and field studies were conducted to address the age origin hydrogeological setting and evolution of the southern sections of the mas rub al khali aquifer system rakas the area identified from the analysis of grace and lsms as being the most suited for sustainable development analysis of grace and lsms revealed 1 the mas central and northern sections are experiencing high groundwater extraction 6 6 km3 yr and depletion rates 2 8 0 8 km3 yr with minimum balancing potential through aquifer capture processes yet sustainability could be achieved by reducing annual extraction by 2 8 km3 and 2 the mas southern sections rub al khali aquifer system rakas are experiencing low groundwater depletion rates eastern rakas 1 8 1 4 mm yr to steady state conditions western rakas 0 73 1 4 mm yr geochemical remote sensing and field investigations over the rakas revealed 1 the presence of west to east trending drainage networks and large scale groundwater flow systems consistent with a meteoric source precipitation over red sea hills 2 increasing 36cl model ages along groundwater flow directions up to 970 000 years indicating aquifer recharge in wet pleistocene periods 3 progressive depletion in the o and h stable isotopic compositions of aquifers with increasing distance from the red sea hills basement outcrops indicating modest recharge during prevailing dry conditions and 4 the presence of relatively fresh tds 800 2800 mg l and non radioactive 226ra 228ra

high resolution strontium isotope stratigraphy and biostratigraphy of the miocene monterey formation central california detailed biostratigraphic and sr isotope studies on two outcrop sections of the miocene monterey formation of california demonstrate the applicability of the sr isotope method for detailed chronostratigraphic correlation multidisciplinary biostratigraphic ages generally agree with sr isotopic ages determined by correlating 87sr 86sr ratios with a standard 87sr 86sr versus age curve constructed of data from deep sea drilling project sites 575 and 590 diagenetic modification of sr isotopic ratios of the monterey formation was negligible strontium isotopes provide age resolutions of 0 1 to 0 2 ma in the lower miocene small faults and slump structures are identified as reversals within a general trend of increasing 87sr 86sr biostratigraphy yields the more definitive age assignments in the younger siliceous rocks where diatoms in particular have more utility than the corresponding flat and polytonal portion of the isotopic curve strontium isotopic correlation of the basal monterey formation with deep sea drilling project site 575 indicates that monterey deposition commenced at 17 85 0 10 ma within planktic foraminiferal zone n6 and calcareous nannofossil zone cn2 concomitant with an increase in slope of the sea water 87sr 86sr versus age curve this event dates 0 35 0 10 m y before the beginning of the pronounced shift of 13c and 1 4 m y before the shift of 18o observed at site 575 it is evident that sr isotope stratigraphy is a valuable supplement to biostratigraphy the techniques are complementary in refining chronostratigraphic interpretations

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

astronomical calibration age for the oligocene miocene boundary the stratotype section for the base of the miocene is at a reversed below to normal above magnetic transition that is claimed to represent magnetic chron c6cn 2n o deep sea drilling project dsdp site 522 is the only location we are aware of that unambiguously records the three normal events of c6cn we have quantitatively determined the range of the short lived nannofossil sphenolithus delphix and the lower limit of s disbelemnos in dsdp holes 522 and 522a in order to calibrate their precise relationship to the magnetostratigraphy and to confirm the completeness of the record at this site astronomical tuning of ocean drilling program odp sites 926 928 and 929 shows that s disbelemnos appears at 22 67 ma and that the entire range of s delphix is from about 22 98 ma to 23 24 ma using these ages linear interpolation in dsdp site 522 suggests that the age of c6cn 2n o and of the oligocene miocene boundary is 22 92 0 04 ma our value conservatively expressed as 22 9 0 1 ma is 0 9 m y younger than the currently accepted age of the oligocene miocene boundary and of c6cn 2n o which was assigned an age of 23 8 ma based on an estimate of 23 8 1 ma for the oligocene miocene boundary the bulk sediment carbon isotope data from dsdp site 522 is correlated to the record from benthic foraminifera at odp site 929 to refine the calibration of magnetic reversals from c6cn 1n o to c7n 2n o at dsdp site 522 on the astronomical time scale

