evidence for shock metamorphism in sandstones from the libyan desert glass strewn field microscopic analysis of sandstones from the southern libyan desert glass strewn field reveals a sequence of progressive deformation features which range from unaffected rock to extreme brecciation the quartz grains show a wide range of deformation features crushing and fracturing undulatory extinction mosaicism oriented cleavage partial isotropization and multiple sets of planar deformation features this preliminary report provides the first description of these shock indicators which are typical for hypervelocity impact in bedrock material that is assumed to be related to the libyan desert glass

potential consequences of a mid pleistocene impact event for the middle stone age occupants of dakhleh oasis western desert egypt abstract while it is expected that prehistoric populations experienced the effects of impacts by extraterrestrial objects there is little record of such events in occupied regions we discuss the ramifications of an impact between 100 and 200 ka into dakhleh oasis at that time experiencing humid phase conditions and inhabited by middle stone age people based on modeling of impact processes using estimated impact parameters the impact blast would likely have felled or dismembered most trees over 280 2400 km 2 of the oasis and inhabitants would have been injured over much of the region although severely only near the blast location the impact would not have vaporized much of the dakhleh paleolake s although some water was probably lost through boiling and through waves initiated by the impact blast water quality would have decreased as lake turbidity increased and soot from regional fires fell into the lake a relatively small event would not have immediately ignited much of the oasis vegetation but sedimentary evidence suggests that impact generated fires did spread to significantly affect the landscape the impact and resulting fires may have triggered mass wasting events as well as significant changes in erosion rates and have substantially affected human uses of the area

evidence for ancient lithospheric deformation in the east european craton based on mantle seismic anisotropy and crustal magnetics abstract we present new shear wave splitting measurements performed at 16 stations on the east european craton and discuss their implications in terms of upper mantle anisotropy for this geophysically poorly known region previous investigations of mantle anisotropy in central europe have shown fast directions aligning smoothly with the craton s margin and various suggestions have been proposed to explain their origin such as asthenospheric flow or lithospheric frozen in deformation here we aim at investigating the continuation of this shear wave splitting pattern further to the east into the east european craton for the craton the interpretation appears to be less ambiguous than for central europe since several arguments support lithospheric anisotropy in this region 1 the large scale coherence within either of the four constituting blocks and the significant variations between the blocks on a small scale 2 the weak correlation with absolute plate motion vectors and 3 the good correlation between anisotropy and crustal features for which we use magnetic field alignments as a proxy rather good correlation of these magnetic features with seismic fast orientations strongly supports the idea of vertically coherent deformation throughout upper mantle and crust the observed splitting orientations thus reflect the last tectonic events of each block frozen in into the lithosphere for hundreds of millions of years

late holocene glacial activity of bridge glacier british columbia coast mountains bridge glacier is a prominent eastward flowing valley glacier located on the east side of the pacific ranges within the southern british columbia coast mountains the terminus of bridge glacier has retreated at rates up to 125 m year over the last 50 years and currently calves into proglacial bridge lake field investigations of the recently deglaciated terrain and moraines led to the discovery of detrital boles and glacially sheared stumps dendroglaciological analyses of this subfossil wood produced five radiocarbon controlled floating tree ring chronologies the relative age and stratigraphic location of these samples revealed that bridge glacier experienced at least four periods of significant advance during the late holocene a tiedemann aged advance ca 3000 14c years bp an unattributed advance ca 1900 14c years bp a first millennium advance ca 1500 14c years bp and a little ice age advance beginning ca 700 14c years bp lichenometric investigations at eight terminal and lateral moraine comple

the sedimentary record and neoglacial history of tide lake northwestern british columbia tide lake was the largest glacier dammed lake in british columbia before its demise in the early twentieth century situated in the northern coast mountains the lake was impounded by frank mackie glacier and its neoglacial end moraine a study of tide lake has provided information on styles of glaciolacustrine sedimentation and the chronology of the neoglacial interval much of the sediment underlying the floor of tide lake was transported by subglacial and proglacial meltwater streams flowing from nearby glaciers during the last phase of the lake large subaqueous fans were built in front of berendon and frank mackie glaciers and deltas formed on the east side of the basin rhythmically bedded fine sediments which cover much of the lake floor but are almost completely lacking on the slopes above were deposited from underflows originating on deltas and subaqueous fans and by fallout from interflows and overflows three major and one minor lake phases are recognized from stratigraphic geomorphic radio

late holocene activity of sherman and sheridan glaciers prince william sound alaska abstract two adjacent glaciers in the chugach mountains of south central alaska have markedly different histories on decadal to perhaps centennial timescales sheridan glacier has advanced and retreated hundreds of metres during the latest holocene its recent fluctuations have markedly altered local base level of sherman river which drains sherman glacier and flows into sheridan lake sheridan glacier advanced to its greatest extent during the little ice age raising base level of sherman river and inducing aggradation there of up to 17 m of sediment retreat of sheridan glacier formed a series of lakes that have coalesced as lower lake outlets have become available base level of sherman river has dropped resulting in the evacuation of substantial volumes of sediment from sherman river valley in about 2000 the terminus of sheridan glacier began to disintegrate retreat accelerated dramatically in 2010 by 2016 the glacier had retreated an average of 600 m from its 2010 terminus although some areas retreated up to 1 9 km and others did not retreat at all meanwhile sherman glacier continued a slow advance initiated by a rock avalanche that blanketed much of its ablation area in the 1964 alaska earthquake

high frequency reflections in granite delineation of the weathering front in granodiorite at pinon flat california we analyze data from two orthogonal seismic lines 336 m in length collected at pinon flat california over weathered granodiorite bedrock each line was made up of 10 reversed segments 84 m in length we analyzed the first arrivals from these data and found dramatic variations in velocity along the profiles an upper layer approximately 2 m thick known from trenching to be composed of soil and sandy grus had measured velocities ranging from 400 to 700 m s velocities inferred from refraction analysis of first arrivals of the reversed lines revealed a heterogeneous lower layer below the soil with measured velocities of 1600 2700 m s by a depth of 15 m we interpret these data to be measuring velocities of a deeply weathered unit characterized by granodiorite corestones embedded in a matrix of saprolite the most remarkable feature of these data emerged from attempting to process the same data as reflection data simple bandpass filtering in the 250 400 hz band revealed a bright impulsive arrival with t

coherence of seismic body waves from local events as measured by a small aperture array eight local earthquakes were recorded during the operation of a small aperture seismic array at pinyon flat california the site was chosen for its homogeneous granitic geology and its planar topography amplitude spectral ratios for the same signal measured at different stations had average values of less than 2 and maximum values of 7 magnitude squared coherences were estimated for all station pairs these estimates were highest for the p wave arrivals on the vertical component and lowest for the p wave recorded on the transverse component at 500 m station separation the p and s waves were incoherent above 15 hz and 10 hz respectively coherence for both the p and s waves decrease as frequency increases and as distance increases the coherence of signals from borehole sensors located at 300 and 150 m depth displays higher average coherence than equally spaced sites located on the surface the results here suggest that even for sites that appear to be very similar that is those which are located on a planar surface within a few meters of granite bedrock the measured seismic wavefield can be distorted substantially over scale lengths of 500 m coherence properties were calculated from synthetic seismograms which were computed for velocity models with exponential and self similar distribution perturbations standard deviations of 10 are not sufficient for the random velocity distributions to approximate the results from the small aperture array

latest pleistocene and holocene behaviour of franklin glacier mt waddington area british columbia coast mountains canada franklin glacier is an 18 km long valley glacier that originates in a broad icefield below the west face of mt waddington in the central british columbia coast mountains canada radiocarbon dated

numerical modelling of impact melt production in porous rocks abstract melting of rocks by impact is a fundamental geologic process that results from shock wave compression and subsequent release from high pressure shock melted material is found in many terrestrial craters however most impact craters in sedimentary targets which are typically porous have been reported as containing significantly less melt than craters in nonporous crystalline targets to investigate the effect of porosity on shock melting we present a numerical modelling approach that combines a porosity compaction model with an equation of state for the solid component to demonstrate that our model accurately calculates shock pressures in porous materials we compare these results with hugoniot data for porous quartzite coconino sandstone and calcite our results show that the presence of porosity significantly reduces the critical pressure required for melting which enhances melt production we show that this effect is reduced but not totally diminished by faster shock wave decay in porous materials so that all other things being equal impact melt production is greater when target porosity is higher we conducted a series of simulations of impacts into targets of different material composition quartzite calcite dunite and porosity of up to 50 and varied the impact velocity between 6 and 50 km s we found a significant increase in the production of impact melt with increasing velocity in agreement with several previous studies and quantify the net increase in impact melt due to target porosity for the nonporous case our results agree well with estimated melt volumes at terrestrial impact craters over a range in size 7 90 km in diameter in porous targets our results contradict the widely cited observation of a melt deficiency in sedimentary target craters however our model results agree well with recently revised estimates of melt volumes at terrestrial craters formed in sedimentary or mixed sedimentary and crystalline targets this further strengthens the view that substantial volumes of impact melt should be produced during impacts into porous sedimentary targets and that the apparent paucity of impact melt in some sedimentary target craters may be due to difficulties in recognizing impact melts derived from sedimentary rocks