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 ocean drilling program holes 744a and 748b represent key sections for calibration of southern ocean eocene oligocene biostratigraphic zonations sites 744 and 748 were above the carbonate compensation depth throughout this time interval and contain good planktonic foraminiferal calcareous nannofossil and diatom biostratigraphic records in particular the southern ocean diatom biostratigraphic zonation for the oligocene critically hinges on calibration of these two holes previous low resolution magnetostratigraphic studies at these sites were hampered by limited sampling and technical difficulties which prompted our high resolution reinvestigation of the magnetostratigraphy magnetic polarity zonations for holes 744a and 748b were constructed after inspection of vector component plots at 1 cm stratigraphic intervals from continuous u channel measurements the magnetizations are generally stable and a robust polarity stratigraphy has been obtained for both holes the increased resolution of our study and identification of persistent secondary overprints which were not recognised in previous studies suggests that the previously published interpretations need to be revised our magnetostratigraphic interpretations for both holes are constrained by foraminiferal and calcareous nannofossil datums as well as by sr isotope ages we have calibrated four diatom datums which are synchronous at the two studied sites to the geomagnetic polarity timescale including the first occurrence fo of lisitzinia ornata 27 8 ma the fo of rocella vigilans var b 27 8 ma the fo of cavitatus jouseanus 30 9 ma and the fo of rhizosolenia oligocaenica 33 8 ma the synchroneity of these datums suggests that diatom biostratigraphy has considerable potential for palaeogene biostratigraphic correlation in the southern ocean although the ages of some datums are obscured by an unconformity in hole 744a our age model from hole 748b suggests age estimates for the last common occurrence of rocella vigilans var a 29 0 ma the fo of rocella vigilans var a 30 0 ma and the fo of rhizosolenia antarctica 33 2 ma it should also be noted that the last occurrence of the calcareous nannofossil chiasmolithus altus occurs in chron c8r rather than c8n in our revised magnetostratigraphic interpretation which indicates that this datum is not diachronous between low and mid latitudes as had previously been suggested significant unconformities are documented in both holes in the middle oligocene and in the middle late oligocene respectively which probably resulted from periods of enhanced circumpolar deep water circulation

petroleum geology and potential hydrocarbon plays in the gulf of suez rift basin egypt the gulf of suez in egypt has a north northwest south southeast orientation and is located at the junction of the african and arabian plates where it separates the northeast african continent from the sinai peninsula it has excellent hydrocarbon potential with the prospective sedimentary basin area measuring approximately 19 000 km 2 and it is considered as the most prolific oil province rift basin in africa and the middle east this basin contains more than 80 oil fields with reserves ranging from 1350 to less than 1 million bbl in reservoirs of precambrian to quaternary age the lithostratigraphic units in the gulf of suez can be subdivided into three megasequences a prerift succession pre miocene or paleozoic eocene a synrift succession oligocene miocene and a postrift succession post miocene or pliocene holocene these units vary in lithology thickness areal distribution depositional environment and hydrocarbon importance geological and geophysical data show that the northern and central gulf of suez consist of several narrow elongated depositional troughs whereas the southern part is dominated by a tilt block terrane containing numerous offset linear highs major prerift and synrift source rocks have potential to yield oil and or gas and are mature enough in the deep kitchens to generate hydrocarbons geochemical parameters sterane distribution and biomarker correlations are consistent with oils generated from marine source rocks oils in the gulf of suez were sourced from potential source rock intervals in the prerift succession that are typically oil prone type i and in places oil and gas prone type ii or are composites of more than one type multiple types i ii or iii for oil prone oil and gas prone or gas prone respectively the reservoirs can be classified into prerift reservoirs such as the precambrian granitic rocks paleozoic cretaceous nubian sandstones upper cretaceous nezzazat sandstones and the fractured eocene thebes limestone and synrift reservoirs such the miocene sandstones and carbonates of the nukhul rudeis kareem and belayim formations and the sandstones of south gharib zeit and

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

special climatological conditions in the deserts of sinai and the negev during the latest pleistocene abstract results of hydrological and geological investigations carried out during the last ten years in the deserts of the sinai and the negev indicate that unique climatological and hydrological conditions prevailed between ca 100 000 and ca 10 000 yr b p the uniqueness was expressed by the following characteristics 1 1 higher precipitation and recharge rates caused the nubian sandstone aquifers to be filled up through the outcrops in central sinai and to overflow through big springs emerging along the faults of the syrian african rift system this water is of special isotopic composition namely depleted in 18o and deuterium and with a lower excess of the latter 2 2 dust laden rainstorms prevailed probably mainly during the autumn season causing the deposition of thick layers of loess the quantity of rain during the humid periods was double that of the present 3 3 the drainage system of many western and northern wadis of sinai as well as the negev could not drain out all the silt loaded water during the rainy season and shallow lakes and marshes extended in many wadis during this season 4 4 the floods and the springs flowing into the dead sea rift valley contributed to the lisan lake which was 200 m above the level of the contemporary dead sea

changing moisture sources over the last 330 000 years in northern oman from fluid inclusion evidence in speleothems speleothems from hoti cave in northern oman provide a record of continental pluvial periods over the last 330 000 yr periods of rapid speleothem deposition occurred from 6000 to 10 500 78 000 to 82 000 120 000 to 135 000 180 000 to 200 000 and 300 000 to 330 000 yr ago with little or no growth during the intervening periods during each of these five pluvial periods d values of water extracted from speleothem fluid inclusions dfi are between 60 and 20 vsmow and 18o values of speleothem calcite 18oc are between 12 and 4 to vpdb these values are much more negative than modern rainfall for d or modern stalagmites for 18o previous work on the isotopic composition of rainfall in oman has shown that northern and southern moisture sources are isotopically distinct combined measurements of the d values of fluid inclusion water with calculated 18o values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern indian ocean moisture source when the monsoon rainfall belt moved northward and reached northern oman during each of these periods

indian ocean climate and an absolute chronology over dansgaard oeschger events 9 to 13 oxygen isotope ratios of a stalagmite from socotra island in the indian ocean provide a record of changes in monsoon precipitation and climate for the time period from 42 to 55 thousand years before the present the pattern of precipitation bears a striking resemblance to the oxygen isotope record from greenland ice cores with increased tropical precipitation associated with warm periods in the high northern latitudes the largest change at the onset of interstadial 12 occurred very rapidly in about 25 years the chronology of the events found in our record requires a reevaluation of previously published time scales for climate events during this period

chronostratigraphic framework for the iodp expedition 318 cores from the wilkes land margin constraints for paleoceanographic reconstruction the integrated ocean drilling program expedition 318 to the wilkes land margin of antarctica recovered a sedimentary succession ranging in age from lower eocene to the holocene excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals drill sites recovered the lower and middle eocene nearly the entire oligocene the miocene from about 17 ma the entire pliocene and much of the pleistocene the paleomagnetic properties are generally suitable for magnetostratigraphic interpretation with well behaved demagnetization diagrams uniform distribution of declinations and a clear separation into two inclination modes although the sequences were discontinuously recovered with many gaps due to coring and there are hiatuses from sedimentary and tectonic processes the magnetostratigraphic patterns are in general readily interpretable our interpretations are integrated with the diatom radiolarian calcareous nannofossils and dinoflagellate cyst dinocyst biostratigraphy the magnetostratigraphy significantly improves the resolution of the chronostratigraphy particularly in intervals with poor biostratigraphic control however southern ocean records with reliable magnetostratigraphies are notably scarce and the data reported here provide an opportunity for improved calibration of the biostratigraphic records in particular we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the paleogene and a substantially improved diatom calibration for the pliocene this paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the wilkes land margin cores it further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region