what spaceguard did a survey of large objects near earth has shown that there is little risk of a cataclysmic impact in the next century alan harris asks if such cataloguing efforts should continue a near mars object that got too near is a possible explanation for one of the most prominent features we see on mars the north south dichotomy of the planet s surface appearance the southern highlands on mars cover about 60 of the planet and are heavily cratered while the northern lowlands are lightly cratered are geologically younger and the underlying crust is significantly thinner than in the south the two favoured explanations for this hemispheric dichotomy are mantle convection and a giant impact but there is little available evidence to distinguish between the theories three letters in this issue provide support for the giant impact model marinova et al present the results of dynamical simulations of dichotomy forming impacts that demonstrate the feasibility of a giant impact origin a snapshot of a simulation with favoured impact conditions is shown on the cover the snapshot is about 30 min after impact and the colour codes for internal energy image s lombeyda caltech center for advanced computing research m marinova and o aharonson california institute of technology andrews hanna et al use the gravity and topography of mars to map the dichotomy boundary beneath the large tharsis volcanic province and find the boundary to be elliptical consistent with an oblique giant impact origin this borealis basin would be the largest impact scar in the solar system nimmo et al use numerical modelling to simulate the effects of vertical impacts they find that the impact model as well as excavating a crustal cavity of the correct size can explain the observed crustal disruption and the formation of the northern lowlands crust by impact generated melt in an accompanying news views walter kiefer sums up the evidence for the impact model elsewhere in this issue the results of a smaller but still enormous impact event are remembered the tunguska event laid waste to a large swath of forest to the north of lake baikal in central siberia on the morning of 30 june 1908 in a news feature duncan steel goes back to basics to sift through the contemporary evidence collected in the days after the blast that combined with modern studies of the area and theoretical work points to a fragment of comet encke as the likely impactor a small group of astronomers began to look for near earth objects neos capable of causing tunguska like events in the 1960s and 1970s and with the realization that an asteroid impact can cause events as drastic as mass extinctions the spaceguard project was begun in the 1998 to search more methodically for neos as alan harris explains in a commentary the results of spaceguard are encouraging it looks like we are safe for the foreseeable future but neo watchers say that we need to keep up our guard eric hand reports on the giant lunar crater that holds the key to a catastrophic bombardment and a gallery feature celebrates the beauty of impact craters from across the solar system

broadband bearing time records of three component seismic array data and their application to the study of local earthquake coda high frequency three component array data are used to study the p and s coda produced by local earthquakes the data are displayed as broadband bearing time records which allow us to examine a complete time history of the propagation directions and arrival times of direct and scattered phases crossing the array this visualization technique is used to examine the wavefield on two scale lengths using two sub arrays of sensors results suggest that p coda is dominated by p energy propagating sub parallel to the diect p arrival thes coda propagates in all directions and appears to be composed predominantly of s and or surface wave energy significantly more s coda appears on the smaller scale length sub array relative to the larger scale array suggesting that much of the s coda remains coherent for only very short distances

the flux of small near earth objects colliding with the earth asteroids with diameters smaller than approximately 50 100 m that collide with the earth usually do not hit the ground as a single body rather they detonate in the atmosphere these small objects can still cause considerable damage such as occurred near tunguska siberia in 1908 the flux of small bodies is poorly constrained however in part because ground based observational searches pursue strategies that lead them preferentially to find larger objects a tunguska class event the energy of which we take to be equivalent to 10 megatons of tnt was previously estimated to occur every 200 300 years with the largest annual airburst calculated to be approximately 20 kilotons kton tnt equivalent ref 4 here we report satellite records of bolide detonations in the atmosphere over the past 8 5 years we find that the flux of objects in the 1 10 m size range has the same power law distribution as bodies with diameters 50 m from this we estimate that the earth is hit on average annually by an object with approximately 5 kton equivalent energy and that tunguska like events occur about once every 1 000 years

near surface scattering effects observed with a high frequency phased array at pinyon flats california analysis of data collected by a high frequency array experiment con ducted at pinyon flat in southern california provides strong evidence that the high frequency wave field from local earthquakes at this hard rock site are strongly dis totted by near surface scattering the seismic array we deployed consisted of 60 2 hz natural frequency three component sensors deployed in a three dimensional array two of the sensors were located in boreholes at 150 and 275 m depth the other 58 sensors were deployed in an areal array above these boreholes thirty six of these were deployed in a 6 by 6 element grid array with a nominal spacing of 7 m centered over the borehole sensors the remaining 22 seismometers were laid out in two 11 element linear arrays radiating outward from the grid coherence calculations reveal a rapid loss of coherence at frequencies over 15 hz at all but the shortest length scales of this array three dimensional visualization techniques were used to closely examine the spatial stability of particle motions of p and s waves this reveals systematic variations of particle motion across the array in which the particle motion tracks tilt drastically away from the backazimuth expected for an isotropic medium these variations however are frequency dependent below around 8 hz the particle motions become virtually identical for all stations at progressively higher frequen cies the wave field particle motion becomes increasingly chaotic frequency wave number analysis of these data provide quantitative measures of the same phenomena we find that direct wave f k spectra are bathed in a background of signal generated noise that varies from 10 to 30 db down from the direct arrival signal this signal generated noise appears to be nearly white in wavenumber indicating the wavelength of this noise on the scale of tens of meters and less refraction measurements we made on two lines crisscrossing the array reveal that the weathered layer velocities are highly variable and define a very strong wave guide measured surface p wave velocities varied from 400 to 1300 rn sec and velocities at depth of approximately 15 m varied from 1600 to 2700 m sec previous measurements in the boreholes showed that the intact granite below about 65 m depth has a velocity of approximately 5400 m sec these results demonstrate the extreme velocity contrast and degree of velocity heterogeneity of the near surface at this site we conclude that all the ob servations we made can be explained by strong scattering of incident body wave signals into a complex mishmash of body wave and surface wave modes in this heterogeneous near surface wave guide

multi wavelet analysis of three component seismic arrays application to measure effective anisotropy at pinon flats california abstract we develop and apply a new technique to determine array averaged particle motions from three component seismic array data the method is based on multi wavelets which are an extension of multi taper spectral methods and is a hybrid of fourier and time domain methods of array processing particle motions are determined by a time domain principal component method a complex singular value decomposition is used on wavelet transformed signals assembled into multiple matrices one for each wavelet the eigenvector of the largest singular value of each matrix is used to estimate the phase between individual signals we determine the relative phase between components to estimate an average particle motion ellipse for the array the estimation procedure is made more stable by the redundancy inherent in the multi wavelets and by m estimators applied to individual phase factors in the complex plane the method is applied to data from three component array experiments conducted at pinon flats california in 1990 and 1991 we find remarkable departures of p wave particle motions from the pure longitudinal motion expected for an isotropic media anomalies as large as 40 are measured from some azimuths the azimuthally varying particle motion anomalies are frequency dependent generally increasing in magnitude as frequency increases borehole measurements from sensors at 153 and 274 m depth below the array show a pattern indistinguishable from the surface sensors the data are fit with a dipping transversely isotropic medium with a symmetry plane having a strike of 70 and a dip of 30 to the northwest we attribute our results to three superimposed effects 1 an anisotropy of the near surface induced by preferential weathering of the grandiorite bedrock along joints 2 a larger scale anisotropy induced by structural and intrinsic anisotropy related to the santa rosa mylonite and 3 near surface scattering