use of chloride mass balance and environmental isotopes for evaluation of groundwater recharge in the alluvial aquifer wadi tharad western saudi arabia groundwater recharge estimation has become a priority issue for humid and arid regions especially in regions like saudi arabia where the precipitation varies over space and time as a result of topography and seasonality wadi tharad is a typical arid area in western saudi arabia within its drainage area of 400 km 2 the groundwater system shows a graded hydrochemical zonation from the hydrocarbonate in the upper reach to the chloride zone in the lower reach the saturation index si varies depending on the concentrations of carbonate minerals the mean for calcite and dolomite is about in equilibrium e g zero value as halite and gypsum indices are negative it is undersaturated isotopic compositions of h and o in the groundwater show that the groundwater recharge resources are mainly from meteoric water the chloride mass balance method was refined to estimate the amount of recharge which is probably 11 of the effective annual rainfall these results can be used to improve the accuracy of future groundwater management and development schemes

assessing seawater basalt exchange of strontium isotopes in hydrothermal processes on the flanks of mid ocean ridges we have measured the87sr 86sr of discharging geothermal waters from three ridge flank hydrothermal systems 1 the galapagos mounds hydrothermal field on 0 7 myr old crust 2 a region with crustal age of 4 6 myr on the west flank of the east pacific rise at 19 s and 3 an area having a crustal age of 3 myr in the mariana trough a back arc spreading center half spreading rates at our study sites range from 1 to 8 cm yr and our sites include both normal spreading centers and a back arc basin our sites thus span the range of ridge flank tectonic environments at each of our study sites the hydrothermal nature of our study samples is confirmed by supporting heat flow and chemical evidence our results show that the87sr 86sr of these ridge flank hydrothermal solutions is virtually identical to that of modern seawater indicating that sr isotope exchange on the ridge flanks occurs too slowly to be quantitatively important in the oceanic mass balance of the sr isotopes

persistent near tropical warmth on the antarctic continent during the early eocene epoch the warmest global climates of the past 65 million years occurred during the early eocene epoch about 55 to 48 million years ago when the equator to pole temperature gradients were much smaller than today1 2 and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume3 4 recently the early eocene has received considerable interest because it may provide insight into the response of earth s climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future5 as a consequence of unabated anthropogenic carbon emissions4 6 climatic conditions of the early eocene greenhouse world however are poorly constrained in critical regions particularly antarctica here we present a well dated record of early eocene climate on antarctica from an ocean sediment core recovered off the wilkes land coast of east antarctica the information from biotic climate proxies pollen and spores and independent organic geochemical climate proxies indices based on branched tetraether lipids yields quantitative seasonal temperature reconstructions for the early eocene greenhouse world on antarctica we show that the climate in lowland settings along the wilkes land coast at a palaeolatitude of about 70 south supported the growth of highly diverse near tropical forests characterized by mesothermal to megathermal floral elements including palms and bombacoideae notably winters were extremely mild warmer than 10 c and essentially frost free despite polar darkness which provides a critical new constraint for the validation of climate models and for understanding the response of high latitude terrestrial ecosystems to increased carbon dioxide forcing

environmental change across the paleocene eocene transition from eastern new zealand a marine palynological approach abstract recent improvements in the resolution and calibration of dinoflagellate cyst dinocyst bioevents across the paleocene eocene p e transition in new zealand allow better understanding of the relation between dinocyst variations and environmental change in southern mid high latitudes during this greenhouse climate combining information from land spore pollen assemblages with coeval dinocyst records allows evaluation of plant changes in a marine based timeframe palynological associations at tawanui and moeraki hampden eastern new zealand fluctuate across the p e transition and local palynological phases are recognized the onset of major fluctuations in dinocyst assemblages coincide with the intense warmth and excess carbon of the initial eocene thermal maximum ietm changes in sea surface temperature sst appear to have been the main environmental factor that affected dinoflagellates short lived intervals of higher ssts suggested by a high relative abundance of the apectodinium complex are seen during the ietm and lower eocene abundant cysts of probable heterotrophic dinoflagellates suggest surface waters remained relatively eutrophic for up to 0 5 myr after the onset of the ietm perhaps in response to enhanced terrigenous input related to changes in the character and pattern of continental weathering in contrast to dinocysts spore pollen assemblages suggest plant communities remained rather stable across the p e transition vegetation was dominated by a mesothermal conifer dominated multistratal rainforest and low latitude nypa mangroves were established by the uppermost paleocene plants in this region show no clear response to the ietm and the predominant vegetation change may have occurred at least 1 5 myr later characterized by an increase in mesothermal megathermal angiosperm plants

groundwater evaporation from salt pans examples from the eastern arabian peninsula summary the major groundwater resources of the arabian peninsula are stored in the large sedimentary basins in its eastern part evaporation from continental salt pans playas is an important process in water resources assessments of its upper principal aquifers the upper mega aquifer system as it constitutes a significant sink however literature values on evaporation rates vary widely and usually report about coastal salt pans where seawater evaporation is assumed the present study applies different methods to provide a comprehensive picture of groundwater evaporation from salt pans of the upper mega aquifer system a remote sensing approach provided the spatial distribution and total salt pan area of about 36 500 km 2 hydrochemical and isotopic investigations revealed that from about 10 3600 km 2 1600 km 2 of the mapped salt pan area seawater evaporates to estimate the groundwater evaporation rate from continental salt pans a laboratory column experiment was set up implying a mean annual evaporation rate of about 42 mm 13 mm in situ analysis of water table fluctuations in the field suggested about 3 mm a 1 originate from recently infiltrated rainwater leading to an annual net groundwater evaporation of 39 mm 13 mm relating this number to the mapped salt pan area from which groundwater evaporates provides a total annual groundwater loss of 1 3 km 3 0 5 km 3 for the upper mega aquifer system

red sea rifting controls on aquifer distribution constraints from geochemical geophysical and remote sensing data highly productive wells in the central eastern desert of egypt are tapping groundwater in subsided blocks of jurassic to cretaceous sandstone taref formation of the nubian sandstone group and oligocene to miocene sandstone nakheil formation now occurring beneath the red sea coastal plain and within the proximal basement complex aquifer development is related to red sea rifting 1 rifting was accommodated by vertical extensional displacement on preexisting nw se to n s trending faults forming a complex array of half grabens and asymmetric horsts and 2 subsided blocks escaped erosion accompanying the red sea related uplift subsided blocks were identifi ed and verifi ed using satellite data geologic maps and fi eld and geophysical investigations interpretations of very low frequency vlf measurements suggest the faults acted as conduits for ascending groundwater from the subsided aquifers stable isotopic compositions d 19 3 to 53 9 18 o 2 7 to 7 1 of groundwater samples from these aquifers are interpreted as mixtures of fossil up to 70 and modern up to 65 precipitation groundwater volumes in subsided blocks are large within the central eastern desert basement complex alone they are estimated at 3 10 9 m 3 and 10 10 9 m 3 for the

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

age calibrated relative paleointensity for the last 1 5 myr at iodp site u1308 north atlantic integrated ocean drilling program iodp site u1308 central north atlantic records paleomagnetic directional and relative paleointensity rpi variations for the last 1 5 myr in 110 m of the sediment sequence at a mean sedimentation rate of 7 3 cm kyr a detailed benthic oxygen isotope record was combined with rpi to produce an integrated high resolution magneto isotopic stratigraphy for site u1308 apart from the well known polarity reversals in this interval the punaruu excursion is recorded at 1092 ka and the cobb mountain subchron in the 1182 1208 ka interval the paleointensity proxies are determined as slopes of nrm versus arm and nrm versus armaq arm acquisition with linear correlation coefficients to monitor the quality of the linear fit the rpi record for site u1308 is compared with the three other paleointensity records one from the western equatorial pacific and two from the north atlantic that cover the same time interval and have accompanying oxygen isotope records the match protocol of lisiecki and lisiecki 2002 is used to optimize the correlation of paleointensity records beginning with the original published age models for each record the match routine is used to optimize the rpi correlations to site u1308 with checks to ensure compatibility with oxygen isotope records squared wavelet coherence wtc indicates significant improvement in rpi and oxygen isotope correlations after matching each rpi record to site u1308 particularly for periods 10 kyr the level of coherence for the atlantic rpi records and the lower resolution pacific record implies synchronous global variability at scales 10 kyr that can be attributed to the axial dipole geomagnetic field