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

direct p wave anisotropy measurements at homestake mine implications for wave propagation in continental crust we measured anisotropic seismic properties of schists of the homestake formation located at a depth of 1478 m in the sanford underground research facility surf in the black hills of south dakota usa we deployed a 24 element linear array of three component geophones in an area in the homestake mine called 19 ledge an airless jackhammer source was used to shoot two profiles 1 a walkaway survey to appraise any distance dependence and 2 a fan shot profile to measure variations with azimuth slowness estimates from the fan shot profile show a statistically significant deviation with azimuth with the expected 180 variation with azimuth we measured p wave particle motion deviations from data rotated to ray coordinates using three methods 1 a conventional principal component method 2 a novel grid search method that maximized longitudinal motion over a range of search angles and 3 the multiwavelet method the multiwavelet results were computed in two frequency bands of 200 600 and 100 300 hz results were binned by azimuth and averaged with a robust estimation method with error bars estimated by a bootstrap method the particle motion results show large statistically significant variations with azimuth with a 180 cyclicity we modelled the azimuthal variations in compressional wave speed and angular deviation from purely longitudinal particle motion of p waves using an elastic tensor method to appraise the relative importance of crystalline fabric relative to fracturing parallel to foliation the model used bulk averages of crystal fabric measured for an analogous schist sample from southeast vermont rotated to the homestake formation foliation directions supplied by surf from old mine records we found with average crustal crack densities crack induced anisotropy had only a small effect on the observables we found strong agreement in the traveltime data the observed amplitudes of deviations of p particle motion showed significantly larger variation than the model predictions and a 20 phase shift in azimuth we attribute the inadequacies of the model fit to the particle motion data to inadequacies in the analogue rock and or near receiver distortions from smaller scale heterogeneity we discuss the surprising variability of signals recorded in this experimental data we show clear examples of unexplained resonances and unexpected variations on a scale much smaller than a wavelength that has broad implications for wave propagation in real rocks

little ice age glacial activity in the mt waddington area british columbia coast mountains canada the establishment of fourteen little ice age lia glacier chronologies in the mt waddington area led to the development of an extended history of glacial activity in this portion of the southern british columbia coast mountains canada the glaciers were located within four different mountain ranges and were of varying size and aspect dendrochronological and lichenometric techniques were used to provide relative age estimates of moraines formed as glacier termini retreated from advanced positions evidence for pre lia glacial events is best preserved at tiedemann glacier where the oldest glacial advances date to a d 620 and 925 933 soil covered and well vegetated moraines built at cathedral pagoda and siva glaciers date to between a d 1203 and 1226 following this event moraines constructed at ragnarok siva and cathedral glaciers in the mid 14th century suggest glaciers in the region underwent a period of downwasting and retreat before readvancing the majority of moraines recorded in the mt waddington area describe late lia glacial events shown to have constructed moraines that date to a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 and 1942 1946 over the last 500 years these moraine building episodes were shown to occur on average every 65 years and suggest there has been prolonged synchronicity in the glaciological response to persistent climate forcing mechanisms nevertheless our analysis suggests that local factors such as aspect and size play an important role in individual glacial response notably ice termini of medium size glaciers facing eastwards showed a quicker response to climatically induced mass balance changes resume l historique de quatorze glaciers de vallee de la region du mont waddington sud de la chaine cotiere de colombie britannique canada durant le petit ge glaciaire pag fut evalue par l utilisation de techniques dendrochronologiques et lichenometriques procurant un ge minimum pour la formation des moraines laterales et frontales multiples les glaciers a l etude d aspect et de taille differents furent selectionnes a partir de quatre chaines de montagnes les evenements qui predatent le pag sont le mieux preserves sur le site du glacier tiedemann ou les plus vieilles avancees glaciaires date de a d 620 et 925 933 des moraines presentant une pedogenese avancee et recouvertes d une dense couverture vegetale furent datees entre a d 1203 et 1226 des moraines construites dans le milieu du 14 e siecle par les glaciers ragnarok siva et cathedral suggerent que les glaciers de la region se sont retires pour par la suite reavancer la majorite des moraines datees le furent vers la fin du pag soit en a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 et 1942 1946 au cours des 500 dernieres annees en moyenne 65 annees separent les differents episodes glaciaires ce qui suggerent un synchronisme des reponses glaciaires aux mecanismes climatiques des donnees preliminaires suggerent que l orientation et la taille des glaciers jouent un role important dans la reponse individualiste des glaciers en fait les terminus glaciaires des moyens glaciers d orientation est semblent repondre plus rapidement a un ajustement de volume interne glaciaire

late holocene glacial activity at bromley glacier cambria icefield northern british columbia coast mountains canada retreating and downwasting glaciers in the british columbia coast mountains are exposing the remains of forests buried during holocene age glacial advances despite recent progress in discerning th

recent volume loss of british columbian glaciers canada 1 we use the shuttle radar topography mission srtm data and digital terrain models from aerial photography to quantify the change of glacier volume in british columbia bc canada for the period 1985 1999 we note substantial elevation bias in the srtm elevations typically on the order of 12 m km 1 the bias corrected thinning rate is 0 78 0 19 m a 1 which yields an annual volume loss of 22 48 5 53 km 3a 1 this rate of glacier volume loss is 65 of the estimate uncorrected for elevation bias 34 7 km 3a 1 and cautions against the use of uncorrected srtm data for glacier change studies glacier recession in bc could account for ca 0 67 0 12 mm of sea level rise over the period 1985 1999 0 05 0 009 mm yr 1 or about 8 3 of the contribution from mountain glaciers and ice caps the recent rate of glacier loss in the coast mountains 17 0 km 3a 1 is approximately double that observed for the previous two decades

mid holocene glacier expansion between 7500 and 4000 cal yr bp in the british columbia coast mountains canada the mid holocene behaviour of five glaciers in the british columbia coast mountains was reconstructed from radiocarbon ages and stratigraphic analysis subfossil wood evidence at canoe fyles jaco

geomorphology and quaternary geology of the dakhla oasis region egypt abstract dakhla oasis 25 5 n 29 e occupies a structurally localized depression at 90 140 m above sea level 1200 km 2 in area below a 300 m escarpment bordering the libyan plateau western desert of egypt semi arid intervals of the quaternary period generated eight sedimentary formations separated by erosion during hyper arid intervals sediments comprise three generations of colluvial fluvial fanglomerates two generations of tabular spring laid clastic and chemical sediments two generations of mound springs and basinal sediments of fluvio lacustrine evaporitic pluvio aeolian and aeolian origins discussion of these sediments is organized according to geomorphic region from north to south plateau scarp and piedmont lowland and cuesta plain chronological evidence is restricted to many radiocarbon dates of holocene cultural material associated with playa sediments 9 4 5 ka a th u isochron age of 62 0 7 6 ka for basinal evaporites and two th u ages of 176 and 170 ka for a boulder of derived travertine the regional quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces it is broadly similar to sequences earlier reconstructed in the topographically similar kharga oasis region 150 km to the east and kurkur oasis 400 km to the south southeast speculations on chronology and driving mechanism are offered in conclusion

faunal remains from a middle pleistocene lacustrine marl in dakhleh oasis egypt palaeoenvironmental reconstructions abstract vertebrates and invertebrates associated with lithic artifacts are reported from a later middle pleistocene horizon in dakhleh oasis probably dating to isotope stage 7 this represents the first middle pleistocene fauna of this stage from a site in the egyptian western desert and demonstrates the presence of extensive permanent lakes along the margin of the libyan escarpment the fauna includes two freshwater snails limnaea stagnalis planorbis planorbis a catfish clarias sp two reptiles varanus cf griseus trionyx sp four water birds grus grus anas platyrhynchos anas sp small arenaria interpres and one land bird struthio camelus and probably eleven mammals phacochoerus aethiopicus hippopotamus amphibius camelus thomasi pelorovis antiquus damaliscus large antelope gazella sp large gazella cf dorcas small antelope equus capensis and possibly hyaena hyaena most of the fossils derive from a near shore marl deposit in a freshwater lake that occupied a depression whose northern boundary coincides with the present southern margin of the oasis in its eastern end casts of the stems of reeds are also present the animals represent a proximal freshwater tied fauna of obligatory aquatics and those who require freshwater during much of their activity a distal savanna fauna of grazers browsers or rooters who migrate to water on a diurnal cycle and probable transitory avian migrants attracted to the palaeolake in passage human presence is attested by flakes and bifaces found in situ