composition and origin of thermal waters in the gulf of suez area egypt abstract thermal waters with discharge temperatures ranging from 32 to 70 c are being discharged along the gulf of suez egypt from springs and shallow artesian wells a comprehensive chemical and isotopic study of these waters supports previous suggestions that the waters are paleometeoric waters from the nubian sandstone aquifer the chemical and isotopic compositions of solutes indicate possible contributions from tertiary sedimentary aquifer rocks and windblown deposits marine aerosols and or evaporite dust in the recharge area there is no chemical or isotopic evidence for mixing with red sea water gas effervescence from the hammam faraoun thermal water contains about 4 ch4 13c 32 6 and 0 03 he having an isotopic ratio consistent with a mixture of crustal and magmatic he 3he 4he 0 26 re geothermometers for the thermal waters indicate maximum equilibration temperatures near 100 c the waters could have been heated by percolation to a depth of several km along the regional geothermal gradient

an integrated approach for identification of potential aquifer zones in structurally controlled terrain wadi qena basin egypt abstract wadi qena basin represents one of the most promising regions for future development in egypt fresh water supplies are crucial for such plans we provide an integrated remote sensing landsat aster dem geoeye 1 geophysical aeromagnetic isotopic 18 o 2 h field stratigraphic and structural interpretation and geochemical major dissolved ions approach to delineate zones of potential groundwater resources in wadi qena basin four water bearing horizons were sampled fractured crystalline aquifer nubian aquifer system nas post nubian aquifer system pnas and the quaternary aquifer findings include 1 spatial analysis of remote sensing data in a gis environment indicates extensive structural deformation by dextral faults trending ne sw i e qena safaga shear zone qs and sinistral faults trending nw se i e najd shear zone and sufficient surface water supply from the east through wadi fattera sub basin 2 analysis of geophysical data indicates that these faults control the water bearing horizons in the subsurface 3 isotopic analysis reveals four isotopic groups including two end members one mixed group and one mixed and evaporated group group i highly depleted fossil nubian waters range 18 o from 6 39 to 6 74 and 2 h from 48 21 to 52 46 group ii modern waters in fractured basement range 18 o from 1 41 to 1 51 and 2 h from 5 46 to 6 04 group iii a mixed cluster between nas and modern waters range 18 o from 4 82 to 5 05 and 2 h from 33 28 to 38 54 and group iv samples which have both mixing between the nubian and meteoric waters and also have a considerable deviation from the global meteoric water line gmwl range 18 o from 0 58 to 4 69 and 2 h from 19 59 to 38 68 4 samples with a mixed isotopic signature in group iii which tap the nas and are located along the main channel of wadi fattera area 3600 km 2 provide evidence for modern recharge along surface exposures of the nas and enhanced infiltration along deep seated faults 5 samples with a mixed isotopic signature in group iv which tap the quaternary and pnas aquifers and are located along deep seated faults provide evidence of artesian upward leakage from the deep nas into the shallower quaternary and pnas aquifers the present study improves our understanding of the role of structural control and modern recharge in exploration for aquifer potential in arid environments

thinking outside the zone high resolution quantitative diatom biochronology for the antarctic neogene abstract developing a coherent neogene history of the antarctic ice sheet and southern ocean requires a high resolution biostratigraphic age model one that is applicable to the array of existing onshore and offshore paleoenvironmental records this study integrates comprehensive diatom biostratigraphy magnetostratigraphy and tephrostratigraphy from 32 neogene sections around the southern ocean and antarctic continental margin framing their correlation as a constrained optimization conop permits the use of computer implemented approaches that resemble multidimensional versions of graphic correlation the method establishes the most parsimonious sequence of events subject to an expert s selection of suitable input data determination of geological feasibility constraints and the most appropriate measure of fit to the data optimization quantitative output includes assessments of record quality and confidence intervals on all age assignments thorough review and testing of conop model settings and input datasets established the solution s sensitivity to these factors and guided the selective removal of unreliable data to produce a robust precise and reproducible biochronology two complementary models based on different assumptions about reworking yield independent estimates of average local ranges and total regional ranges of fossil taxa in the southern high latitudes the resulting composite sequences include range data of 116 diatom taxa as well as 52 paleomagnetic reversals and two radiometrically dated ashes which enable age calibration to within an average of 0 08 m y for first and last appearances as old as 18 ma deviations of new model ages from previously published estimates are generally small and reflect the different sample sizes available for traditional versus new quantitative biostratigraphic calibrations our results confirm the reliability and regional isochroneity of most commonly utilized diatom zonal marker events identify many new potentially useful events and provide up to an order of magnitude greater temporal resolution than traditional zonations the anticipated expansion of this new southern ocean chronostratigraphic framework to new localities and other microfossil groups will pave the way to further age refinement and broader application of this approach in the future

isotope study of moisture sources recharge areas and groundwater flow paths within the eastern batinah coastal plain sultanate of oman oxygen and hydrogen isotope analyses of rainfall samples collected on the eastern batinah coastal plain of northern oman between 1995 and 1998 indicate two different principal water vapor sources for precipitation in the area a northern mediterranean source and a southern indian ocean source as a result two new local meteoric water lines were defined for the study area isotopic analyses of groundwater samples from over 200 springs and wells indicate that the main source of water to the batinah coastal alluvial aquifer is high altitude rainfall from the adjacent jabal akhdar mountains originating from a combination of northern and southern moisture sources the groundwater recharged at high altitude forms two plumes of water which is depleted in the heavy isotopes 18o and 2h and stretches from the mountains across the coastal plain to the sea thereby retaining a chemical homogeneity horizontally and vertically down to a depth exceeding 300 m in contrast in areas adjacent to these two plumes the alluvial aquifer is geochemically stratified near the coast saline intrusion results in abrupt changes in chloride concentrations and isotope values

seismic facies and sedimentary processes on the continental rise off wilkes land east antarctica evidence of bottom current activity abstract the slope and rise areas off wilkes land east antarctica encompass three large scale composite sediment ridges dissected by two broad deep sea valleys jussieu canyon and wega channel large scale depositional architecture revealed from multi channel seismic profiles acquired during the wilkes basin glacial history wega cruise indicates a wide temporal and spatial variability in the dominant depositional processes delivering or redistributing sediments on the slope and rise all three sediment ridges are built on a flat seafloor and resulted from the growth of a thick sediment section at least 2 km with a depositional relief in the order of hundreds of meters on the adjacent deep sea valleys the sediment ridges show their maximum internal complexity in areas shallower than 3000 m where they are also substantially thicker as much as 1 1 5 s in two way travel time high amplitude sediment waves typically 20 30 m and up to 50 70 m have wavelengths ranging from 1500 to 3500 m and occur in the deepest sectors of the continental rise where the sediment ridges toe out in the lower rise the sediment waves display a consistent decrease in wavelength with increasing water depth on seismic profiles the relief of the sediment waves decreases from older to younger sequences possibly indicating a decrease in bottom current intensity throughout their formation sediment waves occur also at the seafloor which is dominated elsewhere by irregular topography and widespread evidence of erosion however no conclusion can be drawn on the possible modern activity of these large scale bedforms in shallower upper rise areas where the sediment ridges are thicker sediment waves are evident in the upper stratigraphic units while the remaining section is characterized by the development of channel levee complexes seen as small scale erosional channels bordered by depositional reliefs consisting of variable amplitude reflector packages wedging out away from the channels channel levee complexes are locally associated with poorly developed sediment waves the origin of these features is likely related to transport by turbidity flows from the edge of the antarctic shelf and implies the presence of a more temperate glacial regime than the one dominating since the late miocene the formation of the sediment waves both in this more proximal area and on the deep rise is indicative of the impact of bottom hugging currents during intervals of the cenozoic history of the margin no constrains are available at present on the nature of these currents nor on the timing of their activity down slope turbidity currents downwelling dense waters or slope parallel contour currents are possible mechanisms despite this substantial uncertainty the observed progressive upward attenuation of the wave amplitudes indicates that substantial variations of sediment delivery and dispersal occurred through time we suggest that the interval of more complex depositional geometry in the proximal areas reflects higher bottom current velocity and or increased sediment input perhaps during conditions of temperate wet based ice sheet on the continent these conditions were conducive to high rates of melt water production formation of dense plumes and enhanced sediment input