evidence for a 200 100 ka meteorite impact in the western desert of egypt abstract in this study we present evidence in the form of unusual silicate glasses for a meteorite impact event 200 100 ka in the dakhleh oasis western desert egypt these glasses known locally as dakhleh glass were derived from the shock melting of a series of unconsolidated sediments underlain by interbedded carbonates sandstones and phosphate rich lithologies hypervelocity impact in to a volatile rich target resulted in the production of impact glasses with cao and al 2 o 3 contents of up to 25 and 18 wt respectively other notable properties include the presence of globules of immiscible calcite and pyrrhotite melt phases shattered quartz grains and fragments of silicified plant matter dating of geoarchaeological artefacts associated with the dakhleh glass support preliminary 40 ar 39 ar data indicating a 200 100 ka age for the impact event geoarchaeological evidence indicates that archaic homo sapiens and early modern humans continually inhabited this region of the western desert during this period while it is unclear at present whether the dakhleh glass was formed during a cratering event or a large aerial burst the effect on the environment and inhabitants of dakhleh would have been catastrophic

age of the dakhleh impact event and implications for middle stone age archeology in the western desert of egypt abstract dakhleh glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occur over an area of ca 400 km2 in and around the dakhleh oasis in central western egypt previous studies establish a meteorite impact origin for the dakhleh glass no impact crater has yet been found suggesting an airburst origin the dakhleh glass forming impact event occurred during the middle stone age time of occupation but the timing of this event has not been well established 40ar 39ar incremental heating of three aliquots from a sample of dakhleh glass yield data that can be ascribed to quenched glass which efficiently purged radiogenic 40ar inherited from the target rocks one of the aliquots yielded data suggestive of an undegassed clast of target material but these are easily resolved the age of the impact event is determined from a compositionally filtered subset of the data that yield an isochron age of 145 19 ka

assessing long term habitability at an eastern sahara oasis esr dating of molluscs and herbivore teeth at dakhleh oasis egypt abstract in the northeastern sahara electron spin resonance esr dating of when animals lived documents their habitability in dakhleh oasis egypt a middle pleistocene paleolake s covered 1700 km 2 at eastern locality dak348 10 m thick remnant lacustrine marls yielded pleistocene fauna rare artefacts and plant casts no obvious unconformity exists within these deposits from upper horizons a hartebeest tooth esr dated at 195 11 ka correlates with marine isotope stage mis 7 while molluscs from a stratigraphically higher horizon averaged 89 10 ka correlating with mis 5a b at western locality dak006 upslope deflation has left a temporally mixed surficial lag numerous lagged tooth fragments independently dated by esr correlate with mis 5 through 17 fragments from a slope sand unit correlate with mis stages 3 through 6 one bovid tooth associated with younger middle stone age artefacts in the base of the sand dated at 84 7 ka mis 5a b molluscs from romano byzantine backdirt at a breached artesian vent dated to 8 15 1 ka suggesting that ponds formed during mis 1 and 2 even without well defined sedimentary contexts esr frequency data indicate that the oasis was habitable for herbivores during at least twelve stages in the mid late quaternary and therefore likely also for humans

p wave array polarization analysis and effective anisotropy of the brittle crust summary p wave polarization constrains local anisotropy in the vicinity of the receivers using three component and array data from the regional geress array in south eastern germany we measure polarization a and propagation vectors s for p phases of 120 events angular deviations a s between these normalized vectors often approach 10 rendering them easily measurable the effect of anisotropy can be distinguished from remote effects since all remote effects such as source mislocation distant lateral heterogeneity or distant anisotropy affect polarization and propagation vectors simultaneously averaging removes sensitivity to near receiver heterogeneity and local anisotropy is left as the sole cause of the effects in a s this method hence gives local effective anisotropy in the near receiver crust averaging over a depth interval of a wavelength 6 km we resolve strike and dip of the symmetry plane and also two dimensionless numbers and which give constraints on four of the elastic parameters the optimum model variance reduction 44 per cent has symmetry plane orientation of strike 113 and dip 49 to the north which corresponds closely to the consistently observed gneiss foliation direction in the area 120 50 60 comparing and with predictions from different physical models we find that the data are fit by a gneiss model assuming that the anisotropy is dominated by the mica if 3 8 per cent of the mica are well aligned this suggests that anisotropy in the region studied is dominated by the effect of local foliation rather than the regional stress field

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

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

late holocene fluctuations of the bear river glacier northern coast ranges of british columbia canada during holocene advances of the bear river glacier in northwestern british columbia ice pushed against a bedrock slope on the north side of bear river pass as it was being diverted eastward and westward along the pass the result is a series of till sheets plastered against the rock slope and separated by wood mats this sequence of tills provides an unusually detailed record of early neoglacial history and shows that neoglacial expansion in the northern coast mountains began earlier than previously known moraines show the extent of little ice age expansion and documents related to the long mining history of the area provide records of post lia recession the oldest deposits in the area are a small lateral moraine outside of a prominent lia moraine and a till in the pass older than c 3500 14c yr bp the small moraine is undated it may be equivalent to the latest pleistocene crowfoot advance which produced similar moraines in the southern coast mountains and eastern cordillera wood mats in the pa

calendar dated glacier variations in the western european alps during the neoglacial the mer de glace record mont blanc massif holocene glacier records from the western european alps are still sparse although a number of sites are well suited to constraining pre and early little ice age lia glacier advances the present study provides the first dendrochronologically based and calendar dated neoglacial glacier chronology for the mont blanc massif french alps it is based on the analysis of over 240 glacially buried pinus cembra subfossil logs and wood remains found either embedded in till or as detrital material in the mer de glace right lateral moraine only a few of the samples were found to be formally in situ but we show that some logs were virtually in situ not rooted but showing little or no evidence of reworking and could be used to accurately reconstruct past glacier margin behavior in space and time uncertainties regarding the other samples may relate to original growth location and or to outer wood decay the resulting dates followed by a were therefore considered maximum limiting ages for glacier advances the main burial events interpreted as glacier advances occurred between ca 1655 and 1544 bc between ca 1230 and 1105 bc between ca 1013 and 962 937 bc at ca 802 777 bc after 608 bc between 312 and 337 ad between ca 485 ad and 606 ad between 1120 and 1178 ad between ca 1248 and 1278 1296 ad and after 1352 ad these advances predate the late lia maxima known from historical sources the magnitude of the advances gradually increased to culminate in three near neoglacial maxima during the 7th 12th and 13th centuries ad followed by a first lia neoglacial maximum in the second half of the 14th century ad the pattern of neoglacial events described here is coherent with central and eastern alpine glacier chronologies this indicates marked synchronicity of late holocene glacier variability and forcing at a regional scale although occasional differences could be detected between western and eastern records the mer de glace record also confirms the link between the timing of sediment erosion in a high elevation glaciated alpine catchment and subsequent deposition in the sub alpine lake bourget

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

dendroglaciological evidence for holocene glacial advances in the todd icefield area northern british columbia coast mountains accelerated glacial recession and downwasting in pacific north america is exposing land surfaces and fea tures buried by glacial advances that in many locations predate the recent little ice age lia dendrochronologic analyses of increment core samples from living trees abies lasiocarpa tsuga mertensiana and samples of subfossil wood collected in the todd icefield area boundary ranges british columbia coast mountains provide the basis for a dendroglaciological and radiocarbon based reconstruction of late holocene glacier activity five intervals of glacier ex pansion were recorded by trees killed or buried by advancing glaciers 1 an advance prior to 3000 14 c years bp 2 an advance at 3000 14 c years bp that coincides with the regional tiedemann advance 3 an unattributed advance at 2300 14 c years bp 4 a two phase advance at 1700 and 1450 14 c years bp that corresponds with the regional first millennium advance 5 an advance with three phases of expansion that began prior to 750 14 c bp and is con sistent with the regional early lia interval and a two phase interval of late lia expansion culminating after 240 and 100 years bp this chronology of late holocene glaciation matches that emerging from similar investigations in the coastal cordillera of pacific north america and provides additional support for the regional significance of both the tiedemann and the first millennium advances resume une recession et une fonte glaciaire accelerees dans l ocean pacifique en amerique du nord exposent des sur faces de terrain et des traits caracteristiques enfouis sous des avancees glaciaires lesquelles dans bien des cas datent d avant le recent petit ge glaciaire des analyses dendrochronologiques d echantillons proportionnels de carottes pris

dendroglaciological investigations of mid to late holocene glacial activity in the mt waddington area british columbia coast mountains canada dendroglaciological investigations near mt waddington in the central british columbia coast mountains provide an enhanced perspective of holocene glacial activity field investigations at confederation franklin and jambeau glaciers led to the discovery of subfossil wood mats encased in glacial deposits and glacially sheared stumps buried beneath till radiocarbon dated wood collected from valley bottom and lateral moraine sites at confederation glacier suggest that an early holocene advance occurred at c 5665 cal yr bp followed by succeeding intervals of glacier expansion at c 3700 and 3500 cal yr bp at jambeau glacier detrital wood mats buried close to the contemporary lateral moraine crests document glacier expansion at c 3000 cal yr bp detrital subfossil wood buried in lateral moraines at the confluence of confederation and franklin glaciers records distinct episodes of little ice age glacier expansion as early as c 1212 cal yr ad and suggests the glacier surface continued to thicken u

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

neoglacial history of the stikine iskut area northern coast mountains british columbia information about neoglacial features was obtained from aerial photograph interpretation observations during low level flights ground checking and historical records terminal moraines at great flood and mud glaciers date from the late seventeenth to early eighteenth centuries and recessional moraines at these glaciers and terminal moraines at glaciers farther east date from the late nineteenth to early twentieth centuries these late neoglacial terminal moraines appear in general to mark the greatest post pleistocene extent of the glaciers radiocarbon dates from overridden trees and soil indicate that 500 600 14c years bp glaciers were considerably more extensive than they are at present and were advancing preservation of a 3800 14c year old caribou antler in a snowbank that is now rapidly shrinking suggests that climate has been relatively cool and moist for the past four millennia

azimuth and slowness deviations from the geress regional array abstract for high signal to noise ratio events body wave travel times at geress stations are well fit by a plane wave model corresponding to travel time uncertainties of about 1 100 sec slownesses obtained in this study are accurate to about 0 5 sec deg while azimuth uncertainties are about 2 for regional events and about 5 for teleseismic nuclear events for illustration we demonstrate performance for nevada and tuamotu nuclear tests and for regional events from poland unbiased measurement requires array topography about 200 m for geress to be taken into account if ignored these elevation variations give rise to a systematic shift of about 0 6 sec deg to eastern directions which is almost independent of source location in principle arrays extending in vertical direction 3d array can measure the vertical slowness and hence local material velocity c for geress we find c 5 2 km sec compared with given accuracies the regional geress array finds statistically significant deviations of slownesses and azimuths these may be used to investigate lateral heterogeneity at regional scale

landsat based inventory of glaciers in western canada 1985 2005 abstract we report on a glacier inventory for the canadian cordillera south of 60 n across the two western provinces of british columbia and alberta containing 30 000 km2 of glacierized terrain our semi automated method extracted glacier extents from landsat thematic mapper tm scenes for 2005 and 2000 using a band ratio tm3 tm5 we compared these extents with glacier cover for the mid 1980s from high altitude aerial photography for british columbia and from landsat tm imagery for alberta a 25 m digital elevation model dem helped to identify debris covered ice and to split the glaciers into their respective drainage basins the estimated mapping errors are 3 4 and arise primarily from seasonal snow cover glaciers in british columbia and alberta respectively lost 10 8 3 8 and 25 4 4 1 of their area over the period 1985 2005 the region wide annual shrinkage rate of 0 55 a 1 is comparable to rates reported for other mountain ranges in the late twentieth century least glacierized mountain ranges with smaller glaciers lost the largest fraction of ice cover the highest relative ice loss in british columbia 24 0 4 6 occurred in the northern interior ranges while glaciers in the northern coast mountains declined least 7 7 3 4

impact metamorphism of caco3 bearing sandstones at the haughton structure canada impact metamorphosed caco3 bearing sandstones at the haughton structure have been divided into 6 classes based to a large extent on a previous classification developed for sandstones at meteor crater class 1a sandstones 10 30 gpa consist almost entirely of lechatelierite a new class of shocked sandstones class 6 consists of sio2 rich melt that recrystallized to microcrystalline quartz calcite within class 4 to 6 sandstones also underwent melting and is preserved as globules and euhedral crystals within sio2 phases demonstrating the importance of impact melting and not decomposition in these caco3 bearing sandstones

dendroglaciological reconstruction of late holocene glacier activity at white and south flat glaciers boundary range northern british columbia coast mountains canada holocene glacier activity in the northern british columbia coast mountains canada is described following investigations in the recently deglaciated forefields of white and south flat glaciers spilling from the cambria icefield glacially overridden stumps and detrital wood was radiocarbon and dendrochronologically dated to describe an advance between ad 250 and 650 expansion and thickening of white glacier by ad 765 resulted in creation of an ice dammed lake in south flat valley that persisted until ad 1080 following this the lake drained before refilling in the early little ice age prior to ad 1300 shortly thereafter white and south flat glaciers became confluent and flowed over the valley side toward white lake the characteristics of the site and the preservation of 1500 yr old deposits indicate that the two glaciers remained confluent throughout the remainder of the little ice age only separating following terminal retreat early in the 20th century the late holocene glacial history of whit

the dakhleh glass product of an impact airburst or cratering event in the western desert of egypt impact cratering is a ubiquitous geological process on the terrestrial planets meteorite impact craters are the most visible product of impact events but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time in this contribution we report on an unusual impact glass the dakhleh glass dg which is distributed over an area of 400 km 2 of the dakhleh oasis egypt this region preserves a rich history of habitation stretching back to over 400 000 years before the emergence of homo sapiens we report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the dg formed during an impact event the wide distribution and large size of dg specimens up to 50 cm across the chemistry e g cao and al2o3 contents up to 25 and 18 wt respectively the presence of lechatelierite and burnt sediments and the inclusion of clasts and spherules in the dg is inconsistent with known terrestrial processes of glass formation the age and other textural characteristics rule out a human origin instead we draw upon recent numerical modeling of airbursts to suggest that the properties of dg coupled with the absence of a confirmed crater can best be explained by melting of surficial sediments as a result of a large airburst event we suggest that glass produced by such events should therefore be more common in the rock record than impact craters assuming that the glass formed in a suitable preserving environment

regional wave propagation in southern california and nevada observations from a three component seismic array we present results from a study conducted to characterize regional wave propagation in southern california and nevada the data are from events whose paths sample the southern coast ranges the southern sierra nevada mountains and the southern basin and range these regional earthquake data were recorded by a small aperture three component seismic array located at the pinon flat observatory southern california the data are analyzed using a statistical array processing algorithm that provides estimates of the propagation direction frequency wavenumber and particle motion polarization characteristics of the coherent arrivals observed at the array perhaps the most striking feature shared by these data is the extent to which the p s and lg wave trains are composed of coherent forward scattered multipathed energy the nature of the p s and lg wave trains suggests that spatially anisotropic scattering plays an important role in regional wave propagation in southern california and nevada and that scattering sources are located not on elliptical shells whose foci are the source and the receiver but instead in a limited volume subparallel to the path of the direct arrivals the high amplitude coherent nature of numerous of the pg and lg coda waves suggests that strong scattering in the source zone plays an important role in shaping the pg and lg wave trains while the p s and lg wave trains for these regional events share some general characteristics they also exhibit fairly significant differences these differences illustrate the important role regional and source zone structure play in shaping the wave field and the need to account for both complex scattering and three dimensional propagation effects in regional waveform modeling the coda for these regional data do not begin to exhibit a character consistent with the random scattering model for coda generation until the arrival of the surface waves the fact that much of the surface wave coda cannot be effectively modeled as plane waves suggests that it is not the product of scattering from distant heterogeneities

fabric related velocity anisotropy and shear wave splitting in rocks from the santa rosa mylonite zone california the directional dependence of p and s wave velocities have been measured at pressures up to 600 mpa and temperatures up to 700 c in rocks from the santa rosa mylonite zone southern california during tectonism these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite the mineralogical and chemical composition of protolith and mylonite is nearly identical thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy velocity anisotropy increases significantly with the degree of deformation whereas average velocities and densities do not change at low pressure 50 mpa the velocity anisotropy ranges from 1 7 in granodiorite up to 19 in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation at high pressure 600 mpa the residual anisotropy up to 12 is mainly due to preferred mineral orientation in particular of biotite significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture these observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks

esr in the 21st century from buried valleys and deserts to the deep ocean and tectonic uplift abstract electron spin resonance esr dating can date many materials including hydroxyapatite in enamel and some fish scales aragonite and calcite in corals molluscs some travertine and calcrete and quartz from ash fluvial deposits and some flint dating studies using these materials have numerous potential applications in many varied quaternary settings esr dating uses signals resulting from trapped charges created by radiation in crystalline solids ages are calculated by comparing the accumulated radiation dose in the dating sample with the internal and external radiation dose rates produced by natural radiation in and around the sample and produced by cosmic radiation when compared to other dating techniques age agreement has been excellent for teeth corals molluscs and quartz recent improvements have included using a more complex modelling technique to calculate the cosmic dose rates and more detailed modelling techniques for dealing with variable external dose rates methods in development include using quartz from buried fluvial valleys to date geomorphic surfaces and using the signals in barnacles and benthic foraminifera for dating fossils or their associated sediment new chronometer applications recently developed include using coral and mollusc dates to build sealevel curves and to monitor volcanic activity and tectonic uplift using tooth and mollusc dates to assess water availability in deserts and using isochron data to assess u uptake processes into teeth when coupled with other geochemical and geomorphological techniques esr can provide the chronometric control to build paleoclimatic and other paleoenvironmental records many other applications are possible from heating studies for artefacts to dating sulphates and other minerals on distant planets