paleomagnetic overprints in ocean sediment cores and their relationship to shear deformation caused by piston coring 1 we use paleomagnetic data from cores collected at ocean drilling program site 1062 on the bahama outer ridge as well as observations from prior cruises to quantify the nature and to assess the causes of drilling overprints the largest overprint arises from an isothermal remanent magnetization that is imparted to the core during coring or core retrieval a second type of overprint is apparent only in soft sediments collected with a piston corer and has coercivities and unblocking temperatures that completely overlap those of the primary remanent magnetization which means it cannot be removed by standard demagnetization methods this demagnetization resistant overprint can produce significant biases in paleomagnetic observations particularly those from split core sections we hypothesize that shearing which occurs as a result of friction on the inside wall of the piston corer as it rips through sediments and cuts a core deflects the ancient magnetization we develop and test a model that predicts how shear deformation can rotate remanence carrying grains and deflect the paleomagnetic remanence of a split core section using the shear model predictions and directions measured on split core sections and u channel samples from the undeformed core center we estimate the average deformation sustained and then correct the split core data for biases caused by shear deformation the reduction in the deviations between corrected split core data and u channel data is statistically significant indicating that the shear model is capable of accounting for a significant portion of the systematic biases observed in paleomagnetic observations obtained from piston cores

noble gas signatures of high recharge pulses and migrating jet stream in the late pleistocene over black mesa arizona united states many semiarid and arid regions of the world are almost entirely dependent on groundwater for water supply yet many of these aquifers were primarily recharged during the late pleistocene here we show that new noble gas data record the high pulses of recharge to the navajo sandstone aquifer at black mesa arizona between 14 and 17 ka which was associated with the passing of the southern branch of the jet stream higher excess neon coincided with high water levels independently deduced from numerical modeling of groundwater fl ow and 14 c data in previous studies this development allows the use of noble gases not only as a tool to reconstruct paleotemperatures but also as a new tool to reconstruct paleohydraulic conditions and to verify the conceptual and hydraulic assumptions of existing groundwater models

plio pleistocene magnetic polarity stratigraphies and diagenetic magnetite dissolution at odp leg 177 sites 1089 1091 1093 and 1094 abstract magnetic polarity stratigraphies from odp leg 177 high resolution sites indicate brunhes sedimentation rates in the 12 25 cm kyr range with a trend of decreasing sedimentation rates with increasing age magnetite is the principal remanence carrying mineral downcore alteration of magnetite and authigenic growth of iron sulfides introduces a high coercivity diagenetic remanence carrier pyrrhotite the change in pore water sulfate with depth in the sediment tends to be in step with the decrease in magnetization intensity indicating the link between sulfate reduction and magnetite dissolution shipboard pass through magnetometer data are generally very noisy due to a combination of weak magnetization intensities drilling related core deformation and the influence of authigenic iron sulfides post cruise progressive demagnetization of discrete samples aids the magnetostratigraphic interpretation as these measurements are less influenced by low magnetization intensities and drilling related deformation the magnetostratigraphic interpretations provide much needed calibration for biostratigraphic events in the high latitude southern oceans apart from the odp hole 745b kerguelen plateau published plio pleistocene magnetostratigraphies from odp sites in the southern ocean are poorly constrained for this reason we compare interpolated ages of 11 radiolarian events and one diatom event that occur at hole 745b and leg 177 sites