shear wave splitting in the anza seismic gap southern california temporal variations as possible precursors shear wave splitting above small earthquakes in the anza seismic gap on the san jacinto fault southern california displays the effective anisotropy of vertical fluid filled microcracks the delays between the split shear waves increase significantly over the 3 years of available records at the only station with arrivals from a wide range of azimuths and angles of incidence these changes can be modeled by increasing the aspect ratio bowing of stressoriented microcracks which is one of the expected elastic effects of an increase of stress on a rock mass containing a distribution of fluid filled microcracks this is the first time that temporal variations of shear wave splitting have been observed and suggests that shear wave splitting can be used to monitor the detailed changes in the buildup of stress before an earthquake

lithospheric imaging via teleseismic scattering tomography summary the coda of the teleseismic p phase consists largely of energy scattered by small inhomogeneities in the receiver side lithosphere given large collections of teleseismic data from dense permanent networks previous workers have successfully back propagated coda energy back to scattering source points using various kinematic migration schemes as well as by inverting using an inverse scattering radon transform approach under the born approximation seismic scattering is a linear process therefore it is possible to approach coda scattering as a linear waveform inversion problem mathematically similar to transmission based tomography assuming ray theoretical propagation and rayleigh scattering we pose the inverse scattering problem in tomographic form and recover perturbations in density and p and s velocities from pp and ps scattered data the method is applied to data from the southern california seismic network scsn covering the san jacinto anza region the results show a considerable correlation between seismicity and velocity perturbation structure particularly in the region between the mission creek and banning fault branches features connecting the coyote creek and elsinore faults at right angles are correlated with seismicity lineations and may represent conjugate faulting with no surface expression

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

three dimensional groundwater flow modeling approach for the groundwater management options for the dakhla oasis western desert egypt in dakhla oasis western desert of egypt groundwater is the only resource for all anthropogenic activities during the last 50 years the nubian sandstone aquifer system nsas has been undergoing serious stress through withdrawing its storage plans for expanding the agricultural areas in dakhla oasis were given by the government this article is an attempt to investigate the best management option that meets development ambitions and groundwater availability based on a calibrated regional three dimensional groundwater flow model for the nsas using feflow a refined high resolution local scale model was developed to simulate and predict the impact of applying the actual and planned extractions rates on dakhla oasis five management scenarios were suggested the application of the actual extraction rate of 1 2 106 m3 day for the oasis for the next 90 years resulted in a drawdown of 75 m and a depth to groundwater up to 75 m with an annual change in hydraulic head of 0 57 m at the end of this simulation only a few wells at the west of the oasis will still be free flowing the application of the planned extraction rate 1 7 106 m3 day resulted in great depths to groundwater 100 m and formed huge cones of depressions that connected together to cover the whole oasis and extend further beyond its borders it was found that the best option for groundwater management in the oasis is the implementation of an extraction rate of 1 46 106 m3 day as the depths to groundwater will never exceed the 100 m limit

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

multiwavelet seismic wave gradiometry abstract a new technique to determine uncertainty estimates for wave parameters obtained by seismic wave gradiometry is established using the multiwavelet transform wave gradiometry uses spatial gradients as measured by a small scale seismic array to estimate the wave parameters of propagation azimuth slowness geometrical spreading and radiation pattern the advantage of wave gradiometry is that the wave parameters are estimated on a point by point basis for the entire seismogram previous work on wave gradiometery employed the continuous wavelet transform to decompose the wave field into narrow band realizations prior to gradiometric analysis so that the wave parameters are resolved as functions of both time and frequency to build on this approach i incorporated the multiwavelet transform the multiwavelet transform decomposes the wave field into a series of mutually orthogonal wavelet coefficients which can then be analyzed by wave gradiometry each result can then be treated as a sample from a statistical population the method is tested on synthetic data with and without noise a relatively low degree of uncorrelated noise can have a significant impact on the quality of the results finally multiwavelet gradiometry is applied to a single earthquake recorded by a small subset of usarray stations and shows that the method accurately and robustly determines the wave parameters

holocene glacier history of frank mackie glacier northern british columbia coast mountains frank mackie glacier repeatedly advanced across the bowser river valley in northwestern british columbia to impound tide lake during the holocene the most recent infilling of tide lake was associa

surface wave propagation in central asia observations of scattering and multipathing with the kyrgyzstan broadband array we studied the propagation of rayleigh waves at regional distances in central asia using a combination of array processing techniques and surface wave analysis we present results from the detailed analysis of three representative events recorded by a 10 station broadband network that has been running in the central asian country of kyrgyzstan since 1991 an ms 5 1 event near ashkhabad turkmenistan an ms 5 8 event in south central tibet and the october 7 1994 nuclear explosion at lop nor we find there is a remarkable difference in the propagation characteristics of surface waves along these three paths the path from the event in turkmenistan is simple and is well approximated by propagation through a laterally homogeneous medium array processing shows the entire rayleigh wave train stacks coherently and arrives from an azimuth close to that predicted by a great circle path furthermore estimates of dispersion curves and fundamental mode signals determined for individual stations show little variation across the array the tibet and lop nor paths are completely different we find strong evidence for complicated multipathing and scattering effects along both of these paths we observe a three stage pattern in the tibet case 1 the early lowest frequency part of the rayleigh wave packet arrives as a coherent signal from close to the great circle path azimuth 2 this is overpowered in the period range around 20 s by a strong multipath signal that propagates across the array from a much more southerly azimuth and 3 periods below 20 s rapidly become incoherent and the signal does not have a well defined direction of propagation the lop nor path shows similar complexity on this path there is little dispersion for measurable periods greater than 10 s so the low frequency energy arrives in an airy phase the airy phase stacks somewhat coherently it stacks but significant power is lost in the best beam and slowness analysis shows it arrives from an azimuth 14 north of the great circle path azimuth like the tibet event the direction of propagation of the shorter periods cannot be resolved these results are consistent with crustal structure in central asia the multipathing and scattering from the tibet and lop nor events are not surprising given these waves propagate across highly variable crust and high topography resulting from the collision of india with eurasia the relative simplicity of the turkmenistan event path reinforces this as almost all of that path traverses the relatively undeformed turan platform of uzbekistan

p wave backazimuth anomalies observed by a small aperture seismic array at pinyon flat southern california implications for structure and source location abstract seismograms of earthquakes and explosions recorded at local regional and teleseismic distances by a small aperture dense seismic array located on pinyon flat in southern california reveal large 15 backazimuth anomalies we investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques the broadband frequency wavenumber bbfk technique the polarization technique and the beamforming technique while each technique provided nearly the same direction as a most likely estimate the beamforming estimate was associated with the smallest uncertainties backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the anza and caltech seismic networks and the preliminary determination of epicenters pde bulletin these backazimuth anomalies have a simple sinelike dependence on azimuth with the largest anomalies observed from the southeast and northwest directions such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array a best fit model of a single interface has a dip and strike of 20 and 315 respectively and a velocity contrast of 0 82 km sec application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions suggesting that this is an upper crustal feature we confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

paleoenvironmental reconstruction and water balance of a mid pleistocene pluvial lake dakhleh oasis egypt mid pleistocene lacustrine sediments exposed as erosional remnants in dakhleh oasis in the western desert of egypt provide evidence for a more humid climate than that which persists today the sediments range in facies from palustrine to fully lacustrine and generally reflect an increase in water depth upward through the strata ironstone spring deposits associated with the lacustrine sediments and modern artesian discharge in the oasis indicate that nubian aquifer water was probably an important component of the water balance but the high carbonate content of the lake sediments requires the input of surface drainage derived from the nearby limestone capped libyan plateau although definitive shorelines have not been observed a maximum lake size of 1735 km2 is derived from extrapolation of the elevations of the deposits onto the modern deflated topography theoretical water balance modeling suggests that in addition to the discharge derived from the nubian aquifer 410 860 mm yr of rainfall would be required over the dakhleh oasis drainage basin in order to maintain the lake at hydrologic steady state the persistence of climatic and hydrologic conditions amenable to maintaining a shallow freshwater lake would have allowed the region to be inhabited by a savanna fauna as well as early human groups

holocene glacier activity in the british columbia coast mountains canada abstract the coast mountains flank the pacific ocean in western british columbia canada subdivided into the southern pacific ranges central kitimat ranges and northern boundary ranges the majority of large glaciers and icefields are located in the boundary and pacific ranges prior descriptions of the holocene glacial history of this region indicate the holocene was characterized by repeated episodes of ice expansion and retreat recent site specific investigations augment our understanding of the regional character and duration of these events in this paper previously reported and new radiocarbon evidence is integrated to provide an updated regional assessment the earliest evidence of glacier expansion in the coast mountains comes from the boundary ranges at 8 9 and 7 8 ka and in the pacific ranges at 8 5 8 2 ka with the latter advance corresponding to an interval of rapid global climate deterioration although generally warm and dry climates from 7 3 to 5 3 ka likely limited the size of glaciers in the region there is radiocarbon evidence for advances over the interval from 7 3 to 6 0 and at 5 4 5 3 ka in the pacific ranges following these advances glaciers in the pacific ranges expanded down valley at 4 8 4 6 4 4 4 0 3 5 2 6 1 4 1 2 and 0 8 0 4 ka while glaciers in boundary ranges were advancing at 4 1 4 0 3 7 3 4 3 1 2 8 2 3 1 7 1 1 and 0 8 0 4 ka after 0 4 ka it appears that most glaciers in the coast mountains continued to expand to attain their maximum holocene extents by the early 18th to late 19th centuries this enhanced record of holocene glacier activity highlights the temporal synchrony in the coast mountains individual expansion events in the mid to late holocene broadly correspond to intervals of regional glacier activity reported in the canadian rocky mountains in alaska and on high elevation volcanic peaks in washington state

alpine glaciers and permanent ice and snow patches in western canada approach their smallest sizes since the mid holocene consistent with global trends most alpine glaciers in the northern hemisphere reached their maximum extents of the holocene between ad 1600 and 1850 since the late 1800s however glaciers have thinned and retreated mainly be

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

paleolandscape and paleoenvironmental interpretation of spring deposited sediments in dakhleh oasis western desert of egypt abstract iron rich sediments in dakhleh oasis western desert of egypt have been recognized as spring mounds and as archaeological sites where paleolithic materials have been recovered detailed sedimentologic investigation and mapping of these features reveal that spring mound sediments were deposited in a shallow vegetated wetland formed by the discharge of iron rich nubian aquifer waters along the southern margin of the oasis controlled largely by localized faulting and the variable paleotopography of the basin floor the spring sediments represent peri lacustrine or lake independent features and can be differentiated from fully lacustrine deposits on the basis of their sedimentary characteristics as well as the presence of goethite and jarosite in a region where authigenic deposition during pleistocene pluvial activity principally resulted in tufas and lacustrine marls spring mound formation incorporated sediment through the ponding of surface water aeolian entrapment by local vegetation and the formation of iron precipitates in a low energy oxidative and acidic environment that was not dependent upon surface water inputs into the dakhleh basin the potentially interpluvial nature of this water resource makes it an important sedimentary archive for archaeological investigations in the basin the dakhleh spring mounds record a unique groundwater controlled paleoenvironment providing the first evidence of a bog iron in egypt and one of the few occurrences of iron rich wetland remnants in the modern sahara

terrestrial impact melt rocks and glasses abstract the effects of meteorite and comet impact on earth are rock brecciation the formation of shock metamorphic features rock melting and the formation of impact structures i e simple craters complex craters and multi ring basins large events such as the 65 ma chicxulub impact are believed to have had catastrophic environmental effects that profoundly influenced the development of life on earth in this review an attempt is made to summarize some of the voluminous literature on impact melting one important aspect of planetary impact provide some comments on this process and to make suggestions for future research the products of impact melting are glasses impact melt rocks and pseudotachylites our treatise deals mainly with the geological setting petrography and major element chemistry of melt rocks and glasses impact glasses in several petrographic aspects are similar to volcanic glasses but they are associated with shock metamorphosed mineral and rock fragments and in places with siderophile element anomalies suggestive of meteoritic contamination they are found in allogenic breccia deposits within fall back suevite and outside fall out suevite impact craters and as spherules in distal ejecta large events such as the k t boundary chicxulub impact are responsible for the formation of worldwide ejecta horizons which are associated with siderophile element anomalies and shock metamorphosed mineral and rock debris impact glasses have a bulk chemical composition that is homogeneous but exemptions to this rule are common on a microscopic scale however impact glasses are commonly strikingly heterogeneous tektites are glasses ejected from craters over large distances they are characterized by very low water and volatile contents and element abundances and ratios that are evidence that tektites formed by melting of upper crustal sedimentary rocks four tektite strewn fields are known three of which can be tied to specific impact craters impact melt rocks form sheets lenses and dike like bodies within or beneath allogenic fallback breccia deposits in the impact crater and possibly on crater terraces and flanks dikes of impact melt rocks also intrude the rocks of the crater floor they commonly contain shock metamorphosed target rock and mineral fragments in various stages of assimilation and are glassy or fine to coarse grained chemically they are strikingly homogeneous but as with impact glasses exemptions to this rule do exist large and thick melt bodies such as the sudbury igneous complex sic are differentiated or may represent a combination of impact melt rocks sensu strictu and impact triggered deep crustal melts a concerted multidisciplinary approach to future research on impact melting and on other aspects of meteorite and comet impact is advocated impact models are models only and uncritical reliance on their validity will not lead to a better understanding of impact processes especially of melting excavation and deposition of allogenic breccias and the spatial position of breccias in relation to sheets and lenses of melt rocks within the crater impact triggered pressure release melting of target rocks beneath the excavation cavity may be responsible for the existence of melt rocks beneath the impact melt rocks sensu strictu this controversial idea needs to be tested by a re evaluation of existing data and models be they based on field or laboratory research only a relatively small number of terrestrial impact structures has been investigated in sufficient detail as it relates to geological and geophysical mapping in this review we summarize observations made on impact melt rocks and impact glasses in a number of north american brent haughton manicouagan new quebec sudbury wanapitei all in canada asian popigai russia zhamanshin kazakhstan two south african structures morokweng and vredefort the henbury crater field of australia and one european crater ries germany our tables listing major element chemical compositions of impact glasses and melt rocks however include also data from structures not dealt with in further detail

derivation of melt factors from glacier mass balance records in western canada melt factors for snow k s and ice k i were derived from specific mass balance data and regionally interpolated daily air temperature series at nine glaciers in the western cordillera of canada fitted k s and k i were relatively consistent across the region with mean values standard deviations of 3 04 0 38 and 4 59 0 59 mm d 1 c 1 respectively the interannual variability of melt factors was investigated for two long term datasets calculated annually snow and ice melt factors were relatively stable from year to year standard deviations for snowmelt factors were 0 48 17 and 0 42 18 at peyto and place glaciers respectively while standard deviations of ice melt factors were 1 17 25 and 0 81 14 while fitted values of k s are comparable to those presented in previous observational and modeling studies fitted k i are substantially and consistently lower across the region fitted melt factors were sensitive to the choice of lapse rate used in the air temperature interpolation melt factors fitted to mass balance data from a single site place glacier provided reasonable summer balance predictions at most other sites representing both maritime and continental climates although there was a tendency for under prediction at several sites the combination of regionally interpolated air temperatures and a degree day model appears capable of generating first order estimates of regional summer balance which can provide a benchmark against which to judge the predictive ability of more complex e g energy balance models applied at a regional scale mass balance sensitivity analyses indicate that a temperature increase of 1 k will increase summer ablation in the region by 0 51 m w e a 1 on average

glacial changes of five southwest british columbia icefields canada mid 1980s to 1999 this study adjusts and compares digital elevation models dems created from photogrammetric and interferometric synthetic aperture radar techniques to determine volume and surface elevation changes of five icefields in a remote region of southwest british columbia canada between the mid 1980s and 1999 preliminary differences between the dems in ice free and vegetation free areas indicated variable elevation offsets with increasing altitude 11 m km 1 and with increasing slope 2 7 m 108 1 results indicate a surface elevation change of 6 0 2 7 m 0 5 0 2 m a 1 and a total volume loss of 19 4 8 8 km 3 1 5 0 7 km 3 a 1 which represents a potential sea level rise contribution of 0 004 0 002 mm a 1 temperature and snowfall data from four nearby meteorological stations indicate that increased temperatures and decreased snowfall throughout the late 1980s and 1990s are a likely cause of the thinning glacier terminus positions were compared between a historical map 1927 and satellite images 1974 1990 91 and 2000 01 all observed glaciers were in retreat between 1927 and 1974 as well as between 1990 91 and 2000 01 but many glaciers advanced or significantly slowed in their retreat between 1974 and 1990 91

open system modelling for u series and esr dating of teeth abstract the study of the constituents of teeth dentine and enamel by a combination of esr and u series techniques offer unique constraints on the history of uranium migration into these materials our results imply that it is inappropriate to assume a simplified u uptake model for neither the components of a single tooth nor for the faunal remains of a given site however the combination of both methods may provide a new technique for establishing reliable chronologies for archaeological quaternary sites of up to several hundred thousand years

3d modeling of fracture induced shear wave splitting in the southern california basin splitting of shear waves generated by local earthquakes in the southern california basin and their polarization changes during propagation through layers with different orientations of anisotropy are investigated from multicomponent seismograms and their hodograms synthetic data for earthquakes in the southern california basin illustrate the effects on polarization caused by dry vertical microcracks with a crack density of 0 04 at the source and receiver locations hodograms for observed and synthetic data show that the polarization at the receiver depends only on the orientation of the anisotropy within two wavelengths of the receiver which qualitatively explains the frequency dependence of anisotropy in previous studies seismograms are simulated for a model with a range of station azimuths and distances if the anisotropy producing crack orientations do not change between the source and a receiver and the source motion is parallel to the cracks there is no shear wave splitting splitting occurs when the anisotropy orientation at the receiver or between the source and receiver is different from the source orientation

extending the place glacier mass balance record to ad 1585 using tree rings and wood density abstract recognizing that climate influences both annual tree ring growth and glacier mass balance changes in the mass balance of place glacier british columbia were documented from increment core records annually resolved ring width rw maximum mxd and mean density md chronologies were developed from engelmann spruce and douglas fir trees sampled at sites within the surrounding region a snowpack record dating to ad 1730 was reconstructed using a multivariate regression of spruce md and fir rw chronologies spruce mxd and rw chronologies were used to reconstruct winter mass balance bw for place glacier to ad 1585 summer mass balance bs was reconstructed using the rw chronology from spruce and net balance was calculated from bw and bs the reconstructions provide insight into the changes that snowpack and mass balance have undergone in the last 400 years as well as identifying relationships to air temperature and circulation indices in southern british columbia these changes are consistent with other regional mass balance reconstructions and indicate that the persistent weather systems characterizing large scale climate forcing mechanisms play a significant glaciological role in this region a comparison to dated moraine surfaces in the surrounding region substantiates that the mass balance shifts recorded in the proxy data are evident in the response of glaciers throughout the region

petrographic studies of the impact melts from meteor crater arizona usa we investigated the ballistically dispersed melts from meteor crater arizona usa to determine the stratigraphic extent of its melt zone from the compositional relationship of melts and target rocks most melt particles are crystallized hydrated and oxidized pristine glasses are rare hydration and oxidation occurred at ambient temperatures long after the impact the preserved glasses are generally clear and texturally homogeneous but unlike typical impact melts they have unusually heterogeneous compositions both within individual particles and from sample to sample for example the average sio2 for individual particles ranges from 43 to 65 the projectile content is unusually high and it is distributed bimodally with specific samples containing either 5 10 or 20 30 feo these compositional heterogeneities most likely reflect the high carbonate content of the target rocks and the release of copious co2 that dispersed the melts thereby terminating melt flow and mixing the high projectile content and the co2 depleted residue of purely sedimentary rocks produced mafic melts that crystallized fine grained olivine and pyroxene the melts fall into three compositional groups reflecting variable proportions of the major target formations moenkopi kaibab and coconino least square mixing calculations revealed one group to contain 55 moenkopi 40 quartz rich upper kaibab and 5 meteorite suggesting a source depth of 90 m or 30 m respectively additional studies especially hydrocode calculations are needed to better understand the source depth of these melts and their exceptionally high projectile content

late holocene glacial activity in manatee valley southern coast mountains british columbia canada the dendroglaciologic and lichenometric research methodologies employed in this study provide a perspective of glaciological conditions from 5 ka to present in a remote headwater area of the british columbia coast mountains since holocene ice fronts of four glaciers at this site periodically extended below treeline previous glacier advances overrode and buried forests beneath till deposits this study suggests that glaciers were expanding into standing forests at 4 76 and 3 78 ka following glacier expansion at 3 78 ka a period of recession ensued when glaciers withdrew upvalley long enough for the development of deep pedogenic surfaces and the growth of trees exceeding 300 years investigations at beluga and manatee glaciers benchmark a subsequent episode of significant glacial expansion at 2 42 ka referred to as the manatee advance this advance has regional correlatives and is distinguished from the tiedemann advance at manatee glacier by documentation of substantive ice front retreat between the

were springline carbonates in the kurkur dungul area southern egypt deposited during glacial periods the tufa deposits in the kurkur dungul area southern egypt date from marine isotope stage mis 11 to mis 1 springs across the region were active during glacial periods with sea level below 50 m reflecting changed atmospheric circulation over the indian ocean as well as peak interglacial periods during times of low sea level reduced indonesian throughflow promoted formation of an indian ocean warm pool and anomalous rainfall on its western margin we suggest that egypt lies at the intersection of westerly maghrebian and easterly mashriqian rainfall provinces which show different timing with relation to orbital forcing and different source water regions tufa growth periods are therefore not mechanistically linked to humid periods or sapropel events identified elsewhere stable isotope and t 47 data are also inconsistent with these spring systems being part of a larger system spanning northern africa and lack a clear interaction between northern hemisphere heating and mid latitude rainfall we also follow previous researchers in concluding that formation of springline deposit formation was probably delayed compared with rainfall owing to aquifer flow distances this delay is unlikely to be sufficient to explain why rainfall is out of phase with movements of the monsoon belts but may complicate interpretation of these records supplementary material a lithofacies description and supplementary figures and tables are available at https doi org 10 6084 m9 figshare c 5246661

tree ring crossdates for a first millennium ad advance of tebenkof glacier southern alaska tree ring crossdates from glacially killed logs show that tebenkof glacier advanced into a forefield forest in the ad 710s and 720s recession from this first millennium ad fma advance occurred before the 950s after which the ice margin readvanced in the 1280s to 1320s at the start of the little ice age lia a more extensive lia advance was underway from the 1640s to 1670s and the terminus stayed at or near its lia maximum until the 1890s these are the first absolute tree ring crossdates for a fma glacier advance in north america and support growing evidence from northwestern north america and europe for a significant cool interval in the centuries around ad 500

impact glasses in fallout suevites from the ries impact structure germany an analytical sem study t impact generated glasses from fallout suevite deposits at the ries impact structure have been investigated using analytical scanning electron microscopy approximately 320 analyses of glass clasts were obtained four glass types are distinguished on the basis of composition and microtextures type 1 glasses correspond to the aerodynamically shaped glass bombs studied previously by many workers major oxide concentrations indicate the involvement of granitic rocks amphibolites and minor al rich gneisses during melting type 2 glasses are chemically heterogeneous even within individual clasts with variations of several wt in most of the major oxides e g 57 70 wt sio2 this suggests incomplete mixing of 1 mineral derived melts or 2 whole rock melts from a wide range of lithologies aluminium rich clinopyroxene and fe mg rich plagioclase quench crystals are present in type 1 and 2 glasses respectively type 3 glasses contain substantial amounts of h2o 12 17 wt low sio2 50 53 wt high al2o3 17 21 wt and high cao 5 7 wt contents this suggests an origin due to shock melting of part of the sedimentary cover type 4 glasses form a ubiquitous component of the suevites based on their high sio2 content 85 100 wt the only possible protolith are sandstones in the lowermost part of the sedimentary succession calcite forms globules within type 1 glasses with which it develops microtextures indicative of liquid immiscibility unequivocal evidence also exists for liquid immiscibility between what are now montmorillonite globules and type 1 2 and 4 glasses indicating that montmorillonite was originally an impact melt glass clearly the melt zone at the ries must have incorporated a substantial fraction of the sedimentary cover as well as the underlying crystalline basement rocks impact melts were derived from different target lithologies and these separate disaggregated melts did not substantially mix in most cases type 2 3 and 4 glasses and carbonate melts